Call drop
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About This Presentation
Telecommunication
Slide Content
1
Telecom Regulatory Authority of India
Technical Paper
on
Call Drop in Cellular Networks
Mahanagar Door Sanchar Bhawan,
J.L. Nehru Marg, (Old Minto Road)
New Delhi – 110 002, India
Telecom Regulatory Authority of India
Technical Paper
on
Call Drop in Cellular Networks
Mahanagar Door Sanchar Bhawan,
J.L. Nehru Marg, (Old Minto Road)
New Delhi – 110 002, India
2
s
For any clarification/information, Shri A. Robert J.
Ravi, Advisor (TD & QoS) may be contacted at Tel.
No.+91-11-23230404, Fax: +91-11-23213036 ,
e-mail: [email protected].
s
For any clarification/information, Shri A. Robert J.
Ravi, Advisor (TD & QoS) may be contacted at Tel.
No.+91-11-23230404, Fax: +91-11-23213036 ,
e-mail: [email protected].
3
CONTENTS
TITLE PAGE
CHAPTER 1: INTRODUCTION 4-9
CHAPTER 2: ANALYSIS OF VARIOUS QUALITY OF SERVICE
PARAMETERS
10- 19
CHAPTER 3: FACTORS RESPONSIBLE FOR CALL DROP 20-25
CHAPTER 4: EFFECT OF NETWORK TRAFFIC ON CALL DROP
RATE
26-30
CHAPTER 5: STEPS THAT NEED TO BE TAKEN BY THE
SERVICE PROVIDERS
31- 38
ANNEXURE-I: THE SERVICE AREAS WHERE TSPS ARE NOT
MEETING THE CALL DROP RATE PARAMETER FOR JUNE 2015.
39
ANNEXURE-II: THE SERVICE AREAS WHERE TSPS ARE NOT
MEETING THE WORST AFFECTED CELLS HAVING MORE THAN
3% TCH DROP IN QE JUNE 2015.
40
ANNEXURE-III: THE SERVICE AREAS WHERE TSPS ARE NOT
MEETING THE CONNECTIONS WITH GOOD VOICE QUALITY
BENCHMARK IN QE JUNE 2015.
41
ANNEXURE IV: DRIVE TESTS AT DELHI, MUMBAI, PUNE,
KOLKATA, BHUBANESHWAR AND SURAT
42-57
ANNEXURE V: COMMON TERMINOLOGIES 58-63
CONTENTS
TITLE PAGE
CHAPTER 1: INTRODUCTION 4-9
CHAPTER 2: ANALYSIS OF VARIOUS QUALITY OF SERVICE
PARAMETERS
10- 19
CHAPTER 3: FACTORS RESPONSIBLE FOR CALL DROP 20-25
CHAPTER 4: EFFECT OF NETWORK TRAFFIC ON CALL DROP
RATE
26-30
CHAPTER 5: STEPS THAT NEED TO BE TAKEN BY THE
SERVICE PROVIDERS
31- 38
ANNEXURE-I: THE SERVICE AREAS WHERE TSPS ARE NOT
MEETING THE CALL DROP RATE PARAMETER FOR JUNE 2015.
39
ANNEXURE-II: THE SERVICE AREAS WHERE TSPS ARE NOT
MEETING THE WORST AFFECTED CELLS HAVING MORE THAN
3% TCH DROP IN QE JUNE 2015.
40
ANNEXURE-III: THE SERVICE AREAS WHERE TSPS ARE NOT
MEETING THE CONNECTIONS WITH GOOD VOICE QUALITY
BENCHMARK IN QE JUNE 2015.
41
ANNEXURE IV: DRIVE TESTS AT DELHI, MUMBAI, PUNE,
KOLKATA, BHUBANESHWAR AND SURAT
42-57
ANNEXURE V: COMMON TERMINOLOGIES 58-63
4
CHAPTER-1
INTRODUCTION
1. Today a number of mobile subscribers are grappling with the issue of
frequent call disconnections or ‘call drop’. Dropped call is the common
term used for describing any unexpected termination of a wireless
mobile call. Consequently, there has been an increase in the consumer
complaints regarding frequent call drops.
2. While the subscriber base in the country is growing very fast, the mobile
telecom infrastructure is not growing at the same pace and immense
pressure is being put on to the existing facilities, leading to a dip in the
quality of services (QoS) provided. Call drop, affecting the quality of
experience of the subscribers, can take place due to a variety of
technical issues, including inadequate coverage; problems with the
quality of signal; interference; network congestion; and network failure.
The rural subscribers primarily face call drops because of lack of
coverage, while in urban areas; this can be due to the increasing gap
between the growth in subscriber base and lack of commensurate
growth in investment in augmenting the network infrastructure,
including setting up of additional base transceiver stations (BTS) and
establishing in-building coverage.
3. The EMF radiation norms for BTS in India, are 10 times more stringent
than many developed countries like USA, Canada, Japan and Australia.
This necessitates lowering of power levels of BTS which may result in
shrinkage of the coverage, most importantly indoor coverage.
4. The Quality of Service performance of the telecom service providers
(TSPs) is monitored against the benchmarks set by the Authority,
through quarterly Performance Monitoring Reports (PMRs) and monthly
congestion reports submitted by the TSPs for all licensed service areas
(LSAs). The performance is reported by the TSPs averaged over a
Quarter for the entire LSA. These reports are released by TRAI on its
CHAPTER-1
INTRODUCTION
1. Today a number of mobile subscribers are grappling with the issue of
frequent call disconnections or ‘call drop’. Dropped call is the common
term used for describing any unexpected termination of a wireless
mobile call. Consequently, there has been an increase in the consumer
complaints regarding frequent call drops.
2. While the subscriber base in the country is growing very fast, the mobile
telecom infrastructure is not growing at the same pace and immense
pressure is being put on to the existing facilities, leading to a dip in the
quality of services (QoS) provided. Call drop, affecting the quality of
experience of the subscribers, can take place due to a variety of
technical issues, including inadequate coverage; problems with the
quality of signal; interference; network congestion; and network failure.
The rural subscribers primarily face call drops because of lack of
coverage, while in urban areas; this can be due to the increasing gap
between the growth in subscriber base and lack of commensurate
growth in investment in augmenting the network infrastructure,
including setting up of additional base transceiver stations (BTS) and
establishing in-building coverage.
3. The EMF radiation norms for BTS in India, are 10 times more stringent
than many developed countries like USA, Canada, Japan and Australia.
This necessitates lowering of power levels of BTS which may result in
shrinkage of the coverage, most importantly indoor coverage.
4. The Quality of Service performance of the telecom service providers
(TSPs) is monitored against the benchmarks set by the Authority,
through quarterly Performance Monitoring Reports (PMRs) and monthly
congestion reports submitted by the TSPs for all licensed service areas
(LSAs). The performance is reported by the TSPs averaged over a
Quarter for the entire LSA. These reports are released by TRAI on its
5
website for the information of stakeholders. Also, the Authority has
been imposing financial disincentives on TSPs for failure, if any, of the
said benchmarks.
5. A call is established once the call set up procedures are completed
successfully and a traffic channel (TCH) is allotted. A call drop occurs
when after a call is established, it gets disconnected for reasons other
than the normal release of the call by either the calling or the called
party. Failure of call during setup phase or drop of the call after it is
established deteriorates the quality of experience of the subscriber and
results in customer dissatisfaction.
6. The Authority monitors the following Network related QoS parameters
in a cellular mobile telephone service network:
a. Network Availability,
b. Connection Establishment,
c. Connection Maintenance and
d. Points of interconnection.
7. Of these parameters, once the call is established, the maintenance of
the call i.e. Connection Maintenance becomes crucial for customer
satisfaction. This is monitored through three parameters -Call Drop
Rate (CDR), worst affected cells having more than 3% Traffic Channel
(TCH) drops and connections with good Voice Quality.
CDR
8. CDR is defined as the ratio of abnormal disconnect of calls to total calls
established. The performance of a TSP relating to call drop is assessed
1
1
The call drop measurement is made via an automatic data collection system, based on the network
counters which register the real traffic of the network. The counter is available on the switch or OMC
and is recorded 24 hours a day, every day of the year. However, for reporting the performance the
measurements have to be taken during the Busy Hour of the day. (Time-Consistent Busy Hour [TCBH]).
website for the information of stakeholders. Also, the Authority has
been imposing financial disincentives on TSPs for failure, if any, of the
said benchmarks.
5. A call is established once the call set up procedures are completed
successfully and a traffic channel (TCH) is allotted. A call drop occurs
when after a call is established, it gets disconnected for reasons other
than the normal release of the call by either the calling or the called
party. Failure of call during setup phase or drop of the call after it is
established deteriorates the quality of experience of the subscriber and
results in customer dissatisfaction.
6. The Authority monitors the following Network related QoS parameters
in a cellular mobile telephone service network:
a. Network Availability,
b. Connection Establishment,
c. Connection Maintenance and
d. Points of interconnection.
7. Of these parameters, once the call is established, the maintenance of
the call i.e. Connection Maintenance becomes crucial for customer
satisfaction. This is monitored through three parameters -Call Drop
Rate (CDR), worst affected cells having more than 3% Traffic Channel
(TCH) drops and connections with good Voice Quality.
CDR
8. CDR is defined as the ratio of abnormal disconnect of calls to total calls
established. The performance of a TSP relating to call drop is assessed
1
1
The call drop measurement is made via an automatic data collection system, based on the network
counters which register the real traffic of the network. The counter is available on the switch or OMC
and is recorded 24 hours a day, every day of the year. However, for reporting the performance the
measurements have to be taken during the Busy Hour of the day. (Time-Consistent Busy Hour [TCBH]).
6
through this parameter. The benchmark set by TRAI for CDR is <2%.
According, to the PMRs submitted by various TSPs it is seen that the
TSPs are mostly complying with the benchmark for the entire service
area as a whole. For the quarter ending March, 2015 and June, 2015
only 3 out of 184 Licensees are not meeting the benchmarks for this
parameter. The service areas where the CDR is not met in the last
quarter is placed at Annexure-I. To get more granular CDR data, the
Authority has further issued directions to TSPs in July, 2015 to report
the same city-wise format for 42 cities across the country.
Worst affected cells having more than 3% TCH drops
9. Since the CDR for the service area as a whole does not reveal the extent
of number of areas or localities where the CDR is poor, the Authority is
monitoring another parameter called “Worst affected cells having more
than 3% Traffic Channel (TCH) drops”. It is defined as, “cells in which
the call drop rate exceeds 3% during cell busy hour, averaged over a
month for a service area.”
10. During the quarter ending June 2015, as per details at Annexure-II, 45
licensees were not able to meet this benchmark. The number of TSPs
defaulting in this parameter has increased from 10 to 45, since the
quarter ending December 2013. The parameter “Worst affected cells
having more than 3% TCH drops” provides a much more localised view
of the network. Complying with this benchmark shall ensure that on an
average not more than 3% of the base transceiver stations (BTS) on a
day are having call drops of more than 3% during the busy hour, thus
improving overall call drop rate.
Connections with good Voice Quality
11. In maintaining the call, quality of voice is also important for the
subscriber. The quality of voice in cellular mobile telecom services is
measured on a scale from 0 to 7 in GSM technology. In case of CDMA
technology, the fundamental measure for voice quality is Frame Error
through this parameter. The benchmark set by TRAI for CDR is <2%.
According, to the PMRs submitted by various TSPs it is seen that the
TSPs are mostly complying with the benchmark for the entire service
area as a whole. For the quarter ending March, 2015 and June, 2015
only 3 out of 184 Licensees are not meeting the benchmarks for this
parameter. The service areas where the CDR is not met in the last
quarter is placed at Annexure-I. To get more granular CDR data, the
Authority has further issued directions to TSPs in July, 2015 to report
the same city-wise format for 42 cities across the country.
Worst affected cells having more than 3% TCH drops
9. Since the CDR for the service area as a whole does not reveal the extent
of number of areas or localities where the CDR is poor, the Authority is
monitoring another parameter called “Worst affected cells having more
than 3% Traffic Channel (TCH) drops”. It is defined as, “cells in which
the call drop rate exceeds 3% during cell busy hour, averaged over a
month for a service area.”
10. During the quarter ending June 2015, as per details at Annexure-II, 45
licensees were not able to meet this benchmark. The number of TSPs
defaulting in this parameter has increased from 10 to 45, since the
quarter ending December 2013. The parameter “Worst affected cells
having more than 3% TCH drops” provides a much more localised view
of the network. Complying with this benchmark shall ensure that on an
average not more than 3% of the base transceiver stations (BTS) on a
day are having call drops of more than 3% during the busy hour, thus
improving overall call drop rate.
Connections with good Voice Quality
11. In maintaining the call, quality of voice is also important for the
subscriber. The quality of voice in cellular mobile telecom services is
measured on a scale from 0 to 7 in GSM technology. In case of CDMA
technology, the fundamental measure for voice quality is Frame Error
7
Rate (FER). It is the probability that a transmitted frame will be received
incorrectly. Good voice quality is 0-4 or 0-4 % FER value. The Authority
is also monitoring this parameter and the existing benchmark for this
parameter is >95%. During the quarter ending June 2015, in 7 LSAs
as per details at Annexure-III, TSPs were not able to meet this
benchmark.
Use of Drive Test in assessing the Network Performance
12. TRAI also conducts sample Drive tests across the country as part of the
audit and assessment of the TSPs. The audit agencies conduct a 300
km drive test over two/three days, in each service area during a month.
High, low and medium dense areas including highways, commercial
complex and residential areas and specially those areas from
consumers have complaints, are covered. As on July 2015, more than
400 areas/cities have been covered across the country. Subsequent to
these drive tests, corrective actions are taken by the TSPs and
compliance is reported to the Authority.
13. A drive test has the following advantages:
It measures the performance of the network from the point of view of a
user and it does not depend upon any program/algorithm within the
network.
While Network Counters do not take into account the user who has no
coverage, such situations are fully taken into account by Drive tests.
14. Even though a simple drive test may not be representative of the
performance of the whole network, it can give a snapshot of the
performance of a network on the limited routes chosen for the test. The
major issues observed during these drive tests are :
In cities/towns there are patches of poor coverage for some of the
operators.
On highways and major roads, complete coverage is not available for
many operators.
Rate (FER). It is the probability that a transmitted frame will be received
incorrectly. Good voice quality is 0-4 or 0-4 % FER value. The Authority
is also monitoring this parameter and the existing benchmark for this
parameter is >95%. During the quarter ending June 2015, in 7 LSAs
as per details at Annexure-III, TSPs were not able to meet this
benchmark.
Use of Drive Test in assessing the Network Performance
12. TRAI also conducts sample Drive tests across the country as part of the
audit and assessment of the TSPs. The audit agencies conduct a 300
km drive test over two/three days, in each service area during a month.
High, low and medium dense areas including highways, commercial
complex and residential areas and specially those areas from
consumers have complaints, are covered. As on July 2015, more than
400 areas/cities have been covered across the country. Subsequent to
these drive tests, corrective actions are taken by the TSPs and
compliance is reported to the Authority.
13. A drive test has the following advantages:
It measures the performance of the network from the point of view of a
user and it does not depend upon any program/algorithm within the
network.
While Network Counters do not take into account the user who has no
coverage, such situations are fully taken into account by Drive tests.
14. Even though a simple drive test may not be representative of the
performance of the whole network, it can give a snapshot of the
performance of a network on the limited routes chosen for the test. The
major issues observed during these drive tests are :
In cities/towns there are patches of poor coverage for some of the
operators.
On highways and major roads, complete coverage is not available for
many operators.
8
In cities/towns, some of the operators have problems in meeting the
benchmarks in indoor tests.
Therefore, while in the LSA as a whole, the average call drop rate may
be negligible, it might be concentrated in certain pockets.
Recent action taken by TRAI
15. In view of complaints on call drops and other network issues, an
independent Drive Test (IDT) was conducted on
23
rd
and 24
th
June 2015 covering various locations in South and
Central Mumbai. The performance of Idea, Airtel, Vodafone, Reliance
(GSM), Aircel & Tata(GSM) was monitored;
9
th
to 11
th
July 2015 covering various locations in South Delhi,
Central Delhi and West Delhi. The performance of Idea, Airtel,
Vodafone, Reliance (GSM), Aircel & Tata (CDMA) was monitored.
15
th
and 16
th
September 2015 covering various locations in West and
South Kolkata. The performance of Idea, Aircel, Airtel, Vodafone,
Reliance (GSM & CDMA), MTS, Tata(GSM & CDMA) & BSNL was
monitored;
14
th
and 15
th
September 2015 covering various locations in Pune.
The performance of Idea, Aircel, Airtel, Vodafone, Reliance (GSM)
Tata(GSM) & BSNL was monitored;
16
th
and 17
th
September 2015 covering various locations in Surat.
The performance of Idea, Airtel, Vodafone, Reliance (GSM)
Tata(GSM) & BSNL was monitored;
18
th
and 19
th
September 2015 covering various locations in
Bhubaneswar. The performance of Idea, Aircel, Airtel, Vodafone,
Reliance (GSM & CDMA), Tata(GSM & CDMA) & BSNL was
monitored;
The Key observations of these drive tests are placed at Annexure-IV.
16. A team from the Authority was present during these Drive tests. The
test results obtained from these drive tests are presented to explain the
network condition in terms of radio frequency (RF) coverage; receive
In cities/towns, some of the operators have problems in meeting the
benchmarks in indoor tests.
Therefore, while in the LSA as a whole, the average call drop rate may
be negligible, it might be concentrated in certain pockets.
Recent action taken by TRAI
15. In view of complaints on call drops and other network issues, an
independent Drive Test (IDT) was conducted on
23
rd
and 24
th
June 2015 covering various locations in South and
Central Mumbai. The performance of Idea, Airtel, Vodafone, Reliance
(GSM), Aircel & Tata(GSM) was monitored;
9
th
to 11
th
July 2015 covering various locations in South Delhi,
Central Delhi and West Delhi. The performance of Idea, Airtel,
Vodafone, Reliance (GSM), Aircel & Tata (CDMA) was monitored.
15
th
and 16
th
September 2015 covering various locations in West and
South Kolkata. The performance of Idea, Aircel, Airtel, Vodafone,
Reliance (GSM & CDMA), MTS, Tata(GSM & CDMA) & BSNL was
monitored;
14
th
and 15
th
September 2015 covering various locations in Pune.
The performance of Idea, Aircel, Airtel, Vodafone, Reliance (GSM)
Tata(GSM) & BSNL was monitored;
16
th
and 17
th
September 2015 covering various locations in Surat.
The performance of Idea, Airtel, Vodafone, Reliance (GSM)
Tata(GSM) & BSNL was monitored;
18
th
and 19
th
September 2015 covering various locations in
Bhubaneswar. The performance of Idea, Aircel, Airtel, Vodafone,
Reliance (GSM & CDMA), Tata(GSM & CDMA) & BSNL was
monitored;
The Key observations of these drive tests are placed at Annexure-IV.
16. A team from the Authority was present during these Drive tests. The
test results obtained from these drive tests are presented to explain the
network condition in terms of radio frequency (RF) coverage; receive
9
quality; network accessibility and network retainability; for which
benchmarks have been prescribed by the Authority or the Licensor. In
addition the carrier to interference ratio (C/I) is also observed.
17. Though the Authority has been monitoring various QoS parameters of
the TSPs, a sliced down analysis of these parameters, various factors
responsible for call drops, modelling of call drop analysis and various
steps TSPs could take to improve CDR are discussed in the subsequent
chapters. This technical paper attempts to give a comprehensive
overview of the call drop and its impact on the Telecom Network. The
common terminologies used in this paper are explained in Annexure-V.
quality; network accessibility and network retainability; for which
benchmarks have been prescribed by the Authority or the Licensor. In
addition the carrier to interference ratio (C/I) is also observed.
17. Though the Authority has been monitoring various QoS parameters of
the TSPs, a sliced down analysis of these parameters, various factors
responsible for call drops, modelling of call drop analysis and various
steps TSPs could take to improve CDR are discussed in the subsequent
chapters. This technical paper attempts to give a comprehensive
overview of the call drop and its impact on the Telecom Network. The
common terminologies used in this paper are explained in Annexure-V.
10
CHAPTER-2
ANALYSIS OF VARIOUS QUALITY OF SERVICE PARAMETERS
2.1. As mentioned in Chapter-1, once a call is established, the maintenance
of the call becomes crucial for customer satisfaction. The parameter related
to connection maintenance -Call Drop Rate (CDR), worst affected cells having
more than 3% Traffic Channel (TCH) drops and connections with good Voice
Quality – as reported by some of the operators are further analysed in this
Chapter.
2.2. CDR: The objective of this parameter is to provide the consumer with
an expectation of how successful a mobile network will be at retaining the
signal throughout the whole duration of the call. ETSI EG 202 057-3 v1.1.1
(2005-04) defined Dropped Call Ratio as “The percentage of calls which, once
they have been correctly established and therefore have an assigned TCH, are
interrupted prior to their normal completion by the user, the cause of the
early termination being within the operator’s network”.
2.3. The formula for calculating the percentage of dropped calls is:
=
E
F
x 100
where: A = the total number of interrupted calls (dropped calls)
B = the total number of calls successfully established (where traffic
channel is allotted)
The formula includes the interrupted calls which consist of failures which
cause the dropping of the call once the TCH has been successfully
established, and the successful seizure of TCH for an originated or terminated
call. The total number of established calls shall include the number of TCH
assignment in a cell for establishment of new call + number of TCH assigned
for incoming handover – number of TCH made free for outgoing handovers.
CHAPTER-2
ANALYSIS OF VARIOUS QUALITY OF SERVICE PARAMETERS
2.1. As mentioned in Chapter-1, once a call is established, the maintenance
of the call becomes crucial for customer satisfaction. The parameter related
to connection maintenance -Call Drop Rate (CDR), worst affected cells having
more than 3% Traffic Channel (TCH) drops and connections with good Voice
Quality – as reported by some of the operators are further analysed in this
Chapter.
2.2. CDR: The objective of this parameter is to provide the consumer with
an expectation of how successful a mobile network will be at retaining the
signal throughout the whole duration of the call. ETSI EG 202 057-3 v1.1.1
(2005-04) defined Dropped Call Ratio as “The percentage of calls which, once
they have been correctly established and therefore have an assigned TCH, are
interrupted prior to their normal completion by the user, the cause of the
early termination being within the operator’s network”.
2.3. The formula for calculating the percentage of dropped calls is:
=
E
F
x 100
where: A = the total number of interrupted calls (dropped calls)
B = the total number of calls successfully established (where traffic
channel is allotted)
The formula includes the interrupted calls which consist of failures which
cause the dropping of the call once the TCH has been successfully
established, and the successful seizure of TCH for an originated or terminated
call. The total number of established calls shall include the number of TCH
assignment in a cell for establishment of new call + number of TCH assigned
for incoming handover – number of TCH made free for outgoing handovers.
11
CDR ANALYSIS IN DELHI
2.4. An analysis of the TCH Call drop rate was carried out for various TSPs
in Delhi circle. Though the operators are generally meeting the TRAI bench
mark of TCH call drop <=2%, a drill down of the values at cell level as
tabulated in Table 2.1 below, shows that there are several cells that have
much higher TCH call drop rate.
Table 2.1: TCH call drop rate
CH drop (in %) COUNT OF
CELLS (TSP 1)
COUNT OF
CELLS (TSP 2)
COUNT OF
CELLS (TSP 3)
2-4% 5 10 473
4-5% 1 0 15
5-10% 0 0 12
>10% 0 0 4
Count of cells not
meeting TRAI benchmark
6 out of 8604 10 out of
15850
504 out of
16117
2.5. To further analyse the causes of call drops, the reasons of the call drops
captured through various other counters associated to each call, reporting the
cause of call termination, were obtained from the various TSPs
2. Table 2.2
depicts the sub-counters that record the reasons of call drop for certain type
of switches.
Table 2.2 Call drop counters
Counter name Reason for call drop
TSUDLOS Dropped calls due to Sudden Loss
TDISSUL Dropped calls due to insufficient signal strength on the
Uplink
TDISSDL Dropped calls due to insufficient signal strength on the
Downlink
TDISSBL Dropped calls due to insufficient signal strength on Both
link
TDISQAUL Dropped calls due to Bad quality on the Uplink
2
Performance Evaluation of Well-Established Cellular Network Using Drop Call Probability Analysis, by
Osunkwor E.O., Atuba S.O., Azi S.O.
CDR ANALYSIS IN DELHI
2.4. An analysis of the TCH Call drop rate was carried out for various TSPs
in Delhi circle. Though the operators are generally meeting the TRAI bench
mark of TCH call drop <=2%, a drill down of the values at cell level as
tabulated in Table 2.1 below, shows that there are several cells that have
much higher TCH call drop rate.
Table 2.1: TCH call drop rate
CH drop (in %) COUNT OF
CELLS (TSP 1)
COUNT OF
CELLS (TSP 2)
COUNT OF
CELLS (TSP 3)
2-4% 5 10 473
4-5% 1 0 15
5-10% 0 0 12
>10% 0 0 4
Count of cells not
meeting TRAI benchmark
6 out of 8604 10 out of
15850
504 out of
16117
2.5. To further analyse the causes of call drops, the reasons of the call drops
captured through various other counters associated to each call, reporting the
cause of call termination, were obtained from the various TSPs
2. Table 2.2
depicts the sub-counters that record the reasons of call drop for certain type
of switches.
Table 2.2 Call drop counters
Counter name Reason for call drop
TSUDLOS Dropped calls due to Sudden Loss
TDISSUL Dropped calls due to insufficient signal strength on the
Uplink
TDISSDL Dropped calls due to insufficient signal strength on the
Downlink
TDISSBL Dropped calls due to insufficient signal strength on Both
link
TDISQAUL Dropped calls due to Bad quality on the Uplink
2
Performance Evaluation of Well-Established Cellular Network Using Drop Call Probability Analysis, by
Osunkwor E.O., Atuba S.O., Azi S.O.
12
TDISQADL Dropped calls due to Bad quality on the Downlink
TDISQABL Dropped calls due to Bad quality on Both link
TDISTA Dropped calls due to excessive Timing Advance
2.6. The following graphs show the contribution of these factors in the total
call drops for Delhi and Mumbai circles collected for four TSPs, during August
2015.
Figure 2.1: Various factors affecting Call Drop
2.7. It can be seen that insufficient signal strength on both links is one of
the prominent causes of dropped calls. Other factors like sudden loss of signal
and insufficient signal strength on the Uplink also play a vital role in the call
drop.
2.8. In certain other systems, where such detailed analysis is not possible,
it is possible to obtain broadly the various factors contributing to call drop
like radio failure, BTS failure, failure to activate a channel during a call
attempt etc. as shown in the next figure.
0
5
10
15
20
25
30
35
40
45
Due to Sudden Loss
Due to insufficient signal
strength on the Uplink
Due to insufficient signal
strength on the Downlink
Due to insufficient signal
strength on Bothlink
Due to Bad quality on the
Uplink
Due to Bad quality on the
Downlink
Due to Bad quality on
Bothlink
Due to excessive Timing
Advance
Others
Various factors affecting Call Drop
TSP 1, Delhi
TSP 2, Delhi
TSP 2, Mumbai
TSP 3, Mumbai
TSP 4, Delhi
TDISQADL Dropped calls due to Bad quality on the Downlink
TDISQABL Dropped calls due to Bad quality on Both link
TDISTA Dropped calls due to excessive Timing Advance
2.6. The following graphs show the contribution of these factors in the total
call drops for Delhi and Mumbai circles collected for four TSPs, during August
2015.
Figure 2.1: Various factors affecting Call Drop
2.7. It can be seen that insufficient signal strength on both links is one of
the prominent causes of dropped calls. Other factors like sudden loss of signal
and insufficient signal strength on the Uplink also play a vital role in the call
drop.
2.8. In certain other systems, where such detailed analysis is not possible,
it is possible to obtain broadly the various factors contributing to call drop
like radio failure, BTS failure, failure to activate a channel during a call
attempt etc. as shown in the next figure.
0
5
10
15
20
25
30
35
40
45
Due to Sudden Loss
Due to insufficient signal
strength on the Uplink
Due to insufficient signal
strength on the Downlink
Due to insufficient signal
strength on Bothlink
Due to Bad quality on the
Uplink
Due to Bad quality on the
Downlink
Due to Bad quality on
Bothlink
Due to excessive Timing
Advance
Others
Various factors affecting Call Drop
TSP 1, Delhi
TSP 2, Delhi
TSP 2, Mumbai
TSP 3, Mumbai
TSP 4, Delhi
13
Figure 2.2: Factors affecting Call Drop
In the above case, the Call drop is predominantly due to Radio link failure
and Radio fail during handover.
In case of CDMA systems, the various call drop factors are depicted in
Figure 2.3.
Figure 2.3: Factors affecting Call Drop in CDMA Systems
0
10
20
30
40
50
60
70
80
radio failure
radio fail during handover
failure in A-interface…
failure in A-interface during…
transcoder failure
transcoder failure during…
LAPD failure (signaling link…
BTS failure
user actions
BCSU restart
reconfiguration of the radio…
failure to activate a channel…
TCH_ABIS_FAIL_CALL
TCH_ABIS_FAIL_OLD
TSP 1, Delhi
TSP 1, Mumbai
TSP 2, Mumbai
0
10
20
30
40
50
60
70
80
90
100
CS Call Drops (A2
interface
abnormal)[Times]
CS Call Drops (Abis
interface
abnormal)[Times]
CS Call Drops (No
reverse frame
received)[Times]
CS Call Drops (Too
many Erasure
frames)[Times]
CS Call Drops (Other
causes)[Times]
CS IS-2000 Call Drops
(HHO fail)[Times]
Various factors affecting Call Drop
TSP 1, Mumbai
TSP 1, Delhi
Figure 2.2: Factors affecting Call Drop
In the above case, the Call drop is predominantly due to Radio link failure
and Radio fail during handover.
In case of CDMA systems, the various call drop factors are depicted in
Figure 2.3.
Figure 2.3: Factors affecting Call Drop in CDMA Systems
0
10
20
30
40
50
60
70
80
radio failure
radio fail during handover
failure in A-interface…
failure in A-interface during…
transcoder failure
transcoder failure during…
LAPD failure (signaling link…
BTS failure
user actions
BCSU restart
reconfiguration of the radio…
failure to activate a channel…
TCH_ABIS_FAIL_CALL
TCH_ABIS_FAIL_OLD
TSP 1, Delhi
TSP 1, Mumbai
TSP 2, Mumbai
0
10
20
30
40
50
60
70
80
90
100
CS Call Drops (A2
interface
abnormal)[Times]
CS Call Drops (Abis
interface
abnormal)[Times]
CS Call Drops (No
reverse frame
received)[Times]
CS Call Drops (Too
many Erasure
frames)[Times]
CS Call Drops (Other
causes)[Times]
CS IS-2000 Call Drops
(HHO fail)[Times]
Various factors affecting Call Drop
TSP 1, Mumbai
TSP 1, Delhi
14
In the above case, around 97% of call drops in Mumbai for the above operator
are due to ‘too many eraser frames’ while, too many eraser frames and HHO
fall is the major cause of call drops in Delhi.
Worst affected cells having more than 3% TCH drops:
2.9. As discussed earlier, the TCH call drop does not reveal the extent of
number of areas or localities with worst call drop rate. Worst affected cells are
defined as cells in which the call drop rate exceeds 3% during cell Bouncing
Busy Hour (CBBH) or at any other hour of a day. An analysis of this parameter
was carried out for various TSPs in Delhi Circle for the month of August 2015
and the results tabulated at Table 2.3 below. Though the operators are
generally meeting the TRAI bench mark of <=3%, a drill down of the values at
cell level shows that for one TSP, there are more than 300 cells not meeting
the benchmark of 3%.
Table 2.3: Worst affected cells having more than 3% TCH drops (Call Drop Rate)
Worst affected cells having
more than 3% TCH drops
(Call Drop Rate)
Count of cells
(TSP 1)
Count of cells
(TSP 2)
Count of cells
(TSP 3)
108 out of
8604
106 out of
15850
335 out of
16117
Connections with good Voice Quality
2.10. An analysis of this parameter was carried out for various TSPs in Delhi
Circle for the month of August 2015 and the results tabulated at Table 2.4
below. Though the operators are generally meeting the bench mark of >95%,
a drill down of the values at cell level shows that there are around 15 % cells
not meeting the benchmark.
In the above case, around 97% of call drops in Mumbai for the above operator
are due to ‘too many eraser frames’ while, too many eraser frames and HHO
fall is the major cause of call drops in Delhi.
Worst affected cells having more than 3% TCH drops:
2.9. As discussed earlier, the TCH call drop does not reveal the extent of
number of areas or localities with worst call drop rate. Worst affected cells are
defined as cells in which the call drop rate exceeds 3% during cell Bouncing
Busy Hour (CBBH) or at any other hour of a day. An analysis of this parameter
was carried out for various TSPs in Delhi Circle for the month of August 2015
and the results tabulated at Table 2.3 below. Though the operators are
generally meeting the TRAI bench mark of <=3%, a drill down of the values at
cell level shows that for one TSP, there are more than 300 cells not meeting
the benchmark of 3%.
Table 2.3: Worst affected cells having more than 3% TCH drops (Call Drop Rate)
Worst affected cells having
more than 3% TCH drops
(Call Drop Rate)
Count of cells
(TSP 1)
Count of cells
(TSP 2)
Count of cells
(TSP 3)
108 out of
8604
106 out of
15850
335 out of
16117
Connections with good Voice Quality
2.10. An analysis of this parameter was carried out for various TSPs in Delhi
Circle for the month of August 2015 and the results tabulated at Table 2.4
below. Though the operators are generally meeting the bench mark of >95%,
a drill down of the values at cell level shows that there are around 15 % cells
not meeting the benchmark.
15
Table 2.4: Connections with good Voice Quality
CONNECTION
QUALITY (in %)
COUNT OF
CELLS (TSP 1)
COUNT OF
CELLS (TSP 2)
COUNT OF
CELLS (TSP 3)
90-95% 701 2473 71
85-90% 91 456 8
80-85% 14 130 3
70-80% 6 83 0
50-70% 3 19 2
40-50% 0 4 0
20-40% 0 3 0
5-20% 0 1 0
<5% 0 0 0
Count of cells
violating TRAI
benchmark
815 OUT OF 7545
CELLS
3169 OUT OF
15348 CELLS
84 OUT
OF16108
CELLS
Call Establishment
2.11. Customer dissatisfaction arises because of calls getting dropped after
establishment. But there could also be customer dissatisfaction, because of
failure during establishment of a call. To analyse these failures, the various
cause codes for failures during the process of establishment of a call, was
obtained from TSPs for the month of August 2015. These cause codes are
recorded by the system, which provide an insight into the major causes due
to which a call was unsuccessful. The various cause codes collected from TSPs
were analysed. Currently there are no regulations concerning these cause
codes. However, ‘The Standards Of Quality Of Service Of Basic Telephone
Service (Wireline) And Cellular Mobile Telephone Service Regulations, 2009’
for Basic (Wireline) Services have defined the benchmark for Call completion
Rate
3 (CCR) within a local network at ≥ 55% or the Answer to Seizure ratio
(ASR) at≥ 75%.
2.12. The results of the analysis of the various cause codes for Delhi and
Mumbai are given in the figure 2.4 and 2.5.
3
Call Completion Rate (CCR) is defined as the ratio of the number of successful calls to the number of call
attempts. Not all call attempts result in successful calls i.e. called party answers. A variety of reasons such as
called line busy, no answer and congestion in the network as well as subscriber behaviour like premature
release, wrong dialing etc. are responsible for the failure. “Answer Seizure Ratio” is defined as the ratio of calls
answered to the calls processed by the switch
Table 2.4: Connections with good Voice Quality
CONNECTION
QUALITY (in %)
COUNT OF
CELLS (TSP 1)
COUNT OF
CELLS (TSP 2)
COUNT OF
CELLS (TSP 3)
90-95% 701 2473 71
85-90% 91 456 8
80-85% 14 130 3
70-80% 6 83 0
50-70% 3 19 2
40-50% 0 4 0
20-40% 0 3 0
5-20% 0 1 0
<5% 0 0 0
Count of cells
violating TRAI
benchmark
815 OUT OF 7545
CELLS
3169 OUT OF
15348 CELLS
84 OUT
OF16108
CELLS
Call Establishment
2.11. Customer dissatisfaction arises because of calls getting dropped after
establishment. But there could also be customer dissatisfaction, because of
failure during establishment of a call. To analyse these failures, the various
cause codes for failures during the process of establishment of a call, was
obtained from TSPs for the month of August 2015. These cause codes are
recorded by the system, which provide an insight into the major causes due
to which a call was unsuccessful. The various cause codes collected from TSPs
were analysed. Currently there are no regulations concerning these cause
codes. However, ‘The Standards Of Quality Of Service Of Basic Telephone
Service (Wireline) And Cellular Mobile Telephone Service Regulations, 2009’
for Basic (Wireline) Services have defined the benchmark for Call completion
Rate
3 (CCR) within a local network at ≥ 55% or the Answer to Seizure ratio
(ASR) at≥ 75%.
2.12. The results of the analysis of the various cause codes for Delhi and
Mumbai are given in the figure 2.4 and 2.5.
3
Call Completion Rate (CCR) is defined as the ratio of the number of successful calls to the number of call
attempts. Not all call attempts result in successful calls i.e. called party answers. A variety of reasons such as
called line busy, no answer and congestion in the network as well as subscriber behaviour like premature
release, wrong dialing etc. are responsible for the failure. “Answer Seizure Ratio” is defined as the ratio of calls
answered to the calls processed by the switch
16
Figure 2.4: Cause Code Analysis for Delhi
Figure 2.5: Cause Code Analysis for Mumbai
The Normal end of the call is less than 50% for all the TSPs. It was also noticed
that the other important cause for unsuccessful calls was ‘Clear/A Onhook
during wait for answer phase’ amongst others.
2.13. Failure during call establishment could also be due to congestion in the
signalling channel known as SDCCH (in respect of GSM network) /Paging
Channel Congestion (in respect of CDMA network) or in the TCH. SDCCH
channel/paging channel is the control channel where majority of the call set
0
10
20
30
40
50NORMAL END OF
THE CALL
B SUBSCRIBER BUSY
ABSENT
SUBSCRIBER
B ANSWER TIME
OUT
CIRCUIT RELEASED
BY CO-EXCHANGE
NO RESPONSE TO
CALL…
NETWORK,
UNALLOCATED…
CLEAR/A ONHOOK
DURING WAIT…
CALL REJECTED
Others
TSP 1
TSP 2
TSP 3
TSP 4
0
50
NORMAL END OF THE
CALL
CLEAR/A ONHOOK
DURING WAIT FOR…
B SUBSCRIBER BUSY
B ANSWER TIME OUT
CLEAR/A ONHOOK
DURING SET-UP PHASE
ABSENT SUBSCRIBER
NO RESPONSE TO CALL
ESTABLISHMENT;…
NETWORK,
UNALLOCATED NUMBER
CALL REJECTED
OUT OF RADIO COVER,
RE-ESTABLISH FAIL
Others
TSP 1
TSP 2
TSP 3
TSP 4
Figure 2.4: Cause Code Analysis for Delhi
Figure 2.5: Cause Code Analysis for Mumbai
The Normal end of the call is less than 50% for all the TSPs. It was also noticed
that the other important cause for unsuccessful calls was ‘Clear/A Onhook
during wait for answer phase’ amongst others.
2.13. Failure during call establishment could also be due to congestion in the
signalling channel known as SDCCH (in respect of GSM network) /Paging
Channel Congestion (in respect of CDMA network) or in the TCH. SDCCH
channel/paging channel is the control channel where majority of the call set
0
10
20
30
40
50NORMAL END OF
THE CALL
B SUBSCRIBER BUSY
ABSENT
SUBSCRIBER
B ANSWER TIME
OUT
CIRCUIT RELEASED
BY CO-EXCHANGE
NO RESPONSE TO
CALL…
NETWORK,
UNALLOCATED…
CLEAR/A ONHOOK
DURING WAIT…
CALL REJECTED
Others
TSP 1
TSP 2
TSP 3
TSP 4
0
50
NORMAL END OF THE
CALL
CLEAR/A ONHOOK
DURING WAIT FOR…
B SUBSCRIBER BUSY
B ANSWER TIME OUT
CLEAR/A ONHOOK
DURING SET-UP PHASE
ABSENT SUBSCRIBER
NO RESPONSE TO CALL
ESTABLISHMENT;…
NETWORK,
UNALLOCATED NUMBER
CALL REJECTED
OUT OF RADIO COVER,
RE-ESTABLISH FAIL
Others
TSP 1
TSP 2
TSP 3
TSP 4
17
up occurs and is used for mobile station (mobile handset) to Base Transceiver
Station (BTS) communications before the mobile station is assigned
TCH/speech channel. TCH is a logical channel which carries either encoded
speech or user data. If there is no free channel in radio access network to
establish a call, it will lead to blocked call. Hence, connection establishment
(accessibility) represents congestion in the radio access network.
SDCCH CONGESTION ANALYSIS IN DELHI
An analysis of the SDCCH congestion was done for three TSPs in Delhi circle
for the month of August 2015, which is shown below in Table 2.6. Though the
operators are generally meeting the TRAI bench mark of SDCCH congestion
<=1%, a drill down of the values at cell level shows that there are several cells
that have SDCCH congestion much higher than the benchmark.
Table 2.6: SDCCH Congestion Rate
SDCCH congestion Count of cells
(TSP 1)
Count of cells
(TSP 2)
Count of cells
(TSP 3)
(in %age)
1-2% 173 24 54
2-4% 123 25 34
4-5% 30 4 6
5-20% 115 8 27
>20% 23 0 9
Cells not meeting
TRAI benchmark
464 out of 7665 61 out of 16108 130 out of 15348
TCH CONGESTION ANALYSIS IN DELHI
2.14. An analysis of the TCH congestion has been done for various TSPs in
Delhi circle for the month of August 2015, is shown in table 2.7 below. Though
the operators are generally meeting the TRAI bench mark of TCH congestion
<=2%, a drill down of the values at cell level shows that there are several cells
that have much higher TCH congestion than the benchmarks.
up occurs and is used for mobile station (mobile handset) to Base Transceiver
Station (BTS) communications before the mobile station is assigned
TCH/speech channel. TCH is a logical channel which carries either encoded
speech or user data. If there is no free channel in radio access network to
establish a call, it will lead to blocked call. Hence, connection establishment
(accessibility) represents congestion in the radio access network.
SDCCH CONGESTION ANALYSIS IN DELHI
An analysis of the SDCCH congestion was done for three TSPs in Delhi circle
for the month of August 2015, which is shown below in Table 2.6. Though the
operators are generally meeting the TRAI bench mark of SDCCH congestion
<=1%, a drill down of the values at cell level shows that there are several cells
that have SDCCH congestion much higher than the benchmark.
Table 2.6: SDCCH Congestion Rate
SDCCH congestion Count of cells
(TSP 1)
Count of cells
(TSP 2)
Count of cells
(TSP 3)
(in %age)
1-2% 173 24 54
2-4% 123 25 34
4-5% 30 4 6
5-20% 115 8 27
>20% 23 0 9
Cells not meeting
TRAI benchmark
464 out of 7665 61 out of 16108 130 out of 15348
TCH CONGESTION ANALYSIS IN DELHI
2.14. An analysis of the TCH congestion has been done for various TSPs in
Delhi circle for the month of August 2015, is shown in table 2.7 below. Though
the operators are generally meeting the TRAI bench mark of TCH congestion
<=2%, a drill down of the values at cell level shows that there are several cells
that have much higher TCH congestion than the benchmarks.
18
Table 2.7: TCH congestion rate for each TSP
Short Duration Calls:
2.15. Another variant to analyse call drops could be an analysis of the Call
Data Records in the billing system. It may be noted that short duration calls
do not necessarily mean a call drop. The Call Data Record analysis in Delhi
was made for some service providers for the month of August 2015.
Surprisingly as shown in figure 2.8, more than 30% of the records were of less
than 30 seconds. This could imply either the calls were made for short
duration or the calls were dropped within 30 seconds.
2.16. It was also noticed that some of these calls are also repeat calls which
might indicate multiple failures in getting connected to the same number. The
repeat calls which last for less than 60 seconds as a percentage of total calls
(i.e. of all possible durations) has been shown in figure 2.9. While this
percentage is small, this might contain calls dropped. The data varies with
the various TSPs, with an average of around 5%. The differences in prepaid
and postpaid call drops are negligible in this regard.
TCH congestion
(in %)
Count of cells
(TSP 1)
Count of cells
(TSP 2)
Count of cells
(TSP 3)
2-5% 190 31 232
5-10% 136 5 158
10-20% 89 0 89
20-50% 75 0 56
>50% 16 0 22
Cells not meeting
TRAI bench mark
506 out of 7665 36 out of
16108
557out of
15348
Table 2.7: TCH congestion rate for each TSP
Short Duration Calls:
2.15. Another variant to analyse call drops could be an analysis of the Call
Data Records in the billing system. It may be noted that short duration calls
do not necessarily mean a call drop. The Call Data Record analysis in Delhi
was made for some service providers for the month of August 2015.
Surprisingly as shown in figure 2.8, more than 30% of the records were of less
than 30 seconds. This could imply either the calls were made for short
duration or the calls were dropped within 30 seconds.
2.16. It was also noticed that some of these calls are also repeat calls which
might indicate multiple failures in getting connected to the same number. The
repeat calls which last for less than 60 seconds as a percentage of total calls
(i.e. of all possible durations) has been shown in figure 2.9. While this
percentage is small, this might contain calls dropped. The data varies with
the various TSPs, with an average of around 5%. The differences in prepaid
and postpaid call drops are negligible in this regard.
TCH congestion
(in %)
Count of cells
(TSP 1)
Count of cells
(TSP 2)
Count of cells
(TSP 3)
2-5% 190 31 232
5-10% 136 5 158
10-20% 89 0 89
20-50% 75 0 56
>50% 16 0 22
Cells not meeting
TRAI bench mark
506 out of 7665 36 out of
16108
557out of
15348
19
Figure 2.8: Call Data Records of less than 30 second duration as a percentage
of total Records
Figure 2.9: Repeat calls as a %age of total calls
0
0.2
0.4
0.6
TSP 1
TSP 2
TSP 3
TSP 4
TSP 5
TSP 6
TSP 7
TSP 1
TSP 2
TSP 3
TSP 4
TSP 5
TSP 6
TSP 7
TSP 1
TSP 3
TSP 4
TSP 5
TSP 6
TSP 7
TSP 1
TSP 3
TSP 4
TSP 5
TSP 6
TSP 7
Delhi Delhi Mumbai Mumbai
Prepaid Postpaid Prepaid Postpaid
%age of CDRs of <30 second
duration
0
2
4
6
TSP 1
TSP 2
TSP 3
TSP 4
TSP 5
TSP 6
TSP 7
TSP 1
TSP 2
TSP 3
TSP 4
TSP 5
TSP 6
TSP 7
TSP 1
TSP 3
TSP 4
TSP 5
TSP 6
TSP 7
TSP 1
TSP 3
TSP 4
TSP 5
TSP 6
TSP 7
Prepaid Postpaid Prepaid Postpaid
Delhi Mumbai
Repeat calls as a %age of total CDRs
Figure 2.8: Call Data Records of less than 30 second duration as a percentage
of total Records
Figure 2.9: Repeat calls as a %age of total calls
0
0.2
0.4
0.6
TSP 1
TSP 2
TSP 3
TSP 4
TSP 5
TSP 6
TSP 7
TSP 1
TSP 2
TSP 3
TSP 4
TSP 5
TSP 6
TSP 7
TSP 1
TSP 3
TSP 4
TSP 5
TSP 6
TSP 7
TSP 1
TSP 3
TSP 4
TSP 5
TSP 6
TSP 7
Delhi Delhi Mumbai Mumbai
Prepaid Postpaid Prepaid Postpaid
%age of CDRs of <30 second
duration
0
2
4
6
TSP 1
TSP 2
TSP 3
TSP 4
TSP 5
TSP 6
TSP 7
TSP 1
TSP 2
TSP 3
TSP 4
TSP 5
TSP 6
TSP 7
TSP 1
TSP 3
TSP 4
TSP 5
TSP 6
TSP 7
TSP 1
TSP 3
TSP 4
TSP 5
TSP 6
TSP 7
Prepaid Postpaid Prepaid Postpaid
Delhi Mumbai
Repeat calls as a %age of total CDRs
20
CHAPTER-3
FACTORS RESPONSIBLE FOR CALL DROP
3.1. Due to the increase in users’ demand for wireless cellular connectivity,
and to accommodate more number of users, the cell size in mobile wireless
cellular networks is getting reduced specially in urban areas. Due to this,
more number of handovers (or handoffs) are taking place and the probability
of calls dropping has increased. Also, if sufficient bandwidth is not available
for new calls, then blocking probability for newly generated calls also
increases. Dropping of calls during handover is less desirable than blocking
of new calls.
4
3.2. Another reason for dropped calls is when a mobile user enters an area
without adequate signal strength, or the signal has been interrupted,
interfered with, or jammed. From the network perspective, this is similar to
leaving the coverage area. Occasionally, calls are dropped upon handoff –
between cells. One possible reason for such occurrences is traffic imbalance
between two cell sites when the new cell site is at capacity and cannot accept
additional traffic from the cell trying to “hand in”.
3.3. In networks there could be sites added or modified or moved even on a
daily basis. This requires constant updating or reconfiguration of the
networks. Wrong network configuration or wrong neighbor definition can be
another reason, which renders one cell site “unaware” of the cell the mobile
user is attempting to hand off to. If the mobile phone cannot find an
alternative cell to provide the handshake, then the call is lost.
3.4. In cellular networks, co-channel and adjacent channel frequency
interference is mainly caused by neighbouring cells
5
. Thus cells in the
coverage area of the serving cell should be checked. The density of the base
4
Modelling the effect of dropped calls on cell traffic in established 3G based Cellular Networks, M.Ekpenyong,
J. Isabona, African Journal of Computing and ICT, June 2014
5
Paunovic D, Neskovic N, Neskovic A. Automatic frequency planning algorithm in a real land mobile radio
system design. In: IEEE Trans. on TELSIKS 2001. Nis, Yugoslavia, 2001: 511-520
CHAPTER-3
FACTORS RESPONSIBLE FOR CALL DROP
3.1. Due to the increase in users’ demand for wireless cellular connectivity,
and to accommodate more number of users, the cell size in mobile wireless
cellular networks is getting reduced specially in urban areas. Due to this,
more number of handovers (or handoffs) are taking place and the probability
of calls dropping has increased. Also, if sufficient bandwidth is not available
for new calls, then blocking probability for newly generated calls also
increases. Dropping of calls during handover is less desirable than blocking
of new calls.
4
3.2. Another reason for dropped calls is when a mobile user enters an area
without adequate signal strength, or the signal has been interrupted,
interfered with, or jammed. From the network perspective, this is similar to
leaving the coverage area. Occasionally, calls are dropped upon handoff –
between cells. One possible reason for such occurrences is traffic imbalance
between two cell sites when the new cell site is at capacity and cannot accept
additional traffic from the cell trying to “hand in”.
3.3. In networks there could be sites added or modified or moved even on a
daily basis. This requires constant updating or reconfiguration of the
networks. Wrong network configuration or wrong neighbor definition can be
another reason, which renders one cell site “unaware” of the cell the mobile
user is attempting to hand off to. If the mobile phone cannot find an
alternative cell to provide the handshake, then the call is lost.
3.4. In cellular networks, co-channel and adjacent channel frequency
interference is mainly caused by neighbouring cells
5
. Thus cells in the
coverage area of the serving cell should be checked. The density of the base
4
Modelling the effect of dropped calls on cell traffic in established 3G based Cellular Networks, M.Ekpenyong,
J. Isabona, African Journal of Computing and ICT, June 2014
5
Paunovic D, Neskovic N, Neskovic A. Automatic frequency planning algorithm in a real land mobile radio
system design. In: IEEE Trans. on TELSIKS 2001. Nis, Yugoslavia, 2001: 511-520
21
station greatly varies in different regions. The distances between base stations
are much longer in rural areas than in cities. Thus, the cell coverage radius
in rural area is much larger than in cities. The cell coverage is then usually
indicated by the base station site layer and the azimuth award side (the
antenna). Co-channel and adjacent channel interference can also be
responsible for dropped calls in a wireless network. Neighboring cells with
same frequencies may interfere with each other to deteriorate the quality of
service and cause dropped calls. Through drive test the C/I ratio could be
checked for levels of the signal strength of the current serving cell to that of
the signal strength of undesired (interfering) signal components. The data
regarding C/I ratio measured during drives tests conducted in Delhi, Mumbai
and other major cities is at Annexure-V. It could be noticed that most of the
TSPs in the metros are having relatively higher C/I.
3.5. Transmission problems also cause dropped calls due to a faulty
transceiver (TRX) within the base station or faulty transmission media. Call
drops could also be because of hardware related issues including equipment
failure. At the receivers’ end, calls may be dropped if a mobile phone loses
battery power and abruptly stops transmitting.
3.6. The calls could also drop because of various antenna related issues like:
If the transmit antennas of two cells are improperly connected; the
uplink signal level in each cell is much lower than the downlink
signal level in the cell. Therefore, call drops are likely to occur at
places far away from the BTS.
If a directional cell has main and diversity antennas, the BCCH and
SDCCH of the cell may be transmitted from different antennas. If the
two antennas have different traffic channel angles or azimuths, the
coverage areas of the two antennas will be different. In this case, the
mobile station (MS) can receive the BCCH signals from one antenna
and when a call is made, the MS cannot seize the SDCCH
transmitted by the other antenna and thus a call drop occurs.
station greatly varies in different regions. The distances between base stations
are much longer in rural areas than in cities. Thus, the cell coverage radius
in rural area is much larger than in cities. The cell coverage is then usually
indicated by the base station site layer and the azimuth award side (the
antenna). Co-channel and adjacent channel interference can also be
responsible for dropped calls in a wireless network. Neighboring cells with
same frequencies may interfere with each other to deteriorate the quality of
service and cause dropped calls. Through drive test the C/I ratio could be
checked for levels of the signal strength of the current serving cell to that of
the signal strength of undesired (interfering) signal components. The data
regarding C/I ratio measured during drives tests conducted in Delhi, Mumbai
and other major cities is at Annexure-V. It could be noticed that most of the
TSPs in the metros are having relatively higher C/I.
3.5. Transmission problems also cause dropped calls due to a faulty
transceiver (TRX) within the base station or faulty transmission media. Call
drops could also be because of hardware related issues including equipment
failure. At the receivers’ end, calls may be dropped if a mobile phone loses
battery power and abruptly stops transmitting.
3.6. The calls could also drop because of various antenna related issues like:
If the transmit antennas of two cells are improperly connected; the
uplink signal level in each cell is much lower than the downlink
signal level in the cell. Therefore, call drops are likely to occur at
places far away from the BTS.
If a directional cell has main and diversity antennas, the BCCH and
SDCCH of the cell may be transmitted from different antennas. If the
two antennas have different traffic channel angles or azimuths, the
coverage areas of the two antennas will be different. In this case, the
mobile station (MS) can receive the BCCH signals from one antenna
and when a call is made, the MS cannot seize the SDCCH
transmitted by the other antenna and thus a call drop occurs.
22
If the feeder cable is damaged, water leaks in the feeder, or the feeder
and the connector are not securely connected, both the transmit
power and receiver sensitivity of the antenna are reduced. This can
also result in call drops.
3.7. In a cellular network, the difference between the uplink signal and the
downlink signal level may be high which can further cause call drop, in the
following situations:
The Transmit power of the BTS is high.
The tower mounted amplifier (TMA) or BTS amplifier malfunction.
The antenna and the connector are not properly connected. As a
result, call drops may occur at the edge of the coverage area.
3.8. Propagation factors on signal behavior such as reflections and
multipath, diffraction and shadowing, building and vehicle penetration,
propagation of signal over water, propagation of signal over vegetation (foliage
loss), fading of the signal, interference could also lead to call failures.
Generally more than 50% of the reasons for dropped calls
6 in a cell, are
reported to be mainly due to electromagnetic causes, as shown at Table: 2.1.
In some cases, where the networks use load control algorithm (typically
located in the radio network controller), Calls can also be dropped to preserve
system quality.
Table 3.1: Occurrence of Call Dropping in a Reference Cell
Drop Call causes Occurrence (%)
Electromagnetic causes
(RF related)
51.4
Irregular User behavior 36.9
Abnormal Network response 7.6
Others 4.1
6
Modeling the effect of dropped calls on cell traffic in established 3G-based Cellular Networks by M.
Ekpenyong and J.Isabona; IEEE vol 7, N0. 2 – June, 2014
If the feeder cable is damaged, water leaks in the feeder, or the feeder
and the connector are not securely connected, both the transmit
power and receiver sensitivity of the antenna are reduced. This can
also result in call drops.
3.7. In a cellular network, the difference between the uplink signal and the
downlink signal level may be high which can further cause call drop, in the
following situations:
The Transmit power of the BTS is high.
The tower mounted amplifier (TMA) or BTS amplifier malfunction.
The antenna and the connector are not properly connected. As a
result, call drops may occur at the edge of the coverage area.
3.8. Propagation factors on signal behavior such as reflections and
multipath, diffraction and shadowing, building and vehicle penetration,
propagation of signal over water, propagation of signal over vegetation (foliage
loss), fading of the signal, interference could also lead to call failures.
Generally more than 50% of the reasons for dropped calls
6 in a cell, are
reported to be mainly due to electromagnetic causes, as shown at Table: 2.1.
In some cases, where the networks use load control algorithm (typically
located in the radio network controller), Calls can also be dropped to preserve
system quality.
Table 3.1: Occurrence of Call Dropping in a Reference Cell
Drop Call causes Occurrence (%)
Electromagnetic causes
(RF related)
51.4
Irregular User behavior 36.9
Abnormal Network response 7.6
Others 4.1
6
Modeling the effect of dropped calls on cell traffic in established 3G-based Cellular Networks by M.
Ekpenyong and J.Isabona; IEEE vol 7, N0. 2 – June, 2014
23
3.9. Call could also drop due to irregular user behavior (mobile equipment
failure, phones switched off after ringing, subscriber charging capacity
exceeded during the call). Other causes can be due to abnormal network
response (e.g. radio and signaling protocol error).
Reasons of increasing Call Drop Rate in Urban areas and Metros
3.10. The increasing rate of call drops, especially in urban and metro areas,
can also be attributed to spectrum related issues. The Authority has
recommended to DoT from time to time, for making additional spectrum
available in existing as well as new bands for commercial use to serve the ever
increasing subscriber base and also to deliver higher data rates. But it has
also been observed that a part of the spectrum remained unsold in the recent
auction (22.5 MHz out of 108.75 MHz in 800 MHz band, 9.8 MHz out of 177.8
MHz in 900 MHz, 5.4 MHz out of 99.2 MHz in 1800 MHz and 15 MHz out of
85 MHz in 2100 MHz) due to various reasons.
3.11. The Table 3.2 below, depicts the number of subscribers, the spectrum
availability and the number of BTS towers available with some TSPs in Delhi.
As can be seen from the table, the spectrum availability has nearly been
constant since 2009 for some operators and has decreased for some
operators, since they have used a portion of the spectrum for new technology
deployments after the auction, despite an increasing number of subscribers.
This has led to an increase in the subscriber density per MHz of spectrum.
Though the TSPs have installed additional towers, but the growth of BTS sites
has not kept up with the growth of the subscriber base. The deficient
spectrum availability or non-installation of BTS by the TSPs has translated
into declining call quality. Moreover, operators who have started to use a
portion of the spectrum obtained in the recent auction for new technologies
after renewal of their license, require extensive rebalancing of voice traffic. If
this exercise is not carried out properly, it could lead to call drops.
3.9. Call could also drop due to irregular user behavior (mobile equipment
failure, phones switched off after ringing, subscriber charging capacity
exceeded during the call). Other causes can be due to abnormal network
response (e.g. radio and signaling protocol error).
Reasons of increasing Call Drop Rate in Urban areas and Metros
3.10. The increasing rate of call drops, especially in urban and metro areas,
can also be attributed to spectrum related issues. The Authority has
recommended to DoT from time to time, for making additional spectrum
available in existing as well as new bands for commercial use to serve the ever
increasing subscriber base and also to deliver higher data rates. But it has
also been observed that a part of the spectrum remained unsold in the recent
auction (22.5 MHz out of 108.75 MHz in 800 MHz band, 9.8 MHz out of 177.8
MHz in 900 MHz, 5.4 MHz out of 99.2 MHz in 1800 MHz and 15 MHz out of
85 MHz in 2100 MHz) due to various reasons.
3.11. The Table 3.2 below, depicts the number of subscribers, the spectrum
availability and the number of BTS towers available with some TSPs in Delhi.
As can be seen from the table, the spectrum availability has nearly been
constant since 2009 for some operators and has decreased for some
operators, since they have used a portion of the spectrum for new technology
deployments after the auction, despite an increasing number of subscribers.
This has led to an increase in the subscriber density per MHz of spectrum.
Though the TSPs have installed additional towers, but the growth of BTS sites
has not kept up with the growth of the subscriber base. The deficient
spectrum availability or non-installation of BTS by the TSPs has translated
into declining call quality. Moreover, operators who have started to use a
portion of the spectrum obtained in the recent auction for new technologies
after renewal of their license, require extensive rebalancing of voice traffic. If
this exercise is not carried out properly, it could lead to call drops.
24
Table 3.2: Spectrum Efficiency for some operators in Delhi
Spectrum Efficiency (Delhi)
Geographic Area=1483 sq km
TSP Year Number of
Subscribers
ending
31st July
(‘000)
Total
Amount
of 2G
spectrum
(Mhz)
Number
of
subs./
sq. km
Subs./
km
2
/
Mhz
Cell
Sites
Cell
Site/
10
sq.
km
TSP
1
2009 5215149
10
3517 352 4177 28
2010 6802779 4587 459 4441 30
2011 8356619 5635 563 4634 31
2014 10561710 13 7122 548 5570 38
2015 10901252 8 7351 919 5988 40
TSP
2
2009 2343017
8
1580 197 3032 20
2010 3002652 2025 253 3142 21
2011 4073799 2747 343 3417 23
2014 5617071 13.6 3788 279 4678 32
2015 6098302 8.6 4112 478 4804 32
TSP
3
2009 4323178
10
2915 292 4141 28
2010 5709471 3850 385 4356 29
2011 7947038 5359 536 4736 32
2014 9188895 13 6196 477 5902 40
2015 9731448 13 6562 505 6115 41
TSP
4
2009 2133275
8.4
1438 171 1063 7
2010 2492269 1681 200 1214 8
2011 2682856 1809 215 1070 7
2014 2308385 8.4 1557 185 1119 8
2015 2341960 8.4 1579 188 1120 8
3.12. Also for some operators in Delhi, there was a major changeover of
frequencies in the 900 MHz and 1800 MHz bands on the live networks after
the auction, requiring proper network tuning. If proper network tuning is not
carried out, then there could be call drops.
3.13. After the auction, there was a shift in the existing frequencies used by
some of the incumbent operators in Delhi. The operators whose new
frequencies are near the CDMA band are required to install additional filters
in the network, which the incumbent operator may not have in the network
Table 3.2: Spectrum Efficiency for some operators in Delhi
Spectrum Efficiency (Delhi)
Geographic Area=1483 sq km
TSP Year Number of
Subscribers
ending
31st July
(‘000)
Total
Amount
of 2G
spectrum
(Mhz)
Number
of
subs./
sq. km
Subs./
km
2
/
Mhz
Cell
Sites
Cell
Site/
10
sq.
km
TSP
1
2009 5215149
10
3517 352 4177 28
2010 6802779 4587 459 4441 30
2011 8356619 5635 563 4634 31
2014 10561710 13 7122 548 5570 38
2015 10901252 8 7351 919 5988 40
TSP
2
2009 2343017
8
1580 197 3032 20
2010 3002652 2025 253 3142 21
2011 4073799 2747 343 3417 23
2014 5617071 13.6 3788 279 4678 32
2015 6098302 8.6 4112 478 4804 32
TSP
3
2009 4323178
10
2915 292 4141 28
2010 5709471 3850 385 4356 29
2011 7947038 5359 536 4736 32
2014 9188895 13 6196 477 5902 40
2015 9731448 13 6562 505 6115 41
TSP
4
2009 2133275
8.4
1438 171 1063 7
2010 2492269 1681 200 1214 8
2011 2682856 1809 215 1070 7
2014 2308385 8.4 1557 185 1119 8
2015 2341960 8.4 1579 188 1120 8
3.12. Also for some operators in Delhi, there was a major changeover of
frequencies in the 900 MHz and 1800 MHz bands on the live networks after
the auction, requiring proper network tuning. If proper network tuning is not
carried out, then there could be call drops.
3.13. After the auction, there was a shift in the existing frequencies used by
some of the incumbent operators in Delhi. The operators whose new
frequencies are near the CDMA band are required to install additional filters
in the network, which the incumbent operator may not have in the network
25
prior to the spectrum auction. Non-installation or delayed installation of these
filters will result in calls being dropped because of interference.
3.14. In metros, some of the operators, who operate in dual-band network,
usually setup a call in a GSM1800 cell and hand over the same to a GSM900
cell in the same site. If the network clocks of GSM900 cell and GSM1800 cell
are not properly synchronized, it could also lead to call drops, especially in
cases of circuit embedded networks.
3.15. In some of the major towns, there are objections raised by resident
welfare associations for installed mobile towers, because of mounting fears
7
about radiation, transmitting from the towers and the perceived health
hazards associated with the same. The protests in residential areas have
resulted in towers being pulled down or in stalling installation of new towers
affecting mobile service quality. Every tower pulled down also exerts
additional loads in the neighbouring adjacent cells resulting in poor call
quality. In fact less number of towers in an area will actually increase the
power levels of the hand sets, since the mobile handset has to ‘shout’ so that
its signal reaches the BTS.
3.16. Also the users, due to weak signal strength in their building or premise,
tend to install signal boosters to boost their received mobile signal strength.
More often these users tend to purchase boosters that are not band specific
to their service provider and boosts the complete GSM band (including all
TSPs), resulting in interference of the signals. In Delhi alone there are more
than 250 identified illegal boosters operating in the network.
7
Telecom industry experts have opined this fear is a case of “misinformation" about radiation, saying that towers
in India exceed World Health Organisation (WHO) safety standards. It is to be noted that the radiation limits
approved by the Government are one of the lowest in the world and 1/10 of the ICNIRP values. The Authority
has also released an information paper on Effects of Electromagnetic Field Radiation from Mobile Towers and
Handsets on July 30, 2014.
prior to the spectrum auction. Non-installation or delayed installation of these
filters will result in calls being dropped because of interference.
3.14. In metros, some of the operators, who operate in dual-band network,
usually setup a call in a GSM1800 cell and hand over the same to a GSM900
cell in the same site. If the network clocks of GSM900 cell and GSM1800 cell
are not properly synchronized, it could also lead to call drops, especially in
cases of circuit embedded networks.
3.15. In some of the major towns, there are objections raised by resident
welfare associations for installed mobile towers, because of mounting fears
7
about radiation, transmitting from the towers and the perceived health
hazards associated with the same. The protests in residential areas have
resulted in towers being pulled down or in stalling installation of new towers
affecting mobile service quality. Every tower pulled down also exerts
additional loads in the neighbouring adjacent cells resulting in poor call
quality. In fact less number of towers in an area will actually increase the
power levels of the hand sets, since the mobile handset has to ‘shout’ so that
its signal reaches the BTS.
3.16. Also the users, due to weak signal strength in their building or premise,
tend to install signal boosters to boost their received mobile signal strength.
More often these users tend to purchase boosters that are not band specific
to their service provider and boosts the complete GSM band (including all
TSPs), resulting in interference of the signals. In Delhi alone there are more
than 250 identified illegal boosters operating in the network.
7
Telecom industry experts have opined this fear is a case of “misinformation" about radiation, saying that towers
in India exceed World Health Organisation (WHO) safety standards. It is to be noted that the radiation limits
approved by the Government are one of the lowest in the world and 1/10 of the ICNIRP values. The Authority
has also released an information paper on Effects of Electromagnetic Field Radiation from Mobile Towers and
Handsets on July 30, 2014.
26
CHAPTER-4
EFFECT OF NETWORK TRAFFIC ON CALL DROP RATE
4.1. An attempt has been made in this chapter to analyse the effects of
carried traffic intensity and utilization factor of the network on the call drop
rate.
Average Traffic Intensity
4.2. Average traffic intensity is a measure of the average occupancy of
a channel during busy hour, measured in traffic units (Erlangs) and is defined
as the ratio of the time during which a channel is occupied (continuously or
cumulatively) to the time this channel is available for occupancy.
4.3. A traffic intensity of one traffic unit (one Erlang) means continuous
occupancy of a channel during the time period under consideration,
regardless of whether or not information is transmitted
8. The traffic intensity
offered by each user is equal to call request rate multiplied by the holding
time. That is, each user generated a traffic intensity of AU (Erlangs) given by:
AU = G X H
Where,
H=average duration of a call and,
G= average number of call requests per unit time for each user.
For a system containing ‘U’ users and an unspecified number of channels,
the total offered traffic intensity ‘A’ is given as:
A= U x AU
4.4. The average carried traffic of each cell has been directly collected from
the TSPs for the month of August 2015. Then the traffic carried by each BSC
has been calculated and a correlation between the average carried traffic
intensity and call drop rate for various operators has been plotted as shown
8
Wireless Communications: Principles and Practice, By Theodore S. Rappaport
CHAPTER-4
EFFECT OF NETWORK TRAFFIC ON CALL DROP RATE
4.1. An attempt has been made in this chapter to analyse the effects of
carried traffic intensity and utilization factor of the network on the call drop
rate.
Average Traffic Intensity
4.2. Average traffic intensity is a measure of the average occupancy of
a channel during busy hour, measured in traffic units (Erlangs) and is defined
as the ratio of the time during which a channel is occupied (continuously or
cumulatively) to the time this channel is available for occupancy.
4.3. A traffic intensity of one traffic unit (one Erlang) means continuous
occupancy of a channel during the time period under consideration,
regardless of whether or not information is transmitted
8. The traffic intensity
offered by each user is equal to call request rate multiplied by the holding
time. That is, each user generated a traffic intensity of AU (Erlangs) given by:
AU = G X H
Where,
H=average duration of a call and,
G= average number of call requests per unit time for each user.
For a system containing ‘U’ users and an unspecified number of channels,
the total offered traffic intensity ‘A’ is given as:
A= U x AU
4.4. The average carried traffic of each cell has been directly collected from
the TSPs for the month of August 2015. Then the traffic carried by each BSC
has been calculated and a correlation between the average carried traffic
intensity and call drop rate for various operators has been plotted as shown
8
Wireless Communications: Principles and Practice, By Theodore S. Rappaport
27
in the following graphs. Assuming the traffic loss by the network to be
negligible, average carried traffic intensity is equal to average offered traffic
intensity. Annexure 5 gives a detailed explanation of carried and offered
traffic.
Figure 4.1: Average Traffic vs. Call drop
It can be inferred from the above graphs that on an average, as the traffic
intensity (on x-axis) increases, the call drop rate increases in a linear fashion.
This explains that when the admissible users exceed the maximum threshold
(till the point where the call maintenance stage is able to control), the call drop
rate increases.
4.5. The system performance begins to degrade as the traffic increases
beyond the network capacity. If the various radio resources are available
during a call maintenance stage, the network becomes stable, thereby
in the following graphs. Assuming the traffic loss by the network to be
negligible, average carried traffic intensity is equal to average offered traffic
intensity. Annexure 5 gives a detailed explanation of carried and offered
traffic.
Figure 4.1: Average Traffic vs. Call drop
It can be inferred from the above graphs that on an average, as the traffic
intensity (on x-axis) increases, the call drop rate increases in a linear fashion.
This explains that when the admissible users exceed the maximum threshold
(till the point where the call maintenance stage is able to control), the call drop
rate increases.
4.5. The system performance begins to degrade as the traffic increases
beyond the network capacity. If the various radio resources are available
during a call maintenance stage, the network becomes stable, thereby
28
providing the required QoS to users accessing the system. This calls for
appropriate suitable load control measures to be taken by the telecom service
providers during congestion periods.
UTILIZATION FACTOR
4.6. The utilization factor is the ratio of the time that the network is in use
to the total time that it could be in use. Utilization factor is the traffic load in
the cellular network. Traffic load signifies the strength of the offered traffic in
the network. By definition, the traffic load is the ratio between the arrival rate
of calls and the service rate of the calls arriving. Utilization factor gives the
product of total traffic offered and the mean service time.
Utilization factor = Traffic Load= Average Traffic Intensity (A) x Mean holding time (H)
4.7. As the traffic load or utilization factor increases, the load on the network
increases and hence the probability of call drops also increases. The
correlation between the utilization factor and call drop rate for various
operators is shown in the following graphs at Figure 4.2. The utilization factor
has been calculated for each day in the month of August 2015 for all the cells
of the respective service providers. The mean holding time has been taken as
140 seconds.
providing the required QoS to users accessing the system. This calls for
appropriate suitable load control measures to be taken by the telecom service
providers during congestion periods.
UTILIZATION FACTOR
4.6. The utilization factor is the ratio of the time that the network is in use
to the total time that it could be in use. Utilization factor is the traffic load in
the cellular network. Traffic load signifies the strength of the offered traffic in
the network. By definition, the traffic load is the ratio between the arrival rate
of calls and the service rate of the calls arriving. Utilization factor gives the
product of total traffic offered and the mean service time.
Utilization factor = Traffic Load= Average Traffic Intensity (A) x Mean holding time (H)
4.7. As the traffic load or utilization factor increases, the load on the network
increases and hence the probability of call drops also increases. The
correlation between the utilization factor and call drop rate for various
operators is shown in the following graphs at Figure 4.2. The utilization factor
has been calculated for each day in the month of August 2015 for all the cells
of the respective service providers. The mean holding time has been taken as
140 seconds.
29
Figure 4.2: Utilization factor vs. Call drop
4.8. It can be inferred from the above graphs that on an average, as the
utilization factor (on x-axis) increases, the call drop rate increases in a linear
fashion. From the above analysis, it can be inferred that the Call Drop Rate
of a cellular network varies linearly with average traffic intensity and
Utilisation factor above a certain threshold in similar fashion.
4.9. The tele-traffic modelling of dropped calls performance in an
established cellular network can be compared for different service providers
to estimate the network capacity problems leading to frequent call drops. Use
of directive antennas with realistic pattern can strongly impact the spectral
efficiency of the systems and help in reduction of call drops, using the
dynamic channel assignment strategy, but this could also load the system.
Figure 4.2: Utilization factor vs. Call drop
4.8. It can be inferred from the above graphs that on an average, as the
utilization factor (on x-axis) increases, the call drop rate increases in a linear
fashion. From the above analysis, it can be inferred that the Call Drop Rate
of a cellular network varies linearly with average traffic intensity and
Utilisation factor above a certain threshold in similar fashion.
4.9. The tele-traffic modelling of dropped calls performance in an
established cellular network can be compared for different service providers
to estimate the network capacity problems leading to frequent call drops. Use
of directive antennas with realistic pattern can strongly impact the spectral
efficiency of the systems and help in reduction of call drops, using the
dynamic channel assignment strategy, but this could also load the system.
30
4.10. In cellular networks, it is also possible to arrive at the probability of call
drops theoretically. The probability that a call is dropped could be calculated
based on handoff rate and handoff call arrival rate as given below:
Where,
pd is the call drop probability;
Pf is the Handoff blocking probability or forced termination probability;
λ is the new call arrival rate;
λh is the handoff traffic arrival rate; and
E[H] is the average number of handoffs during the cell life.
4.11. This indicates that in homogeneous wireless networks, the call
dropping probability (which is a network wide quantity) can be completely
determined by the call arrival rates for new calls, and the handoff blocking
probability in a single cell. This is consistent with the fact that a homogeneous
wireless network can be completely characterized by a single cell in the
wireless network.
4.10. In cellular networks, it is also possible to arrive at the probability of call
drops theoretically. The probability that a call is dropped could be calculated
based on handoff rate and handoff call arrival rate as given below:
Where,
pd is the call drop probability;
Pf is the Handoff blocking probability or forced termination probability;
λ is the new call arrival rate;
λh is the handoff traffic arrival rate; and
E[H] is the average number of handoffs during the cell life.
4.11. This indicates that in homogeneous wireless networks, the call
dropping probability (which is a network wide quantity) can be completely
determined by the call arrival rates for new calls, and the handoff blocking
probability in a single cell. This is consistent with the fact that a homogeneous
wireless network can be completely characterized by a single cell in the
wireless network.
31
CHAPTER-5
STEPS THAT NEED TO BE TAKEN BY THE SERVICE PROVIDERS
COUNTERMEASURES
5.1. Call drop rate is an important QoS parameter for cellular networks.
Therefore, mitigating call drops is a prime obligation of the telecom industry.
The following sections underscore several measures which could be deployed
by the TSPs to reduce call drops. Such measures include handover
prioritization schemes, auxiliary stations, guard channels, call admission
control protocol, smart antennas, in-building solutions and handoff queuing.
5.2. In cellular networks, Time Division Multiple Access (TDMA) based
dynamic channel allocation in heavy load conditions is one of the methods
adopted by various service providers to reduce the call drop probability in
their networks. The performance is evaluated for probability of call drops due
to handover in busy traffic conditions. A bandwidth window is applied, where
the bandwidth window changes its size according to changing network traffic
conditions. With this solution, higher priority and real time handover calls
(voice and multimedia calls) get the requested bandwidth while the lower
priority handover calls (Data calls) get minimum bandwidth and the
probability of dropping of handover calls is reduced to minimum. Hence,
larger number of users can be served by the network with the bandwidth
usage being maximised.
5.3. When in a network, the traffic volume is high and the capacity cannot
be expanded, half-rate TCHs can be used to serve more mobile MSs, thus
decreasing Congestion Ratio on TCH.
5.4. Allocating multiple backhaul routes for same call: The service
providers can allocate multiple routes for specific flows thereby bypassing any
congestion in a particular route. One example of this is the use of Contention-
Free Transmission Opportunities. For example, if calls towards a specific
CHAPTER-5
STEPS THAT NEED TO BE TAKEN BY THE SERVICE PROVIDERS
COUNTERMEASURES
5.1. Call drop rate is an important QoS parameter for cellular networks.
Therefore, mitigating call drops is a prime obligation of the telecom industry.
The following sections underscore several measures which could be deployed
by the TSPs to reduce call drops. Such measures include handover
prioritization schemes, auxiliary stations, guard channels, call admission
control protocol, smart antennas, in-building solutions and handoff queuing.
5.2. In cellular networks, Time Division Multiple Access (TDMA) based
dynamic channel allocation in heavy load conditions is one of the methods
adopted by various service providers to reduce the call drop probability in
their networks. The performance is evaluated for probability of call drops due
to handover in busy traffic conditions. A bandwidth window is applied, where
the bandwidth window changes its size according to changing network traffic
conditions. With this solution, higher priority and real time handover calls
(voice and multimedia calls) get the requested bandwidth while the lower
priority handover calls (Data calls) get minimum bandwidth and the
probability of dropping of handover calls is reduced to minimum. Hence,
larger number of users can be served by the network with the bandwidth
usage being maximised.
5.3. When in a network, the traffic volume is high and the capacity cannot
be expanded, half-rate TCHs can be used to serve more mobile MSs, thus
decreasing Congestion Ratio on TCH.
5.4. Allocating multiple backhaul routes for same call: The service
providers can allocate multiple routes for specific flows thereby bypassing any
congestion in a particular route. One example of this is the use of Contention-
Free Transmission Opportunities. For example, if calls towards a specific
32
destination are commuted through a Gateway A and if these lines are busy,
these calls can be routed through another gateway say, Gateway B.
5.5. Use of Signal Booster: A mobile phone signal (also called reception) is
the strength of the connection to the mobile phone with its network. In an area
where the signal would normally be strong, certain other factors may have an
effect on the mobile phone signal, thereby making it either stronger or weaker,
or may cause complete interference. Additionally, the weather and volume of
network traffic may also impact the signal strength.
5.6. The building construction material can block or reduce the signal
strength inside the home or office. Many underground areas, such as tunnels
and subway station do not have sufficient coverage. For this situation,
specifically tuned cell phone signal booster for each TSP or an in-building
solution will increase the cell phone signal such places, reducing or
eliminating the number of dropped calls.
5.7. As discussed in chapter-2, generally, call drops and handoff losses are
due to inadequate radio resources. By implementation of cell splitting,
sectoring, and efficient handoff management
9
the coverage areas of BTSs
(Base Transceivers) could be maximised reducing handoff and drop call
probabilities. To achieve this reduction, the coverage area of each cell could
be redesigned (split) to accommodate micro-cells and pico-cells. Ironically, cell
splitting increases the rate of handoff. However, since the coverage areas of
the various cells are overlapping, the resulting handoff is smooth one and
does not lead call drops.
5.8. Another strategy commonly used by some of the service providers
worldwide, is through the use of Hybrid Channel Allocation (HCA)
10
9
Handoff and Drop Call Probability: Case Study of Nigeria’s Global System for Mobile Communication Sector, Rex Ndubuisi
Ali, Scholars Journal of Engineering and Technology, 2015
10
Handoff Schemes and its Performance Analysis of Priority within a particular channel in wireless systems, Chandan Singh
Ujarari, Arun Kumar, International Journal for Research in Applied Sciences & Engineering Technology, May 2015
destination are commuted through a Gateway A and if these lines are busy,
these calls can be routed through another gateway say, Gateway B.
5.5. Use of Signal Booster: A mobile phone signal (also called reception) is
the strength of the connection to the mobile phone with its network. In an area
where the signal would normally be strong, certain other factors may have an
effect on the mobile phone signal, thereby making it either stronger or weaker,
or may cause complete interference. Additionally, the weather and volume of
network traffic may also impact the signal strength.
5.6. The building construction material can block or reduce the signal
strength inside the home or office. Many underground areas, such as tunnels
and subway station do not have sufficient coverage. For this situation,
specifically tuned cell phone signal booster for each TSP or an in-building
solution will increase the cell phone signal such places, reducing or
eliminating the number of dropped calls.
5.7. As discussed in chapter-2, generally, call drops and handoff losses are
due to inadequate radio resources. By implementation of cell splitting,
sectoring, and efficient handoff management
9
the coverage areas of BTSs
(Base Transceivers) could be maximised reducing handoff and drop call
probabilities. To achieve this reduction, the coverage area of each cell could
be redesigned (split) to accommodate micro-cells and pico-cells. Ironically, cell
splitting increases the rate of handoff. However, since the coverage areas of
the various cells are overlapping, the resulting handoff is smooth one and
does not lead call drops.
5.8. Another strategy commonly used by some of the service providers
worldwide, is through the use of Hybrid Channel Allocation (HCA)
10
9
Handoff and Drop Call Probability: Case Study of Nigeria’s Global System for Mobile Communication Sector, Rex Ndubuisi
Ali, Scholars Journal of Engineering and Technology, 2015
10
Handoff Schemes and its Performance Analysis of Priority within a particular channel in wireless systems, Chandan Singh
Ujarari, Arun Kumar, International Journal for Research in Applied Sciences & Engineering Technology, May 2015
33
strategies for channel allocation and queuing technique for Quality of Service
(QoS) provisioning. HCA strategy considers new calls in Fixed Channel
Allocation (FCA) method and handoff calls in Dynamic Channel Allocation
(DCA) method to reduce call blocking and call dropping probabilities. The
application of queuing technique applied to HCA strategy increases the
efficiency of the cellular system performance especially in micro and Pico
cellular environments, effectively utilizing available allocated radio spectrum.
This leads to decrease in call blocking and dropping and an increased capacity
for users in the available channels. For Fixed channel assignments, a single
queue for the whole micro-cellular network can be considered or a dedicated
queue for each transceiver.
Prioritization Schemes
11
5.9. Prioritization of handoff calls over new calls is employed, since it is
desirable to complete an ongoing call rather than accepting a new one. Such
schemes permit high utilization of bandwidth while guaranteeing the quality
of service of handoff calls. Basic methods of handoff prioritization schemes
are auxiliary station, guard channels, call admission control (CAC), handoff
queuing schemes. Some of these schemes can be combined together to get
better results.
5.10. Scheme 1: Measurement-Based Prioritization Scheme (MBPS):
12
It
employs a dynamic priority queuing discipline instead of First In/First Out
(FIFO). It uses a signal prediction priority queuing (SPPQ) scheme to improve
MBPS algorithm by using both Received Signal Strength (RSS) and the change
in RSS (ΔRSS) to determine the priority ordering in the handoff queue.
11
Decreasing Call Blocking Rate by Using Optimization Technique Vinay Prakash Sriwastava , Jalneesh Singh , Vinay Kumar
Verma
12
Development of Efficient Hand off Queuing Schemes for minimizing call drop due to handoff failure in GSM Systems,
Aniebiet Kingsley Inyang, F.K. Opara, Uduak Idio Akpan, International Journal of Engineering Research and Technology,
April 2014
strategies for channel allocation and queuing technique for Quality of Service
(QoS) provisioning. HCA strategy considers new calls in Fixed Channel
Allocation (FCA) method and handoff calls in Dynamic Channel Allocation
(DCA) method to reduce call blocking and call dropping probabilities. The
application of queuing technique applied to HCA strategy increases the
efficiency of the cellular system performance especially in micro and Pico
cellular environments, effectively utilizing available allocated radio spectrum.
This leads to decrease in call blocking and dropping and an increased capacity
for users in the available channels. For Fixed channel assignments, a single
queue for the whole micro-cellular network can be considered or a dedicated
queue for each transceiver.
Prioritization Schemes
11
5.9. Prioritization of handoff calls over new calls is employed, since it is
desirable to complete an ongoing call rather than accepting a new one. Such
schemes permit high utilization of bandwidth while guaranteeing the quality
of service of handoff calls. Basic methods of handoff prioritization schemes
are auxiliary station, guard channels, call admission control (CAC), handoff
queuing schemes. Some of these schemes can be combined together to get
better results.
5.10. Scheme 1: Measurement-Based Prioritization Scheme (MBPS):
12
It
employs a dynamic priority queuing discipline instead of First In/First Out
(FIFO). It uses a signal prediction priority queuing (SPPQ) scheme to improve
MBPS algorithm by using both Received Signal Strength (RSS) and the change
in RSS (ΔRSS) to determine the priority ordering in the handoff queue.
11
Decreasing Call Blocking Rate by Using Optimization Technique Vinay Prakash Sriwastava , Jalneesh Singh , Vinay Kumar
Verma
12
Development of Efficient Hand off Queuing Schemes for minimizing call drop due to handoff failure in GSM Systems,
Aniebiet Kingsley Inyang, F.K. Opara, Uduak Idio Akpan, International Journal of Engineering Research and Technology,
April 2014
34
5.11. Scheme 2: Guard- Channel Prioritization Scheme: Guard Channel
schemes improve the probability of successful handoffs by simply reserving a
number of channels exclusively for handoff in each cell. Remaining channels
are shared equally between handoff and new calls. Guard channels are
established only when the number of free channels is equal to or less than
the predefined threshold. Guard channels are feasible because new calls are
less sensitive to delay than the handoffs. To overcome the poor utilization of
bandwidth, the dynamic guard channel scheme can be used.
5.12. Scheme 3: Queuing Handoff Calls: Queuing handoff call prioritization
scheme queues the handoff calls and when a channel is released, it is
assigned only to one of the handoff calls in the priority queue. The Handoff
queuing technique reduces the call blocking rate, as new calls are not
assigned a channel until all the handoff requests in the queue are served.
5.13. In the handoff queuing schemes when the received signal strength of
the BSC in the current cell reaches a certain defined threshold, the call is
queued from a neighbouring cell in the same BSC. Then, a new call request
is assigned a channel if the queue is empty or if there is at least one free
channel in the BSC. The calls would be queued until either a channel is
available in the new cell or the power by the base station in the current cell
drops below the receiver threshold signal. If the call reaches the receiver
threshold and no free channel is found then the call is blocked. Queuing
handoff is possible due to overlapping regions between the adjacent cells in
which the mobile station can communicate with more than one base station
(BS). First in First Out (FIFO) scheme is the most common queuing scheme.
5.14. Scheme 4: Using Auxiliary Station
13: Whenever large number of calls
arrive at the base station, some of them could be blocked due to congestion.
To reduce these problems, auxiliary stations are used. When call arrives and
13
Praveen Kumar ,Vinay Prakash Sriwastava, Rishi Srivastava “Decreasing Call Blocking and Dropping Rate by Implementing
Resource Planning Model Through Auxiliary Station in Search MODE”“Computer Science and Engineering BBD University
Lucknow, India ” I JIRSE Journals Vol 2,Issue-5–May 2014
5.11. Scheme 2: Guard- Channel Prioritization Scheme: Guard Channel
schemes improve the probability of successful handoffs by simply reserving a
number of channels exclusively for handoff in each cell. Remaining channels
are shared equally between handoff and new calls. Guard channels are
established only when the number of free channels is equal to or less than
the predefined threshold. Guard channels are feasible because new calls are
less sensitive to delay than the handoffs. To overcome the poor utilization of
bandwidth, the dynamic guard channel scheme can be used.
5.12. Scheme 3: Queuing Handoff Calls: Queuing handoff call prioritization
scheme queues the handoff calls and when a channel is released, it is
assigned only to one of the handoff calls in the priority queue. The Handoff
queuing technique reduces the call blocking rate, as new calls are not
assigned a channel until all the handoff requests in the queue are served.
5.13. In the handoff queuing schemes when the received signal strength of
the BSC in the current cell reaches a certain defined threshold, the call is
queued from a neighbouring cell in the same BSC. Then, a new call request
is assigned a channel if the queue is empty or if there is at least one free
channel in the BSC. The calls would be queued until either a channel is
available in the new cell or the power by the base station in the current cell
drops below the receiver threshold signal. If the call reaches the receiver
threshold and no free channel is found then the call is blocked. Queuing
handoff is possible due to overlapping regions between the adjacent cells in
which the mobile station can communicate with more than one base station
(BS). First in First Out (FIFO) scheme is the most common queuing scheme.
5.14. Scheme 4: Using Auxiliary Station
13: Whenever large number of calls
arrive at the base station, some of them could be blocked due to congestion.
To reduce these problems, auxiliary stations are used. When call arrives and
13
Praveen Kumar ,Vinay Prakash Sriwastava, Rishi Srivastava “Decreasing Call Blocking and Dropping Rate by Implementing
Resource Planning Model Through Auxiliary Station in Search MODE”“Computer Science and Engineering BBD University
Lucknow, India ” I JIRSE Journals Vol 2,Issue-5–May 2014
35
base station is not free then these new calls are engaged by auxiliary stations
and as soon as the auxiliary station finds that the base station has free
channel, it transfers the call to the base station.
5.15. Scheme 5: Call Admission Control (CAC) Protocol: The CAC scheme
refers to the task of deciding whether new calls are admitted into the network
or not. In this scheme the arrival of new calls is estimated and if they are
higher than the predefined threshold level then some calls are restricted
(blocked) irrespective of whether channel is available or not to decrease the
probability of call drop due to handoff calls. In the CAC both the new calls
and handoff calls have access to all channels. If a new call that is generated
in cell cannot find the idle channel, the call is dropped immediately if there is
no queue provided for the new calls to wait.
5.16. Improvement in Infrastructure: Improvements in Tower and related
infrastructure are elementary solutions that need to be in place for assuring
reliability of telecom services. Certain new technologies can also be considered
for supplementing infrastructural developments for better optimization of
resources.
A. In-Building Solutions
5.17. In-Building Solutions (IBS) provide mobile coverage inside buildings,
where the coverage, capacity or quality otherwise would not have been
satisfactory. It is needed because traditional wireless macro networks do not
provide seamless and uniformly good quality service in whole of the coverage
area. Signals often fade inside buildings, basements, parking garages or
subways.
5.18. Moreover, spectrum is not optimally utilised when wireless coverage is
provided from outside the building by increasing the power of the signal. This
may improve the reception to some extent, but strength of the signal varies a
lot with the location resulting in poor quality of speech and call drops.
base station is not free then these new calls are engaged by auxiliary stations
and as soon as the auxiliary station finds that the base station has free
channel, it transfers the call to the base station.
5.15. Scheme 5: Call Admission Control (CAC) Protocol: The CAC scheme
refers to the task of deciding whether new calls are admitted into the network
or not. In this scheme the arrival of new calls is estimated and if they are
higher than the predefined threshold level then some calls are restricted
(blocked) irrespective of whether channel is available or not to decrease the
probability of call drop due to handoff calls. In the CAC both the new calls
and handoff calls have access to all channels. If a new call that is generated
in cell cannot find the idle channel, the call is dropped immediately if there is
no queue provided for the new calls to wait.
5.16. Improvement in Infrastructure: Improvements in Tower and related
infrastructure are elementary solutions that need to be in place for assuring
reliability of telecom services. Certain new technologies can also be considered
for supplementing infrastructural developments for better optimization of
resources.
A. In-Building Solutions
5.17. In-Building Solutions (IBS) provide mobile coverage inside buildings,
where the coverage, capacity or quality otherwise would not have been
satisfactory. It is needed because traditional wireless macro networks do not
provide seamless and uniformly good quality service in whole of the coverage
area. Signals often fade inside buildings, basements, parking garages or
subways.
5.18. Moreover, spectrum is not optimally utilised when wireless coverage is
provided from outside the building by increasing the power of the signal. This
may improve the reception to some extent, but strength of the signal varies a
lot with the location resulting in poor quality of speech and call drops.
36
5.19. The implementation of dedicated in-building coverage enables new
traffic for the mobile operators in areas that previously were “black holes” and
offloads the macro system in areas with overlapping in-building and macro
network coverage, thereby increasing overall system coverage, capacity and
decreasing call drops.
5.20. The primary reason for limited use of IBS in India is said to be lack of
adequate connectivity with existing mobile networks through suitable media
like optical fibre. Also, providing connectivity to these sites becomes a
problem due to complex procedures for granting Right of Way (ROW)
permissions. Such connectivity requires permission to lay cable into a
building which is the bottleneck.
B. Distributed Antenna System
5.21. Distributed Antenna System (DAS) is a network of spatially separated
antenna nodes connected to a common source that provides wireless service
within a geographic area or structure. DAS can serve many telecom service
providers simultaneously. Such shared DASs are commonly referred to as
neutral host systems.
5.22. The commonly deployed DASs consist of coaxial feeder cables and
components such as antennas, power tappers and power splitters. Wireless
Service Providers can use Shared Distributed Antenna Systems (DAS) for both
in-building and outdoor RF coverage to help alleviate many challenges
associated with the traditional Macro/Micro Cell architecture.
5.23. One way of implementing a Distributed Antenna System is to mount
low powered BTSs on lamp-posts or street furniture which are connected to
the mobile operators’ networks via copper wires or optical fibres. As lamp-
posts are available at short distances a large number of such BTSs can be
planned each with a small coverage area. Optical fibre connectivity would be
preferable over other traditional methods like microwave and satellite from
the point of view of cost-performance benefits, providing a more robust
5.19. The implementation of dedicated in-building coverage enables new
traffic for the mobile operators in areas that previously were “black holes” and
offloads the macro system in areas with overlapping in-building and macro
network coverage, thereby increasing overall system coverage, capacity and
decreasing call drops.
5.20. The primary reason for limited use of IBS in India is said to be lack of
adequate connectivity with existing mobile networks through suitable media
like optical fibre. Also, providing connectivity to these sites becomes a
problem due to complex procedures for granting Right of Way (ROW)
permissions. Such connectivity requires permission to lay cable into a
building which is the bottleneck.
B. Distributed Antenna System
5.21. Distributed Antenna System (DAS) is a network of spatially separated
antenna nodes connected to a common source that provides wireless service
within a geographic area or structure. DAS can serve many telecom service
providers simultaneously. Such shared DASs are commonly referred to as
neutral host systems.
5.22. The commonly deployed DASs consist of coaxial feeder cables and
components such as antennas, power tappers and power splitters. Wireless
Service Providers can use Shared Distributed Antenna Systems (DAS) for both
in-building and outdoor RF coverage to help alleviate many challenges
associated with the traditional Macro/Micro Cell architecture.
5.23. One way of implementing a Distributed Antenna System is to mount
low powered BTSs on lamp-posts or street furniture which are connected to
the mobile operators’ networks via copper wires or optical fibres. As lamp-
posts are available at short distances a large number of such BTSs can be
planned each with a small coverage area. Optical fibre connectivity would be
preferable over other traditional methods like microwave and satellite from
the point of view of cost-performance benefits, providing a more robust
37
system. The commonly deployed DASs consist of coaxial feeder cables and
components such as antennas, power tappers and power splitters. Radiating
feeders work as a combined feeder cable and antenna. They are often used in
tunnels and culverts. IBS/DAS solutions can be put up on Government
buildings including PSU buildings, Airports and Train stations etc. for
ensuring quality of service. Similarly, DAS coverage can be dove-tailed with
urban and rural development programmes. IBS/DAS solutions could also be
deployed in public utility buildings such as hospitals having more than 100
beds and shopping malls of more than 25000 square feet super built area.
C. Smart Antenna
5.24. A smart antenna consists of several antenna elements, whose signal is
processed adaptively in order to exploit the spatial domain of the mobile radio
channel. The smart antenna technology can significantly improve wireless
system performance for a range of potential users.
5.25. A smart antenna enables a higher capacity in wireless networks by
effectively reducing multipath and co-channel interference. This is achieved
by focusing the radiation only in the desired direction and adjusting itself to
changing traffic conditions or signal environments. Multipath is a condition
that arises when a transmitted signal undergoes reflection from various
obstacles in the environment. This gives rise to multiple signals arriving from
different directions at the receiver. Co-channel interference is interference
between two signals that operate at the same frequency. Smart antennas
employ a set of radiating elements arranged in the form of an array.
Self-optimization networks
5.26. Self-optimising networks (SON) offer service providers the opportunity
to replace engineering resource with software that manages and controls
networks to deliver optimum performance from current assets. Optimizing
algorithms such as load balancing and handover parameter optimization,
among others, can be used to improve system performance.
system. The commonly deployed DASs consist of coaxial feeder cables and
components such as antennas, power tappers and power splitters. Radiating
feeders work as a combined feeder cable and antenna. They are often used in
tunnels and culverts. IBS/DAS solutions can be put up on Government
buildings including PSU buildings, Airports and Train stations etc. for
ensuring quality of service. Similarly, DAS coverage can be dove-tailed with
urban and rural development programmes. IBS/DAS solutions could also be
deployed in public utility buildings such as hospitals having more than 100
beds and shopping malls of more than 25000 square feet super built area.
C. Smart Antenna
5.24. A smart antenna consists of several antenna elements, whose signal is
processed adaptively in order to exploit the spatial domain of the mobile radio
channel. The smart antenna technology can significantly improve wireless
system performance for a range of potential users.
5.25. A smart antenna enables a higher capacity in wireless networks by
effectively reducing multipath and co-channel interference. This is achieved
by focusing the radiation only in the desired direction and adjusting itself to
changing traffic conditions or signal environments. Multipath is a condition
that arises when a transmitted signal undergoes reflection from various
obstacles in the environment. This gives rise to multiple signals arriving from
different directions at the receiver. Co-channel interference is interference
between two signals that operate at the same frequency. Smart antennas
employ a set of radiating elements arranged in the form of an array.
Self-optimization networks
5.26. Self-optimising networks (SON) offer service providers the opportunity
to replace engineering resource with software that manages and controls
networks to deliver optimum performance from current assets. Optimizing
algorithms such as load balancing and handover parameter optimization,
among others, can be used to improve system performance.
38
Conclusion
5.27. In light of the reasons discussed above about the increase in call drops,
it must be realised that mobile towers do not have an unlimited capacity for
handling the current network load. There is an urgent need to increase the
number of the towers so as to cater to the demands of a growing subscriber
base. At the same time, problems like removal of towers from certain areas by
Authorities should be adequately addressed. This problem is particularly
evident in urban areas. Moreover, with the increase in the usage of 3G
networks, the growth rate of mobile towers supporting 2G networks has
reduced. This must be addressed.
5.28. The previous sections highlighted some important countermeasures at
TSPs’ end. Measures like Dynamic Channel Allocation, multiple call routing
and optimised resource management can be employed by the TSP’s besides,
usage of mobile signal boosters through the TSPs at users’ buildings or
premises. Some prioritization schemes like MBPS, CAC, Guard Channels,
Handoff Queuing and Auxiliary Stations essentially need to be incorporated
by TSPs to reduce call drops.
Conclusion
5.27. In light of the reasons discussed above about the increase in call drops,
it must be realised that mobile towers do not have an unlimited capacity for
handling the current network load. There is an urgent need to increase the
number of the towers so as to cater to the demands of a growing subscriber
base. At the same time, problems like removal of towers from certain areas by
Authorities should be adequately addressed. This problem is particularly
evident in urban areas. Moreover, with the increase in the usage of 3G
networks, the growth rate of mobile towers supporting 2G networks has
reduced. This must be addressed.
5.28. The previous sections highlighted some important countermeasures at
TSPs’ end. Measures like Dynamic Channel Allocation, multiple call routing
and optimised resource management can be employed by the TSP’s besides,
usage of mobile signal boosters through the TSPs at users’ buildings or
premises. Some prioritization schemes like MBPS, CAC, Guard Channels,
Handoff Queuing and Auxiliary Stations essentially need to be incorporated
by TSPs to reduce call drops.
39
Annexure –I
The Service areas where TSPs are not meeting the Call Drop Rate
parameter for June 2015.
Quarter Benchmark Service Provider Service Area
Call drop
rate
(%age)
Quarter end June
2015
≤ 2%
TSP-1
BH 2.84
NE 3.52
TSP-2 HR 6.37
Annexure –I
The Service areas where TSPs are not meeting the Call Drop Rate
parameter for June 2015.
Quarter Benchmark Service Provider Service Area
Call drop
rate
(%age)
Quarter end June
2015
≤ 2%
TSP-1
BH 2.84
NE 3.52
TSP-2 HR 6.37
40
Annexure -II
The Service areas where TSPs are not meeting the worst affected cells
having more than 3% TCH drop in QE June 2015.
Quarter Benchmark Service Provider Service Area Performance
Quarter
ending
June 2015
≤ 3%
TSP-1
Bihar 8.13
North East 8.30
Punjab 19.17
West Bengal 7.34
TSP-2
Andhra Pradesh 6.11
Assam 15.46
Bihar 10.59
Delhi 6.87
Haryana 4.31
Himachal Pradesh 11.77
Jammu & Kashmir 9.53
Karnataka 7.92
Kerala 3.29
Maharashtra 4.22
Mumbai 5.85
North East 16.78
Orissa 11.28
Rajasthan 3.24
Tamil Nadu 5.93
West Bengal 8.74
TSP-3
Andhra Pradesh 3.19
Gujarat 3.87
Haryana 3.93
Himachal Pradesh 11.68
Karnataka 4.81
Maharashtra 4.92
TSP-4
Mumbai 3.05
Punjab 3.58
Rajasthan 4.11
UPE 5.46
UPW 4.20
TSP-5
Bihar 4.22
Gujarat 5.34
Haryana 4.36
Himachal Pradesh 3.20
Kerala 6.61
Madhya Pradesh 5.23
Maharashtra 4.91
Mumbai 3.32
Orissa 3.47
Punjab 4.36
Rajasthan 5.78
UPE 5.54
UPW 3.52
West Bengal 4.95
Annexure -II
The Service areas where TSPs are not meeting the worst affected cells
having more than 3% TCH drop in QE June 2015.
Quarter Benchmark Service Provider Service Area Performance
Quarter
ending
June 2015
≤ 3%
TSP-1
Bihar 8.13
North East 8.30
Punjab 19.17
West Bengal 7.34
TSP-2
Andhra Pradesh 6.11
Assam 15.46
Bihar 10.59
Delhi 6.87
Haryana 4.31
Himachal Pradesh 11.77
Jammu & Kashmir 9.53
Karnataka 7.92
Kerala 3.29
Maharashtra 4.22
Mumbai 5.85
North East 16.78
Orissa 11.28
Rajasthan 3.24
Tamil Nadu 5.93
West Bengal 8.74
TSP-3
Andhra Pradesh 3.19
Gujarat 3.87
Haryana 3.93
Himachal Pradesh 11.68
Karnataka 4.81
Maharashtra 4.92
TSP-4
Mumbai 3.05
Punjab 3.58
Rajasthan 4.11
UPE 5.46
UPW 4.20
TSP-5
Bihar 4.22
Gujarat 5.34
Haryana 4.36
Himachal Pradesh 3.20
Kerala 6.61
Madhya Pradesh 5.23
Maharashtra 4.91
Mumbai 3.32
Orissa 3.47
Punjab 4.36
Rajasthan 5.78
UPE 5.54
UPW 3.52
West Bengal 4.95
41
Annexure -III
The Service areas where TSPs are not meeting the Connections with good
Voice Quality Benchmark in QE June 2015.
Quarter Benchmark Service
Provider
Service Area Performance
Quarter end
June 2015
≥ 95% TSP-1 Assam 94.39
North East 92.06
TSP-2 Assam 91.37
Jammu & Kashmir 94.82
North East 93.11
TSP-9 Bihar 94.89
UPE 93.79
Annexure -III
The Service areas where TSPs are not meeting the Connections with good
Voice Quality Benchmark in QE June 2015.
Quarter Benchmark Service
Provider
Service Area Performance
Quarter end
June 2015
≥ 95% TSP-1 Assam 94.39
North East 92.06
TSP-2 Assam 91.37
Jammu & Kashmir 94.82
North East 93.11
TSP-9 Bihar 94.89
UPE 93.79
42
Annexure- IV
Drive Tests at Delhi, Mumbai, Pune, Kolkata, Bhubaneshwar
and Surat
A. Drive test at Delhi
1. A drive test was conducted in Delhi in the month of July, 2015. Total six
Operators were benchmarked. In the following figure, the green route depicts
the associated drive route. The total drive route covered is approximately 300
km over a period of 3 days using a vehicle. The drive test was carried out from
9
th
to 11
th
July 2015 during 09:00 hrs. to 20:30 hrs. In all about 3626 calls
were made for all 6 operators.
Sadar Bazar
DRIVE TEST ROUTE OF DELHI
Annexure- IV
Drive Tests at Delhi, Mumbai, Pune, Kolkata, Bhubaneshwar
and Surat
A. Drive test at Delhi
1. A drive test was conducted in Delhi in the month of July, 2015. Total six
Operators were benchmarked. In the following figure, the green route depicts
the associated drive route. The total drive route covered is approximately 300
km over a period of 3 days using a vehicle. The drive test was carried out from
9
th
to 11
th
July 2015 during 09:00 hrs. to 20:30 hrs. In all about 3626 calls
were made for all 6 operators.
Sadar Bazar
DRIVE TEST ROUTE OF DELHI
43
2. Key Areas Covered:
New Delhi Railway
Station
BhimRao Marg Airport T3 INA
Mirdag Marg Akbar Road Uttam Nagar Delhi Haat
LNJP Hospital Teen Murti
Marg
Delhi Gate AIIMS
C.P Outer/Inner circle South Avenue Bahadurshah
Marg
Sri Aurobindo
Marg
R.K Ashram Marg T Point Mathura Road JNU Campus
Outer
Gol Market ITC Maurya Lodhi Road Qutub Minar
GPO CSD Road CGO Interior Saket Metro
RML Jail Road Bhism Pitamah
Road
Batra Hospital
Nehru Place Govind Puri
3. KPI Details
Table 1: Benchmark KPI Operator Table
KPI Aircel Idea Vodafone Airtel Reliance
Tata
(CDMA)
Coverage % 74.32% 87.42% 87.29% 91.26% 57.96% 58.07%
Accessibility
%
97.05% 73.91% 95.31% 91.82% 89.55% 98.89%
Retainability
%
94.82% 97.16% 95.72% 91.96% 82.71% 99.16%
Mobility % 97.85% 98.65% 94.15% 95.94% 96.86% 94.12%
Rx Quality
%
82.69% 91.12% 90.67% 84.32% 85.36% 99.68%
C/I % 53.64% 60.30% 58.82% 43.82% 53.64% 79.96%
2. Key Areas Covered:
New Delhi Railway
Station
BhimRao Marg Airport T3 INA
Mirdag Marg Akbar Road Uttam Nagar Delhi Haat
LNJP Hospital Teen Murti
Marg
Delhi Gate AIIMS
C.P Outer/Inner circle South Avenue Bahadurshah
Marg
Sri Aurobindo
Marg
R.K Ashram Marg T Point Mathura Road JNU Campus
Outer
Gol Market ITC Maurya Lodhi Road Qutub Minar
GPO CSD Road CGO Interior Saket Metro
RML Jail Road Bhism Pitamah
Road
Batra Hospital
Nehru Place Govind Puri
3. KPI Details
Table 1: Benchmark KPI Operator Table
KPI Aircel Idea Vodafone Airtel Reliance
Tata
(CDMA)
Coverage % 74.32% 87.42% 87.29% 91.26% 57.96% 58.07%
Accessibility
%
97.05% 73.91% 95.31% 91.82% 89.55% 98.89%
Retainability
%
94.82% 97.16% 95.72% 91.96% 82.71% 99.16%
Mobility % 97.85% 98.65% 94.15% 95.94% 96.86% 94.12%
Rx Quality
%
82.69% 91.12% 90.67% 84.32% 85.36% 99.68%
C/I % 53.64% 60.30% 58.82% 43.82% 53.64% 79.96%
44
4. Overall Analysis
The Drive Test results revealed that the most of the operators failed to meet
benchmarks of network related parameters. They failed to achieve benchmark
due to High Block Call Rate, High Drop Call Rate, Low Call Setup Success
Rate & Rx Quality Samples.
Table 2: Operator Analysis Table
KPI Aircel Idea Vodafone Airtel Reliance Tata
(CDMA)
Call Attempt 441 782 490 587 603 723
Blocked Call
Rate
3.27% 48.96% 4.71% 8.16% 9.44% 2.80%
Call Setup
Success Rate
(95%)
94.82% 97.16% 95.72% 91.96% 82.71% 99.16%
Dropped Call
Rate (2%)
5.18% 2.84% 4.28% 8.04% 17.29% 0.84%
Rx Quality (0-
5) (95%)
82.69% 91.12% 90.67% 84.32% 85.36% 99.68%
Handover
Success Rate >
95%
97.85% 98.65% 94.15% 95.94% 96.86% 94.12%
4. Overall Analysis
The Drive Test results revealed that the most of the operators failed to meet
benchmarks of network related parameters. They failed to achieve benchmark
due to High Block Call Rate, High Drop Call Rate, Low Call Setup Success
Rate & Rx Quality Samples.
Table 2: Operator Analysis Table
KPI Aircel Idea Vodafone Airtel Reliance Tata
(CDMA)
Call Attempt 441 782 490 587 603 723
Blocked Call
Rate
3.27% 48.96% 4.71% 8.16% 9.44% 2.80%
Call Setup
Success Rate
(95%)
94.82% 97.16% 95.72% 91.96% 82.71% 99.16%
Dropped Call
Rate (2%)
5.18% 2.84% 4.28% 8.04% 17.29% 0.84%
Rx Quality (0-
5) (95%)
82.69% 91.12% 90.67% 84.32% 85.36% 99.68%
Handover
Success Rate >
95%
97.85% 98.65% 94.15% 95.94% 96.86% 94.12%
45
B. Drive test at Mumbai
1.
A drive test was conducted in Mumbai in the month of June, 2015. Total
six Operators were benchmarked. In the following figure, the green route
depicts the associated drive route. The total drive route covered is
approximately 300 km over a period of 2 days per operator using a vehicle.
The drive test was carried out from 09.00 hrs. to 1930 hrs. during 23
rd
and
24
th
June 2015. In all about 3305 calls were made for all 6 operators.
2. Key Areas Covered:
Navy Nagar Colaba Malad East Andheri Lokhandwala
Nariman Point Malad West BPCL Colony Matunga BKC
Peddar Road Charkop Mahul Shivaji Nagar
Peragon center
Mira-Bhayandra
Road Ghatkopar Sakinaka
Malabar Hill AG Nagar Matunga Mankhurd
TJ Eastern Highway Dahisar Sion Govandi Station
ChurchgateArea Malvani Juhu Punam Nagar
Dadar MarineLine
Road Chinchpoli W E Highway JVLR Road
Khar Neelam Nagar
DRIVE TEST ROUTE OF MUMBAI
B. Drive test at Mumbai
1.
A drive test was conducted in Mumbai in the month of June, 2015. Total
six Operators were benchmarked. In the following figure, the green route
depicts the associated drive route. The total drive route covered is
approximately 300 km over a period of 2 days per operator using a vehicle.
The drive test was carried out from 09.00 hrs. to 1930 hrs. during 23
rd
and
24
th
June 2015. In all about 3305 calls were made for all 6 operators.
2. Key Areas Covered:
Navy Nagar Colaba Malad East Andheri Lokhandwala
Nariman Point Malad West BPCL Colony Matunga BKC
Peddar Road Charkop Mahul Shivaji Nagar
Peragon center
Mira-Bhayandra
Road Ghatkopar Sakinaka
Malabar Hill AG Nagar Matunga Mankhurd
TJ Eastern Highway Dahisar Sion Govandi Station
ChurchgateArea Malvani Juhu Punam Nagar
Dadar MarineLine
Road Chinchpoli W E Highway JVLR Road
Khar Neelam Nagar
DRIVE TEST ROUTE OF MUMBAI
46
3. KPI Details
Table 3: Benchmark KPI Operator Table
KPI Idea Airtel Vodafone
Reliance
Communication
(GSM)
Aircel
Tata
(GSM)
Coverage % 95.40% 95.13% 91.08% 89.49% 93.63% 97.07%
Accessibility % 90.00% 96.98% 96.07% 68.87% 95.64% 95.42%
Retainability % 94.44% 99.03% 95.17% 97.71% 96.81% 94.49%
Mobility % 97.87% 96.74% 97.54% 98.01% 96.86% 95.40%
Rx Quality % 86.46% 91.11% 89.56% 85.33% 85.60% 89.50%
C/I % 66.67% 64.83% 65.23% 83.44% 68.13% 69.75%
4. Overall Analysis
The Drive Test results revealed that the most of the operators were failed
to meet benchmarks of network related parameters. They failed to achieve
benchmark due to High Block Call Rate, High Drop Call Rate, Low Call
Setup Success Rate & Rx Quality Samples.
Table 4: Operator Analysis Table
KPI Idea Airtel Vodafone
Reliance
(GSM)
Aircel
Tata
(GSM)
Call Attempt 570 529 535 575 550 546
Blocked Call Rate 10.00% 3.02% 3.93% 31.13% 4.36% 4.58%
Call Setup
Success Rate
(>=95%)
90.00% 96.98% 96.07% 68.88% 95.64% 95.42%
Dropped Call Rate
(<=2%)
5.56% 0.97% 4.83% 2.29% 3.19% 5.51%
Rx Quality (0-5)
(>=95%)
86.46% 91.11% 89.56% 85.53% 85.60% 89.50%
Handover Success
Rate (>=95%)
97.87% 96.74% 97.54% 98.01% 96.86% 95.40%
3. KPI Details
Table 3: Benchmark KPI Operator Table
KPI Idea Airtel Vodafone
Reliance
Communication
(GSM)
Aircel
Tata
(GSM)
Coverage % 95.40% 95.13% 91.08% 89.49% 93.63% 97.07%
Accessibility % 90.00% 96.98% 96.07% 68.87% 95.64% 95.42%
Retainability % 94.44% 99.03% 95.17% 97.71% 96.81% 94.49%
Mobility % 97.87% 96.74% 97.54% 98.01% 96.86% 95.40%
Rx Quality % 86.46% 91.11% 89.56% 85.33% 85.60% 89.50%
C/I % 66.67% 64.83% 65.23% 83.44% 68.13% 69.75%
4. Overall Analysis
The Drive Test results revealed that the most of the operators were failed
to meet benchmarks of network related parameters. They failed to achieve
benchmark due to High Block Call Rate, High Drop Call Rate, Low Call
Setup Success Rate & Rx Quality Samples.
Table 4: Operator Analysis Table
KPI Idea Airtel Vodafone
Reliance
(GSM)
Aircel
Tata
(GSM)
Call Attempt 570 529 535 575 550 546
Blocked Call Rate 10.00% 3.02% 3.93% 31.13% 4.36% 4.58%
Call Setup
Success Rate
(>=95%)
90.00% 96.98% 96.07% 68.88% 95.64% 95.42%
Dropped Call Rate
(<=2%)
5.56% 0.97% 4.83% 2.29% 3.19% 5.51%
Rx Quality (0-5)
(>=95%)
86.46% 91.11% 89.56% 85.53% 85.60% 89.50%
Handover Success
Rate (>=95%)
97.87% 96.74% 97.54% 98.01% 96.86% 95.40%
47
C. RF DRIVE TEST AT PUNE
1. Total seven Operators were benchmarked during the drive test at Pune. In
the following figure, the green route depicts the associated drive route. The
total drive route covered was approximately 300 kms. covered over a period
of 2 days. The drive test was carried out from 09:00 hrs. to 20:30 hrs. on 14
th
and 15
th
September 2015. In all about 3331 calls were made for all 7
operators.
DRIVE TEST ROUTE OF PUNE
C. RF DRIVE TEST AT PUNE
1. Total seven Operators were benchmarked during the drive test at Pune. In
the following figure, the green route depicts the associated drive route. The
total drive route covered was approximately 300 kms. covered over a period
of 2 days. The drive test was carried out from 09:00 hrs. to 20:30 hrs. on 14
th
and 15
th
September 2015. In all about 3331 calls were made for all 7
operators.
DRIVE TEST ROUTE OF PUNE
48
2. Key Areas Covered:
Vivanta by Taj Blue Diamond Bhudhwar Peth Rasta Peth Karve Road
Bajirao Road-BSNL Exchange Khadakwasala Pune Airport Viman Nagar
Kalyani Nagar Dandekar Nal Stop Sasoon Hospital
Shaniwar Wada Railway Station
Pune
Sadashiv Peth Hadapsar
Swargate Agakhan Street Shivaji Nagar Babdhan
Kothrud Shashtri Nagar KEM Hospital Apte Road Salapur Road
Saniper Road Mudaliar Road Koregaon Park Sanewadi
Nigdii Bridge Kalewadi Phata Hinjewadi Prabhat Nagar
Akurdi
Pimpri
Siddeswar Eng.
College
Premlok Park
Bhosari Dattwadi
Pimpri Chikhali
Road
Yamuna Nagar
Road
Chakan Market Transport Nagar
3. KPI details
Table 5: Benchmark KPI Operator Table
KPI Aircel Idea Vodafone Airtel Reliance Tata BSNL
Coverage % 83.15% 97.32% 97.74% 80.59% 69.21% 93.79% 93.08%
Accessibility % 94.19% 98.07% 96.34% 97.07% 92.89% 94.51% 95.50%
Retainability % 97.26% 98.42% 96.64% 98.49% 96.74% 97.30% 94.22%
Mobility % 98.16% 98.39% 99.16% 94.79% 98.75% 95.83% 92.55%
Rx Quality % 89.36% 89.37% 89.23% 92.28% 91.72% 93.05% 87.08%
C/I % 65.64% 69.78% 72.37% 80.11% 71.86% 63.59% 64.83%
SQI % 83.89% 84.43% 78.73% 83.34% 90.31% 86.78% 83.40%
2. Key Areas Covered:
Vivanta by Taj Blue Diamond Bhudhwar Peth Rasta Peth Karve Road
Bajirao Road-BSNL Exchange Khadakwasala Pune Airport Viman Nagar
Kalyani Nagar Dandekar Nal Stop Sasoon Hospital
Shaniwar Wada Railway Station
Pune
Sadashiv Peth Hadapsar
Swargate Agakhan Street Shivaji Nagar Babdhan
Kothrud Shashtri Nagar KEM Hospital Apte Road Salapur Road
Saniper Road Mudaliar Road Koregaon Park Sanewadi
Nigdii Bridge Kalewadi Phata Hinjewadi Prabhat Nagar
Akurdi
Pimpri
Siddeswar Eng.
College
Premlok Park
Bhosari Dattwadi
Pimpri Chikhali
Road
Yamuna Nagar
Road
Chakan Market Transport Nagar
3. KPI details
Table 5: Benchmark KPI Operator Table
KPI Aircel Idea Vodafone Airtel Reliance Tata BSNL
Coverage % 83.15% 97.32% 97.74% 80.59% 69.21% 93.79% 93.08%
Accessibility % 94.19% 98.07% 96.34% 97.07% 92.89% 94.51% 95.50%
Retainability % 97.26% 98.42% 96.64% 98.49% 96.74% 97.30% 94.22%
Mobility % 98.16% 98.39% 99.16% 94.79% 98.75% 95.83% 92.55%
Rx Quality % 89.36% 89.37% 89.23% 92.28% 91.72% 93.05% 87.08%
C/I % 65.64% 69.78% 72.37% 80.11% 71.86% 63.59% 64.83%
SQI % 83.89% 84.43% 78.73% 83.34% 90.31% 86.78% 83.40%
49
4. Overall Analysis
Table 6: Operator Analysis Table
KPI Aircel Idea Vodafone Airtel
Reliance
(GSM)
Tata
(GSM)
BSNL
Call
Attempt
465 519 464 478 464 474 467
Blocked
Call Rate
5.81% 1.93% 3.66% 2.93% 7.11% 5.49% 4.50%
Call Setup
Success
Rate (95%)
94.19% 98.07% 96.34% 97.07% 92.89% 94.51% 95.50%
Call Drop
Rate (2%)
2.74% 1.58% 3.36% 1.51% 3.26% 2.70% 5.78%
Rx Quality
(0-5) (95%)
89.36% 89.37% 89.23% 92.28% 91.72% 93.05% 87.08%
Handover
Success
Rate
98.16% 98.39% 99.16% 94.79% 98.75% 95.83% 92.55%
The Drive Test results revealed that the most of the operators failed to meet
benchmarks of network related parameters. They failed to achieve benchmark
for the parameters Block Call Rate, Call Drop Rate, Call Setup Success Rate &
Rx Quality Samples.
4. Overall Analysis
Table 6: Operator Analysis Table
KPI Aircel Idea Vodafone Airtel
Reliance
(GSM)
Tata
(GSM)
BSNL
Call
Attempt
465 519 464 478 464 474 467
Blocked
Call Rate
5.81% 1.93% 3.66% 2.93% 7.11% 5.49% 4.50%
Call Setup
Success
Rate (95%)
94.19% 98.07% 96.34% 97.07% 92.89% 94.51% 95.50%
Call Drop
Rate (2%)
2.74% 1.58% 3.36% 1.51% 3.26% 2.70% 5.78%
Rx Quality
(0-5) (95%)
89.36% 89.37% 89.23% 92.28% 91.72% 93.05% 87.08%
Handover
Success
Rate
98.16% 98.39% 99.16% 94.79% 98.75% 95.83% 92.55%
The Drive Test results revealed that the most of the operators failed to meet
benchmarks of network related parameters. They failed to achieve benchmark
for the parameters Block Call Rate, Call Drop Rate, Call Setup Success Rate &
Rx Quality Samples.
50
D. RF DRIVE TEST AT KOLKATA
1. In the drive test at Kolkata, ten operators were benchmarked as shown in
the figure below. Route map was designed in such a way that all the major
roads were covered as part of audit. The route also included poor coverage
areas identified during past drive tests. Special emphasis was given to those
areas where the customer complaints received were on the higher side in the
past 2-3 months. Routes including major and secondary roads/streets,
commercial and residential areas, and very congested areas were also covered.
The total drive route covered was approximately 300 kms. covered over a
period of 2 days. The drive test was carried out from 08:30 hrs. to 20:30 hrs.
on 15
th and 16
th September 2015.
DRIVE TEST ROUTE OF KOLKATA
D. RF DRIVE TEST AT KOLKATA
1. In the drive test at Kolkata, ten operators were benchmarked as shown in
the figure below. Route map was designed in such a way that all the major
roads were covered as part of audit. The route also included poor coverage
areas identified during past drive tests. Special emphasis was given to those
areas where the customer complaints received were on the higher side in the
past 2-3 months. Routes including major and secondary roads/streets,
commercial and residential areas, and very congested areas were also covered.
The total drive route covered was approximately 300 kms. covered over a
period of 2 days. The drive test was carried out from 08:30 hrs. to 20:30 hrs.
on 15
th and 16
th September 2015.
DRIVE TEST ROUTE OF KOLKATA
51
2. Key Areas Covered:
Baguihati More Airport Gate No.1 Jassor Road Dum Dum Road
Chiriamore B.T Road Paikpara Paikpara Bus Stand
Tala Park Dutta Bagan R.G Kar Hospital Kolkata Station
Shyam Bazar 5 point Crossing Raja Manindra
Chandra College
Rajballav Para
Bag Bazar Kumartuli Sova Bazar Beniatola
Ahiritola Malapara Ganesh Talkish Girish Park
Jorasanko M G Road APC Road Rajabazar
Narkeldanga Main
Road
CIT Road Belelghata Main
Road
Sealdah Stn.
BB Ganguly St. Amherst Street Ganesh Ch. Avenue C R Avenue
Lalbazar B B D Bag Writes’ Building Stock Exchange
India Exchange Place Brabourn Road Bara Bazar Howrah Bridge
Howrah Station Howrah Mallick
Bazar
Nabannya 2nd Hooghly Bridge
Strand Road Eden Garden Road Auckland Road Strand Road
K S Roy Road Govt. Place West Rani Rasmoni Road Daffrin Road
Mayo Road Red Road Casurina Avenue Khidderpore Road
Hastings Karl Marx Sarani
Kiddirpore
Airport Gate No.1 Kaikhali More
Narayanpur Road Salua More Dashdrone Road Dashdrone More
Rajarhat Baguihati Road Chinar Park VIP Road
Keshtopur Adarsha Pally Road Newtown Express
Way
New Town
Salt Lake Newtown Road Island No. 8 AJ Block Baisakhi
Circle
PNB More CA Island City Centre-I Lalkuthi Island
Karunamoyee-Tank
No. 13
EM Bypass Salt Lake Stadium Beleghata
EZCC Big Bazar Stadium Island Canal Side Road
Wipro College More Godrej Water side EP-GP Block Godrej
Water side
Webel More Nicco Park Chingrighata Science City
Park Circus Dr. Sundari Mohan
Avenue
AJC Bose Road Park Street
Jawaharlal Nehru
Road
Theatre Road Park Circus Lee Road/ Sarat
Bose Road
Elgin Road Sambhunath Pandit
Road
D L Khan Road Zoo / National
Library
Ebalpur Mominpur Judges Court Road Hastings Park Road
Belvedere Road Baker Road Bhawani Bhawan Gopal Nagar
Kalighat Road Patuapara Ramesh Mitra Road Sarat Bose Road
Padmapukur Road Ballygunge Circular
Road
Richi Road Deodar Street
Ballygunge Phari Hazra Road Hazra Manohar
Pukur Road
Aswaii Dutta Road
Panditia Road Dover Lane/Garcha
Road
Garia hat Road Bondel Road
Picnic Garden Road Diamond Harbour Ruby -Gariahat Rasbehari
Chetla Alipore Road Alipore Petrol Pump Burdwan Road
2. Key Areas Covered:
Baguihati More Airport Gate No.1 Jassor Road Dum Dum Road
Chiriamore B.T Road Paikpara Paikpara Bus Stand
Tala Park Dutta Bagan R.G Kar Hospital Kolkata Station
Shyam Bazar 5 point Crossing Raja Manindra
Chandra College
Rajballav Para
Bag Bazar Kumartuli Sova Bazar Beniatola
Ahiritola Malapara Ganesh Talkish Girish Park
Jorasanko M G Road APC Road Rajabazar
Narkeldanga Main
Road
CIT Road Belelghata Main
Road
Sealdah Stn.
BB Ganguly St. Amherst Street Ganesh Ch. Avenue C R Avenue
Lalbazar B B D Bag Writes’ Building Stock Exchange
India Exchange Place Brabourn Road Bara Bazar Howrah Bridge
Howrah Station Howrah Mallick
Bazar
Nabannya 2nd Hooghly Bridge
Strand Road Eden Garden Road Auckland Road Strand Road
K S Roy Road Govt. Place West Rani Rasmoni Road Daffrin Road
Mayo Road Red Road Casurina Avenue Khidderpore Road
Hastings Karl Marx Sarani
Kiddirpore
Airport Gate No.1 Kaikhali More
Narayanpur Road Salua More Dashdrone Road Dashdrone More
Rajarhat Baguihati Road Chinar Park VIP Road
Keshtopur Adarsha Pally Road Newtown Express
Way
New Town
Salt Lake Newtown Road Island No. 8 AJ Block Baisakhi
Circle
PNB More CA Island City Centre-I Lalkuthi Island
Karunamoyee-Tank
No. 13
EM Bypass Salt Lake Stadium Beleghata
EZCC Big Bazar Stadium Island Canal Side Road
Wipro College More Godrej Water side EP-GP Block Godrej
Water side
Webel More Nicco Park Chingrighata Science City
Park Circus Dr. Sundari Mohan
Avenue
AJC Bose Road Park Street
Jawaharlal Nehru
Road
Theatre Road Park Circus Lee Road/ Sarat
Bose Road
Elgin Road Sambhunath Pandit
Road
D L Khan Road Zoo / National
Library
Ebalpur Mominpur Judges Court Road Hastings Park Road
Belvedere Road Baker Road Bhawani Bhawan Gopal Nagar
Kalighat Road Patuapara Ramesh Mitra Road Sarat Bose Road
Padmapukur Road Ballygunge Circular
Road
Richi Road Deodar Street
Ballygunge Phari Hazra Road Hazra Manohar
Pukur Road
Aswaii Dutta Road
Panditia Road Dover Lane/Garcha
Road
Garia hat Road Bondel Road
Picnic Garden Road Diamond Harbour Ruby -Gariahat Rasbehari
Chetla Alipore Road Alipore Petrol Pump Burdwan Road
52
3. KPI Details
Table 7: Benchmark KPI Operator Table
Operator Aircel Airtel BSNL Idea MTS Reliance
CDMA
Reliance
GSM
Tata
CDMA
Tata
GSM
Vodafone
Coverage
Rate
89.57% 95.73% 92.35% 80.28% 98.05% 91.97% 77.65% 89.45% 76.14% 96.62%
CSSR 89.86% 81.24% 96.28% 89.44% 98.06% 98.89% 96.05% 99.00% 95.40% 97.03%
CCSR 97.40% 98.15% 94.40% 99.52% 98.42% 97.19% 98.82% 97.99% 97.69% 97.51%
RxQuality 83.78% 87.44% 86.14% 86.43% 95.64% 97.10% 90.70% 95.10% 84.87% 92.78%
C/I 71.09% 84.41% 74.80% 75.34% 99.90% 98.37% 85.97% 98.31% 72.63% 86.43%
4. Overall Analysis
Table 8: Operator Analysis Table
The Drive Test results revealed that the most of the operators failed to meet
the Rx quality parameter, Blocked call rate and Dropped call rate.
3. KPI Details
Table 7: Benchmark KPI Operator Table
Operator Aircel Airtel BSNL Idea MTS Reliance
CDMA
Reliance
GSM
Tata
CDMA
Tata
GSM
Vodafone
Coverage
Rate
89.57% 95.73% 92.35% 80.28% 98.05% 91.97% 77.65% 89.45% 76.14% 96.62%
CSSR 89.86% 81.24% 96.28% 89.44% 98.06% 98.89% 96.05% 99.00% 95.40% 97.03%
CCSR 97.40% 98.15% 94.40% 99.52% 98.42% 97.19% 98.82% 97.99% 97.69% 97.51%
RxQuality 83.78% 87.44% 86.14% 86.43% 95.64% 97.10% 90.70% 95.10% 84.87% 92.78%
C/I 71.09% 84.41% 74.80% 75.34% 99.90% 98.37% 85.97% 98.31% 72.63% 86.43%
4. Overall Analysis
Table 8: Operator Analysis Table
The Drive Test results revealed that the most of the operators failed to meet
the Rx quality parameter, Blocked call rate and Dropped call rate.
53
E. RF DRIVE TEST AT BHUBANESHWAR
1. In the drive test at Bhubaneshwar, total ten operators were benchmarked
which is shown as below: Route map was designed in such a way that all the
major roads were covered as part of audit. The route also included poor
coverage areas identified during past drive tests. Routes including major and
secondary roads/streets, commercial and residential areas, and very
congested areas were also covered. The total drive route covered was
approximately 300 kms. covered over a period of 2 days. The drive test was
carried out from 08:30 hrs. to 20:30 hrs. on 18
th and 19
th September 2015.
Blue colour road represents Highway
Red colour road represents Major Road
Green colour road represents Within city
DRIVE TEST ROUTE OF BHUBANESHWAR
E. RF DRIVE TEST AT BHUBANESHWAR
1. In the drive test at Bhubaneshwar, total ten operators were benchmarked
which is shown as below: Route map was designed in such a way that all the
major roads were covered as part of audit. The route also included poor
coverage areas identified during past drive tests. Routes including major and
secondary roads/streets, commercial and residential areas, and very
congested areas were also covered. The total drive route covered was
approximately 300 kms. covered over a period of 2 days. The drive test was
carried out from 08:30 hrs. to 20:30 hrs. on 18
th and 19
th September 2015.
Blue colour road represents Highway
Red colour road represents Major Road
Green colour road represents Within city
DRIVE TEST ROUTE OF BHUBANESHWAR
54
2. Key Areas Covered:
Within City Major Road Highway Office / Shopping
Complex
BSNL Telephone
Exchange
Puri City Bhubaneswar Office Complex:
BSNL Telephone
Exchange-Puri
Hans coco palm
beach resort
GHITM
College
Lingipur BSNL Telephone
Bhawan-
Bhubaneswar
Sea beach police
station-
Lakhia Toll
Gate
CIFA Shopping Complex:
I.D. Market
Mayfair Hotel Konark-
Saroda
Siula Nayapalli
Sadar Bedapur Pipili Bhubaneswar,Medi
cal Square
Police Station GOP Mangalpur Konark
Pokhari Temple Nimapada Tesipur
Puri Entrance Khelar Sakhigopal
Purussottamnagar PIPILI Chandanpur
IOCL Fuel station Hatachowk
(Pipili)
Puri
ChhagapatharaNayag
arh
Mathasahi Khurda
New Rajawati Kanti Loknathpur
Devtor Colony Jatni Pubusahi
Lakhanpur Badatota Baghmari
Sagardiha Khurda Pichukuli
Khandapada Road Rameswar Sunakhala
Nabard Office Pandanayaga
rh
Bolagarh
NandanKanan Road Nirakarpur Purussottamp
ur
Patia square Raigiri Nayagarh
Press chak Bhubaneswar
Kalinga Enclave Jatni
Dharmvihar Gangapada
Kapila Prasad Ogolopada
Samantarapur Khurda
Lingipur Kanapura
Satya Vihar Jankia Road
Kesura Rameswar
Crown Hotel
2. Key Areas Covered:
Within City Major Road Highway Office / Shopping
Complex
BSNL Telephone
Exchange
Puri City Bhubaneswar Office Complex:
BSNL Telephone
Exchange-Puri
Hans coco palm
beach resort
GHITM
College
Lingipur BSNL Telephone
Bhawan-
Bhubaneswar
Sea beach police
station-
Lakhia Toll
Gate
CIFA Shopping Complex:
I.D. Market
Mayfair Hotel Konark-
Saroda
Siula Nayapalli
Sadar Bedapur Pipili Bhubaneswar,Medi
cal Square
Police Station GOP Mangalpur Konark
Pokhari Temple Nimapada Tesipur
Puri Entrance Khelar Sakhigopal
Purussottamnagar PIPILI Chandanpur
IOCL Fuel station Hatachowk
(Pipili)
Puri
ChhagapatharaNayag
arh
Mathasahi Khurda
New Rajawati Kanti Loknathpur
Devtor Colony Jatni Pubusahi
Lakhanpur Badatota Baghmari
Sagardiha Khurda Pichukuli
Khandapada Road Rameswar Sunakhala
Nabard Office Pandanayaga
rh
Bolagarh
NandanKanan Road Nirakarpur Purussottamp
ur
Patia square Raigiri Nayagarh
Press chak Bhubaneswar
Kalinga Enclave Jatni
Dharmvihar Gangapada
Kapila Prasad Ogolopada
Samantarapur Khurda
Lingipur Kanapura
Satya Vihar Jankia Road
Kesura Rameswar
Crown Hotel
55
3. KPI details
Table 9: Benchmark KPI Operator Table
Operator Aircel Airtel BSNL Idea Reliance
CDMA
Reliance
GSM
Tata
CDMA
Tata
GSM
Vodafone
Coverage
Rate
72.13% 91.33% 90.23% 81.30% 59.00% 87.57% 67.33% 78.77% 79.47%
CSSR
93.64% 96.46% 98.23% 95.32% 96.44% 93.33% 89.83% 90.72% 93.49%
CCSR
93.71% 97.99% 95.41% 99.05% 90.78% 94.18% 93.20% 98.71% 96.61%
RxQuality
84.45% 88.37% 86.23% 81.66% 87.59% 84.12% 87.77% 89.00% 91.63%
C/I
74.86% 78.03% 74.82% 69.46% 95.73% 73.09% 94.70% 83.10% 87.67%
4. Overall Analysis
Table 10: Operator Analysis Table
KPI Aircel Airtel BSNL Idea Reliance
CDMA
Reliance
GSM
Tata
CDMA
Tata
GSM
Vodafone
Call
Attempt
347 334 337 359 274 327 309 341 339
Blocked
Call Rate
6.36% 3.54% 1.77% 4.68% 3.56% 6.67% 10.17% 9.28% 6.51%
Call
Setup
Success
Rate
(95%)
93.64% 96.46% 98.23% 95.32% 96.44% 93.33% 89.83% 90.72% 93.49%
Call Drop
Rate (2%)
6.29% 2.01% 4.59% 0.95% 9.22% 5.82% 6.80% 1.29% 3.39%
Rx
Quality
%
84.45% 88.37% 86.23% 81.66% 87.59% 84.12% 87.77% 89.00% 91.63%
Handover
Success
Rate
96.88% 94.93% 95.55% 97.02% 100.00% 93.56% 100.00% 95.36% 97.43%
The Drive Test results revealed that the most of the operators failed to meet
the Rx quality parameter, Blocked call rate and Dropped call rate.
3. KPI details
Table 9: Benchmark KPI Operator Table
Operator Aircel Airtel BSNL Idea Reliance
CDMA
Reliance
GSM
Tata
CDMA
Tata
GSM
Vodafone
Coverage
Rate
72.13% 91.33% 90.23% 81.30% 59.00% 87.57% 67.33% 78.77% 79.47%
CSSR
93.64% 96.46% 98.23% 95.32% 96.44% 93.33% 89.83% 90.72% 93.49%
CCSR
93.71% 97.99% 95.41% 99.05% 90.78% 94.18% 93.20% 98.71% 96.61%
RxQuality
84.45% 88.37% 86.23% 81.66% 87.59% 84.12% 87.77% 89.00% 91.63%
C/I
74.86% 78.03% 74.82% 69.46% 95.73% 73.09% 94.70% 83.10% 87.67%
4. Overall Analysis
Table 10: Operator Analysis Table
KPI Aircel Airtel BSNL Idea Reliance
CDMA
Reliance
GSM
Tata
CDMA
Tata
GSM
Vodafone
Call
Attempt
347 334 337 359 274 327 309 341 339
Blocked
Call Rate
6.36% 3.54% 1.77% 4.68% 3.56% 6.67% 10.17% 9.28% 6.51%
Call
Setup
Success
Rate
(95%)
93.64% 96.46% 98.23% 95.32% 96.44% 93.33% 89.83% 90.72% 93.49%
Call Drop
Rate (2%)
6.29% 2.01% 4.59% 0.95% 9.22% 5.82% 6.80% 1.29% 3.39%
Rx
Quality
%
84.45% 88.37% 86.23% 81.66% 87.59% 84.12% 87.77% 89.00% 91.63%
Handover
Success
Rate
96.88% 94.93% 95.55% 97.02% 100.00% 93.56% 100.00% 95.36% 97.43%
The Drive Test results revealed that the most of the operators failed to meet
the Rx quality parameter, Blocked call rate and Dropped call rate.
56
D. RF DRIVE TEST AT SURAT
1. Total seven Operators were benchmarked in the drive test at Surat. There
was no coverage of Aircel in Surat city. In the following figure, the green route
depicts the associated drive route. The total drive route covered was
approximately 200 kms covered over a period of 2 days. The drive test was
carried out from 09:00 hrs. to 20:30 hrs. on 16
th and 17
th September 2015.
In all, about 1967 calls were made for all 7 operators.
2. Key Areas Covered:
Surat Railway
Station Ring Road Hazira
Middle Ring Road Textile Market Rander Road
Udhna Railway Station Mithi Khadi Road Katargam
Guru Nanak Marg Adajan Road SH-170
Bombay Hotel Road Punnagam NH-6
Canal Raod ITC Market Khodiyar Nagar
Athwa Gate Shimla Nagar Ved Road
Bhatha Road Mota Baracha Makki Pool
DRIVE TEST ROUTE OF SURAT
D. RF DRIVE TEST AT SURAT
1. Total seven Operators were benchmarked in the drive test at Surat. There
was no coverage of Aircel in Surat city. In the following figure, the green route
depicts the associated drive route. The total drive route covered was
approximately 200 kms covered over a period of 2 days. The drive test was
carried out from 09:00 hrs. to 20:30 hrs. on 16
th and 17
th September 2015.
In all, about 1967 calls were made for all 7 operators.
2. Key Areas Covered:
Surat Railway
Station Ring Road Hazira
Middle Ring Road Textile Market Rander Road
Udhna Railway Station Mithi Khadi Road Katargam
Guru Nanak Marg Adajan Road SH-170
Bombay Hotel Road Punnagam NH-6
Canal Raod ITC Market Khodiyar Nagar
Athwa Gate Shimla Nagar Ved Road
Bhatha Road Mota Baracha Makki Pool
DRIVE TEST ROUTE OF SURAT
57
3. KPI details
Table 11: Benchmark KPI Operator Table
KPI BSNL Idea Vodafone Airtel Reliance Tata
Coverage % 93.50% 98.73% 89.80% 90.72% 21.69% 78.47%
Accessibility % 84.59% 78.72% 97.63% 77.57% 81.61% 73.00%
Retainability % 97.02% 99.26% 98.38% 97.97% 61.03% 97.15%
Mobility % 96.01% 98.05% 96.79% 96.12% 96.40% 98.55%
Rx Quality % 89.85% 87.68% 88.68% 88.65% 74.82% 88.75%
SQI % 86.44% 82.59% 82.69% 84.27% 77.82% 84.12%
C/I % 67.91% 82.23% 81.29% 85.64% 60.70% 79.43%
4. Overall Analysis
Table 12: Operator Analysis Table
KPI BSNL Idea Vodafone Airtel
Reliance
(GSM)
Tata
(GSM)
Call Attempt 305 343 253 263 261 337
Blocked Call Rate 15.41% 21.28% 2.37% 22.43% 18.39% 27.00%
Call Setup Success
Rate (95%)
84.59% 78.72% 97.63% 77.57% 81.61% 73.00%
Call Drop Rate (2%) 2.98% 0.74% 1.62% 2.03% 38.97% 2.85%
Rx Quality (0-5)
(95%)
89.85% 87.68% 88.68% 88.65% 74.82% 88.75%
Handover Success
Rate
97.85% 98.65% 94.15% 95.94% 96.86% 94.12%
The Drive Test results revealed that the most of the operators failed to meet
the Rx quality parameter, Blocked call rate and Dropped call rate.
3. KPI details
Table 11: Benchmark KPI Operator Table
KPI BSNL Idea Vodafone Airtel Reliance Tata
Coverage % 93.50% 98.73% 89.80% 90.72% 21.69% 78.47%
Accessibility % 84.59% 78.72% 97.63% 77.57% 81.61% 73.00%
Retainability % 97.02% 99.26% 98.38% 97.97% 61.03% 97.15%
Mobility % 96.01% 98.05% 96.79% 96.12% 96.40% 98.55%
Rx Quality % 89.85% 87.68% 88.68% 88.65% 74.82% 88.75%
SQI % 86.44% 82.59% 82.69% 84.27% 77.82% 84.12%
C/I % 67.91% 82.23% 81.29% 85.64% 60.70% 79.43%
4. Overall Analysis
Table 12: Operator Analysis Table
KPI BSNL Idea Vodafone Airtel
Reliance
(GSM)
Tata
(GSM)
Call Attempt 305 343 253 263 261 337
Blocked Call Rate 15.41% 21.28% 2.37% 22.43% 18.39% 27.00%
Call Setup Success
Rate (95%)
84.59% 78.72% 97.63% 77.57% 81.61% 73.00%
Call Drop Rate (2%) 2.98% 0.74% 1.62% 2.03% 38.97% 2.85%
Rx Quality (0-5)
(95%)
89.85% 87.68% 88.68% 88.65% 74.82% 88.75%
Handover Success
Rate
97.85% 98.65% 94.15% 95.94% 96.86% 94.12%
The Drive Test results revealed that the most of the operators failed to meet
the Rx quality parameter, Blocked call rate and Dropped call rate.
58
Annexure- V
Common Terminologies
1. The aggregate calls including call attempts offered or carried by some
defined parts of a network, such as a group of circuits or switches with
account being taken of both the number of calls and their duration is referred
to as traffic.
2. In traffic engineering, any occupancy of a circuit or device caused
directly or indirectly by a subscriber making or attempting to make use of the
system is regarded as a call.
3. The amount of traffic carried by a group of circuits will always exhibit
daily and seasonal variations. Of more significance, however, are the changes
that occur with the time of the day, leading to the concept of the busy hour
when the traffic carried is at its peak. During such a period, the number of
call arrivals and departures are essentially equal and the system is said to be
in a state of statistical equilibrium. In this state, the average number of calls
existing simultaneously gives a measure of the density of the traffic.
Figure 1: Traffic carried, traffic lost and traffic offered
14
14
The Effects of Propagation Environments on Cellular Network Performance, Joseph M. Mom, Nathaniel S. Tarkaa, and
Cosmas I. Ani, American Journal of Engineering Research, 2013
Annexure- V
Common Terminologies
1. The aggregate calls including call attempts offered or carried by some
defined parts of a network, such as a group of circuits or switches with
account being taken of both the number of calls and their duration is referred
to as traffic.
2. In traffic engineering, any occupancy of a circuit or device caused
directly or indirectly by a subscriber making or attempting to make use of the
system is regarded as a call.
3. The amount of traffic carried by a group of circuits will always exhibit
daily and seasonal variations. Of more significance, however, are the changes
that occur with the time of the day, leading to the concept of the busy hour
when the traffic carried is at its peak. During such a period, the number of
call arrivals and departures are essentially equal and the system is said to be
in a state of statistical equilibrium. In this state, the average number of calls
existing simultaneously gives a measure of the density of the traffic.
Figure 1: Traffic carried, traffic lost and traffic offered
14
14
The Effects of Propagation Environments on Cellular Network Performance, Joseph M. Mom, Nathaniel S. Tarkaa, and
Cosmas I. Ani, American Journal of Engineering Research, 2013
59
4. Traffic carried = Traffic Offered – Traffic Lost
The traffic carried is the traffic that actually occupies a group of trunks or
switches. The average number of simultaneously occupied trunks or switches
gives its average intensity in Erlangs. Traffic intensity is the load presented to
a system, that is, the amount or volume of traffic carried by the group of
trunks or switches and is given by:
A = λ*h
λ= mean rate of calls attempted per unit time, h= mean holding time per
successful call, A= average number of calls arriving during average holding
period, for normalized λ and is expressed in Erlang-hours.
5. Call arrival rate, λt refers to the traffic offered expressed as the number
of call attempts per unit time which is given as]:
?P = 0QI>AN KB %=HH #PPAILPO/ 7JEP 6EIA
6. Busy hour traffic is the period which has the highest amount of
blocked or lost calls. If the dimensioning of the equipment at this period is
correct and the blocked calls can be minimized, all other non-busy hour traffic
should then be handled satisfactorily.
7. Channel Utilization The channel utilization is a measure of trunking
efficiency and is defined as:
? = 6N=BBE? +JPAJOEPU/ 0QI>AN KB ?ℎ=JJAHO
8. Cellular network is a radio network distributed over land areas called
cells and each cell is serviced by a station called base station. Each cell is
represented by hexagonal shape, each cell use different set of frequencies from
its neighboring cells. Normally a practical cell is considered to be a circle but
to think on it ideally the boundary portions of any radial cell cannot be
captured easily due to the gap after integration of more than one cell. So on
part of this a hexagon is assumed to be the largest area covering the practical
cell and capturing the gaps after integration of cells too.
4. Traffic carried = Traffic Offered – Traffic Lost
The traffic carried is the traffic that actually occupies a group of trunks or
switches. The average number of simultaneously occupied trunks or switches
gives its average intensity in Erlangs. Traffic intensity is the load presented to
a system, that is, the amount or volume of traffic carried by the group of
trunks or switches and is given by:
A = λ*h
λ= mean rate of calls attempted per unit time, h= mean holding time per
successful call, A= average number of calls arriving during average holding
period, for normalized λ and is expressed in Erlang-hours.
5. Call arrival rate, λt refers to the traffic offered expressed as the number
of call attempts per unit time which is given as]:
?P = 0QI>AN KB %=HH #PPAILPO/ 7JEP 6EIA
6. Busy hour traffic is the period which has the highest amount of
blocked or lost calls. If the dimensioning of the equipment at this period is
correct and the blocked calls can be minimized, all other non-busy hour traffic
should then be handled satisfactorily.
7. Channel Utilization The channel utilization is a measure of trunking
efficiency and is defined as:
? = 6N=BBE? +JPAJOEPU/ 0QI>AN KB ?ℎ=JJAHO
8. Cellular network is a radio network distributed over land areas called
cells and each cell is serviced by a station called base station. Each cell is
represented by hexagonal shape, each cell use different set of frequencies from
its neighboring cells. Normally a practical cell is considered to be a circle but
to think on it ideally the boundary portions of any radial cell cannot be
captured easily due to the gap after integration of more than one cell. So on
part of this a hexagon is assumed to be the largest area covering the practical
cell and capturing the gaps after integration of cells too.
60
In cellular network blocking occurs when base station has no free channels
to allocate mobile users. One distinguishes between two kinds of blocking, the
first is called new call blocking which refers to blocking of new calls, and the
second is called handoff blocking which refers to blocking of ongoing calls due
to the mobility of the users.
Figure 2: Mobile Cell structure
9. The Geographical area is divided into smaller areas in the shape of
hexagon. These hexagonal areas are called as cells. A base station (BS) is
located at each cell. The mobile terminal (MT) within that region is served by
this BS. Before a mobile user can communicate with other mobile user in the
network, a group channels should be assigned. The cell size plays a major
role in the channel utilization. A user has to cross several cells during the
ongoing conversation; the call has to be transferred from one cell to another
to achieve the call continuation during boundary crossing. Here comes the
role of handoff. Transferring the active call from one cell to another without
disturbing the call is called as the process of handoff.
10. A typical Cellular network is shown in the figure 3 below. A limited
frequency is allocated .But it is very successfully utilized because of the
frequency reuse concept. To avoid the interference while neighboring cells are
utilizing the same frequency, the group of channels assigned to one cell
should be different from the neighboring cells.
In cellular network blocking occurs when base station has no free channels
to allocate mobile users. One distinguishes between two kinds of blocking, the
first is called new call blocking which refers to blocking of new calls, and the
second is called handoff blocking which refers to blocking of ongoing calls due
to the mobility of the users.
Figure 2: Mobile Cell structure
9. The Geographical area is divided into smaller areas in the shape of
hexagon. These hexagonal areas are called as cells. A base station (BS) is
located at each cell. The mobile terminal (MT) within that region is served by
this BS. Before a mobile user can communicate with other mobile user in the
network, a group channels should be assigned. The cell size plays a major
role in the channel utilization. A user has to cross several cells during the
ongoing conversation; the call has to be transferred from one cell to another
to achieve the call continuation during boundary crossing. Here comes the
role of handoff. Transferring the active call from one cell to another without
disturbing the call is called as the process of handoff.
10. A typical Cellular network is shown in the figure 3 below. A limited
frequency is allocated .But it is very successfully utilized because of the
frequency reuse concept. To avoid the interference while neighboring cells are
utilizing the same frequency, the group of channels assigned to one cell
should be different from the neighboring cells.
61
11. If the MS is traveling while the call is in progress, the MS need to get a
new channel from the neighboring BS to continue the call without dropping.
The MSs located in the cell share the available channels. The multiple Access
Methods and channel allocation schemes govern the sharing and allocating
the channels in the cell, respectively.
Figure 3: Cellular Hierarchy
15
12. Handoff is the process of changing the channel (frequency, time slot,
spreading code, or combination of them) associated with the current
connection while a call is in progress. Usually, handoff occurs when the
mobile terminal crosses a cell boundary or when there is deterioration in
quality of the signal in the current channel.
13. Handoff initiation: Handoff decision is based on received signal
strengths (RSS) from current BS and neighboring BSs. Handoff initiation is
the process of deciding when a request to a handoff. Handoff is based on
received signal strength (RSS) from the current base station and neighboring
base station. The RSS of BTS1decreases as the mobile station moves away
15
Decreasing call blocking rate by using optimization technique, Vinay Prakash Sriwastava, Jalneesh Singh, Vinay Kumar
Verma, International Journal of Scientific and Research Publication, June 2014
11. If the MS is traveling while the call is in progress, the MS need to get a
new channel from the neighboring BS to continue the call without dropping.
The MSs located in the cell share the available channels. The multiple Access
Methods and channel allocation schemes govern the sharing and allocating
the channels in the cell, respectively.
Figure 3: Cellular Hierarchy
15
12. Handoff is the process of changing the channel (frequency, time slot,
spreading code, or combination of them) associated with the current
connection while a call is in progress. Usually, handoff occurs when the
mobile terminal crosses a cell boundary or when there is deterioration in
quality of the signal in the current channel.
13. Handoff initiation: Handoff decision is based on received signal
strengths (RSS) from current BS and neighboring BSs. Handoff initiation is
the process of deciding when a request to a handoff. Handoff is based on
received signal strength (RSS) from the current base station and neighboring
base station. The RSS of BTS1decreases as the mobile station moves away
15
Decreasing call blocking rate by using optimization technique, Vinay Prakash Sriwastava, Jalneesh Singh, Vinay Kumar
Verma, International Journal of Scientific and Research Publication, June 2014
62
and increases as the mobile station get closer to BTS2 as a result of the signal
propagation.
14. Once a call is established, the set-up channel is not used again during
the call period. Therefore, handoff is always implemented on the voice
channel. The value of implementing handoffs is dependent on the size of the
cell. If a call is dropped in a fringe area, the customer simply redials and
reconnects the call. There are two types of handoff: A. Based on signal
strength. B. Based on carrier-to-interference ratio.
15. There are three critical factors that impact the performance of both
voice and data networks: radio frequency (RF) signal level (in both uplink and
downlink; level of radio interference (also in both uplink and downlink); and
available radio channel capacity.
16. To provide any sort of service, the Received Signal Strength Indicator
(RSSI) of both uplink and downlink transmissions must be sufficiently above
the level of thermal RF noise to allow for successful recovery of the modulated
information stream. The ratio of the desired RF carrier signal power to the
linear sum of interference power is called C/I.
17. The distance travelled by the signal is dependent upon the radio
propagation characteristics in the given area. Radio propagation varies from
region to region and should be studied carefully, before predictions for both
coverage and capacity are made.
18. The signal that is transmitted from the transmitting antenna (BTS/MS)
and received by the receiving antenna (MS/BTS) travels a small and complex
path. This signal is exposed to a variety of man-made structures, passes
through different types of terrain, and is affected by the combination of
propagation environments. All these factors contribute to variation in the
signal level, so varying the signal coverage and quality in the network.
and increases as the mobile station get closer to BTS2 as a result of the signal
propagation.
14. Once a call is established, the set-up channel is not used again during
the call period. Therefore, handoff is always implemented on the voice
channel. The value of implementing handoffs is dependent on the size of the
cell. If a call is dropped in a fringe area, the customer simply redials and
reconnects the call. There are two types of handoff: A. Based on signal
strength. B. Based on carrier-to-interference ratio.
15. There are three critical factors that impact the performance of both
voice and data networks: radio frequency (RF) signal level (in both uplink and
downlink; level of radio interference (also in both uplink and downlink); and
available radio channel capacity.
16. To provide any sort of service, the Received Signal Strength Indicator
(RSSI) of both uplink and downlink transmissions must be sufficiently above
the level of thermal RF noise to allow for successful recovery of the modulated
information stream. The ratio of the desired RF carrier signal power to the
linear sum of interference power is called C/I.
17. The distance travelled by the signal is dependent upon the radio
propagation characteristics in the given area. Radio propagation varies from
region to region and should be studied carefully, before predictions for both
coverage and capacity are made.
18. The signal that is transmitted from the transmitting antenna (BTS/MS)
and received by the receiving antenna (MS/BTS) travels a small and complex
path. This signal is exposed to a variety of man-made structures, passes
through different types of terrain, and is affected by the combination of
propagation environments. All these factors contribute to variation in the
signal level, so varying the signal coverage and quality in the network.
63
Moreover, any signal that is transmitted by antenna will suffer attenuation
during its journey in free space.
19. The received signal strength by an MS at any given point in space will
be inversely proportional to the distance covered by the signal. Unlike fixed
point-to-point systems, there are no simple formulas that can be used to
determine anticipated path loss. By the nature of the continuously varying
environment of the mobile subscriber, there is a very complicated relationship
between the mobile telephone received signal strength and time. As in the
typical call placed form a moving car, the signal variation is a formidable
problem that can be approached only on a statistical level. The received signal
by an MS could be considered as consisting of three components, namely a
free space path loss component, a slow fading component due to
shadowing, and a fast fading component due to vehicle velocity.
Moreover, any signal that is transmitted by antenna will suffer attenuation
during its journey in free space.
19. The received signal strength by an MS at any given point in space will
be inversely proportional to the distance covered by the signal. Unlike fixed
point-to-point systems, there are no simple formulas that can be used to
determine anticipated path loss. By the nature of the continuously varying
environment of the mobile subscriber, there is a very complicated relationship
between the mobile telephone received signal strength and time. As in the
typical call placed form a moving car, the signal variation is a formidable
problem that can be approached only on a statistical level. The received signal
by an MS could be considered as consisting of three components, namely a
free space path loss component, a slow fading component due to
shadowing, and a fast fading component due to vehicle velocity.
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