CELLULAR CONCEPT-SYSTEM DESIGN FUNDAMENTALS

Frequency reuse-Channel assignment strategies-Handoff strategies :Prioritizing handoffs, practical handoff considerations. Interference and System Capacity: Co-channel Interference and system capacity -Channel planning for wireless systems, Adjacent channel Interference, Power control for reducing interference, Trunking and Grade Of Service. Improving coverage and capacity in Cellular Systems: Cell Splitting, Sectoring.

1. THE CELLULAR CONCEPT-SYSTEM
DESIGN FUNDAMENTALS

2. Dr.C.Helen Sulochana, Prof/ ECE,
SXCCE, Nagercoil

Introduction-Frequency reuse-Channel assignment strategies-Handoff
strategies :Prioritizing handoffs, practical handoff considerations.
Interference and System Capacity: Co-channel Interference and system
capacity -Channel planning for wireless systems, Adjacent channel
Interference, Power control for reducing interference, Trunking and
Grade Of Service. Improving coverage and capacity in Cellular Systems:
Cell Splitting, Sectoring.
CO –Design the cellular system.

3. Cellular architecture
Goals of a Cellular System
High capacity
Large coverage area
Efficient use of limited spectrum
Early mobile system
Single Tx, high power, and tall tower(single cell)
Low cost
Large coverage area
Small no of users
Poor spectrum utilization
Low user capacity
Dr.C.Helen Sulochana, Prof/ ECE,
SXCCE, Nagercoil

4. Cellular concept
- Solves the problem of spectral congestion and user capacity.-
frequency reuse
- Consists of many low power transmitter(small cells)
- Each cell covers only a small portion of the service area
- Base station in each cell is allocated a portion of the total number of
channels
-Nearby base stations are assigned different groups of channels so that
interference between base station is minimized
-.
Dr.C.Helen Sulochana, Prof/ ECE,
SXCCE, Nagercoil

5. Offer very high capacity in a limited spectrum without
major technological changes.
-Available channels are distributed throughout the
geographic region and may be reused as many times
as necessary.
-Enable a fixed number of channels to serve an
arbitrarily large number of users by reusing the
channel throughout the coverage region
Dr.C.Helen Sulochana, Prof/ ECE,
SXCCE, Nagercoil
Advantage of cellular system

6. Frequency Reuse
•Service area split into small geographic areas called-cells
•Each cellular base station is allocated a group of radio
channels
•Neighboring cells are assigned different channel groups.
•By limiting the coverage area to within the boundary of the
cell, the same group of channels may be reused by different
cells.
•Frequency reuse or frequency planning-process of
Selecting and allocating channel groups for all cellular base
stations within the system
- Adjacent cells are assigned different frequency to avoid
interference or crosstalk

Dr.C.Helen Sulochana, Prof/ ECE,
SXCCE, Nagercoil

7. Dr.C.Helen Sulochana, Prof/ ECE,
SXCCE, Nagercoil
•footprint of a cell - actual radio coverage area of the cell
determined from propagation prediction model
•Cell Shape – Geometric shape cover the entire region without
overlap and with equal area -square, equilateral triangle,
hexagon
-Hexagon is preferred- fewest no. of cells cover the geographic
region
-approximates circular radiation pattern like Omni directional
antenna
Excitation mode- (i) center excited cells-base station Tx. is in the
center of the cell
-omni directional ant. is used
(ii)Edge excited cells-base station Txs. are on three of
six vertices of the cell
-sectored directional ants. are used

8. -cellular system which has a total of S duplex channels(available spectrum).
-The S channels are divided among N cells.
-Each cell is allocated a group of k channels, ( ) . No channels are reused within
the cluster. The same channels are reused in other cluster(co channel cells) .
-The total number of available radio channels
Cluster- is group of N cells which use the complete set of available channels
cluster size N=4,7,or 12
Frequency reuse factor =
If the cluster is repeated M times within the system. The total number of channels,
C(measure of capacity)
-Capacity is proportional to number of times the cluster is repeated
-If N es, M es to cover the entire area, C es,
co channels are located closer , interference es
- To connect without gap between adjacent cells, total no.
of cells is i,j –non negative integer
Sk
kNS
MSMkNC 
N/1
Eg. For N=7 , i=2, j=1
Dr.C.Helen Sulochana, Prof/ ECE,
SXCCE, Nagercoil

9. Nearest co channel neighbor of particular cell
-move i cell along any chain of hexagon
- turn 60
0
counterclockwise and move j cells
•Hexagonal geometry has
–exactly six equidistance neighbors
–the lines joining the centers of any cell and each of its neighbors
are separated by multiples of 60 degrees.
•Co-channel neighbors of a particular cell, eg, i=3 and j=2. N=19
Dr.C.Helen Sulochana, Prof/ ECE,
SXCCE, Nagercoil

10. Channel Assignment Strategies
Frequency reuse scheme- is for efficient utilization of radio spectrum
–increases capacity objective
–minimize interference
Types of channel assignment strategy
1. Fixed channel assignment
2. Dynamic channel assignment
1. Fixed channel assignment
–each cell is allocated a predetermined set of voice channel irrespective of
no. of customers
–any new call attempt within the cell can only be served by the unused
channels in that particular cell
–the call will be blocked if all channels in that cell are occupied
–Borrowing technique is used- cell is allowed to borrow channels from
neighboring cells, if all of its own channels are occupied. Mobile
switching center(MSC) supervise this procedure
–Used in TDMA/FDMA cellular system
Dr.C.Helen Sulochana, Prof/ ECE,
SXCCE, Nagercoil

11. 2. Dynamic channel assignment
–channels are not allocated to cells permanently.
–allocate channels based on request, based on
likelihood of future blocking within the cell
frequency of use of candidate channel
the reuse distance of the channel to avoid co-channel interference
Advantages
–reduce the likelihood of blocking,
– increase the trunking capacity. –all available channels in the market
are accessible to all the cells
Disadvantages
-MSC need to collect data on channel occupancy, traffic distribution,
radio signal strength identification(RSSI) of all channels
-Increases the storage & computational load of the system

Dr.C.Helen Sulochana, Prof/ ECE,
SXCCE, Nagercoil

12. Handoff (hand
over)
•Process of switching a user from one cell to another while
conversation is in progress.
- This is done by MSC(Mobile switching center).
•Handoff operation
–identifying a new base station
–re-allocating the voice and control channels with the new base
station.
•Handoff strategies requirement
Handoff must be performed
–Successfully
–As infrequent as possible
–Imperceptible(unnoticable) to the user
Dr.C.Helen Sulochana, Prof/ ECE,
SXCCE, Nagercoil

13. •How to meet these strategies
- System designer specify the optimum signal level at which handoff is initiated
–Minimum usable signal for acceptable voice quality is -
90dBm to -100dBm
–Threhold at which handoff is made is slightly greater than min
usable signal
–Handoff margin cannot be too large or too
small.
–If is too large, unnecessary handoffs burden the MSC
–If is too small, insufficient time to complete handoff before a call is lost
due to poor signal condition.
usable minimum,, rhandoffr PP 


Dr.C.Helen Sulochana, Prof/ ECE,
SXCCE, Nagercoil

14. Dr.C.Helen Sulochana, Prof/ ECE,
SXCCE, Nagercoil

15. •Call drop occurs when excess delay in assigning handoff by MSC
excess delay is due to high traffic or no channel available or
computational load of MSC
•Avoid unnecessary handoff
-Ensure that drop in the signal strength is not due to fading and that the
mobile is moving away from the serving base station.
- Base station monitors the signal strength for certain period of time
before handoff is initiated
•Length of time needed to decide handoff
–Depends on the speed of mobile- estimated from the statistics of the received short-
term fading signal at the base station
–If the slope of short term average signal level is steep -> the hand off should be made
quickly
•Dwell time: is the time over which a call may be maintained within a cell
without handoff.
•Dwell time depends on
–Propagation, interference
–Distance between user and BS, other time varying effects
–Speed of user, type of radio coverage Dr.C.Helen Sulochana, Prof/ ECE,
SXCCE, Nagercoil

16. •Received Signal strength measurement
–In first generation analog cellular systems-signal is measured by the base station
and supervised by the MSC.
- Each base station monitors the RSSI(Radio signal strength indicator)
- locator Receiver(spare Rx. in BS) which is controlled by MSC is used
to determine the signal strength of user in the neighboring cells
–In second generation systems (TDMA), handoff decisions are mobile assisted,
called mobile assisted handoff (MAHO)
–Mobile station measure the signal power of nearby base station and report to the
serving base station
–Handoff occurs when power Rx.ed from neighboring cell > than power Rx.ed
from current base station
–Faster , suitable for microcells( 1Km)
•Intersystem handoff is necessary ,when a mobile moves from one cellular system to
a different cellular system controlled by a different MSC.
•Handoff requests is much important than handling a new call.
Dr.C.Helen Sulochana, Prof/ ECE,
SXCCE, Nagercoil

17. Dr.C.Helen Sulochana, Prof/ ECE,
SXCCE, Nagercoil
Soft handoff - a technique in which a cellular user is switched
to another base station before broken the connection with an
existing base station. 
- no change of channel. Used in CDMA system
Hard handoff - user's connection to be entirely broken with an existing
base station before being switched to another base station. 
-in FDMA system

18. Prioritizing Handoff
-To improve the quality of service, priority is given to handoff using
two methods
1.Guard Channel Concept: fraction of the total available
channels in a cell is reserved exclusively for handoff.
Disadvantage: Reducing the total carried traffic. Few channel for
originating calls
-efficient when dynamic allocation with min. no. of guard channels
2. Queuing of Handover Requests: If all channels in the
destination cell are occupied, a handover request is put in the queue
-To prevent forced termination due to lack of available channel.
Queuing of handoffs is possible – because finite time
interval exists between the received signal level drops below the handoff
threshold and termination of call due to insufficient signal level.
Dr.C.Helen Sulochana, Prof/ ECE,
SXCCE, Nagercoil

19. Practical Handoff Consideration
problems in practical cellular system
1.Managing low and High speed users
2. Cell dragging problem
1.Managing low and High speed users(umbrella cell approach)
–High speed users need frequent handoff during a call.
–Pedestrian (Low speed) users may never need a handoff during a
call.
•In Microcells ( es capacity), the MSC can become burdened if high
speed users are constantly being passed between very small cells.
•Minimize handoff interference
- handle the simultaneous traffic of high speed and low speed users,
umbrella cell concept is used.
- provide additional cell and base station in the same physical location
of the existing cell rather than new site location
Dr.C.Helen Sulochana, Prof/ ECE,
SXCCE, Nagercoil

20. Dr.C.Helen Sulochana, Prof/ ECE,
SXCCE, Nagercoil
-The smaller cell is grouped and assumed to be under a large
cell
-Different antenna heights and different power levels can be
used to provide small and large cells located at single site.
-Used to provide a large area to high-speed users while small
area coverage to low speed users
-If a high-speed user in large umbrella cell is near the base
station and if its velocity is decreasing then the
 BS can decide
whether to hand the user into the co-located micro
cell
 without the intervention of the MSC

21. umbrella cell approach
•Large cell (high speed users) and small cells(low speed users) can
be located at a single location (umbrella cell approach)
–different antenna height
–different power level
Dr.C.Helen Sulochana, Prof/ ECE,
SXCCE, Nagercoil

22. 2. Cell dragging problem:
- practical handoff problem in microcell systems
- occurs when there is a line-of-sight (LOS) radio path
between the user and base station.
- pedestrian users provide a very strong signal to the
neighboring cell without handoff.
-This creates a potential interference and traffic
management problem.
- To avoid this
-threshold and other radio coverage parameters are
adjusted
•For first generation analog cellular systems
–10 secs handoff time
– is in the order of 6 dB to 12 dB


Dr.C.Helen Sulochana, Prof/ ECE,
SXCCE, Nagercoil

23. •For second generation cellular systems, e.g., GSM
–1 to 2 seconds handoff time
–mobile assists handoff
– is in the order of 0 dB to 6 dB
–Handoff decisions based on signal strength, co-channel
interference, and adjacent channel interference.
•IS-95 CDMA spread spectrum cellular system
–Mobiles share the channel in every cell.
–No physical change of channel during handoff (soft hand
off)
–MSC decides the base station with the best receiving
signal as the service station
Dr.C.Helen Sulochana, Prof/ ECE,
SXCCE, Nagercoil


24. Interference
•Sources of interference
–another mobile in the same cell
–a call in progress in the neighboring cell
–other base stations operating in the same frequency band
–noncellular system leaks energy into the cellular
frequency band
•Types of cellular interference
1. Co-channel interference
2. Adjacent channel interference
Dr.C.Helen Sulochana, Prof/ ECE,
SXCCE, Nagercoil

25. 1.Co-channel Interference
Co-channel cells
- are several cells that use the same set of frequencies
–interference between signals from these cells is called co-channel
interference
To reduce co-channel interference,
-co-channel cell must be separated by a minimum distance.
When the size of the cell is approximately the same, co-channel
interference is independent of the transmitted power
co-channel interference depends on
•R - Radius of the cell
•D- distance to the center of nearest co-channel cell
co-channel reuse ratio
For a hexagonal geometry

Q=D/R
Dr.C.Helen Sulochana, Prof/ ECE,
SXCCE, Nagercoil

26. - Q es -interference es , transmission quality improves
Q es capacity es
A tradeoff must be made between capacity and voice quality

signal-to-interference ratio (SIR)
Let i
0 number of co-channel interfering cells
For a mobile receiver SIR is
S - desired signal power from the desired base station
I
i
- interference power caused by the i
th
interfering co-channel cell
Co-channel Reuse
Ratio
Dr.C.Helen Sulochana, Prof/ ECE,
SXCCE, Nagercoil

27. Average received power P
r at a distance d from the transmitting antenna
is
When transmission power of each base station is equal, then
Consider only the first layer of interfering cells
- if all the interfering base stations are equidistant D from the desired
base station
P
0
-power received at reference
distance d
0
in the far field region
n - path loss exponent.(value :2 to 4)
i
o
=6
For good voice quality, SIR be greater than 12dB
-N should be at least 6.49 for n=4
-So minimum cluster size is 7
Dr.C.Helen Sulochana, Prof/ ECE,
SXCCE, Nagercoil

28. S/I is worst case when a mobile is at the cell edge
-low signal power from its own base station & high interference
power from other cells
-If the mobile is approximately at a dist. D-R from two cells. Other
cells are at distance D-R/2, D+R/2 , D+R, D
the signal-to-interference ratio is
44444
4
)()2/()2/()(2




DRDRDRDRD
R
I
S
Dr.C.Helen Sulochana, Prof/ ECE,
SXCCE, Nagercoil
For n=4

29. Dr.C.Helen Sulochana, Prof/ ECE,
SXCCE, Nagercoil
If a signal to interference ratio of 15 dB is required for satisfactory
forward channel performance of a cellular system, what is the frequency
reuse factor and cluster size that should be used for maximum capacity if
the path loss exponent is (a) it = 4 , (b) it = 3? Assume that there are 6 co-
channels cells in the first tier, and all of them are at the same distance
from the mobile. Use suitable approximations.
Problem
Solution
(a)n = 4
S/I = 15dB
Assume, no of cells in a cluster N=7 -7 cell reuse pattern.
co-channel reuse ratio = 4.583.
signal-to-noise interference ratio
S/I = (1/6)x(4.583)
4
= 75.3 = 18.66 dB.
Since this is greater than the minimum required S/I, N = 7 can be
used.

30. Dr.C.Helen Sulochana, Prof/ ECE,
SXCCE, Nagercoil

31. 2 Adjacent Channel Interference
-interference from signals which are adjacent in frequency to the
desired signal.
–Imperfect receiver filters allow nearby frequencies to leak into the
passband
desired signal
receiving filter
response
desired signal
interference
interference
signal on adjacent channel
signal on adjacent channel
FILTER
Dr.C.Helen Sulochana, Prof/ ECE,
SXCCE, Nagercoil
–Performance degrade seriously if near-far effect present.

32. Dr.C.Helen Sulochana, Prof/ ECE,
SXCCE, Nagercoil
- when many mobile users share the same channel, the
strongest signal(nearby) is received at a base station.
- stronger received signal levels raise the noise floor of the
weaker signals(far away) at the base station demodulators,
thereby decreasing the probability of weak signal reception
near-far effect

33. Adjacent channel interference is minimized by
•careful filtering and channel assignment.
•Keep the frequency separation between each channel in a given cell
as large as possible
•A channel separation greater than six is needed to bring the
adjacent channel interference to an acceptable level.
•tighter base station filters are needed when close-in and distant
users share the same cell.
•each base station receiver is preceeded by a high Q cavity filter in
order to reject adjacent channel interference.
Dr.C.Helen Sulochana, Prof/ ECE,
SXCCE, Nagercoil

34. Dr.C.Helen Sulochana, Prof/ ECE,
SXCCE, Nagercoil
interference (Co- channel and Adjacent channel is minimized) by
•Power Control
-Ensure each mobile transmits the smallest power necessary to
maintain a good quality link on the reverse channel
•Power control provides
–long battery life
–increase SIR
–solve the near-far problem

35. Trunking and Grade of Service
Trunking allows large number of users to share the small number of
channels in a cell by providing access to each user, on demand, from a pool
of available channels.
-when a user requests service and all of the radio channels are in use, the
user is blocked, denied access or hold on queue
Erlangs: One Erlangs represents the amount of traffic intensity carried by a
channel that is completely occupied.
–Ex: A radio channel that is occupied for 30 minutes during an hour
carries 0.5 Erlangs of traffic.
Grade of Service (GOS): is a measure of ability of a user to access a
trunked system during the busiest hour.
-it is the performance of the trunked system
-likelihood that a call is blocked/delayed
•Each user generates a traffic intensity of Erlangs given by
H: average duration of a call. : average number of call requests per unit time
HA
u

uA
Dr.C.Helen Sulochana, Prof/ ECE,
SXCCE, Nagercoil

36. For a system containing U users, the total traffic intensity A is
•For a C channel trunking system, the traffic intensity per channel
Types of trunked systems
1.Blocked calls cleared(M/M/m queue)
- If no channels are available, the requesting user is blocked
without access and is free to try again later
- Erlang B fomula determines the probability that a call is blocked
and is a measure of GOS for a trunked system which provides no
queuing

C -number of trunked channels
A -total offered traffic.
u
UAA
CUAA
uc
/
cA
Dr.C.Helen Sulochana, Prof/ ECE,
SXCCE, Nagercoil

37. Dr.C.Helen Sulochana, Prof/ ECE,
SXCCE, Nagercoil
(a) there are memoryless arrivals of requests, implying that all users,
including blocked users, may request a channel at any time
(b) the probability of a user occupying a channel is exponentially
distributed, so that longer calls are less likely to occur
(c) there are a finite number of channels available in the trunking pool.

38. 2. Blocked Calls Delayed
- queue is provided to hold calls which are blocked
- If a channel is not available immediately, the call request may be
delayed until a channel becomes available
- Erlang C formula determines the likelihood of a call not having
immediate access to a channel

Trunking efficiency - measure of number of users which can be
offered a particular GOS with a particular configuration of fixed
channels
Dr.C.Helen Sulochana, Prof/ ECE,
SXCCE, Nagercoil
The average delay D for all calls in a queued system

39. Dr.C.Helen Sulochana, Prof/ ECE,
SXCCE, Nagercoil

40. Dr.C.Helen Sulochana, Prof/ ECE,
SXCCE, Nagercoil

41. Set-up Time: The time required to allocate a channel to a requesting
user.
Blocked Call: Call which cannot be completed at time of request, due to
congestion.
Holding Time: Average duration of a typical call.
Traffic Intensity: Measure of channel time utilization, which is the
average channel occupancy.
Load: Traffic intensity across the entire trunked radio system, measured
in Erlangs.
Grade of Service: A measure of congestion which is specified as the
probability of a call being blocked (Erlang B), or the probability of a call
being delayed(Erlang C) beyond a certain amount of time
Request Rate: The average number of call requests per unit time.
Dr.C.Helen Sulochana, Prof/ ECE,
SXCCE, Nagercoil

42. Dr.C.Helen Sulochana, Prof/ ECE,
SXCCE, Nagercoil
maximum possible carried traffic is the total number of channels C(
Erlangs).
 AMPS cellular system is designed for a GOS of 2% blocking.
-2 out of 100 calls will be blocked due to channel occupancy
during the busiest hour.
offered traffic : traffic which is offered to the trunked system.
carried traffic : traffic which is carried by the trunked system, only that
which is offered to the trunked system.
When offered traffic exceeds the maximum capacity of the system, the
carried traffic becomes limited due to the limited capacity (i.e. limited
number of channels).

43. Improving Capacity in Cellular Systems
Number of channels assigned to a cell becomes insufficient to support
the required number of users
•Methods for improving capacity in cellular systems are
1. Cell Splitting: subdividing a congested cell into smaller cells.
2. Sectoring: directional antennas to control the interference and
frequency reuse.
3. Coverage zone : Distributing the coverage of a cell and extends
the cell boundary to hard-to-reach place.
1.es the number of base stations to increase capacity
2. &3. based on base station antenna placements to improve capacity
by reducing co-channel interference
Dr.C.Helen Sulochana, Prof/ ECE,
SXCCE, Nagercoil

44. 1. Cell Splitting
-process of dividing a congested cell into smaller cells(microcells)
between the existing cells
- each with its own base station
-antenna height and transmitter power are reduced
-preserve the frequency reuse

-Radius of the cell R is reduced to smaller cells with radius R/2 .
-to cover the entire service area with smaller cells, four cells are
required
-Increased no. of cells increases the no. of clusters over the coverage
region, which increase the number of channels, and capacity.
-co-channel reuse ratio D/R unchanged
Dr.C.Helen Sulochana, Prof/ ECE,
SXCCE, Nagercoil

45. - original base station A is surrounded
by six new microcell base stations.
-smaller cells are added such that to
preserve the frequency reuse plan of the
system.
-microcell base station labeled G was
placed half way between two larger
stations utilizing the same channel
set G.
-This is for the other microcells
microcell
-As in fig. cell ‘A’ saturated with traffic
-New base stations are needed in the region to increase the number of
channels
Example
Dr.C.Helen Sulochana, Prof/ ECE,
SXCCE, Nagercoil

46. Transmission power
Due to cell splitting, Transmission power reduces from to
•receiving power at the new and old cell boundary
If n = 4 and set the received power equal to each other
•The transmit power must be reduced by 12 dB in order to fill in the
original coverage area.
Disadvantage
•if only part of the cells are splitted
–Different cell sizes will exist simultaneously
•Handoff issues - high speed and low speed traffic can be simultaneously
accommodated
1t
P
2t
P
n
tr RPP


1]boundary cell oldat [
n
tr
RPP

 )2/(]boundary cellnew at [
2
16
1
2
t
t
P
P
Dr.C.Helen Sulochana, Prof/ ECE,
SXCCE, Nagercoil

47. 2. Sectoring
- Technique of decreasing co-channel interference and increasing
system capacity by using directional antennas is called sectoring.
-Achieves capacity improvement by keeping the cell radius unchanged
and decrease the D/R ratio.
-reduce the number of cells in a cluster and thus increasing the capacity
Decrease the co-channel interference
–Replacing single omni-directional antenna by several directional
antennas
– directional antennas radiates within a specified sector
Dr.C.Helen Sulochana, Prof/ ECE,
SXCCE, Nagercoil

48. Drawbacks
- sectoring reduces the coverage area of a particular group of channels,
the number of handoffs increases
- Increasing the load on the switching and control link of the
mobile system
-decreases trunking efficiency
Sector
-A cell is partitioned into three 120
0
sectors
or six 60° sectors.
- channels used in a particular cell are
divided into sector groups and are used only
within a particular sector
-Due to this, for 7-cell reuse with 120°
sectors, the number of interferers is reduced
from 6 to 2.
- S/I increased to 24.2dB
120
0
sectoring
60
0
sectoring
Dr.C.Helen Sulochana, Prof/ ECE,
SXCCE, Nagercoil

49. •Interference Reduction
position of the
mobile
interference cells
Dr.C.Helen Sulochana, Prof/ ECE,
SXCCE, Nagercoil

50. Sl NoCell splitting Sectoring Microtone
increasing system
capacity by dividing a
congested cell into
smaller cells
decreasing co-channel
interference and increasing
system capacity by using
directional antennas
cell radius decreases
and D/R ratio constant
cell radius unchanged and
decrease the D/R ratio
For N=7, No of
interference cell =6
No. of interference cell
reduces to 2
Frequent handoff Increased no. of handoffReduces handoff
Single omnidirectional
antenna
Several directional antenna
Increased load on switching
and control
trunking efficiency not
affected
decreases trunking efficiencytrunking efficiency
not affected
co-channel
interference
reduced
Dr.C.Helen Sulochana, Prof/ ECE,
SXCCE, Nagercoil

51. 3. Microcell Zone Concept
•Three or more zones are connected to a single base station
-Multiple zones and a single base station make up a cell
-antennas are placed at the outer edges of the cell, any base station
channel may be assigned to any zone by the base station.
- mobile travels within the cell is served by the zone with the strongest
signal
-Large central base station is placed by several low power transmitter
on the edge of the cell reduces the interference
•Handoff is done within a cell
–No channel re-assignment
–Switch the channel to a
different zone site
•Reduce interference
–Because of Low power
transmitters
Dr.C.Helen Sulochana, Prof/ ECE,
SXCCE, Nagercoil

52. -each individual hexagon represents a zone.
- zone radius = one hexagon radius
- group of three hexagons represents a cell.
-capacity is related to distance between co-channel cells, and not
zones
-No. of cells in a cluster N=3, then D/R=3
--reduction in cluster size from 7 to 3 increase the capacity by 2.33
Dr.C.Helen Sulochana, Prof/ ECE,
SXCCE, Nagercoil

53. Advantages
-Decreased co-channel interference, improves the signal quality
-increase in capacity, without the degradation in trunking
efficiency
Dr.C.Helen Sulochana, Prof/ ECE,
SXCCE, Nagercoil