Dr. Tanuja Patgar -Wireless Network Architecture �and Operation

The key characteristic of a cellular network is the ability to reuse frequencies to increase both coverage and capacity. Extensive frequency reuse allows for many users to be supported at the same time.

1. Unit-3 Wireless Network Architecture and Operation Dr . TANUJA P B.Tech , M.tech , PhD, Post Doc Department of Electronics and Communication Dr. AIT, Bangalore

2. The Cellular Concept AT & T and Bell Labs offered first mobile telephone service . Use high power BS Txs with elevated antenna provide a larger coverage area . Typically 250 watt FM transmitter used paged a mobile when there was an incoming call for the mobile . The limitation of this system is limited users, no frequency reuse, cell congestion, high power requirement . Improvement: The main objective of cellular concept is to allocate more users in a limited allocated spectrum. The basic system characteristics are Area divided into Cells, each served by base station with lower power transmitter covers a few hundred meters in some cities.. Each cell gets portion of total number of channels, neighboring cells assigned different groups of channels in order to reduce the interference. Multiple lower-power base stations that service mobile users within their coverage area and handoff users to neighboring base stations as users move.

3. 1G Cellular Systems The cellular Advantage. A large subscriber capacity and Efficient use of spectrum resources Nationwide coverage & Adaptability to traffic density Telephone service to both vehicle and portable user terminals including closed user groups with voice dispatch operations with Toll quality Affordability, which could eventually make it a mass-market service Power requirement for mobile is less due smaller cell and low power transmitter Longer battery life and smaller mobile station form factors . Cellular Limitation : Initial implement cost is large due to Deployment of large no. of low power stations Acquisition of lands for cell sites The associated hardware like RBS TxrRXr , controller, Antennas and towers NOTE: But the cellular concept allows a large enough increase in capacity to make these operations economically feasible.

4. Instead of one base station covering an entire city, the city was broken up into cells, or smaller coverage areas. Each of these smaller coverage areas had its own lower-power base station. The radio channels must be allocated to these smaller cells in such way as to minimize interference but at the same time provide the necessary system performance to handle the traffic load within the cells. Implementation of basic cellular architecture :

5. AMPS Characteristics Frequency Reuse: ** (Jan-2015-10M) It is a design process of selecting and allocating channel groups for all of the cellular base stations within a system called frequency reuse. The key characteristic of a cellular network is the ability to reuse frequencies to increase both coverage and capacity. Extensive frequency reuse allows for many users to be supported at the same time. The frequency reuse concept as illustrated in figure 3.1. Total spectrum allocated to the service provider is broken up into smaller bands. A cell is assigned one of these bands. This means all communications (transmissions to and from users) in this cell occur over these frequencies only. Neighboring cells are assigned a different frequency band. This ensures that nearby transmissions do not interfere with each other. The same frequency band is reused in another cell that is far away. This large distance limits the interference caused by this co- frequency cell.

6. AMPS Channels Cluster 2 Cluster 1 Cluster 3

7. Cluster It is a group of cell (see fig 3.1) that makes use of all the available radio spectrum. Cluster has N cells with unique and disjoint channel. Since adjacent cannot use the same frequency channels, the total frequency allocation is divided up over the cluster and then repeated for other clusters in the system. The number of cells in a cluster is known as the cluster size or the frequency reuse factor (1/N)

8. AMPS System Components and Layout Illustration of cellular system capacity: An Example (June-2011-5M) Consider service provider wants to provide cellular communications to a particular geographic area. The provider is licensed = 5MHz. Each system subscriber bandwidth (channel B.W) = 10 KHz. If the service provider was to provide coverage from only one transmitter site, the total theoretical number of possible simultaneous users = Total B.W/ Channel B.W = 5 MHz/ 10kHz / user = 500 users . If, however, the service provider implements a cellular system with 35 transmitter sites, located to minimize interference and provide total coverage of area, determine the new system capacity? Solution: Assume the cluster size N = 7 The allocated B.W/cell= System B.W/ Number of cells in a cluster =5*10 6 /7=714kHz Bandwidth per cell = 714 kHz . No. of cluster 35/7= 5. Each cell has a capacity =714kHz/10kHz/user = 71 users Total system capacity =35 cells*71 users/cell = 2485 users . This is a system capacity increase of =5 times. Conclusion: Smaller cells è higher number of clusters è higher Channel reuse è higher Capacity and + Lower power requirements for mobiles o Undesirable factors : Additional

9. Cellular Hierarchy: It is created in the cellular system based on the cell size, as shown in the below table. All type uses different radio link propagation & different technical cell design concept . Sl. No. Cell Type Cell diameter Operating Environment 1 Femtocells < 10 mts Personal Area network(PAN) 2 Picocells < 100 mt Indoor environment 3 Microcells 100-1000mts Outdoor to indoor and pedestrian 4 Macrocells >1000mts to Few Kms Vehicular and high antenna environment 5 Megacells Global coverage Vehicular and high antenna environment

10. SAT(Supervisory Audio Tones) or DCC(Digital Color Code)– 5970Hz,6000Hz and 6030Hz used to know radio link status Base station adds SAT to Forward Voice Channel(FVC) Mobile station adds SAT to RVC If both SAT mismatches, then mobile receiver will be muted AMPS Forward & Reverse, Control & Voice Channels

11. FOCC transmits three data streams in TDM format Data streams -- Stream A Stream B Busy idle stream LSB = 0 , MIN sent to stream A LSB = 1 , MIN sent to stream B Busy idle stream tells the status about Reverse control channel. AMPS Forward & Reverse , Control & Voice Channels

12. Over Head Messages – Initialization task, system access by mobile station and update by providing latest system parameters MS Control Messages – Order messages to initiate particular operation Control Filler Messages – Used when there is no other message to be sent FOCC Message Format

13. Different Order Messages Alert Order Messages – informs there is incoming mobile call Audit Order Messages – checks for mobile is busy or not Change Power Order Message –changes mobile RF output power Intercept Order Message – any errors in placing a call Maintenance Order Message – checks operation of MS Release Order Message – to disconnect call Reorder Order Message – all facilities are in use Send Called Address Order Message - sends message to base station with dialed digit information Stop Alert Order Message – stop alerting the user

14. AMPS Security and Identification ESN (Electronic Serial Number) – provided by mobile phone manufacturer.32 bit ID No. SID(System Identification Number) – 15 bit binary no. uniquely assigned, gives status of the mobile MIN(Mobile Identification Number) – 34 bit binary no. derived from MS’s 10 digit telephone number. 24-bits- derived from 7 digit local number & 10 bits from area code. 10digit= 7 digit local no.(MIN1) + 3 digit area code(MIN2)

15. Summery of Basic AMPS Operations Operations include AMPS Mobile phone initialisation Mobile generated call Mobile terminated call AMPS network operations (i) AMPS network operations for a mobile originated call (ii) AMPS Handoff operations