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# 3 cellular networks & infarastructure

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### 3 cellular networks & infarastructure

1. 1. A Brief Overview By Engr. Abdul Razzaque Memon Email: uldhdqpia@yahoo.com Web: Http://www.uldhdqpia.webs.com
2. 2. Frequency Carries/Channels  The information from sender to receiver is carrier over a well defined frequency band.  This is called a channel  Each channel has a fixed frequency bandwidth (in KHz) and Capacity (bit-rate)  Different frequency bands (channels) can be used to transmit information in parallel and independently. by: Engr. Abdul Razzaque Memon
3. 3. Example - Frequency Spectrum Allocation in U.S. Cellular Radio Service Reverse Channel 991 992 … 1023 1 2 Forward Channel … 799 824-849 MHz 991 992 … 1023 1 2 … 799 869-894 MHz Channel Number Center Frequency (MHz) Reverse Channel 1 <=N <= 799 991 <= N <= 1023 0.030N + 825.0 0.030(N-1023) + 825.0 Forward Channel 1 <=N <= 799 0.030N + 870.0 991 <= N <= 1023 0.030(N-1023) + 870.0 (Channels 800-990 are unused) Channel bandwidth is 45 MHz by: Engr. Abdul Razzaque Memon
4. 4. Frequency & Wavelength of Some Technologies  AMPS Phones:  frequency ~= 800 Mhz  wavelength ~= 37.5 cm  GSM Phones:  frequency ~= 900 Mhz  wavelength ~= 33 cm  PCS Phones  frequency ~= 1800 Mhz (1.8 Ghz)  wavelength ~= 16.6 cm  Bluetooth:  frequency ~= 2.4 Gz  wavelength ~= 12.5 cm by: Engr. Abdul Razzaque Memon
5. 5. Example  Assume a spectrum of 90KHz is allocated over a base frequency b for communication between stations A and B  Assume each channel occupies 30KHz.  There are 3 channels  Each channel is simplex (Transmission occurs in one way)  For full duplex communication: Channel 1 (b - b+30)  Use two different channels (front and reverse channels) Station  A Channel 2 (b+30 - b+60) Station B Use time division in a channel Channel 3 (b+60 - b+90) by: Engr. Abdul Razzaque Memon
6. 6. Simplex Communication  Normally, on a channel, a station can transmit only in one way.  This is called simplex transmision  To enable two-way communication (called full-duplex communication)  We can use Frequency Division Multiplexing  We can use Time Division Multiplexing by: Engr. Abdul Razzaque Memon
7. 7. Duplex Communication - FDD  FDD: Frequency Division Duplex Mobile Terminal M Forward Channel Reverse Channel Base Station B Forward Channel and Reverse Channel use different frequency bands by: Engr. Abdul Razzaque Memon
8. 8. Duplex Communication - TDD  TDD: Time Division Duplex Mobile Terminal M M B M B M B Base Station B A singe frequency channel is used. The channel is divided into time slots. Mobile station and base station transmits on the time slots alternately. by: Engr. Abdul Razzaque Memon
9. 9. What is Mobility  Initially Internet and Telephone Networks is designed assuming the user terminals are static  No change of location during a call/connection  A user terminals accesses the network always from a fixed location  Mobility and portability  Portability means changing point of attachment to the network offline  Mobility means changing point of attachment to the network online by: Engr. Abdul Razzaque Memon
10. 10. Degrees of Mobility  Walking Users  Low speed  Small roaming area  Usually uses high-bandwith/low-latency access  Vehicles     High speeds Large roaming area Usually uses low-bandwidth/high-latency access Uses sophisticated terminal equipment (cell phones) by: Engr. Abdul Razzaque Memon
11. 11. Very Basic Cellular/PCS Architecture Public Switched Telephone Network Mobility Database Base Station Controller Mobile Switching Center (MSC) Radio Network Base Station (BS) by: Engr. Abdul Razzaque Memon Mobile Station
12. 12. Mobile/Cellular System Definitions:  Mobile Station  A station in the cellular radio service intended for use while in motion at unspecified locations. They can be either hand-held personal units (portables) or installed on vehicles (mobiles)  Base station  A fixed station in a mobile radio system used for radio communication with the mobile stations. Base stations are located at the center or edge of a coverage region. They consists of radio channels and transmitter and receiver antennas mounted on top of a tower. by: Engr. Abdul Razzaque Memon
13. 13. Mobile/Cellular System Definitions:  Mobile Switching Center  Switching center which coordinates the routing of calls in a large service area. In a cellular radio system, the MSC connections the cellular base stations and the mobiles to the PSTN (telephone network). It is also called Mobile Telephone Switching Office (MTSO)  Subscriber  A user who pays subscription charges for using a mobile communication system  Transceiver  A device capable of simultaneously transmitting and receiving radio signals by: Engr. Abdul Razzaque Memon
14. 14. Mobile/Cellular System Definitions:  Control Channel  Radio channel used for transmission of call setup, call request, call initiation and other beacon and control purposes.  Forward Channel  Radio channel used for transmission of information from the base station to the mobile  Reverse Channel  Radio channel used for transmission of information from mobile to base station by: Engr. Abdul Razzaque Memon
15. 15. Mobile/Cellular System Definitions:  Simplex Systems  Communication systems which provide only one-way communication  Half Duplex Systems  Communication Systems which allow two-way communication by using the same radio channel for both transmission and reception. At any given time, the user can either transmit or receive information.  Full Duplex Systems  Communication systems which allow simultaneous two-way communication. Transmission and reception is typically on two different channels (FDD). by: Engr. Abdul Razzaque Memon
16. 16. Mobile/Cellular System Definitions:  Handoff  The process of transferring a mobile station from one channel or base station to an other.  Roamer  A mobile station which operates in a service area (market) other than that from which service has been subscribed.  Page  A brief message which is broadcast over the entire service area, usually in simulcast fashion by many base stations at the same time. by: Engr. Abdul Razzaque Memon
17. 17. Mobile Communications Network by: Engr. Abdul Razzaque Memon
18. 18. CELLUAR TELEPHONY WHY NEED CELLULAR SYSTEM FOR MOBILES Capacity Limitation used a single high power radio transmitter to cover a large area. few channels for many people 1976 Bell Mobile Phone service in New York had 12 channels, serving 543 customer, waiting list of 3,700 and market of 10 million!! by: Engr. Abdul Razzaque Memon
19. 19. Cellular system / Network  Apart from the capacity limitation of these early systems, the other characteristic was that the carrier frequency was only re-used many tens or hundreds of kms away, so that no ‘co–channel’ interference would arise. [co–channel = same frequency) by: Engr. Abdul Razzaque Memon
20. 20. CELLUAR TELEPHONY Cellular systems Cellular systems are based on the concept of dividing the geographic service area into a number of cells and placing a low power transmitter in each of these, usually at the geographic centre. by: Engr. Abdul Razzaque Memon
21. 21. by: Engr. Abdul Razzaque Memon
22. 22. Cellular systems – cont. . .  The transmit frequencies are re-used across these cells and the system becomes interference rather than noise limited.  Needs a method for handling the call as the user crosses the cell boundary i.e. call Handover by: Engr. Abdul Razzaque Memon
23. 23. Mobile Cellular Telephone System by: Engr. Abdul Razzaque Memon
24. 24. Cellular Telephony  Characterized by  High mobility provision  Wide-range  Two-way tetherless voice communication  Handoff and roaming support  Integrated with sophisticated public switched telephone network (PSTN)  High transmit power requires at the handsets (~2W) by: Engr. Abdul Razzaque Memon
25. 25. by: Engr. Abdul Razzaque Memon
26. 26. CELLUAR TELEPHONY What is a Cell?  Cellular Telephony meets demand of multiple users in a metropolitan area (called the market) by breaking the whole market into several smaller regions known as CELLS.  Each cell has its own transmission tower and set of assignable communication channels. A Cell is an area covered by a BASE STATION. by: Engr. Abdul Razzaque Memon
27. 27. CELLUAR TELEPHONY Figure showing mobile telephone tower by: Engr. Abdul Razzaque Memon
28. 28. CELLUAR TELEPHONY Question?  why hexagon is used as a cell? Why not a triangle? a square? a circle? by: Engr. Abdul Razzaque Memon
29. 29. CELLUAR TELEPHONY Answer – Yes Hexagonal  Because to avoid gaps between cells.  If a customer is near the boundary of a cell, it can’t be undertaken by the cell next to it,because of the gap between two cells, therefore communication breakdown occurs.  And also to remain equal distance from a base station to a mobile user. by: Engr. Abdul Razzaque Memon
30. 30. FREQUENCY REUSE  The same frequency is used by many cells (separated by a distance).  Spectral efficiency (or capacity) is greatly increased. See next slide . . . by: Engr. Abdul Razzaque Memon
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35. 35. Example of 2G Digital Cellular The Global System for Mobile communication . . . .
36. 36. Network Architecture by: Engr. Abdul Razzaque Memon
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42. 42. Mobile Station (MS)  The Cellular (GSM) committee has introduced an important powerful innovation by using a Smart Card in conjunction with a mobile telephone. Thus GSM subscribers are provided with a Subscriber Identity Module card (SIM-Card) with its unique identification at the very beginning of the service.  "Confidential information -- may not be copied or disclosed without permission".  The Mobile Station (MS) includes radio equipment and the man machine interface (MMI) that a subscriber needs in order to access the services provided by the Cellular (GSM) network. by: Engr. Abdul Razzaque Memon
43. 43. Mobile Station (MS) by: Engr. Abdul Razzaque Memon
44. 44. Mobile Station (MS)  The mobile station includes provisions for data communication as well as voice.  Each mobile station has an International Mobile Equipment Identity (IMEI) that is permanently stored in the mobile unit. Upon request, the MS sends this number over the signaling channel to the network.  The IMEI is used to identify mobile units that are reported stolen or operating incorrectly. by: Engr. Abdul Razzaque Memon
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47. 47. Um Radio-Interface by: Engr. Abdul Razzaque Memon
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