1 PART I A Brief History PART II Cellular Concepts PART III GSM- Radio Interface CELLULAR MOBILE RADIO

2 MOBILE COMMUNICATION REVOLUTION IN TELECOM. MOBILE COMMUNICATION IS A VERY RAPIDLY GROWING AND A POPULAR SERVICE. MORE THAN 40 FOLD INCREASE IN LAST 10 YEARS IT HAS BECOME A BACKBONE FOR BUSINESS SUCCESS AND EFFICIENCY CHANGED THE LIFE STYLE ALL OVER THE WORLD.

3 History First mobile service started in 1946 in St. Louis, Missouri, USA. –Manually operated service, restricted area of service, only few lucky subscribers. Between , it evolved to be automatic with decreased cost. Mobile telephony service appeared in its useful form in 1960s.

4 Mobile Communications: 1980s Analog systems: 1st Generation AMPS: Advanced mobile phone service USA: 800 MHz band TACS: Total Access communication system UK : 900 MHz band NMT: Nordic Mobile telephone service Scandinavian: 450 MHz & 900 MHz band

5 Mobile Communications:1990s Digital systems: 2nd Generation DAMPS: Digital AMPS USA: 800 MHz band, IS-54, IS-136 CDMA: Code division multiple access system : US: 900 MHz band :IS-95 GSM: Global system for mobile comm. Europe: 900/1800 MHz

6 Any time Anywhere Mobility & Roaming High capacity & subs. density Efficient use of radio spectrum Seamless Network Architecture Low cost Flexibility Innovative Services Standard Interfaces MOBILE COMMUNICATION OBJECTIVES

7 MOBILE COMMUNICATION s 1980s 1990s 2000s Appeared 1G 2G 3G Analog Digital Digital MultiMulti Unified Standard Standard Standard Terrestrial Terrestrial Terr. & Sat

8 MOBILE COMMUNICATION 1 G -analog (cellular revolution) - only mobile voice services WIRELESS GENERATIONS 2 G - digital (breaking digital barrier) - mostly for voice services & data delivery possible 3 G - Voice & data ( breaking data barrier) - Mainly for data services where voice services will also be possible

9 CELLULAR MOBILE CONCEPTS

10 CELLULAR MOBILE CONCEPTS RADIO IN LOCAL LOOP LIMITED AVAILABILITY OF RF SPECTRUM INTERFERENCE PROBLEM INTERFERENCE AND SYSTEM CAPACITY FREQUENCY REUSE PATTERN TRUNKING EFFICIENCY CELLULAR PRINCIPLE CELLULAR ENVIRONMENT CAPACITY CONSIDERATIONS FUTURE TRENDS

11 Propagation loss L in dBs Transmit power P T and antenna gain G T Voice Channels Coverage area Forward path Reverse path Or control channels Lines to MSC Site noice MS Operating distance d Planned cell radius R Cell radio range - radius R max Radio Cell Parameters

12 Fundamental problems Radio range, or coverage no. of channels, or voice circuits Full, seamless service coverage Large no. of subscribers in the range of millions

13 FERQUENCY SCARCITY PROBLEM Tel Ex.    WIRED NETWORK 100,000  50 Khz = 5 Ghz (NOT POSSIBLE) Hence Individual RF Loop is not extended But a Common group of channels is shared CELLULAR MOBILE CONCEPTS BW forTelephony speech: 3KHz increases to 25 KHz with FM for Radio Trans.

14 CELLULAR MOBILE CONCEPTS ASSUMPTIONS Traffic /User = 30 mE, GOS = 1%

15 CELLULAR MOBILE CONCEPTS 360 * 25 KHz * 2 = KHz = 18 MHz FOR A CELL OF 10 KM RADIUS ONLY WHICH IS IMPOSSIBLE TO BE ALLOCATED HENCE FREQUENCY REUSE IS A MUST TO COVER THE TOTAL SERVICE AREA WITH A LIMITED AVAILABLE RF RESOURCES HENCE THE NEED FOR A CELLULAR PRINCIPLE

16 CELLULAR MOBILE CONCEPTS WHAT IS A CELL ? A base station (transmitter) having a number of RF channels is called a cell Each cell covers a a limited number of mobile subscribers within the cell boundaries ( Coverage area) Typical Cell Radius Aprrox = 30 Km (Start up), 1 KM (Mature)

17 A CLUSTER OF CELLS GIVEN FREQ. RESOURCE CELLULAR MOBILE CONCEPTS

D R CELLULAR PRINCIPLE N= Frequency Reuse Pattern “N”=7 Given Freq Resource CELLULAR MOBILE CONCEPTS

19 CELLULAR MOBILE CONCEPTS CO-CHL INTERFERENCE :Interference caused by another cell/mobile using the same frequency D R Co Chl Interference is a Function of “Q” the re-use ratio: Q =D / R Lower Q Increased Co-Chl Interference  Higher Q Reduced Co-Chl Interference 

20 CELLULAR MOBILE CONCEPTS CO - Chl Interference Q = D /R =  3N N =Cluster Size R = Size (Radius of Cell) D = Distance between two Co- Chl Cells N Q=D/R Higher Q Less Interference  Higher N More Cluster Size Less RF freq/cell Less Traffic Handling Capacity of the system  LOWER Q Higher Interference  Increased System Handling Capacity  Higher Q Less Interference  Higher N More Cluster Size Less RF freq/cell Less Traffic Handling Capacity of the system

21 CELLULAR MOBILE CONCEPTS Co- Chl Interference Reduction Technique Antenna Front to Back Coupling Reduces Potential Interference Use Directional Antennas Instead of Omni Directional Antennas Receives interference from lesser directions * 1 2 3f1f1 f2f2 f3f3 Three Sectored Cell Omni Directional

22 CELLULAR MOBILE CONCEPTS Improvement in Co- Chl Interference * 1 2 3f1f1 f2f2 f3f3 Three Sectored Cell Q= 4.6,N=7, S/I=14 db (Omni) S/I= 24.5 dB (Three Sectored) Q= 4.6,N=7, S/I=14 db (Omni) S/I= 29 dB (Six Sectored)

23 CELLULAR MOBILE CONCEPTS FREQUENCY REUSE PATTERN * f1f1 f2f2 f3f3 Three Sectored Cell CDMA = 1/3 ; 1 Cell Pattern & each cell with 3 sectors GSM = 4/12 ; 4 Cell Pattern & each cell with 3 sectors DAMPS = 7/21 ; 7 Cell Pattern & each cell with 3 sectors

24 CELLULAR MOBILE CONCEPTS FREQUENCY REUSE PATTERN 4/12 7/21

25 CELLULAR MOBILE CONCEPTS Extract from Traffic Table - Erlang B Model

26 CELLULAR MOBILE CONCEPTS TRUNKING EFFICIENCY More The Number Of Access Channels In A Cell Further Increase In The System Handling Capacity The Number Of Users Served In A Cell Are Directly Proportional To The Access Channels Allocated In A Cell TRUNKING EFFICIENCY It is better to have a single cell than to split into two with half the number of access channels Subs 50 subs

27 Cellular Environment Cellular Environment is quite different from fixed radio systems -Cellular approach -MOBILITY of the user -Dynamically changing surrounding terrain conditions  RF Signal attenuates, RF  d -   =4 (generally) Multipath Fading  Distortions Signal fluctuations due to mobility of the user

28 CELLULAR ENVIRONMENT  Techniques Power Control Channel Coding Interleaving Equalization Slow Frequency Hopping Antenna Diversity

29 GSM CAPACITY CONSIDERATIONS Access Channels 1--Signaling 7- Voice With 2 % GoS  2.94 E  2.94E/25mE=120 Subs 120 Subs/Sector  3 = 360 Subscribers

30 MOBILE COMMUNICATION WORLD CELLULAR MARKET 1N 2004 ASIA -PACIFIC35%225 M WESTERN EUROPE 30 % M NORTH AMERICA 17 % M LATIN AMERICA8 %51.5 M EASTERN EUROPE 5 % M AFRICA 3 % M MIDDLE EAST2 % 12.5 M

31 Public Land Mobile Network INDIA has adopted GSM standard for PLMN. Digital Cellular System. Operates at 900 MHz. International Roaming facility. Power class 0.8 to 20W. Cell Radius upto 35 Kms. Maximum mobility speed 250 Km/hr.

32 GSM - RADIO INTERFACE

33 Communication - Mobile Telephone Exchange Subscriber Line (2W) Inter-Exchange Junction Mobile Switching Centre (MSC) BSCBTS MS

34 GSM RADIO INTERFACE Most Important Interface Full Compatibility between mobile stations of various Manufacturers & Networks of different vendors to help roaming To increase spectral efficiency -- Large number of simultaneous calls in a given bandwidth -- Frequency Reuse -- Interference -- Use of Interference Reduction Techniques

35 GSM Specifications - II Frequency Bands- Mobile to Cell(UP-LINK) to 915 MHz Cell to Mobile (DOWN -LINK) to 960 MHz Channel Bandwidth KHz Access Method - TDMA/FDMA Modulation - GMSK

36 GSM Specifications - III Number of Channels-124 Voice Channel Coding- ( 13 Kbps) RPE-LTP RPE-LTP - Regular Pulse Excitation Long Term Prediction FULL RATE - 13Kb/s ; HALF RATE Kb/s Bit Rate Kbps

37 GSM - MULTIPLE ACCESS GSM uses both FDMA & TDMA Freq Mhz FDMA Access along Frequency axis Each RF carrier 200khz apart Total 124 RF Channels available. One or more carrier assigned to each base station Absolute Radio Freq Carrier Number ( ARFCN) 0 & 124 not used untill it is co-ordinated with Non -GSM operators in adjacent freq. bands. In most cases 124 RF Channels are used ……...

38 GSM FDMA 25 MHz Mobile to Base ( MHz) Base to Mobile kHz 45MHz Channel layout and frequency bands of operation kHz

39 GSM TDMA MHz Frequency F2’ F1’ (Cell transmit) F2F1 (Cell Rx) Amplitude Typical TDMA/ FDMA frame structure