MOBILE COMMUNICATION

1. MOBILE COMMUNICATION

2. PSTN TRANSFER MODE : CIRCUIT SWITCHING NETWORK TYPE : DIGITAL EXCEPT PART OF ACCESS NETWORK CHANNEL CAPACITY : 64 KBPS

3. CELLULAR SYSTEM

4. CELLULAR MOBILE SYSTEM • A WIRELESS MOBILE COMMUNICATION NETWORK ENABLES USERS TO INITIATE AND RECEIVE PHONE CALLS USING MOBILE PHONES • CELLULAR MOBILE TELEPHONY IS DIFFERENT FROM THE LANDLINE TELEPHONY IN THAT THE MOBILE SUBSCRIBER CAN INITIATE AND RECEIVE CALLS WHILE ON MOVE WITHOUT ANY DISRUPTION IN THE CALL • CELLULAR TELEPHONY DERIVES ITS NAME FROM THE PARTITION OF A GEOGRAPHIC AREA INTO SMALL PARTS CALLED “CELLS”

5. CELLULAR MOBILE SYSTEM (CONTD.) • EACH CELL IS COVERED BY A LOCAL TRANSMITTER AND RECEIVER POWERFUL ENOUGH TO ENABLE CONNECTIVITY WITH CELLULAR PHONES (MOBILE STATIONS / MOBILE TERMINALS / MOBILE EQUIPMENT) WITHIN ITS AREA • A SEPARATE RADIO FREQUENCY IS USED FOR EACH DIRECTION OF COMMUNICATION • MOBILE PHONE TO CELL SITE : UPLINK TRANSMISSION • CELL SITE TO MOBILE PHONE : DOWNLINK TRANSMISSION • THE SPECTRUM OF RADIO FREQUENCIES AVAILABLE FOR COMMUNICATION IS LIMITED AND ARE ALLOCATED TO DIFFERENT CELLULAR TECHNOLOGIES

6. RADIO FREQUENCY ALLOCATION TO MOBILE COMMUNICATION

7. CELLS ANTENNA TOWER CELLS

8. CELLS • CELLS ARE SMALL SECTIONS OF AN AREA WITH ANTENNA, TRANSMITTER AND RECEIVER • CELLS ARE DEFINED BY ITS • PHYSICAL SIZE • SIZE OF POPULATION • CELL RADII CAN VARY FROM HUNDREDS OF METERS IN CITIES TO TENS OF KILOMETERS IN COUNTRY SIDE • CELLS ARE REPRESENTED BY HEXAGON WITH HONEYCOMB PATTERN

9. TYPES OF CELLS • MACRO CELL • LARGE CELL WITH DIAMETER >= 10 KM • TRANSMITTER POWER 1 TO 6 W • MICRO CELL • SMALL CELL WITH DIAMETER OF UPTO 1 KM • TRANSMITTER POWER 01 TO 1 W • PICO CELL • VERY VERY SMALL CELL • USED FOR INDOOR TRANSMISSION IN BUILDINGS OR TUNNELS • SELECTIVE CELL • COVERAGE LESS THAN 360 DEGREES • USED TO FILL GAPS IN THE COVERAGE • UMBRELLA CELL • USED IN MICRO CELL BUT WITH DIFFERENT CHANNEL FOR TRANSMISSION • USAGE EXAMPLE : AT PLACES WHERE HEAVILY USED ROAD CROSSES THE MICRO CELL AREA THE FIRST THREE TYPES ARE BASED ON SIZE OF CELL THE LAST TWO TYPES ARE BASED ON SPECIAL FUNCTIONS

10. EVOLUTION OF MOBILE COMMUNICATION • 1940 : MTS ( MOBILE TELEPHONE SYSTEM ) • MTS USED FREQUENCY MODULATION TECHNIQUE • IT USED SINGLE CARRIER FREQUENCY IN THE RABGE OF 35 TO 45 MHz • HALF DUPLEX OPERATION • ALL CALLS HANDLED THROUGH OPERATOR • MOBILES PHONES HAD PUSH-TO-TALK SWITCH • 5 DIGIT MOBILE NUMBER • NO CONNECTIVITY WITH PSTN – MOBILE TO PSTN AND VICE VERSA NOT POSSIBLE • 1964 : IMTS ( IMPROVED MTS ) • SEVERAL CARRIER FREQUENCIES USED TO HAVE SIMULTANEOUS CALLS • NEED FOR OPERATOR WAS ELEMINATED • WIDE AREA COVERAGE • BASE STATION TRANSMITTER POWER 100 TO 200 W • MOBILE PHONE TRANSMITTER POWER 5 TO 25 W • MOBILE PHONE NUMBERS OF SAME LENGTH AS PSTN NUMBERS. SO MOBILE TO PSTN AND VICE VERSA CLLS WERE POSSIBLE

11. EVOLUTION OF CELLULAR NETWORK

12. EVOLUTION OF CELLULAR NETWORK • NMT • NORDIC MOBILE TELEPHONE ( 450 & 900 MHz ) • AMPS • ADVANCED MOBILE PHONE SYSTEM ( 850 MHz ) • DAMPS • DIGITAL AMPS • CDMA • CODE DIVISION MULTIPLE ACCESS SYSTEM • GSM • GLOBAL SYSTEM FOR MOBILE COMMUNICATION ( TDMA 900 MHz EUROPE) • DCS • DIGITAL CELLULAR SYSTEM ( TDMA GSM 1800 EUROPE ) • PCS • PERSONAL CELLULAR SYSTEM ( TDMA GSM 1900 US ) • UMTS • UNIVERSAL MOBILE TELECOM SYSTEM • IMT • INTERNATIONAL MOBILE SYSTEMS

13. CELLULAR TELEPHONY SERVICES • CELLULAR TELEPHONY HAS EVOLVED FROM BEING JUST A VOICE SERVICE TO PROVIDING A RICH COLLECTION OF VOICE, DATA AND MULTIMEDIA SERVICES • KEY CELLULAR SERVICES : • TEXT MESSAGING (SMS) • INSTANT MESSAGING (CHAT) • MULTIMEDIA MESSAGING (MMS) • EMAIL • EMERGENCY CALLS • WIRELESS INTERNET • VIDEO-ON-DEMAND • MOBILE TV • IP BASED MULTIMEDIA COMMUNICATION

14. COMPARISON OF CELLULAR SYSTEMS

15. MEDIUM ACCESS CONTROL • CHANNELIZATION IS A MULTIPLE ACCESS METHOD IN WHICH THE AVAILABLE BANDWIDTH OF A LINK IS SHARED IN TIME, FREQUENCY OR USING CODE BY NUMBER OF STATIONS • THE MEDIUM ACCESS CONTROL TECHNIQUES ARE : • FDMA ( FREQUENCY DIVISION MULTIPLE ACCESS ) • TDMA ( TIME DIVISION MULTIPLE ACCESS ) • CDMA ( CODE DIVISION MULTIPLE ACCESS )

16. FDMA • FREQUENCY DIVISION MULTIPLE ACCESS • THE BANDWIDTH IS DIVIDED INTO SEPARATE GREQUENCY BANDS

17. TDMA • TIME DIVISION MULTIPLE ACCESS • THE BANDWIDTH IS DIVIDED INTO TIME SLOTS

18. CDMA • CODE DIVISION MULTIPLE ACCESS • DATA FROM ALL STATIONS ARE TRANSMITTED SIMULTANEOUSLY AND ARE SEPARATED BASED ON CODING THEORY

19. COMPONENTS OF CELLULAR NETWORK • BASE TRANCEIVER STATION ( BTS ) • BASE STATION CONTROLLER ( BSC ) • MOBILE SWITCHING CENTRE (MSC ) OR MOBILE TELEPHONE SWITCHING OFFICE (MTSO) • LOCATION REGISTERS ( HLR & VLR ) • AUTHENTICATION CENTRE ( AuC ) • LINKS TO PSTN

20. BASE TRANVEIVER STATION (BTS) • BTS CONSISTS OF • ELECTRONIC SECTION LOCATED AT THE BASE OF ANTENNA TOWER AND INCLUDES • FREQUENCY AMPLIFIER • RADIO TRANCEIVER • RADIO FREQUENCY COMBINER • CONTROL LINKS • COMMUNICATION LINKS TO BSC • POWER SUPPLY WITH BACKUP • ANTENNA AND FEEDER SECTION • INTERFACE BETWEEN BTS AND BSC • CONTROL LOGIC • SOFTWARE

21. BTS • BTS LOCATION IN THE CELL, HEIGHT OF ANTENNA AND ORIENTATION ARE ALL IMPORTANT FACTORS TO ENSURE REQUIRED COVERAGE IN THE CELL • DIFFERENT LOCATIONS OF BTS ARE : • CENTRE EXCITED CELL • CORNER EXCITED CELL • EDGE EXCITED CELL OMNI DIRECTIONAL ANTENNA SECTORED DIRECTIONAL ANTENNA

22. MOBILE SWITCHING CENTRE (MSC) • MSC CONTROLS BSCs • ACTS AS SWITCH AND CONNECTION TO PSTN • ACTS AS AN AUTHENTICATION CENTRE (AuC) • CONTAINS REGISTERS – THE DATABASES MAINTAINING MOBILE LOCATION INFO • CONTROLS CHANNEL ASSIGNMENT, CALL PROCESSING, CALL SETUP AND TERMINATION, SIGNALLING, SWITCHING AND SUPERVISION • CONTAINS FACILITIES TO GENERATE BILLING INFO FOR CUSTOMER ACCOUNTS • IN VIEW OF ITS IMPORTANCE, MANY BACKUP AND DUPLICATE CIRCUITS ARE PROVIDED TO ENSURE THAT THER ARE NO FAILURES

23. AUTHENTICATION CENTRE (AuC) • USER’S IDENTITY IS CHECKED TO PROVIDE AUTHENTICATION AND ENCRYPTION PARAMETERS • AuC MAINTAINS A REGISTRATION DATABASE OF USERS ALLOWED TO USE THE NETWORK • AuC FUNCTION IS NECESSARY FOR SECURITY AS WELL AS BILLING OPERATION

24. EQUIPMENT IDENTITY REGISTER (EIR) • EIR IS A DATABASE HOLDING DETAILS OF MOBILE PHONE EQUIPMENT IN THE FORM OF IMEI NUMBER • IMEI ( INTERNATIONAL MOBILE EQUIPMENT IDENTITY ) NUMBER CAN BE ACCESSED AS FOLLOWS : • BY ENTERING *#06# ON MOBILE • ALSO PRINTED INSIDE THE PHONE • EIR DATABASE IS USED TO PREVENT CALLS FROM STOLEN, UNAUTHORIZED MOBILE PHONES • THE NETWORK OPERATORS MAINTAIN 3 SEPARATE LISTS OF IMEI IN THE EIR • GREY : MOBILE PHONES TO BE TRACKED • BLACK : BARRED MOBILE PHONES • WHITE : VALID MOBILE PHONES

25. LOCATION REGISTERS ( HLR, VLR) • HLR : HOME LOCATION REGISTER • CONTAINS SEMI-PERMANENT INFORMATION OF SUBSCRIBERS • KEEPS USER PROFILE OF USERS REGISTERED WITH THE NETWORK • MSC REFERS TO THE SUBSCRIBER INFORMATION IN THE HLR • THE HLR DATA OF A SUBSCRIBER IS STORED AS LONG AS THE SUBSCRIBER REMAINS WITH MOBILE OPERATOR • HLR ALSO STORES CURRENT LOCATION OF THE SUBSCRIBER AND SERVICES TO WHICH HE/SHE HAS ACCESS

26. LOCATION REGISTERS ( HLR, VLR) • VLR : VISITOR LOCATION REGISTER • CONTAINS TEMPORARY INFORMATION ABOUT THE MOBILE SUBSCRIBERS CURRENTLY LOCATED IN THE SERVICE AREA OF AN MSC BUT WHOSE HLR ARE ELSEWHERE • ROAMING USER RECORD IS ADDED TO VLR WHENEVER AN MSC DETECTS A NEW MOBILE PHONE IN ITS AREA • THE MSC CONTACTS THE HLR OF THE MOBILE SUBSCRIBER’S HOME LOCATION AND GETS THE DETAILS REQUIRED TO VALIDATE THE USER

27. CONNECTING TO NETWORK • WHEN A MOBILE PHONE IS SWITCHED ‘ON’, IT NEEDS TO COMMUNICATE WITH THE CELLULAR NETWORK TO REGISTER • THE MOBILE PHONE USES A ‘PAGING’ OR ‘CONTROL’ CHANNEL TO MAKE THE CONTACT WITH THE BASE STATION AND SENDS ‘ATTACH’ REQUEST • THE AUTHENTICATION CENTRE VERIFIES THE USER’S IDENTITY • ONCE VALIDATED, THE HOME LOCATION REGISTER (HLR) AND THE VISITOR LOCATION REGISTER (VLR) ARE UPDATED • PERIODICALLY, EVEN IF THE MOBILE PHONE IS IDLE, THE MOBILE PHONE COMMUNICATES WITH THE BASE STATION TO UPDATE ITS STATUS AND LOCATION • WHEN MOBILE PHONE IS SWITCHED ‘OFF’, IT SENDS A ‘DETACH’ REQUEST TO THE BASE STATION • THE NETWORK THEN UPDATES THE LAST KNOWN LOCATION OF THE MOBILE IN THE DATABASE

28. CLUSTER • CLUSTER IS A GROUP OF CELLS • THE CELLULAR NETWORK AREA IS DIVIDED INTO NUMBER OF CELLS • THESE CELLS ARE GROUPED INTO NUMBER OF CLUSTERS • FOR HEXAGONAL CELLS, POSSIBLE CLUSTER SIZES ARE GIVEN BY THE FORMULA : c = i^2 + I x j + j^2 Where ‘c’ is cluster size and ‘i’ and ‘j’ are non-negative numbers • FOR EXAMPLE, i = 2 & j = 1 GIVES CLUSTER SIZE OF 7 CELLS

29. CLUSTER (CONTD.) • THE INTEGERS ‘i’ & ‘j’ DETERMINE THE RELATIVE LOCATIONS OF CO-CHANNEL CELLS • CO-CHANNEL CELLS CAN USE THE SAME FREQUENCIES • IN THE DIAGRAM, CELLS WITH THE SAME LABEL ARE “CO-CHANNEL CELLS” • TO LOCATE A CO-CHANNEL CELL, MOVE ‘i’ CELLS, TURN 60 DEGREES COUNTER CLOCKWISE, MOVE ‘j’ CELLS IN THAT DIRECTION

30. LOCATING A CO-CHANNEL CELL

31. CELL PATTERN : CLUSTER OF 3 CELLS

32. CELL PATTERN : CLUSTER OF 7 CELLS

33. NO. OF CHANNELS IN A CLUSTER • NO. OF CHANNELS IN A CLUSTER IS GIVEN BY THE FORMULA : F = G x N • WHERE, • F : NO. OF FULL DUPLEX CHANNELS AVAILABLE IN A CLUSTER • G : NO. OF CHANNELS IN A CELL • N : NO. OF CELLS IN A CLUSTER

34. TOTAL CHANNEL CAPACITY OF AN AREA • TOTAL CHANNEL CAPACITY OF AN AREA IS GIVEN BY THE FORMULA : C = m x G x N = m x F • WHERE, • C : TOTAL CHANNEL CAPACITY OF THE AREA • M : NO. OF CLUSTERS IN THE AREA • G : NO. OF CHANNELS IN A CELL • N : NO. OF CELLS IN A CLUSTER • F : NO. OF CHANNELS IN A CLUSTER

35. CHANNEL CAPACITY • THUS, THE CHANNEL CAPACITY OF CELLULAR NETWORK IS DIRECTLY PROPORTIONAL TO THE NO. OF CLUSTERS IN THAT NETWORK • ‘N’ IS CALLED THE CLUSTER SIZE AND IS TYPICALLY 3, 7, OR 12 CELLS PER CLUSTER

36. FREQUENCY REUSE • FREQUENCY REUSE IS THE PROCESS IN WHICH THE SAME SET OF FREQUENCIES ( CHANNELS ) CAN BE ALLOCATED TO MORE THAN ONE CELL • FREQUENCY REUSE HAS BECOME ESSENTIAL DUE TO • LIMITED FREQUENCY SPECTRUM AVAILABLE FOR CELLULAR MOBILE COMMUNICATION • TREMENDOUS GROWTH IN THE NUMBER OF MOBILE USERS • IT IS POSSIBLE TO REUSE A FREQUENCY OUTSIDE THE RANGE OF THE RADIO TRANSMITTER • CELLS IN A CLUSTER USE UNIQUE FREQUENCY CHANNELS. HOWEVER, DIFFERENT CLUSTERS CAN USE THE SAME SET OF FREQUENCIES

37. FREQUENCY REUSE FACTOR ( FRF ) • THE FREQUENCY REUSE FACTOR IS GIVEN BY THE EQUATION : FRF = N / C • WHERE, • FRF : FREQUENCY REUSE FACTOR • N : TOTAL NO. OF CHANNELS IN AN AREA • C: TOTAL NO. OF CHANNELS IN A CELL

38. 3N 3N REUSE DISTANCE REUSE DISTANCE ‘D’ = ( ) X R WHERE, R : CELL SIDE, AND N: CLUSTER SIZE THE REUSE FACTOR ‘q’ = D/R OR =

39. ADJACENT CHANNEL INTERFERENCE • INTERFERENCE CAUSED BY TRANSMISSION OF ADJACENT FREQUENCIES • GENERALLY THE FREQUENCY CHANNELS USED ARE SEPARATED BY 200 KHz SO AS NOT TO INTERFERE WITH EACH OTHER • HOWEVER, IMPERFECT FILTERS IN RECEIVERS ALLOW NEARBY FREQUENCIES TO ENTER THE RECEIVER AND INTERFERE WITH THE SIGNAL BEING RECEIVED FROM THE BASE STATION • PROPER FILTERS CAN REDUCE THE PROBLEM

40. 3N 3N CO-CHANNEL INTERFERENCE • CELLS FROM DIFFERENT CLUSTERS USING THE SAME FREQUENCIES ARE CALLED “CO-CHANNELS CELLS” • A CERTAIN MINIMUM DISTANCE MUST SEPARATE THESE CO-CHANNEL CELLS IN ORDER TO AVOID THE INTERFERENCE • FOR HEXAGONAL CELLS THE REUSE DISTANCE IS GIVEN BY : REUSE DISTANCE ‘D’ = ( ) X R WHERE, R : CELL SIDE, AND N: CLUSTER SIZE THE REUSE FACTOR ‘q’ = D/R OR =

41. CELL SPLITTING • CELL SPLITTING IS THE PROCES OF SUBDIVIDING THE CELLS INTO SMALLER CELLS EACH WITH ITS OWN BASE STATION AND SET OF CHANNEL FREQUENCIES • SPLITTING OF CELLS ALLOWS AN INCREASE IN THE DEGREE OF FREQUENCY REUSE THUS INCREASING THE CHANNEL CAPACITY OF CELLULAR NETWORK • IF THE RADIUS OF A CELL IS MADE HALF, FOUR TIMES AS MANY SMALLER CELLS COULD BE CREATED TO PROVIDE SERVICE TO THE SAME COVERAGE AREA • MAJOR DRAWBACK OF CELL SPLITTING IS MORE HANDOFFs PER CALL AND MORE PROCESSING LOAD PER SUBSCRIBER

42. CELL SPLITTING (CONTD.) • EXAMPLE OF CELL SPLITTING : • THE CHANNEL CAPACITY OF 7 MACRO CELLS WITH 10 CHANNELS PER CELL= 10 x 7 = 70 CHANNELS • AFTER SPLITTING THE MACRO CELLS INTO 4 MINICELLS, THE CHANNEL CAPACITY = 10 x 7 x 4 = 280 CHANNELS • AFTER SPLITTING MINI CELL INTO 4 MICRO CELLS, THE TOTAL CAPACITY = 10 x 7 X 4 X 4 = 1120 CHANNELS

43. SECTORING • THE CO-CHANNEL INTERFERENCE CAN BE REDUCED BY REPLACING A SINGLE OMNI-DIRECTIONAL ANTENNA AT THE BASE STATION BY SEVARAL DIRECTIONAL ANTENNAS, EACH RADIATING WITHIN A SPECIFIED SECTOR • THIS TECHNIQUE OF IMPROVING SYSTEM PERFORMANCE BY USING DIRECTIONAL ANTENNAS IS CALLED “SECTORING” • A CELL IS NORMALLY PARTITIONED INTO THREE 1200 SECTORS OR SIX 600 SECTORS

44. ROAMING • ROAMING REFERS TO EXTENSION OF CONNECTIVITY SERVICE IN A LOCATION THAT IS DIFFERENT FROM THE HOME LOCATION WHERE THE MOBILE SUBSCRIBER WAS REGISTERED • ROAMING ENSURES THAT THE SUBSCRIBER CAN CONTINUE WITH THE CALL WHEN MOVING AWAY FROM HIS HOME LOCATION WITHOUT LOSING THE CONNECTION • ROAMING IS POSSIBLE ONLY IF THERE IS AN AGREEMENT BETWEEN THE TWO NETWORKS PROVIDING SERVICES TO DIFFERENT AREAS

45. ROAMING PROCESS • WHEN A MOBILE DEVICE IS TURNED ‘ON’ IN A NEW LOCATION, THE “VISITED” NETWORK NOTICES THAT THE MOBILE SUBSCRIBER IS NOT REGISTERED WITH IT AND ATTEMPTS TO IDENTIFY THE HOME NETWORK OF THE SUBSCRIBER • IF ROAMING AGREEMENT EXISTS BETWEEN THE TWO NETWORKS, THE VISITED NETWORK CONTACTS THE HOME NETWORK AND REQUESTS SERVICE INFORMATION USING THE “IMSI” NUMBER • IF SUCCESSFUL, THE VISITED NETWORK MAINTAINS A TEMPORARY RECORD IN ITS DATABASE FOR THE SUBSCRIBER • LIKEWISE, THE HOME NETWORK UPDATES ITS DATABASE WITH THE CURRENT LOCATION OF THE SUBSCRIBER SO THAT IT CAN ROUTE THE CALLS CORRECTLY TO THE MOBILE DEVICE

46. HANDOFF / HANDOVER • CONTINUITY OF SERVICE IS MAINTAINED BY SUPPORTING HANDOFF / HANDOVER PROCESS WHEN A MOBILE SUBSCRIBER MOVES FROM ONE CELL TO ANOTHER • IT IS A PROCESS OF CHANGING THE CHANNEL RESOURCES (FREQUENCIES, TIME SLOT, CODE, ETC) ASSOCIATED WITH THE CURRENT CONNECTION WHILE A CALL IS GOING ON • IT IS INITIATED BY CROSSING A CELL BOUNDARY OR BY DETERIORATION IN THE QUALITY OF SIGNAL IN THE CURRENT CHANNEL

47. TYPES OF HANDOFFs • TWO TYPES OF HANDOFFs ARE USED : • HARD HANDOFF • SOFT HANDOFF

48. HARD HANDOFF • IT IS A “BREAK BEFORE MAKE” PROCESS • CURRENT RESOURCES ARE RELEASED BEFORE NEW RESOURCES ARE USED • PRIMARILY USED IN TDMA / FDMA NETWORKS • THE BREAK IS SHORT ENOUGH TO BE NOTICED BY THE USER

49. SOFT HANDOFF • IT IS A “MAKE BEFORE BREAK” PROCESS • CONNECTION WITH THE TARGET BASE STATION IS MADE BEFORE THE CONNECTION WITH THE EXISTING BASE STATION IS BROKEN • COMMONLY USED IN CDMA NETWORKS • THE SOFT HANDOFF GIVES MORE RELIABLE CONTINUITY WITH LESS CHANCES OF CALL TERMINATION THAN THAT IN HARD HANDOFF

50. FURTHER CLASSIFICATION OF HANDOFFs • NETWORK CONTROLLED HANDOFF • NETWORK MAKES THE HANDOFF DECISION • MOBILE ASSISTED HANDOFF • MOBILE MEASURES THE SIGNAL STRENGTH, BUT NETWORK MAKES THE DECISION OF HANDOFF • MOBILE CONTROLLED HANDOFF • MOBILE IS IN COMPLETE CONTROL OF THE HANDOFF PROCESS