MOBILE COMMUNICATION

PSTN

TRANSFER MODE : CIRCUIT SWITCHINGNETWORK TYPE : DIGITAL EXCEPT PART OF ACCESS NETWORKCHANNEL CAPACITY : 64 KBPS

CELLULAR SYSTEM

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”

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

RADIO FREQUENCY ALLOCATION TO MOBILE COMMUNICATION

CELLS

ANTENNA TOWER

CELLS

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

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 CELLTHE LAST TWO TYPES ARE BASED ON SPECIAL FUNCTIONS

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

EVOLUTION OF CELLULAR NETWORK

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

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

COMPARISON OF CELLULAR SYSTEMSPARAMETER AMPS TACS NMT450 NMT900

FREQUENCY BAND (MHz)

800 900 450 900

CHANNEL SPACING (KHz)

30 25 25 12.5

SPEECH MODULATION

FM FM FM FM

SIGNALLING FSK FSK FSK FSK

SIGNALLINGBIT RATE

10 KBPS 8 KBPS 1200 BPS 1200 BPS

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 )

FDMA

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

TDMA

•TIME DIVISION MULTIPLE ACCESS•THE BANDWIDTH IS DIVIDED INTO TIME SLOTS

CDMA

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

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

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

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

SECTORED DIRECTIONAL ANTENNA

OMNI DIRECTIONAL ANTENNA

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

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

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

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

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

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

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

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

LOCATING A CO-CHANNEL CELL

CELL PATTERN : CLUSTER OF 3 CELLS

CELL PATTERN : CLUSTER OF 7 CELLS

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

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

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

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

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

REUSE DISTANCE

REUSE DISTANCE ‘D’ = ( ) X RWHERE, R : CELL SIDE, AND N: CLUSTER SIZETHE REUSE FACTOR ‘q’ = D/R OR =

3N

3N

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

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 RWHERE, R : CELL SIDE, AND N: CLUSTER SIZETHE REUSE FACTOR ‘q’ = D/R OR =

3N

3N

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

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

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

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

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

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

TYPES OF HANDOFFs

• TWO TYPES OF HANDOFFs ARE USED :– HARD HANDOFF– SOFT HANDOFF

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

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

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

MOBILE TO LANDLINE CALL

MOBILE TO LANDLINE CALL• PRE-ORIGINATION DIALING : WHEN SUBSCRIBER DIALS A NUMBER,

THE DIALED DIGITS ARE NOT TRANSMITTED, BUT ARE STORED IN TH MOBILE MEMORY

• THE CALL PROCESS STARTS WHEN THE USER PRESSES ‘SEND’ KEY• THE MOBILE SCANS ALL THE DEDICATED CONTROL CHANNELS AND

LOCKS ONTO THE STRONGEST CHANNEL. ( CONTROL, PAGING, AND ACCESS FUNCTIONS ARE ON THE SAME CHANNEL)

• WHEN THE REVERSE CONTROL CHANNEL (RECC) IS AVAILABLE, THE MOBILE TRANSMITS A ‘SERVICE REQUEST’ ON THE ‘RECC’ (CONSISTING OF DIALED DIGITS, ‘ESN’ AND ‘MIN’) TO THE CELL SITE

• CELL SITE FORWARDS THE REQUEST TO MSC• MSC VALIDATES THE DATA (DIALED DIGITS, ‘ESN’ AND ‘MIN’) AND

ROUTES HE CALL TO ‘PSTN’

MOBILE TO LANDLINE CALL (CONTD.)

• THE CELL SITE SELECTS AN IDLE VOICE CHANNEL AND TRANSMITS AN ‘IVCDM’ (INITIAL VOICE CHANNEL DESIGNATION MESSAGE) TO THE MOBILE ON FORWARD CONTROL CHANNEL (FOCC)

• ‘IVCDM’ CONTAINS THE VOICE CHANNEL NUMBER, THE SUPERVISORY AUDIO TONE (SAT) AND THE VOICE CHANNEL MOBILE AUTHENTICATION CODE (VMAC)

• SAT IS SNT ON THE ASSIGNED VOICE CHANNEL (FOVC)• MOBILE RECEIVES THE VOICE CHANNEL ASSIGNMENT, TUNES TO IT AND

TRANSPONDS THE SAT ON REVERSE CONTROL CHANNEL ‘REVC’ • IF SAT IS LOST FOR 5 SECONDS OR MORE, THE CALL IS DROPPED• WHEN THE CELL SITE RECEIVES THE SAT ON REVC, BOTH AUDIO PATHS ARE

ENABLED AND MOBILE USER HEARS RINGBACK FROM PSTN• WHEN THE CALLED PARTY ANSWERS, THE CONVERSATION BEGINS• BLANK AND DATA BURST SIGNALLING IS USED TO TRANSMIT CONTROL

INFORMATION TO THE MOBILE DURING THE CALL

LANDLINE TO MOBILE CALL

LANDLINE TO MOBILE CALL• LANDLINE PARTY DIALS THE MOBILE NUMBER• PSTN DETERMINES THAT THE CALL IS TO A MOBILE AND ROUTES THE

CALL TO MSC• MSC PERFORMS VALIDATION OF DIALED DIGITS• A PAGE MESSAGE IS SENT FROM MSC TO THE CELL SITE ON FORWARD

CONTROL CHANNLE (FOCC)• WHEN THE MOBILE SEES THE PAGE MESSAGE ON FOCC, IT RESCANS

THE CONTROL CHANNELS AND LOCKS ON THE STRONGEST ONE• MOBILE TRANSMITS A PAGE RESPONSE MESSAGE ON THE REVERSE

CONTROL CHANNEL (RECC)• CELL SITE RECEIVES THE PAGE RESPONSE AND SELECTS AN IDLE VOICE

CHANNEL

LANDLINE TO MOBILE CALL (CONTD.)

• CELL SITE TRANSMITS ON THE FORWARD CONTROL CHANNEL (FOCC) AN ‘IVCDM’ AND ‘SAT’ ON FORWARD VOICE CHANNEL (FOVC) TO MOBILE

• MOBILE RECEIVES ‘IVCDM’ ON FOCC, TUNES TO THE ASSIGNED VOICE CHANNEL AND TRANSPONDS ‘SAT’ ON REVERSE VOICE CHANNEL (REVC)

• CELL SITE TRANSMITS AN ALERT ON FOVC TO THE MOBILE ASKING THE MOBILE TO RING

• MOBILE STARTS RINGING AND TRNSMITS SIGNAL TONE ‘ST’ CONTINUOUSLY UNTIL THE CALL IS ANSWERED

• LOSS OF ST INDICATES THAT THE CALL HAS BEEN ANSWERED• MSC NOW CONNECTS THE LANDLINE PARTY TO THE MOBILE AND

CONVERSATION BEGINS

MOBILE TO MOBILE CALL• THE ORIGINATING MOBILE INITIATES THE CALL• CELL SITE RECEIVES THE DESTINATION MOBILE NUMBER AND

ORIGINATING MOBILE’S ID ON REVERSE CONTROL CHANNEL (RECC) AND FORWARDS IT TO MSC

• MSC SENDS A PAGING SIGNAL TO ALL CELL SITES TO LOCATE THE DESTINATION MOBILE

• ONCE LOCATED, THE DESTINATION CELL SITE SENDS A PAGING SIGNAL TO THE DESTINATION MOBILE TO DETERMINE IF IT IS ‘ON’

• AFTER RECEIVING A POSITIVE RESPONSE FROM THE DESTINATION MOBILE,VOICE CHANNELS ARE ASSIGNED TO BOTH ORIGINATING AND DESTINATION MOBILES

MOBILE TO MOBILE CALL (CONTD.)• CALL PROGRESS TONES ARE APPLIED IN BOTH THE DIRECTONS

( RING AND RINGBACK)• WHEN THE STSTEM RECEIVES ANSWER FROM THE DESTINATION

MOBILE, CALL PROGRESS TONES ARE TERMINATED AND CONVERSATION BEGINS

• IF THE SYSTEM FINDS THAT– ALL VOICE CHANNELS ARE ALLOCATED

• SENDS ‘RETRY’ SIGNAL– DESTINATION MOBILE IS ON A CALL

• SENDS ‘BUSY’ SIGNAL– DESTINATION MOBILE NUMBER IS INVALID

• SENDS ‘CALL CAN NOT BE PROCESSED’ SIGNAL