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CELLULAR COMMUNICATIONS GSM/GPRS/EDGE. Groupe Speciale Mobile/Global System for Mobile.

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Presentation on theme: "CELLULAR COMMUNICATIONS GSM/GPRS/EDGE. Groupe Speciale Mobile/Global System for Mobile."— Presentation transcript:


2 Groupe Speciale Mobile/Global System for Mobile

3 GSM Air Interface  TDMA with FDD  200Khz channels with 200KHz guard bands  GSM 900 has 124 carriers  GMSK modulation, 270kbps per carrier  Up to 8 users, 24.8kbps per user  FEC reduces to 13kbps per user for voice

4 Physical Channel  RF carrier divided into 8 slots, numbered 0..7  Timeslots carrying data  At most 8 traffic channels  Control messages  At least 1 control channels  More control (logical) channels  Packed into RF carrier

5 Single Burst/Slot

6 Frame Structure

7 Traffic channels (TCH) Signaling channel TCH/F: Full-rate Traffic Channel TCH/H: Half-rate Traffic Channel FCCH: Frequency correction SCH: Synchronization BCCH: Broadcast control PCH: Paging AGCH: Access grant RACH: Random access SDCCH: Stand-alone dedicated control SACCH: Slow associated control FACCH: Fast associated control Two-way Base-to- mobile Two-way Logical Channel List BCH CCCH DCCH

8 Broadcast Control Channels

9 Common Control Channels

10 Dedicated Control Channels

11 Channel Coding





16 16 What is a location area (LA)?  A powered-on mobile is informed of an incoming call by a paging message sent over the PAGCH channel of a cell  One extreme is to page every cell in the network for each call - a waste of radio bandwidth  Other extreme is to have a mobile send location updates at the cell level. Paging cut to 1 cell, but large number of location updating messages.  Hence, in GSM, cells are grouped into Location Areas – updates sent only when LA is changed; paging message sent to all cells in last known LA

17 International Mobile Station Equipment Identity (IMEI)  Type Approval Code (TAC): 6 decimal places, centrally assigned.  Final Assembly Code (FAC): 6 decimal places, assigned by the manufacturer.  Serial Number (SNR): 6 decimal places, assigned by the manufacturer.  Spare (SP): 1 decimal place.

18 International Mobile Subscriber Identity ( IMSI)  Mobile Country Code (MCC): 3 decimal places, internationally standardized.  Mobile Network Code (MNC): 2 decimal places, for unique identification of mobile network within the country.  Mobile Subscriber Identification Number (MSIN): Maximum 10 decimal places, identification number of the subscriber in the home mobile network.

19 Mobile Subscriber ISDN Number ( MSISDN):  Country Code (CC) : Up to 3 decimal places.  National Destination Code (NDC): Typically 2-3 decimal places.  Subscriber Number (SN): Maximum 10 decimal places.

20 SMS  SMS allowed  Two way communications of the text messages  Maximum character length of 160 characters This can change though depending on the operator or the character set used  Character sets supported are ASCII + additional European characters Unicode  First Text  Was sent in December 1992, to a Vodafone device Sent by Neil Papworth, saying “Merry Christmas”  Standard  Defined by ETSI and is known as “GSM 03.40”

21 SMS  SMS Continued  The success is SMS was never planned for!  It was only ever intended as the Pager replacement, with limited use This will explain some of the design decisions made

22 SMS  GSM  At a defined time interval in GSM all devices will listen to a transmission. This is when a Digital Control Channel (DCCH) packet of information is being sent across the network. These DCCH packets are used to transfer essential information into the devices. Information like a call is in coming Paging signals from the Base stations, to work out if a handover is needed One of these packet formats is called SMS point to point messaging, Paging, access control channel (SPACH) This message type can be used to carry a text message. Advantage of this method is a text message can still be delivered during a phone conversation.

23 SMS  SMS Packet format  All data is transferred in a single DCCH SPACH packet SCAService Centre Address MRMessage ReferencePIDProtocol Identifier PDU TypeProtocol Data Unit Type DADestination AddressDCSData Coding Scheme VPValidity PeriodUDLUser Data LengthUDUser Data

24 GPRS: General Packet Radio Service  GSM data  CSD: circuit switched data  Max 14kbps  Similar to voice call  Inefficient usage of spectrum  GPRS packet-based service  Upgrade of infrastructure  GGSN is a gateway to outside world  SGSN is a gateway within the network

25 GPRS architecture

26 GPRS handset classes  Class A Class A terminals have 2 transceivers which allow them to send / receive data and voice at the same time. This class of device takes full advantage of GPRS and GSM. You can be taking a call and receiving data all at the same time.  Class B Class B devices can send / receive data or voice but not both at the same time. Generally if you are using GPRS and you receive a voice call you will get an option to answer the call or carry on.  Class C This device only allows one means of connectivity. An example would be a GPRS data card in a laptop.

27 Page 27  Packet switched  Upgrades the modulation scheme  From GMSK to 8-PSK  Maximum speed ~59 Kb/sec per time slot, ~473.6 Kb/sec for all 8 time slots  Variable data rate – depending on the channel conditions  Defines several different classes of service and mobile terminals Enhanced Data GSM Environment (EDGE) EDGE enabled data mobile

28 Page 28 Practically achievable data rates  Theoretical rates are constrained by mobile power and processing capabilities  Most mobiles support less than the maximum allowed by standard Practically achievable data rates

29 Page 29 Migration: 1.High speed circuits switched data (HSCSD) 2.Packet switched data (GPRS,EDGE) 3.Integrated packet services – possibly under different access scheme (UMTS) GSM Migration Towards 3G

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