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
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
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
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.
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.
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.
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”
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
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.
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
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
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.
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
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
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