Presentation on 2G Technologies
Standard name is IS-54
30 KHz channel spacing of AMPS and frequency bands (824-849 and 869-894‚MHz) as AMPS
This system is most often referred to as TDMA
IS-136 added feature to IS-54 text messaging & circuit switched data.
IS-54 stands for Interim Standard-54 and specifies 84 control channels, 42 of which are shared with AMPS
The channel transmission bit rate for digitally modulating the carrier is 48.6 kbit/s. Each frame has six time slots of 6.67-ms duration.
Also, as with GSM, the known sequence acts as a training pattern to initialize an adaptive equalizer.
The modulation scheme for IS-54 is 7C/4 differential quaternary phase shift keying (DQPSK), otherwise known as differential 7t/4 4-PSK or p/4 DQPSK
The technical specifications can be summarized as below:
Mobile Frequency Range Rx: 869-894 ‚ MHz; Tx: 824-849 ‚ MHz
Multiple Access Method: TDMA/FDM
Duplex Method: FDD
Number of Channels: 832 (3 users per channel)
Channel Spacing/Bandwidth :30 ‚ kHz
Modulation /4 DQPSK
Channel Bit Rate: 48.6 kbit/s
Spectrum Efficiency:1.62 bit/s/Hz
Interleaving: 2 slot interleaver
IS-136 eventually added an extra channel to the IS-54 hybrid design.
Unlike IS-54, IS-136 utilizes time division multiplexing for both voice and control channel transmissions
IS-136 added a number of features to the original IS-54 specification, including text messaging, circuit switched data (CSD), and an improved compression protocol.
IS-136 TDMA traffic channels use p/4-DQPSK modulation at a 24.3-kbaud channel rate and gives an effective 48.6 kbit/s data rate across the six time slots comprising one frame in the 30 ‚ kHz channel.
The origins of the Global System for Mobile Communications (GSM) can be found in Europe ‚
in the early 1980s.
Has to meet the following criteria:
Good subjective speech quality; ‚
Low terminal and service cost; ‚
Support for international roaming; ‚
Ability to support handheld terminals; ‚
Support for range of new services and facilities; ‚
Variants of GSM
Network Architecture ‚
Few terms related to GSM
International Mobile Equipment Identity (IMEI) number
Subscriber Identity Module (SIM)
Personal Identification Number (PIN)
International Mobile Subscriber Identity (IMSI) number
Enables access to subscribed services
Base Station Subsystem (BSS) ‚
It comprises two parts, the Base Station (BS) and the Base Station Controller (BSC).
These communicate across the standardized Abis interface
BSCs are quite intelligent and perform many of the necessary functions to enable the link between the BSs and the MSs.
Forms the central component of the network subsystem.
MSC performs switching of user calls.
The MSC contains no information about particular mobile stations.
The information of MS is stored in the two location registers of GSM.
These are the Home Location Register
(HLR) and the Visitor Location Register (VLR).
HLR, VLR, EIR, AuC
The HLR contains all the administrative information for the subscribers.
This information includes the current locations of the MSs
The Visitor Location Register (VLR) contains selected administrative information from the HLR, necessary for call control and provision of the subscribed services, for each mobile roaming in the area controlled by the VLR
The EIR is a database that contains a list of all valid MSs on the network, each uniquely identified by its IMEI as mentioned above.
Voice needs to be converted from its analog form to a digital form that will be transmitted over the digital GSM wireless network
PCM in not suitable as it has high capacity demands (64 kbps).
Regular Pulse Excited-Linear Predictive Coder (RPE-LPC) with a long term predictor loop is used.
Speech is divided into 20 ms samples, each of which is encoded as 260 bits, giving a total bit rate of 13 kbps.
Radio Transmission Characteristics
Modulation scheme that is used is Gaussian Minimum Shift Keying (GMSK).
This achieves 270.8 kbps ‚over each of the 200-kHz wide GSM channels.
GSM is split into 124 carriers, each 200 kHz wide.
GSM uses a combination of Time and Frequency Division Multiple Access (TDMA/FDMA) for user separation.
Each time period is called a slot and lasts 0.577 ms.
The GSM slot( 8 slots= 1 frame)
A traffic channel (TCH) is used to carry speech and data traffic.
TCHs for the uplink and downlink are separated in time by 3 slots so that the mobile station does not have to transmit and receive simultaneously, thus simplifying the electronics.
Eighth-rate TCHs are also specified, and are used for signalling. They are called Standalone Dedicated Control Channels (SDCCH).
Control channels can be accessed both by idle and active mobiles. They are:
Broadcast Control Channel (BCCH).
Frequency Correction Channel (FCCH)
Random Access Channel (RACH).
Paging Channel (PCH)
Access Grant Channel (AGCH).
Each of these channels finds their use in call initiation from a MS or calling a MS
Handover:Handover is performed by the Radio Resources layer
Handover of a call between channels (slots) in the same cell.
Handover of a call between cells under the control of the same BSC.
Handover of a call between cells under the control of different BSCs, which belong to the same MSC.
Handover of a call between cells under the control of different MSCs.
There are five classes of MS defined (three in North American GSM standards), according to their peak transmitter power, rated at 20, 8, 5, 2, and 0.8 W. To minimize co-channel interference and to conserve power, both the mobiles and the base transceiver stations operate at the lowest power level that will maintain an acceptable signal quality.