Overview of GSM Architecture · 2013. 6. 18. · GSM Call Flow Scenarios . GSM Call Flow Scenarios . GSM Call Flow Scenarios • Handoff – MS scans transmission from surrounding

Overview of GSM Architecture

2EC359 Advanced Communication System

B.Tech Sem-VII (EC)

GSM: History • 1982 CEPT establishes Groupe Speciale Mobile

– Motivation develop Pan-European mobile network – Support European roaming and interoperability in landline – Increase system capacity – Provide advanced features – Emphasis on STANDARDIZATION, supplier independence – Low cost infrastructure and terminals

• 1989 European Telecommunications Standardization Institute (ETSI) takes over standardization – changes name: Global System for Mobile Communication

• 1990 First Official Commercial launch in Europe • 1995 GSM Specifications ported to 1900 MHz band • GSM is the most popular 2G technology

GSM Overview • FDD/ FDMA/TDMA – channel structure - 200 KHz channels – each

carries 8 voice channels • Higher Quality than Analog Systems • Digital Voice compressed to 13.3Kbps • Slow frequency hopping, adaptive equalizer, error control coding,

DTX • Low power handsets – support sleep mode • Security with encryption • Subscriber Identity Modules (SIM cards) • personalization of the mobile terminal, stores user parameters • Low bit rate digital data service • fax, circuit switched data • SMS short messaging service • Additional features: call waiting, voice mail, group calling, caller id…

GSM Services

GSM Services

GSM System Architecture

GSM System Architecture

GSM Interfaces

GSM Air Interface Um

Mobile Station • Mobile Station Types – Vehicle-mounted stations – portable stations – handheld stations • Mobile Station Power Classes – Vehicular & portable units can be either class I or class II – Handheld units can be class III, IV, & V

Identities of Mobile Station

• Mobile station has three identities

– International Mobile Subscriber Identity (IMSI) – International Mobile Equipment Identity (IMEI) – Temporary Mobile Subscriber Identity (TMSI)

Identities of Mobile Station • International Mobile Subscriber Identity

– IMSI is assigned to an MS at subscription time – It uniquely identifies a given MS – It contains 15 digits

• Mobile Country Code (MCC) – 3 digits (home country)

• Mobile Network Code (MNC) – 2 digits (home GSM PLMN)

• Mobile Subscriber Identification(MSIN) • National Mobile Subscriber Identity(NMSI) eg. 262 02 454 275 1010


• International Mobile Equipment Identity (*#06#)

– IMEI uniquely identifies the MS equipment – It is assigned by the equipment manufacturer – It contains 15 digits

• Type Approval Code (ATC) – 6 digits

• Final Assembly Code (FAC) – 2 digits

• Serial Number (SNR) – 6 digits

• Spare (SP) – 1 digit


• Temporary Mobile Subscriber Identity

– TMSI is assigned to MS by the Visitor Location Register (VLR)

– TMSI uniquely identifies an MS within the area controlled by a given VLR

– A maximum of 32 bits can be used for TMSI


• Subscriber Identity Module Card (SIM card)

– IMSI – Authentication Key – Subscriber information – Access control class – Cipher key – Additional GSM services – Location Area Identity – Forbidden PLMN

Summary of Identities

Base Station Subsystem

• Base Station Subsystem (BSS) contains 2 Parts

– Base Station Controller (BSC) – Base Transceiver System (BTS)

• It contains the Transcoder Rate Adopter Unit (TRAU) – GSM-specific speed encoding & decoding is carried

out, as well as the rate adaptation function for data • Power class are also classified in a similar way to

MS with 8 classes in 3 dB - steps from 2.5 W to 320 W

Network and Switching Subsystem

• Network and Switching Subsystem contains

– Switching functions of the GSM

• MSC & GMSC – Database required for the subscriber – Mobility management

Operational & Maintenance Subsystem

• The OMS is responsible for handling system security based on validation of identities of various telecommunication entities. Performed by • Authentication Center (AUC): The AUC is accessed by HLR

to determine whether an MS will be granted services • Equipment Identity Register (EIR): The EIR provides MS

information used by the MSC. The EIR maintain a list of legitimate, fraudulent or faulty MSs.

• In charge of remote operation and maintenance of PLMN.

• Operational and Maintenance Center (OMC) – The functional entity through which the service provider

monitors and controls the system.

GSM QoS Requirements

High-Level View of Some Scenarios

GSM Call Flow Scenarios






• Handoff – MS scans transmission from surrounding BSs in

the spare timeslots • It then reports the measured results back to the

fixed network via BS, where the handoff decision is made

• Classifications • Internal Handoff – Inter-BSS Handoff • External

– Intra-MSC Handoff – Inter-MSC Handoff

GSM-INTRA MSC HAND OFF

GSM Time Slot Structure

Frequency Bands and Bandwidth




• Time Slot Structure or Burst types in GSM – Normal Bursts – Random Access Burst – Frequency Correction Bursts – Synchronization Bursts



68.25 bits = 0.252 msec which is equivalent to 75.5 km propagation delay. That is, the max. allowed distance between mobile station and BTS is 37.75 km. Max. cell size is 35 km


An all zeros sequence can meet the purpose of frequency correction due to the nature of GMSK.


In the beginning , it only detects the frequency of base channel and needs to know the training seq. and system parameters. This is done by the synchronization burst. In addition to a longer synchronization seq., coded data contains the BSIC (base station information code) including BCC (BS color code) and NCC (national color code) and shortened TDMA frame number.

GSM Logical Channels


Traffic Channel – Are used to transmit user information (speech or data) – 2 categories

• TCH/Full (TCH/F) – Allows the transmission of 13 Kbps of speech • TCH/Half (TCH/H) – Allows the speech coded at a half rate

GSM Logical Channels Control Channel (CCH)

– Are used to transmit control and signaling information • Broadcast Channel (BCH) • Common Control Channel (CCH) • Dedicated Control Channel (DCCH)


Control Channel (CCH) – Broadcast Channel (BCH) • Are point-to-multipoint, downlink-only channels • Classification – Broadcast Control Channel (BCCH) – Frequency Correction Channel (FCCH) – Synchronization Channel (SCH)

GSM Logical Channels Control Channel (CCH) – Common Control Channel (CCCH)

• Are point-to-multipoint, downlink-only channels that are used for paging & access except for RACH.

• Classifications – Paging Channel (PCH) – Access Grant Channel (AGCH) – Random Access Channel (RACH)

GSM Logical Channels Control Channel (CCH) – Dedicated Control Channel

(DCCH) • Are bidirectional, point-to-point channels • Classifications – Stand-Alone Dedicated Control Channel (SDCH) – Associated Control Channel (ACCH)

• Slow Associated Control Channel (SACCH) • Fast Associated Control Channel (FACCH)


GSM Frame Structure

GSM Frame Structure

GSM Frame Structure

GSM Frame Structure

GSM Frame Structure

GSM Frame Structure

GSM Frame Structure

GSM Frame Structure

GSM Frame Structure

• T1, T2 & T3 Counters – T1 counter counts the super-frames

• Whenever a super-frame is completed, T1 is incremented by 1 & 0 < = T1 < =2047

– T2 counter counts the speech frames, which only occur in 26 multi-frame structure & 0 <=T2 <= 25

– T3 counter counts the signaling frames, which are 51-multi-frame structure & 0 <= T3 <= 50

GSM Frame Structure

GSM Frame Structure

Location Updating Scenarios

Call Establishment Scenarios


GSM signal Processing

GSM Signal Processing







Security in GSM

Authentication and Encoding

Authentication Procedure in GSM

Ciphering in GSM

GSM Frequency Hopping

Frequency Hopping

Handset Hardware

Block Diagram of Base Station

GSM Protocol Stack

GSM Protocol Stack

Location Management

Documents

Overview of GSM Architecture · 2013. 6. 18. · GSM Call Flow Scenarios . GSM Call Flow Scenarios . GSM Call Flow Scenarios • Handoff – MS scans transmission from surrounding