1. ECE Department Florida Institute of Technology Wireless Data Communication Networks Lecture 19: Introduction to GSM

2. ECE Department Florida Institute of Technology Outline  Brief history  GSM network architecture  Elements of the air interface organization Page 2

3. ECE Department Florida Institute of Technology Global System for Mobile Communication  Most popular cellular standard  Started as Groupe Special Mobile  2 nd generation global digital standard  Important time stamps: o1982 CEPT created Groupe Special Mobile o1987 MoU – 13 European countries o1989 Transferred to ETSI o1991 Publishing of Phase 1 specs o1991 Radiolinia Finland – first GSM network o1993 Telstra Australia – first non-European GSM network o1995 US implements GSM in PCS band o1996 Russia and China implement GSM oSince 1996 tremendous growth all over the world Page 3 Official GSM logo

4. ECE Department Florida Institute of Technology GSM in the World Page 4 GSM currently holds about 80% of the market share worldwide

5. ECE Department Florida Institute of Technology Page 5 GSM Network Layout GSM architecture is first standardized cellular system architecture  GSM network can be divided into three main subsystems:  Base Station Subsystem - BSS  Mobile Station Subsystem - MSS  Network Switching Subsystem - NSS

6. ECE Department Florida Institute of Technology Page 6 GSM Network Components  Network has many functional components  Components are integrated through a network protocol – MAP  Majority of GSM interfaces are standardized – allows interworking of equipment from different vendors  Major equipment vendors: Ericsson, Nokia-Siemens, Alcatel-Lucent, Huawei, Motorola, etc.

7. ECE Department Florida Institute of Technology Page 7 Overview of GSM - Mobile Station  Offered as a phone for voice services  Data services will bring new devices to the market  Two functional parts:  HW/SW radio interface  SIM Two types of SIM (Subscriber Identity Module) –Smart Card –Plug-in GSM Mobile Architectural Diagram

8. ECE Department Florida Institute of Technology Page 8 Overview of GSM - Base Transceiver Station  BTS is a set of transceivers (TX/RX).  GSM BTS can host up to 16 TX/RX.  In GSM one TX/RX is shared by 8 users.  The main role of TX/RX is to provide conversion between traffic data on the network side and RF communication on the MS side.  Depending on the application, it can be configured as megacell, macrocell, microcell, pico and femto cell, omni, sectored, etc. Typical BTS installations

9. ECE Department Florida Institute of Technology Page 9 Overview of GSM - Base Station Controller  Provides a small digital exchange with some mobility tasks  Connects to one or several BTS on the Abis Interface  Connects to the MSC on the A Interface  Designed to offload most of the radio link related processes from the MSC  Provides clock distribution to BTS  Communicates with the OMC In GSM, BSC handles majority RRM functions Handoff Power control Channel assignment

10. ECE Department Florida Institute of Technology Page 10 Overview of GSM - TRAU  TRAU is responsible for trans-coding the user data from 16Kb/sec to standard ISDN rates of 64Kb/sec.  It can physically reside on either BSC side or MSC side. If it resides on the MSC side, it provides substantial changes in the backhaul – 4 users over a single T-1/E-1 TDMA channel. TRAU, BSC and BTSs form Base Station Subsystem (BSS) Location of TRAU in GSM

11. ECE Department Florida Institute of Technology Page 11 Overview of GSM - MSC  Responsible for connecting the mobile to the landline side  GSM MSC is commonly designed as a regular ISDN switch with some added functionality for mobility support  GSM Network can have more than one MSC One of the MSC has an added functionality for communication with public network – Gateway MSC (GMSC) All calls from the “outside networks” are routed through GMSC GSM MSC and Gateway MSC

12. ECE Department Florida Institute of Technology Page 12 Overview of GSM - HLR/AuC  Database for permanent or semi-permanent data associated with the user  Logically, there is only one HLR per network  Typical information stored in HLR: International Mobile Service Identification Number (IMSI), service subscription information, supplementary services, current location of the subscriber, etc.  HLR is usually implemented as an integral part of MSC  AUC is an integral part of HLR responsible for ciphering and encryption.  GSM specifies elaborate encryption schemes.  There are three levels of the encryption:  A5/1 – Used by countries in Europe and USA  A5/2 – Used by countries and the so called COCOM list  No encryption – used by all other countries Introduction to GPRS

13. ECE Department Florida Institute of Technology GSM frequency bands  14 bands defined  Most dominant oGSM-900 (P-GSM+ E-GSM) oDCS-1800 oGSM-850 (US) oPCS-1900 (US)  It is common that a phone is capable of multiband operation oDual band - 2 bands oQuad band - 4 bands Page 13

14. ECE Department Florida Institute of Technology GSM – Frequency ARFCN calculations Page 14 ARFCN – Absolute Radio Frequency Channel Number Example – US PCS allocation 22

15. ECE Department Florida Institute of Technology Overview of GSM - Air Interface  GSM is a FDMA/TDMA based technology  Transmissions are discontinuous  Each user is assigned a timeslot  Each frequency is divided into eight timeslots  Each channel has a 200 kHz bandwidth  Overhead signaling is required for coordination and control  Information is sent in bursts  Several types of bursts Page 15 GSM as a FDMA/TDMA Interface

16. ECE Department Florida Institute of Technology Page 16 Overview of GSM - Burst Types  Used to carry information on both control and traffic channels  Mixture of data and overhead  GSM defines 8 training sequences assigned in color code mode  Both on the forward and reverse link  Facilitates the synchronization of the MS to the network at the base band  Commonly referred to as S-burst  Only on the forward link  The same sync sequence is used in all GSM networks Synchronization Burst Normal Burst

17. ECE Department Florida Institute of Technology Page 17 Overview of GSM - Burst Types  Used when the MS is accessing the system  Shorter in length – burst collision avoidance  Extended synchronization sequence  Used only on the reverse link Supports MAHO Used to ensure constant power level of the broadcast control channel Only on the forward link Dummy Burst Access Burst GSM mobiles use slotted ALOHA to access the system In the case of collision – a hashing algorithm is provided

18. ECE Department Florida Institute of Technology Page 18 Overview of GSM - Burst Types  Sometimes referred to as the F-burst  Provides mobile with precise reference to the frequency of the broadcast control channel  Inserting the F-bursts on the control channel produces spectral peak 67.7 KHz above the central frequency of the carrier  Only on the forward link Spectral characteristics of the control channel. The peak in the spectrum allows for easier MS network acquisition Frequency synchronization burst

19. ECE Department Florida Institute of Technology Page 19 Overview of GSM - Physical Channels  A GSM physical channel can carry several different types of logical channels  Can be divided into two categories: traffic and signaling  Signaling channels can be further categorized as:  Broadcast  Common Control  Dedicated Control

20. ECE Department Florida Institute of Technology Page 20 Overview of GSM - Frame Hierarchy  Different organization on the superframe level for different logical channels

21. ECE Department Florida Institute of Technology Page 21 GSM Time Division Duplex  Communication on the forward and reverse link does not happen simultaneously  Delay of three slots between TX and RX  Time division duplexing avoids RF duplexer at the RF stage oReduces the cost of mobile oSaves battery

22. ECE Department Florida Institute of Technology Review questions  What are the elements of GSM system?  What is a BTS?  What is a BSC?  What is a MSC?  What is a HLR?  What is a VLR?  What is TRAU?  What is a SIM card?  What is the Abis? Page 22  What are four most prevalent frequency bands for GSM deployment?  Explain GSM FDMA/TDMA access?  How many time slots are on one GSM ARFCN?  What is an ARFCN?  Name 2 basic channel types in GSM?  Name five burst types used in GSM?

23. ECE Department Florida Institute of Technology Review questions  Draw GSM TDMA hierarchy for traffic channel.  Draw GSM TDMA hierarchy for control channel.  What is the bandwidth of a GSM channel?  What is the difference between DCS-1800 and PCS-1800?  What is a quad-band phone?  Do GSM mobiles use RF duplexers? Please explain. Page 23