Chapter 9: Existing Wireless Systems: 2G, GSM System

1. Chapter 9:Existing Wireless Systems:2G, GSM System Associate Prof. Yuh-Shyan Chen Dept. of Computer Science and Information Engineering National Chung-Cheng University

2. Introduction • Global System for Mobile communication or Groupe Speciale Mobile (GSM) communication • Initiated by European Commission • Second-generation mobile cellular system • Aimes at developing a Europe-wide digital cellular system • Created in 1982 to have a common European mobile telephone standard that would formulate specifications for a pan-European mobile cellular radio system operating at 900 MHz • The main objective of GSM is to remove any incompatibility among the systems by allowing the roaming phenomenon for any cell phone

3. Introduction • It also supports speed transmissions between MSs, emergency calls, and digital data transmission • Specific functions of different constituents are as follows • Base Station Controller (BSC): • Mobile Switching Center (MSC): • Authentication Center (AC): • Equipment Identity Register (EIR):

4. GSM infrastructure

5. Frequency Bands and Channels • GSM has been allocated an operational frequency from 890 MHz and 960 MHz • MSs employ 890 MHz to 915 MHz • BS operates in 935 MHz and 960 MHz • GSM follows FDMA and allows up to 124 MSs to be serviced at the same time • The frequency band of 25 MHz is divided into 124 frequency division multiplexing (FDM) channels, each of 200 kHz (Fig. 10.9) • A guard frame of 8.25 bits is used between any two frames transmitted either by the BS or the MS

6. Frequency band used by GSM

7. GSM uses a variety of multiplexing techniques • GSM uses a variety of multiplexing techniques to create a collection of logical channels • Three control channels are used for broadcasting some information to all MSs • Broadcast control channel (BCCH) • Frequency correction channel (FCCH) • Synchronization channel (SCH)

8. Channel in GSM

9. Cont. • Three common control channels are used for establishing links between the MS and the BS • Random access channel (RACH): • Used by the MS to transmit information regarding the requested dedicated channel from GSM • Paging channel: • Used by the BS to communicate with individual MSs in the cell • Access grant channel: • Used by the BS to send information about timing and synchronization

10. Cont. • Three dedicated control channels are used • Slow associated control channel (SACCH): • Stand-alone dedicated control channel (SDCCH): • Fast associated control channel (FACCH):

11. Frames in GSM • GSM system uses the TDMA scheme with a 4.615 – ms long frame • Dividing into eight time slots each of 0.557 ms • Each frame measured in terms of time is 156.25 bits long, of which 8.25 period bits are guard bits for protection • The 148 bits are used to transmit the information • The frame contains 26 training bits allow the receiver to synchronize itself • Many such frames are combined to constitute multiframes, superframes, and hyperframes

12. Frame structure of TDMA

13. Identify Numbers used by a GSM System • International Mobile Subscriber Identity (IMSI)

14. Format of IMSI

15. Cont. • Subscriber Identify Module (SIM) • Every time the MS has to communicate with a BS, it must correctly identify itself. • A MS does this by storing the phone number, personal identification number for the station, authentication parameters, and so on in the SIM card • Smart SIM cards have a flash memory • The main advantage of SIM is that is supports roaming with or without a cell phone, also called SIM roaming • Mobile System ISDN (MSISDN)

16. Format of MSISDN

17. Cont. • Location Area Identify (LAI) • The GSM service area is usually divided into a hierarchical structure that facilitates the system to access any MS quickly • Each PLMN is divided into many MSCs • Each MSC typically contains a VLR to tell the system if a particular cell phone is roaming • If it is roaming, the VLR of the MSC in which the cell phone is reflects the fact • Each MSC is divided into many location areas (LAs) • A location area is a cell or a group of cells and is useful when the MS is roaming in a different cell but the same LA

18. Cont. • Since any LA has to be identified as the part of the hierarchical structure • The identifier should contain the country code, mobile network code, and LA code

19. GSM layout

20. Cont. • International MS Equipment Identity (IMSEI)

21. Format of IMSEI

22. Cont. • MS Roaming Number (MSRN)

23. Format of MSRN

24. Layout, Planes, and Interfaces of GSM

25. Interface of GSM

26. Cont. • The GSM system can be divided into five planes • OAM • CM • MM • RR • Physical

27. Functional planes in GSM

28. Authentication • Authentication is done with the help of a fixed network that is used to compare the IMSI (International Mobile Subscriber Identity) of the MS reliably

29. Authentication process in GSM

30. Handoff in GSM • Intracell/intra-BTS handoff • Intercell/intra-BSC handoff • Inter-BSC/intra-MSC handoff • Inter-MSC handoff

31. Inter-MSC handoff

32. Personal Communication Service (PCS) • PCS employs an inexpensive, lightweight, and portable handset to communicate with a PCS BS • The PCS is classified into high-tier and lower-tier standards • High-tier system includes high-mobility units with large batteries • An MS in a car • Low-tier system includes system with low mobility, capable of providing high-quality portable communication service over a wide area • The PCS lower-tier standards based on PACS (Personal Access Communication Systems) and DECT (Digital European Cordless Telecommunication) are given in Table 10.6.

33. FCC view of PCS

34. PCS High-Tier Standards

35. PCS Low-Tier Standards

36. Chronology of PCS Development • CT2 (Cordless Telephone) • Using FDMA with a speed rate of 32 kbps using Adaptive Differential Pulse Code Mudulation (ADPCM) • The transmitter data rate is 72 kbps • Uses TDD, which allows BS and MS share one channel • D is called D-channel which includes 4 bits of control information • DECT (Digital European Cordless Telecommunication)

37. CT2 TDD Slot (First Generation)

38. DECT (Digital European Cordless Telecommunication) • The second-generation cordless telephone system • DECT operates on frequencies ranging from 1880 MHz to 1900 MHz • Uses ADPCM with 32 kbps speed rate • Uses TDD with two frames with 10-ms periods • Supports both voice and data transmission

39. DECT TDD Slot (Second Generation)

40. Bellcore View of PCS • The Bellcore view of PCS is based on five different service provided between the Bellcore client company (BCC), BCC network, and the PCS wireless provider network • PCS access service for networks (PASN) • A connection service to and from the PCS service provider (PSP) • PCS access service for controllers (PASC) • A service for use with PCS wireless provider (PWP) across radio channels and some type of automatic link transfer capability

41. Bellcore View of PCS • PCS access service for ports (PASP) • An interface into PWP • PCS access service for data (PASD) • A database information transport service • PCS access service for external service providers (PASE) • Is used to support specialized PCS service like voice mail and paging

42. Bellcore PCS Architecture Signaling System 7 Radio Port Radio Port Control Unit Operation, Administration, & Maintenance

43. Description of the PCS Air Interface:Forward TDMA Frame for PCS