1. Yschen, CSIE, CCU1 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. Yschen, CSIE, CCU2 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. Yschen, CSIE, CCU3 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. Yschen, CSIE, CCU4 GSM infrastructure

5. Yschen, CSIE, CCU5 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. Yschen, CSIE, CCU6 Frequency band used by GSM

7. Yschen, CSIE, CCU7 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. Yschen, CSIE, CCU8 Channel in GSM

9. Yschen, CSIE, CCU9 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. Yschen, CSIE, CCU10 Cont.  Three dedicated control channels are used Slow associated control channel (SACCH): Stand-alone dedicated control channel (SDCCH): Fast associated control channel (FACCH):

11. Yschen, CSIE, CCU11 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. Yschen, CSIE, CCU12 Frame structure of TDMA

13. Yschen, CSIE, CCU13 Identify Numbers used by a GSM System International Mobile Subscriber Identity (IMSI)

14. Yschen, CSIE, CCU14 Format of IMSI

15. Yschen, CSIE, CCU15 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. Yschen, CSIE, CCU16 Format of MSISDN

17. Yschen, CSIE, CCU17 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. Yschen, CSIE, CCU18 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. Yschen, CSIE, CCU19 GSM layout

20. Yschen, CSIE, CCU20 Cont.  International MS Equipment Identity (IMSEI)

21. Yschen, CSIE, CCU21 Format of IMSEI

22. Yschen, CSIE, CCU22 Cont.  MS Roaming Number (MSRN)

23. Yschen, CSIE, CCU23 Format of MSRN

24. Yschen, CSIE, CCU24 Layout, Planes, and Interfaces of GSM

25. Yschen, CSIE, CCU25 Interface of GSM

26. Yschen, CSIE, CCU26 Cont.  The GSM system can be divided into five planes OAM CM MM RR Physical

27. Yschen, CSIE, CCU27 Functional planes in GSM

28. Yschen, CSIE, CCU28 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. Yschen, CSIE, CCU29 Authentication process in GSM

30. Yschen, CSIE, CCU30 Handoff in GSM Intracell/intra-BTS handoff Intercell/intra-BSC handoff Inter-BSC/intra-MSC handoff Inter-MSC handoff

31. Yschen, CSIE, CCU31 Inter-MSC handoff

32. Yschen, CSIE, CCU32 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. Yschen, CSIE, CCU33 FCC view of PCS

34. Yschen, CSIE, CCU34 PCS High-Tier Standards

35. Yschen, CSIE, CCU35 PCS Low-Tier Standards

36. Yschen, CSIE, CCU36 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. Yschen, CSIE, CCU37 CT2 TDD Slot (First Generation)

38. Yschen, CSIE, CCU38 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. Yschen, CSIE, CCU39 DECT TDD Slot (Second Generation)

40. Yschen, CSIE, CCU40 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. Yschen, CSIE, CCU41 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. Yschen, CSIE, CCU42 Bellcore PCS Architecture Radio Port Control Unit Signaling System 7 Operation, Administration, & Maintenance

43. Yschen, CSIE, CCU43 Description of the PCS Air Interface: Forward TDMA Frame for PCS