GSM (Global System for Mobile communications) is a digital cellular network developed to provide improved spectrum efficiency, international roaming, and compatibility with other networks. It uses TDMA to allow multiple users to access the same radio frequency channel at different time slots. The GSM architecture consists of mobile stations, a base station subsystem including base transceiver stations and base station controllers, and a network subsystem including mobile switching centers and databases like the home location register.

2. PRESENTATION CONTEMPORARY STUDENTS NAME: AZIZ ZOAIB ID: FA06-BS-0013 COURSE: SWITCHING THEORY TOPIC: GSM ARCHITECTURE

3. What is Telecommunication Telecommunications means to change information into electric signals for remote transmission. Getting Wireless---What's the Advantage? Saving Transmission Cost. Fast Deployment. Easy and Fast Access Challenges Interference Multipath Fading LOS and NLOS (RAN and Backhaul) Changing Terrain and Air Interface Characteristics(weather)

4. History of Cellular Mobile Radio and GSM(Global Systems for Mobile) Early 1980s there was analog technologies: Advanced Mobile Phone Services(AMPS)in North America. Total Access Communications System(TACS)in the UK. Nordic Mobile Telephone(NMT) in Nordic countries.

5. Contd Each country developed its own system, which caused problems: System worked only within the boundaries of each country. Mobile equipment manufacturers Markets were limited by the operating system. Solution was GSM, which is digital technology and was developed by CEPT(Conference of European Posts and Telecommunications)

6. The Goals of GSM Improved spectrum efficiency International roaming Low-cost mobile sets and base stations High-quality speech Compatibility with ISDN and other telephone company services. Support for new services QoS

7. Gsm facts(2003) Used in over 170 countries Over 400 GSM network operators Over 550 million people were subscribers to GSM

9. FDMA, CDMA FDMA (FREQUENCY DIVISON MULTIPLEXING) 1) Each user on a different frequency. 2) A channel is a frequency. CDMA (CODE DIVISION MULTIPLEXING) 1) Each user uses the same frequency all the time, but mixed with different distinguishing code patterns. 2) A channel is a unique set of code patterns.

10. Gsm uses TDMA Short for T ime D ivision M ultiple A ccess, a technology for delivering digital wireless service using time-division multiplexing (TDM). TDMA works by dividing a radio frequency into time slots and then allocating slots to multiple calls. In this way, a single frequency can support multiple, simultaneous data channels.TDMA is used by the GSM digital cellular system. Time Frequency 0 1 2 3 4 5 6 7 Time Slot

11. CONTD Time Division Multiple Access Each carrier frequency subdivided in time domain into 8 time slots Each mobile transmits data in a frequency, in its particular time slot - Burst period = 0.577 milli secs. 8 time slots called a TDMA frame. Period is .577 * 8 = 4.616 milli secs 0 1 2 3 4 5 6 7 4.616 ms 0.577 ms

12. FDD/ TDD

13. UP / Down-Link Down-link: the transmission path from Base Station to Mobile Station Up-link: the transmission path from Mobile Station to Base Station

14. GSM Cell Structure The power level of a transmitter within a single cell must be limited to reduce the interference with the neighboring cells.

15. Contd Neighboring cells cannot share the same channels Different size of patterns: 4,7,12 or 21cells in one cluster

16. Types of Cells Macrocells(3 to 35 km) Microcells(0.1 to 1 km) 1) Picocells(0.01 to 1km) 2) Nanocells(1m to 10m)

17. GSM Architecture Mobile Station (MS) Used by the subscriber to access the GSM network via the air interface Contains the hardware and software specific to the radio interface Need a Subscriber Identity Module (SIM) which contains the subscriber-specific data to access GSM network, except emergency call SIM cards are embedded with a microprocessor Stores customer identity information and is made to fit inside the cellular phone Memory capacity 1K, 3K, 8K, 16K

18. Base Transceiver Station(BTS) serves a single cell usually placed in the center of a cell. multiplexing modulating synchronizing

19. Base Station Controller(BSC) Frequency hopping Time and frequency synchronization Power management Time delay measurements

20. The Transcoder and adaptation unit(TRAU) (13Kbps speech or data + 3Kbps additional synchronizing data)*4 =64Kbps (TRAU Standard rate)

21. Base Station Subsystem(BSS) = BTS + BSC

22. Mobile Switching Center(MSC) The central component of the Network Subsystem (30 + 2)* 64Kbps = 2,048Mbps(E1) or better to the other network interfaces(PSDN,ISDN) Billing Location registration Gateway to SMS Synchronizing BSS Handover management

23. GSM Architectures 3 broad parts Subscribers carries MOBILE STATION BSS controls the radio link with the mobile station NETWORK SUBSYSTEM (NSS), which main part is MSC

26. The Registers Completing the NSS Home Location Register (HLR) contains all information of each subscriber registered in the corresponding GSM network Visitor location Register (VLR) contains selected information from the HLR, which is necessary for call control and provision of the subscribed services, for each mobile currently located in the geographical area controlled by the VLR NSS = HLR + VLR + MSC

27. Equipment Identity Register (EIR) contains a list of all valid mobile equipment on the network Authentication Center (AUC) stores a copy of the secret key stored in each subscribers SIM card EIR and AUC are used for security and authentication purposes EIR has three databases., White list - For all known, good IMEI’s Black list - For all bad or stolen handsets Grey list - For handsets/IMEI’s that are on observation

28. GSM IS A HALF DUPLEX

29. Trunking theory and EARLANG Trunking theory: Cellular radio systems rely on trunking theory to accommodate a large number of users in a limited radio spectrum. The fundamentals of trunking theory was developed by Earlang, a Danish mathematician in the late 1990s. EARLANG: Earlang represents the amount of traffic intensity carried by a channel that is completely occupied.

30. CONTD EARLANG B: ( Also called Block calls Cleared) that is for every user who requests service it is assumed that user is given a immediate access to a channel if one is available. If no channel is available the user is blocked without access and is free to try again later. EARLANG B: (Also called Block calls Delayed) is one in which a que is provided to hold calls which are blocked. If a channel is not available immediately the call request may be delayed until a channel becomes available.

31. Channel concept Physical channel: One timeslot of a TDMA-frame on one carrier is referred to as a physical channel. There are 8 physical channels per carrier in GSM,channel 0-7(timeslot 0-7). Logical channel: A great variety of information must be transmitted between BTS and the MS,for e.g. user data and control signaling. Depending on the kind of information transmitted we refer to different logical channels. These logical channels are mapped on physical channel.

32. GSM CHANNELS

33. CONTD Control channels are intended to carry signaling or synchronization data. Three are defined: Broadcast Channels (BCHs), Common Control Channels (CCCHs), Dedicated Control Channels (DCCHs). Broadcast channels are point to multipoint unidirectional (downlink) control channels from the the fixed subsystem to the mobile telephone. First, BCHs include a Frequency Control Channel ( FCCH ) that allows an MS to accurately tune to a Base Transceiver Station (BTS). Then BCHs contain the Synchronization Channel ( SCH ), which provide TDMA frame oriented synchronization data to a MS. Last, BCHs include the Broadcast Control Channel ( BCCH ) intended to broadcast a variety of information to MSs, including cues necessary for the MS to register in the network.

34. CONTD Common Control Channels (CCCHs) are point to multipoint channels that is primarily intended to carry signaling information for access handling functions. The CCCHs include: Paging Channel ( PCH ), which is down channel used to page (call terminating) MSs. Access Grant Channel ( AGCH ) that is a downlink channel used to assign a MS to a specific Dedicated Control Channel (DCCH). Cell Broadcast Channel ( CBCH ), which is down channel used to broadcast miscellaneous short messages to the MSs. Random Access Control Channel (RACH ) is an uplink channel which allows MS to initiate a call.

35. CONTD Stand Alone control channel (SDCCH) it is used to send sms. Slow Associated control channel (SACCH) It is used to gather the information of surrounding area and updates the network. Fast Associated control channel (FACCH) It has the authority to discard speech channel while executing the handoff.

36. Types of handoffs Intra cell handover: The MS in handed over to another channel on the same cell, under the same BTS. Intra BSC handover: The MS is handed over to the another channel on a d/f cell, under the control of the d/f BTS of the same BSC. Inter BSC Handover: the MS is handed over to the another channel on a d/f cell, under the control of a d/f BSC of the same MSC. Inter MSC Handover: The MS is handed over to another MSC.

38. THANKS Q/A.?