gsm and tdma technology
- 1. GSM AND TDMA TECHNOLOGY Mr.Narayana Swamy.R Assoc.Prof,Dept of ECE T.John Institute of Technology, Bangalore
- 2. GSM SYSTEM OVERVIEW • INTRODUCTION TO GSM AND TDMA – In 1982 frequency bands of 890-915MHz and 935-960MHz i.e. 25MHz bandwidth and 45MHz duplex spacing, were allocated for a PAN-European second generation digital cellular system (GSM 900) which would allow roaming on an international basis and would replace the incompatible first generation systems . – 1982- task force, 1987 – formally adopted by European commission, 1989-ETSI Took over, 1990- standard published, 1992-deployment of functional system, 1997- GSM 1800 (DCS 1800), GSM1900 (PCS). • GSM Services – First Generation Analog cellular systems were designed for basic voice service. Data services for fax or circuit switched data transmission using a voice band modem were classified as “overlay” services that run on top of the voice service. – Second Generation Digital Cellular systems (GSM) were designed for integrated wireless voice-data service network that offered several services like teleservices, bearer services and supplementary services (can be added to teleservices) over GSM network. – GSM System development and deployment to implement services happens in two phases shown in table 5-1 (Phase-1), 5-2(Phase-2), Phase-2+ (addition of high speed packet data services to GSM(EDGE and GPRS)). • GSM Radio frequency carriers – GSM900-FDMA divides 25MHz bandwidth into 124 carrier frequencies each of 200khz bandwidth. – GSM1800 – 374 Carrier frequencies – GSM1900 – 299 Carrier frequencies – Since each carrier can be shared by up to 8 users, the total number of channels for each system is • 124 x 8 = 992 channels for GSM900 • 374 X 8 = 2992 channels for GSM1800 • 299x 8 = 2392 channels for GSM 1900/PCS1900 System Direction Frequency band (MHz) GSM 900 Uplink 890-815 Downlink 935-960 GSM/DCS1800 Uplink 1710-1785 Downlink 1805-1880
- 6. GSM Network and System Architecture
- 7. Mobile Station • Consists of two elements – Mobile equipment – SIM • Is the device that provides radio link between GSM subscriber and wireless mobile network. • Provides subscriber means to control their access to PSTN and PDN and also to facilitate their mobility once connected to the network. • Supports setup and clearing of radio channels used for the TX of various forms of subscriber traffic. • Constantly performing power and BER measurements on signals being received from BTS. This along with handover algorithms performed BSS supports mobility. • SIM – Makes MS functional – Subscriber IMSI number – Mobile MSISDN number – SIM PIN – Address book – Stored SMS – Additional services (video)
- 8. Base station system • Consists of two elements – Base transceiver system (BTS) – Base station controller (BSC) • Provide translation between MS (wireless protocols) and MSC (wireline protocol). • Communication Between BTS and BSC is through LAPD protocol (data link, ISDN (Network layer)). • Components of BTS (RBS (radio base station)) – Radio transceiver units, – Switching and distribution unit – RF Power combining and distribution units, – Environmental control units, – Power system, – Processing and database storage unit. • BSC components – Input and output interface multiplexers – Timeslot interchange group switch – Subrate switch – Speech coder/decoders – Transcoders and rate adaptors (stand alone TRC) – SS7 signaling points – Environment control units – Power supply and power distribution units – Various signal and control processing.
- 9. Network switching system • Provides necessary interface for connection of the wireless network to other networks and provides support for the mobility. • NSS includes – Atleast one MSC – A gateway MSC – VLR and HLR – Equipment identity register(EIR) – Authentication center(AuC) – Flexible numbering register (FNR) – Inter working location register • To handle SMS – GMSC, IWMSC and GPRS for high speed data TX/Rx requires additional SGSN and GGSN.
- 10. Operation and support system and other nodes • Supports operation and maintenance of entire network • System operator – Perform configuration – Performance evaluation – Security management along with display of fault or alarms
- 11. GSM Network interfaces and protocols • GSM Interfaces
- 12. GSM Network interfaces and protocols • GSM protocols and signaling model Layered structured or OSI Model • GSM signaling protocol’s third layer is divided into three sub layers: – Radio Resource Management (RR), – Mobility Management (MM), and – Connection Management (CM).
- 13. • Figure 5-6 shows signaling model for the GSM System. As shown by the figure, the MS communicate with the MSC to provide system connection, mobility, and radio resource management by sending messages back and forth over the air interface from the MS to the BTS, between the BTS and the BSC and between the BSC and the MSC. • Um interface The "air" or radio interface standard that is used for exchanges between a mobile (ME) and a base station (BTS / BSC). For signaling, a modified version of the ISDN LAPD, known as LAPDm is used. – Major differences are LAPDm no error detection is employed (built into Layer 1 signaling) – LAPDm messages are segmented into shorter messages than LAPD to be compatible with the TDMA frame length. • Abis interface This is a BSS internal interface linking the BSC and a BTS, and it has not been totally standardised. The Abis interface allows control of the radio equipment and radio frequency allocation in the BTS. There are some radio resource management messages handled by BTS.(BTSM(BTS Management) example encryption) • A interface The A interface is used to provide communication between the BSS and the MSC. Signaling over A interface is done according to BSSAP (base station signaling application part) using the network service part of SS7. – In MSC in direction of MS layer 3 is subdivided into three parts: RR, CM, MM – The protocol used to transfer CM and MM messages is BSSAP and is subdivided into DTAP(Direct transfer application part) and BSSMAP (Base station system management application part) – DTAP is used to send CM and MM messages between MSC and MS transparently through BSS. – BSSMAP is used to send messages between MSC and BSC.
- 14. • Ater Interface – Only exists in GSM systems that have separate units for the transcoder controller and BSC . Signaling between the BSC and the TRC Is performed by the use BSC/TRC application part (BTAP) protocol. • MSC interface – MTP,SCCP, TCAP, MAP and ISUP/TUP Protocols – MTP (Message Transfer Part) is used to transport messages and for routing and addressing.MTP corresponds to OSI Layer 1,2 and Parts of 3 – SCCP (signaling connection control part)adds functions to SS7 signaling to provide for more extensive addressing and routing. – Together MTP and SCCP form the network service part(NSP) and corresponds to layers 1-3 in the OSI Model. – TCAP and MAP are layer 7 protocols. TCAP provides services based on connection less network services.MAP is a protocol specifically designed for mobile communications. MAP-n signaling between databases (HLR, VLR, EIR, AUC..Etc). – ISDN-UP (ISDN User part) and temporary user part (TUP) are used from layer 3 up to layer 7and are used between MSC and the ISDN/PSTN for call setup and supervision. • B interface The B interface exists between the MSC and the VLR . It uses a protocol known as the MAP/B protocol. As most VLRs are collocated with an MSC, this makes the interface purely an "internal" interface. The interface is used whenever the MSC needs access to data regarding a MS located in its area. • C interface The C interface is located between the HLR and a GMSC or a SMS-G. When a call originates from outside the network, i.e. from the PSTN or another mobile network it ahs to pass through the gateway so that routing information required to complete the call may be gained. The protocol used for communication is MAP/C, the letter "C" indicating that the protocol is used for the "C" interface. In addition to this, the MSC may optionally forward billing information to the HLR after the call is completed and cleared down. • D interface The D interface is situated between the VLR and HLR. It uses the MAP/D protocol to exchange the data related to the location of the ME and to the management of the subscriber. • E interface The E interface provides communication between two MSCs. The E interface exchanges data related to handover between the anchor and relay MSCs using the MAP/E protocol. • F interface The F interface is used between an MSC and EIR. It uses the MAP/F protocol. The communications along this interface are used to confirm the status of the IMEI of the ME gaining access to the network. • G interface The G interface interconnects two VLRs of different MSCs and uses the MAP/G protocol to transfer subscriber information, during e.g. a location update procedure. • H interface The H interface exists between the MSC the SMS-G. It transfers short messages and uses the MAP/H protocol.
- 15. GSM Channel Concept • TDMA provides additional user capacity over a limited amount of RF Spectrum. – Divides air interface connection period into eight equal and repeating Timeslots know as Frames each timeslots can be considered logical channels, that can be used by different subscribers for voice, data traffic and also for transmission of required system signaling and control information. system can use several different types of repeating frame (depending on information transmitted) structures known as Multiframes.
- 16. • Logical Channels – Logical channels may carry either subscriber traffic or signaling and control information to facilitate subscriber mobility. – Presently there and three types of traffic channels(TCHs). • Full rate traffic channels (TCH/F or Bm) carries one conversation by using one timeslot (voice encoded at 13kbps rate with additional channel overhead bits at 22.8kbps and data at rates of 14.4,9.6,4.8 and 2.4kbps). • Half rate traffic channel (TCH/H or Lm) carries two conversations or one conversation and a data transfer or two data transfers by using one timeslot (voice encoded at 6.5kbps or data at rates of 4.8 or 2.4kbps with additional overhead bits data rate becomes 11.4kbps). • Enhanced full rate (EFR) encodes voice at 12.2kbps rate . – Three sub categories of Signaling and control channels. • Broadcast channels • Common control channels • Dedicate control channels
- 17. • GSM Cellular system uses broadcast channels (BCHs) to provide information to the mobile station about various system parameters and also information about the location area identity(LAI). • Three types of BCHs are • Broadcast control channel, • Frequency correction channel, • Synchronization channel. – Using information transmitted over these three BCHs , the MS can tune to a particular base transceiver system(BTS) and synchronize its timing with frame structure and timing in that cell. – Broad cast control channel(BCCH) • BCCH Is only transmitted in downlink from BTS to MS. • Type of information broadcast include – LAI (Location Area Identity) – The maximum output power allowed in cell – BCCH Carrier frequencies for the neighboring cells (helps possible handover) – Frequency correction channel • FCCH is broadcast on downlink • Transmits bursts of zeros (unmodulated carrier signal ) to the MS.this signaling is done for two reasons – MS can use this signal to synchronize itself to correct frequency and – the MS can verify that this is the BCCH carrier – Synchronization channel • SCH is broadcast in downlink • Synchronize MS with timing in a particular cell • By listening to SCH the MS can learn about the frame number in this cell and about BSIC(base station identity code) of the BTS it is attached to ,
- 18. • Common Control Channels (CCCHs) – Provide paging messages to the MS and a means by which the mobile can request a signaling channel that it can use to contact the network. – Three types of CCCHs • Paging channel • Random access channel • Access grant channel – Paging channel (PCHs) • Transmitted in downlink direction only • Used by system to send paging messages to the mobiles attached to the cell. • MS listens to PCH at certain time intervals to learn if the network wants to make contact with it. • Mobile will be paged when ever the network has an incoming call ready for the mobile or some type of message (SMS,MMS) to deliver to the mobile. • Information transmitted contains paging message and mobile identity number (ISMI, TMSI). – Random Access channels • Transmitted in uplink direction only • Is used by mobile to respond to a paging message requesting for a signaling channel. • To setup mobile originated calls • Allow to calculate distance of the mobile from the BTS , this measured time delay is then translated into a timing advance (TA) that is sent to MS. • The use of TA allows any mobile with in cell to transmit information that will arrive at the BTS in correct synchronization with start of TDMA frame (max cell radius of 35km). – Access grant channels • Transmitted in downlink direction only • Used by network to assign a signaling channel to MS.
- 19. • Dedicated Control Channels (DCCHs) – Used for specific call setup, handover, measurement, and short message delivery functions. – Four DCCHs are • Stand alone dedicated control channel (SDCCH) • The Slow associated control channel (SACCH) • Fast associated control channel (FACCH) • Cell broadcast channel (CBCH) – Stand alone dedicated control channel (SDCCH) • Transmitted in both uplink and downlink directions. • Call setup procedure is performed over SDCCH once complete switch to available traffic channel. – Slow associated control channel (SACCH) – Fast associated control channel (FACCH) –
- 20. Speech processing Speech is digitized and broken up into 20ms segments. It is then coded to reduce the bit rate and to control errors. Channel Model is created
- 21. • Time Slots and TDMA frames
- 22. • TDMA Frames
- 23. • Time Slots
- 24. • GSM Traffic and control bursts
- 25. • Mapping of logical channels to physical channels
- 27. Traffic Channels
- 28. GSM Identities