*Tempus Telcosys*ADA CELLWORKS PVT LTD

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INTRODUCTION The global system for mobile communications (GSM) is a set of recommendations and specifications for a digital cellular telephone network (known as a Public Land Mobile Network, or PLMN). These recommendations ensure the compatibility of equipment from different GSM manufacturers, and interconnectivity between different administrations, including operations across international boundaries.*Tempus Telcosys*

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THE GSM NETWORK The GSM network is comprised of the following components: Network Elements The GSM network incorporates a number of network elements to support mobile equipment. They are listed and described in the GSM network elements section of this chapter. GSM subsystems In addition, the network includes subsystems that are not formally recognized as network elements but are necessary for network operation. These are described in the GSM subsystems (non-network elements) section of this chapter. Standardized Interfaces GSM specifies standards for interfaces between network elements, which ensure the connectivity of GSM equipment from different manufacturers. These are listed in the Standardized interfaces section of this chapter.*Tempus Telcosys*

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THE GSM NETWORK - CONTINUED Network Protocols For most of the network communications on these interfaces, internationally recognized communications protocols have been used These are identified in the Network protocols section of this chapter.

GSM Frequencies The frequency allocations for GSM 900, Extended GSM and Digital Communications Systems are identified in the GSM frequencies section of this chapter.*Tempus Telcosys*

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DIGITAL NETWORKS GSM networks are digital and can cater for high system capacities. They are consistent with the world wide digitization of the telephone network, and are an extension of the Integrated Services Digital Network (ISDN), using a digital radio interface between the cellular network and the mobile subscriber equipment.*Tempus Telcosys*

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INCREASED CAPACITY The GSM system provides a greater subscriber capacity than analogue systems. GSM allows 25 kHz. Per user, that is, eight conversations per 200kHz. Channel pair (a pair comprising one transmit channel and one receive channel). Digital channel coding and the modulation used makes the signal resistant to interference from the cells where the same frequencies are re-used (co-channel interference); a Carrier to Interference Ratio (C/I) level of 9 dB is achieved, as opposed to the 18 dB typical with analogue cellular. This allows increased geographic reuse by permitting a reduction in the number of cells in the reuse pattern. Since this number is directly controlled by the amount of interference, the radio transmission design can deliver acceptable performance.*Tempus Telcosys*

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CGI : CELL GLOBAL IDENTITY*Tempus Telcosys*MCCMNCLACCILAICGIMCC = Mobile Country CodeMNC = Mobile Network CodeLAC = Location Area CodeCI = Cell Identity

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MSISDN*Tempus Telcosys*CCNDCSN98XXX12345CC = Country CodeNDC = National Destination CodeSN = Subscriber Number

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MSISDN The Mobile Subscriber ISDN (MSISDN) number is the telephone number of the MS. This is the number a calling party dials to reach the subscriber. It is used by the land network to route calls towards the MSC.*Tempus Telcosys*

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IMSI IMSI (International Mobile Subscriber Identity) Network Identity Unique To A Sim.*Tempus Telcosys*MCCMNCMSIN404XX12345..10SIM = Subscriber Identity ModuleMCC = Mobile Country CodeMNC = Mobile Network CodeMSIN = Mobile Subscriber Identity Number

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IMEIIMEI : Serial number unique to each mobile*Tempus Telcosys*TACFACSNRSP6261IMEI = International Mobile Equipment IdentityTAC = Type Approval CodeFAC = Final Assembly CodeSNR = Serial NumberSP = Spare

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SUBSCRIBER IDENTIFICATIONInternational Mobile Subscriber Identity (IMSI) Just the IMEI identifies the mobile equipment, other numbers are used to identify the mobile subscriber. Different subscriber identities are used in different phases of call setup. The International Mobile Subscriber Identity (IMSI) is the primary identity of the subscriber within the mobile network and is permanently assigned to that subscriber.Temporary Mobile Subscriber Identity (TMSI) The GSM system can also assign a Temporary Mobile Subscriber Identity (TMSI). After the subscribers IMSI has been initialized on the system, the TMSI can be used for sending backward and forward across the network to identify the subscriber. The system automatically changes the TMSI at regular intervals, thus protecting the subscriber from being identified by someone attempting to monitor the radio channels. The TMSI is a local number and is always transmitted with the Local numbers and is always transmitted with the Location Area Identification (LAI) to avoid ambiguities.*Tempus Telcosys*

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SUBSCRIBER IDENTIFICATION MODULE (SIM) By making a distinction between the subscriber identity and the mobile equipment identity, a GSM PLMN can route calls and perform billing based on the identity of the subscriber rather than the mobile equipment being used. This can be done using a removable Subscriber Information Module (SIM). A smart card is one possible implementation of a SIM module.

IMSI. This is transmitted at initialization of the mobile equipment. TMSI This is updated periodically by the PLMN MSISDN This is made up of a country code, a national code and a subscriber number. Location Area Identity (LAI) This identified the current location of the subscriber. Subscriber Authentication Key (KI) This is used to authenticate the SIM.*Tempus Telcosys*

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EQUIPMENT IDENTITY NUMBER International Mobile station Equipment Identity (IMEI) Each MS is identified by an International Mobile station Equipment Identity (IMEI) number which is permanently stored in the mobile equipment. On request, the MS sends this number over the signalling channel to the MSC. The IMEI can be used to identify MS,s that are reported stolen or operating incorrectly.

Equipment Identity Register ( EIR ) A listing of the allowed IMEI is maintained by the PLMNs in the Equipment Identity Register (EIR) to validate the mobile equipment.*Tempus Telcosys*

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Frequency BandsUplink890 915 MHz25 MHz*Tempus Telcosys*Downlink935 960 MHz25 MHzA 200 KHz carrier spacing has been chosen. Excluding 2x100 KHz edges ofthe band, this gives 124 possible carriers for the uplink and downlink. The use of carrier 1 and 124 are optional for operators.

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GSM Network Architecture*Tempus Telcosys*BTSBTSBTSBTSBTSBSCBSCTRAUMSCHLRAUCVLREIRPSTNSMSC

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MS Mobile StationMobile station provides user access to GSM network for voice and dataAll GSM mobiles comply to GSM standardsSubscriber data is read from a SIM card that plugs into ME*Tempus Telcosys*SIMMEMS

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MS (cont..)Each MS has a unique number called as IMEI number, which is stored in EIR for authentication purposesMobile camps on to the GSM network through the BTS serving the cellMobile also scans neighboring cells and reports signal strengthsMobile transmits and receives voice at 13 kb/s over the air interface*Tempus Telcosys*

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Mobile Station Output PowerCLASS 120 watts Vehicle and PortableCLASS 28 wattsPortable and VehicleCLASS 35 wattsHand-HeldCLASS 42 wattsHand-Held (GSM)CLASS 5 0.8 wattsHand-Held (DCS 1800)Output power determines:Accessibility in areas of coverageTalk Time and Standby time*Tempus Telcosys*

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Mobile Station IdentitiesCC Country CodeNDC National Destination CodeSN Serial Number*Tempus Telcosys*MSISDN : Mobile Station ISDN NumberIt is the human identity used to call a Mobile StationCCSNNDCMSISDN9825000134

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IMSI (International Mobile Subscriber Identity)MCC Mobile Country CodeMNC Mobile Network CodeMSIN Mobile Subscriber Identity Number

*Tempus Telcosys*MCCMSINMNCIMSI3 2 or 3 Not more than 15NMSI

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IMEI (International Mobile Equipment Identity)TAC Type Approval CodeFAC Factory Assembly CodeSNR Serial NumberSP Spare digit (usually used to specify software version)*Tempus Telcosys*TACSPFACIMEISNR616215

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SIM ( Subscriber Identity Module)Removable module inserted when the subscriber wants to use the METwo sizes: credit card size and stamp sizeSIM features and contents are personalized by the Service ActivatorROM 6kb to 16 kbRAM 128 bytes to 256 bytesEEPROM 3kb to 8 kb*Tempus Telcosys*Space to insert SIM photo

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Contents of SIMSerial NumberIMSI, Subscriber Key Ki, Ciphering Key KcAlgorithms for authentication and cipheringNetwork CodePIN, PUKCharging InformationAbbreviated DiallingSupplementary Features (e.g. Call barring)*Tempus Telcosys*

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SIM SecurityTwo level protectionWhen mobile is turned on, it will ask for user to enter PIN (Personal Id Number)3 tries for PIN, after that PIN lockedTo unblock PIN, there is PUK (Pin Unblock Key)10 attempts of PUK allowedAfter that SIM is blocked*Tempus Telcosys*

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BTS (Base Transceiver Station)BTS has a set of Transceivers (TRXs) to communicate with mobiles in its areaOne BTS covers one or more than one cellThe capacity of a cell depends on number of transceivers in the cellBTS is connected to the BSC through Abis Interface which is 2MbpsBTS transmits and receives voice at 13kbps over air interface to the mobiles.BTS commands mobiles to set Tx. Power, timing advance and Handovers*Tempus Telcosys*

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BTS*Tempus Telcosys*

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BSC Base Station ControllerSeveral BTSs are connected to the BSCBSC Manages channel allocation, handovers and release of channels at connected BTSsBSC connects to the BTS via the Abis interface and to the MSC on A interfaceBSC has the entire database of cell parameters associated with the BTSs.No mobile data is stored in the BSCLess connections for MSC as intelligence is made common to all BTSs by the BSC*Tempus Telcosys*

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BSC*Tempus Telcosys*

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TRAU Transcoder Rate Adaptation Unit*Tempus Telcosys*BTSBSCPSTN13 kbps16 kbps16 kbps64 kbpsMSC and TRAU

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TRAU (cont..)The MSC is based on ISDN switching. The Fixed Network is also ISDN based.ISDN has speech rate of 64 kbps. Mobile communicates at 13 kbps.TRAU converts the data rates between 13kbps GSM rate to 64kbps Standard ISDN rateTRAU can be collocated with the BTS, BSC or MSC or it can be a separate unit.*Tempus Telcosys*

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Location of TranscoderCollocated with MSC, BSC, BTSSeparate Unit*Tempus Telcosys*MSCTranscoderBSC

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MSC Mobile Switching Centre*Tempus Telcosys*BSCBSCBSCBTSsPSTNHLRVLR

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MSC (cont..)Exchange where calls are established, maintained and releasedDatabase for all subscribers and their associated features.Communicates with the BSCs on the A interface and with PSTN on fixed line.MSC is weighted on the number of subscribers it can support. E.g. an MSC of 1 lac subscribers means one MSC is enough till subscriber base increases upto 1 lac, beyond which another MSC is required.*Tempus Telcosys*

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Multiple MSCsWhen there is more capacity, there are more than one MSCs.All MSCs have to communicate with one another and to the outside world.Very complicated to connect each MSC to each other and each MSC to PSTNSo there is a concept of GMSC (Gateway MSC)*Tempus Telcosys*BSCBSCMSCMSCGMSCPSTN

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HLR Home Location RegisterMSC has all subscriber database stored in HLRHLR has all permanent subscriber databaseHLR has a database which describes the subscribers profile i.e. basic features and supplementary servicesMSC communicates with the HLR to get data for subscribers on call*Tempus Telcosys*

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VLR Visiting Location RegisterA subscription when activated is registered in VLRVLR has all the subscriber numbers which are active.VLR has a temporary database of all active subscribers (on/off, location information)*Tempus Telcosys*MSCVLRHLR

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VLR (cont..)MSC communicates with HLR for subscribers coming from different MSCs. If the subscriber is found valid, then it registers the subscriber in the VLR*Tempus Telcosys*MSCMSCVLRHLRVLR

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AUC Authentication CentreAuthentication is a process by which a SIM is verifiedSecret data and the verification process algorithm are stored in AUCAUC is the element which carries out the verification of the SIMAUC is associated with the HLR

*Tempus Telcosys*MSMSCHLRAUC

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EIR (Equipment Identity Register)EIR is the Mobile Equipment Database which has a series of IMEIsMSC asks the Mobile to send its IMEIMSC then checks the validity of IMEI with the EIRAll IMEIs are stored in EIR with relevant classifications*Tempus Telcosys*EIRMSC

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Classification of IMEIs*Tempus Telcosys*White list: This contains the IMEI of type approved mobilesBlack List: List of IMEIs which should be barred because either they are stolen or are not functioning properlyGrey list: List of IMEIs which are to be evaluated before they are put in black list

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Billing Centre (BC)BC Generates the billing statement for each subscriberBC may be directly connected to the MSC or through a mediation deviceMSC sends CDRs (Call Detail Records) to the BCAccording to the template of pulse rates and units set, BC creates a bill according to the destination called and the call duration *Tempus Telcosys*

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Billing Centre (BC) (cont..)*Tempus Telcosys*CDRsTemplates for unit costs

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OMC Operations and Maintenance CentreAlso called the NOC (Network Operations centre)It is the central monitoring and remote maintenance centre for all network elementsOMC has links to BSCs and MSCs*Tempus Telcosys*

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OMC Operations and Maintenance CentreAlso called the NOC (Network Operations centre)It is the central monitoring and remote maintenance centre for all network elementsOMC has links to BSCs and MSCs*Tempus Telcosys*

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OMC*Tempus Telcosys*OMC SystemBSCBSCBSCOMC Terminals

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*Tempus Telcosys*GSM Channels

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GSM ChannelsPhysical ChannelOne time slot on one carrier is called physical channel.Logical ChannelInformation carried by physical channels is called logical Channels.Logical channels are mapped on physical channels.

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Logical ChannelsTraffic channels: Used for speech and data Full Rate(TCH/F) Half Rate(TCH/H) Control channels: Used for signaling .i.e. setting up a radio connection, call or controlling an MS during conversationBCH(Broadcast channels)CCCH(common control channels)DCCH(dedicated control channels)

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Traffic Channels(TCH)*Tempus Telcosys*

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Control Channels(CCH)*Tempus Telcosys*CCH(Control Channel)BCHCCCHDCCHCCHRACHCBCHSDCCHACCHSynch.ChanelsSACCHFACCHPCH/AGCHFCCHSCH

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BCH(Broadcast Channels)BCCH(Broadcast Control Channels)Downlink Only.Broadcast information of the serving cell (System Information).Transmitted on timeslot zero of BCCH carrier.Reads only by idle mobile at least once every 30 secs.

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BCH(Broadcast Channels) contdSCH(Synchronisation Channels)Downlink OnlyCarries information for frame synchronisation.Contains frame number and BSIC(Base Station Identity Code).

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BCH(Broadcast Channels) contdFCCH(Frequency Correction Channels)Downlink Only.Enable MS to synchronies to the frequency.

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CCCH(Common Control Channel)RACH(Random Access Channel)Uplink only.Used by the MS when making its first access to the Network.The reason for access could be initiation of a call or a page response.

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CCCH(Common Control Channel) contdAGCH(Assess Grant Channel)Downlink only.Used for acknowledgement of the access attempt sent on RACH.Used by the network to assign a signaling cannel upon successful decoding of access bursts.

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CCCH(Common Control Channel) contdPCH(Paging Channel)Downlink only.The network will page the MS ,if there is a incoming call or a short Message.It contains the MS identity number, the IMSI or TMSI.

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DCCH(Dedicated Control Channel)SDCCH (Stand-alone Dedicated Control Channel)Uplink and Downlink.Used for call setup, authentication, ciphering location update and SMS.

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DCCH(Dedicated Control Channel) contdSACCH(Slow Associated Control Channel)Downlink and Uplink.Used to transfer signal while MS have ongoing conversation on traffic or while SDCCH is being used.On the forward link, the SACCH is used to send slow but regularly changing control information to each mobile on that ARFCN, such as power control instructions and specific timing advance instructions

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SACCH(Slow Associated Control Channel) contdThe reverse SACCH carries information about the received signal strength and quality of the TCH, as well as BCH measurement results from neighboring cells.*Tempus Telcosys*

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DCCH(Dedicated Control Channel) contdFACCH(Fast Associated Control Channel)Downlink and uplink.Associate with TCH only.It is used to send fast message like hand over message.Work by stealing traffic bursts.

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Mapping on Physical ChannelsThe Logical channels are mapped on the physical channels.The TDMA frames are grouped together into multi-frame.26 TDMA multi-frame for Traffic.51 TDMA multi-frame for control signal.

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Channel CombinationCombined All the controlling signals are in the time slot 0 of the Multi-frame. Non CombinedDedicated controlling signals are in time slot 1 of the Multi-frame.*Tempus Telcosys*

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CombinedCell with single carrier.Timeslot 0 :BCCH+CCCH+SDCCH.Timeslot 1-7 :TCH/FACCH+SACCH.*Tempus Telcosys*

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Non CombinedCell with Two carrierTimeslot 0 (of carrier 1) BCCH+CCCH.Timeslot 1 (of carrier1) SDCCH+SACCH.Timeslot 2-7 & 0-7(of both carriers) TCH/FACCH+SACCH.*Tempus Telcosys*

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BROADCAST MESSAGESSystem information 5 and 6 sent on the SACCH immediately after Handover or whenever nothing else is being sent.Downlink SACCH is used for system information messages while uplink SACCH is used for measurement reports.System Information types 7 and 8 (optional) are an extension to type 4 and broadcast on the BCCH.*Tempus Telcosys*

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SYSTEM INFORMATION*Tempus Telcosys*

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SYSTEM INFORMATION 1When frequency hopping is used in cell MS needs to know which frequency band to use and what frequency within the band it should use in hopping algorithm.Cell channel descriptionCell Allocation Number(CANO)-Informs the band number of the frequency channels used. 00-Band 0(current GSM band)Cell Allocation ARFCN(CA ARFCN):- ARFCNs used for hopping.It is coded in a bitmap of 124 bits.*Tempus Telcosys*

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SYTEM INFORMATION 1*Tempus Telcosys*

124123122121

024023022021020019018017016015014013012011010009008007006005004003002001

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SYSTEM INFORMATION 1RACH Control ParametersAccess Control Class(ACC) :-Bitmap with 16 bits. All MS spread out on class 0 9 . Priority groups use class 11-15. A bit set to 1 barred access for that class. Bit 10 is used to tell the MS if emergency call is allowed or not.0 All MS can make emergency call.1 - MS with class 11-15 only can make emergency calls. Cell barred for access(CB):-0- Yes1- No*Tempus Telcosys*

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SYSTEM INFORMATION 1RACH Control ParametersRe-establishment allowed(RE):-0- Yes1- NoMax_retransmissions(MAXRET):-Number of times the MS attempts to access the Network [1,2,4 or 7].Tx-integer(TX):- Number of slots to spread access retransmissions when a MS attempts to access the system.Emergency call allowed:- Yes/No.*Tempus Telcosys*

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SYSTEM INFORMATION 2System Information Type 2 message consists of the Double BA list which defines the BCCH frequencies used in the neighboring cells. The Double BA list provides the MS with different frequencies on which to measure, depending on whether the MS is in idle or active mode.In active mode, the MS should measure on a reduced number of frequencies in order to improve the accuracy of measurements.*Tempus Telcosys*

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SYSTEM INFORMATION 2In Idle mode,the MS should measure on larger number of frequencies, so that the time required for the MS to access the network after power on is reduced.The MS is also informed which PLMNs it may use.As well as System Information Type 2,it is also possible to have System Information Type 2 Bis and System information Type 2 Ater, depending on the size of the BA List.System Information Type 2 Bis/Ter are optional.*Tempus Telcosys*

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SYSTEM INFORMATION 2Neighbor Cell Description:-BA Indicator(BA IND):- Allows to differentiate measurement results related to different list of BCCH frequencies sent to MS.BCCH Allocation number(BANO):- Band 0 is used.PLMN Permitted(NCCPERM):-This the PLMN color codes permitted and tells the MS which network color codes(NCC) on the BCCH carriers it is allowed to monitor when it is in this cell..*Tempus Telcosys*

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SYSTEM INFORMATION 2RACH Control ParametersAccess Control Class(ACC) :-Bitmap with 16 bits. All MS spread out on class 0 9 . Priority groups use class 11-15. A bit set to 1 barred access for that class. Bit 10 is used to tell the MS if emergency call is allowed or not.0 All MS can make emergency call.1 - MS with class 11-15 only can make emergency calls. Cell barred for access(CB):-0- Yes1- No

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SYSTEM INFORMATION 2Re-establishment allowed(RE):-0- Yes1- NoMax_retransmissions(MAXRET):-Number of times the MS attempts to access the Network [1,2,4 or 7].Tx-integer(TX):- Number of slots to spread access retransmissions when a MS attempts to access the system.Emergency call allowed:- Yes/No.

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SYSTEM INFORMATION 2 BCCH ARFCN Number(BAIND):- ARFCNs used for in a Bitmap of 124 bits*Tempus Telcosys*

124123122121

024023022021020019018017016015014013012011010009008007006005004003002001

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SYSTEM INFORMATION 3The System Information Type 3 contains information on the identity of the current LA and cell identity, because a change means that the MS must update the network.System Information 3 also as Control Channel Description parameters used to calculate the Paging group.When the MS is in idle mode it decides which cells to lock to. Information needed by the MS for cell selection is also broadcast in the Type 3 information.*Tempus Telcosys*

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SYSTEM INFORMATION 3*Tempus Telcosys*

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Sheet1

LOCATION AREA IDENTITTY(LAI)

87654321

MCC DIG 2MCC DIG 1

1111MCC DIG 1

MNC DIG 2MNC DIG 1

LAC

LAC

CELL IDENTITY

CI

CI

Sheet2

Sheet3

SYSTEM INFORMATION 3Control Channel DescriptionAttach / Detach(ATT):-0 = Allowed 1 = Not Allowedbs_agblk:-Number of block reserved for AGCH [0-7]Ba_pmfrms:-Number of 51 frame multi-frames between transmission of paging messages to MS of the same groupT3212:- Periodic location update timer . [1-255 deci hours].*Tempus Telcosys*

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SYSTEM INFORMATION 3*Tempus Telcosys*

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Sheet1

cch_confPhysical channelscombinedNo. of CCH

01 timeslot(0)No9

11 timeslot(0)Yes3

22 timeslot(0,2)No18

43 timeslot(0,2,4)No27

64 timeslot(0,2,4,6)No36

Sheet2

Sheet3

SYSTEM INFORMATION 3Cell optionsDTX:-Whether Discontinuous Transmission used or not.PWRC:-Power control on the downlink.0 = Not used.1 = Used.Radio link timeout(RLINKT):-Radio link time-out is the time before an MS disconnects due to failure in decoding SACCH message. Sets the timer T100 in the MS.*Tempus Telcosys*

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SYSTEM INFORMATION 3Cell Selection ParametersRxlev_access_min:- Minimum received signal level at the MS for which it is permitted to access the system.0-63 = -100 dBm to 47 dBm.Mx_txpwr_cch:- Maximum power the MS will use when accessing the system.Cell_reselect_hysteresis:- Used for cell reselection.RACH Control Parameters.

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SYSTEM INFORMATION 4Location Area Identification.Cell Selection ParametersRxlev_access_min:- Minimum received signal level at the MS for which it is permitted to access the system.0-63 = -100 dBm to 47 dBm.Mx_txpwr_cch:- Maximum power the MS will use when accessing the system.Cell_reselect_hysteresis:- Used for cell reselection.

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SYSTEM INFORMATION 4RACH Control Parametersmax_retransmissions(MAXRET)tx_integer(TX)Cell barred for access(CB).Re-establishment allowed(RE)Emergency Call AllowedAccess Control Class (ACC)*Tempus Telcosys*

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SYSTEM INFORMATION 4CBCH Description(Optional) :CHN:- This is the channel number for CBCH. It is controlled internally in BSC.TSC:- Training Sequence Code. Base Station Color Code(BCC) part of BSIC is used. CBCHNO:- Absolute RF channel number of CBCH.MAC:- Mobile Allocation in the cell, describes the frequencies to be used in the hopping sequence if frequency hopping is used.*Tempus Telcosys*

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SYSTEM INFORMATION 4Hopping Channel(H):-Informs if CBCH Channel is hopping or single.ARFCN:- If H=0;MAIO:- If H=1, informs the MS where to start hopping. Values [0-63].HSN:- If H=1, informs the MS in what order the hopping should take place. Values[0 63]. HSN=0 Cyclic Hopping.MA:-Indicates which RF Channels are used for hopping. ARFCN numbers coded in bitmap.*Tempus Telcosys*

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SYSTEM INFORMATION 5Sent on the SACCH on the downlink to the MS in dedicated mode.On SAACH, the MS also receives information about the BCCH carrier in each neighboring cell. This may differ from those sent in System information type 2.It is also possible to have system Information Type 5 Bis and System Information Type 5Ter, depending on the size of the BA list.*Tempus Telcosys*

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SYSTEM INFORMATION 5Neighbor Cell Description:-BA-IND:-Used by the Network to discriminate measurements results related to different lists of BCCH carriers sent by the MS(Type 2 or 5).Values 0 or 1(different from type 2).BCCH Allocation number:-00-Band 0(current GSM band).

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SYSTEM INFORMATION 5BCCH ARFCN:-Neighboring cells ARFCNs. Sent as a bitmap.0-Not used1-Used.*Tempus Telcosys*

124123122121

024023022021020019018017016015014013012011010009008007006005004003002001

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SYSTEM INFORMATION 6Ms in dedicated mode needs to know if the LA has changed.If so, it must perform location updating when the call is released.MS may change between cells with different Radio link timeout and DTX.Cell Identity.Location Area Identification.PLMN permitted.*Tempus Telcosys*

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SYSTEM INFORMATION 6Cell options:DTXPWRCRadio Link timeout.*Tempus Telcosys*

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SYSTEM INFORMATION 7/8System Information Types 7 and 8 contain Cell Reselect parameters. Their function is to supplement System Information Type 4.*Tempus Telcosys*

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GSM Interfaces

(Um) Air interface -MS to BTSA bis interface-BTS to BSCA Interface-BSC to MSCB Interface-MSC to VLRC interface-MSC to HLR

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MSCBSCVLRHLRAUCEIRGMSCMS A InterfaceA bis Interface Air Interface B Interface

C InterfaceF Interface D Interface H InterfaceTo otherNetworks*Tempus Telcosys*

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GSM InterfacesThe interfaces between MSC and MS is called A, Abis and Um interfaces. On these interfaces only three layers are defined.They are not corresponding to the OSI (Open System Interconnection) model.*Tempus Telcosys*

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A InterfaceA interface between the BSC and the MSC The A interface provides two distinct types of information, signalling and traffic, between the MSC and the BSC.The speech is transcoded in the TRC and the SS7 (Signalling system) signalling is transparently connected through the TRC or on a separate link to the BSC. *Tempus Telcosys*

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Abis InterfaceThe A-bis interface responsible for transmitting traffic and signalling information between the BSC and the BTS.The transmission protocol used for sending signalling information on the A-bis interface is Link Access Protocol on the D Channel (LAPD)

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(Um) Air Interface This is the interface between the mobile station and the Base station. The Air interface uses the Time Division Multiple Access (TDMA) technique to transmit and receive traffic and signalling information between the BTS and MS.The TDMA technique is used to divide each carrier into eight time slots.These time slots are then assigned to specific users,allowing up to eight conversations to be handled Simultaneously by the same carrier. *Tempus Telcosys*

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7 5 6 3 4 1 2 0 1 2 43 5 7 6Down LinkUp Link 0Time Slot*Tempus Telcosys* This interface is the radio interface between the mobile station and the network and uses layer Three messages. On Layer three messages we have the division of message types into CM (communication Management), MM (Mobility Management), and RR (Radio Resource Management).

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Connection Management (CM) There are three entities within CM:Call Control(CC) Which handles the procedures concerning call control. e.g. setup,Change of bearer service.Supplementary Service (SS) Which handles such as call bearing, call waiting , call forwarding etc. Short Message Service (SMS) Enables the MS to handle short message transfer to and from the network.

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Mobility Management (MM)Mobility management handles functions for authentication, location updating, identification and others concerning the mobility of the mobile station. *Tempus Telcosys*

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Radio Resource Management (RR)

It contains the functions concerning the radio link. Here we find the capability to establish,maintain and release the radio connection between the network and the mobile station, which includes the handover procedure.*Tempus Telcosys*

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B InterfaceThe B interface between the MSC and the VLR uses the MAP/TCAP protocol. Most MSCs are associated with a VLR, making the B interface "internal". Whenever the MSC needs access to data regarding a MS located in its area, it interrogates the VLR using the MAP/B protocol over the B interface.

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C Interface

The C interface is between the HLR and a MSC. Each call originating outside of GSM (i.e., a MS terminating call from the PSTN) has to go through a Gateway to obtain the routing information required to complete the call, and the MAP/TCAP protocol over the C interface is used for this purpose. Also, the MSC may optionally forward billing information to the HLR after call clearing. *Tempus Telcosys*

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D InterfaceThe D interface is between the VLR and HLR.It uses the MAP/TCAP protocol to exchange the data related to the location of the MS and to the management of the subscriber. *Tempus Telcosys*

Tempus Telcosys

E InterfaceThe E interface interconnects two MSCs. The E interface exchanges data related to handover between the anchor and relay MSCs using the -MAP/TCAP+ISUP/TUP protocol. *Tempus Telcosys*

Tempus Telcosys

F InterfaceThe F interface connects the MSC to the EIR.It uses the MAP/TCAP protocol to verify the status of the IMEI that the MSC has retrieved from the MS. *Tempus Telcosys*

Tempus Telcosys

G InterfaceThe G interface interconnects two VLRs of different MSCs.It uses the MAP/G protocol to transfer subscriber information, during e.g. a location update procedure.

*Tempus Telcosys*

Tempus Telcosys

*Tempus Telcosys*

Tempus Telcosys

Topics for discussionSpeech EncodingData EncodingInterleaving for Voice,Control and Data signals*Tempus Telcosys*

Tempus Telcosys

Speech EncodingWe shall start with a raw voice signal fed into the microphone, travel through the various stages involving vocoding, channel coding etc till it reaches the final burst format on the Air Interface.*Tempus Telcosys*

Tempus Telcosys

Speech Encoding ckt*Tempus Telcosys*Voice EncodingChannel codinginterleavingRF ModulationRaw Voicesignal

Tempus Telcosys

Speech Encoding cktThe voice is sampled at the rate of 50 samples per second.This results in 20 msec blocks of speechEach of this 20 msec block is passed on to the 13Kbps vocoder.There are 260 information bits from the output of the vocoder for every 20 msec input i.e.; 13Kbps *20msec = 260 bits.*Tempus Telcosys*

Tempus Telcosys

Voice Encoding ckt*Tempus Telcosys*Vocoder I/p20 msec speechblocks13Kbps Vocoder

Vocoder O/p260 bits

Tempus Telcosys

Channel codingChannel Coding is done to protect the logical channels from transmission errors introduced by the radio path.The coding schemes depend on the type of the logical channels, hence the coding can differ from speech, control and data .*Tempus Telcosys*

Tempus Telcosys

Channel Coding for speech*Tempus Telcosys*Class class 1b class 21a 3 132 4 tailBits parity bitsConvolutional coder coder, k=5456 bits=378 bits from Convolution coder + 78 class 2 bits260 bits

Tempus Telcosys

Channel coding for SpeechThe 260 bits of speech info from the vocoder is broken down into three parts.Class 1a- 50 bits , these represent the filter coefficients of the speech and are the most important for proper detection of the speech at the receiver and hence are given maximum protection. 3 additional parity bits are derived from the class 1a bits for cyclic redundancy check (CRC).*Tempus Telcosys*

Tempus Telcosys

Channel coding for Speech contdClass 1b - 132 bits are not parity checked but are fed into the convolutional coder along with 4 tail bits which are used to set the registers in the receiver to a known state for decoding purpose.Class 1b- 78 bits, these are not so important and are not protected but are combined with the output of the convolution coder.*Tempus Telcosys*

Tempus Telcosys

Convolutional coder CCThe Convolutional coder is a series of shift registers implemented using logic gates, where for every one input bit we get 2 output bits. Hence it is called coder.Here k=5 is the constraint length, it means there are 5 shift register and each bit has memory depth of 4 , meaning it can influence the output of up to four next successive bits. This is useful during reception as bits can be derived even if a few consecutive bits are lost due to errors or corruption.*Tempus Telcosys*

Tempus Telcosys

Convolutional coder*Tempus Telcosys*R1R2R3R5R4++C0outputC1output0110..Input bits+ EX-OR R=register

Tempus Telcosys

Convolutional coder contdThe output of the CC* is now 378 bits. (50+3+132+4)*2=378The total number of bits now is 378+78=456 bits.*Note : The bit rate from the vocoder was 13Kbps for the 20 msec speech block, but after CC the bit rate increases to 22.8Kbps. 456 bits *20msecs=22.8Kbps * CC = Convolutional Coder.*Tempus Telcosys*

Tempus Telcosys

Control Channel Coding*Tempus Telcosys*184 bits Control data 184 40 4 tailFire coded parity bits Convolutional Coder456 bits output

Tempus Telcosys

Control Channel CodingThe control information is received in blocks of 184 bits.These bits are first protected with a cyclic code called as Fire code, which is useful in correction and detection of burst errors.40 Parity bits are added, along with 4 tail bits.These 228 bits are given to the CC whose output is again 456 bits at a bitrate of 22.8Kbps.The control channels include the RACH, PCH, AGCH etc.*Tempus Telcosys*

Tempus Telcosys

Data Channel Coding*Tempus Telcosys* 240 bits 4 tail Data bits Convolutional CoderOutput= 488 bitsAfter PuncturingOutput=456 bits

Tempus Telcosys

Data Channel CodingThe data bits are received in blocks of 240 bits. These are directly convolution coded after adding 4 tail bits.The output of the CC is now 488 bits, which actually increases the bitrate to 24.4 Kbps.To keep the bitrate constant on the air interface we need to puncture the output of the CC. Hence, we have a final bitrate of 22.8 Kbps again .*Tempus Telcosys*

Tempus Telcosys

Channel Coding contdThe above explanation was given keeping in view a full rate Traffic, Control, or Data channel.For Half rate or Lesser rates the same principle of channel coding holds good, with slight differences in the encoding process.*Tempus Telcosys*

Tempus Telcosys

Interleaving Having encoded the logical channel information, the next step is to build its bit stream into bursts that can be transmitted within the TDMA frame structure. This is the stage where the interleaving process is carried out.Interleaving spreads the content of one information block across several TDMA timeslots or bursts.*Tempus Telcosys*

Tempus Telcosys

Interleaving contdThe following interleaving depths are used :Speech 8 blocksControl 4 blocksData 22 blocksThe interleaving process for a speech block is shown wherein which a 456 bit speech block is divided into 8 blocks of 57 bits each and each of these odd and even 57 bit blocks are interleaved diagonally on to alternate bursts on the TDMA frame.*Tempus Telcosys*

Tempus Telcosys

Speech Interleaving*Tempus Telcosys*8* 57 bits each = 456 bitsOf Speech block N57EvenOf N-157EvenOf NSpeech blockN-157oddOf N-157oddOf NThe speech is spread over 8 such normal burstsEach normal burst consists of two blocks of 57 bit speech from different 20msec blocks (say N, N-1) along with26 bit training sequence T and 2 flag F plus 6 start stop bits .T+FT+FT+F456 bit speech data

Tempus Telcosys

Control Data Interleaving*Tempus Telcosys*114 114 114 114 456 bits control dataThe control data is spread over 4 blocks using rectangular interleaving instead of diagonal interleaving as in speech the receiver will have to wait for at least 2 multiframes before being able to decode the controlmessageTDMABurst blocks

Tempus Telcosys

Data Interleaving*Tempus Telcosys*114 114 114 114 Burst 1Burst 22Burst 2Burst 3Burst 4Burst 19First 6bitsFirst 6bitsLast 6bitsLast 6bits456 bit data block

Tempus Telcosys

Data Interleaving contdHere the data block of 456 bits is divided into 4 blocks of 114 bits each.The first 6 bits from each of the 114 bit blocks is inserted in to each frame, the second 6 bits from each of the 114 bits into the next frame and so on spreading each 114 block over 19 TDMA bursts while the entire 456 bits is spread over 22 TDMA bursts.Thus the data interleaving is said to have a depth of 22 bursts.*Tempus Telcosys*

Tempus Telcosys

Data Interleaving contdThe reason why data is spread over such along period of time is that if data burst is corrupted or lost, only a small part of it is lost which can be reproduced at the receiver.This wide interleaving depth does produce a time delay during transmission but that is acceptable since it does not affect the data signal quality at the receiver, unlike speech where delay could result in bad quality of signal to the subscriber.*Note The interleaving used in data is diagonal interleaving.

*Tempus Telcosys*

Tempus Telcosys

Before Deinterleaving3 successive bursts corruptedAfter DeinterleavingThe corrupted bursts are spread over a length equal to the interleaving depth so that the effect of the errors isminimized.*Tempus Telcosys*Interleaving Advantage

Tempus Telcosys

Air Interface BitrateThe information which is now coded and interleaved at 22.8 Kbps now has to be transmitted over the Air interface to the BTS. The information burst is not sent directly , but is sent in ciphered form within a burst envelope. This ciphering is done using ciphering keys and algorithms known both by the mobile and the BSS. *Tempus Telcosys*

Tempus Telcosys

Air Interface Bitrate contdThe Kc is the ciphering key and A5 algorithm are applied to the information(speech or data) which increases the bitrate to a final rate of 33.8 Kbps from/to each mobile.If we assume all 8 timeslots of the cell to be occupied then the bitrate of the Air interface comes to 33.8 * 8= 270.4 Kbps/channel.

*Tempus Telcosys*

Tempus Telcosys

Air Interface Bitrate contd*Tempus Telcosys*A5 AlgorithmKcInformation Block 22.8 KbpsSent on Air interface

Ciphered information burst33.8 Kbps

Tempus Telcosys

Air Interface Bitrate contd*Tempus Telcosys*1 2 3 4 5 6 7 8Mobile Txs at 33.8 Kbps Cell rxs 8*33.8 KBps = 270.4 KbpsPer TDMA frameCell coverage areaTDMA FnTDMA Fn+1

Tempus Telcosys

Decoding and Deinterleaving at the ReceiverAt the receiver the reverse process of Deinterleaving and decoding have to take place respectively, so as to recover the information from the signal.After Deinterleaving the signal will be decoded which is the reverse process of the Convolutional coding, using Viterbi decoders.The decoder can recover lost or corrupted data up to 4 successive bits, because the memory depth of the CC is 4(for k=5).*Tempus Telcosys*

Tempus Telcosys

ChannelizationFrequency band has several application segmentsCertain blocks of the Band are reserved for certain applications by regulating authoritiesTechnologies have decided their frequency bandsE.g. AMPS/DAMPS: 824-894 MHz*Tempus Telcosys*

Tempus Telcosys

Channelization methodsChannelization can be done primarily by three methods:FDMA (Frequency Division Multiple Access)TDMA (Time Division Multiple Access)CDMA (Code Division Multiple Access)*Tempus Telcosys*

Tempus Telcosys

FDMA E.g. AMPS band is divided into 30 KHz channels (1666 Freq. channels)Television Channels (Star, Zee, Sony,..)*Tempus Telcosys*FrequencyTimePower

Tempus Telcosys

TDMAE.g. AMPS has 3 timeslots on each 30 KHz channel

*Tempus Telcosys*FrequencyTimePower

Tempus Telcosys

CDMAFrequency channel is divided into code channelsE.g. in IS-95 CDMA, 1.228 MHz channel is divided into 64 Code ChannelsEach user has a particular codeCodes are orthogonal to each other, do not interfere with each other*Tempus Telcosys*

Tempus Telcosys

Duplex Access MethodsFrequency Division Duplex (FDD)Transmit on one frequency and receive on another frequency*Tempus Telcosys*F1F2FrequencyAmplitudeTimeTxRx

Tempus Telcosys

Time Division DuplexTime division duplexTx and Rx is on the same frequency but on different times*Tempus Telcosys*F1FrequencyAmplitudeTimeTxRx

Tempus Telcosys

GSM Air InterfaceSeparate Bands for Uplink and DownlinkDownlink: 935-960Mhz (EGSM: 925-960MHz)Uplink: 890-915 MHz (EGSM: 880-915 MHz)*Tempus Telcosys*TDMA and TDMA Multiplex124 Frequency Channels (ARFCN) for GSM9001 to 124 fro current band975 to 1023 for E-GSM 200kHz Channels8 Mobiles share ARFCN by TDMA

Tempus Telcosys

GSM Air interface (1800)1800: Downlink: 1805-1880 MHz1800: Uplink: 1710-1785 MHx374 ARFCNsSeparation of 95 MHzARFCNs are numbered from 512 to 885 inclusive

*Tempus Telcosys*

Tempus Telcosys

The GSM Burst*Tempus Telcosys*33572615718.25Tail BitsDataControl BitMidambleControl BitDataTail BitsGuard Period

Tempus Telcosys

Speech CoderRPE/LTP coder (Regular Pulse excitation/Long term Prediction)Converts 64 kbps speech to 13 kbpsAt the end we get 13kbps speech i.e. 260 bits in 20 ms*Tempus Telcosys*20 ms blocksSpeech CoderBits Ordered50 very important bits132 important bits78 other bits

Tempus Telcosys

Error Correction*Tempus Telcosys*Type 1a 503(CRC)Type 1b 132Type II 78Reordering2566366254Type II 78Type 1aType 1bType 1bType 1aTailHalf rate convolutional code378Type II 78456 bits from 20 ms of speech

Tempus Telcosys

Diagonal InterleavingTraffic channel (TCH) bursts carry two 57 bit blocks (114) Each 120 ms of speech = 456*6 = 2736 bits2736/114 = 24 bursts i.3. 24 frames Multiframe has 26 frames in 120ms.There are 2 spare frames .. 1 SACCH, 1 Idle*Tempus Telcosys*456 bits from 20ms of speech456 bits from 20ms of speech57575757575757575757575757575757

Tempus Telcosys

Convolutional Coding and InterleavingBits to be Tx ed: HELLOConvolutionally encoded: HHEELLLLOOInterleaved:EE HH LL LL OO

Bits Rx ed: EE HH LL LL OODe-Interleaved: HHEELLLLOOViterbi Decoded: HELLO*Tempus Telcosys*

Tempus Telcosys

Speech Coding Process*Tempus Telcosys*20 msSpeech Coder260 bits13 kbps50 1a132 1b78 IIChannel Coder456 bits 22.8 kbpsTransceiver (BTS)Transcoder Handler260 bits456 bits 16 kbpsTRAU frame260 + 60 = 320 bitsAbis13 kbps

Tempus Telcosys

TRAU frame260 bits info + 60 TRAU bits = 320 bits/20ms = TRAU frame60 bits contain frame Information data which indicates speech, data, O&M, full rate/half rate60 bits = 35 synchronization + 21 control + 4 timing*Tempus Telcosys*

Tempus Telcosys

Midamble or Training Bits8 midamble patterns (Colour codes) of 26 bits (BSIC)RACH and SCH have longer 41 and 64 bit MidamblesEqualizer estimates channel impulse response from midambleMathematically construct inverse filterUses inverse to decode bits*Tempus Telcosys*

Tempus Telcosys

Downlink and UplinkUplink lags downlink by 3 timeslotsUplink and downlink use same timeslot numberUplink and downlink use same channel number (ARFCN)Uplink and downlink use different bands (45 MHz apart for GSM 900)*Tempus Telcosys*

Tempus Telcosys

Measurements made by MS and BTS*Tempus Telcosys*RxQual0< 0.2%10.2 0.4 %0.4 0.8 %40.8 0.16 %1.6 3.2 %63.2 6.4 %76.4 12.8 %Uplink RXLEV (-48 to -110 dbm)Uplink RXQUAL (0-7)Uplink RXLEV (-48 to -110 dbm)Uplink RXQUAL (0-7)

Tempus Telcosys

Mobile Power Control*Tempus Telcosys*Mobile is commanded to change its Transmit PowerChange in Power is proportionate to the Path LossChange in Power is done in steps of 2 dbsPath LossPower Command

Tempus Telcosys

Timing AdvanceTDMA approach requires signals to arrive at BTS at the correct timeA mobile at 30 km will be late by 100micro secondsTiming advance is in the range of 0-62One unit is 550mSo maximum cell size is 63*0.55 = ~35 kms*Tempus Telcosys*

Tempus Telcosys

Concepts of Channels in GSMA company vehicle is used for several purposes in a daySimilarly in GSM, the timeslots are used for different purposes at different times

*Tempus Telcosys*

Tempus Telcosys

Frames and Multiframes*Tempus Telcosys*065432173Data1Midamble1Data38.25 bits156.25 bits576.92 micro sec4.615 msTimeSlotFrameControl Channel MultiframeTraffic Channel Multiframe

Tempus Telcosys

GSM OperationsLocation UpdateMobile Originated CallMobile Terminated CallHandoverSecurity ProceduresCell BarringDTXCell BroadcastShort Message ServiceEmergency callsSupplementary ServicesRoaming

*Tempus Telcosys*

Tempus Telcosys

Mobile Turn OnMobile Searches for Broadcast Channels (BCH)Synchronizes Frequency and TimingDecodes BCH sub-channels (BCCH)Checks if Network Allowed by SIMLocation UpdateAuthentication

*Tempus Telcosys*

Tempus Telcosys

Location Area*Tempus Telcosys*Location Area 1LocationArea 2BTSBTSBTSBTSBTSBTSBTSBTSBSCBSCBSCMSC

Tempus Telcosys

Location Area IdentityLocation area is the area covered by one or more BTSs where a mobile can move freely without updating the systemOne Location area can be covered by one or more BSCs, but ony one MSC.*Tempus Telcosys*MCCLACMNC

Tempus Telcosys

Importance of Location AreaReduce Paging loadResource Planning

Smaller Location Areas Location update increases

Larger Location Areas Paging load increases*Tempus Telcosys*

Tempus Telcosys

What is Location Update?MSC should know the location of the Mobile for pagingMobile is continuously changing location areaMobile when changes Location Area informs the MSC about its new LAProcess of informing MSC about new Location area is Location Update

*Tempus Telcosys*

Tempus Telcosys

Types of Location UpdatesNormal Location UpdateIMSI AttachPeriodic Location Update*Tempus Telcosys*Hi,I am in Location area xxx

Tempus Telcosys

IMSI AttachMobile turns off and sends an IMSI Detach to MSCMobile turns on again and compares LAIIf same, sends an IMSI attach to MSC*Tempus Telcosys*Is the received LAI same as beforeIf same,Sends IMSI attach

Tempus Telcosys

Normal Location UpdateMobile Turns on PowerReads the new LAIIf different, does a Location Update

*Tempus Telcosys*Is the received LAI same as beforeIf different,does Location Update

Tempus Telcosys

Periodic Location UpdateThe periodic location Update time is set from OMC/MSCAfter the periodic location update timer expires, the mobile has to do a location update

*Tempus Telcosys*

Tempus Telcosys

What happens at Location Update?Mobile changes location areaReads the new Location Area from BCCHSends a RACH (request for channel)Gets a SDCCH after AGCHSends its IMSI and new and old LAI in a Location Update request to MSC on SDCCH*Tempus Telcosys*

Tempus Telcosys

What happens at location update cont.... . .MSC starts AuthenticationIf successful, Updates the new Location area for the Mobile in the VLRSends a confirmation to the MobileMobile leaves SDCCH, and comes to idle mode*Tempus Telcosys*

Tempus Telcosys

Mobile Originated Call*Tempus Telcosys*Channel RequestImmediate AssignService RequestCall ProceedingSet UpCipheringAuthenticationAlertingAssignmentConnection

Tempus Telcosys

Mobile Terminated Call*Tempus Telcosys*PagingChannel RequestImmediate AssignSet UpCipheringAuthenticationPaging ResponseAssignmentCall ConfirmedAlertingConnection

Tempus Telcosys

Security FeaturesAuthenticationProcess to verify Authenticity of SIMMobile is asked to perform an operation using identity unique to SIM*Tempus Telcosys*CipheringProcess of coding speech for secrecyThe speech bits are EXORed with bit stream unique to MS

Tempus Telcosys

Security Features (TMSI Reallocation)*Tempus Telcosys*GSM InfrastructureMobileLocation UpdateTMSI AllocationCall SetupTMSI ReallocationTMSI- Temporary Mobile Subscriber Identity

Tempus Telcosys

Security Features (Identity Check)*Tempus Telcosys*EIRSends IMEIIdentity CheckWhite listed /Grey Listed/ Black Listed mobiles

Tempus Telcosys

Handover*Tempus Telcosys*Cell 1Cell 2Handover is a GSM feature by which the control/communication of a Mobile is transferred from one cell to another if certain criterias are met. It is a network initiated process.

Tempus Telcosys

Criteria for HandoverReceive Quality (RXQUAL) on uplink and downlinkReceive Signal Strength (RXLEV) on uplink and downlinkDistance (Timing Advance)Interference LevelPower Budget*Tempus Telcosys*

Tempus Telcosys

Handover DecisionBSC process the measurements reported by Mobile and the BTS*Tempus Telcosys*Mobile has measurements of six neighbors

Tempus Telcosys

Handover Decision (cont..)BSS performs averaging function on these measurements every SACCH frame (480ms)

Handover Decision algorithm is activated after a set number of SACCH frame periods by comparison against thresholds

*Tempus Telcosys*

Tempus Telcosys

Types of HandoversINTRA-CELL HANDOVERSINTER-CELL HANDOVERSINTRA-BSC HANDOVERSINTER-BSC HANDOVERSINTER-MSC HANDOVERS*Tempus Telcosys*

Tempus Telcosys

INTRA-CELL HANDOVER*Tempus Telcosys*C0C1Handover between timeslots of same frequencyHandover between different frequencies of the same cell (to reduce interference)MSC is not aware about this

Tempus Telcosys

Inter-cell Handover*Tempus Telcosys*Handover between cells of the same BTSBTSCell 1Cell 2

Tempus Telcosys

Inter-cell Handover (cont..)MSC is told about HOBTS -> BSC -> MSCWhy MSC is informed?In case of change of LA, MSC may need LAC for paging. As MS is busy, a link already exists. So, MSC can send a tone in case of call waiting, and does not need to page again.This is needed also for billing and call tracing*Tempus Telcosys*

Tempus Telcosys

INTRA-BSC Handover*Tempus Telcosys*MSCBSCBTSThis HO takes place if the cell to which handover is to be done belongs to the same BSC

Tempus Telcosys

Inter BSC Handover*Tempus Telcosys*MSCBSCBTSBSCThe MSC is completely involved in this Handover

Tempus Telcosys

Inter MSC Handover*Tempus Telcosys*BSCBSCMSCMSCGMSC/PSTN/BackboneIn this case the handover takes place through the interconnecting element which can be GMSC or PSTN or private Backbone between the MSCs

Tempus Telcosys

Cell Barring*Tempus Telcosys*Cell Barring is a GSM feature by which certain mobiles could be barred access to certain cellsCell barring is activated/deactivated at BTS levelCell barring is done for mobile categories and priorities

Tempus Telcosys

Cell BarringEvery mobile has an access classThe access class is stored in the SIMClasses 0-9 are termed normal calssesClasses 11-15 are emergency classes

*Tempus Telcosys*Every cell has a set parameter which defines which access classes are barred for the particular cell. This parameter is broadcasted on the BCCH

Tempus Telcosys

What is DTX?DTX (Discontinous Transmission)Each direction of Transmission is only 50% Transmitter is switched ON for useful information frames*Tempus Telcosys*Need for DTXTo increase battery lifeTo reduce the average interference levelDTX is done by DTX handlers which have the following functions.

Tempus Telcosys

VAD (Voice Activity Detector)Senses for speech in 20ms blocks Removes stationary noiseVAD is an energy detectorCompares Energy of filtered speech thresholdIt determines which 20ms blocks contain speech and it only forwards those frames*Tempus Telcosys*

Tempus Telcosys

Evaluation of Background NoiseBackground noise is always present with speechDTX cuts off this noise with speechGives an uncomfortable feeling to the listenerVAD takes care of this by inserting comfort noise at the receiving end when speech discontinues.*Tempus Telcosys*

Tempus Telcosys

Emergency CallsGSM specs define 112 as an emergency number112 is accessible with or without SIMWithout SIM it is sent on the best channelMobile on sensing 112 sets the establishment cause to emergency call in the RACHRouting of this call be done to a desired location defined in the switch*Tempus Telcosys*

Tempus Telcosys

Cell (Re)selectionCell reselection is done using C1 path loss criterion.The purpose is to ensure that the MS is camped on to the cell with the best transmission quality.The MS will camp on to the cell with the highest C1 value if C1 > 0.*Tempus Telcosys*

Tempus Telcosys

The following parameters are used to calculate the C1 criterionThe received signal at the MS side.Rxlev_access_min - broadcast on the BCCH - The minimum received level at the MS required for access to the network.Ms_txpwr_max_cch - the maximum power that an MS may use when initially accessing the network.The maximum power of the MS

*Tempus Telcosys*

Tempus Telcosys

C1 = A - Max(B,0)

A = Received level Average - Rxlev_access_min.

B = MS_txpwr_max_cch - maximum output power of the MS*Tempus Telcosys*

Tempus Telcosys

Cell Reselect HysteresisCell reselection on the border of two location areas result in a location update. When an MS moves on the border of two location areas lots of location updates take place. To avoid these location updates, the reselect hysteresis is introduced.A location update is performed only if:The C1 value of the new location area is higher than the C1 value in the current location area andThe received signal strengths have at least a difference of the reselect hysteresis.*Tempus Telcosys*

Tempus Telcosys

Cellular concept*Tempus Telcosys*

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Why to use the cellular concept ?Solves the problem of Spectral congestion and user capacity by means of frequency reuse.Offers high capacity in a limited spectrum allocation.Offers system level approach, using low power transmitters instead of a single, high power transmitter (large cell) to cover larger area.

*Tempus Telcosys*

Tempus Telcosys

A portion of the total channels available is allocated to each base station.Neighboring base stations are assigned different groups channels, in order to minimize interference.*Tempus Telcosys*

Tempus Telcosys

Cell shape*Tempus Telcosys*

Tempus Telcosys

*Tempus Telcosys*

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1-Omni-directional cell-site (Omni-directional antenna).2-Rhombus-shaped sectors (Directive antenna).3-Hexagonal shaped sectors (Directive antenna).*Tempus Telcosys*

Tempus Telcosys

Cell sizeLarge cell : (up to 70km in diameter)It exists where :1-Radio waves are unobstructed.2-Transmission power can cover the area.3-low subscriber density.Small cell : (up to 2km in diameter)It exists where :1-Radio waves are obstructed.2-Low transmission power to decrease interference.3-High subscriber density.*Tempus Telcosys*

Tempus Telcosys

Types of cells1-Macro-cells 2-Micro-cells. 3-Pico-cells. 4-Umbrella-cells.

*Tempus Telcosys*

Tempus Telcosys

What is a cluster ?A cluster is a group of cells.No channels are reused within a cluster.It is the unit of design.

*Tempus Telcosys*

Tempus Telcosys

Cluster sizeDefinition : It is The number of cells per cluster N = i^2 + ij + j^2

Where : i = 0, 1, 2.& j = 0,1,2. etc. N = 1 , 3 , 4 ,7, 9 , 12 ,

*Tempus Telcosys*

Tempus Telcosys

Types of clusters1-N=7 omni frequency plan (2-directional).2-N=7 trapezoidal frequency plan (1-directional).3-N=9 omni frequency plan.4-Tricellular plans a) N=3 tricellular plan (3/9). b) N=4 tricellular plan (4/12).*Tempus Telcosys*

Tempus Telcosys

Channel assignment strategiesConsiderations : 1) Max. capacity. 2) Min interference. 3) Perfect handover.

Types of assignment strategies : 1) Fixed :Each cell has permanent predetermined set of voice channels.New calls served by unused channels of this cell.Borrowing strategy if all channels are occupied.High probabiltity that call is Blocked if channels are occupied.( disadv.)*Tempus Telcosys*

Tempus Telcosys

2) Dynamic :

Channels are not allocated to different cells permanently.

Each new call BTS requests new channel from MSC.

MSC allocate a channel, by using an algorithm that takes into account: 1- Frequency is not already in use. 2- Min. reuse distance to avoid co-channel interference. *Tempus Telcosys*

Tempus Telcosys

Adv. of dynamic assignment strategy :

1) Increase channel utilization ( Increase trunking efficiency ).

2) Decrease probability of a blocked call.*Tempus Telcosys*

Tempus Telcosys

Frequency reuseConcept*Tempus Telcosys*

Tempus Telcosys

*Tempus Telcosys*

Tempus Telcosys

Reuse cluster*Tempus Telcosys*

Tempus Telcosys

Co-channel Reuse ratio (Q) :R : cell radius.D : reuse distance.

Q = D/R. = sqrt(3N).Where :N : cluster size

*Tempus Telcosys*

Tempus Telcosys

Handover*Tempus Telcosys*

Tempus Telcosys

Definition : procedure that allows MS to change the cell or time-slot to keep as good link as possible during all the call.*Tempus Telcosys*

Tempus Telcosys

Types of handover IntraCell : bet. 2 channels of same cell.

InterCell : bet. 2 channels of 2 different cell & same BTS.

InterBTS (intra BSC) : 2 cells of different BTS Same BSC.

InterBSC : bet. 2 cells of different BSCs & same MSC.

*Tempus Telcosys*

Tempus Telcosys

Measurements before handover1- Measurements from MS to BSC : a) Strength of BTS signal. b) Quality of BTS signal. c) Signal strength of 6 neighbor BTSs.

2-Measurements from BTS to BSC : a) Strength of MS signal. b) Quality of MS signal. c) Distance between serving BTS & MS.

*Tempus Telcosys*

Tempus Telcosys

Different causes of handover*Tempus Telcosys*Better cell HOEmergency HOLevelQualityPBGTTraffic causesInterferenceDistanceDifferent causes ofHandover

Tempus Telcosys

Basic handover algorithmsa)Min. acceptable performance algorithm: MS power is increased when quality deceases till handover is the only way.b) Power budget algorithm: Prefer direct handover when quality deceases without increasing MS power first .*Tempus Telcosys*

Tempus Telcosys

Handover priority1) UL quality cause (or interference).2) DL quality cause (or interference).3) UL level cause.4) DL level cause.5) Distance cause.6) Better cell cause.*Tempus Telcosys*

Tempus Telcosys

Interference*Tempus Telcosys*

Tempus Telcosys

Sources of interference include:

1) Another mobile in the same cell. 2) A call in progress in the neighboring cell. 3) Other BTSs operating in the same frequency band.

*Tempus Telcosys*

Tempus Telcosys

Interference effects :In voice channel causes crosstalk

In control channels it leads missed and blocked calls due to errors in the digital signaling.

*Tempus Telcosys*

Tempus Telcosys

Main types of interference :1) Co-channel interference.

2) Adjacent channel interference.*Tempus Telcosys*

Tempus Telcosys

1) Co-channel interference Source : Near cell using same frequency. It is a function of reuse distance(D/R).General rule :

io = No. of co-channel interfering cells.S = Signal power from a desired BS.Ii = interference power caused by the ith interfering co-channel cell BS.

*Tempus Telcosys*

Tempus Telcosys

Another form : C/I = 10 log {(1/n)(D/R)*m} Where : m = propagation constant (deps on nature of environment) n = number of co-channel interferers.

Can be minimized by : Choosing minimum reuse distance = (2.5.3)(2R).*Tempus Telcosys*

Tempus Telcosys

2) Adjacent channel interferenceSource : A cell using a frequency adjacent to the one in another cell due to imperfect recievers filter.

*Tempus Telcosys*

Tempus Telcosys

Can be minimized by :1-careful filtering2-careful channel assignments3-Directional antenna.

General rule : ACI= -10 Log[(d1/d2)*m] Adj ch isolation. Where : d1: distance between MS & proper BTs d2: dist. Bet MS & adj BTS causing interference. Adj ch isolation = Filter isolation = - 26db. *Tempus Telcosys*

Tempus Telcosys

Traffic engineering theory*Tempus Telcosys*

Tempus Telcosys

Why do we need to know traffic?The amount of traffic during peak hours allows us to dimension our wireless system for a certain GOS.

GOS : probability of having a call blocked during busy hour (block rate).*Tempus Telcosys*

Tempus Telcosys

Traffic intensity (E)Erlang : A unit of traffic intensity measure.

1 Erlang = 1 circuit in use for 1 hour.

T ( in Erlangs) = [No. of calls per hour*average call holding time(sec.)] / [3600]*Tempus Telcosys*

Tempus Telcosys

Typical traffic profile*Tempus Telcosys*

Tempus Telcosys

Traffic tables*Tempus Telcosys*

Tempus Telcosys

Erlang B tableP(N;T) = [ (T^N)*exp(-T) ] / N!*Tempus Telcosys*

Tempus Telcosys

TrunkingSharing channel among several users.

Trunking efficiency (nT) : Measures the number of subscribers that each channel in every cell can accommodate.

nT = (traffic in Erlangs / no. of channels)*100.

*Tempus Telcosys*

Tempus Telcosys

Trunking efficiency in presence of one operator :

N = 7 , 312 one direction voice channelsNo. of channels / cell = 312 / 7 = 44 ch./cell.From Erlang-B table @GOS 2%,thiss equivalent to 35 ErlangsnT = 35 / 44 = 79.55.Trunking efficiency in presence of two operators :

N = 7 , 312 / 2 = 156 one direction voice channel for each operator.No. of channels / cell = 156 / 7 = 22 ch./cell.From Erlang-B table @GOS 2%,thiss equivalent to 15 Erlangs.nT = 15 / 22 = 68.18.*Tempus Telcosys*

Tempus Telcosys

System capacity*Tempus Telcosys*

Tempus Telcosys

S : total duplex channels available for use = k*N

Where: N : cluster size. k : No. of channels / cell.

C : total No. of duplex channels in system;

C = M*k*N.

Where : M : No. of times the cluster is repeated.*Tempus Telcosys*

Tempus Telcosys

Improving system capacityCell splitting.Sectoring. *Tempus Telcosys*

Tempus Telcosys

Cell splitting*Tempus Telcosys*

Tempus Telcosys

Sectoring We use directional antennas instead of being omnidirectional*Tempus Telcosys*

Tempus Telcosys

What does sectoring mean?We can now assign frequency sets to sectors and decrease the re-use distance to fulfill : 1) More freq reuse. 2) Higher system capacity. 3) Improve S/I ratio ( better signal quality ).How S/I ratio is improved? -e.g. In 120 degree sectoring theres only 2 interferers instead of 6 incase of omnidirectional N=7 cluster.*Tempus Telcosys*

Tempus Telcosys

*Tempus Telcosys*

Tempus Telcosys

*Tempus Telcosys*

Tempus Telcosys

Directional frequency reuse

Here we use 7/21 pattern for frequency allocation.*Tempus Telcosys*

Tempus Telcosys

Comparison between various types of clusters*Tempus Telcosys*

Tempus Telcosys

N = 7 omni frequency plan :n = 6 , m = 4.

D / R = 4.583.

1) Co-channel interference ratio : C / I = 18.6 dB.

2) Adjacent channel interference : ACI = -26 dB @ d1= d2.*Tempus Telcosys*

Tempus Telcosys

N = 7 trapezoidal frequency plann = 2 , m = 4.

D / R = 6.245.

1) Co-channel interference ratio : C / I = 28.8.

2) Adjacent channel interference : disappears because the channels are assigned alternatively to the cells.*Tempus Telcosys*

Tempus Telcosys

Trunking efficiency :312 one direction voice channels N = 7 312 / 7 = 44.57 ~ 44 ch./cell.

From Erlang-B table @ GOS = 2%T = 35 E. nT = 35 / 44 = 79.55 %.*Tempus Telcosys*

Tempus Telcosys

N = 9 omni frequency plann = 4 , m = 4.

D / R = sqrt ( 3 * 9 ) = 5.2.

1) Co-channel interference : C / I = 22.6 dB.

2) Adjacent channel interference : ACI = -38 dB @ d2 = 2 (d1).*Tempus Telcosys*

Tempus Telcosys

Trunking efficiency :312 one direction voice channels N = 9 312 / 9 = 34.67 ~ 34 ch./cell.From Erlang-B table @ GOS = 2%T = 25.529 E. nT = 25.529 / 34 = 75.085 %.Conclusion : nT 7 > nT 9 But C/I 7 > C/I 9 ACI 7 > ACI 9

*Tempus Telcosys*

Tempus Telcosys

4 / 12 cell patternn = 1 , m = 4.D / R = sqrt (3* 4) = 3.732.

C / I = 22.87 dB.

Trunking efficiency :No. of channels/cell = 312 / 12 = 26 ch./cell.From Erlang-B table @ GOS = 2 %. T = 18.4 E/cell.nT = 18.4 / 26= 70.77%.*Tempus Telcosys*

Tempus Telcosys

3 / 9 cell patternn = 1 , m = 4.D / R = sqrt (3* 3) = 3.

C / I = 19.1 dB.

Trunking efficiency :No. of channels/cell =312 / 9 = 34 ch./cell.From Erlang-B table @ GOS = 2 %. T = 25.5 E/cell.nT = 25.5 / 24 = 75 %.*Tempus Telcosys*

Tempus Telcosys

120 degree cell sectoringn = 2 , m = 4.D / R = sqrt(3 * 7) = 4.583.

Co-channel interference : C / I = 23.436 + 6dB(due to isolation) = 29.436 dB.

Trunking efficiency :No. of channels/cell = 312 / 21 = 14.857.From Erlang-B @ GOS=2% T= 8.2003.nT = 8.2003 / 14.857 =56.216%.*Tempus Telcosys*

Tempus Telcosys

References :Motorola CP02NOKIA SYSTRA*Tempus Telcosys*

Tempus Telcosys

If any QueryContact9903867731TempusTelcosys@gmail.com*Tempus Telcosys*

Tempus Telcosys

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