Total GSM Concept

5,931 views

Published on

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.
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.
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
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.

Published in: Education, Business, Technology
4 Comments
26 Likes
Statistics
Notes
No Downloads
Views
Total views
5,931
On SlideShare
0
From Embeds
0
Number of Embeds
2
Actions
Shares
0
Downloads
0
Comments
4
Likes
26
Embeds 0
No embeds

No notes for slide

Total GSM Concept

  1. 1. TEMPUS TELCOSYS(P)LIMITEDTelecom Tutorials5/31/2013www.TempusTelcosys.com1
  2. 2. GSM INTRODUCTION5/31/2013www.TempusTelcosys.com2
  3. 3. INTRODUCTION The global system for mobile communications (GSM) is a set ofrecommendations and specifications for a digital cellulartelephone network (known as a Public Land Mobile Network, orPLMN). These recommendations ensure the compatibility ofequipment from different GSM manufacturers, andinterconnectivity between different administrations, includingoperations across international boundaries.5/31/2013www.TempusTelcosys.com3
  4. 4. THE GSM NETWORK The GSM network is comprised of the following components: Network Elements The GSM network incorporates a number of network elements tosupport mobile equipment. They are listed and described in the GSMnetwork elements section of this chapter. GSM subsystems In addition, the network includes subsystems that are not formallyrecognized 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 differentmanufacturers. These are listed in the Standardized interfaces section ofthis chapter.5/31/2013www.TempusTelcosys.com4
  5. 5. THE GSM NETWORK - CONTINUED Network Protocols For most of the network communications on theseinterfaces, internationally recognized communications protocols havebeen used These are identified in the Network protocols section of this chapter. GSM Frequencies The frequency allocations for GSM 900, Extended GSM and DigitalCommunications Systems are identified in the GSM frequencies section ofthis chapter.5/31/2013www.TempusTelcosys.com5
  6. 6. DIGITAL NETWORKS GSM networks are digital and can cater for high systemcapacities. They are consistent with the world widedigitization of the telephone network, and are anextension of the Integrated Services Digital Network(ISDN), using a digital radio interface between the cellularnetwork and the mobile subscriber equipment.5/31/2013www.TempusTelcosys.com6
  7. 7. INCREASED CAPACITY The GSM system provides a greater subscriber capacity than analoguesystems. GSM allows 25 kHz. Per user, that is, eight conversations per 200kHz.Channel pair (a pair comprising one transmit channel and one receivechannel). Digital channel coding and the modulation used makes the signalresistant to interference from the cells where the same frequencies are re-used (co-channel interference); a Carrier to Interference Ratio (C/I) level of 9dB is achieved, as opposed to the 18 dB typical with analogue cellular. Thisallows increased geographic reuse by permitting a reduction in the number ofcells in the reuse pattern. Since this number is directly controlled by theamount of interference, the radio transmission design can deliver acceptableperformance.5/31/2013www.TempusTelcosys.com7
  8. 8. CGI : CELL GLOBAL IDENTITY5/31/2013www.TempusTelcosys.com8MCC MNC LAC CILAICGIMCC = Mobile Country CodeMNC = Mobile Network CodeLAC = Location Area CodeCI = Cell Identity
  9. 9. MSISDN5/31/2013www.TempusTelcosys.com9CC NDC SN98 XXX 12345CC = Country CodeNDC = National Destination CodeSN = Subscriber Number
  10. 10. MSISDN The Mobile Subscriber ISDN (MSISDN) numberis the telephone number of the MS. This is thenumber a calling party dials to reach thesubscriber. It is used by the land network toroute calls towards the MSC.5/31/2013www.TempusTelcosys.com10
  11. 11. IMSI IMSI (International Mobile SubscriberIdentity) Network Identity Unique To ASim.5/31/2013www.TempusTelcosys.com11MCC MNC MSIN404 XX 12345..10SIM = Subscriber Identity ModuleMCC = Mobile Country CodeMNC = Mobile Network CodeMSIN = Mobile Subscriber Identity Number
  12. 12. IMEI IMEI : Serial number unique to each mobile5/31/2013www.TempusTelcosys.com12TAC FAC SNR SP6 2 6 1IMEI = International Mobile Equipment IdentityTAC = Type Approval CodeFAC = Final Assembly CodeSNR = Serial NumberSP = Spare
  13. 13. SUBSCRIBER IDENTIFICATION International Mobile Subscriber Identity (IMSI) Just the IMEI identifies the mobile equipment, other numbers are used toidentify the mobile subscriber. Different subscriber identities are used in differentphases of call setup. The International Mobile Subscriber Identity (IMSI) is theprimary identity of the subscriber within the mobile network and is permanentlyassigned to that subscriber. Temporary Mobile Subscriber Identity (TMSI) The GSM system can also assign a Temporary Mobile Subscriber Identity (TMSI).After the subscriber’s IMSI has been initialized on the system, the TMSI can be usedfor sending backward and forward across the network to identify the subscriber.The system automatically changes the TMSI at regular intervals, thus protecting thesubscriber from being identified by someone attempting to monitor the radiochannels. The TMSI is a local number and is always transmitted with the Localnumbers and is always transmitted with the Location Area Identification (LAI) toavoid ambiguities.5/31/2013www.TempusTelcosys.com13
  14. 14. SUBSCRIBER IDENTIFICATION MODULE (SIM) By making a distinction between the subscriber identity and the mobileequipment identity, a GSM PLMN can route calls and perform billing based on theidentity of the subscriber rather than the mobile equipment being used. This canbe done using a removable Subscriber Information Module (SIM). A ”smart card” isone 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 subscribernumber. Location Area Identity (LAI) This identified the current location of the subscriber. Subscriber Authentication Key (KI) This is used to authenticate the SIM.5/31/2013www.TempusTelcosys.com14
  15. 15. EQUIPMENT IDENTITY NUMBER International Mobile station Equipment Identity (IMEI) Each MS is identified by an International Mobile station EquipmentIdentity (IMEI) number which is permanently stored in the mobileequipment. On request, the MS sends this number over the signallingchannel to the MSC. The IMEI can be used to identify MS,s that arereported stolen or operating incorrectly. Equipment Identity Register ( EIR ) A listing of the allowed IMEI is maintained by the PLMN’s in theEquipment Identity Register (EIR) to validate the mobile equipment.5/31/2013www.TempusTelcosys.com15
  16. 16. FREQUENCY BANDSUplink 890 – 915 MHz 25 MHz5/31/2013www.TempusTelcosys.com16Downlink 935 – 960 MHz 25 MHz100 KHz 200 KHz 100 KHz1 43 1242 …………….A 200 KHz carrier spacing has been chosen. Excluding 2x100 KHz edges ofthe band, this gives 124 possible carriers for the uplink and downlink. Theuse of carrier 1 and 124 are optional for operators.
  17. 17. GSM NETWORK ARCHITECTURE5/31/2013www.TempusTelcosys.com17BTSBTSBTSBTSBTSBSCBSCTRAUMSCHLRAUCVLREIRPSTNSMSC
  18. 18. MS – MOBILE STATION Mobile station provides user access to GSM networkfor voice and data All GSM mobiles comply to GSM standards Subscriber data is read from a SIM card that plugsinto ME5/31/2013www.TempusTelcosys.com18SIM MEMS
  19. 19. MS (CONT..) Each MS has a unique number called as IMEInumber, which is stored in EIR for authenticationpurposes Mobile camps on to the GSM network throughthe BTS serving the cell Mobile also scans neighboring cells and reportssignal strengths Mobile transmits and receives voice at 13 kb/sover the air interface5/31/2013www.TempusTelcosys.com19
  20. 20. MOBILE STATION OUTPUT POWER CLASS 1 20 watts Vehicle and Portable CLASS 2 8 watts Portable and Vehicle CLASS 3 5 watts Hand-Held CLASS 4 2 watts Hand-Held (GSM) CLASS 5 0.8 watts Hand-Held (DCS1800) Output power determines: Accessibility in areas of coverage Talk Time and Standby time5/31/2013www.TempusTelcosys.com20
  21. 21. MOBILE STATION IDENTITIES CC – Country Code NDC – National Destination Code SN – Serial Number5/31/2013www.TempusTelcosys.com21MSISDN : Mobile Station ISDN NumberIt is the human identity used to call a MobileStationCC SNNDC MSISDN98 250 00134
  22. 22. IMSI (INTERNATIONAL MOBILESUBSCRIBER IDENTITY) MCC – Mobile Country Code MNC – Mobile Network Code MSIN – Mobile Subscriber Identity Number5/31/2013www.TempusTelcosys.com22MCC MSINMNC IMSI3 2 or 3Not more than 15NMSI
  23. 23. IMEI (INTERNATIONAL MOBILEEQUIPMENT IDENTITY) TAC – Type Approval Code FAC – Factory Assembly Code SNR – Serial Number SP – Spare digit (usually used to specifysoftware version)5/31/2013www.TempusTelcosys.com23TAC SPFAC IMEISNR6 162 15
  24. 24. SIM ( SUBSCRIBER IDENTITY MODULE) Removable module inserted when thesubscriber wants to use the ME Two sizes: credit card size and stamp size SIM features and contents are personalized bythe Service Activator ROM – 6kb to 16 kb RAM – 128 bytes to 256 bytes EEPROM – 3kb to 8 kb5/31/2013www.TempusTelcosys.com24Space to insert SIM photo
  25. 25. CONTENTS OF SIM Serial Number IMSI, Subscriber Key Ki, Ciphering Key Kc Algorithms for authentication and ciphering Network Code PIN, PUK Charging Information Abbreviated Dialling Supplementary Features (e.g. Call barring)5/31/2013www.TempusTelcosys.com25
  26. 26. SIM SECURITY Two level protection When mobile is turned on, it will ask for user toenter PIN (Personal Id Number) 3 tries for PIN, after that PIN locked To unblock PIN, there is PUK (Pin Unblock Key) 10 attempts of PUK allowed After that SIM is blocked5/31/2013www.TempusTelcosys.com26
  27. 27. BTS (BASE TRANSCEIVER STATION) BTS has a set of Transceivers (TRXs) to communicatewith mobiles in its area One BTS covers one or more than one cell The capacity of a cell depends on number oftransceivers in the cell BTS is connected to the BSC through Abis Interfacewhich is 2Mbps BTS transmits and receives voice at 13kbps over airinterface to the mobiles. BTS commands mobiles to set Tx. Power, timingadvance and Handovers5/31/2013www.TempusTelcosys.com27
  28. 28. BTS5/31/2013www.TempusTelcosys.com28
  29. 29. BSC – BASE STATION CONTROLLER Several BTSs are connected to the BSC BSC Manages channel allocation, handoversand release of channels at connected BTSs BSC connects to the BTS via the Abis interfaceand to the MSC on A interface BSC has the entire database of cell parametersassociated with the BTSs. No mobile data is stored in the BSC Less connections for MSC as intelligence ismade common to all BTSs by the BSC5/31/2013www.TempusTelcosys.com29
  30. 30. BSC5/31/2013www.TempusTelcosys.com30
  31. 31. TRAU – TRANSCODER RATEADAPTATION UNIT5/31/2013www.TempusTelcosys.com31BTSBSC PSTN13 kbps 16 kbps 16 kbps 64 kbpsMSC and TRAU
  32. 32. TRAU (CONT..) The MSC is based on ISDN switching. TheFixed Network is also ISDN based. ISDN has speech rate of 64 kbps. Mobilecommunicates at 13 kbps. TRAU converts the data rates between13kbps GSM rate to 64kbps Standard ISDNrate TRAU can be collocated with the BTS, BSCor MSC or it can be a separate unit.5/31/2013www.TempusTelcosys.com32
  33. 33. LOCATION OF TRANSCODER Collocated with MSC, BSC, BTS Separate Unit5/31/2013www.TempusTelcosys.com33MSCTranscoderBSC
  34. 34. MSC – MOBILE SWITCHING CENTRE5/31/2013www.TempusTelcosys.com34BSCBSCBSCBTSs PSTNHLRVLR
  35. 35. MSC (CONT..) Exchange where calls are established, maintainedand released Database for all subscribers and their associatedfeatures. Communicates with the BSCs on the A interface andwith PSTN on fixed line. MSC is weighted on the number of subscribers itcan support. E.g. an MSC of 1 lac subscribers meansone MSC is enough till subscriber base increasesupto 1 lac, beyond which another MSC is required.5/31/2013www.TempusTelcosys.com35
  36. 36. MULTIPLE MSCS When there is more capacity, there are more than oneMSCs. All MSCs have to communicate with one another and to theoutside world. Very complicated to connect each MSC to each other andeach MSC to PSTN So there is a concept of GMSC (Gateway MSC)5/31/2013www.TempusTelcosys.com36BSCBSCMSCMSCGMSC PSTN
  37. 37. HLR – HOME LOCATION REGISTER MSC has all subscriber database stored inHLR HLR has all permanent subscriberdatabase HLR has a database which describes thesubscriber’s profile i.e. basic features andsupplementary services MSC communicates with the HLR to getdata for subscribers on call5/31/2013www.TempusTelcosys.com37
  38. 38. VLR – VISITING LOCATION REGISTER A subscription when activated is registered in VLR VLR has all the subscriber numbers which areactive. VLR has a temporary database of all activesubscribers (on/off, location information)5/31/2013www.TempusTelcosys.com38MSC VLRHLR
  39. 39. VLR (CONT..) MSC communicates with HLR for subscriberscoming from different MSCs. If the subscriberis found valid, then it registers the subscriberin the VLR5/31/2013www.TempusTelcosys.com39MSC MSCVLRHLRVLR
  40. 40. AUC – AUTHENTICATION CENTRE Authentication is a process by which a SIM isverified Secret data and the verification process algorithmare stored in AUC AUC is the element which carries out theverification of the SIM AUC is associated with the HLR5/31/2013www.TempusTelcosys.com40MS MSC HLR AUC
  41. 41. EIR (EQUIPMENT IDENTITY REGISTER) EIR is the Mobile Equipment Database which has a series ofIMEIs MSC asks the Mobile to send its IMEI MSC then checks the validity of IMEI with the EIR All IMEIs are stored in EIR with relevant classifications5/31/2013www.TempusTelcosys.com41EIRMSC
  42. 42. CLASSIFICATION OF IMEIS5/31/2013www.TempusTelcosys.com42White list: This contains the IMEI oftype approved mobilesBlack List: List of IMEIs which should bebarred because either they are stolen orare not functioning properlyGrey list: List of IMEIs which are to beevaluated before they are put in black list
  43. 43. BILLING CENTRE (BC) BC Generates the billing statement for eachsubscriber BC may be directly connected to the MSC orthrough a mediation device MSC sends CDRs (Call Detail Records) to theBC According to the template of pulse rates andunits set, BC creates a bill according to thedestination called and the call duration5/31/2013www.TempusTelcosys.com43
  44. 44. BILLING CENTRE (BC) (CONT..)5/31/2013www.TempusTelcosys.com44CDRsTemplates for unit costs
  45. 45. OMC – OPERATIONS AND MAINTENANCECENTRE Also called the NOC (Network Operationscentre) It is the central monitoring and remotemaintenance centre for all network elements OMC has links to BSCs and MSCs5/31/2013www.TempusTelcosys.com45
  46. 46. OMC – OPERATIONS AND MAINTENANCECENTRE Also called the NOC (Network Operationscentre) It is the central monitoring and remotemaintenance centre for all network elements OMC has links to BSCs and MSCs5/31/2013www.TempusTelcosys.com46
  47. 47. OMC5/31/2013www.TempusTelcosys.com47OMC SystemBSCBSCBSCBTSsBTSsBTSsOMC Terminals
  48. 48. 5/31/2013www.TempusTelcosys.com48GSM CHANNELS
  49. 49. GSM CHANNELS Physical Channel One time slot on one carrier is called physicalchannel. Logical Channel Information carried by physical channels is calledlogical Channels. Logical channels are mapped on physical channels.5/31/2013www.TempusTelcosys.com49
  50. 50. LOGICAL CHANNELS Traffic channels: Used for speech and data Full Rate(TCH/F) Half Rate(TCH/H) Control channels: Used for signaling .i.e. setting up aradio connection, call or controlling an MS duringconversation BCH(Broadcast channels) CCCH(common control channels) DCCH(dedicated control channels)5/31/2013www.TempusTelcosys.com50
  51. 51. TRAFFIC CHANNELS(TCH)5/31/2013www.TempusTelcosys.com51TCH/F(full Rate)TCH/H(half Rate)Traffic Channels(TCH)
  52. 52. CONTROL CHANNELS(CCH)5/31/2013www.TempusTelcosys.com52CCH(Control Channel)BCH CCCH DCCHCCH RACH CBCH SDCCH ACCHSynch.ChanelsSACCHFACCHPCH/AGCHFCCHSCH
  53. 53. BCH(BROADCAST CHANNELS) BCCH(Broadcast Control Channels) Downlink Only. Broadcast information of the serving cell (SystemInformation). Transmitted on timeslot zero of BCCH carrier. Reads only by idle mobile at least once every 30 secs.5/31/2013www.TempusTelcosys.com53
  54. 54. BCH(BROADCAST CHANNELS) CONT’D SCH(Synchronisation Channels) Downlink Only Carries information for frame synchronisation. Contains frame number and BSIC(Base StationIdentity Code).5/31/2013www.TempusTelcosys.com54
  55. 55. BCH(BROADCAST CHANNELS) CONT’D FCCH(Frequency Correction Channels) Downlink Only. Enable MS to synchronies to the frequency.5/31/2013www.TempusTelcosys.com55
  56. 56. CCCH(COMMON CONTROL CHANNEL) RACH(Random Access Channel) Uplink only. Used by the MS when making its first access to theNetwork. The reason for access could be initiation of a call or apage response.5/31/2013www.TempusTelcosys.com56
  57. 57. CCCH(COMMON CONTROL CHANNEL) CONT’D AGCH(Assess Grant Channel) Downlink only. Used for acknowledgement of the access attemptsent on RACH. Used by the network to assign a signaling cannelupon successful decoding of access bursts.5/31/2013www.TempusTelcosys.com57
  58. 58. CCCH(COMMON CONTROL CHANNEL) CONT’D PCH(Paging Channel) Downlink only. The network will page the MS ,if there is a incomingcall or a short Message. It contains the MS identity number, the IMSI or TMSI.5/31/2013www.TempusTelcosys.com58
  59. 59. DCCH(DEDICATED CONTROL CHANNEL) SDCCH (Stand-alone Dedicated Control Channel) Uplink and Downlink. Used for call setup, authentication, ciphering locationupdate and SMS.5/31/2013www.TempusTelcosys.com59
  60. 60. DCCH(DEDICATED CONTROL CHANNEL) CONT’D SACCH(Slow Associated Control Channel) Downlink and Uplink. Used to transfer signal while MS have ongoingconversation on traffic or while SDCCH is being used. On the forward link, the SACCH is used to send slowbut regularly changing control information to eachmobile on that ARFCN, such as power controlinstructions and specific timing advance instructions5/31/2013www.TempusTelcosys.com60
  61. 61.  SACCH(Slow Associated Control Channel) cont’d The reverse SACCH carries information aboutthe received signal strength and quality of theTCH, as well as BCH measurement results fromneighboring cells.5/31/2013www.TempusTelcosys.com61
  62. 62. DCCH(DEDICATED CONTROL CHANNEL) CONT’D FACCH(Fast Associated Control Channel) Downlink and uplink. Associate with TCH only. It is used to send fast message like hand overmessage. Work by stealing traffic bursts.5/31/2013www.TempusTelcosys.com62
  63. 63. MAPPING ON PHYSICAL CHANNELS The Logical channels are mapped on the physicalchannels. The TDMA frames are grouped together intomulti-frame. 26 TDMA multi-frame for Traffic. 51 TDMA multi-frame for control signal.5/31/2013www.TempusTelcosys.com63
  64. 64. CHANNEL COMBINATION Combined All the controlling signals are in the time slot 0 of theMulti-frame. Non Combined Dedicated controlling signals are in time slot 1 of theMulti-frame.5/31/2013www.TempusTelcosys.com64
  65. 65. COMBINED Cell with single carrier. Timeslot 0 :BCCH+CCCH+SDCCH. Timeslot 1-7 :TCH/FACCH+SACCH.5/31/2013www.TempusTelcosys.com65
  66. 66. NON COMBINED Cell with Two carrier Timeslot 0 (of carrier 1) BCCH+CCCH. Timeslot 1 (of carrier1) SDCCH+SACCH. Timeslot 2-7 & 0-7(of both carriers)TCH/FACCH+SACCH.5/31/2013www.TempusTelcosys.com66
  67. 67. BROADCAST MESSAGES System information 5 and 6 sent on the SACCH immediately afterHandover or whenever nothing else is being sent. Downlink SACCH is used for system information messages whileuplink SACCH is used for measurement reports. System Information types 7 and 8 (optional) are an extension totype 4 and broadcast on the BCCH.5/31/2013www.TempusTelcosys.com67
  68. 68. SYSTEM INFORMATION5/31/2013www.TempusTelcosys.com68
  69. 69. SYSTEM INFORMATION 1 When frequency hopping is used in cell MS needs to know whichfrequency band to use and what frequency within the band itshould use in hopping algorithm. Cell channel descriptionCell Allocation Number(CANO)-Informs the band numberof the frequency channels used.00-Band 0(current GSM band)Cell Allocation ARFCN(CA ARFCN):- ARFCN’s used forhopping.It is coded in a bitmap of 124 bits.5/31/2013www.TempusTelcosys.com69
  70. 70. SYTEM INFORMATION 15/31/2013www.TempusTelcosys.com70124 123 122 121024 023 022 021 020 019 018 017016 015 014 013 012 011 010 009008 007 006 005 004 003 002 001
  71. 71. SYSTEM INFORMATION 1 RACH Control ParametersAccess Control Class(ACC) :-Bitmap with 16 bits. All MSspread out on class 0 –9 . Priority groups use class 11-15. A bitset to 1 barred access for that class. Bit 10 is used to tell theMS if emergency call is allowed or not.0 – All MS can make emergency call. 1- MS with class 11-15 only canmake emergency calls.Cell barred for access(CB):-0- Yes 1-No5/31/2013www.TempusTelcosys.com71
  72. 72. SYSTEM INFORMATION 1 RACH Control Parameters Re-establishment allowed(RE):-0- Yes1- NoMax_retransmissions(MAXRET):-Number of times the MSattempts to access the Network [1,2,4 or 7].Tx-integer(TX):- Number of slots to spread accessretransmissions when a MS attempts to accessthe system.Emergency call allowed:- Yes/No.5/31/2013www.TempusTelcosys.com72
  73. 73. SYSTEM INFORMATION 2 System Information Type 2 message consists of theDouble BA list which defines the BCCH frequencies usedin the neighboring cells. The Double BA list provides the MS with differentfrequencies on which to measure, depending onwhether the MS is in idle or active mode. In active mode, the MS should measure on a reducednumber of frequencies in order to improve the accuracyof measurements.5/31/2013www.TempusTelcosys.com73
  74. 74. SYSTEM INFORMATION 2 In Idle mode,the MS should measure on larger numberof frequencies, so that the time required for the MS toaccess the network after power on is reduced. The MS is also informed which PLMN’s it may use. As well as System Information Type 2,it is also possibleto have System Information Type 2 Bis and Systeminformation Type 2 Ater, depending on the size of the BAList. System Information Type 2 Bis/Ter are optional.5/31/2013www.TempusTelcosys.com74
  75. 75. SYSTEM INFORMATION 2 Neighbor Cell Description:- BAIndicator(BA IND):- Allows to differentiate measurementresults related to different list of BCCH frequencies sent to MS.BCCH Allocation number(BANO):- Band 0 isused. PLMN Permitted(NCCPERM):-This the PLMN colorcodes permitted and tells the MS which network colorcodes(NCC) on the BCCH carriers it is allowed to monitor whenit is in this cell..5/31/2013www.TempusTelcosys.com75
  76. 76. SYSTEM INFORMATION 2 RACH Control ParametersAccess Control Class(ACC) :-Bitmap with 16 bits. AllMS spread out on class 0 –9 . Priority groups use class11-15. A bit set to 1 barred access for that class. Bit10 is used to tell the MS if emergency call is allowed ornot.0 – All MS can make emergency call. 1- MS with class 11-15 only canmake emergency calls.Cell barred for access(CB):-0- Yes 1-No5/31/2013www.TempusTelcosys.com76
  77. 77. SYSTEM INFORMATION 2Re-establishment allowed(RE):-0- Yes1- NoMax_retransmissions(MAXRET):-Number of times the MSattempts to access the Network [1,2,4 or 7].Tx-integer(TX):- Number of slots to spread accessretransmissions when a MS attempts to accessthe system.Emergency call allowed:- Yes/No.5/31/2013www.TempusTelcosys.com77
  78. 78. SYSTEM INFORMATION 2BCCH ARFCN Number(BAIND):- ARFCN’s used for ina Bitmap of 124 bits5/31/2013www.TempusTelcosys.com78124 123 122 121024 023 022 021 020 019 018 017016 015 014 013 012 011 010 009008 007 006 005 004 003 002 001
  79. 79. SYSTEM INFORMATION 3 The System Information Type 3 contains information on theidentity of the current LA and cell identity, because a changemeans that the MS must update the network. System Information 3 also as Control Channel Descriptionparameters 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 broadcastin the Type 3 information.5/31/2013www.TempusTelcosys.com79
  80. 80. SYSTEM INFORMATION 38 7 6 5 4 3 2 11 1 1 1LACLOCATION AREA IDENTITTY(LAI)MCC DIG 1MCC DIG 2MCC DIG 1MNC DIG 1MNC DIG 2CICICELL IDENTITYLAC5/31/2013www.TempusTelcosys.com80
  81. 81. SYSTEM INFORMATION 3 Control Channel DescriptionAttach / Detach(ATT):-0 = Allowed1 = Not Allowedbs_agblk:-Number of block reserved for AGCH [0-7]Ba_pmfrms:-Number of 51 frame multi-frames betweentransmission of paging messages to MS of the same groupT3212:- Periodic location update timer .[1-255 deci hours].5/31/2013www.TempusTelcosys.com81
  82. 82. SYSTEM INFORMATION 3cch_conf Physical channels combined No. of CCH0 1 timeslot(0) No 91 1 timeslot(0) Yes 32 2 timeslot(0,2) No 184 3 timeslot(0,2,4) No 276 4 timeslot(0,2,4,6) No 365/31/2013www.TempusTelcosys.com82
  83. 83. SYSTEM INFORMATION 3 Cell optionsDTX:-Whether Discontinuous Transmission used ornot.PWRC:-Power control on the downlink.0 = Not used.1 = Used.Radio link timeout(RLINKT):-Radio link time-out isthe time before an MS disconnects due to failure indecoding SACCH message. Sets the timer T100 inthe MS.5/31/2013www.TempusTelcosys.com83
  84. 84. SYSTEM INFORMATION 3 Cell Selection ParametersRxlev_access_min:- Minimum received signal level at theMS for which it is permitted to access the system.0-63 = -100 dBmto –47 dBm. Mx_txpwr_cch:- Maximumpower the MS will use when accessing the system.Cell_reselect_hysteresis:- Used for cell reselection. RACH Control Parameters.5/31/2013www.TempusTelcosys.com84
  85. 85. SYSTEM INFORMATION 4 Location Area Identification. Cell Selection ParametersRxlev_access_min:- Minimum received signal level at theMS for which it is permitted to access the system.0-63 = -100 dBmto –47 dBm. Mx_txpwr_cch:- Maximumpower the MS will use when accessing the system.Cell_reselect_hysteresis:- Used for cell reselection.5/31/2013www.TempusTelcosys.com85
  86. 86. SYSTEM INFORMATION 4 RACH Control Parametersmax_retransmissions(MAXRET)tx_integer(TX) Cellbarred for access(CB). Re-establishment allowed(RE) Emergency CallAllowedAccess Control Class (ACC)5/31/2013www.TempusTelcosys.com86
  87. 87. SYSTEM INFORMATION 4 CBCH Description(Optional) :CHN:- This is the channel number for CBCH. It iscontrolled internally in BSC.TSC:- Training Sequence Code. Base Station ColorCode(BCC) part of BSIC is used.CBCHNO:- Absolute RF channel number of CBCH.MAC:- Mobile Allocation in the cell, describes thefrequencies to be used in the hopping sequence iffrequency hopping is used.5/31/2013www.TempusTelcosys.com87
  88. 88. SYSTEM INFORMATION 4Hopping Channel(H):-Informs if CBCH Channel is hoppingor single.ARFCN:- If H=0;MAIO:- If H=1, informs the MS where tostart hopping.Values [0-63]. HSN:- IfH=1, informs the MS in what order the hoppingshould take place. Values[0 –63]. HSN=0 Cyclic Hopping.MA:-Indicates which RFChannels are used for hopping. ARFCN numberscoded in bitmap.5/31/2013www.TempusTelcosys.com88
  89. 89. SYSTEM INFORMATION 5 Sent on the SACCH on the downlink to the MS in dedicatedmode. On SAACH, the MS also receives information about the BCCHcarrier in each neighboring cell. This may differ from those sent inSystem information type 2. It is also possible to have system Information Type 5 Bis andSystem Information Type 5Ter, depending on the size of the BAlist.5/31/2013www.TempusTelcosys.com89
  90. 90. SYSTEM INFORMATION 5 Neighbor Cell Description:-BA-IND:-Used bythe Network to discriminate measurements results relatedto different lists of BCCH carriers sent by the MS(Type 2 or 5).Values 0 or 1(different from type 2).BCCH Allocationnumber:-00-Band 0(current GSM band).5/31/2013www.TempusTelcosys.com90
  91. 91. SYSTEM INFORMATION 5BCCH ARFCN:-Neighboring cells ARFCN’s. Sent as abitmap.0-Not used1-Used.124 123 122 121024 023 022 021 020 019 018 017016 015 014 013 012 011 010 009008 007 006 005 004 003 002 0015/31/2013www.TempusTelcosys.com91
  92. 92. SYSTEM INFORMATION 6 Ms 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 timeoutand DTX. Cell Identity. Location Area Identification. PLMN permitted.5/31/2013www.TempusTelcosys.com92
  93. 93. SYSTEM INFORMATION 6 Cell options:DTXPWRC RadioLink timeout.5/31/2013www.TempusTelcosys.com93
  94. 94. SYSTEM INFORMATION 7/8 System Information Types 7 and 8 contain Cell Reselectparameters. Their function is to supplement SystemInformation Type 4.5/31/2013www.TempusTelcosys.com94
  95. 95. GSM INTERFACES (Um) Air interface - MS to BTS A bis interface - BTS to BSC A Interface - BSC to MSC B Interface - MSC to VLR C interface - MSC to HLR5/31/2013www.TempusTelcosys.com95
  96. 96. MSCBSCVLRHLRAUCEIRGMSCMSA InterfaceA bis InterfaceAir InterfaceB InterfaceC InterfaceF InterfaceD InterfaceH InterfaceTo otherNetworks5/31/2013www.TempusTelcosys.com96
  97. 97. GSM INTERFACES The interfaces between MSC and MS is called A, Abisand Um interfaces. On these interfaces only three layers are defined.Theyare not corresponding to the OSI (Open SystemInterconnection) model.5/31/2013www.TempusTelcosys.com97
  98. 98. A INTERFACE A interface between the BSC and the MSC The A interface provides two distinct types ofinformation, signalling and traffic, between the MSC andthe BSC. The speech is transcoded in the TRC and the SS7(Signalling system) signalling is transparently connectedthrough the TRC or on a separate link to the BSC.5/31/2013www.TempusTelcosys.com98
  99. 99. ABIS INTERFACE The A-bis interface responsible for transmitting traffic andsignalling information between the BSC and the BTS. The transmission protocol used for sending signalling informationon the A-bis interface is Link Access Protocol on the D Channel(LAPD)5/31/2013www.TempusTelcosys.com99
  100. 100. (UM) AIR INTERFACE This is the interface between the mobile station and theBase station. The Air interface uses the Time Division Multiple Access(TDMA) technique to transmit and receive traffic andsignalling information between the BTS and MS. The TDMA technique is used to divide each carrier intoeight time slots.These time slots are then assigned tospecific users,allowing up to eight conversations to behandled Simultaneously by the same carrier.5/31/2013www.TempusTelcosys.com100
  101. 101. 7 56 34 12 01 2 43 5 76Down LinkUp Link 0Time Slot5/31/2013www.TempusTelcosys.com101• This interface is the radio interface between themobile station and the network and uses layerThree messages.• On Layer three messages we have the divisionof message types into CM (communicationManagement), MM (Mobility Management), andRR (Radio Resource Management).
  102. 102. CONNECTION MANAGEMENT (CM)There are three entities within CM: Call Control(CC) – Which handles the proceduresconcerning call control. e.g. setup,Change of bearerservice. Supplementary Service (SS) – Which handles such as callbearing, call waiting , call forwarding etc. Short Message Service (SMS) – Enables the MS to handleshort message transfer to and from the network.5/31/2013www.TempusTelcosys.com102
  103. 103. MOBILITY MANAGEMENT (MM) Mobility management handles functions forauthentication, location updating, identification andothers concerning the mobility of the mobile station.5/31/2013www.TempusTelcosys.com103
  104. 104. RADIO RESOURCE MANAGEMENT (RR) It contains the functions concerning the radio link. Here we findthe capability to establish,maintain and release the radioconnection between the network and the mobile station, whichincludes the handover procedure.5/31/2013www.TempusTelcosys.com104
  105. 105. B INTERFACE The B interface between the MSC and the VLR uses theMAP/TCAP protocol. Most MSCs are associated with a VLR, making the B interface"internal". Whenever the MSC needs access to data regarding a MS locatedin its area, it interrogates the VLR using the MAP/B protocol overthe B interface.5/31/2013www.TempusTelcosys.com105
  106. 106. C INTERFACE The C interface is between the HLR and a MSC. Each call originating outside of GSM (i.e., a MS terminating callfrom the PSTN) has to go through a Gateway to obtain the routinginformation required to complete the call, and the MAP/TCAPprotocol over the C interface is used for this purpose. Also, the MSC may optionally forward billing information to theHLR after call clearing.5/31/2013www.TempusTelcosys.com106
  107. 107. D INTERFACE The D interface is between the VLR and HLR. It uses the MAP/TCAP protocol to exchange the data related tothe location of the MS and to the management of the subscriber.5/31/2013www.TempusTelcosys.com107
  108. 108. E INTERFACE The E interface interconnects two MSCs. The E interface exchanges data related to handover between theanchor and relay MSCs using the -MAP/TCAP+ISUP/TUP protocol.5/31/2013www.TempusTelcosys.com108
  109. 109. F INTERFACE The F interface connects the MSC to the EIR. It uses the MAP/TCAP protocol to verify the status of the IMEIthat the MSC has retrieved from the MS.5/31/2013www.TempusTelcosys.com109
  110. 110. G INTERFACE The G interface interconnects two VLRs of different MSCs. It uses the MAP/G protocol to transfer subscriberinformation, during e.g. a location update procedure.5/31/2013www.TempusTelcosys.com110
  111. 111. ENCODING AND INTERLEAVINGOF INFORMATION SIGNALINGSM5/31/2013www.TempusTelcosys.com111
  112. 112. TOPICS FOR DISCUSSION Speech Encoding Data Encoding Interleaving for Voice,Control and Data signals5/31/2013www.TempusTelcosys.com112
  113. 113. SPEECH ENCODING We shall start with a raw voice signal fed into themicrophone, travel through the various stagesinvolving vocoding, channel coding etc till itreaches the final burst format on the AirInterface.5/31/2013www.TempusTelcosys.com113
  114. 114. SPEECH ENCODING CKT5/31/2013www.TempusTelcosys.com114VoiceEncodingChannelcodinginterleavingRF ModulationRawVoicesignal
  115. 115. SPEECH ENCODING CKT The voice is sampled at the rate of 50 samplesper second. This results in 20 msec blocks of speech Each of this 20 msec block is passed on to the13Kbps vocoder. There are 260 information bits from the outputof the vocoder for every 20 msec input i.e.;13Kbps *20msec = 260 bits.5/31/2013www.TempusTelcosys.com115
  116. 116. VOICE ENCODING CKT5/31/2013www.TempusTelcosys.com116Vocoder I/p20 msec speechblocks13Kbps Vocoder Vocoder O/p260 bits
  117. 117. CHANNEL CODING Channel Coding is done to protect the logicalchannels from transmission errors introduced bythe radio path. The coding schemes depend on the type of thelogical channels, hence the coding can differfrom speech, control and data .5/31/2013www.TempusTelcosys.com117
  118. 118. CHANNEL CODING FOR SPEECH5/31/2013www.TempusTelcosys.com118Class class 1b class 21a50 3 132 4 tailBits parity bitsConvolutional coder½ coder, k=5456 bits=378 bits from Convolution coder + 78 class 2 bits260 bits
  119. 119. CHANNEL CODING FOR SPEECH The 260 bits of speech info from the vocoder is brokendown into three parts. Class 1a- 50 bits , these represent the filter coefficientsof the speech and are the most important for properdetection of the speech at the receiver and hence aregiven maximum protection. 3 additional parity bits arederived from the class 1a bits for cyclic redundancycheck (CRC).5/31/2013www.TempusTelcosys.com119
  120. 120. CHANNEL CODING FOR SPEECH CONT’D Class 1b - 132 bits are not parity checked but arefed into the convolutional coder along with 4 tailbits which are used to set the registers in thereceiver to a known state for decoding purpose. Class 1b- 78 bits, these are not so important andare not protected but are combined with theoutput of the convolution coder.5/31/2013www.TempusTelcosys.com120
  121. 121. CONVOLUTIONAL CODER CC The Convolutional coder is a series of shift registersimplemented using logic gates, where for every oneinput bit we get 2 output bits. Hence it is called ½ coder. Here k=5 is the constraint length, it means there are 5shift register and each bit has memory depth of 4, meaning it can influence the output of up to four nextsuccessive bits. This is useful during reception as bitscan be derived even if a few consecutive bits are lostdue to errors or corruption.5/31/2013www.TempusTelcosys.com121
  122. 122. ½ CONVOLUTIONAL CODER5/31/2013www.TempusTelcosys.com122R1 R2 R3 R5R4++C0outputC1output0110..Input bits+ EX-ORR=register
  123. 123. CONVOLUTIONAL CODER CONT’D The 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 the20 msec speech block, but after CC the bit rate increasesto 22.8Kbps.456 bits *20msecs=22.8Kbps* CC = Convolutional Coder.5/31/2013www.TempusTelcosys.com123
  124. 124. CONTROL CHANNEL CODING5/31/2013www.TempusTelcosys.com124184 bitsControl data184 40 4 tailFire coded parity bits½ Convolutional Coder456 bits output
  125. 125. CONTROL CHANNEL CODING The control information is received in blocks of 184 bits. These bits are first protected with a cyclic code called asFire code, which is useful in correction and detection ofburst errors. 40 Parity bits are added, along with 4 tail bits. These 228 bits are given to the CC whose output is again456 bits at a bitrate of 22.8Kbps. The control channels include the RACH, PCH, AGCH etc.5/31/2013www.TempusTelcosys.com125
  126. 126. DATA CHANNEL CODING5/31/2013www.TempusTelcosys.com126240 bits 4 tailData bits½ Convolutional CoderOutput= 488 bitsAfter PuncturingOutput=456 bits
  127. 127. DATA CHANNEL CODING The data bits are received in blocks of 240 bits. Theseare directly convolution coded after adding 4 tail bits. The output of the CC is now 488 bits, which actuallyincreases the bitrate to 24.4 Kbps. To keep the bitrate constant on the air interface weneed to puncture the output of the CC. Hence, we havea final bitrate of 22.8 Kbps again .5/31/2013www.TempusTelcosys.com127
  128. 128. CHANNEL CODING CONT’D The above explanation was given keeping in viewa full rate Traffic, Control, or Data channel. For Half rate or Lesser rates the same principle ofchannel coding holds good, with slightdifferences in the encoding process.5/31/2013www.TempusTelcosys.com128
  129. 129. INTERLEAVING Having encoded the logical channelinformation, the next step is to build its bitstream into bursts that can be transmitted withinthe TDMA frame structure. This is the stagewhere the interleaving process is carried out. Interleaving spreads the content of oneinformation block across several TDMA timeslotsor bursts.5/31/2013www.TempusTelcosys.com129
  130. 130. INTERLEAVING CONT’D The following interleaving depths are used : Speech – 8 blocks Control – 4 blocks Data – 22 blocks The interleaving process for a speech block is shownwherein which a 456 bit speech block is divided into 8blocks of 57 bits each and each of these odd and even57 bit blocks are interleaved diagonally on to alternatebursts on the TDMA frame.5/31/2013www.TempusTelcosys.com130
  131. 131. SPEECH INTERLEAVING5/31/2013www.TempusTelcosys.com1318* 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 speechfrom 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
  132. 132. CONTROL DATA INTERLEAVING5/31/2013www.TempusTelcosys.com132114 114 114 114456 bits control dataThe control data is spread over 4 blocks using rectangularinterleaving instead of diagonal interleaving as inspeech the receiver will have to wait for at least2 multiframes before being able to decode the controlmessageTDMABurst blocks
  133. 133. DATA INTERLEAVING5/31/2013www.TempusTelcosys.com133114 114 114 114Burst 1 Burst 22Burst 2 Burst 3 Burst 4 Burst 19First 6bitsFirst 6bitsLast 6bitsLast 6bits456 bit data block
  134. 134. DATA INTERLEAVING CONT’D Here the data block of 456 bits is divided into 4 blocks of114 bits each. The first 6 bits from each of the 114 bit blocks isinserted in to each frame, the second 6 bits from eachof the 114 bits into the next frame and so on spreadingeach 114 block over 19 TDMA bursts while the entire456 bits is spread over 22 TDMA bursts. Thus the data interleaving is said to have a depth of 22bursts.5/31/2013www.TempusTelcosys.com134
  135. 135. DATA INTERLEAVING CONT’D The reason why data is spread over such along period oftime is that if data burst is corrupted or lost, only a smallpart of it is lost which can be reproduced at the receiver. This wide interleaving depth does produce a time delayduring transmission but that is acceptable since it doesnot affect the data signal quality at the receiver, unlikespeech where delay could result in bad quality of signalto the subscriber. *Note – The interleaving used in data is diagonalinterleaving.5/31/2013www.TempusTelcosys.com135
  136. 136. Before Deinterleaving3 successive bursts corruptedAfter DeinterleavingThe corrupted bursts are spread over a length equal to theinterleaving depth so that the effect of the errors isminimized.5/31/2013www.TempusTelcosys.com136INTERLEAVING ADVANTAGE
  137. 137. AIR INTERFACE BITRATE The information which is now coded and interleaved at22.8 Kbps now has to be transmitted over the Airinterface to the BTS. The information burst is not sent directly , but is sent inciphered form within a burst envelope. This ciphering isdone using ciphering keys and algorithms known bothby the mobile and the BSS.5/31/2013www.TempusTelcosys.com137
  138. 138. AIR INTERFACE BITRATE CONT’D The Kc is the ciphering key and A5 algorithm areapplied to the information(speech or data) whichincreases the bitrate to a final rate of 33.8 Kbpsfrom/to each mobile. If we assume all 8 timeslots of the cell to beoccupied then the bitrate of the Air interfacecomes to 33.8 * 8= 270.4 Kbps/channel.5/31/2013www.TempusTelcosys.com138
  139. 139. AIR INTERFACE BITRATE CONT’D5/31/2013www.TempusTelcosys.com139A5 AlgorithmKc InformationBlock 22.8 KbpsSent on Air interfaceCiphered information burst33.8 Kbps
  140. 140. AIR INTERFACE BITRATE CONT’D5/31/2013www.TempusTelcosys.com1401 2 3 4 5 6 7 8MobileTx’s at33.8 KbpsCell rx’s 8*33.8KBps = 270.4 KbpsPer TDMA frameCell coverage areaTDMA Fn TDMA Fn+1
  141. 141. DECODING AND DEINTERLEAVING AT THERECEIVER At the receiver the reverse process of Deinterleavingand decoding have to take place respectively, so as torecover the information from the signal. After Deinterleaving the signal will be decoded which isthe reverse process of the Convolutional coding, usingViterbi decoders. The decoder can recover lost or corrupted data up to 4successive bits, because the memory depth of the CC is4(for k=5).5/31/2013www.TempusTelcosys.com141
  142. 142. CHANNELIZATION Frequency band has several applicationsegments Certain blocks of the Band are reserved forcertain applications by regulating authorities Technologies have decided their frequency bands E.g. AMPS/DAMPS: 824-894 MHz5/31/2013www.TempusTelcosys.com142
  143. 143. CHANNELIZATION METHODSChannelization can be done primarily by threemethods: FDMA (Frequency Division Multiple Access) TDMA (Time Division Multiple Access) CDMA (Code Division Multiple Access)5/31/2013www.TempusTelcosys.com143
  144. 144. FDMA E.g. AMPS band is divided into 30 KHzchannels (1666 Freq. channels) Television Channels (Star, Zee, Sony,..)5/31/2013www.TempusTelcosys.com144FrequencyTimePower
  145. 145. TDMA E.g. AMPS has 3 timeslots on each 30 KHzchannel5/31/2013www.TempusTelcosys.com145FrequencyTimePower
  146. 146. CDMA Frequency channel is divided into code channels E.g. in IS-95 CDMA, 1.228 MHz channel is dividedinto 64 Code Channels Each user has a particular code Codes are orthogonal to each other, do notinterfere with each other5/31/2013www.TempusTelcosys.com146
  147. 147. DUPLEX ACCESS METHODS Frequency Division Duplex (FDD) Transmit on one frequency and receive onanother frequency5/31/2013www.TempusTelcosys.com147F1 F2 FrequencyAmplitudeTimeTx Rx
  148. 148. TIME DIVISION DUPLEX Time division duplex Tx and Rx is on the same frequency but ondifferent times5/31/2013www.TempusTelcosys.com148F1 FrequencyAmplitudeTimeTxRx
  149. 149. GSM AIR INTERFACE Separate Bands for Uplink and Downlink Downlink: 935-960Mhz (EGSM: 925-960MHz) Uplink: 890-915 MHz (EGSM: 880-915 MHz)5/31/2013www.TempusTelcosys.com149• TDMA and TDMA Multiplex– 124 Frequency Channels (ARFCN) for GSM900– 1 to 124 fro current band– 975 to 1023 for E-GSM– 200kHz Channels– 8 Mobiles share ARFCN by TDMA
  150. 150. GSM AIR INTERFACE (1800) 1800: Downlink: 1805-1880 MHz 1800: Uplink: 1710-1785 MHx 374 ARFCNs Separation of 95 MHz ARFCNs are numbered from 512 to 885 inclusive5/31/2013www.TempusTelcosys.com150
  151. 151. THE GSM BURST5/31/2013www.TempusTelcosys.com1513 357 261 571 8.25Tail BitsDataControlBitMidambleControlBitDataTail BitsGuardPeriod
  152. 152. SPEECH CODER RPE/LTP coder (RegularPulse excitation/Long termPrediction) Converts 64 kbps speech to13 kbps At the end we get 13kbpsspeech i.e. 260 bits in 20ms5/31/2013www.TempusTelcosys.com15220 ms blocksSpeech CoderBits Ordered50 veryimportantbits132importantbits78 otherbits
  153. 153. ERROR CORRECTION5/31/2013www.TempusTelcosys.com153Type 1a 50 3(CRC) Type 1b 132 Type II 78Reordering25 66366 25 4 Type II 78Type 1aType 1b Type 1bType 1aTailHalf rate convolutional code378 Type II 78456 bits from 20 ms of speech
  154. 154. DIAGONAL INTERLEAVING Traffic channel (TCH) bursts carry two 57 bit blocks(114) Each 120 ms of speech = 456*6 = 2736 bits2736/114 = 24 bursts i.3. 24 framesMultiframe has 26 frames in 120ms.There are 2 spare frames .. 1 SACCH, 1 Idle5/31/2013www.TempusTelcosys.com154456 bits from 20ms of speech 456 bits from 20ms of speech57 57575757575757 57 5757575757575757 57 57 5757 5757 5757 5757 5757 5757 57
  155. 155. CONVOLUTIONAL CODING ANDINTERLEAVING Bits to be Tx ed: HELLO Convolutionally encoded: HHEELLLLOO Interleaved: EE HH LL LL OO Bits Rx ed: EE HH LL LL OO De-Interleaved: HHEELLLLOO Viterbi Decoded: HELLO5/31/2013www.TempusTelcosys.com155
  156. 156. SPEECH CODING PROCESS5/31/2013www.TempusTelcosys.com15620 msSpeech Coder260 bits 13 kbps50 1a 132 1b 78 IIChannel Coder456 bits 22.8 kbpsTransceiver (BTS)Transcoder Handler260 bits456 bits16 kbpsTRAU frame260 + 60 = 320 bitsAbis13 kbps
  157. 157. TRAU FRAME 260 bits info + 60 TRAU bits = 320 bits/20ms =TRAU frame 60 bits contain frame Information data whichindicates speech, data, O&M, full rate/half rate 60 bits = 35 synchronization + 21 control + 4timing5/31/2013www.TempusTelcosys.com157
  158. 158. MIDAMBLE OR TRAINING BITS 8 midamble patterns (Colour codes) of 26 bits (BSIC) RACH and SCH have longer 41 and 64 bit Midambles Equalizer estimates channel impulse response frommidamble Mathematically construct inverse filter Uses inverse to decode bits5/31/2013www.TempusTelcosys.com1583 357 261 571 8.25Tail BitsDataControl BitMidambleControl BitDataTail BitsGuardPeriod
  159. 159. DOWNLINK AND UPLINK Uplink lags downlink by 3 timeslots Uplink and downlink use same timeslotnumber Uplink and downlink use same channelnumber (ARFCN) Uplink and downlink use different bands (45MHz apart for GSM 900)5/31/2013www.TempusTelcosys.com159
  160. 160. MEASUREMENTS MADE BY MS AND BTS5/31/2013www.TempusTelcosys.com160 RxQual0 < 0.2% 1 0.2 – 0.4 %3 0.4 – 0.8 % 4 0.8 – 0.16 %5 1.6 – 3.2 % 6 3.2 – 6.4 %7 6.4 – 12.8 %Uplink RXLEV (-48 to -110 dbm)Uplink RXQUAL (0-7)Uplink RXLEV (-48 to -110 dbm)Uplink RXQUAL (0-7)
  161. 161. MOBILE POWER CONTROL5/31/2013www.TempusTelcosys.com161 Mobile is commanded to change its TransmitPower Change in Power is proportionate to the PathLoss Change in Power is done in steps of 2 dbsPath LossPower Command
  162. 162. TIMING ADVANCE TDMA approach requires signals to arrive at BTSat the correct time A mobile at 30 km will be late by 100microseconds Timing advance is in the range of 0-62 One unit is 550m So maximum cell size is 63*0.55 = ~35 kms5/31/2013www.TempusTelcosys.com162
  163. 163. CONCEPTS OF CHANNELS INGSM A company vehicle is used for several purposes in aday Similarly in GSM, the timeslots are used for differentpurposes at different times5/31/2013www.TempusTelcosys.com163
  164. 164. FRAMES AND MULTIFRAMES5/31/2013www.TempusTelcosys.com1640 654321 73 Data 1Midamble1 Data 3 8.25 bits156.25 bits 576.92 micro sec4.615 msTimeSlotFrame0 50 0 25Control ChannelMultiframeTraffic ChannelMultiframe
  165. 165. GSM OPERATIONS Location Update Mobile OriginatedCall MobileTerminated Call Handover SecurityProcedures Cell Barring DTX Cell Broadcast Short MessageService Emergency calls SupplementaryServices Roaming5/31/2013www.TempusTelcosys.com165
  166. 166. MOBILE TURN ON Mobile Searches for Broadcast Channels(BCH) Synchronizes Frequency and Timing Decodes BCH sub-channels (BCCH) Checks if Network Allowed by SIM Location Update Authentication5/31/2013www.TempusTelcosys.com166
  167. 167. LOCATION AREA5/31/2013www.TempusTelcosys.com167Location Area 1LocationArea 2BTSBTSBTSBTSBTSBTSBTSBTSBSCBSCBSCMSC
  168. 168. LOCATION AREA IDENTITY Location area is the area covered by one ormore BTSs where a mobile can move freelywithout updating the system One Location area can be covered by oneor more BSCs, but ony one MSC.5/31/2013www.TempusTelcosys.com168MCC LACMNC
  169. 169. IMPORTANCE OF LOCATION AREA Reduce Paging load Resource PlanningSmaller Location Areas – Location update increasesLarger Location Areas – Paging load increases5/31/2013www.TempusTelcosys.com169
  170. 170. WHAT IS LOCATION UPDATE? MSC should know the location of theMobile for paging Mobile is continuously changing locationarea Mobile when changes Location Areainforms the MSC about its new LA Process of informing MSC about newLocation area is Location Update5/31/2013www.TempusTelcosys.com170
  171. 171. TYPES OF LOCATION UPDATES1. Normal LocationUpdate2. IMSI Attach3. Periodic LocationUpdate5/31/2013www.TempusTelcosys.com171Hi,I am in Location areaxxx
  172. 172. IMSI ATTACH Mobile turns off and sends an IMSI Detach toMSC Mobile turns on again and compares LAI If same, sends an IMSI attach to MSC5/31/2013www.TempusTelcosys.com172Is the receivedLAI same asbefore
  173. 173. NORMAL LOCATION UPDATE Mobile Turns on Power Reads the new LAI If different, does a Location Update5/31/2013www.TempusTelcosys.com173Is the receivedLAI same asbefore
  174. 174. PERIODIC LOCATION UPDATE The periodic location Update time is setfrom OMC/MSC After the periodic location update timerexpires, the mobile has to do a locationupdate5/31/2013www.TempusTelcosys.com174
  175. 175. WHAT HAPPENS AT LOCATION UPDATE? Mobile changes location area Reads the new Location Area fromBCCH Sends a RACH (request for channel) Gets a SDCCH after AGCH Sends its IMSI and new and old LAI in aLocation Update request to MSC onSDCCH5/31/2013www.TempusTelcosys.com175
  176. 176. WHAT HAPPENS AT LOCATION UPDATE CONT.. MSC starts Authentication If successful, Updates the new Location areafor the Mobile in the VLR Sends a confirmation to the Mobile Mobile leaves SDCCH, and comes to idlemode5/31/2013www.TempusTelcosys.com176
  177. 177. MOBILE ORIGINATED CALL5/31/2013www.TempusTelcosys.com177Channel RequestImmediate AssignService RequestCall ProceedingSet UpCipheringAuthenticationAlertingAssignmentConnection
  178. 178. MOBILE TERMINATED CALL 5/31/2013www.TempusTelcosys.com178PagingChannel RequestImmediate AssignSet UpCipheringAuthenticationPaging ResponseAssignmentCall ConfirmedAlertingConnection
  179. 179. SECURITY FEATURES AuthenticationProcess to verify Authenticity of SIMMobile is asked to perform an operationusing identity unique to SIM5/31/2013www.TempusTelcosys.com179• Ciphering–Process of coding speech for secrecy–The speech bits are EXORed with bitstream unique to MS
  180. 180. SECURITY FEATURES (TMSI REALLOCATION)5/31/2013www.TempusTelcosys.com180GSMInfrastructureMobileLocation UpdateTMSI AllocationCall SetupTMSI ReallocationTMSI- Temporary Mobile Subscriber Identity
  181. 181. SECURITY FEATURES(IDENTITY CHECK)5/31/2013www.TempusTelcosys.com181EIRSends IMEIIdentity CheckWhite listed /Grey Listed/ BlackListed mobiles
  182. 182. HANDOVER 5/31/2013www.TempusTelcosys.com182Cell 1 Cell 2Handover is a GSM feature by which thecontrol/communication of a Mobile is transferredfrom one cell to another if certain criteria’s aremet. It is a network initiated process.
  183. 183. CRITERIA FOR HANDOVER Receive Quality (RXQUAL) on uplink anddownlink Receive Signal Strength (RXLEV) on uplink anddownlink Distance (Timing Advance) Interference Level Power Budget5/31/2013www.TempusTelcosys.com183
  184. 184. HANDOVER DECISION BSC process the measurements reported by Mobileand the BTS5/31/2013www.TempusTelcosys.com184BTSBTSBTSBTSBTSBTSMobile has measurements of six neighbors
  185. 185. HANDOVER DECISION (CONT..) BSS performs averaging function on thesemeasurements every SACCH frame (480ms) Handover Decision algorithm is activated aftera set number of SACCH frame periods bycomparison against thresholds5/31/2013www.TempusTelcosys.com185
  186. 186. TYPES OF HANDOVERS INTRA-CELL HANDOVERS INTER-CELL HANDOVERS INTRA-BSC HANDOVERS INTER-BSC HANDOVERS INTER-MSC HANDOVERS5/31/2013www.TempusTelcosys.com186
  187. 187. INTRA-CELL HANDOVER5/31/2013www.TempusTelcosys.com187C0C1Handover between timeslots of same frequencyHandover between different frequencies of the same cell(to reduce interference)MSC is not aware about this
  188. 188. INTER-CELL HANDOVER5/31/2013www.TempusTelcosys.com188Handover between cells of the same BTSBTSCell 1 Cell 2
  189. 189. INTER-CELL HANDOVER (CONT..) MSC is told about HO BTS -> BSC -> MSC Why MSC is informed? In case of change of LA, MSC may need LAC forpaging. As MS is busy, a link already exists. So,MSC can send a tone in case of call waiting, anddoes not need to page again. This is needed also for billing and call tracing5/31/2013www.TempusTelcosys.com189
  190. 190. INTRA-BSC HANDOVER5/31/2013www.TempusTelcosys.com190MSC BSCBTSBTSThis HO takes place if the cell to which handoveris to be done belongs to the same BSC
  191. 191. INTER BSC HANDOVER5/31/2013www.TempusTelcosys.com191MSCBSC BTSBTSBSCThe MSC is completely involved in this Handover
  192. 192. INTER MSC HANDOVER5/31/2013www.TempusTelcosys.com192BSCBSCMSCMSCBTSBTSGMSC/PSTN/BackboneIn this case the handover takes place through theinterconnecting element which can be GMSC orPSTN or private Backbone between the MSCs
  193. 193. CELL BARRING5/31/2013www.TempusTelcosys.com193BTSCell Barring is a GSM feature by which certainmobiles could be barred access to certain cellsCell barring is activated/deactivated at BTS levelCell barring is done for mobile categories andpriorities
  194. 194. CELL BARRING Every mobile has an access class The access class is stored in the SIM Classes 0-9 are termed normal calsses Classes 11-15 are emergency classes5/31/2013www.TempusTelcosys.com194• Every cell has a set parameter whichdefines which access classes are barredfor the particular cell. This parameter isbroadcasted on the BCCH
  195. 195. WHAT IS DTX? DTX (Discontinous Transmission) Each direction of Transmission is only 50% Transmitter is switched ON for usefulinformation frames5/31/2013www.TempusTelcosys.com195Need for DTX•To increase battery life•To reduce the average interference levelDTX is done by DTX handlers which havethe following functions.
  196. 196. VAD (VOICE ACTIVITY DETECTOR) Senses for speech in 20ms blocks Removes stationary noise VAD is an energy detector Compares Energy of filtered speech threshold It determines which 20ms blocks contain speechand it only forwards those frames5/31/2013www.TempusTelcosys.com196
  197. 197. EVALUATION OF BACKGROUND NOISE Background noise is always present with speech DTX cuts off this noise with speech Gives an uncomfortable feeling to the listener VAD takes care of this by inserting comfort noiseat the receiving end when speech discontinues.5/31/2013www.TempusTelcosys.com197
  198. 198. EMERGENCY CALLS GSM specs define 112 as an emergencynumber ‘112’ is accessible with or without SIM Without SIM it is sent on the best channel Mobile on sensing ‘112’ sets theestablishment cause to emergency call inthe RACH Routing of this call be done to a desiredlocation defined in the switch5/31/2013www.TempusTelcosys.com198
  199. 199. CELL (RE)SELECTION Cell reselection is done using C1 path losscriterion. The purpose is to ensure that the MS is campedon to the cell with the best transmission quality. The MS will camp on to the cell with the highestC1 value if C1 > 0.5/31/2013www.TempusTelcosys.com199
  200. 200. THE FOLLOWING PARAMETERS ARE USED TOCALCULATE THE C1 CRITERION The received signal at the MS side. Rxlev_access_min - broadcast on the BCCH - Theminimum received level at the MS required foraccess to the network. Ms_txpwr_max_cch - the maximum power thatan MS may use when initially accessing thenetwork. The maximum power of the MS5/31/2013www.TempusTelcosys.com200
  201. 201. C1 = A - MAX(B,0) A = Received level Average - Rxlev_access_min. B = MS_txpwr_max_cch - maximum outputpower of the MS5/31/2013www.TempusTelcosys.com201
  202. 202. CELL RESELECT HYSTERESIS Cell reselection on the border of two location areas result in alocation update. When an MS moves on the border of twolocation areas lots of location updates take place. To avoid theselocation 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 C1value in the current location area and The received signal strengths have at least a difference of thereselect hysteresis.5/31/2013www.TempusTelcosys.com202
  203. 203. CELLULAR CONCEPT5/31/2013www.TempusTelcosys.com203
  204. 204. WHY TO USE THECELLULAR CONCEPT ? Solves the problem of Spectral congestion anduser capacity by means of frequency reuse. Offers high capacity in a limited spectrumallocation. Offers system level approach, using low powertransmitters instead of a single, high powertransmitter (large cell) to cover larger area.5/31/2013www.TempusTelcosys.com204
  205. 205.  A portion of the total channels available isallocated to each base station. Neighboring base stations are assigneddifferent groups channels, in order tominimize interference.5/31/2013www.TempusTelcosys.com205
  206. 206. CELL SHAPE5/31/2013www.TempusTelcosys.com206
  207. 207. 5/31/2013www.TempusTelcosys.com207
  208. 208. 1-Omni-directional cell-site (Omni-directionalantenna).2-Rhombus-shaped sectors (Directiveantenna).3-Hexagonal shaped sectors (Directiveantenna).5/31/2013www.TempusTelcosys.com208
  209. 209. 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.5/31/2013www.TempusTelcosys.com209
  210. 210. TYPES OF CELLS1-Macro-cells 2-Micro-cells.3-Pico-cells. 4-Umbrella-cells.5/31/2013www.TempusTelcosys.com210
  211. 211. WHAT IS A CLUSTER ? A cluster is a groupof cells. No channels arereused within acluster. It is the unit ofdesign.5/31/2013www.TempusTelcosys.com211
  212. 212. CLUSTER SIZE Definition : It is The number of cells perclusterN = i^2 + ij + j^2Where :i = 0, 1, 2….& j = 0,1,2…. etc.N = 1 , 3 , 4 ,7, 9 , 12 ,……5/31/2013www.TempusTelcosys.com212
  213. 213. 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 plansa) N=3 tricellular plan (3/9).b) N=4 tricellular plan (4/12).5/31/2013www.TempusTelcosys.com213
  214. 214. CHANNEL ASSIGNMENTSTRATEGIES Considerations :1) Max. capacity.2) Min interference.3) Perfect handover. Types of assignment strategies :1) Fixed : Each cell has permanent predetermined set of voicechannels. New calls served by unused channels of this cell. Borrowing strategy if all channels are occupied. High probabiltity that call is Blocked if channels areoccupied.( disadv.)5/31/2013www.TempusTelcosys.com214
  215. 215. 2) Dynamic : Channels are not allocated to different cellspermanently. Each new call BTS requests new channel fromMSC. MSC allocate a channel, by using an algorithmthat takes into account:1- Frequency is not already in use.2- Min. reuse distance to avoid co-channelinterference.5/31/2013www.TempusTelcosys.com215
  216. 216.  Adv. of dynamic assignment strategy :1) Increase channel utilization( Increase trunking efficiency ).2) Decrease probability of a blocked call.5/31/2013www.TempusTelcosys.com216
  217. 217. FREQUENCY REUSECONCEPT5/31/2013www.TempusTelcosys.com217
  218. 218. 5/31/2013www.TempusTelcosys.com218
  219. 219. REUSE CLUSTER5/31/2013www.TempusTelcosys.com219
  220. 220. CO-CHANNEL REUSERATIO (Q) : R : cell radius. D : reuse distance. Q = D/R. =sqrt(3N).Where :N : cluster size5/31/2013www.TempusTelcosys.com220
  221. 221. HANDOVER5/31/2013www.TempusTelcosys.com221
  222. 222. Definition : procedure that allows MS tochange the cell or time-slot to keep asgood link as possible during all the call.5/31/2013www.TempusTelcosys.com222
  223. 223. 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 SameBSC. InterBSC : bet. 2 cells of different BSC’s & sameMSC.5/31/2013www.TempusTelcosys.com223
  224. 224. MEASUREMENTS BEFOREHANDOVER1- Measurements from MS to BSC :a) Strength of BTS signal.b) Quality of BTS signal.c) Signal strength of 6 neighbor BTS’s.2-Measurements from BTS to BSC :a) Strength of MS signal.b) Quality of MS signal.c) Distance between serving BTS & MS.5/31/2013www.TempusTelcosys.com224
  225. 225. DIFFERENT CAUSES OF HANDOVER5/31/2013www.TempusTelcosys.com225Better cell HOEmergency HOLevel QualityPBGTTraffic causesInterferenceDistanceDifferent causes ofHandover
  226. 226. BASIC HANDOVERALGORITHMSa)“Min. acceptable performance” algorithm:MS power is increased when qualitydeceases till handover is the only way.b) “Power budget “ algorithm:Prefer direct handover when qualitydeceases without increasing MS power first.5/31/2013www.TempusTelcosys.com226
  227. 227. 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.5/31/2013www.TempusTelcosys.com227
  228. 228. INTERFERENCE5/31/2013www.TempusTelcosys.com228
  229. 229. SOURCES OFINTERFERENCE INCLUDE:1) Another mobile in the same cell.2) A call in progress in the neighboringcell.3) Other BTS’s operating in the samefrequency band.5/31/2013www.TempusTelcosys.com229
  230. 230. INTERFERENCE EFFECTS : In voice channel causes crosstalk In control channels it leads missed and blockedcalls due to errors in the digital signaling.5/31/2013www.TempusTelcosys.com230
  231. 231. MAIN TYPES OFINTERFERENCE :1) Co-channel interference.2) Adjacent channel interference.5/31/2013www.TempusTelcosys.com231
  232. 232. 1) CO-CHANNELINTERFERENCE 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 ithinterfering co-channel cell BS.5/31/2013www.TempusTelcosys.com232
  233. 233.  Another form :C/I = 10 log {(1/n)(D/R)*m}Where :m = propagation constant(dep’s on nature of environment)n = number of co-channel interferers.Can be minimized by :Choosing minimum reuse distance= (2.5….3)(2R).5/31/2013www.TempusTelcosys.com233
  234. 234. 2) ADJACENT CHANNELINTERFERENCE Source : A cell using a frequency adjacent tothe one in another cell due to imperfectreciever’s filter.5/31/2013www.TempusTelcosys.com234
  235. 235. Can be minimized by :1-careful filtering2-careful channel assignments3-Directional antenna. General rule : ACI= -10 Log[(d1/d2)*m] – Adj chisolation.Where :d1: distance between MS & proper BTs d2:dist. Bet MS & adj BTS causinginterference.Adj ch isolation = Filter isolation = - 26db.5/31/2013www.TempusTelcosys.com235
  236. 236. TRAFFIC ENGINEERING THEORY5/31/2013www.TempusTelcosys.com236
  237. 237. WHY DO WE NEED TOKNOW TRAFFIC? The amount of traffic during peak hoursallows us to dimension our wireless system fora certain GOS. GOS : probability of having a call blockedduring busy hour (block rate).5/31/2013www.TempusTelcosys.com237
  238. 238. 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*averagecall holding time(sec.)] / [3600]5/31/2013www.TempusTelcosys.com238
  239. 239. TYPICAL TRAFFIC PROFILE5/31/2013www.TempusTelcosys.com239
  240. 240. TRAFFIC TABLESBlocked calls are notheldErlang BTableBlocked calls are held inthe queue indefinitelyErlang CTableBlocked calls are held inthe queue for a time =the mean holding timePoissonTable5/31/2013www.TempusTelcosys.com240
  241. 241. ERLANG – B TABLE P(N;T) = [ (T^N)*exp(-T) ] / N!GOS2%GOS1%N0.2230.15321.0930.86945.0844.461013.18212.02030.99729.0405/31/2013www.TempusTelcosys.com241
  242. 242. TRUNKING Sharing channel among several users. Trunking efficiency (nT) : Measures thenumber of subscribers that each channel inevery cell can accommodate.nT = (traffic in Erlangs / no. ofchannels)*100.5/31/2013www.TempusTelcosys.com242
  243. 243.  Trunking efficiency inpresence of oneoperator :N = 7 , 312 one directionvoice channelsNo. of channels / cell = 312 /7 = 44 ch./cell.From Erlang-B table @GOS2%,this’s equivalent to 35ErlangsnT = 35 / 44 = 79.55. Trunking efficiencyin presence of twooperators :N = 7 , 312 / 2 = 156 onedirection voice channel foreach operator.No. of channels / cell = 156/ 7 = 22 ch./cell.From Erlang-B table @GOS2%,this’s equivalent to 15Erlangs.nT = 15 / 22 = 68.18.5/31/2013www.TempusTelcosys.com243
  244. 244. SYSTEM CAPACITY5/31/2013www.TempusTelcosys.com244
  245. 245.  S : total duplex channels available for use = k*NWhere: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.5/31/2013www.TempusTelcosys.com245
  246. 246. IMPROVING SYSTEMCAPACITY Cell splitting. Sectoring.5/31/2013www.TempusTelcosys.com246
  247. 247. CELL SPLITTING5/31/2013www.TempusTelcosys.com247
  248. 248. SECTORING We use directional antennas instead of beingomnidirectional5/31/2013www.TempusTelcosys.com248
  249. 249. WHAT DOES SECTORINGMEAN? We can now assign frequency sets to sectorsand 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 there’s only2 interferers instead of 6 incase of omnidirectional N=7cluster.5/31/2013www.TempusTelcosys.com249
  250. 250. 5/31/2013www.TempusTelcosys.com250
  251. 251. 5/31/2013www.TempusTelcosys.com251
  252. 252. DIRECTIONAL FREQUENCYREUSE Here we use 7/21pattern forfrequency allocation.5/31/2013www.TempusTelcosys.com252
  253. 253. COMPARISON BETWEENVARIOUS TYPES OFCLUSTERS5/31/2013www.TempusTelcosys.com253
  254. 254. N = 7 OMNI FREQUENCYPLAN : n = 6 , m = 4. D / R = 4.583. 1) Co-channelinterference ratio :C / I = 18.6 dB. 2) Adjacent channelinterference :ACI = -26 dB @ d1= d2.5/31/2013www.TempusTelcosys.com254
  255. 255. N = 7 TRAPEZOIDALFREQUENCY PLAN n = 2 , m = 4. D / R = 6.245. 1) Co-channel interferenceratio :C / I = 28.8. 2) Adjacent channelinterference : disappearsbecause the channels areassigned alternatively to thecells.5/31/2013www.TempusTelcosys.com255
  256. 256.  Trunking efficiency : 312 one direction voice channelsN = 7 312 / 7 = 44.57 ~ 44 ch./cell. From Erlang-B table @ GOS = 2%T = 35 E. nT = 35 / 44 = 79.55 %.5/31/2013www.TempusTelcosys.com256
  257. 257. N = 9 OMNI FREQUENCY PLAN n = 4 , m = 4. D / R = sqrt ( 3 * 9 ) = 5.2. 1) Co-channel interference:C / I = 22.6 dB. 2) Adjacent channelinterference :ACI = -38 dB @ d2 = 2 (d1).5/31/2013www.TempusTelcosys.com257
  258. 258.  Trunking efficiency : 312 one direction voice channelsN = 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 9But C/I 7 > C/I 9ACI 7 > ACI 95/31/2013www.TempusTelcosys.com258
  259. 259. 4 / 12 CELL PATTERN n = 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%.5/31/2013www.TempusTelcosys.com259
  260. 260. 3 / 9 CELL PATTERN n = 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 %.5/31/2013www.TempusTelcosys.com260
  261. 261. 120 DEGREE CELL SECTORING n = 2 , m = 4. D / R = sqrt(3 * 7) = 4.583. Co-channel interference :C / I = 23.436 + 6dB(due toisolation) = 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%.5/31/2013www.TempusTelcosys.com261

×