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EEE 464 Wireless Communications Lecture 7

EEE 464 Wireless Communications Lecture 7. Shahzad Malik, Ph.D. smalik@comsats.edu.pk. Mobile Cellular Wireless Networks. This lecture presents system details of 2G/3G mobile cellular networks: GSM/GPRS, CdmaOne (IS-95) and UMTS/ Cdma2000. Organization of Lecture 7.

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EEE 464 Wireless Communications Lecture 7

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  1. EEE 464Wireless CommunicationsLecture 7 Shahzad Malik, Ph.D. smalik@comsats.edu.pk

  2. Mobile Cellular Wireless Networks This lecture presents system details of 2G/3G mobile cellular networks: GSM/GPRS, CdmaOne (IS-95) and UMTS/ Cdma2000

  3. Organization of Lecture 7 • Global System for Mobile (GSM) • GPRS • SMS • EDGE

  4. GSMGlobal System for Mobile

  5. CT0/1 FDMA AMPS CT2 NMT IMT-FT DECT IS-136 TDMA D-AMPS EDGE IMT-SC IS-136HS UWC-136 TDMA GSM GPRS PDC IMT-DS UTRA FDD / W-CDMA IMT-TC UTRA TDD / TD-CDMA IMT-TC TD-SCDMA CDMA IS-95 cdmaOne IMT-MC cdma2000 1X EV-DO cdma2000 1X 1X EV-DV (3X) 2G 3G 1G 2.5G Cellular Systems – Generation

  6. Digital PLMN systems (PLMN = Public Land Mobile Network) 2nd Generation (2G) 3rd Generation (3G) 4G IMT-2000 GSM FDD UMTS: GPRS More radio capacity UTRA FDD ? Packet services UTRA TDD EDGE IS-136 USA CDMA 2000 IS-95

  7. GSM: Overview • GSM - Global System for Mobile • formerly: Groupe Spéciale Mobile (founded 1982) • now: Global System for Mobile Communication • Pan-European standard (ETSI, European Telecommunications Standardisation Institute) • simultaneous introduction of essential services in three phases (1991, 1994, 1996) by the European telecommunication administrations  seamless roaming within Europe possible • today many providers all over the world use GSM (more than 184 countries in Asia, Africa, Europe, Australia, America) • more than 1000 million subscribers • more than 70% of all digital mobile phones use GSM • over 10 billion SMS per month in Germany, > 360 billion/year worldwide

  8. GSM • Objectives: • Broad offering of speech and data services • Compatible with wireline networks, eg, ISDN • Automatic roaming and handoff • Highly efficient use of frequency spectrum • Support for different types of mobile terminal equipment (eg, cars, portable handsets) • Digital signaling and transmission • Low cost infrastructure and terminal equipment

  9. Performance characteristics of GSM • Communication • mobile, wireless communication; support for voice and data services • Total mobility • international access, chip-card enables use of access points of different providers • Worldwide connectivity • one number, the network handles localization • High capacity • better frequency efficiency, smaller cells, more customers per cell • High transmission quality • high audio quality and reliability for wireless, uninterrupted phone calls at higher speeds (e.g., from cars, trains) • Security functions • access control, authentication via chip-card and PIN

  10. Architecture of the GSM system • GSM is a PLMN (Public Land Mobile Network) • several providers setup mobile networks following the GSM standard within each country • components • MS (mobile station) • BS (base station) • MSC (mobile switching center) • LR (location register) • subsystems • RSS (radio subsystem): covers all radio aspects • NSS (network and switching subsystem): call forwarding, handover, switching • OSS (operation subsystem): management of the network

  11. GSM: overview OMC, EIR, AUC fixed network HLR GMSC NSS with OSS VLR MSC VLR MSC BSC BSC RSS

  12. GSM: elements and interfaces radio cell BSS MS MS Um radio cell RSS MS BTS BTS Abis BSC BSC A MSC MSC NSS signaling VLR VLR ISDN, PSTN HLR GMSC PDN IWF O OSS EIR AUC OMC

  13. GSM: system architecture fixedpartner networks network and switching subsystem radiosubsystem MS MS ISDNPSTN MSC Um Abis BTS BSC EIR BTS SS7 HLR VLR BTS ISDNPSTN BSC BTS MSC A IWF BSS PSPDNCSPDN

  14. Components MS (Mobile Station) BSS (Base Station Subsystem):consisting of BTS (Base Transceiver Station):sender and receiver BSC (Base Station Controller):controlling several transceivers Interfaces Um : radio interface Abis : standardized, open interface with 16 kbit/s user channels A: standardized, open interface with 64 kbit/s user channels System architecture: radio subsystem radiosubsystem network and switchingsubsystem MS MS Um Abis BTS MSC BSC BTS A BTS MSC BSC BTS BSS

  15. Radio subsystem • The Radio Subsystem (RSS) comprises the cellular mobile network up to the switching centers • Components • Base Station Subsystem (BSS): • Base Transceiver Station (BTS): radio components including sender, receiver, antenna - if directed antennas are used one BTS can cover several cells • Base Station Controller (BSC): switching between BTSs, controlling BTSs, managing of network resources, mapping of radio channels (Um) onto terrestrial channels (A interface) • BSS = BSC + sum(BTS) + interconnection • Mobile Stations (MS)

  16. Radio subsystem - BSS • Base Station Subsystem • It is the wireless point of contact of the network with users • It forms Radio Access Network (RAN) • It translates between the air interface and the wired infrastructure protocols • The two network segments need different protocols because the difference of the nature of wireless links • Unreliable, bandwidth limited, supports mobility • Speech Conversion • The MS generates radio-efficient 13 kbps digitized voice packets using speech coder. The backbone PSTN requires 64 kbps PCM digitized voice. The BSS converts 13 to 64 kbps code. • Signaling • The multi-tone frequency signaling is used in POTS in the wired backbone, whereas GSM performs several packet exchange to establish a call. The signaling conversion takes place at the BSS

  17. Radio subsystem - BSS • Tasks of a BSS are distributed over BSC and BTS • BTS comprises radio specific functions • BSC is the switching center for radio channels

  18. TE TA MT Um R S Radio subsystem - Mobile station • Terminal for the use of GSM services • A mobile station (MS) comprises several functional groups • MT (Mobile Terminal): • offers common functions used by all services the MS offers • end-point of the radio interface (Um) • TA (Terminal Adapter): • terminal adaptation, hides radio specific characteristics • TE (Terminal Equipment): • peripheral device of the MS, offers services to a user • does not contain GSM specific functions • SIM (Subscriber Identity Module): • personalization of the mobile terminal, stores user parameters

  19. network and switching subsystem networksubsystem fixed partnernetworks • Components • MSC (Mobile Services Switching Center): • IWF (Interworking Functions) • ISDN (Integrated Services Digital Network) • PSTN (Public Switched Telephone Network) • PSPDN (Packet Switched Public Data Net.) • CSPDN (Circuit Switched Public Data Net.) • Databases • HLR (Home Location Register) • VLR (Visitor Location Register) • EIR (Equipment Identity Register) ISDNPSTN MSC EIR SS7 HLR VLR ISDNPSTN MSC IWF PSPDNCSPDN

  20. Network and switching subsystem • NSS is the main component of the public mobile network GSM • switching, mobility management, interconnection to other networks, system control • Components • Mobile Services Switching Center (MSC)controls all connections via a separated network to/from a mobile terminal within the domain of the MSC - several BSC can belong to a MSC • Databases (important: scalability, high capacity, low delay) • Home Location Register (HLR)central master database containing user data, permanent and semi-permanent data of all subscribers assigned to the HLR (one provider can have several HLRs) • Visitor Location Register (VLR)local database for a subset of user data, including data about all user currently in the domain of the VLR

  21. Mobile Services Switching Center • The MSC (mobile switching center) plays a central role in GSM • switching functions • additional functions for mobility support • management of network resources • interworking functions via Gateway MSC (GMSC) • integration of several databases • Functions of a MSC • specific functions for paging and call forwarding • termination of SS7 (signaling system no. 7) • mobility specific signaling • location registration and forwarding of location information • provision of new services (fax, data calls) • support of short message service (SMS) • generation and forwarding of accounting and billing information

  22. Operation subsystem • The OSS (Operation Subsystem) enables centralized operation, management, and maintenance of all GSM subsystems • Components • Authentication Center (AUC) • generates user specific authentication parameters on request of a VLR • authentication parameters used for authentication of mobile terminals and encryption of user data on the air interface within the GSM system • Equipment Identity Register (EIR) • registers GSM mobile stations and user rights • stolen or malfunctioning mobile stations can be locked and sometimes even localized • Operation and Maintenance Center (OMC) • different control capabilities for the radio subsystem and the network subsystem

  23. higher GSM frame structures 5 7 8 1 2 4 6 3 4.615 ms 546.5 µs 577 µs GSM - FDMA/TDMA 935-960 MHz 124 channels (200 kHz) downlink frequency 890-915 MHz 124 channels (200 kHz) uplink time GSM TDMA frame GSM time-slot (normal burst) guard space guard space S user data tail tail user data S Training 1 3 1 57 bits 3 bits 57 bits 26 bits

  24. GSM FDMA … 4 2 3 124 1 200 KHz Carrier Spacing BW = 25 MHz Downlink Frequency Band: 890-915 MHz Downlink Frequency Band: 935-960 MHz Bc = 200 KHz Bg = 100 KHz Number of Channels = 124 Data rate for each carrier = 270.833 kbps Bit time = 3.69 s Slot time (or burst time) = 577 s Number of bits/slot = 156.25 bits Burst Types: 1. Normal Burst (NB) 2. Frequency Correction Burst 3. Synchronization burst 4. Random Access Burst (RAB) 100 KHz guard band

  25. GSM Physical Channels TDMA frame = 4.615 ms Timeslot 1 2 3 4 5 6 7 8 Frequency 1 Ch 1 Ch 2 Ch 3 Ch 4 Ch 5 Ch 6 Ch 7 Ch 8 Frequency 2 Ch 1 Ch 2 Ch 3 Ch 4 Ch 5 Ch 6 Ch 7 Ch 8 : : : : Frequency 124 Ch 1 Ch 2 Ch 3 Ch 4 Ch 5 Ch 6 Ch 7 Ch 8 ARFCN – Absolute Radio Frequency Channel Number

  26. GSM Air Interface

  27. GSM Logical and Physical Channels • Um interface: various logical channels are mapped to physical channels • A physical channel is a timeslot with timeslot number in a sequence of TDMA frames on a particular ARFCN • 8 physical channels mapped onto 8 timeslots within TDMA frame per frequency carrier

  28. 2048 super frames: Hyper frame (3 hr 28 min 53.76 s) 51 traffic or 26 control multi frames: Super frame (6.12 s) 51control frames: Multi frame (235.4 ms) 26 traffic frames: Multi frame (120 ms) 8 slots: Frame (4.615 ms) 156.25 bits: Burst (0.577 ms) GSM Frame Hierarchy

  29. GSM hierarchy of frames hyperframe 0 1 2 ... 2045 2046 2047 3 h 28 min 53.76 s superframe 0 1 2 ... 48 49 50 6.12 s 0 1 ... 24 25 multiframe 0 1 ... 24 25 120 ms 0 1 2 ... 48 49 50 235.4 ms frame 0 1 ... 6 7 4.615 ms slot burst 577 µs

  30. GSM Logical Channels • 3 groups of logical channels, TCH, CCH and CBCH • TCH is used to carry voice or data traffic • CCH is used for control functions • CBCH is used for broadcast functions • Logical traffic channels = full rate (TCH/F) at 22.8 kb/s or half rate (TCH/H) at 11.4 kb/s • Physical channel = full rate traffic channel (1 timeslot) or 2 half rate traffic channels (1 timeslot in alternating frames) • Full rate channel may carry 13 kb/s speech or data at 12, 6, or 3.6 kb/s • Half rate channel may carry 6.5 kb/s speech or data at 6 or 3.6 kb/s


  32. GSM Logical Channels, cont.. • CCH consists of 3 groups of logical control channels, BCH, CCCH and DCCH • BCH (broadcast channel): point-to-multipoint downlink only. Contains three sub-channels, BCCH, FCCH and SCH • BCCH (broadcast control channel): send cell identities, organization info about common control channels, cell service available, etc • FCCH (frequency correction channel): send a frequency correction data burst containing all zeros to effect a constant frequency shift of RF carrier • SCH (synchronization channel): send TDMA frame number and base station identity code to synchronize MSs

  33. GSM Logical Channels, cont… • CCCH (common control channel): Consists of three sub-channels, PCH, AGCH and RACH. This channels is used for paging and access • PCH (paging channel): to page MSs • AGCH (access grant channel): to assign MSs to stand-alone dedicated control channels for initial assignment • RACH (random access channel): for MS to send requests for dedicated connections

  34. GSM Logical Channels, cont… • DCCH (dedicated control channel): bi-directional point-to-point -- main signaling channels. Consist of two sub-channels, SDCCH and ACCH • SDCCH (stand-alone dedicated control channel): for service request, subscriber authentication, equipment validation, assignment to a traffic channel • ACCH consist of two sub-channels, SACCH and FACCH • SACCH (slow associated control channel): for out-of-band signaling associated with a traffic channel, eg, signal strength measurements • FACCH (fast associated control channel): for preemptive signaling on a traffic channel, eg, for handoff messages

  35. GSM Logical Channels , cont…

  36. GSM Logical Channels , cont…

  37. Speech packet (13 kbps) 260 bits (20 ms) 50 bits 260 bits CRC coding 53 bits 132 bits ½ convolutional coding ½ convolutional coding ½ convolutional coding 4 tail bits 78 bits 378 bits 456 bits (20 ms) Transmitted packet 184 bits (20 ms) Signaling packet 9600 bps data packet 192 bits (20 ms) 40 parity bits 48 bits signaling info 4 tail bits 4 tail bits 456 bits (20 ms) 456 bits (20 ms) Transmitted packet Transmitted packet GSM Packet Encoding

  38. GSM Data Bursts

  39. GSM Operation

  40. Um Air Interface A-bis A CM CM MM MM RRM RRM RRM RRM SCCP SCCP MTP LAPDm LAPD LAPD LAPDm MTP 64kbps Radio Radio 64kbps 64kbps 64kbps MSC MS BSC BTS Protocol Stack CM: Connection Management RRM: Radio Resource Management MM: Mobility Management MTP: Message Transfer Part SCCP: Signal Connection Control part LAPD: Link access protocol-D

  41. GSM Protocol Layers • RF : Physical Layer • LAPD: Link Layer, ISDN protocol based • SCCP: Signal Connection Control Layer, part of link layer • RR: Radio Resource • MM: Mobility Management • CC: Call Control

  42. GSM Network Layer • Network layer consists of 3 sublayers • Radio resource management (RR) sublayer • Establishment, maintenance, and termination of radio channel connections • Mobility management (MM) sublayer • Registration, authentication, and location tracking • Call control (CC) sublayer • Establishment, maintenance, and termination of circuit-switched calls

  43. HLR MSC VLR MS BSC BTS 1. Channel Request 2. Activation Response 3. Activation ACK 4. Channel Assigned 5. Location Update Request 6. Authentication Request 7. Authentication Response 8. Authentication Check 9. Assigning TMSI 10. ACK for TMSI 11. Entry for VLR and HLR 12. Channel Release Registration

  44. 1, 2: connection request 3, 4: security check 5-8: check resources (free circuit) 9-10: set up call PSTN Mobile Originated Call VLR 3 4 6 5 GMSC MSC 7 8 2 9 1 MS BSS 10

  45. 1: calling a GSM subscriber 2: forwarding call to GMSC 3: signal call setup to HLR 4, 5: request MSRN from VLR 6: forward responsible MSC to GMSC 7: forward call to current MSC 8, 9: get current status of MS 10, 11: paging of MS 12, 13: MS answers 14, 15: security checks 16, 17: set up connection PSTN Mobile Terminated Call 4 HLR VLR 5 8 9 3 6 14 15 7 calling station GMSC MSC 1 2 10 13 10 10 16 BSS BSS BSS 11 11 11 11 12 17 MS

  46. MS MTC BTS MS MOC BTS paging request channel request channel request immediate assignment immediate assignment paging response service request authentication request authentication request authentication response authentication response ciphering command ciphering command ciphering complete ciphering complete setup setup call confirmed call confirmed assignment command assignment command assignment complete assignment complete alerting alerting connect connect connect acknowledge connect acknowledge data/speech exchange data/speech exchange MTC/MOC

  47. MSC MS BSC BTS 1. Channel Request (RACH) 2. Channel Assigned (AGCH) 3. Call Establishment Request (SDCCH) 4. Authentication Request (SDCCH) 5. Authentication Response (SDCCH) 6. Ciphering Command (SDCCH) 7. Ciphering Ready (SDCCH) 8. Send Destination Address (SDCCH) 9. Routing Response (SDCCH) 10. Assign Traffic Channel (SDCCH) 11. Traffic Channel Established (FACCH) 12. Available/Busy Signal (FACCH) 13. Call Accepted (FACCH) 14. Connection Established (FACCH) 15. Information Exchange (TCH) GSM Channel Use Example

  48. GSM Numbers • International mobile station equipment identity (IMEI). IMEI= TAC + FAC + SNR + SP • TAC = Type Approval Code, 6 decimals • FAC = Final Assembly Code, 6 decimals, assigned by manufacturer • SNR = Serial Number, 6 decimals, assigned by manufacturer • SP = Spare, 1 decimal place • EIR has white, black and optionally grey list. • International mobile Subscriber Identity (IMSI): Stored on the SIM (Subscriber Identity Module) card. IMSI is obtained at the time of subscription. IMSI is not made public. • IMSI = MCC + MNC + MSIN • MCC = Mobile Country Code, 3 decimals • MNC = Mobile Network Code, 2 decimals • MSIN = Mobile Subscriber Identification Number, maximum 10 decimal digits

  49. GSM Numbers • Mobile Station ISDN number (MSISDN), is the real phone number of the subscriber. Stored in HLR and on SIM card • MSISDN = CC + NDC + SN • CC = Country Code, up to 3 decimals • NDC = National Destination Code, typically 2-3 decimals • SN = Subscriber Number, maximum 10 decimals. • Mobile Station Roaming Number (MSRN), same format as MSISDN. A temporary location dependent ISDN number; assigned in two cases, at registration or at call set up. • Location Area Identity (LAI). Regularly sent on BCCH; LAI = CC + MNC + LAC, • LAC = Location Area Code, max 5 decimals (<FFFFhex). • Temporary Mobile Subscriber Identity (TMSI). Stored only in the VLR and SIM card. Consists of 4*8 bits excluding value FFFF FFFFhex • TMSI has only local meaning and can be defined according to operator’s specifications. • LAI + TMSI uniquely identifies the user, i.e. IMSI is no longer needed for ongoing communication

  50. GSM Handoffs • 3 types of handoffs • Intra-BSS: if old and new BTSs are attached to same base station • MSC is not involved • Intra-MSC: if old and new BTSs are attached to different base stations but within same MSC • Inter-MSC: if MSCs are changed

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