Wireless Telecommunication Systems Lec 04 14/03/2010 ECOM 6320

2 Outline Market GSM

Mobile phone subscribers worldwide year Subscribers [million] approx. 1.7 bn GSM total TDMA total CDMA total PDC total Analogue total W-CDMA Total wireless Prediction (1998) 2009: >4 bn!

Development of mobile telecommunication systems 1G 2G3G 2.5G IS-95 cdmaOne IS-136 TDMA D-AMPS GSM PDC GPRS IMT-DS UTRA FDD / W-CDMA EDGE IMT-TC UTRA TDD / TD-CDMA cdma2000 1X 1X EV-DV (3X) AMPS NMT IMT-SC IS-136HS UWC-136 IMT-TC TD-SCDMA CT0/1 CT2 IMT-FT DECT CDMA TDMA FDMA IMT-MC cdma2000 1X EV-DO HSPA

How does it work? r How can the system locate a user? r Why don’t all phones ring at the same time? r What happens if two users talk simultaneously? r Why don’t I get the bill from my neighbor? r Why can an American use his phone in Cairo? Why can’t I simply overhear the neighbor’s communication? How secure is the mobile phone system? What are the key components of the mobile phone network?

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

Disadvantages of GSM r There is no perfect system!! m no end-to-end encryption of user data m no full ISDN bandwidth of 64 kbit/s to the user r reduced concentration while driving r electromagnetic radiation r abuse of private data possible r roaming profiles accessible r high complexity of the system r several incompatibilities within the GSM standards

GSM: Mobile Services r GSM offers m several types of connections voice connections, data connections, short message service m multi-service options (combination of basic services) r Three service domains m Bearer Services m Telematic Services m Supplementary Services

Bearer Services r Telecommunication services to transfer data between access points r Specification of services up to the terminal interface (OSI layers 1-3) r Different data rates for voice and data (original standard) m data service (circuit switched) synchronous: 2.4, 4.8 or 9.6 kbit/s asynchronous: bit/s m data service (packet switched) synchronous: 2.4, 4.8 or 9.6 kbit/s asynchronous: bit/s r Today: data rates of approx. 50 kbit/s possible

Tele Services I r Telecommunication services that enable voice communication via mobile phones r All these basic services have to obey cellular functions, security measurements etc. r Offered services m mobile telephony primary goal of GSM was to enable mobile telephony offering the traditional bandwidth of 3.1 kHz m Emergency number common number throughout Europe (112); mandatory for all service providers; free of charge; connection with the highest priority (preemption of other connections possible)

Tele Services II r Additional services m Non-Voice-Teleservices group 3 fax voice mailbox (implemented in the fixed network supporting the mobile terminals) electronic mail (MHS, Message Handling System, implemented in the fixed network)... Short Message Service (SMS) alphanumeric data transmission to/from the mobile terminal (160 characters) using the signaling channel, thus allowing simultaneous use of basic services and SMS (almost ignored in the beginning now the most successful add-on!)

Supplementary services r Services in addition to the basic services, cannot be offered stand-alone r Similar to ISDN services besides lower bandwidth due to the radio link r May differ between different service providers, countries and protocol versions r Important services m identification: forwarding of caller number m automatic call-back m conferencing with up to 7 participants m locking of the mobile terminal (incoming or outgoing calls) m...

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

Ingredients 1: Mobile Phones, PDAs & Co. The visible but smallest part of the network!

Ingredients 2: Antennas Still visible – cause many discussions…

Ingredients 3: Infrastructure 1 Base Stations Cabling Microwave links

Ingredients 3: Infrastructure 2 Switching units Data bases Management Monitoring Not „visible“, but comprise the major part of the network (also from an investment point of view…)

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

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

UmUm A bis A BSS radio subsystem MS BTS BSC BTS BSC BTS network and switching subsystem MSC fixed partner networks IWF ISDN PSTN PSPDN CSPDN SS7 EIR HLR VLR ISDN PSTN GSM: system architecture

System architecture: radio subsystem r Components m MS (Mobile Station) m BSS (Base Station Subsystem): consisting of BTS (Base Transceiver Station): sender and receiver BSC (Base Station Controller): controlling several transceivers r Interfaces m U m : radio interface m A bis : standardized, open interface with 16 kbit/s user channels m A: standardized, open interface with 64 kbit/s user channels UmUm A bis A BSS radio subsystem network and switching subsystem MS BTS BSC MSC BTS BSC BTS MSC

System architecture: network and switching subsystem 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) network subsystem MSC fixed partner networks IWF ISDN PSTN PSPDN CSPDN SS7 EIR HLR VLR ISDN PSTN

Radio subsystem r The Radio Subsystem (RSS) comprises the cellular mobile network up to the switching centers r Components m 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 (U m ) onto terrestrial channels (A interface) BSS = BSC + sum(BTS) + interconnection m Mobile Stations (MS)

possible radio coverage of the cell idealized shape of the cell cell segmentation of the area into cells GSM: cellular network r r use of several carrier frequencies r not the same frequency in adjoining cells r cell sizes vary from some 100 m up to 35 km depending on user density, geography, transceiver power etc. r hexagonal shape of cells is idealized (cells overlap, shapes depend on geography) r if a mobile user changes cells handover of the connection to the neighbor cell

Base Transceiver Station and Base Station Controller r Tasks of a BSS are distributed over BSC and BTS r BTS comprises radio specific functions r BSC is the switching center for radio channels

Mobile station r Terminal for the use of GSM services r A mobile station (MS) comprises several functional groups m MT (Mobile Terminal): offers common functions used by all services the MS offers corresponds to the network termination (NT) of an ISDN access end-point of the radio interface (Um) m TA (Terminal Adapter): terminal adaptation, hides radio specific characteristics m TE (Terminal Equipment): peripheral device of the MS, offers services to a user does not contain GSM specific functions m SIM (Subscriber Identity Module): personalization of the mobile terminal, stores user parameters RS UmUm TETAMT

Network and switching subsystem r NSS is the main component of the public mobile network GSM m switching, mobility management, interconnection to other networks, system control r Components m 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 m 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

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

Operation subsystem r The OSS (Operation Subsystem) enables centralized operation, management, and maintenance of all GSM subsystems r Components m 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 m Equipment Identity Register (EIR) registers GSM mobile stations and user rights stolen or malfunctioning mobile stations can be locked and sometimes even localized m Operation and Maintenance Center (OMC) different control capabilities for the radio subsystem and the network subsystem

higher GSM frame structures MHz 124 channels (200 kHz) downlink MHz 124 channels (200 kHz) uplink frequency time GSM TDMA frame GSM time-slot (normal burst) ms µs 577 µs tailuser dataTrainingS guard space Suser datatail guard space 3 bits57 bits26 bits 57 bits1 13 GSM - TDMA/FDMA

GSM hierarchy of frames hyperframe superframe multiframe frame burst slot 577 µs ms 120 ms ms 6.12 s 3 h 28 min s

GSM protocol layers for signaling CM MM RR MM LAPD m radio LAPD m radio LAPD PCM RR’ BTSM CM LAPD PCM RR’ BTSM 16/64 kbit/s UmUm A bis A SS7 PCM SS7 PCM 64 kbit/s / Mbit/s MS BTSBSCMSC BSSAP

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

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

MTC/MOC BTSMS paging request channel request immediate assignment paging response authentication request authentication response ciphering command ciphering complete setup call confirmed assignment command assignment complete alerting connect connect acknowledge data/speech exchange BTSMS channel request immediate assignment service request authentication request authentication response ciphering command ciphering complete setup call confirmed assignment command assignment complete alerting connect connect acknowledge data/speech exchange MTCMOC

4 types of handover MSC BSC BTS MS 1 234

Handover decision receive level BTS old receive level BTS old MS HO_MARGIN BTS old BTS new

Handover procedure HO access BTS old BSC new measurement result BSC old Link establishment MSC MS measurement report HO decision HO required BTS new HO request resource allocation ch. activation ch. activation ack HO request ack HO command HO complete clear command clear complete