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DESCRIPTIONGSM and UMTS
Introduction, History, Overview of Wireless Systems
1GSM + UMTSWireless CommunicationContentsIntroductionNetwork architecture Fundamental functionalityPhysical layer / radio interfaceUMTS
2GSM The idea of a common European mobile communications system1982: A Nordic group is considering the next generation of mobile telephone. NMT (Nordisk Mobil Telefon), the analogue first generation system has only just been startedThese ideas are presented to CEPT (European Conference of Postal and Telecommunications Administrations) in June 1982September 1982: The first meeting in CEPT GSM Groupe Spcial MobileIn 1988 ETSI (European Telecommunications Standards Institute) is established and the work is continued under a new name: SMG Special Mobile Group
GSM - SpecificationsOriginal specifications for the GSM system:Good subjective voice qualityLow terminal and service costSupport for international roamingSupport for handheld terminalsSupport for new servicesSpectrum efficientCompatible with ISDN
GSM - Growth1991: First operational GSM network in Finland: Radiolinja1993: Tele-mobil (later: Telenor Mobil) and NetCom GSM open their networks in Norway1998: GSM 1800 is deployed to increase capacity in cities and other densely populated areas02004006008001 0001 2001 4001 6001 8002 0002 2002 4002 6002 8003 0003 200198219831984198519861987198819891990199119921993199419951996199719981999 20000 %10 %20 %30 %40 %50 %60 %70 %80 %TM NMTTM GSMNetCom 9M01GSM improvements 2.5 G and 3 GThe need for data services increase:In 1998-99 the HSCSD High Speed Circuit Switched Data - is standardised. Introduced in Norway 1. July 2001 (Telenor)I 1999 packet switching using GPRS (General Packet Radio Service) is standardised. Introduced in Norway 1. February 2001 (Telenor)Theoretical data rates up to 171 kbit/s
"2.5 G" EDGE Enhanced Data rates for GSM EvolutionStandardised in 2001-2002Introduced in September 2004 Theoretical data rates up to 373 kbit/s3 G" EDGE Enhanced Data rates for GSM Evolution/UMTS
Standardised in 2001-2002Introduced in September 2004 deployment ongoing Theoretical data rates up to 2 Mbps
Some GSM terminalsDevelopment..HTC P4350Pocket computer running Windows
iPhone ApplesMobile phone initiativeHigh level network architecture (1/2)
SIMME:Mobile equipmentServices / ApplicationsCore Network(CN)Ext.networkUE: User equipmentAccess Network(AN)8High level network architecture (2/2)The network contains functionally of: User Equipment (UE), Access Network (AN), and Core Network (CN)User equipment: Interfaces the user, handles radio functionalityAccess network: Communication to and from the user equipment, handles all radio related functionality in the networkCore network: Communication between access network and external networks, handles all switching and routing
Services and applications lie above the network10GSMThe European TDMA Digital Cellular StandardGeneral Architecture Of GSM MESIMBTSBTSBSCBSCMSCVLREIRHLRAuCAUmAbisPSTN,ISDNMobile stationBase Station SubsystemNetworkSubsystem MSBSSNSNetwork Overview11
Network OverviewA GSM system is basically designed as a combination of three major subsystems: Network Sub-System (NSS), Radio subsystem called the Base station Sub-System (BSS),Operation Sub-System (OSS).
The Network Sub-System (NSS)
includes the equipment and functions related to end-to-end-calls, management of subscribers, mobility, and interfaces with the fixed network (PSTN). It is built on the switch of the system called Mobile-services Switching Center (MSC).
The Base station Sub-System (BSS)
includes the equipment and functions related to the management of the connection on the radio path. It mainly consists of Base Transceiver Stations (BTS) communicating with the Mobile Station (MS) and one Base Station Controller (BSC) managing the flow of information between the BTSs and the MSC.
12Network OverviewThe Operation Sub-System (OSS)mainly contains Operation and Maintenance Center for NSS (OMC-S) and Operation and Maintenance Center devoted to the BSS (OMC-R). It is connected to all equipment in the switching system and to the BSC (BTSs are not connected to the OSS).
13Mobile StationThe Mobile Station (MS) is composed of three parts:The handset includes the radio equipment (receiver-transmitter) and the Man-Machine Interface (MMI),The SIM card (Subscriber Identity Module-card): allows the identification of any subscriberThe battery.
The International Mobile Subscriber Identity (IMSI) is the primary identification of the subscriber within the GSM network and is permanently assigned to him.
The Mobile Subscriber ISDN Number (MSISDN) is the number that the calling party dials in order to reach the GSM subscriber. It is used by the land networks to route calls toward an appropriate GSM network. MSISDN is stored in HLR.
15BSS ArchitectureThe Base Station Sub-System (BSS) is a set of equipment (aerials, transceivers and a controller) that is viewed by the Mobile Switching Center through a single A interface as being the entity responsible for communicating with mobile telephones or Mobile Stations (MSs) in a certain area.
The radio equipment of a BSS may be composed of one or more cells, such a BSS may contain one or more Base Transceiver Stations (BTSs).
The interface between the BSC and the BTSs is called an Abis interface16BSSBSC: Base station ControllerIt manages radio resources for one or more BTS.Allocation and De-allocation of channels.Transmitter power control.Handoff controlBTS : Base Transceiver stationIt defines the cell .It handles the radio link protocol with the mobile station
A BSS contains only one Base Station Controller (BSC).The function split is basically between a transmission equipment, the BTS, and the BSC.
17NSS Architecture18Network SubsystemMSC: Mobile Switching CenterHLR: Home Location RegisterVLR: Visitor Location registerAuC: Authentication CenterEIR: Equipment Identity RegisterBSCMSCVLREIRHLRAuCPSTN,ISDNNSS ArchitectureBSCs of a same area are connected to a switch. In a GSM system this switch is called MSC (Mobile Switching Center). MSCs are connected to each others.Mobile Switching center:(MSC)call set up/supervision/release/routingbilling information collectionmobility managementpaging, alertingconnection to BSC, other MSC and other local exchange networksAccess to HLR and VLRUsually, each MSC is associated to four databases.
The Visitor Location Register (VLR)memorizes information about the subscribers physically present in a geographic area. Temporary visitors databaseOne VLR per MSC
19NSS Architecture Home Location Register (HLR) One HLR per GSM operator Contains permanent database of all the subscribers in the networkcontains MSRN(mobile station routing no.)It is referred for every incoming call
Authentication Center (AuC): Provides securityAuthentication and encryption
The Equipment Identity Register (EIR) contains list of all the Mobile Equipment: it contains valid and invalid mobile equipment.Contains IMEI
20Identification of users:Mobile number: MS-ISDN number follows numbering plan for telephony/ISDN (max. 15 digits):
Calling number associated with a subscriptionUsed on interface towards users
Identification of a mobile subscription:IMSI : International Mobile Subscription Identity
Identification of terminal:IMEI : International Mobile Equipment Identity. Not used in fundamental service handling, but to identify stolen or black listed equipmentIdentifying users and mobile terminals MCC mobile country codeSubscription Identification NC[2-3]network codeCountry codeNational mobile number(1- 3)Fundamental functionality The following functions are described:Circuit switched connectivityPacket switched connectivityMobile messagingSecurityRoamingChoice of networkLocation updateHandover
Circuit Switched connectivity
ISDNMobile networkFixed connection and reserved resources while the communication lasts. (Mobile) telephony Circuit switched data, e.g. WAP, mobile office solutions using data cards etc. Transparent channel with defined performanceBilling typically per time unit and dependant on transport data rateStandard GSM: up to 14.4 kbit/s (more using HSCSD - High Speed Circuit Switched Data)
Packet Switched connectivityResources allocated only when data is transferred Same path through network can be maintained (but not necessarily)Billing typically dependant on amount of data transferred (or fixed tarrifs)GPRS: Theoretically up to 171 kbit/s, typically 40 50 kbit/s4 different quality classes for packet bearer services:
Internet ordifferent IP networkMobile networkBackgroundTypically automatic download of email, MMSInteractiveTypically web/WAP-browsing, MMS, games StreamingNetwork radio, video streaming, web TVConversationalVoice, video conferencing
Mobile messaging formats SMS: Short Message ServiceText based service to transfer up to 160 characters per message (solutions exist to connect messages into longer messages, and also to carry other types of content ring tones, logos)
MMS: Multimedia Messaging ServiceA service for multimedia content, such as text, picture, sound, video
Both SMS and MMS are store and forward services, i.e. messages are intermediately stored in the network
Security functionsThe purpose of security functions is to protect users and network against improper and illegal use:Verify that the user has a valid subscriptionProtect the users identity against trackingProtection against wiretapping on the radio connection
The mechanisms in GSM are based on secure storage of information in the users SIM card
International networkRoaming (1/2)Circuit switched call to a mobile in a visiting network Home network Visiting networkISDN (country A)ISDN (country B)
International networkRoaming (2/2)Mobile to mobile call in a visiting network Effect referred to as tromboningHome network Visiting networkISDN (country A)ISDN (country B)
Choice of networkIn GSM the following procedure is followed:The latest used network is stored on the SIMAs long as a cell that fulfils the criteria is available from this network, the mobile will not search for alternatives (the exception is national roaming, in which case the mobile will periodically search for the home network and connect when this becomes available)If the previously used network is not available, the mobile searches for alternative networksThe mobiles can perform manually or automatic choice of network Location updateA location update is performed when:The mobile is connecting to a cell and discovers that the LAI read is different than the one stored in the mobileThe mobile has been turned on, but not used, for a pre-defined period of time since the last location update (periodic location update) IMSI detach/attach:An additional function where the mobile informs that it is turned on or off (in the same LA), saves resources on the radio interface and leads to faster response on incoming callsPeriodic detachA network functionality where the network assumes that the mobile has been turned off if periodic location update has not been performed and no other activity has been observed for a pre-defined amount of time30Fortelle nettet hvor man er (blant annet med tanke p motta anrop).
HandoverTo connect a call or communication session from one cell to another (or to a different channel in the same cell) Is normally performed because the signal level from the current cell is becoming to low, but can also be done for different reasons, such as too much traffic in a cellTypes of handoverIntra cell (to another channel in the same cell) (1)Inter cell, intra BSC (2)Inter BSC, intra MSC (3)Inter MSC (4)
In addition inter system handover can sometimes be performed, e.g. GSM to UMTS Complicated, special rules apply
Type of handover has network implications, but the algorithms to decide handover are the same
Physical layer/Radio interface
GSM Radio Aspects :GSM 900: 890 915 MHz: Uplink (MS transmit) 935 - 960 MHz: Downlink (MS receive)GSM 1800: 1710 - 1885 MHz: Uplink1805 - 1880 MHz: Downlink
Carrier bandwidth: 200 kHzChannels / carrier:8Multiple access: TDMA / FDMADuplex:FDDModulation:GMSK full rate calls 13 KbpsIf half-rate used16 calls at 6.5 kbps
3345 MHz960 MHz935 MHz200 kHzMS transmitMS receive4123412412318234567182345671231241234915 MHzTotal Frequency range(Uplink)=25MhzSpacing between two carriers= 200kHzNo. of Carriers=25MHz/200KHz = 124Suggested use: only 122Use top & bottom as additional guard
35GSM uses TDMA within each carrierEach user occupies the entire carrier one time slot/time frame8 slots per frame
0712450333567TimeFreqDown Link carrier Up Link carrier200 KHzTime slots4.6 ms0.57ms36542135TDMA Frame360126537122524401035757261DataData TrainingTdma FrameFrame MultiframeFormat of a single BurstDuration=120msDuration=4.615msDuration=0.577ms25Classification of channels in GSM
Channels are used to carry speech , data and control information.Two typesTraffic channels (TCH)Typically uses one time slot per frameGross data rate per TCH: 22 kbpsEffective data rate lower because of forward error correction Control channels (CCH)Traffic Channels are defined using 26 TDMA frame multi-frame.Length of 26 TDMA frames = 120 msecLength of 1 TDMA frame =120/26 = 4.615 msec1 TDMA frame consists of 8 burst framesLength of 1 burst frame = 0.577msecOut of 26 frames 24 are TCH used for traffic,1 is SACCH used for control,1 is unused
Logical channelsLogical channels built up of physical channels Traffic channelsControl channels
Logical channels divided between: Dedicated channelsCommon channels
Traffic (TCH)SpeechFull rate 22.8 kb/sHalf rate 11.4 kb/sData9.6kb/s,4.8kb/s,2.4kb/s
Control (CCH)Broadcast (BCCH)Freq correction (FCCH)Synchronization (SCH)Common (CCH)Paging (PCH)Access grant (AGCH)Random Access (RACH)Dedicated (DCCH)Fast Associative (FACCH)Slow Associative (SACCH)Stand alone (SDCCH)
40Control ChannelBCCH (Broadcast Control Channel )Continuously transmitted from the BTS. Contains information about cell identity, frequency etc. FCCH/SCH (Frequency Correction Channel / Synchronisation Channel )Used to correct/synchronise the frequency (FCCH) + time synchronise to the frame structure. Each cell has a FCCH and a SCHRACH (Random Access Channel )Used by the mobile to send a request to the network for access. AGCH (Access Grant Channel ) Used by the network to inform the mobile that access has been granted and information about which channel to usePCH (Paging Channel)Used by the network to notify users about incoming calls. 41ModulationAssuming that everyone is familiar with digital modulation :-)
Considerations upon choosing modulations scheme:Spectrum efficiency Out of band emission (rapid drop off desired to limit adjacent channel interference)Constant envelope desired for low cost amplifiers, e.g. in handheld equipment
In GSM: GMSK Gaussian Minimum Shift Keying is used
42GMSKGaussian Minimum Shift KeyingBandwidth-time productDescribes the amount the symbols overlapBT = 0.3 for GSM networks Characterized by the value of BTT = bit durationB = 3dB Bandwidth of the shaping filterBT = 0.3 for GSMBT = 0.5 for DECTGood spectral efficiencyAt the expense of some inter-symbol interference (ISI)43GMSKGMSK further reduces side lobes by using a Gaussian filterCost: introduces inter-symbol-interference (ISI)Figures show time and frequency responseGSM uses BT = 0.3
UMTSUMTS Universal Mobile Telecommunication systems45SYSTEM ARCHITECTUREFunctional network elementsUser Equipment (UE)interfaces with user and radio interfaceRadio Access Network (RAN, UMTS Terrestrial RAN = UTRAN)handles all radio-related functionalityCore Networkswitches and routes calls and data connections to external networks
SYSTEM ARCHITECTUREPLMN (Public Land Mobile Network)operated by a single operatordistinguished from each other with unique identitiesconnected to other PLMNs as well as to other types of network, such as ISDN, PSTN, Internet, etc47
4748UE consists of two partsMobile Equipment (ME)the radio terminal used for radio communication over Uu interfaceUMTS Subscriber Identity Module (USIM)a smartcard that holds the subscriber identityperforms authentication algorithmsstores authentication and encryption keyssome subscription information that is needed at the terminalUser Equipment (UE)UTRAN consists of two elementsNode Bconverts data flow between Iub and Uu interfacesparticipates in radio resource managementchannel coding and interleavingrate adaptationSpreadingRadio Network Controller (RNC)owns and controls radio resources in its domain the service access point (SAP) for all services that UTRAN provides to the CNe.g., management of connections to UE49UTRANCore NetworkMain elements of CNHLR (Home Location Register)MSC/VLR (Mobile Services Switching Centre/Visitor Location Register)GMSC (Gateway MSC)SGSN (Serving GPRS (General Packet Radio Service) Support Node)GGSN (Gateway GPRS Support Node)
50Core Network- HLR (Home Location Register)
a database located in users home system that stores the master copy of users service profileservice profile consists of, e.g., information on allowed services, forbidden roaming areassupplementary service information such as status of call forwarding and the call forwarding numberit is created when a new user subscribes to the system, and remains stored as long as the subscription is activefor the purpose of routing incoming transactions to UE (e.g. calls or short messages)HLR also stores the UE location on the level of MSC/VLR and/or SGSN
51Core Network - MSC/VLR and GMSC(Mobile Services Switching)Centre/Visitor Location Register)the switch (MSC) and database (VLR) that serve the UE in its current location for Circuit Switched (CS) servicesthe part of the network that is accessed via MSC/VLR is often referred to as CS domainMSCused to switch CS transactionsVLRholds a copy of the visiting users service profile, as well as more precise information on the UEs location within the serving systemGMSC (Gateway MSC)the switch at the point where UMTS PLMN is connected to external CS networksall incoming and outgoing CS connections go through GMSC
52Core Network - SGSN and GGSNSGSN (Serving GPRS (General Packet Radio Service) Support Node)functionality is similar to that of MSC/VLR but is typically used for Packet Switched (PS) servicesthe part of the network that is accessed via SGSN is often referred to as PS domain
GGSN (Gateway GPRS Support Node)functionality is close to that of GMSC but is in relation to PS services
53External NetworksExternal networks can be divided into two groupsCS networksprovide circuit-switched connections, like the existing telephony serviceISDN and PSTN are examples of CS networksPS networksprovide connections for packet data servicesInternet is one example of a PS network
54Main open interfaces
Cu interfacethe electrical interface between USIM smartcard and MEUu interfacethe WCDMA radio interfacethe interface through which UE accesses the fixed part of the systemIu interfaceconnects UTRAN to CNIur interfaceallows soft handover between RNCsIub interfaceconnects a Node B and an RNC
UMTS Band : 1900-2025 MHz and 2110-2200 MHz for 3G transmission.
Terrestrial UMTS (UTRAN) : 1900-1980 MHz, 2010-2025 MHz, and 2110-2170 MHz bandsUMTS Frequency Spectrum Radio Interface
UMTS uses Wideband-Code Division Multiple Access (W-CDMA)Also known as IMT-2000 Direct SpreadExtremely complex algorithmsUses 10x the 2G processing power!Modulation is done with Quadrature phase shift keying (QPSK)This encodes 2 bits with each change Supports two modes of operationFrequency Division Duplex (FDD)Time Division Duplex (TDD)57UMTS - Air InterfaceUMTS FDD (Frequency Division Duplex)Uplink: 1920 - 1980 MHzDownlink: 2110 - 2170 MHz190 MHz duplex distanceca. 5MHz (variable) carrier spacing (DS CDMA Direct Sequence CDMA)12 bands in uplink & downlink
UMTS - Air InterfaceUMTS TDD (Time Division Duplex)Uplink & Downlink: 1900 - 1920 MHz and 2020 - 2025 MHz5 carriers in total, 15 timeslots per framea user may use one or several timeslotsa timeslot can be assigned to either uplink or downlink
UMTS history and planned standardsFebruary 1995 UMTS Task Force established; "The Road to UMTS" reportDecember 1996 The UMTS Forum established. "European" WCDMA standard known as Universal Mobile Telecommunications System (UMTS) June 1997 UMTS Forum produces first report: "A regulatory Framework for UMTS"October 1997 ERC decided on UMTS core band.January 1998 ETSI meeting: W-CDMA and TD-CDMA proposals combined to UMTS air interface specificationJune 1998 Terrestrial air interface proposals (UTRAN, WCDMA(s), CDMA2000(s), EDGE, EP-DECT, TD-SCDMA) were handed into ITU-R3GPP Release 99
60UMTS history and planned standardsMarch 2001 in Palm Springs 3GPP approves UMTS Release 4 specificationRelease 4 and 5 specifies an All IP standardStreaming services (fast handover)Seamless UMTS/WLAN integration, interworkingPush-to-Talk over cellularPresence for chat, instant messaging, ...Release 6Extended location based services (LBS)Packet switches streaming services, with adaptation to available network resources (GERAN/GPRS, UTMS, WLAN) Charging Management Framework (for extended payment systems)For more see www.3gpp.org