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8/26/2013

IT 2404 Mobile Communication ByDr T Gnanasekaran

Cellular Network OrganizationUse multiple low-power transmitters (100 W or less)Areas divided into cellsEach served by its own antennaServed by base station consisting of transmitter, receiver, and control unitBand of frequencies allocatedCells set up such that antennas of all neighbors are equidistant (hexagonal pattern)

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GSM GLOBAL SYSTEM FOR MOBILE COMMUNICATION

DISCUSSION TOPICSHistory

Building Blocks

System Architecture

Features (Basic and Advanced)

Advantages of GSM

Future whats next

HISTORY

Early 80s Europe was experiencing rapid growth in the analog cellular telephone systems1982 Conference of European Posts and Telegraphs (CEPT) GSM (Groupe Special Mobile) group was formed to study and develop a pan-European public land mobile systemGSM mandate was to develop a standard to be common for the countries that created it provide service to the entire European continent

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HISTORYcontd.GSM criteria Good subjective speech qualityLow terminal and service costSupport for international roaming one system for all of EuropeAbility to support handheld terminalsSupport for range of new services and facilitiesEnhanced FeaturesISDN compatibilityEnhance privacySecurity against fraud

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HISTORYcontd.Late 1980s GSM work was transferred to the European Telecommunication Standards Institute (ETSI) and SGM (Special Mobile Group) was created

Document the functionality and interaction of every aspect of the GSM network

1987 ETSI oversees the creation of GSM MoU (Memorandum of Understanding) Association

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HISTORYcontd.Formal objective of the GSM MoU Association is the promotion and evolution of the GSM systems and GSM platforms

Concepts of a published international standard and a constantly evolving common standard are unique to GSM

Work groups throughout the world specifically designed to allow interested parties to meet and work on finding solutions to systems enhancements that will fit into existing programs of GSM operators

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HISTORYcontd.Phase I of GSM specifications was published in 1990International demand was so great that the system name was changed from Groupe Special Mobile to Global Systems for Mobile Communications (still GSM)Commercial service started in mid-19911992 first paying customers were signed up for serviceBy 1993 there were 36 GSM networks in 22 countriesEarly 1994 there were 1.3 million subscribers worldwideBy 1996 there were more than 25 million subscribers worldwideThe total base of GSM subscribers has now crossed the 250 million-mark and stands at 257.85 million as on Dec 31, in India.

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Building BlocksAMPS Advanced Mobile Phone System

TACS Total Access Communication System

NMT Nordic Mobile Telephone System

Building Blockscontd.AMPS Advanced Mobile Phone System

analog technology

used in North and South America and approximately 35 other countries

operates in the 800 MHz band using FDMA technology

Building Blockscontd.TACS Total Access Communication System

variant of AMPS

deployed in a number of countries

primarily in the UK

Building Blockscontd.NMT Nordic Mobile Telephone System

analog technology

deployed in the Benelux countries and Russia

operates in the 450 and 900 MHz band

first technology to offer international roaming only within the Nordic countries

System ArchitectureMobile Station (MS)Mobile Equipment (ME)Subscriber Identity Module (SIM)Base Station Subsystem (BBS)Base Transceiver Station (BTS)Base Station Controller (BSC)Network SubsystemMobile Switching Center (MSC)Home Location Register (HLR)Visitor Location Register (VLR)Authentication Center (AUC)Equipment Identity Register (EIR)

System ArchitectureMobile Station (MS)The Mobile Station is made up of two entities:

Mobile Equipment (ME)

2.Subscriber Identity Module (SIM)

System ArchitectureMobile Station (MS) contd.Mobile Equipment

Produced by many different manufacturersMust obtain approval from the standardization bodyUniquely identified by an IMEI (International Mobile Equipment Identity)

System ArchitectureMobile Station (MS) contd.Subscriber Identity Module (SIM)

Smart card containing the International Mobile Subscriber Identity (IMSI)Allows user to send and receive calls and receive other subscribed servicesEncoded network identification detailsProtected by a password or PINCan be moved from phone to phone contains key information to activate the phone

System ArchitectureBase Station Subsystem (BSS)Base Station Subsystem is composed of two parts that communicate across the standardized Abis interface allowing operation between components made by different suppliers

Base Transceiver Station (BTS)

Base Station Controller (BSC)

System ArchitectureBase Station Subsystem (BSS) contd.Base Transceiver Station (BTS)

Houses the radio transceivers that define a cellHandles radio-link protocols with the Mobile StationSpeech and data transmissions from the MS are recodedRequirements for BTS:ruggednessreliabilityportabilityminimum costs

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System ArchitectureBase Station Subsystem (BSS) contd.Base Station Controller (BSC)

Manages Resources for BTSHandles call set upLocation updateHandover for each MS

System ArchitectureNetwork SubsystemMobile Switching Center (MSC)

Switch speech and data connections between:Base Station ControllersMobile Switching CentersGSM-networksOther external networksHeart of the networkThree main jobs: 1) connects calls from sender to receiver2) collects details of the calls made and received3) supervises operation of the rest of the network components

System ArchitectureNetwork Subsystem contd.Home Location Registers (HLR)- contains administrative information of each subscriber- current location of the mobileVisitor Location Registers (VLR)- contains selected administrative information from the HLRauthenticates the usertracks which customers have the phone on and ready to receive a callperiodically updates the database on which phones are turned on and ready to receive calls

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System ArchitectureNetwork Subsystem contd.Authentication Center (AUC) mainly used for securitydata storage location and functional part of the networkKi is the primary element

Equipment Identity Register (EIR)- Database that is used to track handsets using the IMEI (International Mobile Equipment Identity)Made up of three sub-classes: The White List, The Black List and the Gray ListOptional database

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System Architecture

Basic Features Provided by GSMCall Waiting- Notification of an incoming call while on the handsetCall Hold- Put a caller on hold to take another callCall Barring- All calls, outgoing calls, or incoming callsCall Forwarding- Calls can be sent to various numbers defined by the userMulti Party Call Conferencing- Link multiple calls together

Advanced Features Provided by GSMCalling Line ID- incoming telephone number displayedAlternate Line Service- one for personal calls- one for business callsClosed User Group- call by dialing last for numbersAdvice of Charge- tally of actual costs of phone callsFax & Data- Virtual Office / Professional OfficeRoaming- services and features can follow customer from market to market

Future -- UMTS (Universal Mobile Telephone SystemReasons for innovationsnew service requirementsavailability of new radio bands

User demandsseamless Internet-Intranet accesswide range of available servicescompact, lightweight and affordable terminalssimple terminal operationopen, understandable pricing structures for the whole spectrum of available services

Advantages of GSM Crisper, cleaner quieter callsSecurity against fraud and eavesdroppingInternational roaming capability in over 100 countriesImproved battery lifeEfficient network design for less expensive system expansionEfficient use of spectrumAdvanced features such as short messaging and caller IDA wide variety of handsets and accessoriesHigh stability mobile fax and data at up to 9600 baudEase of use with over the air activation, and all account information is held in a smart card which can be moved from handset to handset

Frequency ReuseAdjacent cells assigned different frequencies to avoid interference or crosstalkObjective is to reuse frequency in nearby cells10 to 50 frequencies assigned to each cellTransmission power controlled to limit power at that frequency escaping to adjacent cellsThe issue is to determine how many cells must intervene between two cells using the same frequency

Approaches to Cope with Increasing CapacityAdding new channelsFrequency borrowing frequencies are taken from adjacent cells by congested cellsCell splitting cells in areas of high usage can be split into smaller cellsCell sectoring cells are divided into a number of wedge-shaped sectors, each with their own set of channelsMicrocells antennas move to buildings, hills, and lamp posts

Cellular System Overview

Cellular Systems TermsBase Station (BS) includes an antenna, a controller, and a number of receiversMobile telecommunications switching office (MTSO) connects calls between mobile unitsTwo types of channels available between mobile unit and BSControl channels used to exchange information having to do with setting up and maintaining callsTraffic channels carry voice or data connection between users

Steps in an MTSO Controlled Call between Mobile UsersMobile unit initializationMobile-originated callPagingCall acceptedOngoing callHandoff

Additional Functions in an MTSO Controlled CallCall blockingCall terminationCall dropCalls to/from fixed and remote mobile subscriber

Mobile Radio Propagation EffectsSignal strengthMust be strong enough between base station and mobile unit to maintain signal quality at the receiverMust not be so strong as to create too much cochannel interference with channels in another cell using the same frequency bandFadingSignal propagation effects may disrupt the signal and cause errors

Handoff Performance MetricsCell blocking probability probability of a new call being blockedCall dropping probability probability that a call is terminated due to a handoffCall completion probability probability that an admitted call is not dropped before it terminatesProbability of unsuccessful handoff probability that a handoff is executed while the reception conditions are inadequate

Handoff Performance MetricsHandoff blocking probability probability that a handoff cannot be successfully completedHandoff probability probability that a handoff occurs before call terminationRate of handoff number of handoffs per unit timeInterruption duration duration of time during a handoff in which a mobile is not connected to either base stationHandoff delay distance the mobile moves from the point at which the handoff should occur to the point at which it does occur

Handoff Strategies Used to Determine Instant of HandoffRelative signal strengthRelative signal strength with thresholdRelative signal strength with hysteresisRelative signal strength with hysteresis and thresholdPrediction techniques

Power ControlDesign issues making it desirable to include dynamic power control in a cellular systemReceived power must be sufficiently above the background noise for effective communicationDesirable to minimize power in the transmitted signal from the mobileReduce cochannel interference, alleviate health concerns, save battery powerIn SS systems using CDMA, its desirable to equalize the received power level from all mobile units at the BS

Types of Power ControlOpen-loop power controlDepends solely on mobile unitNo feedback from BSNot as accurate as closed-loop, but can react quicker to fluctuations in signal strength Closed-loop power controlAdjusts signal strength in reverse channel based on metric of performanceBS makes power adjustment decision and communicates to mobile on control channel

Traffic EngineeringIdeally, available channels would equal number of subscribers active at one timeIn practice, not feasible to have capacity handle all possible loadFor N simultaneous user capacity and L subscribersL < N nonblocking systemL > N blocking system

Blocking System Performance QuestionsProbability that call request is blocked?What capacity is needed to achieve a certain upper bound on probability of blocking?What is the average delay?What capacity is needed to achieve a certain average delay?

Traffic IntensityLoad presented to a system:

= mean rate of calls attempted per unit timeh = mean holding time per successful callA = average number of calls arriving during average holding period, for normalized

Factors that Determine the Nature of the Traffic ModelManner in which blocked calls are handledLost calls delayed (LCD) blocked calls put in a queue awaiting a free channelBlocked calls rejected and droppedLost calls cleared (LCC) user waits before another attemptLost calls held (LCH) user repeatedly attempts callingNumber of traffic sourcesWhether number of users is assumed to be finite or infinite

First-Generation AnalogAdvanced Mobile Phone Service (AMPS)In North America, two 25-MHz bands allocated to AMPSOne for transmission from base to mobile unitOne for transmission from mobile unit to baseEach band split in two to encourage competitionFrequency reuse exploited

AMPS OperationSubscriber initiates call by keying in phone number and presses send keyMTSO verifies number and authorizes userMTSO issues message to users cell phone indicating send and receive traffic channelsMTSO sends ringing signal to called partyParty answers; MTSO establishes circuit and initiates billing informationEither party hangs up; MTSO releases circuit, frees channels, completes billing

Differences Between First and Second Generation SystemsDigital traffic channels first-generation systems are almost purely analog; second-generation systems are digitalEncryption all second generation systems provide encryption to prevent eavesdroppingError detection and correction second-generation digital traffic allows for detection and correction, giving clear voice receptionChannel access second-generation systems allow channels to be dynamically shared by a number of users

Mobile Wireless TDMA Design ConsiderationsNumber of logical channels (number of time slots in TDMA frame): 8Maximum cell radius (R): 35 kmFrequency: region around 900 MHzMaximum vehicle speed (Vm):250 km/hrMaximum coding delay: approx. 20 msMaximum delay spread (m): 10 sBandwidth: Not to exceed 200 kHz (25 kHz per channel)

GSM Network Architecture

Mobile StationMobile station communicates across Um interface (air interface) with base station transceiver in same cell as mobile unitMobile equipment (ME) physical terminal, such as a telephone or PCSME includes radio transceiver, digital signal processors and subscriber identity module (SIM)GSM subscriber units are generic until SIM is insertedSIMs roam, not necessarily the subscriber devices

Base Station Subsystem (BSS)BSS consists of base station controller and one or more base transceiver stations (BTS)Each BTS defines a single cellIncludes radio antenna, radio transceiver and a link to a base station controller (BSC)BSC reserves radio frequencies, manages handoff of mobile unit from one cell to another within BSS, and controls paging

Network Subsystem (NS)NS provides link between cellular network and public switched telecommunications networksControls handoffs between cells in different BSSsAuthenticates users and validates accountsEnables worldwide roaming of mobile usersCentral element of NS is the mobile switching center (MSC)

Mobile Switching Center (MSC) DatabasesHome location register (HLR) database stores information about each subscriber that belongs to itVisitor location register (VLR) database maintains information about subscribers currently physically in the regionAuthentication center database (AuC) used for authentication activities, holds encryption keysEquipment identity register database (EIR) keeps track of the type of equipment that exists at the mobile station

TDMA Format Time Slot FieldsTrail bits allow synchronization of transmissions from mobile unitsEncrypted bits encrypted dataStealing bit - indicates whether block contains data or is "stolen"Training sequence used to adapt parameters of receiver to the current path propagation characteristicsStrongest signal selected in case of multipath propagationGuard bits used to avoid overlapping with other bursts

GSM Speech Signal Processing

GSM Signaling Protocol Architecture

Functions Provided by ProtocolsProtocols above the link layer of the GSM signaling protocol architecture provide specific functions:Radio resource managementMobility managementConnection managementMobile application part (MAP)BTS management

Advantages of CDMA CellularFrequency diversity frequency-dependent transmission impairments have less effect on signalMultipath resistance chipping codes used for CDMA exhibit low cross correlation and low autocorrelationPrivacy privacy is inherent since spread spectrum is obtained by use of noise-like signalsGraceful degradation system only gradually degrades as more users access the system

Drawbacks of CDMA CellularSelf-jamming arriving transmissions from multiple users not aligned on chip boundaries unless users are perfectly synchronizedNear-far problem signals closer to the receiver are received with less attenuation than signals farther awaySoft handoff requires that the mobile acquires the new cell before it relinquishes the old; this is more complex than hard handoff used in FDMA and TDMA schemes

Mobile Wireless CDMA Design ConsiderationsRAKE receiver when multiple versions of a signal arrive more than one chip interval apart, RAKE receiver attempts to recover signals from multiple paths and combine themThis method achieves better performance than simply recovering dominant signal and treating remaining signals as noiseSoft Handoff mobile station temporarily connected to more than one base station simultaneously

Principle of RAKE Receiver

Types of Channels Supported by Forward LinkPilot (channel 0) - allows the mobile unit to acquire timing information, provides phase reference and provides means for signal strength comparisonSynchronization (channel 32) - used by mobile station to obtain identification information about cellular systemPaging (channels 1 to 7) - contain messages for one or more mobile stationsTraffic (channels 8 to 31 and 33 to 63) the forward channel supports 55 traffic channels

Forward Traffic Channel Processing StepsSpeech is encoded at a rate of 8550 bpsAdditional bits added for error detectionData transmitted in 2-ms blocks with forward error correction provided by a convolutional encoderData interleaved in blocks to reduce effects of errorsData bits are scrambled, serving as a privacy mask

Forward Traffic Channel Processing Steps (cont.)Power control information inserted into traffic channelDS-SS function spreads the 19.2 kbps to a rate of 1.2288 Mbps using one row of 64 x 64 Walsh matrixDigital bit stream modulated onto the carrier using QPSK modulation scheme

ITUs View of Third-Generation CapabilitiesVoice quality comparable to the public switched telephone network144 kbps data rate available to users in high-speed motor vehicles over large areas384 kbps available to pedestrians standing or moving slowly over small areasSupport for 2.048 Mbps for office useSymmetrical / asymmetrical data transmission ratesSupport for both packet switched and circuit switched data services

ITUs View of Third-Generation CapabilitiesAn adaptive interface to the Internet to reflect efficiently the common asymmetry between inbound and outbound trafficMore efficient use of the available spectrum in generalSupport for a wide variety of mobile equipmentFlexibility to allow the introduction of new services and technologies

Alternative Interfaces

CDMA Design ConsiderationsBandwidth limit channel usage to 5 MHzChip rate depends on desired data rate, need for error control, and bandwidth limitations; 3 Mcps or more is reasonableMultirate advantage is that the system can flexibly support multiple simultaneous applications from a given user and can efficiently use available capacity by only providing the capacity required for each service

8/26/2013Department of Information Technology8/26/2013Department of Information TechnologyTraditional SMS Architecture

GMSC : Gateway Mobile [service] Switching CenterHLR : Home Location RegisterMSC : Mobile Service Switching CenterSMS : Short Messaging ServiceSMSC : Short Messaging Service Center

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GPRS

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GSM Network ElementModification or Upgrade Required for GPRS.Mobile Station (MS)New Mobile Station is required to access GPRS services. These new terminals will be backward compatible with GSM for voice calls.BTSA software upgrade is required in the existing base transceiver site.BSCThe base station controller (BSC) requires a software upgrade and the installation of new hardware called the packet control unit (PCU). The PCU directs the data traffic to the GPRS network and can be a separate hardware element associated with the BSC.GPRS Support Nodes (GSNs)The deployment of GPRS requires the installation of new core network elements called the serving GPRS support node (SGSN) and gateway GPRS support node (GGSN).Databases (HLR, VLR, etc.)All the databases involved in the network will require software upgrades to handle the new call models and functions introduced by GPRS.

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THANK YOU8/26/2013Department of Information Technology8/26/2013Department of Information Technology