Satnam Singh +9198936506991GSM System Engineering.GSM System Engineering.1. Introduction2. Modulation & modulation tech.3. Circuit Switching & Packet Switching4. The Mobile & Air Interface5. The base station sub system6. The core network7. Logical ChannelsWEEK - 01
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Satnam Singh +9198936506999INTRODUCTIONINTRODUCTIONDefinition Global system for mobile communication (GSM) is a globallyaccepted standard for digital cellular communication. GSM is thename of a standardization group established in 1982 to create acommon European mobile telephone standard that would formulatespecifications for a pan-European mobile cellular radio systemoperating at 900 MHz. It is estimated that many countries outside ofEurope will join the GSM partnership.Overview This tutorial provides an introduction to basic GSM concepts,specifications, networks, and services. A short history of networkevolution is provided in order set the context for understanding GSMindex
Satnam Singh +919893650699101. Introduction: The Evolution of MobilTelephone SystemsCellular is one of the fastest growing and most demanding telecommunicationsapplications. Today, it represents a continuously increasing percentage of all newtelephone subscriptions around the world. Currently there are more than 45 millioncellular subscribers worldwide, and nearly 50 percent of those subscribers arelocated in the United States. It is forecasted that cellular systems using a digitaltechnology will become the universal method oftelecommunications. By the year 2005, forecasters predict that there will bemore than 100 million cellular subscribers worldwide. It has even been estimatedthatsome countries may have more mobile phones than fixed phones by the year2000 (see Figure 1).index
Satnam Singh +91989365069911The concept of cellular service is the use of low-powertransmitters where frequencies can be reused within ageographic area. The idea of cell-based mobile radio servicewas formulated in the United States at Bell Labs in the early1970s. However, the Nordic countries were the first tointroduce cellular services for commercial use with theintroduction of the Nordic Mobile Telephone (NMT) in1981.Cellular systems began in the United States with the releaseof the advanced mobile phone service (AMPS) system in1983. The AMPS standard was adopted by Asia, LatinAmerica, and Oceanic countries, creating the largest potentialmarket in the world for cellular. In the early 1980s, mostmobile telephone systems were analog rather than digital, liketodays newer systems. One challenge facing analog systemswas the inability to handle the growing capacity needs in acost-efficient manner. As a result, digital technology waswelcomed. The advantages of digital systems over analogsystems include ease of signaling, lower levels ofinterference, integration of transmission and switching, andincreased ability to meet capacity demands..index
Satnam Singh +91989365069912Table 1 charts the worldwide development of mobile telephone systems
Satnam Singh +91989365069913index2. GSMThroughout the evolution of cellular telecommunications,various systems have been developed without the benefitof standardized specifications. This presented manyproblems directly related to compatibility, especiallywith the development of digital radio technology. TheGSM standard is intended to address these problems.From 1982 to 1985 discussions were held to decidebetween building an analog or digital system. Aftermultiple field tests, a digital system was adopted forGSM. The next task was to decide between a narrow orbroadband solution. In May 1987, the narrowband timedivision multiple access (TDMA) solution was chosen.A summary of GSM milestones is given in Table
Satnam Singh +91989365069915index3. The GSM NetworkGSM provides recommendations, not requirements. TheGSM specifications define the functions and interfacerequirements in detail but do not address the hardware.The reason for this is to limit the designers as little aspossible but still to make it possible for the operators tobuy equipment from different suppliers.The GSM network is divided into three major systems: theswitching system (SS), the base station system (BSS),and the operation and support system (OSS).The basic GSM network elements are shown in Figure 2.
Satnam Singh +91989365069917The Switching SystemThe switching system (SS) is responsible for performing call processing andsubscriber-related functions. The switching system includes the followingfunctional units:• home location register (HLR)—The HLR is a database used forstorage and management of subscriptions. The HLR is considered themost important database, as it stores permanent data aboutsubscribers, including a subscribers service profile, locationinformation, and activity status. When an individual buys asubscription from one of the PCS operators, he or she is registered inthe HLR of that operator.• mobile services switching center (MSC)—The MSC performs thetelephony switching functions of the system. It controls calls to andfrom other telephone and data systems. It also performs such functionsas toll ticketing, network interfacing, common channel signaling, andothers.
Satnam Singh +91989365069918• visitor location register (VLR)—The VLR is a database thatcontains temporary information about subscribers that is needed bythe MSC in order to service visiting subscribers. The VLR is alwaysintegrated with the MSC. When a mobile station roams into a new MSCarea, the VLR connected to that MSC will request data about themobile station from the HLR. Later, if the mobile station makes a call,the VLR will have the information needed for call setup without havingto interrogate the HLR each time.• authentication center (AUC)—A unit called the AUC providesauthentication and encryption parameters that verify the users identityand ensure the confidentiality of each call. The AUC protects networkoperators from different types of fraud found in todays cellular world.• equipment identity register (EIR)—The EIR is a database thatcontains information about the identity of mobile equipment thatprevents calls from stolen, unauthorized, or defective mobile stations.The AUC and EIR are implemented as stand-alone nodes or as acombined AUC/EIR node.
Satnam Singh +91989365069919The Base Station System (BSS)All radio-related functions are performed in the BSS, which consists of base stationcontrollers (BSCs) and the base transceiver stations (BTSs).• BSC—The BSC provides all the control functions and physical linksbetween the MSC and BTS. It is a high-capacity switch that providesfunctions such as handover, cell configuration data, and control ofradio frequency (RF) power levels in base transceiver stations. Anumber of BSCs are served by an MSC.• BTS—The BTS handles the radio interface to the mobile station. TheBTS is the radio equipment (transceivers and antennas) needed toservice each cell in the network. A group of BTSs are controlled by aBSC.The Operation and Support SystemThe operations and maintenance center (OMC) is connected to all equipment inthe switching system and to the BSC. The implementation of OMC is called theoperation and support system (OSS). The OSS is the functional entity from whichthe network operator monitors and controls the system. The purpose of OSS is tooffer the customer cost-effective support for centralized, regional, and localoperational and maintenance activities that are required for a GSM network. Animportant function of OSS is to provide a network overview and support themaintenance activities of different operation and maintenance organizations.index
Satnam Singh +91989365069920Additional Functional ElementsOther functional elements shown in Figure 2 are as follows:• message center (MXE)—The MXE is a node that providesintegrated voice, fax, and data messaging. Specifically, the MXEhandles short message service, cell broadcast, voice mail, fax mail, email,and notification.• mobile service node (MSN)—The MSN is the node that handles themobile intelligent network (IN) services.• gateway mobile services switching center (GMSC)—A gatewayis a node used to interconnect two networks. The gateway is oftenimplemented in an MSC. The MSC is then referred to as the GMSC.• GSM interworking unit (GIWU)—The GIWU consists of bothhardware and software that provides an interface to various networksfor data communications. Through the GIWU, users can alternatebetween speech and data during the same call. The GIWU hardwareequipment is physically located at the MSC/VLR.index
Satnam Singh +91989365069921The cell is the area given radio coverage by one base transceiver station. The GSMnetwork identifies each cell via the cell global identity (CGI) number assigned toeach cell. The location area is a group of cells. It is the area in which thesubscriber is paged. Each LA is served by one or more base station controllers,yet only by a single MSC (see Figure 4). Each LA is assigned a location areaidentity (LAI) number.index
Satnam Singh +919893650699224. GSM Network AreasThe GSM network is made up of geographic areas. As shown in Figure 3, theseareas include cells, location areas (LAs), MSC/VLR service areas, and public landmobile network (PLMN) areas.An MSC/VLR service area represents the part of the GSM network that iscovered by one MSC and which is reachable, as it is registered in the VLR ofthe MSC (see Figure 5).index
Satnam Singh +91989365069923The PLMN service area is an area served by one network operator (see Figure 6).5. GSM SpecificationsBefore looking at the GSM specifications, it is important to understand thefollowing basic terms:• bandwidth—the range of a channels limits; the broader thebandwidth, the faster data can be sent• bits per second (bps)—a single on-off pulse of data; eight bits areequivalent to one byte• frequency—the number of cycles per unit of time; frequency ismeasured in hertz (Hz)• kilo (k)—kilo is the designation for 1,000; the abbreviation kbpsrepresents 1,000 bits per second• megahertz (MHz)—1,000,000 hertz (cycles per second)• milliseconds (ms)—one-thousandth of a second• watt (W)—a measure of power of a transmitterindex
Satnam Singh +91989365069924Specifications for different personal communication services (PCS) systems varyamong the different PCS networks. Listed below is a description of thespecifications and characteristics for GSM.• frequency band—The frequency range specified for GSM is 1,850 to1,990 MHz (mobile station to base station).• duplex distance—The duplex distance is 80 MHz. Duplex distance isthe distance between the uplink and downlink frequencies. A channelhas two frequencies, 80 MHz apart.• channel separation—The separation between adjacent carrierfrequencies. In GSM, this is 200 kHz.• modulation—Modulation is the process of sending a signal bychanging the characteristics of a carrier frequency. This is done in GSMvia Gaussian minimum shift keying (GMSK).• transmission rate—GSM is a digital system with an over-the-air bitrate of 270 kbps.• access method—GSM utilizes the time division multiple access(TDMA) concept. TDMA is a technique in which several different callsmay share the same carrier. Each call is assigned a particular time slot.• speech coder—GSM uses linear predictive coding (LPC). The purposeof LPC is to reduce the bit rate. The LPC provides parameters for afilter that mimics the vocal tract. The signal passes through this filter,leaving behind a residual signal. Speech is encoded at 13 kbps.index
Satnam Singh +919893650699256. GSM Subscriber ServicesThere are two basic types of services offered through GSM: telephony (also referred to as teleservices)and data (also referred to as bearer services). Telephony services are mainly voice services that providesubscribers with the complete capability (including necessary terminal equipment) to communicate withother subscribers. Data services provide the capacity necessary to transmit appropriate data signalsbetween two access points creating an interface to the network. In addition to normal telephony andemergency calling, the following subscriber services are supported by GSM:• dual-tone multifrequency (DTMF)—DTMF is a tone signaling scheme often used for various controlpurposes via the telephone network, such as remote control of an answering machine. GSMsupports full-originating DTMF.• facsimile group III—GSM supports CCITT Group 3 facsimile. As standard fax machines are designedto be connected to a telephone using analog signals, a special fax converter connected to the exchangeis used in the GSM system. This enables a GSM–connected fax to communicate with any analog fax inthe network.• short message services—A convenient facility of the GSM network is the short message service. Amessage consisting of a maximum of 160 alphanumeric characters can be sent to or from a mobilestation. This service can be viewed as an advanced form of alphanumeric paging with a number ofadvantages. If the subscribers mobile unit is powered off or has left the coverage area, the message isstored and offered back to the subscriber when the mobile is powered on or has reentered the coveragearea of the network. This function ensures that the message will be received.• cell broadcast—A variation of the short message service is the cell broadcast facility. A message of amaximum of 93 characters can be broadcast to all mobile subscribers in a certain geographic area.Typical applications include traffic congestion warnings and reports onaccidents.index
Satnam Singh +91989365069926• voice mail—This service is actually an answering machine within the network, which iscontrolled by the subscriber. Calls can be forwarded to the subscribers voice-mail box and thesubscriber checks formessages via a personal security code.• fax mail—With this service, the subscriber can receive fax messages at any fax machine.The messages are stored in a service center from which they can be retrieved by the subscribervia a personal security code to the desired fax number.Supplementary ServicesGSM supports a comprehensive set of supplementary services that can complement andsupport both telephony and data services. Supplementary services are defined by GSM and arecharacterized as revenue-generating features. A partial listing of supplementary servicesfollows.• call forwarding—This service gives the subscriber the ability to forward incoming calls toanother number if the called mobile unit is not reachable, if it is busy, if there is no reply, or ifcall forwarding is allowed unconditionally.• barring of outgoing calls—This service makes it possible for a mobile subscriber to preventall outgoing calls.• barring of incoming calls—This function allows the subscriber to prevent incoming calls.The following two conditions for incoming call barring exist: baring of all incoming calls andbarring of incoming calls when roaming outside the home PLMN.index
Satnam Singh +91989365069927• advice of charge (AoC)—The AoC service provides the mobile subscriber with anestimate of the call charges. There are two types of AoC information: one that provides thesubscriber with an estimate of the bill and one that can be used for immediate chargingpurposes. AoCfor data calls is provided on the basis of time measurements.• call hold—This service enables the subscriber to interrupt an ongoing call and thensubsequently reestablish the call. The call hold service is only applicable to normaltelephony.• call waiting—This service enables the mobile subscriber to be notified of an incoming callduring a conversation. The subscriber can answer, reject, or ignore the incoming call. Callwaiting is applicable to all GSM telecommunications services using a circuit-switchedconnection.• multiparty service—The multiparty service enables a mobile subscriber to establish amultiparty conversation—that is, a simultaneous conversation between three and sixsubscribers. This service is only applicable to normal telephony.• calling line identification presentation/restriction—These services supply the calledparty with the integrated services digital network (ISDN) number of the calling party. Therestriction service enables the calling party to restrict the presentation. The restrictionoverrides the presentation.• closed user groups (CUGs)—CUGs are generally comparable to a PBX. They are a groupof subscribers who are capable of only calling themselves and certain numbers.index
Satnam Singh +91989365069928GLOSSARYGLOSSARYADC American Digital CellularAMPS advanced mobile phone serviceAoC advice of chargeAUC authentication centerbps bits per secondBSC base station controllerBSS base station systemBTS base transceiver stationCGI cell global identityCUG closed user groupDCS digital cellular systemDTMF dual-tone multifrequencyEIR equipment identity registerGIWU GSM interworking unitGMSC gateway mobile services switching centerGMSK Gaussian minimum shift keyingGSM global system for mobile communicationHLR home location registerHz hertzISDN integrated services digital networkk kilokbps kilobits per secondindex
Satnam Singh +91989365069929GLOSSARYGLOSSARYLA location areaLAI location-area identityLPC linear predictive codingMHz megahertzMSC mobile services switching centerMSN mobile service nodeMXE message centerNMT Nordic Mobile TelephoneOMC operations and maintenance centerOSS operation and support systemPCS personal communications servicesPDC personal digital cellularPLMN public land mobile networkSS switching systemTACS total access communication systemTDMA time division multiple accessVLR visitor location registerindex
Satnam Singh +91989365069930Modulation & Modulation tech.Modulation & Modulation tech. IntroductionThe purpose of analog modulation is to impressan information-bearing analog waveform onto acarrier for transmission. The purpose of digitalmodulation is to convert an information-bearingdiscrete-time symbol sequence into a continuous-time waveform (perhaps impressed on a carrier).Key concerns bandwidth eciency andimplementation complexity. These are aected by: baseband pulse shape phase transition characteristics envelope uctuations (channel non-linearities?)index
Satnam Singh +91989365069932Modulation & Modulation tech.Modulation & Modulation tech. FM Demodulation Methods Limiter-discriminator FM feedback (FMFB) Phase-locked loop (PLL) FM PerformanceCharacterized by signal-to-noise ratio (SNR): thedemodulator input CNR (carrier-to-noise ratio)for AMPS is specied to be 18dB, resulting in anoutput SNR of 40 dB.
Satnam Singh +91989365069933Modulation & Modulation tech.Modulation & Modulation tech. Digital ModulationCriteria for selection: BER perrformance-Mobile/personal channel-severe fading-cellular architecture-interference-Typically, reqt is 10-2or better (speech) Spectral efficiency Adjacent channel interface Power efficiency(esp. at mobile) Implementation complexity/cost (may require dual-modemobile)
Satnam Singh +91989365069934Modulation & Modulation tech.Modulation & Modulation tech. Digital Modulation | ClassicationConstant-envelope methods: Allow use of lessexpensive amplication (not dependent on signalamplitude) at the expense of out-of-bandemissions. Limited to a spectral eciency of about1 bit/sec/Hz. Examples: MSK, GMSK Linear methods: Higher spectral eciency, butmust use linear ampliers to maintain performanceand to limit out-of-band emissions. Examples: PSK, QAM
Satnam Singh +91989365069935Modulation & Modulation tech.Modulation & Modulation tech. Spectral EciencySpectral occupancy (per channel) is roughlyS0=B+2f where B = bandwidth occupied of RF signal powerspectrum and f is the maximum (one-way) carrier frequency(oscillator) drift. Remark: Per-channel spectral eciencyfor narrowband systems onlyWe can express the bandwidth asB=Rd/n where Rd is the channel data rate and n is the spectraleciency (in bits/sec/Hz).
Satnam Singh +91989365069936 Combining,S0=Rd/n+2f Thus, to minimize spectral occupancy (thusmaximizing capacity in number of users) we can:1. Lower speech encoder rate (trade: cost, delity),or2. Improve spectral eciency of modulation (trade:complexity), or3. Improve transmitter/receiver oscillators (trade:cost).
Satnam Singh +91989365069937State of the technology:Bandwidth eciency: 1 < n < 2Speech encoder rate: Rd = 4 - 8 kb/secOscillator stability: = 1x10-6/year implyingf<= 1 kHz at 900 MHz (long-term)Examples: NADC (TDMA): 48.6 kbps in 30 kHz GSM: 34 kbps in 25 kHz
Satnam Singh +91989365069938Circuit Switching & PacketCircuit Switching & PacketSwitchingSwitchingSwitching Networks Long distance transmission is typically done overa network of switched nodes Nodes not concerned with content of data End devices are stations– Computer, terminal, phone, etc. A collection of nodes and connections is acommunications network Data routed by being switched from node to nodeindex
Satnam Singh +91989365069939NodesNodesNodes may connect to other nodes only, or to stations and othernodesNode to node links usually multiplexedNetwork is usually partially connectedSome redundant connections are desirable for reliabilityTwo different switching technologiesCircuit switchingPacket switchingindex
Satnam Singh +91989365069941Switching ActivitiesSwitching ActivitiesSome nodes connect only to other nodes(intermediary nodes). Sole purpose is toswitch dataSome nodes have one or more stationsattached. They accept from and deliverdata to the attached station.Node-to-node links are usuallymultiplexedMultiple paths enhance reliabilityindex
Satnam Singh +91989365069942Circuit SwitchingCircuit Switching Originated in public telephone networks Well suited to analog transmission of voice signal Dedicated communication path between two stations Three phases– Establish– Transfer– Disconnect Must have switching capacity and channel capacity toestablish connection Must have intelligence to work out routingindex
Satnam Singh +91989365069943Circuit Switching - ApplicationsCircuit Switching - ApplicationsInefficient– Channel capacity dedicated for duration ofconnection– If no data, capacity wastedSet up (connection) takes timeOnce connected, transfer is transparentDeveloped for voice traffic (phone)index
Satnam Singh +91989365069945Telecom ComponentsTelecom Components Subscriber– Devices attached to network Subscriber line– Link between subscriber and network Also called Local Loop or Subscriber Loop– Almost all Local Loops are TPW– Range from Few km up to tens of km Exchange– Switching center in the network– End office specific switching center that supports subscribers Trunks– Branches between exchanges– Multiplexedindex
Satnam Singh +91989365069947Circuit Switching ConceptsCircuit Switching Concepts Digital Switch– Provide transparent signal path between devices– Typically allows full duplex transmission Network Interface Functions and h/w needed to connect digitaldevices to the network Control Unit– Establish connections - Generally on demand, Handle andacknowledge requests, Determine if destination is free,constructpath– Maintain connection– Disconnectindex
Satnam Singh +91989365069948Blocking or Non-blocking CircuitBlocking or Non-blocking CircuitSwitchingSwitching Blocking– A network may not be able to connect stationsbecause all paths are in use (more stations than path)– Used on voice systems Short duration calls Non-blocking– Permits all stations to connect (in pairs) at once (atleast as many paths as stations)– Used for some data connectionsindex
Satnam Singh +91989365069949Space Division SwitchingSpace Division SwitchingDeveloped for analog environment, butcarried over into digitalSignal paths are physically separate (slide15)Each connection requires dedicated path(crossbar switch)index
Satnam Singh +91989365069950Crossbar switchCrossbar switchNumber of crosspoints grows as square ofnumber of stationsLoss of crosspoint prevents connection– Inefficient use of crosspoints– If all stations connected, only a fewcrosspoints in useNon-blockingindex
Satnam Singh +91989365069952Multistage SwitchMultistage SwitchReduced number of crosspointsMore than one path through network– Increased reliabilityMore complex controlMay be blockingindex
Satnam Singh +91989365069953Three StageThree Stage Space DivisionSpace DivisionSwitchSwitchindex
Satnam Singh +91989365069954Time Division SwitchingTime Division SwitchingModern digital systems rely on intelligentcontrol of space and time divisionelementsUse digital time division techniques to setup and maintain virtual circuitsPartition low speed bit stream into piecesthat share higher speed streamindex
Satnam Singh +91989365069955Control Signaling FunctionsControl Signaling Functions Audible communication with subscriber Transmission of dialed number Call can not be completed indication Call ended indication Signal to ring phone Billing info Equipment and trunk status info Diagnostic info Control of specialist equipmentindex
Satnam Singh +91989365069956Control Signal SequenceControl Signal Sequence Both phones on hook Subscriber lifts receiver (off hook) End office switch signaled Switch responds with dial tone Caller dials number If target not busy, send ringer signal to target subscriber Feedback to caller– Ringing tone, engaged tone, unobtainable Target accepts call by lifting receiver Switch terminates ringing signal and ringing tone Switch establishes connection Connection release when Source subscriber hangs upindex
Satnam Singh +91989365069957Switch to Switch SignalingSwitch to Switch SignalingSubscribers connected to differentswitchesOriginating switch seizes interswitch trunkSend off hook signal on trunk, requestingdigit register at target switch (for address)Terminating switch sends off hookfollowed by on hook (wink) to showregister readyOriginating switch sends addressindex
Satnam Singh +91989365069958In Channel SignalingIn Channel Signaling Use same channel for signaling control and call– Requires no additional transmission facilities Inband– Control signals have same electromagnetic properties(frequency) as voice signal– Can go anywhere a voice signal can– Impossible to set up a call on a faulty speech path Out of band– Voice signals do not use full 4kHz bandwidth– Narrow signal band within 4kHz used for control– Can be sent whether or not voice signals are present– Need extra electronics– Slower signal rate (narrow bandwidth)index
Satnam Singh +91989365069959Drawbacks of In ChannelDrawbacks of In ChannelSignalingSignalingLimited transfer rateDelay between entering address (dialing)and connectionOvercome by use of common channelsignalingindex
Satnam Singh +91989365069960Common Channel SignalingCommon Channel Signaling Control signals carried over paths independent ofvoice channel One control signal channel can carry signals fora number of subscriber channels Common control channel for these subscriberlines Associated Mode– Common channel closely tracks interswitch trunks Disassociated Mode– Additional nodes (signal transfer points)– Effectively two separate networksindex
Satnam Singh +91989365069962Signaling System Number 7Signaling System Number 7 SS7 Common channel signaling scheme ISDN Overall purpose to provide internationalstandardized common channel signaling system Performs call management (setup, maintenance,termination) and network management functions Network is circuit switched, but control is packetswitchedindex
Satnam Singh +91989365069963Softswitch ArchitectureSoftswitch ArchitectureLatest trend in circuit-switchingtechnology General purpose computer running software tomake it a smart phone switch Lower cost, greater functionality Can packetize digitized voice data, allowingvoice over IP Performs call routing Separates call processing from hardware functionof switchindex
Satnam Singh +91989365069966Circuit Switching ShortcomingsCircuit Switching ShortcomingsInefficient for data because of idle timeProvides for transmission at constant rate –must transmit and receive at same datarate. Limits versatilitindex
Satnam Singh +91989365069967Packet Switching Basic OperationPacket Switching Basic Operation Data transmitted in small packets– Typically 1000 octets (8 bit byte)– Longer messages split into series of packets– Each packet contains a portion of user data plus somecontrol info Control info– Routing (addressing) info Packets are received, stored briefly (buffered)and passed on to the next node– Store and forwardindex
Satnam Singh +91989365069968Use of PacketsUse of Packetsindex
Satnam Singh +91989365069969AdvantagesAdvantages Line efficiency– Single node to node link can be shared by manypackets over time– Packets queued and transmitted as fast as possible Data rate conversion– Each station connects to the local node at its ownspeed– Nodes buffer data if required to equalize rates Packets are accepted even when network is busy– Delivery may slow down Priorities can be usedindex
Satnam Singh +91989365069970Switching TechniqueSwitching TechniqueStation breaks long message into packetsPackets sent one at a time to the networkPackets handled in two ways– Datagram– Virtual circuitindex
Satnam Singh +91989365069971DatagramDatagramEach packet treated independentlyPackets can take any practical routePackets may arrive out of orderPackets may go missingUp to receiver to re-order packets andrecover from missing packetsindex
Satnam Singh +91989365069972Virtual CircuitVirtual Circuit Preplanned route established before any packetssent Call request and call accept packets establishconnection (handshake) Each packet contains a virtual circuit identifierinstead of destination address No routing decisions required for each packet Clear request to drop circuit Not a dedicated pathindex
Satnam Singh +91989365069973Virtual Circuits v DatagramVirtual Circuits v Datagram Virtual circuits– Network can provide sequencing and error control– Packets are forwarded more quickly No routing decisions to make– Less reliable Loss of a node loses all circuits through that node Datagram– No call setup phase Better if few packets– More flexible Routing can be used to avoid congested parts of the networkindex
Satnam Singh +91989365069974Circuit vs. Packet SwitchingCircuit vs. Packet Switching Circuit Switched Bandwidth guaranteed Circuit capacity notreduced by othernetwork traffic Circuit costsindependent of amountof data transmitted,resulting in wastedbandwidthPacket Switched Bandwidth dynamicallyallocated on as-neededbasis May have concurrenttransmissions overphysical channel May have delays andcongestion More cost-effective,offer better performance
Satnam Singh +91989365069975Switch to Switch SignalingSwitch to Switch SignalingSubscribers connected to differentswitchesOriginating switch seizes interswitch trunkSend off hook signal on trunk, requestingdigit register at target switch (for address)Terminating switch sends off hookfollowed by on hook (wink) to showregister readyOriginating switch sends addressindex
Satnam Singh +91989365069976Location of SignalingLocation of SignalingSubscriber to network– Depends on subscriber device and switchWithin network– Management of subscriber calls and network– More complexindex
Satnam Singh +91989365069977In Channel SignalingIn Channel Signaling Use same channel for signaling control and call– Requires no additional transmission facilities Inband– Control signals have same electromagnetic properties(frequency) as voice signal– Can go anywhere a voice signal can– Impossible to set up a call on a faulty speech path Out of band– Voice signals do not use full 4kHz bandwidth– Narrow signal band within 4kHz used for control– Can be sent whether or not voice signals are present– Need extra electronics– Slower signal rate (narrow bandwidth)index
Satnam Singh +91989365069978Drawbacks of In ChannelDrawbacks of In ChannelSignalingSignalingLimited transfer rateDelay between entering address (dialing)and connectionOvercome by use of common channelsignalingindex
Satnam Singh +91989365069979Common Channel SignalingCommon Channel Signaling Control signals carried over paths independent ofvoice channel One control signal channel can carry signals fora number of subscriber channels Common control channel for these subscriberlines Associated Mode– Common channel closely tracks interswitch trunks Disassociated Mode– Additional nodes (signal transfer points)– Effectively two separate networksindex
Satnam Singh +91989365069981Signaling System Number 7Signaling System Number 7 SS7 Common channel signaling scheme ISDN Overall purpose to provide internationalstandardized common channel signaling system Performs call management (setup, maintenance,termination) and network management functions Network is circuit switched, but control is packetswitchedindex
Satnam Singh +91989365069982Softswitch ArchitectureSoftswitch ArchitectureLatest trend in circuit-switchingtechnology General purpose computer running software tomake it a smart phone switch Lower cost, greater functionality Can packetize digitized voice data, allowingvoice over IP Performs call routing Separates call processing from hardware functionof switchindex
Satnam Singh +91989365069985Packet Switching Basic OperationPacket Switching Basic Operation Data transmitted in small packets– Typically 1000 octets (8 bit byte)– Longer messages split into series of packets– Each packet contains a portion of user data plus somecontrol info Control info– Routing (addressing) info Packets are received, stored briefly (buffered)and passed on to the next node– Store and forwardindex
Satnam Singh +91989365069986Use of PacketsUse of Packets
Satnam Singh +91989365069987AdvantagesAdvantages Line efficiency– Single node to node link can be shared by manypackets over time– Packets queued and transmitted as fast as possible Data rate conversion– Each station connects to the local node at its ownspeed– Nodes buffer data if required to equalize rates Packets are accepted even when network is busy– Delivery may slow down Priorities can be usedindex
Satnam Singh +91989365069988Switching TechniqueSwitching TechniqueStation breaks long message into packetsPackets sent one at a time to the networkPackets handled in two ways– Datagram– Virtual circuitindex
Satnam Singh +91989365069989DatagramDatagramEach packet treated independentlyPackets can take any practical routePackets may arrive out of orderPackets may go missingUp to receiver to re-order packets andrecover from missing packetsindex
Satnam Singh +91989365069991The Mobile & Air InterfaceThe Mobile & Air Interface
Satnam Singh +91989365069992 A1 InterfaceThe A1 interface carries signaling information between the Call Control andMobility Management functions of the MSC (Mobile Switching Centre) and thecall control component of the BSC (Base Station Controller). A2 InterfaceThe A2 interface carries 64Kbps/56Kbps PCM (Pulse Code Modulation)information (voice/data) or 64Kbps UDI (Unrestricted Digital Information)between the MSC (Mobile Switching Centre) and the channel element componentof the BSC (Base Station Controller). A5 InterfaceThe A5 interface carries a full duplex stream of bytes between the IWF(Interworking Function) and the Selection / Distribution unit function. A5/1 - Encryption Algorithm A5/1Algorithm used in the GSM ciphering process between a MS (MobileStation) and the GSM network A5/2 - Encryption Algorithm A5/2Algorithm used in the GSM ciphering process between a MS (Mobile Station) andthe GSM network. This algorithm is simpler than A5/1 and was developed by ETSI(European Telecommunications Standards Institute) for use in Eastern Europeanstates that had restrictions to certain Western technologies. A3 InterfaceThe A3 interface carries coded user information (voice/data) and signalinginformation between the Selection / Distribution unit function and the channelelement component of the BTS (Base Transceiver System). The A3 interface iscomposed of two parts: Signaling - the signaling information is carried across aseparate logical channel from the user traffic channel, and controls the allocationand use of channels for transporting user traffic User traffic - the user traffic istransported in traffic channels A7 InterfaceThe A7 interface carries signaling information between a source BS (Base Station)and a target BS.index
Satnam Singh +91989365069993 A8 - Ciphering Key Generating Algorithm A8This algorithm is used in conjunction with Ki theauthentication key and RAND (Random Number) togenerate Kc (Cipher Key). This is used with A5/X to cipherthe data stream between the MS (Mobile Station) and theGSM network.
Satnam Singh +91989365069994 A8 InterfaceThe A8 interface carries user traffic between the BS (Base Station) and thePCF (Packet Control Function). A9 InterfaceThe A9 interface carries signaling information between the BS (BaseStation) and the PCF (Packet Control Function). A10 InterfaceThe A10 interface carries user traffic between the PCF (PacketControl Function) and the PDSN (Packet Data Serving Node). A11 InterfaceThe A11 interface carries signaling information between the PCF(Packet Control Function) and the PDSN (Packet Data Serving Node). A38A single algorithm in GSM that performs the functions of A3 and A8 . A LinkAn "A" (Access) link is a SL (Signalling Link) that connects a signalling endpoint, i.e. a SP (Signalling Point), to an STP (Signalling Transfer Point).Only messages that are originating from or destined to the signalling endpoint are transmitted on this link.
Satnam Singh +91989365069995Abis InterfaceThe interface within the GSM architecture, betweenthe BTS (Base Transceiver Station) and BSC (BaseStation Controller). This interface is usuallyconfigured using a 16Kbps slot structure.
Satnam Singh +91989365069996Voice is not sent as a series of tones, but coded into data bursts. A mobile is onlyactually logged onto one cell at a time, but that cell may have several other mobilesusing it at the same time. A basic single-channel cell uses Time Division MultipleAccess (TDMA), which allows eight mobiles to take turns to actively use the channel.There are around 100 to 200 channels using different pairs of uplink (mobile to base)and downlink (base to mobile) frequencies within each of the GSM bands (900MHz,1800MHz and 1900MHz). To minimise the effects of interference, the mobile and thebase frequency-hop during a call. Far more than eight mobiles can be logged on to acell, as long as they dont all want to make or receive a call at once.How a GSM mobile handset communicates with the base station
Satnam Singh +91989365069997Speech is analogue: In an analogue system, varying air pressures are captured by a microphone and delivered by an earpieceor loudspeaker, passing the signal between the two ends through an analogue connection. GSM mobile phone systems aredigital: they pass data to and fro, so speech has to be encoded at the microphone end and decoded at the speaker end.There are three systems in use: Full rate (FR) (described here), Half Rate (HR), which increases capacity at the expense ofaudio quality, and Enhanced Full Rate (EFR) which improves sound quality with only a small processing overhead.Educated guessesThe coding system used is called Regular Pulse Excitation Long-Term Prediction (RPE-LTP). Basically, it uses previous samples to predict whatthe next sounds will be, and uses that as a basis for working out how best to turn it into data.CutThe handset chops the sound into 20ms samples, which are passed to the encoder, running at 13kbps. This means that the result is 260 bits ofsampled data.ShuffledIt chooses the most important 50 bits and encodes them with 3 parity bits for error correction. The next 132 bits are addedwithout parity bits, and the result is encoded before the least important 78 bits are added. At the other end, if the importantTop 50 data bits are corrupted, they are discarded, and the Top 50 from the previous data burst are reused instead. This iswhat causes the metallic twang echo sound of a poor GSM connection. Better than no sound at all, though!Dealt outThis 456bit long block of data, representing 20ms of sound, is then split up and shared across four pairs of 57bit data bursts.By being interleaved in this way, lost data will make a section fuzzy instead of losing the whole of a smaller section.ConcealedThe data is encrypted before being sent.The data is sent over the radio link using a modulation system called Gaussian Modulation Shift Keying (GMSK).Back againA similar process goes on at the other end to reverse the coding and restore audio tones.DelayedAll this processing and interleaving causes a time delay, and unless measures are taken to prevent it, there can be a problem with echo. Handsetsare designed so that they do not pass sound from the earpiece to the microphone, and there are echo-suppressors built into the network, but theycan only do so much. If echo is a problem, it is often because the earpiece volume is set too high, or because a phone case is reflecting earpiecesound back to the microphone.how speech is encoded
Satnam Singh +91989365069998How a GSM phone keeps in touch with the network between callsIdle mode refers to when the handset is on "standby" and not in a call. It is a bit of a misnomer,because it isnt entirely idle!It listens to several common (shared) channels:Broadcast Channels:The Broadcast Control Channel (BCCH) sends information including the identity of the basestation, its frequency allocations, and the frequency-hopping sequences it uses as well as a list ofneighbouring cells that the mobile might like to consider.The Frequency Correction Channel (FCCH) and Synchronisation Channel (SCH) send out amarker that allows the mobile to precisely synchronise the frequencies it transmits on, andidentifies precisely when each timeslot sequence begins. Every cell in a GSM network broadcastsone FCCH and one SCH, in time slot number 0 (the first of a TDMA frame).Common Control ChannelsThe Random Access Channel (RACH) is used by mobiles to request a connection, so it is notused for anything else. Mobiles dont actually listen to this one, but it is a "common channel"The Paging Channel (PCH) alerts the mobile of an incoming call. This is divided intosubchannels. To save power, handsets can only listen to "their" sub-channel, and doze for the restof the time.The Access Grant Channel (AGCH) is used to allocate an SDCCH (a slow data channel) to amobile so that it can request a channel to carry a call.In Idle Mode
Satnam Singh +91989365069999Because mobile phones move around, they dont stay in coverage of one cell. As a result, there has to be a mechanism to transfer calls from cellto cell without interrupting the call.Between CallsWhen in Idle Mode, the mobile only reports when it transfers to another VLR by doing a Location Update.Every so often (controlled by an interval time setting the Network chooses) each mobile reports its position by sending a Location Update, justin case the network has mislaid it through a database or signalling error. The mobiles decide when to do this, so that they dont allreport in at once.In practice, you may suddenly get old SMS messages or be told of long-waiting Voicemail when a Location Update occurs.When the mobile is switched off, it signals a log-off (known as an IMSI Detach) to the network so that it wont try to search for a switched-offmobile. It is possible that this doesnt happen (if switched off out of coverage, for example). In such a case, the network wont noticeuntil the next scheduled Location Update has been missed.During a CallWhen a call is in progress, during the time between sending and receiving data, the handset monitors the signal it gets from the 16 nearby cellslisted in the current cells Neighbour List, and every second it reports the signal level of the best six of them to the BSC, using a SlowAccess Control Channel (SACCH).How the decision to switch cells is made can vary, but generally the idea is to switch to the cell with the best signal to economise on power inthe mobile, but the alternative of staying put till the signal quality fades is sometimes used.To trigger and coordinate a handoff is a time-critical function, so the Fast Access Control Channel (FACCH) needed to do this "commandeers"an entire databurst on the control channel to do this.The decision to switch to another cell can be made by the mobile or by the BTS: the latter usually because it is getting too busy. Occasionally,the handoff fails, and the mobile has to start again, scanning for a network for a fresh start. This can happen when unusual signalpropagation has led it to register on a far distant cell, over the hilltops, which has a neighbour list of cells nowhere near the mobile!Types of HandoffsThere are five types of handoff, but only four are supported in the GSM standard.From one time slot to another in the same cell. This is managed by the BSC and reported to the MSC.From one cell to another under the control of the same BSC. This is managed by the BSC and reported to the MSC.From one BSC area to another, but still under the control of the same MSC. The MSC manages this transfer.From one MSC area to another. This leaves the original MSC in charge of the call, but the new MSC manages any new handoffs.From one network to another: this is the one you cant do! Cross a national boundary, or move into coverage of a different network whenroaming, and youll have to redial to continue the call on the new network. Note that some partner networks have made specialarrangements for this to happen, but its exceptional.Handoffs
Satnam Singh +919893650699100How the network reaches a mobile phone for an incoming callWhen a mobile phone makes an outgoing call, it is easy: the network just has toallocate a channel and send the call to the destination number. Incoming calls are not soeasy. The network has to find the mobile before the caller rings off!Finding the MobileThe incoming call is routed to the Gateway Mobile Switching Centre (GMSC), whichasks the NPDB if it has a record for that number (and for details if it has) and then asksthe HLR where to send it.The HLR knows which sim card is associated with that phone number, and rememberswhich VLR/MSC is currently looking after it, whether on the home network, or theVLR of a roaming partner.The VLR/MSC returns the current location and status of the mobile and thisinformation passes back to the GMSC, The GMSC passes the call to the appropriateMSC, which in turn passes it to the BSC, which tells the BTS to page the mobile on thePaging Channel (PCH) to say there is a call for it.Trying to Connect You...Once the BTS has paged the mobile, it offers a channel and waits for the mobilesresponse. If it finds the mobile, it authenticates the mobiles identity and then the call isset up.
Satnam Singh +919893650699101The base station sub systemThe base station sub system GSM provides recommendations, notrequirements. The GSM specifications define thefunctions and interface requirements in detail butdo not address the hardware. The reason for thisis to limit the designers as little as possible butstill to make it possible for the operators to buyequipment from different suppliers. The GSM network is divided into three majorsystems: the switching system (SS), the basestation system (BSS), and the operation andsupport system (OSS). The basic GSM networkelements are shown in Figure.index
Satnam Singh +919893650699102The base station sub systemThe base station sub system
Satnam Singh +919893650699103The base station sub systemThe base station sub systemThe Switching SystemThe switching system (SS) is responsible for performing call processing andsubscriber-related functions. The switching system includes the followingfunctional units:• home location register (HLR)—The HLR is a database used forstorage and management of subscriptions. The HLR is considered themost important database, as it stores permanent data aboutsubscribers, including a subscribers service profile, locationinformation, and activity status. When an individual buys asubscription from one of the PCS operators, he or she is registered inthe HLR of that operator.• mobile services switching center (MSC)—The MSC performs thetelephony switching functions of the system. It controls calls to andfrom other telephone and data systems. It also performs such functionsas toll ticketing, network interfacing, common channel signaling, andothers.
Satnam Singh +919893650699104The base station sub systemThe base station sub system• visitor location register (VLR)—The VLR is a database thatcontains temporary information about subscribers that is needed bythe MSC in order to service visiting subscribers. The VLR is alwaysintegrated with the MSC. When a mobile station roams into a new MSCarea, the VLR connected to that MSC will request data about themobile station from the HLR. Later, if the mobile station makes a call,the VLR will have the information needed for call setup without havingto interrogate the HLR each time.• authentication center (AUC)—A unit called the AUC providesauthentication and encryption parameters that verify the users identityand ensure the confidentiality of each call. The AUC protects networkoperators from different types of fraud found in todays cellular world.• equipment identity register (EIR)—The EIR is a database thatcontains information about the identity of mobile equipment thatprevents calls from stolen, unauthorized, or defective mobile stations.The AUC and EIR are implemented as stand-alone nodes or as acombined AUC/EIR node.
Satnam Singh +919893650699105The Base Station System (BSS)All radio-related functions are performed in the BSS, which consists ofbasestation controllers (BSCs) and the base transceiver stations (BTSs).BSC—The BSC provides all the control functions and physical linksbetween the MSC and BTS. It is a high-capacity switch that providesfunctions such as handover, cell configuration data, and control ofradio frequency (RF) power levels in base transceiver stations. Anumber of BSCs are served by an MSC.• BTS—The BTS handles the radio interface to the mobile station. TheBTS is the radio equipment (transceivers and antennas) needed toservice each cell in the network. A group of BTSs are controlled by aBSC.
Satnam Singh +919893650699106The Operation and Support SystemThe operations and maintenance center (OMC) is connected to all equipment inthe switching system and to the BSC. The implementation of OMC is called theoperation and support system (OSS). The OSS is the functional entity fromwhichthe network operator monitors and controls the system. The purpose of OSS istooffer the customer cost-effective support for centralized, regional, and localoperational and maintenance activities that are required for a GSM network. Animportant function of OSS is to provide a network overview and support themaintenance activities of different operation and maintenance organizations.
Satnam Singh +919893650699107Additional Functional ElementsOther functional elements shown in Figure 2 are as follows:• message center (MXE)—The MXE is a node that providesintegrated voice, fax, and data messaging. Specifically, the MXEhandles short message service, cell broadcast, voice mail, fax mail, email,and notification.• mobile service node (MSN)—The MSN is the node that handles themobile intelligent network (IN) services.• gateway mobile services switching center (GMSC)—A gatewayis a node used to interconnect two networks. The gateway is oftenimplemented in an MSC. The MSC is then referred to as the GMSC.• GSM interworking unit (GIWU)—The GIWU consists of bothhardware and software that provides an interface to various networksfor data communications. Through the GIWU, users can alternatebetween speech and data during the same call. The GIWU hardwareequipment is physically located at the MSC/VLR.
Satnam Singh +919893650699108The core networkThe core networkIt provides an overview of the GSM networkarchitecture. This includes a brief explanation of thedifferent network subsystems and a description ofthe functionality of the elements within each of thesubsystems. Topics include: General architecture overview The Mobile Station (MS) Subsystem and Elements The Base Station Subsystem (BSS) and Elements The Network Subsystem (NSS) and Elements Introduction to network interfacesindex
Satnam Singh +919893650699110A GSM network is made up of three subsystems:• The Mobile Station (MS)• The Base Station Sub-system (BSS) – comprising a BSCand several BTSs• The Network and Switching Sub-system (NSS) –comprising an MSC and associated registersThe interfaces defined between each of these sub systemsinclude:• A interface between NSS and BSS• Abis interface between BSC and BTS (within the BSS)• Um air interface between the BSS and the MS
Satnam Singh +919893650699111Abbreviations:MSC – Mobile Switching CenterBSS – Base Station Sub-systemBSC – Base Station ControllerHLR – Home Location RegisterBTS – Base Transceiver StationVLR – Visitor Location RegisterTRX – TransceiverAuC – Authentication CenterMS – Mobile StationEIR – Equipment Identity RegisterOMC – Operations and Maintenance CenterPSTN – Public Switched Telephone Network
Satnam Singh +919893650699112Mobile StationMobile StationThe Mobile Station (MS) consists of thephysical equipment used by a PLMNsubscriber to connect to the network. Itcomprises the Mobile Equipment (ME) andthe Subscriber Identity Module (SIM). TheME forms part of the Mobile Termination(MT) which, depending on the applicationand services, may also include various typesof Terminal Equipment (TE) and associatedTerminal Adapter (TA).
Satnam Singh +919893650699114 The IMSI identifies the subscriber within the GSMnetwork while the MS ISDN is the actual telephonenumber a caller (possibly in another network) uses toreach that person. Security is provided by the use of an authentication keyand by the transmission of a temporary subscriberidentity (TMSI) across the radio interface where possibleto avoid using the permanent IMSI identity. The IMEI may be used to block certain types ofequipment from accessing the network if they areunsuitable and also to check for stolen equipment.
Satnam Singh +919893650699115MS and SIMMS and SIMThe mobile station consists of :• mobile equipment (ME)• subscriber identity module (SIM)The SIM stores permanent and temporary data about themobile, the subscriber and the network, including :• The International Mobile Subscribers Identity (IMSI)• MS ISDN number of subscriber• Authentication key (Ki) and algorithms forauthentication checkThe mobile equipment has a unique International MobileEquipment Identity (IMEI), which is used by the EIR
Satnam Singh +919893650699116Base Station Subsystem (BSS)Base Station Subsystem (BSS)
Satnam Singh +919893650699117Base Station Subsystem (BSS)Base Station Subsystem (BSS)The BSS comprises: Base Station Controller (BSC)• One or more Base Transceiver Stations (BTSs)The purpose of the BTS is to: provide radio access to the mobile stations• manage the radio access aspects of the systemBTS contains: Radio Transmitter/Receiver (TRX)• Signal processing and control equipment Antennas and feeder cables
Satnam Singh +919893650699118Base Station Subsystem (BSS)Base Station Subsystem (BSS)The BSC:allocates a channel for the duration of acallmaintains the call:monitors qualitycontrols the power transmitted by theBTS or MSgenerates a handover to another cellwhen required
Satnam Singh +919893650699119Network Switching System (NSS)Network Switching System (NSS)The NSS combines the call routingswitches (MSCs and GMSC) withdatabase registers required to keeptrack of subscribers’ movements anduse of the system. Call routingbetween MSCs is taken via existingPSTN or ISDN networks. Signalingbetween the registers uses SignalingSystem No. 7 protocol.
Satnam Singh +919893650699120Base Station Subsystem (BSS)Base Station Subsystem (BSS)Functions of the MSC: Switching calls, controlling calls and loggingcalls• Interface with PSTN, ISDN, PSPDN• Mobility management over the radio networkand other networks Radio Resource management - handoversbetween BSCs Billing Information
Satnam Singh +919893650699122Logical ChannelsLogical Channels Physical channelPhysical channel - Each timeslot on a carrier is referredto as a physical channel. Per carrier there are 8 physicalchannels. Logical channelLogical channel - Variety of information is transmittedbetween the MS and BTS. There are different logicalchannels depending on the information sent. The logicalchannels are of two types– Traffic channel– Control channelindexDownlinkUplink
Satnam Singh +919893650699125Logical ChannelsLogical Channels BCH ChannelsBCH Channels BCCH( Broadcast Control Channel )BCCH( Broadcast Control Channel )– Downlink only– Broadcasts general information of the serving cell called SystemInformation– BCCH is transmitted on timeslot zero of BCCH carrier– Read only by idle mobile at least once every 30 secs. SCH( Synchronisation Channel )SCH( Synchronisation Channel )– Downlink only– Carries information for frame synchronisation. Contains TDMA framenumber and BSIC. FCCH( Frequency Correction Channel )FCCH( Frequency Correction Channel )– Downlink only.– Enables MS to synchronise to the frequency.– Also helps mobiles of the ncells to locate TS 0 of BCCH carrier.
Satnam Singh +919893650699126Logical ChannelsLogical Channels CCCH ChannelsCCCH Channels RACH( Random Access Channel )RACH( Random Access Channel )– Uplink only– Used by the MS to access the Network. AGCH( Access Grant Channel )AGCH( Access Grant Channel )– Downlink only– Used by the network to assign a signalling channel upon successfulldecoding of access bursts. PCH( Paging Channel )PCH( Paging Channel )– Downlink only.– Used by the Network to contact the MS.
Satnam Singh +919893650699127Logical ChannelsLogical Channels DCCH ChannelsDCCH Channels SDCCH( Standalone Dedicated Control Channel )SDCCH( Standalone Dedicated Control Channel )– Uplink and Downlink– Used for call setup, location update and SMS. SACCH( Slow Associated Control Channel )SACCH( Slow Associated Control Channel )– Used on Uplink and Downlink only in dedicated mode.– Uplink SACCH messages - Measurement reports.– Downlink SACCH messages - control info. FACCH( Fast Associated Control Channel )FACCH( Fast Associated Control Channel )– Uplink and Downlink.– Associated with TCH only.– Is used to send fast messages like handover messages.– Works by stealing traffic bursts.
Satnam Singh +919893650699129NORMAL BURSTNORMAL BURST DataData - Two blocks of 57 bits each. Carries speech, data or controlinfo. Tail bits - Used to indicate the start and end of each burst. Three bitsalways 000. Guard periodGuard period - 8.25 bits long. The receiver can only receive anddecode if the burst is received within the timeslot designated forit.Since the MS are moving. Exact synchronization of burst is notpossible practically. Hence 8.25bits corresponding to about 30us isavailable as guard period for a small margin of error. Flag bitsFlag bits - This bit is used to indicate if the 57 bits data block is usedas FACCH. Training SequenceTraining Sequence - This is a set sequence of bits known by both thetransmitter and the receiver( BCC of BSIC). When a burst ofinformation is received the equaliser searches for the trainingsequence code. The receiver measures and then mimics the distortionwhich the signal has been subjected to. The receiver then comparesthe received data with the distorted possible transmitted sequenceand chooses the most likely one.
Satnam Singh +919893650699130FREQUENCY CORRECTION BURSTFREQUENCY CORRECTION BURST0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7142 bits 33FRAME1(4.615ms) FRAME2Fixed DataTailBitsTailBitsGuardPeriodGuardPeriod0.546ms0.577ms• Carries FCCH channel.• Made up of 142 consecutive zeros.• Enables MS to correct its local oscillator locking it to that of the BTS.
Satnam Singh +919893650699131SYNCHRONISATION BURSTSYNCHRONISATION BURST0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 739 bits 33FRAME1(4.615ms) FRAME2SynchronisationSequenceTailBitsTailBitsGuardPeriodGuardPeriod0.546ms0.577ms64 bits 39 bitsEncryptedBitsEncryptedBits• Carries SCH channel.• Enables MS to synchronise its timings with the BTS.• Contains BSIC and TDMA Frame number.
Satnam Singh +919893650699132DUMMY BURSTDUMMY BURST0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 757 bits 57 bits26 bits 33FRAME1(4.615ms) FRAME2TrainingsequenceData DataTailBitsTailBitsFlagBitFlagBitGuardPeriodGuardPeriod0.546ms0.577ms• Transmitted on the unused timeslots of the BCCH carrier in thedownlink.
Satnam Singh +919893650699133AACCESS BURSTCCESS BURST0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 741 bits 68.25 bits8FRAME1(4.615ms) FRAME2TailBitsTailBitsGuardPeriod0.577ms36 bitsSynchronisationSequenceEncryptedBits3• Carries RACH.• Has a bigger guard period since it is used during initial access andthe MS does not know how far it is actually from the BTS.
Satnam Singh +919893650699134NEED FOR TIMESLOT OFFSETNEED FOR TIMESLOT OFFSET0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 70 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7BSS DownlinkMS Uplink• If Uplink and Downlink are aligned exactly, then MS will have totransmit and receive at the same time. To overcome this problem aoffset of 3 timeslots is provided between downlink and uplink
Satnam Singh +9198936506991350 1 2 3 4 5 6 7 0 1 2 3 4 5 6 75 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4BSS DownlinkMS Uplink503 timeslotoffsetNEED FOR TIMESLOT OFFSETNEED FOR TIMESLOT OFFSET• As seen the MS does not have to transmit and receive at the sametime. This simplifies the MS design which can now use only onesynthesizer.
Satnam Singh +919893650699136Components of Nokia BTSComponents of Nokia BTSThere are two type of Nokia BTS Nokia ULTRAUltra IndoreUltra Outdoor Nokia METROThere is some basic different inthese BTS which are goanna to bediscussed later on.
Satnam Singh +919893650699137Ultrasite BTS TechnicalUltrasite BTS TechnicalSpecificationsSpecificationsCommon coremechanics in NokiaUltraSite EDGE BTSOutdoor and NokiaUltraSite EDGE BTSIndoorCommon plug-in units
Satnam Singh +919893650699138 1940 x 770 x 750 mm (H x W x D)– Identical footprint to CityTalk BTS Weight– Max weight (12 TRX) 340 kg– Heaviest single part 58 kg (coremechanics)– Heaviest plug-in unit 18 kg (RTC) Acoustic noise (max): 68 dB(A) Climatic conditions:– w/o heater -10°C ... +50°C– with optional heater -33°C ... +50°C Ingress Protection Class: IP 55 Two level environmental protection:– BTS core and cabinet door provides EMC shielding– Outdoor kit provides additional weather proofing
Satnam Singh +919893650699139Nokia UltraSite EDGE BaseNokia UltraSite EDGE BaseStationStationwith GSM/EDGE and WCDMAwith GSM/EDGE and WCDMANokia UltraSite EDGE BTS cabinet– up to 6 GSM/EDGE TRXs– 3 WCDMA carriers (Rel.1), sectorised 1+1+1– 6 WCDMA carriers (Rel.2), sectorised 2+2+2WCDMA output power– 5 W per sector in 1+1+1– 2 W per sector in 2+2+2common transmissionsharing feeders through triplexerscommon site support provided byNokia UltraSite SupportGSM/EDGEWCDMA
Satnam Singh +919893650699140Mechanical CharacteristicsMechanical Characteristics 1800 x 600 x 570 mm (H x W x D)– Identical footprint to IntraTalk BTS– Additional 50 mm free space requiredbehind cabinet Weight– Max weight (12 TRX) 270 kg– Heaviest single part 58 kg(core mechanics)– Heaviest plug-in unit 18 kg(RTC) Acoustic noise (max): 73dB(A) Climatic conditions: -5°C ... +50 °C Ingress Protection Class: IP 20 BTS core and cabinet doorprovides EMC shielding
Satnam Singh +919893650699141Temperature Control SystemTemperature Control SystemSW controlled coolingwith variable speed fans–11 unit cooling fans–1 cabinet cooling fan in UltraSiteEDGE BTS OutdoorNo heat exchangers norair-conditionersHeater unit–for cold start (< -10ºC)–optional for UltraSite EDGEBTS OutdoorIndoorOutdoor
Satnam Singh +919893650699142Transmission Interface UnitsTransmission Interface UnitsPDH radio transmission– FXC RRI 2 Flexbus interfaces with2..16 x 2 Mbit/s capacityWire line transmission– FXC E1 & FXC E1/T1 4 E1 (or T1) interfaces– FC E1/T1 1 E1 or T1 interfaces
Satnam Singh +919893650699143Power Consumption with GSMPower Consumption with GSMTRXsTRXsBTS type With VACWith VDCIndoor 3.2 kW2.7 kW3.4 kW2.9 kWOutdoor1.8 kW1.5 kWMidi IndoorMidi Outdoor 2.2 kW 2.5 kWMaximum configurations with– GSM 1800 / GSM 1900– 12 TRX in Indoor and Outdoor– 6 TRX in Midi Indoor– full output power in alltimeslots– 1 transmission unit (no radios)Power supply redundancy– with DC full redundancy for 1-12 TRX configurations– with AC full redundancy for 1-6 TRX configurations– number of microwave radios may cause limitationsNominal power consumption:GSM 900 TRX ~ 200 WGSM 1800 TRX ~ 220-230 WGSM 1900 TRX ~ 220-230 W
Satnam Singh +919893650699151Material req. for installationMaterial req. for installation• TRANSCEIVERConsists of two parts:– Transceiver RF Unit– Transceiver Baseband Unit– Consists of one transmitter, one mainreceiver and one diversity receiver
Satnam Singh +919893650699153DUAL BASEBAND UNITDUAL BASEBAND UNITDual Baseband Unit (1-6 units)– Performs DSP functions– Consists of two independent Transceiver BasebandModules– Each Baseband module independently supports itsown Transceiver RF Unit.– Each module independently controls its ownfrequency hopping function
Satnam Singh +919893650699154DUAL BASEBANDDUAL BASEBAND99584316B B 2 A 1 1B B 2 A 1 1S T A T U SS T A T U SAABB
Satnam Singh +919893650699155DUAL BASEBANDDUAL BASEBANDF-bus signalsClock andControl signalsD-bus signalsUplink andDownlink signalsSection AD-busInterfaceSection BD-busInterfaceSection AControlBlockSection BControlBlockSection ADSP BlockSection BDSP BlockF-bus for bothSection A andSection B
Satnam Singh +919893650699156DUAL DUPLEXDUAL DUPLEX– Performs duplex operation of the TX and RX signalsinto a common antenna– Provides filtering and amplification for main anddiversity receive signals– Contains variable low and high gain LNAs foroptimal amplification of the receive signal from theoptional masthead amplifier– Sub-banded for the GSM 1800 to increase TX/RXseparation and achieve better performance
Satnam Singh +919893650699157DUAL DUPLEXDUAL DUPLEX99614746Combines outputs from GSM 900 and GSM 1800 DDUsor RTCs into one antenna feeder
Satnam Singh +919893650699158DUAL BAND DUPLEXDUAL BAND DUPLEX99614797AntennaRX/TXGSM1800bandRX/TXGSM900band
Satnam Singh +919893650699159COMBINERCOMBINERWideband Combiner (0-9 units)– Combines the output of two transmitters into oneantenna (with 1 WBC)– Combines the output of four transmitters into oneantenna (with 3 WBC)Remote Tune Combiner (0-2 units)– Combines the output of up to six transmitters into oneantenna
Satnam Singh +919893650699162MULTICOUPLERMULTICOUPLER Distributes RX signals to the TRX RF units Performs signal splitting for both main anddiversity branches– 2-way Receive Multicoupler (0-6 units) Used in most wideband combining or combining by-passconfigurations– 6-way Receive Multicoupler (0-2 units) Used in conjunction with the RTC configuration
Satnam Singh +919893650699164MASTHEAD AMPLIFIREMASTHEAD AMPLIFIRE– Provide 33 dBRX gain for theGSM 1800/GSM1900 BaseStations– Provide 32 dBRX gain for theGSM 900 BaseStations
Satnam Singh +919893650699165BIAS-TEEBIAS-TEE– Provides DC power to theMHA via an RF cable– Two versions of Bias-Teeavailable: Bias-Tee without VSWRantenna monitoring Bias-Tee with VSWRantenna monitoring Bias-Tee with VSWRmonitoring– Checks the condition of theantenna line– Creates alarm if measuredparameters exceed the limits– Can be used with or withoutthe MHA Bias-Tee without VSWRmonitoring– No VSWR monitoringcapabilities– Solely used with the MHA
Satnam Singh +919893650699167TRANSMISSION UNITTRANSMISSION UNIT Interconnects UltraSite BTSs Connects other components of the network such as BSCs,and other BTSs through the Abis interface. Transmission media can be either a radio linktransmission, E1/T1 wire line transmission, or a fibreoptic transmission (STM-1) UltraSite BTS supports 16, 32,and 64 kbits/sec data ratesfor transceiver RF signaling via Abis interface O&M signaling data rate can be 16 or 64 kbits/s
Satnam Singh +919893650699168TRANSMISSION UNITTRANSMISSION UNITFC E1/T1 (Wire line transmission)– No cross-connection capability– Only 1 FC E1/T1 unit is allowed perBTS cabinet– Provides 1x2 Mbit/s 75/120 ohms OR1x1.5 Mbit/s 100 ohms interfaces
Satnam Singh +919893650699169TRANSMISSION UNITTRANSMISSION UNITRXlineT X li n eRX/TXline7 5 1 2 0 / 1 0 0 99591936
Satnam Singh +919893650699170TRANSMISSION UNITTRANSMISSION UNITFXC E1 and FXC E1/T1 (Wire line transmission)– Provides cross-connection capability at 8 kbit/s– Supports grooming, branching and loop protection– FXC E1 4x2 Mbit/s interfaces 4 coaxial 75 ohms TX/RX interfaces– FXC E1/T1 4x2/1.5 Mbit/s interfaces 4 twisted pair 120/100 ohms TX/RX interfacesRX/TX (Flexbus radio 2)RX/TX (Flexbus radio 1)
Satnam Singh +919893650699171TRANSMISSION UNITTRANSMISSION UNITFXC STM (SDH Fibre Optic RadioTransmission)– FXC STM-1 Optical interface with 63 x 2 Mbit/s– FXC Bridge Always used with FXC STM-1 for BTS internal 21x2 Mbit/sadd/drop capacity– 2 optical STM-1 interfaces– Add and drop functionality– Loop and equipment protection
Satnam Singh +919893650699172TRANSMISSION UNIT fxc stmTRANSMISSION UNIT fxc stmOpticalSTM-1interface2OpticalSTM-1interface1TXRXTXRXPowerinterface2Powerinterface100133344
Satnam Singh +919893650699173TRANSMISSION UNIT fxc stmTRANSMISSION UNIT fxc stmQ interfaceX
Satnam Singh +919893650699174BOIBOIBase Operationand Interface units(1 unit)– Responsible for thecontrol functionscommon to all otherunits such as O&Mfunctions, main clockfunctions, andexternal alarmscollection00129021BOIABOIASTATUSSTATUSRESETRESETLMPLMPFCLKFCLK13 MHz13 MHzMONITORINTERFACEMONITORINTERFACE
Satnam Singh +919893650699175POWER SUPPLYPOWER SUPPLY PWSA (AC)– Operates on AC inputpower and provides theDC output power voltage– BTS can accommodate upto 2 AC power supplies– PWSA supports fullredundancy up to 6 TRXconfiguration– Provide power feed to theMHAs99584258R(FLT)Y(STANDBY)G(OPR)
Satnam Singh +919893650699176POWER SUPPLYPOWER SUPPLY PWSB (1-3 units)– Operates on DC inputpower and provides theDC output power voltage– BTS can accommodate upto 3 DC power supplies– PWSB Supports fullredundancy for up to 12TRX configuration– Provide power feed to theMHAsR(FLT)Y(STANDBY)G(OPR)99584285
Satnam Singh +919893650699177TEMPRATURE CONTROL SYSTEMTEMPRATURE CONTROL SYSTEM Controls– Door mounted Cabinet Cooling Fan (1) part of the Outdoor Application Kit(OAKA)– Unit fans (11) of the cabinet core– BOIA unit controls the speed of the fan units according to the temperatureinformation from other units– Cooling is performed depending on the temperature of the particular unit Heater Unit (1)– Needed in the Outdoor BTS cabinet to cold start when the operating temperatureis in the range of -10 and -33oC (+14 and -27oF)– Maintain interior cabinet temperature
Satnam Singh +919893650699180UNIT FANSUNIT FANS3 Unit fans(Transceiver area)3 Unit fans(Transceiver or IBBU area)NOTE:11 Unit fans per cabinet1 Unit fan(BB2x, BOI)CabinetInterfaceArea for installation ofWCxx/ DVxx or RTxx1 Bottom RF Filter unit fan(Horizontal mounting,notused with IBBU configuration)1 Top RF Filter unit fan(Horizontal mounting)2 Unit fans(Power supply area)
Satnam Singh +919893650699181ELECTRICAL REQUIREMENTELECTRICAL REQUIREMENTTYPE OF POWER SUPPLY BATAACPWSAACPWSBDCNominal Voltage 208-230 V 208-230 V -48 / 60 VPermitted Voltage Range 166-276 V 166-276 V -36 to-72VAC Voltage frequency range 50-60Hz 50-60Hz N/AConfiguration: Input voltage Circuit Breaker /Fuse Rate:External DC supply DC -48 V 125AExternal DC supply DC -60 V 100AIBB + 6 TRX AC 230 V 3 X 16AIBB + 6 TRX + Heater AC 230 V 3 X 25ASSU + 12 TRX AC 230 V 3 X 25ASSU + 12 TRX + Heater AC 230 V 3 X 35AConfiguration Typical Watts Maximum watts Heat dissipation / W1 TRX TRX alone 190 295 1681 BTx Booster alone 310 391 2016 TRX With Cabinet 2300 240212 TRX With Cabinet 3900 48031BATA Rectifier 1444
Satnam Singh +919893650699182InstallationInstallationProperty Value Connector TypeAntenna Connectors 6 + 6 optionalMax. 48dBm / TRX7/16 (DIN) femaleAC Supply 166 - 276 V Screw latch 0.5…16mmDC Supply - 36 to - 72V Screw latch 16…50mmGrounding ≤ 10 Ω. Busbar, 5 and 8mmscrewESD StudExternal Alarm s And Controls TTL D - 37 pin or optionalscrew latchFrame Number, Frame Clock,Mains and SISU alarm inputRS - 485 D - 15 pinFrame Number, Frame Clock,Mains and SISU alarm outputRS - 485 D - 15 pinAbis 2 Mbit/s (E1) or 1.5Mbit/s (T1) PCMTQ female for 120ohm / BT43 femalefor 75 ohmDTRU FXC RRI Radiolink i/o TNCQ1 Interface -SISU RS - 485 TQQ1 Interface RS - 485 TQMMI / ILMT RS - 232 BQ13 MHz test clock At BOI front panel 50 ohm SMB femaleTest FCLK At BOI front panel 50 ohm SMB femaleTest / Monit or Interface BOIA unit LVTTL D - 25 female
Satnam Singh +919893650699183CABLE ENTRY BLOCKCABLE ENTRY BLOCKNut (7x)BracketCaptivebolt (7x)Roof hinge pin,spring loaded(2x)Top of cabinet withcover removedCable entryblock, 6 sections
Satnam Singh +919893650699184EXTERNAL INTERFACEEXTERNAL INTERFACECabinetinterfaceInput/OutputQx connectors to be changed to D-9External interfaceExternal Alarms InputsControl OutputsQ1_, Q1_2, Q1_SSS
Satnam Singh +919893650699185EXTERNAL INTERFANCEEXTERNAL INTERFANCECabinetInterfaceCustomerInterfaceSite SupportInterfaceEMC Cover forTransmission units12 TX/RX Antennas(also 6 on back)as requiredAbis Interfaceaccess toTransmission UnitDC PowerInput - Right side(AC Powerinput - Left side, optional)
Satnam Singh +919893650699188GROUNDING CONNECTIONGROUNDING CONNECTIONCabinetground cableCabinetground cableCRMA backAntenna boxM8M5Ground nutGround boltGround lugTop view of cabinet Side view of cabinetCabinetground cableBack coverAntenna box
Satnam Singh +919893650699189AC SINGLE PHASE POWER CONNECTIONAC SINGLE PHASE POWER CONNECTIONL1L2L3NPEAC Powerinput cableShorting barNOTE: Power input wiring must adhere to local codes.L1, L2, L3 (Short Circuited)=Phase 1N= Phase 2, PE= Ground
Satnam Singh +919893650699210Steps1. Connect the LMP cable.2. Power on the UltraSite EDGE BTS.3. Install BTS Manager.4. Install BTS Hub Manager.
Satnam Singh +919893650699211Commission the UltraSite EDGE BTSCommission the UltraSite EDGE BTSCommission the UltraSite EDGE BTS with IBBU.a. Check the BIOS.b. Upgrade the BIOS.c. Upgrade CCUA software.d. Prepare to commission with PSM Node Manager.e. Connect to PSM Node Manager remotely.f. Connect to PSM Node Manager locally.g. Enter system type and set up details.h. Enter product code, serialisation and configuration details for SiSSnode.i. Enter documentation, site details and cabinet mechanics details.j. Enter product code and serialisation details for rectifiers.k. Enter product code and serialisation details for batteries.l. Enter product code and serialisation details for climatic controlunit.m. Check the configuration and complete commissioning.n. Print a commissioning report.o. Check power management settings.p. Check climatic control settings.q. Check system settings.r. Check identifications.
Satnam Singh +919893650699212Before you start Before commissioning, the physical installationof the BTS (units, cabling, antennas and radios)must be complete. Steps 1. Connect the LMP cable. 2. Power on the UltraSite EDGE BTS. 3. Set the BOIx unit 13 MHz clock. 4. Install BTS Manager. 5. Install BTS Hub Manager. 6. Install PSM Manager. 7. Commission the BTS.
Satnam Singh +919893650699213BTS Manager Nokia BTS Manager hasthe following mainfeatures: auto-detected base stationhardware in a graphicalEquipment view support for transmissionconfiguration advanced BTS diagnosticsand alarm management BTS testing Commissioning Wizard
Satnam Singh +919893650699214LMP CABLE CONFIGRATIONLMP CABLE CONFIGRATION Steps 1. Remove the protective coverfrom the LMP port on theBOIx for GSM/EDGEconnection. 2. Connect the D9 femaleconnector to the PC. 3. Connect the D9 maleconnector to the LMP port onthe BOIx for GSM/EDGEconnection.LMP cable conenction