Mobile CommunicationsOverview

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Definition Enjoy communication services while movingA mobile communication link is a communication link in which at least one terminal is mobile

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PLMNPublic Land Mobile NetworkA generic term for a mobile wireless network that is centrally operated and administrated by an organization and uses land-based radio frequency transmitters or base stations as network hubs. PLMNs can stand alone and interconnect with one another or connect to a fixed system such as the PSTN. Cellular phones and mobile Internet access are two common uses of a PLMN

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1GFirst Generation wireless technology (1G) is the original analog, voice-only cellular telephone standard, developed in the 1980s. Analog cellular service is being phased out in most places worldwideExamplesNMT (Nordic Mobile Telephone), used in Nordic countries, Eastern Europe and RussiaAMPS (Advanced Mobile Phone System) used in the USTACS (Total Access Communications System) in the UKJTAGS in Japan, C-Netz in West Germany, Radiocom 2000 in France, and RTMI in Italy.

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2GSecond generation of mobile wireless communication technology (digital)Can be divided into TDMA-based, and CDMA-based standardsAllows slow data communication, but its primary focus is voiceExamplesGSMCDMA

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2.5GThe bridging technology between 2G and 3GA digital communication allowing e-mail and simple Web browsing, in addition to voice.ExamplesGPRSWiDEN

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3GThird generation of wireless communication technologiesSupport broadband voice, data and multi-media communications over wireless networksExamplesCDMA2000UMTS

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3.5G Generally refers to the technologies beyond the well defined 3G wireless/mobile technologiesHSDPAHigh Speed Downlink Packet AccessCurrently considered as the primary 3.5G technologySoftware upgrade of WCDMAProvides high speed broadband wireless access

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4G The next generation of technology for high-speed wireless communicationsCurrently in research and development stageWill be designed for new data services and interactive TV through mobile network

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GSM, GPRS, and UMTSGSMA digital mobile radio standard developed for mobile wireless voice communicationsGPRSAn extension of GSM networks that provides mobile wireless data communications UMTSAn extension of GPRS networks that moves towards an all-IP network by delivering broadband information including commerce and entertainment services to mobile users via fixed, wireless and satellite networks

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1xRTT1xRTT is a cellular data technology for CDMA networks. RTT stands for Radio Transmission Technology1xRTT has a theoretical maximum of 144 Kbps of bandwidth, but achieves a practical throughput of only 50 to 70 Kbps in the real world.

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1xEV-DO 1xEV-DO, also known as Evolution Data Optimized (EV-DO)A 3G cellular data technology for cellular phones, networks and handheld devicesIts bandwidth is up to 3.1Mbps

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1xEV-DV 1xEV-DV, also known as Evolution Data/Voice (EV-DV)A 3G cellular data technology for cellular phones, networks and handheld devicesIts bandwidth is up to 3.1Mbps

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PCSPersonal Communications Service, the U.S. Federal Communications Commission (FCC) term used to describe a set of digital cellular technologies being deployed in the U.S. Work over CDMA (IS-95), GSM, and North American TDMA (IS-136) air interfacesCompletely digital Operate at the 1900MHz frequency range They can be used internationally A 2G mobile communications technology.

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3GPP / 3GPP2The 3rd Generation Partnership Project (2)A collaboration agreement that was established in December 1998A co-operation between ETSI (Europe), ARIB/TTC (Japan), CCSA (China), ATIS (North America) and TTA (South Korea)The scope of 3GPP was to make a globally applicable third generation (3G) mobile phone system specification within the scope of the ITU's IMT-2000 project3GPP specifications are based on evolved GSM specifications, now generally known as the UMTS system.3GPP2, in practice, is the standardization group for CDMA2000, the set of 3G standards based on earlier 2G CDMA technology

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A-KeyA-key is a secret number issued to a cellular phone that is used in conjunction with a subscriber's shared secret data information for authentication

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Air InterfaceIn wireless communications, the air interface is the radio frequency (RF) part of the network that transmits signals between base stations and end-user equipment. The air interface is defined by specifications for a specific format such as GSM, cdma2000, GPRS, or UMTS

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APAccess PointWLAN transceiver or "base station" that can connect a network to one or many wireless devices. APs can also bridge to one another

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BasebandBaseband is the transmission of a digital or analogue signal at its original frequencies and in its original form before being changed by modulation

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BSBase StationA transmitter and receiver serves as a bridge between all mobile users in a cell and connects mobile calls to the mobile switching centre

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BSCBase Station ControllerA device and software associated with a base station that permits it to register mobile phones in the cellassign control and traffic channelsperform handoff and process call setup and termination

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BSICBase Station Identity CodeA unique code contained in messages on the broadcast channels of a cell or base station that uniquely identifies the base station.

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BSSThe Base Station SubsystemThe section of a cellular network which is responsible for handling traffic and signalling between a mobile phone and the Network Switching SubsystemCarries out transcoding of speech channelsallocation of radio channels to mobile phonesPagingquality management of transmission and reception over the Air Interface, and many other tasks related to the radio network

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Cellular SystemIn wireless communications, cellular refers most basically to the structure of the wireless transmission networks which are comprised of cells or transmission sites. The purpose of this division is to make the most use out of a limited number of transmission frequencies. Each connection, or conversation, requires its own dedicated frequency, and the total number of available frequencies is limited. To support large number of simultaneous conversations (more than the number of available frequencies), cellular systems allocate a set of number of frequencies for each cell. Two cells can use the same frequency for different conversations as long as the cells are not adjacent to each other. For digital communications, several competing cellular systems exist, including GSM and CDMAThe terms "cellular phone" or "cell phone" are used interchangeably to refer to wireless phones

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CellIn wireless communication, Cell is the geographic area encompassing the signal range from one base stationWireless transmission networks are comprised of many hexagonal, overlapping cell sites to efficiently use radio spectrum for wireless transmissions. Basis for the term "cellular phone

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Cell SiteCell Site, also called the Base Station, is the local cellular tower and radio antenna (including the radios, controller, switch interconnect, etc.) that handles communication with subscribers in a particular area or cell. A cellular network is made up of many cell sites, all connected back to the switch via landline or microwave.

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ChannelIn wireless communication, a channel describes a communications path between two systems. They may be either physical or logical depending on the application An RF channel is a physical channel, whereas control and traffic channels within the RF channel would be considered logical channels Downlink (forward) is the transmission path from the base station down to the mobile stationUplink (reverse) is the transmission path from the mobile station up to the base station

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DSSSDirect-Sequence Spread SpectrumUsed in WLAN 802.11 and 802.11b physical layerMultiplies a "noise" signal to the data being transmitted This noise signal is a pseudorandom sequence of 1 and -1 values, at a frequency much higher than that of the original signal, thereby spreading the energy of the original signal into a much wider band.

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Eb/N0 Bit Energy-to-Noise DensityThe ratio of bit energy to noise densityUsed to specify the lower limit of operation in most digital communications systems andmeasure radio channel performance

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FadingFading is the variation in signal strength from its normal valueFading is normally negative and can be either fast or slowIt is normally characterized by the distribution of fades, Gaussian, Rician, or Rayleigh

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Handoff or HandoverThe transfer of a cellular phone transmission from one radio frequency within a cell to another radio frequency in an adjacent cell. Handoffs occur when a cellular phone user passes out of the range that the cell can handle and into another cells range, and the signal is passed from one base station to the next. The handoff is transparent to the user and typically will not result in a loss of service unless the user moves out of range of a cells base station. The transition and the process required to make the transition are both referred to as the handoff.

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Handoff (cont)Soft handoffIt is a process of establishing a link with a target sector before breaking the link with the serving sectorSofter handoffLike the soft handoff, but the handoff is occurred between multi-sectors in the same base stationHard handoffHard handoff occurs when the two sectors are not synchronized or are not on the same frequency. Interruption in voice or data communication occurs but this interruption does not effect the user communication

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Transmission TechniquesCDMATDMAFDMATraffic channels: different users are assigned unique code and transmitted over the same frequency band, for example, WCDMA and CDMA2000Traffic channels: different time slots are allocated to different users, for example, GSM and DAMPSTraffic channels: different frequency bands are allocated to different users,for example, AMPS and TACS

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Development of Mobile CommunicationsEDGE: Enhanced Data rates for Global Evolution or Enhanced Data GSM Environment or Enhanced Data rates for GSM Evolution A faster version of GSM wireless service that enables data to be delivered at rates up to 384 KbpsAlthough technically a 3G network technology, it is generally classified as the unofficial standard 2.75G, due to its slower network speed

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Difference of 3G StandardsCWTS: China Wireless Telecommunication StandardTD-SCDMA: Time Division Synchronous CDMA

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CDMAPrinciples

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Development of CDMA SystemHigher spectrum efficiency and network capacity Higher packet data rate and more diversified services Smooth transit to 3G

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CDMA2000 Network Structure (1) Mobile Station (MS)The mobile subscriber equipment, which can originate and receive calls and communicate with the BTS.Base Transceiver Station (BTS)Transmits and receives radio signals, realizing communication between the radio system and the mobile station.Base Station Controller (BSC)Performs management and control of BTS, call, mobility, handoff, power, and radio resourcesPacket Control Function (PCF)Performs the radio packet connection managementPacket Data Service Node (PDSN)Performs the switching of packet data services of mobile subscribers. One PDSN can be connected to multiple PCFs. It provides the interface between the radio network and the packet data network.

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CDMA2000 Network Structure (2) Home Location Register (HLR)A database for mobile subscriber managementResponsible for storing subscription information, MS location information, MS identity numbersAC (Authentication Center) A database that is physically combined with the HLR. A functional entity of the HLR, specially dedicated to the security management of the CDMA system. It stores the authentication information. It also prevents unauthorized subscribers from accessing the system

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CDMA2000 Network Structure (3)Home Agent (HA)An HLR like agent located at the home network of the Mobile NodeBroadcasts the accessible information of MNTunnels data for the MN when it is in a foreign networkMobile Switching Center (MSC) The MSC implements the service switching between the calling and called subscribers. One MSC is connected with multiple BSCs, and can also be connected to the PSTN, ISDN or other MSCs.Visitor Location Register (VLR) It is a dynamic database, stores the temporary information (all data necessary to set up call connections) of the roaming subscribers in the local MSC area

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CDMA 2000 Network Structure (4)

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Direct Spread (DS)Direct Sequence Spread spectrum system mixes the input data with a fast sequence and transmits a wideband signal. The spreading sequence is independently regenerated at the receiver and mixed with the incoming wideband signal to recover the original information.TransmissionReceiving

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Spectrum-domain Analysis

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Communication ModelSource codingChannel CodingModulationRF transit1011011 1011011 BitSymbolChipReverseForwardSource DecodingChannel DecodingSpread De-SpreadDemodulationRF receiveScrambling Unscrambling10011000111001101001

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Source CodingThere are 3 types of source coding in CDMA 2000 system:8K QCELP13K QCELPEVRCCharacteristic:Support voice activityVocoder: voice encoder

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Channel Coding: ConvolutionConvolution code or TURBO code is used in channel encoding (send some redundant bits)Encoding efficiency= (total input bits / total output symbols)RegisterMUX0011000100100111Channel coding is for reliability issues (fading and interference impact)

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Channel Coding: Interleaving123456781234567812345678Input:Output:Transmission directionInterleaverTransmission directionWrite by rowRead by column

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Scrambling and SpreadingM Sequence for scramblingLong CodeShort CodeWalsh Code for spreading

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Scrambling and Spreading: Long Code The long code is a PN sequence with period of 242-1chipsThe functions of a long code: Scramble the forward CDMA channelControl the insertion of power control bitSpread the information on the reverse CDMA channel to identify the mobile stationsEach MS uses a unique User LCLong code is a period sequence. Generated at 1.2288 Mcps, this sequence requires 41 days, 10 hours, 12 minutes and 19.4 seconds to complete.

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Scrambling and Spreading: Short Code Short code is a PN sequence with period of 215 chipsSequence with different time offset is used to distinguish different sectors512 PN offsets are available to identify the CDMA sectors

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Scrambling and Spreading: Walsh Code64-order Walsh function is used as a spreading function and each Walsh code is orthogonal to otherA Walsh can be presented by Wim where ith (row) is the position and m is the order. For example, W24 means 0101 code in W4 matrixWalsh code is used to spread the forward traffic channelWalsh Code is one kind of orthogonal code.

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MS: Which BTS ? 512 total PN available to identify the 512 sectors/BTSs. BTS BBTS APN 4PN 108BTS CPN 52

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Each MS has unique Walsh codeMS-AMS-BMS-CMS-DMS-EMS-FMS-GMS-H0000000. A0101010 B0000111 C0101010 0MS-B: Which is my signal?

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BTS: Which MS?A PN sequence (long code) is used to Spread the information on the reverse CDMA channel and identify the MS MS-AMS-BMS-CMS-DMS-EMS-FMS-GMS-H

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ModulationQPSKHPSKFor CDMA 2000QPSK: Quadrature Phase Shift Keying HPSK: Hybrid Phase Shift Keying

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Power Control: Far/near problem no power controlafter power controlIf every mobile station transmits at the same power level, the base station could receive a very strong signal from a nearby mobile station, together with a weaker signal from a distant one; and the weaker would be drowned by the stronger one.To overcome this problem, different MSs should not send signals with the same power. The purpose of Power Control is to ensure that all signals arrive at the base station at approximately the same level

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Power Control: CDMA is a self-interference systemAll mobiles transmit at the same frequency, internal interference generated within the system plays a critical role in determining system capacity and traffic quality. The transmit power from each mobile must be controlled to limit interference

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Power Control ClassificationAccording to the direction Reverse power control Forward power control According to the type Reverse power control Reverse open loop power control Reverse closed loop power control Forward power control Measurement report power control EIB power control Fast power control

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The mobile transmission power is determined by the following factors:Distance from the base stationLoad of the cellCircumstance of the code channels Reverse Open Loop Power ControlThe MS adjusts its transmit power based on total power received in the whole band. If the received power is high/low, the mobile reduces/increases its transmit powerIn open-loop power control, the BS is not involved. The MS determines the initial power transmitted to access the system. Thought the open-loop power, mobile should access the system with the most reasonable power to reduce interference to others. The prime goal in CDMA system is to transmit just enough power to meet the required performance objective

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Reverse Closed Loop Power ControlThe reverse link closed-loop power control mechanism is much faster than the open-loop method It consists of two parts: inner-loop power control and outer-loop power control. The inner-loop power control keeps the mobile as close to its target (Eb/Nt) set point as possible, whereas the outer-loop power control adjusts the base station target (Eb/Nt) set point for a given mobile.

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Fast Forward Power ControlDuring the communication of the mobile station, the mobile station measures the Eb/Nt value of the received forward traffic channels, compares them with the threshold and orders the base station to increase or decrease the transmission power to keep constant the traffic channel Eb/Nt

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RAKE ReceiverDelays on the reflected path may add to (strengthen) or subtract from (fade) the main path. Solution: multiple receive antennas or frequency hopping.

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Pilot Set (1)An MS always track the pilot channel of different BTSs (or sectors).It determines the pilot signal strength and if it is strong, reports to the BSC through the current BTS for new connectivityMS arranges the different detected Pilots into groups or SetsActive setA set of pilots which are being used by MS for communication. A CDMA system can have up to 6 pilots in this setCandidate setPilots which are not being used by MS but have enough signal strength that MS can use it for connectivityNeighbor setPilots which are of neighboring BTSs to the serving one.Once a good signal is received from any neighbor pilot, MS updates his information and put this pilot in to the candidate or active set.Remaining Set

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Pilot Sets (2)

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Soft Handoff And Softer HandoffMS can keep traffic channel with two or more sectors.Soft handoffinvolves traffic channel from more than one BTS and Multi-path combination in the BSC.Softer handoffinvolves traffic channel from two or more sectors of one BTS and Multi-path combination in the BTS.

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Dynamic Soft Handoff

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Definition of Coverage Areas

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MIN/IMSI (identity/international mobile subscriber identity )Mobile subscriber identity/international mobile subscriber identityFor example, 0907550001/46003090755000115 digits3 digits2 digitsIMSIMCCMNCMSINNMSIMCC: Mobile Country Code, 460 for China.MNC: Mobile Network Code03 used in Unicom CDMA.

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MIN/IMSIIMSI is the only number to identify a mobile user in a CDMA digital public land cellular mobile communication network. This code is valid in all locations including a roaming areaIMSI adopts E.212 coded system.IMSI is stored in the mobile station/UIM card, HLR and VLR and transmitted on a wireless interface and MAP interface.

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ESN (Electronic Serial Number )A unique Electronic Serial Number (ESN) is used to identify single MS. An ESN includes 32 bits and has the following structure:For example, FD 03 78 0A (the 10th Motorola 378 mobile phone)The equipment serial number is allocated by a manufacturer.

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MDN (Mobile directory number)CC+MAC+H0H1H2H3+ABCDInternational mobile subscriber DNNational valid mobile subscriber number subscriber numberIs the dialed no when a mobile user is in home network MDN adopts E.164 coded system.MDN is stored in HLR and VLR, and transmitted on a MAP interfaceCC: country code, e.g., 249MAC: Mobile Access Code, network number plan adopted in home networkABCD: mobile user number, allocated by various HLRs.H0H1H2H3 regulator dependent

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TLDN (Temporary local directory number)+CCMACH0H1H2 ABC+++44TLDN is a number temporarily allocated by the VLR of the visiting office to a visiting mobile user for the sake of network routing when a call is made to a mobile user.TLDN is part of a mobile user MDN and its number structure is shown in the figure: CC: country code MAC: mobile access code H0H1H2: identify a certain MSC/VLR. ABC: defined by MSC/VLR itself.

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Location Area Identity (LAI)PAGING message is broadcast within a local area, the size of which depends on traffic, paging bearer capability, signaling flow , etc.Format: MCC+MNC+LACMCC: Mobile Country Code, 3 digitsMNC: Mobile Network Code, 2 digits. For example, the MNC of Unicom is 03.LAC: Location Area Code, a 2-byte-long hexadecimal BCD code. 0000 cannot be used with FFFE

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Global Cell Identity (GCI)The unique ID of a cell in PLMNFormat: LAI+CICI: Cell Identity, a 2-byte-long hexadecimal BCD code, pre defined by the engineering department. The first 3 digits and the last digit represent the base station number and the sector number respectively. For an omni-directional site, the last digit of CI is 0.For example, 4600301001230 shows base station number 123 contains an omni-directional site

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SID/NIDIn the CDMA2000 1X network, the service area consists of systems and networks that are identified respectively by the system identification (SID) and network identification (NID).The system judges whether the MS is roaming according to the SID and NID.

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Number AnalyzingBTSBSCMSC1/VLRMSC2/VLRBSCBTS13316882234Number Analysis1331688XXXXFind HLRAccording to MDN, get the IMSI that can be used to query VLR LocationAccording to IMSI, allocate TLDN that will be sent back to HLRTransfer TLDN to MSC1With TLDN, connect to MSC2With IMSI, send paging information to BHere is a call for youHLR

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AMPSAdvanced Mobile station System (AMPS) uses 800MHz frequency band .It is widely used in North America, South America and some round-the-Pacific countries.TACSTotal Access Communication System (TACS) uses 900MHz frequency band. There are two versions of TACS: ETACS (Europe) and NTACS (Japan). This standard is widely used in England, Japan and some Asian countries.GSMGlobal System of Mobile Communication (GSM) uses 900MHz frequency band and the system using 1800MHz frequency band is called DCS 1800. GSM originated from Europe and was designed as the TDMA standard of global digital cellular communication. GSM supports 64kbit/s data and can be interconnected with ISDN. GSM adopts FDD duplex mode and TDMA multiple access mode. Each carrier supports 8 channels and uses 200kHz bandwidth. IS-54North America Digital Cell (IS-54) standard uses 800MHz frequency band and is also called D-AMPS. IS-54 is the earlier one in the two North America Digital Cell standards and is specified to use TDMA.IS-95North America Digital Cell (IS-95) standard uses 800MHz frequency band or 1.9GHz frequency band. IS-95 is specified to use CDMA, which becomes the first choice of American PCS network. Currently, there are 54% license bearers using CDMA. CDMA One is the brand name of IS-95. CDMA2000 wireless communication standard evolves based on IS-95.

The 3GPP(Third Generation Partnership Project) was formed in December 1998 as a collaboration agreement bringing together a number of telecommunication standards bodies. These standards bodies are referred to as Organizational Partners. The original aim of the 3GPP was to produce globally applicable technical specifications for third generation mobile systems based on evolved GSM core networks and the radio access technology UTRA (Universal Terrestrial Radio Access). This was subsequently amended to include the maintenance and development of the GSM standards including GPRS and EDGE (Enhanced Data rates for Global Evolution).The 3GPP2 (Third Generation Partnership Project2) is a sister project to 3GPP and is a collaboration agreement dealing with North American and Asian interests regarding third generation mobile networks. It is comprised of five Standards Development Organizations similar to the Organizational Partners in the 3GPP. The partnership is comprised of a number of Technical Specification Groups which meet around ten times per year and are responsible for the following five areas: A-interface system, CDMA2000 , ANSI-41 (American National Standards Institute-41), wireless packet data interworking and services and systems aspects.CWTS(China Wireless Telecommunication Standard ) is another standard of 3G coming from China. This standard can use the same core network with WCDMA system.Both WCDMA and CDMA 2000 system use FDD (Frequency Division Duplex ) technique . Frequency Division Duplex is employed in radio systems to provide an uplink and downlink radio channel between the network and the user. The frequencies separated by a duplex spacing. Users tune between the uplink and downlink frequencies to transmit and receive respectively. TD-SCDMA (Time Division Synchronous CDMA ) works in TDD (Time Division Duplex ) mode. In a Time Division Duplex system a common carrier is shared between the uplink and downlink, the resource being switched in time. Users are allocated one or more timeslots for uplink and downlink transmission. The main advantage of TDD operation is that it allows asymmetric flow which is more suited to data transmission.Development motivation of CDMA2000 EV: Voice and high-speed packet data have different QoS requirements:Voice: low-speed, symmetric, low-speed burstData: high-speed burst, asymmetric, lower BER requirementsWhen evolving into high-speed packet data services, CDMA2000 system minimizes the influence on a base station system and terminal system.Evolution process of CDMA2000 EV: phase 1: 1XEV-DO ( Data Only / Data Optimized )Providing the support for packet data services alone instead of real-time voice services.phase 2: 1XEV-DV ( Data and Voice )Providing non-real time packet data services and real-time voice services

Mobile Station (MS)The MS is the mobile subscriber equipment, which can originate and receive calls and communicate with the BTS.Base Transceiver Station (BTS)The BTS transmits and receives radio signals, realizing communication between the radio system and the mobile station.Base Station Controller (BSC)The BSC implements the following functions:Base Transceiver Station (BTS) control and management, call connection and disconnection, mobility management, stable and reliable radio link provision for the upper-layer services by soft/hard handoff, power control, and radio resource management.Packet Control Function (PCF)The PCF implements the R-P connection management. Because of the shortage of radio resources, some radio channels should be released when subscribers do not send or receive data, but the PPP connection is maintained continuously. The PCF can shield radio mobility for the upper-layer services via handoff.Packet Data Service Node (PDSN)The PDSN implements the switching of packet data services of mobile subscribers. One PDSN can be connected to multiple PCFs. It provides the interface between the radio network and the packet data network.Home Agent (HA)The agent locates at the place where the Mobile Node open its account, receive the registration information from MN. Similar as HLR in mobile network. Broadcast the accessible information of MN. Setup the tunnel between FA&HA. Transfer the data from other computer to the MN via the tunnel.Mobile Switching Center (MSC) The MSC implements the service switching between the calling and called subscribers. One MSC is connected with multiple BSCs. The MSC can also be connected to the PSTN, ISDN or other MSCs. It provides the interface between the radio network and PSTN.Visitor Location Register (VLR) It is a dynamic database, stores the temporary information (all data necessary to set up call connections) of the roaming subscribers in the local MSC area. VLR is used to store the subscriber information of all the MSs in its local area, which can be used to establish the incoming/outgoing call connections, to support basic services, supplementary services and mobility management. Home Location Register (HLR)It is a database for mobile subscriber management, the HLR (Home Location Register) is responsible for storing subscription information (telecom service subscription information and subscriber status), MS location information, MDN, IMSI (MIN), etc. The AC (Authentication Center) is physically combined with the HLR. It is a functional entity of the HLR, specially dedicated to the security management of the CDMA system. It stores the authentication information. It also prevents unauthorized subscribers from accessing the system and prevents the radio interface data from being stolen.

Direct Sequence Spread Spectrum is based on the multiplying of the baseband signal data with a broadband spreading code. The result is termed the chip rate. The characteristics of the broadband spreading code are that of pseudorandom noise. Consequently the receiver synchronized to the code will obtain the narrowband signal. All other receivers will see the spread signal as white noise. In CDMA 2000 1X system, the chip rate is 1.2288Mcps, and the Bandwidth is 1.25MHZ.

Traditional radio communication systems transmit data using the minimum bandwidth required to carry it as a narrowband signal. Direct-Sequence Spread Spectrum systems mix their input data with a fast spreading sequence and transmit a wideband signal. The spreading sequence is independently regenerated at the receiver and mixed with the incoming wideband signal to recover the original data. The de-spreading gives substantial gain proportional to the bandwidth of the spread-spectrum signal. The gain can be used to increase system performance and range, or allow multiple coded users, or both. A digital bit stream sent over a radio link requires a definite bandwidth to besuccessfully transmitted and received. The actual spectrum occupied by a digital signal depends on its bit rate and type of radio modulation (AM, FSK, QPSK, etc.).Source coding can increase the transmitting efficiency.FEC Coding (channel coding) can make the transmission more reliably.Scrambling can make transmission in security.Spreading can increase the capability of overcoming interference.Through the modulation, the signals will transfer to radio signals from digital signals.

Adopted in CDMA system is a QCELP vocoder with variable rates, which is actually a device converting a sound signal into the signal which can be transmitted in a circuit. The method adopted generally in a wire communication system is to first sample (8,000 sample values generated per second) a voice signal with a 8KHZ signal and then implement 8-bit quantization coding for each sample value. Therefore, each voice channel in a wired system has the rate of 64K. However, because the air resource in a wireless system is very precious, a more effective coding mode is needed to use a rate as low as possible in the case where voice quality is guaranteed. QCELP vocoder with variable rates is such a device. The main principles of it are to extract some voice feature parameters when a person speaks and transmit these feature parameters to the peer party. Then,the peer party will recover the voice with these parameters based on the promise between the two parties. Thus, a far lower rate is needed. Lets give an example. The information of a triangle can be transmitted from one place to another in two ways: one is to obtain some points by means of sampling and transmit the information of these points to the peer party. The two parties connect these points to obtain a triangle. The other is to transmit the length of a side and the degrees of two angles of this triangle to the peer party, who can likewise recover this triangle based on these pieces of information. Obviously, there is far less information to be transmitted in the second method. What a vocoder does is similar to the latter method, but what a vocoder actually does is more complex than this. But the principles are the same.Meanwhile, the codes transmitted from the transmit end to the receive end and describing voice feature parameters vary with the rhythm or loudness of a speech. In summary, variable rates mean that a vocoder can change its own code rates based on the loudness or rhythm of a speech to further reduce a code rate. Thus, a code with a higher rate will be adopted when there is a high voice while a code with a lower rate will be adopted when there is a low voice. In a silent period (when a person makes no sound during a speech), the lowest code rate will be adopted. Thus, a code rate can be decreased to reduce the interference with other users.

During the transmission, there are many interferences and fading. To guarantee reliable transmission, system should overcome these influence through the channel coding which includes convolution and interleaving. The first is convolution that is used for anti-interference. Through the technology, many redundant bits will be inserted in original information. When error code is caused by interference, the redundant bits can be used to recover the original information.In CDMA 2000 1X network, both convolution code and TURBO code are used. Convolution code applies to voice service while TURBO code applies to high rate data service. The performance of a Turbo code is superior to that of a convolution code. But the time delay is also higher than convolution code. In channel coding , there is another technology named interleaving. Communications over radio channel are characterized by fast fading that can cause large numbers of consecutive errors. Most coding schemes perform better on random data errors than on blocks of errors. By interleaving the data, no two adjacent bits are transmitted near to each other, and the data errors are randomized.Actually, interleaving is used to overcome fast fading.

Scrambling is the processing of making signals randomization. M sequence can perform this function in CDMA2000.Spreading is the processing that can wide the spectrum. Walsh code can perform the function in CDMA2000.

In CDMA system, user information is encrypted by means of scrambling. Long code is used for scrambling on the Forward CDMA Channel and spreading on the Reverse CDMA Channel . That is meaning in a reverse direction, through different long code offset the base station can identify different mobile station. Each mobile station uses a unique User Long Code Sequence generated by applying a mask, based on its 32-bit ESN, to the 42-bit Long Code Generator which was synchronized with the CDMA system during the mobile station initialization. Portions of the Users Long Codes generated by different mobile stations for the duration of a call are not exactly orthogonal but are sufficiently different to permit reliable decoding on the reverse link.Long code is a period sequence. Generated at 1.2288 Mcps, this sequence requires 41 days, 10 hours, 12 minutes and 19.4 seconds to complete.

In one network, usually a MS is surrounded by many base stations with sectors. If MS wants to get service from system, first MS should distinguish different signals from different sectors. In CDMA system, all the sectors use the same frequency ,so MS can not get any information thought the frequency. Here short PN sequences are used. As we know, there are 215 offsets in one period. One sector will be allocated one offset that is called PN. So we can get the result that MS uses different PN to discriminate different sector. In CDMA system, the chip rate is 1.2288Mcps that is fixed. So one short code can also stand for 1/1.2288M seconds. We can get another useful conclusion that we will use in PN planning: 1 chip is standing for 244 meters. Among the short PN sequence, we define every 64 chips as one unit. So totally there are 512 (215/64) units in the short PN sequence. Actually these units are PN information. We also can say there are 512 PN that can be used in one network.Orthogonal codes are easily generated by starting with a seed of 0, repeating the 0 horizontally and vertically, and then complementing the 1 diagonally. This process is to be continued with the newly generated block until the desired codes with the proper length are generated. Sequences created in this way are referred as Walsh code.In forward direction, each symbol is spread with Walsh code. Walsh code is used to distinguish the different channel. For forward channel, Walsh functions are used to eliminate multiple access interference among users in the same cell. On downlink, all Walsh function are synchronized in the same cell and have zero correction between each other. IS95A/B or CDMA2000 RC1RC2 system adopts 64-bit Walsh code to spread one symbol. But upper than the CDMA2000 RC3 (included), system adopts variable length Walsh code to spread one symbol in order to realize different channel rate (from 4.8kbps to 307.2kbps).In reverse link, for IS95A/B or CDMA2000 RC1RC2, every 6 symbols correspond to one Walsh code. For example, if the symbol input is 110011,the output after spreading is W5164 (110011=51).This process is called Orthogonal Modulation. But for CDMA2000 RC39, in the reverse, Walsh code is used to define the types of channel.

QPSK: Quadrature Phase Shift Keying . Phase shift keying in which four different phase angles are used. Sometimes called quadriphase or quaternary phase shift keying. In an actual application, the system implements the modulation in this way: as shown above, I and Q channel sequences in the figure represent two channels of cyclic PN short code sequences. The cyclic period of each channel of PN short codes is 215. For different sectors, there are different starting locations of I and Q sequence cycles (that is to say, different sectors have different time offsets). In this way, different PN short code sequences can be obtained and a mobile station can recognize the information from different sectors.Of course, for IS 95 , both I sequence and Q sequence are the same. So for IS95, actually the modulation is BPSK in forward link and reverse link. But for CDMA 2000, in forward link, the modulation is QPSK ,and in reverse link, the modulation is HPSK ( Hybrid Phase Shift Keying ).In any wireless system ,there is a famous problem named far/near problem. The distributing of subscriber is random. Some mobile stations may be close to the base station, while others may be located far from it. As a result, the path losses and multi-path environments affecting the signals from different mobile stations show a great variability. If every mobile station transmits at the same power level, the base station could receive a very strong signal from a nearby mobile station, together with another signal from a distant one; and the weaker signal would be drowned by the stronger one.To overcome this problem, each mobile station can not send signals with the same power. The technology controlling power is called power control. The purpose of Power Control is to ensure that all signals arrive at the base station at approximately the same level. This requirement makes power control in the reverse direction extremely critical and demanding.

CDMA is an interference-limited system---since all mobiles transmit at the same frequency, internal interference generated within the system plays a critical role in determining system capacity and traffic quality. The transmit power from each mobile must be controlled to limit interference. However, the power level should be adequate for satisfactory traffic quality. The reverse link power control affects the access and reverse traffic channels. It is used for establishing the link while originating a call and reacting to large path-loss fluctuation. The reverse power control includes the open-loop power control and closed-loop power control. The closed-loop power control involves the inner-loop power and the outer-loop power control.The forward link power control (FLPC) aims at reducing the interference on the forward link. The FLPC not only limits the in-cell interference, but it is especially effective in reducing other cell interference. For IS95A, forward power control is based on measurement report. For IS95B, system can support EIB power control. And for CDMA 2000 system , the highest priority is fast power control. Reverse power control is based on the principle that a mobile closer to the base station needs to transmit less power as compared to a mobile that is farther away from base station. The mobile adjusts its transmit power based on total power received in the whole band. If the received power is high, the mobile reduces its transmit power. On the other hand, if the power received is low, the mobile increase its transmit power.In open-loop power control, the base station is not involved. The mobile determines the initial power transmitted to access the system. Thought the open-loop power, mobile should access the system with the most reasonable power to reduce interference to others. The prime goal in CDMA system is to transmit just enough power to meet the required performance objective. But the frequency of open-loop power is only 50HZ that is not fast enough to resist fast fading. So we need anther type power control to solve this problem.

Fading sources in multipath require a much faster power control than the open-loop power control. The additional power adjustment required to compensate for fading losses are handled by the reverse link closed-loop power control mechanism whose frequency is 800HZ. The quicker response time gives the closed-loop power control mechanism the ability to override the open-loop power mechanism in practical application. The closed-loop power control provides correction to open-loop power control. Actually, two independent power control mechanisms work together to overcome interference and fading.The reverse link closed-loop power control mechanism consists of two parts---inner-loop power control and outer-loop power control. The inner-loop power control keeps the mobile as close to its target (Eb/Nt) set point as possible, whereas the outer-loop power control adjusts the base station target (Eb/Nt) set point for a given mobile.There are three types of forward power control. To CDMA 2000, the highest priority is fast power control. Measurement report power control attempts to set each traffic channel transmit power to the minimum required to maintain the desired FER at the mobile. The mobile continuously measures forward traffic channel FER. It reports this measurement to the base station on a periodic basis.After receiving the measurement report, the base station takes the appropriate action to increase or decrease power on the measured logical channel. Usually, this type power control is used in RC1 .For RC2, EIB (Erasure Indicator Bit) power control should be used. For RC2, 1 bit per reverse link frame (the E or erasure bit) is dedicated to confirm the base station whether or not the last link frame was received without error at the mobile. This allows more rapid and precise control offorward link power than the scheme used for RC1.A new fast-forward power control algorithm for the forward link is used in CDMA2000. The standards specify a fast closed-loop power control at 800HZ. During the communication of the mobile station, the mobile station measures the Eb/Nt value of the received forward traffic channels, compares them with the threshold and orders the base station to increase or decrease the transmission power to keep constant the traffic channel Eb/Nt of whole-rate services. Actually the principle is similar with reverse closed-loop power control . Fast-forward power control has the highest priority in RC3 and RC4.

In all the wireless systems, there is a common problem named multi-path that is a form of radio fading caused by the existence of two or more paths between the transmitter and receiver. Delays on the reflected path may add to (strengthen) or subtract from (fade) the main path. Multi-path may be overcome by using multiple receive antennas or frequency hopping. How does an MS detect different BTS (pilots)? That is which BTS (pilot) MS needs to search for connectivity and which BTS (pilot) MS can use in future? An MS always track the pilot channel of different BTSs (or sectors). It determines the pilot signal strength and if the signal is strong then reports to the BSC through the current BTS for new connectivity. To distinguish different pilots of different BTSs/sectors, an MS maintains several lists. Each list contains the relevant pilots. For example a list of pilots which are connected or a list of pilots which are neighbor etc. These lists in fact are the sets of pilots and can be classified in four sets, which are, Active set, Candidate set, Neighbor set and Remaining set. Here also note that all sets have the same frequency but different PN sequence offset. Active set: A set of pilots which are being used by MS for communication. According to the protocol, a CDMA system can have up to 6 pilots in this set. This set is maintained by MS.Candidate set: A set of pilots which are not being used by MS but have enough signal strength that MS can use it for connectivity. This set is maintained by MS.Neighbor set: A set of pilots which are of neighboring BTSs to the serving one. This information is updated to the MS from BS. And MS always tries to search for it. Once the good signal is received from any neighbor pilot, MS updates his information and put this pilot in to the candidate or active set.

Soft handoff: This is a handoff in which the mobile station starts communications with a new base station without interrupting communications with the old one. Soft handoff can only be used between CDMA channels having identical frequency assignments. Soft handoff provides diversity of Forward and Reverse Traffic Channel paths on the boundaries between base stations.Soft handoff, in addition to reducing dropped calls, improves their quality. When the mobile station is in soft handoff, the two or three Forward Traffic Channels it receives contain identical modulation symbols with the exception of the power control subchannel. The mobile station provides diversity by combining these different Forward Traffic Channels.The requirements for a Soft Handoff are the following: all links must be on the same CDMA frequency all links must use the same traffic frame offset (frame staggering)Softer handoff: This is a special case of soft handoff between two or three sectors of the same base station. The DMS-MTX is aware of the softer handoff but does not participate. All the activities are managed by the BTS.

CDMA2000 system can support dynamic soft handoff.This graph illustrates the dynamic soft handoff process. The steps shown in this diagram are:Pilot P2 strength 2 exceeds T_ADD. Mobile station transfers the pilot to the Candidate Set.Pilot P2 strength exceeds [(SOFT_SLOPE/8) * 10 * log10(PS1) + ADD_INTERCEPT/2].Mobile station sends a Pilot Strength Measurement Message. Mobile station receives an Extended Handoff Direction Message, a General Handoff Direction Message or a Universal Handoff Direction Message, transfers the pilot P2 to the Active Set, and sends a Handoff Completion Message.Pilot P1 strength drops below [(SOFT_SLOPE/8) * 10 * log10(PS2) +DROP_INTERCEPT/2 Mobile station starts the handoff drop timer.Handoff drop timer expires. Mobile station sends a Pilot Strength Measurement Message.Mobile station receives an Extended Handoff Direction Message, a General Handoff Direction Message or a Universal Handoff Direction Message, transfers the pilot P1 to the Candidate Set and sends a Handoff Completion Message.Pilot P1 strength drops below T_DROP. Mobile station starts the handoff drop timer.Handoff drop timer expires. Mobile station moves the pilot P1 from the Candidate Set to the Neighbor Set.

IMSI is the only number to identify a mobile user in a CDMA digital public land cellular mobile communication network. This code is valid to all location including a roaming area.IMSI adopts E.212 coded system.IMSI is stored in the mobile station/UIM card, HLR and VLR and transmitted on a wireless interface and MAP interface. Unicom uses MIN-based IMSI. IMSI is a 15-digit decimal number and its number structure is shown in the figure.MCC: Mobile Country Code, 460 for China.MNC: Mobile Network Code03 used in Unicom CDMA.MSIN: Mobile Subscriber Identification Number, a 10-digit decimal number. Unicom requires that MIN is the latter 10 digits of an IMSI, namely, MSIN.For the users of in the original Great Wall network in Unicom, the MSIN number structure is shown below: 3 + H1H2H3 + ABCDEF H1H2H3 equals that in a MDN.ABCDEF is obtained after the scrambling of ABCD in a MDN.For new Unicom users, MSIN is the IRM number resource obtained by China Unicom. Unicom first uses the number segment between 09 1000 0000 and 09 4999 9999 and the number structure is as follows: 09 + M0M1M2M3 +ABCDM0M1M2M3: the same as the H0H1H2H3 in a MDN. (Note: in the number segment first used by Unicom, M0M1M2M3 may be the same as H0H1H2H3. Because the IRM number obtained by China Unicom is a discontinuous number segment. In the number segment used at a late time, M0M1M2M3 and H0H1H2H3 are different.ABCD: user number, to be obtained based on the scrambling of ABCD in a MDN in a certain mode, the scrambling mode to be defined by Unicom headquarters.

IMSI is the only number to identify a mobile user in a CDMA digital public land cellular mobile communication network. This code is valid to all location including a roaming area.IMSI adopts E.212 coded system.IMSI is stored in the mobile station/UIM card, HLR and VLR and transmitted on a wireless interface and MAP interface. Unicom uses MIN-based IMSI. IMSI is a 15-digit decimal number and its number structure is shown in the figure.MCC: Mobile Country Code, 460 for China.MNC: Mobile Network Code03 used in Unicom CDMA.MSIN: Mobile Subscriber Identification Number, a 10-digit decimal number. Unicom requires that MIN is the latter 10 digits of an IMSI, namely, MSIN.For the users of in the original Great Wall network in Unicom, the MSIN number structure is shown below: 3 + H1H2H3 + ABCDEF H1H2H3 equals that in a MDN.ABCDEF is obtained after the scrambling of ABCD in a MDN.For new Unicom users, MSIN is the IRM number resource obtained by China Unicom. Unicom first uses the number segment between 09 1000 0000 and 09 4999 9999 and the number structure is as follows: 09 + M0M1M2M3 +ABCDM0M1M2M3: the same as the H0H1H2H3 in a MDN. (Note: in the number segment first used by Unicom, M0M1M2M3 may be the same as H0H1H2H3. Because the IRM number obtained by China Unicom is a discontinuous number segment. In the number segment used at a late time, M0M1M2M3 and H0H1H2H3 are different.ABCD: user number, to be obtained based on the scrambling of ABCD in a MDN in a certain mode, the scrambling mode to be defined by Unicom headquarters.

MDN is the number the caller needs to dial when a mobile user in home network is the called. MDN adopts E.164 coded system.MDN is stored in HLR and VLR, and transmitted on an MAP interface. The structure of a MDN is shown in the figure.CC: country code, 86 used in China.MAC: Mobile Access Code, network number plan adopted in home network, 133 used in China.H0H1H2H3: HLR identity number, allocated by Unicom headquarters on a uniform basis.ABCD: mobile user number, allocated by various HLRs.H0H1H2H3 China Unicom allocation plan:This allocation plan takes into consideration IRM (international roaming MIN) number resource and user development prediction controlled by China Unicom. In actual applications, the starting point should be H0 equal to 0~9 and MDN can be gradually used. Currently, the number segment with H0 equal to 0 is used by users in the original Great Wall network and includes TLDN number and user number. For allocation arrangement, refer to the requirements of the Great Wall network. The numbers with H0 equal to 1~9 are used new users. The allocation plan of H0H1H2H3 is decided by Unicom headquarters on a uniform basis.

TLDN is a number temporarily allocated by the VLR of the visiting office to a visiting mobile user for the sake of network routing when a call is made to a mobile user.TLDN is part of a mobile user MDN and its number structure is shown in the figure: CC: country code, 86. MAC: mobile access code, 133. H0H1H2: identify a certain MSC/VLR. ABC: defined by MSC/VLR itself.