ORA000003 CDMA2000 Principle ISSUE4.0

HUAWEI, Mobile Network Curriculum Development Section

ObjectivesAfter this presentation, you will be familiar with:

the development of mobile communication system the structure of CDMA2000 network the number planning in CDMA2000 network the techniques used by CDMA system including: source coding, channel coding, interleaving, scrambling, spreading and modulation etc.power control, soft handoff, RAKE receiverF-PCH,F-PICH,F-SYNCH,F-FCH,F-SCH,R-ACH,R-PICH Long code, short code and Walsh code

Course OrganizationChapter 1: IntroductionChapter 2: CDMA Techniques & TechnologiesChapter 3: CDMA Air InterfaceChapter 4: CDMA Core NetworksChapter 5: CDMA Number Planning

Development of Mobile Communications

1st Generation 1980s (analog) 2nd Generation 1990s (digital) 3rd Generation current (digital)3G provides: Complete integrated service solutions High bandwidth Unified air interface Best spectral efficiency and a step towards PCS AMPSAnalog to DigitalTACSNMTOTHERSGSMCDMA IS95TDMA IS-136PDCUMTS WCDMACDMA 2000TD-SCDMAIntroductionVoice to Broadband

Transmission Techniques

Traffic channels: different users are assigned unique code and transmitted over the same frequency band, for example, WCDMA and CDMA2000Traffic channels: different frequency bands are allocated to different users,for example, AMPS and TACSTraffic channels: different time slots are allocated to different users, for example, DAMPS and GSMFDMATDMACDMAUser User User User User User Introduction

TDMAFrequencyTimePoweruseruseruseruseruserIntroduction

3G Objectives

3G is developed to achieve:Universal frequency band for standard and seamless global coverage High spectral efficiency High quality of service with complete security and reliability Easy and smoothly transition from 2G to 3G, compatible with 2G Provide multimedia services, with the rates:Vehicle environment: 144kbpsWalking environment: 384kbpsIndoor environment: 2MbpsIntroduction

Standards for 3G 3G systemCDMA20003GPP2FDD mode WCDMA 3GPPFDD modeTD-SCDMA CWTSTDD modeIntroduction

A Comparison b/w 3G standards

WCDMACDMA2000TD-SCDMAReceiver type RAKERAKERAKEClose loop power control SupportedSupportedSupportedHandoffSoft/hard handoff Demodulation modeCoherentChip rate (Mcps) 3.84N*1.22881.28Transmission diversity modeTSTD, STTDFBTDOTD, STSNoSynchronizationmode AsynchronousSynchronousAsynchronousCore network GSM MAPANSI-41GSM MAPCoherentCoherentSoft/hard handoff Soft/hard handoff Introduction

Development of CDMA

Higher spectrum efficiency and network capacity Higher packet data rate and more diversified services Smooth transit to 3G CDMA2000 307.2kbps Heavier voice service capacity ; Longer period of standby time 1995199820002003Introduction

Frequency Allocation In CDMA2000Band Class 0 and Spreading Rate 1IntroductionThe transmit frequence point for Base Station is computed by:F=870+N*0.03N: CDMA Channel Number

Frequency Allocation In CDMA2000Band Class 1 and Spreading Rate 1IntroductionThe transmit frequency point for Base Station is computed by:F=1930+N*0.05N: CDMA Channel Number

CDMA2000 1X Network StructureMS: Mobile Station BTS: Base Transceiver StationBSC: Base Station Controller MSC: Mobile Switching CenterHLR :Home Location Register VLR: Visitor Location RegisterPCF: Packet data Control Function PDSN: Packet Data Service Node HA: Home Agent FA: Foreign Agent SCP: Service Control Point Radius: Remote Authentication Dial-in User ServiceAbisA1(Signaling)A2(Traffic)A11(Signaling)A10(Traffic)A3(Signaling & Traffic)A7(Singaling)Introduction

Course ContentsChapter 1 IntroductionChapter 2 CDMA Techniques & TechnologiesChapter 3 CDMA Air InterfaceChapter 4 CDMA Core NetworksChapter 5 CDMA Number Planning

Correlation

(a)(b)Correlation 100% so the functions are parallel Correlation 0% so the functions are orthogonal CDMA Techniques & Technologies+1-1+1-1+1-1+1

Orthogonal Function

Orthogonal functions have zero correlation. Two binary sequences are orthogonal if their XOR output contains equal number of 1s and 0s000001010101EXAMPLE:CDMA Techniques & Technologies101001011111

Information spreading over orthogonal codes

CDMA Techniques & Technologies

Information recovery

CDMA Techniques & Technologies

Spreading and De-spreading

information pulse interferenceWhite noiseThe improvement of time-domain information rate means that the bandwidth of spectrum-domain information is spread.S(f) is the energy density.fSfThe spectrum before spreadinginformationf0The spectrum before despreadinginformationInterference/noiseSff0ff0The spectrum after despreadinginformationInterference/noiseSffThe spectrum after spreadinginformationf0SffCDMA Techniques & Technologies

Signal flow

InterleavingSource codingConvolution &InterleavingScramblingSpreadingModulationRF transmission CDMA Techniques & Technologies

Common Technical Terms Bit, Symbol, Chip:A bit is the input data which contain informationA symbol is the output of the convolution, encoder, and the block interleavingA chip is the output of spreadingProcessing Gain:Processing gain is the ratio of chip rate to the bit rate. The processing gain in IS-95 system is 128, about 21dB.Forward direction: Information path from base station to mobile stationReverse direction: Information path from mobile station to base stationCDMA Techniques & Technologies

Source Coding

Vocoder: 8K QCELP13K QCELPEVRCCharacteristicsSupport voice activityIn a typical duplex call, the duty ratio is less than 35%. To achieve better capacity and low power consumption, base station reduces its transmission power.CDMA Techniques & Technologies

Channel Coding

Convolution code or TURBO code is used in channel encodingConstraint length=shift register number+1.Encoding efficiency= (total input bits / total output symbols)convolution encoderInput (bits)Output (symbols)CDMA Techniques & Technologies

Turbo Code Turbo code is used during the transmission of large data packet.Characteristics of the Turbo code: The input information is encoded twice and the two output codes can exchange information with each other during decoding.The symbol is protected not only by the neighborhood check bits, but also by the separate Check Bits.The performance of a Turbo code is superior to that of a convolution code.CDMA Techniques & Technologies

Interleaving

The direction of the data stream1287364512873645128736451287364512873645128736451287364512873645128736451287364511111111222227777777766666666333333334444444412873645128736455555555588888888interleavingCDMA Techniques & Technologies222

Scrambling (M) sequence

Two points are important here: Maximum number of shift register (N)MaskThe period of out put sequence is 2N-1 bitsOnly sequence offset is change when the mask is changedPN stands for Pseudorandom Noise sequenceCDMA Techniques & Technologies

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 stationsCDMA Techniques & Technologies

Short Code

Short code is a PN sequence with period of 215 chipsSequence with different time offset is used to distinguish different sectors

Minimum PN sequence offset used is 64 chips, that is, 512 PN offsets are available to identify the CDMA sectors (215/64=512). PNaPNcPNbCDMA Techniques & Technologies

Walsh Code

W2n=WnWnWnWnW1=0W2=0001W4=Walsh code64-order Walsh function is used as a spreading function and each Walsh code is orthogonal to other.Walsh Code is one kind of orthogonal code.A 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 matrixCDMA Techniques & Technologies1 11 0

Walsh Code

In forward direction, each symbol is spread with Walsh code

Walsh code is used to distinguish the user in forward link

For IS95A/B, in the reverse, every 6 symbols correspond to one Walsh code. For example, if the symbol input is 110011,the output after spreading is W5164 (110011=51).

For CDMA2000, in the reverse, Walsh function is used to define the type of channel (RC 3-9)CDMA Techniques & Technologies

Variable Walsh codes

Data rate -bps-The different Walsh codes corresponding to different data ratesCDMA Techniques & Technologies

Modulation-QPSK

IQI channel PN sequence1.2288McpsQ channel PN sequence1.2288McpsBaseband filterBaseband filterCos(2pfct)Sin(2pfct)I(t)Q(t)s(t)A1.2288Mcps: the PN chip rate of the system.After being spread, all the forward channels in the same carrier are modulated by means of QPSK(OQPSK in the reverse), converted into simulation signals and transmitted after clustering.CDMA Techniques & Technologies

Power ControlHandoff Diversity and RAKECDMA Techniques & Technologies

Power Control

Reverse power controlOpen loop power controlClosed loop power controlInner loop power control: 800 HzOuter loop power controlForward power controlMessage transmission mode: threshold transmissionperiodic transmission Closed loop power control .CDMA Techniques & Technologies

Reverse Open Loop Power Control

The transmission power required by the mobile station is determined by the following factors: Distance from the base station Load of the cell Circumstance of the code channels The transmission power of the mobile station is relative to its received power. Transmitting PowerCDMA Techniques & Technologies

Reverse Closed Loop Power Control

BTSPower Control BitEb/Nt ValueFER ValueInner Loop Power ControlOuter Loop Power ControlChange in Eb/Nt ValueCDMA Techniques & TechnologiesBSCBTS

Forward Power Control MS measures the frame quality and informs the base station to the result i.e. whether it is in the threshold or periodical mode. Base station determines whether to change the forward transmitting power or not. In IS-95 system, the forward power control is slow but in CDMA2000 system it is fast.CDMA Techniques & TechnologiesMessage Transmission Mode

Forward Closed Loop Power Control

Compared with IS-95 system, CDMA2000 the forward quick power control is fast.Power Control BitEb/Nt ValueCDMA Techniques & TechnologiesBTS

Handoff

Soft handoffIt is a process of establishing a link with a target sector before breaking the link with the serving sector

Softer handoffLike the soft handoff, but the handoff is occurred between multi-sectors in the same base station

Hard 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 communicationCDMA Techniques & Technologies

Soft/Softer Handoff

Multi-path combination in the BSC during soft handoff Multi-path combination in the BTS during softer handoffsCDMA Techniques & Technologies

Pilot Set

ActiveSetCandidateSetNeighborSetRemaining SetThe pilot set, corresponding to the base station being connectedThe pilot set, not in the active set but potential to be demodulatedThe pilot set, not included in the active set or the candidate set but being possible to be added in the candidate setOther pilot setsthe set of the pilots having same frequency but different PN sequence offset CDMA Techniques & Technologies

T_ADD,T_DROP,T_TDROP

T_ADD, T_DROP and T_TDROP affect the percentage of MS in handoff. T_ADD & T_DROP is the standards used to add or drop a pilot.T_DROP is a timer.CDMA Techniques & Technologies

Comparison Threshold

Pilot P1Pilot P2Pilot P0t0T_COMP0.5dBt1t2T_ADDPilot strengthP0-Strengh of Pilot P0 in Candidate Set.P1,P2-Stength of Pilot P1,P2 in Active Set.t0-Pilot strength Measurement Message Sent, P0>T_ADDt1-Pilot strength Measurement Message Sent, P0>P1+T_COMP*0.5dBt2 -Pilot strength Measurement Message Sent, P0>P2+T_COMP*0.5dBCDMA Techniques & Technologies

Transition Between Pilot Sets

T_ADDT_DROPPilot 1Pilot strengthPilot 2T_TDROPT_TDROPNeighborSetCandidateSetActiveSetCandidateSetNeighborSetTIME12345678CDMA Techniques & Technologies

Transmit Diversity

Time diversityBlock interleaving, error-correctionFrequency diversityThe CDMA signal energy is distributed on the whole 1.23MHZ bandwidth.Space diversityThe introduction of twin receive antennas .The RAKE receivers of the mobile station and the base station can combine the signals of different time delay.During a handoff, the mobile station contacts multiple base stations and searches for the strongest frameCDMA Techniques & Technologies

Transmission Diversity

The forward transmission diversity types in CDMA2000 1X areTD (Transmit Diversity)OTD (Orthogonal Transmit Diversity)The data stream is divided into two parts, which will be spread by the orthogonal code sequence, and transmitted by two antennas.STS (Space Time Spreading)All the forward code channels are transmitted by the multi-antennas.Spread with the quasi-orthogonal code Non-TDCDMA Techniques & Technologies

Transmission Diversity

The Transmission Diversity Technology enhances the receive performance of MS.CDMA Techniques & Technologies

The Principle of RAKE Receiver

RAKE antennas help to overcome on the multi-path fading and enhance the receive performance of the systemCDMA Techniques & Technologies

Course ContentsChapter 1 IntroductionChapter 2 CDMA Techniques & TechnologiesChapter 3 CDMA Air interface Chapter 4 CDMA Core Network Chapter 5 CDMA Number Planning

Physical Channel in IS-95A

Forward channel Forward Pilot Channel Forward Sync Channel Forward Paging Channel Forward Traffic Channel (including power control sub-channel)

Reverse channel Access Channel Reverse Traffic ChannelCDMA Air Interface

Pilot Channel

A pilot channel:Assist mobile station to be connected with CDMA networkHandles multi-path searchingProvide the phase reference for coherent demodulation and help the mobile station estimate the transmission powerThe mobile station measures and compares the pilot channel powers from the base stations during the handoffForward pilot channel is spread over W0 and modulated with short code directly

BTS transmits the pilot channel continuously

CDMA Air Interface

Sync Channel

The sync channel is used by the mobile station to synchronize with the network. W32 is used to spread Sync Channel.The synchronization message includes: Pilot PN sequence offset: PILOT_PNSystem time: SYS_TIMELong code state: LC_STATEPaging channel rate: P_RATHere note that, sync channel rate is 1200bpsTo QPSK coder2.4kbps4.8kbps4.8kbpsCode symbolRepetitive code symbol1.2kbpsConvolution encoderr=1/2,K=9symbol repetitionBlock interleavingSync Ch bitsW3264CDMA Air Interface

Paging Channel

The paging channel transmits:System parameters messageAccess parameters Neighbors list CDMA channels list messageThe paging channel accomplishes: Paging to MSAssign traffic channel to MSThe frame length of a paging channel is 20msW1 ~ W7 are spared for the Paging Channels spreadingTo QPSK coderPaging channel bits19.2/9.6Kbps19.2kbps19.2kbpsCode symbol9.6/4.8 kbpsConvolution encoderr=1/2,K=9Symbol repetitionBlock interleaving Paging channel address maskLong code PN generatordecimator1.2288Mcps19.2kbpsRepetitive code symbolCDMA Air Interface W164

Forward Traffic Channel

I Ch PN sequence (1.2288 Mcps)PN 1.2288 McpsRepetitive symbol19.2kbps8.6kbps9.6kbps4.8kbps2.4kbps1.2kbpsAdd frame quality indicator bits(12,10,8,6)Add 8 encoded tail bitsConvolution encoderr=1/2,K=9Symbol repetitionForward traffic channal(172/80/40 or 16bits/frame) Block interleaver19.2kbpsMUXLong code generatorPower control bitsQ Ch PN sequence (1.2288 Mcps)Baseband filterI(t)Q(t)decimator+QPSK Modulation4.0kbps2.0kbps0.8kbps19.2ksybps9.6ksybps4.8ksybps2.4ksybpsSin(2pfct)Cos(2pfct)is used to transmit data and signaling information.Walsh codeCDMA Air Interface decimatorBaseband filter

Reverse Access Channel

4.8 kbps (307.2kbps)PN chips1.2288 McpsOrthogonal spreadingRepetitive symbol8.8 kbpsCode symbol14.4 kbps4.4 kbps4.8 kbpsAdd 8 encoder tail bitsConvolutionencoderr=1/3,K=9Symbol repetitionAccess channel (80 bits/frame)Block interleaving28.8 kbpsData burst randomizerLong code PN generatorFrame rateLong code maskRepetitive symbolused by MS to initiate communication or respond to Paging ChannelWalsh codeCDMA Air Interface I Ch PN sequence (1.2288 Mcps)Baseband filterI(t)Q(t)QPSK ModulationSin(2pfct)Cos(2pfct)Baseband filterQ Ch PN sequence (1.2288 Mcps)1/2 PN chips Delayed time=406.9ns

Reverse Traffic Channel

used to transmit data and signaling informationCDMA Air Interface 8.6kbps9.6kbps4.8kbps2.4kbps1.2kbpsAdd frame quality indicator bits(12,10,8,6)Add 8 encoded tail bitsconvolution encoderr=1/3,K=9Symbol repetitionReverse traffic channel(172/80/40 or 16 bits/frame) Block interleaver4.0kbps2.0kbps0.8kbps28.8Ksybps14.4Ksybps7.2Ksybps3.6Ksybps4.8 kbps (307.2kbps)PN chips1.2288 McpsOrthogonal spreadingData burst randomizerLong code PN generatorFrame rateLong code maskWalsh code I Ch PN sequence (1.2288 Mcps)Baseband filterI(t)Q(t)QPSK ModulationSin(2pfct)Cos(2pfct)Baseband filterQ Ch PN sequence (1.2288 Mcps)1/2 PN chips Delayed time=406.9ns

Initialization of the MS

Synchronous Channel message contains the LC_STATE, SYS_TIME, P_RAT, and synchronizes with the system.CDMA Air Interface BTS

CDMA2000 Forward Channel

Forward CDMA2000 channelF-CACHF-CPCCHF-PICHF-CCCHF-DCCHF-FCHF-PCF-SCCHF-SCHF-PICHF-TDPICHF-APICHF-ATDPICHF-SYNCHF-TCHF-BCHF-PCHF-QPCHsubchannel(RC1~2)(RC3~9)Note: Only the channels with black color are being implemented in Huawei equipment. The function of F-PICH, F-SYNCH, F-FCH, F-PC, F-SCCH, F-PCH are the same as those of IS95. We will only discuss F-SCH, F-QPCH F-DCCH in the following slides. CDMA Air Interface

Forward channel

These channels are newly defined in CDMA2000 system.CDMA physical channels are classified in common channels and dedicated channels: Common physical channels: Forward Pilot Channel(F-PICH)Forward Synchronous Channel(F-SYNC)Forward Paging Channel(F-PCH)Forward Broadcast Control Channel(F-BCCH)Forward Quick Paging Channel(F-QPCH)Forward Common Power Control Channel(F-CPCCH)Forward Common Assignment Channel(F-CACH)Forward Common Control Channel(F-CCCH)These channels are compatible with IS-95 system Dedicated physical channel: Forward Dedicated Control Channel(F-DCCH)Forward Fundamental Channel(F-FCH) Forward Supplemental Channel(F-SCH)These channels are used to establish the connection between a base station and a specific mobile station. The CDMA2000 system adopts multiple data rates and the different combinations of channels can achieve a performance superior to that in IS-95 system.CDMA Air Interface

F-QPCH

It transmits OOK-modulated signal which can be demodulated by MS simply and rapidly. The channel adopts 80ms as a QPCH timeslot. Each timeslot is divided into paging indicators, configuration change indicators and broadcast indicators, all of which are utilized to inform the MS whether to receive paging message, broadcast message or system parameters in the next F-PCH.

Rapid and simple demodulation. MS no need to monitor F-PCH for long time, so the standby time is prolonged.CDMA Air Interface

F-SCH

F-SCH is typically used for high speed data applications, while F-FCH is used for common voice and low speed data application.

When a data call is established, firstly, F-FCH will be allocated to the user. If the speed of data for user exceeds 9.6kbps, F-SCH will be allocated.CDMA Air Interface

F-DCCH

It is used for the transmission of specific user signaling information during a call.

Each forward traffic channel may contain one F-DCCH.

Support 5ms frame.

Support discontinuous transmission.CDMA Air Interface

Forward Radio Configuration (RC)

Radio Configuration(RC): A set of Forward Traffic channel and Reverse Traffic Channel transmission formats that are characterized by physical parameters such as data rates, modulation characteristics, and spreading rate.

Spreading Rate: Equivalent to chips rate, e.g., 1.2288Mcps.** Same as IS95CDMA Air Interface

Reverse Channel

Reverse CDMA2000 channelR-ACHR-TCH operation(RC1~2)R-EACH operationR-CCCH operationR-SCCHR-FCHR-TCH operation (RC3~6)R-EACHR-PICHR-CCCHR-PICHR-DCCHR-PICH0~70~1R-SCHR-FCH0~20~1subchannelR-PCOnly the channels in dark color are used in Huawei equipment. The function of R-ACH,R-FCH,R-SCCH are the same as those in IS95. We will only discuss R-PICH,R-SCH in the following slides.CDMA Air Interface

Types of Reverse Channel

Reverse channel includes reverse common channel and reverse dedicated channel.Reverse common channel:Reverse Access Channel(R-ACH)Reverse Enhanced Access Channel(R-EACH)Reverse Common Control Channel(R-CCCH)Reverse Dedicated ChannelReverse Pilot Channel(R-PICH)Reverse Dedicated Control Channel(R-DCCH)Reverse Fundamental Channel(R-FCH)Reverse Supplemental Channel(R-SCH)Reverse Supplemental Code Channel (R-SCCH) CDMA Air Interface

R-PICH

The Function of Reverse Pilot ChannelInitializationTracing Reverse Coherent DemodulationPower Control MeasurementBase station enhances the received performance and increases the capacity by means of coherent demodulation of the Reverse Pilot Channel.N is the Spreading Rate numberReverse Pilot ChannelCDMA Air Interface

Reverse Channels

Fundamental Channel: Fundamental Channel is used for the transmission of user information to the base station during a call, and can be used to transmit defaulted voice services as an independent Traffic Channel.Dedicated Control ChannelThe Dedicated Control Channel is used for the transmission of user and signaling information to a base station during a call.Supplemental Channel/Supplemental Code ChannelThese channels are used for the transmission of user information, mainly data services, to the MS. The Reverse Traffic Channel contains up to two supplemental channels and up to seven supplemental code channels.CDMA Air Interface

Reverse Radio Configuration (RC)

RC: Radio ConfigurationRC1~RC2:IS-95A/BRC3~RC4:CDMA2000 1XRC5~RC6: CDMA2000 3x** Same as IS95CDMA Air Interface

Sheet1

Radio ConfigurationSpreading RateMax Data Rate* (kbps)Effective FEC Code RateOTD AllowedFEC EncodingModulation

1**19.61/3NoConv64-ary ortho

2**114.41/2NoConv64-ary ortho

31153.61/4YesConv or TurboBPSK

(307.2)(1/2)

41230.43.8YesConv or TurboBPSK

53153.61/4YesConv or TurboBPSK

(614.4)(1/3)

63460.81/4YesConv or TurboBPSK

(1036.8)(1/2)

Sheet2

Sheet3

RC Combination Regulation

RC1 and RC2 corresponds respectively to rate set 1 and rate set 2 in IS- 95A/B system.

CDMA2000 Forward RC: RC1~RC5 Reverse RC: RC1~RC4

Rules: Forward RC1, Reverse RC1Forward RC2, Reverse RC2Forward RC3 or RC4,Reverse RC3Forward RC5, Reverse RC4CDMA Air Interface

Course ContentsChapter 1 IntroductionChapter 2 CDMA Techniques & TechnologiesChapter 3 CDMA Air InterfaceChapter 4 CDMA Core NetworkChapter 5 CDMA Number Planning

A typical CDMA Network CDMA Core Network

CDMA Interfaces MSC: Mobile-service Switching Center BSC: Base Station ControllerMC: Short Message Center HLR: Home Location RegisterBTS: Base Transceiver Station VM: Voice MailboxVLR: Visitor Location Register OMC: Operation & Maintenance Center AC: Authentication Center SCP: Service Control PointOther MSCsMC/VMMSC/SSP/VLROMCHLR/ACSDHGMSC/SSPSCPSTPIOS4.0SS7IS-41IS-41IS-41IS-41Mobile Customer Service CenterSS7TCP/IPSS7IS-41BTSBTSBSCMSIS95----CDMA2000INTERNETOther PLMNsPSTN/ISDNCDMA Core Network PDSN

Network Interface

CDMA Core Network

CDMA Services

Businesses, enterprisesMobile virtual private networkMobile high-speed network accessAdvertising servicesFree phoneFamilyFamiliarity numberLife & amusement

Schools, groupsUniversal account numberSectorized and time-shared chargeBroadcast newsIndividualsIndividualized servicesPrivacyCDMA Core Network

CDMA Feature Services---Example 1

Where is my mobile phone? It is lucky to have Ruyi lock!Ruyi lockFeatures: a mobile phone user can dial the access code and input the PIN code to lock/unlock his mobile phone by using any fixed telephone instead of registering and paying at a business hall.Why cant I make a call the moment I picked it up?CDMA Core Network

CDMA Feature Services---Example 2

FOLLOW MEFeatures: a user can activate call forwarding of his/he MS from any phone to ensure that any incoming call of a mobile phone user will not be lost. You can register for a forwarding service on your own I forgot to bring my mobile phone, but I will have an important customer to meet this afternoon. What should I do?CDMA Core Network

CDMA Feature Services---Example 3

Does that guy still bother you recently?He can no longer reach me!Why? Ask me to input a password?FriendshipcomFeatures: After a called user subscribes for this service, the system requires password to caller. A call is accomplished only if the password is correct. Otherwise, the call will be rejected or transferred. CDMA Core Network

CDMA Feature Services---Example 4

Intra-group userLOOK FOR serviceFeature 1: When a user makes a call to an intra-group user, the terminals of all intra-group users ring in-turn or simultaneously until there is a reply.CDMA Core Network

CDMA2000---Data Services

032649.61281443842,000Video StreamingVoiceText MessagingStill ImagingAudio StreamingElectronic newspaperHigh-quality videoconferenceTelephone (Voice)Voice MailE-MailFax Electronic bookSports, news and weather report on demand Singing roomLow-quality videoconferenceJPEG Still PhotosMobile RadioVideo Surveillance,Video Mail, TravelImageDataWeather, transportation, news, sports and securitiesMobile TVE-commerceRemoteMedical ServiceData rate in KbpsCDMA Core Network

Locating Services

GPS-aided measurementAccuracy: suburbs---10m. City zone---30~70m. Indoor --unable to locateResponse time: 3~10sMeasurement of base station pilot phaseAccuracy: 50~200mResponse time: 3~6sLocating of a cell IDAccuracy: depends on the size of a cellResponse time: within 3s3GPP2 uses the following 3 standards for MS location: CDMA Core Network

Locating Services

The system transfers the alarm to the nearest alarm processing center based on the location.An emergency button can be set on a users mobile phone to so that an alarm can be reported without any conversation or delay.110! Bandit!CDMA Core Network

Equal Access of Toll Calls

Help mobile operators to absorb large quantities of toll services Users subscribe to select toll operators to ensure quality of service. Enable users to save toll call charge (premium strategy) Make an IP toll call without dialing a preamblePSTNCDMA/INTERNETUsers who subscribe for toll servicesOriginal toll routeToll route after subscriptionMSC/GMSCHLROperators who subscribe for toll servicesCDMA Core Network

Course ContentsChapter 1 IntroductionChapter 2 CDMA Techniques & TechnologiesChapter 3 CDMA Air Interface Chapter 4 CDMA Core NetworkChapter 5 CDMA Number Planning

Definition of Coverage Areas Location areaMSC areaPLMN areaService areaSectorareaCDMA Number Planning Cell area

Parameters Involved

In a CDMA system, the following parameters are defined to identify a user and his location:MIN/IMSI MDN ESN TLDN SID/NID LAI GCI SIN SSN

CDMA Number Planning

MIN/IMSI

Mobile subscriber identity/international mobile subscriber identityFor example, 0907550001/460030907550001Not more than 15 digits3 digits2 digitsIMSIMCCMNCMSINNMSICDMA Number Planning

MDN

CC+MAC+H0H1H2H3+ABCDInternational mobile subscriber DNNational valid mobile subscriber number Mobile directory numberFor example, 8613307550001CDMA Number Planning

ESN

A unique Electronic Serial Number (ESN) is used to identify single MS. An ESN includes 32 bits and has the following structure:

31......24 23......18 17......0 bitManufacturers number retained equipment SNFor example, FD 03 78 0A (the 10th Motorola 378 mobile phone)The equipment serial number is allocated by a manufacturer.CDMA Number Planning

TLDN

Temporary local directory numberFor example, 8613344755001CDMA Number Planning

SID/NID

MSCID (Exchange Identity)= System Identity (SID) + Exchange number (SWIN)is used to represent a certain set of equipment in an NSS network. For example, Unicom CDMA Shenzhen MSC is labeled as 3755+01CDMA Number Planning

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 digits. For example, China is 460.MNC: 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.For example, 460030100CDMA Number Planning

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 siteCDMA Number Planning

Sender Identification Number (SIN)

MSC number The MSC number stipulated by Unicom is 460 + 03 + 09 + H0H1H2H3 + 1000.HLR numberThe HLR number stipulated by Unicom is 460 + 03 + 09 + H0H1H2H3 + 0000.SMC numberThe SMC number stipulated by Unicom is 460 + 03 + 09 + H0H1H2H3 + 2000.SCP numberThe SCP number stipulated by Unicom is 460 + 03 + 09 + H0H1H2H3 + 3000.CDMA Number Planning

Sub-System Number (SSN

SSN of MSC: 8 SSN of VLR: 7SSN of HLR: 6SSN of AC: 10SSN of SMC: EESSN of SCP: EFSSN of A interface: FE/FCSSN of SCCP management: 1CDMA Number Planning

Voice Channel Routing

CDMA Number Planning

Signaling Route

CDMA Number Planning

Example of Signaling Network

Route from an LSTP to the LSTP not located in the same placeHLR in Chongqin to MSC in Fujian (two LSTPs respectively at the transmit end and receive end)CDMA Number Planning

Interconnection of CDMA with PSTN

CDMA Number Planning

Review

Chips rate: 1.2288Mcps IS-95A/B is a subset, RC1/RC2 Apply the coherent demodulation to the reverse pilot channel Forward transmit diversity: OTD and STSForward quick power control at 800HZ rateImprove the standby time by introducing the quick paging channel.Variable frames: 5ms, 20ms, 40ms and 80ms Introduce TURBO code into channel encoding The maximum rate of a physical layer is up to 307.2KCDMA Technology

Development of CDMA Standards in ChinaCDMA standards currently adopted in China are mainly based on the USA standards with few alterations. For example, in USA the emphasis is put on the dual service support i.e. CDMA and AMPS compatibility, while in China there is no such requirement. Therefore, the settings of frequency and basic channels, IMSI and others parameters need to be modified. Likewise, there is also the need to modify network interface IS-41 series of standards.

Case study: China Unicom Network In China Unicom CDMA project, phase 1, a narrow-band CDMA network, named IS-95B (enhanced IS-95) is being constructed. With total capacity is 15,000,000, subscribers handling, covering over 200 cities.

Currently, both nationwide and international roaming tests have conducted successfully with the CDMA networks of HongKong, South Korea and Japan via the TSI international gateway bureau.

Besides, a CDMA intelligent network will be constructed to provide intelligent value-added services like Pre-Paid Charging (PPC) and Virtual Private Network (VPN) etc.

The whole CDMA20001X network was launched in air in the second half of 2002.

Why CDMA2000? Increase the system capacityForward quick power controlForward transmit diversity: OTD,STSCoherent modulation applied on the pilot channel.(about 3dB)The introduction to Turbo codeThe stronger ability to resist interference The improved error-correcting encoding (applying Turbo code in medium/high rate data transmission)

Why CDMA2000?Support high rate SCH, with the maximum rate of a single channel being up to 307.2kbps. Improve the standby timeUse the quick paging channelForward compatibilityRadio-frequency partBaseband part, such as RC

SummaryBrief Development History of Mobile CommunicationAnalog--digital--code divisionObjectives of 3G and comparison of 3 systemsTechnical features of CDMAKey technologies: power control, soft handoff,RAKE receiver and cell breathOther technologies: source coding, channel coding, interleaving, scrambling, spreading and modulationChannel structure: pilot, synchronization, paging, access and serviceTechnical features of CDMA2000 1XWalsh and Turbo codes

QuestionsWhat power control modes are there in CDMA2000 system and how are they implemented?Describe the soft handoff process?Describe the process and functions of cell breath?Describe the implementation process of service channels (forward and reverse)?Describe the technical features of CDMA2000?Describe the initialization process of a mobile phone?What are the functions of a long code, short code and Walsh code in CDMA system?

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.

Frequency Division Multiple Access: frequency division, sometimes called channelization, means dividing the whole available spectrum into many single radio channels (transmit/receive carrier pair). Each channel can transmit one-way voice or control information. Under the control of the system, any user can be accessed to any of these channels. Analog cellular system is a typical example of FDMA structure. Similarly, FDMA can also be used in a digital cellular system,except that pure frequency division is not adopted. For example, FDMA is adopted in GSM and CDMA. Time Division Multiple Access means that the wireless carrier of one bandwidth is divided into multiple time division channels in terms of time (or called timeslot). Each user occupies a timeslot and receives/transmits signals within this specified timeslot. Therefore, it is called time division multiple access. This multiple access mode is adopted in both a digital cellular system and a GSM. TDMA is a complex architecture and the simplest case is that a single channel carrier is divided into many different timeslots, each of which transmits one-way burst-oriented information. The key part in TDMA is the user part, in which each user is allocated with one timeslot (allocated when a call begins). The user communicates with a base station in a synchronous mode and counts the timeslot. When his own timeslot comes, the mobile station starts a receiving and demodulation circuit to decode the burst-oriented information sent from the base station. Likewise, when a user wants to send any information, he should first cache the information and waits for his timeslot to come. After a timeslot begins, the information is transmitted at a double rate and next burst-oriented transmission begins to be accumulated. CDMA is a multiple access mode implemented by Spread Spectrum Modulation. Unlike FDMA and TDMA, both of which separate the user information in terms of time and frequency, CDMA can transmit the information of multiple users on a channel at the same time. That is to say,mutual interference between users is permitted. The key is that every information before transmission should be modulated by different Spread Spectrum Code-Sequence to broadband signal, then all the signals should be mixed and send. The mixed signal would be demodulated by different Spread Spectrum Code-Sequence at the different receiver.Because all the Spread Spectrum Code-Sequence is orthogonal,only the information that was be demodulated by same Spread Spectrum Code-Sequence can be reverted in mixed signal.

Time Division Multiple Access means that the wireless carrier of one bandwidth is divided into multiple time division channels in terms of time (or called timeslot). Each user occupies a timeslot and receives/transmits signals within this specified timeslot. Therefore, it is called time division multiple access. This multiple access mode is adopted in both a digital cellular system and a GSM. TDMA is a complex architecture and the simplest case is that a single channel carrier is divided into many different timeslots, each of which transmits one-way burst-oriented information. The key part in TDMA is the user part, in which each user is allocated with one timeslot (allocated when a call begins). The user communicates with a base station in a synchronous mode and counts the timeslot. When his own timeslot comes, the mobile station starts a receiving and demodulation circuit to decode the burst-oriented information sent from the base station. Likewise, when a user wants to send any information, he should first cache the information and waits for his timeslot to come. After a timeslot begins, the information is transmitted at a double rate and next burst-oriented transmission begins to be accumulated.

(1) Capable of roaming globally: users can roam within the whole system,even in the whole world , and can be provided with guaranteed quality of service at different rates and in different statuses of motion. (2) Providing diversified services: providing voice, data with variable rates, active video non-voice services, especially multimedia services. (3) Capable of adapting to many kinds of environment: can integrate the existing Public Switched Telephone Network (PSTN), Integrated Service Digital Network (ISDN), cordless system, land mobile communication system and satellite communication system to provide seamless coverage. (4) Sufficient system capacity, powerful management capability of multiple users, high security performance and quality of service.

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.

Correlation is measure of similarity of any two arbitrary signals. It is computed by multiplying the two signals and then summing (integrating) the result over a defined time windows. The two signals of figure (a) are identical and therefore their correlation is 1 or 100 percent. In figure (b) , however, the two signals are uncorrelated, and therefore knowing one of them does not provide any information on the other.The principle behind spreading and despreading is that when a symbol is XORed with a known pattern, and the result is again XORed with the same pattern, the original symbol is recovered. In other words, the effect of an XOR operation if performed twice using the same code is null. In orthogonal spreading, each encoded symbol is XORed with all 64 chips of the Walsh code. By spreading ,each symbol is XORed with all the chips in the orthogonal sequence (Walsh Sequence) assigned to the user. The resulting sequence is processed and is then transmitted over the physical channel along with other spread symbols. In this figure, a 4-digit code is used. The product of the user symbols and the spreading code is a sequence of digits that must be transmitted at 4 times the rate of the original encoded binary signal.The receiver despreads the chips by using the same Walsh code used in the transmitter. Notice that under no-noise conditions, the symbols or digits are completely recovered without any error. In reality, the channel is not noise-free, but cdma system employ Forward Error Correction techniques to combat the effects of noise and enhance the performance of the system. When the wrong Walsh sequence is used for despreading, the resulting correlation yields an average of zero. This is a clear demonstration of the advantage of the orthogonality property of the Walsh codes. Whether the wrong code is mistakenly used by the target user or other users attempting to decode the received signal, the resulting correlation is always zero because of the orthogonality property of Walsh sequences.The processing gain is calculated as follows: 10*log10128=21db

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. convolution code is an error correcting code. Convolution aims to associate a previous signal with a subsequent one and the association of the previous signal and the subsequent one actually means that this signal is capable of detecting and/or correcting an error. Error correcting or error detecting certainly will increase some redundancy signals, therefore the output bit rate increases to 3 times that at the input terminal of a convolution encoder.

It can be seen from the figure that the data are read row by row into an interleaver at the transmit end,read column by column out (this process is called interleaving) and propagated after other modulation process. Then, the data enter the interleaver at the receive end row by row and are read out column by column (this process is called de-interleaving). Currently, we assume that in the course of propagation, when row 2 data are transmitted, consecutive error codes occur to the 2nd, 3rd and 4th bits as a result of fading or other reasons, as shown by the left side of the figure. If the original data had been transmitted after the interleaving, the second bit of row 2 ,the second bit of row 3 and the second bit of row 4 would have been error codes after being read out column by column at the receive end. Because common error correcting codes can very easily process discrete error codes, the receive end can very easily recover the signals after the anti-interleave into the original signals by means of error correcting,but always cannot recover those signals not interleaved as a result of consecutive error codes. Therefore, the interleave can overcome fast fading caused during the signals transmission in air. The interleave code seldom functions in correcting error codes caused by slow fading, because slow fading may result in long consecutive error codes,even the whole frame may be error.Therefore, there will occur consecutive error codes after de-interleaving . The above figure is the simplest interleave and the interleave in an actual application is far more complex.In CDMA system, user information is encrypted by means of scrambling. The scramble code used here is M-sequence. Shown in the figure is an M-sequence generator made up of a shifting register sequence and a mask. The period of the output sequence is 2N-1 (N being the number of shifting registers). That is to say, the shifting register sequence resumes to the initial status when every 2N-1 pieces of codes are output. In a CDMA system, there are two kinds of M-sequence, one being the long code with its period of 242-1 and the other being the short code with its period of 215-1. Used for scrambling is the long code while used for subsequent demodulation is the short code.It can be seen that for different masks, a shifting register sequence outputs different M-sequences, which we call different phases. Actually, different masks in CDMA are allocated to different users,who are enabled to obtain different M-sequences. In a reverse direction, different long codes are used for the information sent by different users and these are known to the base station and these users. Thus, the base station can identify different mobile stations.

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.The Walsh code is used to separate the user in the forward CDMA link. In any given sector, each forward code channel is assigned a distinct Walsh code.Enhancements of CDMA2000 include the use of Walsh spreading factor to attain high data rates on the forward link. Variable Walsh spreading uses the tree structure for recursively constructing Walsh codes of the longer lengths. Higher data rates for the user can be obtained by using the shorter Walsh code. However ,use of one of the shorter codes precludes using any longer code that are derived from it. 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.

Reverse open loop power control means that based on the detected signals from a base station, a mobile station makes a preliminary judgement of the attenuation of an air path and specifies what transmitting power should be used to transmit signals. If the mobile station receives strong signals, it shows there is weak air attenuation and the mobile station transmits signals at a smaller power. If the mobile station receives weak signals, it shows there exists strong air attenuation and the mobile station will transmit signals at a greater power. Reverse closed loop power control means that after receiving a signal from a mobile station , a base station will judge its strength. If the signal is higher than the threshold needed by the base station, the base station sends an instruction that the mobile station should decrease the transmitting power. If the signal is lower than the threshold needed by the base station, the base station sends an instruction that the mobile station should increase its transmitting power. Forward power control is similar to reverse power control, but the former controls the signals a base station transmits to various users.

Inner loop power controlThe base station compares the measured Eb/Nt with the corresponding objective and the mobile station will be ordered to decrease the transmission power if the measured Eb/Nt exceeds the objective. Otherwise, the mobile station will be ordered to increase the transmission power. The adjustment frequency is 800HZ.Outer loop power controlEstimate Eb/Nt objective based on the measured Frame Error Rate(FER) Eb/Nt=bit energy/density of interference power spectrum, similar to signal-to-noise ratio.

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. Soft handoff means that during the handoff of a mobile station at the coverage edge areas of two or multiple base stations, the mobile station receives the signals from multiple base stations (two in most cases) at the same time and the base stations receive the signals from this mobile station at the same time. The mobile station will not disconnect from the original base station until some conditions are satisfied. The reasons for soft handoff are as follows: 1. CDMA system can implement the frequency multiplexing of adjacent cells with the same frequency. 2. For each channel, the mobile station and base station adopt multiple RAKE receivers to receive multi-path signals at the same time. In the course of soft handoff, the signals from various base stations, for a mobile station, are equal to multi-path signals and the receiving of these signals by the mobile station is equal to a kind of space diversity. This soft handoff or softer handoff can improve the quality of service during the handoff in a real sense. That is to say, the conversation quality at the coverage edge is improved and the call dropping rate greatly reduced. This is not common commercial propagation, but a fundamental solution because call dropping in a GSM system mostly takes place during the handoff.

Pilot Detection Threshold (T_ADD)Any Pilot that is strong but is not in the Handoff Direction Message is a source of interference. This Pilot should be immediately moved into the active set for handoff to avoid voice/data degradation or a possible drop call. T_ADD affects the percentage of MS in handoff. It should be low enough to quickly add useful Pilots and high enough to avoid false alarms due to noise.Pilot Drop Threshold (T_DROP)This affects the percentage of MS in handoff. It should be low enough to avoid dropping a good Pilot that goes into a short fade . It should be high enough not to remove quickly useful Pilots in the active or candidate state.Pilot Drop Timer (T_TDROP)This is a timer. Whenever the strength of a Pilot in the active set falls below a value of T_DROP, a timer is started by the MS. If the Pilot strength goes back above T_DROP, the timer is reset; otherwise the timer expires when a T_TDOP has elapsed since the Pilot strength has fallen below T_DROP. Every MS maintain a handoff drop timer for each Pilot in the Active and Candidate Sets.The Comparison Threshold: T_COMPAn additional parameter, T_COMP, is used to control handoff signaling. When the strength of a new Pilot exceeded the strength of the current serving Pilot by the amount of the comparison threshold, the MS will signal the BTS.This graph illustrates the soft handoff process. The steps shown in this diagram are:Pilot 2>T_ADD.MS sends PSMM (Pilot Strength Measurement Message) and adds Pilot 2 to the Candidate Set.Pilot 2>Pilot1+T_COMP*0.5. MS sends another PSMM. BTS decides to add Pilot 2 to the Active Set and sets up the soft handoff.MS receives message and moves Pilot 2 to the Active Set.Pilot 1