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Hệ thống CMDA NỘI DUNG: ) Thuận lợi CDMA ) Các Frequency channels CDMA ) Các tốc độ mã hoá thoại ) CDMA Call Processing ) Điều khiển công suất ) Chuyển giao mềm (Soft handoff) Nguồn tham khảo: univ.zte.com.cn Bài giảng Mạng TT di động Slice Thuận lợi CDMA Bài giảng Mạng TT di động Slice Vùng phủ sóng rộng large coverage almost times than GSM, save money for operator Example:cover 1000 km2： GSM need 200 BTS ，CDMA only need 50 BTS Attention: exact result need “Link Budget ” Bài giảng Mạng TT di động Slice Dung lượng lớn High spectrum capacity，8 10 times than AMPS,4—6 times than GSM FDMA FDMA -Different user use different frequency Power T im TACS、AMPS TDMA -Different user use different time slot of one frequency y nc TDMA Power GSM、DAMPS CDMA -Different user use same frequency at the same time,but with different spreading code e ue eq Fr Ti m e e qu Fr e y nc CDMA Power Tim e Bài giảng Mạng TT di động ue eq Fr y nc Slice Độ bảo mật cao ¾High privacy, hard to wiretapping Each user is below the noise deeply Spread signal Information signal Demodulated signal TX Spread code RX Spread code Bài giảng Mạng TT di động Slice Chuyển giao mềm → tin cậy Use soft handoff, decrease drop-call rate z CDMA：”make before break” -soft handoff z Other systems: “make after break” -hard handoff Bài giảng Mạng TT di động Slice Chất lượng thoại cao Good voice quality, use 8k,13K(QCELP,EVRC)voice coding—the best coding method in the world Voice quality (MOS) 64k PCM 13k GSM 8k 13k CDMA CDMA 8kEVRC CDMA Bài giảng Mạng TT di động Slice Ít ảnh hưởng sức khoẻ Perfect Power Control and voice activation make the MS Power low, healthy for body—green mobile phone Mean Power Max Power GSM: 125mW 2W CDMA: 2mW 200mW Bài giảng Mạng TT di động Slice Các cơng thức tính tần số sóng mang CDMA Frequency Calculation： 450MHz BS receiver(Uplink): 450.00+0.025(N-1) BS sender(downlink): 460.00+0.025(N-1) 800MHz BS receiver(Uplink): 825.00+0.03N BS sender(downlink):870.00+0.03N 1900MHz BS receiver(Uplink): 1850.00+0.05N BS sender(downlink):1930.00+0.05N Bài giảng Mạng TT di động Slice Frequency channels: tần số sóng mang B Band 799 A Band 716 715 667 666 334 333 991 1023 A” A’ B’ Channel Numbers 1019 37 78 119 160 201 242 283 384 425 466 507 548 589 630 691 1 * CDMA A-Band Carriers CDMA B-Band Carriers * 736 777 ** * Requires frequency coordination with non-cellular interferers ** Requires frequency coordination with A-band carrier A Band Primary Channel A Band Secondary Channel Channel number? Center frequency 283 691 B Band Primary Channel B Band Secondary Channel 384 777 Up link: 825.00MHz+0.03MHz*N Down link: 870.00MHz+0.03MHz*N Bài giảng Mạng TT di động Slice 10 Frequency channels: tần số sóng mang CDMA 800 MHz Cellular Spectrum Assignment Primary Channel Secondary channel A段 B段 825MHz A’ 840MHz 835MHz B’ 段 845MHz 849MHz 846.5MHz N= 37 78 119 160 201 242 283 384 425 466 507 548 Total 10M Total 5M Frequency Carries Frequency Carries A Band Primary Channel B Band Primary Channel 283 384 589 630 691 736 777 Not allocation A Band Secondary Channel B Band Secondary Channel Bài giảng Mạng TT di động 691 777 Slice 11 Frequency channels: tần số sóng mang CDMA 1900 MHz Cellular Spectrum Assignment N= 925 950 975 925 1900M 1895M （Uplink：1895-1900） 950 975 1975M 1980M （Downlink：1975-1980） Bài giảng Mạng TT di động Slice 12 Mã hoá thoại với tốc độ thay đổi Variable Rate Vocoding bits Rate Set Frame Sizes bits Rate Set Frame Sizes 192 Full Rate Frame 288 Full Rate Frame 96 1/2 Rate Frame 48 144 1/2 Rate Frame 1/4 Rt 72 24 1/8 1/4 Rt 36 1/8 Rate set1(8KQCELP & EVRC): Rate set2 (13KQCELP ): Full rate：9.6Kbps Full rate ：14.4Kbps Half rate：4.8Kbps Half rate ：7.2Kbps 1/4 rate：2.4Kbps 1/4 rate ：3.6Kbps 1/8 rate ：1.2Kbps 1/8 rate ：1.8Kbps Bài giảng Mạng TT di động Slice 13 CDMA Call Processing Power-Up Initialization Mobile station has fully acquired system timing Mobile station is in idle handoff with NGHBR_CONFG equal to ‘011’ or is unable to receive Paging Channel Message Mobile station ends use of the Traffic Channel Idle Mobile station receives a Paging Channel message requiring ACK or response, originates a call, or performs registration Mobile station receives an ACK to an Access Channel transmission other than an Origination Message or a Page Response Message System Access Mobile station is directed to a Traffic Channel Traffic Bài giảng Mạng TT di động Slice 14 Điều khiển công suất Power control All CDMA users occupy the same frequency at the same time! Frequency and time are not used as discriminators CDMA operates by using CODES to discriminate between users CDMA interference comes mainly from nearby users Transmit power on all users must be tightly controlled so their signals reach the base station -at the same signal level - at the absolute minimum power level necessary to ensure acceptable service quality Figure of Merit: Ec/Io, Eb/No (energy per chip [bit] / interference [noise] spectral density) CDMA: Ec/Io -17 to -2 dB CDMA: Eb/No ~6 to7 dB Bài giảng Mạng TT di động Slice 15 Phân loại điều khiển công suất Reverse Power Control Open-loop Power Control Closed-loop Power Control (Forward traffic Channel) 9Outer-loop Power Control 9Inner-loop Power Control Forward Power Control IS-95 Power Control IS-2000 Fast Power Control (Reverse Pilot Channel) 9Outer-loop Power Control 9Inner-loop Power Control Bài giảng Mạng TT di động Slice 16 Reverse Open-loop Power Control Reverse Open Loop Power Control Mobile BTS Reverse open loop power is mobile station controlling its transmit power Reverse open loop power control consists of : estimating how strong the mobile station should transmit based on a coarse measurement of how much power it is receiving from the base station some correcting parameters delivered in the access parameters message The Reverse open loop method of power control provides a quick response to changes in signal conditions Bài giảng Mạng TT di động Slice 17 Reverse Open-loop Power Control Problems with Reverse Open Loop Power Control ) Assumes same exact path loss in both directions; therefore, cannot account for asymmetrical path loss ) Estimates are based on total power received; therefore the power received from other cell sites by mobile station introduces inaccuracies Bài giảng Mạng TT di động Slice 18 Reverse Closed Loop Power Control Mobile BTS or Reverse Closed Loop Power Control Signal Strength Measurement Setpoint Compensates for asymmetries between the forward and reverse paths Consists of power up (0) & power down (1) commands sent to the mobile stations, based upon their signal strength measured at the Base Station and compared to a specified threshold (setpoint) Each command requests a 1dB increase or decrease of the mobile station transmit power Transmitted 800 times per second, always at full power Allows to compensate for the effects of fast fading Bài giảng Mạng TT di động Slice 19 Reverse Outer Loop Power Control Mobile BSC BTS or Reverse Closed Loop Power Control Signal Strength Measurement Setpoint Reverse Outer Loop Power Control FER ) Setpoint is varied/dynamic according to the FER (Frame Error Rate) level, typically 1% on the Reverse Traffic Channel (determined at the Base Station Controller), ) Sampled at a rate of 50 frames per second (20 ms / frame) ) Setpoint adjusted every 1-2 seconds Bài giảng Mạng TT di động Slice 20 Closed-loop Power Control Procedure Received the Frame Quality Information from the Reverse Link Outer-loop Algorithm Outer Loop Correction Eb/No Closed-loop Control Threshold No Demodulate and measure Eb/Nt Eb/Nt>Eb/No? Up Power Control Bit Yes Down Power Control Bit Base Station Puncture to Power Control Subchannel Mobile Power Control Command Measurement Power Control Command Measurement Bài giảng Mạng TT di động Slice 21 Forward Power Control in IS-95 Mobile BTS BSC Adjust Fwd power FER Forward Link Power Control The base station continually and slowly decreases power to each mobile station(each user’s forward traffic channel) As the FER (determined at the mobile station) increases, the mobile station requests a Forward Traffic Channel power increase Bài giảng Mạng TT di động Slice 22 Forward Quick Power Control in IS-2000 In CDMA2000, there is a faster method used for Forward Power Control operating much like the IS-95 Reverse Link Power control described next In order to implement Forward Link Quick Power Control,we use Reverse Pilot channel which includes power control subchannel Bài giảng Mạng TT di động Slice 23 Forward Quick Power Control Procedure Received the Frame Quality Information from the Forward Link Outer-loop Algorithm Outer Loop Correction Closed-loop Control Demodulate and measure Eb/Nt Eb/No No Eb/Nt>Eb/No? Up Power Control Bit Yes Down Power Control Bit Mobile Station Puncture to Power Control Subchannel Base Station Power Control Command Measurement Power Control Command Measurement Bài giảng Mạng TT di động Slice 24 Summary of Power Control Reverse Open Loop Power Control Mobile BSC BTS or Reverse Closed Loop Power Control FER Signal Strength Measurement Setpoint Adjust Fwd power Reverse Outer Loop Power Control FER Forward Link Power Control All types of power control work together to minimizes power consumption at the mobile stations, and increases the overall capacity of the system transmit power Bài giảng Mạng TT di động Slice 25 Chuyển giao mềm - Soft handoff Handoff is the process by which a mobile station maintains communications with the Mobile Telephone Switching center (MSC), when traveling from the coverage area of one base station to that of another Handoff keep the call established during the following conditions: ) Subscriber crosses the boundaries of a cell ) Subscriber experiences noise or other interference above a specified threshold ) A base station component experiences an out-of-service condition during a call Bài giảng Mạng TT di động Slice 26 Phân loại: CDMA Handoffs While in the Idle State Idle Handoff Soft Handoff Softer Handoff Inter-System Soft Handoff During a Call CDMA-to-CDMA Handoff CDMA-to-Analog Handoff Bài giảng Mạng TT di động Slice 27 CDMA Idle Handoff PN 108 Ec/Io 104 108 A ng gi a P ne an h C n Sy s sg M l cC sg lM e nn It’s not soft and hard handoff! PN 104 Bài giảng Mạng TT di động Slice 28 CDMA Idle Handoff PN 108 >3dB Ec/Io 104 108 ng gi a P e nn a Ch s sg M l C nc y S sg lM e nn A It’s easy to meet Access failure? PN 104 Bài giảng Mạng TT di động Slice 29 CDMA Soft Handoff CDMA Cell Site B Cell Site B Cell Site A Cell Site A Soft Handoff:The mobile station starts communications with a target base station without interrupting communications with the current serving base station ) Make-before-break ) Directed by the mobile not the base station,Undetectable by user ) Improves call quality Can involve up to three cells simultaneously and use all signals ) Mobile station combines the frames from each cell Bài giảng Mạng TT di động Slice 30 CDMA Soft Handoff Mechanics CDMA soft handoff is driven by the handset Handset continuously checks available pilots Handset tells system pilots it currently sees System assigns sectors (up to max.), tells handset Handset assigns its fingers accordingly Each end of the link chooses what works best, on a frame-by-frame basis Users are totally unaware of handoff Bài giảng Mạng TT di động Slice 31 CDMA Softer Handoff Softer Handoff is between sectors of the same cell, that means multiple sectors of one BTS simultaneously serve a handset Softer handoff occurs in BTS in a single channel element alpha beta gamma Communications are maintained across both sectors until the mobile station transition has completed MSC is aware but does not participate All activities are managed by the cell site Signals received at both sectors can be combined for improved quality Bài giảng Mạng TT di động Slice 32 CDMA-to-CDMA Hard Handoff PSTN PSTN MSC MSC MSC T1 or E1 Links TIA/EIA-41D BSC A (ƒ1) B (ƒ2) BSC BSC A B Between cells operating on different frequencies Between cells that could be on the same frequency, but which are subordinated to different MSC Bài giảng Mạng TT di động Slice 33 Handset Structure Review Digital Rake Receiver Symbols Chips Traffic Correlator PN xxx Receiver RF Section IF, Detector RF PN xxx PN xxx Open Loop Duplexer Traffic Correlator Walsh xx Traffic Correlator AGC RF Walsh xx Transmitter RF Section Walsh xx Pilot Searcher PN xxx Walsh Symbols Σ Viterbi Decoder Messages Bit Packets Audio CPU Vocoder Transmit Gain Adjust Transmitter Digital Section Long Code Gen Audio Messages Bit Packets Bài giảng Mạng TT di động Slice 34 Pilot Sets Pilot Sets Active Candidate Neighbor Remaining There are memorizer (pilot set) in handset, to save the related PN offset index.After power off, all memorizer will be cleared automatically ) Active Set: Pilots associated with the forward traffic channels assigned to the mobile station (max pilots) ) Candidate Set: Pilots not currently in the Active Set, but received by the mobile with sufficient strength to indicate that the corresponding Traffic Channels can be successfully demodulated (max pilots) ) Neighbor Set: Pilots not currently on the Active or Candidate Sets, that are likely handoff candidates (at most 20 pilots) ) Remaining Set: All other possible pilots in the current system on the current CDMA frequency assignment All pilots in a set have the same frequency assignment Bài giảng Mạng TT di động Slice 35 Rules of Soft Handoff The MS assists the BS in the handoff process by measuring and reporting the strengths of received pilots using a Pilot Strength Measurement Message Handset sends PSMM to the system whenever: It notices a pilot in neighbor or remaining set exceeds T_ADD An active set pilot drops below T_DROP for T_TDROP time A candidate pilot exceeds an active by T_COMP Bài giảng Mạng TT di động Slice 36 IS-95 Soft Handoff Signaling Bài giảng Mạng TT di động Slice 37 Power Control during Soft Handoff During soft handoff, the mobile station receives power control bits from multiple base stations If two or more power control subchannels are identical, their power control bits are diversity combined into one per 1.25 ms time slot If the mobile station receives different power control bits from different power control subchannels, it decreases its mean power output level by dB Only if the power control bits from ALL power control subchannels request a power increase, the mobile station increases its mean power output level by dB Bài giảng Mạng TT di động Slice 38 ... Frame 48 144 1/2 Rate Frame 1 /4 Rt 72 24 1/8 1 /4 Rt 36 1/8 Rate set1(8KQCELP & EVRC): Rate set2 (13KQCELP ): Full rate：9.6Kbps Full rate ： 14. 4Kbps Half rate 4. 8Kbps Half rate ：7.2Kbps 1 /4 rate：2.4Kbps... Assignment Primary Channel Secondary channel A段 B段 825MHz A’ 840 MHz 835MHz B’ 段 845 MHz 849 MHz 846 .5MHz N= 37 78 119 160 201 242 283 3 84 425 46 6 507 548 Total 10M Total 5M Frequency Carries Frequency... Band 799 A Band 716 715 667 666 3 34 333 991 1023 A” A’ B’ Channel Numbers 1019 37 78 119 160 201 242 283 3 84 425 46 6 507 548 589 630 691 1 * CDMA A-Band Carriers CDMA B-Band Carriers * 736 777 **
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