3G的三種制式編碼方式

1、編碼方式：CDMA2000 和 UMTS 的擾碼均采用的是偽隨機(jī)序列 PN Code。CDMA2000CDMA2000 采用的是偽隨機(jī)碼自相關(guān)特性，整個(gè)系統(tǒng)只有一個(gè)短碼215 和一個(gè)242GPS 同步時(shí)鐘的控制下，按照一定的規(guī)則，每個(gè)基站和手機(jī)得到相應(yīng)的PN Offset，從而實(shí)現(xiàn)扇區(qū)以及手機(jī)反向信道的區(qū)分，同時(shí)又保證所有在空中出現(xiàn)的信號(hào)近似于噪聲，以減少相互之間的干擾。技術(shù)上實(shí)現(xiàn)最簡(jiǎn)單。 ShortPN（15 位）用于區(qū)分不同的基站或扇區(qū) (64 Walsh code)用于區(qū)分不同的前向信道 LongPN （42 位）用于分不同的反向信道相同的偽隨機(jī)碼當(dāng)時(shí)間對(duì)齊時(shí),其自相關(guān)的歸一化值為 1.

2、相同的偽隨機(jī)碼當(dāng)時(shí)間不對(duì)齊時(shí),其自相關(guān)的歸一化值為-1/L.當(dāng) L 趨于較大值時(shí), 該值趨于 0.UMTS-FDD：偽隨機(jī)碼的互相關(guān)特性沒有自相關(guān)特性那樣強(qiáng)的規(guī)律性. 只有一些特殊的碼組之間有一定的規(guī)律性.優(yōu)選對(duì)Preferred :m-sequences .-1- 2+1 and + 2-1n=odd- 2+1 and + 2-1n=even例: n=3, -1, -5, +3n=4, -1, -9, +7GOLDCODE :利用一對(duì)優(yōu)選對(duì)Preferred Pair, 即可得到一個(gè)新的序列GOLDCODE.m-squences 2 -1,GOLD CODE :2+1(包含兩個(gè)原始 pref

3、erred pair m-sequences)GOLDCODE m-sequence )GOLDCODE 的自相關(guān)特(Auto-correlation): 歸一化: Ci(t)Cj(t) = 1i =jGOLDCODE (Cross-correlation)():歸一化:|Ci(t)Cj(t) |1i j(最大不超過(guò)| 2|)WCDMA 中Uplinkn=25(024)Downlink n=18(017)則有,最差情況: Uplink |2+ 1 /2|=0.00024由于每個(gè)扇區(qū)分配不同的擾碼，相互之間的互相關(guān)特性與時(shí)間沒有對(duì)應(yīng)關(guān)系，因此UMTS FDD 系統(tǒng)可以不使用 GPS，但技術(shù)實(shí)現(xiàn)相

4、對(duì)復(fù)雜。UMTS-TDD：TD-SCDMA 體制中采用的擾碼嚴(yán)格意義上講與前面介紹的兩種擾碼有很大不同；首先這里的擾碼序列長(zhǎng)度很短，因此所謂的自相關(guān)和互相關(guān)特性都不是很理想；其次，由于采用的擾碼序列長(zhǎng)度非常短，只有 16chips,因此隨機(jī)化的效果會(huì)比較有限。因此擾碼在這里主要是識(shí)別扇區(qū)的作用，扇區(qū)隔離和將信號(hào)隨機(jī)化的作用相對(duì)比較薄弱。實(shí)際使用中，每個(gè)扇區(qū)會(huì)分配給一個(gè)擾碼，周圍相鄰小區(qū)不能使用相同的擾碼。16 128 個(gè)擾碼。對(duì)擾碼的識(shí)別和解調(diào)主要是利用了自相關(guān)特性，也就是相同序列，當(dāng)時(shí)間對(duì)齊的時(shí)候結(jié)果為11OVSF 1.28Mcps。OVSF code CDMA 信道。ScramblingC

5、oding,用于區(qū)分不同的扇區(qū)。PN Sequence Midamble Code。1.28Mcps。TD-SCDMA 中，非常規(guī)時(shí)隙是沒有加擾的（Dwpts,Gp,UpPts 時(shí)隙是不加擾的）。The TDMA frame has a duration of 10 ms and is divided into 2 sub-frames of 5ms. The frame structure for each sub-frame in the 10ms frame length is the same.Subframe 5ms (6400chip) Switching Point1.28Mcp

6、sSubframe 5ms (6400chip) Switching PointDwPTS(96chips)GP (96chips)UpPTS(160chips)Switching PointData Symbols 352 chipsData Symbols 352 chipsMidamble144chipsData Symbols 352chipsGp16ChipsFigure 18B: Structure of the sub-frame for 1.28Mcps TDD optionTime slot#n (n from 0 to 6): the nthtraffic time slo

7、t, 864 chips duration; DwPTS: downlink pilot time slot, 96 chips duration;UpPTS: uplink pilot time slot, 160 chips duration;GP: main guard period for TDD operation, 96 chips duration;bps:通常描述的是原始數(shù)據(jù)速率；sps:FEC 編碼之后的數(shù)據(jù)速率；cps:譜編碼之后的數(shù)據(jù)速率。7 個(gè)時(shí)隙，常規(guī)時(shí)隙的時(shí)間長(zhǎng)度為 675us 即 864 個(gè) chips,DwPTS 的時(shí)間長(zhǎng)度為 75us,UpPTS為 125us

8、,Gp 為 75us。功率控制的頻率為 200 次/秒=1000(ms)/5(ms)。TS0 只能是下行時(shí)隙，TS1 只能是上行時(shí)隙；TS2-TS6 可以根據(jù)需要確定發(fā)射方向。常規(guī)時(shí)隙的格式如下：SS symbol(s)SS symbol(s)TPC symbol(s)Data symbolsMidambleData symbolsGP144 chips864 ChipsFor the number of TPC symbols per time slot there are 3 possibilities, that can be configured by higher layers in

9、dividually for each timeslot:one TPCsymbolno TPCsymbols16/SF TPCsymbolsSo, in case 3), when SF=1, there are 16 TPC symbols which correspond to 32 bits (for QPSK) and 48 bits (for 8PSK).In the following the uplink is described only. For the description of the downlink, downlink (DL) and uplink (UL) h

10、ave to be interchanged.三個(gè)特殊時(shí)隙：DwPTS :GPGP（32Chips）SYNC-DL（64chips）下行導(dǎo)頻時(shí)隙 downlink pilot time slot，長(zhǎng)度為 96chips。UpPTS:SYNC-ULSYNC-UL（128chips）GP（32Chips）上行導(dǎo)頻時(shí)隙 uplink pilot time slot ,長(zhǎng)度 160chips。GP：（DwPTS/UpPTS 中）mainguardperiod96chipsExamples for symmetric and asymmetric UL/DL allocations are given

11、in figure 18C.5 ms5 mssymmetric DL/UL allocation 對(duì)稱模式5 ms5 msasymmetric DL/UL allocation 非對(duì)稱模式Figure 18C: 1.28Mcps TDD sub-frame structure examplesDPCH： SF=16OVSF SF=1SF=2-8 不使用。 SF 根據(jù)需要可以變化，SF=1-16SF 來(lái)改變 速率。 SF=1.28MCPS/Symbol rate（糾錯(cuò)編碼之后），擴(kuò)譜系數(shù)隱含數(shù)據(jù)速率的影子，和數(shù)據(jù)速率直接相關(guān)。每個(gè)數(shù)據(jù)塊對(duì)應(yīng)的 Number of Symbols, 不同的 SF

12、對(duì)應(yīng)不同數(shù)量的 Symbols;這里一QPSK 2 bits,下表中右邊的數(shù)值代表的是一個(gè)數(shù)據(jù)塊對(duì)應(yīng)的符號(hào)數(shù)。Table 8A: number of symbols per data field in a traffic burstSpreading factor (Q)124816Number of symbols (N) per data field in Burst352176884422TFCI： TFCI：transportformat combinationIndicator DPCH 傳送的數(shù)據(jù)結(jié)構(gòu)、格式和組成。是系統(tǒng)正常工作的重要控制參數(shù)。 TFCI code Word 4 s

13、ub-frame TFCI 需10ms 的發(fā)射時(shí)間。 TFCI code word OVSF data block 的部分空間。TPC SS 的情況：1 1 st partofTFCI codeword2 ndpartofTFCI codeword3 rd part ofTFCI code word4 thpartofTFCI codewordData symbolsMidambleData symbolsGPData symbolsMidambleData symbolsGPTime slot x (864 Chips)Timeslotx(864Chips)Sub-frame 5msSub-

14、frame 5msRadio Frame 10msTPC SS 的情況：1 st part of TFCI code wordTPCsymbols3 rd part of TFCI code wordTPCsymbolsSSsymbols2 ndpart of TFCI code GSS4 th part of TFCI code wordGDatasymbolsMidambleDataTime slot x (864 Chips) Sub-frame 5msDatasymbolsMidambleDatasymbolsPPTimeslotx(864Sub-frame5msRadio Frame

15、 10ms從上面 TFCI 的結(jié)構(gòu)，我們發(fā)現(xiàn) TD 是以幀為單位改變業(yè)務(wù)類型的；同時(shí)，我們發(fā)現(xiàn)TPC、TFCI、SS 都是隨路控制信息。TPC： TPC：Transmitter Power Control,功率控制信息，是保證系統(tǒng)正常工作的重要參數(shù)，上行下行均可以發(fā)送，以控制對(duì)方的信號(hào)發(fā)射功率。 sub-frame 200 /秒。 TPC TFCI datablock 空間。The TPC symbols are spread with the same spreading factor (SF) and spreading code as the data parts of the resp

16、ective physical channel.SS symbol(s)SS symbol(s)TPC symbol(s)Data symbolsMidambleData symbolsGP144 chips864 ChipsFigure 18G: Position of TPC information in the traffic burst in downlink and uplinkFor the number of TPC symbols per time slot there are 3 possibilities, that can be configured by higher

17、layers individually for each timeslot:one TPCsymbolno TPCsymbols16/SF TPCsymbolsSo, in case 3), when SF=1, there are 16 TPC symbols which correspond to 32 bits (for QPSK) and 48 bits (for 8PSK).In the following the uplink is described only. For the description of the downlink, downlink (DL) and upli

18、nk (UL) have to be interchanged.Each of the TPC symbols for uplink power control in the DL will be associated with an UL time slot and an UL CCTrCH pair. This association varies withthe number of allocated UL time slots and UL CCTrCHs on these time slots (time slot and CCTrCH pair)andthe allocated T

19、PC symbols in theDL.In case a UE hasmore than one channelisationcodeand/orchannelisation codes being of lower spreading factor than 16 and using 16/SF SS and 16/SF TPCsymbols,The relationship between the TPC Bits and the transmitter power control command for 8PSK is given in table 8CTable 8C: TPC Bi

20、t Pattern for 8PSKTPC BitsTPC Bits000110TPCDownUpMeaningDecrease Tx Increase Tx PowerCoding of the TPC Bit Pattern for QPSKTPC BitsTPC commandMeaning00DownDecrease Tx Power11UpIncrease Tx PowerSS：SS ：Synchronisation Shift ,TD-SCDMA 基站的時(shí)間要完全同步。Transmission of uplink synchronization control (ULSCGSM Timing Advance.SS 就是發(fā)送該控制信息。 TFCI datablock 空間。 SS Timing Adjustment 的步長(zhǎng)可以是：每Msub-frames，調(diào)整（k/8）Tc,Tc