WiMax System Design10MHzMIMO

1、wimax mimo demo system design documentationsystem engineeringtable of contentsadaptix proprietary and confidentialitable of contentstable of contents .i1wimax mimo demo system specifications.11.1overall system parameters.11.2mimo demo system setup.22delta specs over baseline system.22.1frame structu

2、re.22.2subcarrier mapping.22.2.1downlink subcarrier mapping.22.2.2uplink subcarrier mapping .32.3coding and modulation.42.3.1coding .42.3.2modulation .42.4adaptive antenna systems.42.4.1antenna configuration.42.4.2downlink.52.4.3uplink.52.4.4transmitter block diagram for stc and sm.52.4.5receiver bl

3、ock diagram for stc and sm.52.4.6supported acm combinations.62.5preamble.72.6map support for mimo .82.6.1frame control messages (fcm) and channel quality feedback .82.6.2mimo operation procedure.83phy layer algorithms.93.1downlink agc algorithm.93.2downlink preamble processing.103.2.1timing/frequenc

4、y acquisition using preamble auto-correlation.123.2.2cell/sector id detection and frequency integer part estimation.133.2.3channel profiling, fine timing adjustment, full band channel estimation.133.2.4post sinr estimation and subchannel selection .143.2.5mobile/fixed mode detection.143.3frequency t

5、racking and sampling clock error estimation.153.4phase noise compensation.163.5downlink channel estimation.163.6power control.173.7uplink channel estimation.173.8metrics generation.173.9uplink maximum ratio combining (mrc) .174platform and task partitioning .174.1hardware platform overview.184.2bs f

6、unction partitioning overview.194.3ss function partitioning overview.19page 1 of 211 wimax mimo demo system specifications1.1overall system parameterschannel bandwidth: 10mhzsampling frequency: 10mspsfft size: 1024 (102.4us)cp length: 1/8*1024=128 (12.8us)symbol duration: fft + cp = 1152 (115.2us)do

7、wnlink subcarrier mapping: pusc & amc, frequency reuse factor 1 (single-sector cell) uplink subcarrier mapping: pusc, frequency reuse factor 1frame duration: 5mstotal samples per frame: 50000total ofdm symbols per frame: 42ttg: 606 samples (121.2us)rtg: 202 samples (40.4us)dl/ul symbol ratio: 32

8、:9antennas configuration: 2x2dl highest spectrum efficiency: 2x spatial multiplexing x 64qam x 5/6 coding = 10 bits/s/hzpage 2 of 211.2 mimo demo system setup2 delta specs over baseline system2.1 frame structureframe control messages (fcm, pusc)fixed downlink data(amc, spatial multiplexing)ttg (121.

9、2us)uplink traffic(pusc, alamouti code)rtg (40.4us)mobile dl data(pusc, alamouti code)freqtimedownlinkuplinkpreamble5 ms framethree ranging symbolsstatically configured through oam&pdynamically changeable based on mobile/fixed traffic8.75mhz4 or2 symbolsfigure 1 frame structurethe frame structur

10、e of the mimo demo system is basically the same as that of the baseline siso system, which is illustrated in figure 1. 2.2 subcarrier mapping2.2.1 downlink subcarrier mappingpusc dl permutationcorrigendum 8.4.8.1.2.1.1page 3 of 21amc dl permutation 16ed6 ch. 8.4.8.3.1.12.2.2 uplink subcarrier mappin

11、gpusccorrigendum d1 ch. 8.4.8.1.5page 4 of 212.3 coding and modulation2.3.1 codingctc for dl, rate = 1/2, 3/4, 5/63gpp,ctc for ul , rate = 1/2, 3/43gpp,2.3.2 modulationdl data: qpsk, 16qam, 64qam ch. 8.4.9.4.2,ul data: qpsk, 16qamch. 8.4.9.4.2,2.4 adaptive antenna systems2.4.1 antenna configurationb

12、oth bs and ss are equipped with 2 complete rf/if branches.page 5 of 212.4.2 downlinkamc subcarrier mapping: adaptive switch between alamouti code, spatial multiplexing and antenna selection.pusc subcarrier mapping: alamouti code.2.4.3 uplinkalamouti code.2.4.4 transmitter block diagram for stc and s

13、mfigure 2 transmitter block diagram for sm (figure 251b in 16ed7)figure 3 transmitter block diagram for alamouti code (figrue 251a in 16ed7)2.4.5 receiver block diagram for stc and smfigure 4 receiver block diagram for alamouti code (figure 251a in 16ed7)page 6 of 212.4.6 supported acm combinationsz

14、onemimostream 1stream 2spectral efficiencymodulationcodingmodulationcodingpuscalamoutiqpsk1/21alamoutiqpsk3/41.5alamouti16qam1/22alamouti16qam3/43alamouti64qam1/23alamouti64qam2/34alamouti64qam5/65amcsm16qam1/2n/a2sm16qam1/2qpsk1/23sm16qam1/2qpsk3/43.5sm16qam1/216qam1/24sm16qam3/4n/a3sm16qam3/4qpsk1

15、/24sm16qam3/4qpsk3/44.5sm16qam3/416qam1/25sm16qam3/416qam3/46sm64qam1/2same with 16qam 3/4sm64qam2/3n/a4sm64qam2/3qpsk1/25sm64qam2/3qpsk3/45.5sm64qam2/316qam1/26sm64qam2/316qam3/47sm64qam2/364qam2/38sm64qam5/6n/a5sm64qam5/6qpsk1/26sm64qam5/6qpsk3/46.5sm64qam5/616qam1/27sm64qam5/616qam3/48sm64qam5/66

16、4qam2/39page 7 of 21sm64qam5/664qam5/6102.5 preamblethe preamble structure is based on that of the baseline system, which is similar to the common sync symbol (css) in 16e, section 8.4.6.1.1. the following figure from the 16e illustrates the preamble structure.note in the baseline system, two minor

17、modifications are made to the css specifications in 16e:the css is transmitting on every frame instead of every 4 frames. as we replace the legacy preamble with css, css should be present in every frame for more regular processing;instead of transmitting the same css symbol across the whole network,

18、 we modulate css with different pn code for cell/sector identification. the pn code uses a truncate version (the first 425 bits) of 2048-fft preamble sequence as defined in table 309 of 16d. to facilitate the channel estimation in the mimo demo system, 2 transmit antennas at the bs shall transmit th

19、e preamble simultaneously. the first antenna should use the pn sequence specified above, and the second antenna shall transmit the sequence obtained by modulating the original one by +1,-1,+1,-1, . to be more specific,let p(n) be the pn sequence used by antenna 1, the preamble for the 2nd antenna, q

20、(n), isq(n) = p(n) * exp(j*pi*n) for n = 0,1,.the algorithms related to the preamble processing, including timing and frequency acquisition, channel profiling and channel quality estimation are explained in the subsequent section.page 8 of 212.6 map support for mimo2.6.1 frame control messages (fcm)

21、 and channel quality feedbackthe coding/modulation scheme for fcm is 16qam 1/2 with stc (alamouti code), without repetition. among all the map_ies defined in the baseline siso system, the following are modified to support mimo operation:dl_amc_map_iedescriptorbitsnotecid8diuc for antenna 14diuc for

22、antenna 24subchannel index6number of subchannels2channel quality feedbacksyntaxbitsnotesmobile_mode_indication4fixed mode = 0b0000; mobile mode = 0b1111;if (mobile_mode_indication = 0b1111) diuc4reserved168shall be set to zero else for (i=0;i= pinstantaneousdecision=mobileinstantaneousdecision=mobil

23、einstantaneousdecision=fixed3.3 frequency tracking and sampling clock error estimationdue to the lack of commonly used continuous pilot tones (cpt), the frequency tracking, sampling clock error estimation, and the common phase error (cpe) caused by the phase noise have to use the scattered pilot ton

24、es.pilot arrangement in pusc and amc are different. the pusc has pilots on the same subcarrier every two symbols, while in amc zone the scattered pilot repeats every 6 symbols. therefore, the tracking parameter has to be calculated with different parameters in pusc and amc respectively, though the a

25、lgorithm used is about the same. we will use pusc as an example to describe the algorithmthe received pilot tones in certain subcarriers are extracted first and differentiated in time dimension. the phases of differentiated pilot tones contain the frequency offset and sampling clock error informatio

26、n. specifically, the intercept of the phase sequence, i.e. the common phase rotation among all pilot tones can be used to estimate the fine frequency offset. the slope of the phase sequence conveys the information on the sampling clock error. when selected pilot tones for the tracking purpose are ev

27、enly distributed between lower half and higher half frequency band, some simplifications can be made to find the intercept and the slope. the following figure illustrates the idea.page 16 of 21the carrier and sampling clock error are estimated using pusc and amc respectively and the result is averag

28、e for adjustment/compensation in the next frame. also, moving average can be applied across several frames to smooth out noise. for algorithm details, please refer to the paper below:3.4 phase noise compensationdue to the limited ss processing power and relative low snr requirement in pusc, we imple

29、ment phase noise compensation algorithm only in amc zone.8 subchannels in the amc zone with the best channel gain are used for cpe compensation. first of all, the channel response on these 8 subchannels is estimated. cpe introduced by the phase noise can be estimated from the remaining (after channe

30、l estimation) phase rotation of all pilot tones in a symbol. and such cpe is then compensated in all the other data subcarriers to remove the phase noise effect.3.5 downlink channel estimationdownlink channel can be estimated using the standard 2 1-d mmse channel estimations, in which the time-dimen

31、sion estimation is performed first followed by the frequency-dimension interpolation.several sets of estimator coefficients suitable for different channel profile can be pre-computed and stored. dsp will choose the set that provides the best estimation quality.for both amc and pusc mapping, time-dim

32、ension estimation may use 3-4 closest received pilot tones, resulting in an estimation window of 6-8 symbols as pilot tones is spaced 2 symbols apart in page 17 of 21the time dimension. note the estimation window size is limited by the processing delay requirement and the available memory for storin

33、g the received pilots.frequency dimension estimator can consist of 4-6 taps. similar to time dimension estimation, frequency estimation can also be performed in a sliding-window style. note the pilot spacing in subcarriers after the time dimension interpolation is not uniform for both amc and pusc m

34、apping. a careful implementation is required to choose the appropriate estimator coefficients and to align the estimated channels. 3.6 power controlthe power control contains open loop and close loop mechanisms. the open loop algorithm performs the power control based on the downlink preamble. with

35、the knowledge of bs transmitting power and the ss agc gain settings, the path loss for the downlink can be calculated. due to the reciprocal tdd channel, the uplink transmitting power is controlled to ensure the ss signal reaching at the bs with a pre-determined power level (determined by the uplink

36、 coding/modulation scheme being used).the close loop power control is based on the initial/periodic ranging signal. the ss first transmits the ranging signal using the power calculated through open-loop algorithm. the bs measures the received ranging signal and compares it against a predefined refer

37、ence value. the difference is then fed to the terminal for fine power adjustment. the frequency of ss doing periodic ranging is yet to be studied.we may need to implement subchannel-based pre-boosting on top of power control.3.7 uplink channel estimationfor pusc, use 2d mmse within each tile. the 12

38、 x 4 mmse matrix is calculated offline and stored in memory. please refer to reference xxx for algorithms on how to generate the matrix. 3.8 metrics generationrefer to the module design for details on the bit metric calculation. 3.9 uplink maximum ratio combining (mrc)the standard mrc combining is p

39、erformed at the bs to achieve higher diversity and snr gain.4 platform and task partitioningpage 18 of 214.1 hardware platform overviewfpgaxilinx xc2v40004m gatesdacad6640/ad6620adc/ducad9857difdac/ddcad6640/ad6620adc/ducad9857difrf transceiver rf transceiver mcuintel ipx 425emifhpiif data interface

40、dsp interconnectiondsp 1yti c64141ghzdsp 1xti c64141ghzif data interfacedsp interconnectionhpiemifdsp 2ti c64161gmhzemifemifhpiemiffigure 6 baseband hardware platform for the mimo demo systemfor the mimo demo system, both bs and ss use the same baseband platform, as illustrated in the above figure.

41、this baseband board consists of two 2 separate dif interfaces and one 4m gates virtex ii fpga, 2 1ghz ti c6414 dsp (dsp 1x and dsp 1y), one 1 ghz ti c6416 dsp (dsp 2), and one intel ipx 425 mcu.page 19 of 214.2 bs function partitioning overview down sample fftup sample ifftfram-ingdeframingchannel estimationranging detectionmodula-tionencod-ingalamouti decodingmetric generationdecodingfpgad