gusucode.com > wlan工具箱matlab源码程序 > wlan/wlan/wlanHTDataRecover.m
function [bits, eqDataSym, varargout] = wlanHTDataRecover( ...
rxHTData, chanEst, noiseVarEst, cfgHT, varargin)
%wlanHTDataRecover Recover information bits from HT-Data field signal
%
% BITS = wlanHTDataRecover(RXHTDATA, CHANEST, NOISEVAREST, CFGHT)
% recovers the information bits in the HT-Data field for a HT-Mixed
% format transmission.
%
% BITS is an int8 column vector of length 8*CFGHT.PSDULength containing
% the recovered information bits.
%
% RXHTDATA is the received time-domain HT-Data field signal. It is a
% Ns-by-Nr matrix of real or complex values, where Ns represents the
% number of time-domain samples in the HT-Data field and Nr represents
% the number of receive antennas. Ns can be greater than the HT-Data
% field length; in this case additional samples at the end of RXHTDATA
% are not used.
%
% CHANEST is the estimated channel at data and pilot subcarriers based on
% the HT-LTF. It is a real or complex array of size Nst-by-Nsts-by-Nr,
% where Nst represents the total number of occupied subcarriers.
%
% NOISEVAREST is the noise variance estimate. It is a real, nonnegative
% scalar.
%
% CFGHT is the format configuration object of type <a href="matlab:help('wlanHTConfig')">wlanHTConfig</a>, which
% specifies the parameters for the HT-Mixed format.
%
% BITS = wlanHTDataRecover(..., CFGREC) allows different algorithm
% options for data recovery via the input CFGREC, which is a
% <a href="matlab:help('wlanRecoveryConfig')">wlanRecoveryConfig</a> configuration object. When the CFGREC input is not
% specified, the default property values of the <a href="matlab:help('wlanRecoveryConfig')">wlanRecoveryConfig</a> object
% are adopted in the recovery.
%
% [..., EQDATASYM, CPE] = wlanHTDataRecover(...) also returns the
% equalized subcarriers and common phase error.
%
% EQDATASYM is a complex Nsd-by-Nsym-by-Nss array containing the
% equalized symbols at data carrying subcarriers. Nsd represents the
% number of data subcarriers, Nsym represents the number of OFDM symbols
% in the HT-Data field, and Nss represents the number of spatial streams.
%
% CPE is a column vector of length Nsym containing the common phase error
% between each received and expected OFDM symbol.
%
% Example:
% % Recover a HT-Data field signal through a SISO AWGN channel using
% % ZF equalization.
%
% cfgHT = wlanHTConfig('PSDULength', 1024); % HT format configuration
% txBits = randi([0 1], 8*cfgHT.PSDULength, 1); % Payload bits
% txHSig = wlanHTData(txBits, cfgHT); % Generate HT-Data signal
%
% % Pass through an AWGN channel with noise variance of 1
% rxHTSig = awgn(txHSig, 1, 1);
%
% % Configure recovery object
% cfgRec = wlanRecoveryConfig('EqualizationMethod', 'ZF');
% % Recover payload bits
% rxBits = wlanHTDataRecover(rxHTSig, ones(56,1), 1, cfgHT, cfgRec);
%
% [numerr, ber] = biterr(rxBits, txBits); % Compare bits
% disp(ber)
%
% See also wlanHTConfig, wlanRecoveryConfig, wlanHTData.
% Copyright 2015-2016 The MathWorks, Inc.
%#codegen
narginchk(4,5);
nargoutchk(0,3);
% Calculate CPE if requested
if nargout>2
calculateCPE = true;
else
calculateCPE = false;
end
% HT configuration input self-validation
validateattributes(cfgHT, {'wlanHTConfig'}, {'scalar'}, mfilename, ...
'HT-Mixed format configuration object');
s = validateConfig(cfgHT, 'MCS');
% Validate rxHTData
validateattributes(rxHTData, {'double'}, {'2d','finite'}, ...
'rxHTData', 'HT-Data field signal');
% Validate chanEst
validateattributes(chanEst, {'double'}, {'3d','finite'}, ...
'chanEst', 'channel estimates');
% Validate noiseVarEst
validateattributes(noiseVarEst, {'double'}, ...
{'real','scalar','nonnegative','finite'}, ...
'noiseVarEst', 'noise variance estimate');
numSTS = cfgHT.NumSpaceTimeStreams;
numRx = size(rxHTData, 2);
mcsTable = wlan.internal.getRateTable(cfgHT);
pNcbpssi = mcsTable.NCBPS/mcsTable.Nss;
numDBPS = mcsTable.NDBPS;
rate = mcsTable.Rate;
numOFDMSym = s.NumDataSymbols;
numSS = mcsTable.Nss;
STBC = numSTS - numSS;
mSTBC = 1 + (STBC~=0);
% If PSDU is empty there is no data to return
if cfgHT.PSDULength == 0
bits = zeros(0, 1, 'int8');
eqDataSym = zeros(mcsTable.NSD, 0, mcsTable.Nss);
if calculateCPE==true
varargout{1} = []; % CPE
end
return;
end
% Optional recovery configuration input validation
if nargin == 5
validateattributes(varargin{1}, {'wlanRecoveryConfig'}, {'scalar'}, ...
mfilename, 'recovery configuration object');
symOffset = varargin{1}.OFDMSymbolOffset;
pilotPhaseTracking = varargin{1}.PilotPhaseTracking;
eqMethod = varargin{1}.EqualizationMethod;
maxLDPCIterationCount = varargin{1}.MaximumLDPCIterationCount;
earlyTermination = varargin{1}.EarlyTermination;
else % use defaults
symOffset = 0.75;
pilotPhaseTracking = 'PreEQ';
eqMethod = 'MMSE';
maxLDPCIterationCount = 12;
earlyTermination = false;
end
% Get OFDM related parameters
[cfgOFDM,dataInd,pilotInd] = wlan.internal.wlanGetOFDMConfig( ...
cfgHT.ChannelBandwidth, cfgHT.GuardInterval, 'HT', numSTS);
% Cross validate input
numST = numel([dataInd; pilotInd]); % Total number of occupied subcarriers
coder.internal.errorIf(size(chanEst, 1) ~= numST, ...
'wlan:wlanHTDataRecover:InvalidHTChanEst1D', numST);
coder.internal.errorIf(size(chanEst, 2) ~= numSTS, ...
'wlan:wlanHTDataRecover:InvalidHTChanEst2D', numSTS);
coder.internal.errorIf(size(chanEst, 3) ~= numRx, ...
'wlan:wlanHTDataRecover:InvalidHTChanEst3D');
% Extract data and pilot subcarriers from channel estimate
chanEstData = chanEst(dataInd,:,:);
chanEstPilots = chanEst(pilotInd,:,:);
% Cross-validation between inputs
minInputLen = numOFDMSym*(cfgOFDM.FFTLength+cfgOFDM.CyclicPrefixLength);
coder.internal.errorIf(size(rxHTData, 1) < minInputLen, ...
'wlan:wlanHTDataRecover:ShortHTDataInput', minInputLen);
% Processing for all streams/numRx
% OFDM demodulation
[ofdmDemodData, ofdmDemodPilots] = wlan.internal.wlanOFDMDemodulate(...
rxHTData(1:minInputLen, :), cfgOFDM, symOffset);
if calculateCPE==true || strcmp(pilotPhaseTracking, 'PreEQ')
% Get reference pilots, from IEEE Std 802.11-2012, Eqn 20-58/59
% For HT-MF, offset by 3 to allow for L-SIG and HT-SIG pilot symbols
z = 3;
refPilots = wlan.internal.htPilots(numOFDMSym, z, ...
cfgHT.ChannelBandwidth, numSTS);
% Estimate CPE and phase correct symbols
cpe = wlan.internal.commonPhaseErrorEstimate(ofdmDemodPilots, ...
chanEstPilots, refPilots);
if strcmp(pilotPhaseTracking, 'PreEQ')
ofdmDemodData = wlan.internal.commonPhaseErrorCorrect(ofdmDemodData, cpe);
end
if calculateCPE==true
varargout{1} = cpe.'; % Permute to Nsym-by-1
end
end
% Equalization
if mcsTable.Nss < numSTS
[eqDataSym, csiData] = wlan.internal.wlanSTBCCombine(ofdmDemodData, ...
chanEstData, mcsTable.Nss, eqMethod, noiseVarEst);
else
[eqDataSym, csiData] = wlan.internal.wlanEqualize(ofdmDemodData, ...
chanEstData, eqMethod, noiseVarEst);
end
% LLR Demodulation: per Nss, account for nVar
qamDemodOut = wlan.internal.wlanConstellationDemodulate(eqDataSym, ...
mcsTable.NBPSCS, noiseVarEst);
% Apply bit-wise CSI
qamDemodOut = bsxfun(@times, ...
reshape(qamDemodOut, mcsTable.NBPSCS, [], numOFDMSym, mcsTable.Nss), ...
reshape(csiData, 1, [], 1, mcsTable.Nss)); % [Nbpscs Nsd Nsym Nss]
% Deinterleave per OFDM symbol
deintlvrOut = zeros(pNcbpssi*numOFDMSym, mcsTable.Nss);
if strcmp(cfgHT.ChannelCoding,'BCC')
for symIdx = 1:numOFDMSym
deintlvrOut((symIdx-1)*pNcbpssi+(1:pNcbpssi), :) = ...
wlan.internal.wlanBCCDeinterleave( ...
reshape(qamDemodOut(:,:,symIdx,:), [], mcsTable.Nss), ...
'HT', pNcbpssi, mcsTable.NBPSCS, 20*cfgOFDM.FFTLength/64, mcsTable.Nss);
end
else
% Deinterleaving is not required for LDPC
deintlvrOut = reshape(real(qamDemodOut), [], numSS);
end
% Stream deparsing
streamDeparserOut = wlan.internal.wlanStreamDeparser(deintlvrOut, ...
mcsTable.NES, mcsTable.NBPSCS);
% Channel decoding
if strcmp(cfgHT.ChannelCoding,'BCC')
% BCC Channel decoding per Nes
htDataBits = zeros(round(size(streamDeparserOut, 1)*mcsTable.Rate), ...
mcsTable.NES, 'int8');
for nesIdx = 1:mcsTable.NES
htDataBits(:, nesIdx) = wlan.internal.wlanBCCDecode( ...
streamDeparserOut(:, nesIdx), mcsTable.Rate);
end
descramMat = htDataBits.';
descramIn = descramMat(:);
else
% LDPC Channel decoding
numPLD = cfgHT.PSDULength*8 + 16; % Number of payload bits
% LDPC decoding parameters, IEEE Std 802.11-2012, Section
% 20.3.11.17.5.
cfg = wlan.internal.getLDPCparameters(numDBPS, rate, mSTBC, numPLD);
descramIn = wlan.internal.wlanLDPCDecode(streamDeparserOut(:), cfg, ...
maxLDPCIterationCount, earlyTermination);
end
% Combine bits from multiple decoders, descramble with derived initial state
iniY = descramIn(1:7,1); % Extract the first 7 scrambler init bits
scramInit = [iniY(3)+iniY(7) iniY(2)+iniY(6) iniY(1)+iniY(5) ...
iniY(4)+iniY(3)+iniY(7) iniY(3)+iniY(2)+iniY(6) ...
iniY(2)+iniY(1)+iniY(5) iniY(1)+iniY(4)+iniY(3)+iniY(7)];
scramInit = mod(scramInit, 2);
% Remove the padded and tail bits to output only the data bits
descramOutData = wlan.internal.wlanScramble( ...
descramIn(1:(16+8*cfgHT.PSDULength),:), scramInit);
% Remove the 16 service bits
bits = descramOutData(17:end);
end