105 lines
3.6 KiB
Matlab
105 lines
3.6 KiB
Matlab
function steeringMat = heUserBeamformingFeedback(rx,cfgNDP,varargin)
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%heUserBeamformingFeedback HE user beamforming feedback
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%
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% STEERINGMAT = heUserBeamformingFeedback(RX,CFGNDP) returns the steering
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% matrix recommended to beamform towards the user of interest. The
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% steering matrix is calculated using SVD.
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%
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% STEERINGMAT = heUserBeamformingFeedback(RX,CFGNDP,CFOCOMP) performs
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% carrier frequency offset estimation and compensation on the received
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% waveform before calculating the steering matrix if CFOCOMP is set to
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% TRUE.
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%
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% STEERINGMAT is a Nst-by-Nr-by-Nsts array containing the recommended
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% full band beamforming steering matrix. Nst is the number of occupied
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% subcarriers, Nr is the number of receive antennas, and Nsts is the
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% number of space-time-streams.
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%
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% RX is the received NDP at the station.
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%
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% CFGNDP is the format configuration object of type <a href="matlab:help(wlanHESUConfig')">wlanHESUConfig</a>.
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% Copyright 2017-2018 The MathWorks, Inc.
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narginchk(2,3);
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if nargin == 3
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cfoCompensate = varargin{1};
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validateattributes(cfoCompensate,{'logical'},{'nonnan','finite'},mfilename,'',3);
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else
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cfoCompensate = false;
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end
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chanBW = string(cfgNDP.ChannelBandwidth);
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ind = wlanFieldIndices(cfgNDP);
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fs = wlanSampleRate(cfgNDP);
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% Packet detect and determine coarse packet offset
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coarsePktOffset = wlanPacketDetect(rx,chanBW);
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if isempty(coarsePktOffset) % If empty no L-STF detected; try 0
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% Synchronization failed, return empty steering matrix
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steeringMat = [];
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return;
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end
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if cfoCompensate
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% Extract L-STF and perform coarse frequency offset correction
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lstf = rx(coarsePktOffset+(ind.LSTF(1):ind.LSTF(2)),:);
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coarseFreqOff = wlanCoarseCFOEstimate(lstf,chanBW);
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rx = helperFrequencyOffset(rx,fs,-coarseFreqOff);
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end
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% Extract the non-HT fields and determine fine packet offset
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nonhtfields = rx(coarsePktOffset+(ind.LSTF(1):ind.LSIG(2)),:);
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finePktOffset = wlanSymbolTimingEstimate(nonhtfields,chanBW);
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% Determine final packet offset
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pktOffset = coarsePktOffset+finePktOffset;
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% If packet detected outwith the range of expected delays from
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% the channel modeling; packet error
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if pktOffset>50
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% Synchronization failed, return empty steering matrix
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steeringMat = [];
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return;
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end
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if cfoCompensate
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% Extract L-LTF and perform fine frequency offset correction
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rxLLTF = rx(pktOffset+(ind.LLTF(1):ind.LLTF(2)),:);
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fineFreqOff = wlanFineCFOEstimate(rxLLTF,chanBW);
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rx = helperFrequencyOffset(rx,fs,-fineFreqOff);
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end
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% Demodulate HE-LTF with info for all RUs
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rxHELTF = rx(pktOffset+(ind.HELTF(1):ind.HELTF(2)),:);
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demodHELTF = wlanHEDemodulate(rxHELTF,'HE-LTF',cfgNDP);
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% Extract the demodulated HE-LTF RU
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demodHELTFRU = demodHELTF;
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% Channel estimate with info from current RU
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chanEstUser = heLTFChannelEstimate(demodHELTFRU,cfgNDP);
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% Get cyclic shift and inverse
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numSTS = cfgNDP.NumSpaceTimeStreams;
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csh = -wlan.internal.getCyclicShiftVal('VHT',numSTS,wlan.internal.cbwStr2Num(chanBW));
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Nfft = (fs/20e6)*256;
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% Indices of active subcarriers in the NDP
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ndpOFDMInfo = wlanHEOFDMInfo('HE-Data',cfgNDP);
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k = ndpOFDMInfo.ActiveFrequencyIndices;
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chanEstMinusCSD = permute(wlan.internal.cyclicShift(permute(chanEstUser,[1 3 2]),csh,Nfft,k),[1 3 2]);
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chanEstPerm = permute(chanEstMinusCSD,[3 2 1]); % Nr-by-Nsts-by-Nst
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% Compute the feedback matrix using singular value decomposition
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% for the streams allocated to the user
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Nst = size(chanEstPerm,3);
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numRx = size(demodHELTF,3);
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V = complex(zeros(Nst,numSTS,numRx)); % Nst-by-Nsts-by-Nr
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for ist = 1:Nst
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[~,~,V(ist,:,:)] = svd(chanEstPerm(:,:,ist),'econ');
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end
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steeringMat = permute(V,[1 3 2]); % Nst-by-Nr-by-Nsts
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end
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