gusucode.com > wlan工具箱matlab源码程序 > wlan/wlan/+wlan/+internal/wlanWindowing.m
function y = wlanWindowing(x, FFTLen, wLength, guardInterval, preambleLength)
%wlanWindowing Window time-domain OFDM symbols
%
% Note: This is an internal undocumented function and its API and/or
% functionality may change in subsequent releases.
%
% Y = wlanWindowing(X,FFTLEN,WLENGTH,GUARDINTERVAL,PREAMBLELENGTH)
% returns the time-domain windowed signal for the OFDM signal. The
% windowing function for OFDM waveform is defined in IEEE Std
% 802.11-2012.
%
% Y is a complex Ns-by-Nt matrix containing the windowed signal, where Ns
% is the number of time domain samples, and Nt is the number of transmit
% antennas.
%
% X is a complex Ns-by-Nt matrix array containing the time-domain OFDM
% signal.
%
% FFTLEN is the FFT length used to modulate the OFDM symbols. The FFT
% length depends on channel bandwidth of the input signal and should be
% equal to 32, 64, 128, 256 or 512.
%
% WLENGTH is the windowing length in samples to apply. The WLENGTH of
% zero samples means no windowing.
%
% GUARDINTERVAL is the cyclic prefix for the data field within a packet,
% specified as 'Long' or 'Short'.
%
% PREAMBLELENGTH is the number of samples in the preamble field of the
% input signal.
%
% Example:
% % Window a time domain waveform for an 802.11ac VHT transmission.
%
% cfgVHT = wlanVHTConfig; % Create format configuration
% lstf = wlanLSTF(cfgVHT); % Preamble generation
% lltf = wlanLLTF(cfgVHT);
% lsig = wlanLSIG(cfgVHT);
% vhtsiga = wlanVHTSIGA(cfgVHT);
% vhtstf = wlanVHTSTF(cfgVHT);
% vhtltf = wlanVHTSTF(cfgVHT);
% vhtsigb = wlanVHTSIGB(cfgVHT);
% preamble = [lstf;lltf;lsig;vhtsiga;vhtstf;vhtltf;vhtsigb];
% % Generate Data field
% rng(0);
% txPSDU = randi([0,1], cfgVHT.PSDULength*8,1);
% data = wlanVHTData(txPSDU,cfgVHT);
% txWaveform = [preamble; data];
% % Window transmit signal
% wLength = 16; % Windowing samples for Transition time of 100nsec
% sizeFFT = 256; % FFT size for 80MHz bandwidth
% windowedWaveform = wlanWindowing(txWaveform,sizeFFT, ...
% wLength,cfgVHT.GuardInterval,length(preamble));
% % Display the spectrum
% spectrumAnalyzer = dsp.SpectrumAnalyzer('SampleRate',80e6, ...
% 'ShowLegend',true,'Window','Flat Top','ChannelNames', ...
% {'Transmit Waveform','Windowed waveform'});
% % Oversample the signal by a factor of 2 before the display
% spectrumAnalyzer([resample([txWaveform;zeros(15,1)],2,1), ...
% resample(windowedWaveform,2,1)]);
%
% See also wlanWaveformGenerator, wlanTGnChannel.
% Copyright 2015-2016 The MathWorks, Inc.
%#codegen
validateattributes(x,{'double'},{'2d','finite','nonempty'}, ...
mfilename,'signal input');
if wLength == 0
y = x;
return;
end
% Initialize parameters
switch FFTLen
case 32
shortCyclicPrefix = 4;
sampleRate = 10e6;
case 128
shortCyclicPrefix = 16;
sampleRate = 40e6;
case 256
shortCyclicPrefix = 32;
sampleRate = 80e6;
case 512
shortCyclicPrefix = 64;
sampleRate = 160e6;
otherwise % 64 for 20/10/5 MHz
shortCyclicPrefix = 8;
sampleRate = 20e6; % nominal 20 MHz
end
longCyclicPrefix = FFTLen/4;
longSymLength = 4e-6*sampleRate; % In samples, works for 5/10/20 MHz
shortSymLength = 3.6e-6*sampleRate;
% Number of transmit antennas
numTx = size(x,2);
y = complex(zeros(0,numTx));
% Standard defined windowing indices and magnitude for Long symbols
[indLong, magLong] = windowingEquation(wLength,longSymLength);
ofdmSymLen = FFTLen+longCyclicPrefix;
% Check the wLength to be less than or equal to twice the CP
if strcmp(guardInterval,'Long')
coder.internal.errorIf(wLength>(2*longCyclicPrefix),'wlan:wlanWindowing:InvalidWindowLength');
else
coder.internal.errorIf(wLength>(2*shortCyclicPrefix),'wlan:wlanWindowing:InvalidWindowLength');
end
if FFTLen==32 % Special case for S1G 1 MHz mode packet structure
% Window the STF (4 symbols) as one symbol
stfSym = x(1:(4*ofdmSymLen),:);
stfSymExtended = windowLSTFandLLTF(stfSym,FFTLen, ...
2*ofdmSymLen,2*longSymLength,wLength,numTx);
suffixstfSym = stfSymExtended(end-(wLength)+2:end,:);
% Window the first half of LTF (2 symbols)
ltfSymPart1 = x((4*ofdmSymLen)+(1:(2*ofdmSymLen)),:);
ltfSymPart1Extended = windowLSTFandLLTF(ltfSymPart1,FFTLen, ...
ofdmSymLen,longSymLength,wLength,numTx);
prefixltfSym = ltfSymPart1Extended(1:wLength-1,:);
suffixltfSym = ltfSymPart1Extended(end-(wLength)+2:end,:);
suffixTrainingSym = suffixltfSym;
% Combine STF and LTF and overlap prefix and suffix
trainingSymOut = [stfSymExtended(1:end-wLength+1,:); ...
(suffixstfSym+prefixltfSym); ....
ltfSymPart1Extended(wLength:end,:)];
remainingSym = x((6*ofdmSymLen)+1:end,:);
preambleLessFirstTwoFields = x((6*ofdmSymLen)+1:preambleLength,:);
else % All other bandwidths have the same packet structure
% Windowing first two fields; the L-STF and L-LTF or STF and LTF1 (S1G)
trainingSym = x(1:(4*ofdmSymLen),:);
trainingSymExtended = windowLSTFandLLTF(trainingSym,FFTLen, ...
ofdmSymLen,longSymLength,wLength,numTx);
trainingSymOut = windowSym(trainingSymExtended,wLength);
suffixTrainingSym = trainingSymOut(end-(wLength)+2:end,:);
remainingSym = x((4*ofdmSymLen)+1:end,:);
preambleLessFirstTwoFields = x(4*ofdmSymLen+1:preambleLength,:);
end
if strcmp(guardInterval,'Long')
% Process remaining symbols
numSym = length(remainingSym)/ofdmSymLen;
% Check input length
coder.internal.errorIf(mod(numSym,1)~=0,'wlan:wlanWindowing:IncorrectInputLength');
% Reshape by SymLength-NumSym-NumTx
remainingSym = reshape(remainingSym,ofdmSymLen,numSym,numTx);
% Extend symbol length before windowing
remainingSymExt = [remainingSym(end-(abs(indLong(1))+FFTLen/4)+1:end-FFTLen/4,:,:); ...
remainingSym; remainingSym(FFTLen/4+(1:wLength/2),:,:)];
% Apply windowing on the extended symbol portion
remaingSymExtWin = bsxfun(@times,remainingSymExt,magLong);
remaingSymOut = windowSym(remaingSymExtWin,wLength);
prefixSym = remaingSymOut(1:wLength-1,:);
y = [trainingSymOut(1:end-wLength+1,:); ...
(suffixTrainingSym+prefixSym); ....
remaingSymOut(wLength:end,:)];
elseif strcmp(guardInterval,'Short')
% Extract data field
data = x(preambleLength+1: end,:);
% Reshape preamble (less L-LTF and L-STF) by SymLength-NumSym-NumTx
numSym = size(preambleLessFirstTwoFields,1)/longSymLength;
preambleSym = reshape(preambleLessFirstTwoFields,ofdmSymLen,numSym,numTx);
% Extend symbol length
preambleSymExt = [preambleSym(end-(abs(indLong(1))+FFTLen/4)+1:end-FFTLen/4,:,:); ...
preambleSym; preambleSym(FFTLen/4+(1:wLength/2),:,:)];
% Apply windowing to all preamble symbols
remaingSymExtWin = bsxfun(@times,preambleSymExt,magLong);
preambleSym = windowSym(remaingSymExtWin,wLength);
prefixPreambleSym = preambleSym(1:wLength-1,:);
suffixPreambleSym = preambleSym(end-(wLength)+2:end,:);
% Number of data symbols
numDataSym = length(data)/(FFTLen+shortCyclicPrefix);
% Check input length
coder.internal.errorIf(mod(numDataSym,1)~=0,'wlan:wlanWindowing:IncorrectInputLength');
if isempty(data) % NDP
% Only the preamble fields
y = [trainingSymOut(1:end-wLength+1,:); ...
(suffixTrainingSym+prefixPreambleSym); ...
preambleSym(wLength:end-wLength+1,:); ...
suffixPreambleSym];
else
% Window the data symbols
% Reshape data by SymLength x NumSym x NumTx
dataSym = reshape(data,FFTLen+shortCyclicPrefix,numDataSym,numTx);
% Standard defined windowing equations
[index, magnitude] = windowingEquation(wLength,shortSymLength);
% Extend symbol length
dataSymExt = [dataSym(end-(abs(index(1))+FFTLen/8)+1:end-FFTLen/8,:,:); ...
dataSym;dataSym(FFTLen/8+(1:wLength/2),:,:)];
% Apply windowing to all symbols
dataSymExtWin = bsxfun(@times,dataSymExt,magnitude);
dataSym = windowSym(dataSymExtWin,wLength);
prefixdataSym = dataSym(1:wLength-1,:);
y = [trainingSymOut(1:end-wLength+1,:); ...
(suffixTrainingSym+prefixPreambleSym); ...
preambleSym(wLength:end-wLength+1,:); ...
(suffixPreambleSym+prefixdataSym);...
dataSym(wLength:end,:)];
end
end
end
function out = windowSym(inputSym, wlength)
% This function is performing the overlap and add operation on the extended
% window potion.
% Set the windowing length equal to the preIndx window length.
W = wlength-(wlength>0);
firstRegion = inputSym(1:end-W,1,:);
overlapRegion = inputSym(end-W+1:end,1:end-1,:)+inputSym(1:W,2:end,:);
middleRegion = [overlapRegion; inputSym(W+1:end-W,2:end,:)];
lastRegion = inputSym(end-W+1:end,end,:);
out = [firstRegion;reshape(middleRegion,[],1,size(inputSym,3));lastRegion];
end
function [windowIdx,windowMag] = windowingEquation(TTR, symLength)
% The windowing function for the OFDM symbols is defined in IEEE Std
% 802.11-2012, Section 18.3.2.5, Equation 18-4.
preIdx = -TTR/2+1:TTR/2-1;
midIdx = TTR/2:(symLength-TTR/2)-1;
postIdx = symLength-TTR/2:(symLength+TTR/2)-1;
windowIdx = [preIdx midIdx postIdx].';
preMag = sin(pi/2*(0.5+(preIdx)/(TTR))).^2;
midMag = ones(1,length(midIdx));
postMag = sin(pi/2*(0.5-((postIdx)-symLength)/TTR)).^2;
windowMag = [preMag midMag postMag].';
end
function out = windowLSTFandLLTF(sym,sizeFFT,ofdmSymLen, ...
longSymLength,wLength,numTx)
% Standard defined windowing equations
[index,magnitude] = windowingEquation(wLength,2*longSymLength);
% Number of initial symbols
numSym = length(sym)/(2*ofdmSymLen);
% Reshape by SymLength - NumSym - NumTx
sym = reshape(sym,2*ofdmSymLen,numSym,numTx);
% Extend symbol length
initialSymExtended = [sym(end-(abs(index(1))+sizeFFT/2) ...
+ 1:end-sizeFFT/2,:,:);sym; ...
sym(sizeFFT/2+(1:wLength/2),:,:)];
% Apply windowing to first two preamble symbols
out = bsxfun(@times,initialSymExtended,magnitude);
end
% [EOF]