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Impl task1 some part of task2

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ti_mo
2026-05-19 21:56:06 +02:00
parent fca31532d1
commit 1561016689
8 changed files with 849 additions and 187 deletions
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lab_3/from_matlab_example/recoverPreamble.m
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function [status,res] = recoverPreamble(rx,chanBW,searchOffset,varargin)
%recoverPreamble Preamble signal recovery
% [STATUS,RES] = recoverPreamble(RX,CHANBW,SEARCHOFFSET) detects a packet
% and performs analysis of the non-HT preamble.
%
% STATUS is the processing status and is either 'Success' or 'No packet
% detected'.
%
% RES is a structure containing signal analysis.
%
% RX is the received time-domain waveform. It is a Ns-by-Nr matrix of
% real or complex values, where Ns represents the number of time-domain
% samples in the waveform, and Nr represents the number of receive
% antennas.
%
% CHANBW is the channel bandwidth and must be 'CBW20', 'CBW40', 'CBW80',
% 'CBW160', or 'CBW320'.
%
% SEARCHOFFSET is the offset from the start of RX in samples to begin
% searching for a packet.
%
% [STATUS,RES] = recoverPreamble(...,CFGALG) optionally allows
% algorithm options to be used as specified in the structure CFGALG.
% Copyright 2019-2025 The MathWorks, Inc.
persistent wpd
cfgAlg = algorithmConfig(varargin{:});
if isempty(wpd)
wpd = hWLANPacketDetector(rx,chanBW);
else
wpd.Waveform = rx;
wpd.ChannelBandwidth = chanBW;
end
wpd.Threshold = cfgAlg.PacketDetectionThreshold;
cfgBase = wlanEHTMUConfig(chanBW);
index = wlanFieldIndices(cfgBase);
sr = wlanSampleRate(cfgBase);
if cfgAlg.EnergyDetection
movrms = dsp.MovingRMS;
movrms.WindowLength = cfgAlg.EnergyDetectionWindow;
threshold = 10^(cfgAlg.EnergyDetectionThreshold/20);
end
% Minimum packet length is L-STF, L-LTF, L-SIG + 1 Data symbol
lstfLen = double(index.LSTF(2)); % Number of samples in L-STF
minPktLen = lstfLen*3;
% Minimum number of samples to skip before searching for next packet
minAdvLen = lstfLen*4/10;
rxWaveformLen = size(rx,1);
% Do not search for packets if waveform is too short
if (searchOffset+minPktLen)>rxWaveformLen
status = 'No packet detected';
res = defaultResults();
return
end
% Initialize incase no packets detected
packetOffset = nan;
cfoEstimate = nan;
lstfPower = nan;
lltfPower = nan;
chanEstNonHT = [];
noiseEstNonHT = nan;
lltfSNREst = nan;
status = 'No packet detected';
wpd.SearchOffset = searchOffset;
while (wpd.SearchOffset+minPktLen)<=rxWaveformLen
% Detect a packet
if cfgAlg.SkipPacketDetection
packetOffset = 0;
else
packetOffset = findPacketStart(wpd);
end
% Adjust packet offset
if isempty(packetOffset) || (packetOffset<0) || (packetOffset+double(index.LSIG(2))>rxWaveformLen)
status = 'No packet detected';
break
end
if cfgAlg.EnergyDetection
% Run RMS over part of the waveform of interest - where we expect a ramp up
reset(movrms)
idx = (packetOffset+(-movrms.WindowLength+1:(2*movrms.WindowLength)));
idx(idx<1) = []; % In case waveform detected as start
rxRMS = movrms(rx(idx,:));
if all(mean(rxRMS(movrms.WindowLength+1:end,:),2)<threshold)
% If energy detected is not high enough continue searching
wpd.SearchOffset = packetOffset+minAdvLen;
continue;
end
end
% Coarse Frequency Offset Estimation
% Extract non-HT fields and perform coarse frequency offset correction
% to allow for reliable symbol timing
preamble = rx(packetOffset+(index.LSTF(1):index.LSIG(2)),:);
coarseFreqOffset = wlanCoarseCFOEstimate(preamble,chanBW);
preamble = frequencyOffset(preamble,sr,-coarseFreqOffset);
% Timing Synchronization
% Symbol timing synchronization: 4 OFDM symbols to search for L-LTF
if cfgAlg.SkipPacketDetection
lltfStartOffset = 0;
else
lltfStartOffset = wlanSymbolTimingEstimate(preamble,chanBW);
end
% If packet offset is significantly less than search offset then
% likely a false detection
if (packetOffset+lltfStartOffset)<=(wpd.SearchOffset-minAdvLen)
% Skip 4/10 of L-STF length of samples and continue searching
wpd.SearchOffset = packetOffset+minAdvLen;
continue
end
% End search if min packet length is outside of waveform
packetOffset = packetOffset+lltfStartOffset;
if (packetOffset+minPktLen)>rxWaveformLen
break
end
% Force packet offset not to be 0 to prevent hard errors
packetOffset = max(packetOffset,0);
% Extract preamble with fine timing sync
preamble = rx(packetOffset+(index.LSTF(1):index.LLTF(2)),:);
preamble = frequencyOffset(preamble,sr,-coarseFreqOffset);
% Fine Frequency Offset Estimation
% Perform fine frequency offset correction on the synchronized and
% coarse corrected Non-HT fields
lltf = preamble(index.LLTF(1):index.LLTF(2),:); % Extract L-LTF
fineFreqOffset = wlanFineCFOEstimate(lltf,chanBW);
preamble = frequencyOffset(preamble,sr,-fineFreqOffset);
cfoEstimate = coarseFreqOffset+fineFreqOffset; % Total CFO
% AGC
% Scale preamble by rx power before performing channel estimation
lstf = preamble(index.LSTF(1):index.LSTF(2),:);
lstfPower = mean(lstf(:).*conj(lstf(:)));
preamble = preamble/sqrt(lstfPower);
% Channel and noise estimation using L-LTF
lltf = preamble(index.LLTF(1):index.LLTF(2),:);
demodLLTF = wlanLLTFDemodulate(lltf,chanBW);
chanEstNonHT = wlanLLTFChannelEstimate(demodLLTF,chanBW,cfgAlg.LLTFChannelEstimateSmoothingSpan);
noiseEstNonHT = wlanLLTFNoiseEstimate(demodLLTF);
lltfPower = mean(lltf(:).*conj(lltf(:)))*lstfPower; % Subtract AGC scaling
% Test if carrier lost (L-LTF power substantially less than L-STF)
if cfgAlg.DetectCarrierLoss
if lltfPower<(0.25*lstfPower)
% Skip 4/10 of L-STF length of samples and continue searching
wpd.SearchOffset = packetOffset+minAdvLen;
continue
end
end
% Test large difference in energy between L-STF and L-LTF which is suspicious
if cfgAlg.DetectPowerFluctuation
if lstfPower<(0.125*lltfPower)
% Skip 4/10 of L-STF length of samples and continue searching
wpd.SearchOffset = packetOffset+minAdvLen;
continue
end
end
% Estimate SNR from L-LTF
lltfSNREst = 10*log10(mean(abs(chanEstNonHT(:)).^2)/noiseEstNonHT);
% Test if SNR it too low or isnan (when channel and noise estimate are 0)
if cfgAlg.DetectLLTFSNRTooLow
if isnan(lltfSNREst) || lltfSNREst<cfgAlg.LLTFSNRDetectionThreshold
% Skip L-STF length of samples and continue searching
wpd.SearchOffset = packetOffset+minAdvLen;
continue
end
end
% Packet detected
status = 'Success';
break
end
if strcmp(status,'No packet detected')
res = defaultResults();
wpd = [];
else
res = struct;
res.PacketOffset = packetOffset;
res.CFOEstimate = cfoEstimate;
res.LSTFPower = lstfPower;
res.LLTFPower = lltfPower;
res.ChanEstNonHT = chanEstNonHT;
res.NoiseEstNonHT = noiseEstNonHT;
res.LLTFSNR = lltfSNREst;
res.DemodLLTF = demodLLTF;
end
end
function res = defaultResults()
res = struct;
res.PacketOffset = nan;
res.CFOEstimate = nan;
res.LSTFPower = nan;
res.LLTFPower = nan;
res.ChanEstNonHT = nan;
res.NoiseEstNonHT = nan;
res.LLTFSNR = nan;
res.DemodLLTF = nan;
end
function cfg = algorithmConfig(varargin)
if nargin>0
cfg = varargin{1};
if ~isfield(cfg,'DetectCarrierLoss')
cfg.DetectCarrierLoss = true;
end
if ~isfield(cfg,'DetectPowerFluctuation')
cfg.DetectPowerFluctuation = true;
end
if ~isfield(cfg,'DetectLLTFSNRTooLow')
cfg.DetectLLTFSNRTooLow = true;
end
if ~isfield(cfg,'SkipPacketDetection')
cfg.SkipPacketDetection = false;
end
else
cfg = struct;
cfg.PacketDetectionThreshold = 0.5;
cfg.EnergyDetection = false;
cfg.EnergyDetectionThreshold = 0;
cfg.EnergyDetectionWindow = 20;
cfg.LLTFChannelEstimateSmoothingSpan = 1;
cfg.DetectCarrierLoss = true;
cfg.DetectPowerFluctuation = true;
cfg.DetectLLTFSNRTooLow = true;
cfg.LLTFSNRDetectionThreshold = 0;
cfg.SkipPacketDetection = false;
end
end