Impl task1 some part of task2

2026-05-19 21:56:06 +02:00
parent fca31532d1
commit 1561016689
8 changed files with 849 additions and 187 deletions
@@ -0,0 +1,141 @@
+function [decBits,decParams,searchOffset,res] = recoverOFDMBits(rx,searchOffset)
+%recoverOFDMBits Performs non-HT OFDM signal recovery
+%   [DECBITS,DECPARAMS,SEARCHOFFSET,RES] = recoverOFDMBits(RX,SEARCHOFFSET)
+%   detects a OFDM packet and performs analysis of the non-HT preamble,
+%   L-SIG, data fields.
+%
+%   DECBITS is a vector containing the decoded bits in a non-HT packet.
+%
+%   DECPARAMS is a structure containing the decoded signal parameters.
+%
+%   SEARCHOFFSET is the offset from the start of RX in samples to the
+%   next point from which to search for a packet.
+%
+%   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.
+
+%   Copyright 2024 The MathWorks, Inc.
+
+% recoverPreamble detects a packet and performs analysis of the non-HT preamble.
+    decBits = [];
+
+    decParams = struct;
+    decParams.modulation = nan;
+    decParams.codeRate = nan;
+    decParams.MCS = nan;
+    decParams.PSDULength = nan;
+    decParams.failCheck = nan;
+
+    cbw = "CBW20";
+    cfg = wlanNonHTConfig(ChannelBandwidth=cbw);
+    ind = wlanFieldIndices(cfg);
+    sampleRate = 20e6;
+    maxNonHTPacketTime = 5.484e-3;
+    maxNonHTPacketSamples = maxNonHTPacketTime*sampleRate;
+
+    [preambleStatus,res] = recoverPreamble(rx,cbw,searchOffset);
+
+    if matches(preambleStatus,"No packet detected")
+        searchOffset = length(rx);
+        return;
+    end
+
+    % Retrieve synchronized data and scale it with LSTF power as done
+    % in the recoverPreamble function.
+    if maxNonHTPacketSamples <= (length(rx) - res.PacketOffset)
+        endIdx = maxNonHTPacketSamples + res.PacketOffset;
+    else
+        endIdx = length(rx);
+    end
+    syncData = rx(res.PacketOffset+1:endIdx)./sqrt(res.LSTFPower);
+    syncData = frequencyOffset(syncData,sampleRate,-res.CFOEstimate);
+
+    % Need only 4 OFDM symbols (LSIG + 3 more symbols) following LLTF
+    % for format detection
+    fmtDetect = syncData(ind.LSIG(1):(ind.LSIG(2)+4e-6*sampleRate*3));
+
+    [LSIGBits, failcheck] = wlanLSIGRecover(fmtDetect(1:4e-6*sampleRate*1), ...
+                                            res.ChanEstNonHT,res.NoiseEstNonHT,cbw);
+
+    decParams.failCheck = failcheck;
+
+    if ~failcheck
+        format = wlanFormatDetect(fmtDetect,res.ChanEstNonHT,res.NoiseEstNonHT,cbw);
+        if matches(format,"Non-HT")
+
+            % Extract MCS from first 3 bits of L-SIG.
+            rate = double(bit2int(LSIGBits(1:3),3));
+            if rate <= 1
+                cfg.MCS = rate + 6;
+            else
+                cfg.MCS = mod(rate,6);
+            end
+            [modulation,coderate] = getRateInfo(cfg.MCS);
+            decParams.modulation = modulation;
+            decParams.coderate = coderate;
+            decParams.MCS = cfg.MCS;
+
+            % Determine PSDU length from L-SIG.
+            cfg.PSDULength = double(bit2int(LSIGBits(6:17),12,0));
+            decParams.PSDULength = cfg.PSDULength;
+            ind.NonHTData = wlanFieldIndices(cfg,"NonHT-Data");
+
+            if double(ind.NonHTData(2)-ind.NonHTData(1))> ...
+                    length(syncData(ind.NonHTData(1):end))
+                % Exit function as full packet not captured.
+                searchOffset = length(rx);
+                return;
+            end
+
+            nonHTData = syncData(ind.NonHTData(1):ind.NonHTData(2));
+            decBits = wlanNonHTDataRecover(nonHTData,res.ChanEstNonHT, ...
+                                           res.NoiseEstNonHT,cfg);
+            % Shift packet search offset for next iteration of while loop.
+            searchOffset = res.PacketOffset + double(ind.NonHTData(2));
+        else
+            % Packet is NOT non-HT; shift packet search offset by 10 OFDM symbols (minimum
+            % packet length of non-HT) for next iteration of while loop.
+            searchOffset = res.PacketOffset + 4e-6*sampleRate*10;
+        end
+    else
+        % L-SIG recovery failed; shift packet search offset by 10 OFDM symbols (minimum
+        % packet length of non-HT) for next iteration of while loop.
+        searchOffset = res.PacketOffset + 4e-6*sampleRate*10;
+    end
+end
+
+function [modulation,coderate] = getRateInfo(mcs)
+% GETRATEINFO returns the modulation scheme as a character array and the
+% code rate of a packet given a scalar integer representing the modulation
+% coding scheme
+    switch mcs
+      case 0 % BPSK
+        modulation = 'BPSK';
+        coderate = '1/2';
+      case 1 % BPSK
+        modulation = 'BPSK';
+        coderate = '3/4';
+      case 2 % QPSK
+        modulation = 'QPSK';
+        coderate = '1/2';
+      case 3 % QPSK
+        modulation = 'QPSK';
+        coderate = '3/4';
+      case 4 % 16QAM
+        modulation = '16QAM';
+        coderate = '1/2';
+      case 5 % 16QAM
+        modulation = '16QAM';
+        coderate = '3/4';
+      case 6 % 64QAM
+        modulation = '64QAM';
+        coderate = '2/3';
+      otherwise % 64QAM
+        modulation = '64QAM';
+        coderate = '3/4';
+    end
+end