Detect a received 802.11n packet at a signal-to-noise ratio (SNR) of 20 dB.

Create an HT configuration object and TGn channel object. Generate a transmit waveform.

cfgHT = wlanHTConfig;
tgn = wlanTGnChannel('LargeScaleFadingEffect','None');

txWaveform = wlanWaveformGenerator([1;0;0;1],cfgHT);

Pass the waveform through the TGn channel with an SNR of 20 dB. Detect the start of the packet.

snr = 20;
fadedSig = tgn(txWaveform);
rxWaveform = awgn(fadedSig,snr,0);

startOffset = wlanPacketDetect(rxWaveform,cfgHT.ChannelBandwidth)

startOffset = 1

The packet is detected at the first sample of the received waveform, specifically the returned startOffset indicates an offset of zero samples from the start of the received waveform.

Detect a received 802.11ac packet that has been delayed. Specify an offset of 25 to begin the autocorrelation process.

Create an VHT configuration object and generate the transmit waveform.

cfgVHT = wlanVHTConfig;

txWaveform = wlanWaveformGenerator([1;0;0;1],cfgVHT,...
    'WindowTransitionTime',0);

Delay the signal by appending zeros at the start. Specify an offset of 25 for the beginning of autocorrelation processing. Detect the start of the packet.

rxWaveform = [zeros(100,1);txWaveform];
offset = 25;
startOffset = wlanPacketDetect(rxWaveform,cfgVHT.ChannelBandwidth,offset)

startOffset = 48

Calculate the detected packet offset by adding the returned startOffset and the input offset.

pktOffset = offset + startOffset

pktOffset = 73

The offset from the first sample of the received waveform to the start of the packet is detected to be 73 samples. This coarse approximation of the packet-start offset is useful for determining where to begin autocorrelation for the first packet and for subsequent packets when a multipacket waveform is transmitted.

Detect a received 802.11a packet that has been delayed. No channel impairments are added. Set the input offset to 5 and use a threshold setting very close to 1.

Create an non-HT configuration object. Generate the transmit waveform.

cfgNonHT = wlanNonHTConfig;

txWaveform = wlanWaveformGenerator([1;0;0;1],cfgNonHT,...
    'WindowTransitionTime',0);

Delay the signal by appending zeros at the start. Set an initial offset of 5 and a threshold very close to 1. Detect the delayed packet.

rxWaveform = [zeros(20,1);txWaveform];

offset = 5;
threshold = 1-10*eps;
startOffset = wlanPacketDetect(rxWaveform,...
    cfgNonHT.ChannelBandwidth,offset,threshold)

startOffset = 15

Calculate the detected packet offset by adding the returned startOffset and the input offset.

totalOffset = offset + startOffset

totalOffset = 20

Using a threshold close to 1 and an undistorted received waveform increases the accuracy of the packet detect location. The detected offset from the first sample of the received waveform to the start of the packet is determined to be 20 samples.

Return the decision statistics of a WLAN waveform that consists of five 802.11a packets.

Create a non-HT configuration object and a five-packet waveform. Delay the waveform by 4000 samples.

cfgNonHT = wlanNonHTConfig;
txWaveform = wlanWaveformGenerator([1;0;0;1],cfgNonHT, ...
    'NumPackets',5,'IdleTime',20e-6);

rxWaveform = [zeros(4000,1);txWaveform];

Setting the threshold input to 1, generates packet decision statistics for the entire waveform and suppresses the startOffset output. Plot the decision statistics, M.

offset = 0;
threshold = 1;
[startOffset,M] = wlanPacketDetect(rxWaveform,cfgNonHT.ChannelBandwidth,...
    offset,threshold);
plot(M)

Since threshold = 1, the decision statistics for the entire waveform are included in the output M. The decision statistics show five peaks. The peaks corresponds to the first sample of each packet detected. View startOffset.

startOffset

startOffset =

     []

The returned startOffset is empty because threshold was set to 1.