gusucode.com > wlan工具箱matlab源码程序 > wlan/wlanexamples/VHTMIMOPacketErrorRateExample.m
%% 802.11ac Packet Error Rate Simulation for 8x8 TGac Channel
%
% This example shows how to measure the packet error rate of an IEEE(R)
% 802.11ac(TM) VHT link using an end-to-end simulation with a fading TGac
% channel model and additive white Gaussian noise.
% Copyright 2015-2016 The MathWorks, Inc.
%% Introduction
% In this example an end-to-end simulation is used to determine the packet
% error rate for an 802.11ac [ <#11 1> ] VHT link with a fading channel at
% a selection of SNR points. At each SNR point multiple packets are
% transmitted through a channel, demodulated and the PSDUs recovered. The
% PSDUs are compared to those transmitted to determine the number of packet
% errors and hence the packet error rate. Packet detection, timing
% synchronization, carrier frequency offset correction and phase tracking
% are performed by the receiver. The processing for each packet is
% summarized in the following
%
% <<VHTMIMOPERDiagram.png>>
%
% This example also demonstrates how a <matlab:doc('parfor') parfor> loop
% can be used instead of the <matlab:doc('for') for> loop when simulating
% each SNR point to speed up a simulation. <matlab:doc('parfor') parfor>,
% as part of the Parallel Computing Toolbox(TM), executes processing for
% each SNR in parallel to reduce the total simulation time.
%% Waveform Configuration
% An 802.11ac VHT transmission is simulated in this example. A VHT format
% configuration object contains the format specific configuration of the
% transmission. The object is created using the
% <matlab:doc('wlanVHTConfig') wlanVHTConfig> function. The properties of
% the object contain the configuration. In this example the object is
% configured for a 80 MHz channel bandwidth, 8 transmit antennas, 8
% space-time streams, no space time block coding and 256-QAM rate-5/6 (MCS
% 9).
% Create a format configuration object for a 8-by-8 VHT transmission
cfgVHT = wlanVHTConfig;
cfgVHT.ChannelBandwidth = 'CBW80'; % 80 MHz channel bandwidth
cfgVHT.NumTransmitAntennas = 8; % 8 transmit antennas
cfgVHT.NumSpaceTimeStreams = 8; % 8 space-time streams
cfgVHT.APEPLength = 3000; % APEP length in bytes
cfgVHT.MCS = 9; % 256-QAM rate-5/6
%% Channel Configuration
% In this example a TGac N-LOS channel model is used with delay profile
% Model-D. For Model-D when the distance between transmitter and receiver
% is greater than or equal to 10 meters, the model is NLOS. This is
% described further in <matlab:doc('wlanTGacChannel') wlanTGacChannel>. An
% 8x8 MIMO channel is simulated in this example therefore 8 receive
% antennas are specified.
% Create and configure the channel
tgacChannel = wlanTGacChannel;
tgacChannel.DelayProfile = 'Model-D';
tgacChannel.NumReceiveAntennas = 8;
tgacChannel.TransmitReceiveDistance = 10; % Distance in meters for NLOS
tgacChannel.ChannelBandwidth = cfgVHT.ChannelBandwidth;
tgacChannel.NumTransmitAntennas = cfgVHT.NumTransmitAntennas;
tgacChannel.LargeScaleFadingEffect = 'None';
%% Simulation Parameters
% For each SNR point in the vector |snr| a number of packets are
% generated, passed through a channel and demodulated to determine the
% packet error rate.
snr = 40:5:50;
%%
% The number of packets tested at each SNR point is controlled by two
% parameters:
%
% # |maxNumErrors| is the maximum number of packet errors simulated at each
% SNR point. When the number of packet errors reaches this limit, the
% simulation at this SNR point is complete.
% # |maxNumPackets| is the maximum number of packets simulated at each SNR
% point and limits the length of the simulation if the packet error limit
% is not reached.
%
% The numbers chosen in this example will lead to a very short simulation.
% For meaningful results we recommend increasing the numbers.
maxNumErrors = 10; % The maximum number of packet errors at an SNR point
maxNumPackets = 100; % Maximum number of packets at an SNR point
%%
% Set the remaining variables for the simulation.
% Get the baseband sampling rate
fs = helperSampleRate(cfgVHT);
% Get the number of occupied subcarriers in VHT fields and FFT length
[vhtData,vhtPilots] = helperSubcarrierIndices(cfgVHT,'VHT');
Nst_vht = numel(vhtData)+numel(vhtPilots);
Nfft = helperFFTLength(cfgVHT); % FFT length
% Set the sampling rate of the channel
tgacChannel.SampleRate = fs;
% Indices for accessing each field within the time-domain packet
ind = wlanFieldIndices(cfgVHT);
rng(1); % Set random state for repeatability
%% Processing SNR Points
% For each SNR point a number of packets are tested and the packet error
% rate calculated.
%
% For each packet the following processing steps occur:
%
% # A PSDU is created and encoded to create a single packet waveform.
% # The waveform is passed through a different realization of the TGac
% channel model.
% # AWGN is added to the received waveform to create the desired average
% SNR per subcarrier after OFDM demodulation.
% <matlab:doc('comm.AWGNChannel') comm.AWGNChannel> is configured to
% provide the correct SNR. The configuration accounts for normalization
% within the channel by the number of receive antennas, and the noise
% energy in unused subcarriers which are removed during OFDM demodulation.
% # The packet is detected.
% # Coarse carrier frequency offset is estimated and corrected.
% # Fine timing synchronization is established. The L-STF, L-LTF and L-SIG
% samples are provided for fine timing to allow for packet detection at the
% start or end of the L-STF.
% # Fine carrier frequency offset is estimated and corrected.
% # The VHT-LTF is extracted from the synchronized received waveform. The
% VHT-LTF is OFDM demodulated and channel estimation is performed.
% # The VHT Data field is extracted from the synchronized received
% waveform. The PSDU is recovered using the extracted field and the channel
% estimate.
%
% A <matlab:doc('parfor') parfor> loop can be used to parallelize
% processing of the SNR points, therefore for each SNR point an AWGN
% channel is created and configured with <matlab:doc('comm.AWGNChannel')
% comm.AWGNChannel>. To enable the use of parallel computing for increased
% speed comment out the 'for' statement and uncomment the 'parfor'
% statement below.
S = numel(snr);
packetErrorRate = zeros(S,1);
%parfor i = 1:S % Use 'parfor' to speed up the simulation
for i = 1:S % Use 'for' to debug the simulation
% Create an instance of the AWGN channel per SNR point simulated
awgnChannel = comm.AWGNChannel;
awgnChannel.NoiseMethod = 'Signal to noise ratio (SNR)';
% Normalization
awgnChannel.SignalPower = 1/tgacChannel.NumReceiveAntennas;
% Account for energy in nulls
awgnChannel.SNR = snr(i)-10*log10(Nfft/Nst_vht);
% Loop to simulate multiple packets
numPacketErrors = 0;
numPkt = 1; % Index of packet transmitted
while numPacketErrors<=maxNumErrors && numPkt<=maxNumPackets
% Generate a packet waveform
txPSDU = randi([0 1],cfgVHT.PSDULength*8,1); % PSDULength in bytes
tx = wlanWaveformGenerator(txPSDU,cfgVHT);
% Add trailing zeros to allow for channel delay
tx = [tx; zeros(50,cfgVHT.NumTransmitAntennas)]; %#ok<AGROW>
% Pass through channel fading channel model
rx = tgacChannel(tx);
% Reset channel to create a different realization
reset(tgacChannel);
% Add noise
rx = awgnChannel(rx);
% Packet detect
pktOffset = wlanPacketDetect(rx,cfgVHT.ChannelBandwidth);
if isempty(pktOffset) % If empty no L-STF detected; packet error
numPacketErrors = numPacketErrors+1;
numPkt = numPkt+1;
continue; % Go to next loop iteration
end
% Extract L-STF and perform coarse frequency offset correction
lstf = rx(pktOffset+(ind.LSTF(1):ind.LSTF(2)),:);
coarseFreqOff = wlanCoarseCFOEstimate(lstf,cfgVHT.ChannelBandwidth);
rx = helperFrequencyOffset(rx,fs,-coarseFreqOff);
% Extract the Non-HT fields and determine start of L-LTF
nonhtfields = rx(pktOffset+(ind.LSTF(1):ind.LSIG(2)),:);
lltfIdx = helperSymbolTiming(nonhtfields,cfgVHT.ChannelBandwidth);
% Synchronize the received waveform given the offset between the
% expected start of the L-LTF and actual start of L-LTF
pktOffset = pktOffset+lltfIdx-double(ind.LLTF(1));
% If no L-LTF detected or if packet detected outwith the range of
% expected delays from the channel modeling; packet error
if isempty(lltfIdx) || pktOffset<0 || pktOffset>50
numPacketErrors = numPacketErrors+1;
numPkt = numPkt+1;
continue; % Go to next loop iteration
end
rx = rx(1+pktOffset:end,:);
% Extract L-LTF and perform fine frequency offset correction
lltf = rx(ind.LLTF(1):ind.LLTF(2),:);
fineFreqOff = wlanFineCFOEstimate(lltf,cfgVHT.ChannelBandwidth);
rx = helperFrequencyOffset(rx,fs,-fineFreqOff);
% Estimate noise power in VHT fields
lltf = rx(ind.LLTF(1):ind.LLTF(2),:);
demodLLTF = wlanLLTFDemodulate(lltf,cfgVHT.ChannelBandwidth);
nVarVHT = helperNoiseEstimate(demodLLTF,cfgVHT.ChannelBandwidth, ...
cfgVHT.NumSpaceTimeStreams);
% Extract VHT-LTF samples from the waveform, demodulate and perform
% channel estimation
vhtltf = rx(ind.VHTLTF(1):ind.VHTLTF(2),:);
vhtltfDemod = wlanVHTLTFDemodulate(vhtltf,cfgVHT);
chanEst = wlanVHTLTFChannelEstimate(vhtltfDemod,cfgVHT);
% Recover the transmitted PSDU in VHT Data
% Extract VHT Data samples from the waveform and recover the PSDU
vhtdata = rx(ind.VHTData(1):ind.VHTData(2),:);
rxPSDU = wlanVHTDataRecover(vhtdata,chanEst,nVarVHT,cfgVHT);
% Determine if any bits are in error, i.e. a packet error
packetError = any(biterr(txPSDU,rxPSDU));
numPacketErrors = numPacketErrors+packetError;
numPkt = numPkt+1;
end
% Calculate packet error rate (PER) at SNR point
packetErrorRate(i) = numPacketErrors/(numPkt-1);
disp(['SNR ' num2str(snr(i)) ' completed after ' ...
num2str(numPkt-1) ' packets, PER: ' ...
num2str(packetErrorRate(i))]);
end
%% Plot Packet Error Rate vs SNR Results
figure
semilogy(snr,packetErrorRate,'-ob');
grid on;
xlabel('SNR (dB)');
ylabel('PER');
title('802.11ac 80MHz, MCS9, Direct Mapping, 8x8 Channel Model D-NLOS');
%% Further Exploration
% The number of packets tested at each SNR point is controlled by two
% parameters; |maxNumErrors| and |maxNumPackets|. For meaningful results it
% is recommend that these values should be larger than those presented in
% this example. Increasing the number of packets simulated allows the PER
% under different scenarios to be compared. Try changing the transmission
% and reception configurations and compare the packet error rate. As an
% example, the figure below was created by running the example for longer.
%
% <<VHTMIMOPERExample.png>>
%% Appendix
% This example uses the following helper functions:
%
% * <matlab:edit('helperFFTLength.m') helperFFTLength.m>
% * <matlab:edit('helperFrequencyOffset.m') helperFrequencyOffset.m>
% * <matlab:edit('helperNoiseEstimate.m') helperNoiseEstimate.m>
% * <matlab:edit('helperSampleRate.m') helperSampleRate.m>
% * <matlab:edit('helperSubcarrierIndices.m') helperSubcarrierIndices.m>
% * <matlab:edit('helperSymbolTiming.m') helperSymbolTiming.m>
%% Selected Bibliography
% # IEEE Std 802.11ac(TM)-2013 IEEE Standard for Information technology -
% Telecommunications and information exchange between systems - Local and
% metropolitan area networks - Specific requirements - Part 11: Wireless
% LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications -
% Amendment 4: Enhancements for Very High Throughput for Operation in Bands
% below 6 GHz.
displayEndOfDemoMessage(mfilename)