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Verify Viterbi Decoder Using MATLAB System Object and Cadence Incisive

This example shows you how to use MATLAB® System objects and Cadence® Incisive® to cosimulate a Viterbi decoder implemented in VHDL.

Set Simulation Parameters and Instantiate Communication System Objects

The following code sets up the simulation parameters and instantiates the system objects that represent the channel encoder, BPSK modulator, AWGN channel, BPSK demodulator, and error rate calculator. Those objects comprise the system around the Viterbi decoder and can be thought of as the test bed for the Viterbi HDL implementation.

EsNo = 0;	% Energy per symbol to noise power spectrum density ratio in dB
FrameSize = 1024;  % Number of bits in each frame

% Convolution Encoder
hConEnc = comm.ConvolutionalEncoder;
% BPSK Modulator
hMod    = comm.BPSKModulator;
% AWGN channel
hChan   = comm.AWGNChannel('NoiseMethod', ...
                           'Signal to noise ratio (Es/No)',...
                           'SamplesPerSymbol',1,...
                           'EsNo',EsNo);
% BPSK demodulator
hDemod  = comm.BPSKDemodulator('DecisionMethod','Log-likelihood ratio',...
                               'Variance',0.5*10^(-EsNo/10));
% Error Rate Calculator
hError  = comm.ErrorRate('ComputationDelay',100,'ReceiveDelay', 58);

Instantiate the Cosimulation System Object

The hdlcosim function returns an HDL cosimulation System object, which represents the HDL implementation of the Viterbi decoder in this simulation system.

hDec    = hdlcosim('InputSignals', {'/viterbi_block/In1','/viterbi_block/In2'}, ...
                   'OutputSignals', {'/viterbi_block/Out1'}, ...
                   'OutputSigned', false, ...
                   'OutputFractionLengths', 0, ...
                   'TCLPreSimulationCommand', 'force :clk B"0" -after 0ns B"1" -after 5ns -repeat 10ns; force reset B"1" -after 0ns B"0" -after 8ns; force :clk_enable B"1" -after 0ns', ...
                   'TCLPostSimulationCommand', 'echo "done";', ...
                   'PreRunTime', {10,'ns'}, ...
                   'Connection', {'Shared'}, ...
                   'SampleTime', {10,'ns'});

Launch HDL Simulator

The nclaunch command launches Incisive. The launched Incisive session compiles the HDL design and loads the HDL simulation. You are ready to perform cosimulation when the HDL simulation is fully loaded in Incisive.

disp('Waiting for HDL simulator to launch ...');
nclaunch('tclstart',viterbi_tclcmds_incisive('hdlsimmatlabsysobj'));
processid = pingHdlSim(240);
disp('Ready for cosimulation ...');

Run Cosimulation

This example simulates the BPSK communication system in MATLAB incorporating the Viterbi decoder HDL implementation via the cosimulation System object. This section of the code calls the processing loop to process the data frame-by-frame with 1024 bits in each data frame.

for counter = 1:20480/FrameSize
    data            = randi([0 1],FrameSize,1);
    encodedData     = step(hConEnc, data);
    modSignal       = step(hMod, encodedData);
    receivedSignal  = step(hChan, modSignal);
    demodSignalSD   = step(hDemod, receivedSignal);
    quantizedValue  = fi(4-demodSignalSD,0,3,0);
    input1          = quantizedValue(1:2:2*FrameSize);
    input2          = quantizedValue(2:2:2*FrameSize);
    receivedBits    = step(hDec,input1, input2);
    errors          = step(hError, data, double(receivedBits));
end

Display the Bit-Error Rate

The Bit-Error Rate is displayed for the Viterbi decoder.

sprintf('Bit Error Rate is %d\n',errors(1))

Destroy Cosimulation System Object to Release HDL Simulator

The HDL simulator is unblocked when the HDL cosimulation System object is destroyed in MATLAB. Close the Incisive session manually.

clear hDec;

% This concludes the "Verifying Viterbi Decoder Using MATLAB System Object
% and Cadence Incisive" example.
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