EQBER_ADAPTIVE - Simulation of linear and DFE equalizers

This script runs a simulation loop for either a linear or a DFE equalizer. It uses the RLS algorithm to initially set the weights, then uses LMS thereafter to minimize execution time. It plots the equalized signal spectrum, then generates and plots BER results over a range of Eb/No values. It also fits a curve to the simulated BER points, and plots the burst error performance of the linear and DFE equalizers. The adaptive equalizer objects automatically retain their state between invocations of their "equalize" method.

This script uses another script, eqber_siggen to generate a noisy, channel-filtered signal.

% Set parameters based on linear or DFE equalizer setting
if (strcmpi(eqType, 'linear'))
    refTap     = linEq1.RefTap; % set reference tap
    eq1        = linEq1;        % set RLS equalizer for first data block
    eq2        = linEq2;        % set LMS equalizer for remaining data blocks
    hSpecPlot  = hLinSpec;      % set spectrum plot line handle
elseif (strcmpi(eqType, 'dfe'))
    refTap     = dfeEq1.RefTap;
    eq1        = dfeEq1;
    eq2        = dfeEq2;
    hSpecPlot  = hDfeSpec;
end

firstErrPlot = true;   % for burst error plot - reset for each eq method

% Main simulation loop
for EbNoIdx = 1 : length(EbNo)

    % Initialize channel and error collection parameters
    chanState = [];
    numErrs   = 0;
    numBits   = 0;
    firstBlk = true;  % RLS for first data block, LMS thereafter

    while (numErrs < maxErrs && numBits < maxBits)

        eqber_siggen;  % generate a noisy, channel-filtered signal

        if (numErrs < maxErrs)

            % Equalize the signal with an adaptive equalizer.  Use a truncated
            % version of the transmitted signal as the training signal.  Use RLS
            % to initially set the weights in the first data block, and LMS
            % thereafter, for speed purposes.
            trainSig = txSig(1 : end-refTap+1);
            if (firstBlk)
                [PreD, PostD] = equalize(eq1, noisySig, trainSig);

                % Set the weights and weight inputs of the LMS equalizer to
                % those of the RLS equalizer for future data blocks.
                eq2.Weights = eq1.Weights;
                eq2.WeightInputs = eq1.WeightInputs;
            end

            % Equalize all blocks, including a re-equalization of the first
            % block.  Do not use a training sequence.  The performance of the
            % DFE equalizer will be enhanced if called with a training sequence,
            % but a real system would be implemented without the training
            % sequence.
            [PreD, PostD] = equalize(eq2, noisySig);

            % Plot the spectrum of the equalized signal
            hSpecPlot = eqber_graphics('sigspec', eqType, hSpecPlot, ...
                nBits, PreD);

            % Demodulate the signal
            demodSig = (1-sign(real(PostD)))/2;

            range1 = 1 : length(msg)-refTap+1;
            range2 = refTap : length(demodSig);
            [currErrs, ratio] = biterr(msg(range1), demodSig(range2));
            numErrs = numErrs + currErrs;       % cumulative
            numBits = numBits + length(range1); % cumulative
            BER(EbNoIdx) = numErrs / numBits;

            % Plot the burst error performance for this data block
            [hErrs, hText1, hText2] = eqber_graphics('bursterrors', eqType, ...
                mlseType, firstErrPlot, msg(range1), demodSig(range2), ...
                nBits, hErrs, hText1, hText2);
            firstErrPlot = false;
        end

        % Update the BER plot
        [hBER, hLegend, legendString] = eqber_graphics('simber', eqType, ...
            mlseType, firstBlk, EbNoIdx, EbNo, BER, hBER, hLegend, ...
            legendString);
        firstBlk = false;  % done processing first data block

    end     % end of simulation while loop

    % Fit a plot to the new BER points
    hFit = eqber_graphics('fitber', eqType, mlseType, hFit, EbNoIdx, EbNo, BER);

    % Reset the RLS equalizer for the next Eb/No
    if (strcmpi(eqType, 'linear'))
        eq1 = lineareq(nWts, alg1);
        eq1.RefTap = round(nWts/2);
    elseif (strcmpi(eqType, 'dfe'))
        eq1 = dfe(nFwdWts, nFbkWts, alg1);
        eq1.RefTap = round(nFwdWts/2);
    end
    eq1.ResetBeforeFiltering = 0;

end     % end of 'for EbNoIdx' loop

Copyright 1996-2004 The MathWorks, Inc.
Published with MATLAB® 7.0