ddemodce.m

数字通信第四版原书的例程

function [x, z] = ddemodce(y, Fd, Fs, method, M, opt1, opt2, opt3, opt4)
%DDEMODCE Demodulates complex envelope of a digital modulated signal.
%       DDEMODCE(Y, Fd, Fs) plots eye-pattern diagram for the signal Y. The
%       sampling frequency for Y is Fs (Hz) and the digital sampling
%       frequency is Fd (Hz). When Fd is a two element vector, the second
%       element is the offset value for the decision point. The offset should
%       be an integer. The offset timing in the plot is offset/Fs. Fc is not
%       used.
%
%       X = DDEMODCE(Y, Fd, Fs, METHOD, OPT1, OPT2, OPT3, OPT4, OPT5)
%       demodulates a digital modulated signal Y with digital signal frequency
%       Fd (Hz), and computation sampling frequency Fs (Hz). This function 
%       requires Fs/Fd be a positive integer. When Fd is a two element
%       vector, the second element is the offset value for the decision point.
%       The offset timing in the plot is offset/Fs. The default offset is 0.
%       The received digital signal is sampled at time point i/Fd + offset/Fs.
%       The output keeps the same sample value until the next sample point is
%       taken place, which is at time (i+1)/Fd + offset/Fs. The demapping
%       process finds the distance from the sample value to all of the
%       possible digital symbols. The digital symbols with the shortest
%       distance to the current sampling point are the demodulated output.
%       When Fs is a two element vector, the second element specifies the
%       initial phase of the carrier signal in modulation.
%
%       METHOD is a string, which can be one of the following:
%       'ask'       M-ary Amplitude shift keying modulation.
%       'psk'       M-ary Phase shift keying modulation.
%       'qask'      M-ary Quadrature amplitude shift keying modulation, with
%                   choice of 'qask/cir', 'qask/arb' for different mapping table.
%       'fsk'       M-ary Frequency shift keying modulation.
%       'msk'       Minimum shift keying modulation.
%       'sample'    Down sampling from a higher sampling frequency signal.
%
%       When there is a '/eye' or 'scat' string appended to the end of the
%       variable METHOD, the function plots eye-pattern diagram or the scatter
%       plot.
%
%       Use DDEMODCE(METHOD) to view the help for a specific method.
%
%       See also MODMAP, AMOD, ADEMOD, DMODCE, DEMODCE.

%       Wes Wang 1/9/95, 10/2/95
%       Copyright (c) 1995-96 by The MathWorks, Inc.
%       $Revision: 1.1 $  $Date: 1996/04/01 17:56:16 $

%position for optional parameters.
opt_pos = 6;
plot_const = 0;
if nargin < 1
    feval('help','ddemodce');
    return;
elseif isstr(y)
    method = lower(deblank(y));
    if length(method) < 3
        error('Invalid method option for ddemodce.')
    end
    if nargin == 1
        addition = 'See also DMODCE, DMOD, DDEMODE, AMOD, ADEMOD.';
        if method(1:3) == 'qas'
          callhelp('ddemodce.hlp',method(1:4),addition);
        else
          callhelp('ddemodce.hlp',method(1:3),addition);
        end
        return;
    else
        disp('Warning: Worng number of input variable, use MODMAP for plotting constellations.');
        return
    end;
end;

if length(Fs) > 1
    ini_phase = Fs(2);
    Fs = Fs(1);
else
    ini_phase = 0;
end;
if length(Fd) > 1
    offset = Fd(2);
    Fd = Fd(1);
else
    offset = 0;
end;
if (Fs == 0) | (Fd == 0) | isempty(Fd) | isempty(Fs)
    FsDFd = 1;
    offset = 0;
else
    FsDFd = Fs / Fd;
    if (ceil(FsDFd) ~= FsDFd) | (FsDFd <= 0)
        error('Fs / Fd must be a positive integer.')
    end;
end;

offset = rem(offset, FsDFd);
if offset < 0
    offset = rem(offset + FsDFd, FsDFd);
end;

[r, c] = size(y);
if r * c == 0
    x = [];
    return;
end;
if r == 1
    y = y(:);
    len_y = c;
else
    len_y = r;
end;

if nargin < 3
    disp('Usage: Y=DDEMODCE(X, Fd, Fs, METHOD, OPT1, OPT2, OPT3) for modulation mapping');
    return;
elseif (nargin < opt_pos  - 2)
    if nargout < 1
        method = 'eye';
    else
        method = 'sample';
    end;
end;

method = lower(method);

if strcmp(method(1:2), 'as')
    % M has to be specified in 'ask' option.
    if nargin < opt_pos - 1
        error('Not enough input varibale for DDEMODCE.')
    end;
    if offset == 0
        offset = FsDFd;
    end;
    index = ([0 : M - 1] - (M - 1) / 2) * 2 / (M - 1);
    if nargin < opt_pos
        num = 1;
        den = 1;
    else
        num = opt1;
        den = opt2;
    end;
    if findstr(method, '/cos')
        y = ademodce(y, [Fs, ini_phase], 'amdsb-sc/costas', num, den);
    else
        y = ademodce(y, [Fs, ini_phase], 'amdsb-sc', num, den);
    end;
    if findstr(method, '/eye')
        ddemodce(y, [Fd, offset], [Fs, ini_phase], 'eye')
    end;
    if findstr(method, '/sca')
        ddemodce(y, [Fd, offset], [Fs, ini_phase], 'sca')
    end;
    yy = y([offset : FsDFd : len_y], :);
    x = [];
    for i = 1 : size(y, 2)
        [tmp, x_p] = min(abs(yy(:, i*ones(1, M)) - index(ones(1, size(yy, 1)), :))');
        x = [x x_p'-1];
    end;
elseif findstr(method, 'fsk')
    if nargin < opt_pos
        Tone = 2 * Fd / M;
    else
        Tone = opt1;
    end;

    %calculate the correlation of fsk.
    z = [0: M-1] * Tone;
    z = [0; ones(FsDFd-1, 1)] * z;
    z = exp(j * 2 * pi / Fs * cumsum(z) + j * ini_phase);
    zz = exp(j * 2 * pi / Fs * cumsum(z) + j * 2 * ini_phase);
    x = real(y([offset+1 : FsDFd : len_y], :));
    if findstr(method, '/eye')
        t = [0 : FsDFd-1]/Fs;
        t = t + offset/Fs;
        plot([min(t), max(t), max(t)], [-1/2, NaN, 1])
        axis([min(t) max(t), -1/2, 1]);
        hold on
    end;
    [len_x, wid_x] = size(x);
    for i = 1 : wid_x
        comp_low = 1;
        if offset <= 0
            comp_upp = FsDFd;
        else
            comp_upp = offset;
        end;
        for k = 1 : len_x
            corr = (real(y(comp_low : comp_upp)) * ones(1, M)) .* real(z(1 : comp_upp-comp_low + 1, :)) + ...
                (imag(y(comp_low : comp_upp)) * ones(1, M)) .* imag(z(1 : comp_upp-comp_low + 1, :));
            if findstr(method, '/eye')
                if findstr(method, '/nonc')
                    cor2 = (real(y(comp_low : comp_upp)) * ones(1, M)) .* real(zz(1 : comp_upp-comp_low + 1, :)) + ...
                        (imag(y(comp_low : comp_upp)) * ones(1, M)) .* imag(zz(1 : comp_upp-comp_low + 1, :));
                    corr = cumsum(corr).^2 + cumsum(cor2).^2;
                else
                    corr = cumsum(corr);
                end;
                corr = corr / max(max(max(abs(corr))), eps);
                if k == 1
                    plot(t(FsDFd-size(corr, 1)+1 : FsDFd)', corr);
                else
                    plot(t(1:size(corr, 1))', corr)
                end
                corr = corr(size(corr, 1), :);
            else
                corr = sum(corr);
                if findstr(method, '/nonc')
                    cor2 = (real(y(comp_low : comp_upp)) * ones(1, M)) .* real(zz(1 : comp_upp-comp_low + 1, :)) + ...
                        (imag(y(comp_low : comp_upp)) * ones(1, M)) .* imag(zz(1 : comp_upp-comp_low + 1, :));
                    corr = corr.^2 + sum(cor2).^2;
                end;
            end;
            [tmp_v, tmp_i] = max(corr);
            x(k, i) = tmp_i - 1;
            comp_low = min(comp_low + FsDFd, len_y);
            comp_upp = min(comp_upp + FsDFd, len_y);
        end
    end
    if findstr(method, '/eye')
        hold off
    end;
%psk has combined with qask.
elseif findstr(method, 'msk')
    %This is a special case of fsk call back to get fsk
    method(1) = 'f';
    M = 2;
    Tone = Fd;
    x = ddemodce(y, [Fd, offset], [Fs, ini_phase], method, M, Tone);
elseif ~isempty(findstr(method, 'qask')) |...
         ~isempty(findstr(method, 'qam')) |...
         ~isempty(findstr(method, 'qsk')) |...
         ~isempty(findstr(method, 'psk'))
    if offset <= 0
        offset = FsDFd;
    end;
    if findstr(method, '/ar')
        % arbitraryly defined I, Q. 
        if nargin < opt_pos
            error('In correct format for METHOD=''qask/arbitrary''.');
        end;
        I = M;
        Q = opt1;
        if nargin < opt_pos + 2
            num = 1;
            den = 1;
        else
            num = opt2;
            den = opt3;
        end;
        M = length(I);
    elseif ~isempty(findstr(method, '/ci')) | ~isempty(findstr(method, 'psk'))
        % circle defined NIC, AIC, PIC.
        if nargin < opt_pos - 1
            if findstr(method, 'psk')
                error('M-ary number must be specified for psk demap.')
            else
                error('Incorrect format for METHOD=''qask/arbitrary''.');
            end;
        end;
        NIC = M;
        M = length(NIC);
        if nargin < opt_pos
            AIC = [1 : M];
        else
            AIC = opt1;
        end;
        if nargin < opt_pos + 1
            PIC = NIC * 0;
        else
            PIC = opt2;
        end;
        if nargin < opt_pos + 3
            num = 1;
            den = 1;
        else
            num = opt3;
            den = opt4;
        end;
        inx = apkconst(NIC, AIC, PIC);
        I = real(inx);
        Q = imag(inx);
        M = sum(NIC);
    else
        %consider as square style.
        [I, Q] = qaskenco(M);
        if nargin < opt_pos + 1
            num = 1;
            den = 1;
        else
            num = opt1;
            den = opt2;
        end;
    end;
    y = ademodce(y, [Fs, ini_phase], 'qam', num, den);
    if findstr(method, '/eye')
        ddemodce(y, [Fd, offset], [Fs, ini_phase], 'eye')
    end;
    if findstr(method, '/sca')
        ddemodce(y, [Fd, offset], [Fs, ini_phase], 'sca')
    end;
    yy = y([offset : FsDFd : len_y], :);
    [len_y, wid_y] = size(yy);
    if (ceil(wid_y/2) ~= wid_y/2)
        error('qask demap requires input is a matrix with even number of columns.');
    end;
    x = []; I = I(:)'; Q = Q(:)';
    for i = 1 : 2 : wid_y
        [tmp, x_p] = min(...
            ((yy(:, i*ones(1, M)) - I(ones(1, len_y), :)).^2 + ...
            (yy(:, (i+1)*ones(1, M)) - Q(ones(1, len_y), :)).^2)');
        x = [x x_p'-1];
    end;
elseif findstr(method, 'samp')
    %This is made possible to convert an input signal from sampling frequency Fd
    %to sampling frequency Fs.
    if offset <= 0
        offset = FsDFd;
    end;
    x = y([offset : FsDFd : len_y], :);
elseif findstr(method, 'eye')
    % plot eye-pattern plot
    eyescat(y, Fd, Fs, offset, offset);
elseif findstr(method, 'scat')
    if nargin >= opt_pos
        if isstr(M)
            M = M(1);
        else
            M = '.';
        end;
    else
        M = '.';
    end;
    eyescat(y, Fd, Fs, offset, M);
else
    %The choice is not a valid one.
    disp('You have used an invalid method. The method should be one of the following string:')
    disp('  ''ask'' Amplitude shift keying modulation;')
    disp('  ''psk'' Phase shift keying modulation;')
    disp('  ''qask'' Quadrature amplitude shift-keying modulation, square constellation;')
    disp('  ''qask/cir'' Quadrature amplitude shift-keying modulation, circle constellation;')
    disp('  ''qask/arb'' Quadrature amplitude shift-keying modulation, user defined constellation;')
    disp('  ''fsk'' Frequency shift keying modulation;')
    disp('  ''msk'' Minimum shift keying modulation;')
    disp('  ''sample'' Convert sample frequency Fd input to sample frequency Fs output.')
end;