dmodce.m

数字通信第四版原书的例程

function y = dmodce(x, Fd, Fs, method, M, opt2, opt3)
%DMODCE Complex envelope of digital modulation. 
%       Y = DMODCE(X, Fd, Fs, METHOD, OPT1, OPT2, OPT3) output Y, the complex
%       envelope of a digital modulated signal. The sampling frequency for X
%       is Fd (Hz). The sampling frequency for Y is Fs (Hz). Fs must be larger
%       than Fd. Fs/Fc must be a positive integer. The time interval between
%       two successive points in X is 1/Fd. The column number of the modulated
%       signal Y is Fs/Fd times the length of the input signal X. The time
%       interval between two successive points in Y is 1/Fs. When Fs is a two
%       element vector, the second element specifies the initial phase (rad)
%       in the 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.
%       'fsk'       M-ary Frequency shift keying modulation.
%       'msk'       Minimum shift keying modulation.
%       'sample'    Up sample the input signal.
%
%       With a switch '/nomap' appended to the string of METHOD variable, the
%       function will not process the digital to analog mapping part. The
%       input signal is assumed to have sampling frequency Fs.
%
%       DMODCE(METHOD, OPT1, OPT2, OPT3) plots constellation layout.
%
%       Use DMODCE(METHOD) to view the help for a specific method.
%
%       See also DDEMODCE, MODMAP. DEMODMAP, COMMOD, COMDEMOD.
%

%       Wes Wang 1/9/95, 10/5/95
%       Copyright (c) 1995-96 by The MathWorks, Inc.
%       $Revision: 1.1 $  $Date: 1996/04/01 17:56:52 $

%position for optional parameters.
opt_pos = 5;
plot_const = 0;
if nargin < 1
    feval('help','dmodce')
    return;
elseif isstr(x)
    method = lower(deblank(x));
    if length(method) < 3
        error('Invalid method option for dmodce.')
    end
    if nargin == 1
        % help lines for individual modulation method.
        addition = 'See also DDEMODCE, DMOD, DDEMOD, MODMAP, DEMODMAP, AMOD, ADEMOD.';
        if method(1:3) == 'qas'
          callhelp('dmodce.hlp',method(1:4),addition);
        else
          callhelp('dmodce.hlp',method(1:3),addition);
        end
        return;
    else
        plot_const = 1;
        opt_pos = opt_pos - 3;
        M = Fd;
        if nargin > opt_pos
            opt2 = Fs;
        end;
        if nargin > opt_pos+1
            opt3 = method;
        end;
    end;
else
    len_x = length(x);
    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;
    else
        FsDFd = Fs / Fd;
        if (ceil(FsDFd) ~= FsDFd) | (FsDFd <= 0)
            error('Fs / Fd must be a positive integer.')
        end;
        [r, c] = size(x);
        if r * c == 0
            y = [];
            return;
        end;
        if r == 1
            x = x(:);
            len_x = c;
        else
            len_x = r;
        end;
        if isempty(findstr(method, '/nomap'))
            yy = [];
            for i = 1 : size(x, 2)
                tmp = x(:, ones(1, FsDFd)*i)';
                yy = [yy tmp(:)];
            end;
            x = yy;
            clear yy tmp
        end;
    end;
end;

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

if (nargin < 3) & ~isstr(x)
    disp('Usage: Y=DMODCE(X, Fd, Fs, METHOD, OPT1, OPT2, OPT3) for modulation mapping');
    return;
elseif nargin < opt_pos-1
    method = 'samp';
end;


% determine M
if nargin < opt_pos
    % this will happen only 
    M = max(max(x)) + 1;
    M = 2^(ceil(log(M)/log(2)));
    M = max(2, M);
end;
method = lower(method);

if length(method) < 3
    method = [method '   '];
end;

if strcmp(method(1:3), 'ask')
    if plot_const
        plot([0 0], [-1.1 1.1], 'w-', [-1.1, 1.1], [0 0], 'w-', ([0:M-1] - (M - 1) / 2 ) * 2 / (M - 1), zeros(1, M), '*');
        axis([-1.1 1.1 -1.1 1.1])
        xlabel('In-phase component');
        title('ASK constellation')
    else
        if isempty(findstr(method, '/nomap'))
            y = (x - (M - 1) / 2 ) * 2 / (M - 1);
        else
            y = x;
        end;
        if ini_phase
            y = y * exp(j * ini_phase);
        end;
    end;
elseif findstr(method, 'fsk')
    if nargin < opt_pos + 1
        Tone = 2 * Fd / M;
    else
        Tone = opt2;
    end;
    if plot_const
        x = [0 : M-1] * Tone;
        x = x([1 1 1], :);
        x = x(:)';
        tmp = [0 1 0];
        tmp = tmp(ones(1, M), :)';
        tmp = tmp(:)';
        tmp(2) = 2;
        plot(x, tmp);
        xlabel('Baseband spectrum for FSK (Hz)')
        title('FSK constellation')
    else
        if isempty(findstr(method, '/nomap'))
            x = x * Tone;
        end;
        y = x;
        [len_y, wid_y] = size(y);
        for i = 1 : ceil(len_y/FsDFd)
            y((i-1)*FsDFd+1 : min(i*FsDFd, len_y), :) = ...
            exp(j * 2 * pi / Fs * cumsum([zeros(1, wid_y); y((i-1)*FsDFd+1 : min(i*FsDFd, len_y)-1, :)]) ...
                    + j*ini_phase);
%           exp(j * 2 * pi / Fs * cumsum(y((i-1)*FsDFd+1 : min(i*FsDFd, len_y), :)) ...
        end;
    end;
elseif findstr(method, 'psk')
    if plot_const
        apkconst(M);
    else
       if isempty(findstr(method, '/nomap'))
            method = 'qask/cir';
        else
            method = 'qask/cir/nomap';
        end;
        y = dmodce(x, Fs, [Fs, ini_phase], method, M, 1, 0);
    end;
elseif strcmp(method, 'msk')
    %This is a special case of fsk call back to get fsk
    if plot_const
        Fd = M;
        x = [0 0 0 Fd Fd Fd];
        tmp = [0 2 0 0 1 0];
        plot(x, tmp);
        xlabel('Baseband spectrum for FSK')
        title('FSK constellation')
    else
        M = 2;
        Tone = Fd;
        if isempty(findstr(method, '/nomap'))
            y = x * Tone;
        else
            y = x;
        end;
        len_y = size(y, 1);
        method(1) = 'f';
        for i = 1 : ceil(len_y/FsDFd)
            y((i-1)*FsDFd+1 : min(i*FsDFd, len_y), :) = ...
                exp(j * 2 * pi / Fs * cumsum(y((i-1)*FsDFd+1 : min(i*FsDFd, len_y), :)) ...
                    + j*ini_phase);
        end;
    end;    
elseif ~isempty(findstr(method, 'qas')) |...
         ~isempty(findstr(method, 'qam')) |...
         ~isempty(findstr(method, 'qsk'))
    if findstr(method, '/nomap')
        y = amodce(x, [Fs, ini_phase], 'qam');
    else
        if findstr(method, '/ar')
            % arbitraryly defined I, Q. 
            if nargin < opt_pos + 1
                error('In correct format for METHOD=''qask/arbitrary''.');
            end;
            I = M;
            Q = opt2;
            M = length(I);
            if plot_const
                axx = max(max(abs(I))) * [-1 1] + [-.1 .1];
                axy = max(max(abs(Q))) * [-1 1] + [-.1 .1];
                plot(I, Q, 'r*', axx, [0 0], 'w-', [0 0], axy, 'w-');
                axis('equal')
                axis('off');
                text(axx(1) + (axx(2) - axx(1))/4, axy(1) - (axy(2) - axy(1))/30, 'QASK Constellation');
                return;
            else
                % leave to the end for processing
                CMPLEX = I + j*Q;
            end;
        elseif findstr(method, '/ci')
            % circle defined NIC, AIC, PIC.
            if nargin < opt_pos
                error('In correct format for METHOD=''qask/circle''.');
            end;
            NIC = M;
            M = length(NIC);
            if nargin < opt_pos+1
                AIC = [1 : M];
            else
                AIC = opt2;
            end;
            if nargin < opt_pos + 2
                PIC = NIC * 0;
            else
                PIC = opt3;
            end;
            if plot_const
                apkconst(NIC, AIC, PIC);
                return;
            else
                CMPLEX = apkconst(NIC, AIC, PIC);
                M = sum(NIC);
            end;
        else
            %consider as square style.
            if plot_const
                qaskenco(M);
                return;
            else
                [I, Q] = qaskenco(M);
                CMPLEX = I + j * Q;
            end;
        end;
        y = [];
        x = x + 1;
        if (min(min(x)) < 1)  | (max(max(x)) > M)
            error('Element in input X exceeded range.');
        end;
        if max(max(x)) > length(CMPLEX)
            error(['Maximum element in x exceeds limit M = ' num2str(length(CMPLEX))])
        elseif min(min(x)) < 1
            error('Element in input X cannot be a negative number.')
        end;
        for i = 1 : size(x, 2)
            tmp = CMPLEX(x(:, i));
            y = [y tmp(:)];
        end; 
        if ini_phase
            y = y * exp(j * ini_phase);
        end;
    end;
elseif findstr(method, 'sam')
    %This is made possible to convert an input signal from sampling frequency Fd
    %to sampling frequency Fs.
    y = x;
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;