dmod.m

Proakis《contemporarycommunication systems using matlab》matlab源代码

function [y, t] = dmod(x, Fc, Fd, Fs, method, M, opt2, opt3)
%DMOD   Digital modulation.
%       Y = DMOD(X, Fc, Fd, Fs, METHOD, OPT1, OPT2, OPT3) modulates signal X
%       with carrier frequency Fc (Hz) using the given method in the input 
%       variable METHOD. The sampling frequency for X is Fd (Hz). The sampling
%       frequency for the complex envelope output is Fs (Hz). It is required
%       that Fs>Fc. 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 as 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. For baseband simulation or complex
%       envelope simulation, please use DMODCE.
%
%       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 the switch '/nmap' appended to the string of METHOD variable, the
%       function will not process the digital to analog mapping. The input
%       signal is assumed having sampling frequency Fs.
%
%       DMOD(METHOD, OPT1, OPT2, OPT3) plot constellation layout.
%
%       Use DMOD(METHOD) to view the help for a specific method.
%
%       See also DDEMOD, DMODCE, DDEMOD, MODMAP. DEMODMAP, AMOD, ADEMOD.
%

%       Wes Wang 1/9/95, 10/5/95
%       Copyright (c) 1995-96 by The MathWorks, Inc.
%       $Revision: 1.1 $  $Date: 1996/04/01 17:56:46 $

%position for optional parameters.
opt_pos = 6;
plot_const = 0;
if nargin < 1
    feval('help','dmod')
    return;
elseif isstr(x)
    method = lower(deblank(x));
    if length(method) < 3
        error('Invalid method option for dmod.')
    end
    if nargin == 1
        % help lines for individual modulation method.
        addition = 'See also DDEMOD, DMODCE, DDEMODCE, MODMAP, DEMODMAP, AMOD, ADEMOD.';
        if method(1:3) == 'qas'
          callhelp('dmod.hlp',method(1:4),addition);
        else
          callhelp('dmod.hlp',method(1:3),addition);
        end
    else
        %plot constellation, make a shift.
        opt_pos = opt_pos - 3;
        M = Fc;
        if nargin >= opt_pos
            opt2 = Fd;
        else
            modmap(method, M);
            return;
        end;
        if nargin >= opt_pos+1
            opt3 = Fs;
        else
            modmap(method, M, opt2);
            return;
        end;
        %take care of all plot by using modmap
        modmap(method, M, opt2, opt3);
    end;
    return;
end;
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;
end;

%turn to the right position.
[r, c] = size(x);
if r * c == 0
    y = [];
    return;
end;
if r == 1
    x = x(:);
    len_x = c;
else
    len_x = r;
end;

%expand x from Fd to Fs.
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;

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

if (nargin < 3)
    disp('Usage: Y=DMOD(X, Fc, 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 isempty(findstr(method, '/nomap'))
        y = (x - (M - 1) / 2 ) * 2 / (M - 1);
    else
        y = x;
    end;
    [y, t] = amod(y, Fc, [Fs, ini_phase], 'amdsb-sc');
elseif findstr(method, 'fsk')
    if nargin < opt_pos + 1
        Tone = 2 * Fd / M;
    else
        Tone = opt2;
    end;
    if isempty(findstr(method, '/nomap'))
        x = x * Tone;
    end;
    [len_y, wid_y] = size(x);
    t = (0:1/Fs:((len_y-1)/Fs))';
    t = t(:, ones(1, wid_y));
    x = 2 /Fs * pi * x;
    for i = 1 : ceil(len_y/FsDFd)
        y((i-1)*FsDFd+1 : min(i*FsDFd, len_y), :) = ...
            cos(2 * pi * Fc * t(1:min(FsDFd, len_y-(i-1)*FsDFd), :) ...
             + cumsum([zeros(1, wid_y); x((i-1)*FsDFd+1 : min(i*FsDFd, len_y)-1, :)]) ...
             + ini_phase);
    end;
    t = (0:1/Fs:((len_y-1)/Fs))';
elseif findstr(method, 'psk')
    %PSK is a special case of QASK.
    [len_y, wid_y] = size(x);
    t = (0:1/Fs:((len_y-1)/Fs))';
    if findstr(method, '/nomap')
        y = dmod(x, Fc, Fs, [Fs, ini_phase], 'qask/cir/nomap', M);
    else
        y = dmod(x, Fc, Fs, [Fs, ini_phase], 'qask/cir', M);
    end;
elseif findstr(method, 'msk')
    %This is a special case of fsk call back to get fsk
    M = 2;
    Tone = Fd;
    if isempty(findstr(method, '/nomap'))
        x = x * Tone;
    end;
    [len_y, wid_y] = size(x);
    t = (0:1/Fs:((size(x,1)-1)/Fs))';
    t = t(:, ones(1, size(x, 2)));
    x = 2 /Fs * pi * x;
    for i = 1 : ceil(len_y/FsDFd)
        y((i-1)*FsDFd+1 : min(i*FsDFd, len_y), :) = ...
         cos(2 * pi * Fc * t(1:min(FsDFd, len_y-(i-1)*FsDFd), :)+...
         cumsum([zeros(1,wid_y); x((i-1)*FsDFd+1:min(i*FsDFd,len_y)-1, :)])...
                + ini_phase);
    end;
elseif ~isempty(findstr(method, 'qas')) |...
         ~isempty(findstr(method, 'qam')) |...
         ~isempty(findstr(method, 'qsk'))
    if findstr(method,'nomap')
        [y, t] = amod(x, Fc, [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);
            % leave to the end for processing
            CMPLEX = I + j*Q;
        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;
            CMPLEX = apkconst(NIC, AIC, PIC);
            M = sum(NIC);
        else
            %consider as square style.
            [I, Q] = qaskenco(M);
            CMPLEX = I + j * Q;
        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;
        y = [real(y) imag(y)];
        wid_y = size(y, 2);
        y = [y(:,1:2:wid_y) y(:,2:2:wid_y)];
        [y, t] = amod(y, Fc, [Fs, ini_phase], 'qam');
    end;
elseif findstr(method, 'sam')
    %This is made possible to convert an input signal from sampling frequency Fd
    %to sampling frequency Fs.
    [len_y, wid_y] = size(x);
    t = (0:1/Fs:((len_y-1)/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;

%---end of dmod.m