simrscod.m

数字通信第四版原书的例程

function [sys, x0, str, ts] = simrscod(t, x, u, flag, n, k, pg, tp, dim);
%SIMBCHDC SIMULINK S-function for Reed-Solomon encode.
%       The m-dile is designed to be used in a SIMULINK S-Function block.
%       This function will encode the input integer vector using RS-code.
%       Parameters: n -- length of code word.
%                   k -- length of message.
%                   pg-- generator polynomial
%                   tp-- list of all GF(2^M) elements. n=2^M-1.
%                   dim -- M.
%
%       The output has length n.

%       Wes Wang
%       Copyright (c) 1995-96 by The MathWorks, Inc.

if (flag == 3)
    % refresh the state only when there is a trigger signal
    len_u = length(u);
    if u(len_u)
        % main calculation
        t2 = n - k;
        pgg = fliplr(pg(1:length(pg)-1));       % pg is a monic polynomial
        msg = u(1 : len_u-1) - 1;
        msg = [flipud(msg); -ones(t2,1)];
        for main_j = 1 : len_u-1
            if msg(main_j)>= 0
                for main_k = 1: t2
                    msg(main_j + main_k) = gfadd(msg(main_j + main_k), gfmul(msg(main_j), pgg(main_k), tp), tp);
                end;
            end;
        end;
        sys = [flipud(msg(len_u:n))+1; u(1:len_u-1)];
        indx = find(~(sys >= 0));
        sys(indx) = indx - indx;
    else
        % if there is no trigger, no calculation.
        sys = zeros(n, 1);
    end;
elseif flag == 0
    if 2^dim-1 ~= n
        error('Ree-Solomon encode has illegal code word length')
    end;
    sys(1) = 0; % no continuous state
    sys(2) = 0;
    sys(3) = n;   % number of output, code word length plus one.
    sys(4) = k + 1;       % number of input, message length.
    sys(5) = 0;
    sys(6) = 1;       % direct through flag.
    sys(7) = 1;       % one sample rate
    x0 = [];
    ts = [-1, 0];
else
    sys = [];
end;