simrsdbv.m

数字通信第四版原书的例程

function [sys, x0, str, ts] = simbchdc(t, x, u, flag, n, k, tp, dim);
%SIMBCHDC SIMULINK S-function for BCH decode.
%       The m-dile is designed to be used in a SIMULINK S-Function block.
%       This function will decode the cyclic code using BCH decod method.
%       Parameters: n -- length of code word.
%                   k -- length of message.
%                   t -- error-correction capability.
%                   tp-- list of all GF(2^M) elements. n=2^M-1.
%
%       The output has length n+1, the last digit is the error signal err.
%       A non-negative err indicates number of errors have been corrected.
%       A nagative err indicates that more than t error have been found in
%       in the code, the routine cannot correct such error.

%       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)
        % output the decode result.
        % main calculation
        code_word = bi2de(vec2mat(u(1:len_u-1), dim)) - 1;
        [sys, err] = rscore(code_word, k, tp, dim, n);
        % output is the combination of message and error information.
        sys = sys +1;
        indx = find(~(sys>=0));
        sys(indx) = indx-indx;
        sys = de2bi(sys, dim)';
        sys = [sys(:); err];
%        disp(['should output ', num2str(k * dim + 1), 'it is now ', num2str(length(sys))])
    else
        % if there is no trigger, no calculation.
        if t <= 0
            sys = zeros(m*k+1, 1);
        end;
    end;
elseif flag == 0
    if 2^dim-1 ~= n
        error('Reed-Solomon decode has illegal code word length')
    end;
    sys(1) = 0; % no continuous state
    sys(2) = 0;
    sys(3) = k * dim + 1;   % number of output, code word length plus one.
    sys(4) = n * dim + 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;