sova.m - function L_all = sova(rec_s g L_a ind_dec This...

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function L_all = sova(rec_s, g, L_a, ind_dec) % This function implememts Soft Output Viterbi Algorithm in trace back mode % Input: % rec_s: scaled received bits. rec_s(k) = 0.5 * L_c(k) * y(k) % L_c = 4 * a * Es/No, reliability value of the channel % y: received bits % g: encoder generator matrix in binary form, g(1,:) for feedback, g(2,:) for feedforward % L_a: a priori information about the info. bits. Extrinsic info. from the previous % component decoder % ind_dec: index of the component decoder. % =1: component decoder 1; The trellis is terminated to all zero state % =2: component decoder 2; The trellis is not perfectly terminated. % Output: % L_all: log ( P(x=1|y) ) / ( P(x=-1|y) ) % % Copyright: Yufei Wu, Nov. 1998 % MPRG lab, Virginia Tech % for academic use only % Frame size, info. + tail bits L_total = length(L_a); [n,K] = size(g); m = K - 1; nstates = 2^m; Infty = 1e10; % SOVA window size. Make decision after 'delta' delay. Decide bit k when received bits % for bit (k+delta) are processed. Trace back from (k+delta) to k. delta = 30; % Set up the trellis defined by g.
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