msg = randint(4000,1,2,139);   %產生隨機數
t = poly2trellis(7,[171 133]);   %定義trellis
code = convenc(msg,t);     %卷積編碼
ncode = awgn(code,6,'measured',244); %加噪聲
qcode = quantiz(ncode,[0.001,.1,.3,.5,.7,.9,.999]);     %量化以進行軟判決

tblen = 48; delay = tblen;       %回歸的路徑長
decoded = vitdec(qcode,t,tblen,'cont','soft',3);   %Viterbi譯碼
%計算誤比特率
[number,ratio] = biterr(decoded(delay+1:end),msg(1:end-delay))