卷积码编码译码 维特比译码

%Hard Decision Viterbi Decoder %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %Function gets an encoded message 'rcvd(encoded by a convolutional encoder) %as argument and returns the decoded message 'dec_op' %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% function [dec_op]=viterbidec(rcvd) %Concatenate two consecutive bits of recieved encoded sequence to %make up a symbol input=[]; for j=1:2:length(rcvd) input=[ input (rcvd(j))* 2 + (rcvd(j+1))]; end %initializing all arrays op_table=[00 00 11; 01 11 00; 10 10 01; 11 01 10]; %OUTPUT array ns_table=[0 0 2; 1 0 2; 2 1 3; 3 1 3]; %NEXT STATE array transition_table=[0 1 1 55; 0 0 1 1; 55 0 55 1; 55 0 55 1]; %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% % A R R A Y S - U P D A T I N G Part %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% st_hist(1:4, 1:17)=55; %STATE HISTORY array aem=zeros(4, 17); %ACCUMULATED ERROR METRIC (AEM) array ssq=zeros(1, 17); %STATE SEQUENCE array input=rcvd; input(1, :)=bin2dec(rcvd) input=[0 3 3 0 1 2 1 3 3 2 0 0 3 0 3 2 3] %INPUT vector rcvd=['00';'11';'11';'00';'01';'10';'01';'11';'11';'10';'00';'00';'11';'00';'11';'10'; '11'] lim=length(input); %number of clock cycles for (t=0:1:lim) %clock loop disp('------------------------------------------------------') t; %display current clock instance if(t==0) st_hist(1,1)=0; %start at state 00 else temp_state=[];%vector to store possible states at an instant temp_metric=[];%vector to store metrics of possible states temp_parent=[];%vector to store parent states of possible states for (i=1:1:4) i; in=input(t); if(st_hist(i, t)==55) %if invalid state %do nothing else ns_a=ns_table(i, 2)+1; %next possible state-1 ns_b=ns_table(i, 3)+1; %next possible state-2 op_a=op_table(i, 2); %next possible output-1 op_b=op_table(i, 3); %next possible output-2 cs=i-1; %current state M_a=hamm_dist(in, op_a); %branch metric for ns_a M_b=hamm_dist(in, op_b); %branch metric for ns_b indicator=0; %flag to indicate redundant states for k=1:1:length(temp_state) %check redundant next states %if next possible state-1 redundant if(temp_state(1,k)==ns_a) indicator=1; %ADD-COMPARE-SELECT Operation %em_c: error metric of current state %em_r: error metric of redundant state em_c=M_a + aem(i,t); em_r=temp_metric(1,k) + aem(temp_parent(1, k)+1,t); if( em_c< em_r)%compare the two error metrics st_hist(ns_a,t+1)=cs;%select state with low AEM temp_metric(1,k)=M_a; temp_parent(1,k)=cs; end end %if next possible state-2 redundant if(temp_state(1,k)==ns_b) indicator=1; em_c=M_b + aem(i,t); em_r=temp_metric(1,k) + aem(temp_parent(1, k)+1,t); if( em_c < em_r)%compare the two error metrics st_hist(ns_b,t+1)=cs;%select state with low AEM temp_metric(1,k)=M_b; temp_parent(1,k)=cs; end end end %if none of the 2 possible states are redundant if(indicator~=1) %update state history table st_hist(ns_a,t+1)=cs; st_hist(ns_b,t+1)=cs; %update the temp vectors accordingly temp_parent=[temp_parent cs cs]; temp_state=[temp_state ns_a ns_b]; temp_metric=[temp_metric M_a, M_b]; end %print the temp vectors temp_parent; temp_state; temp_metric; end end %update the AEMs (accumulative error metrics) for all states for %current instant 't' for h=1:1:length(temp_state) xx1=temp_state(1, h); xx2=temp_parent(1, h)+1; aem(xx1, t+1)=temp_metric(1, h) + aem(xx2, t); end end end %end of clock loop %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% % T R A C E - B A C K Part %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% for(t=0:1:lim) slm=min(aem(:, t+1)); slm_loc=find( aem(:, t+1)==slm ); sseq(t+1)=slm_loc(1)-1; end dec_op=[]; for p=1:1:length(sseq)-1 p; dec_op=[dec_op, transition_table((sseq(p)+1), (sseq(p+1)+1))]; end