(完整word版)matlab卷积码程序

1、卷积码编码
function [output]=cnv_encd(input)
%output=cnv_encd(g,k0,input) 卷积码编码函数
%g 生成矩阵
%k0 输入码长
%input 输入信源序列
%output 输出卷积编码序列
g=[1 1 1;1 0 1];编码矩阵
k0=1;
input=[1 1 0 1];
if rem(length(input),k0)>0
input=[input,zeros(size(1:k0-rem(length(input),k0)))]; end
n=length(input)/k0;
if rem(size(g,2),k0)>0
error('Error,g is not of the right size.')
end
li=size(g,2)/k0;
n0=size(g,1);
u=[zeros(size(1:(li-1)*k0)),input,zeros(size(1:(li-1)*k0))];
u1=u(li*k0:-1:1);
for i=1:n+li-2
u1=[u1,u((i+li)*k0:-1:i*k0+1)];
end
uu=reshape(u1,li*k0,n+li-1);
output=reshape(rem(g*uu,2),1,n0*(n+li-1));
2、Viterbi译码程序
1）
function y=bin2deci(x)
l=length(x);
y=(l-1:-1:0);
y=2.^y;
y=x*y';
2）
function y=deci2bin(x,l)
y=zeros(1,l);
i=1;
while x>=0 & i<=l
y(i)=rem(x,2);
x=(x-y(i))/2;
i=i+1;
end
y=y(l:-1:1);
3）
function distance=metric(x,y)
if x==y
distance=0;
else
distance=1;
end
4）
function [next_state,memory_contents]=nxt_stat(current_state,input,L,k)
binary_state=deci2bin(current_state,k*(L-1));
binary_input=deci2bin(input,k);
next_state_binary=[binary_input,binary_state(1:(L-2)*k)];
next_state=bin2deci(next_state_binary);
memory_contents=[binary_input,binary_state];
5）
function [decoder_output,survivor_state,cumulated_metric]=viterbi(channel,snr_db)
G=[1 1 1;1 0 1]; % G 卷积编码矩阵，如（2,1,3)卷积码生成矩阵[1 1 1;1 0 1],可以根据自己的需要输入编码矩阵
k=1; % k 信息源输入端口数k=1
channel=[1 1 0 1 0 1 0 0 1 0 1 1 ]; %信源编码
snr_db=6;%信噪比，可以通过调节信噪比大小观察viterbi译码的性能
%bpsk调制
channel_output=bpsk(channel,snr_db);%调用bpsk函数,得到信道编码
n=size(G,1); % n 编码输出端口数量,(2,1,3)中n=2
if rem(size(G,2),k)~=0 %当G列数不是k的整数倍时error('Size of G and k do not agree') %发出出错信息
end
if rem(size(channel_output,2),n)~=0 %当输出量元素个数不是输出端口的整数倍时error('channel output not of the right size')
end
N=size(G,2)/k; %得出移位数，即寄存器的个数
M=2^k;
number_of_states=2^(k*(N-1)); %状态数
for j=0:number_of_states-1 %j表示当前寄存器组的状态因为状态是从零
%开始的,所以循环从0到number_of_states-1 for m=0:M-1 %m为从k个输入端的信号组成的状态，总的状
%态数为2^k，所以循环从0到2^k-1
% nxt_stat完成从当前的状态和输入的矢量得出下寄存器组的一个状态
[next_state,memory_contents]=nxt_stat(j,m,N,k);%调用nxt_stat函数
input(j+1,next_state+1)=m;
branch_output=rem(memory_contents*G',2);
nextstate(j+1,m+1)=next_state;
output(j+1,m+1)=bin2deci(branch_output);
end
end
% state_metric数组用于记录译码过程在每状态时的汉明距离
% state_metric大小为number_of_states 2，（:,1）当前
% 状态位置的汉明距离，为确定值，而（:,2）为当前状态加输入
% 得到的下一个状态汉明距离，为临时值
state_metric=zeros(number_of_states,2);
depth_of_trellis=length(channel_output)/n;
channel_output_matrix=reshape(channel_output,n,depth_of_trellis);
survivor_state=zeros(number_of_states,depth_of_trellis+1);
for i=1:depth_of_trellis-N+1
flag=zeros(1,number_of_states);
if(i<=N)
step=2^(k*(N-i));
else
step=1;
end
for j=0:step:number_of_states-1
for m=0:M-1
branch_metric=0;
binary_output=deci2bin(output(j+1,m+1),n);
for ll=1:n
branch_metric=branch_metric+metric(channel_output_matrix(ll,i),binary_output(ll));
end
% 选择码间距离较小的那条路径
% 选择方法：
% 当下一个状态没有被访问时就直接赋值，否则，用比它小的将其覆盖
if(( state_metric(nextstate(j+1,m+1)+1,2)>state_metric(j+1,1)+branch_metric) | flag(nextstate(j+1,m+1)+1)==0 )
state_metric(nextstate(j+1,m+1)+1,2)=state_metric(j+1,1)+branch_metric;
survivor_state(nextstate(j+1,m+1)+1,i+1)=j;
flag(nextstate(j+1,m+1)+1)=1;
end
end
end
state_metric=state_metric(:,2:-1:1);
end
for i=depth_of_trellis-N+2:depth_of_trellis
flag=zeros(1,number_of_states);
% 状态数从number_of_states→number_of_states/2→...→2→1
%程序说明同上，只不过输入矢量只为0
last_stop=number_of_states/(2^(k*(i-depth_of_trellis+N-2)));
for j=0:last_stop-1
branch_metric=0;
binary_output=deci2bin(output(j+1,1),n);
for ll=1:n
branch_metric=branch_metric+metric(channel_output_matrix(ll,i),binary_output(ll));
end
if( (state_metric(nextstate(j+1,1)+1,2)>state_metric(j+1,1)+branch_metric) | flag(nextstate(j+1,1)+1)==0 )
state_metric(nextstate(j+1,1)+1,2)=state_metric(j+1,1)+branch_metric;
survivor_state(nextstate(j+1,1)+1,i+1)=j;
flag(nextstate(j+1,1)+1)=1;
end
end
state_metric=state_metric(:,2:-1:1);
end
% 从最佳路径中产生解码
% 译码过程可从数组survivor_state的最后一个位置向前逐级译码
state_sequence=zeros(1,depth_of_trellis+1);
state_sequence(1,depth_of_trellis)=survivor_state(1,depth_of_trellis+1);
for i=1:depth_of_trellis
state_sequence(1,depth_of_trellis-i+1)=survivor_state((state_sequence(1,depth_of_trellis+2-i)+1), depth_of_trellis-i+2);
end
decoder_output_matrix=zeros(k,depth_of_trellis-N+1);
for i=1:depth_of_trellis-N+1
% 根据数组input的定义来得出从当前状态到下一个状态的输入信号矢量
dec_output_deci=input(state_sequence(1,i)+1,state_sequence(1,i+1)+1);
dec_output_bin=deci2bin(dec_output_deci,k);
% 将一次译码存入译码输出矩阵decoder_output_matrix相应的位置
decoder_output_matrix(:,i)=dec_output_bin(k:-1:1)';
end
decoder_output=reshape(decoder_output_matrix,1,k*(depth_of_trellis-N+1));
cumulated_metric=state_metric(1,1);
3、卷积码译码误码性能分析
clear all;
clc;
cycl = 50;
snr_db = 0:1:10;
% 输入信息
msg = randint(1,1024);
ber0 = zeros(cycl,length(snr_db));
ber1 = zeros(cycl,length(snr_db));
ber2 = zeros(cycl,length(snr_db));
% Trellises
trel = poly2trellis(3,[5 7]); %Define trellis for rate 1/2 code. for n = 1:cycl
for x = 1:length(snr_db)
% Code words
code = convenc(msg,trel); % Encode.
% Interleaver
state = 20;
inter = randintrlv(code,state);
% BPSK 调制
s0 = sign(msg - 0.5);
s1 = sign(inter-0.5);
s2 = sign(code-0.5);
% AWGN Channel
add_noise0=awgn(s0,snr_db(x),'measured');
add_noise1=awgn(s1,snr_db(x),'measured');
add_noise2=awgn(s2,snr_db(x),'measured');
% Deinterleaver with noise for soft decoding
deinter_noise = randdeintrlv(add_noise1,state);
% 解调
r_0 = 0.5*sign(add_noise0) + 0.5;
r_1 = 0.5*sign(add_noise1) + 0.5;
r_2 = 0.5*sign(add_noise2) + 0.5;
% Deinterleaver
deinter_1 = randdeintrlv(r_1,state);
% Traceback length
tblen = 5;
% vitdec 硬判决
decoded1 = vitdec(deinter_1,trel,tblen,'cont','hard');
% vitdec 软判决
[y,qcode] = quantiz(deinter_noise,[-.75 -.5 -.25 0 .25 .5 .75],7:-1:0); decoded2 = vitdec(qcode,trel,tblen,'cont','soft',3);
% 比较误码率
[num0,rat0] = biterr(r_0,msg);
[num1,rat1] = biterr(double(decoded1(tblen+1:end)),msg(1:end-tblen)); [num2,rat2] = biterr(double(decoded2(tblen+1:end)),msg(1:end-tblen)); ber0(n,x) = rat0;
ber1(n,x) = rat1;
ber2(n,x) = rat2;
end
end
ber0 = mean(ber0);
ber1 = mean(ber1);
ber2 = mean(ber2);
semilogy(snr_db,ber0,'b-o',snr_db,ber1,'r-s',snr_db,ber2,'k-p');
xlabel('SNR (dB)');
ylabel('BER');
legend('Uncoded','Hard Coded','Soft Coded');
title('Performance of convolutional code with rate 1/2');。