gusucode.com > LTE基带收发仿真系统matlab源码程序 > LTE baseband simulation/logmapo.m
function L_all = logmapo(rec_s,g,L_a,ind_dec) % 函数实现的主要功能:对解调信号进行Log-Map译码,计算LLR % 输入变量: % rec_s: 接受比特的加权. % rec_s = 0.5 * L_c * yk = ( 2 * a * rate * Eb/N0 ) * yk % g: 生成矩阵. % L_a: 另一个分量译码器的先验信息 % ind_dec: 分量译码器的索引号 % 输出变量: % L_all: 概率对数似然比值. % Author: 程式小组(徐萌 张妙 张晓庆) % Date: 2010-07-11 % ========================================================== % Total number of bits: Inftyo. + tail L_total = length(rec_s)/2; [n,K] = size(g); m = K - 1; nstates = 2^m; % number of states in the trellis % Set up the trellis [next_out, next_state, last_out, last_state] = trellis(g); Infty = 1e10; % Initialization of Alpha Alpha(1,1) = 0; Alpha(1,2:nstates) = -Infty*ones(1,nstates-1); % Initialization of Beta if ind_dec==1 Beta(L_total,1) = 0; Beta(L_total,2:nstates) = -Infty*ones(1,nstates-1); elseif ind_dec==2 Beta(L_total,1:nstates) = zeros(1,nstates); else fprintf('ind_dec is limited to 1 and 2!\n'); end % Trace forward, compute Alpha tempmax = zeros(1,L_total+1); for k = 2:L_total+1 for state2 = 1:nstates gamma = -Infty*ones(1,nstates); gamma(last_state(state2,1)) = (-rec_s(2*k-3)+rec_s(2*k-2)*last_out(state2,2)).... -log(1+exp(L_a(k-1))); gamma(last_state(state2,2)) = (rec_s(2*k-3)+rec_s(2*k-2)*last_out(state2,4)).... +L_a(k-1)-log(1+exp(L_a(k-1))); if(sum(exp(gamma+Alpha(k-1,:)))<1e-300) Alpha(k,state2)=-Infty; else Alpha(k,state2) = log( sum( exp( gamma+Alpha(k-1,:) ) ) ); end end tempmax(k) = max(Alpha(k,:)); Alpha(k,:) = Alpha(k,:) - tempmax(k); end % Trace backward, compute Beta for k = L_total-1:-1:1 for state1 = 1:nstates gamma = -Infty*ones(1,nstates); gamma(next_state(state1,1)) = (-rec_s(2*k+1)+rec_s(2*k+2)*next_out(state1,2)).... -log(1+exp(L_a(k+1))); gamma(next_state(state1,2)) = (rec_s(2*k+1)+rec_s(2*k+2)*next_out(state1,4)).... +L_a(k+1)-log(1+exp(L_a(k+1))); if(sum(exp(gamma+Beta(k+1,:)))<1e-300) Beta(k,state1)=-Infty; else Beta(k,state1) = log(sum(exp(gamma+Beta(k+1,:)))); end end Beta(k,:) = Beta(k,:) - tempmax(k+1); end % Compute the soft output, log-likelihood ratio of symbols in the frame L_all=zeros(1,L_total); temp0=zeros(1,nstates); temp1=zeros(1,nstates); for k = 1:L_total for state2 = 1:nstates gamma0 = (-rec_s(2*k-1)+rec_s(2*k)*last_out(state2,2)).... -log(1+exp(L_a(k))); gamma1 = (rec_s(2*k-1)+rec_s(2*k)*last_out(state2,4))... +L_a(k)-log(1+exp(L_a(k))); temp0(state2) = exp(gamma0 + Alpha(k,last_state(state2,1)) + Beta(k,state2)); temp1(state2) = exp(gamma1 + Alpha(k,last_state(state2,2)) + Beta(k,state2)); end L_all(k) = log(sum(temp1)) - log(sum(temp0)); end