deqam16.m

OFDm模型里面的调制和解调相关源程序代码

function [llr]=deqam16(x,h,SNR)
%本程序是计算经过16QAM调制信号的对数释然比信息，为软维特比译码提供信息源
%这里是根据输入信息点在坐标中的位置情况来判断对应二进制信息为的似然比的大小
%这里应该是对应四位二进制比特的释然比
%根据二进制对应比特数位置，分别求离输入信息点最近的0和1对应星座的似然比即位该比特的似然比
%具体理论公式见第一阶段文档附件中的均衡和解调方案
%输入参数：x：  经过16QAM调制的信号，长度为L
%          h：  信号经过的信号估计序列
%          SNR：经过的高斯信道的信噪比
%输出参数：llr：信号对应二进制序列的对数释然比信息
%                    8    7  |   3    4
%                    6    5  |   1    2
%             －－－－－－－－－－－－－－－        
%                   14    13 |   9    10
%                   16    15 |   11   12
%
%王东洋
%2005－10－19
%星座图表
constel_diagram=[sqrt(2)/2+j*sqrt(2)/2, 1.5*sqrt(2)+j*sqrt(2)/2, sqrt(2)/2+j*1.5*sqrt(2), 1.5*sqrt(2)+j*1.5*sqrt(2),...%第一象限
                -sqrt(2)/2+j*sqrt(2)/2,-1.5*sqrt(2)+j*sqrt(2)/2,-sqrt(2)/2+j*1.5*sqrt(2),-1.5*sqrt(2)+j*1.5*sqrt(2),...%第二象限
                 sqrt(2)/2-j*sqrt(2)/2, 1.5*sqrt(2)-j*sqrt(2)/2, sqrt(2)/2-j*1.5*sqrt(2), 1.5*sqrt(2)-j*1.5*sqrt(2),...%第四象限
                -sqrt(2)/2-j*sqrt(2)/2,-1.5*sqrt(2)-j*sqrt(2)/2,-sqrt(2)/2-j*1.5*sqrt(2),-1.5*sqrt(2)-j*1.5*sqrt(2)]/sqrt(5);%第三象限
%SNR为信道信噪比，信号功率为1,转化为线性值
SNR_linr=10^(SNR/10);
%得到信道估计值的平方
h_square=abs(h).^2;
%len为输入信号的长度
len=length(x);
%存储似然比信息
llr=zeros(1,4*len);
%计算信号到各个星座点的映射距离
temp=[abs(x-constel_diagram(1)),abs(x-constel_diagram(2)),abs(x-constel_diagram(3)),abs(x-constel_diagram(4)),abs(x-constel_diagram(5)),abs(x-constel_diagram(6)),...
    abs(x-constel_diagram(7)),abs(x-constel_diagram(8)),abs(x-constel_diagram(9)),abs(x-constel_diagram(10)),abs(x-constel_diagram(11)),abs(x-constel_diagram(12)),...
    abs(x-constel_diagram(13)),abs(x-constel_diagram(14)),abs(x-constel_diagram(15)),abs(x-constel_diagram(16))].^2;
%下面是计算各个信息比特的似然比信息llr
for m=1:len
    temp2=temp(m:len:16*len);
    [y,z]=sort(temp2);
    
    switch z(1)
        case 1
        llr(4*(m-1)+1)=h_square(m)*(temp2(5)-temp2(1));
        llr(4*(m-1)+2)=h_square(m)*(temp2(9)-temp2(1));
        llr(4*(m-1)+3)=h_square(m)*(temp2(2)-temp2(1));
        llr(4*(m-1)+4)=h_square(m)*(temp2(3)-temp2(1));
        case 2
         llr(4*(m-1)+1)=h_square(m)*(temp2(5)-temp2(2));
         llr(4*(m-1)+2)=h_square(m)*(temp2(10)-temp2(2));
         llr(4*(m-1)+3)=h_square(m)*(temp2(2)-temp2(1));
         llr(4*(m-1)+4)=h_square(m)*(temp2(4)-temp2(2));
        case 3
         llr(4*(m-1)+1)=h_square(m)*(temp2(7)-temp2(3));
         llr(4*(m-1)+2)=h_square(m)*(temp2(9)-temp2(3));
         llr(4*(m-1)+3)=h_square(m)*(temp2(4)-temp2(3));
         llr(4*(m-1)+4)=h_square(m)*(temp2(3)-temp2(1));
        case 4
         llr(4*(m-1)+1)=h_square(m)*(temp2(7)-temp2(4));
         llr(4*(m-1)+2)=h_square(m)*(temp2(10)-temp2(4));
         llr(4*(m-1)+3)=h_square(m)*(temp2(4)-temp2(3));
         llr(4*(m-1)+4)=h_square(m)*(temp2(4)-temp2(2));
        case 5
         llr(4*(m-1)+1)=h_square(m)*(temp2(5)-temp2(1));
         llr(4*(m-1)+2)=h_square(m)*(temp2(13)-temp2(5));
         llr(4*(m-1)+3)=h_square(m)*(temp2(6)-temp2(5));
         llr(4*(m-1)+4)=h_square(m)*(temp2(7)-temp2(5));
        case 6
         llr(4*(m-1)+1)=h_square(m)*(temp2(6)-temp2(1));
         llr(4*(m-1)+2)=h_square(m)*(temp2(14)-temp2(6));
         llr(4*(m-1)+3)=h_square(m)*(temp2(6)-temp2(5));
         llr(4*(m-1)+4)=h_square(m)*(temp2(8)-temp2(6));
        case 7
         llr(4*(m-1)+1)=h_square(m)*(temp2(7)-temp2(3));
         llr(4*(m-1)+2)=h_square(m)*(temp2(13)-temp2(7));
         llr(4*(m-1)+3)=h_square(m)*(temp2(8)-temp2(7));
         llr(4*(m-1)+4)=h_square(m)*(temp2(7)-temp2(5));
        case 8
         llr(4*(m-1)+1)=h_square(m)*(temp2(8)-temp2(3));
         llr(4*(m-1)+2)=h_square(m)*(temp2(14)-temp2(6));
         llr(4*(m-1)+3)=h_square(m)*(temp2(8)-temp2(7));
         llr(4*(m-1)+4)=h_square(m)*(temp2(8)-temp2(6));
        case 9
         llr(4*(m-1)+1)=h_square(m)*(temp2(13)-temp2(9));
         llr(4*(m-1)+2)=h_square(m)*(temp2(9)-temp2(1));
         llr(4*(m-1)+3)=h_square(m)*(temp2(10)-temp2(9));
         llr(4*(m-1)+4)=h_square(m)*(temp2(11)-temp2(9));
        case 10
         llr(4*(m-1)+1)=h_square(m)*(temp2(13)-temp2(10));
         llr(4*(m-1)+2)=h_square(m)*(temp2(10)-temp2(2));
         llr(4*(m-1)+3)=h_square(m)*(temp2(10)-temp2(9));
         llr(4*(m-1)+4)=h_square(m)*(temp2(12)-temp2(10));
        case 11
         llr(4*(m-1)+1)=h_square(m)*(temp2(15)-temp2(11));
         llr(4*(m-1)+2)=h_square(m)*(temp2(11)-temp2(1));
         llr(4*(m-1)+3)=h_square(m)*(temp2(12)-temp2(11));
         llr(4*(m-1)+4)=h_square(m)*(temp2(11)-temp2(9));
        case 12
         llr(4*(m-1)+1)=h_square(m)*(temp2(15)-temp2(12));
         llr(4*(m-1)+2)=h_square(m)*(temp2(12)-temp2(2));
         llr(4*(m-1)+3)=h_square(m)*(temp2(12)-temp2(11));
         llr(4*(m-1)+4)=h_square(m)*(temp2(12)-temp2(10));
        case 13
         llr(4*(m-1)+1)=h_square(m)*(temp2(13)-temp2(9));
         llr(4*(m-1)+2)=h_square(m)*(temp2(13)-temp2(5));
         llr(4*(m-1)+3)=h_square(m)*(temp2(14)-temp2(13));
         llr(4*(m-1)+4)=h_square(m)*(temp2(15)-temp2(13));
        case 14
         llr(4*(m-1)+1)=h_square(m)*(temp2(14)-temp2(9));
         llr(4*(m-1)+2)=h_square(m)*(temp2(14)-temp2(6));
         llr(4*(m-1)+3)=h_square(m)*(temp2(14)-temp2(13));
         llr(4*(m-1)+4)=h_square(m)*(temp2(16)-temp2(14));
        case 15
         llr(4*(m-1)+1)=h_square(m)*(temp2(15)-temp2(11));
         llr(4*(m-1)+2)=h_square(m)*(temp2(15)-temp2(5));
         llr(4*(m-1)+3)=h_square(m)*(temp2(16)-temp2(15));
         llr(4*(m-1)+4)=h_square(m)*(temp2(15)-temp2(13));
       otherwise 
         llr(4*(m-1)+1)=h_square(m)*(temp2(16)-temp2(11));
         llr(4*(m-1)+2)=h_square(m)*(temp2(16)-temp2(6));
         llr(4*(m-1)+3)=h_square(m)*(temp2(16)-temp2(15));
         llr(4*(m-1)+4)=h_square(m)*(temp2(16)-temp2(14));
     end
 end
 llr=llr/SNR_linr;