Nt = 2 ;
Nr = 2 ;
Len = 10000 ;
M= 4 ;
bitsPerSymbol = log2(M) ;
bitsTotal = bitsPerSymbol * Nt * Len ;ALP = [-1+1i  ;-1-1* 1i ;1+1i ;1-1i] * sqrt(3/(2*(M-1)))  ; %QAM符号
%ALPbin = dec2bin( 0:M-1 , log2(M))  ; %QAM的二进制编码
SNRVect = 0:2:20 ;
SER = zeros( 1 ,length(SNRVect) )  ;
for snrLoop =  1: length (SNRVect)fprintf(' snrLoop = %d \n',snrLoop) ;%计算信噪比SNRdB = SNRVect(snrLoop) ;SNR  = 10^(SNRdB/10) ;%此处我们假设每根天线发送的信号能量为1   %N0 表示噪声的能量N0 = Nt * 1 / SNR ;   %产生随机比特流send = round(rand(1,bitsTotal)) ;sendReshape = reshape(send , Nt * bitsPerSymbol , Len ) ;symbols = zeros(Nt, Len) ;symbolsModulation = zeros(Nt ,Len) ;%发送端 4QAM调制fprintf('\n正在调制并发送 \n') ;for sendLoop = 1 :Lenfor antennaLoop = 1: NttwoBits = sendReshape ( 2* antennaLoop-1 :2* antennaLoop, sendLoop) ;symbols  ( antennaLoop ,sendLoop)  = 2 * twoBits(1) + 1 * twoBits(2) +1 ;symbolsModulation ( antennaLoop ,sendLoop) = ALP(symbols  ( antennaLoop ,sendLoop) ) ;endend%经过信道H = (randn(Nr, Nt) + sqrt(-1) * randn(Nr , Nt))/ sqrt(2)  ; % 除以sqrt(2) 保证信道的能量为1n = (randn(Nr , Len) + sqrt(-1)*randn(Nr, Len )) * sqrt(N0) /sqrt(2) ; %保证噪声 n ~N(0,N0)y = H* symbolsModulation + n ;%接收端fprintf('\n正在译码 \n') ;symbolsDetect = zeros(2 , Len) ;for sendLoop = 1 :Lenfprintf('%d %d \n',snrLoop ,sendLoop) ;%得到M*M种组合dml = zeros(M ,M ,Len) ;for i1 = 1:Mfor i2 = 1:Mdml(i1, i2, sendLoop) = (norm (  y(: , sendLoop) - H * [ALP(i1) ; ALP(i2)] ) )  .^2 ; % 共16种组合endenddml_min = min( reshape(dml( :, :, sendLoop ) .' , 1, M*M)  ) ;%找到最合适的  然后译码for j1 = 1: M ;for j2 = 1:Mif dml(j1 , j2, sendLoop) ==dml_min ;symbolsDetect(1, sendLoop) = j1 ;symbolsDetect(2, sendLoop) = j2 ;endendendend% 一个信噪比结束  统计SERSER(snrLoop)  = sum ( reshape(symbolsDetect , 1, Len * Nt) ~= reshape (symbols , 1, Len *Nt) )/ (Len * Nt) ;
endsemilogy( 0: 2 : 20 , SER)

L=1000时，仿真结果如下：