1.问题描述：

 MRC误码率的matlab仿真

2.部分程序：

%Comparison of Decode and F,Detect and F and Amplify and Forward 
%BPSK in flat fading with WGN: 
%plot simulation results of BER and theoratical results for it. 
%combining the two signals using MRC 
%using averaged BER 

%%%%%%%%%house hold instuctions%%%%%%%%%%%%%%%%%% 
clc 
clear all 
close all 

sum_dcf = 0; 
sum_dtf = 0; 
sum_af = 0; 
%%%%%%%%%%%%%%%%%%%User1:Source%%%%%%%%%%%%%% 
N_bits = 15000; %Number of data bits 

%number of iterations over which the results are going to be averaged 
N_iter = 15; 
for iter = 1:N_iter 

data = round(rand(N_bits,1));%random data bits 
%channel coding using rate 1/2 convolutional code: 
trellis = poly2trellis(3,[5 7]); %trellis structure 
c_data = convenc(data,trellis); 

%BPSK modulation 
tx = 2*c_data - 1; 

%%%%%%%%%Channel characteristics%%%%%%%%%%%%%%%% 
SNRdB = -3:20; %Range of SNR for which BER is investigated. 

%additive noise and channel response for the relay channel: 
%Source uplink channel: 
noise_d = 1/sqrt(2) * (randn(2 * N_bits,1) + j * randn(2 * N_bits,1)); 
h_d = 1/sqrt(2) * (randn(2 * N_bits,1) + j * randn(2 * N_bits,1)); 

%interuser channel: 
noise_r1 = 1/sqrt(2) * (randn(2 * N_bits,1) + j * randn(2 * N_bits,1)); 
h_r1 = 1/sqrt(2) * (randn(2 * N_bits,1) + j * randn(2 * N_bits,1)); 

%for Relay uplink: 
noise_r2 = 1/sqrt(2) * (randn(2 * N_bits,1) + j * randn(2 * N_bits,1)); 
h_r2 = 1/sqrt(2) * (randn(2 * N_bits,1) + j * randn(2 * N_bits,1)); 

for k = 1:length(SNRdB) 

SNR = 10^(SNRdB(k)/10); %convert SNRdB to linear value SNR 

ftx_r1 = sqrt(SNR) * h_r1 .* tx + noise_r1; 

%%%%%%%%%%%%%%%%% At the Relay %%%%%%%%%%%%% 
%%%%%%%%%%%%%%%%%%%%%%%%%Decode n F%%%%%% 
%equalizing at relay 
eq_rx1 = ftx_r1 .* conj(h_r1); 
%hard decision and converting from bipolar to bits 
r_bits = (sign(real(eq_rx1)) + 1)/2; 
%channel decoding: 
dec_dcf_r1 = vitdec(r_bits,trellis,3,'term','hard'); 
%re-encoding using the same procedure as Source: 
c_data2 = convenc(dec_dcf_r1,trellis); 
%BPSK signal for the relay coded data: 
tx2_dcf = 2 * c_data2 - 1; 
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 

%%%%%%%%%%%%%%%%%%Detect n F%%% 

dec_dtf_r1 = sign(real(eq_rx1)); 
tx2_dtf = dec_dtf_r1; 

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%Apmlify n F%% 

beta = sqrt(1./((SNR * abs(h_r1).^2) + 1)); 
%amplification: 
ftx_amp = ftx_r1 .* beta; 

%%%%%%%%%%%%%%%%%%%%%%%%%%Relay to Destination% 
%DCF 
ftx_dcf_r2 = sqrt(SNR) * tx2_dcf .* h_r2 + noise_r2 ; 
%DTF 
ftx_dtf_r2 = sqrt(SNR) * tx2_dtf .* h_r2 + noise_r2 ; 
%AF 
ftx_af_r2 = sqrt(SNR) * ftx_amp .* h_r2 + noise_r2 ; 

%%%%%%%%%%%%%%%%% At the Destination%%%%%%%%%%% 
ftx_d = sqrt(SNR)* tx .* h_d + noise_d; 

%%%%%%%%%%%%%%%%%%%%%%%%DCF%%%%%%%%%%% 
%%%%%%%%%%%%%%%%%%%MRC%%%%%%%%%%%%%%% 
R_dcf = ftx_dcf_r2 .* conj(h_r2) + ftx_d .* conj(h_d); 
%hard decisioning 
dec_com_dcf = sign(real(R_dcf)); 

%%%%%%%%%%%BER calculations%%%%%%%%%%%%%%%%%% 
%at destination: 
err_com1(k) = sum(abs(dec_com_dcf - tx)/2); 
simber_com1(k) = err_com1(k) / (2 * N_bits); 

%%%%%%%%%%%%%%%%%%%%%%%%DTF%%%%%%%%%%% 
%%%%%%%%%%%%%%%%%%%MRC%%%%%%%%%%%%%%% 
R_dtf = ftx_dtf_r2 .* conj(h_r2) + ftx_d .* conj(h_d); 
%hard decision 
dec_com_dtf = sign(real(R_dtf)); 
%%%%%%%%%%%BER calculations%%%%%%%%%%%%%%%%%% 
%at destination: 
err_com2(k) = sum(abs(dec_com_dtf - tx)/2); 
simber_com2(k) = err_com2(k) / (2 * N_bits); 

%%%%%%%%%%%%%%%%%%%%%%%%AF%%%%%%%%%%% 
%%%%%%%%%%%%%%%%%%%MRC%%%%%%%%%%%%%%% 
R_af = ftx_af_r2 .* conj(h_r2) .* conj(h_r1) + ftx_d .* conj(h_d); 
dec_com_af = sign(real(R_af)); 
%%%%%%%%%%%BER calculations%%%%%%%%%%%%%%%%%% 
%at destination: 
err_com3(k) = sum(abs(dec_com_af - tx)/2); 
simber_com3(k) = err_com3(k) / (2 * N_bits); 

theberawgn(k) = 0.5 * erfc (sqrt(SNR));%theoratical BER for AWGN 
theberrayleigh(k) = 0.5 * (1 - sqrt(SNR./(1 + SNR))); %theoratical rayleigh 

mue = sqrt(SNR/(1+SNR)); 
mrcth(k) = 0.25 * (2 + mue) * (1-mue)^2;%theoratical 2Rx MRC 

end 

sum_dcf = sum_dcf + simber_com1; 
sum_dtf = sum_dtf + simber_com2; 
sum_af = sum_af + simber_com3; 
end 

%average BER: 
avgber_dcf = sum_dcf/N_iter; 
avgber_dtf = sum_dtf/N_iter; 
avgber_af = sum_af/N_iter; 

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 
%%%%%%%%%BER plots%%%%%%%%%%%%%%%%%%%%%%%%%% 
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 

figure 
semilogy(SNRdB,avgber_dcf,SNRdB,avgber_dtf,SNRdB,avgber_af,SNRdB,theberawgn,SNRdB,theberrayleigh,SNRdB,mrcth); 
axis([SNRdB(1) max(SNRdB) 10^-5 0.5]); 
grid on 
legend('DCF','DTF','AF','AWGN','Rayleigh','MRC 2 senders'); 
xlabel('SNR dB'); 
ylabel('BER'); 
title(['BER curves for comparison,(averaged for ',num2str(N_iter),' iterations)']); 

3.仿真结论：

D69