Pls help me spot errors in the code..I don't get a decaying BER

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Janet 2012-3-21

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https://ww2.mathworks.cn/matlabcentral/answers/33018-pls-help-me-spot-errors-in-the-code-i-don-t-get-a-decaying-ber

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clc;
clear all;
close all;
%input
M=1024;
nt=2;
nr=1;
L=65;
%Generate random data
m=4;
msg1=randint(M,1,m);
msg2=randint(M,1,m);
msg=vertcat(msg1,msg2);
% QPSK modulation
qpsk_modulated_data1=pskmod(msg1,m);
qpsk_modulated_data2=pskmod(msg2,m);
%IFFT
x1=ifft(qpsk_modulated_data1);
x2=ifft(qpsk_modulated_data2);
x=vertcat(x1,x2);
%channel
temp=randsrc(1,L-1);
temp=[temp zeros(1,960)];
temp1=transpose(temp);
h1=gallery('circul',temp1);
h1=h1';
temp2=randsrc(1,L-1);
temp2=[temp2 zeros(1,960)];
temp3=transpose(temp2);
h2=gallery('circul',temp3);
h2=h2';
h=horzcat(h1,h2);
%r
r=h*x;
%--- Joint estimation of channel response and I/Q imbalance
%ek
e=eye(M);
%y due to cfo
y=e*r;
y1=conj(y);
%z due to cfo and i/q
u=(1+exp(-j*10))/2;
u1=conj(u);
v=(1-exp(j*10))/2;
z=(u*y)+(v*y1);
z1=conj(z);
%a
a=(v/u1);
%ur
a1=abs(a)^2;
e1=conj(e);
ur=(e1*(z-(a*z1))/(1-a1));
%p
p=M/nt;
%MIMO channel response
a1=randn(M,L);
a2=randn(M,L);
A=horzcat(a1,a2);
a11=randn(M,p-L);
a22=randn(M,p-L);
B=horzcat(a1,a11,a2,a22);
B1=inv(B);
ud=B1*ur;
%CRE
q = M-(L*nt);
P = zeros(q,M);
P(:,2:2:end) = (p-L)*eye(q,M/2);
cre=norm(P*ud)^2;
CRE =norm(P*B1*(z-(a*z1)))^2;
%I/Q_imbalance
o=ctranspose(P*B1*z1); %traspose_conj of p*B1*z1
aopt=(o*(P*B1*z))/(norm(P*B1*z1))^2;
%channel response
aopt1=abs(aopt)^2;
cha_res=B1*(z-(aopt*z1))/(1-aopt1);
%--------------------------------------------------
%fft
 fft_recdata=fft(r);
%Demodulate the data
qpsk_demodulated_data = pskdemod(fft_recdata,M);
%estimated signal
est_sgl=r*cha_res';
%calculating BER
errors=0;
snr=0:1:35;
for k=1:length(snr)
for i=1:M
if est_sgl(i) ~= msg(i)
 errors=errors+1;
end
end 
ber(k)=errors/M;
Q=sort(ber,'descend');
end
figure(1)
semilogy(smooth(snr),smooth(Q));
title('BER vs SNR');
ylabel('BER');
xlabel('SNR');

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Jan 2012-3-22

Please, Janet, explain what error you see. Do you get an error message (if so, post it completely) or do the results differ from your expectations?

Janet 2012-3-22

My Ber curve is not decaying..It has errors upto 10^2

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回答（1 个）

Walter Roberson 2012-3-22

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/33018-pls-help-me-spot-errors-in-the-code-i-don-t-get-a-decaying-ber#answer_41679

The problem is the same as I told you before more than once: you are not recalculating your noise signal as you change your snr, so your number of errors is coming out constant for each snr.