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

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');

[Janet]

pls help me spot it

[Jan]

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]

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

Answer 1

[Walter Roberson]

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.

[Janet]

Can u pls say me how to do it? I really don't know how to proceed

[Janet]

i don't get a straight line now...rather it is growing

[Walter Roberson]

Have you considered zeroing "errors" for each snr, so that your error count does not accumulate between different SNR?

[Janet]

@walter : I am new to this sir and I tried my best to bring out this project...I really don't get what u say...

I actually need a decaying ber with low error rate...but i am getting a growing ber

[Walter Roberson]

for snr=0:1:35

errors = 0; %HERE HERE HERE HERE HERE

for i=1:1:128

<etc>

[Janet]

so what should i give in this line?

[Oleg Komarov]

Janet, please read again Walter's comments. Carefully this time.

[Janet]

actually,I want to decrease my ber in my project

[Janet]

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

ber(k)=errors/M;

Q=sort(ber,'descend');

end

figure(1)

semilogy(smooth(snr),smooth(Q));

title('BER vs SNR');

ylabel('BER');

xlabel('SNR');

is this correct?

[Walter Roberson]

Fixing *only* the most immediate problem:

snr = 0:1:35

for k = 1:length(snr)

errors = 0; %THIS GOES HERE

for i = 1 : M

if est_sig(i) ~= msg(i)

errors = errors + 1;

end

ber(k)=errors/M;

%GET RID OF Q HERE

end

figure(1)

semilogy(smooth(snr),smooth(ber)); %NO NOT Q

title('BER vs SNR');

ylabel('BER');

xlabel('SNR');

Do *not* go around sorting your BER: the results you produce will be near meaningless.

But the key point for now is that errors has to be initialized to 0 for *each* snr value.

WARNING: This will only take you as far as showing you that you are getting a completely flat BER graph. The above corrections do not attempt to fix your fundamental problem with your BER calculation that you are failing to change your est_sgl according to the "current" snr.

[Janet]

how should i change my est_sgl acc to current snr

[Janet]

i get very high ber..how can i bring it down?