Is my BER curve right?

clc;
clear all;
close all;

%input

M=128;
nt=2;
nr=1;
L=16;

%Generate random data

m=4;
msg1=randint(M/2,1,m);
figure(1)
stem(msg1)
grid on
xlabel('data points')
ylabel('transmitted data phase representation')
title('Transmitted Data "O"')
msg2=randint(M/2,1,m);
figure(2)
stem(msg2)
grid on
xlabel('data points')
ylabel('transmitted data phase representation')
title('Transmitted Data "O"')
msg=vertcat(msg1,msg2);

% QPSK modulation

qpsk_modulated_data1=pskmod(msg1,m);
qpsk_modulated_data2=pskmod(msg2,m);
%scatterplot(qpsk_modulated_data1);
%title('qpsk modulated transmitted data1');
%scatterplot(qpsk_modulated_data2);
%title('qpsk modulated transmitted data2');

%IFFT

x1=ifft(qpsk_modulated_data1);
x2=ifft(qpsk_modulated_data2);
%scatterplot(x1)
%scatterplot(x2)
x=vertcat(x1,x2);

%channel

h1=gallery('circul',M:M);
h2=gallery('circul',M:M);
e=horzcat(h1,h2);
f=vertcat(h1,h2);
h=e*f;

%r

r=h*x;

%fft

 fft_recdata=fft(r);

%Demodulate the data

qpsk_demodulated_data = pskdemod(fft_recdata,M);

%ek

e=eye(M);

%y due to cfo

y=e*r;

%z due to cfo and i/q

u=(1+exp(-j*10))/2;
v=(1-exp(j*10))/2;
y1=conj(y);
z=(u*y)+(v*y1);

%a

u1=conj(u);
a=(v/u1);

%ur

z1=conj(z);
a1=abs(a)^2;
e1=conj(e);
ur=(e1*(z-(a*z1))/(1-a1));

%p

p=M/nt;

%ud

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 = 96; %p-L
P = zeros(q,M);
P(:,2:2:end) = (48)*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*z1))/(norm(P*B1*z1))^2;
scatterplot(aopt)
title('I/Q imbalance')

%channel response

aopt1=abs(aopt)^2;
cha_res=B1*(z-(aopt*z1))/(1-aopt1);
scatterplot(cha_res)
title('Channel Response')

%Recovering signal

est_sgl= r*cha_res'

%calculating BER

errors=0;
count=1;
for snr=0:1:35
ber(count) = mean(est_sgl(1:M) ~= msg(1:M));
count=count+1;
end

semilogy(0:1:snr,smooth(ber));
title('BER vs SNR');
ylabel('BER');
xlabel('SNR (dB)');
grid on

[Janet]

get a BER of 0.9922..Pls share ur ideas of minimising

Answer 1

[Walter Roberson]

You assign M=128 in the Input section and reassign it in the CR section. Why?

In your BER section, you "for i=1:1:128", but you do not divide by 128, you divide by M. Why?

Why do you use the "for i" loop at all?

ber(count) = mean(qpsk_demodulated_data(1:M) ~= msg(1:M));

Why does your demodulated data not depend upon the value of the "snr" that you are looping over?

[Janet]

I have changed the program now as u said..but still get errors..Pls help

[Janet]

Now I get BER as a straight line

[Walter Roberson]

Why does your est_sgl data not depend upon the value of the "snr" that you are looping over?

[Janet]

@Walter: I don't how to do it..pls help me in doing it

[Walter Roberson]

The data that you demodulate for comparison to msg(1:M) need to be data that was affected by noise with the SNR equal to the level indicated by your "for snr" loop. In your code, it is not: each time through the "for snr" loop, you compare the same data. Of course you end up with a straight line: nothing has changed in the loop for the two values you are comparing.

Which portion of your code changes the modulated signal according to a known SNR before demodulating the signal, this simulating transmission along a noisy channel?

[Janet]

@Walter : I can get what u say, but i don't know hw to implement...

i wanted to compare est_sgl with msg(1:M)

R u asking me that est_sgl is not affected by snr?

[Janet]

Pls help me with codings..i tried for the full day,but couldn't get it

Answer 2

[rao raghavendra]

sir, i m doing project on non binary ldpc codes.i wrote the code for ldpc ber vs snr,but i m not getting correct result.plz check my code.

clc; clear all;

% LDPC matrix size, rate must be 1/2 % Warning: encoding - decoding can be very long for large LDPC matrix! rows = 4; cols =8;

% Method for creating LDPC matrix (0 = Evencol; 1 = Evenboth) method = 1;

% Eliminate length-4 cycle noCycle = 1;

% Number of 1s per column for LDPC matrix onePerCol = 3;

% LDPC matrix reorder strategy (0 = First; 1 = Mincol; 2 = Minprod) strategy = 2;

% EbN0 in dB EbN0 = [ 5 10 15 20]; % Number of iteration; iter = 5;

% Number of frame (N bits per frame) frame = 1;

% Make the LDPC matrix H = makeLdpc(rows, cols, 1, 1, onePerCol);

for i = 1:length(EbN0)

   ber1(i) = 0;
   ber2(i) = 0;

% Make random data (0/1)
 dSource = round(rand(rows, frame));

   for j = 1:frame
      fprintf('Frame : %d\n', j);

% Encoding message [c, newH] = makeParityChk(dSource(:, j), H, strategy); u = [c; dSource(:, j)];

%%%%%%%%%%%%%%% reorder u¢to get the CW u %%%%%%%%%%%%%%%%%%%

      % BPSK modulation
      bpskMod = 2*u - 1;
      % Additional white gaussian noise
      N0 = 1;
      tx = bpskMod + sqrt(N0/2)*randn(size(bpskMod));

      % Decoding (select decoding method)
      %vhat = decodeProbDomain(tx, H, newN0, iter);
      % Uncoded
      %a=sort(rand(1,8).*[0.1 0.07 0.05 0.02 0.01 0.005 0.001   0.0001],'descend');
      EbN0_uncoded = [ 1:0.5:4.5 ];
     ber_uncoded = [ 0.1241 0.11 0.0974 0.0850 0.0730 0.0618 0.0514 0.0420 ];

     vhat1 = decodeLogDomain(tx, H, N0, iter);
    [num1, rat1] = biterr(vhat1', u);
   ber1(i) = (ber1(i) + rat1);
    ber1(i) = ber1(i)/frame;
     ber1(i) = ber1(i)/frame;

   % Get bit error rate (for brevity, BER calculation includes parity bits)

      vhat = decodeBitFlip(tx, H, iter);
      [num2, rat2] = biterr(vhat', u);
     ber2(i) = (ber2(i) + rat2);
      ber2(i) =ber2(i)/frame;

    end % for j

   % Get average of BER
   end % for i
figure
semilogy(EbN0_uncoded,ber_uncoded,'r')
hold on
semilogy(EbN0,ber1, 's-')

hold on semilogy(EbN0,ber2 , 'g-') hold on

legend('Uncoded', 'log domain','bit flipping') xlabel('EbN0') ylabel('ber')

%title('(3,6)-regular code, 1000 bits') grid on hold off

 results