I have a written qpsk Code but am not getting correct ber o/p please help.

FRM=100;

EbNo_vector=0:10;

Modulator = comm.QPSKModulator('BitInput',true);
AWGN = comm.AWGNChannel;
DeModulator = comm.QPSKDemodulator('BitOutput',true,'DecisionMethod','Log-likelihood ratio');
for EbNo = EbNo_vector
snr = EbNo + 10*log10(2);
u = randi([0 1], FRM,1); % Generate random bits
mod_sig = Modulator(u); % QPSK Modulator
rx_sig = AWGN(mod_sig); % AWGN channel% Receiver
y = DeModulator(rx_sig); % QPSK Demodulator
x = DeModulator(rx_sig);

for s = 1:10
  if y(s) > 0
       y(s) = 0;
   else
       y(s) = 1;
  end


errorRate = comm.ErrorRate('ComputationDelay',3);
    errors = errorRate(u,y);
    BER(s) = errors(1);
end
end

[KALYAN ACHARJYA]

Is it program (code) error

or

result is not as per expected?

[Nitin Sapre]

its result not as expected

am able to get o/p y bits...but there is some problem in ber

[Renato SL]

I'm curios in why you generate 100 bits

FRM = 100
...
u = randi([0 1], FRM,1); % Generate random bits

but here,

for s = 1:10
  if y(s) > 0
       y(s) = 0;
   else
       y(s) = 1;
  end

you only check the first 10 bits.

Perhaps what you want is to check all 100 bits?

[Nitin Sapre]

Thank you for letting me know my mistake.

I wanted to take Ber for different EbNo values....

Now am stuck now to take Ber for differnt EbNo Values

[Renato SL]

I would do something like this

Please read the comments that I put because some things are still questionable for me.

FRM=100;
EbNo_vector=0:10;
Modulator = comm.QPSKModulator('BitInput',true);
AWGN = comm.AWGNChannel;
DeModulator = comm.QPSKDemodulator('BitOutput',true,'DecisionMethod','Log-likelihood ratio');
BER = []; %initialize empty space to keep BER values that are computed later
for EbNo = EbNo_vector
    snr = EbNo + 10*log10(2);
    u = randi([0 1], FRM,1); % Generate random bits
    mod_sig = Modulator(u); % QPSK Modulator
    rx_sig = AWGN(mod_sig); % AWGN channel% Receiver
    y = DeModulator(rx_sig); % QPSK Demodulator
    x = DeModulator(rx_sig);
    %I am not sure why you have the line above because x is never used below
    for s = 1:10 %or 1:100, as you want
        if y(s) > 0
            y(s) = 0;
        else
            y(s) = 1;
        end
    end
    %basically, put the lines below on this level of the loop
    %rather than inside the second for loop like what you put in your question
    %because it is for each value of EbNo, not for each value of s
    errorRate = comm.ErrorRate('ComputationDelay',3);
    %I assume the line above is used to call a function (?)
    %it is strange for me since I have never done anything like it
    %and I don't have comm so I cannot check by myself
    errors = errorRate(u,y);
    %I think with the line above you want to compute the difference
    %between u (original bits) to y (bits after error is introduced + demodulation)
    %Seems ok to me, but how you call errorRate before is just strange to me
    BER = [BER errors(1)];
    %Then you get the BER from results inside errors
    %while keeping values obtained from previous loops
end

[Nitin Sapre]

Thanks I got what you are saying ....

But I Need Ber only for EbNo values now it is giving for all FRM Values

[Renato SL]

What does FRM stand for? I genuinely don't know.

And what's the output of errors? What's its size?

[Nitin Sapre]

fixed symbol rate modulation (FRM)

error size depends on FRM and BER for SNR values 1:10

[Nitin Sapre]

btw i got the ans thanks for all your help

instead of objects i Defined ber

nErrors = biterr(u,y);

numErrs = numErrs + nErrors;

numBits = numBits + k;

berEst(EbNo) = numErrs/numBits;

[Renato SL]

I'm glad you found something that works for you.