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What is the correct SNR vs BER plot for OFDM in awgn channel for 1-QAM modulation?

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commworld

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hi..
can nyone pls show me snr vs ber plot for OFDM in awgn channel for 4-QAM.
modulation.
I got the plot but I fear its wrong, m getting prob. of error = 10^-3 at 24db..!!

plz gv a rply...:|
 

Re: Snr vs BER plot

commworld said:
hi..
can nyone pls show me snr vs ber plot for OFDM in awgn channel for 4-QAM.
modulation.
I got the plot but I fear its wrong, m getting prob. of error = 10^-3 at 24db..!!

plz gv a rply...:|
Click to expand...

BER=10^-3 we get for SNR around 10 dB
 

Re: Snr vs BER plot

ya u two r rite... i dono wer I am mistakening..
I added awgn to the ofdm signal which is made up of 58 ofdm symbols=ofdm_strm

xt=ofdm_strm;
xt=awgn(xt,n);
then I did the reverse process of removal of CP, fft and then demodulation.
then I converted bak the decimal values to binary values... and compared it with my transmitted bit sequence to calculate the BER
[error, pe]=biterr(rx_bit,dat_strm);
then for 40 values of SNR/EbNo I calculated Pe and ploted it
semilogy(EbNo,Pe,'k*-');

plz tel me what step m I missing..
I verified all my functions of ofdm demodulation are working correctly..

I ve attached the plot...
 
Re: Snr vs BER plot

commworld said:
ya u two r rite... i dono wer I am mistakening..
I added awgn to the ofdm signal which is made up of 58 ofdm symbols=ofdm_strm

xt=ofdm_strm;
xt=awgn(xt,n);
then I did the reverse process of removal of CP, fft and then demodulation.
then I converted bak the decimal values to binary values... and compared it with my transmitted bit sequence to calculate the BER
[error, pe]=biterr(rx_bit,dat_strm);
then for 40 values of SNR/EbNo I calculated Pe and ploted it
semilogy(EbNo,Pe,'k*-');

plz tel me what step m I missing..
I verified all my functions of ofdm demodulation are working correctly..

I ve attached the plot...
Click to expand...

in my code i generated random noise for every snr (for loop use)

then gaussian noise would be n=sqrt(1/(snr))*randn(1,(2*N+Ncp)))

where N is the num of subcarriers and Ncp the cyclic prefix. hope this helps:D
 

Re: Snr vs BER plot

thnks for ur response I got the plot after that change, i.e. BER=10^-3 at SNR=14dB.
:)
 

Re: Snr vs BER plot

anta said:
in my code i generated random noise for every snr (for loop use)

then gaussian noise would be n=sqrt(1/(snr))*randn(1,(2*N+Ncp)))

where N is the num of subcarriers and Ncp the cyclic prefix. hope this helps:D
Click to expand...

where you found this equation, can you support it by any reference? i see it is useful but we must support it by a reference before i use it :) thanks
 

Re: Snr vs BER plot

Dear brother,

We use for wgn,

rand(1,N+Ncp)*10^(-snr/20), where snr is assumed to be in dB

but if the snr is in linear scale,

rand(1,N+Ncp)*sqrt(1/snr)


Same thing

---------- Post added at 11:53 AM ---------- Previous post was at 11:45 AM ----------

In fact, it can also be done in the following way

Data_corrupted = Data*sqrt(snr) + rand(1,N+Ncp)

for eg, snr = 10, then either increase amplitude of user data by sqrt(snr) or decrease amplitude of channel noise by sqrt(1/snr)
 
Re: Snr vs BER plot

i just want to design an LTE transciver based on ODFM technique . so i want coding of OFDM transmitter and OFDM receiver part so please provide me if anyone have, as soon as possible .
 


Re: Snr vs BER plot

hello Communication_Engineer
for ofdm matlab simulations, at the receciver end when to do the equalization, is it after the Cyclic prefix removal or before that...??:?:
 

Re: Snr vs BER plot

Hi commworld, it would be after you remove the cyclic prefix. In fact, it will be immediately after the DFT (FFT)

---------- Post added at 04:05 PM ---------- Previous post was at 04:04 PM ----------

Because we go for Frequency Domain equalization
 
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    Damien

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Re: Snr vs BER plot

so u mean to say dat
ifft->conv with channel--> awgn-->CP removal-->fft.
h=[0.2 0.4 0.7 0.8] % 4-tap rayleigh channel
=> CP should be removed in time domain itself.. rite!!
 

Re: Snr vs BER plot

ok.
can u please tell me whether the BER curve for 4QAM modulation with ofdm and without ofdm over awgn channel should be
1. same or
2. slightly better..!
 

Re: Snr vs BER plot

It should be same...

IF it is not then the SNR has not been scaled properly.

I suggest you ask your teacher/supervisor to help you understand the scaling of SNR in simulation of wireless communication
 
hi guys
please giev me the tranciever LTE matlab using ofdm and MIMO
please make it urgent
 

Re: Snr vs BER plot

@Communications_Engineer
how to model a frequency flat fading channel on matlab, which requires the Bandwidth of signal > bandwidth of channel and the delay spread> symbol period..??
if the bandwidth of singal is 20MHz..
 

Re: Snr vs BER plot

@communication engineer, can u please help me on hw to go by modelling an Ofdm simulink system with convolutional encoder, viterbi decoder and interleaver with deinterleaver?
 

Re: Snr vs BER plot

@omotayour, I am also looking for Ofdm simulink with turbo encoder and turbo decoder for my project work of masters degree. Please keep posted in same forum if you get any breakthrough.
 

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