# Q) OFDM and BER verification

Started by February 18, 2007
```Hello. Could I have some help & discussion please?

I built an OFDM simulator with IEEE 802.20 channel model.
But, I'm not sure if my BER results are correct or not.

Thus, I checked BER of OFDM  in AWGN  first.
Then, I checked BER of OFDM in very very low bit rate. For example when a
channel shows rms delay spread of 0.37usec, I tested with Rb = 1E4 bps.
Then, I checked BER of OFDM with higher data rate.

Here is my question: With OFDM, can we realize gaussian performance ( for
example, 16-QAM in Gaussian channel performance)? My result is that
always, OFDM BER is far away from Gaussian BER. I'm not sure if I did the
right or not.

I'd highly appreciate any suggestion or discussion.

Thank you very much.
```
```>Hello. Could I have some help & discussion please?
>
>I built an OFDM simulator with IEEE 802.20 channel model.
>But, I'm not sure if my BER results are correct or not.
>
>Thus, I checked BER of OFDM  in AWGN  first.
>Then, I checked BER of OFDM in very very low bit rate. For example when
a
>channel shows rms delay spread of 0.37usec, I tested with Rb = 1E4 bps.
>Then, I checked BER of OFDM with higher data rate.
>
>Here is my question: With OFDM, can we realize gaussian performance (
for
>example, 16-QAM in Gaussian channel performance)? My result is that
>always, OFDM BER is far away from Gaussian BER. I'm not sure if I did
the
>right or not.
>
>I'd highly appreciate any suggestion or discussion.
>
>Thank you very much.
>

Hi,

let us define the following equation

r(t)=s(t)*H(t)+w(t)

s(t)=transmitted OFDM signal
H(t)=channel impulse response

when performance of OFDM is studied only in AWGN, the above equation
becomes

r(t)=s(t)+w(t)

In this case the plot of SNR vs BER matches the theoritical BER given in
the literature,irrespective of modulation(QPSK,16QAM) used in OFDM.

when channel is assumed along with AWGN, the equation is
r(t)=s(t)*H(t)+w(t)

depending on the channel properties, we see some delay spread in the

In this case, there is no way that the plot of SNR vs BER matches the
theoritical BER. This is because, the thoritical BER given in
literature(John G Proakis) is only in the presence of AWGN.
In fact BER is worse in this case when compared with BER in the presence
of only AWGN.

I hope you got my point.
Aamer

```