I did simulation of OFDM over rayleigh channel (BPSK). But I am confused what theory BER equation I should use to compare this simulation result with? Can you please let me know or give me the theory equation to use. So I can compare them both and see if my simulation is correct or not. Thank you so much.
Now usually, when you are using OFDM, this means that the Rayleigh fading channel is an ISI channel. So, you can compare the results you got with non ISI channel.
Why did you use OFDM in the first place? Did you assume that the channel is ISI channel? Usually, OFDM is used when the frequency response of the channel is not flat. So, this non-flat frequency response is divided into a number of sub-bands where the amplitude of the channel and the noise power is approximately constant. In this case you are communicating with ISI-free channels, especially when using CP. So, I think it may be correct to compare your results with the non ISI case, i.e.: when the channel is flat fading.