Esakki Muthu Kadarkarai,

You could record the data stream which is transmitted and to compare it (offline) to the received data stream.

Esakki Muthu Kadarkarai,

you will  have to generate a random sequence with N bits. In general we use 

N ~ 3x(1/BER), wher BER is the value you intend to measure in your experiment/simulation.

You'll have to generate the RF signal, send it to the optical modulator (a laser or an external modulator) and receive it with a photodiode.

After the photodiode you have to recover the RF signal and compare the bit sequences.

Thank you all

You will need to simulate a huge number of bits. We usally measure the EVM (Error Vector Magnitude). From EVM we estimate BER.

 You have to synchronize the received sequence with that of transmitted one and feed to the ex-or gate inputs whose output will be fed to a counter. The time duration over which the counter was on can be calibrated w.r.t data rate (clock rate) to find number of counted errors per transmitted data.

Thank you very much Sir,

With Best Regards,

K.Esakki Muthu