Hi Nithin,
I do not understand why do you use S/P converter after PRBS. if you would like to transmit the same data, you can use fork instead of S/P converter.
Your design did not work because
1- the input of the QAM sequence generator have to be in serial (not in parallel like what you have in your design)
2- as far as I know, when you use the S/P converter you are not copy the data to two OFDM system. S/P will divide the data to two output (for example the PRBS generate 101110100101 so the output of the S/P will be:
output 1====> 111100
output 2====> 010011
kind regards
mohamed