I am so confused to calculate the relationship between bandwidth and bit rate. I use #OFDM file benchmark_tx to transmit. I set the bandwidth = 10 MHz, FFT Length =1024,  and I assume the cyclic prefix and the occupied FFT bins to be the default numbers.  CP=128, Occupied = 200.  

So my problem is what is the bit rate ? Thanks

I do not know the GNU radio OFDM implementation but from the few parameters you have listed the following calculation / logic may give you an answer.

FFT size is 1024 with CP of 128 each OFDM symbol is 1024+128=1152 samples.

Assuming the "bandwidth" you stated is the DAC reconstruction rate this can be used to calculate the "OFDM symbol rate": 1152/10e6 = 115.2 usec or ~8680.6 symbols per second.

If you set the number of occupied bins to 200 and assuming BPSK (1 bit per bin) you get:

1/115.2e-6 * 200 = 1736111.1 bps = ~1.736 Mbps

Hope this helps,

Moti

You are really hopeful. Thanks