I was simulating a simple OFDM transceiver system without a channel (just the transmitter and the receiver directly connected). I saw that if I use the "Find Delay" block in Simulink between the transmitted and received bits, I find that it keeps changing, because of which it becomes difficult to decide a specific receiver delay to calculate the BER. This however shows a constant value of delay in just a simple BPSK transceiver system without the OFDM. Can anyone please tell me what is actually happening and what are the things to consider while calculating the BER of an OFDM system?
In basically all simulations I've done, you just send known (but, depending on what you want to simulate, seemingly random) data. Then you correlate the received bits with the transmitted ones, and look for a peak.
That's your end-to-end bit delay, which you don't really care about, but it's how you know which bit you compare to which.
If you data has no significant autocorrelation, and assuming your transceiver basically works with a BER much smaller than 0.5, this is pretty reliable.