Should the blocks of transmitted bits be the same for repeated transmission at a specific SNR?

I am transmitting bits through a AWGN channel with multipath. A block of 200 bits are transmitted repeatedly at a certain SNR so as to obtain the BER. Firstly, should the block of bits be same each time, by using the rng(-) function before using randi? How to choose the value for the argument of rng function? Also, if the function rng is not used, then for the same SNR, the amount of errors differ greatly.

Please advise on usual way such simulation should be carried out.

Answer 1

[Andrew Schenk]

You should not need to seed the random number generator since the bit error rate should not depend on the underlying data. A common problem in BER calculations is not properly delaying the source data before the error calculation to account for simulation delays in the transmitted signal.

Take a look at the following example which calculates the BER for a full QPSK Transmitter and Receiver with AWGN:

http://www.mathworks.com/help/comm/examples/qpsk-transmitter-and-receiver.html

[S.B]

Thank you Andrew for the help. What do you mean by delaying the data before error calculation?