Minimum Number of Errors required for BER Curves in Matlab Simulation
I have done a fair number of BER simulations and have not found a definitive answer on this. It depends on the error behavior of your channel, Gaussian or some other pdf. My process for AWGN was as follows. First I determine the approximate BER I am expecting. Say that it is 10-3. The inverse of that is 1000 bits. So I would run at least 10x that to start, or a length of 10,000 bits as a minimum. For coded signals, or those with fading, I might use a larger multiplier, such as 50 to 100 times. By watching the error pattern we can often tell if steady state has been achieved. For coded channels with BERs of 10-8 etc., the run lengths quickly become an issue.

This applies to Monte Carlo simulations. You can do semi-analytic methods that do not require such large runs. However semi-analytic methods are generally not that good for non-AWGN channels. Importance sampling is one such semi-analytic method which is used with coded signals. All of these are estimates.