Possible Duplicate:
Do you use “a” or “an” before acronyms?
I searched google for "a MPR" and "an MPR". The first one returns about 52000 hits while the second one returns about 34000 hits. None of them actually looks incorrect to me. MPR stands for multi-packet reception. So, which one is the correct one, "a MPR ..." or "an MPR ..."?