  We present a generic approximation of the packet error rate (PER) function of
uncoded schemes in the AWGN channel using extreme value theory (EVT). The PER
function can assume both the exponential and the Gaussian Q-function bit error
rate (BER) forms. The EVT approach leads us to a best closed-form
approximation, in terms of accuracy and computational efficiency, of the
average PER in block-fading channels. The numerical analysis shows that the
approximation holds tight for any value of SNR and packet length whereas the
earlier studies approximate the average PER only at asymptotic SNRs and packet
lengths.
