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We derive simple uniform approximations (UAs) for the bit error rate (BER), the symbol error rate (SER), and the outage of wireless digital communication systems impaired by fading, noise, and interference. The striking feature of the UAs is their accuracy over the whole range of signal-to-noise ratio (SNR) values, whereas the existing high-SNR approximations break down as the SNR decreases. The UAs require slightly more information than that for high-SNR expressions. The additional information required in the case of error probabilities is the several moments (fractional) of channel gain, which can be extracted readily from the PDF, MGF or the Mellin transform of the PDF. The computation of the UA is simple and requires only the solution of a set of linear equations. Additionally, we also generalize the previous asymptotic results of Wang and Giannakis. The unified asymptotic results of the average of an arbitrary performance measure are thus derived. Various BER and SER expressions then become special cases of this unified approach.