Approximating the Outage Probability of Parallel Fading Channels

We develop an approximation for the outage probability of a parallel channel where the subchannel statistics satisfy mild conditions. The main result is in the form of a functional of the density function that describes the statistics of the subchannel powers. The error of the approximation is quantified to be O(y^-n(q+1)-2), where y is the end-to-end SNR of a given subchannel, n is the number of subchannels, and q represents the inherent subchannel diversity. We illustrate the versatility and accuracy of the approximation by studying different statistical subchannel models, which reflect practical wireless communication systems, including line-of-sight links (Rician fading), transmissions affected by interference, and relay systems subject to amplifier distortion.