  In this paper, we present an analysis of the outage probability for
fixed-gain amplify-and-forward (AF) multihop relay links operating in the high
SNR regime. Our analysis exploits properties of Mellin transforms to derive an
asymptotic approximation that is accurate even when the per-hop channel gains
adhere to completely different fading models. The main result contained in the
paper is a general expression for the outage probability, which is a functional
of the Mellin transforms of the per-hop channel gains. Furthermore, we
explicitly calculate the asymptotic outage probability for four different
systems, whereby in each system the per-hop channels adhere to either a
Nakagami-m, Weibull, Rician, or Hoyt fading profile, but where the
distributional parameters may differ from hop to hop. This analysis leads to
our second main result, which is a semi-general closed-form formula for the
outage probability of general fixed-gain AF multihop systems. We exploit this
formula to analyze an example scenario for a four-hop system where the per-hop
channels follow the four aforementioned fading models, i.e., the first channel
is Nakagami-m fading, the second is Weibull fading, and so on. Finally, we
provide simulation results to corroborate our analysis.
