Distributed Differential Modulation over Asymmetric Fading Channels

The present work quantifies the effects of asymmetric fading conditions on differentially modulated amplify-and-forward relaying systems. To this end, novel bit error rate expressions are derived for the case that the source-relay and relay-destination links experience non-line-of-sight multipath fading whilst the source-destination link is subject to: multipath fading, shadowing, and composite fading. Simple and tight approximate and asymptotic expressions are also derived, leading to useful insights into the system design. It is shown that the incurred performance variations range from one to few orders of magnitude compared to the standard case of symmetric Rayleigh scenarios, which verifies the importance to account for fading conditions realistically. In addition, differential phase-shift keying is shown to provide adequate performance in severe fading conditions in the moderate and high-signal-to-noise ratio regimes.