A New Perspective on Maximal-Ratio Combining

The realization of ultra-reliable low latency communications (URLLC) is a highly relevant problem that remains unsolved. Multi-connectivity (MC) is regarded as one of the main enablers as it has the potential to boost reliability by orders of magnitude. Typically, selection combining (SC) is implemented due to its simplicity. However, it is not optimal regarding the effective signal-to-noise ratio (SNR), in contrast to maximal-ratio combining (MRC). Furthermore, research focus is typically led on the outage probability only, but for reliable communications also the temporal behavior is relevant, which is better reflected by metrics like level crossing rate (LCR) and average fade duration (AFD). In this paper, we introduce a transformation which facilitates such an analysis by decoupling the dependence of the envelope or SNR from their time derivatives in MRC. Thereby, we present a thorough comparison between the investigated schemes of not only the outage but also the temporal behavior.