Outage probability and optimal cache placement for multiple amplify-and-forward relay networks

We present a novel framework for analyzing and optimizing the outage performance of a multiple amplify-and-forward relay network, where N relays, each with finite cache capacity, are deployed to assist the transmission from a base station equipped with L antennas to the destination. In this network, if the requested file is cached at the relays and the associated relay channels are in good condition, then the data are directly transmitted from the relays to the destination; otherwise, traditional two-hop transmission is performed. Based on this concept, we propose a relay-selection criterion to choose the best relay, which maximizes the received signal-to-noise ratio at the destination. For this criterion, we derive exact and asymptotic analytical expressions for the system outage probability in Nakagami-m fading. To further improve the network outage performance, we optimize the cache placement, which minimizes the outage probability. Numerical and simulation experiments are performed to validate the analysis and demonstrate the conditions where the proposed cache placement strategy outperforms the existing ones.