Heterogeneous Relay Selection

Relay selection, a simple and efficient method of operating multi-relay networks, has in the past been considered only when all relays follow the same protocol. This work studies relay selection in heterogeneous relay networks where relays with different protocols can co-exist. The new techniques for the analysis of such networks are demonstrated on a mixture of decode-forward relays and amplify-forward relays, as well as a mixture of non-orthogonal amplify-forward (NAF) and dynamic decode-forward (DDF) relays, and also a mixture of NAF and compress-forward relays. In each case the diversity-multiplexing tradeoff is calculated. In the process, a noteworthy limitation of previous relay selection schemes is also relaxed and removed: In the past in multi-relay networks the direct source-destination link has been ignored whenever it introduces dependencies among selection decision variables, as it often does. This has been motivated chiefly by the lack of suitable analytical techniques for order statistics of dependent random variables. In this work, relay selection analysis is extended to allow the presence of a direct source-destination link. As a side benefit, the relay selection results in homogeneous networks (where relays are all of the same type) are also extended to include the presence of a source-destination link.