Multi-Layer Transmission and Hybrid Relaying for Relay Channels with Multiple Out-of-Band Relays

摘要

In this work, a relay channel is studied in which a source encodercommunicates with a destination decoder through a number of out-of-band relaysthat are connected to the decoder through capacity-constrained digital backhaullinks. This model is motivated by the uplink of cloud radio access networks. Inthis scenario, a novel transmission and relaying strategies are proposed inwhich multi-layer transmission is used, on the one hand, to adaptively leveragethe different decoding capabilities of the relays and, on the other hand, toenable hybrid decode-and-forward (DF) and compress-and-forward (CF) relaying.The hybrid relaying strategy allows each relay to forward part of the decodedmessages and a compressed version of the received signal to the decoder. Theproblem of optimizing the power allocation across the layers and thecompression test channels is formulated. Albeit non-convex, the derived problemis found to belong to the class of so called complementary geometric programs(CGPs). Using this observation, an iterative algorithm based on the homotopymethod is proposed that achieves a stationary point of the original problem bysolving a sequence of geometric programming (GP), and thus convex, problems.Numerical results are provided that show the effectiveness of the proposedmulti-layer hybrid scheme in achieving performance close to a theoretical(cutset) upper bound.