Transmission Latency Minimization in Full-Duplex Relaying Network Operating With Finite Blocklength Codes

In this paper, we consider a multi-hop full-duplex (FD) relaying system that supports low-latency communication, and aim to explore the potential of FD technology in suppressing transmission latency. Specifically, we begin with a two-hop relaying system, where a source node is expected to transmit a large message to the destination node via a relaying node operating in FD mode. We assume the large message is equally divided into multiple smaller packets, while the whole transmission is operated in a packet-by-packet manner and retransmissions are scheduled against decoding failures. Notably, we have for the first time characterized the expected transmission latency while taking into account the finite blocklength (FBL) impact on transmission reliability. Through a proposed error probability propagation policy, we have recursively derived the expected number of transmissions required to successfully conveying the entire message via FD relaying system. An optimization problem is then formulated to minimize the expected transmission latency by jointly optimizing packet division, blocklength allocation, and transmit power control. To deal with the inherent nonconvexity of the problem, we reformulate it using variable substitution and subsequently construct a tight convex approximation based on an arbitrary feasible point. This facilitates an iterative algorithm that progressively refines the solution until convergence to a suboptimal point. The whole approach for latency characterization and minimization is then extended to the multi-hop relaying scenario. Finally, simulation results validate the convergence behaviours of our proposed algorithms and highlight the latency benefits of our solution compared to both half-duplex relaying and full-duplex relaying without optimal power control.