Precoding for Low-Latency Full-Duplex MIMO Relays: A Dynamic Approach

Ultra-reliable low-latency communications (URLLC) is increasingly necessary for contemporary and future wireless networks. In-band full-duplex (IBFD) relaying has potential to boost spectral efficiency and decrease latency, but is limited by self-interference (SI) in practice. Many works investigate the overall capacity of the IBFD relay with SI, but few, if any, attempt to minimize the overall delay in a transmission of a block of information. We introduce a dynamic programming algorithm that shows how precoding at the relay transmitter may be dynamically leveraged to balance SI suppression and downlink rate optimization across channel uses to minimize the overall delay. We show the precoder at the relay transmitter is biased towards reducing SI early in a transmission before switching to a precoder biased towards improving the downlink rate. On average, our algorithm significantly exceeds the performance of using the overall relay capacity maximizing precoder for all channel uses and provokes interesting future research directions.