Transmit power minimisation for full‐duplex two‐way relaying systems with asymmetric packet‐rates and quality‐of‐service requirements

This study solves the transmit power minimisation problem subject to a target quality‐of‐service constraint of a full‐duplex (FD) two‐way decode‐and‐forward relaying system with asymmetric packet‐rates, where the two‐way relaying system can operate in two different styles, i.e. half‐duplex sources with full‐duplex relaying (HDS‐FDR) and full‐duplex sources with full‐duplex relaying (FDS‐FDR) styles. For the FDS‐FDR style, the relay node can use two strategies to handle the received signals from the sources, namely, physical‐layer network coding (PNC) and physical‐layer superposition coding (PSC), both of which are referred to as FDS‐FDR‐PNC and FDS‐FDR‐PSC styles, respectively. By transforming the transmit power minimisation problem into a two‐stage problem, optimum power control (OPC) techniques are developed for the HDS‐FDR, FDS‐FDR‐PNC and FDS‐FDR‐PSC styles, respectively, giving closed‐form solutions for individual transmit power at the relay and the sources. Computer simulations are conducted and the results validate the proposed OPC techniques. It is shown that the FDS‐FDR‐PNC style performs best in terms of energy saving when the two sources' packet‐rates are moderately asymmetric or symmetric. For the case that the packet‐rates are strongly asymmetric, the FDS‐FDR‐PSC style can save more energy than the other two styles.