On the Design of NOMA-Enhanced Backscatter Communication Systems

Non-orthogonal multiple access (NOMA) and backscatter communication (BackCom) are two emerging technologies for low-power Internet of Things (IoT) applications. This paper addresses the performance of a monostatic BackCom system employing the hybrid time-division multiple-access (TDMA)/power-domain (PD) NOMA, where a reader simultaneously serves multiple backscatter nodes (BNs). While the conventional schemes are mainly for static NOMA-aided monostatic BackCom systems, we instead introduce the design framework for dynamic systems. Moreover, we also present novel schemes to further improve the performance of such conventional static systems. Specifically, as for the static NOMA-enhanced monostatic BackCom systems, we investigate two schemes: (i) a two-node pairing (TNP) scheme to increase the possibility of successfully decoding NOMA groups by not randomly pairing BNs for such groups as in conventional approach and (ii) an adaptive power reflection coefficient (APRC) scheme to enhance the system performance by adjusting BN’s power reflection coefficient based on the channel conditions. Regarding the dynamic NOMA-enhanced monostatic BackCom systems, two schemes, namely dynamic-sized pairing (DSP) and hybrid APRC/DSP, are proposed, in which the number of BNs in a NOMA group is not necessarily to be a fixed size. To illustrate the enhanced system using the proposed schemes, we analyze the performance of the BackCom system in terms of the number of successful backscatter nodes and the number of bits that can be successfully decoded by a controller/reader. The obtained results confirm the effectiveness of our proposed schemes compared to the conventional ones over the state-of-the-art.