Enhancing Backscatter Communication Networks: Optimization and Integration with Emerging Technologies
Creators: Hakimi Najafabadi, Azar
Publisher: name: University of Alberta Library
Year: 2024

<p>Future wireless networks require low cost, high spectral efficiency, and high energy efficiency. To achieve these goals, backscatter communication (BackComm) networks rely on passive reflective backscatter devices (tags). However, passive transmission causes low data rates and ranges. To address these, this thesis aims to address (1) BackComm optimization algorithms and (2) integration of BackComm with other wireless technologies. </p>

<p>The thesis starts with examining a monostatic backscatter Communication (Monostatic BackComm) network consisting of multiple tags with a full-duplex (FD) multiple-input multiple-output (MIMO) reader (backscatter receiver) that is subject to self-interference (SI), which reduces the achievable data rate, throughput, and coverage. Practical SI cancellation methods cannot fully remove it but rather leave residual self-interference (RSI). Thus, to remedy this problem, an algorithm is designed to optimize the reader’s precoder and combiner filters and the tag reflection coefficients. The constraints limit the effects of the RSI and allow the energy harvested by the tags to exceed a minimum. </p>

<p>To enhance spectral efficiency, this thesis integrates BackComm as a secondary network with a downlink non-orthogonal multiple access (NOMA) system as the primary network in a spectrum-sharing environment. In the secondary network, backscatter device (BD) reflects the primary signal while modulating its data onto it. An intelligent reflecting surface (IRS) with backscattering is integrated as a BD to leverage its transmit diversity. The downlink NOMA users are the cooperative receivers who decode both primary and secondary signals. However, a power-splitting (PS) technique is proposed to prevent interference where the downlink signal can be split into modulated and unmodulated parts. Then, the IRS uses ii the latter to transfer its data. It is shown that the interference from the secondary system (IRS-backscattering) on the primary system can be controlled without any performance degradation.</p>

<p>Cooperative symbiotic radio (SR) backscattering is introduced within a spectrum-sharing system. The primary motivation is to address the Backcomm limitations by exploiting an active node, such as the User Equipment (UE). An innovative system model comprising two transmission phases is proposed to achieve this objective. The initial phase involves a traditional SR phase, where the assigned BD utilizes the UE’s uplink signal to modulate its data towards a common base station (BS). In the subsequent phase, the UE decodes and embeds the associate BD’s signal within its data, employing power splitting techniques to allocate distinct power levels to each stream. The analysis of this system encompasses the throughput optimization for both UE and BD. </p>

<p>Also, integrated sensing and communication (ISAC) has emerged to improve spectrum utilization. The thesis proposes an integrated sensing and SR network to study the coexistence and spectrum-sharing among systems. The downlink system leverages SR assisted by an IRS-empowered BackComm system, while the uplink BS performs target sensing. System parameters are optimized to maximize the communication rate while ensuring that sensing and backscatter signals meet their required quality of service (QoS).</p>