Energy Efficiency Optimization for Backscatter Enhanced NOMA Cooperative V2X Communications under Imperfect CSI

Abstract

Automotive-Industry 5.0 will use beyond fifthgeneration (B5G) technologies to provide robust, computationally intelligent, and energy-efficient data sharing among various onboard sensors, vehicles, and other devices. Recently, ambient backscatter communications (AmBC) have gained significant interest in the research community for providing battery-free communications. AmBC can modulate useful data and reflect it towards near devices using the energy and frequency of existing RF signals. However, obtaining channel state information (CSI) for AmBC systems would be very challenging due to no pilot sequences and limited power. As one of the latest members of multiple access technology, non-orthogonal multiple access (NOMA) has emerged as a promising solution for connecting large-scale devices over the same spectral resources in B5G wireless networks. Under imperfect CSI, this paper provides a new optimization framework for energy-efficient transmission in AmBC enhanced NOMA cooperative vehicle-to-everything (V2X) networks. We simultaneously minimize the total transmit power of the V2X network by optimizing the power allocation at BS and reflection coefficient at backscatter sensors while guaranteeing the individual quality of services. The problem of total power minimization is formulated as non-convex optimization and coupled on multiple variables, making it complex and challenging. Therefore, we first decouple the original problem into two subproblems and convert the nonlinear rate constraints into linear constraints. Then, we adopt the iterative sub-gradient method to obtain an efficient solution. For comparison, we also present a conventional NOMA cooperative V2X network without AmBC. Simulation results show the benefits of our proposed AmBC enhanced NOMA cooperative V2X network in terms of total achievable energy efficiency.

Ergodic Capacity Analysis of NOMA-Based Two-Way Relaying Systems

“…The slope of the stream χ is defined as S χ = lim ρ→∞ Ce χ rg log ρ , where ρ b = ρ r = ρ. By substituting the high-SNR approximations of the ECs in (9) into S χ , we observe that the high-SNR slope of all streams are equal to zero. This result demonstrates that all streams converge to throughput ceilings with zero slope due to the interference introduced by NOMA spectrum sharing, which seriously impacts the slope.…”

Ergodic Capacity Analysis of NOMA-Based Two-Way Relaying Systems

“…Owing to the improvements expected in terms of system capacity, spectral efficiency, and massive users' access for the fifth generation (5G) wireless networks, NOMA has been proposed for many applications [2]- [9] to serve multiple users within the same resource block (i.e., frequency, code, and time) by multiplexing their messages in the power domain. This type of NOMA is known in the literature as power-domain NOMA (PD-NOMA) [10]- [12].…”