Energy-Efficient Cooperative Backscattering Closed-Form Solution for NOMA

Abstract

In this paper, the energy efficiency of multi-user non orthogonal multiple access (NOMA) systems in the presence of a backscatter device is investigated. The energy efficiency maximization problem is formulated as a tradeoff between the sum rate and the total power consumption and shown to be nonconvex. We then derive a closed-form expression of the optimal reflection coefficient. Remarkably, the obtained expression allows the reformulation of the optimization in terms of the power allocation policy into a convex optimization problem that has recently been solved in closed form. This overall solution can then be exploited to reduce the computational complexity of Dinkelbach's algorithm for maximizing the ratio sum rate vs. total power. Simulation results show that the presence of backscatter devices significantly improve the energy efficiency of NOMA systems and reach up to 450% relative gains compared to OMA.

Energy-Efficient Solutions in Two-user Downlink NOMA Systems Aided by Ambient Backscattering

“…In this paper, we study the energy efficiency of a twouser downlink NOMA system aided by several backscatter devices, extending our previous work [14], in which only a single backscatter device was considered. To the best of our knowledge, this is the first work to investigate the energy efficiency of a two-user downlink NOMA system aided by several backscatter devices.…”

“…(10) We can show that GEE can be maximized using Dinkelbach's method [16] and that our closed-form solution reduces the inner loop of the algorithm to a simple line search, similarly to [14]…”

“…The problem (EE1) is not convex due to the joint optimization of the reflection coefficients ρ 1 and ρ 2 and the allocated powers P 1 and P 2 . Nevertheless, we can exploit a similar approach as in [14] and solve the problem by decoupling it into two sub-problems without loss of optimality such that we first optimize (ρ 1 , ρ 2 ) for an arbitrary power allocation and then optimize (P 1 , P 2 ) with the obtained optimal reflection coefficients ρ * 1 and ρ * 2 .…”

“…Compared to our previous work in [14], the novel contributions are two-fold. First, when moving from one to two backscatter devices, although the methodology is similar, finding the closed-form expressions of the optimal reflection coefficients is not trivial.…”

NOMA-Based Backscatter Communications: Fundamentals, Applications, and Advancements

“…According to an investigation into the results, the proposed scheme's performance is far better than the baseline approaches in terms of EE. Similarly, in another work, El Hassani et al [57] assessed the EE of the NOMA-enhanced BC system by considering the data rate and the overall energy usage. By considering the ideal RC, they constructed the EE maximization problem as a nonconvex problem and obtained a closed-form solution.…”