Robust Transmit Beamforming for SWIPT-Enabled Cooperative NOMA With Channel Uncertainties

Abstract

In this paper, we study the robust beamforming design for a simultaneous wireless information and power transfer (SWIPT) enabled system, with cooperative nonorthogonal multiple access (NOMA) protocol applied. A novel cooperative NOMA scheme is proposed, where the strong user with better channel conditions adopts power splitting (PS) scheme and acts as an energy-harvesting relay to transmit information to the weak user. The presence of channel uncertainties is considered and incorporated in our formulations to improve the design robustness and communication reliability. Specifically, only imperfect channel state information (CSI) is assumed to be available at the base station (BS), due to the reason that the BS is far away from both users and suffers serious feedback delay. To comprehensively address the channel uncertainties, two major design criteria are adopted, which are the outage-based constraint design and the worst-case based optimization. Then, our aim is to maximize the strong user's data rate, by optimally designing the robust transmit beamforming and PS ratio, while guaranteeing the correct decoding of the weak user. With two different channel uncertainty models respectively incorporated, the proposed formulations yield to challenging nonconvex optimization problems. For the outage-based constrained optimization, we first conservatively approximate the probabilistic constraints with the Bernstein-type inequalities, which are then globally solved by two-dimensional exhaustive search. To further reduce the complexity, an efficient low-complexity algorithm is then proposed with the aid of successive convex approximation (SCA). For the worst-case based scenario, we firstly apply semidefinite relaxation (SDR) method to relax the quadratic terms and prove the rank-one optimality. Then the nonconvex max-min optimization problem is readily transformed into convex approximations based on S-procedure and SCA. Simulation results show that for both channel uncertainty models, the proposed algorithms can converge within a few iterations, and the proposed SWIPT-enabled robust cooperative NOMA system achieves better system performance than existing protocols. Index Terms-Non-orthogonal multiple access, simultaneous wireless information and power transfer (SWIPT), outage-based constrained optimization, worst-case based optimization.

Hybrid User Pairing for Spectral and Energy Efficiencies in Multiuser MISO-NOMA Networks With SWIPT

“…Regarding MISO-NOMA SWIPT systems, the power splitting architecture was addressed in [18], where a user with better channel condition is acted as an EH relay for the poor channel condition one, with the goal of maximizing its data rate under serious feedback delay at the BS. Considering non-linear EH model, Zhang et al in [19] formulated the transmission power and the total EH trade-off problem by using multi-objective optimization approach.…”

Edge Cache-Assisted Secure Low-Latency Millimeter-Wave Transmission

“…Solve the relaxed problem (44) and obtain the solution Combing Lemma 1, (39a) and (39c), we can obtain the following convex linear matrix inequality (LMI)…”

“…However, by removing (44c), the above problem becomes a convex SDP and can be solved efficiently by numerical solvers such as SDPT3 [43]. To obtain the solution of P2, we need to iteratively solve the relaxed problem of (44). The procedure is summarized as Algorithm 2.…”

“…The same conclusions can be obtained for (34) and (43) following a similar procedure, and they are thus omitted here. As a result, the solution of problem (44) at the ith iteration is also a feasible solution for the (i+1)th iteration.…”

“…Finally, we need to consider whether the obtained solution satisfies the rank-one constraint or not. The rank-one solution is satisfied if the following condition holds [44]:…”