Energy Efficiency Maximization in Multi-user Cooperative SWIPT-NOMA Networks with nonlinear EH and Imperfect SIC

With the rapid growth of the Internet of Things, the demand for low-power, high-speed communication in terminal devices is increasing, highlighting the need for effective wireless resource allocation strategies. Non-Orthogonal Multiple Access improves spectral efficiency and multi-user access, and when combined with Simultaneous Wireless Information and Power Transfer, it enables simultaneous energy harvesting and information transmission. However, optimizing energy efficiency while balancing energy harvesting and information transmission in energy-constrained multi-user scenarios remains a challenge.This paper proposes a cooperative transmission algorithm for SWIPT-NOMA networks under nonlinear energy harvesting and imperfect successive interference cancellation conditions. The base station transmits information to all users, while cooperative users relay information to remote users, enhancing throughput and supplementing energy via wireless power transfer. The algorithm optimizes transmission time and power allocation to maximize energy efficiency, subject to constraints on user throughput, energy harvesting, and base station power.The problem is formulated as a Mixed-Integer Nonlinear Programming problem, which is transformed into a convex problem using the Dinkelbach and Successive Convex Approximation methods, with the Lagrangian dual method employed for the optimal solution. Simulation results show that the proposed algorithm achieves good convergence and outperforms benchmark schemes in terms of energy efficiency.