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Energy efficient resource allocation for Non-Orthogonal Multiple Access (NOMA) systems Fang, Fang


Non-orthogonal multiple access (NOMA) is a promising technique for the fifth generation (5G) mobile communication due to its capability of achieving high spectral efficiency and high data rate. A popular NOMA scheme uses power domain to achieve multiple access. By applying successive interference cancellation (SIC) technique at the receivers, multiple users with different power levels can be multiplexed on the same frequency band, providing higher sum rate than that of conventional orthogonal multiple access (OMA) schemes. The energy consumption has increased rapidly in recent years. To save energy and meet the requirement of green communications in 5G, we focus on the energy efficient resource optimization for NOMA systems. Our research aim is to maximize the system energy efficiency in NOMA systems by considering perfect channel state information (CSI) and imperfect CSI via resource management. We first study the energy efficient resource allocation for a downlink single cell NOMA network with perfect CSI. The energy efficient resource allocation is formulated as a nonconvex problem. A low-complexity suboptimal algorithm based on matching theory is proposed to allocate users to subchannels. A novel power allocation is designed to further maximize the system energy efficiency. However, the perfect CSI is challenging to obtain in practice. We subsequently investigate energy efficiency improvement for a downlink NOMA single cell network by considering imperfect CSI. To balance the system performance and computational complexity, we propose a new suboptimal user scheduling scheme, which closely attains the optimal performance. By utilizing Lagrangian approach, an iterative power allocation algorithm is proposed to maximize the system energy efficiency. Implementing NOMA in Heterogeneous networks (HetNets) can alleviate the cross-tier interference and highly improve the system throughput via resource optimization. By considering the cochannel interference and cross-tier interference, an iterative algorithm is proposed to maximize the macro cell and small cells energy efficiency. Simulations results show that the proposed algorithm can converge within ten iterations and can achieve higher system energy efficiency than that of OMA schemes.

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