Power Allocation for Energy Efficiency Optimization in Multi-User mmWave-NOMA System With Hybrid Precoding

Xiangbin Yu,Kai Yu,Fangcheng Xu,Xiaoyu Dang

doi:10.1109/access.2019.2933328

Abstract

Recently, the non-orthogonal multiple access (NOMA) scheme has been applied in millimeter-wave (mmWave) communication system to support more users and further improve the performance. In this paper, an energy-efficient power allocation (PA) scheme is designed for a downlink multi-user mmWave-NOMA system with hybrid precoding (HP), where two typical HP architectures, namely the fully-connected HP architecture (FHPA) and the sub-connected HP architecture (SHPA), are both considered. Firstly, we pair users in term of their channel difference and correlation. Then, analog beamforming schemes are proposed for the system with fully-connected and sub-connected HP architectures, respectively. Based on this, a two-step HP design with the proposed analog beamforming and zero-forcing precoding is presented. With these results, the optimization problem is formulated to maximize the energy efficiency (EE) of the system. This is a non-convex optimization problem, and can be approximately decomposed into independent convex sub-problems by applying the fractional programming theory. Using the coordinate descent method, the closed-form solutions of each sub-problem are derived. On these basis, an effective iterative algorithm is proposed to obtain the suboptimal power allocation. Simulation results verify the effectiveness of the proposed PA scheme, it has the same EE performance as the existing scheme with relatively low complexity, and can obtain the EE close to the exhaustive search scheme as well as the chaotic accelerated particle swarm optimization scheme. Moreover, the proposed analog beamforming obviously outperforms the conventional finite resolution analog beamforming, and the system with SHPA has higher EE than that with FHPA.

Highlights

Yu et al.: Power Allocation for Energy Efficiency Optimization in Multi-User mmWave-non-orthogonal multiple access (NOMA) System station (BS) in order to guarantee the security of NOMA networks, while in [3], joint trajectory and precoding optimization problem is studied for NOMA networks with unmanned aerial vehicle (UAV)
SIMULATION RESULTS simulation results are provided to testify the effectiveness of the proposed energy-efficient power allocation scheme in the multiuser mmWave-NOMA system, where the Monte-Carlo method is employed for simulation
The CAPSO scheme has the same EE performance as the exhaustive search scheme, which proves that the CAPSO scheme can effectively converge to the global optimal power allocation

Summary

ANALOG PRECODING

One principle of the analog precoding design is to maximize the array gain for the strong user in the g-th cluster The optimal solution for the sub-connected HP architecture is a(gsub) λmax hg,1h Hg,1 + hg,2h Hg,. The users in each cluster will be resorted such that hHg,1A 2 ≥ hHg,2A 2 C. DIGITAL PRECODING After the user pairing and analog precoding, the equivalent channel vector for the k-th user in the g-th cluster can be expressed as h Hg,k = hHg,k A,. The digital precoding is designed to eliminate the inter-cluster interference by the low-complexity ZF precoding [23]. The digital precoding vector for the g-th cluster can be obtained by normalizing dg, i.e., dg =.

ENERGY EFFICIENCY OPTIMIZATION

3: Initialize power allocation p

SIMULATION RESULTS

CONCLUSION