Abstract
A symmetry-based hybrid precoder and combiner is a high spectral efficiency structure in millimeter-wave (mmWave) massive multiple-input multiple-output (mMIMO) non-orthogonal multiple access (NOMA) system. To improve the spectral efficiency of the mmWave mMIMO-NOMA system, we first propose a user grouping scheme to suppress the strong inter-user interference caused by NOMA, then the hybrid precoder based on user channel alignment and the zero-forcing algorithm is constructed to further improve the signal-to-interference-plus-noise ratio (SINR) of the receiver. Subsequently, the non-convex spectral efficiency optimization problem is transformed into a convex optimization problem of inter-cluster power allocation and the closed-form solution for the optimal power under the minimum rate constraint is obtained by solving the KKT condition to further improve the spectral efficiency. The simulation results show that the proposed scheme can achieve higher spectral efficiency compared to orthogonal multiple access (OMA), fixed power allocation (FPA), K-means, and cluster head selection (CHS).
Highlights
The massive multiple-input multiple-output (mMIMO) communication networks which operate in the mmWave band are characterized by high frequency and a larger number of antennas, resulting in high path loss, large power consumption, and server interference
There are two serious technical obstacles in the mMIMONOMA communication system, The first problem is that the number of users is much larger than the number of radio frequency (RF) chains, which can lead to severe inter-beam and intra-beam interference, i.e., inter-user interference problem [5,6]
For the inter-user interference in the mmWave mMIMO-non-orthogonal multiple access (NOMA) system, we propose a hybrid precoder scheme based on the user channel alignment and a zero-forcing algorithm to solve the interference problem and further improve the signal-to-interference-plus-noise ratio (SINR) of users
Summary
The mMIMO communication networks which operate in the mmWave band are characterized by high frequency and a larger number of antennas, resulting in high path loss, large power consumption, and server interference. These problems make the spectrum efficiency largely reduced; how to improve the spectral efficiency is a significant research issue for 6G communication [1,2]. The other problem is that the number of users in the 6G communication system has increased dramatically, making the energy consumption greatly increased, i.e., power allocation problem [7]. Inter-user interference and power allocation are the two essential challenges that need to be solved in 6G communication systems
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