Abstract
Based on the high-direction characteristic of millimeter wave (mmWave) transmission, randomly directional beamforming (RDB) can be used for the mmWave massive multiple-input single-output (MISO) non-orthogonal multiple access (NOMA) system to reduce the number of radio frequency (RF) chains. However, the impact of RDB on the signal-to-interference-plus-noise ratio (SINR) of each user is related to the corresponding beamforming gain and interference from other users. Thus, in this paper, we investigate the max-min SINR among all users to evaluate user fairness. In particular, we focus on the single-cell downlink mmWave MISO-NOMA system with RDB, where single-antenna users are divided into multiple NOMA clusters according to their azimuth angles. We formulate the minimum achievable SINR maximization problem associated with power allocation and propose the sum of power allocation coefficients based iterative algorithm (SPACIA) to find the max-min SINR. We also prove that the max-min SINR monotonically decreases as the number of paired users in an NOMA cluster increases as well as the number of beams in the cell with large-scale base station (BS) antenna array increases. Moreover, we derive the upper bound of the max-min SINR. Simulation results verify our theoretical analyses and demonstrate that the proposed algorithm guarantees user fairness, thus outperforming existing schemes.
Highlights
Non-orthogonal multiple access (NOMA), millimeter wave communication, and massive multiple-input multiple-output (MIMO) have been considered as three promising technologies in future wireless networks to meet demands for high data rate and massive connectivity [1]–[3]
This paper focused on the max-min signal-to-interference-plus-noise ratio (SINR) in the singlecell downlink millimeter wave (mmWave) massive multipleinput single-output (MISO)-non-orthogonal multiple access (NOMA) system with randomly directional beamforming (RDB)
We formulated the minimum SINR maximization problem associated with power allocation
Summary
Non-orthogonal multiple access (NOMA), millimeter wave (mmWave) communication, and massive multiple-input multiple-output (MIMO) have been considered as three promising technologies in future wireless networks to meet demands for high data rate and massive connectivity [1]–[3]. The strong channel correlation of paired users in NOMA system can be satisfied by highly directional nature of mmWave transmission [10]–[13]. The mmWave massive MIMO-NOMA system relies on analog processing or hybrid processing to reduce hardware cost and power consumption [18], [22]. Randomly directional beamforming (RDB), which is a form of analog precoding, can be applied to the mmWave massive multipleinput single-output (MISO) NOMA system where one base station (BS) is communicating with multiple single-antenna users.
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