Abstract
Hybrid beamforming (HB) is a solution for reducing radio frequency (RF) chains in millimeter-wave (mmWave) massive MIMO systems. By reducing RF chains, HB can achieve energy efficient transmission compared to fully digital beamforming of massive MIMO system. However, if the resolution of RF precoder is not quantized, the energy consumption of HB may become similar to fully digital beamforming. And, if the resolution of RF precoder is heavily quantized, the spectral efficiency of HB is decreased significantly. Non-orthogonal multiple access (NOMA) is one of the emerging technologies for the fifth generation (5G) or beyond fifth-generation (B5G) wireless communication to support high spectral efficiency. Especially, power domain NOMA (PD-NOMA) can share same resources to transmit signals and divide the signals in power domain by using successive interference cancellation (SIC). In this paper, the adoption of NOMA shows increase of spectral efficiency in a low-resolution RF precoder. To apply NOMA, two users with high channel correlation are selected according to the proposed criterion. Then, the RF precoder and digital precoder that are applied to both users at the same time are determined. Finally, intra-pair user fairness is achieved by power allocation. The ratio of channel power is compared for each user in each pair. Then, users with high channel power are assigned with low power. It is shown that the spectral efficiency of the proposed scheme is higher than the conventional scheme in heavily quantized RF precoder.
Highlights
The emergence of the millimeter-wave communications operating from 30–300 GHz provides an opportunity to satisfy the rapid increase of mobile data traffic for the 5th generation (5G) of wireless communication systems [1]
The simulation results of full complexity (FC) ZF, Phased zero-forcing (PZF) Hybrid beamforming (HB), and proposed HB Non-orthogonal multiple access (NOMA) schemes are presented
In this paper, a new HB scheme based on power domain NOMA (PD-NOMA) in massive multiple-input and multiple-output (MIMO) systems is proposed
Summary
The emergence of the millimeter-wave (mmWave) communications operating from 30–300 GHz provides an opportunity to satisfy the rapid increase of mobile data traffic for the 5th generation (5G) of wireless communication systems [1]. Lee et al.: HB With Reduced RF Chain Based on PZF and PD-NOMA in mmWave Massive MIMO Systems analog beamformers in the RF domain and digital beamformers in baseband [15]–[17]. This combination allows hybrid beamformer to maximize the achievable data by joint optimization [18], [19]. The RF precoder components with the index of higher normalized channel power value are adopted Through this process, two users can share one beam. The ratio of channel power is used for user allocation. In the fully connected HB system, each RF chain is connected to every antenna including phase shifters (PS)
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