Abstract
Non-orthogonal multiple access (NOMA) has been recognized as a promising multiple access technology for fifth generation (5G) mobile communication system. However, the advantage of NOMA is only verified under the ideal condition that the transmitter has the perfect knowledge of channel state information (CSI). In this paper, NOMA downlink multiuser system, in which the transmitter acquires the CSI through limited feedback channel, is studied. Two traditional beamforming technologies, zero-forcing beamforming and random beamforming, are investigated in the NOMA downlink multiuser system. Making use of the imperfect CSI feedback, channel direction information (CDI), and channel quality indicator (CQI), we propose the user selection scheme to reduce the interference between the NOMA users. Furthermore, a power allocation scheme is proposed to improve the sum-rate of NOMA system. Numerical results show that NOMA system with limited feedback channel still gains larger system rate than traditional orthogonal multiple access system. It is also shown that random beamforming is more suitable for the NOMA system with limited CSI feedback.
Highlights
As a promising multiple access technology for fifth generation (5G) wireless systems, non-orthogonal multiple access (NOMA) has received many attentions recently, as it can improve the system capacity and spectrum efficiency [1,2,3]
With the imperfect channel state information (CSI), we propose the user selection scheme to reduce the interference between the NOMA users and the power allocation scheme to improve the sum-rate of NOMA system
We introduce the zero-forcing beamforming and random beamforming into NOMA downlink multiuser system and give the feedback forms of channel direction information and channel quality indicator, which are transmitted by the candidate users via a limited rate channel
Summary
As a promising multiple access technology for fifth generation (5G) wireless systems, non-orthogonal multiple access (NOMA) has received many attentions recently, as it can improve the system capacity and spectrum efficiency [1,2,3]. In [23], the performance of downlink NOMA system with channel estimation error was analyzed and it was shown that NOMA still obtains system rate gains compared to traditional OMA systems. A channel correlation matrix-based CSI feedback scheme was proposed in massive-antenna NOMA system [24]. We intend to investigate the performance of NOMA system in downlink multiuser beamforming system with limited CSI feedback.. Numerical results show that the NOMA-BF system with our proposed schemes can improve the sum-rate performance under condition of the limited CSI feedback. AT(aT) denotes the transpose of a matrix A (vector a), AH(aH).
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