Non-orthogonal multiple access in a downlink multiuser beamforming system with limited CSI feedback

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.

Efficient message exchange protocols exploiting state-of-the-art PHY layer

“…A more straightforward extension to this work is the assessment of OFDM, given that this is a modulation designed to cope with wide-band frequency selective channels and used in the recent versions of the 802.11 family of standards, as well as in 4G celular systems. Another very recent technology that is presently at an early stage of research is power-domain non-orthogonal multiple access (NOMA) [42][43][44][45], and the exploration of NOMA with MIMO-IBFD is a major research problem that needs to be addressed. Moreover, as PLNC can be seen as akin to the NOMA concept, a fruitful interplay between these two techniques can be expected.…”

Reconsidering Design of Multi-Antenna NOMA Systems With Limited Feedback

“…The spectral efficiency improvement of NOMA technique over orthogonal multiple access (OMA) has been well investigated for single-antenna systems [3][4][5][6][7][8]. The spatial multiplexing property of multi-antenna systems can be naturally combined with power-domain NOMA to further enhance the spectral efficiency [9][10][11][12][13][14][15][16][17][18][19][20][21]. NOMA was also regarded as a spectrum sharing technique in [22].…”

“…While in frequency division duplex (FDD) systems, the downlink CSI is usually first estimated and quantized using a pre-determined codebook at each receiver, and then conveyed to transmitter via feedback channel. Specifically, the NOMA schemes in [9,16,17] were designed based on the kind of CSI acquisition in TDD mode, whilst the NOMA schemes in [18][19][20] were designed based on the kind of CSI acquisition in FDD mode. Particularly, the work in [21] had tried to employ a unified channel model to embrace both TDD and FDD modes.…”

“…Specifically, the outage performance of NOMA was investigated in [18] for each group decomposed from a massive-antenna system with one-bit feedback. [19] investigated the traditional zeroforcing BF (ZFBF) and random BF technologies for the downlink NOMA systems. A joint user selection and power allocation scheme was proposed to reduce the multiuser (MU) interference and improve the sum-rate performance based on both quantized channel vector and perfect SINR feedback.…”

“…The authors in [21] had also tried to jointly optimize the transmit power and feedback bits of each users. However, [21] did not use the well recognized practical CSI model for FDD systems as in [19,20,23,24]. One can see the model used by [21] actually assumed some terms in the practical CSI model that should vary at the same speed of channel fading to be constant 2 , which is impractical for FDD systems.…”