A New View of Multi-User Hybrid Massive MIMO: Non-Orthogonal Angle Division Multiple Access

Abstract

Abstract-This paper presents a new view of multi-user (MU) hybrid massive multiple-input and multiple-output (MIMO) systems from array signal processing perspective. We first show that the instantaneous channel vectors corresponding to different users are asymptotically orthogonal if the angles of arrival (AOAs) of users are different. We then decompose the channel matrix into an angle domain basis matrix and a gain matrix. The former can be formulated by steering vectors and the latter has the same size as the number of RF chains, which perfectly matches the structure of hybrid precoding. A novel hybrid channel estimation is proposed by separately estimating the angle information and the gain matrix, which could significantly save the training overhead and substantially improve the channel estimation accuracy compared to the conventional beamspace approach. Moreover, with the aid of the angle domain matrix, the MU massive MIMO system can be viewed as a type of non-orthogonal angle division multiple access (ADMA) to simultaneously serve multiple users at the same frequency band. Finally, the performance of the proposed scheme is validated by computer simulation results.Index Terms-Massive MIMO, array signal processing, angle of arrival (AOA), channel estimation, hybrid precoding, angle division multiple access (ADMA).

An Overview of Enhanced Massive MIMO With Array Signal Processing Techniques

“…The authors of [85] then proposed to add zero at the end of h(t) before the DFT operation, such that the angle domain is sampled in a much denser way. In this case, a better angle estimation can be obtained compared to beamspace method.…”

“…Matching the columns in F RF with the true steering vector a(θ dl p , 0, 0) is named as anglespace beamforming, and the corresponding beams are shown in Fig. 3(a), [85], [131], [132]. Alternatively, if F RF only supports M fixed directions, then the best beamforming vectors should be selected from a predetermined codebook, i.e., beamspace beamforming, [82], [83], [133], [134].…”

“…Alternatively, if F RF only supports M fixed directions, then the best beamforming vectors should be selected from a predetermined codebook, i.e., beamspace beamforming, [82], [83], [133], [134]. Obviously, the beamspace precoding can be achieved with low complexity but can only be viewed as "angle on the grid" approach and will suffer from power leakage [62], [85], as shown in Fig. 3(b).…”

On fair power optimization in nonorthogonal multiple access multiuser networks

“…Recently, nonorthogonal multiple access (NOMA) schemes have gained much attention where multiple users share the same channel, simultaneously. Various methods of NOMA have been proposed in literature, eg, angle domain multiple access, multiuser shared access, sparse code multiple access, and power division multiple access . In power domain NOMA, superposed signals of multiple users are received simultaneously and then receiver employs successive interference cancelation (SIC) to obtain the desired symbols .…”

Decoupled beamforming techniques for distributed MIMO two-way multi-relay networks with imperfect CSI

“…Recently, cooperative and multiple-input multiple-output (MIMO) systems [1][2][3][4] have been widely considered as a candidate for the fifth generation (5G) wireless communication due to their transmission reliability, where multiple users (MU) are simultaneously served at the same frequency band by the base station (BS) equipped with number of antennas. Cooperative two-way relay network (TWRN) technology has attracted significant interests due to the superior spectral efficiency.…”