User Selection for Massive MIMO under Line-of-Sight Propagation

Abstract

This paper provides a review of user selection algorithms for massive multiple-input multiple-output (MIMO) systems under the line-of-sight (LoS) propagation model. Although the LoS propagation is extremely important to some promising technologies, like in millimeter-wave communications, massive MIMO systems are rarely studied under this propagation model. This paper fills this gap by providing a comprehensive study encompassing several user selection algorithms, different linear precoders and simulation setups, and also considers the effect of partial channel state information (CSI). One important result is the existence of practical cases in which the LoS propagation model may lead to significant levels of interference among users within a cell; these cases are not satisfactorily addressed by the existing user selection algorithms. Motivated by this issue, a new user selection algorithm based on inter-channel interference (ICI) called ICI-based selection (ICIBS) is proposed. Unlike other techniques, the ICIBS accounts for the ICI in a global manner, thus yielding better results, especially in cases where there are many users interfering with each other. In such scenarios, simulation results show that when compared to the competing algorithms, the proposed approach provided an improvement of at least 10.9% in the maximum throughput and 7.7% in the 95%-probability throughput when half of the users were selected.

User Selection Scheme based on Reference Frames

“…SOS and ICIBS present in [25]. Table I records the number of multiplications, additions, divisions that are necessary for these algorithms.…”

“…In literature [25], user channel vectors have a single path. That is ∥h∥ 2 = √ M without multiplication operation.…”

“…This also results in the above algorithms not being very practical. Motivated by this, alternative algorithms, semi-orthogonal selection (SOS) in [25,[16][17][18][19][20] and correlation-based selection (CBS) algorithms in [21][22], have been proposed that not only achieve better performance but also significantly reduce computational effort.…”

“…Thus, the CBS aims to maximize the SINR of a particular user without considering the SINR of the remaining users. In [25], the inter-channel interference-based user selection (ICIBS) algorithm was proposed. Compared to the CBS algorithm, the algorithm takes into account global interference in order to overcome problems in the CBS algorithm.…”

User Selection Methods for Overcoming Growing Number of Served Users in Massive MIMO Systems

“…Ref. [25] reviews the Semi-orthogonal Selection method and the Correlation-based Selection method. The Semi-orthogonal Selection chooses the user with the most semi-orthogonal channel with the other users.…”