On the Multiplexing Capability of mmWave Doubly-Massive MIMO Systems in LOS Environments

Abstract

This paper is concerned with the potential of spatial multiplexing in a millimeter wave (mmWave) multiple-input multiple-output (MIMO) downlink system in which the base station (BS) is equipped with multiple distributed massive antenna subarrays to serve multiple users. The paper first introduces the concept of multiplexing gain when the number of antennas goes to infinity and the transmit power is finite. Assume that each of the user terminals is equipped with a large antenna array, the paper focuses on the simple and cost-effective analog beamforming scheme for the MIMO system operating in mmWave line-of-sight propagation environments. We obtain simple and approximate expressions for the sum rate of the system based on asymptotic analysis in the limit of the numbers of antennas at the BS and at the user terminals when the total transmit power is fixed or scaled down. The approximate expressions show that the employed analog beamforming scheme can achieve a multiplexing gain that is equal to the product of the number of subarrays at the BS and the number of users when the total transmit power is fixed, whereas the multiplexing gain decreases proportionally to such a product when the total transmit power is scaled down. Extensive numerical results are also provided to corroborate analytical results. INDEX TERMSMassive MIMO, millimeter-wave, multiplexing gain, distributed antenna subarrays, analog beamforming, line-of-sight environment.

mmWave Doubly-Massive-MIMO Communications Enhanced With an Intelligent Reflecting Surface: Asymptotic Analysis

“…By the optimal control of phase shifts in (31), we can have that |ξ k 11 | 2 = 1. However, without control of phase shifts, due to the fact that V k = I N in this case, we can show in a similar fashion as in [6] that |ξ k 11 | 2 will tend to zero when N grows without bound.…”

“…To confirm this, Fig. 8 plots the average number of useful paths for four different values of K (K = 0, 3,6,9) when N increases from 100 to 1000. Note that K = 0 stands for the special case where there is no IRS.…”

“…Denote by H TR the channel matrix between the transmitter and the receiver. In general, the matrix H TR consists of a LOS matrix and a scattered matrix [6], [38], i.e.,…”

“…Since a very large antenna array can be realized in a very small volume, it is practical to mount large numbers of antennas at both the transmit and receive terminals. Such a MIMO system is called a mmWave doublymassive MIMO system [4], [5], [6]. In this paper, we shall consider mmWave doubly-massive MIMO systems that are enhanced by making use of an intelligent reflecting surface (IRS).…”

Energy Optimization in Massive MIMO UAV-Aided MEC-Enabled Vehicular Networks

“…Nevertheless, there exist some practical barriers (e.g., energy consumption and hardware complexity) towards the implementation of large-scale antennas, especially when fully digital beamforming is used. Recently, less complex hybrid analog-digital [42] and fully analog [42], [43] beamforming architectures were studied. Also, low-complexity transceivers with perfect [41] and partial [44] channel state information (CSI) requirements were proposed.…”