Energy-Efficient Hybrid Analog and Digital Precoding for MmWave MIMO Systems With Large Antenna Arrays

Millimeter wave (mmWave) MIMO will likely use hybrid analog and digital precoding, which uses a small number of RF chains to reduce the energy consumption associated with mixed signal components like analog-to-digital components not to mention baseband processing complexity. However, most hybrid precoding techniques consider a fully connected architecture requiring a large number of phase shifters, which is also energy-intensive. In this paper, we focus on the more energy-efficient hybrid precoding with subconnected architecture, and propose a successive interference cancelation (SIC)-based hybrid precoding with near-optimal performance and low complexity. Inspired by the idea of SIC for multiuser signal detection, we first propose to decompose the total achievable rate optimization problem with nonconvex constraints into a series of simple subrate optimization problems, each of which only considers one subantenna array. Then, we prove that maximizing the achievable subrate of each subantenna array is equivalent to simply seeking a precoding vector sufficiently close (in terms of Euclidean distance) to the unconstrained optimal solution. Finally, we propose a low-complexity algorithm to realize SIC-based hybrid precoding, which can avoid the need for the singular value decomposition (SVD) and matrix inversion. Complexity evaluation shows that the complexity of SIC-based hybrid precoding is only about 10% as complex as that of the recently proposed spatially sparse precoding in typical mmWave MIMO systems. Simulation results verify that SIC-based hybrid precoding is near-optimal and enjoys higher energy efficiency than the spatially sparse precoding and the fully digital precoding.

I. Introduction

The integration of millimeter-wave (mmWave) and massive multiple-input multiple-output (MIMO) technique can achieve orders of magnitude increase in system throughput due to larger bandwidth [1] and higher spectral efficiency [2], which makes it promising for future 5G wireless communication systems [3]. On one hand, massive MIMO with a very large antenna array (e.g., 256 antennas) at the base station (BS) can simultaneously serve a set of users through the use of precoding [4]. It has been theoretically proved that massive MIMO can achieve orders of magnitude increase in spectral efficiency, since it can provide more multi-user gain [2]. On the other hand, mmWave with high frequencies enables such large antenna array in massive MIMO to be packed in small physical dimension [5]. Furthermore, the large antenna array can also provide sufficient array gain by precoding [6], [7] to overcome the free-space pathloss of mmWave signals and establish links with satisfying signal-to-noise ratio (SNR)  [8].