Location-assisted precoding for three-dimension massive MIMO in air-to-ground transmission

Abstract

This paper investigates the low-complexity precoding for air-to-ground transmission, where an air platform (AP) is equipped with a two-dimension (2D) rectangular antenna array and communicates with a number of user equipments (UEs) on the ground. By exploiting the slow time-varying parameters and clustering UEs properly, we propose a location-assisted precoding scheme for downlink transmission. The scheme consists of two-layer precoding. The first-layer precoding is to decompose the original system into several small MIMO systems based on the location information of UEs, and is designed as a constant-envelope matrix. In this way, the number of required radio frequency (RF) chains at AP can be substantially reduced. The second-layer precoding matrix is designed to control the interference within small MIMO system. Simulation results show that the proposed scheme outperforms match filter precoding and DFT precoding in the air-to-ground transmission scenarios. Moreover, the results show that when the altitude of AP is high, increasing the number of RF chains at AP cannot improve the spectral efficiency of the system.