Downlink Performance of Pilot-Reused HetNet with Large-Scale Antenna Arrays

TL;DR

This paper analyzes the downlink performance of a HetNet with large-scale antenna arrays at macro and small cell base stations, proposing new pilot reuse patterns, deriving capacity bounds, and developing low-complexity user scheduling algorithms.

Contribution

It introduces a novel pilot reuse pattern for channel estimation and derives capacity bounds considering imperfect CSI in massive MIMO HetNets.

Findings

Capacity bounds accurately predict system performance.

Asymptotic analysis validates the effectiveness of proposed algorithms.

User scheduling algorithms improve system throughput and are computationally efficient.

Abstract

Considering a heterogeneous network (HetNet) where both macro base station (BS) and small cell (SC) nodes are equipped with massive antennas, this paper studies the performance for multiple-input multiple-output (MIMO) downlinks when the macro and small cells share the same spectrum and hence interfere with each other. Suppose that the large-scale antenna arrays at both macro BS and SC nodes employ maximum-ratio transmission (MRT) or zero-forcing transmission (ZFT) precoding, and transmit data streams to the served users simultaneously. A new pilot reuse pattern among SCs is proposed for channel estimation. Taking into account imperfect channel state information (CSI), capacity lower bounds for MRT and ZFT are derived, respectively, in closed-form expressions involving only statistical CSI. Then asymptotic analyses for massive arrays are presented under specific power scaling laws. Subsequently, two user scheduling algorithms, greedy scheduling algorithm and asymptotical scheduling algorithm (ASA), are proposed based on derived capacity lower bounds and asymptotic analyses, respectively. ASA is demonstrated to be a near optimal in the asymptotic regime and has low complexity. Finally, the derived closed-form expressions are verified to be accurate predictors of the system performance by Monte-Carlo simulations. Numerical results demonstrate the effectiveness of asymptotic analysis and proposed user scheduling schemes.