Impact of Pilot Overhead and Channel Estimation on the Performance of Massive MIMO

Atchutaram K Kocharlakota,Sergiy A Vorobyov,Karthik Upadhya

doi:10.1109/tcomm.2021.3112213

Abstract

This paper studies the impact of additional pilot overhead for covariance matrix estimation in a time-division duplexed (TDD) massive multiple-input multiple-output (MIMO) system. We choose average uplink (UL) and downlink (DL) spectral efficiencies (SEs) as performance metrics for the massive MIMO system, and derive closed form expressions for them in terms of the additional pilot overhead. The expressions are derived by considering linear minimum mean squared error (LMMSE)-type and element-wise LMMSE-type channel estimates that represent LMMSE and element-wise LMMSE with estimated covariance matrices, respectively. Using these expressions, a detailed theoretical analysis of SE behavior as a function of pilot overhead for both LMMSE-type and element-wise LMMSE-type channel estimation are presented, followed by simulations, which also demonstrate and validate theoretical results.

Highlights

A MULTI-USER massive multiple-input multiple-output (MIMO) system comprises multiple cells, each having a base station (BS) with a large number of antennas to serve multiple users within the cell
We demonstrate the impact of pilot overhead and channel estimation method on the performance of the massive MIMO system with imperfect covariance information at BSs
We consider a massive MIMO system with L = 7 cells, each comprising a BS with M = 100 antennas and K = 10 users

Summary

Introduction

A MULTI-USER massive multiple-input multiple-output (MIMO) system comprises multiple cells, each having a base station (BS) with a large number of antennas (hundreds) to serve multiple users (tens) within the cell. It is considered to be one of the key technologies for the fifth-generation (5G) cellular systems due to the considerable improvement in spectral efficiency (SE) through spatial multiplexing [1]–[5] achieved with low computational complexity [1], [6], [7]. Acquiring channel state information (CSI) at the base station (BS) is essential to realize the benefits of a massive MIMO system. We consider a time-division duplexing (TDD) massive MIMO system where the CSI is acquired through uplink (UL) pilots. The channel has to be estimated in each coherence

Results

Discussion

Conclusion