T-11: Practical Massive MIMO: Performance Bottlenecks and How to Overcome Them: Part 1

This is a three hour (half day) tutorial that discusses the causes and effects of different impairments in a practical massive MIMO system, along with techniques to mitigate them. The recent popularity of massive MIMO systems is due to the high spectral and energy efficiencies offered by them, even with simple linear signal processing techniques being employed at the BS. These advantages require the availability of accurate and up-to-date channel state information (CSI) at the BS. However, the accuracy of the CSI at the BS is compromised due to several reasons, e.g. as pilot contamination, channel aging and reciprocity imperfections in massive MIMO system and severely limit the performance of these systems. In the context of millimeter wave (mmWave) communications, the hybrid analog-digital architecture and low resolution ADCs further limit the performance. While these effects have been studied independently, in this tutorial, we aim to bring all these effects under a common umbrella. We will first discuss the modelling of the effects of these impairments. Following this, we will use signal processing tools based on blind channel estimation and tracking to present techniques for mitigating the effects of these impairments. Finally, we will describe more recent attempts at mitigating these imperfections using machine learning (ML) based methods.