This module will act as a bridge between multi-user MIMO and massive MIMO systems. The module will explain when a multi-user MIMO system can be called a massive MIMO system. You will learn about different properties of massive MIMO, for example, channel hardening and favorable propagation. You will learn why channel estimation is an important aspect, mainly when you consider a massive MIMO system. The focus will be on how to calculate an estimate of channels with limited overhead. Further, it will discuss different ways to estimate channels, such as the minimum mean square error (MMSE), least-square (LS), semi-blind, and superimposed channel estimation techniques.