LTE-Advanced and Next Generation Wireless Networks: Channel Modelling and Propagation

Chapter 7

Multi-User MIMO Channels

Fredrik Tufvesson¹, Katsuyuki Haneda² and Veli-Matti Kolmonen²

¹ Lund University, Sweden

² Aalto University, Finland

7.1 Introduction

Multiple Input Multiple Output (MIMO) technologies are nowadays used in the major cellular and wireless standards such as LTE, and the IEEE 802.11 family. For single-link MIMO, correlation effects between antennas are of high interest since they will determine the ability to use spatial multiplexing in an efficient way. In addition, the received signal strength for each link is of course also of major interest since it ultimately determines the possibility to detect and decode the data transmitted. Usually the antennas used for a single link MIMO are located quite close to each other, though there are concepts like distributed MIMO, cooperative communication and Coordinated Multipoint (CoMP) communication as will be discussed in the next chapter. A close proximity of the antennas means that the power levels usually are quite similar, though variations might be present due to polarization effects, variations in antenna patterns and so on. Shadowing by larger objects typically affects all antennas simultaneously.

In multi-user MIMO those properties of course still hold for the individual links, but in addition to this it is important to consider the joint behavior of the individual MIMO links. It has been shown that there can be correlation between the links even if the units (different base stations/access points, ...