MIMO Communications - Motivation and a Practical Realization

Abstract

Under rich scattering environment, Multiple Input Multiple Output (MIMO) systems have the potential to achieve capacities inconceivable by Single Input Single Output (SISO) systems. This makes it one of the most exciting developments to have occurred in wireless communications. Within a short duration, it has matured from a reasearch topic into a technology to find a place in upcoming wireless communication standards. This paper focuses on the spatial multiplexing aspects of MIMO. Starting from AWGN channels, we bring out how fading, which is typically an undesirable phenomenon, can be gainfully exploited to attain large capacities under MIMO configuration. We first briefly discuss some MIMO architectures initially designed to realize a large portion of the theoretical MIMO capacity, namely V-BLAST (Vertical Bell Labs Layered Space-Time) and D-BLAST (Diagonal BLAST), and then describe briefly the conventional V-BLAST receivers and a receiver that attains near optimal performance while keeping the complexity low. The combination of Orthogonal Frequency Division Multiplexing (OFDM) and MIMO is introduced as a simple method to apply MIMO communication in a delay spread environment. Taking the example of Wireless Local Area Network (WLAN) standard IEEE 802.11n , we see how the research developments have been incorporated in a practical system.