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MIMO Systems and Transmit Diversity 1 Introduction

Summary: MIMO Systems and Transmit Diversity
1 Introduction
So far we have investigated the use of antenna arrays in interference cancellation and for receive
diversity. This final chapter takes a broad view of the use of antenna arrays in wireless communi-
cations. In particular, we will investigate the capacity of systems using multiple transmit and/or
multiple receive antennas. This provides a fundamental limit on the data throughput in multiple-
input multiple-output (MIMO) systems. We will also develop the use of transmit diversity, i.e.,
the use of multiple transmit antennas to achieve reliability (just as earlier we used multiple receive
antennas to achieve reliability via receive diversity).
The basis for receive diversity is that each element in the receive array receives an independent
copy of the same signal. The probability that all signals are in deep fade simultaneously is then
significantly reduced. In modelling a wireless communication system one can imagine that this
capability would be very useful on transmit as well. This is especially true because, at least in the
near term, the growth in wireless communications will be asymmetric internet traffic. A lot more
data would be flowing from the base station to the mobile device that is, say, asking for a webpage,
but is receiving all the multimedia in that webpage. Due to space considerations, it is more likely
that the base station antenna comprises multiple elements while the mobile device has only one or
In addition to providing diversity, intuitively having multiple transmit/receive antennas should
allow us to transmit data faster, i.e., increase data throughput. The information theoretic analysis


Source: Adve, Raviraj - Department of Electrical and Computer Engineering, University of Toronto


Collections: Engineering