Digital Signal Processing Reference
In-Depth Information
4.1
Introduction
This chapter considers the principles of multiple-input multiple-output (MIMO) wire-
less communication systems as well as some recent accomplishments concerning their
implementation. By employing multiple antennas at both transmitter and receiver, very
high data rates can be achieved under the condition of deployment in a rich-scattering
propagation medium. This interesting property of MIMO systems suggests their use
in the future high-rate and high-quality wireless communication systems. Several con-
cepts in MIMO systems are reviewed in this chapter. We first consider MIMO channel
models and recall the basic principles of MIMO structures and channel modeling. We
next study the MIMO channel capacity and present the early developments in these
systems concerning the information theory aspect. Iterative signal detection is consid-
ered next; it considers iterative techniques for space-time decoding. As the capacity is
inversely proportional to the spatial channel correlation, MIMO antennas should be
sufficiently separated, usually by several wavelengths. In order to minimize antennas'
deployment, we present advanced polarization diversity techniques for MIMO systems
and explain how they can help to reduce the spatial correlation in order to achieve high
transmission rates. We end the chapter by considering the application of MIMO systems
in local area networks, as well as their potential in enhancing range, localization, and
power efficiency of sensor networks.
4.2
MIMO Systems and Channel Models
In this section, we present briefly a general MIMO communication structure. The defi-
nition of MIMO channel is then described with some related characteristics of wireless
communication channels. Some recent MIMO channel models are also reported.
4.2.1
MIMO Communication Systems
Using multiple antennas [1] at both transmitter and receiver permits the increasing of
the data rate by creating multiple spatial channels. Multiple receiving antennas can also
be used to combat fading without expanding the bandwidth of the transmitted signal.
In particular, with
M
T
transmitting and
M
R
receiving antennas, it is possible to achieve
an
M
-time capacity of a single transmitting and single receiving antenna configuration
where
M
= min{
M
T
,
M
R
}. Figure 4.1 demonstrates a general system employing multiple
transmitting and multiple receiving antennas to increase the data rate. A sequence of
Input
sequences
Output
sequences
Propagation
environment
H(
t
, τ)
+
M
T
M
R
η(
t
)
FIgure 4.1
General configuration of a MIMO communication system.
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