The advantages of multiple-input multiple-out
-
put (MIMO) systems have been widely acknowl-
edged, to the extent that certain transmit
diversity methods (i.e., Alamouti signaling) have
been incorporated into wireless standards.
Although transmit diversity is clearly advanta
-
geous on a cellular base station, it may not be
practical for other scenarios. Specifically, due to
size, cost, or hardware limitations, a wireless
agent may not be able to support multiple trans-
mit antennas. Examples include most handsets
(size) or the nodes in a wireless sensor network
(size, power).
This article presents a tutorial overview of a
class of techniques known as
cooperative commu-
nication
, which allow single-antenna mobiles to
reap some of the benefits of MIMO systems.
The basic idea is that single-antenna mobiles in
a multi-user scenario can “share” their antennas
in a manner that creates a virtual MIMO system.
Several important milestones in this area have
been achieved, leading to a flurry of further
research activity. It is our hope that this article
will serve to illuminate the subject for a wider
audience, and thus accelerate the pace of devel-
opments in this exciting technology.