MIMO Systems: Principles, Iterative Techniques, and Advanced Polarization - Adaptive Signal Processing in Wireless Communications - page 127

RF and IF
MOD
DEMO

Micro battery

FIgure 4.21 Typical wireless sensor node.

is a very important design consideration, and energy-efficient transmission schemes
must be used for the data transfer in sensor networks.
In add it ion, because sensor nodes w i l l be deployed i in remote a nd otent i mes da ngerous
locations, their maintenance (in particular, battery replacement) will be unlikely [84].
Sensor networks are a new attraction for many potential applications, such as indus-
trial, military, geolocalization, surveillance, intrusion detection, and environmental
monitoring [84, 85].
Robust communications between sensor nodes are highly demanded at low power. As
was shown, MIMO communication promises performance enhancements over conven-
tional single-input single-output (SISO) technology without increasing the bandwidth
consumed by the system or the total power radiated from a transmitter. MIMO technol-
ogy has promising characteristics that make it a serious candidate for sensor network
communication technology. Signal processing techniques that use multiple transmit and
receive antennas, such as space-time coding (ST coding), have been shown to increase
transmission reliability.
In a surveillance application, the ability of sensor nodes to relay data is critical to the
utility and effectiveness of the sensor network.
For a given node density, nodes are more likely to be out of range, thus inhibiting
communication. In a situation such as this, the extended range of MIMO is of greater
importance because it enables cohesion (the ability of the sensor nodes to form a com-
pletely connected network), which guarantees the success of the final application [86].
New protocols for target reporting and a procedure for target localization that con-
serve energy have recently been developed [86, 87]. In [88], the authors summarize and
compare several routing MIMO technologies.
Mean path length provides a measurement of the impact of MIMO communications
on a wireless sensor network. Mean path length provides a rough estimate of the amount
of time and energy expended in a data transmission from one node to another in the
network.
Most significant mean path length reduction is provided by MIMO in the low or mid
range of node densities because the internode spacing is such that MIMO can reliably