Agriculture Reference
In-Depth Information
industrial areas such as radio frequency (RF) technology, integrated circuits, micro-
processors, smart sensors, and microelectromechanical systems (MEMS) (Mahfuz
and Ahmed, 2005). These latest advancements have enabled the mass production of
low-cost, low-power consumption, high-reliability, multifunctional, intelligent, min-
iature sensor and controller nodes with networking capability. The networked nodes
are commonly deployed to application environments to collect real-time data and
implement simple control strategies. Through them, more detailed knowledge about
the environment is acquired, especially for those dangerous, hazardous, and remote
areas and locations. Precise implementation of agricultural operations such as irriga-
tion and chemical application can be realized.
13.4.1 AB
RIEF
I
NTRODUCTION
TO
W
IRELESS
S
ENSOR
N
ETWORKS
A wireless sensor network (WSN) system consists of multiple nodes, each of which is
comprised of RF transceivers (motes), sensors, microcontrollers, and power sources.
Their self-organizing, self-configuring, self-diagnosing, and self-healing capabilities
enable them to form
ad hoc
single-/multi-hop networks. This reduces and simplifies
wiring and connectors, provides installation flexibility for sensors and controllers,
and reduces maintenance complexity and costs. Most wireless nodes have signal
conditioning and processing units that can convert analog to digital signals. As a
result, noise pickup becomes a less significant problem. Through advanced micro-
electronic technology, nodes have become much smaller with lower power require-
ments while maintaining their functionality. Furthermore, wireless sensor networks
allow a remote user (e.g., farm manager) to send commands to selected nodes in a
field to assign new tasks, change configurations, and diagnose problems. With these
advantages, WSN technology has been playing a very important role to realize unin-
terrupted data acquisition, processing, and controls with fine spatial and temporal
resolution.
13.4.2 A
VAILABLE
W
IRELESS
S
ENSOR
N
ETWORK
T
ECHNOLOGY
Development of WSNs is mainly based on three major components: hardware, oper-
ating system, and network communication. The hardware consists of (1) multiple
nodes distributed in a target site to form a wireless communication network, each of
which has one or more sensors and/or controllers, onboard signal conditioning and
processing units, limited data storage, a radio transceiver, and a power unit; and (2) one
or multiple sink or gateway bridging units to relay measurement data to a remote con-
trol center through wireless LAN, cellular, or other networks (Boegena et al., 2006).
The operating systems are tied to the hardware and running on the nodes to coor-
dinate onboard components to complete the assigned tasks such as data acquisition,
processing, transmission, and storage (Gay et al., 2003). The network communica-
tion defines network topology and communication protocols with the consideration
of routing, power and resource management, node localization, etc. Table 13.1 shows
the most common commercial wireless sensing and controlling systems.
Various international standards have been established for WSN applications in
past decades. Among them, the standards for wireless LAN, IEEE 802.11b (“WiFi”)
