Introduction - Energy Harvesting Autonomous Sensor Systems - page 5

multiple pervasive sensor nodes, sink, public networks, manager nodes, and
end user [4]. Many tiny, smart, and inexpensive sensor nodes are scattered in
the targeted sensor field to collect data and route the useful information back
to the end user. These sensor nodes cooperate with each other via a wireless
connection to form a network and collect, disseminate, and analyze data com-
ing from the environment. To ensure full connectivity, fault tolerance, and a
long operational life, WSNs are deployed in an ad hoc manner, and the net-
works use multihop networking protocols to obtain real-world information
and perform control ubiquitously [5]. As illustrated in Figure 1.5 , the data
collected by nod e A is routed within the sensor field by other nodes. When
the data reaches the boundary, nod e E ,itisthen transferred to the sink. The
sink serves as a gateway with a higher processing capacity to communicate
with the task manager node. The connection between the sink and task man-
ager node is the public network in the form of the Internet or a satellite. Once
the end user receives the data from the task manager node, some processing
actions are then performed on the received data.
In Figure 1.5 , the sink is essentially a coordinator between the deployed
sensor nodes and the end user, and it can be treated like a gateway node. The
need of a sink in WSN architecture is due to the limited power and comput-
ing capacity of each of the wireless sensor nodes. The gateway node, typically
powered by the readily available power source from the AC (alternating cur-
rent) main, is equipped with a better processor and sufficient memory space
that it is able to provide the need for extra information processing before
data is transferred to the final destination. The gateway node can therefore
share the loadings posed on the wireless sensor nodes and hence prolong
their working lifetime. To understand how data is communicated within the
sensor nodes in a WSN as shown in Figure 1.5 , the protocol stack model of
the WSN as shown in Figure 1.6 is investigated. With this understanding, the
energy-hungry portions of the wireless sensor node can be identified, and

Internet and
Satellite

B

D

C

Sink

E

A

Ta sk Manager
Node
User

Sensor Field Sensor Nodes

FIGURE 1.5
Architecture of a WSN to facilitate smart environments. (From I.F. Akyildiz, W.L. Su, S. Yogesh,
and C. Erdal, “A survey on sensor networks,” IEEE Communications Magazine , vol. 40, no. 8,
pp. 102-114, 2002 [4].)