Information Technology Reference
Fig. 6.1 WSN, mobile entities and possible reaction to events
mobile sensor nodes are summarized. Cooperative communications are further
discussed as an efficient way for exploiting multi-user diversity for data propagation.
Mobile Entities in WSN
Each sensor node in the WSNs comprises sensing unit , transceiver , processing unit,
and power supply (usually battery ) . If mobile, sensor nodes can be equipped with
various locomotion devices and, additionally, they may contain different position
finding systems (Fig. 6.2 ).
The sensor's sensing range defines the coverage , while the transmission and recep-
tion range of transmitter defines the connectivity of the sensor network. It is signifi-
cant to provide connectivity and coverage at the same time since a sensed data is not
beneficial if it cannot be sent to the sink due to poor connectivity [ 1 ]. These aspects
are also addressed in [ 2, 3 ]. The authors in [ 2 ] evaluate the minimum transmission
range needed for connectivity in static WSNs modeled by random geometric graphs,
while [ 3 ] provides necessary and sufficient relation between the transmission range
and the sensing range to simultaneously guarantee coverage and connectivity.
Sensor devices run on batteries, which makes the power consumption another key
factor in the design of nodes and network protocols. This introduces another important
performance parameter of WSNs, i.e. network lifetime . Power consumption affects all
aspects of WSNs, from choosing hardware components to programming efficient network
protocols for minimizing the use of the radio, and efficient power control algorithms that
will switch off hardware components when necessary. Another aspect is the limited
computation capabilities of the microcontrollers and the reduced memory space to run
the programs. These limitations restrict the protocol stacks and computation algorithms
requiring the programming of the sensor devices to be hardware specific [ 4 ].
Coverage , connectivity, and network lifetime are the most important performance
metrics that can be improved by enabling the sensor nodes with motion capability.