Image Processing Reference
In-Depth Information
7.1 General Remarks on Routing in Wireless Sensor Networks
A wireless sensor network (WSN) is a collection of nodes organized into a cooperative network,
typically operating in an unattended environment. Each node is equipped with a processing element,
a radio-frequency transceiver (usually with a single omnidirectional antenna), a number of sensors
andactuators,memories(data,program,andlash),andapowersource.Sincethenodesareequipped
with small, often irreplaceable, batteries with limited capacity, it is crucial that the network be energy-
efficient in order to maximize its lifetime.
The nodes in a WSN are also capable of performing other functions such as data processing and
routing.
Routing in WSNs is quite different from traditional routing in wired networks. Table . sum-
marizes the main differences between WSNs and traditional distributed systems relying on wired
connections, while Table . shows the factors which make the difference between routing in WSNs
and traditional routing on the Internet.
Very simple approaches to relaying data in WSNs are Flooding and Gossiping [Hed]. In looding,
each packet received by a sensor node is broadcast to all its neighbors, until the destination is reached.
With a similar approach, if a path between the source and destination nodes exists, it will be found.
However, as a large number of duplicate packets will be generated, a maximum hop count is needed
in order to prevent infinite loops.
he Gossiping protocol works by selecting a random neighbor (other than the source of the incom-
ing packet) at every hop, until the packet reaches its destination. Both Flooding and Gossiping are
easy to implement, as they do not require topology information. However, these mechanisms have a
few major drawbacks. One negative aspect is that they suffer from the well-known problem of data
overlap between nodes belonging to the same area (as sensor nodes often cover overlapping areas,
sensed data also overlaps). In addition, flooding algorithms also suffer from the implosion problem,
which occurs when multiple nodes send the same data to the same destination node. he Gossiping
protocol avoids the problem of implosion, but can cause very large end-to-end delays in data delivery,
especially with large networks. Finally, the major drawback of both approaches is that they do not
take power consumption into account.
TABLE .
Features Which Make WSNs Very Different from
Traditional Distributed Systems
Distributed Systems
WSNs
Wired
Wireless
Reliable connections
Error-prone connections (depending
on the link quality, signal strength,
noise, interference, atmospheric
conditions, etc.)
Symmetric links
Asymmetric links
Unlimited power
Scarce power
Generally not real-time
Typically real-time
Each individual node is important
Aggregate behavior counts
Location-independent
Location-dependent
Resources not an issue
Resource-limited
TABLE .
Factors Which Make the Difference between WSN
Routing and Traditional Internet Routing
Variable Link Properties
Traffic patterns
Routing decisions usually based on geographic coordinates and/or data seman-
tics, instead of node IDs
Unicast, area multicast or anycast semantics
Node sleep/wakeup for power management
Voids on the routing path
