  Routing algorithms for wireless sensor networks can be broadly divided into
two classes - proactive and reactive. Proactive routing is suitable for a
network with a fixed topology. On the other hand, reactive routing is more
suitable for a set of mobile nodes where routes are created on demand and there
is not much time to evaluate the worthiness of a route, the prime concern being
reachability due to constantly changing node positions. Sensor networks route
events of interest from source(s) to destination(s) where appropriate actions
could be taken. However, with mobile sensor nodes, it is not only important to
know the events but the location of the nodes generating the events. Most
sensor nodes are not equipped with expensive GPS or accurate RSSI computation
hardware to aid localization. Keeping these in view, we propose a modified
reactive routing algorithm, with added support for localization, to localize
mobile sensor nodes on the basis of information received from fixed sensor
nodes during mutual exchange of routing control packets. The accuracy of
localization depends on the ratio of the number of fixed nodes to the number of
mobile nodes and the topology of the fixed nodes. A typical application
scenario would be a mix of mobile nodes and fixed nodes, where fixed nodes know
their absolute location and the location of mobile nodes is derived from the
fixed nodes, in step with the reactive routing protocol in action. The modified
algorithm would be suitable for deployments where the approximate position of a
mobile node (i.e. the event location) is required but there is no external
support infrastructure available for localization.
