Routing in Mobile Wireless Sensor Networks

In this report we have considered the problem of routing in wireless sensor networks (WSNs) with mobile sinks. The introduction of non-static data collectors has been shown to bring contrasting effects on the design of networking protocols: on one hand mobile sinks can be exploited to increase network capacity and connectivity at the expense of a higher delay; on the other hand, if delivery latency is a major constraint, routing algorithms that are usually employed in WSNs incur significant performance losses. Starting from these remarks, two classes of solutions, network centric and sink centric ones, have been analyzed.

The basic principle of network centric approaches is to take advantage of the mobility of some nodes in order to simplify the routing procedures. A sensor node tends to send data only to mobile units (either the sink itself or any other mobile terminal) that are close to it. If the desired destination is in the proximity of a source, a single hop communication is sufficient to deliver the payload. Otherwise, a source node transmits its data to a close-by mobile user. Such a mobile node stores the received information until its trajectory brings it in the proximity of the final destination, and then delivers the payload. In both cases, only one hop communications take place in the network and no routing algorithm is required. The use of such routes significantly reduces interference and overhead, leading to important gains in terms of network capacity.

Sink centric solutions are addressed to scenarios that do not tolerate high delivery delays. They divide routing into two phases: first, data generated at a source are forwarded inside the static WSN towards a sensor node close to the mobile sink; once this has been accomplished, a local routing procedure to the final destination takes place. Here efficient forwarding procedures or geographic routing can be exploited. Moreover, the paths from the edge of the WSN (i.e., the destination of the routing phase within the static network) to the sink are composed of few hops, and therefore mobility can be handled more easily. These benefits come at the expense of the procedures required to efficiently identify and maintain routes to a node in the WSN that is close to the final destination. Sink centric solutions can be significantly improved if the mobile sink is able to predict its trajectory because if the information is spread in the network, data can be routed much more precisely towards the exact location of the destination.

An integration of network and sink centric solutions may be interesting and beneficial, in particular in scenarios with multiple mobile nodes and with reliable trajectory prediction models. Mobile units could be used to physically forward information towards the region where the sink is located, reducing the multihop induced overhead while limiting delivery latency.

By: Andrea Munari and Wolfgang Schott

Published in: RZ3707 in 2008


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