Mobility-assisted resolution of queries in large-scale mobile sensor networks (MARQ)

One of the most crucial aspects of the design of sensor networks is provisioning of efficient query resolution and resource discovery. In many cases sensor networks are expected to be large-scale (i.e., consist of potentially thousands of nodes), and in some cases these sensors maybe installed on moving objects, rendering the query resolution problem even more challenging. Flooding techniques, including global flooding or expanding ring search techniques, may be very inefficient in large-scale networks, especially in wireless (spatial) networks where the diameter of the network maybe quite high. More so is the case when queries are one-shot and frequent. In this study, a novel architecture is presented for query resolution in large-scale mobile sensor networks. A salient feature of our architecture is that it takes advantage of mobility to increase the efficiency of query resolution. The architecture borrows from the concept of small worlds and introduces the concept of contacts that act as short cuts to reduce the degrees of separation between the sources of the query and the targeted objects. Contacts are initially chosen from nearby neighbors, as they move away they discover new neighbors and hence become more effective in query resolution. Unlike approaches for routing protocols, route or delay optimization is not the primary design goal of our architecture, but reducing communication overhead is. This is especially true in energyconstraint environments, as are many sensor networks, particularly for one-shot queries, where no path is established to be used for further communication. We design our protocol to be scalable, self-configuring, and highly adaptive to mobility. In fact, it utilizes mobility. We evaluate our protocol through extensive simulations and present a detailed analysis of its performance. We further compare our approach to other query resolution protocols. Our results clearly indicate the drastic improvement obtained by using contacts, especially in high mobility scenarios. For non-replicated objects, we obtain 60-70% improvement over edge-of-zone flooding, 80-90% improvement in communication overhead over flooding, and even greater improvements over expanding ring search approaches. Our protocol responds extremely well to replication, as the number of transmitted packets per query drops significantly.