Efficient and Robust Geocasting Protocols for Sensor Networks
  Geocasting is the delivery of packets to nodes within a certain geographic area. For many applications in wireless ad hoc and sensor networks, geocasting is an important and frequent communication service. The challenging problem in geocasting is distributing the packets to all the nodes within the geocast region with high probability but with low overhead. According to our study we notice a clear tradeoff between the proportion of nodes in the geocast region that receive the packet and the overhead incurred by the geocast packet especially at low densities and irregular distributions. We present two novel protocols for geocasting that achieve high delivery rate and low overhead by utilizing the local location information of nodes to combine geographic routing mechanisms with region flooding. We show that the first protocol Geographic-Forwarding-Geocast (GFG) has close-to-minimum overhead in dense networks and that the second protocol Geographic-Forwarding-Perimeter-Geocast (GFPG) provides guaranteed delivery without global flooding or global network information even at low densities and with the existence of region gaps or obstacles. An adaptive version of the second protocol (GFPG*) has the desirable property of perfect delivery at all densities and close-to-minimum overhead at high densities. We evaluate our mechanisms and compare them using simulation to other proposed geocasting mechanisms. The results show the significant improvement in delivery rate (up to 63% higher delivery percentage in low density networks) and reduction in overhead (up to 80% reduction) achieved by our mechanisms. We hope for our protocols to become building block mechanisms for dependable sensor network architectures that require robust efficient geocast services. 
Karim Seada, Ahmed Helmy