Geocasting in ad hoc and sensor networks

In a geocasting problem in ad hoc networks, a message is sent from one node to all the nodes located in a designated region. For example, monitoring center needs to contact all active sensors within a monitored area to either gather data from them periodically, or to provide its location to sensors covering certain area for event reporting. Intelligent flooding methods exist for this task when all active sensors belong to the monitored area. However, when a particular area containing only a small subset of active sensors needs to be monitored, the problem reduces to geocasting. This article surveys existing solutions to the geocasting problem, with particular consideration on whether or not they guarantee delivery. Most existing solutions are shown not to guarantee delivery. Three approaches to guarantee delivery are then described. Two of them are face traversal schemes and are based on depth-first search of the face tree and traversal of all faces that intersect the border of geocasting region, respectively. In the entrance zone multicasting based approach, the monitoring center divides entrance ring of geocast region into zones of diameter equal to the transmission radius. The problem is decomposed into multicasting toward centers of each zone, and flooding from these nodes. Improvements to all methods can be made by applying neighbor or area dominating sets and coverage, and converting nodes that are not selected to sleep mode.