|We present a new approach, the GeoQuorums approach, for implementing atomic read/write shared memory
in mobile ad hoc networks. Our approach is based on associating abstract atomic objects with certain geographic
locations. We assume the existence of focal points, geographic areas that are normally “populated” by mobile nodes.
For example, a focal point may be a road junction, a scenic observation point, or a water resource in the desert. Mobile
nodes that happen to populate a focal point participate in implementing a shared atomic object, using a replicated state
machine approach. These objects, which we call focal point objects, are then used to implement atomic read/write
operations on a virtual shared object, using our new GeoQuorums algorithm. The GeoQuorums algorithm uses a
quorum-based strategy in which each each quorum consists of a set of focal point objects. The quorums are used to
maintain the consistency of the shared memory and to tolerate limited failures of the focal point objects, caused by
depopulation of the corresponding geographic areas. We present a mechanism for changing the set of quorums on
the fly, thus improving efficiency. Overall, the new GeoQuorums algorithm efficiently implements read and write
operations in a highly dynamic, mobile network.