Distributed decision fusion with a random-access channel for sensor network applications

The envisioned use of sensor networks for military and civilian applications calls for the deployment of a large number of sensors for extended periods over wide geographical areas. Due to energy and bandwidth constraints, most sensor fields would be "dormant," initiating communication only when a threat is detected. Many architectures under consideration call for compression of locally sensed data into binary "target/no target" decisions. These schemes use a common channel for communication between local detectors (LDs) and the decision fusion center (DFC) that integrates the multiple detector decisions. Unlike most parallel fusion schemes, which use a dedicated communication channel between every LD and the DFC, sensor fields would employ a single shared, time-slotted communication link for all LDs to transmit decisions to the DFC. In this paper, we introduce two window-based methods for managing traffic over this channel. The first allows simultaneous messages to collide. The DFC uses the statistics of the channel states (i.e., the numbers of successful transmissions, idle slots, and collisions during a specified time period) to make its global target/no target decision. The second method uses a simple collision resolution algorithm (CRA), similar to slotted-ALOHA, with dynamically updated retransmission probability. With this scheme, the DFC makes its decision based on data communicated successfully within a specified time window. Overall performance of the two approaches are presented and compared. Simple rules are developed for assessing the conditions under which each one is preferred.