A Probabilistic Acknowledgment Mechanism for Wireless Sensor Networks

The inherently unreliable communication infrastructure compel WSN protocols to employ error control mechanisms. Traditionally, error control is achieved by a retransmission scheme using acknowledgment mechanisms. WSN architectures are severely resource constrained and the additional energy expense of transmitting error control messages can seriously degrade network lifetime. In this paper, we analyze performance of error control schemes for the case of point-to-multipoint communication. An explicit acknowledgment mechanism may provide for reliable communication, but has two major drawbacks: 1) the over head is significant for small data messages, and 2) in case of asymmetrical communication links, multi-hop dissemination of acknowledgments is required. As an alternative to such explicit acknowledgment schemes we propose the use of probabilistic acknowledgments. In this probabilistic scheme, a sender estimates the probability that a message has been successfully delivered, based on information about the quality of the radio channel. A message is then retransmitted until the probability of successful delivery reaches a defined threshold value. Network capacity available for error control can be distributed prudently among all information items to be disseminated, possibly taking into account different application requirements. We formulate are transmission control strategy which results in minimal latency and maximal message delivery ratio.