MAC Layer Dynamic Backoff Scheme for Message Delivery Reliability in Wireless Sensor Networks

Abstract

We propose using dynamic backoff on CSMA-type MAC layer protocols to improve message delivery reliability in wireless sensor networks. It is assumed that the MAC layer is able to determine message reliability requirements by reading a reliability data bit embedded within the message. The basic concept is to apply shorter random backoff times to important messages. This gives them the opportunity to test the availability of the communication channel more frequently, enhancing their chance of finding the medium idle. However, this technique might produce the opposite result by allowing the MAC layer to retry sending the important messages in a higher frequency. As a result important messages may reach their maximum retry limit, and get removed from the network. To counteract, we also propose giving the messages a maximum retry limit based on their type. In this setting, important messages will have a higher maximum retry limit. We developed a simulation program to validate our proposed dynamic backoff scheme. The results obtained show that under reasonable network utilization level, the latency is reduced for important messages. Under heavy network utilization conditions, the dynamic backoff scheme drops normal messages leaving the network resources available to handle the delivery of important messages.