DGRAM: A Delay Guaranteed Routing and MAC Protocol for Wireless Sensor Networks

This paper presents an integrated MAC and routing protocol called Delay Guaranteed Routing and MAC (DGRAM) for delay-sensitive wireless sensor network (WSN) applications. DGRAM is a TDMA-based protocol designed to provide deterministic delay guarantee in an energy-efficient manner. The design is based on slot reuse to reduce latency of a node in accessing the medium, while ensuring that the medium access is contention-free. The transmission and reception slots of nodes are carefully computed so that data is transported from the source toward the sink while the nodes could sleep at the other times to conserve energy. Thus, routes of data packets are integrated into DGRAM, i.e., there is no need for a separate routing protocol in a DGRAM network. We provide a detailed design of time slot assignment and delay analysis of the protocol. We have simulated DGRAM using ns2 simulator and compared the results with those of FlexiTP, which is another TDMA protocol that claims to provide delay guarantee, and with those of a basic TDMA MAC. Simulation results show that the delay experienced by data packets is always less than the analytical delay bound for which the protocol is designed. Also, the TDMA frame size with DGRAM is always lesser compared to that of FlexiTP, which makes the maximum possible delay much lesser than that of FlexiTP. The average delay experienced by packets and the average total energy spent in the network are much lesser in a network using DGRAM than that using FlexiTP or the basic TDMA MAC.