The scarcest resource for most of the wireless sensor networks (WSNs) is energy and the major factor in energy consumption for WSNs is communication. Not only transmission, but also reception is the source of energy consumption. The lore to decrease energy consumption is to turn off the radio circuit when it is not needed. This is why TDMA is advantageous over contention based methods. A time slot assignment algorithm is an essential part of TDMA based systems. Although centralized time slot assignment protocols are preferred in many WSNs, a centralized approach is not scalable. In this article, a new energy efficient, delay sensitive, and fault tolerant distributed time slot assignment algorithm, referred to as ft_DTSM, is proposed for sensor networks under convergecast traffic pattern. ft_DTSM aims at operating with low delay and low energy under faulty nodes assumption. Instead of random access based periods, it assigns slots with the help of tiny request slots. While traditional slot assignment algorithms do not allow assigning the same slot within two hop neighbors, because of the hidden node problem, ft_DTSM can assign, if the assignment is suitable for convergecast traffic. Simulation results have shown that both delay and energy consumption performances of ft_DTSM is superior to existing distributed slot assignment protocols for WSNs. ft_DTSM can also distribute the slots so that the network can continue its operation against a single point of failure. Although ft_DTSM has a somewhat longer execution time, its scalability characteristic may provide application specific time durations.
An optimal fixed-priority assignment algorithm for supporting fault-tolerant hard real-time systems
