Binary TDMA scheduler by means of egyptian fractions for real-time WSNs on TMotes

In Wireless Sensor Networks (WSNs), the user should not be bothered with configuring the network, depending on the kind of sensors that he/she is using. It should only be a matter of deploying the sensors and they should do the necessary effort to construct a network. Since most of these networks use low power devices, the energy consumption is vital. The most suited medium access method in order to waste as few energy as possible, is Time Division Multiple Access (TDMA). TDMA has however the reputation of being a rigid access method. In this paper, we present a TDMA access method for passive sensors, i.e. sensors are constant bitrate sources. The presented protocol does not only take into account the energy, but it also ensures that every sensor gets its data on time at the sink and this in a fair fashion. Even more, the latency of the transmission is deterministic. We could say that real-time communication is possible. The protocol is developed keeping in mind the practical limitations of actual hardware by limiting the memory usage and the communication overhead. The schedule that determines which sensor can send when, which can be encoded in a very small footprint, and needs to be sent only once. To prove our statement, we implemented our scheduling protocol on TMotes.