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

Abstract

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.

Analysis of TDMA scheduling by means of Egyptian Fractions for real-time WSNs

“…Furthermore, this article analyzes in detail the theoretical real-time behavior of our protocol and deduces a formula that predicts the latency that can be expected. The measurements in [1] verify whether this formula also applies when using a practical implementation.…”

“…Therefore, the protocol can be combined with several TDMA MACs. In [1], we provided an example implementation, based upon a tree topology, where we first let the sensors synchronize to each other. Afterwards, the new sensor needs to announce its required bandwidth by sending an identification packet to its parent, which it forwards to the sink.…”

“…To prove the previous statement, an actual implementation of the protocol on Tmotes was described in our previous paper [1]. It describes superficially the protocol itself, and is more focused on an actual implementation of the protocol than the analysis of the operation of the protocol.…”