Adaptive Collision Avoidance through Implicit Acknowledgments in WSNs

The large number of nodes, typical of many sensor network deployments, and the well-known hidden terminal problem make collision avoidance an essential goal for the actual employment of WSN technology. Collision avoidance is traditionally dealt with at the MAC Layer and plenty of different solutions have been proposed, which however have encountered limited diffusion because of their incompatibility with commonly available devices.In this paper we propose an approach to collision avoidance which is designed to work over a standard MAC Layer, namely the IEEE 802.15.4 MAC, and is based on application-controlled delays of packet transmission times. The proposed scheme is simple, decentralized and scalable. We present two variants of the algorithm and we evaluate our work through simulations. Discussed results show that our scheme provides a considerable boost of performance in IEEE 802.15.4 tree-based networks, effectively addressing the hidden terminal problem and keeping radio utilization efficient.