Why collisions happen: A pathology of CSMA for wireless sensor networks in high contention

Contention is highly prevalent in wireless sensor network applications, especially those where the measured physical phenomenon is triggered by spatially and temporally co-located events, such as in distributed acoustic localisation. As a fundamental performance aspect, characterising and understanding the impact of contention on the packet reception rate is an important step towards building robust real-world communication protocols. As a step forward, based on measurements taken with CC2420-equipped iMote2 nodes, this paper empirically identifies two areas of packet reception with contrasting link characteristics in relation to the contention level. It also reveals the “deaf node problem”, which causes conflicting carrier sense results and can thereby lead to packet collisions, even in optimal topologies.