ACR: Active Collision Recovery in Dense Wireless Sensor Networks

Packet collision causes packet loss and wastes resources in wireless networks. It becomes even worse in dense WSNs, due to burst-traffic and congestion around sinks. In this paper, we propose a novel protocol to recover collided packets. Our experiments on a testbed reveal that collisions between long packets and short packets cause a partial error pattern on collided packets, which can be used for efficient recovery. We give a theoretical analysis that demonstrates that combining such collision recovery with CSMA protocols achieves a significant performance improvement. Then, we design ACR, an Active Collision Recovery protocol, which actively converts most potential collisions into LS-collisions, and then applies a lightweight FEC scheme to recover collided packets with such partial error patterns. We implement ACR on a Tmote testbed, and compare its performance with other packet recovery schemes. Results show that ACR significantly reduces the number of retransmissions, and achieves around 25% improvement on transmission efficiency over other schemes.