Scheduling messages with deadlines in multi-hop real-time sensor networks

Consider a team of robots equipped with sensors that collaborate with one another to achieve a common goal. Sensors on robots produce periodic updates that must be transmitted to other robots and processed in real-time to enable such collaboration. Since the robots communicate with one another over an ad-hoc wireless network, we consider the problem of providing timeliness guarantees for multihop message transmissions in such a network. We derive the effective deadline and the latest start time for per-hop message transmissions from the validity intervals of the sensor data and the constraints imposed by the consuming task at the destination. Our technique schedules messages by carefully exploiting spatial channel reuse for each per-hop transmission to avoid MAC layer collisions, so that deadline misses are minimized. Extensive simulations show the effectiveness of our channel reuse-based SLF (smallest latest-start-time first) technique when compared to a simple per-hop SLF technique, especially at moderate to high channel utilization or when the probability of collisions is high.