SPEED design is guided by the key observation that unlike wired networks, where the delay is independent of the physical distance between the source and destination, in multi-hop wireless sensor networks, the end-to-end delay depends on not only single hop delay, but also on the distance a packet travels. In view of this, the key design goal of the SPEED algorithm is to support a soft real-time communication service with a desired delivery speed across the sensor network, so that end-to-end delay is proportional to the distance between the source and destination.
SPEED Architecture
SPEED is an adaptive real-time routing protocol that aims to reduce the end-to-end deadline miss ratio in sensor networks. Similar to geographic routing, each node only maintains the states of one-hop neighbors. The core of SPEED is feedback-based adaptation algorithms that enforce per-hop speed in face of unpredictable traffic. The first adaptation mechanism is a neighborhood feedback loop on each node that periodically computes the probability of forwarding a packet to every neighbor based on its measured delay and per-hop speed violation in the last sampling period. The feedback loop ensures that more congested neighbors (with longer delays and higher miss ratios) get lower probabilities of receiving packets. When all of its neighbors have deadline misses in the last sampling period, a node performance rate control to drops packets. The packet-drops subsequently cause upstream neighbors to redirect packets away from it, a process called back pressure rerouting. The back pressure can propagate upstream until it reaches outside the congestion region or the sources. The combination of neighborhood feedback loop and back pressure rerouting significantly enforces the per-hop deadline in steady states and reduces the end-to-end deadline miss ratio.
feedback-based adaptation controller
Simulation experiments given in showed that SPEED can achieve significantly lower deadline miss ratio than geographic routing, DSR, and AODV in face of sudden congestion. Meanwhile, SPEED's number of overhead packets is comparable to geographic routing and significantly smaller than DSR and AODV. SPEED demonstrates that localized feedback control is a promising approach for real-time communication in sensor networks. Remaining challenges in this direction include establishing stability analysis and providing statistical guarantees on end-to-end delays.
For more detail see PDF
กก
กก