Optimal candidate set for opportunistic routing in asynchronous wireless sensor networks

In asynchronous wireless sensor networks, finding an optimal candidate set can significantly improve the efficiency of an opportunistic routing protocol by balancing the one-hop cost from a sender to a relay and the remaining cost from the relay to the sink. A larger candidate set indicates smaller one-hop waiting cost to wait for a candidate to wake up, however, a packet is more likely to deviate from the shortest path, which will induce larger remaining cost. Remaining cost of each candidate can be used to construct a coordinate system. Neighbors of a node with high coordinate value is excluded from the candidate set, thus, we can select the next-hop relay by simply taking the first wake-up candidate. In this paper, we propose a distributed algorithm which is similar to the Bellman-Ford algorithm to construct a coordinate system and find an optimal candidate set for each node. Moreover, we propose an algorithm which induces acceptable overhead to maintain the coordinate system and each node's optimal candidate set. We also use simulation results to show that our proposed opportunistic routing protocol is more efficient than conventional strategies in terms of delay, energy efficiency, and miss ratio.