Distributed Scheduling for Real-Time Convergecast in Wireless Sensor Networks

Wireless sensor networks (WSNs) need to support real time periodic or sporadic queries of physical environments. In this work, we focus on the periodic queries. For each periodic query issued by control applications in a WSN, the data from the source sensors should be collected and/or aggregated to the control center within a certain end-to-end delay. We first propose almost-tight necessary conditions for a set of queries to be schedulable by a WSN. We then develop a family of efficient and effective data collection/aggregation algorithms that can meet the real-time requirement for quality of service (QoS) under resource constraints by addressing three tightly coupled tasks: (1) routing tree construction for data aggregation/collection, (2) link activity scheduling, and (3) packet scheduling at nodes. Our theoretical analysis for the schedulability of these algorithms show that they can achieve a constant fraction of the maximum schedulable load. For the case of overloaded networks where not all queries can be possibly satisfied, we propose an efficient algorithm for query selection that approximately maximizes the total weight of selected schedulable queries. Extensive simulations validating the proposed algorithms corroborate our theoretical analysis.