Real-Time Data Aggregation for Contention-Based Sensor Networks in Cyber-Physical Systems

Abstract

Wireless sensor network plays an important role in information collection and data gathering in cyber-physical systems. We study real-time data aggregation problem for wireless sensor networks that use CSMA/CA MAC layer protocols. The problem is, for a given sink, a set of sensor nodes and a delay bound, to maximize the average transmission success probability of all sensor nodes within the delay bound. In CSMA/CA protocols, the success probability and the expected transmission delay are highly sensitive to node interference, and the node interference is often very high in the large scale cyber-physical systems. We divide the system time into time-frames with fixed size and schedule the transmission of nodes into time-frames. The size of time-frame is much larger than the time-slot in pure TDMA protocols. The transmissions of all child nodes under the same parent are scheduled in the same time-frame and they compete the channel access in CSMA/CA fashion. In this system model, the construction of data aggregation trees becomes very important in maximizing the success probability of data collection. We solve the joint routing and scheduling problem by first constructing an aggregation tree that minimizes the node interference. Then, we propose an efficient greedy scheduling method to assign time-frames to sensor nodes. Extensive simulations have been done and the results show that our proposed method can improve the success probability significantly.