Routing in Duty-Cycled Surveillance Sensor Networks

Abstract

In many surveillance sensor networks, sensors are scheduled to work in a duty-cycled mode (i.e., periodically switching between active states and sleeping states) in order to prolong the network lifetime. The duty-cycled mode saves sensors' energy but brings other issues. In surveillance applications (e.g., forest fire alarm or intruder detection), it is desired to report detected events to the sink node as soon as possible. However, the duty-cycled mode may increase the data delivery latency. In this paper, we study minimum-delay routing in duty-cycled surveillance sensor networks. As the minimum-delay routes are time dependent (i.e., they change with time) in duty-cycled sensor networks, routing becomes a challenging task. We propose a distributed routing algorithm to find the minimum-delay routes at any time from all nodes to the sink node. Further, all minimum-delay routes can be found in one execution of our routing algorithm. We further provide a distributed route maintenance algorithm for finding the minimum-delay routes when the network dynamically changes. We theoretically prove the correctness of the proposed algorithm, and extensive simulation results show that the performance of our algorithm outperforms other existing algorithms. IntroductionWireless sensor networks (WSNs) have been used in many surveillance applications such as traffic monitoring, forest fire detection, and target tracking. Typically, in surveillance system, sensors (or nodes) detect events and then report the events to the base station (or the sink node). To build longterm operating surveillance systems, sensors are expected to work for months or even years, but they only have limited battery energy. For example, the battery of a sensor can only last for a few days if running continuously. One viable technique is to schedule sensors switching between active mode and sleeping mode, while active sensors perform surveillance tasks. Energy-efficient scheduling algorithms [1][2][3][4][5][6][7] are proposed in the literature to prolong network lifetime, as well as to guarantee event detection. In these algorithms, sensors are scheduled to be active for a period of time and then to sleep for another period of time, which forms a duty-cycled WSN.As pointed out by [8], the effectiveness of a surveillance system lies in two aspects: accurately detecting events and timely reporting the events. The second aspect is highly related to routing problem. Routing in WSNs has been extensively studied and many routing algorithms or protocols are proposed. The research on routing evolves from early flooding-based protocols to location-based routing protocols (with the help of localization methods [9,10]) and to stateof-the-art gradient-based routing protocols [11]. Collection tree protocol (CTP) [12] and routing protocol for low-power and lossy networks (RPL) [13] are two well-known gradientbased routing protocols. CTP uses expected transmissions (ETX) as the gradient that indicates the expected number of transmissions needed for the packet to reach t...