Mobile nodes path design and deployment for data collection in wireless sensor networks

Abstract

Recent years have seen the deployments of wireless sensor networks (WSNs) in data-intensive applications. WSNs in these applications often produce high-bandwidth sensor data that need to be collected under stringent delay constraints. On the other hand, sensors in such applications must operate on limited power supplies like batteries for extended lifetime up to years. Therefore, a fundamental challenge for these WSNs is to support Time-sensitive data collection with minimum network energy consumption. Motivated by these factors, we introduce mobile nodes (MNs) for collecting high-bandwidth data which can greatly save the energy of sensor nodes since the energy consumption of mobile nodes is less constrained as they can replenish their energy supplies because of the mobility. The major work of this thesis can be summarized as follows. First, we introduce mobile elements (MEs) to collect data to the base station (BS). A subset of nodes serve as the rendezvous points (RPs) that buffer data originated from sources and transfer to MEs when they arrive, which can achieve a desirable balance between network energy saving and data collection delay. We prove that the optimal schedule problem is NP-hard and develop two rendezvous planning algorithms: RP-CP and RP-UG. RP-CP finds the optimal RPs when MEs move along the data routing tree, while RP-UG greedily chooses the RPs with maximum energy saving to travel distance ratios. Our approach is validated through extensive simulations. Second, some urgent data may need to be sent to the BS through a routing tree before the arriving of MEs, but the nodes on this tree may consume much more energy, which is a bottleneck for the whole network. Our solution is to make some mobile nodes (MNs) to "cover" the routing paths for forwarding data originally transferred by sensors. We study two MN deployment problems that aim to maximize the MN coverage and to minimize the MN deployment cost, respectively. Both problems are proved to be NP-hard and we design optimal solution and approximation algorithm with provable bounds. The effectiveness of our algorithm is validated through both theoretical analysis and simulations. Third, we investigate the issue of data collection when the base station itself is mobile. A rendezvous-based data collection approach is proposed and we jointly optimize data routing paths and the BS tour. Furthermore, data aggregation model is considered. We propose efficient rendezvous design algorithms with provable performance bounds for mobile base stations with both variable and fixed tracks, respectively. The effectiveness of our approach is validated through both theoretical analysis and extensive simulations. Finally, when mobile base stations are used to collect data, they are required to inform sensor nodes about their new location information since the urgent data can be sent to BSs directly through routing methods. However, frequent location updates from mobile BSs may lead to both rapid energy consumption of sensor nodes and increased collisions in wireless transmissions. We propose a new solution with adaptive location updates for mobile BSs to resolve this problem. When a BS moves, it only needs to broadcast its location information within a local area other than among the entire network. In this way, lots of energy can be saved. Both theoretical analysis and simulation studies show that this solution consumes less energy.

Date of Award	3 Oct 2011
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Wei Jia JIA (Supervisor)