The Deployment, Dispatch, and Packet-scheduling Issues of Mobile Wireless Sensor Networks

• Main Authors: You-Chiun Wang, 王友群
• Other Authors: Yu-Chee Tseng
• Format: Others
• Language: en_US
• Published: 2006
• Online Access: http://ndltd.ncl.edu.tw/handle/01156060809124690967

博士 === 國立交通大學 === 資訊科學與工程研究所 === 95 === Wireless sensor networks have become one emerging technology that greatly enrich our life. Such a network consists of many tiny, wireless devices that can gather information from the environment and communicate with each other. In this dissertation, we will study the deployment, dispatch, and packet-scheduling issues of a mobile wireless sensor network, in which some or all nodes in the network have a mobile capability. In particular, the deployment issue discusses how to determine the minimum number of sensors and their locations to be placed in the region of interest so that every point in the region can be covered by sensors and the network is connected. The dispatch issue addresses how to efficiently schedule mobile sensors to reach certain locations to perform some missions so that their energies can be conserved as much as possible. After the network is constructed or mobile sensors arrive at their destinations, the packet-scheduling issue considers how to manage the messages reported from sensors so that the delays of important real-time messages can be bounded while other non-real-time messages will not be starved. For the deployment issue, we first propose a general deployment solution that allows the deployed region to be arbitrary-shaped and possibly contain obstacles. Our solution also allows an arbitrary relationship of sensors' communication distances rc and their sensing distances rs, which is ignored by previous works. Our solution first computes the positions to place the least number of sensors according to the condition of deployed region and the relationship of rc and rs. Then we dispatch sensors to these locations under certain constraints of energy consumptions. In this way, our solution can relax the limitations of previous works and is more complete to the deployment problem. In this dissertation, we further investigate how to deploy a sensor network for multi-level coverage, which is an essential assumption required by many applications and protocols in wireless sensor networks. For this deployment problem, we also propose a general solution in which the relationship of rc and rs can be arbitrary. Our solution can use fewer sensors compared with other schemes. In addition, we also propose two distributed dispatch schemes to help deploy sensors. For the dispatch issue, we propose an efficient dispatch method for mobile sensors to visit event locations in a hybrid sensor network. Our dispatch method is general in which the numbers of event locations and mobile sensors can be arbitrary. Our dispatch method can balance the moving distances of mobile sensors while preserve their energies as much as possible during each round of dispatch. In this way, we can maximize the system time for mobile sensors to perform their missions with their limited energies. For the packet-scheduling issue, we propose two wireless packet fair scheduling algorithms, Traffic-Dependent wireless Fair Queuing (TD-FQ) and Multi-Rate wireless Fair Queuing (MR-FQ). TD-FQ takes traffic types of flows into account when scheduling packets. It gives a higher priority for real-time flows to alleviate their queuing delays, but still guarantees the fairness among all flows. MR-FQ considers a more complicated multi-rate environment in which sensors can adopt different modulation techniques to transmit their packets under different channel conditions. MR-FQ adjusts a flow's transmission rate according to the flow's channel condition and its lagging degree, so that both fairness and system performance can be taken care of. In this dissertation, we also implement a mobile sensor platform, called the integrated mobile surveillance and wireless sensor (iMouse) system. The iMouse system integrates the context-aware capability of wireless sensor network into surveillance system so that the real critical information in the environment can be retrieved and immediately send to users. In this way, the overheads of traditional visual surveillance systems can be reduced. We demonstrate the iMouse system with a home/office security scenario in this dissertation.