摘要: | 研究期間：10108~10207;Wireless sensor networks (WSNs) with mobile sensor nodes require a scalable, rapid, accurate and low-cost localization scheme to localize the mobile nodes (target nodes). As a WSN node with an embedded omni-directional antenna receives signals emitted from a directional antenna, the received signal strength indication (RSSI) varies with the angle of arrival (AoA) of the received signal. From our preliminary experiments of Maxim AP-12 panel directional antennas, we have the following two observations about the RSSI values of signals which a sensor node receives from a directional antenna. (1) If the distance of the node and the antenna is fixed, RSSI varies like a parabola function of AoA between −90◦ and 90◦ with a symmetry axis at AoA=0◦. (2) If we put two same-type directional antennas with perpendicular orientation at the same position, then the difference of the signal RSSI values which the node receives from the two antennas varies like a linear function of AoA between 0◦ and 90◦. By the preliminary experiment results, we found that it is possible to rapidly determine AoA with a very small average angle error by measuring the RSSI values of perpendicular-orientationed directional antennas. Therefore, we propose a two-year project to design and implement localization schemes to localize mobile sensor nodes in WSNs. In the first year, we plan to design and implement a localization scheme with RSSI differences and AoA values of directional antennas for a target node to estimate AoA and then its position by measuring RSSI value differences of two perpendicular-orientationed directional antennas. The proposed localization scheme consists of two phases: the measuring phase and the localizing phase. In the measuring phase, we measure the RSSI values of signals received from a directional antenna at different distances and angles. For a fixed distance d, we perform regression analysis on the measured RSSI values to obtain two approximation functions: a quadratic function Rd = f(θ) and a linear functions Dd = g(θ), where θ is AoA, Rd is RSSI, and Dd is the RSSI difference of two signals received from two perpendicular directional antennas at the same position. These approximation functions, rather than all measured RSSI values, are then loaded into the limited storage of the sensor nodes to calculate AoA values and sensor node locations. In the localizing phase, two location-known beacon nodes, either of which is equipped with two same-type perpendicular directional antennas, are deployed to transmit beacon signals periodically. By the approximation functions and the RSSI values received from two antennas of one beacon node, a sensor node can roughly estimate the distance d to the beacon node. By the Dd functions and RSSI difference, the sensor node can estimate AoA. With estimated AoA values of two distinct beacon nodes, a sensor node can then calculate its position. In the second year, we plan to extend the result of the first-year project to localize high-speed mobile sensor nodes in a large field. The extended scheme also consists of the measuring phase and the localizing phase. In the extended scheme, target nodes, rather than beacon nodes, transmit signals for the purpose of localization. The beacon nodes are equipped with four directional antennas whose orientations are East, West, South and North, respectively. Once receiving a signal from a target node with the four antennas simultaneously, the beacon node can estimate the AoA and distance corresponding to the target node by the similar method used in the first-year project. The extended scheme suits for localizing high-speed mobile sensor nodes because only one signal is required to estimate the location of the target node. Moreover, the extended scheme can be applied in a large field because the target nodes need not store the approximation functions. In summary, we plan to design and implement, in two years, localization schemes to localize WSN mobile sensor nodes rapidly and accurately. We also plan to compare the proposed schemes with other related schemes comprehensively to demonstrate that our proposed schemes indeed outperform others. |