The Study of Relay Node Placement and Localization Problems in Wireless Sensor Networks

• Main Authors: Chi-Yu Chang, 張圻毓
• Other Authors: Chi-Chang Chen
• Format: Others
• Language: en_US
• Published: 2014
• Online Access: http://ndltd.ncl.edu.tw/handle/22483516411275875958

博士 === 義守大學 === 資訊工程學系 === 102 === In the thesis, we propose a linear time approximation algorithm for the minimum geometric disk cover (MGDC) problem in wireless sensor networks (WSNs). The proposed algorithm can be applied to the relay node placement problem of wireless sensor networks. Given a set P with n points in the Euclidean plane, the MGDC problem is to identify the smallest set of congruent disks with prescribed radius r that covers all points in P. It is known that the MGDC problem is NP-complete. A novel linear time approximation algorithm for the MGDC problem is proposed, which identifies covering disks using the regular hexagon tessellation of the plane. The approximation ratio of the proposed algorithm is (5+ϵ), where 0<ϵ≤15. Experiment results show that the worst case is rare, and on average, the proposed algorithm uses less than 1.7 times the optimal disks of the MGDC problem. Suppose in a WSN, the deployed relay nodes are homogeneous, and their communication ranges are circles with radius r, the WSN relay node placement problem can be resolved by first solving the MGDC problem and placing the relay nodes at the centers of the covering disks, and then, if necessary, deploying additional relay nodes to meet the connection requirement of relay nodes. For the case that needs to promptly deploy the relay nodes, this study provides a fast 7-approximation algorithm which uses on average less than twice the optimal number of relay nodes in the experiments. For the localization problem of the WSNs, we presents a low-cost yet effective scheme which uses only two anchor nodes and uses bilateration to estimate the coordinates of unknown nodes. Many localization algorithms of WSNs require the installation of extra components, such as a GPS, ultrasonic transceiver, and unidirectional antenna. The proposed localization scheme is range-free (i.e., not demanding any extra devices for the sensors). In this scheme, two anchor nodes are installed at the bottom-left corner (Sink X) and the bottom-right corner (Sink Y) of a square monitored region of the WSN. Sensors are identified with the same minimum hop counts pair to Sink X and Sink Y to form a zone, and the estimated location of each unknown sensor is adjusted according to its relative position in the zone. This study compares the proposed scheme with the well-known DV-Hop method. Simulation results show that the proposed scheme outperforms the DV-Hop method in localization accuracy, communication cost, and computational complexity.