The Research Of Wireless Sensor Network Protocol For Urban Transportation

Characterized by flexible networking, strong environment adaptability, low power consumption and low cost, etc., wireless sensor networks has become the supporting technology of intelligent transportation systems. Communication protocols play the core role of wireless sensor networks. According to many wireless network protocols with greatly different performance, wireless sensor network protocol for urban transportation system is surveyed in this paper by considering the feature of urban transportation scenarios. The main research in this paper includes evaluation of avaliability and improvement of protocols.Firstly, the major protocols are evaluated from the aspects of reliability, lantency, mobility supporting, etc. The communication condition of urban scenarios is the major consideration in this performance comparision. Secondly, by researching the IEEE 802.15.4 standard, a reliable vehicle recognition method based on dense RSUs and an adaptive data rate changing scheme based on node number are proposed as the fundamental applications of urban transportation system. With the modification of message interaction procedure between OBU and RSU, OBU could exchange its identification information with multi-RSU in shorter interval, so that high recognition rate is achieved as compared with IEEE 802.15.4 protocol. Then, based on the analytical models of throughput and delivery reliability of IEEE 802.15.4 specified MAC mechanism, the adaptive data rate scheme is developed by changing the data rate with the node number in the PAN, so as to optimize the communication performance in both typical scenarios such as peak hours and normal traffic. Experiments show that the proposed methods can significantly improve the performance of IEEE 802.15.4 protocol in urban transportation system.This paper is organized as follows. Chapter 1 presents the research efforts of wireless sensor network protocols for urban transportation systems which have already been made. The typical application scenarios for urban transportation system are described and the comparison of wireless sensor network protocols is included in Chapter 2. Characteristics of application situations are considered and theoretical analysis and simulations are provided for the performance comparison of protocols. Chapter 3 introduces the IEEE 802.15.4 standard, including the association procedure, scan process and CSMA-CA mechanism. The optimization and improvementation suggestions are also provided based on the IEEE 802.15.4 specifications and the features of urban transportation scenarios. The proposed reliable vehicle recognition method is showed in Chapter 4. The basic ideas, communication interactions and algorithms of this recognition method are offered. Besides, simulations and experiments are presented for performance evaluation. An adaptive data rate scheme for ZigBee is detailed in Chapter 5. The communication performance optimization in both typical scenarios of peak hours and normal traffic are mainly surveyed. By analysis of CSMA-CA model, the data rate adaptively changes according to the current node number of PAN, so as to realize the comprehensive optimization of throughput and reliability. Chapter 6 is the summary and the prospects.