The vehicular ad hoc network is one of the key enabling components in Intelligent Transportation Systems that has been developed for safe and smooth driving without excessive delays. A major hurdle in the development of the networks for time-dependent safety-critical services is the lack of established models and metrics. These enable one to determine the effectiveness of the network design mechanisms for predictable quality of service, and allow the evaluation of the tradeoff between network parameters.
This collaborative research project between Oral Roberts University and Duke University analyzes and suggests enhancements of safety-critical services in vehicular ad hoc networks. Several key issues are investigated in the project. First, the project develops stochastic modeling techniques to address some open problems, such as hidden terminal issues and rebroadcast coverage problems in two-dimensional broadcast vehicular networks under typical traffic scenarios. Second, new analytical models are developed for time-dependent analysis of time-critical safety services. Consequently, performance, reliability, and survivability metrics for the safety services are defined and analyzed. Third, new solutions to assure reliable delivery of emergency messages and novel analytical model based cross-layer protocols are designed and studied. Broad impact of the work is that the outcome of this research is deemed to be beneficial to the design and analysis of general mobile ad hoc networks for critical missions. This project creates new collaborative opportunities with the industry. Both graduate and under-graduate level courses are developed to integrate the scientific findings of the project with current teaching activities at the two universities.
Vehicle to vehicle communication will soon be common place in order to enhance safety of road traffic. Communication network used for this purpose thus needs to be highly reliable. This NSF project concentrated on the analysis and enhancement of Dedicated Short Range Communication (DSRC) based vehicular ad hoc networks (VANET) for safety-critical applications. A major hurdle in the development of VANET for time-dependent safety-critical services in the DSRC system is the lack of established models and metrics that enable one to determine the effectiveness of VANET design mechanisms for predictable quality of service and allow one to evaluate the tradeoff between network parameters. So far, there has been no practical MAC protocol and channel design suited for vehicle safety messaging in the DSRC system, with predictable quality of service (QoS) guarantees. This collaborative research project has investigated and made contributions to several key issues of VANET for safety-critical applications: (1) Definition of new QoS metrics in both MAC level and Application level New metrics of performance and reliability in both MAC level and Application level have been introduced and defined to reflect QoS requirements of individual safety applications so that current DSRC system settings or new protocols can be evaluated and designed in a more objective way. The new metrics include: 1) MAC level packet delivery probability (transmitter centric reliability index), packet delivery ratio (receiver centric reliability index), packet reception ratio, packet transmission delay, channel throughput, and the effective range, 2) application level reliability and application-level delay. (2) Development of cost-effective and accurate stochastic modeling techniques to compute the designed metrics to characterize dynamic behavior of VANET safety-critical services under practical DSRC environments and traffic scenarios. Novel analytical and simulation models are proposed to characterize dissemination of both the periodic beacon safety messages (BSM) and event-driven safety messages (ESM) in DSRC multi-channel based VANET on highway, rural roads and urban intersections. Consequently, various performance and reliability metrics are evaluated and significant observations are made. (3) Development of effective and robust solutions to enhance reliability of emergency message broadcast Effective solutions to the design of the control channel in DSRC with three levels of safety-related broadcast services that are critical to most safety applications are proposed, which include 1) a priority scheme for three levels of safety services; 2) a dynamic new application-level receiver-oriented (AROR) repetition scheme for reliable one-hop emergency message broadcast 3) a robust relay selection scheme for multi-hop propagation of emergency notification messages; 4) suppression of hidden terminals via long range multi-frequency busy tone. Consequently, a systematic protocol for VANET safety-related services is proposed. As a result of the work in this project, 24 papers (9 journal papers, 15 peer-reviewed conference papers) are published. A complete NS2 based simulation platform is built for VANET on highway, intersections on rural roads, and urban intersections. Intellectual Merit: This project has addressed some open problems in analytical models such as solutions to two-dimensional broadcast hidden terminal problem (or rebroadcast coverage problem), the performance and reliability of safety-related message broadcast in vehicular ad hoc networks (VANETs) at intersections with non-homogeneous Poisson process (NHPP) for node distribution, accurate performance evaluation of DSRC BSM communication with multi-channel schemes and periodic packet generation and out-dated information replacement, and derivation in k-dimensional broadcast ad hoc networks in the presence of channel fading with path loss. The project also concludes that the current IEEE 802.11p fails to meet QoS requirements of some critical safety applications under some situations and provided solutions to the issues. The outcome of the project will speed up development and dissemination of next-generation cars equipped with ad hoc wireless network capability. Broader Impact: The following activities were conducted to promote diversity and broad dissemination of the results produced: (1) The project created new collaborative opportunities and stronger ties with GM. The project sent a graduate student as a summer intern for three months at a GM site in Palo Alto, California. Both PIs visited the GM office discussing with engineers to elaborate the research plan. (2) The project created new research opportunities for undergraduate students and graduate students at both universities. The project has supported one Ph.D student at Duke and 13 undergraduate students at Oral Roberts University (ORU). The research team includes 5 women and 6 under-represented students. (3) The project has supported a wireless laboratory in the College of Engineering and Science at ORU. (4) Both PIs gave many invited talks related to the project in US, and other countries. Dr. Ma proposed a special issue on "Reliable and secure VANETs" in IEEE Trans. on Dependable and Secure Computing and served as one of three Guest Editors. (5) Research results from this project have been exposed to high-school students through participation in the annual engineering summer academy event hosted at ORU.
