Robust QoS Control of DSRC Vehicle Networks for Collaborative Road Safety Applications

道路交通安全一直是全世界关注的问题。每年全国因交通事故造成的损失非常高。在过去十年中，在道路安全系统方面作出了广泛的努力，以主动预防事故或被动地减少事故的后果。随着无线通信和移动自组织网络的发展，由车辆通信实现的所谓协同安全应用（CSA）被广泛认为是未来道路安全的关键。配备了车辆间通信（IVC）和GPS，车辆可以帮助驾驶员识别无法由驾驶员或本地传感器单独检测到的事件。例如，在高速公路上抛锚的车辆可以使用IVC向后面的车辆通报紧急情况，避免可能发生的碰撞。除了安全方面的应用外，车辆网络也可应用多种非安全方面的应用，例如有效的路线规划，以减少燃油消耗和碳排放。专用短距离通信（DSRC）是IVC的主要技术。它被认为是唯一能够提供一个强大的媒介和负担得起的技术，足以建立大规模的CSA。小型现场试验验证了DSRC用于CSA的通信能力。然而，除非大部分车辆配备了IVC，否则CSA将不会有效。如何在DSRC车辆网络上提供高效、稳健的QoS支持是大规模CSA成功的关键问题。原因是CSA生成的安全消息在吞吐量、可靠性和延迟方面都有非常严格的QoS要求。过度的延迟和消息丢失可能使正确的CSA操作无效，甚至产生意想不到的负面后果。然而，为CSA提供有效和健壮的QoS支持是非常具有挑战性的。现有的CSA研究工作主要集中在通过现场测试或仿真方法从较低层（物理层和MAC层）进行DSRC的可行性研究，而对支持CSA QoS的DSRC网络的有效QoS控制尚未进行研究。DSRC在较低层提供的功能与大规模CSA所需的QoS支持之间存在很大差距。本项目旨在开发鲁棒且带宽高效的DSRC QoS控制方案，为大规模的CSA提供QoS支持，这对实际的CSA部署至关重要。我们将把工作重点放在两项密切相关的任务上：(a)开发最先进的离线分析和优化工具，以支持大规模云计算服务和服务规划目的。这里脱机是指可用于QoS控制决策的全局网络知识。这些工具将基于马尔可夫链、排队论和注水法进行开发；(b)开发新颖的在线鲁棒和带宽高效的拥塞控制方案，以提供QoS支持，其中通过跨层交互、反馈和车辆合作共同控制发射功率和消息速率。在线QoS控制只有局部知识可用。在任务(a)中获得的对QoS支持的见解将提供给任务(b)中的在线控制方案设计。提出的研究是新颖的，并建立在调查员和他的研究小组在网络性能建模，网络协议设计和优化领域的专业知识。据我们所知，提出的工作是同类中第一个关于DSRC网络的鲁棒拥塞控制和QoS支持的工作。本研究的启示有望在理论和应用方面直接为DSRC网络QoS支持做出贡献，最终为实现安全、环保、舒适的驾驶做出贡献。

Road traffic safety has been a subject of worldwide concern. The annual national lost due to road accidents is tremendously high. During the last decade extensive efforts have been made on road safety systems to actively prevent accidents or passively minimize the consequences of accidents. With the advances in wireless communications and mobile ad hoc networking, the so-called collaborative safety applications (CSA) enabled by vehicular communications is widely regarded as a key to future road safety [19]. Equipped with inter-vehicle communication (IVC) and GPS, vehicles can assist drivers to recognize events that can not be detected by the drivers or local sensors alone. For example, a vehicle broken in highway can use IVC to inform the following vehicles the emergency event and avoid possible collisions. Apart from safety applications, a wide range of non-safety applications can also be deployed over vehicle networks, e.g. efficient route planning to reduce fuel consumption and carbon emission. Dedicated short range communications (DSRC) is a leading technique for IVC. It is regarded as the only technology able to provide a robust medium and affordable enough to build large scale CSA. Small scale field tests have demonstrated the communication capabilities of DSRC for CSA. However, CSA will not be effective unless a large proportion of vehicles are equipped with IVC. For the success of large scale CSA a critical issue is how to provide efficient and robust QoS support over DSRC vehicle networks. The reason is that safety messages generated by CSA have very strict QoS requirements in terms of throughput, reliability and delay. Excessive delay and message losses can nullify proper CSA operations and even produce negative unanticipated consequences. However providing effective and robust QoS support for CSA is very challenging. Existing research work on CSA has been primarily focused on the feasibility study of DSRC from the lower layers (physical and MAC layers) by field test or simulation approaches, while efficient QoS control of DSRC networks for CSA QoS support has not been studied. There is a big gap between the capabilities provided by DSRC at the lower layers and QoS support required by large scale CSA. This project aims to develop solutions for robust and bandwidth-efficient DSRC QoS control schemes to provide QoS support for large scale CSA, which is of utmost importance to practical CSA deployment. We will focus our work on two closely related tasks: (a) development of state of the art offline analytical and optimization tools for QoS support of large scale CSA and service planning purposes. Here offline means global network knowledge available for QoS control decisions. The tools will be developed based on Markov chain, queuing theory and water-filling method; and (b) development of novel online robust and bandwidth efficient congestion control schemes to provide QoS support, where transmit power and message rate are jointly controlled with cross-layer interaction, feedback and vehicle cooperation. Only localized knowledge is available for online QoS control. The insights into QoS support obtained in task (a) will be feed into the online control scheme design in task (b). The proposed research is novel and built upon the expertise of the investigator and his research group in the field of network performance modeling, network protocols design and optimization. To the best of our knowledge, the proposed work is the first of its kind on the robust congestion control and QoS support of DSRC networks. The implications of this research are expected to contribute directly to DSRC network QoS support in both theory and applications sides, which will eventually contribute to realize safe, environment friendly and comfortable driving.