1. INTRODUCTION A robust wireless communication network is the foundation for connected transportation systems. Reliable and seamless vehicle-to-vehicle (V2V) and vehicle-to-infrastructure (V2I) data communication is the critical component of Connected Vehicle Technology (CVT) applications. Though there are several communication technologies/options available, such as Wi-Fi, WiMAX, LTE, and DSRC, not all can support low latency, accuracy, and the reliability of data transmission required for CVT safety applications (RITA, 2015a). While dedicated short-range communication (DSRC) provides low latency, fast network connectivity, highly secure and highspeed communication for safety applications, reliance on DSRC only may prove detrimental to diverse CVT applications. As a result, research efforts for wireless technologies that can enhance V2V and V2I communications for diverse applications have been undertaken. The wireless communication research community has been exploring combinations of DSRC with Wi-Fi, WiMAX and LTE communication technologies to provide a robust next-generation communication network for connected vehicles (Dar et al., 2010). Moreover, it is expected that DSRC roadside units will be installed at key locations such as intersections and interchanges. Thus, the limited coverage of DSRC (approximately 300 meters) and integration of existing Wi-Fi, WiMAX, and LTE network creates a heterogeneous wireless network (Het-Net) for CVT applications. For continuous connectivity, the shift from one communication network to another relies on the successful handoffs between the networks that ensure optimal utilization of available communication options (i.e., eliminate the need of using multiple communication options at the same time) and corresponding backhaul communication infrastructure requirements depending on the connected vehicle application requirements. In this study, the authors investigated the potential of a Het-Net to provide connectivity for V2V and V2I communications with optimal network resource allocation based on the connected vehicle application requirements. The objectives of this research were to evaluate the performance of Het-Net for i) V2I communications for collecting traffic data, and ii) V2V communications for a collision warning application. For field experiments, the authors utilized the Clemson University Wi-Fi network, and the National Science Foundation (NSF) sponsored Science Wireless Network (SciWiNet) infrastructure at Clemson, South Carolina that supports WiMAX, 3G and LTE, and DSRC infrastructure installed in test vehicles and roadsides. SciWiNet project supports a mobile virtual network operator (MVNO) for academic research communities (Martin et al., 2015). In additional, an ns-3 simulation experiment was conducted to evaluate Het-Net performance when there are larger numbers of vehicles within close proximity, and validate field test findings. 2. PREVIOUS STUDIES Various wireless technologies have been used to support the data transfer requirements of diverse intelligent t...

The connected vehicle (CV) system promises unprecedented safety, mobility, environmental, economic, and social benefits, which can be unlocked using the enormous amount of data shared between vehicles and infrastructure (e.g., traffic signals, centers). Real-world CV deployments, including pilot deployments, help solve technical issues and observe potential benefits, both of which support the broader adoption of the CV system. This study focused on the Clemson University Connected Vehicle Testbed (CU-CVT) with the goal of sharing the lessons learned from the CU-CVT deployment. The motivation of this study was to enhance early CV deployments with the objective of depicting the lessons learned from the CU-CVT testbed, which includes unique features to support multiple CV applications running simultaneously. The lessons learned in the CU-CVT testbed are described at three different levels: (i) the development of system architecture and prototyping in a controlled environment, (ii) the deployment of the CU-CVT testbed, and (iii) the validation of the CV application experiments in the CU-CVT. Field experiments with CV applications validated the functionalities needed for running multiple diverse CV applications simultaneously using heterogeneous wireless networking, and meeting real-time and non-real-time application requirements. The unique deployment experiences, related to heterogeneous wireless networks, real-time data aggregation, data dissemination and processing using a broker system, and data archiving with big data management tools, gained from the CU-CVT testbed, could be used to advance CV research and guide public and private agencies for the deployment of CVs in the real world.

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