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With the rapid development of the Intelligent Transportation System (ITS), vehicular communication networks have been widely studied in recent years. Dedicated Short Range Communication (DSRC) can provide efficient real-time information exchange among vehicles without the need of pervasive roadside communication infrastructure. Although mobile cellular networks are capable of providing wide coverage for vehicular users, the requirements of services that require stringent realtime safety cannot always be guaranteed by cellular networks. Therefore, the Heterogeneous Vehicular NETwork (HetVNET), which integrates cellular networks with DSRC, is a potential solution for meeting the communication requirements of the ITS. Although there are a plethora of reported studies on either DSRC or cellular networks, joint research of these two areas is still at its infancy. This paper provides a comprehensive survey on recent wireless networks techniques applied to HetVNETs. Firstly, the requirements and use cases of safety and non-safety services are summarized and compared. Consequently, a Het-VNET framework that utilizes a variety of wireless networking techniques is presented, followed by the descriptions of various applications for some typical scenarios. Building such HetVNETs requires a deep understanding of heterogeneity and its associated challenges. Thus, major challenges and solutions that are related to both the Medium Access Control (MAC) and network layers in HetVNETs are studied and discussed in detail. Finally, we outline open issues that help to identify new research directions in HetVNETs. IndexTerms-Vehicle-to-Vehicle (V2V),

OBJECTIVES: Although it is widely believed that China is facing a major shortage of pediatricians, the real situation of the current national status of pediatric human resources and their working conditions has not been evaluated to date. METHODS: We administered a survey to 54 214 hospitals from all 31 provinces in mainland China from 2015 to 2016. Hospital directors of all secondary and tertiary hospitals with pediatric services and a random sample (10%) of primary hospitals provided information on number of pediatricians and their educational levels, specialties, workloads, dropout rates, and other hospital characteristics. A data set of medical resources and socioeconomic information regarding each region (1997–2016) was constructed from the Chinese National Statistics Bureau. The Gini coefficient was used to describe the geographical distributions of pediatricians and hospitals. RESULTS: There were 135 524 pediatricians in China or ∼4 pediatricians per 10 000 children. Pediatricians’ average educational level was low, with ∼32% having only 3 years of junior college training after high school. The distribution of pediatricians was extremely skewed (Gini coefficient 0.61), and the imbalance of highly educated pediatricians was even more skewed (Gini coefficient 0.68). The dropout rate of pediatricians was 12.6%. Despite an increase in the Chinese government’s financial investment in health over the last decade, physicians have been burdened with a greater workload. CONCLUSIONS: Uneven development of the pediatric care system, inadequately trained pediatricians, low job satisfaction, and unmet demand for pediatric care are the major challenges facing China’s pediatric health care system.

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Heterogeneous Vehicular NETworks (HetVNETs) can meet various quality-of-service (QoS) requirements for intelligent transport system (ITS) services by integrating different access networks coherently. However, the current network architecture for HetVNET cannot efficiently deal with the increasing demands of rapidly changing network landscape. Thanks to the centralization and flexibility of the cloud radio access network (Cloud-RAN), soft-defined networking (SDN) can conveniently be applied to support the dynamic nature of future HetVNET functions and various applications while reducing the operating costs. In this paper, we first propose the multi-layer Cloud RAN architecture for implementing the new network, where the multi-domain resources can be exploited as needed for vehicle users. Then, the high-level design of soft-defined HetVNET is presented in detail. Finally, we briefly discuss key challenges and solutions for this new network, corroborating its feasibility in the emerging fifth-generation (5G) era.

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Autonomous driving technology has been regarded as a promising solution to reduce road accidents and traffic congestion, as well as to optimize the usage of fuel and lane. Reliable and high efficient Vehicleto-Vehicle (V2V) and Vehicle-to-Infrastructure (V2I) communications are essential to let commercial autonomous driving vehicles be on the road before 2020. The current paper firstly presents the concept of Heterogeneous Vehicular NETworks (HetVNETs) for autonomous driving, in which an improved protocol stack is proposed to satisfy the communication requirements of not only safety but also non-safety services.We then consider and study in detail several typical scenarios for autonomous driving. In order to tackle the potential challenges raised by the autonomous driving vehicles in HetVNETs, new techniques from transmission to networking are proposed as potential solutions.Index Terms-Autonomous driving, Heterogeneous vehicular networks, Vehicle-to-Vehicle (V2V), Vehicle-to-Infrastructure (V2I).