# Connected Vehicles: Technology Review, State of the Art, Challenges and Opportunities
## 1 Introduction
This is followed by the European market, which comes second in place but is soon expected to be surpassed by the fast-growing CV market of Asia Pacific by the end of 2027. These are followed by the Middle East, Africa, and Central and South America. The CV global market is an increasingly highly competitive market due to industrial contributions and fast paced dominance by major market players, such as General Motors (GM), Volkswagen, Google, Tesla, Volvo, Mercedes, Bosch, IBM, Intel, Qualcomm, Huawei, and Vodafone [7]. Statistics and forecasting values reflect CVs' promising future. IHS Markit predicts an expected worldwide sale of 72.5 million sold units by 2023. According to Statista [8], the revenue in the connected cars segment amounted to USD 21,811 million in 2019. Hence, they predicted an overall market growth from USD 46 billion to USD 140 billion. Moreover, based on the Juniper report [9], CVs are expected to reach around USD 775 million in the year 2023. Everyday technological advancements bring CVs one step closer with enabling technologies and widespread adoption. We have noticed a growing interest from all stakeholders to make CVs a reality. Therefore, in recent years, CVs have attracted researchers to explore the enabling technologies, challenges, opportunities and to study the different aspects of the CV technologies. [PERSON] et al. [10] conduct a focused review on the potential challenges and alternatives to achieve robust and reliable wireless communication technologies that enable V2X connectivity. The authors discuss the challenges that arise based on wired technologies for intra-vehicle communication, lower-layer-level (physical and medium access control) issues of dedicated short range protocols and Internet connectivity for inter-vehicle communication. [PERSON] et al. [11] investigate the design aspects of CV technologies and applications and review outstanding challenges in terms of privacy, scala bility, and extensibility. The authors in [12] provide a precise overview on the features and functionalities of CV services along with the hardware and software technical challenges. In [13], the authors discuss the need for viable safety-based verification systems and point out the main three-fold aspects (modeling, analysis, and blueprints) associated with the control of the longitudinal and handling dynamics of self-driving vehicles. They further introduce the social and economic effects and provide suggestions on enhancements for traffic dynamics based on the adoption of connected and autonomous (CAV) vehicles. Although these studies focus on different aspects of CVs, we did not find a comprehensive review of CVs that provides a deep understanding of the enabling technologies, open challenges, and potential opportunities. This study provides a holistic review on the recent advancements of CVs technologies to comprehend the fast pace of the technological development in this field. Our contributions in this study are summarized as follows:  
* Provided a comprehensive review with technical insights on the current standardization efforts of the key enabling communication technologies including Wi-Fi 6 and 5G. * Discussed the challenges in regards to cooperative computation, privacy/security, and over-the-air updates facing CV technology and pointed out open research issues that need attention by the research community. * Presented safety and non-safety applications and directed the reader's attention to some unnoticed innovative applications' research scope. * Drew the boundaries of the opportunities that the CV technology brings to our life. This article is organized as follows. Section 2 highlights the current enabling technologies that are suitable and most convenient for meeting CV technology requirements. Section 3 describes CV applications ranging from safety to commercial applications with an emphasis on applications that will have great potential in the CV environment. Recommendations upon fundamental challenges are presented in Section 4.