# Connected Vehicles: Technology Review, State of the Art, Challenges and Opportunities
## 2 Enabling Technologies
### 5G-Cellular Technology  
Cellular technology such as the fifth generation (5G) is another strong competing candidate to achieve efficient and reliable wireless communication to support CV applications. The network capacity in cellular technology is high, which provides higher bandwidth and which can have the ability to support a variety of data-based applications. Cellular technology covers a wide coverage range, which diminishes frequent horizontal handovers. In this case, vehicles can stay connected to the base station for a large amount of time, in contrast to the small duration of time between vehicle and RSU, where the communication link remains valid [28]. Moreover, it precisely focuses on the performance measures related to achieving ultra-low latency, improving reliability, decreasing the power usage, and maximizing network throughput per session [29]. The rise of 5G mobile cellular networks as a new innovative technology opens up the potential to enable fully mobile and interconnected systems. The Third Generation Partnership Project (3 GPP) release 15 [30] and Technical Specifications (TS) 23.501 [31] provide a reference framework for a collective number of requirements and functionalities needed to advance and establish 5G networks [32]. Moreover, 5G automotive association (5 GAA) is an organization, where major automotive and telecommunication corporations including BMW, Audi, Ericsson, Intel, Nokia, and many others come together to advance, employ, and provide mobility and transit solutions for cellular-based V2X communication [32; 33]. 5G networks will depend on long-term evolution-advanced (LTE-A), millimeter WAVE (mm WAVE), Wi-Fi, and Wireless Gigabits (WiGig), which are recent radio-supportingtechnologies, operating from ultra-density-based cells to device to device (D2D) [32]. The design of LTE-A meets the safety- and non-safety-based application specifications including high mobility, wide coverage range, improved quality of service (QoS), and multicast communication. LTE-A downlink and uplink access technologies will utilize OFDMA and single-carrier frequency division multiple-access (SC-FDMA) techniques allowing for scheduling based on frequency-time resources to be achieved with high resilience and effectiveness. Spectral competence can also be achieved in a highly dynamic environment depending on advanced multiple input multiple output (MIMO) potentials. Even with the previously mentioned benefits, LTE-A still suffers from latency issues where the maximum achievable latency is around 80 ms, which is not convenient for applications that require a maximum latency of 10 ms [29]. Whereas, mmWave incorporates beamforming technology that allows higher data rates, in addition to its bandwidth of 30-300 GHz that significantly enhances system operations [29; 33]. The Doppler effect at mmWave frequencies can be controlled in a highly dynamic environment due to the presence of directive transmissions and narrow beam-based antennas [33]. The fundamental technological design of 5G is dependent on the automation of the resources of the network that utilizes network slicing (NS), which is dependent on network function virtualization (NFW) and software-defined networks (SDN). Issues such as improper connectivity and the packet loss rate can be solved through the integration of SDN and edge computing. Vehicular networks based on SDN can benefit from such technology such as improving resource utilization [34]. (1) Challenges of 5G-Cellular Technology: With the high expectations that 5G will meet the dynamic change of vehicular networks, high mobility endorsed by vehicles and the huge volume of data transmission involved within the CV technology [32], 5G telecommunication is still facing several challenges, which are further discussed below:  
* **Service and Business Models. ** The increasing number of connected IoT devices to the internet through 5G necessitates the requirement for new business and service paradigms.