## 2 Internet of Vehicles (IoV)
### Radio Access Technologies  
There is a need to combine short-range technologies, such as Bluetooth, with long-range technologies for seamless network availability. In this section, we describe their basic characteristics, summarized in Table 2.  
1. _IEEE 802.11p / WAVE_: The 802.11p (WAVE: wireless access in vehicular environments) protocol adapted the IEEE 802.11 PHY/MAC layer specification to the vehicular environment and termed it dedicated short-range communications (DSRC). It provides V2V and V2I communication using a 10 MHz wide channel at 5.9 GHz. Various regional bodies define spectrum utilization for IoV. In Europe, ITS-G5 allocated a total of 40 MHz in the frequency range of 5875-5915 MHz for safety-related road ITS. In addition, the frequency range 5915-5925 MHz was prioritized for urban rail ITS, but could also be used for road ITS once ETSI establishes polite protocols and proper co-channel sharing mechanisms between road ITS and urban rail ITS [32]. IEEE 802.11p uses binary convolutional coding (BCC) which is weaker than low-density parity-check coding (LDPC) or turbo-coding in higher modulation and coding schemes (MCS). This is addressed in the IEEE 802.11 bd amendment which offers twice the performance, supporting speeds up to 500 km/h, and twice the communication range of 802.11p, due to its use of LDPC coding and 256 QAM modulation. 802.11 bd is expected to be approved in 2022. Similarly, the US Federal Communication Commission had allocated 75 MHz (frequency range from 5850 MHz to 5925 MHz) for V2X applications. However, on 3 May 2021 it decided to reallocate 45 MHz of the 75 MHz spectrum to unlicensed devices, such as Wi-Fi. As a result, from this date on, only the 30 MHz between 5895 and 5925 will remain for safety applications using vehicle-to-everything (V2X) communication [33]. 2. _LTE Cellular V2X (C-V2X)_: LTE cellular vehicle-to-everything (C-V2X) is a 3 GPP standard that uses the PC5 interface at 5.9 GHz. Employing high capacity, large cell infrastructure, it enables communication between vehicles, humans, and infrastructure. It consists of vehicle-to-vehicle (V2V), vehicle-to-infrastructure (V2I) and vehicle-to-person (V2) communication. It represents an alternative to the IEEE 802.11p standard, that supports direct vehicle-to-vehicle communication even without cellular base station involvement. C-V2X is continually evolving over 3 GPP releases. It was introduced in 3 GPP release 14, completed in 2017. In Release 15, further enhancements were introduced. In 5G, further performance improvements will be attained, replacing C-V2X with New Radio (NR). It should be noted that C-V2X and DSRC are not compatible with each other. 3. _5G and Beyond 5G NR V2X_: Some IoV applications, such as self-driving vehicles, require that the transmission delay is less than one millisecond. The IoV of tomorrow will require higher throughput, lower latency, higher reliability and multicast capabilities, while supporting mobility up to 500 km/h and application-aware services. Thus, NR C-V2X in release 16 offers backward compatibility with Rel. 14 and Rel. 15 for safety, multicast messages, and advanced-use-case (transport profile) capabilities. Spectrum and energy efficiencies are improved by deploying massive multi-input multi-output (MIMO) and millimeter-wave technologies. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Application** & **Examples** & **Communication Support** & **Bandwidth Req.** & **Latency Req.** \\ \hline Traffic Safety & Pre-sense Crash Warning & VRU, V2V, V2P & Low & 20–100 ms \\ \hline Traffic Efficiency & Navigation System, Traffic Light & V2R, V2I & High & 100–500 ms \\ \hline Cooperative Driving & CACC & V2V, V2I, V2S & High & 2–10 ms \\ \hline Infotainment & Video and Music Streaming, News & V2I, V2U & High & 500–1000 ms \\ \hline \hline \end{tabular}
\end{table} 
Table 1: IoV applications and characteristics. Figure 3 shows the spectrum allocation in Europe and the US.