## 3 Background
### A V2I Overview  
Over the past twenty years, V2I has emerged as a well-established research and development domain within the scope of ITS. This is described in [28], which summarises some of that research and lists the perceived advantages in helping to aid traffic management, improve road safety, and enhance access to services:  
* Reduce traffic accidents and improve road safety;
* Aid in the management and efficiency of traffic flows and alleviate congestion;
* Aid road safety services;
* Provide information services.  
However, V2I adoption has not yet been widely accepted. In [28], the authors list some of the challenges with V2I systems. These challenges may be why V2I has not experienced widespread deployment:  
* The high cost of deploying and maintaining V2I communication infrastructure and road-side units (RSUs);
* Maintaining the accuracy and timeliness of distributed information;
* Gathering, processing, and fusing enough data to ensure correct decision-making;
* Drivers and future autonomous vehicles responding correctly to V2I-distributed information;
* Concerns about the privacy and security of data flowing around the V2I and ITS systems;
* Managing the ad hoc communication connections in the highly dynamic vehicular environment.  
This lack of adoption of V2I is why the United States Federal Communications Commission (FCC) reduced the amount of radio spectrum available to V2I devices [29]. However, continuing research in the V2I domain aims to address those challenges, with our application investigating the use of an FSO-QKD-based method to maintain the privacy and security of V2I data.  
A V2I system, as with any connected system, is a potential target for a cyber attack. Connected transportation infrastructures and vehicles represent enticing targets due to their vital role in society and their inherent financial value [30]. The V2I system could be subjected to denial of service attacks, message alteration, message spoofing, message spamming, eavesdropping, and malware [31]. This is because V2I's dedicated short-range communication (DSRC) is a derivative of the Wi-Fi standard, tailored for roadside deployment. It uses a 5.9 GHz communications channel and is specified in the wireless access for vehicular environment (WAVE) standards, IEEE 802.11p, and IEEE 1609 [32].  
The DSRC infrastructure has relied on the deployment of dedicated devices. These include roadside units (RSUs) mounted to lamp-posts, traffic lights, or separate poles, and on-board units (OBUs) for vehicles. Data are exchanged between OBUs and RSUs that act as access points (APs) for OBU-equipped vehicles. The RSUs and OBUs operate at 5.9 GHz to ensure the low latency necessary for V2I applications. V2I messages come in several standardised formats, including [33]:  
* DENMs--Decentralised environmental notification messages, for road profiles, zones, and hazards.
* CAMs--Cooperative awareness messages, for vehicle status and capabilities.
* SPATEMs--Signal phase and timing messages, for the state of signals at intersections.
* MAPEMs--Map message, for geographic information.
* CPMs--Collective perception messages, for object and obstacle detection.
* IVIM--In-vehicle information message, to relay electronic sign indications to vehicles.  
An alternative to deploying the DSRC-based V2I systems is to use the cellular communication networks designed for mobile phone communications. The 3 rd Generation Partnership Project (3 GPP), which is the body that develops cellular standards, incorporatedsupport for vehicular communications in the 2019 5G New Radio (5G NR) standards [34]. Cellular vehicle-to-everything (C-V2X) is another area that is being actively researched [35].  
Having provided an introduction to the AirQKD project, V2I, and QKD, the next section covers the integration of FSO-QKD within the AirQKD V2I application.