## 2 State-of-the-Art V2X Technology
### Protocols of V2X Communication  
#### 2.1.1 DSRC Protocol  
DSRC is a wireless communication protocol specifically developed for V2X communication. It operates at the 5.9 GHz frequency band and allows vehicles to exchange information within a range of up to 300-1000 m. DSRC supports direct V2V, V2I and V2P communication. It facilitates the exchange of safety-related information, such as vehicle position, speed, acceleration and basic safety messages. DSRC has been widely deployed and tested in various research projects and pilot programs around the world [24].  
DSRC supports multiple communication modes to enable various types of V2X interactions, including:  
* Vehicle-to-Vehicle (V2V): communication between vehicles. It allows nearby vehicles to exchange safety-critical information, such as speed, location, acceleration and braking status, enabling cooperative maneuvers and collision avoidance.
* Vehicle-to-Infrastructure (V2I): communication between vehicles and infrastructure components like traffic signals, roadside units, and toll booths. It enables the exchange of traffic-related data, such as signal phase and timing information, traffic conditions, and road hazards. V2I communication enhances traffic efficiency and supports applications like signal prioritization for emergency vehicles.
* Vehicle-to-Pedestrian (V2P): communication between vehicles and pedestrians carrying DSRC-enabled devices. This communication mode enhances pedestrian safety by providing alerts to both the driver and the pedestrian in potentially hazardous situations. Other, less common uses of V2X include, but not limited to:
* Vehicle-to-Network (V2N): Involves communication between vehicles and the broader communication network, enabling access to cloud-based services, traffic information, and other centralized data sources.  
* Vehicle-to-Grid (V2G): Allows electric vehicles to communicate with the power grid, enabling bidirectional flow of energy. This can be utilized for vehicle charging, discharging excess energy back to the grid, and participating in demand response programs.
* Vehicle-to-Cloud (V2C): Involves communication between vehicles and cloud-based platforms, enabling access to a wide range of services, including over-the-air updates, infotainment and personalized settings.
* Vehicle-to-Home (V2H): Enables communication between vehicles and smart home systems, allowing the integration of electric vehicles with home energy management for charging optimization and energy sharing.
* Vehicle-to-Device (V2D): Involves communication between vehicles and other connected devices, such as smartphones or wearables, to enhance the overall connected experience and provide additional services.  
DSRC utilizes a standardized set of message formats to exchange information between vehicles and infrastructure. These messages follow the IEEE 802.11p standard, which is an amendment to the WiFi standard tailored specifically for vehicular communication [25]. Security is also a critical aspect of DSRC communication to prevent unauthorized access and ensure the integrity of the exchanged messages. DSRC incorporates security measures, including authentication, encryption and message integrity verification, to protect the confidentiality and authenticity of communication. DSRC has been standardized by organizations such as the IEEE and the SAE. Standardization ensures interoperability between different DSRC-enabled devices from various manufacturers, allowing seamless communication and compatibility across different V2X deployments.  
DSRC has been extensively researched, tested and deployed in pilot programs and field trials worldwide. It has shown promising results in improving road safety, traffic efficiency, and enabling advanced V2X applications.