## 5 Obstacles and Challenges in Evolving V2X Communication
### Main Concepts Forseen for 6G-V2X  
This section briefly summarizes the main concepts that are foreseen to affect 6G-V2x.  
According to [8], there are technologies that are evolving in 5G and beyond and becoming mature for 6G, while others are revolutionary in the sense that their appearance will enable groundbreaking new results. The evolving technologies are the following:  
* Hybrid RF-VLC V2X--providing higher data rates and demanding a low setup cost;
* Multiple radio access technologies--having the benefits of sub-6 GHz carriers but with a longer range;
* Non-orthogonal multiple access (NOMA)--allowing the combination of massive connectivity with ultra-low latency;
* The new multicarrier scheme--for higher spectrum and power effectiveness, even against the Doppler effect;
* Advanced resource allocation--for enhanced context awareness and to support cross-layer resource allocation;
* Integrated sensing, localization, and communication--for improved situation awareness;
* Satellite/UAV-aided V2X--as one of the common expectations for 6G infrastructure, to provide flexible, aerial base stations and wider coverage;
* Integrated computing--faster computing with lower operational costs;
* Integrated control and communications--the co-design of control and communications.  
There are revolutionary technologies that are quite mature [8], so they could become an important part of 6G-based ecosystems:  
* Blockchain--as it could significantly enhance security for some services;
* ML-aided V2X design--as it could provide significant performance enhancement for highly adaptive and complex V2X environments.  
Furthermore, there are some revolutionary technologies--called revolutionary for 6G by [8]--that are less mature but might still be considered to support 6G:  
* A programmable V2X environment--especially for enhancing the robustness and resilience of the radio interface;
* Tactile communication--as real-time haptic information transmission is one of the generic expectations for 6G;
* Quantum computing--as the ultimate superior computation mechanism that also enhances security;
* Brain-vehicle interfacing--as brain communication interfacing evolves, it could enable various supporting functions;
* THz communications--allowing an extremely high throughput.  
Some research areas are receiving specific attention. Offloading and resource management is an important aspect; hence, [117] proposed a federated learning empowered computation offloading and resource management (FLOR) method, which offloads and manages the resources with low latency. Another aspect is data privacy, as information is passed among V2X users, often in open channels of heterogeneous technologies. Certain security and privacy issues can be handled by blockchain technologies, and processes can be optimized by federated learning (FL) at the edge. Hence, the BFLEdge [113] framework is proposed to cover the gap between these technologies. Positioning for V2X is also a key issue; advances from 5G to 6G are discussed in [21].  
Although our current article does not focus on UAVs, 6G is expected to solve various issues around UAV control, communication, and management. Survey papers are already available for the anticipated 5G to 6G visions for UAV communication [115] and for green UAV communication for 6G [116].