Car-Fi – fault – tolerant ITS “modem” device that allows to ensure fail-aware, fail-safe, and fail-operational principles. Car-FI means “Car Fidelity”, by analogy of Wi-Fi – Wireless Fidelity such that it will provide trusty V2X and reliable services what are enabled by:
- Fail – awareness – system should indicate whenever there is fault in the system.
- Fail – safety – system should not cause any scenarios harming any humans.
- Fail – operationality – system has ability to continue operating in case of failure.
To achieve all these principles, we identified that system should include redundancy, and this redundancy should be aligned with the available urban environment communication technologies. As the primary technology we chose the 802.11p communication stack as this is the dedicated technology for V2X to be able to deploy VANET (Vehicular ad-hoc network). For the second redundancy stage the regular mobile such as 4G-LTE was chosen, since this technology is ubiquitous in urban environments. For the third stage of redundancy the special LoRa PHY based communication protocol was developed which uses TDMA for accessing media and broadcasting. In comparison to the LoRaWAN network stack, the LoRa TDMA has higher bandwidth for safety critical information. The LoRa modulation itself has good properties being resistant to fading and Doppler effects [12], which makes it suitable for vehicular communication.
The redundancy is achieved also at the different levels of the OSI network representation model, e.g. at physical level there are different RF bands being used, at the network level for 802.11p PHY Geonetworking protocol is used for network layer and CAM/DEMN messaging for application layer (ETSI ITS-G5 specification [13]), TCP/IP is used on top of 4G-LTE. For all these communication protocols Car – Fi is providing a united API interface, making the system technology agnostic.