# Integration and Field Evaluation of an IoV System for Enhancing Road Safety
## 2 System Architecture  
### General Architecture  
The ODOS2020 integrated system comprises several modules and is depicted in Figure 1.  
Several pairs of sensor stripes comprising MEMS magnetometers detect passing vehicles and help to determine several critical parameters of their movement, such as their speed and direction. Sensor data are collected by On-the-Road Units (ORUs) using the versatile and highly scalable I\({}^{2}\)C protocol. The ORUs calculate the critical parameters of the vehicles' movement and send them to a Road-Side Unit (RSB) via LoRa. The ORUs also communicate with the passing vehicles via Bluetooth Low Energy (BLE) to identify passing vehicles so that personalized information can then be sent to each specific vehicle from the RSB.  
Each RSB acts as a central point where data from several ORUs are collected and from there are sent to the Cloud for further processing. The RSB also communicates with each passing vehicle via MQTT over LTE for vehicles with older communication capabilities (non-equipped vehicles) and via ITS-G5 for vehicles with modern communication systems that allow connectivity via BLE, ITS-G5 and several other protocols (equipped vehicles).  
A dedicated HMI is used in each passing vehicle in order to display warnings issued by the system to the driver. The HMI displays useful warnings in a simple yet intuitive way using easy to understand images and sounds so that the driver can avoid a potential accident by accordingly adjusting his/her behavior. The HMI has been developed so that it can be used with both contemporary and older vehicles. It can be installed in the existing hardware infrastructure of the vehicle or the driver's mobile device.  
Figure 1: ODOS2020 system architecture.  
Several aspects of the developed system's scalability and versatility can already be traced in this initial description of the system's general architecture. The use of the I\({}^{2}\)C protocol for communication between the ORUs and the sensors located on the road allows for easy expansion of the system's sensing capabilities in several additional traffic lanes, without the need for additional cabling, as the I\({}^{2}\)C protocol employs only two (2) wires to form a bus where several sensors can be connected. Moreover, several ORUs can be placed along a road or highway/motorway and be spaced according to the traffic conditions of the road in order to effectively monitor the road's traffic. The LoRa protocol employed for communication between the ORUs and the RSB can be used to cover a wide area and to support a large number of connected devices, as long as the data exchange between them remains within certain limits dictated by the protocol limitations [23]. In this way, data can be accumulated for processing in a centralized cloud infrastructure with very few communication units deployed. The versatility of the developed HMI makes the system easy to integrate into practically every vehicle and easily used by nearly every driver.  
In the following sections, each module of the ODOS2020 system is presented in greater detail, outlining the special features of each and its specific role in the entire system.