## 2 ITS Applications and Communication Technologies, Critical Design Requirements, and Related Works
### Low-Cost GNSS Receivers  
The Location-based Services (LBS) market is constantly growing, predicted to reach hundreds of billions of USD by 2025, while tens of billion LBS-based devices will be operating by 2025. Although high-end GNSS receivers are currently sitting on top of the positioning and navigation industry due to their high precision, accuracy, and reliability, a significant demand for low-cost and ultra-low-cost GNSS receivers will soon emerge to satisfy ITS deployment [18; 19]. For instance, ITS applications, such as vehicle platooning, data transactions, and the remote control of Unmanned Aerial Vehicles (UAVs), employ low-cost LBS devices, e.g., smartphones, trackers, and wearables [9; 12]. The expansion of GPS, the addition of new satellite navigation systems, and the attainment of higher sampling rates (>10 Hz) have greatly benefited low-cost GNSS receivers. They typically support a single- or dual-band functionality, have small size and mass, can operate with low-drain batteries, can form wireless networks, and are not dependent on temperature conditions while a patch-antenna is attached to them [10; 18; 19]. On the other hand, the commercial single-band low-cost GNSS stations are lacking in accuracy, reliability, and robustness compared to dual-band ones with geodetic antennas [18; 19]. The design discrepancies between them lead to a greater radio noise/interference level, more severe multipath effects, and a decreased integer ambiguity fixing of the low-cost GNSS station. Moreover, their low availability in city environments has restricted their use, especially for vehicular, safety-critical applications. As a result, low-cost GNSS receivers alone cannot reach the full potential of satellite positioning, and, therefore, they are used complementary to other sensor types to increase redundancy and reliability in position fixing [20; 21]. Many researchers have studied and proposed solutions to enhance the performance of low-cost GNSS receivers. In [18], the authors propose a positioning apparatus comprised of two low-cost GNSS receivers placed in close proximity (up to a few cms) to model the noise and multipath errors between them. Assuming that the two GNSS stations experience identical error sources, the dual low-cost GNSS system solely evaluates the noise characteristics and mitigates the noise effects in the GNSS coordinate time series. In [19], a real-time, continuous, low-cost positioning solution for autonomous vehicles is proposed. A single-frequency, low-cost Precise Point Positioning (PPP) GNSS receiver is integrated with an equally low-cost INS. The considered PPP/INS scheme reaches sub-meter root mean square (rms) accuracy in benign clear-sky environments and circumvents the navigation issues during GNSS blockages. In [20], the authors performed kinematic experiments in rural, interurban, urban, and freeway environments to evaluate the positioning performance of a low-cost receiver using network RTK (NRTK) positioning. They achieved a centimeter-level accuracy with correction data provided from SmartNet. Collaborative or Cooperative Positioning (CP) solutions to empower the performance of low-cost GNSS receivers in C-ITS scenarios have also been proposed. In [21], a lane-level localization tool is proposed based on infrastructure lacking CP. The participating vehicles \begin{table}
\begin{tabular}{l c c c c} \hline \hline
**ITS Application** & **Sampling Rate (Hz)** & **Latency (ms)** & \
\begin{tabular}{c} **Data Rate** \\ **(Mbps)** \\ \end{tabular} &
\begin{tabular}{c} **Reliability** \\ **(\%)** \\ \end{tabular} \\ \hline Safety-critical vehicular CP & 10–20 & 1–50 & 10–50 & \(\geq\)99.999 \\ Traffic efficiency & 1–5 & 50–100 & 50–65 & \(\geq\)99.9 \\ Infotainment & On Demand & \(\geq\)100 & 10–1000 & 90–99.9 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Taxonomy of ITS applications’ technical radio requirements. form vehicular sensor networks (VSNs) by equipping image sensors and are able to share lane position information through DSRC.