# Passive RFID-Based Inventory of Traffic Signs on Roads and Urban Environments
## 5 Discussion: Comparison with Related Works  
A comparison with the similar works [9; 10; 11; 24; 12] referenced in Section 1 is detailed in Table 7. To the best of our knowledge, these approaches are the most related to that proposed in this paper in terms of their applications. Having said that, we observe that some of their features (e.g., the frequency band or the selected technology, active RFID in most cases) are clearly distinct from those proposed in the present paper. Therefore, Table 7 is focused on highlighting how employing the selected technology, band, and equipment is possible to meet the requirements for the intended inventory-making application, with some benefits (such as costs) over the similar previously presented approaches. First of all, note that we present a system dedicated to inventory and location purposes, whereas that [9; 10; 24] propose ADAS implementations to display digital sign traffics, and [11; 12] proposes the attachment of RFID tags at traffic signs as part of a high accuracy vehicle speed controller system. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & [9] & I[0] & [11] & [12] & **This Work** \\ \hline
**Type** & Passive & Active & Active & Active & Passive \\ \hline Application & In-vehicle traffic signing & In-vehicle traffic signing & Traffic sign alert system & Intelligent speed controller & Inventory and location \\ \hline Carrier frequency & \multirow{2}{*}{13.56} & \multirow{2}{*}{2400–2483} & \multirow{2}{*}{867} & \multirow{2}{*}{433} & \multirow{2}{*}{866.5} \\ (MHz) & & & & & \\ \hline On average read range & \multirow{2}{*}{0.4} & \multirow{2}{*}{30} & \multirow{2}{*}{10} & \multirow{2}{*}{23} & \multirow{2}{*}{71  \\ (m/h) & & & & & \\ \hline Tag ID capacity (bits) & 64 & 24 & 192 & - & 96 \\ \hline Price/tag (US8) & 1.31 & - & 20 & 10–20 & 3.3 \\ \hline Maximum reading rate & \multirow{2}{*}{503  (10 3)} & \multirow{2}{*}{103  (10 3)} & \multirow{2}{*}{-} & \multirow{2}{*}{-} & \multirow{2}{*}{400  (10 3)} \\ (Tags/s) & & & & & \\ \hline Data rate (Kbps) & 3.2 & 250 & - & - & 40 \\ \hline Tag area (mm \(\times\) mm) & \(76\times 45\) & - & \(80\times 40\) & \(123\times 80\) & \(51.5\times 47.5\) \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Comparison between traffic signs detection systems based on RFID. Figure 14: Number of detections for each studied case. Apart from the present work, only [9] proposes the use of passive RFID technologies. However, ref [9] is implemented by using tags with a short distance range, no ruggedized and no designed for metallic environment applications. This implies that these tags are placed at the road lane instead of on the traffic sign, unlike the others referenced works, losing the capability of detecting displacements or thefts of the traffic signs. Moreover, the tags used in [9] limit the speed of the car to 20 Km/h, which would interfere with the normal traffic flow in many cases. Finally, although the main advantage of these tags is their price, this cost difference is decreased considering that [9] employs three tags per traffic sign, whereas the others works employ one. In fact, [24] presents an improvement of the encoding proposed in [9] in order to reduce the number of tags. Regarding the active RFID systems [10; 11; 12], it is possible to observe that the distance range achieved by the present work is lower, as expected, but still enough to detect all the traffic signs and urban facilities when using a vehicle running at a normal speed, while benefiting, at the same time, from the advantages of passive RFID technologies, such as costs, tag size, and no need for battery replacement. An additional feature of [12] is the use of two independent readers for redundancy, in order to avoid the occasional missed tags detections that may occur by using only one reader. This feature can be also implemented in our system, since the employed reader is equipped with four antenna ports that can be orientated in multiple directions.