# Passive RFID-Based Inventory of Traffic Signs on Roads and Urban Environments
## 4 System Validation
### Experimental Comparison between Passive and Active Technologies
#### 4.1.2 Test Setup and Experimental Results  
In order to compare the performance of both technologies, the test configuration shown in Figure 5 was implemented for passive and active cases. The test setup consists of a mobile support, where the RFID tag was installed over a metallic plate (45 \(\times\) 15 cm\({}^{2}\)), and the RF antenna was connected to the RFID reader, which is controlled by a computer in order to visualize the results. Active Case  
(a) Maximum coverage range  
Previously to measure the coverage range for this technology, a preliminary test was conducted with the objective to evaluate the performance of the three active tags referenced in Section 4.1.1 (b) in a metallic environment, in order to select one of these models for the rest of the experiment and be compared with the passive case. All these active tags were detected when faced to the reader and separated by a distance of 7 m, which was the experimental range for passive case. However, the main observed difference between the three active tags is their behavior when placed on a metallic plate: the speed of reading of the NT02 model was enormously decreased on a metallic environment. Thereby, placing samples of NT02, RT02, and ZT02 at the same metallic plate, we only made two readings per scan for the NT02 tag, while we had obtained 68 readings without the plate. However, for the rugged models (RT02 and ZT02), the number of readings is much less decreased, mainly for the case of ZT02. These results are shown in Table 4.  
The next task for the active case was to measure the maximum distance range using the rugged active tags (RT02 and ZT02) over the metallic plate. The results are shown in Table 5, for a fixed tag-floor distance of 1.5 m, being possible to observe how this maximum range is pretty longer than that in the passive case, as expected. (b) Multiple readings capabilities  
Also from the results illustrated in Table 4, it is possible to observe how the collision problems are less accused than in the passive case (see Table 3). This effect is predictable, because manufacturers of active tags usually provide anti-collision protocols (>100 tags can be simultaneously read for the proposed tags). However, this should be not a decisive factor to select the technology since usually only one tag will be placed at each traffic sign or urban facility. In any case, even if a multiple reading is required, Table 3 shows that it is also possible to read up to three and four tags placed at the same metallic plate for a distance from the reader of 4 and 2 m, respectively, using passive technology. Moreover, as will be validated by simulation in Section 4.2, the same tag is usually read several times while the vehicle is inside its cover area, thus decreasing the impact of possible collisions over the inventory process, as will be corroborated in experimental results presented in Section 4.3, where multiple simultaneous readings are performed with the reader mounted in the vehicle. Finally, in the best observed case (i.e., using a ZT02 tag and the antenna faced at the same height and at the maximum distance range of 30 m) the number of readings starts to decrease (<3 readings/s) when the horizontal distance between the antenna and the tag is higher than 0.8 m (using the setup of Figure 6), decreasing the efficiency of the active system in comparison to the case when the transmitter and the receiver are faced (>10 readings/s). Recall that, for the passive case, tags were detected at \begin{table}
\begin{tabular}{c c c} \hline \hline  & **Readings without Metallic Plate** & **Readings with Metallic Plate** \\ \hline NT02 & 68 & 2 \\ RT02 & 37 & 26 \\ ZT02 & 37 & 30 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Readings for the active tags in a 3-s test time. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Reader Antenna Distance from Floor (m)** & **Maximum Range for RT02 (m)** & **Maximum Range for ZT02 (m)** \\ \hline -0 & 25 & 30 \\
0.75 & 28 & 31 \\
1.5 & 30 & 34 \\ \hline \hline \end{tabular}
\end{table}