## 2 Materials and Methods
The depicted and expected radiation pattern of both mentioned antennas gives us presupposition of the difference in RSSI values of tag right under the interrogator antenna and in the neighboring 2 m distance. Therefore, we were forced to rely completely on experimental character data and its statistical comparison based on measured RSSI. The localization subsystem must be able to distinguish between two neighboring locations. The smallest logistic units used in the selected warehouse has dimensions of 2 m by 2 m. The distinguishing process and its result are based on the value of RSSI (received signal strength indication), while the statistically significantly stronger signal (we decided that 95% confidence level is fully sufficient) is considered to come from the tag that is located directly under the reading antenna. The selected RFID tag (Confidex Survivor) must be placed in the center of the top side of the logistic unit, therefore the distance between two different RFID tags is at least 2 m. To test the boundary conditions of the identification and distinction process, a specific test scenario was proposed. \begin{table}
\begin{tabular}{c c} \hline
**Reading Distances** & **Received Signal Strength** \\ \hline
4 m & \(-\)55.5 dB \\
6 m & \(-\)63 dB \\
8 m & \(-\)68 dB \\
10 m & \(-\)71.9 dB \\ \hline \end{tabular}
\end{table} 
Table 4: Received signal strength by RFID reader. \begin{table}
\begin{tabular}{c c c c c} \hline
**RFID Tag** & **Type** & **Chip** & **Size [mm]** & **Read Range** & **Op. Temp** \\  & & & & **[m]** & [\({}^{\circ}\)C] \\ \hline Omni-ID & passive & Impinj Monza 4 QT & 39 \(\times\) 53.0 \(\times\) 14.9 & 20 (on metal) & \(-\)40 to \(+\)85 \\ Exo 2000 & passive & Impinj Monza 4 QT & 174 \(\times\) 70.0 \(\times\) 17.8 & 33 (on metal) & \(-\)40 to \(+\)85 \\ Everest & passive & Alien Higgs-3 & 130 \(\times\) 42 \(\times\) 10.5 & 28 (on metal) & \(-\)30 to \(+\)80 \\ OPP130 & passive & NXP UCODE & 155 \(\times\) 26 \(\times\) 14.5 & 18 (on metal) & \(-\)35 to \(+\)85 \\ Survivor & passive & G2 iM+ & 155 \(\times\) 26 \(\times\) 14.5 & 16 (off metal) & \(-\)35 to \(+\)85 \\ Confidex & battery & EM4325 & 155 \(\times\) 26 \(\times\) 14.5 & up to 60 & \(-\)35 to \(+\)85 \\ Survivor B & assisted & & & 12 (on metal) & \\ Xerdy Cargo & passive & Alien Higgs-3 & 100 \(\times\) 26 \(\times\) 8.9 & 6 (off metal) & \(-\)40 to \(+\)85 \\ Trak & & & & 20 (on metal) & \\ Container & passive & Impinj Monza R6-P & 138.8 \(\times\) 42 \(\times\) 12 & 15 (off metal) & \(-\)40 to \(+\)85 \\ Trak & & & & \\ \hline \end{tabular}
\end{table} 
Table 5: UHF RFID reader with long read range and suitable for outdoor usage. To perform the experiment, the overall power of the reading system (reader power and antenna gain) of 33 dBm ERP was used. The minimum distance between the tag under test (in figures denoted as AA) and the reader's antenna was specified at 2 m. At this distance the reader tried to identify the tag under test as well as the neighboring tag (in figures denoted as BB) and measure RSSI values of both (if read). The measurement was made 100 times. In the next iteration the same procedure was used to obtain RSSI values of both tags from a distance of 2 m more and the process continued to a distance of 8 m between reader antenna and the tag under test, that appeared to be the maximum read distance in accordance with the datasheet values. Based on the data hypothesis test for a difference in two population means and medians that were performed for each measured distance, the significance of the difference between pairs of measurements (for tag AA and BB) were determined. The determination was based on the set of hypothesis tests for a difference in means as well as for medians of two populations (measurements for tags AA and BB) that were performed at various distances. Based on the hypothesis tests it could be possible to find a maximal distance that allows for the distinction between the tag under test and surrounding tags.