## 4 Conclusions  
In this paper, the approach for simulation of radio signal propagation for passive UHF RFID technology in an indoor environment using the RTg method is proposed. Using a combination of the 3D modeling tool SketchUp and the V-Ray plugin for computer rendering of images, the use of the RTg method to render a heat map over a 2D floor plan in a 3D scene is demonstrated. The heat map thus presents the signal intensity in the \begin{table}
\begin{tabular}{c c c} \hline \hline
**Resolution** & **1 Source [s]** & **2 Sources [s]** \\ \hline
2560 \(\times\) 1440 (2K) & 29 & 35 \\
1920 \(\times\) 1080 (Full HD) & 17 & 20 \\
1280 \(\times\) 720 (HD) & 8 & 10 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Test of time consumption for different resolutions of the heat map and a different number of emitters. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**RSSI range (dBm)** & \(-1\); \(-20\) & \(-20\); \(-30\) & \(-30\); \(-40\) & \(-40\); \(-60\) & \(-60\); \(-70\) & \(-70\); \(-80\) & \(-80\); \(-100\) \\
**Original (\%)** & 17.6 & 14.2 & 4.3 & 27.1 & Null & Null & 0.9 \\
**Simulation (\%)** & 24.1 & 7.5 & 4.0 & 28.8 & Null & Null & Null \\
**Difference (\%)** & 6.5 & 6.7 & 0.3 & 1.7 & Null & Null & 0.9 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Percentage of pixels in the heat map by RSSI ranges for antenna 1. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**RSSI range (dBm)** & \(-1\); \(-20\) & \(-20\); \(-30\) & \(-30\); \(-40\) & \(-40\); \(-60\) & \(-60\); \(-70\) & \(-70\); \(-80\) & \(-80\); \(-100\) \\
**Original (\%)** & 30.5 & 19.2 & 4.0 & 8.9 & Null & Null & Null \\
**Simulation (\%)** & 27.8 & 20.6 & 4.7 & 7.5 & Null & Null & Null \\
**Difference (\%)** & 2.7 & 1.4 & 0.8 & 1.4 & Null & Null & Null \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Percentage of pixels in the heat map by RSSI ranges for antenna 2.  
environment as RSSI values. This approach has the potential to reduce the time and cost requirements for planning an RFID system infrastructure. It also provides a comprehensive view of the signal range in a real environment, which can improve the approach to the coexistence of multiple telecommunication technologies in a given environment. A comparison of the RTg method with the Multi-Wall method and its verification based on the comparison of visual results of heat maps over a 2D plan in a 3D environment is presented. Two heat maps are generated in one environment for two different antenna locations, i.e., antennas 1 and 2. The largest difference of 6.7% is achieved for the RSSI value range of \(-20\) to \(-30\) dBm. The difference of 6.5% is achieved for the range of \(-1\) to \(-20\) dBm. These differences come at the strongest signal. Hence they have practically no effect on the functionality of the RFID system. We believe that this difference is negligible from a practical point of view. Practically, the most interesting results are the RSSI levels at which the signal is lost or almost lost. The maximum difference for the lowest RSSI range, i.e., \(-80\) to \(-100\) dBm, is 0.9% for antenna 1. In terms of time, the entire simulation up to the resulting heat map can be created in 10 min. However, this strongly depends on the complexity of the scene and the number of signal sources. It is affected by the increase in time required to create a 3D model and the time required to calculate reflections and refractions from a larger number of objects. Although this approach shows results comparable to other methods for radio signal prediction, further experimental investigation is needed. One possible goal is to make corrections to the set parameters in this approach based on real measurements or a larger number of validated simulation results. Furthermore, there is a need to minimize the time to create a 3D scene, which increases significantly with the complexity of the floor plan. Furthermore, the position and rotation of the RFID tag relative to the RFID antenna need to be considered, which is not currently accounted for in this approach.