# Analysis of Passive RFID Applicability in a Retail Store: What Can We Expect?
## 3 Influence of Retail Store Products and Propagation Phenomena on a Tag Sensitivity
### Simulation Model and Setup  
For the purpose of obtaining the realistic simulation model of a retail store, a radio propagation software Wireless InSite is used [21]. Ray-tracing models and high-fidelity EM solvers are used for the analysis of wireless communication systems and radio propagation channels. It gives efficient predictions of EM propagation and, also important, the visualization of the EM wave propagation for better understanding of the scattering phenomena in complex environments.  
\begin{table}
\begin{tabular}{l c c c} \hline \hline
**Scenario** & **Z (\(\Omega\))** & **\(e_{r}\) (\%)** & **Gain (dBi)** \\ \hline d = 3 mm & 12.5 + j172.8 & 75.8 & 2.63 \\ d = 6 mm & 32.4 + j161.6 & 81.0 & 3.98 \\ Minor antenna part in air & 7.1 + j155.0 & 49.9 & 0.60 \\ Major antenna part in air & 12.2 + j178.1 & 80.0 & 2.30 \\ Tag attached (d = 0.1 mm) to larger cylinder & 3.2 + j200.3 & 42.9 & 3.1 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Impedance, radiation efficiency and gain results of tag antenna attached to plastic product in different scenarios at 920 MHz.  
Figure 3: 3D directivity patterns at 920 MHz for tag attached to the twice larger plastic cylinder (**left**), with minor part in the air (**center**), and at 3-mm distance from the plastic cylinder (**right**).  
A real retail store was built in Wireless InSite according to the given floor plan with dimensions of 8.6 \(\times\) 6.2 \(\times\) 3.1 m, concrete floor and ceiling, metallic shelves, refrigerators, wooden baskets and beverage packs as shown in Figure 4 for different views. Walls depicted with light gray color are made of concrete; white color represents glass material; dark gray is metal; brown is wood, and blue is for water. All materials' electrical properties in the model, except for plastic, are listed in Table 3. Their parameters are taken from Wireless InSite database of material properties given or calculated according to International Telecommunication Union (ITU) references [21]. The calculation is done with the X3D propagation model with five reflections, two transmissions, one diffraction, and ray spacing of 0.25 m for each receiver considered. The transmitter antenna is a directional circularly polarized antenna, with gain of 5 dBi supplied with power of 30 dBm at \(f=866\) MHz, whereas the receiver tag antenna is modeled as an omnidirectional horizontally polarized antenna with 2 dBi gain (as in FEKO simulations in free space, see Figure 1). The transmitter was placed at one place for simulations and measurements, whereas three different receiver setups were used to examine the impact of receiver height, random position in the store by taking some route around the shelves. Also, various scenarios of products' materials, position and setup are investigated: store with empty shelves and refrigerators; store with shelves and refrigerators filled with products of water (water is representing all liquids, as in Section 2), metal and plastic; mixed products positioned in the simulation model as in a real store and the last one, mixed products scenario in which the receiver antenna has significantly lower gain (\(-12\) dBi) in order to represent the case when the tag is attached to a bottle of water.  
and 3D view of propagation paths. It is shown that the received power at each receiver position depends on the multipath channel, i.e., on the scattering from the objects in the vicinity of reader and tag antenna. Even in LOS between the reader and tag, there is a possibility that tag is not read due to multipath reception.