## 2 Derivation and Analysis for Statistical Indoor EZ
Therefore, the electromagnetic waves produced by the transmitting antenna propagate relatively evenly in all azimuth directions without significant interference from the interior structures as shown in Figure 3a. However, since the heights of equipment \(A\) and \(C\) are both above 2 m, there is a shaded area on the back of the equipment. On the other hand, when the transmitting antenna is located at \(Tx\). 2 (\(x_{t}\) = 13.5 m and \(y_{t}\) = 1.5 m), as shown in Figure 3b, the radiated electromagnetic waves are more affected by the indoor wall than in Figure 3a. Stronger electromagnetic fields are even observed around equipment \(A\), which is further away from the transmitting antenna, due to the reflection effect caused by the wall. In Figure 4, the black line is the EZ assuming the NPP as free space, which is reported in _Regulatory Guide 1.180_. When the input power and the gain of the transmitting antenna are 1 W and 2.15 dBi, respectively, it has a circular shape with a radius of 1.75 m. On the other hand, the red line indicates the statistical indoor EZ boundary (\(d_{n}\)) in terms of the azimuth angle regions (_Region n_) based on the environment in Figure 3 (the height of the receiving antenna (\(h_{rx}\)) is 1.4 m). In contrast to the free space EZ, it can be seen that the EZ boundary (\(d_{n}\)) differs depending on the directions of the azimuth angle. In Figure 4a, when the transmitting antenna is placed at \(Tx\). 1, the EZ boundary (\(d_{n}\)) in all regions is observed from a minimum of 2.8 m to a maximum of 7.4 m. The maximum of 7.4 m (\(d_{4}\)) at _Region 4_ (\(\phi_{T}\) = 90-120\({}^{\circ}\)) is examined because of stronger electromagnetic fields due to the reflection by the equipment \(A\). On the other hand, in _Region 12_ (\(\phi\) = 330-360\({}^{\circ}\)), there is no structure that generates strong reflections near the transmitting antenna in order for the distance (\(d_{12}\)) of _Region 12_ to be shorter than the distance (\(d_{4}\)) of _Region 4_. In Figure 4b, the EZ boundary (\(d_{n}\)) in all regions is observed from a minimum of 1.3 m (at _Region 1_) to a maximum of 11.7 m (at _Region 4_) when the transmitting antenna is located at \(Tx\). 2. In this case, the electromagnetic field distribution is affected by equipment \(A\) as well as the indoor wall, and thus the maximum \(d_{n}\) is greater than in the case of Figure 4a. Additionally, to understand the EZ in a 3D environment, the EZ is extended into a 3D volume space by investigating at various heights. When the height of the receiving antenna (\(h_{rx}\)) is 1.2 m, as shown by the blue line in Figure 4, the distance (\(d_{7}\)) of _Region 7_ is greater than the red line, because the wave reflected by structure \(D\) and \(F\) is stronger than when \(h_{rx}\) is 1.4 m. On the other hand, when \(h_{rx}\) is 1.6 m (the green line in Figure 4), the EZ boundary is much more  
Figure 3: Received power distribution according to transmitting antenna position: (**a**) \(Tx\). 1; (**b**) \(Tx\). 2.  
reduced than the red line. This is because, in the line-of-sight direction, both the influence of the structure and the antenna gain are reduced.