## 2 Implementation of Active Localization: Signal Model, Processing, and Feasibility Test
### Preliminary Experiments in Ideal Conditions  
This section presents the experimental results in an anechoic chamber. If the proposed method is directly applied in an actual space, exactly matching the analysis with the experimental results becomes difficult because of the various spatial effects (R\({}_{\text{m}}^{\text{effect}}\)). Therefore, the experimental procedure was performed in anechoic space to quantitatively verify the accuracy of the proposed approach. In other words, we excluded the environmental elements of the control space and confirmed that the proposed concept exhibited no problem under ideal conditions.  
Figure 8 depicts the proposed SRP results obtained from the experiment when a PVC pipe or a person is a silent intruder. Each image shows the intruder position using relative power values (dB).  
In Case 1 (Figure 8a-d), when examining the position estimation of the intruder (i.e., a PVC pipe), although the angle had no error, the error of the distance was observed to reach up to 0.04 m (for position A).  
In Case 2 (Figure 8e-h), the error for the angle was confirmed to reach 5\({}^{\circ}\) (for position C) and the error for the distance ranged up to 0.13 m (position D) if a person was in each intrusion position. According to these results, when reviewing the energy maps again in terms of the maximum error, Case 1 indicated that the intruder position was estimated with a relatively small error. This was because the PVC pipe had a specific boundary condition at a fixed location without moving. As a result, a consistent reflection wave was measured by the active localization system. However, Case 2  
Figure 7: Experimental configuration for the verification of the proposed approach in terms of localization performance using a polyvinyl chloride (PVC) pipe or a human intruder in an anechoic chamber or a classroom. A, B, C, and D are the positions of the silent intruder. The superscripts represent the distance and the subscripts describe the angle (measured counterclockwise) between the microphone array and the intruder.  
indicated that the reflected signals measured by the microphone array were not constant when a person was in the intruder position. The reason was that a slight movement occurred although the person remained in the same position. From this difference, the position estimations of the intruder in the two cases had different results in terms of the maximum error. Nonetheless, we confirmed the feasibility of position estimation through reflections.  
Two important conclusions can be drawn. Firstly, the position of a person can be detected using the proposed active localization. Secondly, the energy maps of a person are similar to those of a PVC pipe, which is a circular object. The result indicates that the active localization method can detect the position of an object or a person, and it was the basis for modeling a person as a circular object in the subsequent simulation.  
Figure 8: Energy maps of Case 1 and Case 2 for verification of the localization performance in an anechoic chamber: The Case 1 of a PVC pipe in (**a**) position A; (**b**) position B; (**c**) position C; (**d**) position D; Case 2 of a person in (**e**) position A; (**f**) position B; (**g**) position C; (**h**) position D.