## 3 CSI Measurement Environments  
### Experimental Scenarios  
Prior research has predominantly focused on CSI measurements in scenarios where there is a line-of-sight (LoS) between a Wi-Fi transmitter and a CSI receiver. In addition, these studies typically concentrate on counting the number of stationary individuals in the environment. In this study, as shown in Figure 1, we collect CSI data in several challenging scenarios that push the boundaries of traditional Wi-Fi sensing. These challenging environments are chosen to rigorously test the robustness and versatility of the CSI-based people-counting system. By showing the successful operation of our method under these conditions, we aim to demonstrate the potential of our approach in real-world situations where ideal line-of-sight conditions are rarely available. Figure 1: CSI measurement environments (Tx represents a Wi-Fi transmitter, and Rx represents a CSI receiver). In the first scenario named TTW (Through The Wall), we set up an environment where the Wi-Fi transmitter and the CSI measurement device are separated by two walls. This setup tests the system's ability to penetrate physical obstacles. In this scenario, people are in the typical seminar room. To capture the diverse scenarios that may occur in a typical seminar room, we conduct a series of CSI measurements. During these measurements, we systematically vary the location and movement patterns of occupants within the seminar room. This approach allows us to encompass a wide range of potential spatial configurations and mobility dynamics that are commonly encountered in seminar room environments. The specific variations we implement are as follows: all people are sitting in a chair and do not move around, all people are standing in a row along a wall and do not move, people are clustered and the number of cluster is changed, some people are walking around while the others are sitting, and all people are moving around in a random direction and velocity. We do not impose any restrictions on their movement. Since each participant is free to decide their movement speed and direction based on their own judgment, the measured CSI data include various CSI patterns caused by movement of people. We vary the number of people in a room from zero to five. For each variation in the seminar room, we also conduct CSI measurements in a setting where the Wi-Fi signal propagation is disrupted by individuals moving at random speeds and directions through the corridor between two rooms. We also do not impose any restrictions on the movement patterns of each individuals disturbing Wi-Fi signals. Thus, their movements are reflected as noise in the measured CSI. The second CSI measurement scenario is called Queuing. For this scenario, we position individuals in a linear formation between the Wi-Fi transmitter and the CSI receiver at the front of a classroom. This arrangement creates a challenging environment for the system. Since people are overlapped between a transmitter and a CSI receiver, the differences in the CSI characteristic change patterns between classes are small. Thus, it becomes difficult for a Wi-Fi sensing system to accurately determine the number of people. In this scenario, we change the number of people in a row from zero to four. The third scenario is named Corner. In this scenario, we explore situations where a measurement target is not directly visible from the location of Wi-Fi transceivers. This setup tests the system's capability to detect a person in occluded areas. We position one person around a corner in a hallway. In addition, we colocate the Wi-Fi transmitter and a CSI receiver at the other corner so that the subject is not within direct line-of-sight of the Wi-Fi transceivers. The Corner scenario is designed to address a specific safety concern: preventing collisions with an individual emerging from blind corners. This approach is different from our previous experiment scenarios, which focus on counting people within a defined area.