6 Yafeng Yin et al. 5.1 Focusing Process The focusing process aims to adjust the interrogation region to be focused on the specified area S by adjusting r,P,while ignoring the tags outside S.It contains three phases,selecting the initial power,establishing the boundary and power stepping.The process aims to get the optimal power P,whose corresponding interrogation region is just enough to cover the area S. Selecting the Initial Power Before the reader identifies the tags,it selects the initial power instead of the default (maximum)one to control the interrogation region.In RFID systems,the reader's interrogation region of an antenna is like an ellipsoid.The larger the angle 0.between the radiation direction and the an- tenna's surface,the longer the reader's scanning range.However,in the realistic environment,the tag size,the reader's power Po,the radiation angle 0r,and the distance d all affect the effective interrogation region,as mentioned in section 3. Therefore,in the realistic environments,we measure the minimum power P based on 6,and d,and use them to calculate the initial power.In this paper,we measure P (r,d)with the distances dj=0.5m x j,j[1,7]and the angles 9=90°-15°×i,i∈[0,6.For example,we get Pmin(90°，1.0)=15.7dBm, Pwmin(75°，1.5)=l8.8dBm,Pwn(60°，2.0)=23.4dBm.The reader first selects the reference angle 0i closest to r,0r-il <0r-(k E [0,6]and k i). Then,it uses d to calculate the initial power Pm(r,d) Pwmn(0,d） if d=di Pwmin (0dj)+Pmind ifd∈[d,dj+l (1) However,the power is only used as the initial power.In order to identify more tags,the reader can repeatedly increase the power by AP.We set AP= 1dBm,which is achievable by most of the commercial readers 14. Establishing the boundary The 3D camera can recognize the specified area by RGB camera and measure distance by 3D depth sensors.However,the reader can hardly find the boundary of S,due to the unknown distribution of tag IDs Therefore,PID first establishes the boundary S of the area S based on the in- terference tags located around S,as shown in Fig.4.PID uses the 3D camera to calculate the minimum distance do between the interference tags in So and the antenna,and the distance ds between the center of S and the antenna.Further- more,it calculates the rotation angle=arccos(是)，p∈(0°，90).Then,the antenna rotates degree to face the interference tags in So for identification. The identified tags are used as reference tags to describe S. ▣▣ 口口 Fig.4.Identify the tags in the specified area with a 3D camera In PID,the antenna always faces towards the center of the objects,r= 90.Then,the reader selects the initial power Pb according to the distance d,6 Yafeng Yin et al. 5.1 Focusing Process The focusing process aims to adjust the interrogation region to be focused on the specified area S by adjusting θr, Pw, while ignoring the tags outside S. It contains three phases, selecting the initial power, establishing the boundary and power stepping. The process aims to get the optimal power P ∗ w, whose corresponding interrogation region is just enough to cover the area S. Selecting the Initial Power Before the reader identifies the tags, it selects the initial power instead of the default (maximum) one to control the interrogation region. In RFID systems, the reader’s interrogation region of an antenna is like an ellipsoid. The larger the angle θr between the radiation direction and the an￾tenna’s surface, the longer the reader’s scanning range. However, in the realistic environment, the tag size, the reader’s power Pw, the radiation angle θr, and the distance d all affect the effective interrogation region, as mentioned in section 3. Therefore, in the realistic environments, we measure the minimum power Pwmin based on θr and d, and use them to calculate the initial power. In this paper, we measure Pwmin (θr, d) with the distances dj = 0.5m × j, j ∈ [1, 7] and the angles θi = 90◦ − 15◦ × i, i ∈ [0, 6]. For example, we get Pwmin (90◦ , 1.0) = 15.7dBm, Pwmin (75◦ , 1.5) = 18.8dBm, Pwmin (60◦ , 2.0) = 23.4dBm. The reader first selects the reference angle θi closest to θr, |θr − θi | ≤ |θr − θk| (k ∈ [0, 6] and k ̸= i). Then, it uses d to calculate the initial power Pwmin (θr, d) { Pwmin (θi , dj ) if d = dj Pwmin (θi,dj )+Pwmin (θi,dj+1) 2 if d ∈ [dj , dj+1]. (1) However, the power is only used as the initial power. In order to identify more tags, the reader can repeatedly increase the power by ∆Pw. We set ∆Pw = 1dBm, which is achievable by most of the commercial readers [14]. Establishing the boundary The 3D camera can recognize the specified area by RGB camera and measure distance by 3D depth sensors. However, the reader can hardly find the boundary of S, due to the unknown distribution of tag IDs. Therefore, PID first establishes the boundary Sb of the area S based on the in￾terference tags located around S, as shown in Fig. 4. PID uses the 3D camera to calculate the minimum distance db between the interference tags in Sb and the antenna, and the distance ds between the center of S and the antenna. Further￾more, it calculates the rotation angle φ = arccos( ds db ), φ ∈ (0◦ , 90◦ ). Then, the antenna rotates φ degree to face the interference tags in Sb for identification. The identified tags are used as reference tags to describe Sb. Specified area (S) Interrogation region Tag (S) db ds Antenna ¶ Fig. 4. Identify the tags in the specified area with a 3D camera In PID, the antenna always faces towards the center of the objects, θr = 90◦ . Then, the reader selects the initial power Pwb according to the distance d