Focus and Shoot:Efficient Identification Over RFID Tags 353 The only difference between PID and PIA is how to determine the boundary of S.We only describe how to find the boundary in PIA,while ignoring the others. Without the 3D camera,PIA cannot calculate any distance,it explores the boundary by rotating the antenna,as shown in Fig.5.Firstly,the application appoints S and the antenna rotates towards S.Then the reader sets its initial power equal to the minimum power min P and identifies ns tags in S.If ns<ne, the reader repeatedly increases the power by AP and identifies the tags until ns ne,the identified target tags are N.=(ID1,ID2,...,IDn}.If Pw maxP,PIA gets P=maxP.Otherwise,the antenna rotates away from S to get the interference tag IDs in the boundary,as shown in Algorithm 3. Anicmna Interrogation region Fig.5.Identify the tags in the specified area without any auxiliary equipment Algorithm 3.PIA:Exploring the boundary Input:The specified area S Pw=nin Pu,ns=0,nu=0,△0r1=0°. while ns<ne and P<marPu do Get ns tag IDs,Pe min(P +AP,mar P). if P maxPe then P maxPw,Return. Get tag IDs Ns={ID1,ID2...,IDn,} while n<ne and0r∈[0°，90]do The antenna rotates to the left by△or,△omn=△ar+△ar. while P<maxP do △ns tag IDs in Ns disappear,ns=ng-△ns· Get An new tag IDs,nn+An,update the set of new tags Ni ifl≥ne then Break. if Ans >0 then P min(P+AP,maxP).else Break. N6=V. The antenna rotates to the right in[O°，△orJ,gets Nr,it rotates△0 r degree. if△0n=△0 r.then N%=NUNr.else if△0r>△0r,then N=Nr. Output:Tag IDs in the boundary N When the antenna rotates to another direction(called as left),ns decreases As shown in Algorithm 3,when the radiation angle decreases by Aor,Ans tags in Ns disappear.The reader gets n new tag IDs,which are considered as the tag IDs from the boundary.If n ne,the reader collects enough tag IDsFocus and Shoot: Efficient Identification Over RFID Tags 353 The only difference between PID and PIA is how to determine the boundary of S. We only describe how to find the boundary in PIA, while ignoring the others. Without the 3D camera, PIA cannot calculate any distance, it explores the boundary by rotating the antenna, as shown in Fig. 5. Firstly, the application appoints S and the antenna rotates towards S. Then the reader sets its initial power equal to the minimum power minPw and identifies ns tags in S. If ns < nε, the reader repeatedly increases the power by ΔPw and identifies the tags until ns ≥ nε, the identified target tags are Ns = {ID1,ID2,...,IDns }. If Pw = maxPw, PIA gets P∗ w = maxPw. Otherwise, the antenna rotates away from S to get the interference tag IDs in the boundary, as shown in Algorithm 3. Fig. 5. Identify the tags in the specified area without any auxiliary equipment Algorithm 3. PIA: Exploring the boundary Input: The specified area S Pw = minPw, ns = 0, nl = 0, Δθrl = 0◦. while ns < nε and Pw < maxPw do Get ns tag IDs, Pw = min(Pw + ΔPw, maxPw). if Pw = maxPw then P∗ w = maxPw, Return. Get tag IDs Ns = {ID1,ID2 ...,IDns }. while nl < nε and θr ∈ [0◦, 90◦] do The antenna rotates to the left by Δθr, Δθrl = Δθrl + Δθr. while Pw < maxPw do Δns tag IDs in Ns disappear, ns = ns − Δns. Get Δnl new tag IDs, nl = nl + Δnl, update the set of new tags Nl. if nl ≥ nε then Break. if Δns > 0 then Pw = min(Pw + ΔPw, maxPw). else Break. Nb = Nl. The antenna rotates to the right in [0◦, Δθrl ], gets Nr, it rotates Δθrr degree. if Δθrl = Δθrr then Nb = Nl ∪ Nr. else if Δθrl > Δθrr then Nb = Nr. Output: Tag IDs in the boundary :Nb When the antenna rotates to another direction (called as left), ns decreases. As shown in Algorithm 3, when the radiation angle decreases by Δθr, Δns tags in Ns disappear. The reader gets nl new tag IDs, which are considered as the tag IDs from the boundary. If nl ≥ nε, the reader collects enough tag IDs