888 EEE TRANSACTIONS ON COMPUTERS,VOL.65,NO.3.MARCH 2016 Focus and Shoot:Exploring Auto-Focus in RFID Tag ldentification Towards a Specified Area Yafeng Yin,Student Member,IEEE,Lei Xie,Member,IEEE,Jie Wu,Fellow,IEEE,and Sanglu Lu,Member,IEEE Abstract-With the rapid proliferation of RFID technologies,RFID has been introduced into applications such as inventory and sampling inspection.Conventionally,in RFID systems,the reader usually identifies all the RFID tags in the interrogation region with the maximum power.However,some applications may only need to identify the tags in a specified area,which is usually smaller than the reader's default interrogation region.An example could be identifying the tags in a box,while ignoring the tags out of the box.In this paper,we respectively present two solutions to identify the tags in the specified area.The principle of the solutions can be compared to the picture-taking process of an auto-focus camera,which firstly focuses on the target automatically and then takes the picture. Similarly,our solutions first focus on the specified area and then shoot the tags.The design of the two solutions is based on the extensive empirical study on RFID tags.Realistic experiment results show that our solutions can reduce the execution time by 44 percent compared to the baseline solution,which identifies the tags with maximum power.Furthermore,we improve the proposed solutions to make them work well in more complex environments. Index Terms-RFID,tag identification,auto-focus,specified area,experimental study,algorithm design 1 INTRODUCTION ECENTLY,RFID tags have been widely used in various Moreover,identifying the tags out of the area is rather time- Lapplications,such as inventory control,sampling consuming.Due to the large number of tags,time-efficiency inspection,and supply chain management.Each RFID tag is very important.Therefore,it is essential to identify the has a unique ID,thus the reader can recognize the object by tags in the specified area efficiently without moving the tags. identifying its attached tag.Many existing research works on Fortunately,we note that tag identification in the speci- RFID have concentrated on tag identification [1],[21,[3],[4],fied area can be compared to the picture-taking process in [51,[61,[71,[81,aiming to identify a large number of tags as an auto-focus camera.The camera automatically focuses on quickly as possible.While detecting the missing tags and the object before shooting,aiming to lock the target object searching a particular subset of tags only concentrate on the while ignoring the others.In this paper,we propose the part of tags.However,all the literature do not research the photography based identification method,which works in a problem of tag identification in a specified area,which is similar way.It first focuses on the specified area by adjust- rather important in many applications,e.g.,inventory and ing the antenna's angle and the reader's power,and then sampling inspection in warehouse management.Taking the identifies the tags in the area.When the reader's interro- inventory for example,in order to have a knowledge of the gation region is just enough to cover the specified area,it tags in the target area,we may only need to identify the tags achieves the best performance.To solve this problem,we in some specified boxes while ignoring the others,i.e.,identi- respectively propose two solutions working in the realistic fying the tags in the specified area.In regard to a sampling environments.Both solutions conform to the EPC-C1G2 inspection,it also requires focusing on the tags in the current standards. area,while ignoring the others.Sometimes,it is difficult to However,efficiently identifying the tags in realistic move the objects out for tag identification,especially for environments is difficult.There are a few research works the objects obstructed by obstacles.A traditional solution is concentrating on this problem.The reading performance to identify the tags with the maximum power (MaxPw).in the realistic experiments is still unknown,especially for However,this solution will identify the tags out of the area,a large number of tags.Hence,we conduct a series of leading to lower accuracy of the identification process. measurements over RFID tags in realistic settings,inves- ting the factors which affect the reading performance.For- tunately,we have a few important new findings.For .Y.Yin,L.Xie,and S.Lu are with the State Key Laboratory for Novel Soft- example,we find that the tag density affects the effective ware Technology,Nanjing University,Nanjing 210023,China. scanning range,i.e.,the larger the tag density,the smaller E-mail:yyf@dislab.nju.edu.cn,(lxie,sanglu@nju.edu.cn. I.Wu is with the Department of Computer and Information Sciences the effective scanning range.The findings are crucial for Temple UIniversity,Philadelphia,PA 19122.E-mail:jiewu@temple.edu. improving the performance of our solutions.They indicate Manuscript received 28 June 2014;revised 26 Feb.2015;accepted 22 Apr. that the reader should adaptively adjust its interrogation 2015.Date of publication 19 May 2015;date of current version 10 Feb.2016. region,considering the actual situation.We propose the Recommended for acceptance by G.Min. two solutions based on the extensive experimental study, For information on obtaining reprints of this article,please send e-mail to: in order to make the solutions work well in the realistic reprints@ieeeorg,and reference the Digital Object Identifier below. Digital Object Identifier no.10.1109/TC.2015.2435749 environments.Focus and Shoot: Exploring Auto-Focus in RFID Tag Identification Towards a Specified Area Yafeng Yin, Student Member, IEEE, Lei Xie, Member, IEEE, Jie Wu, Fellow, IEEE, and Sanglu Lu, Member, IEEE Abstract—With the rapid proliferation of RFID technologies, RFID has been introduced into applications such as inventory and sampling inspection. Conventionally, in RFID systems, the reader usually identifies all the RFID tags in the interrogation region with the maximum power. However, some applications may only need to identify the tags in a specified area, which is usually smaller than the reader’s default interrogation region. An example could be identifying the tags in a box, while ignoring the tags out of the box. In this paper, we respectively present two solutions to identify the tags in the specified area. The principle of the solutions can be compared to the picture-taking process of an auto-focus camera, which firstly focuses on the target automatically and then takes the picture. Similarly, our solutions first focus on the specified area and then shoot the tags. The design of the two solutions is based on the extensive empirical study on RFID tags. Realistic experiment results show that our solutions can reduce the execution time by 44 percent compared to the baseline solution, which identifies the tags with maximum power. Furthermore, we improve the proposed solutions to make them work well in more complex environments. Index Terms—RFID, tag identification, auto-focus, specified area, experimental study, algorithm design Ç 1 INTRODUCTION RECENTLY, RFID tags have been widely used in various applications, such as inventory control, sampling inspection, and supply chain management. Each RFID tag has a unique ID, thus the reader can recognize the object by identifying its attached tag. Many existing research works on RFID have concentrated on tag identification [1], [2], [3], [4], [5], [6], [7], [8], aiming to identify a large number of tags as quickly as possible. While detecting the missing tags and searching a particular subset of tags only concentrate on the part of tags. However, all the literature do not research the problem of tag identification in a specified area, which is rather important in many applications, e.g., inventory and sampling inspection in warehouse management. Taking the inventory for example, in order to have a knowledge of the tags in the target area, we may only need to identify the tags in some specified boxes while ignoring the others, i.e., identi￾fying the tags in the specified area. In regard to a sampling inspection, it also requires focusing on the tags in the current area, while ignoring the others. Sometimes, it is difficult to move the objects out for tag identification, especially for the objects obstructed by obstacles. A traditional solution is to identify the tags with the maximum power (MaxPw). However, this solution will identify the tags out of the area, leading to lower accuracy of the identification process. Moreover, identifying the tags out of the area is rather time￾consuming. Due to the large number of tags, time-efficiency is very important. Therefore, it is essential to identify the tags in the specified area efficiently without moving the tags. Fortunately, we note that tag identification in the speci- fied area can be compared to the picture-taking process in an auto-focus camera. The camera automatically focuses on the object before shooting, aiming to lock the target object while ignoring the others. In this paper, we propose the photography based identification method, which works in a similar way. It first focuses on the specified area by adjust￾ing the antenna’s angle and the reader’s power, and then identifies the tags in the area. When the reader’s interro￾gation region is just enough to cover the specified area, it achieves the best performance. To solve this problem, we respectively propose two solutions working in the realistic environments. Both solutions conform to the EPC-C1G2 standards. However, efficiently identifying the tags in realistic environments is difficult. There are a few research works concentrating on this problem. The reading performance in the realistic experiments is still unknown, especially for a large number of tags. Hence, we conduct a series of measurements over RFID tags in realistic settings, inves￾ting the factors which affect the reading performance. For￾tunately, we have a few important new findings. For example, we find that the tag density affects the effective scanning range, i.e., the larger the tag density, the smaller the effective scanning range. The findings are crucial for improving the performance of our solutions. They indicate that the reader should adaptively adjust its interrogation region, considering the actual situation. We propose the two solutions based on the extensive experimental study, in order to make the solutions work well in the realistic environments.
Y. Yin, L. Xie, and S. Lu are with the State Key Laboratory for Novel Soft￾ware Technology, Nanjing University, Nanjing 210023, China. E-mail: yyf@dislab.nju.edu.cn, {lxie, sanglu}@nju.edu.cn.
J. Wu is with the Department of Computer and Information Sciences, Temple University, Philadelphia, PA 19122. E-mail: jiewu@temple.edu. Manuscript received 28 June 2014; revised 26 Feb. 2015; accepted 22 Apr. 2015. Date of publication 19 May 2015; date of current version 10 Feb. 2016. Recommended for acceptance by G. Min. For information on obtaining reprints of this article, please send e-mail to: reprints@ieee.org, and reference the Digital Object Identifier below. Digital Object Identifier no. 10.1109/TC.2015.2435749 888 IEEE TRANSACTIONS ON COMPUTERS, VOL. 65, NO. 3, MARCH 2016 0018-9340
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