cate with the data acquisition module through WiFi. 3 Demonstration We start by randomly place books into the bookshelf.The LD tag user is invited to search a book by entering the keywords in- to the search box in the tablet embedded in the bookshelf. By clicking on one of the results,information such as the abstract and cover of the book are crawled from the Internet and illustrated on the user interface.The user can further lo- cate the book's position by clicking the"location"button,i- Bookshelfreturns the location graphically as shown in Fig.4, along with less probable locations and the respective proba- 4a- X-axis bilities.Due to space limitation,we can show a video of the Figure 2.The design model of iBookshelf system at the demo,and present a smaller live version 2.1 Indexing and Searching The indexing/search module is working as follows:once a book with tag attached is placed into the bookshelf,the tag'ID and keyword information is sensed by the data ac- quisition module.Then,the keywords are incorporated into the search index,meanwhile,the web crawlers use these key- words to crawl more detail information from web sites such as Wikipedia in the Internet.The crawled data are further Theya stored and indexed.When a user wants to search a book. The x axis he/she enters the keyword and the system returns the search (a)The similarity between the target(b)The probability of each grid for tag and the reference tags the target book to be located to results by fast retrieving data from the index 2.2 Localization Figure 3.Experiment results:the target book is deployed in Grid (3,2)in the X-Y axis among the 4 x 4 grids The objective of the localization module is to accurately locate the target tags in a real-time approach.In order to offset the impact from the ambient noises and interferences. we uniformly deploy 15 reference tags inside the grids,as shown in Fig.2.The position of each reference tag in X-Y axis is fixed and known in advance.We propose an algorithm to estimate the target tag's position,as shown in Alg.1. Algorithm 1 Localization Algorithm 1:Set the reader to issue m query cycles from each of the 4 antennas. 2:Get the signal strength vector of the target tag as V={s1,s2,53,s4),sj is the average signal strength of the target tag perceived on antennas / Figure 4.The user interface of iBookshelf where j∈[l,4. 3:Get the signal strength vector of the reference tags as= 4 Acknowledgments {s.1,2,s.3,s.4},where i∈[l,15. This work is supported by the National Basic Research 4:for i 1,15]do Program of China(973)under Grant No.2009CB320705: Compute the similarity between and Vi as follows the National Natural Science Foundation of China under V.V mK,闭=个 =1 Grant No..61100196,61073028,61021062:the JiangSu V=了V= Natural Science Foundation under Grant No.BK2011559. References 6 end for 7:Sort the value of sim(.)in decreasing order.Find the first k refer- [1]S.Inoue,Y.Nohara,T.Masaki,and K.Sakuragawa.Location recogni- tion in rfid bookshelves.IEICE Transactions,pages 1147-1152,2011. ence tags with the position (x)according to sim(V.V). 8:Compute the position of the target tag [2]L.M.Ni,Y.Liu,Y.C.Lau,A.P.Patil,and A.P.Patil.Landmarc: Indoor location sensing using active rfid.Wireless Nenorks,pages (.y)()-w.here.= 1/(1-sim(V,)+e) 701-710,2004 1 I-m(化月+g>0叭， [3]C.Peng,G.Shen,Y.Zhang,Y.Li,and K.Tan.Beepbeep:a high accuracy acoustic ranging system using cots mobile devices.In Proc. According to the localization algorithm,suppose we place ofACM SenSys,2007. a target book in Grid (3,2)in the X-Y axis,Fig.3(a)shows the [4]A.Sample,C.Macomber,L.-T.Jiang,and J.R.Smith.Optical local- similarities between this target tag and the reference tags in ization of passive uhf rfid tags with integrated leds.In Proc.of /EEE terms of the received signal strength,Fig.3(b)further shows RFID,2012. the probability of each grid that the target book is located to, [5]M.Youssef,M.Mah,and A.Agrawala.Challenges:device-free passive on average the target book is located to the right grid with localization for wireless environments.In Proc.of ACM MobiCom, 85%accuracy 2007.cate with the data acquisition module through WiFi. RFID Reader (Alien-9900) Antenna Antenna Books attached with RFID tag Antenna Antenna Tablet PC Reference RFID tags X-axis Y-axis (1,3) (2,3) (3,3) (4,3) (5,3) (1,2) (2,2) (3,2) (4,2) (5,2) (1,1) (2,1) (3,1) (4,1) (5,1) 1 2 3 4 1 1 2 3 4 Figure 2. The design model of iBookshelf 2.1 Indexing and Searching The indexing/search module is working as follows: once a book with tag attached is placed into the bookshelf, the tag’ ID and keyword information is sensed by the data ac￾quisition module. Then, the keywords are incorporated into the search index, meanwhile, the web crawlers use these key￾words to crawl more detail information from web sites such as Wikipedia in the Internet. The crawled data are further stored and indexed. When a user wants to search a book, he/she enters the keyword and the system returns the search results by fast retrieving data from the index. 2.2 Localization The objective of the localization module is to accurately locate the target tags in a real-time approach. In order to offset the impact from the ambient noises and interferences, we uniformly deploy 15 reference tags inside the grids, as shown in Fig.2. The position of each reference tag in X-Y axis is fixed and known in advance. We propose an algorithm to estimate the target tag’s position, as shown in Alg. 1. Algorithm 1 Localization Algorithm 1: Set the reader to issue m query cycles from each of the 4 antennas. 2: Get the signal strength vector of the target tag as V = {s1,s2,s3,s4}, sj is the average signal strength of the target tag perceived on antennas j, where j ∈ [1,4]. 3: Get the signal strength vector of the reference tags as Vi = {si,1,si,2,si,3,si,4}, where i ∈ [1,15]. 4: for i ∈ [1,15] do 5: Compute the similarity between V and Vi as follows: sim(V,Vi) = V ·Vi |V|·|Vi | = ∑ 4 j=1 si, j ·sj q ∑ 4 j=1 s 2 j · q ∑ 4 j=1 s 2 i, j . 6: end for 7: Sort the value of sim(V,Vi) in decreasing order. Find the first k refer￾ence tags with the position (xi ,yi) according to sim(V,Vi). 8: Compute the position of the target tag (x,y) = k ∑ i=1 (xi ,yi)·wi ,here,wi = 1/(1−sim(V,Vi) +ε) ∑ k i=1 1/(1−sim(V,Vi) +ε) (ε > 0). According to the localization algorithm, suppose we place a target book in Grid (3,2) in the X-Y axis, Fig.3(a) shows the similarities between this target tag and the reference tags in terms of the received signal strength, Fig.3(b) further shows the probability of each grid that the target book is located to, on average the target book is located to the right grid with 85% accuracy. 3 Demonstration We start by randomly place books into the bookshelf. The user is invited to search a book by entering the keywords in￾to the search box in the tablet embedded in the bookshelf. By clicking on one of the results, information such as the abstract and cover of the book are crawled from the Internet and illustrated on the user interface. The user can further lo￾cate the book’s position by clicking the “location” button, i￾Bookshelf returns the location graphically as shown in Fig.4, along with less probable locations and the respective proba￾bilities. Due to space limitation, we can show a video of the system at the demo, and present a smaller live version. 1 2 3 4 5 1 2 3 0 0.5 1 The value of y The value of x The value of similarity (a) The similarity between the target tag and the reference tags 1 2 3 4 1 2 3 4 0 20 40 60 80 100 The x axis The y axis The detection ratio (%) (b) The probability of each grid for the target book to be located to Figure 3. Experiment results: the target book is deployed in Grid (3,2) in the X-Y axis among the 4 × 4 grids Figure 4. The user interface of iBookshelf 4 Acknowledgments This work is supported by the National Basic Research Program of China (973) under Grant No. 2009CB320705; the National Natural Science Foundation of China under Grant No. 61100196, 61073028, 61021062; the JiangSu Natural Science Foundation under Grant No. BK2011559. References [1] S. Inoue, Y. Nohara, T. Masaki, and K. Sakuragawa. Location recogni￾tion in rfid bookshelves. IEICE Transactions, pages 1147–1152, 2011. [2] L. M. Ni, Y. Liu, Y. C. Lau, A. P. Patil, and A. P. Patil. Landmarc: Indoor location sensing using active rfid. Wireless Networks, pages 701–710, 2004. [3] C. Peng, G. Shen, Y. Zhang, Y. Li, and K. Tan. Beepbeep: a high accuracy acoustic ranging system using cots mobile devices. In Proc. of ACM SenSys, 2007. [4] A. Sample, C. Macomber, L.-T. Jiang, and J. R. Smith. Optical local￾ization of passive uhf rfid tags with integrated leds. In Proc. of IEEE RFID, 2012. [5] M. Youssef, M. Mah, and A. Agrawala. Challenges: device-free passive localization for wireless environments. In Proc. of ACM MobiCom, 2007