Fig.12.Scheduling rounds Fig.13.Throughput Fig.14.Delays procedure,such as the asynchronization,background noise,[13]J.Waldrop.D.W.Engels,and S.E.Sarma,"Colorwave:An Anticol- and the like. lision Algorithm for the ReaderCcollision Problem,"in Proceedings of IEEE ICC.2003. [14]Z.Zhou.H.Gupta.S.R.Das,and X.Zhu."Slotted Scheduled Tag ACKNOWLEDGMENT Access in Multi-Reader RFID Systems,"in Proceedings of ICNP.2007 We thank Qinsong Yao and Yiyang Zhao for their kind help [15]S.Tang.J.Yuan,X.Y.Li,G.Chen,Y.Liu,and J.Zhao,"RASPberry: A Stable Reader Activation Scheduling Protocol in Multi-reader RFID in our experiment.This work is supported in part by National Systems,"in Proceedings of ICNP,2009 Natural Science Foundation of China (NSFC)(No.60933003. [16]L.S.Leong.N.M.Ng.A.R.Grasso,and P.H.Cole,"Synchronization No.60736016,No.60873262,and No..60903155),National of RFID Readers for Dense RFID Reader Environments,"in Proceedings of SAINT Workshops 2006. High Technology Research and Development Program of [17]J.F.Kuros and K.W.Ross,Computer Networking:A Top-Down China(863 Program)under Grants No.2009AA01Z116,Na- Approach Featuring the Internet,2005. [18]F.C.Schoute,"Dynamic Frame Length ALOHA,"IEEE Transactions tional Basic Research Program of China (973 Program) on Communications,1983. under Grants No.2011CB302705.No.2010CB328004 and [19]M.Kodialam andT.Nandagopal,"Fast and Reliable Estimation Schemes No.2010CB328101,China Postdoctoral Science Foundation in RFID Systems,"in Proceedings of MobiCom,2006. [20]C.Qian,H.Ngan,and Y.Liu,"Cardinality Estimation for Large-scale funded project (No.20090461298),Hong Kong Innovation RFID Systems,"in Proceedings of PerCom,2008. and Technology Fund GHP/044/07LP and ITP/037/09LP,the [21]T.Li.S.Wu.S.Chen,and M.Yang"Energy Efficient Algorithms for Science and Technology Research and Development Program the RFID Estimation Problem,"in Proceedings of INFOCOM,2010. (22]H.Han,B.Sheng.C.Tan,Q.Li,W.Mao and S.Lu,"Counting RFID of Shaanxi Province under Grant No.2008KW-02.and IBM Tags Efficiently and Anonymously,"in Proceedings of INFOCOM,2010. Joint Project.This work also Partially supported by the Danish [23]S.Basagni,"Finding a Maximal Weighted Independent Set in Wireless Agency for Science,Technology and Innovation,International Networks."Telecommunication Systems,2001. (24]E.Welbourne,K.Koscher,E.Soroush,M.Balazinska,and G.Borriello, Network Program. "Longitudinal Study of a Building-scale RFID Ecosystem,"in Proceed- ings of ACM MobiSys,2009. REFERENCES [25]http://rfid.cs.washington.edu/deployment/ (26]S.R.Lee,S.D.Joo,and C.W.Lee,"An Enhanced Dynamic Framed [1]B.Sheng,C.C.Tan,Q.Li,and W.Mao,"Finding Popular Categories Slotted ALOHA Algorithm For RFID Tag Identification,"in Proceedings for RFID Tags,"in Proceedings of MobiHoc,2008. of MobiQuitous,2005. [2]T.Kriplean,E.Welbourne,N.Khoussainova,V.Rastogi,M.Balazinska, [27]B.Sheng.Q.Li,and W.Mao,"Efficient Continuous Scanning in RFID G.Borriello,T.Kohno,and D.Suciu,"Physical Access Control for Systems,"in Proceedings of INFOCOM,2009. Captured RFID Data,"Pervasive Computing,2007. [28]L.Xie,B.Sheng.C.C.Tan,H.Han.Q.Li,and D.Chen,"Efficient Tag [3]C.C.Tan.S.Bo.and L.Qun,"How to Monitor for Missing RFID tags," Identification in Mobile RFID Systems,"in Proceedings of INFOCOM. in Proceedings of ICDCS,2008. 2009. [4]L.M.Ni,Y.Liu,Y.C.Lau,and A.P.Patil,"LANDMARC:Indoor [29]J.Myung and W.Lee."Adaptive Binary Splitting:A RFID Tag Colli- Location Sensing Using Active RFID,"in ACM Wireless Networks, sion Arbitration Protocol for Tag Identification,"Mobile Networks and Volume 10,Issue 6,November 2004,Pages 701-710. Applications,2006. [5]M.Kodialam,T.Nandagopal,and W.C.Lau,"Anonymous Tracking [30]H.Gupta,Z.Zhou,S.R.Das,and Q.Gu,"Connected Sensor Cover: Using RFID Tags",in Proceedings of INFOCOM,2007. Self-organization of Sensor Networks for Efficient Query Execution." [6]Y.Liu,Z.Yang,X.Wang,and L.Jian,"Location,Localization,and IEEE/ACM Transaction on Networking,2006. Localizability,"in Journal of Computer Science and Technology,2010. [31]J.Ho.D.W.Engels.and S.E.Sarma."HiQ:A Hierarchical Q-leaming [7]Z.Yang.and Y.Liu,"Quality of Trilateration:Confidence based Algorithm to Solve the Reader Collision Problem,"in Proceedings of Iterative Localization",in IEEE Transactions on Parallel and Distributed IEEE SAINT Workshops 2006. Systems,Vol.21,No.5,May 2010,Pages 631-640. (32]C.Floerkemeier and E.Zurich,"Transmission Control Scheme for Fast [8]Z.Yang.Y.Liu,X-Y.Li,"Beyond Trilateration:On the Localizability of RFID Object Identification,"in Proceedings of PerCom Workshop,2006 Wireless Ad-hoc Networks",in IEEE/ACM Transactions on Networking [33]L Yang,J.Han,Y.Qi,Y.Liu,"Identification-Free Batch Authentication (TON).Vol.18,No.6.December 2010,Pages 1806-1814. for RFID Tags".in Proceedings of IEEE ICNP.2010. [9]"EPCglobal RFID Class-1 Gen2 UHF RFID Protocol,"Standard,2005. [34]L.Lu,J.Han,L.Hu,Y.Liu,and L.M.Ni,"Dynamic Key-Updating: [10]"RFID For Item Management Air Interface.Part-6,"ISO 18000-6 Privacy-Preserving Authentication for RFID Systems,"in Proceedings Standard,2003. of IEEE PerCom 2007. [11]J.R.Cha and J.H.Kim,"Novel Anti-collision Algorithms for Fast [35]L.Lu,J.Han,R.Xiao,and Y.Liu,"ACTION:Breaking the Privacy Object Identification in RFID System,"in Proceedings of ICPADS.2005. Barrier for RFID Systems,"in Proceedings of IEEE INFOCOM,2009 [12]D.W.Engels and S.E.Sarma."The Reader Collision Problem."in Proceedings of IEEE SMC.2002.Warehouse Tracking Sparse Moderate Dense 0 10 20 30 40 50 60 70 80 90 100 110 120 Scheduling rounds (# of time slots) DCS Colorwave Season Fig. 12. Scheduling rounds Warehouse Tracking Sparse Moderate Dense 0 2 4 6 8 Throughput DCS Colorwave Season Fig. 13. Throughput Warehouse Tracking Sparse Moderate Dense 0 5000 10000 15000 20000 25000 30000 35000 40000 45000 50000 55000 60000 65000 Delay(# of time slots) DCS Colorwave Season Fig. 14. Delays procedure, such as the asynchronization, background noise, and the like. ACKNOWLEDGMENT We thank Qinsong Yao and Yiyang Zhao for their kind help in our experiment. This work is supported in part by National Natural Science Foundation of China (NSFC) (No.60933003, No.60736016, No.60873262, and No.60903155), National High Technology Research and Development Program of China (863 Program) under Grants No.2009AA01Z116, Na￾tional Basic Research Program of China (973 Program) under Grants No.2011CB302705, No.2010CB328004 and No.2010CB328101, China Postdoctoral Science Foundation funded project (No.20090461298), Hong Kong Innovation and Technology Fund GHP/044/07LP and ITP/037/09LP, the Science and Technology Research and Development Program of Shaanxi Province under Grant No.2008KW-02, and IBM Joint Project. This work also Partially supported by the Danish Agency for Science, Technology and Innovation, International Network Program. REFERENCES [1] B. Sheng, C. C. Tan, Q. Li, and W. Mao, “Finding Popular Categories for RFID Tags,” in Proceedings of MobiHoc, 2008. [2] T. Kriplean, E. Welbourne, N. Khoussainova, V. Rastogi, M. Balazinska, G. 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