Probabilistic Optimal Tree Hopping for RFID Identification Muhammad Shahzad Alex X. Liu Dept. of Computer Science and Engineering Michigan State University East Lansing, Michigan, 48824, USA
2 RFID is everywhere Muhammad Shahzad
3 Radio Frequency Identification Muhammad Shahzad
4 Tree Walking (EPCGlobal Standard) Number of queries: Muhammad Shahzad
5 Optimizing Tree Walking Muhammad Shahzad Total queries = successful + collisions + empty Minimize total queries
6 Limitations of Prior Art All prior work proposes heuristics to reduce identification time ─ MobiHoc’06, PerCom’07, INFOCOM’09, ICDCS’10 No formal model of the Tree Walking process ─ No optimality results Muhammad Shahzad
7 Our Modeling of Tree Walking (Hypergeometric distribution) Level l Position p n=16 m=4 Muhammad Shahzad
8 Proposed Approach 1.Estimate unidentified tag population size 2.Find optimal level and the first unvisited node 3.Perform Tree Walking. Go to step 1 Muhammad Shahzad
9 Population Size Estimation First time estimation: rough, but fast ─ We adapt a fast scheme proposed by Flajolet and Martin in the database community in ─ Did not use accurate RFID estimation schemes Subsequent estimation = estimated tags - identified tags Muhammad Shahzad
10 Calculating Optimal Level Muhammad Shahzad
11 Muhammad Shahzad
12 Tree Hopping vs. Tree Walking Muhammad Shahzad
13 Tree Hopping Example Number of queries: 11 (compared to 16 of TW) Muhammad Shahzad
14 Experimental Evaluation Implemented 8 protocols in addition to TH 1.BS (IEEE Trans. on Information Theory, 1979) 2.ABS (MobiHoc, 2006) 3.TW (DIAL-M 2000) 4.ATW (Tanenbaum, 2002) 5.STT (Infocom, 2009) 6.MAS (PerCom, 2007) 7.ASAP (ICDCS 2010) 8.Frame Slotted Aloha (IEEE Transactions on Communications, 2005) Muhammad Shahzad
15 Improvement of TH over prior art Uniformly distributed populations ─ Total number of queries: 50% ─ Identification time: 10% ─ Average responses per tag: 30% Non-uniformly distributed populations ─ Total number of queries: 26% ─ Identification time: 37% ─ Average responses per tag: 26% Muhammad Shahzad
16 Normalized Queries Muhammad Shahzad
17 Identification Speed Muhammad Shahzad
18 Normalized Collisions Muhammad Shahzad
19 Normalized Empty Reads Muhammad Shahzad
20 Conclusion First effort towards modeling the Tree Walking process Proposed a method to minimize the expected number of queries More in the paper ─ Method to make TH reliable in the presence of communication errors ─ Continuous scanning of dynamically changing tag populations ─ Multiple readers environment with overlapping regions Comprehensive side-by-side comparison of TH with 8 major prior tag identification protocols Muhammad Shahzad
21 Questions? Muhammad Shahzad