1. Recovering Data From Corrupt Packets SENSYS 2013 EWSN 2014

2. Typical procedure of transmission  Techniques for overcoming bit errors  ARQ : Automatic Repeat reQuest  FEC : Forward Error Correction  Or the combination : HARQ  Interesting things happened when it finds a corrupted packet during the CRC detection process!  All IS NOT LOST(ANL): a opportunistic approach  TVA: an novel method of CRC correcting

3. DSSS in 802.15.4 Standard  A byte = 2 four-bit symbols  Echo symbol is finally represented by a 32-bit log chip sequence (i.e. the rightmost table)  What happened when takes noise into consideration ?  Corruption may happen

4. ANL : Observation  Deployment  16 nodes  One year from 2012 to 2013  Mutation Matrix:  Each entry denotes a mutation frequency  One Observation:  Mutations are not uniformly distributed

5. ANL : Recovering Data

6. ANL : Left questions  How to generate the mutation matrix?  Through Simulation  How to estimate p chip : using LQI  Is the actual sent word is assigned the highest rank?(95% of them are)

7. TVA-A reliable protocol  Procedure  Feature:  A novel method of CRC error correction  Compact and computationally efficient  Designed to correct the most common error patterns observed in WSNs

8. CRC error correction Theory ……CRC(e1)CRC(e2)CRC(e3)……......e1e2e3……

9. Reliability of TVA:verify ……CRC(e 2 )=c…… e2e2

10. Searching for Polynomials:results

11. Performance Comparison

12. Conclusion of two work  Solve the same issue  Recovering information from corrupt packet  Different method  ANL : a probabilistic approach  TVA : CRC error correcting  Combination Possibility?

13. 谢谢！

18. Comparison with other protocol

20. Outline 1.All is not lost the distinct pattern of how 802.15.4 packets are corrupted an probabilistically approach infers the original content of a corrupt packet 2.Unlocking the full power of the CRC a novel method of CRC error correction a protocol TVA making use of the error correcting ability of CRC

21. Comparision with ANL

22. Observations  Observation 1:Mutations are not uniformaly distributed  Observation 2:The most significant bit of a symbol is more stable than other bits  Observation 3:Symbols s0 to s7 are more stable than other symbols

23. Explanation

24. Exploitation COMPUTE A DISTRIBUTION: