1. Scrutinizing bit-and symbol-errors of IEEE 802.15.4 Communication in Industrial Environments Filip Barac, Student Member, IEEE, Mikael Gidlund, Member, IEEE, and Tingting Zhang, Member, IEEE TIM(2013)

2. Why study error properties 1.first step in protocol design Crucial for designing higher layer protocals Facilitates the design of FEC coding,interleaving,retransmission schemes 2.bit and symbol-level errors offer more subtle channel-state information The commonly observed parameters can’t (packet loss,delay) e.g error pattern,burstiness,ber Works: 1.Study of error properties 2.Optimal choice of channel coding

3. Error Sources 1.Physical Environment

4. Error Sources 2.Electromagnetic Interference (e.g WLAN)

5. Experimental Setup: wlan setup beacon predefined content 1.Error distribution 2.Burstiness 3.Channel memory 4.Ber

6. 1. Bit-Error Distribution

7. 1.randomly placed bit-errors2.periodic ——Without Wifi Interference

8. 1. Bit-Error Distribution a ramp like pattern ——With Wifi Interference

9. 2.Bit- and Symbol-Error Burst Length 1.90% bursts are no more than 5 bits 2.single-symbol-error bursts dominate in 802.15.4

10. 3. Channel Memory Length The burst nature of WLAN-affected errors

11. 4.The Bounds on BER The performance of FEC codes depends on how often the number of errors exceeds the correcting capability 99.14% of packets corrupted by MFA had a BER≤10% and the mean BER is 1.88%. The mean BER averaged over all WLAN experiments is 9.51%

12. Implication on channel coding selection Two criteria Error correction performance Computational complexity Turbo and LDPC Good correcting ability En/decoding slow: hardware-accelerated implementations result in encoding times in the order of 6–7 ms Reed-Solomon code A tradeoff require decoding times below 1 ms for certain block lengths

13. RS(?,?) 1.Suitability With Respect to Bit-Error Burst Properties Burst length is no more than 5 bits m = 4,n = 2^4 – 1 = 15;RS(15,?) 2.Timing Constraints of IEEE 802.15.4-2006-Based Standards RS(15,7) is the strongest code satisfy the following constraints:

14. codeword symbol codeword Interleaving

15. Implication 1: The Lower Bound of Plain RS(15,7) Performance Under MFA a measurable named packet salvation ratio (PSR) Absoulte improvements of pdr introduced by RS(15,7) in several experiments on links under MFA it is not possible to bring quantitative conclusions about RS(15,7) performance under WLAN interference.

16. Implication 2: BI Versus SI and the Optimal Interleaving Depth 1.SI outperforms BI on both types of link 2.The optimal interleaving depth corresponds to the codeword length

17. Implication 3: The Gain of SI on Links Affected by MFA In MFA experiments The contribution of SI negligible BI reduces the PSR in corrupted packets So interleaving is not recommendable for default use should be activated when interference occurs FEC and interleaving are preferable to retransmissions 2,700 times more energy to send one bit than to execute an instruction

18. Conclusion Scrutinizing nature of bit- and symbol-errors of IEEE 802.15.4-2006 transmissions Bers,symbol burst lengths Channel memory Bit-error-bursts : less than five in most cases The evaluation on channel coding and interleaving BI should not be considered for practical implementations

19. Thanks

21. Contributions 1.a number of conclusions about bit- and symbol-error behavior 2.two distinct error patters are identified 3.the performance of a sufficiently lightweight channel code is evaluated on the collected error traces 4.it shows that SI(symbol interleaving) outperforms it counterpart 5.the interleaving gain is proven to be negligible on links affected by MFA 6.FEC and interleaving are a must on links under IEEE802.11 interference