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Scrutinizing bit-and symbol-errors of IEEE 802.15.4 Communication in Industrial Environments

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). Why study error properties. 1.first step in protocol design

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Scrutinizing bit-and symbol-errors of IEEE 802.15.4 Communication in Industrial Environments

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  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,retransmissionschemes • 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 1.Error distribution 2.Burstiness 3.Channel memory 4.Ber beacon predefined content

  6. 1. Bit-Error Distribution

  7. 1. Bit-Error Distribution ——Without Wifi Interference 1.randomly placed bit-errors 2.periodic

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

  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. Interleaving codeword codeword codeword codeword symbol

  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 codewordlength

  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-errorsof 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

  20. 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

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