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Andrea Bardella, Nicola Bui, Andrea Zanella and Michele Zorzi

Andrea Bardella, Nicola Bui, Andrea Zanella and Michele Zorzi {bardella,bui,zanella,zorzi}@dei.unipd.it Signet Research Group http://dgt.dei.unipd.it Department of Information Engineering, University of Padova, Italy. SIGNET. Special Interest Group on NEtworking & Telecommunications.

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Andrea Bardella, Nicola Bui, Andrea Zanella and Michele Zorzi

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  1. Andrea Bardella, Nicola Bui, Andrea Zanella and Michele Zorzi {bardella,bui,zanella,zorzi}@dei.unipd.it Signet Research Group http://dgt.dei.unipd.it Department of Information Engineering, University of Padova, Italy SIGNET Special Interest Group on NEtworking & Telecommunications An Experimental Study on IEEE 802.15.4 Multichannel Transmission to Improve RSSI-Based Service Performance

  2. Outline • motivation • experimental setup • wireless channel characterization • multi-channel analysis • communication protocol • conclusion

  3. Motivation RSSI: ReceivedSignalStrengthIndicator Supportedbymost commercial RF transceivers Largelyusedtoassesschannelquality and/or used in manylocalizationalgosforranging High variability • Goals: • Experimental characterization of RSSI • Reducing RSSI variability by multi-channel samples harvesting

  4. Outline • motivation • experimental setup • wireless channel characterization • multi-channel analysis • communication protocol • conclusion

  5. Tmote Sky platform • CC2420 transceiver • 250 kbps @ 2.4 Ghz • external isotropic antenna (5 dBi) 5 MHz 3 MHz fm = 2405 + 5(m-11) Mhz m = 11, …, 26 2405 MHz 2480 MHz

  6. Experimental setup • indoor & outdoor • N fixed nodes • 1 mobile node for each position for each couple of nodes for each channel 10 RSSI samples collected over time

  7. Outline • motivation • experimental setup • wireless channel characterization • multi-channel analysis • communication protocol • conclusion

  8. Classical path loss model with Gaussian shadowing fast fading rx power (in [dBm]) actual distance slow fading (shadowing) path loss coefficient tx power (in [dBm]) constant (free space atten., antenna gain,…) reference distance free space + shadowing Least Mean Square criterion to estimateKandη

  9. Parameter estimation For each couple of nodes and channel →10 RSSI samples collected over time

  10. Ψ: fitting the normal pdf indoor →σΨ = 4.6 dB outdoor →σΨ = 3.5 dB

  11. Rx signal statistic Weibull distributed [1] Extreme Value distributed EV(θlocation, θscale) [1] Sagias, N.C., Karagiannidis, G.K.: “Gaussian Class Multivariate Weibull Distribution: Theory and Applications in Fading Channels”, IEEE Trans. on Information Theory (Oct 2005)

  12. Ψ: fitting the Extreme Value pdf Indoor (Kullback-Leibler divergence) KL(emp,norm) = 0,0824 KL(emp,ev) = 0,0169 Outdoor (Kullback-Leibler divergence) KL(emp,norm) = 0,1371 KL(emp,ev) = 0,0146 Extreme Value distribution fits better the empirical data than the Normal distribution

  13. Outline • motivation • experimental setup • wireless channel characterization • multi-channel analysis • communication protocol • conclusion

  14. Narrowband fading amplitude • Tds→delay spread • B→tx signal bandwidth • u(t)→baseband signal • τn→delay associated with the n-th component t τ1 τ2 τ3

  15. Example: two rays phase associated with n-th component d TX @ 2405[MHz] (m=11) TX @ 2455[MHz] (m=21) d1' d1'' if δ1 = (d1' +d1'') – d = 3[m] thenτ1 = δ1/vp = 10[ns] and Δϕ = |ϕ1,11 – ϕ1,21| = π

  16. Multichannel Averaging RSSI samples over frequencies

  17. Outline • motivation • experimental setup • wireless channel characterization • multi-channel analysis • communication protocol • conclusion

  18. Communication protocol I’m in CH1! (Next CH2) Anybody in CH1? (Next CH2) I’m in CH1! (Next CH2) Everybody’s switching on CH2. Let’s follow them!

  19. Inquirer scheduled channels: default, NC(1), ..., NC(end) next channel = NC(1) start REQ T.O. TX REQUEST next channel = NC(i) start REQ T.O. TX REQUEST no RX REPLY i>end yes REQ T.O. elapsed no yes restart REQ T.O. channel = next channel i = i+1 no reply RX REPLY yes REQ T.O. elapsed no END

  20. Replier IDLE channel = default IDLE channel = next channel RX REPLY RX REQUEST no no yes yes TX REPLY

  21. Conclusion • RSSI characterization • parametric and statistical • statistic model validation • RSSI variability mitigation • RSSI averaged over time  • RSSI averaged over frequency  • Communication protocol simulation tools Indoor & Outdoor 802.15.4 RSSI and LQI measurements http://telecom.dei.unipd.it/pages/read/59/

  22. Questions? THANK YOU FOR YOUR ATTENTION! An Experimental Study on IEEE 802.15.4 Multichannel Transmission to Improve RSSI-Based Service Performance Andrea Bardella, Nicola Bui, Andrea Zanella and Michele Zorzi {bardella,bui,zanella,zorzi}@dei.unipd.it

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