Underwater Backscatter Channel: Theory, Link Budget, and Climate Monitoring

In response to the significant impacts of climate change on the world's oceans, a new technology called underwater backscatter is being developed for distributed ultra-low-power underwater sensor networks. This technology aims to enable climate monitoring, sea-level measurement, and hurricane response in coastal regions. The research includes theoretical modeling, experimental validation, and analysis of the communication range and capabilities of underwater backscatter systems.

• Underwater Technology
• Climate Monitoring
• Backscatter Communication
• Ocean Research
• Experimental Validation

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1. The Underwater Backscatter Channel: Theory, Link Budget, and Experimental Validation Waleed Akbar Ahmed Allam Fadel Adib

2. This Work is Motivated by Climate Change The ocean plays the largest role in the world s climate, and has been significantly impacted by climate change Significant need to monitor the ocean, especially in coastal regions Food security + climate-friendly food We have been developing underwater backscatter, a new technology for distributed ultra-low-power underwater sensor networks [SIGCOMM'19, SIGCOMM'20, OCEANS 20, Nature Communications 22, HotNets 22, HotMobile 22, SIGCOMM 23] Climate monitoring Sea-level + hurricane response

3. Backscatter Communication Traditional Acoustic Communication Acoustic waves Reflects an existing acoustic signal Consumes a ?? few of power Generates its own acoustic signal Consumes 10s of watts of power Backscatter Node

4. How far can we communicate using underwater backscatter?

5. End-to-End Link Budget Model Channel Transmitter ?2 ? ??? = 159.8 + 10log ?? + ???+ 10log + 2?????+ ???? 2?? ?? Signal-to-Noise Ratio Backscatter Node

6. End-to-End Link Budget Model First closed-form analytical model of underwater backscatter network ?2 ? Validated through empirical and numerical evaluation with a median error of ??? = 159.8 + 10log ?? + ???+ 10log <0.76dB across frequencies + 2?????+ ???? 2?? ?? Shows that the backscatter range can be extended to multiple kilometers even in its current form

7. Theory vs Practice ?2 ? ??? = 159.8 + 10log ?? + ???+ 10log + 2?????+ ???? 2?? ?? Tx Rx (hydrophone) Node 1 m Experimental Setup in the Charles River

8. Theory vs Practice Analytical (Theory) ??? ?2 ? = 159.8 + 10log ?? + ???+ 10log + 2?????+ ???? 2?? ?? Experimental Validation Tx Median deviation < 0.76 dB Rx Node (hydrophone) 1 m

9. Theory vs Practice Analytical (Theory) ??? ?2 ? = 159.8 + 10log ?? + ???+ 10log + 2?????+ ???? 2?? ?? Experimental Validation Tx Rx Node (hydrophone) 1 m

10. Let us focus on the key novel component of our end-to-end link budget

11. Backscatter Communication Traditional Acoustic Communication Rx Rx Tx ?? =????? ?? Differential Scattering Cross Section Incident Intensity (??) Reflected Power (?????) Channel Channel Tx

12. Differential Scattering Cross Section (??) ????? ?? ?? =

13. Differential Scattering Cross Section (??) ????? ?? ?? = Electrical ?? ????? ?? ?? ?? ? ?? ??? ?? Acoustic Directivity Piezoelectric Differential Reflection Coefficient Wavelength ??=?2?? 2 ???122 ????22+??2 ????? ?????2 ??1 |???+??1||???+??2| Electrical impedance mismatch = 2 4?

14. End-to-End SNR Tx 159.8 + 10log ?? + ??? Channel 2?? + ?? =?2?? 2 4? ??

15. End-to-End SNR ??? = ) + 10 ???( 159.8 + 10log ?? + ??? ?? Backscatter Node Gain ) ( 2?? + ?? Tx Gain Pathloss ?2 ? ??? = 159.8 + 10log ?? + ???+ 10log + 2?????+ ???? 2?? ?? Input Electrical Power Noise Impedance Mismatch

16. How far can we Communicate using Underwater Backscatter? = 0 dB

17. Link-Budget Tool

18. End-to-End Link Budget Model First closed-form analytical model of underwater backscatter Validated through empirical and numerical evaluation with a median error of <0.76dB across frequencies 01010101 Shows that the backscatter range can be extended to several kilometers ?? An interactive open-source tool to study backscatter systems: https://github.com/signalkinetics/linkbudget Datasets (1,500+ experimental trials) & Open-Source Code [SIGCOMM 23]: https://github.com/signalkinetics/vab