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

 
The Underwater Backscatter Channel:
Theory, Link Budget, and Experimental Validation
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
Sea-level +
hurricane response
Food security +
climate-friendly
food
Climate
monitoring
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]
Traditional Acoustic
Communication
Backscatter
Communication
 
 
Acoustic waves
 
Backscatter
Node
 
How far can we communicate using underwater
backscatter?
End-to-End Link Budget Model
 
Signal-to-Noise
Ratio
 
Backscatter
Node
 
Transmitter
 
Channel
End-to-End Link Budget Model
 
First closed-form 
analytical model 
of underwater backscatter network
Validated through empirical and numerical evaluation with a median error of
<0.76dB 
across frequencies
Shows that the backscatter range can be extended to multiple 
kilometers
even in its 
current form
Tx
Node
Rx (hydrophone)
1 m
 
Experimental Setup in the Charles River
Theory vs Practice
Tx
Node
Rx
(hydrophone)
1 m
Theory vs Practice
Analytical (Theory)
Experimental Validation
 
Median deviation < 0.76 dB
Tx
Node
Rx
(hydrophone)
1 m
Theory vs Practice
Analytical (Theory)
Experimental Validation
 
Let us focus on the key novel component of our
end-to-end link budget
Traditional Acoustic
Communication
Backscatter
Communication
 
 
 
 
Differential
Reflection
 
Coefficient
 
Wavelength
 
Directivity
 
Electrical impedance
mismatch
 
End-to-End SNR
 
End-to-End SNR
 
Input Electrical
Power
 
Tx Gain
 
Backscatter
Node Gain
 
Impedance
Mismatch
 
Pathloss
 
Noise
How far can we Communicate using Underwater Backscatter?
= 0 dB
Link-Budget Tool
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
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
Slide Note

Hello Everyone! My name is Waleed Akbar and I am a PhD student at MIT. Today, I will tell you about our work on The Underwater Backscatter Channel. This work is in collaboration with my colleagues Ahmed Allam and Fadel Adib

Before I start my talk, I want to say why we are working on this. This talk will go into a fair level of theory, but there is a major real-world problem that drives the work I’ll be talking about today. 

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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.


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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

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