Enabling Higher-Order Modulation for Underwater Backscatter Communication

Oct. 5, 2020


Sayed Saad Afzal, Reza Ghaffarivardavagh, Waleed Akbar, Osvy Rodriguez, and Fadel Adib. 2020. Enabling Higher-Order Modulationfor Underwater Backscatter Communication. Global OCEANS 2020.


Piezo-acoustic bacskcatter (PAB) is a recently-introduced ultra-low-power underwater communication technol-ogy. In contrast to traditional underwater acoustic modems,which need to generate power-consuming carrier signals, PABnodes communicate by simply reflecting (i.e., backscattering)existing acoustic signals in the environment. This reflection-basedapproach enables them to communicate at net-zero power butalso imposes significant constraints on their throughput andmodulation schemes.We presentPAB-QAM, the first underwater backscatter designcapable of achieving higher-order modulation.PAB-QAMexploitsthe electro-mechanical coupling property of piezoelectric trans-ducers to modulate their reflection coefficients. Specifically, bystrategically employing reactive circuit components (inductors),we demonstrate howPAB-QAMnodes can modulate the phaseand amplitude of acoustic reflections and realize higher-orderand spectrally-efficient modulation schemes such as QAM.We designed and built a prototype ofPAB-QAMand empiri-cally evaluated it underwater. Our empirical evaluation demon-strates thatPAB-QAMcan double the throughput of underwaterbackscatter without requiring additional power, spectrum, orcost. Looking ahead, such increased throughput paves way forvarious subsea IoT applications in ocean exploration, underwaterclimate monitoring, and marine life sensing.

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