PAB-QAM: Higher-Order Modulation for Underwater Backscatter

Sayed Saad Afzal


PAB-QAM  is a new system that achieves higher-order modulation with the current PAB sensor design. PAB relies on the piezoelectric effect to enable underwater communication and sensing at near-zero power and these sensors differ from traditional communication modems in that they do not expend their own energy for transmission. Instead, they communicate by modulating the reflections of existing underwater acoustic signals. PAB-QAM builds on the design of PAB to enable higher-order modulation schemes such as QAM which will allow us to support high throughput applications like streaming images in the ocean

How does PAB-QAM work?

Piezo-electric materials have electromechanical coupling which means that the backscatter reflection from the piezo depends not just on the piezo itself, but also depends on the load  that it is attached to. PAB-QAM exploits this idea of electromechanical coupling by switching between different electrical loads at the PAB node  to achieve higher order modulation. 

We tested PAB-QAM in a controlled environment and our results show that PAB-QAM can deliver twice the throughput compared to the traditional PAB design in high SNR scenarios. This technology has many applications in low power and low cost subsea IoT for monitoring, exploration, and marine life sensing.

If you are interested in this, check out  our other ocean research projects: