Mobile Underwater Backscatter Networking

Abstract

Underwater backscatter is a promising technology for ultra-low-power underwater networking, but existing systems break down in mobile scenarios. This paper presents EchoRider, the first system to enable reliable underwater backscatter networking under mobility. EchoRider introduces three key components. First, it incorporates a robust and energy-efficient downlink architecture that uses chirp-modulated transmissions at the reader and a sub-Nyquist chirp decoder on backscatter nodes—bringing the resilience of LoRa-style signaling to underwater backscatter while remaining ultra-low-power. Second, it introduces a NACK-based full-duplex retransmission protocol, enabling efficient, reliable packet delivery. Third, it implements a Doppler-resilient uplink decoding pipeline that includes adaptive equalization, polar coding, and dynamic retraining to combat channel variation. We built a full EchoRider prototype and evaluated it across over 1,200 real-world mobile experiments. EchoRider improves bit error rate by over 125× compared to a state-of-the-art baseline and maintains underwater goodput of 0.8 kbps at speeds up to 2.91 knots. In contrast, the baseline fails at speeds as low as 0.17 knots. Finally, we demonstrate EchoRider in end-to-end deployments involving mobile drones and sensor nodes, showing its effectiveness in practical underwater networked applications.