November 13, 2025

Improving Underwater Communication with Subnero Multi-Receiver Modems

Underwater acoustic communication faces several physical limitations: restricted bandwidth, long propagation delays, severe multipath—especially in shallow waters—Doppler effects, and high ambient noise. Traditional modems with a single receiver rely heavily on sophisticated signal processing, but performance is ultimately constrained by the quality of the signal captured at that one location. If the receiving element happens to sit in a deep null or a locally noisy patch, recovery becomes difficult. Many underwater systems also require localization and tracking, which often rely on separate hardware such as USBL arrays or dedicated receivers, adding to overall operational complexity.

Subnero’s multi-receiver modems address both needs at once—capturing multiple spatially separated signals for improved communication robustness while also enabling bearing estimation and positioning capabilities within the same platform. This enhances communication performance, reduces hardware requirements, simplifies integration, and streamlines operations in the field.

Why Multiple Receiving Channels Matter?

Adding multiple receivers introduces receive diversity. Each hydrophone receives a slightly different version of the signal, giving the modem more information to work with. Even in degraded conditions, combining information from all hydrophones increases the likelihood of successful decoding. This forms the basis of Single-Input–Multiple-Output (SIMO) systems, which provide higher receive gain, improved signal-to-noise ratio, and more resilient communication performance.

Practical Impact on Throughput and Range

The benefits are often substantial.

A user experiencing 30–40% packet loss with a single-receiver modem may see losses drop to under 5% with just one additional receiver, depending on spatial placement.
With three or four receivers, overall loss can approach near-zero, resulting in a highly stable link even in difficult environments.

These gains translate directly into higher effective throughput, longer communication ranges, and far more consistent performance in dynamic or shallow-water deployments.

Multiple receivers unlock capabilities that are particularly valuable for research users:

Acoustic communications research: Users can test SIMO-based techniques, spatial combining, direction-of-arrival estimation, multipath mitigation strategies, or advanced PHY/MAC concepts. Subnero modems provide access to raw data streams from all receivers, making them flexible testbeds for developing and validating new communication algorithms.
Navigation and tracking research: With hydrophones placed at different spatial locations, researchers can implement Time Difference of Arrival (TDOA), Phase Difference of Arrival (PDOA), or hybrid methods to estimate range, bearing, or full 3D position. This enables experiments in underwater localization using the same hardware platform.

These features allow teams to use Subnero’s multi-receiver modems not only as communication devices but also as versatile platforms for scientific experimentation and algorithm development.

Operational Applications Enabled by Multiple Receiving Channels

Beyond research, multiple receiving hydrophones support a wide range of real-world applications:

Bearing estimation of underwater sources
Target tracking, depending on array geometry
Array-based sensing and environmental characterization
Custom USBL-style processing using user-developed algorithms

Subnero modems additionally support external GPS PPS (Pulse-Per-Second) input for absolute timing and optional AHRS sensors (Attitude and Heading Reference System) to provide orientation information when required.

Beyond Communications: Passive Acoustic Sensing

Multi-receiver modems can also act as capable passive acoustic monitoring systems. By fusing information from multiple receivers, users can estimate the range and bearing of acoustic sources—useful for rapid environmental assessment, situational awareness, or wildlife monitoring. Subnero’s multi-receiver modem has already been used by research groups for tracking marine mammals and other field studies.

Learn More About Subnero’s Multi-Receiver Modems