An acoustic modem is a device designed for underwater wireless communication using acoustic signals, typically functioning as a simple data transmitter. In contrast, an acoustic smart modem, like those from Subnero, is comparable to a smartphone. Just as a smartphone can run apps and customize its behavior for different tasks, a smart modem allows users to tailor its functionality to specific applications. It supports advanced features, such as running custom algorithms, managing multiple tasks seamlessly, and adapting to the underwater environment when needed. This flexibility makes smart modems far more versatile and capable than traditional acoustic modems.

Acoustic modems face challenges like limited bandwidth, multipath interference, and environmental variability, which can affect performance. Subnero addresses these with software-defined modems that allow real-time adaptation to channel conditions, customizable communication protocols, and advanced error correction, ensuring reliable and efficient underwater communication.

Subnero modems have been tested in diverse environments, including shallow coastal waters, deep seas, and noisy tropical regions, demonstrating reliable performance across varying conditions.

For more information, including relevant publications and magazine articles from Subnero and our customers, visit https://subnero.com/quicklinks/#publications.

Subnero modems are categorized by frequency bands, each optimized for specific needs:

• L12L Series (Low Frequency, 9-16 kHz): Long-range communication, tested over 10 km with data rates between 100 bps and 7 kbps.
• M25M Series (Medium Frequency, 20-32 kHz): Balanced range and data rate, tested over 4 km with rates of up to 15 kbps.
• S40H Series (High Frequency, 25-55 kHz): High-speed communication, with data rates up to 33 kbps under 1 km range.

Each series is suited for specific applications, from long-range deployments to high-speed communication. For more details about these frequency bands, please visit https://subnero.com/products/modem.html.

Subnero modems are available in Platinum, Silver, and Research editions.

For more information about the different editions, visit: https://subnero.com/products/modem.html

Subnero modems are available in Standalone, OEM, and Multichannel configurations, each suited for specific use cases:

• Standalone Configuration: Pressure-housed and ideal for surface or seabed deployments.
• OEM Configuration: Compact and designed for seamless integration into platforms like AUVs.
• Multichannel Configuration: Equipped with multiple receiving channels, it is designed for enhanced communication performance.

For more information about the different configurations, visit: https://subnero.com/products/modem.html

Standalone configurations are pressure-housed for external deployments, while OEM configurations are compact (without a pressure hull) and designed for integration into platforms like AUVs.

The multichannel configuration features multiple receiving channels for enhanced communication performance and supports additional functionalities like positioning and passive acoustic monitoring.

Relevant Links

• Brochure
• Magazine article

The Research Edition modem is only available in the standalone configuration for MF band.

Yes, Subnero Gen4 modems include a compatibility mode that allows them to interoperate with Gen3 modems.

Subnero modems are configured to use Frequency Hopping Binary Frequency Shift Keying (FH-BFSK) and Orthogonal Frequency Division Multiplexing (OFDM) for CONTROL and DATA channels out-of-the-box, with user customization options. An auxiliary channel supports standards like JANUS and SWiGAcoustic Level 1, and a user-defined channel allows custom modulation schemes.

Subnero modems support multiple Forward Error Correction (FEC) schemes, including convolutional codes, Golay codes, LDPC (Low-Density Parity-Check) codes, and BCH (Bose-Chaudhuri-Hocquenghem) codes.

The achievable throughput and communication range in ideal channel conditions are listed in the technical specifications for each Subnero modem. However, actual performance can vary significantly depending on environmental factors such as channel and noise conditions. As software-defined devices, Subnero modems allow users to dynamically trade off throughput for range or vice versa, adapting to real-time conditions to meet specific application needs effectively.

Subnero modems feature a Link Tuner to optimize communication between modems and preconfigured profiles for various environments.

For a detailed guide, refer to this step-by-step article, which explains how to tune your communication link effectively.

UnetStack is a comprehensive collection of technologies designed to extend communication networks underwater featuring components such as the Unet framework, basic stack, premium stack, simulator, and Unet audio, each serving specific functions.

UnetStack is available in three editions:

• Community Edition: Freely available for non-commercial use. Includes Unet Simulator, Unet audio (v3 only)
• Commercial Edition: Same as Community Edition, but with a license for commercial use.
• OEM Edition: Pre-installed on Subnero modems, tailored for integrated use.

For detailed information about the various editions and their applications, refer to this UnetStack website or whitepaper.

Contact us at [email protected] for more details about licensing the UnetStack Commercial edition.​​

Several components of UnetStack are open source, including the fjåge framework, Virtual Acoustic Ocean, and a collection of agents available in the Unet Contrib Repository. All gateway API interfaces are also open source.

To get started with UnetStack:

• Visit the UnetStack website.
• Explore the Unet Handbook for comprehensive documentation: Unet Handbook.
• Access API documentation and examples in the Unet Contributions Repository and Unet Sockets Repository.
• Join the Unet Support Forum for community discussions: Unet Support Forum.
• Explore use cases and examples in the Unet Blog: Unet Blog.

UnetStack provides a flexible framework for developing custom features in any part of an underwater communication network. The Unet Handbook offers detailed guidance on this process.

Relevant Links

• Developing your own acoustic PHY with UnetStack
• Harnessing the power of Julia in UnetStack — Part II

If you are an OEM developer, you can license the UnetStack OEM Edition through Subnero and design your modem hardware around it. For non-commercial users, UnetStack provides tools and guidance for building your own modems using off-the-shelf components. A detailed step-by-step process can be found in this blog article.

If you create a modem based on UnetStack, we’d love to hear from you! Contact us at [email protected] to have your project showcased on our social media channels.

For detailed information about the various editions and their applications, refer to this UnetStack whitepaper.

UnetStack provides a flexible framework for developing custom modem drivers, enabling users to integrate their hardware seamlessly into the UnetStack environment.

For detailed guidance, refer to this blog article on developing modem drivers for UnetStack, for step-by-step instructions.

To set up and use MATLAB with UnetStack, refer to this blog article.

Unet audio, available as part of UnetStack3 Community Edition, converts a laptop into an acoustic modem using its built-in speaker and microphone. Freely available for non-commercial use, it helps test and develop communication protocols.

For example, you can use Unet audio to convert your laptop into a JANUS-compliant modem. For more information, refer to this blog article and video.

Yes, Subnero modems can interface with various external sensors, including ADCPs, tide gauges, and CTDs, through the Subnero Wireless Integrated Suite (SWIS). UnetStack APIs also allow software-level or custom integrations.

For more details about custom integrations, contact us at [email protected].

Subnero modems typically support one RS232 and one Ethernet interface.

For more details about customizations, contact us at [email protected].

Yes, Subnero modems can be integrated with ROS2 for marine robots using the UnetStack ROS2 Gateway. This gateway is available as an open-source utility at UnetStack ROS2 Gateway GitHub repository.

Yes, Subnero modems can interoperate with third-party devices that support standards like JANUS or SWiG Acoustic Level 1. Users can also implement custom communication algorithms for interoperability. Over the years, Subnero modems have demonstrated interoperability with various third-party modems (commercial or research variants).

For more details about interoperability, contact us at [email protected].

Relevant Links

• Subnero Successfully Demonstrates Interoperability using SWiG Standard at WUWNET 2024

Subnero modems operate with a nominal input voltage of 24 VDC, with an acceptable range of 22 - 28 VDC.

Subnero modems are compatible with any subsea battery capable of providing a 24 VDC (nominal) output. Users can source their own batteries or purchase rechargeable batteries from a preferred partner, which are available in varying capacities based on specific deployment requirements.

The required battery capacity depends on several factors related to the deployment, including:

• Amount of data download
• Frequency of downloads
• Range of communication

To help estimate battery requirements, Subnero provides an online battery calculator tailored for SWIS applications, available here.

For assessments based on your deployment needs, contact us at [email protected].

Subnero modems support three operating modes:

• Transmit Mode: between 2 - 40 W during transmission, fully adjustable.
• Receive Mode: ~3-4 W while listening for incoming packets.
• Deep Sleep Mode: <1 mW

Subnero modems support three wake-up modes:

1. Scheduled wake-up: Modems can wake up at pre-configured schedules.
2. External wake-up interrupt: A 3.3V external signal (~100 ms) can trigger the modem to wake up.
3. Power cycle: Disconnecting and reconnecting the power supply wakes up the modem.
4. Acoustic wake-up (on selected models only): Receiving a specific acoustic signal can wake up the modem.

Yes, Subnero modems support acoustic ranging out-of-the-box using the ranging agent. With appropriate software upgrades, the multi-channel modems can function as USBL systems for positioning and tracking.

For more on localization with multiple modems, see this blog article: https://blog.unetstack.net/on-underwater-localization-using-unetstack

Subnero modems use two-way travel time measurements for range estimation with COTS transponders. This leverages the arbitrary waveform transmission feature.

Refer to this blog article for a step-by-step guide: https://blog.unetstack.net/AUV-to-transponder-Range-Estimation-Application-using-UnetStack

Subnero modems feature two types of clocks to support time synchronization: the system clock and the baseband clock.

• The system clock provides OS time and retains time during power-off using an RTC. It is synchronizable via NTP.
• The baseband clock is used for timestamping and ranging, with a drift of ±100 ppb. External synchronization between modems is supported via PPS signal for timestamp alignment across modems. The captured timestamps are available on the baseband agent as bb.syncSystemTime and bb.syncBasebandTime which can be used for synchronization.

For applications requiring even lower drift, an optional OCXO clock (±25 ppb) is available. For more details about clock synchronization, contact us at [email protected].

Yes, Subnero modems support JANUS in the appropriate frequency bands.

To prevent interference with other acoustic devices, you can use these methods:

1. Time Division: Schedule transmissions or use the MAC layer to avoid simultaneous operation, with the option to use an external hardware sync signal for coordination.
2. Frequency Division: Configure the modems to operate in non-overlapping frequency bands. See this blog article for details: https://blog.unetstack.net/frequency-band-control-in-unetstack

Yes, Subnero modems support encryption via external hardware compliant with AES-256 and relevant key management standards. A scrambler sequence provides basic eavesdropping protection out-of-the-box.

For more details, contact us at [email protected].

Subnero modems come with 32 GB of default storage, upgradable to 1 TB, depending on deployment requirements.

Yes, users can develop and run their own protocols or applications on the modem as Groovy scripts or UnetStack agents written in Java or Groovy. These agents can be managed using the modem’s web-based UI, which includes a fully featured file manager and editor.

For compute-intensive tasks, such as implementing a custom physical layer, Subnero modems offer the option to include an additional coprocessor, such as the NVIDIA Jetson Orin Nano, to handle high-demand processing requirements.

Yes, Subnero modems can be tested in air with reduced power settings (e.g., -42 dB). Power above -20 dB may damage the transducer. A safety parameter, bb.maxInAirPowerLevel, limits power during air tests if depth data is available.

The standalone configuration includes a 25 m underwater cable terminating with power (barrel jack) and Ethernet (RJ45) connectors. Cable length is customizable based on user requirements. For RS232 termination, the maximum length is 15 m.

For more details on customized cables, contact us at [email protected].

The default transducer cable length in the OEM configuration is 1 m, which can be customized to up to 10 m upon request. Custom lengths may affect the lead time for your order.

The Silver Edition standalone configuration modems are rated for 300 m depth, with optional hull upgrades for 2000 m, 4000 m, and 6000 m. Multi-channel configurations are rated for 300 m. For more details, refer to Subnero’s hull options.

To configure a static IP:

1. Locate the modem’s pre-assigned static IP address (default range: 192.168.42.2-254) on its label.
2. Connect the modem by plugging in the modem cable’s Ethernet connector to the user’s computer.
3. Access the modem’s web interface:
   • Assign a static IP (e.g., 192.168.42.1) to your computer on the same subnet.
   • Open a browser and navigate to the modem’s IP.
4. Use the shell to set or update the static IP:
   • staticIP '192.168.1.214' to assign a new IP.
   • staticIP none to remove the static IP.
   • statcIP auto to revert to the factory-assigned IP.

RS232 interfaces on Subnero modems can be configured for specific modes (e.g., Groovy shell, AT commands, or UnetStack API). To enable the Groovy shell:

1. Access the modem’s web interface and open the startup.groovy from the files menu.
2. Modify/uncomment the relevant line, e.g.: iface API, '/dev/rs232', 115200, 'N81'
3. Save the changes and reboot the modem.

Transparent mode in Subnero modems is enabled through the use of Portals. Refer to the Portals chapter in the Unet Handbook for information about how to configure the transparent mode.

Acoustic modems offer a safer, cost-effective alternative by enabling wireless communication between the seabed and the surface. This approach eliminates the need for physical retrieval or cumbersome cables which are costly, risky, and prone to failures. ensuring continuous monitoring and reliable data collection.

The Subnero Wireless Integrated Suite (SWIS) - ADCP Edition is a tailored solution for the wireless transfer of data from ADCPs like Nortek’s Signature series. It uses Subnero’s WNC series of acoustic smart modems, powered by SWIS software, to overcome challenges associated with underwater acoustic communication.

Key differentiators include:

• Advanced communication algorithms that can adapt to changing environmental conditions for consistent communication.
• Seamless integration and edge intelligence that processes data at the edge for efficient, content-aware transmission.
• Intuitive user interface for data access, fault detection, and smart scheduling with minimal effort.

The communication range for SWIS - ADCP Edition depends on the series of modem being used:

• M25M Series: Recommended range is up to 2 km.
• S40H Series: Recommended range is up to 500 m.

Actual performance may vary based on environmental factors and deployment conditions.

The topside modem can be deployed using a buoy, boat (manual deployment), or an Unmanned Surface Vessel (USV). Depending on your use case, you can configure the system for on-demand mode to retrieve data at ad hoc intervals or on-schedule mode for automated data retrieval at regular intervals.

After a data transfer from the seabed unit, the files are stored on the topside modem. You can access these files through the modem’s web interface or via REST APIs. Additionally, the topside modem can be configured to upload the data to a remote server, such as a cloud service, FTP server, or a data logger.

For a list of supported external services and devices, contact us at [email protected].

The SWIS - ADCP Edition offers a preview functionality that allows you to extract relevant information from the raw files. Preview files are much smaller in size and can be easily transferred to the topside modem, making data access efficient even with large raw files.

Subnero modems include a standard 12-month warranty covering defective parts, excluding damage from accidents or user negligence. Upon receiving a modem for service, Subnero assesses and informs you about what is covered under warranty.

Warranty extensions are available through an additional service package. Repairs or major services outside this agreement are charged separately.

For more details, contact us at [email protected].

The M25M and S40H series modems are not subject to any export restrictions. For the L12L series, we require end-user information to meet export compliance regulations. Export policies are subject to change based on updates from the Singapore government.

The standard lead time for Subnero modems is two months upon receiving an acceptable purchase order (PO). We can provide the most updated shipment date at the time of placing an order.

Subnero offers flexible training options:

• Online Training: An introductory session covering modem setup and configuration. Typically conducted after purchase and delivery of at least a pair of modems.
• Onsite Training at Subnero Facilities: Held in Subnero office in Singapore, this option can cover setup, configuration, application development, including (but not limited to) in-water testing.

For more details or to schedule training, contact us at [email protected].

Subnero provides multiple tiers of support:

• Forum Support: Community-driven assistance, free and unlimited.
• Tier 1 [Basic]: Basic inquiries via email with guaranteed responses, free and unlimited.
• Tier 2 [Standard]: Dedicated support via email for standard use cases, included with warranty. Renewable as a paid plan.
• Tier 3 [Advanced]: In-depth technical assistance from engineers via email or calls. Renewable as a paid plan after the initial 3-month period from the date of purchase.

For more details on these support options, contact us at [email protected].