Frequently Asked Questions

  1. Who use LinkQuest's underwater acoustic modems?

  2. What kind of environments have LinkQuest's acoustic modems been used in? 

  3. What kind of technology is used in the modem communication?

  4. How can LinkQuest assist customers in field deployment?

  5. Is there any need to modify the existing software of the underwater instruments to work with LinkQuest's modems?

  6. How many instruments can an acoustic modem interface to?     

  7. What is the payload data rate?

  8. What does it mean by a bit error rate of less than 10?

  9. How does the modem deal with noisy environment?

  10. Do the modems utilize coded communications?

  11. Can one modem communicate with several modems?

  12. How much power is required to transmit 1 megabytes of data?

  13. Does the modems have internal battery?

  14. What kind of modulation scheme do you use to communicate between the modems?

  15. Are LinkQuest's acoustic modems integrated with its TrackLink USBL systems and LBL positioning systems? 

  16. Can I obtain any additional technical information about the modems?

  17. Does LinkQuest offer any other modems other than the four standard models?

 


1.  Who use LinkQuest's underwater acoustic modems?

LinkQuest's modems are used by major offshore oil companies, commercial survey companies, government agencies, universities and naval defense contractors.  Users include: Fugro GEOS,  Fugro Chance,  Simrad,  Boeing,  Oceaneering,  BP,  Shell,  ExxonMobil,  Total, C&C Technologies, Mitsubishi,  Onyx Special Services,  NOAA PMEL, NOAA AOML, NOAA NOS,  NOAA National Data Buoy Center,  USGS,  Environmental Canada,  Japan Marine Safety Agency,  Japan Marine Science and Technology Center,  Woods Hole Oceanographic Institution,  Dunstaffnage Marine Lab (UK),  CEFAS (UK),   Institute of Marine Research (Norway),  ENEA (Italy),  Australian Institute of Marine Science,  The University of Maryland,  Virginia Institute of Marine Science,  National University of Singapore,  US Navy Naval Oceanographic Office,  US Navy NUWC (Naval Undersea Warfare Center) Keyport,  US Navy Coastal Systems Station,  The Spanish Navy

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2.  What kind of environments have LinkQuest's acoustic modems been used in?

LinkQuest's underwater acoustic modems have been used very extensively in deepwater and costal oceans, bays, harbors, lakes and rivers all over the world.  All models perform well in near-vertical and horizontal environments.  These modems have been used extensively in horizontal environments for AUV command and control, remote control of undersea sensors and environmental monitoring.  The UWM3000H and UWM2000H modems, tailored for long-range shallow and very-shallow water environments, perform particularly well in environments with very harsh multi-paths (acoustic signals reflected from surface, bottom and other boundaries). Field tests and customer deployments show these systems can achieve reliable communication with bit error rate of less than 10 in very shallow water, immune from the impact of very harsh multi-paths. Examples are communication in costal ocean up to 3000 meters of range at 5 meters of water depth using UWM3000H modems and communication in San Diego bay up to 1000 meters of range at 5 to 10 meters of water depth using UWM2000H modems. 

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3.  What kind of technology is used in the modem communication?

LinkQuest uses advanced broadband spread spectrum technologies in its underwater acoustic modems.  The patent pending technologies are invented by its in-house communication experts under intensive R&D. The technologies combine the modern wireless and high speed digital communication such as DSL with broadband underwater acoustics. The results are the phenomenally improved reliability, data rate and user friendliness.

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4.  How can LinkQuest assist customers in field deployment?

LinkQuest takes utmost pride in making systems friendly to end users and robust in typical field deployments. Vast majority of our customers have no need to contact LinkQuest for any after-sale support.

In order to assist field deployments when needed, LinkQuest has implemented comprehensive test tools to collect and analyze field data. Information such as channel conditions, noise conditions of the surface and bottom modems, signal strengths of both modems and signal spectrum can be easily obtained by running a few software utilities. LinkQuest has used these tools to pin point problems such as faulty radio modem and faulty installation caused by strong wave in customer's deployments.

One of the software utilities in the modem even provides the range between the modems. This effectively makes each modem a ranging transponder.

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5.  Is there any need to modify the existing software of the underwater instruments to work with LinkQuest’s modems? 

LinkQuest’s modems forms a completely transparent RS-232 connection between two end equipment as if they directly connected through an RS-232 cable.   As long as the  user is able to set the RS-232 configuration of the instrument/application software to 9600 baud, 1 start bit, 1 stop bit, no parity bit and no flow control there is no need to modify the instrument software. For example, LinkQuest’s modems has been integrated seamlessly with some popular Doppler Current Profilers and CTDs.

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6. How many instruments can an acoustic modem interface to?  

With the Data Fusion option, a modem can interface to 8 instruments using RS232 interface and sample up to 16 analog inputs simultaneously.  A modem can also provide up to 1 Gbytes of permanent storage on a compact flash disk.

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7. what is the payload data rate?

The payload data rate is the user information data rate.  With the additional 1 start bit, 1 stop bit of the RS-232 interface and modem protocol overhead, the RS-232 data rate becomes 9600 bits/sec. Before transmission the RS-232 data is further modulated and coded, and the resulting acoustic data rate is 17.8k bits/sec.

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8.  What does it mean by a bit error rate of less than 10?

A bit error rate of 10 means there is only one bit error in 10 million user information bits.  LinkQuest's modems provides unprecedented high quality communication for underwater environment. The quality of the communication is similar to the quality of the  modems used with your home computer.  

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9How does the modem deal with noisy environment?

LinkQuest's proprietary modulation and equalization scheme allows the modems to work under very low SNR. LinkQuest’s modems also employ automatic rate adaptation algorithm which reduces the data rate to 1200 baud payload data rate when excessive noise is present. Once the noise level is lowered, the modems automatically restores to high data rate (9600 baud).

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10.  Do the modems utilize coded communications?

Yes. LinkQuest’s modems utilized advanced coded communication and other error correction methods to improve robustness through greater signal-to-noise ratio and to achieve bit error rate of less than 10.  For purposes of fair comparison with other company’s modems, please be sure to compare our data rate with other company modem’s highest data rate with coded communication and be sure to ask what kind of bit error rate is guaranteed. 

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11.  Can one modem communicate with several modems?

Yes. One surface modem can communicate with up to 25 underwater modems in a deployment. Each modem can be configured with a unique address. For certain models, one surface modem can communicate with up to 255 underwater modems. 

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12.  How much power is required to transmit 1 megabytes of data?

Our UWM1000 modem takes only 20 minutes and as little as 0.3 watt-hour (3% of a "D" cell battery) to collect 1 megabytes of data. Our UWM2000 modem takes 20 minutes and 1.2 watt-hour (12% of a "D" cell battery) to collect the same amount of data.  In other words, a "D" cell battery is capable of transmitting 10 to 40 megabytes of data.

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13Does the modems have internal battery?

The modem’s power can be provided by the battery supply of the underwater instruments or an external underwater DC power supply. An external underwater DC power supply may be ordered separately through LinkQuest. LinkQuest also provides an optional internal power supply. 

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14 What kind of modulation scheme do you use to communicate between the modems?

LinkQuest uses a proprietary hybrid modulation scheme which we refer to as the “Acoustic Broadband Spread Spectrum Technology”. LinkQuest does not disclose the specifics of its proprietary technologies.

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15Are  LinkQuest's acoustic modems integrated with its TrackLink USBL systems and LBL acoustic positioning systems?

Yes. The acoustic modems are integrated with TrackLink 1500, 5000 and 10000 USBL positioning systems and LinkQuest's line of LBL acoustic positioning systems.

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16Can I obtain any additional technical information about the modems?

Yes. Please click on the sidebar for the 3 technical notes below.

  • Working Principles of LinkQuest's Acoustic Modems.

  • How to Interface LinkQuest's Modems to Your Instrument.

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17.  Does LinkQuest offer any other modems other than the four standard models?

Yes. LinkQuest offers customized design to tailor to your needs.

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© LinkQuest, Inc. 1999    Last Updated May 2004