CHIPS Articles: TALON — Robust Tactical Optical Communications

NRL researchers designed the TALON FSO system to augment existing Marine Corps line-of-sight radio frequency communication links during Marine Air-Ground Task Force operations. TALON FSO terminals, which can augment current tactical systems, are eye-safe out of the aperture and capable of providing higher speed, more secure, line-of-sight communications than radio frequency communications, while also alleviating RF spectrum congestion.

Because atmospheric turbulence and inclement weather can significantly affect a free space optical system’s performance at operationally useful ranges, numerous past FSO research and development programs have attempted to use complex technology to reduce the impact of turbulence and weather effects and improve performance. However, the successes from these systems came at a significant price in cost, size, weight, power and complexity.

Advantages and Design

TALON’s benefits are many, including:

• Mitigation of atmospheric turbulence by incorporating optimized tracking and modem technologies designed for operationally useful ranges;
• Does not require filing a DD1494 for spectrum authorization because there is no spectrum deconfliction needed;
• Can scale to high bandwidths, beyond 1 Gbps;
• Offers low probability of intercept and low probability of detection, due to highly directional beams;
• Is jam-resistant;
• May be used in RF-constrained conditions; and
• Is sized and priced for fielding in tactically significant quantities.

NRL researchers note another benefit of the TALON system: key components of the system were developed fully under government funding. The modems and commercial gimbals are the only components subject to limited rights because they are treated as vendor-supplied components.

• Active tracking for elevated installations — tracking is maintained without use of any beacon or GPS aid.
• Automated acquisition — TALON terminals self-determine their respective orientation, search for each other, find each other, and lock-on to initiate data transmission.
• Acquisition without GPS — TALON is designed to accept manually entered bearing and elevation angles to initiate the acquisition process. This is important for terrestrial mast installs.
• Fast fine tracking loops — TALON’s custom algorithms are designed to compensate for high frequency beam motion caused by the atmosphere.
• Robust modem — the goal is to make the TALON link appear like any other RF line of sight or wireline communications link by ensuring data is delivered without errors, and with low latency.
• Security — TALON is designed following information assurance best practices.
• Network management — TALON uses advanced networking features, including congestion control.
• Environmental considerations — TALON is designed to Military Standard (MIL-STD) 810F, as well as electromagnetic interference and electromagnetic compatibility standards.
• Space, Weight and Power (SWAP)-optimized for tactical mast installs; small form factor and similar weight as current RF mast-mounted systems and gimbals.
Unit cost — Goal of reducing engineering development unit cost in production for tactically relevant quantities.

NRL’s TALON is unique in its approach; optimizing performance at useful ranges (up to 70 km) and data rates (100 Mbps) for the warfighter, while maintaining lower cost, size, weight, and simplicity. This approach results in a system that provides the attributes of FSO that are most important to the warfighter today, while creating options for improvements in capabilities later.

The NRL-developed TALON offers highly capable compact terminals that are an order of magnitude lower in cost and SWAP than previous Defense Department attempts to develop free space optical systems. As a result of NRL’s efforts, both the Marine Corps and the Navy have expressed an interest in transitioning TALON FSO terminals for operational use.

TALON Testing

TALON is entering the third phase of a three-phase program to incrementally develop terminals capable of transitioning to environmental testing and validation followed by operational employment. Phase 2 culminated in June 2013 with rigorous system performance evaluations at both Camp Pendleton and Naval Air Weapons Station China Lake using the engineering development units.

NRL researchers conducted primary testing on TALON using NRL’s Multi-Generator (MGEN) testing software to quantitatively measure packet error rate and latency at data rates of 95 Mbps. Goals for this testing were to demonstrate packet error rates less than 0.1 percent and latencies less than 50 milliseconds. Secondary testing evaluated the TALON system’s ability to autonomously acquire and maintain a link using each terminal’s coordinates as manual inputs, and assessments of link quality for typical user data, including VoIP, standard and high definition video cameras, chat, and file transfers.

Results

System evaluation was conducted between 100-foot masts at Camp Pendleton over a four-kilometer link. This testing evaluated the TALON system’s ability to establish and maintain a low packet error rate and latency 100 Mbps communications link while mounted on relatively unstable masts. The tests at Camp Pendleton successfully demonstrated the primary goal of establishing and maintaining a low packet error rate and latency link. Average raw packet error rates were less than 1 percent and latencies were less than 50 milliseconds. Autonomous link establishment based on coordinates was also successfully performed, but not with 100 percent reliability. Phase 3 efforts will improve the reliability of the autonomous link establishment process.

Autonomous link maintenance after acquisition was completely successful with tracking maintained 100 percent of the time with no drops in tracking despite the very high winds of more than 30 knots present during the testing.

Qualitative assessments were completely successful with researchers using VoIP, video teleconferencing and chat as the primary communication methods between the two test sites after link establishment. These applications were also useful for demonstrations to base personnel and visitors.

Researchers also performed the Phase 2 testing at NAWS China Lake in a harsh environment over a 50-km range between Cinder Peak and Laurel Mountain in mid-summer with outdoor temperatures exceeding 100 F. The China Lake tests were similar to the Camp Pendleton performance tests except that an autonomous link establishment was not tested. Systems were primarily evaluated for link quality over a long-range, highly turbulent, desert link.

As with Camp Pendleton, China Lake’s average packet error rate and latency were well below the goals of less than 0.1 percent and 50 milliseconds, respectively. Tracking was excellent as well, although a few short drops occurred. In these cases, the link was automatically reestablished in less than one second. Like Camp Pendleton, researchers at China Lake used VoIP, video teleconferencing and chat as the primary forms of communication between the two sites.

Conclusions

Overall, NRL researchers are pleased with the excellent TALON Phase 2 testing results. Fundamental questions of whether the systems could operate in harsh conditions at long range and whether the systems could acquire and track from relatively unstable masts at a maximum extension of approximately 100 feet were clearly answered successfully.

In Phase 3, researchers are currently focusing on improvements to harden the system and to advance the automated operation of the system to allow users to reliably use these systems with minimal training and effort.

Moving forward, NRL researchers are confident that TALON offers a robust optical communications solution to augment the Marine Corps’ existing line-of-sight RF communications portfolio. The TALON free space optical system leverages the unlicensed optical frequencies in the electromagnetic spectrum to bring a high bandwidth, directional, eye-safe, spectrum-friendly communications solution to the warfighter.

U.S. Naval Research Laboratory
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