UGVs: Satellite-Linked Robots Not Common Yet
In mid-May, the German Federal Armed Forces hosted the European Land-Robot Trial 2006 in Hammelburg, Germany, which was intended to showcase European unmanned ground vehicle (UGV) technology. The Roboscout UGV team, led by Base Ten Systems GmbH, was one of the many teams participating which arrived with a satellite-linked UGV, a SOTM land robotic system with a pair of video cameras dubbed KLT, and a satellite link provided by ND Satcom Defence. "ND Satcom provides the complete communications package to application-oriented system integrators for their SOTM systems," says Harald Reder, the company's CEO. "The SkyWAN satellite modem allows the transmission of live video at data rates of more than 2 megabits per second from the moving vehicle, as well as control of the vehicle. Communication is very stable and the driver has no problem remotely controlling KLT in real time." According to Reder, the use of a 75-centimeter parabolic reflectors helps the system avoid interference created by adjacent satellites.
Signal blockage and loss problems also abound in the UGV world, especially as the vehicles operate in and around urban and forested zones where shadowing frequently occurs. The terrain itself can rapidly pitch a UGV, and this, along with frequent rapid turns made by the vehicle, means much stronger motors for rapid repointing must be installed. Modems are stressed, too. "The rapid re-acquisition of the satellite signal after signal blockages is very important," Reder says. "A modem is required to work temporarily at very low Es/No (energy-per-symbol to noise density ratio) values and stay locked. If this is not possible within a few seconds, the overall moving system would not be usable for online control. Our SkyWAN modem shows re-acquisition times in the order of a few seconds, even if the blockage time was more than one minute." With its SOTM component, KLT is the exception to the rule.
Other UGV or unmanned ground combat vehicle (UGCV) program are using satellite communications infrequently at this point, if at all. This is true, for example, of the UGCV Perceptor Integration project at Carnegie Mellon University's National Robotics Engineering Center, which is funded by the U.S. Army and the Defense Advanced Research Projects Agency. The Perceptor project's six-wheel, 6.5-ton Crusher UGCV is not equipped with SOTM. "To date, we have not considered SOTM," says John Barnes, principal investigator for the project. "... In general, our vehicles move in and out of woods and go through erratic pitching and rolling of 20 to 30 degrees. I am not sure that satellite comms would work."
As for unmanned platforms in the sky and under the sea, SOTM options abound not only because the challenges associated with maintaining link integrity are much reduced, but because the need for operational flexibility in near-space and littoral environments is becoming a high priority.
SOTM: The Push Has Been On Since Desert Storm
Only within the past decade has there been a big push for SOTM for ground applications, a situation driven by shortcomings in communications exposed during Operation Desert Storm and advances in miniaturization and the increased affordability of antennas and tracking technology, according to Darlington. As part of the High Capacity Communications Capability program, Raytheon developed a Humvee-mounted mobile command and control SOTM system that allows operational commanders the ability to conduct tactical command and control while in full motion. Raytheon also is involved in the Future Combat System Communications program and has demonstrated mobile ad hoc networking capability which involves links between multiple moving vehicles where each vehicle has a satellite communications link. "Cross-vehicle and [satellite communications] links are monitored for quality and as a single link is degraded by foliage or blockage, data is automatically passed to adjacent connected vehicles until the quality of the link is reestablished. This provides a true ad hoc self healing network that ensures connectivity for the warfighter," says Darlington.
One SOTM technological breakthrough achieved by Raytheon is a Variably Inclined Continuous Transfer Stub antenna which uses the simple rotation of two coplanar plates to provide beam steering. "This approach provides dramatically reduced costs and reduced probability of intercept via precision sidelobe control and improved instantaneous bandwidth," says Darlington. Raytheon is focused on integrated Internet Protocol (IP) networks, "that support user requirements in both planned and ad hoc networks, and this definitely includes video, voice, data, and other applications well beyond these core media." Because this entails WiMAX and Wi-Fi connectivity, SOTM network management is appreciably more complex. Besides the need for adequate bandwidth, link budgets and forward error correction, SOTM assets will transit spot beams and the resultant handovers between beams is not a simple task, according to Darlington.
ViaSat, for example, has delivered both SOTM network hub and user terminal equipment directly to the organization for evaluation, along with operational trials by V Corp. in Germany. ViaSat's approach taps into ubiquitous Ku-band space segment and high-performance user terminals to provide cable-like broadband IP service, along with portable L-band systems capable of providing speeds of more than 400 kilobits per second and trailer-mounted systems currently deployed throughout the U.S. Army for the Joint Network Node. "The systems support multiple applications, including video, Voice over IP, Web access, Blue Force Tracking, messaging, e-mail and large file transfers," says VanderMeulen. "We are continuing to progress with the development of a production deployable capability," he adds. "We have been working with both Connexion by Boeing and Arinc on their broadband airborne services and have delivered over 300 terminals for airborne and maritime use."
ViaSat uses dynamic bandwidth allocations and quality of service systems that are broadly used throughout the commercial broadband VSAT product lines, says VanderMeulen. "We are using both random instant access and managed scheduled access dynamic bandwidth allocation systems to increase the network capacity while providing high speed access. PCMA capability also allows us to reuse the same channel frequencies simultaneously for the forward and return traffic," he says. "... The random instant access system is particularly well suited to the ground SOTM system which can experience blockage that would interrupt a managed scheduled access system. The [quality of service] capability allows user applications requiring low jitter to be processed with priority over jitter-tolerant applications."
So, SOTM is on a roll. The challenges are substantial, but they must be addressed because mobility is critical and lives are on the line. Whether UGV and UGCV research comes to fruition by the end of the decade or not, the SOTM-enabled operator link is one of numerous elements in these increasingly complex weapon systems which are being evaluated. However, while proponents of robotic warfare address the real value and role of SOTM in this arena, soldiers on the ground today are being presented with real world challenges and threats that SOTM can help them to overcome in the quickest and most user-friendly manner possible. And that is what really matters.
Peter Brown is Via Satellite's senior Multimedia and Homeland Security editor.
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