SOTM: Satellite Links In Motion

Ongoing military operations in Afghanistan and Iraq are putting more emphasis on the need for reliable, robust and bandwidth-rich satcom-on-the-move (SOTM) solutions. The U.S. military and Allied Forces relies primarily on small portable, fixed VSAT terminals which can be deployed rapidly, as existing SOTM programs are limited in number and in scope.

Among other things, the emphasis on keeping out of the line of fire has taken on a new sense of urgency with the mounting number of casualties resulting from improvised explosive devices – IEDs – and the growing number SOTM solutions beyond Blue Force Tracking is enabling U.S. forces to get the job done on the move while minimizing the exposure to enemy fire which might occur when small fixed VSAT deployments take place.

"The greatest influence that the Iraq and Afghanistan deployments have had is to accelerate user acceptance of ‘current force’ solutions, and the urgency of these deployments had vastly accelerated the acceptance of equipment and systems when appropriate to the deployed warfighters," says Ric VanderMeulen, director of government satellite communications at California-based ViaSat Inc.

SOTM can be accomplished in Ka-, Ku-, L-, Q- and X-bands, though military applications primarily are limited to Ka-, Q- and X-bands via Defense Satellite Communications System satellites, Milstar spacecraft and the planned Wideband Gapfiller and Advanced Extremely High Frequency constellations, says Fred Darlington, director, satellite communications systems at Raytheon Co. "Lower frequency provides better SOTM connectivity through rain and foliage. Higher frequencies have narrower beam widths requiring precise pointing algorithms but are more jam resistant," he says. "As frequency increases, pointing becomes increasingly difficult, and with Ku-band, as a result of spacecraft spacing, there is the potential for locking onto the wrong satellite or satellite sidelobes after loss of tracking."

Existing SOTM systems include the U.S. Marine Corps Systems Command’s C2 On-the-move Network Digital Over-the-horizon Relay, or CONDOR system, and the U.S. Army’s Mounted Battle Command on the Move system. However, these systems may need to be adapted to meet new requirements from the U.S. Department of Defense that call for lighter, more mobile satellite communications networking solutions which enable interoperability between forces and fully support the Pentagon’s Everything over Internet Protocol objectives, which are driven by IPv6 along with the multi-phased Joint Tactical Radio System. With the increased efficiency and addressability that IPv6 offers, Everything over Internet Protocol is critical to the process of netcentric transformation as it pertains to Brigade and Below operations in particular. "SOTM will continue the drive of smaller, cheaper, faster battlefield tools," says David Helfgott, president and CEO of Americom Government Solutions Inc. (AGS), a subsidiary of SES Americom. "Key will be a stable and robust system that will respond to demand and institutionalize the service throughout the armed forces and hopefully become one or more programs of record. This institutionalization could drive Ka- band and perhaps other band SOTM solutions."

AGS has a SOTM system undergoing testing at the Pentagon’s Joint Interoperability Test Command, which is responsible for end-to-end interoperability certification of joint C4ISR systems. This service employs a low-profile antenna and the Arclight spread spectrum modem from ViaSat Inc. "The core of the SOTM challenge is to reliably deliver the desired performance levels via a small antenna, without causing adjacent satellite interference," says Helfgott. The operational infrastructure for the system in the continental United States has been operational since early 2006, while AGS expects to have the infrastructure for the Indian Ocean region operational midyear.

Signal blockage is mitigated by using satellites in orbits high enough to prevent most blockage created by natural or man-made obstacles, along with advanced modulation technology used to reinforce connectivity and ensure an immediate reconnection in case of signal loss. "The primary effect of [Operation Enduring Freedom] and [Operation Iraqi Freedom] has been to keep the pressure on the military to bring a reliable solution to the market," says Helfgott, who added that the military has realized video is a key part of collaborative battlefield management tools. "In fact, the need for video is part of the driver to utilize a Ku-band solution as opposed to L-band due to the much higher bandwidth."

Datapath Inc. of Georgia supports the U.S. military’s net-centric philosophy by delivering communications networks that include mobile and portable satellite terminals to the Joint Network Node. The company won an $8.3 million contract in September 2005 for operation and maintenance support services on deployable Ku-band earth terminals for the U.S. Army Communications-Electronics Command. "Solutions for the [Joint Network Node] deliver what we describe as Communication on the Quick Halt, which allows forces to stop and within 30 minutes set-up a rapidly deployed terminal to establish connectivity," says Daniel White, vice president of engineering at Datapath. "We will continue to focus on how to deliver increased mobility to the edge of the network. The goal is to create a complete SOTM solution that could provide speeds of greater than 1 megabit per second while traveling at 50 miles per hour."

But meeting the demand high-bandwidth SOTM in a mesh environment using a very small antenna poses a completely different challenge than providing Communication on the Quick Halt, says White. "Most requirements are for a mesh solution that will allow all remote mobile terminals to communicate with all others," he says. "The issue is how to close the satellite link with two small antennas on either end. We think there is a hybrid approach that employs a wireless component along with a satellite piece to give complete functionality and allow for higher speeds." The January acquisition of New Hampshire-based Third Rail Americas Inc. has bolstered Datapath’s ability to provide hybrid SOTM/wireless networking solutions, he says.

To be effective, the SOTM systems must have the ability to handle all data rates, including video, White says. "Forces in the field are requesting speeds that are higher than the currently recommended specifications, which in turn require larger antennas. We expect that these specifications will shake out within the year – defined in large part by Warfighter Information Network-Tactical requirements – and that a hybrid satellite communication and wireless terrestrial communication solution will be required to meet the [space, weight and power] required for mobile forces," he says.

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.