Engineers who develop satellite-based comms-on-the-move (COTM) systems face efficiency and bandwidth management challenges with physics that prevent 100 percent signal efficiency, according to a panel of engineers at SATELLITE 2010.
   The panel session, “COTM: Meeting Military Technical Requirements,” featured viewpoints from across the bandwidth and customer spectrums. Andy Beegan, vice president of engineering at Segovia, said engineering satellite signals to effectively hit VSAT and other small terminals often go unnoticed by the customer. “From the end user’s perspective, they are mostly concerned with the application delivery to the terminal,” he said.
   One of those customers, U.S. Air Force Col. William Harding, oversees a $46 billion portfolio for military satellite communication systems and like other end users, faces challenges following the April termination of the TSAT (Transformational Satellite System) program. “The reality we are looking at now is that we are trying to provide the capabilities with the satellite systems we have now and add prudent enhancements and capabilities to those systems, rather than going off and pursuing a large TSAT program. TSAT essentially was going to push the fiber and the network and the routers into space. At this point, we are not taking this approach anymore. Essentially now, the systems we are now providing are providing bandwidth to the networks that are kind of on the edge, and allow those networks to connect to each other and the Global Information Grid.”
   Unfortunately for the COTM customer, the application in question often is complex and requires a lot of bandwidth, which can get expensive just due to the physics of the mobile infrastructure, said SatProf President Ralph Brooker. Geostationary “satellites are closely spaced together. This results in some of the uplink signal hitting neighboring satellites when that energy is meant for the target satellite,” he said. “COTM antennas are very small, resulting in a wide beamwidth with low gain. [Geostationary] networks are often bent-pipe and shared by multiple customers. They may have spot beams, but those beams aren’t everywhere. These factors create significant interference issues.”
   Brooker also mentioned that the spatial density of COTM beams falls under strict International Telecommunication Union (ITU) and even stricter U.S. Federal Communications Commission (FCC) standards. “Regardless of beam, the spatial density and bandwidth required to both meet regulatory standards and the needs of military customers can get expensive, especially for applications like unmanned aerial vehicles (UAVs), which move very fast from one beam coverage to another. You can’t solve these problems by placing the satellite at a low horizontal angle, because then you deal with physical obstacles and other interference,” he said.
   Brooker even listed radiation as one of the concerns involved with COTM. “The antennas that are mounted to the roofs of these military vehicles are often a few feet from a soldier’s head, which can be dangerous. All of this is considered in the design phase of these architectures.”
   COTM markets traditionally have been divided by air, sea and land uses, with the highest demand coming from military UAVs, vessels, patrol vehicles and ground troop connectivity applications. The more complex the applications, the more difficult it is for satellite engineers to solve the problems that occur. “The challenges keep building on themselves,” said Karl Fuchs, iDirect Government Technologies’ vice president of engineering. “We have developed several products which deal with direct sequence and frequency hopping, or the two types of spread spectrum. The military customer also has security demands, and we need to provide them with a single IP address as the remote moves from location to location. We also need to know how many remotes the military will be operating at one time when we consider our bandwidth management. All of the architecture created to meet U.S. Department of Defense requirements is very broad to meet transmission security compliance.”
   EMS Technologies Defense and Space Systems Principal Engineer William Hafner said that COTM technology is still new and has progressed significantly in its short existence. “Highly mobile satellite communications is a new market in a world where requirements have more typically been based on an assumption of large reflector-based Earth terminals,” he said.