Advances Boost Tactical Nodes

The Defense Advanced Research Projects Agency Network Centric Radio System provides secure backbone battlefield communications that dynamically and automatically maintain connectivity on the move. Transitioning to the U.S. Special Operations Command, this system’s realistic demonstration at Fort Benning, Georgia, works with the Command Post of the Future for situational awareness.

Technologies developed for the new Network Centric Radio System will provide reliable, mobile and secure backbone battlefield communications. Designed for use with a maneuver force, the system’s ad hoc capability dynamically reconfigures itself to maintain network connectivity automatically. Vehicles in the network can communicate routinely whenever within range of each other without manual configuration.

The Defense Advanced Research Projects Agency (DARPA), Arlington, Virginia, is transitioning this wideband waveform network system with on-the-move communications and high data rates to the U.S. Special Operations Command, MacDill Air Force Base, Florida. The system operates as a gateway rather than as a router network, Dr. Larry B. Stotts explains. Stotts is the Network Centric Radio System (NCRS) program manager and deputy director of DARPA’s strategic technology office. His background includes serving as the director of technology for U.S. Army and U.S. Navy programs as well as a previous assignment at DARPA.

This gateway technology allows interoperability among various existing and future communications systems via the network but not by using a radio. The gateway technology demonstrates that it is possible to have previously incompatible tactical radios, including coalition partner radios, communicate seamlessly even with more modern systems, Stotts says. He holds a bachelor’s degree in applied physics and information sciences and a doctorate in electrical engineering, both from the University of California at San Diego.

Radio interoperability has been a problem plaguing the U.S. Defense Department for decades. Stotts points out that the new system’s technical capability is based on using the Internet protocol (IP) layer of the network. “Harnessing IP technology offers a potentially more affordable path for military communications interoperability in the future.”

The communications capabilities, networking technologies and architectures of this system support emerging warfighting concepts. The technologies and systems integration are demonstrating high-data-rate and low-latency communications for real-time fire control and robotic missions, Stotts states. “Since NCRS must operate in a hostile electromagnetic environment, the system must also provide robustness to jamming and significantly improve low probability of detection/intercept characteristics. The approach to meeting these opposing constraints is through multi-tiered directional antennas at low bands and highly directional antennas at high band millimeter wave frequencies,” he says.

This DARPA radio system development began as the Future Combat Systems–Communications (FCS-C) project, a joint DARPA and Army effort. It was proposed as the communications network for the transformation of the Army. The program’s name recently changed to reflect the transition from DARPA to special operations, along with changes in Army plans and service funding issues related to significant cost growth of the Army’s Joint Tactical Radio System.

In January 2006, a demonstration of the DARPA system was carried out at Fort Benning, Georgia. The NCRS operated up to 14 mobile network elements, or nodes, with a variety of communications systems and user applications, Stotts explains. “The nodes were deployed as a mechanized infantry battalion with battalion and company units. Communications systems included tactical stub-nets, which operated as lower echelon, intra-company links. This high-data-rate backbone communications system provided connectivity between higher echelon elements, battalion-company links,” he notes.

During the operational exercises, all 14 nodes operated for more than six hours in scenarios that spanned geographic ranges up to 100 kilometers (60 miles), the distance from the battalion forward command post to the mission objective. During the tests, soldiers operated unscripted through cities and down roads lined with trees to simulate communications under realistic, complex urban terrain, Stotts states. Signal Corps soldiers operated the network without DARPA assistance. A backbone radio network, developed by the Raytheon Company, played a significant role as the broadband interconnection between legacy radio systems.

Tactical radio networks consist of a collection of heterogeneous radio types distributed across an area of operations. Interconnecting the multiple radios requires a network-centric backbone between forward-deployed units and the tactical operations center. A combination of terrestrial and satellite backbone transport networks provides both high bandwidth and reliable connectivity. This capability to interconnect multiple distributed feeder networks with autonomous selection between terrestrial and satellite backbone paths was successfully executed during the Fort Benning demonstration, Stotts maintains.

“The broadband mobile ad hoc radio system incorporates innovative networking features to deliver many breakthrough capabilities. Multiple discontiguous 1.2-megahertz-wide bandwidth segments are aggregated by the system into a single radio frequency waveform to ease frequency planning in crowded ultrahigh frequency spectrum bands,” Stotts confirms. “The DARPA system provides both high data rates and long-range communications, autonomously adapting each link in the ad hoc network topology to deliver the maximum possible throughput under dynamically changing link conditions.”

The various tiers of the system were all interconnected using the U.S. Marine Corps’ command and control on-the-move network digital over-the-horizon relay (CONDOR) system. Applying this disruption-tolerant networking technology enabled IP routers to route application data automatically between various elements using the most efficient routes and radio systems. Stotts continues that applications supported by the DARPA NCRS exercise included the command post of the future (CPoF) and command and control personal computer (C2PC) for situational awareness and battlefield command and control; video data streams from IP cameras with selected elements, both airborne and ground-based simultaneously; IP chat; voice over IP; and network maintenance data.

Signal soldiers directed airborne relays, including unmanned aerial vehicles (UAVs), to maintain the backbone network. “They clearly demonstrated rapid, autonomous, mobile and ad hoc network formation and maintenance during tactical mobility scenarios, with self-forming and self-healing capabilities. Link ranges in excess of 60 kilometers [40 miles] at 5-megabit-per-second data rates were demonstrated. The maximum link range at lower rates with operationally useful data was demonstrated at more than 120 kilometers [75 miles] with 800-kilobit-per-second rate,” Stotts says.

Adaptive data rate shifts were demonstrated between links to maintain reliable data transfer under changing link conditions, Stotts maintains. Low-latency, multi-hop relay capabilities were demonstrated with adaptive throughput under varying link conditions, including arbitrary airplane, helicopter and vehicle speeds. “Soldiers had to learn where to place airborne nodes and network management for the demonstration. We did not have an automatic way to move UAVs to optimum connectivity positions.”

Radios turned on automatically and were assigned an IP address, an amount of spectrum and a center frequency. Aircraft links had to remain within range and within the line of sight of each other. Maneuver vehicles communicated directly; however, when a vehicle broke lock, the computer system automatically looked for the next available asset to maintain connectivity. Global positioning system tracking was used so the system connected that vehicle to the nearest airborne relay within milliseconds. The user in the vehicle did not even know the shift had occurred. If an airborne link flew out of range, the NCRS connected automatically to a satellite, which could relay to another satellite or to another airborne asset to maintain the link.

The NCRS demonstration maintained communications via Ku-band satellite for on-the-move operations, Inmarsat, Global Star, Iridium, the Boeing Company’s satellite radio system and two secure wireless local area network 11 radios—whatever was available. DARPA’s NCRS validated the Army’s vision of using a mobile infrastructure for on-the-move communications with reliable data transfer under dynamically changing link conditions.