Missions in remote, forward operating locations often suffer from a lack of connectivity to tactical operation centers and access to valuable intelligence, surveillance, and reconnaissance (ISR) data. The assets needed for long-range, high-bandwidth communications capabilities are often unavailable to lower echelons due to theater-wide mission priorities. DARPA’s Mobile Hotspots program aims to help overcome this challenge by developing a reliable, on-demand capability for establishing long-range, high-capacity reachback that is organic to tactical units. The program is building and demonstrating a scalable, mobile millimeter-wave communications backhaul network mounted on small unmanned aerial vehicles (UAVs) and providing a 1 Gb/s capacity. DARPA performers recently completed the first of three phases in which they developed and tested key technologies to be integrated into a complete system and flight tested in subsequent phases.
“We’re pleased with the technical achievements we’ve seen so far in steerable millimeter-wave antennas and millimeter-wave amplifier technology,” said Dick Ridgway, DARPA program manager. “These successes—and the novel networking approaches needed to maintain these high-capacity links—are key to providing forward deployed units with the same high-capacity connectivity we all enjoy over our 4G cell-phone networks.”
Phase 1 accomplishments include:
- Smaller, steerable millimeter-wave antennas: During field testing, the program successfully demonstrated steerable, compact millimeter-wave antennas that rapidly acquire, track, and establish a communications link between moving platforms. Steerable millimeter-wave antennas will enable the formation of a high-capacity backhaul network between aerial and ground platforms.
- Low-noise amplifiers: Performers also demonstrated an advanced low-noise amplifier (LNA), which boosts the desired communications signal while minimizing unwanted noise. The prototype achieved the record for the world’s lowest noise millimeter-wave LNA at about half the noise figure of a typical LNA.
- More efficient and capable power amplifiers: Efficient millimeter-wave amplification is required to achieve the long ranges (> 50 km) desired in the Mobile Hotspots program. During Phase 1, performers demonstrated output power exceeding 1 watt and 20% power added efficiency (PAE) from a single gallium nitride (GaN) chip operating at E-Band frequencies (71 GHz to 86 GHz). Output powers exceeding 20 watts and approaching 20% PAE were also achieved using power-combining techniques.
- New approaches for robust airborne networking: Mobile ad-hoc networking approaches were developed to maintain the high-capacity backhaul network among mobile air and ground platforms. Phase 1 performers developed unique solutions to overcome connectivity and network topology challenges associated with mobility and signal blockages due to terrain and platform shadowing.
- Low-Size, Weight, and Power (SWAP) pod design to carry it all: Performers created engineering designs for small, lightweight pods to be mounted on an RQ-7 Shadow UAV. The pods, with all of the Mobile Hotspots components inside, are designed to meet the challenging program goals of widths no more than 8 inches, weight less than 20 pounds, and power consumption less than 150 watts.
Phase 2 of the program began March 2014. Two performers, L-3 Communications and FIRST RF, were chosen to lead teams comprising several Phase 1 performers. Phase 2 goals include the integration of the selected Phase 1 technologies into Shadow-compatible aerial pods and ground vehicles. Phase 2 will conclude with a ground demonstration of at least four Shadow-compatible pods, two ground vehicles and a fixed ground node. A planned third phase will encompass field testing of the Mobile Hotspot systems on networks of multiple SRQ-7 Shadow UAVs and mobile ground vehicles.
Providing high-bandwidth communications for troops in remote forward operating locations is not only critical but also challenging because a reliable infrastructure optimized for remote geographic areas does not exist. To overcome the challenge of data transmission in remote areas, the Agency’s Mobile Hotspots program intends to develop and demonstrate a scalable, mobile, millimeter-wave communications backbone with the capacity and range needed to connect dismounted warfighters with forward-operating bases (FOBs), tactical operations centers (TOCs), intelligence, surveillance and reconnaissance (ISR) assets, and fixed communications infrastructure. The backbone should also provide reliable end-to-end data delivery between hotspots, as well as from ISR sources and command centers.
The program envisions air, mobile and fixed assets, most of which are organic to the deployed unit, that provide a gigabit-per-second tactical millimeter-wave backbone network extending to the lowest-echelon warfighters. To achieve this capability, the program seeks to develop advanced millimeter-wave pointing, acquisition and tracking (PAT) technologies that are needed to provide high connectivity to the forward-located mobile hotspots. Advanced PAT technology is key for connectivity to small UAVs, for example, enabling them to serve as flying nodes on the mobile high-speed backbone. Additionally, the program seeks novel technologies to increase the transmission power of millimeter-wave amplifiers to provide adequate ranges within the small size, weight, and power (SWAP) constraints required for company-level unmanned aerial vehicles (UAVs).