Unmanned Aerial Vehicle (UAV) is defined as a powered, aerial vehicle that does not carry a human operator, uses aerodynamic forces to provide vehicle lift, can fly autonomously or be piloted remotely, can be expendable or recoverable, and can carry a lethal or nonlethal payload. Unmanned aerial vehicles (UAVs) are quickly becoming ubiquitous in military command and control operations. With reduced radar signatures, increased endurance, and the removal of humans from
immediate threat, unmanned (also known as uninhabited) aerial vehicles have become indispensable assets to militarized forces around the world, as proven by the extensive use of the Shadow and Predator in recent conflicts. UAVs have become indispensable to modern military for large number and variety of missions; intelligence & reconnaissance missions like signal intelligence, image intelligence; communications mission like radio relay; electronic warfare missions like electronic attack and electronic protection, and Nuclear, Biological and Chemical (NBC) missions.
A typical unmanned aircraft is made of light composite materials to reduce weight and increase maneuverability. This composite material strength allows military drones to cruise at extremely high altitudes. Typical tactical UAV like SEARCHER consists of many functional systems, including Command Datalink system , payloads Optical and COMINT, Flight control and Navigation systems. UAVs also differ on the level of autonomy programmed in it. Most UAVs however have both remote controlled and autonomous modes. Despite the absence of a crew onboard any of these UAVs, human operators are still needed for supervisory control.
The requirement for UAVs is growing exponentially. At the same time, their capabilities need to increase in terms of data rates, area coverage and operation in a hostile environment. The traditional command and control links in UAVs were line of sight microwave links which connect it to ground Control systems. However these data links are limited to hundreds of kilometers depending on UAV height.
One critical need is to provide data connectivity for control and non-payload communication (CNPC), also known as command and control (C2) communication. The non-payload communication link is dedicated to secure and reliable communications between the remote pilot ground control station and the aircraft to ensure safe and effective UAV flight operation. This link can be either a line of sight (LOS) air-ground (AG) link between the two entities or a beyond-line-of-sight (BLOS) link using another platform such as a satellite or high altitude platform (HAP). Data rates for such links are expected to be modest (e.g., a maximum of 300 kbps for compressed video, which would not be used continuously). In contrast, the payload communication link is usually used for data applications, and often requires high throughput.
The disruption of payload links—albeit inconvenient—is not critical, whereas CNPC link disruption can be critical. The functions of CNPC can be related to different types of information such as telecommand messages, non-payload telemetry data, support for navigation aids, air traffic control (ATC) voice relay, air traffic services data relay, target track data, airborne weather radar downlink data, non-payload video downlink data, etc
High-altitude long-endurance (HALE) AISR aircraft can fly 60,000 feet or higher, for up to 32 hours over vast stretches of oceans and terrain. Other variants of unmanned systems cover a wide range of mission profiles and geographies. These variances and complexities of missions reflect modern military operations, all of which depend upon the “anytime/anywhere” transmission of reliable and secure video and data.These sophisticated drones use satellite command and control links which can extend the range of command and control links to thousands of kilometers. Additionally both methods of communications are used during a single mission. For example, a direct line-of-sight communication is used during take off and landing; then, during flight the drone is switched over to satellite communication so the drone can be controlled remotely from halfway across the globe.
Another advantage of the the tandem approach is the avoidance of the infamous one-second delay that is present during the satellite portion of the drone’s flight. When flying in the open expanse of the skies, the one-second delay does not cause that much of an issue. However, it does pose a threat to delicate maneuvers that are required during landing and take off. However, with line-of-sight communication, the drone can be controlled in real-time without a delay. Allowing the crew at the Ground Control Station (GCS ) to control the drone and it respond immediately lessening the threat of the drone crashing during these portions of the mission.
The disparate links (LOS and BLOS) mean different channel conditions and frequencies of operation, with different latency and range, and this increases challenges for the very high reliability required of CNPC links. In addition to existing cellular frequency bands (600 MHz to 6 GHz), the 5th generation (5G) cellular community is also considering the use of spectrum in the millimeter wave (mmWave) bands (24–86 GHz). In these bands, large free-space and tropospheric attenuations limit the link range, thus if the mmWave link is the only LOS link, when beyond the LOS mmWave range, BLOS capability will be needed. Such BLOS links are also of course required when in remote areas, out of range of any ground station (GS). Although satellites are an obvious choice for BLOS communications, the choice of satellite orbit, i.e., low-earth orbiting (LEO) or geosynchronous earth orbiting (GEO), distinctly affects the latency, link budget parameters, Doppler, and handoffs/handovers.
Military surveillance drones typically communicate via satellites that have wide beam coverage so the aircraft always stays in the same footprint. Newer satellites have multiple high-powered spot beams, each covering narrow geographic areas. The challenge for the unmanned airplane was to switch beams in flight at about the 600 mile-point.
UAVs require human guidance to varying degrees and often through several operators, which is what essentially defines a UAS (Unmanned Aerial System). For example, the Predator and Shadow each require a crew of two to be fully operational. However, with current military focus on streamlining operations and reducingmanning, there has been an increasing effort to design systems such that the current many-to-one ratio of operators to vehicles can be inverted.
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