Today, airborne downlinks are no longer limited to strategic command applications. More and more, first responders, fire departments, EMS personnel, and others are employing airborne downlinks to meet a diverse array of needs. Through the use of digital downlink technology, these systems are easier to use, eliminating the need for highly trained technical personnel to operate them. They also now have full-featured infrared cameras and secure digital COFDM transmitters, allowing users to share the video intelligence, surveillance, and reconnaissance information across multiple organizations and agencies.

Whether the downlink platform is a fixed-wing aircraft, helicopter, unmanned aerial vehicle (UAV), or even a rapidly deployable blimp, these vehicles carry with them an arsenal of high-quality imagers. These imagers can be daylight cameras, infrared cameras, or other sensors capable of chemical or biological detection. Infrared imagers are able to see through smoke from an industrial fire or track a perpetrator under the cover of darkness. Depending on the operational need, these platforms can be positioned far away from the situation — covertly spying on a perpetrator — or right on top of it.

The video from the aerial platform has a tremendous value to operations. Sharing this effectively requires a digital downlink transmitter. The transmitter accepts the high-definition video from the imager or other onboard sensor and compresses the video so that it can be transmitted in an effective manner. The compressed digital video is then encrypted using a universal standard AES encryption method known as BCRYPT. The encrypted signal is then applied to a COFDM RF modulator and transmitter, which takes the data intended to be transmitted and converts it into a format optimized for aerial downlink transmission. The transmitter is set to transmit at a specific RF frequency, typically between 6.4 GHz and 6.5 GHz, and is divided into 12 discrete channels. It is important to understand that these bands require a license, and often require coordination with a local frequency coordinator.

Once the signal is prepared for transmission, the RF output of the transmitter is connected to an antenna system. This system can be composed of a single, omnidirectional antenna, or a more complex hybrid-directional or downward- facing antenna.

Several factors dictate the type of antenna system needed for a specific application. The terrain of the area will determine the best type of system, as mountainous and city locations require a different solution than a more rural area. Also, the distance between receive sites is a major factor.

Mobile tactical receivers stream video directly to a vehicle’s in-board computer system, where the video is decoded and displayed.

Once the video has been transmitted, several individuals can review it simultaneously. Sharing real-time video minimizes the need for voice instructions over a two-way radio. The video is typically transmitted back to a strategic command center, where it is displayed on a display wall and archived for forensic use. This type of video is especially useful for tactical operations. Video can be shared with such ground personnel as, for example, a firefighter looking to position water for optimal effect, a policeman in a squad car helping to identify suspects during a drug intervention, or even first responders needing video surveillance during a rescue.

The downlink feed can be used more effectively with the deployment of the right type of system. With the correct camera, encoding, BCRYPT AES encryption, and COFDM digital transmission, video can be shared without bounds. Proprietary systems will limit the ability to share feeds, ultimately costing additional money and potentially the loss of the valuable aerial platform during budget-tightening. With the universal COFDM standard, a multitude of receivers are available, ranging from a small, body-worn application, to a county- or state-wide system.

System Options

Advanced aircraft transmitters feature both MPEG-2 and MPEG-4 encoding, BCRYPT AES encryption, and COFDM modulation packaged in an airframe-friendly NVG ARINC fast-deployable rugged chassis, intended to be mounted directly into an aircraft’s console. They are designed for any application requiring reliable video downlink from an aircraft. Fire departments use these systems with infrared cameras, as they can view a fire from the air and see where all the hotspots are without having to send personnel into a dangerous situation. Law enforcement also finds these systems useful in monitoring a potentially dangerous system from above.

Police receiver applications differ from those for firefighters. Today’s police cars are filled with technology, basically functioning as a mobile command center. In contrast, the typical fire truck is usually equipped with a standard two-way radio, with its command center set up on-site. Law enforcement personnel typically have several central receive sites overlapping each other, with a control center for the whole network. For firefighting applications, most of the work is done outside of the truck, requiring a more mobile solution. This way, regardless of where someone is in relation to the fire, they have access to the video feed from the helicopter above.

Mobile tactical receivers are diversity COFDM receivers that will receive the downlinked transmission and stream the video directly to the vehicle’s in-board computer system device, where the video is decoded and displayed. This allows a police officer in the squad car to monitor a suspect’s activity from the road. This enables officers to make a visual identification and execute an arrest much more smoothly.

Self-contained receivers and decoders with a display unit are used for viewing downlink video on a self-contained package. It is specially designed to function under the rigorous environment requirements of a firefighter. They are lightweight, waterproof, and fit inside the pocket of the fireman’s jacket. Advanced versions feature video and audio outputs allowing the video to be viewed on a large-screen display, dismountable antennas, and an outboard high-endurance battery.

Remote strategic command post receivers feature a large-format display, daylight-readable monitor, and a multiband diversity receiver with a DVR and dismountable antennas. Real-time video can be received and shared on a self-contained system. These systems are designed to be a temporary command center for use in a remote location where there may not be a truck. This is especially useful in covert applications, as it is discrete and can be easily set up.

Airborne microwave downlink solutions enable uninterrupted transmission of live aerial images, as well as real-time information critical for situational awareness applications.

This article was written by John Payne IV, Chief Technology Officer at Integrated Microwave Technologies, Mt. Olive, NJ. For more information, Click Here 


RF & Microwave Technology Magazine

This article first appeared in the June, 2012 issue of RF & Microwave Technology Magazine.

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