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Using COFDM microwave links in mission-critical apps

Posted: 25 Jul 2011 ?? ?Print Version ?Bookmark and Share

Keywords:Aerial downlinking? COFDM? coded orthogonal frequency division multiplexing? microwave?

There is now an increasing need for mission-critical microwave video solutions for defense, security and law enforcement applications. In situations that require field deployment and mobility in uncertain conditions, coded orthogonal frequency division multiplexing (COFDM) microwave links provide an alternative to IP wireless or SATCOM technologies. These non line-of-sight links can deliver range lengths from several 100m (low power) to 50 miles or more (for airborne systems). Range is dependent on power, antenna placement, path, and more.

Older, conventional, single-carrier microwave transmission is susceptible to signal fading caused by multipath reflections when a line-of-sight path is not available. Fading can cause picture distortion in analog receivers, and loss of demodulator lock in digital receivers.

COFDM modulation can overcome these impairments by using multiple carriers rather than single carrier transmission schemes. Even if multiple carriers are lost due to fading, additional error correction techniques enable a receiver to recover the intended video data.

COFDM offers significant advantages when using microwave links to transport video in portable, field-deployable, or non-engineered situations. COFDM systems:
- Deliver robust signals even when analog paths don't work.
- Can be used in remote monitoring, mobile command or airborne applications.
- Can provide received video signals that are equal to the field inputs. After compression, the video signals retain their carrier-to-noise ratio even as the transmitted signal approaches the threshold of the microwave receiver.
- Can use less bandwidth than analog techniques.
- Provide extremely effective adjacent channel and co-channel interference rejectionreducing interference with the transmission.
- Can achieve transmission distances equal or greater than analog techniques.
- Enable the application of small format, low-profile, covert systems.

Advancements in COFDM technologies have resulted in microwave systems that are ideal for a growing range of video surveillance applications, minimizing operational failures and maximizing success rates in covert and situational awareness/surveillance.

Integrated Microwave Technologies' COFDM Mobile Diversity Receiver (MobilCMDR) is an example of a device designed for reception for situational awareness in tactical and strategic settings. The main application of this handheld device is for video downlinking for tactical applications, including airborne, ground, and remote surveillance.

An airborne tracking operation is one application where the COFDM and the MobilCMDR can be used. By having a law enforcement helicopter or airplane follow a suspect from above, it allows ground officers to stay well behind the suspect while being able to watch the aerial video on the ground at a safe distance. Tailing a vehicle (subject) also allows the arresting crew to remain well out of vision so the perpetrator does not think (or know) that he or she is being followed. By keeping the element of surprise, the police are afforded the upper hand, which can prove critical in keeping everyone involved safe.

Another application where the MobilCMDR could be used is firefighting. Having the ability to fly above a fire and downlink the thermal video down to the firefighters is a major breakthrough in this field. The firefighters on the ground are now able to use the MobilCMDR to see where the infrared hotspots are and can ultimately direct their efforts for quicker and faster results.

In the past, a helicopter crew would have to explain to the hose crew on the ground (if communication was even possible) whether or not the hose crew's aim was on target. The MobilCMDR provides a much more efficient way of getting information to the ground team. This not only saves critical time and resources, it can also significantly impact a department's budget.

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