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RF/Microwave??

Examine interoperability issues when selecting airborne downlinks

Posted: 28 Jun 2012 ?? ?Print Version ?Bookmark and Share

Keywords:interoperability? components? downlink system? Digital Video Broadcasting?

Coded orthogonal frequency division multiplexing (COFDM) was designed to meet the demands of a highly multipath-rich environment. Developed to support commercial markets, it has no ITAR restrictions and is a widely deployed, truly open standard published by Digital Video Broadcasting (DVB, also known as DVB-T). DVB-T has been adopted universally in the commercial markets because of its unmatched ability to move video reliably. Deploying DVB-T on airborne downlink platforms removes much of the restrictions on how video can be shared; making real-time video available even on small handheld receivers equipped with omni-directional antennas. COFDM digital transmission can be secured with encryption, an important feature for command and control, which makes it ideal for tactical, covert and surveillance operations.

Figure 1: Example of the effects of multipath on a FM signal.

Figure 2: Example of the effects of multipath in a CDL signal.

Figure 3: Example of the effects of multipath on a COFDM signal.

Encryption
Encryption has been evolving over the last few years. For a long time, the basic interoperable scrambling system (BISS) was the standard used within the broadcast industry. The National Institute of Standards and Technology (NIST) determined that BISS was not as strong as it could be and superseded the standard with the Advanced Encryption Standard (AES) as described by FIPS-192. FIPS-192 described how the core encryption is performed but lacked how it is applied to digital video. This led manufacturers to develop proprietary implementations that were generally referred to as AES. To address interoperability problems, an organization within the Department of Justice (DOJ) developed a standard describing how to apply the core AES algorithm to digital video. This standard is referred to as BCRYPT. BCRYPT is the only published standard applying AES to digital video applications. To maximize the utilization of your downlink, the transmitter needs to conform to BCRYPT.

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