Communications

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COFDM Audio and Video Transmission

Cobham Surveillance has introduced a new family of COFDM (Coded Orthogonal Frequency Division Multiplexed) digital video products called SOLO, with domo technology at their core. These products support narrowband (625 KHz, 1.25MHz and 2.5MHz) and full DVB-T compliant (6, 7, or 8MHz) channelisation. This line has specifically been developed for worldwide customers in the law enforcement and military markets, and for the manufacturers of Unmanned Ground Vehicles and Unmanned Aerial Vehicles who support their missions.

Digital technology has made rapid advancements in key areas over the past few years. Notably the size, weight, power consumption and cost have dropped by about 30% per year. Cobham now offers digital systems that represent good value to users and are a better fit for operational requirements than analogue systems. It also develops specific implementations of COFDM technology for the public safety and military markets. Cobham Surveillance is committed to working with customers on developing products that meet specific needs, and invites you to discuss your requirements with its team.

The migration from analogue microwave systems to digital transmission offers several key benefits to users:

Better Performance - By using digital modulation and compression techniques, digital microwave provides superior performance in non-line of sight and high multipath applications. Unmanned Ground Vehicles operating in buildings or urban environments, as well as low fl ying Unmanned Aerial Vehicles, will be able to transmit dramatically clearer video with less break up to remote receive stations. Covert surveillance cameras no longer need to have a clear line of sight to the receive location to have good picture quality. Unlike analogue, digital video picture quality is noise free regardless of distance

Efficient Spectrum Utilisation - Digital video systems operate in a fraction of the spectrum utilised by typical analogue transmitters, offering up to 16 digital video streams in the spectrum previously used to transmit a single analogue channel. Cobham SOLO products support 625 KHz, 1.25MHz or 2.5MHz channels in the narrowband configuration or 6-8MHz channels in the full DVB-T compliant confi guration. This compares to up to 25MHz for a typical analogue channel. In addition, digital channels can be located adjacent to each other without a guard interval. Analogue systems tend to bleed over their allotted spectrum, requiring several Megahertz of separation between channels at a minimum. As regulatory agencies worldwide reallocate spectrum, it’s clear that digital transmission enables more users to co-locate channels in an increasingly crowded RF spectrum.

Secure Transmission Using Encryption – Digital transmission enables the secure transmission of video by using AES128 or 256 bit encryption. There is no penalty to the user in terms of performance. Analogue systems don’t offer this capability as a feature. Analogue “cut and rotate” encryption modules are expensive, often doubling the price of a system, and not nearly as effective in securing the video data stream. In addition, they add to the size of both the transmitter and the receiver. Digital offers true encryption with no additional size penalty. In the case of the Cobham receiver, AES encryption can be carried on over the IP network

Set up for Internet Access - Many customers are looking at how to access their video from anywhere, at any time, over the internet. Digital transmission makes it easier to send data over the internet, avoiding the need for a separate analogue-todigital conversion. Cobham receivers have been designed to offer internet connectivity by means of an optional TCP/IP Ethernet network interface, accessed via a convenient RJ45 connection.