Cobham Tactical Communications and Surveillance COFDM Digital Video Products
How SOLO Technology works
It’s helpful to think of the transmitter and receiver in three distinct steps:
The first step is the conversion of your analogue camera’s output to a digital, compressed signal consisting of “1s” and “0s”, your digital data stream. Cobham has chosen to use the MPEG2 and MPEG4 standard, which is mature and well defined.
The next step is to optionally encrypt the data using AES, and then modulate the data and prepare it for RF transmission. COFDM utilises significant redundancy, producing excellent results in high-multipath environments.
The data is duplicated many times during interleaving process. Because of the interleaving and redundancy the information is presented in different carriers or even within different frames. If one carrier is corrupted, it has little impact on video quality, as the data is repeated on another carrier. This provides the robustness in the system. Digital Signal Processing on the receive side is able to recombine all this data into a single video stream.
In the SOLO product range, you have the option of narrowband transmission at 1.25MHz or 2.5MHz channelisation, or wideband transmission, at 6, 7, or 8MHz per channel.
In the narrowband configuration, approximately 400 carriers are used, versus about 2000 in the wideband configuration. A major benefit of using the 400 carriers, is that fewer carriers give you more power per carrier, which extends the coverage area. 1.25MHz and 2.5MHz are inherently lower noise due to a narrower bandwidth. Although fewer carriers are more susceptible to multipath, this is negated by the full time spatial maximum ratio combining technology that is used. The second benefit simplifies the RF front end design where phase noise is easier to manage.
In testing, the narrower channelisation is often found to be the best mode of operation, in particular when transmitters are within close proximity to each other.
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