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Decibel Engineering

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Digital Video for Mobile Surveillance

The dVMo (Digital Video for Moving Objects) link provides a flexible platform for the transmission of video, sound and data signals either in point to point or mobile to mobile applications or for mobile to base. The dVMo uses advanced COFDM (Coherent Orthogonal Frequency Division Multiplexing) which provides a dramatically enhanced link performance in the presence of multipath signals making it highly suited to users such as Emergency Services and Law Enforcement who require high quality, encrypted video for both static and mobile surveillance scenarios including ground, air and maritime. COFDM, which is also used in digital TV broadcasting, also provides significant spectral efficiency over other technologies.

UAV Navy ship Robot Two water policemen

Key features of the dVMo are : -

  • COFDM modulation providing multipath resilience
  • Wide range of frequency bands
  • Multi-service bearer with PAL or NTSC operation
  • Transport stream input
  • 50 - 200mW RF power output with optional power amplifiers
  • Spectrally efficient, WB (7 MHz) and NB (2.5MHz) typical occupied bandwidth
  • Diversity operation
  • easily carried and weighs less than 1kg

Anlogue video links have always suffered from the effects of multipath interference. This is the problem whereby signals arriving at the receiver antenna via slightly different radio paths can cancel each other out. This has the effect of degrading what might well have been a good quality image. Frequency modulated analogue links are also very spectrally inefficient requiring a channel spacing raster of 25MHz or more.

The dVMo uses modern technology to overcome both of these issues. Use of a COFDM modulation scheme with an MPEG CODEC results in a multipath immune spectrally efficient signal of only 7MHz occupied bandwidth. The coding process thrives on multipath situations making mobile camera operation a delight to watch.

The standard receiver can be deployed using two antenna RF units allowing diversity operation which further improves the multipath rejection process and upto 8-antenna diversity can be used if a receive site using high-gain sectored antennas is required.

The MPEG encoding module uses a protocol that is a dedicated derivative of the DVB-T standard meaning that it can't be casually intercepted by a consumer digital TV or set top box. The encoder card has the facility to multiplex an external ASI stream with the on board encoded video, two audios and data circuit. This allows multiple videos to be carried down a single link which is particularly useful for a vehicle or aircraft repeater/rebroadcast scenario.

Police helicopterDigital encoding naturally provides a level of casual interception immunity. For users requiring a higher level of immunity against intercept by unauthorised parties, AES encryption is available as an option.

While the 100mW RF output may seem low, it provides line of sight coverage of upto 5km and its the enhanced performance over a conventional analogue link at the same power output is most noticeable. A video CD of tests at 100mW and 1W at S Band which clearly shows the difference between analogue and digital performance is available on request.

Because of the nature of the COFDM signal, any amplification of the modulated signal must be very linear in its characteristics. Power amplifiers to boost the dVMo 100mW output will be relatively inefficient and therefore hot and bulky. This is an important consideration when deploying this type of hardware and users, particularly in covert applications or on UAV platforms, must consider the optimum system configuration to achieve physical range, battery economy etc.

The dVMo is available in a Wide range of frequency bands from UHF (320 - 360 MHz) through L-band (1.4 - 1.6 GHz), S Band (1.9 - 2.7 GHz) 3.0 - 3.6 GHz and 5 GHz.

If your application requires a full command and control system including camera or vehicle control, then the dVMo can be integrated with radio telemetry hardware.

Download the dVMo Product Presentation including deployment scenarios > 31 slides (6MB pps format)

Download the dVMo Data Sheet > four page glossy (2.3MB pdf format)