SubscribeIn 1963, development of lightweight, solid-state microwave systems by Microwave Associates Communications Equipment Division (M/A) marked the beginning of live airborne video for the public safety and military community.
NYPD installed Microwave Associates airborne transmitters in the late 1960's and broadcast live video to receive antennas on the 81st floor of the Empire State building. M/A portable radios were deployed by the USMC on helicopter drones in Vietnam and live video from U.S Navy helicopters broadcast the Mercury and Apollo recovery missions using rugged M/A transmitters. M/A-Com was established in 1978 and a select group of M/A Com employees founded Microwave Radio Communications (MRC) in 1986. Over the course of forty years, MRC has furthered downlink technology in conjunction with the airframe manufacturers, integrators and suppliers of gyro stabilized electro optical and infrared camera solutions.
Today MRC has the largest share of video microwave systems in domestic and global broadcast markets. MRC has an install base of over 100,000 microwave radios in over 60 countries around the world. In addition to the broadcast community, MRC continues to provides mission critical real-time encrypted Standard Definition and High Definition live video in support of the law enforcement, fire, military, and intelligence community.
Starting in 2000 with MRC's introduction of digital Coded Orthogonal Frequency Division Multiplexing (COFDM) systems, the industry continues to expand its adoption of digital mobile solutions over legacy analog equipment for nearly all but simple predominantly rural applications.
Figure 1: Multi-Path
In Figure 1, the straight black line denotes a direct path from the helicopter to the tactical receiver case and the red colored lines represent indirect signal reflections off a mountain and nearby vehicle. Receive sites are also often blocked by buildings in urban environments when a mobile unit transmits to a static receiver and the bounce or reflection is the only signal received. The combination of direct and indirect signals is commonly called multi-path. Prior to the development of digital transmission technology, multi-path was a constant problem for analog systems as it results in severe distortion or blocking of the direct signal completely. The issue stems from the fact that analog devices use a single frequency carrier for all data transmitted and the carrier is prone to distortion. An analog receiver must distinguish between inconsistent signals given reflections and blockage plus the receiver must compensate for the time delay associated with such reflections when the desired direct path signal arrives in advance of the reflected signal.
Figure 2: Analog vs. Digital
As illustrated in Figure 2, the development of COFDM, which is a digital multi-carrier transmission technology, actually minimizes the effects of multi-path by spreading the information over a range of closely spaced carrier frequencies then processing for the time based delay of reflections and lost data with forward error correction. To a certain degree, the multiple carriers and the associated reflections actually improve overall reception and signal quality in the presence of severe multi-path conditions.
The latest COFDM digital technology from MRC, Max Ratio Combining diversity reception is a rugged and simple to use downlink solution with greater range facilitated as a consequence of improved receiver threshold. Multiple receive antennae are employed in the application and MRC combines the energy from all antenna inputs simultaneously and blends the individual carriers on a COFDM symbol basis to produce the best signal possible. The MRC Tactical Receiver Case diversity can be deployed in less than one minute with extended range antennae and robust performance in support of persistent or tactical surveillance missions.
The solution was originally developed in conjunction with Mohawk Technologies in response to a Department of the Army Multi-National Forces Camp Victory Baghdad requirement for short; medium and long-range full motion live airborne video surveillance solution. The solution was designed for instant deployment and ease of use given untrained ground personnel and operation in harsh environments under extreme temperature ratings. The receiver was designed as a best in breed solution to complement the airborne components of the downlink, which significantly reduce aircraft payload in respect to other downlink solutions. Many promote equipment that is twice the weight and requires nearly three times the volume given a separate transmitter, amplifier, and GPS unit plus associated cables.
In addition to the benefit of decreasing the airborne payload, there may be a considerable cost savings when one removes the need for a high gain pod type aircraft antenna and a high gain tracking antenna control system on the ground. Both are replaced with passive simple to use omni or sector antennae. There is also a potential security benefit when GPS data is neither broadcast nor tracked during covert applications.
As detailed below, the MRC solution includes a Strata DO-160D RTCA certified 128 bit AES encrypted transmitter and a simple omni antenna on the aircraft. The Tactical Receiver Case Diversity includes the digital MRC diversity receiver, plus a day light readable 700 nit TFT LCD monitor in a NEMA 6P/IP68 outdoor housing, plus an accessible lithium ion 2590 rechargeable military battery and two omni antennae in a MIL-STD-810 (F) Hardigg Storm Case. The City of Baltimore has already accepted delivery of five units for portable deployment throughout the downtown metropolitan area as a complement the existing terrestrial based downlink network.
Transmitter, monitor and Hardigg Storm Case
The solution outlined above is part of MRC's Mobile Network Centric Solutions (MNCS). MNCS provides deployable communications support for phone, video and Internet connectivity. Included in these customizable solutions is on demand, self-sufficient network solutions that do not require existing infrastructure such as a power grid of communication network. MNCS is ideal for applications such as:
- Airborne Downlinks
- Body Worn Video
- Central Command
- Crowd Control
- GPS Tracking
- Harbor Security
- Mobile Command
- Surveillance
- Tactical Video
- Satellite Uplink
For more information on any of the topics discussed throughout this article please contact Microwave Radio Communications at 978-671-5881, or rhughes@mrcbroadcast.com, for further detail or assistance.