The Troposcatter Family of Systems

Spectra Group is a specialist provider of secure voice, data and satellite communications systems and is the global distributor of the Comtech Troposcatter Family of Systems (FoS) except for USA, Canada and Mexico which Comtech retains. 

The Troposcatter FoS is a range of high-capacity, low-latency data links for over-the-horizon communications, which works without the need to rely on satellites or multiple line-of-sight repeaters and is being used by regular and specialist forces around the world to provide strategic communication links between command headquarters down to company level.

How Troposcatter Works

Tropospheric scatter uses the Troposphere (up to about 13km altitude) to provide long-range high data capacity, low-latency and hard-to-detect communications. Troposcatter systems use high-power radio signals (often in the UHF and SHF frequency ranges, around 300 MHz to 3 GHz) that are transmitted toward the troposphere, the lowest layer of the atmosphere. As the radio signal encounters irregularities in the troposphere—like changes in temperature, humidity, or density—it scatters in multiple directions. While most of the signal continues to travel forward, a small fraction is scattered back toward the ground in multiple directions in the common volume. The scattered signal is picked up by a distant receiving antenna. Because only a small part of the original signal is captured after scattering, troposcatter systems require high-powered transmitters and highly sensitive receivers with complex software to detect these weak signals and decode the fragmented data. For this reason, in the past, troposcatter systems were enormous systems with massive dishes and essentially static capabilities. However, with the advancement of technology and a need to use such systems in a mobile context that is no longer the case.

Spectra Group supplies three main systems; the larger, but more powerful 500-Watt Mobile Transportable Transmission Systems (MTTS) capable of delivering 210Mbps of data throughput up to ranges of 250km depending on conditions, and the COMET which is smaller and more lightweight. COMET has a maximum transmit power of 10-watts, using a 1-meter dish and is designed to provide low latency (typically 9-20mS), large data rates (originally up to 60Mbps) and a range of 70 kilometers. However, COMET often far exceeds the designed data rate and, with careful siting, can exceed the specified range. Spectra Group recently developed an OTM option (On The Move) for mobile applications such as land vehicles or maritime vessels. It has demonstrated the capability to deliver up to 7 Mbps at a range of 112 km, even when positioned just a couple of metres above sea level.

Critically, Troposcatter is satellite independent and works in a GPS/GNSS denied environment, so is suitable for use in a Peer-on-Peer conflict/Multi Domain Integration. The low latency, large bandwidth, enables analysis and manipulation of large data, which combined with its low operating cost makes it suitable for deployed battlegroup or even company headquarters. Unlike geostationary satellites, it is also effective in polar regions.  As a point-to-point system, it is very directional, requires low power and uses complex waveforms so has a Low Probability of Detection (LPD) and Low Probability of Interception (LPI) which means it is highly suitable for many of the challenges NATO faces today.

Modular Transportable Transmission System (MTTS)

The Troposcatter MTTS is the most flexible, rapidly deployable, modular transit case troposcatter system available for when the operational situation demands high power (500 Watts), high bandwidth (<210Mbps) and long ranges (< 250km dependent on conditions).

The core MTTS Modem (CS67PLUS) is common across the troposcatter family of systems and is the first software-defined adaptive troposcatter modem and radio packaged in a compact sealed module. This adaptive architecture can support Line- of-sight (LOS), Obstructed LOS and Troposcatter beyond line-of-sight (BLOS) communications with a capacity of < 210 Mbps of full duplex data throughput.

To maximize link availability and data throughput, the CS67PLUS features Adaptive Coding Modulation (ACM). ACM continuously selects the best modulation and error correction coding scheme on a frame-by-frame basis based upon troposcatter link conditions to continuously provide maximum throughput and link availability.

Transit Case Modularity

The modular design allows users to take a building block approach to deployment, only utilising the cases needed for a specific mission objective, with the ability to increase the power of the systems as those requirements change. The Radio Baseband Transit Case (paired with a C-Band antenna) can function as a stand-alone line-of-sight transmission system for shorter range and unobstructed links. The addition of a single RF section enables dual diversity troposcatter and diffraction links for medium range and obstructed communications. A second RF section (with antenna) provides Quad Diversity troposcatter communications for maximum range.

The portable transit case design allows more flexible deployment options than traditional trailer or vehicle based troposcatter systems. The MTTS cases can be transported to areas that are inaccessible by vehicles to optimise transmission paths. Spectra Group offers a 2.4 m troposcatter antenna solution, but the MTTS is compatible with any C-band antenna.

Compact Over-the horizon Mobile Expeditionary Terminal (COMET)

The COMET uses the same CS67Plus modem as the MTTS but is a much smaller and more lightweight system. It is designed to support rapid, mobile operations that require high bandwidth and ranges up to 70km.

The COMET system uses a 1-metre dish and the COMTECH CS67Plus Modem capable of up to 210Mbps, which takes the IP stream and directly converts to two RF outputs in the range 4.4-5Ghz to provide two frequencies, amplified by Dual 10W GaN amps (Dual LNA on the receive path). This allows for dual frequency/polarisation diversity that compensates for any fading/multi path.

In suitable conditions, the bandwidth, range, and data transfer speeds can be much greater than predicted.