Network Centric Warfare: C2 on the move | ADM November 2011

Tom Muir | Canberra

Despite the advantages of the high-capacity digital combat radios that the ADF is acquiring for the networking of deployed battle groups, their VHF/UHF voice and data networks are limited by terrain and range. Full coverage of the battlespace must necessarily rely on range extension systems, such as terrestrial and airborne radio relays, and of course satellite communications.

And one aspect of the latter, in which the DSTO has shown considerable interest, is military command-on-the-move via satellite, whereby commanders in vehicles can receive and transmit satellite feeds while moving.

In 2008 EM Solutions (EMS) won a CTD contract for battle command-on-the-move Ka band communications. This aimed to demonstrate broadband satellite feeds directly into battle group and below command vehicles, and thus its potential as a key NCW enabler.

There are of course significant advantages in having robust beyond-line-of-sight (BLOS) communications available on and behind the battlespace. Broadband satcom, as promised by the WGS capability with its X-band and one-way and two-way Ka-band communications, will be able to deliver data, voice and video directly down to battle group and lower echelon commanders. This CTD for C2OTM has been a first step to providing tactical commanders with important new capabilities, especially in fast moving counter insurgency or similar operations.

The development of a Ka-band satellite tracking antenna system was a strategic decision by EMS. Until now  the company had concentrated on development of RF components as part of military systems developed by other vendors. The CTD Project provided EMS with the opportunity to develop an antenna subsystem where a high level of integration of the RF and antenna was required to achieve product performance targets. Team mate BAE Systems provided valuable experience and competencies in system and antenna design, baseband architecture, vehicle integration and system testing.

Assuming command vehicles could be operating close to or within hostile territory, a major challenge for both EMS and BAES was to design a low profile antenna that could provide continuous connectivity in conditions where commercial terminals would be expected to fail, providing up to 1 Mbps continuous data rates for command elements on the move. The antenna had to be able to automatically and rapidly recover from signal blockages due to buildings, terrain or foliage or weather and other atmospheric conditions (Ka-Band is susceptible to attentuation from rain).

Commenting on the development of the C2 OTM Ka band terminal, EMS Director John Ness points out that the antenna terminal was designed to track the Optus-C1 satellite while mounted on a moving Bushmaster PMV. While WGS operation was not required for the CTD it was an important consideration at every stage of the design which was driven by two main requirements.

First, the RF and antenna performance had to support the required uplink and downlink data rates of 1 Mbps and 4 Mbps respectively under typical operating conditions.  Second, the antenna had to track the satellite to within an allowed pointing error, the determination of which was no trivial matter, due to a number of factors that had to be considered. In the event a design target of 0.3 degree maximum pointing-error was chosen.

Unfortunately, phased array operation at Ka-band presents many technical difficulties. In particular, it is very difficult to share the physical aperture between transmit and receive because of the large frequency separation between the bands. This means the phased array antenna must be nearly twice the size of a conventional reflector, if it is to achieve the same gain.

Ness says there were other difficulties too and the technical challenges of phase array operation at Ka-band made the conventional reflector antenna a more attractive solution and a novel implementation of the well proven parabolic reflector antenna was selected. This offered the best electromagnetic performance, defined tracking requirements, within acceptable size constraints.

Having selected the antenna type, consideration was turned to the two main types of tracking. One approach is to use inertial navigation where a high performance Inertial Navigation Unit (INU) is used to determine the vehicle’s position and attitude, which is used to steer the antenna to the satellite. The other approach involves closed loop tracking, where the pointing error is determined from the satellite’s beacon. A closed loop approach was selected allowing the use of an INU of lower precision (and cost) and which was more robust.

As designed, the antenna terminal has a number of operating states visible to the operator. These are Searching; Tracking; and Gyro Holding. The searching mode is basically an open loop tracking mode and is used for initial acquisition, and for re-acquisition when the satellite has not been tracked for extended periods of time.

Field trials were conducted in August last year (2010), with assistance from the DSTO, teammate BAE Systems and 8/9 RAR based at Gallipoli Barracks, Enoggera. Integration of the antenna terminal on the Bushmaster was performed by BAE Systems. The terminal was fitted to the rear-hatch opening using a temporary mounting plate. A baseband system was installed inside the vehicle, and included an MD-1366 EBEM modem, an ethernet router, a reference oscillator and a PC for monitoring.

Satellite services were provided by DSTO, which included a digital TV video signal streamed to the vehicle; video from a forward looking IP camera streamed out of the vehicle; VoIP services allowing phone calls to be placed and received from inside the vehicle; and web-based management displays to assist with monitoring terminal performance.

During field trials, the SOTM antenna terminal was operated as the vehicle drove on main highways, suburban roads, dirt roads and off-road. Good performance was observed during highway driving. Modem events, such as sync-loss and bit errors, were only observed when obstructions were present.

In general, obstruction by trees was not a problem on major highways, as the trees were generally back from the road. On suburban roads, tree obstruction was common as were obstruction from light poles and overpasses. Between obstructions the pointing error was generally less than about 0.06 degrees. Pointing performance during off-road testing was not as good as during highway driving and most pointing error recordings were less than 0.1 degree, however the maximum pointing error recording was nearly 0.2 degrees, still within the acceptable error limits of 0.3 degrees.

This CTD has resulted in the development and field testing of a Ka-band SOTM antenna terminal, demonstrating downlink data rates of 8Mbps and uplink data rates of 2Mbps on the Optus-C1 satellite.

So what are the next steps to the achievement of a WGS-capable command-on-the-move capability from this initial work? We understand that to achieve WGS ADF inservice capability it would require a suitable modem such as a Linkway S2, an L-band to Ka-band block upgrade converter (BUC) and signal amplifier on the transmitter, and a low noise block (LNB) converter on the signal receiver, together with an antenna control unit (ACU) and other peripherals.

Our understanding is that EMS has been developing a production version of the C2OTM prototype and has joined the BAE Systems team to offer it for the JP2072 Phase 2B’s SOTC requirement.   

Subject: Defence Industry