L-3 SAASM Innovation

September 7, 2012  - By
Image: GPS World

By Tony Murfin.

A new SAASM receiver with multiple key features is set to play a major role in the UAS/UAV market, as well as those traditional weapons programs where SAASM has been employed in the past. The maker, L-3, has also taken a “commercial” approach to bringing those greater capabilities to authorized military users.


At the Association for Unmanned Vehicles International (AUVSI) convention in Las Vegas in August, it seemed that everybody and anybody in the industry was either there with a booth or was walking the exhibit.

So picking and choosing the subject for this article was tough, and we may have to run one or more follow-on pieces on unmanned aerial vehicles/systems (UAV/UAS) in the future.

We ended up selecting a notable breakthrough in SAASM technology with direct applications in the UAV/UAS world as the big news from AUVSI. True, L-3 Interstate Electronics Corporation (L-3/IEC) did announce and demonstrate its TruTrak receiver at the Joint Navigation Conference (JNC) in June in Colorado Springs, but given the focus on threats to GNSS and the explosion of interest in UAV/UAS, we felt we should look into this achievement a little closer.

There was a buzz on the floor and in the conference related to civil applications of UAS/UAVs and the coming need for civil certification — somewhat fueled by the appearance and opening pitch by no less than acting U.S. Federal Aviation Administrator Michael Huerta. But while civil certification is still a couple of years off, the business of UAV/UAS today is still to supply the military with advanced and flexible unmanned vehicles, which can take on what seems like virtually any task — principally using GPS for guidance.

L-3/IEC has been developing GPS-based guidance and navigation products for more than 20 years. In the process, IEC has become a recognized leader in SAASM and modernized GPS, and has produced and fielded more than 60,000 SAASM-based GPS receivers for a number of programs, including the Combat Survivor Evader Locator (CSEL) radio, Advanced Medium Range Air-to-Air Missile (AMRAAM), and precision-guided munitions including M982 Excalibur, XM1156 Precision Guidance Kit (PGK), and the Accelerated Precision Mortar Initiative (APMI).

Typically the PGK turns “dumb bombs” and artillery shells into precision guided munitions — this is now commonplace in the U.S. weapons arsenal — while L-3/IEC has been a significant contributor to the improvements in accuracy and reliability that these weapons have brought to modern warfare.

Nevertheless, L-3/IEC’s largest volume program has been more oriented to saving lives — the CSEL program has provided military pilots with emergency location and communications capability. CSEL’s advanced technology is credited with saving many lives by increasing U.S. forces’ ability to reach and rescue isolated pilots or combat personnel faster than earlier survival radios have previously permitted. CSEL is DoD’s program for personnel recovery survival radios — all services use it. The Navy and the Army purchased most of the early CSEL variants and the Air Force is currently fielding radios to active-duty, Guard, and Reserve organizations.


Now, enter the L-3/IEC next-generation TruTrak SAASM receiver, which is something of an anomaly in today’s world of military products developed through the mil-spec procurement system.

Typically a supplier will bid against a requirement and, if successful, goes on to develop and build something exactly meeting those requirements — no more, no less.

Well, the background to this GB-GRAM Type II receiver evolution instead involves significant L-3/IEC internal IR&D investment — and a desire to considerably exceed the existing requirements. Knowing that commercial receivers already blow the doors off most mil-spec receivers in terms of capability and performance, L-3/IEC set out to create a new level of capability for the military market.

Given that the environment this receiver will live in now has high electromagnetic interference (EMI) and jammers, the first place IEC focused was on the RF front-end. While focusing on robust RF performance, the near in-band and out-of-band interference rejection was improved considerably. And fully shielding the whole receiver lead to a much quieter receiver in terms of radiated EMI and susceptibility to external EMI. The applications L-3/IEC is targeting also require more flexibility in antenna choices, so along with the existing passive antenna capability, they improved the supported active antenna range all the way out to 0-40 dB. This now gives TruTrak much greater integration flexibility and this means more places where it can readily be used.


The other major improvements came on the digital side. Existing GB-GRAM receivers have quite limited interface capability. Eight serial ports were included, and with three processors on-board, there is significant integration capacity for data from external aiding sensors. The typical mix that’s been demonstrated includes a Honeywell inertial, a low-cost MEMS inertial, and an altimeter. This allows a lot of flexibility in building a high-integrity nav solution for mil UAV/UAS — but L-3’s targeted market is not exactly for nav systems on-board UAVs.

And the PowerPC processor which is available for user applications allows integrators to pull hardware out of their nav suite and integrate existing software solutions within the TruTrak receiver — in an on-board user capability that the commercial world has offered its OEM customers for many years. For UAV’s this is a godsend in potential space, power and weight savings.

L-3 still wants significant business in the UAV/UAS space — but their focus is on providing secure guidance for the weapons that mil UAVs now carry on a regular basis. This receiver is really small, lightweight, and highly capable, and L-3/IEC sees the added integration and performance of TruTrak winning them increased opportunities with UAV ordinance suppliers.

As we have seen, the existing SAASM receivers that L3 supplies have found a home with precision munitions/artillery, requiring performance under very high g’s, and with lightning fast acquisition. TruTrak is no exception, and this fast acquisition was demonstrated at JNC with 2-3 second direct P-code acquisition following time and data transfer. One of the new capabilities demonstrated was the addition of inertial and altimeter inputs when the signal strength of simulated satellites was reduced and poor DOP was added to replicate a GPS-challenged, signal-denied environment.

And L-3/IEC is involved in the M-code initiative as one of the Air Force Space and Missile Command’s developers of next-generation GPS user equipment. Modernized M-code GPS User Equipment (MGUE) is expected to provide significant tactical advantages and cost benefits to military users in the future. The TruTrak receiver design uses the same footprint for SAASM and M-code chipsets alike so that the receiver can be configured for either SAASM or M-code depending on which chipset is populated onto the board. This backward- and forward-compatible approach will help to ensure a seamless transition to next-generation M-code.

The other key ingredient is very high quality carrier phase measurements.

What’s that using carrier-phase in a military UAV integrated solution?

Surely this is the last thing anyone in a uniform would want to do? Too much opportunity for jamming of radio links and/or detection by the enemy — these are the typical responses I’ve heard to using RTK in military applications. Well, that’s maybe how it used to be. Today’s UAVs use RTK for take-off and landing — generally in friendly territory, so RTK is a must. L-3/IEC could have taken on this segment of the market alone, but instead it chose to seek a partner and work with one of the industry’s best at civilian RTK — it partnered with NovAtel.

NovAtel’s dual-frequency receivers have been widely accepted into the UAV industry to provide high-quality RTK for precision take-off/landing/capture for a number of years. This position has been challenged, not only by equally capable GNSS competitors, but also by regulations which spell the end of waivers that permit the use of civilian C/A code receivers on mil UAVs. So NovAtel’s answer was to integrate the XFACTOR SAASM module (core DSP for TruTrak) onto the new OEM-6 dual-frequency receiver. This new receiver is known as the OEM625S, and is expected to hit the streets in production quantities after approvals are granted later this year.

With digital outputs that look exactly like those of their regular OEM dual-frequency receivers on board existing fielded UAVs, the OEM625S receiver will be readily integrated and will provide compliant SAASM capability for mil UAVs. NovAtel and L-3/IEC have agreed that NovAtel will lead UAV receiver sales efforts, particularly for RTK applications. L-3/IEC integrates the SAASM module on the NovAtel receiver and ships the receivers to military customers in the U.S. — so both share actively in this market.

So a new SAASM receiver. . . which on the face of it seems to have all the capabilities that you would normally associate with those of a commercial OEM dual-frequency receiver. And an equally innovative commercial partnering scheme for nav systems on UAVs . . . These are welcome departures from the norm for a defense contractor who appears to have matched its technical innovation with an innovative new approach to at least one new market segment. Let’s hope that real business growth comes out of L-3/IEC’s bold moves with TruTrak.

Tony Murfin
GNSS Aerospace

About the Author: Tony Murfin

Tony Murfin is managing consultant for GNSS Aerospace LLC, Florida. Murfin provides business development consulting services to companies involved in GNSS products and markets, and writes for GPS World as the OEM Professional contributing editor. Previously, Murfin worked for NovAtel Inc. in Calgary, Canada, as vice president of Business Development; for CMC Electronics in Montreal, Canada, as business development manager, product manager, software manger and software engineer; for CAE in Montreal as simulation software engineer; and for BAe in Warton, UK, as senior avionics engineer. Murfin has a B.Sc. from the University of Manchester Institute of Science and Technology in the UK, and is a UK Chartered Engineer (CEng MIET).