An Evolving SAASM Receiver Story

By Tony Murfin

Whatever happed to Allen Osborne Associates (AOA)? As a 1994 report (seeking a receiver for a “GPS Sounder” task) stated, “Signal-to-noise ratio tests of three high-performance GPS receivers in severe multipath conditions clearly show the Alllen Osborne Associates TurboRogue SNR-8000 is superior in locking and tracking C/A, P1 and P2 codes at very low receiver-to-satellite elevation angles.”

The advanced features of the TurboRogue may well have been key in AOA receivers being used for a large number of ground reference applications, including Monitor Station Receivers for the U.S. Air Force GPS Operational Control Segment (OCS).

Just to refresh your memory, AOA was acquired in 2004, and the GPS group now resides and thrives within the Communication Systems Division of ITT Exelis Corporation (ITT). Those AOA products and technology have contributed to the ITT military GPS receiver group in Van Nuys, California, becoming a leading SAASM receiver supplier.

ITT Exelis also has a Geospatial Systems group headquartered in Rochester, New York, which is home to the GPS Payload, Receiver and Control Systems group who are currently developing the ground reference receiver as part of the Raytheon team for the next-generation GPS Operational Control Segment (OCX).

Geospatial Systems has also been continuously involved in the supply of GPS payloads on every GPS satellite launched and has accumulated more than 500 years of on-orbit payload life.Geospatial Systems is also part of the Lockheed Martin team that is developing and building the satellite payloads for tomorrow’s GPS III space segment. ITT is developing and integrating the navigation payloads for eight GPS IIIA satellites.

An Exelis SINCGARS radio.

SINCGARS

SINCGARS

So, today, ITT boasts that it is the only GPS systems developer to have been a key contributor to all three GPS program segments (space, OCS and user) with both legacy and modernized equipment.

The receiver guys in Van Nuys have fielded a series of SAASM-based receivers over the years, beginning with the EGR-1020 which has gone into a large number of SINCGARS radio systems.. This adds position and GPS time-sync to each radio terminal. The handheld control display allows each radio operator to see the location in real-time of all SINCARS-equipped friendly force groups, providing active situational awareness on the battlefield.

The EGR-2000 Small Serial Interface (SSI) SAASM receiver.

The next generation EGR-2000 Small Serial Interface (SSI) SAASM receiver has been integrated into “an in-country GPS designed and manufactured system of a U.S. International Ally,” and can be found in terminals, radios and handhelds.

This brings us to the current ITT receiver product — known as the EGR-2500. ITT-funded IR&D investment in more integration and miniaturization has reduced the size of the EGR-2500 to half that of the SSI receiver. With the same capability to track through reduced signal levels and producing high-precision carrier phase and pseudorange, its not surprising that the EGR-2500 has found a few new OEM applications.

Both Geodetics and Technology Advancement Group (TAG) have worked with ITT to integrate the EGR-2500 into their products in order to achieve centimeter-level RTK positioning. The EGR provides high-quality, variable rate observations at up to 10 Hz for up to 24 different satellite signals, and this allows Geodetics and TAG to offer anti-spoofing RTK performance. With the addition of external inertial aiding, the EGR is also able to maintain a high quality RTK solution even under high dynamics.

The ITT EGR-2500.

But the SAASM receiver world is becoming even more competitive, and ITT is responding by maintaining its IR&D investment in yet another generation of receiver. The main objective is to even further improve power consumption and performance. A pair of ARM 9 processors has been added, along with circuitry that is software-controlled to reduce power to blocks not being used, so the next-generation EGR will have reduced size, weight and cost and is targeted to consume 500 milliwatts in low-power mode. The new enhanced correlator array design will also dramatically reduce time-to-first fix, and with today’s operational environment in mind, a front end filter has been added to reduce the effects of interference and jamming.

So anti-spoofing with reduced interference and jamming — sounds like a good solution for UAVs and others operating in a hostile environment. From a rack of monitoring equipment to a single board 1.1 gram OEM module, and more integration underway for the next generation receiver — another example of electronic GNSS evolution in action…

Tony Murfin
GNSS Aerospace