Radical Change in the Air for GLONASS - GPS World
HOME   ABOUT US   MEDIA KIT   SUBSCRIBE: MAGAZINE   SUBSCRIBE: E-NEWSLETTERS  
SEARCH
Radical Change in the Air for GLONASS
GPS World
An intriguing memo regarding GPS-GLONASS interoperability has appeared on the websites of the National Space-Based Positioning, Navigation, and Timing (PNT) Executive Committee and the Russian Space Agency regarding the December 13-14 meeting, in Moscow, of the GPS-GLONASS Interoperability and Compatibility Working Group (WG-1).

The memorandum (also available here) states "Both sides noted that concerning the question of the use of FDMA and CDMA, significant progress was made in understanding the benefit to the user community of using a common approach."

Whether or not this means that the Russian satnav system will convert its broadcast from a frequency division multiple access (FDMA) to a code division multiple access (CDMA) signal remains open to speculation. Sources close to the negotiations have  clammed up  very effectively.

The December meeting was the third for the working group. The statement calls the proceedings "highly successful" and adds that it "resolved many questions regarding interoperability and compatibility between the GPS and GLONASS systems."

At the September 2006 meeting of the Institute of Navigation, Sergey Revnivykh, deputy director of Mission Control Center of Central Research Institute of Machine Building of the Russian Federal Space Agency (RFSA) spoke of CDMA as an "option" for GLONASS and added that the system "probably will be able to implement CDMA signals" on the new third frequency, to be added on GLONASS-K satellites during Phase 3 of GLONASS modernization, and at L1. Such a change would be far from trivial — but it would leapfrog GLONASS back into viability as a GNSS partner with modernized GPS and Galileo. At the moment, it risks fading into obsolescence.

Receiver operation in the GPS and Galileo mode is simpler with CDMA. A GLONASS switch to CDMA would make manufacture of combined receivers far easier.

The change, of course, would require significant commitment of resources (time and expertise) and money, a perennially short commodity in contemporary Russia. Russian officials have promised to focus on the subject in the first quarter of 2007. GLONASS has already had to modify its frequency band — more than once — because of interference to radio astronomy.

The GLONASS signal uses FDMA technology to broadcast a common code on different carrier frequencies. GPS and Galileo use CDMA signals that transmit different codes on the same frequency. Some manufacturers — Javad Navigation Systems, Leica, NovAtel, Topcon, and Trimble — currently offer combined GPS/GLONASS receivers, principally for the survey market. For surveying use, GLONASS has been to this point a fairly good GPS augmentation system, filling in at times of day when not enough GPS satellites are visible for high-precision use. But that will only hold true until Galileo broadcasts enough signals to be useful. Then, according to Eric Gakstatter, GPS World's Survey and Construction e-newsletter editor, "GLONASS risks being ignored. But if the Russians are serious about addressing the CDMA/FDMA issue, that makes things a bit more interesting."

The differences between FDMA and CDMA signals make offering combined GPS/GLONASS receivers a complex and costly venture, one unlikely to expand beyond the current high-precision sectors where users will pay for a high-cost receiver if it adds value. Such a scenario is extremely unlikely, if not dismissable out of hand, in the rapidly developing low-cost mass market of cell phones, personal navigation, and location-based services.

The Working Group memo concludes that "The Russian side noted that a decision in this regard would be made by the end of 2007." One spokesperson who requested anonymity stated that "I expect we will be able to say something during the Moscow forum in April," referring to the planned International Satellite Forum 2007 to be held April 9-10, 2007, in Moscow. The Working Group memo characterizes the conference as "a unique opportunity to demonstrate the benefits of GLONASS and GPS interoperability in the Russian Federation for civil applications."

MORE GPS WORLD ARTICLES
Galileo Industries Told to Put House in Order
Radical Change in the Air for GLONASS
Galileo Faces Challenge over Use of Name
Global Locate, SiRF Vie for ONE Position
CSR Acquires NordNav, Cambridge Positioning

NEWSLETTERS

GPS DIGITAL EDITION


Click here
to
view GPS Digital archives
Click here to Subscribe

ADVERTISEMENT

RSS feeds for this site