GLONASS-K for Airborne Applications
Issues and Perspective
As the Russian GLONASS constellation approaches completion, the planned addition of new CDMA signals has renewed interest in use of GLONASS in combination with other GNSSes for civil aviation. This article describes the work of an international team of engineers to develop and test an integrated GLONASS/ Galileo/GPS aviation receiver that can process the new Russian L3 CDMA signal.
As is well known, Galileo will become the European complement to the U.S. Global Positioning system.
But what about Russia’s GLONASS?
Although this constellation has been in operation for nearly three decades, the limited number of available satellites along with an uncertain governmental commitment to GLONASS performance until recent years had seriously restricted its use for aviation.
However, the ongoing and planned modernization of the GLONASS space and ground segments, as well as an increasing number of satellites in orbit, will lead in the mid-term to an attractive additional constellation for airborne receivers.
Moreover, international regulatory agreements already allow the use of GLONASS L1 receivers onboard civil aircraft. Standards and recommended practices (SARPS) for GLONASS L1 receivers have been published for several years by ICAO (International Civil Aviation Organization). In addition, a recent Russian regulation mandates the integration of a GLONASS receiver onboard Russian-manufactured aircraft.
So, why don’t we take a fresh look at this GNSS system and assess its potential benefit for aviation? This article will examine the utility of the GLONASS, particularly its new signal plan initiated with the K-generation of satellites, in the context of a multi-constellation receiver development project.
Using Multiple GNSSes
A lot has been done regarding combined GPS/Galileo aviation equipment. Standards have been discussed for years and are currently developed in the leadership of working groups of the European Organization for Civil Aviation Equipment (EUROCAE) and RTCA Inc. (formerly Radio Technical Commission for Aeronautics).
However, until now, standards have not been achieved to support Galileo/ GLONASS capability for civil airborne receivers, mainly due to the fact that no obvious signal compatibility and spectrum commonality exists at the receiver level. The frequencies and types of modulations of the two GNSS systems are indeed different and require two separate RF chains for L1 to comply with interference rejection–mask requirements (see Figure 1, above right).
However, the recently introduced GLONASS-K modulation scheme creates new opportunities for synergy between Galileo and GLONASS.
GLONASS Constellation Roadmap and GLONASS-K
The first experimental GLONASS-K satellite actually launched on February 26, 2011, will broadcast a new type of civil signal on L3. Although an official GLONASS-K interface control document (ICD) is not expected to be available before end of this year, some L3 signal characteristics have been made public.
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Interference Rejection Masks
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Standards for Civil Aviation
The MOPS document provides very detailed and stringent requirements describing receiver development, performance, test procedures, and internal algorithms. MOPS are discussed and elaborated by RTCA and EUROCAE technical working groups.
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Pulse Mitigation Technique
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The receiver mock-up embeds state-of-the-art technology at the RF and signal-processing level and provides a triple-constellation capability. At the same time, a GLONASS-K constellation simulator was developed, paving the way to future multi-constellation receiver development.
For the complete story, including figures, graphs, and images, please download the PDF of the article, above.
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