GPS+GLONASS RTK: Making the Choice Between Civilian and Military L2 GLONASS

Frank Boon, Jean-Marie Sleewaegen, Andrew Simsky, Wim De Wilde

Abstract:	After several years of moderate activity, the GLONASS constellation has undergone significant maintenance. Currently, 16 satellites are present, resulting in a valuable surplus for positioning accuracy and reliability. More interestingly, the GLONASS constellation is now almost fully based on GLONASS-M satellites, which feature L2CA, an open-access civilian code on L2, while GPS currently still supports L2C on a limited number of satellites. Because old GLONASS satellites did not transmit L2CA, the military L2P signal was the only choice for dualfrequency receivers, which was simplified by the fact that on old satellites L2P was data-less. The new GLONASSM satellites transmit civilian open-access L2CA signal, while the transmission of the L2P of GLONASS-M is complicated by a navigation message with undocumented contents and structure. Receiver designers have two choices: either deal with the increased complexity of L2P tracking or consider a transfer to the use of L2CA. Because, to our knowledge, nothing has yet been reported on the structure of the navigation message on GLONASS L2P, we have undertaken our own investigation which resulted in the values of 250 bps for the bit rate and 4s for the frame periodicity. The knowledge of the bit rate is in principle sufficient for the code and phase tracking, although the aiding by CA code is necessary for the resolution of half-cycle phase ambiguity, which is a requirement for RTK applications. Preliminary performance analysis of code and phase noises has shown that although L2CA code is predictably noisier than L2P code, its overall performance shall be sufficient to ensure reliable use in phase-based GPS/GLONASS applications. The fact that the use of L2P requires behind-the-scene manipulations and is without official guarantee compels receiver designers to tune their future receivers to the use of GLONASS L2CA.
Published in:	Proceedings of the 21st International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2008) September 16 - 19, 2008 Savannah International Convention Center Savannah, GA
Pages:	2860 - 2867
Cite this article:	Boon, Frank, Sleewaegen, Jean-Marie, Simsky, Andrew, De Wilde, Wim, "GPS+GLONASS RTK: Making the Choice Between Civilian and Military L2 GLONASS," Proceedings of the 21st International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2008), Savannah, GA, September 2008, pp. 2860-2867.
Full Paper:	ION Members/Non-Members: 1 Download Credit Sign In