Indian Regional Navigation Satellite Starts Signal Transmissions

July 25, 2013  - By

By Richard B. Langley

Update (July 29, 2013): The spectrum recorded by the German Aerospace Center researchers appears to be consistent with a combination of BPSK(1) and BOC(5,2) modulation. This is the signal structure that ISRO announced would be used for IRNSS transmissions in the L-band:

“The IRNSS signals consist of two special services namely Standard Positioning Service (SPS) and a Restricted Service (RS) [that] will be carried on L5 and S bands. The SPS will be modulated by a 1 MHz BPSK signal and RS will use BOC(5,2) modulation.”

(“Spectral Compatibility of BOC(5,2) Modulation with Existing GNSS Signals” by S.B. Sekar, S. Sengupta, and K.Bandyopadhyay in Proceedings of IEEE/ION Position Location and Navigation Symposium (PLANS) 2012, Myrtle Beach, SC, April 23–26, 2012, pp.886–890, doi: 10.1109/PLANS.2012.6236831.)

Scientists from the German Aerospace Center’s Institute of Communications and Navigation in Oberpfaffenhofen, Germany, have received signals from IRNSS-1A, the first satellite in the Indian Regional Navigation Satellite System.

Launched on July 1, 2013, the satellite reached its designated inclined geosynchronous orbit by July 18 with an inclination of 27 degrees and an equator crossing of 55 degrees east longitude. Indian Space Research Organisation (ISRO) chairperson Dr. K. Radhakrishnan announced on July 18 that testing of the satellite’s navigation payload would begin within a week.

On July 23, the German Aerospace Center scientists pointed their 30-meter dish antenna at Weilheim towards the satellite and found that it was already transmitting a signal in the L5 frequency band.

FIGURE 1. Spectrum of IRNSS-1A L5 signal.

FIGURE 1. Spectrum of IRNSS-1A L5 signal. Source: Richard B. Langley

Figure 1 shows the spectrum of the received signal. Centered at 1176.45 MHz, the signal has a single symmetrical main lobe and a number of side lobes characteristic of a spread-spectrum signal. The corresponding IQ constellation diagram is shown in Figure 2. The signal structure appears to be unlike those used by the GPS, GLONASS, Galileo, or BeiDou constellations. Further analysis will be required to sleuth the signal details as ISRO, so far, has not publicly released an IRNSS interface control document (ICD). ICDs characteristically describe a satellite system’s signal structure in detail.

FIGURE 2. IQ constellation diagram of IRNSS-1A L5 signal.

FIGURE 2. IQ constellation diagram of IRNSS-1A L5 signal. Source: Richard B. Langley

The German scientists caution that “this is a very early snapshot of the current signal transmission and probably both the signal power and the signal quality will change and possibly improve during the in-orbit-testing phase of the satellite’s operation.”

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About the Author: Richard B. Langley

Richard B. Langley is a professor in the Department of Geodesy and Geomatics Engineering at the University of New Brunswick (UNB) in Fredericton, Canada, where he has been teaching and conducting research since 1981. He has a B.Sc. in applied physics from the University of Waterloo and a Ph.D. in experimental space science from York University, Toronto. He spent two years at MIT as a postdoctoral fellow, researching geodetic applications of lunar laser ranging and VLBI. For work in VLBI, he shared two NASA Group Achievement Awards. Professor Langley has worked extensively with the Global Positioning System. He has been active in the development of GPS error models since the early 1980s and is a co-author of the venerable “Guide to GPS Positioning” and a columnist and contributing editor of GPS World magazine. His research team is currently working on a number of GPS-related projects, including the study of atmospheric effects on wide-area augmentation systems, the adaptation of techniques for spaceborne GPS, and the development of GPS-based systems for machine control and deformation monitoring. Professor Langley is a collaborator in UNB’s Canadian High Arctic Ionospheric Network project and is the principal investigator for the GPS instrument on the Canadian CASSIOPE research satellite now in orbit. Professor Langley is a fellow of The Institute of Navigation (ION), the Royal Institute of Navigation, and the International Association of Geodesy. He shared the ION 2003 Burka Award with Don Kim and received the ION’s Johannes Kepler Award in 2007.

1 Comment on "Indian Regional Navigation Satellite Starts Signal Transmissions"

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  1. Crazy Motts says:

    good to know about IRNSS. I did a simulation-based analysis of IRNSS and IRNSS-1A to look into the orbital characteristics, related opportunities and challenges that IRNSS may face:

    Here’s my analysis of IRNSS:

    There are many regional and global navigation satellite systems under implementation and very soon all countries will have access to at least one such system.

    Here are my analysis of GNSS applications in commercial aviation industry and the possible business opportunities it may open up: