Inside GNSS Media & Research

SEP-OCT 2018

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Page 10 of 67 S E P T E M B E R / O C T O B E R 2 0 1 8 Inside GNSS 11 Some Quick Considerations GPS signals broadcast at 27 Watts which are received at 158 x 10 -18 Watts on earth. Signals of OneWebb and SpaceX Starlink are 1000 x (30dB) stronger compared to LEO vs. MEO (GNSS). But, it takes seven LEOs to match the cover- age of 1 MEO. 200+ LEOs are needed for similar coverage – but no problem, as both mentioned LEO systems have significantly more than 200 satellites. us, the geometry (Dilution of Precision - DOP values) is consequently 3 x better than that of present GNSS. When you consider further, that a positioning error is approximately SIS URE (signal-in-space (SIS) user range error (URE)) x geometry, then we can recognize that the 3x better geometry of a LEO system relaxes the URE. A con- stellation like OneWeb/SpaceX Starlink could have a URE 3x worse and give comparable positioning performance to GPS (about 3 meters horizontally, 4-5 meters vertically). e chip-scale atomic clocks (low power < 120mW, small size 17 cc volume, low-cost < 1000 USD … 300 USD) in the LEO satellites are approximately 100 x worse at one day compared to GPS atomic clocks. However, we may get com- parable performance if they are updated once per LEO orbit (approx. 100min) instead of once every 12 hours (GPS). Simple computations of the LEO orbits by ground sta- tions indicate that it is possible to achieve 3m RMS, using in addition cross-links approximately 1.5 meters. And the costs? No taxpayer's money has to be provided by governments…? Also, a new feature of satellite positioning in the near future might come up. If the high doppler of the LEO satel- lites can be used for fast carrier phase ambiguity resolu- tion in conjunction with the GNSS MEO signals – an old proposal by Brad Parkinson and Stanford University (more than 20 years old) – then centimeter positioning from our GNSS in real time can be achieved. A hybrid LEO/MEO solution! In conclusion: 5G wireless networks and New Space LEO systems for communication and the internet are being built up in the next 10-15 years. Advanced RAIM may make SBAS aer 2035 obsolete. So, how does the future of satellite navigation look? No more RNSS and GNSS? Or only mili- tary operations with RNSS and GNSS in future? I follow the customs of the tax authorities (writing-off a GNSS receiver within three years), as it is hard or even impossible to predict the future of satellite navigation over more than 3-5 years. Don't we live in an exciting (satellite navigation) time and future? Defeat GPS threats to airborne assets. No signal degradation. Every asset you put into the sky can face increasingly sophisticated jamming threats to its GPS signal. Deny those threats and keep your signal strong with our Digital GPS Anti-jam Receiver (DIGAR). It gives any airborne platform superior nulling and beamforming GPS for assured PNT. Multiple configurations make DIGAR simpler than ever to integrate. Protect your mission-critical functions so you can stay in the fight. © 2018 Rockwell Collins. All rights reserved.

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