A Vision on New Frequencies, Signals and Concepts for Future GNSS Systems

Jose-Angel Avila-Rodriguez, Stefan Wallner, Guenter W. Hein, Bernd Eissfeller, Markus Irsigler, and Jean-Luc Issler

Abstract:	The RNSS bands are scarce while the worldwide interest in Satellite Navigation is getting stronger every day. Over the last decade product designers and manufacturers have considerably increased GNSS receiver sensitivity and today satellite navigation even works with attenuated signals in environments where GNSS was never thought to serve. This has awakened the interest of many countries and nowadays all superpowers of the world have set up or plan to set up their own navigation system. But as it occurs with all finite resources, the room for new customers and new services comes at some point to an end. The Radio-Navigation Satellite Service (RNSS) portion of the Radio Frequency (RF) spectrum is overcrowded already now and the bands suitable for usage are very limited. This is especially true for the E1/L1 band occupied today by GPS, GALILEO and QZSS and potentially by GLONASS in the future. Furthermore, COMPASS also intends to use E1/L1. But this is not the unique case. In fact, even those bands that have not been used yet will certainly be shared by many systems in the near future. Thus, the search for other free frequency resources is something that will occur with a high probability in the next years. In the Course of the World Radio Communications Conference 2000 (WRC-2000) the frequency band between 5010 MHz and 5030 MHz was already allocated as C-band portion for RNSS applications. The general idea was to have access to a frequency band which were not yet overloaded by other signal sources and were thus not too susceptible to interfering signals. This paper gives us the opportunity to analyze the pros as well as the cons of the C-band and S-band frequencies for GNSS use, in addition to the L-band. In fact, this last one will also have to be preserved in the future to guarantee the backward compatibility that all GNSS systems pursue. In this paper we will thus look also beyond the C-band for GNSS use towards further suitable portions of the RF spectrum. Some major Asian countries are already considering the use of the S-band as it offers significant advantages in view of future applications. A problem that especially concerns scientists of the GNSS community since many years is that of the interference and interoperability among all the already existing, respectively planned satellite navigation systems. The coexistence of civil and military signals has proved to be extremely difficult particularly in the E1/L1 band. But if the technical aspects were solved and new bands at other frequencies that are available today could be employed for navigation purposes, one could imagine interesting scenarios where civil and military signals could be transmitted in different bands. This will be a further important aspect that will be assessed in this paper. In addition, Inter-Satellite Links (ISL) could be something quite common in not so many years. The Galileo program has studied the possibility but for financial reasons among others did not employ them in its first generation. GPS has carried out first tests with ISL. GLONASS and GPS will implement them in one of the next generations. But this is not the only solution to provide high positioning performance. A promising alternative to ISL could be the use of a ground-based network of directive pseudolites like the presently designed C-band uplink stations. Finally, if new frequency allocations were found without the stringent restrictions that the existing bands present, one could imagine of completely new concepts in signal design and code architectures. This paper will try to discuss possible scenarios and visions of the future GNSS world. Together with new frequency allocations, new signal designs and new concepts will also be scope of this paper.
Published in:	Proceedings of the 20th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2007) September 25 - 28, 2007 Fort Worth Convention Center Fort Worth, TX
Pages:	517 - 534
Cite this article:	Avila-Rodriguez, Jose-Angel, Wallner, Stefan, Hein, Guenter W., Eissfeller, Bernd, Irsigler, Markus, Issler, Jean-Luc, "A Vision on New Frequencies, Signals and Concepts for Future GNSS Systems," Proceedings of the 20th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2007), Fort Worth, TX, September 2007, pp. 517-534.
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