Exploration of possible GNSS signals in S-band

Satellite navigation has become such a worldwide priority that many countries are actively deploying or considering their own systems or modernizing those that already exist. As a consequence, the number of signals transmitted in L band will be significantly increased in the next few years so that only scant spectrum will be available for new systems or signals. Since current signals will have to be maintained many years in order to guarantee backward compatibility for legacy receivers, we can foresee that the search for new frequency allocations will be ranked at the highest level with a view to future evolutions of current systems. In this context S-band spectrum between 2483.5 and 2500 MHz, which is already allocated to the radio determination satellite service (RDSS), can be used for satellite navigation - although the allocation in the Radio Regulations is only primary in parts of Asia, Africa and the Americas - is a particularly interesting possibility as synergies with future mobile communication systems in the band immediately above could be exploited to provide both navigation and communication services using one unique S-band terminal with an efficient, common antenna. Only at the next World Radiocommunications Conference in 2012 will the decision be made whether to make the existing patchwork of RDSS allocations global, but the studies completed so far show this to be promising. A global allocation will provide an important opportunity for a worldwide convergence between systems of the mobile satellite service (MSS) and the radio determination/navigation satellite service (RDSS / RNSS). This paper aims to analyze the suitability of this band for navigation purposes as well as the effects that the introduction of these kind of signals would produce on the other radio services present in the same and adjacent bands. We will also present the results obtained from link and error budget calculations and interference assessment that have been performed using various hypothethical of navigation signals in S band. Opportunities for Galileo-2 signals are currently being studied having in mind possible additional frequencies in C and/or S band and/or L band, in complement to the E5a, E5b, E6 and E1 legacy OS, SoL, CS and PRS signals. The paper will give special attention to possible synergies between a hypothetical Galileo-2 S-band signal, IRNSS/GINS and Beidou/COMPASS, which will use L and S bands, other RNSS/RDSS systems and mobile satellite service systems such as GLOBALSTAR-2. These signals will be compared, and synergies between them explored. Several possible waveforms centred on a frequency close to 2491 MHz will be analysed in terms of intersystem interference and in terms of navigation and data transmission performance. The analysed waveforms in Sband will be BPSK(1*1.023 Mcps), BPSK(4*1.023 Mcps), BPSK(8*1.023 Mcps), BOC(1,1) and MBOC.. Power flux density (pfd) and interference computations showing compatibility between a potential Galileo-2 Sband component, S-band GNSS signals, GLOBALSTAR, mobile services (MS) and fixed services (FS) will be presented.