On the Use of Meta-Signals to Counteract Ionospheric Phase Advance Effects on Wideband LEO PNT Signals

The recent, massive deployment of Low-Earth Orbit (LEO) satellites constellations for broadband communication services is attracting the attention of the Positioning, Navigation and Timing (PNT) community concerning the possibility of complementing current Global Navigation Satellite System (GNSS) through LEO radionavigation signals. Motivated by lower free-space path loss brought in by smaller orbital radia, legacy radionavigation frequency bands as well as less congested bands such as S, C, X, Ka and Ku could host dedicated radionavigation signals or combined solutions that hybridize them with communications signals. However, as per current GNSS signals, LEO radionavigation counterparts will still suffer the effects of intense ionospheric activity. In particular, in spite of higher carrier frequencies which limit the impact of their interaction with the ionosphere, non-negligible ionospheric-induced phase advance has the potential of impoverishing the correlation performance of wideband modulation schemes that may be intrinsically of interest in the design of wide and ultra-wideband navigation signals from LEO. Building on insights from previous literature on Galileo wideband signals and their interactions with ionosphere, we analyze the dispersive effect of the ionosphere on a sample wideband channel of 128 MHz hosting signals with different modulations. We then propose the use of metasignals to overcome the limitation of native wideband signals such as high-order Binary Offset Carrier modulations. The results demonstrate that simplistic BPSK-based meta-signals can be designed to be more robust than wideband BPSK modulations and bandwidth-equivalent BOC signals.