Comparison of several signal designs based on chirp spread spectrum (CSS) modulation for a LEO PNT system

One of the main challenges of GNSS receivers is the provision of a effective solution for low-power devices. This is driven by the proliferation of Internet of Things (IoT) devices, which are low-power by nature. Furthermore, the complimentarity with telecommunication systems is another characteristic of IoT devices. Satellite communications is a solution that has started to be considered by the IoT industry. In particular, low-Earth orbit (LEO) satellite constellations are appearing for broadband IoT connectivity. In this paper, we consider a Chirp Spread Spectrum (CSS) modulation as a possible approach to enable positioning with LEO satellites. The use of CSS is intended to address low complexity and low consumption positioning for IoT devices, tackling the complexity issue of the classic direct-sequence spread spectrum (DSSS) acquisition. Indeed, CSS has been considered as possible candidate for low-power LEO satellite communications due to its resistance to Doppler effect. The target is to use CSS for ranging and low-power communications, as well as to exploit the properties of CSS to design a very simple, thus low-cost and low-power receiver. The study will address also possible approaches to obtain multi-satellite access. The idea is to get advantage of the work already done in radar and low-range communications with CSS and apply it to the design of a new CSS-based PNT signal for LEO satellites. A preliminary design of the considered CSS schemes for a LEO constellation will be provided in this paper. This design will be the base for a complexity analysis of the proposed CSS design as well as for the comparison with the classic DSSS signal.