On the Integration of Tone-Like Signals-of-Opportunity Within a Geodetic Grade GNSS SDR

The signals of opportunity (SOP) concept exploits certain elements of communication signals in addition or as a replacement for conventional global navigation satellite system (GNSS) signals. Due to the enormous number of communication satellites in low earth orbit (LEO), tools to receive and process SOP signals become more and more important. In this work, we extend the functionalities of a existing GNSS software-defined radio (SDR) by elements to track tone-like signals as they occur in the context of SOP processing. Those functionalities include detection of signals in the Fourier domain, adaptation of code-division multiple access (CDMA)-tracking to conventional frequency locked-loop (FLL) tracking of tones and some other signal processing features. At observation level algorithms to identify transmitter ids are introduced and the combined processing of GNSS and SOP signals resulting in a combined receiver independent exchange format (RINEX) file is outlined. The techniques are first tested with simulated tone signals (continuous and pulsed) and then demonstrated with real Starlink and Iridium signals.