1 Quality Monitoring of BOC Signals through Codeless Techniques Daniele Borio, Marco Rao, Cillian O’Driscoll Abstract Codeless and semi-codeless techniques are recently finding new and unexpected applications. For example, they can be used as an effective means for signal authentication and spoofing detection. In this paper, codeless tracking is adopted for processing Binary Offset Carrier (BOC) modulated signals where a Subcarrier Lock Loop (SLL) is used to remove the subcarrier component. The developed system is then used for signal quality monitoring of encrypted Global Navigation Satellite System (GNSS) signals. In this respect, a multi-correlator codeless architecture and a codeless Carrier-to-Noise density power ratio (C/N 0 ) estimator are developed and tested under different operating conditions. The effectiveness of the proposed codeless framework is tested using real data collected from the Galileo IOV satellites. The analysis supports the validity of the proposed architecture which enables quality monitoring of encrypted GNSS signals. Index Terms Codeless Tracking, Global Navigation Satellite Systems, GNSS, Signal Monitoring, Subcarrier Lock Loop, SLL I. I NTRODUCTION Coexistence between Global Navigation Satellite System (GNSS) and communications services is becoming a more and more significant issue that is gathering the attention of the scientific community. This is due, on one side, to the spectrum scarcity that is pushing communications providers to ask for frequency bands previously reserved for other services. On the other side, new GNSS signals with larger frequency occupations and different centre frequencies are being Institute for the Protection and Security of Citizen (IPSC), Joint Research Centre, Ispra (VA), Italy. Email: daniele.borio@ieee.org, {marco.rao, cillian.odriscoll}@jrc.ec.europa.eu,