1-bit processing of composite BOC (CBOC) signals

Olivier Julien (1) , Christophe Macabiau (1) , Jean-Luc Issler (2) , Lionel Ries (2)

1 ENAC - Ecole Nationale de l'Aviation Civile
2 CNES - Centre National d'Études Spatiales [Toulouse]

The US and EU agreed recently to share a common normalized Power Spectral Density (PSD) function for their civil signal on L1. This PSD, referred to as Multiplexed Binary Offset Carrier (MBOC), because of its frequency definition, can lead to different temporal implementations. Two modulations were proposed to implement the MBOC: the Composite BOC (CBOC) seems to be the leading candidate for Galileo L1 OS signal, and the Time-Multiplexed BOC (TMBOC) seems to be the main candidate to be used by the GPS L1C signal. These two modulations use the BOC(1,1) and BOC(6,1) waveforms, but in different ways. The CBOC adds them linearly, creating a multi-level waveform, while the TMBOC multiplexes them. Thus, although very close, the two MBOC implementations would require different architectures that will make the receiver more complex if traditional tracking techniques are used, especially for GPS/Galileo combined receivers (need for a local generation of a multi-bit replica and a time-multiplexed replica). The goal of this paper is to present two tracking techniques that significantly simplify the receiver architecture of future GPS/Galileo L1 receivers (one-bit local replica, no time-multiplexing, ?) while maintaining good performances in presence of thermal noise and multipath. This means that the tracking techniques are easily adaptable to both CBOC and TMBOC signals. Taking advantage of the GPSIII L1C and Galileo E1 OS interoperability and compatibility, these methods are a first step towards the development of combined GPS/Galileo receivers. The first technique, based on the use of either a pure BOC(1,1) or a pure BOC(6,1) subcarrier in the correlation process, allows a drastic simplification of the receiver architecture, but implies a degradation of the tracking noise compared to traditional CBOC or TMBOC tracking, although improving the multipath resistance. The second technique is more demanding in terms of correlators since it requires the use of both a pure BOC(1,1) and a pure BOC(6,1) sub-carrier for the correlation process. However it brings improved tracking performances compared to traditional CBOC and TMBOC tracking and a high flexibility to the receiver architecture. These two techniques, though, seem more suited for CBOC tracking since a slightly more complex architecture is needed for relevant TMBOC tracking.

Domaines: Traitement du signal et de l'image [eess.SP]; Traitement du signal et de l'image [eess.SP]

Olivier Julien, Christophe Macabiau, Jean-Luc Issler, Lionel Ries. 1-bit processing of composite BOC (CBOC) signals. CNES-ESA, 1st Workshop on GALILEO Signals and Signal Processing, Oct 2006, Toulouse, France. ⟨hal-01022447⟩