Method for the unambiguous tracking of Binary Offset Carrier (BOC) signals

668 - Abstract:
The invention relates to a method for the unambiguous tracking of BOC signals, which is a relevant problem for GNSS receivers working in harsh propagation conditions (typical in urban or suburban environments) when high-order BOC signals are to be tracked.

Description:

Global navigation satellite systems (GNSS) are becoming increasingly important in a wide range of applications, including in-car navigation support, location-based services for smartphones, and so on.

Current and future generations of GNSS, such as GPS, Compass or Galileo, have chosen binary offset carrier (BOC) signals for the modulation of the transmitted navigation signals.

A typical GNSS receiver estimates its position based on, among others, the code delay estimation of the  navigation signals received from different GNSS satellites. For this reason, an accurate estimation of the code delay is of interest to minimise the receiver position error. In the particular case of BOC navigation signals being transmitted, the code delay estimation can be biased if the code delay ambiguity is not resolved properly. The presence of a bias in the code delay estimation is translated into a position error. Therefore, the resolution of the code delay ambiguity when tracking a BOC signal in a GNSS receiver is a very significant aspect. 

The invention is based on a multi-correlator architecture and defines the unambiguous tracking as the minimization of a cost function subject to constrain. By doing so the problem is split in two targets: 1) the accurate tracking of the main peak (main cost function) and 2) the identification of the main peak (constraint imposed to the main cost function). Both type of optimisations can be implemented using existing numerical methods such as gradient descent least mean square approach. 

Innovations and advantages:

The method provides a solution for the ambiguity problem of high-order BOC signals (used by Galileo) thus greatly enhancing the Galileo PRS receivers performance in realistic mobile exploitation environments. Previous state-of-the-art techniques failed to solve the unambiguity in a stable way in the same simulation conditions. The present inventions has demonstrated higher performance in harsh propagation conditions for land mobile satellite channels. 

Commercialisation aspects

Applications and Markets

The proposed method it is applicable to the tracking of Galileo PRS signals, in particular in urban, suburban or forest environment where harsh propagation conditions are present creating large ranging errors in the state-of-the-art Galileo PRS receivers. The technique may be attractive for other GNSS constellations using BOC type signals. Ground applications are foreseen, in particular all those applications based on the usage of Galileo PRS signals. This invention may be of interest for GNSS receivers manufacturers. 

Intellectual property status

A European patent application has been filed.

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