Improvements and additions to the Double Estimation Technique

The Double Estimation Technique (DET) is a GNSS signal-tracking concept. DET has the capability to produce reliable unambiguous, full-precision delay estimates from the Binary Offset Carrier (BOC) signals which have been adopted by the modernized and new GNSS, including the European Galileo constellation. DET is robust, being able to function under conditions of low C/N₀, strong multipath and filtering distortion. It achieves the higher precision inherent of BOC by directly tracking the sub-carrier component of the BOC modulation using a sub-carrier locked loop (SLL). The inherent ambiguities are automatically corrected by simultaneous and interactive tracking of the code component using a delay locked loop (DLL). The concept of DET is readily applicable in principle to any of the BOC modulation family. This paper is focused on the sine-phased BOC(1,1) signal: the limited bandwidth component of the multiplexed binary offset carrier - MBOC(6,1,1/11) as agreed by the US and the EU. The DET generalizes to a Triple Estimator Technique (TET) for optimal reception of the full-bandwidth MBOC with another interactive tracking loop of the second subcarrier. This TET has shown promising results (not given here). Investigative work by the authors has identified improvements to implementation of the DET concept. Three algorithmic enhancements, detailed in this paper, have been tested in simulation which increase the DET´s robustness to noise and multipath, and potentially reduce the computational burden on a receiver. These enhancements are: 4- point discriminators; Adaptive Early-Late discriminator spacing; Improved DLL-to-SLL correction scheme.