Jinghui Wu

Effect of pre-correlation filter on BOC-Gated-PRN discriminator

In this paper the authors analyze the effect of signal pre-correlation filtering in the ldquoBOC-Gated-PRNrdquo (ldquoBOC-GPRNrdquo) discriminator technique, recently proposed for use within Global Navigation Satellite System receivers to handle the new signal modulation scheme). The proposed discriminator is introduced to eliminate the tracking ambiguity for Delay Locked Loops and strengthen multipath resistance for precise GNSS applications. In practice, a pre-correlation filter with insufficient bandwidth can, in general, increase the error due to multipath and noise. However, it is preferred that the bandwidth of the front end filter is kept as narrow as possible for other limitation. Hence focusing on the multipath error and discriminator gain optimization of the DLL, the tracking performance with the BOC-GPRN discriminator is investigated by adjusting the parameters of the proposed discriminator and the pre-correlation filter (e.g. the double-sided bandwidth and transition bandwidth). The relationship among those parameters is discussed.

Improvement to Multi-resolution Collective Detection in GNSS Receivers

Collective detection is a promising approach to positioning in a weak signal environment, in which the navigation solution is directly obtained by acquisition search in a multidimensional position and common clock bias uncertainty space. By combining the correlation values from multiple satellites and fully utilizing the coherence between them, the detectable C/N0 of individual satellites can be lowered. However, the lack of a computationally efficient optimization algorithm due to high dimensionality and complexity has hindered its application. A multi-resolution collective detection is therefore proposed to be a coarse-to-fine searching approach to solve for the position and common clock bias estimation. Although it reduces the computation time of collective detection, there is a gap in the efficiency study, which is the contribution of this research. The features of different levels of search in a multi-resolution algorithm are investigated. For a coarse search with large horizontal position step size, a smaller common clock bias step size is proposed instead of an averaging correlogram to reduce computation complexity as well as to obtain high time resolution. For the fine search with small horizontal space step size, a 3-D Dichotomous searching scheme is designed and applied to reduce the number of searching grids. Computer simulation results using experimental raw data are provided, to demonstrate the performance improvement against the conventional methods.

Dichotomous search of coarse time error in collective detection for GPS signal acquisition

Abstract Coarse time error (CTE) is an additional systematic absolute-timing-related bias that must be compensated in an assisted GPS (A-GPS)-based snapshot receiver where the complex baseband signal available for processing is finite and short. Resolving for CTE instead of waiting for the time of week string in the satellite’s navigation message allows A-GPS receivers to achieve faster time to first fix in cold start and warm start conditions. This paper highlights the problem of CTE that is conventionally resolved using coarse time positioning (CTP)—a least-squares-based algorithm. Following this, the same problem is shown to occur when collective detection (CD)—a direct position estimation algorithm—is applied in place of CTP. Previous literature on CD has not discussed nor presented any resolution to the CTE problem. Directly augmenting CTE to be resolved together with the user’s position and common clock bias in CD requires huge computational resources, which is impractical to be implemented using current generation consumer-grade computers. Therefore, the main contribution of this research is to propose and implement a dichotomous search jointly with CD to resolve for the CTE and position-common-clock-bias vector, respectively, at a relatively low computational burden. Empirical results using live satellite signals show that the proposed method is capable of effectively eliminating the positioning error biases caused by CTE. It is shown that the proposed compensation method can achieve equivalent performance to the conventional CTP method without losing the benefits of CD.