High Performance Tracking And Acquisition Loop Algorithms For A GNSS Receiver

In China, many universities and research centers have been devoted to the design of a high performance GNSS receiver with independent intellectual property rights and represented very great achievements at present. It contributes to an increasing marketization of domestic GNSS receiver chips. Digital baseband signal processing is the key topic in the design for a GNSS receiver. It has a great influence on the receiver performance. In this thesis, tracking and acquisition loop algorithms in digital baseband signal processing for a GNSS receiver are investigated. It is helpful to improving the receiver performance, reducing resources in the design of GNSS receivers and enhancing cost performance of domestic GNSS receivers. The main contributions of this thesis are summarized as follows:Firstly, the positioning accuracy of a delay-locked loop in a GNSS receiver is seriously affected by multipath. Multipath effects on common DLLs are approached by comparisons under non-fading and fading conditions. Furthermore, the characteristics of tracking errors induced by multipath in DLL discriminators are evaluated and analyzed. A proper DLL for the specialized multipath environment is given.Secondly, in order to reduce discriminator complexity of carrier tracking loops in a GPS receiver, an improved discriminator algorithm based on the four-quadrant arctangent function is proposed. The phase and frequency discriminators share only one four-quadrant arctangent function. A phase discriminator is insensitive to the navigation message data and a frequency discriminator overcomes the frequency uncertainty by correction functions. Through theoretical analysis and simulation, the proposed discriminator algorithm with a small calculation amount and low complexity is validated. Therefore, carrier tracking loops occupy less system resources.Thirdly, a loop filter structure affects the complexity of a GPS carrier tracking loop critically. A novel loop filter design based on a boxcar digital integrator is given. On this basis, a low complexity design for a GPS carrier tracking loop is represented. The theoretical analysis and simulation results confirm that this novel design not only has low complexity, but also exhibits excellent dynamic tracking performance. Finally, in view of the calculation amount of acquisition algorithms in frequency domain, a new modified averaging circular correlation algorithm based on FFT is proposed and its implementation method is described. This novel algorithm reduces calculation amount in frequency domain by making use of the second sampling and spectrum asymmetry. Simulation results show that it has faster acquisition ability and is easy to be realized without a deleterious effect on the acquisition accuracy.Therefore, the proposed algorithms to improve the performance of GNSS receivers in this thesis are based on theoretical investigation and experiments with the simulated and real GPS signals, and then show expectable results. It has a great theoretical and practical significance on the design of high performance and cost performance receivers.