Research And Design Of The Tracking Loops In GPS Receiver

Global Positioning System is considered as the most important position navigation and timing development. The key part of GPS application is the baseband processing unit in the receive device, including two parts: the acquisition loop and the tracking loop. The research focuses on signal processing algorithms and hardware realization of the tracking loop in GPS receiver.Firstly, this paper analyzes algorithms of GPS base-band tracking loop, and then realizes tracking algorithms in the GPS software receiver by establishing a C++ model. In the tracking process of GPS signals, a digital Phase Lock Loop is used in the carrier tracking loop. The code tracking loop is implemented in a modified method, based on block adjustment of synchronizing signal. This design using the following modified scheme:1) The arctan phase detector based CORDIC algorithm is used in carrier tracking loop and simple logic computations are used to replace the complex loop-up table in carrier Digital Control Oscillator.2)Second order loop filter which is sensitive to acceleration is used in tracking loop, its coefficient is modified to simplify structure and reduce resources.3) Based on block adjustment of synchronizing signal modified the traditional method to improve the performance .The usage of adder and computation delay are reduced by simplifying code discriminator. The basic idea of block adjustment of synchronizing signal is: when the phase of local code is not aligned with the phase of the input signal, bit synchronization is achieved by adjusting the input signal or the local code, not by using the traditional method—changing the code frequency.The modified method which is proposed in this paper reduces the required time for locking the tracking loop and hardware resource consumption. And the required performance of the tracking loop is ensured.