The Research And Matlab Implementation Of GPS Software Receiver

GPS is global positioning system,and which has the characteristics of global coverage and all-weather work. Currently, GPS receiver is more widely used in the land, air and maritime field and has played a great role in the positioning and navigation for users. With the upgrade of GPS and the development of new satellite navigation system,compared to traditionnal GPS receiver, GPS software receiver with the features of low cost and high flexibility is more prominent. This paper mainly studys the capture part and the tracking part, and also calculates the position in Matlab.First of all, the paper introduces the main content of the GPS signal. Then the capture part discusses the algorithms of serial search acquisition, parallel frequency space search acquisition and parallel code phase search acquisition, and also captures the GPS digital signal with the parallel code phase search acquisition algorithm. In the tracking part,the code tracking loop is a non-coherent delay lock loop(DLL). The carrier tracking loop is a Costas loop. The tracking part tracks the signal using the initial code phase and frequency obtained in the capture part. Finally, after the synchronization and parity-check procedure to the GPS signal which has been processed in the acquisition and tracking parts, the paper extracts the navigation message and calculates the user's position coordinates according to the parameters in the navigation message.In the acquisition part, the paper selects the parallel code phase search acquisition algorithm which has the short execution time and high performance in Matlab. The speed and positioning accuracy of GPS software receiver is improved. Using the Costas loop which is not sensitive to the phase conversion of 180°in the carrier tracking loop ensures that the carrier tracking loop can track the signal correctly. Code tracking loop uses the normalized early minus late power discriminator that has great property. The loop is still able to track the signal when the chip error is larger than a 1/2 chip. Combination of the code tracking loop and the carrier tracking loop in the tracking part reduces the complexity of tracking loop. Also in Matlab, this paper prepares the acquisition, tracking and data-processing code and achieves the user's position using software approach. This method saves the cost ,and can set the different thresholds and parameters according to the environment. It also can be used to process signal of other satellite positioning system by changing the code and has great flexibility.