GPS C/ A Code Signal Structure Trong những chương trước, người sử dụng vị trí được tính toán. Để thực hiện việc tính toán vị trí người dùng, vị trí của các vệ tinh và pseudoranges các vệ tinh phải được đánh giá. Nhiều thông số cần thiết để tính toán vị trí của các vệ tinh và chúng được truyền đi trong các tín hiệu vệ tinh. Chương này cung cấp các chi tiết liên quan với các tín hiệu GPS. Spilker (1,2) không chỉ cung cấp cho một cuộc thảo luận rất tốt về tín hiệu, nó. | Fundamentals of Global Positioning System Receivers A Software Approach James Bao-Yen Tsui Copyright 2000 John Wiley Sons Inc. Print ISBN 0-471-38154-3 Electronic ISBN 0-471-20054-9 CHAPTER FIVE GPS C A Code Signal Structure INTRODUCTION 2 In the previous chapters user positions are calculated. In order to perform the user position calculation the positions of the satellites and pseudoranges to the satellites must be measured. Many parameters are required to calculate the positions of the satellites and they are transmitted in the satellite signals. This chapter provides the details associated with the GPS signals. Spilker 1 2 not only gives a very good discussion on the signal it also gives the reasons these signals are selected. The discussion in this chapter is limited to the fundamentals of the signals such that a receiver design can be based on the signals. There are basically two types of signals the coarse or clear acquisition C A and the precision P codes. The actual P code is not directly transmitted by the satellite but it is modified by a Y code which is often referred to as the P Y code. The P Y code is not available to civilian users and is primarily used by the military. In other words the P Y code is classified. The P Y code has similar properties of the P code. In order to receive the P Y code one must have the classified code. Therefore only the fundamentals of the P code will be mentioned in this book. The discussion will be focused on the C A code. In general in order to acquire the P Y code the C A code is usually acquired first. However in some applications it is desirable to acquire the P Y code directly which is known as direct Y acquisition. The radio frequency RF of the C A code will be presented first then the C A code. The generation of the C A code and its properties will be presented because they are related closely to acquiring and tracking the GPS signals. Finally the data carried by the signals will be presented. The applications
