The GNSS signal is a modulated wave broadcasted by GNSS satellites to users for navigation, positioning and timing. There are three reasons for using modulated waves: (1) The ranging code and navigation message used for user positioning are digital signals, which cannot be directly transmitted in wireless channels; (2) It can effectively shift the spectrum and make rational use of spectrum resources; (3) Modulating low-frequency navigation information into high-frequency signals is beneficial for signal propagation, which improves anti-interference ability, and reduces the size of the receiver antenna. Since the GNSS signal is a modulated wave, it should include a low-frequency data wave and a high-frequency signal carrier wave. The low-frequency data wave includes a pseudorandom ranging code and a navigation message.