Three System Navigation Receiver Baseband Signal Processing Technology Research

This paper mainly makes a research on baseband signal processing of tri-system and tri-frequency satellite navigation receiver, analyzes the civil signal structure of L1frequency in GPS navigation system, L1frequency in GLONASS navigation system, and B1frequency in BDS navigation system, and discusses the impact of the signal structure on acquisition, tracking, and bit-frame synchronization.Three kinds of signal acquisition algorithms are discussed and compared, and they are sliding correlation algorithms, FFT-IFFT algorithms, and partial matched filter (PMF) with FFT algorithm of short length. The advantages and disadvantages of these three acquisition algorithms are discussed, and a tri-system acquisiton engine (AE) with the FFT-IFFT algorithm is designed and implemented according to the present DSP-FPGA hardware platform, thus, rough code phase and carrier doppler frequency can be estimated quickly by the acquisition engine. A kind of tri-mode tracking engine (TE) is designed and implemented, in which the code delayed locked loop (DLL) is composed of a early-late power code discriminator and a second-order loop filter, the phase locked loop (PLL) is made up by ATAN phase discriminator and a trird-order loop filter, the frequency locked loop (FLL) is composed of ATAN2frequency discriminator and a second-order loop filter, and the PLL is assisted by FLL. The loop filter is implemented with a kind of multiplexing structure which can load errors, parameters and intermediate data from a selected channel. By simulation, verification and test, the engine can track GPS, GLONASS and BDS signal channel, meets the actual requirement, can track up to hundreds of channels, and reduces the processing load of DSP chips. In order to save FPGA hardware resources, a multi-channel multiplexed method is used to achieve bit-frame synchronization for12channels.