Data demodulation method of global positioning system (GPS) receiver for weak satellite signals
A technology for GPS receivers and satellite signals, which is applied in the field of data demodulation of weak satellite signals by GPS receivers, can solve problems such as affecting navigation messages, and achieve the effects of improving accuracy and eliminating residual frequency differences.
Active Publication Date: 2013-03-27
RDA TECH
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For weak satellite signals, there will be a frequency difference between the locally reconstructed carrier of the tracking module and the carrier of the intermediate frequency signal, and the existence of the residual frequency difference will affect the judgment of the polarity of each bit of the navigation message
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[0033] The navigation message is sent out in units of frames, and the length of each frame is 1500 bits. A complete set of navigation messages consists of 25 frames, totaling 37,500 bits. Each frame is composed of 5 subframes (subframe), and the length of each subframe is 300 bits. The first 8 bits of each subframe are always 10001001, called frame synchronization code. Since the transmission rate of the navigation message is 50bps, the frame synchronization code appears every 6s.
[0034] If the symbol of the binary number "1" is defined as the decimal number 1, and the symbol of the binary number "0" is defined as the decimal number -1, then the symbols of the frame synchronization code are 1, -1, -1, -1, 1, - 1, 1, 1.
[0035] see Figure 5 , where O point represents the center of the earth, A point represents the location of the GPS receiver, S point represents the GPS satellite on the same horizontal plane as the GPS receiver, and B point represents the GPS satellite ...
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The invention discloses a data demodulation method of a global positioning system (GPS) receiver for weak satellite signals. The data demodulation method comprises a first step of performing 20ms coherent integration on navigation data from the initial positions of each bit of data of navigation messages in the navigation data for the bit-synchronization-finished navigation data of the weak satellite signals, and only retaining the latest K coherent integration results; a second step of finding the positions of the navigation data corresponding to frame synchronization codes of the navigation messages of the weak satellite signals by utilizing a time interval of -20ms-20ms of reception time of frame synchronization codes of navigation messages of strong satellite signals; and a third step of utilizing fast Fourier transform (FFT) to judge polarity of each bit of data after the frame synchronization codes of the navigation messages of the weak satellite signals. According to the data demodulation method, the positions of the navigation data corresponding to the frame synchronization codes of the weak satellite signals are found rapidly by utilizing N point FFT under the assistance of the strong satellite signals so as to serve as initial values, the coherent integration time is prolonged to 180ms by utilizing M point FFT, and influence of residual frequency difference is eliminated.
Description
technical field [0001] The present application relates to a signal processing method of a GPS receiver, in particular to a method for the GPS receiver to demodulate navigation messages in weak satellite signals. Background technique [0002] The GPS system is currently the most widely used global satellite navigation system. The GPS receiver determines its position on the earth's surface by receiving GPS satellite signals. [0003] GPS satellite signals include L1 carrier and L2 carrier. The L1 carrier is modulated with C / A code (Coarse / Acquisition Code, also known as coarse code, acquisition code) and navigation messages (Navigation Messages, also known as Data Message, data code, D code), using binary phase shift keying (BPSK) technology, which is a kind of phase modulation. When the modulated signal is modulated on the carrier by phase modulation, the rate at which the phase of the modulated signal changes is usually called the code rate. C / A code is a two-phase modula...
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IPC IPC(8): G01S19/37
Inventor 李倩吴林钊张旭
Owner RDA TECH