Weak Signal Acquisition And Tracking Algorithm Based On The GPS Software Receiver

In recent years, with the GPS receiver applied in multi-purpose and wide fields on aglobal scale, satellite navigation and positioning technology is also put forward higherrequirements. GPS software receiver based on software radio using a relatively commonhardware platform, you can achieve different functions and complex high-performancealgorithms by loading a different program, it provides a convenient and possible for thedevelopment of high complexity algorithm under the special circumstances applicable. As oneof the key technologies of high-performance navigation, weak satellite signal receivertechnology is currently a hot research. Under normal circumstances, the SNR of satellitesignal received by the receiver is about-20dB. But in weak signal environments, the SNR canbe reduced about20dB. In this case, it is difficult for the common receiver to acquisition andtracking the signal, and can not realize the positioning function. The dissertation focuses onthe algorithm for weak signal acquisition and tracking, the primary work and conclusions areas follows:1. The structure and operation of the GPS receiver is introduced. The modulation andmultiplexing of GPS satellite signals are analyzed. The correlation properties of C/A code andthe Doppler Effect on the carrier frequency and the C/A code length are studied. The model ofGPS intermediate frequency (IF) signal is studied for simulating digital IF signal.2. The basic principles and methods of GPS satellite signal acquisition is studied, and theusual weak signal acquisition algorithm is introduced. The characteristics of the coherentintegration algorithm, non-coherent integration algorithm and differential coherent integrationalgorithm are analyzed. To solove the problem that the coherent integration duration is limitedby the navigation data bit flipping, two algorithms that improve the SNR gain by detecting theflip-bit are proposed. The first algorithm draws on the principle of the whole-bit algorithm. Firstly, the possible position of bit-fip is detected in1ms through the comparison of thecoherent integration results of the several groups of signal blocks. Then the rest signal whichis at intervals of20ms with the flip bit is removed, and block coherent integration is applied toits subblock signal. The second algorithm extends the traditional differential coherentintegration algorithm to the processing of the block data. Firstly, the5ms signal with possibleinvolve bit-flipping, which was detected through the comparison of the coherent integrationresults of the several blocks of data, was canceled. Then block differential coherentintegration is applied to its sub-block signal in rest15ms. The simulation results show thatthese two algorithms can improve the acquisition sensitivity and acquisition efficiency.3. The traditional phase-locked loop tracking algorithm is studied deeply. Because of itsflaws the Kalman Filter algorithm is introduced to the GPS satellite signal track, and thetracking loop models of measurement and dynamics are built. The Standard Kanlman Filtermade an ideal assumption on the noise statisitical characteristics which is inconsistent withthe facts, and it is highly dependent on the initial. To solove these problems, a StrongTracking Suge-Husa Adaptive Kalman Filter algorithm is proposed. The algorithm usesSuge-Husa Adaptive Kalman Filter to estimate the noise in real time, and take the advantageof the Stong Tracking which have a good robustness and strong ability to adapt the mutation.The simulation results show that the algorithm can track the weak GPS signal continuouslyand stably.