High Sensitivity Receiving Techniques For Navigation Signal And Channel Code Design Research

The satellite navigation service has been used widely since the running of Global Positioning System. But the service is restricted by environments, the performance can not be assured in weak signal environments such as indoor rooms and city canyons. The sensitivity of receiver has been the bottleneck of enlarging the use of satellite navigation service. To increase the sensitivity of satellite navigation receivers, the acquisition and track of satellite navigation signal with high sensitivity and high-gain channel coding scheme for satellite navigation system are researched in this dissertation.The main contents included are as follows.(1) To analyze the influence of high-order dynamic on the coherent integration time, the length of coherent integration with minimum detection loss is deduced. The relation of acquisition performance and the number of noncoherent accumulation is analyzed. Under the same total accumulation time and the same number of accumulations, The optimizing method based on variable integration time has better performance than the method based on equal integration time. The higher the frequency rate and the bigger the number of accumulations are, the bigger the performance gap is.(2) To overcome the restriction on the coherent integration of unknown data bits, an acquisition method based on ordering data bit combinations by Gray code is presented. Compared to the acquisition method directly searching all possible data bit combinations, the presented method can reduce the calculation complexity by(N-1) times, where N is the number of data bits contained in the coherent integration. The simulations show that the presented method has better performance than BACIX(Block Accumulating Coherent Integration over Extended Length) algorithm when the length of coherent integration is not less than 100 ms. The required CNR of the presented method is 1.7 d B less than BACIX algorithm to achieve the same performance when the signal’s length is 240 ms for the GPS C/A code signal. Although the presented acquisition method based on Gray code has reduced complexity compared to method directly searching all possible data bit combinations, it still has exponential complexity. To reduce the calculation complexity, modified BACIX algorithm is presented, which has linear calculation complexity being proportion to the length of signal. The presented method has better performance than BACIX algorithm when each group in the presented algorithm contains five data bits at least.(3) To enhance the stability of the carrier loop, a kind of tracking loop based on FFT discriminator and data bits estimation is presented. Based on the estimation of the data bit combination and bit edge, long signal can be used to discriminate the frequency error through FFT in the presented carrier tracking loop. Besides, discriminator based on FFT has a wider pull-in range than traditional discriminator, which can strengthen the stability of carrier loop. Simulation results indicate that the presented tracking method can handle signals with CNR 12 d BHz with Doppler frequency rate 1Hz/s.(4) To increase the data bit demodulating sensitivity of receivers without external aid, a kind of channel coding scheme fitting for navigation data bits is presented. The presented code has linear encoding complexity being proportion to code length. The decoder of the presented code can be updated p notes in a parallel way, where p is the block column’s dimension of H1 of the parity check matrix of the presented code. Simulations show that the presented code has approximately the same performance as the LDPC code used in GPS L1 C signal.At last, all the work of this dissertation is summarized, and the next research to be carried out is presented. The main achievements of this dissertation have been used in signal system design and receiving terminal projects of Bei Dou satellite navigation system.