The Method Of Image Depth Estimation Based On Texture Feature Probability Model

In recent years, along with the continuous development of satellite navigation and positioning technology in military and civilian applications, higher requirements have been put forward for the performance of the navigation receiver. As one of the key technologies for the high-performance navigation, GPS signal acquisition technology serves as the core link for base-band digital signal processing of the receiver. The weak satellite signal acquisition technology for complex circumstances such as urban areas, canyons and indoor environment has become the current research focus. As for the shortcomings and blind spots in domestic and international researches on the acquisition of the receiver, the article has put forward profound analysis and research on the C/A code acquisition algorithm of the GPS navigation receiver under weak signal environment.Firstly, the article analyzes the fundamental principles of direct sequence spread spectrum communication technology, the structure of GPS signals and relevant characteristics of pseudo-random code in GPS signals, establishes the model for GPS digital intermediate-frequency signals and generates intermediate-frequency signals through simulation. It puts forward the research on signal detection theories and threshold deciding methods, elaborates the fundamental principles of weak signal acquisition by GPS receiver, makes theoretical analysis on the detection characteristics, process gains, calculation amount and possible loss of the three major integration algorithm, including coherent integration, non-coherent integration and differential integration. Through simulation and comparison, it also analyzes the variation of the detection probabilities of the three algorithms along with the Carrier-to-Noise Ratio.Secondly, by focusing on the possible turning of navigation message data during the acquisition process, the article primarily makes the analysis through comparison between the two kinds of edge estimation algorithms for navigation message, namely the half-bit algorithm and full-bit algorithm. As for the shortcomings and defects of the current edge estimation methods for navigation message, the article proposes an improved edge detection method for navigation data, namely the continuous turning data symbol method. The simulation result has indicated that, the algorithm is capable of successfully estimating code phase and Carrier Doppler Shift. Furthermore, under the environment with the same Carrier-to-Noise Ratio, the maximum detection probability of the algorithm is higher than the full-bit, half-bit and circumference algorithm.Then, based on the theoretical analysis on the influences of navigation message turning on Doppler Shift and the position of self-correlation peak, the article comes to the conclusion that the navigation data turning of the self-correlation peak of C/A code features insensitive properties. Meanwhile, on the basis of relevant traditional averaging technology, the article introduces the improved methods for compensating various data blocks through the Doppler Shift before averaging. Based on the two-point analysis, the article designs a weak signal C/A code acquisition algorithm based on the insensitive characteristics of C/A code navigation data turning, the simulation result of which indicates that, the algorithm is capable of realizing the effective estimation on C/A code time lag and Carrier Doppler Shift without estimating the position of the edge of navigation message.Finally, the article puts forward theoretical analysis and simulation verification for the near orthogonal properties of cross correlation sequences of the C/A code. Additionally, it designs a multiple satellite C/A parallel acquisition algorithm under the weak signal environment on the basis of the near orthogonal properties of cross correlation sequences of the C/A code, focusing on the interference of strong signals on the weak signal acquisition and the pending issue of reducing the required time for the simultaneous acquisition through multiple satellites. By putting forward simulation analysis and comparing with the traditional acquisition algorithm that has been based on the cross correlation characteristics of C/A code, the article discovers that the algorithm requires much less calculation in the case of successful acquisition of satellite C/A code time lag and Carrier Doppler Shift at the same time, which has effectively increased the acquisition efficiency.