Research On The Tracking Theory Of GNSS Signal And High Precious Angle Measurment Technology

Global navigation satellite systems (GNSS) become more and more important in the military and national economic construction. Many countries have begun the construction of their independent GNSS. The development of the America's global positioning system (GPS) is the earliest and most mature; Russia's GLONASS and the European Union's Galileo are constantly being improved; China is building the COMPASS system. In the construction of GNSS, the signal design is crucial, which is directly related to the performance of navigation system. The evaluation theory of receiver performance can provide the guide for the signal design. Under the same receiver parameter, the receiver performance for different signal structuers can reveal the difference between different signals. In the next, we use the expression that is the tracking performance of GNSS signal instead of the expression that is the tracking performance of the receiver for a given GNSS signal for convenience. The main achievements and contributions are given as follows:1) This dissertation established the model of the frequency tracking error of phase locked loop (PLL) in the finite frontend bandwidth case. Currently, the frequency tracking error is usually obtained mainly from simulation. Although the analytic expression of the frequency tracking error for frequency locked loop (FLL) has been presented, in most of the cases, the discriminator output of the frequency locked loop will be cut off after the loop is convergent. Thus, only the PLL is working and the analytic expression of the frequency tracking error for FLL is not suitable to describe the frequency tracking error of the loop. Focusing on the problem, we derived the frequency tracking error of PLL for coherent and non-coherent discriminators with considering the effect of finite frontend bandwidth. The analysis of the difference between the simulation results and the theoretical results of frequency tracking error was pefromed under different normalized equivalent loop bandwidth. It is shown that when the normalized equivalent loop bandwidth is not much more less than 1, the analytic expression obtained from discrete time domain accords with simulation results much more well compared with the analytic expression obtained from continuous time domain.2) This dissertation established the model of the phase tracking error of PLL with considering the effect of finite frontend bandwidth. The currently used analytic expression of the phase tracking error for PLL is presented without considering the effect of finite frontend bandwidth. Although the conclusion that effect of the finite frontend bandwidth on phase tracking error is not obvious is mentioned in some references, it is still lake of theoretically analytic expression to describe the tracking error under the finite frontend bandwidth case. Therefore, we derived the analytic expressions of the phase tracking error of PLL using coherent and non-coherent discriminator with the consideration of the finite frontend bandwidth. The different effect of finite frontend bandwidth on phase and code tracking loop is compared and discussed. The analysis of the difference between the simulation results and the theoretical results of phase tracking error was presented under different normalized equivalent loop bandwidth. It is shown that when the normalized equivalent loop bandwidth is not much more less than 1, the analytic expression obtained from discrete time domain accords with simulation results much more well compared with the analytic expression obtained from continuous time domain.3) This dissertation established the model of evaluating the code tracking performance in the presence of continuous wave (CW) interference for GNSS signals. The currently used models of analyzing the impact of interference on tracking performance are based on the assumptions that the interference obeys the Gaussian distribution and that the effect of the discrete spectral line of Pseudo-Random Noise (PRN) code is ignored. Now, the conclusions based on these models are not applicable for the tracking of the pilot channel. Meanwhile, the signal-to-noise ratio after correlator with consideration of spectral line of PRN code cannot indicate the code tracking performance. Considering these facts, we established the tracking error models under C W interference with consideration of spectral line of PRN. The analytic expressions of the code tracking error for delay lock loop (DLL) using coherent early-minus-late discriminator, non-coherent early-minus-late power discriminator and non-coherent dot-product discriminator were derived. The theoretical results were validated by computer simulation. The detailed analysis of the tracking error under different discriminators and the other receiver parameters were performed. A further analysis shows that for the finite frontend bandwidth case, the tracking error cannot be always reduced, and limitation value exists as the correlator spacing is approaching to zero. It shows the code tracking performance gain obtained from the narrowing of correlator spacing. The code tracking performance of the GPS L5 signal and the Galileo EIOS signal under CW interference were analyzed in details by using the derived mathematics findings. It is shown that part of the PRN codes are more vulnerable to the interference compared with the average level. By using the analytic expressions presented in this dissertationas the criterion, we can optimize these PRN codes. These obtained conclusions can provide the theoretical support and guide of the optimization of the GNSS signal structure.4) This dissertation presented a method of high precise angle measurement based on short baseline. The problem of obtaining the high precise angle measurement between the aircraft with the short baseline and the others in real time was investigated. It is shown that to obtain the high precise angle measurement based on short baseline(less than 10 m), high frequency carrier (larger than GHz) needs to be used. Then the problem of carrier-cycle ambiguity is introduced, while the currently used method of fixing the carrier-cycle in the interferometer cannot resolve this problem well with considering various aspects in this scene. Inspired by the thought of wide lane in the GPS ranging system, we provided a method of high precise angle measurement using carrier aided by PRN code based on short baseline. Then, the accuracy of the angle measurment is analyzed, which provides the guide for the project implementation.