Study On Simulation Of Galileo Signal And The Key Algorithm Of The Software Receiver

Most signals broadcast by Galileo use BOC modulations. BOC modulations have good spectral separation properties, and this is important to avoid inter-system interference. In addition, it brings better tracking performance and flexibility. BOC modulations are becoming a promising direction. This paper will study on the most respective Galileo E1 signal, which is BOC(1,1) modulated. This thesis focuses on simulating E1 intermediate frequency (IF) digital signal and studying the key algorithms of software receiver. The main work and contributions are summarized as follows:1. The structure and characteristic of Galileo E1 signal are analysed thoroughly. The principle and characteristics of BOC, AltBOC and MBOC are analyzes. The mathematical simulation model is established based on the signal structure and the principles of creating IF digital signal, including various error sources exactly, and it is easy to be realized by software. It is convenient for you to change the status of signal by specifying the parameters. The concrete realization of navigation satellite signal is proposed. When calculating the status of signal, iterative method is used to obtain the transmission time. Interpolation and extrapolation methods are used to calculate the pseudorange and carrier Doppler at each sampling time.2. The technique of acquisition for E1-B signal is similar to GPS C/A signal. As we know, the ranging code period of E1-B is the same as data bit period. If correlation is implemented using 4ms signal directly, it is possible that no correlation peak will be visible if a change of sign happens in the incoming signal. A zero padding strategy is adopted to solve the problem in this paper. There will probably be two correlation peaks in the acquisition results. If two occurs, the code phase correspondging to the first peak is the desired result.3. The output, normalization as well as tracking precision of two typical discriminators are dicussed thoroughly. It is validated that BOC signal has a more robust and precise tracking as compared to BPSK signal. The classical tracking architecture offen suffers from short tracking region and false lock at 0.55chips. An unambiguous ASPeCT tracking is proposed to remove the side-peaks of autocorrelation and false lock tracking points. The outputs of ASPeCT discriminators are analyzed, as well as how the thermal noise affects the precision of tracking. The analyzing results show that ASPeCT can remove the side-peaks of autocorrelation thoroughly without degrading the tracking accuracy. Moreover it brings a wider stability region. All these improvements can improve the reliability and robustness of tracking.4. A concrete design project and full realization of the software receiver of Galileo E1-B is put forward. A set of real data is collected to validate the software receiver's function and usability. Finally, the simulated signal is verified indirectly by simulated GPS signal and softGNSS software receiver.On the basis of the above theory and technique, the author programmed the process of signal simulation, acquisition and tracking for Galileo E1 signal.