Key Techniques In Baseband Signal Processing Algorithms Of Beidou Receiver

At present, the Global Navigation Satellite System(GNSS) develops with each passing day and has become an important battlefield in space territory, technology and military power among developed and some developing countries. The GPS(Global Positioning System) of the U.S., GLONASS of Russia, GALILEO of Europe, and Bei Dou Satellite Navigation System of China occupy important positions in the GNSS. Solid development of the Beidou system has broadened it coverage in positioning, navigation and short-message communication covering Asia- Pacific regions. Multiple modes of user experience are offered for authorized users and open users, supporting mass application of positioning and navigation with increased precision. The system aims at global coverage by 2020. Meanwhile, however, challenges come with burgeoning market in stricter demand in positioning accuracy and streaming speed. By contrast, more adverse environment for receivers has been observed, which puts forward challenges and opportunities for all systems. Therefore, this paper is set to study the baseband signal processing algorithms of navigation and positioning receivers and to look into possible ways of improvement. It is believed that improved performance of navigation and positioning receivers is realistically important and promising.Beidou receiver is an important platform of the Beidou system on users’ end. Work including satellite signal acquisition, navigation and positioning computation, data generation and support to auxiliary functions all takes place on the receiver level. Mechanisms and approaches employed for signal optimizing to enhance navigation and positioning performance in each of the major systems often involve overall planning, rendering them hard to execute. Better locations for antenna location are usually restricted by terrain features. Antenna innovation suggests a higher hardware costing. On the link of baseband signal processing in receivers, it is more operationally efficient, functionally effective and economically reasonable to optimize the two key baseband signal processes, i.e. acquisition and tracking, through software so as to improve overall signal processing in receivers for more accurate, faster positioning and navigation.This paper primarily studies enhancement and optimization of baseband signal acquisition and tracking as two key processing actions in Beidou receivers. It first reviews positioning principles of the Beidou system, signal and system composition, and working principles of the receiver to lay a theoretical foundation for follow-up discussion.It moves on to illustrate the signal acquisition mechanisms of Beidou receiver and reviews the status quo of acquisition technology at home and abroad. Addressing added inference in the urban environment which undermines acquisition performance, the author puts forward an anti-interference acquisition algorithm based on wavelet transform for the Beidow system. This approach starts with correlation integral and differential accumulation on incoming signal. Next Meyer wavelet is used to decompose signal waves, which then are compared for energy of each frequency range. The results help determine the frequency range of narrowband noise, the coefficient of which will be attenuated to reconstruct signal and further to remove interference from narrowband noise. Simulations have showed that this approach can achieve resistance to inference from continual narrowband waves in single-antenna condition, with an average gain of 5 db.In the third part, tracking principles of Beidou receivers are explained and status quo of tracking technology internationally reviewed. Responding to the deficiency that signals are often blocked by urban barriers, which causes computational failures of navigational data due to loss of locking in tracking loops, this paper proposes improved vector tracking algorithm based on Kalman filter. By coupling features of signals from various channels, enhanced tracking can by gained through strong signals assisting weaker ones. It is, therefore, possible to maintain accuracy in positioning even when satellite signals are partially blocked. Empirical evidence shows that this model has enabled relatively more accurate positioning when the receiver captures from less than four satellites in urban scenario.This research divides processing of baseband signals into two steps of acquisition and tracking. Optimized algorithms are designed for each catering to their own features. Computing efficiency and accuracy have been effectively improved without compromising hardware comsumption and computational complexity, providing reference to software-based improved in Beidow receivers.