Research On Self-alignment GPS Transceiver Pseudolite And Its System Design

Currently,Global Navigation Satellite System(GNSS)has been applied in many scenarios.Nonetheless,satellite navigation systems also have their inherent limits.If the current location of a user receiver is in a semi-occluded location or in a fully occluded environment,the positioning function may be unavailable.A pseudolite is actually a ground-based device that simulates an authentic satellite transmitting simulated GNSS signals.When the signal structure of a pseudolite is exactly the same as that of an authentic satellite,it can be seamlessly synchronized by a universal receiver and used for positioning.In this case,compatibility is optimal and there can be no changes in a universal receiver.However,due to its low cost and other limitations,its performance,one of which is signal stability,is much poorer than GNSS signals transmitted by an authentic satellite.Therefore,improving the stability of pseudolite signals is also a critical issue.In view of the above problems,this paper designs a self-alignment GPS non-intrusive pseudolite,which has two characteristics.Firstly,the transmitting end is non-intrusive type.The navigation message transmitted by the GPS pseudolite is exactly the same as transmitted by a GPS satellite.Secondly,a receiver is added into the GPS pseudolite in an attempt to receive its own signal and then analyze it.Adjusting frequency of the baseband signal in the transmitter in real time aims to ensure signal stability.The main research contents and results of this paper are shown as follows:Firstly,the transmitter of pseudolite is introduced.The inverse algorithm of generating navigation message is proposed.It is shown that the signal transmitted by the GPS pseudolite received by the commercial receiver can be stably tracked and the navigation message can be resolved.Secondly,problems related to the signals transmitted by a pseudolite are analyzed.Singal assesment parameters are detailed to evaluate the pseudolite signal quality.Then,an intermediate frequency front-end and software receiver are used to analyze the problem that the frequency of GPS pseudolite signal is unstable.Finally,the FPGA implementation of the GPS receiver is introduced and it is shown that the FPGA receiver can stably track the GPS signal.Thirdly,a self-alignment structure is designed to ameliorate signal stability.A receiver is added into the pseudolite.Then,the transmitting end and the receiving end are combined to form a negative feedback loop in the pseudolite.The PID compensation method is used to ameliorate the ability of the system to resist external noise.The equivalent root locus is used to determine the parameters of the PID compensation.It is found that the self-alignment pseudolite can indeed ameliorate the stability of the GPS pseudolite signal by simulations.Finally,self-aligment structure implemention is detailed.The self-alignment GPS pseudolite is materialized on the hardware platform.It is found that the signal becomes more stable.Especially,performance of carrier frequency of the signal has about 10% improvement.