Research On Simulation Technology Of Time Domain Companding Signals And Satellite Navigation Signals

Signal simulator of satellite navigation in various complex environments is an important equipment for modern navigation receivers to develop and test.However,it is still very difficult to realize high-dynamic and high-precision signal simulator of satellite navigation,and which becomes the key technology of simulator.Based on the relative motion between satellite and user,this paper analyzes the time-domain companding characteristics of the received signal and explores the high-precision signal simulation algorithm of satellite navigation from time-domain companding mechanism.The main work is as follows:1.This paper analyzes the mechanism of leading-edge jitter error in conventional numerically controlled oscillator(NCO)method,and presents a digital-domain representation and generation method by means of time amplitude modulation.The fractional arrival time is converted into a fixed interval sample amplitude modulation.The FPGA generation software is designed to simulate the timing and clock waveforms of time amplitude modulation.It is possible to provide a new idea for digital generation and digital processing of low jitter clock signals.2.An improved direct digital synthesizer(DDS)algorithm based on double accumulators is proposed,which only needs a small look-up table.The normal single accumulator is divided into two components,one with the look-up table approach,and the other approximation algorithm.The two accumulators control mutually to produce the precise sampling time in each cycle and to synthesize the required sinusoidal signal.The analysis and simulation results show that the proposed algorithm can significantly reduce the sine table capacity,improve the frequency resolution,reduce the output signal phase noise.It is suitable for subcarrier generation of high resolution satellite navigation signal Doppler frequency offset.3.Based on the relative motion between satellite and user,a dynamic time-domain companding model of satellite navigation signal is established.The pseudo-range signal is generated by time-amplitude modulation clock,and the improved DDS is used to produce the sub-carrier signal with Doppler deviation.IF signal and multipath signal of satellite navigation are simulated,the signal acquisition and the estimation of multipath parameter are carried out,which proves the correctness of the proposed simulation algorithm.