Research On Parasitic Transmitting System Of Navigation Information

The parasitic transmitting system of navigation information is an auxiliary system of satellite navigation system,whose spread spectrum signal can be parasitized in the communication signal of other satellite communication system for transmission to realize the function of transmitting back the information of navigation terminal.The system does not need to lauch a dedicated satellite,and has good ability of concealment,strong performance of anti-interference and high confidentiality,which has broad application prospect in military and civilian fields.In this thesis,the transmitting technique of communication link in the parasitic transmitting system is studied.The main work and results of the study are as follows:1.The parasitic transmitting system and its communication link are studied.From the point of view of link budget,the effects of information rate,antenna aperture of ground center station,spread spectrum gain and background interference suppression on the whole system are studied,and a solution of communication link based on background interference suppression and channel coding is proposed.Theoretical analysis shows that it can surpport reliable transmission with low bit error under background interference.2.An improved background interference suppression technique based on Amplitude Domain Processing?ADP?is proposed.With the method of Continuous Polynomial Approximation?CPA?for expressing mathematically the Probability Density Function?PDF?,nonlinear function derived from this PDF can be applied into nonlinear processing on amplitude domain of received signal to suppress interference.This technique reduces the error caused by inaccurate PDF estimation,and obtains strong interference suppression performance.At the same time,it does not need any training sequence,nor does it have the problem of slow convergence.Simulation results indicate that the proposed technique can improve both INR and SINR of the system greatly under background interference with different intensity.3.An improved adaptive decoding algorithm for Polar codes is proposed,which not only improves the decoding performance,but also reduces the average computational complexity of decoding.In order to solve the problem that hard decision decoding algorithm results in loss of channel information and poor decoding performance in M-ary spread spectrum system,a soft decision decoding algorithm based on bit interleaving for M-ary spread spectrum and Polar code is proposed.The simulation results show that this algorithm can provide the coding gain of about 6.6dB when the BER is 10^-6,and its performance is 3dB better than that of hard decision decoding algorithm.The Matlab simulation platform of parasitic transmitting system is built,and the overall performance of the system is simulated.The simulation results show that the system can meet the requirements of BER below 10^-6 when ISR is 30dB.