| With the rapid development of the space technology and the communication technology,Global Navigation Satellite System(GNSS)has been deeply and widely applied in many fields.However,L band is overcrowded due to an increase in the number of the satellite navigation systems,the system's compatibility and the spectrum's security problems become severe as a result.Therefore,it is very necessary to develop the C band and enhance our navigation spectrum occupancy,improve the international competitiveness and hold the initiative in the future navigation development.Signal design is one of the most important parts in the global navigation satellite system.The performance of the navigation system,the receiver accuracy and anti-jamming ability depend on the navigation signal.Coding,modulation and the ranging code are the important parts in the navigation signal design.At present,the coding and modulation in GNSS system are isolated and it is difficult to keep a balance between the reliability and validity.To solve the problem,the joint coded modulation technology is introduced.Coded continuous phase modulation is an effective scheme of joint coded modulation.The Turbo iterative principle can improve the performance of the system.Serial cascade systems that are cascaded by Turbo code or Binary Low-Density Parity-Check(LDPC)and CPM are the hot spots of the present research.When the Binary code cascades the M-ary CPM,the conversion process between symbols and bit is essential and would cause the decrease in the amount of the information and increase the bit error rate of the system.In order to improve the detection probability of the the system and match the M-ary CPM modulation,a more advanced encoding scheme,Q-ary LDPC is used in this paper which has a better performance.Besides,a ranging code with better balance and stronger confidentiality is designed.This paper aims at designing a satellite navigation signal which is suitable for the C band.The satellite navigation signal combines the Q-ary LDPC,the M-ary CPM and the chaotic spread spectrum to enhance the accuracy of positioning,timing,speed measurement and promote the interoperability,confidentiality and anti-interference ability of the navigation,providing some references for the satellite navigation signal waveform design of C band.Based on above targets,the main contents of this paper are as follows:1.The implementation scheme of Q-ary LDPC code suitable for the GNSS system is researched.This paper selects the coding and decoding algorithm with less hardware resource occupation and computational complexity and analyses the impact of the amount of iterations for the decoding convergence with EXIT chart.2.The basic properties of CPM modulation in AWGN and Rayleigh channel are deduced.The basic principle of Multi-h CPM is derived and the approximate power spectral density is introduced.3.The performance of CPM modulation in C band is evaluated.Performance of rang precision,anti-interference and anti-multipath of MSK modulation,GMSK modulation and CPM modulation are analyzed and the theory support for the GNSS signal waveform design of C band is provided.4.The performance of the ranging code is evaluated.This paper analyses classical chaotic sequences including the weighted optimizing chaotic sequence as the performance of ranging code based on the peaks of autocorrelation and crosscorrelation,and the Welch bound.A ranging code based on the weighted optimizing chaotic sequence with better performance is proposed.5.The way to improve the real-time performance of the Multiple LDPC-CPM system is studied.This paper analyses the exchange mode of external information,and combines the weighted external information exchange mode with iterative stop criterion,effectively optimizing the amount of positive feedback and average iterations and improving the system real-time property. |
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