Coding And Modulation Of Satellite Navigation Signals For High Rate Transmission

The rapid development of real-time,high-precision and reliable positioning services has put forward higher requirements for the navigation messages transmission rate of Global Navigation Satellite System(GNSS).However,the existing GNSS signal modulation methods still have certain shortcomings when realizing high-rate data transmission.Meanwhile,GNSS signal is susceptible to interference and noise during space transmission,its reliability is low.A high-gain channel coding scheme must be considered to reduce the bit error rate.Therefore,this thesis studies the satellite navigation signal coding and modulation technology for high-rate transmission,aiming to achieve high-rate and high-reliability navigation message transmission.The specific work is as follows:This thesis briefly describes satellite navigation signal modulation technology,introduces the principle of code shift keying(CSK)modulation and demodulation,simulates and analyzes the bit error rate of CSK modulation and demodulation,and compares it with direct sequence spread spectrum binary phase shift keying(BPSK)modulation.Based on the requirements of high-rate message transmission and system reliability,this thesis designs CSK and BPSK coding modulation schemes based on nonbinary low density parity check(LDPC)codes,and derives the variable node log likelihood ratio(LLR)expression of LDPC codes.For CSK modulation,an LLR calculation method based on correlation output is proposed.This method can directly calculate the LLR of the variable node of the nonbinary LDPC codes using the correlation value of the CSK demodulation output.Compared with existing methods,the LLR calculation method based on correlation output has lower computational complexity.The simulation verifies the feasibility of this method.This thesis introduces the commonly used decoding algorithms for LDPC codes,and discusses the main factors affecting the decoding performance.The CSK modulation and direct sequence spread spectrum BPSK modulation based on nonbinary LDPC coding are simulated,their advantages and disadvantages are analyzed.Experimental results show that under the same nonbinary LDPC coding conditions,CSK modulation is better than direct sequence spread spectrum BPSK modulation in error correction performance and data transmission rate,but there is a problem of high demodulation complexity.