Research On The All-digital Despread Receiver For DS-MSK Signals

The Direct Sequence Spread Spectrum MSK(DSSS-MSK)communication system is widely used in the military and civilian domain.Holding the advantages of anti-interface performance and high confidentiality in the spread-spectrum communication technology,the DSSS-MSK system also owes the characteristics of MSK signals,for instance,the constant envelope,the concentrated energy,high spectrum efficiency and insensitivity to the non-linear distortion.The requirements on high speed communication environment,have been increasing,which leads research significance on the DSSS-MSK dispreading and demodulation under high dynamic environments.The thesis firstly introduces the theoretical basis of the DSSS communication and the parallel and serial methods of DSSS-MSK.The thesis studies the matched filtering method,one of the traditional methods in DSSS-MSK signal acquisition,which has the problem on its correlation peak and is easily affected by the Doppler shift,and proposed a delay-correlation based acquisition algorithm.The algorithm eliminates the effect by estimating the Doppler shift value and compensating based on its feedback.The acquisition precision decreases as the code phase acquisition process after the Doppler shift evaluation,thus the thesis proposed a code-Doppler joint acquisition algorithm based on the two-dimension compressed correlation(TDCC).The algorithm realizes the fast acquisition,as the compressed correlator compresses and searches the adjoining and Doppler shift simultaneously.By introducing the compressed sensing(CS)into the spread spectrum fast acquisition,the thesis proposed a multi-cycle co-acquisition algorithm based on CS,which has characteristics of high-precision and fast acquisition speed,while considering the sparse characteristics of DSSS-MSK signal.By comparing the simulations of proposed algorithms,the thesis finds that the CS has a better performance under the high dynamic,low SNR environments,with a balance on the acquisition precision and complexity.The thesis uses the full digital early-delay locked loop for the code tracking and the Costas loop for the carrier phase tracking for the DSSS-MSS signal tracking,and gains the optimized parameters by analyzing their phase characteristic curves and the simulation results.The thesis finally simulates the bit error rate performance of the DSSS-MSK signal correlated demodulation system.It verifies that DSSS-MSK system is suitable for high dynamic and low SNR environment.