Research On Key Technology Of Synchronization For PCSS System

Parallel Combination Spread Spectrum(PCSS)communication is a new and efficient spread spectrum communication,while inheriting the advantage of Direct Sequence Spread Spectrum(DSSS)communication such as anti-interference,low probability of intercept and superior multiple access communication ability,has a broad application prospects.Because of the combinatory sequence modulation signal is transmitted in PCSS communication system,so the signal synchronization will be affected by the cross-correlation between sequences,the system computation and other issues,which is a technical problem needed to be resolved urgently.The appropriate synchronization methods are studied based on the principle of PCSS system,and the main contents are as follows:(1)A combinatory sequence sliding correlation acquisition algorithm is first introduced thorough combining the principle of PCSS system with the sequence acquisition algorithms of DSSS system,and the principle of the algorithm is elaborated using the probability of the combinatory sequence amplitude distribution.Then,a combinatory sequence time-frequency domain algorithm based on FFT is exploited to solve the problem of the rapid acquisition of long period sequence,and the correlation characteristics of the combinatory sequence is analyzed,while the relationship between Doppler offset and acquisition correlation peak is illustrated.Finally,an adaptive gate rule of CFAR theory is studied.(2)A carrier tracking algorithm based on Costas loop is quoted to track the remaining frequency difference generated by the first carrier frequency acquisition,and the principle of the loop is analyzed via the QPSK signal unequal probability theory,while a weighted approach for dual channel demodulated data is presented aiming to restore data after carrier tracking.Next,the design of the loop components is detailed introduced and the phase ambiguity is discussed,and an eliminating phase ambiguity method is presented by utilizing the first period of sequence integral accumulation decision results of the two channels.Finally,the loop parameters setting is elaborated specifically.(3)Two improved algorithms are introduced to solve the traditional time-frequency domain acquisition algorithm based on FFT cannot achieves the right acquisition correlation peak under low SNR and wide frequency offset,which are FFT combinatory sequence time-frequency domain acquisition algorithm based on multiple peak accumulation and FFT combinatory sequence time-frequency domain acquisition algorithm based on segment correlation respectively.The accumulation number is analyzed for the former algorithm acquisition performance in low SNR,and the number of the segments and the FFT points is discussed for the latter algorithm acquisition performance.