DSSS Rapid Acquisition And Tracking Technology Research MSK Signal

MSK, which has many advantages such as a constant envelope, high spectrum efficiency, low out-of-band emission and insensitive to nonlinear distortion, is particularly suitable for the wireless communication fields that are power-limited and with nonlinear distortion, Doppler shift and multipath fading. MSK combining with spread spectrum communication that has advantages both of MSK and spread spectrum system (good security, low capture probability and strong anti-interference ability), has been widely used in many areas, such as tactical data link, civil aerial ground-air data link, guided missile command transmission, satellite communication and other fields, so the research on rapid acquisition and tracking technology of DS-SS MSK has important significance.The paper firstly studies the characteristics of the pseudo-random sequences, and then selects the Gold sequences which have good self-correlation and mutual-correlation performance as the spreading codes. Based on Type Ⅱ MSK modulation, it proposes a dual pseudo-code DS-SS MSK communication system, and designs the implementation scheme of DS-SS MSK modulator and IF digital despreading and demodulation receiver, at the same time, the simulation analyzes the generation of DS-SS MSK and the processing of despreading and demodulation. Focusing on the high dynamic environment, the paper carries out a deep study on acquisition and tracking technology of DS-SS MSK. It adopts a rapid DS-SS MSK signal acquisition scheme based on FFT frequency compensating and time domain matching. For the problem of limited frequency estimation precision of FFT that has impact on the performance of the code acquisition, the paper proposes an improved high-precision frequency estimation algorithm, while maintaining the same points of FFT, the algorithm can greatly improve the frequency estimation precision, and then analyzes the performance of the entire rapid acquisition system. The paper adopts all-digital incoherent early-late delay locked loop for code phase tracking, presenting the methods of parameters’ selection and design of the loop, at the same time, analyzing the impact of the loop’s parameters (?) and Bl, on the code tracking loop in detail. At last, the paper proposes a Costas loop structure for dual pseudo-code DS-SS MSK carrier tracking with a detail derivation of the Coatas loop’s phase-detector characteristic, and the MATLAB simulation verifies that the Costas loop can achieve carrier phase tracking effectively.