Research On Key Techniques Of Onboard Digitized Multicarrier QPSK Demodulation

Recent advancement of satellite communication is closely related to on-board base-band processing(BBP) techniques. This dissertation studies on some key BBP techniques to focus on multi-carrier demodulation(MCD), including some algorithms of FDMA signal demultiplexing, fuiiy digitized integral demodulation of FDMAIQPSK signals, carrier frequency tracking and bit-timing synchronization in MCD, etc., Computer simulation experiments on the main key techniques have been done. A real-time demonstration system of demultiplexing and demodulation of 32 channel FDMAIQPSK signals with a single DSP chip, TMS320C6201, has been implemented. The author抯 main contributions are as follows; (1) Studying and proving an algorithm of fully digitized integral demodulation of multi- carrier QPSK signals. It combines the demultiplexing algorithm with that of demodulation and makes them as a whole. So that, the concept of integral demodulation can be reached. (2) A novel algorithm for large frequency offset estimating and rectifying has been proposed. It turns the direct estimation of frequency offset into the estimation of the period of a known sequence. So that it can estimate and correct rather great relative difference of carrier frequency. (3) Proposing a new algorithm for bit-timing recover. By replacing the squaring operation for attaining bit-timing error in bit energy compared-based with weighted mean of the absolute value of samples. The bit-timing signal recovered with this algorithm is characterized by higher stability, better anti-noise ability, and high computational efficiency. (4) Proposing a method of parameter adaptive adjusting in phase-locked loop(PLL), This PLL not only can realized quickly synchronization acquisition when larger frequency offset occurs, but also get the output signals with very little phase jitter noise. The MCD demonstration system has been implemented, to which the algorithm (1 ),(2) and (3) are employed.