Research On Techniques For Carrier Synchronization And Channel Equalization In Data Transmission System Of DRSS

Recently, high rate data transmission technology in DRSS becomes an active research field in wireless communication, and is one of the key problems of our country's spatial information systems. Research was carried out grounded on the design of two high speed modems. Two main subjects were discussed in this thesis: the carrier synchronization for broad-band quadrature modulation signals and the nonlinear equalization for the DRSS channel.In the first section, the thesis investigated the carrier recovering techniques for broad-band quadrature modulation signals.Based on the ML estimate theory, several CRBs of carrier parameters for quadrature modulation signals were deduced and concluded. These CRBs act as a measurement for evaluating the carrier recovering algorithms. An improved difference feed-forward frequency estimate algorithm was presented, which increased the precision and the range of frequency estimation. The performance of first order decide directed DPLL and second order decide directed DPLL were analyzed in detail, and the methods of carrier parameter designing were also given. At last, the influences of carrier phase errors on coherent demodulation were analyzed and simulated. The research above offers a theoretical basis for the carrier recovering module design.In the second section, the thesis investigated the nonlinear equalization techniques for the DRSS channel.Firstly, Aiming at the actual links, the nonlinear models for the DRSS channel were described, and the influences of nonlinear on the system performance were analyzed.Secondly, nonlinear pre-distortions, namely pre-equalizations, for the HPA in user satellite and for the transponder system in relay satellite were analyzed and simulated, and improved nonlinear pre-distortion methods were presented. The simulation results show that the scheme combining nonlinear pre-distortion and power back-off is efficient to compensate the nonlinear distortion in the DRSS channel.Thirdly, nonlinear equalization, namely post-equalization, for the DRSS channel was studied. Nonlinear equalization based on sparse Volterra filter was especially investigated. An improved genetic algorithm for constructing the sparse Volterra filter was proposed. An improved QRD-RLS adaptive algorithm was presented, which increases the convergent speed for the sparse Volterra filter. Furthermore, the quantified effects on the Volterra filter was analyzed. The simulation results show that the nonlinear equalizer removes the nonlinear ISI in the DRSS channel effectively.In the last chapter of this section, the reduced rank nonlinear equalization was studied. MWF was introduced to the Volterra filter for the first time. A reduced rank algorithm for nonlinear equalization was proposed. The new algorithm reduces the samples for training the equalizer greatly. Furthermore, a pipeline implementation for the Volterra filter was presented, which reduces the computation complexity of the Volterra filter.In the third section, a carrier recovering module for 300Mbps TCM-8PSK demodulator and a blind equalizer for 800Mbps 8PSK demodulator were designed and realized in FPGA. Furthermore, an efficient debug method for high speed digital demodulator was proposed and used in practice.