Research And Implementation Of Digital Baseband Satellite Communication System For Remote Station

Software radio is a new technique that is used in the development of communication system. It can give the communication system high adapting ability and broad expansibility. So research of software radio can contribute a lot to the development of new generation communication system. This paper makes a deep research on the technique of software radio and discusses a lot about the key techniques in the communication field based on a satellite communication system which is designed by the author.QPSK demodulator is the first part and has been realized by two ASIC which are HSP50110/HSP50210. From discussing some details of the two chips, it can give a full explanation of QPSK demodulation and frequency acquisition and tracking. Also a common issue, false lock, has been introduced. Through the deduction based on Costas loop, it is clearly to understand the principium of the false lock and verify the false lock position. In the end, experimental data and chart are given to show the two chips can work well.Secondly, this dissertation focuses on the implementation of Viterbi algorithm by FPGA. There are two problems in the design of Viterbi decoder which are overflow of path metric and trace back algorithm and they have been resolved respectively by Two's Complement Modulo technique and pipeline memory management. Then this paper goes through the details of different modules of the Viterbi decoder and the simulation results of Modelsim have been given to testify the validation of the design.Thirdly, this dissertation researches on SNR Estimator and introduces two algorithms which are signal decomposition algorithm and Four-Order Moments algorithm. An improvement on Four-Order Moments algorithm is proposed and based on the simulation result, and there are two conclusions as follows:1. The signal decomposition algorithm can work well under enough SNR(>5dB), while it would lost accuracy for small signal.2. The Four-Order Moments algorithm can give wonderful estimation of small signal (>-10dB) and the improvement of this algorithm owns better result for extreme small signal(<-10dB).In the satellite communication system, signal decomposition algorithm has been realized by DSP and actual experimental results are given.Finally, an introduction of this satellite communication system is given and some improvements are made according to the weakness of the former design. Based on the improved one, the author has turned it into a real product which has all the functions finished. On the base of the implementation of the improved design, a whole new design scheme is proposed, a design that absolutely incarnating the software radio spirit. By utilizing the guiding frequency, the frequency acquisition and tracking can be realized more easily.