The All-digital Demodulator For High-speed Burst Communication Design And Realization

GMSK, a typical continonous phase modulation, has the virtue of good performance of out-of-band suppression, constant envelope, excellent anti-jamming. It can cut down the interference of adjacent channel effectively and enhance the efficiency of non-linear power amplifier. It's widely used in areas of mobile communication, satellite communication and broadband data transmission of versatile Radar. Therefore, developing the research of all-digital GMSK modulation and demodulation based on FPGA is of important significance.Firstly, this dissertation introduces the present situation of digital modulation and demodulation technology, mainly a detailed description of the development and hardware platform of GMSK. Then, the article analyzes the basic principle and composition of GMSK system, mainly gaussian filter, phase shape and some important parts of demodulation included, such as digital down convert, burst detect, carrier synchronization, symbol synchronization and so on. Based on this, simulations are taken to verify the performance of every module by MATLAB. Advantages and disadvantages of two burst-detect algorithms are compared. Performance of three kinds of algorithms of open-loop carrier frequency offset estimation are analyzed. An feed-forward symbol sychronization based on digital and square filter algorithm is proposed. Next, it accomplishes the design of the hardware platform by Cadence, including both schematic, PCB design and board test. Finally, a scheme which is fit for practical application is proposed. A modulation and demodulation system for burst communication with lOMbps symbol rate is realized by FPGA. The performance of the designed system is tested and the simulation and realization results are both gived. It is proved that the system designed is corrected and could put to pratical use.