Research On Synchronization And Modulation Of Short-wave Data Communication

This paper is mainly concerned about the synchronization and demodulation for short-wave data communication and software realization of the digital demodulation system .In the first part, the characters of HF channel are briefly introduced. Taking account of multipath propagation, fading, dropper shift and external disturbances on short-wave channel, the frame form of instruction data is designed. A scheme of using Liner Frequency Modulation (LFM) signal passing through matched filter to implement quick and reliable bit synchronization is realized, and some related computer-based simulations are finished. A scheme of using Barker code identifier to realize frame synchronization is also discussed in details. The paper expounds three kinds of algorithm that demodulate FSK signal using Discrete Fourier Transform (DFT) method, Shifted Discrete Fourier Transform (SDFT) method, and Discrete Short Time Fourier Transform (DSTFT) method. Choices of system parameters are presented by using the simulation results which based on the demodulation performance of different system parameters of that algorithm. Their performances at different level of SNR and frequency offset are discussed by simulations, and improved algorithms are proposed. In the last part, the software design of this demodulation system is presented. Under the plat of TMS320C5409 digital signal processor, the synchronization program flow, modulation program flow, and demodulation program flow are designed.