High Speed Transmission System Of HF Communication Based On 3kHz Bandwidth

HF communication has been widely used as an important way of remote distance wireless communication. However, due to the multipath interference, fading and Doppler frequency shift in the HF channel, not only the synchronous receiving performance is affected, but also the received signal occurred severe intersymbol interference and signal distortion, so that the system transmission performance is decreased greatly. As to these problems, some key technologies, such as signal capture, channel estimation and equalization in the HF high speed system, have been designed and implemented in this thesis.Firstly, the synchronous scheme at the receiver side has been provided according to the frame structure and the transmission scheme in MIL_STD₁88₁10C with 3k Hz bandwidth. The synchronous technology with the sliding correlation FFT and the method of the frequency shift estimation based on the FFT peak position are emphatically discussed. At the same time, the method of detecting the data rate and the interleave ways in the synchronous leader sequence has been also provided.Secondly, several common channel estimation algorithms and the Turbo equalization technology in frequency domain based on the sub-blocks have been researched. According to the characteristic that the unknown data length is longer in the data frame structure, the interpolation algorithm at the unknown data position has been emphatically discussed. And in the equalization part, in order to avoid the equalization performance degradation because of ignoring the channel transition in the long unknown data part, the Turbo equalization technology in frequency domain based on the sub-blocks has been adopted. In the Turbo equalization algorithm, the MMSE equalization has been used at the first iteration stage because there was no prior information, while in the later iterations, the SIC equalization has been adopted. Finally, the system has been debugged and tested on the hardware platform, and the results meets the requirements of the military standard.