| HF frequency selection is a key technique about HF communications. The reflected wave of ionosphere has a significant window effect and the window of available frequencies varies with time. In early HF communication process, manual operation is used to select frequency and change frequency. Along with the development of various technologies, the second generation and the third generation of HF communication system have emerged, which realize the automatic link establishment, automatic link maintenance, link quality analysis and other functions. Because of this, HF link establishment efficiency is greatly improved. But the link establishment process takes a lot of time, its magnitude reached the second level. Taking into account a realistic situation, when users need to transmit a frame of short emergency data in a relatively short time, the above link establishment process can’t meet the time requirement. Therefore, a novel HF robust transmission technology is proposed, which leaves out the channel sounding and link establishment.Firstly, the basic characteristics, development history, current situation and development trend of HF communication are introduced. Then the process and characteristics of the link establishment about the second generation HF communication system and the third generation HF communication system are mainly explained.Secondly, the channel quality estimation techniques in HF communication are described, and the method of the signal to noise ratio estimation based on LMS algorithm is given. Then, a novel channel quality estimation method based on SNR and FER are proposed.Afterwards, the baseband simulation environment about this system is set up. The waveform design, coding, modulation, interleaving and channel selection are discussed, and a novel type of diversity and combining techniques is proposed.Soon, the simulation data is summarized and processed. The performances of the four channel and the every single channel are respectively analyzed, including throughput, average number of retransmissions and FER(Frame Error Ratio). The performances about the diversity combining algorithm mentioned in this thesis are analyzed.Finally, hopping sequence is described. To accommodate hopping sequence with this system, two different hopping sequence is designed, including interval non repeated scanning sequence based on prime sequence and random hopping sequence based on compression mapping. |
