Research On Technology Of Fast Sounding And HF Link Establishing

HF communication is of the advantages of simple equipment,low cost and strong invulnerability,especially in the military is always one of the important means of communication command.HF communication mainly relies on the reflection of the ionosphere to achieve long-distance communication.The time-varying nature of the ionosphere causes HF channel into time-variant channel.In order to ensure the reliability of communication,HF channel must be sounded in real time,then the channel parameters are obtained and the high-quality communication frequency is selected.On the basis of the US military standard MIL-STD-188-141 B,a shortwave fast link establishment system is designed and implemented,which can realize real-time sounding,independent frequency selection and other functions.Chirp sounding technology be thoroughly researched in this thesis.First of all,the asynchronous fast link establishment protocol under the 3G-ALE standard is discussed,the frame structure of the burst waveform is introduced,and the data format is explained in detail.Then,the processes of sounding,link establishing,link breaking,scanning and the protocol data unit of each process are introduced in detail.Secondly,the hardware platform of the system is introduced.The ALE module of the system is mainly composed of two FPGAs,a DSP and a Master.FPGA2 completes the downconversion processing of the RF sampling signal,and outputs 360-channel baseband complex signal.FPGA1 completes the capture of 360-channel baseband complex signals,and selects the signal with the largest peak value and higher than the capture threshold.DSP completes the waveform sending,receiving and signal processing functions.The Master completes the control of the overall process of the system.Next,the system clock and interface design and the interface protocol between DSP and FPGA are explained.Then,the key technologies used in the system,including modulation technology,synchronization capture technology and CRC check technology and their implementation are introduced.At the same time,several spectrum sensing technologies are given.According to the analysis,the spectrum energy detection technology is selected to be applied to this system.The system is tested.The results show that the system indicators meet the project requirements.Finally,the principle of Chirp sounding technology,channel parameter extraction technology of Chirp sounding signal and the relationship between signal energy and delay and multipath delay spread are simulated and studied.At the same time,two solutions to the synchronization problem of Chirp sounding are proposed,and the synchronization process,advantages and disadvantages are explained.