The Design Of The HF Sweeping Replying Sounding System And The Study Of Its Key Technology

The long distance communication can be realized by the shortwave communication with the assistance of reflection by the ionosphere.This method has the advantages as follows:no infrastructure is needed as the relay,the link can be maintained with low cost;and it is hard to destroy the reflecting medium.So theshortwave communication shows great importance in the fields of the military communication,emergent communication,disaster relief and so on.The ionosphere,which is the propagating medium of the shortwave communication,is influenced much by the sun and is randomly varied.So many users lead to the severe inference.In this condition,it is important to supply the optimal operating frequency for available communication quality.There are three ways realizing the frequency selection:the long-term forecasting,the short-term forecasting and the real-time channel evaluation.The oblique sounding and the third generation automatic link establishing technology are methods for the real-time channel evaluation.The oblique sounding uses the networking systems to achieve frequency management for all the communication equipments in the covering area.The third generation automatic link establishing technology is deployed in the transceiver,which can carry out both the sounding and the communication.A new method for the selection of the optimal frequency is developed based on the advantages of both the oblique sounding and the third generation automatic link establishing technology.The GPS synchronization and twice hand-shaking,which are applied in the third generation automatic link establishing technology,are adopted in the new system.The pulse compression,CFAR detection and time integrating,which are applied in the oblique sounding,are also adopted in the new system to overcome the hostile environment.The new system can realize the common function of the optimal frequency selection.In the condition of the harsh environment,the system can assist to determine whether the condition is caused by the ionosphere,the background noise or the interference,and whether the user should give up or adopt other technology to maintain the link.Burst communication becomes the main operating mode in the modern shortwave communication.The carrier synchronization,which is accomplished by the traditional phase-locked loop or the carrier recovery with the assistant data,has the disadvantage of wasting time and low efficiency.Frequency tracking in the hopping frequency technology is a serious problem in the military application.A new method using particle filter is employed to supply a solution for the carrier synchronization and frequency tracking in the hopping frequency technology.The conclusions in this paper can be mainly outlined as follows:1.A new protocol for the HF Sweeping Replying sounding system is developed,which contains the sounding process,the sounding time,the waveform,the signal processing methods and the rule of the frequency selection.The criterion is built.up for the design of the system.2.The architecture of the system and the mark of the components are designed and realized.The embedded architecture leads to the dwindling in size,the stable running and the real time property.3.The algorithm for the frequency selection is designed.The matched filtering,CFAR detection,and time integrating are used to process the signals.The SNR is extracted and sequenced for the selection of the optimal frequency.The experimental data of oblique sounding are processed to validate the algorithm and optimize the waveform.4.The programs for the DSPs and FPGA are developed.The programs for the DSPs are designed to control the process and realize the algorithm for the signal processing.The programs for the FPGA are designed to control the transmitter and receiver,and supply interface for the interaction of the DSPs and the host machine.The programs for the DSPs are loaded with the flash to maintain the running of the system.5.The experiments are designed and accomplished to validate the performance of the system.6.A new method using particle filter is employed to realize the carrier synchronization in the burst communication.The algorithm is efficient for large frequency offset in the simulation.Frequency tracking in the hopping frequency communication is also fast accomplished by the particle filter.