Research On Diversity Receiving Technology Of High Frequency Multi-carrier Signal

Compared with other communication methods,high frequency(HF)communication has a longer communication distance.At the same time,the device used in HF communication is small in size,flexible and convenient to use,and it can still ensure effective communication under extremely harsh conditions.Its unique advantages are irreplaceable by other communication methods.By combining HF communication with multi-carrier modulation,HF communication has the advantages of fully utilizing spectrum resources,combating multipath fading and high-speed data transmission,and is getting more and more widely used in wireless communication.The key technologies involved in diversity reception and reconstruction processing for HF multi-carrier communication systems is studied and made emulate analysis in this paper,including signal acquisition,time-frequency synchronization,soft demodulation about differential modulation,diversity combination and target signal reconstruction.Major work is described as follows:The first chapter introduces the research background and significance of the paper from three aspects of HF channel,HF communication and multi-carrier modulation technique,and gives the research status and development from three aspects of time-frequency synchronization,differential demodulation and diversity combining under HF channel.In the second chapter,the statistical model of the HF channel is analyzed and gives the key channel parameters involved in the simulation process;secondly,this chapter takes orthogonal frequency division multiplexing(OFDM)signals as the main signal model and introduces the principle and implementation of multi-carrier modulation;this chapter also takes the transmission signal of the ARD9900 modem as the main research object,introduces its signal specifications,and sets a unified signal standard for subsequent simulation tests;The design of the ARD9900 HF multi-carrier signal diversity receiving and processing system is described in terms of single-channel demodulation,multi-diversity processing,and combined signal reconstruction.The third chapter studies the time-frequency synchronization module in the ARD9900 HF multi-carrier signal diversity receiving and processing system.It mainly studies the symbol-level target signal acquisition and coarse synchronization algorithm based on the signal-to-noise ratio(SNR)of the preamble pilot,Sampling-level timing synchronization based on early-late gate synchronization algorithm with preamble pilot SNR and energy decision timing synchronization algorithm with reference to single carrier signal.In this chapter,Candan frequency offset estimation algorithm based on preamble pilot and multiple square spectrum of reference single carrier signal frequency offset estimation algorithm are also been studied.The above algorithms are simulated the performance under different channel conditions,and compared with different algorithms of the same function,analyzed the advantages and disadvantages,and at the same time organically combined to minimize the synchronization error and the HF multi-carrier diversity reception processing system,guarantee the robustness of synchronization and provides a strong guarantee for subsequent demodulation,combing and reconstruction.In the fourth chapter,the differential soft demodulation,merging and reconstruction modules of the ARD9900 shortwave multi-carrier signal diversity receiving and processing system are studied.The differential soft demodulation algorithms mainly include single-symbol differential quadrature reference phase shift keying(DQPSK)differential soft demodulation and dual-symbol DQPSK differential soft demodulation.The combing algorithms mainly include selective combing,equal gain combing,maximum ratio combing,hybrid combing,and Max-SNR non-coherent hybrid combing.ARD9900 signal reconstruction is studied from two aspects of modulation data subcarrier reconstruction and noise subcarrier reconstruction.Simulate the research algorithm under different channel conditions and diversity numbers.By comparing and analyzing different algorithms with the same function,the algorithm with better performance and lower complexity is selected as the final demodulation and merging algorithm.The reconstructing multi-carrier waveform-level signal is recaptured,synchronized,and demodulated to verify the final performance of the system.