Design And Implementation Of Shortwave Non-real Time Data Transmission System

Short wave communication has the advantages of flexibility,invulnerability and so on.Which has always been developed in military communications.However,because of the single function and the poor expansibility of the traditional short wave communication,which is difficult to adapt to the digital network and broadband demands of modern communication,The idea of software radio in short wave communication can solve this dilemma very well,which improves the quality of short wave communication.Digital modulation and demodulation technology is a key technology in short wave communication,and it is also the focus of software radio research,In this paper,A short wave non real time data transmission system is realized based on digital modulation and demodulation technology.First of.all,in the data transmission part,based on the Visual C++ compiling environment,the PC message transmission control software is developed,Designing and implementing the communication protocol between the host computer PC and the baseband modulation module,Then the baseband signal modulation circuit of software radio based on DSP chip is completed,The circuit schematic diagram and PCB circuit diagram and welding and debugging of the hardware circuit are designed,In DSP's compiling environment CCS3.3,The 4FTSK modulation program and other circuit sub module programs are developed by using C language and assembly language,and the message sending control software includes data interleaving module,coding module,format assembling module and serial communication module,The message sending control software completes the functions of encoding the original message data(Golay),interleaving and diversity processing,which achieved the data three diversity function.The baseband modulation terminal is composed of serial communication module,4FTSK modulation module,digital to analog conversion module,modulation signal balanced output module and sub module,Basing on the principle of direct digital frequency synthesis,the 4FTSK modulation function of the baseband signal is realized,and data demodulation and decoding software has been developed,The software has completed the decoding and decoding of the stored audio information,and the software demodulation part includes sample rate conversion module,matched filter module,low-pass filter module,likelihood decision module and its sub module,and the decoding part includes interleaving module,bit synchronization module,frame synchronization module,diversity combination module,Chase algorithm and soft error correction module.Finally,The performance of each part of the data transmission system is tested,and then the performance of data transmission and reception is tested.And the experimental results show that the performance of the system meets the requirements of the project design.