Design And Implementation Of Wireless Data Transmission Scheme Based On Shortwave Radio

For the characteristics of long-distance, easy-realized, and non-destroyed, HF (High Frequency) communication plays the irreplaceable part in military and people life. However, as society progressing, data service, not just voice communication, is required, which can't come true depending on traditional shortwave radio with voice function only. In this thesis, a shortwave data transmission system has been designed base on the existing shortwave radio, which can transmit computer data point-to-point.Firstly, this thesis analyzes the transmission characteristics of HF channel, and fixes on the system modulation scheme 2DPSK, according to the comparison of ASK, FSK and PSK (DPSK). Base on the structure of existing shortwave radios, communication scheme and system structure are designed, and particular functions are assigned to the parts of system. According to the band of SSB analog voice channel of shortwave radio, the thesis designs a SSB Modem, using C8051F330 SCM as the core, and introduces in detail structures and working principles of the interface circuit and the sending and receiving circuits. The realization scheme of modulation and demodulation in C8051F330 is given: in modulation, the wave sequences will be outputted by table look-at, and in demodulation, a particular method, using exclusive-or instead of multiplier, is adopted.Secondly, base on the hardwired connection of SSB Modem, the scheme of data transmission is designed, and related software is written. The system operation interface is designed using MFC, which provides with the functions of serial-port setting and sending-receiving of data (files and messages). The specific scheme of data sending-receiving is given: data transmits in frames, and data contents are recognized by the different frame-heads. The scheme is designed also in the thesis that the data exchange by setting and inquiring the state of CTS and RTS of serial-port. And the programs of (8,4) hamming coding-decoding, interweave coding-decoding of 8*152, differential coding and data sending-receiving are written. And the related programs of SCM are finished, that provide the SSB Modem with the functions of 2DPSK modulation-demodulationIn order to verify the performance of the system, the paper gave the test waveforms of some key processing results of SSB Modem, and the sending-receiving tests of messages and files were also performed. The test results showed that SSB Modem can work normally, messages and files can be received rightly, and the whole system can work in good state with the symbol transmission rate of 400B and the information transmission rate of 130bps.