| Modern short-wave communication, an important way of communication, is widely used in the area of long distance or mobile communication, owing to its various advantages such as low cost, easiness to be generated, convenience in maintenance, strong resistance to damage.Taking account of multipam propagation, fading. Doppler Shift and external disturbances on the short-wave channel, the whole framework of short-wave MODEM is presented in this dissertation. Finally the prototype of the MODEM based-on DSP is also developed. The primary endeavor and contributions of this dissertation are as follows:Firstly, the whole framework of the MODEM is presented .The fundamental theories and the key technologies of multi-channel parallel data modulation and demodulation are researched. A scheme, to use Linear Frequency Modulation (LFM) signal passing through matched filter to implement quick and reliable bit synchronization, and to use Barker code identifier to realize frame synchronization, is also discussed in details. In addition, the scheme to control bit error rate through CRC check is proposed.Secondly, the short-wave MODEM hardware platform . based-on DSP is developed, and on the basis of which, the algorithms such as. bit synchronization algorithm, multi-channel parallel modulation and demodulation algorithm, and CRC-16 table lookup algorithm are implemented.Finally, taking account of the characteristics of short-wave channel, and combining the hardware and software system demand of MODEM, data link layer protocol, as an important part of short-wave communication system, is designed preliminarily. |
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