Research On Rate Adaption Techniques In The Elastic Troposcattering Communication

Elastic troposcattering communication technique is based on the rate adaption, which choses the best rate and modulation waveform through the channel estimation and transmission rate selection. The study of rate adaption technology is the key for building an elastic troposcattering communication system.This thesis analyzes the propagation mechanism of troposcatter channel. Based on analyzing slow and fast fading channels, a troposcatter channel model is built. Then the thesis endeavors to rearch on rate adaption techniques. Several rate adaptation algorithms are introduced, and their advantages and disadvantages have been analyzed. A rate adaptation algorithm is proposed, which is suitable for troposcatter channel. After presenting and analyzing some related SNR estimation algorithms, the thesis proposes an SNR estimation algorithm combining the spectrum of the signal, and has validated its performance through simulation. The simulation shows that this arithmetic has many advantages, such as broad estimate dynamic range and high testing precision.The thesis also researches on the design and implementation of rate adaption MODEM, including designs of the signal form and the MODEM modes, and endeavors to make them meet requirement of the information transmission. According to system requirements, the author has designed and implemented the adapt MODEM. Besides, a hardware implementation diagram of modem block is given, and based on this platform the FPGA program of the rate adaption algorithm is realized. Then the algorithm’s performance is tested. The results show that the SNR estimation algorithm can be applied to elastic scattering communication system. It has a good estimate performance both at constant channel and variable channel.Finally, the test system is established using the channel simulator, the rate adapt modem’s performance is tested in AWGN channel and is test the system’s performance increases. Results show that the throughput performance increases7times relative to the fixed rate scatter systems, and transmission reliability also be improved. At the same time, the feasibility of rate adaptation has been proved.