RESEARCH OF Modern SATELLITE COMMUNICATION MODULATIONS TECHNIQUES AND SATELLITE TCP

The channel of satellite communication is described to be the typical band-limited and non-linear channel. Based on its special characteristic, we have the principles to select a type of modulation techniques for satellite communication systems. By theory and practice simulation, the several types of constant envelope modulation techniques are analyzed and compared, including theirs modulation principle, phase path, the modulated wave envelope, power spectrums, error bit rate and the influence of its power spectrums of the band-limited and non-linear, etc. Especially we have researched the IJF-OQPSK modulation technique, and the performance of its inter-symbol interference and time jitter free, and its strongly resisting of spectral spreading. By the eye diagram pattern, we have researched the ideal channel's respond-Nyquist Pulse, and have got its eye diagram model. Based on this , a type of base-band codes called IJF codes have been derived. By the pre-election wave function, simulation and digital hardware circuit has been done to realize the IJF coding. IJF-OQPSK is actually to modulate the IJF codes by the Offset Quadrature Phase Shift Keying. From the analyzing, there is 3 dB Envelope fluctuation of this modulation technique. We have designed a new type of IJF code to reduce the Envelope fluctuation, and have also got the reduced Envelope fluctuation IJF-OQPSK. It has faster roll off of the power spectrum and lower energy of band out. From the research of IJF-OQPSK, we draw the conclusion that,compared with BPSK, QPSK and MSK modems, in the band-limited and non-linear channel, it has nearly constant Envelope, less spectral spreading, better Pe performance and the less interference of the adjacent channel, et. So, it is more suitable for the satellite communication channel.The satellite communication has become an important apartment of Internet because of its unique ability to provide network access from almost everywhere on the globe. It is a tendency to Broadband accesses the Internet. Naturally, the TCP/IP protocols will be used in the satellite link. But because of the high latencies and high bit error and the dissymmetry satellite link, the end-to-end TCP performance will be sharply degraded, so it is necessary to modify the TCP/IP to improve its performance. The paper has discussed several solution schemes, which used to enhance the satellite TCP performance. We have pointed out the advantages and the shortages of these schemes, they need further investigation and discussed in the future.