Research Of Broadband Quasi-orthogonal Time Division Multiplexing Transmission System

As a realization method of time-division multiplexing technology, Quasi-orthogonal time division multiplexing(QOTDM) technique can be applied to satellite transparent transponding systems due to its advantages of easy operation and low complexity of on-board signal processing. Therefore, it has great application value in satellite communication. In the thesis, a systematic theoretical study of QOTDM technique is made. Moreover, a broadband QOTDM transmission system is established by taking account of the characteristics of Ka-band satellite communication channels. And that the performance analysis and FPGA implementation of this transmission system is also provided. The main work and achievable research results of this thesis are as follows:1. The broadband QOTDM transmission system is investigated theoretically in detail. Firstly, the fundamental principle of the basic QOTDM transmission system based on the direct interweaved mode and its specific implementation method is presented. Secondly, an improved QOTDM transmission method based on multi-carrier modulated technique is proposed, which can enhance the ability to resist multipath fading and frequency selective fading.2. The channel characteristics of the GEO satellite communication on Ka wave-band is analyzed. The channel simulation model for GEO satellite communication on Ka wave-band is set up, and the effect of different weather conditions on the performance of the basic QOTDM transmission system is also analyzed. Simulation results show that the impact of envelope fading on this system is very serious, while that of phase distortion can be ignored.3. Synchronization techniques of the broadband QOTDM transmission system are studied. According to the analysis of the effect of sampling bias on the performance of this system,a system synchronization scheme utilizing the fixed threshold algorithm and the group-delay matched filter bands is put forward in this thesis. Simulation results demonstrate that this synchronization scheme is able to achieve the accurate sampling and frame synchronization, and that the synchronization precision of this system reaches 5% of the sampling interval.4. The FPGA implementation of the broadband QOTDM transmission system based on multi-carrier modulated technique is completed. The whole transmission system is modularized to many sub-modules and they are also designed on the FPGA hardware platform, respectively. Moreover, their hardware simulation analysis are also provided.