Downlink Transmission Of Broadband Satellite Based On QOTDM And Its FPGA Design

As a time division multiplexing method of continuous wave signals, Quasi-orthogonal time division multiplexing(QOTDM) technique is always used for the non-regenerative on-board processing, and it can also simplify the on-board equipment and improve the satellite downlink performance. Therefore, it is of important application value to utilize this technique in broadband satellite systems. This thesis deals mainly with the structure design of QOTDM based broadband satellite downlink transmission and its key techniques and completes its FPGA design simultaneously. The main work and research results of this thesis are summarized as follows:1. The fundamental principle of QOTDM technique is investigated, and a realization method of QOTDM transmission systems based on multi-rate transformation is proposed. The theoretical analysis shows that this method is able to improve the flexibility of on-board processing and the downlink bandwidth efficiency compared with the traditional realization approach of QOTDM transmission systems.2. A novel parameter adjustment algorithm for samples timing synchronization loop is put forward. In this algorithm, loop parameters of the accurate sample synchronization loop based on polynomial interpolation algorithm are determined through analyzing step response characteristics of this synchronization loop. Simulation results demonstrate that this algorithm is able to adjust unknown parameters of sample synchronization loop flexibly. Moreover, the accurate sample synchronization loop enables the system sampling precision to reach 2% of the sampling interval.3. A scheme combining the frame acquisition and coarse frequency offset estimation is presented, and the algorithm of parallel search based on FFT is adopted to realize frame synchronization. Simulation results show that this scheme requires only 0.113 ms to achieve the synchronization acquisition and reduces the frequency offset 40 times when there exists a frequency offset of ±30KHz in the satellite downlink.4. The FPGA design of the QOTDM transmission system based on multi-rate transformation technique is completed. Firstly, a simplified hardware implementation scheme of the parallel search algorithm based on FFT method is proposed. Secondly, a whole FPGA design scheme of the multi-rate transformation based QOTDM transmission system is given. Besides, the design of each sub-module of this system is completed on the FPGA hardware platform. Finally, the simulation verifies the correctness of the whole FPGA design is verified by means of computer simulations.