Research On Techniques Of Downlink Transmission Of Ka-band Mobile Satellite Based On QOTDM

As an efficient continuous wave time division multiplexing technique,Quasi-orthogonal time division multiplexing?QOTDM?technique applied to the satellite downlink transmission system,can increase the user capacity,reduce the complexity of on board processing.Ka-band frequency is rich in resources.Therefore,it is of great application to study the transmission characteristics of QOTDM in Ka-band mobile satellite downlink.In this thesis,the key technique of Ka-band mobile satellite downlink communication system based on QOTDM is studied,and the design of the transmitter sub-module is given.The main work of this thesis and the research results are as follows:1.The realization procedure of QOTDM technique at the transmitter and receiver is investigated,and an improved QOTDM transmission scheme is proposed.The theoretical analysis shows that the improved QOTDM transmission system can eliminate its spectrum gap,reduce the bandwidth of the downlink and increase the bandwidth efficiency of the downlink compared with the basic QOTDM system when transmitting the data of the same information rate.2.Aiming at the rain attenuation channel of the Ka-band,under different modulation modes.,the influence of different weather conditions on the performance of improved QOTDM transmission system is analyzed.The simulation results show that the envelope fading determines the performance of the transmission system under BPSK modulation.The envelope fading and phase fading determine the performance of the transmission system in 8PSK modulation mode.Also,the improved QOTDM transmission system is the same as the basic QOTDM system and the single carrier system in the Ka-band rain attenuation channel.3.Aiming at the multipath fading channel of the ground part of Ka-band mobile satellite channel,an efficient PN-assisted QOTDM frequency-domain equalization model is proposed.At the transmitter,the PN sequence and the data QOTDM transmit are alternately transmitted at intervals.At the receiver,a channel estimation algorithm using the PN sequence as a synchronization and training is designed,and a frequency domain equalization algorithm is proposed which uses PN sequence and estimated time domain channel information to eliminate inter-frame interference and reconstruct cyclic convolution.The equalization algorithm can use multipath energy to suppress noise interference,and improve the spectrum utilization and data transmission efficiency of QOTDM.The simulation results show that when the bit error rate is 10^-3,compared with the orthogonal frequency division multiplexing system,the model can obtain the signal-to-noise ratio gain of about 5dB under the condition of slow time-varying Rice fading channel.4.The FPGA design of transmitter module based on the improved QOTDM system is given.The hardware design of each sub-module of the transmission module is transmitted.Finally,the rationality of the FPGA design of the transmitter is verified by simulation.