Research On Nonlinear Distortion Suppression Technology Of Ka-band OFDM Satellite Communications

Ka-band satellite communication system has numerous advantages,such as large communication capacity,fast information rate,narrow antenna beam,small user terminal size,and more satellites accommodated by orbital planes.The current market demand for data information transmission rate is increasing.It will make Ka-band satellites an important method of future high-capacity multimedia applications and long-distance communications.Traditional digital modulation and demodulation schemes have been difficult to meet the requirements of Ka-band satellite communication.Orthogonal Frequency-Division Multiplexing(OFDM)technology is the cornerstone of 5G(fifth-generation)terrestrial wireless networks.Due to its many advantages,it will become the first choice for high-speed data transmission between the satellites and the earth.However,the most important obstacle to the application of OFDM technology to the Ka-band satellite system is its inherent sensitivity to nonlinear distortion.Because of OFDM symbols' high Peak-to-Average Power Ratio(PAPR),satellite High-Power Amplifier(HPA)generates a huge Output Back-Off(OBO),which greatly affects the efficiency of energy-starved satellite communication systems.In order to solve this problem,this thesis studies the principle and solution of nonlinear distortion of Ka-band OFDM satellite communication system.Since the channel environment and working environment between satellite communication and terrestrial communication are different,this thesis builds a wideband satellite OFDM system referring to DVB-S2 and DVB-S2 X standards that can be used in Ka-band,including transmitter,satellite transponder and receiver,and combines Bit-Interleaved Coded Modulation Iterative Decoding(BICM-ID)technology.On this basis,a computationally efficient nonlinear distortion model is established.Meanwhile the transmitter-based successive data predistortion algorithm is designed.And the receiver-based soft information iterative distortion elimination algorithm is introduced.The statistic two-dimensional normal distribution model is introduced to optimize the Log-Likelihood Ratio(LLR).In view of the evaluation and analysis of the performance of nonlinear distortion suppression algorithm under various conditions,this thesis employs two scientific and effective performance evaluation schemes.One is to use the information-theoretic channel capacity concept,and to plot channel capacity and Signal Noise Ratio(SNR)combined with HPA's OBO parameters.The other is the performance total degradation curve based on coded Bit Error Rate(BER)parameter.The simulation shows the gain of the two algorithms under different conditions and the joint operation,which shows that the system performance degradation caused by nonlinear distortion can be significantly reduced when using the proposed distortion suppression algorithm,and compared with receiver-based algorithm,the transmitter-based algorithm has higher gain.In addition,when the constellation mapping order becomes higher,the gain of both algorithms is improved,and when the frequency division multiplexing technique is used,the receiver-based algorithm gain is significantly reduced.