Research On Interference Cancellation Techniques In Full Duplex Based On Polarization Information Processing

With the fast development of the fifth generation of mobile communication technology research, the requirement of massive data transmission speed is getting higher and higher, spectrum resources shortage problem is becoming increasely outstanding, hence it is especially important to develop the more efficient communication technologies with high transmission speed. Full duplex is a technology which enables the equipment to transmit signals and receive signals in the same frequency band simultaneously. Compared with the time division duplex (TDD) and frequency division duplex (FDD) systems, full duplex systems can achieve as much as twice the data transmission speed than them, and the key to realize the full duplex is to cancel the interference efficiently in the system.The research work is supported by Chinese National Nature Science Foundation Project "Research on power amplifier energy efficience based on cognitive and polarization signal processing (61271177)" and"Research on polarimetric self-interference cancellation in full-duplex system based on additive Gaussianized phase noise (61501050)". Based on the polarization information processing technology, developing the property of the signal polarization state that it is not affected by the nonlinearity of the power amplifier (PA), two kinds of self-interference cancellation methods are proposed in the single transmit antenna full duplex communication system and the MIMO full duplex communication system in order to cope with the PA nonlinearity. Meanwhile, an inter-user interference cancellation method is proposed in the multi-user full duplex system, and the main research work and achievements of this thesis are as follows:(1) The research status of full duplex communication as well as related polarization information processing research are summarized and analyzed. Fistly, full duplex communication technologies are summarized overview its main research contents, summarize the full duplex interference technologies in terms of its classification and research status,and point out the problems in existing interference technologies. Then polarization information processing technologies research status is summarized and analyzed, based on this, its application prospect in full duplex communication is discussed.(2) In the single transmit antenna full duplex communication system,the self-interference induced by the PA nonlinearity is a key limitation for the self-interference cancellation, aiming at canceling nonlinear self-interference, a method based on polarization mismatch is proposed to cope with the PA nonlinearity. Firstly, the self-interference cancellation at the RF terminal is designed. Some of the self-interference is eliminated by using the attenuator, the power divider and the phase shifter, and meanwhile the polarization state of the self-interference will not be changed. Secondly, taking advantage of the property that the polarization state of the self-interference is immune to the PA nonlinearity, the polarization information processing is implemented by using dual polarized antennas at the receiver, and then polarization mismatch matrix is constructed at the baseband to be orthogonal to the polarization state of the nonlinear self-interference induced by PA nonlinearity. Theoretical analysis and simulation show that the proposed method can effectively eliminate the nonlinear self-interference and improve the data rate of the system.(3) In the MIMO full duplex system, PA nonlinearity can cause nonlinear distortion in each transmit radio frequency (RF) chain, when the multi-channel nonlinear self-interference are superposed at the receiver, it can lead to serious cancellation performance deterioration.Aiming at addressing this problem, a self-interference cancellation method based on polarization oblique projection is proposed to cope with the PA nonlineartiy. In this method, the oblique projection operator is constructed by using the polarization state information matrices of the multi-channel self-interference and the desired signal, which can oblique project all the self-interference to the null subspace of the operator and oblique project the desired signal to range subspace of itself, which can eliminate the self-interference while retaining the desired signal. Since only the polarization state information of the signal is used to design the cancellation method, so this method can avoid to estimate the PA nonlinearity coefficients, which can eliminate the effect of the PA nonlineartiy. The upper bounds of the system's signal-to-noise ratio and data rate are derived. Finally, the simulation results show that the proposed method can effectively cancel the nonlinear self-interference induced by the PA nonlinearity, and system performance is improved compared with the existing cancellation methods in terms of the signal-to-noise ratio and the data rate.(4) In the multi-user full duplex system, because the co-channel interference channel information between uplink and downlink users is difficult to obtain, aiming at addressing this problem an inter-user interference cancellation method based on blind polarization oblique projection is proposed. The proposed method does not need to obtain the inter-user interference channel information, and constructs the oblique projection operator by using the covariance matrix information of the received signal, and then a denoising method based on subspace decomposition is proposed to obtain the covariance matrix information of the received signal. The final simulation results show that the proposed method can effectively cancel the interference between uplink and downlink users and improve the data rate of the system, and the more the number of antennas, the better performance of the proposed system is.