Study On MIMO-LTE Based Full Duplex System Interference Cancellation Technology

As we all know, spectrum resources are extremely precious in the field of wireless communication. However, the current LTE system duplex modes, including TDD(Time Division Duplex) and FDD(Frequency Division Duplex). No matter which kind of duplex mode, a node can not simultaneously transmit and receive signals in the same frequency band, and this resulted in the waste of half of the radio spectrum resources. Until CCFD(Co-frequency Co-time Full Duplex) technology has emerged, and achieve the true sense of the full duplex communication. However,recent research has found that the full duplex communication based on SISO can be realized. In this thesis the full duplex technique is applied to the LTE system based on MIMO. However, it is to realize the system there are three main technical difficulties. First, eliminate the local co frequency interference signal. Second,cancellation performance is affected by bandwidth. Third, it is too long to adjust the disturbance rejection circuit in order to cancellation the dynamic. In order to solve the above technical difficulties, and this thesis first analyzes the various components of the interference signal. Then through the design of specific solutions to various components of the interference signals are reduced to the noise floor of the acceptable range. Therefore, in this thesis, to cancel the local self-interference we used the multi-layered interference cancellation architecture: antenna interference cancellation, analog cancellation and digital interference cancellation. To cancel the local cross-interference, using the cancellation system based on self interference signals again, and the way through the cascade transmission function. So as to achieve the full duplex LTE system based on MIMO.In this thesis, we studied antenna interference cancellation utilize a antenna with a new circular isolator, and using this way can offset 20 d B around. We studied the three-antenna technology to achieve antenna cancellation. we also studied the analog cancellation technology. This method is the interference signal is constructed by the linear combination of the signal of the fixed delay device and the programmable attenuator. The attenuator coefficient is calculated by using the multidimensional gradient descent algorithm. Analog cancellation can be offset by50 d B. Because of the interference signal contains nonlinear components and transmission noise. Therefore, this thesis proposes a new cancellation structure, and using this structure to the digital base band interference signal containing a nonlinear component and a transmission noise can is eliminate by a linear digital interference cancellation. The method can be used to offset 44 d B.In this thesis, we also study analog cancellation technology of two kinds of mutual interference signals. One is way of copying analog cancellation system of the self interference signal for each interfering link. The innovative ways of this thesis is using the analog cancellation system based on self interference signals again, and the way through the cascade transmission function. The delay lines used in innovative ways are less than the traditional way. Using innovative ways of this thesis can reduce the time which adjust the analog cancellation system for adapt to the constantly changing environment.