Design And Analysis Of Feedback Approach In Interference Alignment Communication System

For the decades of the development of wireless communications, the number of users become larger as well as the terminals.Accompanied by the increasing of the number of users, the interference problem becomes severely at the same time. The method used in the current traditional interference management approach such as noise processing or multiple access technology which makes such single user's efficiency of spectral low. In order to deal with overlapping interference between multiple users, Interference alignment(IA) adopt a new perspective by using pre-coding technology at the transmitting end to alignment interference in to the same sub-space and using decoding technology to cancel the interference at the receiving end. Interference alignment is such a technology which needs to know the global channel information, however in the most of the existed theoretical research, it is often assumed that all nodes have been known the CSI perfectly. On the contrary, the channel estimation error will always exist,as well as the feedback channel feedback overhead that bring adverse influence to the whole systems. Therefore, in the actual scenario, we must find a method of reducing error caused by the amount of channel information feedback overhead and the channel estimation, and design a rational frame structure.This paper relies on the National Natural Science Funding Project "Interference Management and Capacity of Wireless Networks" in order to study the impact of interference alignment performance feedback, and we propose a kind of interference alignment link control protocol and demonstrate the feasibility of such channel information feedback protocol in the TDD-LTE background.To begin with, we study the influence caused channel estimation and feedback to the performance of interference alignment. By studying the analog CSI feedback scheme,the authors deduce interference alignment's loss in performance comes from the non-orthogonal feature between the receiver's decoding matrix and the transmitter's pre-coding matrix, and such non-orthogonal feature comes from channel estimation error and the CSI feedback overhead. Further, compared with the CSI error, the author also demonstrate that the digital quantization error is almost negligible. In such known sources of error, the author also propose a algorithm under a TDD, by using a mixed interference alignment scheme relied on the the channel reciprocity. through simulation analysis,we demonstrate that the mixed interference alignment scheme cost a smaller expense feedback but greatly improve system performance.Further, the authors propose a radio-link control protocol could used in actual interference experiment platform. The proposed solution meets the characteristics of interference alignment algorithm based on the reference LTE-TDD radio frame structure,and it maximize the efficiency of the protocol for the target design. This protocol includes the selection of the scene, setting frame structure, pilot asserting and feedback mechanisms. According to the characteristics of MIMO-OFDM system, the author mentions mean square error, protocol efficiency and system rate of combined three users as the standard to demonstrate the feasibility of the time domain or frequency domain channel feedback scheme.To sum up, the computing simulation and operation results show that the feedback overhead could be less when adopting time domain channel feedback scheme.