Research On Technology Of Interference Management In Cognitive MIMO System

Interference management is one of the key technologies for cognitive radio system to implement spectrum sharing.Compared with traditional cognitive radio systems,interference management of cognitive MIMO system is faced with new opportunities and challenges: on one hand,the introduction of MIMO adds spatial information to the interference,making interference management issues more complicated;on the other hand,MIMO technology provides spatial domain based solutions to interference management because of its advantage in spatial processing.Based on the analysis of new features and possible problems that may arise of co-channel interference of cognitive MIMO system,this paper explores effective methods of interference management in order to achieve highly efficient spectrum sharing and ease the growing contradiction between supply and demand of spectrum resource.The main work and research achievement of this paper are as follows:1.System modeling according to typical scenarios of cognitive MIMO spectrum sharing is conducted here,which forms the basis of this research.This paper then elaborates on the necessity of implementation of interference management through analyzing the influence of interference on the channel capacity of primary user from the perspective of information theory.Finally,based on two interference management methods,i.e.,interference suppression and interference elimination,the author analyzes and deduces the influences of interference management on the channel capacity and degree of freedom(Do F)of secondary user respectively,providing theoretical guidance for the follow-up detailed design of interference management.2.A partial projection interference management algorithm based on the idle dimension of primary users is proposed for cognitive MIMO point-to-point channel.Firstly,the spatial transmission features of primary user are analyzed and the idle dimensions of primary transmission are explored as a new kind of access opportunity for secondary user.Then,in order to eliminate primary user's interference,the secondary transmission channel is projected to the idle dimensions of primary user based on analysis of the spatial structure of primary user's interference signal.Finally,the secondary transmission is optimized by singular value decomposition(SVD)and water-filling of the equivalent projected channel.Theoretical analysis and simulation results show that,compared with the classical projection-based algorithm,the proposed algorithm with better applicability enables the secondary user to achieve higher transmission rates.3.A gradational interference management algorithm based on joint transceiver SLNR is proposed for cognitive MIMO broadcast channel.Based on the fundamental differences between primary and secondary user in the spectrum access privileges,the proposed algorithm proposes different processing methods for two different types of co-channel interference: the primary user's interference is forced to zero by introducing orthogonal projection preprocessing at secondary base station,so as to realize orthogonal transmission of primary and secondary users.Then,for the secondary downlink channel,after incorporating the postprocessing into the definition of SLNR,the co-channel interference between secondary users is also effectively suppressed by jointly design the precoding and postprocessing matrix iteratively,taking the modified SLNR as the optimization target.Theoretical analysis and simulation results show that the proposed algorithm can effectively suppress interference,relax the requirements of antenna configuration,and enable the secondary system to obtain better BER and sum-rate performance when compared to classic algorithms.4.An alternating minimization based joint interference alignment algorithm is proposed for cognitive MIMO interference network.The algorithm covers the two types of co-channel interference existing in the system in a comprehensive way,establishes a problem model of joint interference alignment and deduces the upper bound of DoF accessible to secondary users and theoretical feasibility conditions of the joint interference alignment.Then,as to the issue of joint interference alignment,the joint alignment of both types of interference can be achieved provided that a new indicator of optimization of interference alignment that goes for both types of interference is introduced and that the indicator is minimized through alternating design of the preprocessing and postprocessing matrix.Theoretical analysis and simulation results show that the proposed algorithm realizes nearly the same performance in terms of interference suppression and sum-rate of system as the classic iterative cognitive interference alignment algorithm under the same conditions;what's more,the former,which is not premised on channel reciprocity,can be applied to a far wider range than the latter.