Research On The Interference Cancellation In Multi-user MIMO Systems

MIMO technology can improve the reliability and availability of the system with multi-antenna equipped at transmitters and receivers,which is one of the key technologies of 4G and 5G.In the actual system,multi-user send signals to the base station or receive signals from the base station simultaneously,which result in multi-user interference and affect the communication quality.Therefore,the interference cancellation method is critical to improve the performance of MIMO systems.In this paper,the advantages and disadvantages of the existing interference cancellation method in different scenarios are analyzed.Aiming at the problems in the existing scheme,the corresponding improvement methods are put forward.The main works and innovation of this paper are as follows:(1)An interference cancellation method based on space time code and dual-precoding is proposed for MIMO X channels.Space-time code with dimension of 3×6 is adopted at each user.Each codeword is dual-precoded,which make the undesired codeword alignment and make the desired codeword orthogonal transmission.At the receivers,the zero forcing algorithm is used to eliminate the interference codewords,and then the wanted codewords is obtained by the orthogonal characteristics.(2)A new space-time processing scheme is proposed for MIMO interference channel with three users.The multi-user interference can be eliminated without feedback information.All of the user adopt the space-time code with dimension of 2 ×2,while consists of 4 modulation symbols and have an Alamouti structure.The interference at the third receiver is cancelled by introduction of two columns zero vectors in each codeword,and the interference at the first two receivers is reduced as well.Then,the multi-user interference is cancelled by separating codewords at the first two receivers.(3)An interference cancellation method based on space-time code and precoding is proposed for MIMO Y channel with three users and a relay node.All of the users and the relay node adopt Alamouti code with 2 ×2.During the MA stage,all the nodes exchange the CSI.Each codeword pair is aligned through precoding designed based on the CSI.Then each codeword pair is separated and the elements of each codeword pair is estimated.During the BC stage,the interference between codewords pair is eliminated by using the orthogonal characteristic of effective channel matrix of Alamouti codeword,and the CSI is not required during the BC stage.(4)An efficient uplink transmission method is proposed for large-scale MIMO system,which consists of K users and a base station.Precoding matrices with Alamouti structure are appointed between the users and the base station.The number of Alamouti code transmitted each time at each user is determined by the number of antennas at the base station and the number of users.All of the Alamouti codewords are transmitted after precoding.Using the orthogonal property of effective channel matrix for Alamouti code,the base station adopts iterative method to separate each codeword and decode each element of the codewords.