Lens Antenna Array-based Off-grid Channel Estimation And Anti-interference Research

To solve the problem of spectrum shortage caused by the surge in spectrum demand,a millimeter wave massive MIMO system has been widely used in next-generation wireless communication networks.Although the millimeter wave massive MIMO system can significantly increase the system capacity,it also faces many challenges including the serious path loss of millimeter wave systems and the radio frequency chain limitation in massive MIMO systems.Compared with a traditional uniform planar antenna array,a lens antenna array has the following advantages in solving the above challenges: First,it has a narrower beam and higher directivity,so it is more suitable for the millimeter wave communication;Second,it can solve the problem of the radio frequency chain limitation by combining a simple switching circuit,which greatly saves the cost.Therefore,the lens antenna array has begun to receive widespread attention in millimeter wave systems.In order to make full use of the advantages of the lens antenna array,an excellent channel estimation scheme is essential,so this paper studies the channel estimation scheme which is suitable for the lens antenna array,but it only performs uplink channel estimation to reduce the pilot overhead.Due to the path reciprocity of the lens antenna array,when multiple users use the same time-frequency resource,the inter-user interference may occur in the downlink,so this paper studies the anti-interference technology which is suitable for the lens antenna array.The main contributions of this article are as follows:(1)Firstly,this paper investigates and analyzes the key technologies of the current millimeter wave massive MIMO system,including antenna selection mechanisms,channel estimation schemes,and anti-interference technologies.The basic principles and technical details of typical channel estimation schemes are summarized and compared.Finally,the performance of various estimation schemes is discussed from the perspective of grid.(2)Secondly,this paper studies the channel estimation scheme which is suitable for the lens antenna array.Considering channel characteristics of the millimeter wave,this paper uses the spatial domain method.First,this paper proposes a two-stage antenna selection mechanism using the energy focusing characteristic of the lens and the sparsity of the millimeter wave channel.Based on the two-stage antenna selection mechanism,for scenarios requiring low computational complexity,the least square algorithm can be directly used to obtain the estimated channel response matrix.In order to obtain a more accurate channel response matrix and separate the angle of arrival,this paper further proposes an antenna selection based off-grid channel estimation scheme.The simulation verifies the effectiveness of the antenna selection mechanism and channel estimation scheme proposed in this paper.(3)Finally,in order to solve the problem of the multi-user interference,this paper uses the idea of space division multiplexing to re-select antennas for the interfering users,and considers the goal of maximizing the sum-rate and fairness of the system to establish optimization equations.To reduce the computational complexity,this paper divides all possible interference situations into three cases and considers them separately.For the most important primary antenna interference situation,this paper proposes a partitioned search algorithm to obtain a suboptimal solution,and removes the interference-free group to further reduce the computational complexity.The effects of different parameters on system performance are studied through simulation,and the effectiveness of the proposed scheme is verified.The full text consists of 5 chapters,with 22 figures,6 tables,and 72 references.