Capacity Analysis And Array Topology Design For Compact Arrays

With the development of communication systems,the scale of array is becoming larger and larger.Massive MIMO has been one of the key technologies in the 5th generation mobile communication system,and is expected to achieve great development in the future.However,the challenges brought by the limited physical space resources need to be considered when deploying massive MIMO systems.When physical size is limited,in order to deploy more antennas,the element spacing will decrease and the array will become more compact.At this time,the electromagnetic mutual coupling effect between adjacent antennas cannot be ignored,which will change the radiation power and pattern of the antenna,and then affect the performance of the communication system.Therefore,for the layout design of the arrays with fixed aperture,two contradictory phenomena must be considered: On the one hand,when more antennas are deployed,the multiplexing effect is enhanced,the spatial degree of freedom is improved,and the system capacity can be improved.On the other hand,deploying more antennas in a fixed aperture array will reduce the element spacing,enhance the electromagnetic mutual coupling effect,and cause the loss of system performance.In this paper,for compact uniform linear array and compact uniform planar array,the relationship between the capacity and the array aperture is analyzed,and the optimal spacing is designed under the constraint of fixed array aperture.The main contributions are listed as follows:(1)Considering the mutual coupling characteristic of massive MIMO array under compact condition,the theoretical expression between the capacity and the number and spacing of elements is given.Firstly,the multi-user downlink transmission model and the mutual coupling model of the compact array are analyzed.Based on the classical Shannon formula,the capacity is characterized as a function of the array aperture by using the Toeplitz property of the coupling matrix and the Mar?cenko–Pastur theorem.Numerical simulation results show that the channel capacity obtained by the proposed algorithm is not different from Shannon formula,which verifies the accuracy of the algorithm.(2)Aimed at the two contradictory phenomena caused by changing the element spacing of compact massive MIMO array with fixed aperture,the optimal element spacing of compact uniform array is designed.Taking the maximization of capacity as the optimization goal,the optimization problem of the element spacing is established.Through equivalent transformation and relaxation,it is transformed into a convex optimization problem,which can be solved by one-dimensional search algorithms.In addition,the transmission system is built using Qua DRi Ga to simulate the real transmission scenario and verify the proposed optimal array structure.The results show that the optimal spacing proposed in this paper can significantly improve the capacity compared with the traditional half-wavelength spacing.