Research On Pilot Design Scheme In Massive MIMO

Massive multiple-input multiple-output(MIMO)technology increases system capacity,spectrum efficiency and energy efficiency by deploying hundreds of thousands of antennas on the base station.It has received wide attention as one of the key technologies of 5G.The performance of massive MIMO depends to a large extent on whether the base station can obtain accurate channel state information(CSI).The actual wireless system often obtains the CSI of the current channel by transmitting pilots,but the consequent problems of pilot contamination and excessive consumption of pilot resources limit the further development of massive MIMO technology.This thesis studies the pilot design schemes in massive MIMO systems for the above problems.Firstly,a pilot reuse method based on continuous pilot reuse factor is proposed.This method groups users in a cell and different groups of users use different pilot multiplexing factors.The pilot reuse factor can take any value including a decimal.It increases the flexibility of pilot reuse method.A method for finding the optimal pilot multiplexing based on continuous pilot reuse factor is given.Theoretical analysis shows that the pilot reuse method has a certain improvement in spectral efficiency compared with the traditional single-factor pilot reuse method.Secondly,under the pilot reuse method based on continuous pilot multiplexing factor,combined with the priority of users,a continuous pilot reuse method with weighted spectral efficiency optimization is proposed.The method uses completely mutually orthogonal pilots between different priority user groups,and uses a continuous pilot reuse factor based pilot reuse method for the users with the same priority.A method for finding the optimal continuous pilot reuse factor with weighted spectral efficiency is given when the priority user ratio and weighting factor are given.Finally,a dynamic migration pilot allocation algorithm is proposed for the problem of pilot allocation when users move in massive MIMO systems.The algorithm selects a user to exchange pilots between two time slots for users who have migrated and does not change the original allocated pilots for other users.The complexity analysis and simulation results show that the proposed algorithm can considerably reduce the computational complexity and have similar spectral efficiency comparing with the traditional pilot allocation method.