| The MIMO-LPWAN technology is to solve the problems of existing LPWAN systems(such as NB-Io T,Lo Ra,etc.),when facing massive terminal access,which are high signaling overhead,low access success rate,and insufficient system capacity.In response to these problems,theoretical analysis and practical verification have been completed with an LP-WAN system with uplink MIMIO.To further improve the performance of the LPWAN system,it is necessary to extend the LPWAN system to support downlink MIMO.In this dissertation,in the MIMO-LPWAN downlink communication,a variety of beamforming schemes are designed for single-user and multi-user cases respectively,and tested in realistic scenarios.The test data is used to analyze the performance impact of various beamforming schemes in the MIMO-LPWAN system on the improvement of the received signal strength of the user terminal and the suppression of interference signals,thereby providing a suitable solution for the downlink beamforming of the MIMO-LPWAN system.In the MIMO-LPWAN system,due to the difference in the transmission and reception chain within each radio frequency module,the overall uplink-downlink channel of the system is not reciprocal.Using the uplink channel estimation information directly as the downlink channel estimation information will affect the MIMO-LPWAN downlink performance.One of the major tasks of this dissertation is to design and implement the reciprocity calibration in the MIMO-LPWAN system,and use the calibration factors obtained by the reciprocity calibration in downlink beamforming.The second major work of this dissertation is to design and implement conjugate beamforming and zero-forcing beamforming schemes with various antenna number forsingle-user beamforming and multi-user beamforming in the MIMO-LPWAN system,and complete them in realistic scenarios.For single-user downlink beamforming,conjugate beamforming schemes with various number of antennas were designed to verify the impact of number of antennas on downlink beamforming performance in MIMO-LPWAN systems.As the number of antennas increases,the received signal strength of users also increases.Compared with a fixed single antenna,8-antenna conjugate beamforming can improve the received signal strength by 9.06 dB,which is consistent with theory.For multi-user downlink beamforming,several commonly used beamforming algorithms and implementation complexity were evaluated,and two schemes,conjugate beamforming and zero-forcing beamforming,were designed and implemented.The test results show that in improving the received signal strength,8-antenna conjugate beamforming is the best choice;In terms of interference suppression capability,8-antenna zero-forcing beamforming has very obvious advantages over 8-antenna conjugate beamforming. |
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