Research On Space-time Channel Reconstruction Theory And High-Presicion Reconstruction Methods

Massive multiple-input multiple-output(MIMO)is regarded as an important technique for the fifth generation(5G)mobile communication,which can provide users with reliable and fast data transmission.How to quickly and reliably evaluate the performance of massive MIMO devices to accelerate the development and deployment of 5G systems is an urgent challenge.Given that the field tests under realistic propagation environments are unreproducible and the conducted testing will no longer be applicable for massive MIMO devices,the dissertation focuses on the over-the-air(OTA)channel reconstruction theories and methods for the massive MIMO OTA test.The main contents and innovations of this dissertation includes:1.Research on OTA channel reconstruction method for assessing directional-antenna devicesUnlike the MIMO OTA testing,the BS is usually equipped with a large number of directional-antennas which will produce different gains for directions of received/transmitted signals,affecting the weights of probes in massive MIMO OTA testing,thereby defecting the accuracy of channel emulations.Therefore,the antenna pattern of the devices under test(DUTs)should be taken into account in the target channel when reconstructing OTA channel for testing massive MIMO BSs.In addition,the target Doppler profile is accurately recreated in OTA testing when testing omni-directional antenna devices under the prefaded signal synthesis(PFS)technique which requires that each probe contributing to the cluster has independently and identically distributed(i.i.d.)fading sequences.However,the DUTs may consist of directional-antennas which produce different antenna gains in impinging angles.The Doppler emulation may be inaccurate using conventional PFS technique due to neglecting the dependency of the Doppler spectrum on impinging ray angles.Rather than the conventional PFS method,an improved channel emulation method is proposed in this dissertation,which outperforms the conventional PFS method for Doppler emulations while unaffecting the reconstructed spatial characteristics.The dissertation proposes an effective research method for channel emulation more accurately to evaluate the performance of directional-antenna devices,which can supplement the theory of the channel emulation.2.A non-Kronecker structured PFS method for channel emulationThe target channel is a typical geometry-based stochastic channel model(GBSC),which is non-Kronecker structured.However,the emulated channel under the conventional PFS technique is Kronecker structured in OTA testing.In other words,the surrounding environment on one end of the link only affects the correlation between the antennas at one end of the link,but has no effect on the spatial correlation at the other end of the link,resulting in the statistical independence between the antennas at both ends of the link.Therefore,even if the spatial correlation of the target channel can be reconstructed accurately,the spatial-time characteristics of the channel can not be reconstructed accurately.In order to reconstruct the target channel accurately,the spatial correlation based metric is unapplicable for channel evaluation in OTA testing.Therefore,a non-Kronecker structured PFS method is proposed in this dissertation.Furthermore,an objective function of spatial-time correlation with constraint conditions is established to address the aforementioned problem,thus improving the accuracy of the link characteristics and guaranteeing the accuracy of the marginal correlations for emulation in OTA testing.This study is of great significance for channel emulation in an anechoic chamber,which can supplement the existing channel reconstruction schemes.3.The method for channel emulation based on spatial spectrum metricThe beamforming is regarded as an important performance of the massive MIMO BS,which can greatly improves the performance of 5G communication systems.However,the spatial correlation which is used as the metric may be less relevant for massive MIMO OTA testing due to ignoring the beamforming of the BS.Therefore,the selected metric should be able to emphasize the characteristics of the massive MIMO array.This dissertation will propose an angular spectrum based metric to determine probe antenna weights to characterize the beamforming of a massive MIMO BS,which can improve the accuracy of the channel emulation in terms of array performance and increase the accuracy of measuring massive MIMO BSs.4.Reconstruction method for dynamic channels based on amplitude and phase modulation(APM)networkIn massive MIMO OTA testing,it is very important to establish dynamic channel environments to evaluate the real end-to-end performance of millimeter wave(mmWave)devices.In view of the drawbacks of the current mm Wave OTA testing system with switches,the dissertation will propose an APM network,which is fully-connected and digital,to replace the mechanical switch in the multi-probe anechoic chamber(MPAC)setup.The MPAC setup with a cascaded model of the APM network and the channel emulator(CE)is presented.Rather than the existing mechanical switches,first,the proposed dynamic channel reconstruction method does not need to increase the number of channel emulators,and it can more accurately reconstruct the radio channel environment in the test area and control the cost of the system as much as possible;second,the proposed cascaded MPAC setup can overcome the shortcomings of mechanical switches,which not only greatly improves the dynamic performance in the test area but also is achievable;third,the channel reconstruction method based on a APM network is not only applicable for dynamic channel emulation,but also for static channel emulation.The method proposed in this dissertation has a specific guiding significance for the design of mm Wave OTA test system.As a summary,by taking into account the technical characteristics of massive MIMO equipments,the dissertation proposes a channel reconstruction method for measuring directional-antenna equipments,a non-Kronecker structured PFS method for channel emulation,a channel reconstruction criterion based spatial spectrum similarty,and a channel reconstruction scheme cascaded with a new APM network for dynamic channel reconstruction.These theories and methods can improve the accuracy of the channel emulation and provide theoretical support for massive MIMO OTA testing.