| The International Telecommunication Union(ITU)gives performance metrics for the Fifth Generation Mobile Communication System(5G),including 20 Gbit/s peak data rate and 100 Mbit/s user experience data rate.Millimeter-wave bands have a wealth of available spectrum resources,e.g.,more than 1 GHz of continuous spectrum,that can greatly increase system throughput.Thus,millimeter wave technology has received much attention as one of the key technologies of 5G.Due to the increase in frequency,the propagation characteristics of millimeter waves are quite different from those of conventional microwaves.Studying the characteristics of millimeter-wave mobile communication channels is the key to the research and application of millimeter-wave technologies.And,it is necessary to study the millimeter wave mobile communication channel,understand the millimeter wave propagation characteristics,and model the millimeter wave channel,and then use the millimeter wave channel model to verify the performance of the millimeter wave technology.In this paper,we study the millimeter wave channel measurements and modeling,millimeter wave wideband channel parameter estimating and effects of millimeter wave characteristics on millimeter wave technologies.The specific research work and innovations are as follows:(1)Millimeter-wave and wideband channel measurement platform construction and measurement.The millimeter-wave and wideband channel measurement platform is the precondition for studying the characteristics of millimeter-wave channels.Currently,most channel measurement platforms can only work at low frequencies or have limited bandwidth(below 200 MHz).This paper introduces the basic principle of channel measurement,and gives a detailed method for building a millimeter-wave and wideband channel measurement platform,including Single Input Single Output(SISO)measurement platform and Multiple Input Multiple Output(MIMO)measurement platform.The built millimeter-wave measurement platform has an 800 MHz bandwidth,2.5 ns delay resolution,and a measurement distance range of over 200 m.Based on the built-in millimeter-wave measurement platform,we conducted millimeter-wave channel measurements in three common communication scenarios,including the urban microcell(UMi)scenario,indoor office scenario,and indoor conference room scenario.The UMi scenario and indoor scenario are typical scenarios for 5G enhanced mobile broadband communications evaluated by the ITU.(2)Millimeter-wave channel modeling in indoor office and conference room scenarios.The indoor scenario is one of the typical environments for 5G enhanced mobile broadband communications evaluated by the ITU.At present,the research on millimeter wave channel characteristics for indoor scenarios is relatively insufficient,mainly focusing on the study of large-scale fading characteristics.Based on the channel data collected by the millimeter-wave channel measurement platform in indoor office and conference room scenarios,the millimeter-wave channel characteristics of these two common mobile communication scenarios,including large-scale fading characteristics and small-scale fading characteristics,are studied.At the same time,the channel parameter models are given,including path loss,shadow fading,root mean square(RMS)delay spread(DS),Ricean factor,azimuth angle spread,elevation angle spread,cluster number and intra-cluster RMS DS.Then,statistical results of these channel parameters are modeled and model parameters are given.(3)Millimeter-wave wideband Ricean factor estimation and deviation analysis.The traditional method of moments can only be used to estimate the Ricean factor of narrow-band time-varying channels,and it can not be used to estimate the Ricean factor in millimeter wave wideband channels.This paper proposes a wideband Ricean factor estimation method,which uses the method of moments to extract the Ricean factor from the channel frequency domain response samples.This method can be applied to millimeter-wave wideband channels and does not require that the channel is time-varying.Therefore,the proposed method can extract the Ricean factor from the millimeter-wave fixed-point measurement data.Secondly,the estimation bias of the proposed method is derived.Theoretical analysis and simulation analysis show that the estimation bias is related to the channel Ricean factor,the number of samples,and the correlation between samples.Besides,the estimation bias increases as the channel Ricean factor increases;the estimation bias decreases as the number of samples increases;the estimation bias increases as the correlation between samples grows.Finally,this paper uses the proposed Ricean factor estimation method for wideband channel to extract the Ricean factor in the millimeter wave channel in the UMi scenario,and studies the distance dependence characteristics of the Ricean factor in this scenario.(4)Performance analysis of the millimeter-wave hybrid beamforming(HBF)technology.The design of millimeter-wave HBF algorithms usually only considers the algorithm optimization itself,rather than the effects of channel characteristics on the algorithms.Through simulation experiments,this paper studies the effects of millimeter-wave channel correlation,channel sparsity and channel spatial dispersion on HBF algorithms.Simulation analysis shows that the change of channel characteristics has different effects on different HBF algorithms,which depends on the principle of HBF algorithms.When the HBF algorithm uses the complete channel information for precoding design,the increase of the degree of freedom of the channel will improve the performance of the HBF algorithm.In summary,this paper aims at the design requirements for 5G,and studies the characteristics of millimeter-wave channels for the application of millimeter-wave technologies.Firstly,by constructing a millimeter-wave channel measurement platform,millimeter-wave channel data is collected in three common mobile communication scenarios(UMi,indoor office,indoor conference room).Secondly,using the channel parameter extraction algorithm,the millimeter-wave channel parameters are extracted,analyzed and modeled from the acquired millimeter-wave channel datas;the millimeter-wave channel models in the indoor scenario are given.Thirdly,a new Ricean factor estimation method is proposed,and the correctness and estimation bias of the method are verified by simulation and theoretical bias.Finally,the effects of millimeter-wave channel characteristics on the HBF algorithms are analyzed.The above research results provide the basis for the research and application of 5G millimeter wave technology. |
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