A novel wideband space‐time channel simulator based on the geometrical one‐ring model with applications in MIMO‐OFDM systems

In this paper, we extend the geometrical one‐ring multiple‐input multiple‐output (MIMO) channel model with respect to frequency selectivity. Our approach enables the design of efficient and accurate simulation models for wideband space‐time MIMO channels under isotropic scattering conditions. Two methods will be provided to compute the parameters of the simulation model. Especially, the temporal, frequency and spatial correlation properties of the proposed wideband space‐time MIMO channel simulator are studied analytically. It is shown that any given specified or measured discrete power delay profile (PDP) can be incorporated into the simulation model. The high accuracy of the simulation model is demonstrated by comparing its statistical properties with those of the underlying reference model with specified correlation properties in the time, frequency and spatial domain. As an application example of the new MIMO frequency‐selective fading channel model, we study the influence of various channel model parameters on the system performance of a space‐time coded orthogonal frequency division multiplexing (OFDM) system. For example, we investigate the influence of the antenna element spacings of the base station (BS) antenna as well as the mobile station (MS) antenna. It turns out that an increasing of the antenna element spacing at the BS side results in a higher diversity gain than an increasing of the antenna element spacing at the MS side. Furthermore, the diversity gain brought in by space‐time block coding schemes is investigated by simulation. Our results show that transmitter diversity can significantly reduce the symbol error rate (SER) of multiple antenna systems. Finally, the influence of the Doppler effect and the impact of imperfect channel state information (CSI) on the system performance is also investigated. Copyright © 2009 John Wiley & Sons, Ltd.     

Measurement‐Based Stochastic Cross‐Correlation Models of a Multilink Channel in Cooperative Communication Environments

In this paper, stochastic models for the cross‐correlation of multiple channels are established based on measurement data collected using a wideband multiple‐input multiple‐output relay Band Exploration and Channel Sounder system at 3.7 GHz. We propose models for the cross‐correlation characteristics of large‐scale parameters (LSPs) between two links, that is, the base station and mobile station (MS) link and the relay station and MS link. The LSPs include shadow fading, Rician K‐factor, delay spread, angle spread of arrival, and angle spread of departure. Furthermore, models are established for the cross‐correlation of the small‐scale fading in the impulse responses of two links. The statistics of these model parameters are investigated as functions of geometrical features of the multilink. They are extracted from a large amount of cross‐correlation observations, which are obtained in three measurement sites along more than one hundred measurement routes. These models can be used together with the standard single‐link channel models for the generation of correlated components, for example, path clusters, in two separate channels.     

Simulation Models for Investigation of Multiuser Scheduling in MIMO Broadcast Channels

Spatial correlation is a result of insufficient antenna spacing among multiple antenna elements, while temporal correlation is caused by Doppler spread. This paper compares the effect of spatial and temporal correlation in order to investigate the performance of multiuser scheduling algorithms in multiple‐input multiple‐output (MIMO) broadcast channels. This comparison includes the effect on the ergodic capacity, on fairness among users, and on the sum‐rate capacity of a multiuser scheduling algorithm utilizing statistical channel state information in spatio‐temporally correlated MIMO broadcast channels. Numerical results demonstrate that temporal correlation is more meaningful than spatial correlation in view of the multiuser scheduling algorithm in MIMO broadcast channels. Indeed, the multiuser scheduling algorithm can reduce the effect of the Doppler spread if it exploits the information of temporal correlation appropriately. However, the effect of spatial correlation can be minimized if the antenna spacing is sufficient in rich scattering MIMO channels regardless of the multiuser scheduling algorithm used.     

三维空间统计信道的空时参数AOA和TOA分析

针对在均匀散射体分布以及空间对称的3-D室内移动通信环境,细化了对于基站（BS,Base Station）以及移动台（MS,Mobile Station）端空间角度的研究。对在指向性天线覆盖下的室内微小区移动通信环境下,模型能估计多径衰落信道的重要空时信道参数,如波达信号在水平面以及竖直平面上的信号到达角度（AOA,Angle of Arrival）以及到达时间（TOA,Time of Arrival）。数值仿真结果与2一D多径衰落信道对比表明本模型的信道参数估计结果符合理论和经验,扩展了3一D空间统计信道模型的研究和应用。     

Blind downlink channel estimation for TDD‐based multiuser massive MIMO in the presence of nonlinear HPA

In time division duplex (TDD)‐based multiuser massive multiple input multiple output (MIMO) systems, the uplink channel is estimated and the results are used in downlink for signal detection. Owing to noisy uplink channel estimation, the downlink channel should also be estimated for accurate signal detection. Therefore, recently, a blind method was developed, which assumes the use of a linear high‐power amplifier (HPA) in the base station (BS). In this study, we extend this method to a scenario with a nonlinear HPA in the BS, where the Bussgang decomposition is used for HPA modeling. In the proposed method, the average power of the received signal for each user is a function of channel gain, large‐scale fading, and nonlinear distortion variance. Therefore, the channel gain is estimated, which is required for signal detection. The performance of the proposed method is analyzed theoretically. The simulation results show superior performance of the proposed method compared to that of the other methods in the literature.     

3G共存干扰分析

在WCDMA和CDMA2000组成的共存系统中,邻频干扰是影响系统性能的重要因素,分别从上下行链路两个方面理论分析了由CDMA2000系统引起的邻频干扰对WCDMA系统产生的影响。仿真结果表明,基站与移动台之间的距离、干扰移动台数、两系统之间的保护带宽都将不同程度地影响WCDMA基站的最小允许接收功率和WCDMA移动台的SIR,从而导致系统容量的下降。     

无线通信系统的MIMO信道测量与建模

在多径信道中,使用多天线的M IMO(多输入多输出)无线系统能够比单天线系统提供更高的信道容量,而信道测量与建模是决定通信性能的一个重要因素。文中对目前国际范围内现有的M IMO信道测量和建模进行了研究,并进行了归纳和分类,同时分析了M IMO信道测量和建模的方法,指出了目前信道测量和建模中存在的问题,并给出了一些针对M IMO信道测量系统设计的建议。     

天线匹配对莱斯信道下紧凑MIMO系统性能的影响

深入研究了存在天线互耦和空间相关时,天线匹配网络对莱斯信道下多输入多输出MIMO系统性能的影响,建立了包含相关莱斯信道、天线互耦和匹配网络的(MIMO)系统模型.通过仿真分析了匹配阻抗、天线互耦、空间相关性以及信道衰落环境对包络相关性和信道容量的影响.实验结果表明:莱斯信道下匹配阻抗对MIMO系统的影响与瑞利信道情况下有所不同,适当地选择天线匹配阻抗可以改善MIMO系统的性能.     

Enhanced redesigned spatial modulation: Design and performance evaluation under correlated fading channels

Spatial modulation techniques (SMTs) have emerged as promising multiple‐input and multiple‐output (MIMO) technology for fifth generation (5G) networks, which can achieve an appealing trade‐off between conflicting design objectives such as reliability, hardware cost, complexity, spectral efficiency, and energy efficiency. Most of the SMTs suffer from significant performance deterioration under correlated fading channels. In this paper, a novel spectral efficient SMT referred as enhanced redesigned spatial modulation (EReSM) is proposed, which is robust against adverse channel correlation effects. At any time instant, EReSM activates either one or two transmit antennas and employs a robust bits to antenna index mapping that ensures the selection of antenna subsets with maximum spatial separation to mitigate the effect of spatial correlation. EReSM also exploits phase rotation of transmitted symbols as an additional dimension to convey an extra information bit. The rotation angles used for bit mapping are optimized for various modulation schemes to maximize the minimum euclidean distance between the symbols. To analyze the performance, analytical upper bound expression for average bit error probability (ABEP) is derived for both uncorrelated and spatially correlated channel conditions. Monte Carlo simulation results substantiate the accuracy of the analytical results and also demonstrate that the proposed EReSM outperform conventional redesigned spatial modulation (ReSM) by at least 4 dB.     

Adaptive antennas at the mobile and base stations in an OFDM/TDMAsystem

Several smart antenna systems have been proposed and demonstrated at the base station (BS) of wireless communications systems, and these have shown that significant system performance improvement is possible. We consider the use of adaptive antennas at the BS and mobile stations (MS), operating jointly, in combination with orthogonal frequency-division multiplexing. The advantages of the proposed system includes reductions in average error probability and increases in capacity compared to conventional systems. Multiuser access, in space, time, and through subcarriers, is also possible and expressions for the exact joint optimal antenna weights at the BS and MS under cochannel interference conditions for fading channels are derived. To demonstrate the potential of our proposed system, analytical along with Monte Carlo simulation results are provided     

Transmission Scheme for 2D Antenna Array MIMO Systems with Limited Feedback

Three-dimensional (3D) multiple-input multiple-output (MIMO) systems exploit spatial richness and provide another degree of freedom to transmit signals and eliminate spatial interference. Currently, however, there is no 3D codebook for two-dimensional (2D) antenna array MIMO systems with limited feedback. In this paper, based on the existing 2D codebook, we present a limited feedback and transmission scheme for 2D antenna array MIMO systems. In this scheme, the mobile station (MS) has imperfect channel knowledge, and the base station (BS) only acquires partial information relating the channel instantiation. MS must feed back two channel state information (CSI) instances, i.e., the horizontal and vertical CSIs. After receiving the two CSI instances, the BS interpolates a new vertical precoding vector using the vertical CSI. Then, the BS re-constructs a 3D beamforming vector using horizontal and vertical precoding vectors and compensates the reported horizontal channel quality indicator. System level simulation is employed, and the simulation results show that the proposed method improves the system spectral efficiency and the cell-edge SE significantly.     

Research on the spatial characterization of a 3D UAV air-to-ground channel model

To cope with the problem that the distribution assumptions of arrival angle and departure angle in existing geometry-based stochastic modeling (GBSM) for the unmanned aerial vehicle (UAV) air-to-ground (A2G) channel are too ideal to describe the spatial statistical property of the UAV A2G propagation environment precisely,considering the three-dimensional (3D) cylindrical A2G channel model,the spatial geometric characteristics of scattering regions were investigated analytically as corresponding to the angles of arrival and departure in both elevation and azimuth planes,which derived the probability density function (PDF) for the distribution of each angle.The effects of various parameters of channel model on the PDF were studied and simulation results prove that the derived PDF can describe the spatial statistical properties of UAV A2G channels more accurately,and can support the modeling of A2G communication channels well.     

Geometrical statistical channel model arisen from scatterers around the mobile with an inverted-parabolic spatial distribution

In this paper,firstly presented a geometrically based statistical channel model with scatterers that are with an inverted parabolic spatial distribution around mobile station(MS) within a circle wherein the base station(BS) and MS are included.This paper proposed a technique to simply derive probability density functions(PDFs) of angle of arrival(AOA),time of arrival(TOA) and Doppler spectra to characterize the outdoor macrocell and microcell environments by employing various distances between BS and MS,or different size of circular region.Employing this channel model,we analyze the impacts of a directional antenna at BS with the main-lobe width 2 on the fading and the Doppler spectra.     

Generalized multiuser orthogonal space-division multiplexing

This paper addresses the problem of performing orthogonal space-division multiplexing (OSDM) for downlink, point-to-multipoint communications when multiple antennas are utilized at the base station (BS) and (optionally) all mobile stations (MS). Based on a closed-form antenna weight solution for single-user multiple-input multiple-output communications in the presence of other receiver points, we devise an iterative algorithm that finds the multiuser antenna weights for OSDM in downlink or broadcast channels. Upon convergence, each mobile user will receive only the desired activated spatial modes with no cochannel interference. Necessary and sufficient conditions for the existence of OSDM among the number of mobile users, the number of transmit antennas at the BS, and the number of receive antennas at the MS, are also derived. The assumption for the proposed method is that the BS knows the channels for all MS's and that the channel dynamics are quasi-stationary.     

Optimal Planar Array Architecture for Full‐Dimensional Multi‐user Multiple‐Input Multiple‐Output with Elevation Modeling

Research interest in three‐dimensional multiple‐input multiple‐output (3D‐MIMO) beamforming has rapidly increased on account of its potential to support high data rates through an array of strategies, including sector or user‐specific elevation beamforming and cell‐splitting. To evaluate the full performance benefits of 3D and full‐dimensional (FD) MIMO beamforming, the 3D character of the real MIMO channel must be modeled with consideration of both the azimuth and elevation domain. Most existing works on the 2D spatial channel model (2D‐SCM) assume a wide range for the distribution of elevation angles of departure (eAoDs), which is not practical according to field measurements. In this paper, an optimal FD‐MIMO planar array configuration is presented for different practical channel conditions by restricting the eAoDs to a finite range. Using a dynamic network level simulator that employs a complete 3D SCM, we analyze the relationship between the angular spread and sum throughput. In addition, we present an analysis on the optimal antenna configurations for the channels under consideration.     

协作空分复用CSM系统中的信道估计算法研究

文章就当前MIMO应用过程中终端多天线受限制问题,阐述了单天线终端协作与基站组成虚拟MIMO多天线阵列——基于OFDMA的CSM协作空分复用系统结构。同时,提出对OFDMA系统中时频二维的资源进行分“块”独立进行信道估计,简化了OFDMA系统信道估计模型的复杂度。然后从应用的角度对比分析了基于OFDMA的CSM系统的信道估计算法LS和MMSE两种算法性能与优缺点。通过在PB3信道模型中仿真,得出适用于慢变信道的平滑滤波后的LS信道估计算法。     

Body-Worn Distributed MIMO System

In this paper, we analyze the performance of novel wearable multiple-input-multiple-output (MIMO) systems, which consist of multiple electrotextile wearable antennas distributed at different locations on human clothing. For wearable applications, a semidirectional radiation pattern of the wearable patch antenna is preferred over an omnidirectional radiation of conventional dipole antennas to avoid unnecessary radiation exposure to the human body and radiation losses. Additionally, the spatial distribution of the antennas is not constrained as a typical handheld unit. Through theoretical modeling and simulation, the wearable MIMO system is shown to demonstrate a significantly higher channel capacity than a conventional system on a handheld platform (e.g., a compact dipole array or a single dipole), due to enhanced spatial diversity and antenna pattern diversity. The unique effects of antenna directivity and location on the MIMO system capacity are investigated in terms of antenna correlation and effective gain under different wireless channel models. The advantage of a wearable system over a conventional system was further confirmed by detailed physical modeling through the combination of full-wave electromagnetic and ray-tracing simulations. Finally, complex channel response matrices were measured to characterize the performance of a body-worn MIMO system in comparison with a reference full-size dipole antenna. The 319% improvement in 10% outage capacity for the body-worn system over the reference system made of a full-size dipole antenna is consistent with the 288% improvement projected by theoretical modeling and the average 300% improvement found in the physical simulation of two typical indoor scenarios.     

毫米波时变信道仿真中实现空间一致性的方法研究

为满足终端移动场景下5G毫米波信道建模及仿真的需求,开展了毫米波时变信道仿真中实现空间一致性的研究.基于通用的5G毫米波信道模型开展了仿真和分析,将终端移动轨迹进行分割,确定连续仿真窗口间大尺度参数的相关性.同时,引入马尔可夫链实现窗口间多径簇数目的动态演化.对于窗口内信道小尺度参数,基于多径的几何分布结构实现对其状态...     

Deconstructing multiantenna fading channels

Accurate and tractable channel modeling is critical to realizing the full potential of antenna arrays in wireless communications. Current approaches represent two extremes: idealized statistical models representing a rich scattering environment and parameterized physical models that describe realistic scattering environments via the angles and gains associated with different propagation paths. However, simple rules that capture the effects of scattering characteristics on channel capacity and diversity are difficult to infer from existing models. We propose an intermediate virtual channel representation that captures the essence of physical modeling and provides a simple geometric interpretation of the scattering environment. The virtual representation corresponds to a fixed coordinate transformation via spatial basis functions defined by fixed virtual angles. We show that in an uncorrelated scattering environment, the elements of the channel matrix form a segment of a stationary process and that the virtual channel coefficients are approximately uncorrelated samples of the underlying spectral representation. For any scattering environment, the virtual channel matrix clearly reveals the two key factors affecting capacity: the number of parallel channels and the level of diversity. The concepts of spatial zooming and aliasing are introduced to provide a transparent interpretation of the effect of antenna spacing on channel statistics and capacity. Numerical results are presented to illustrate various aspects of the virtual framework.     

Modelling and Simulation of Direction-Selective and Frequency-Selective Mobile Radio Channels

This paper presents a new approach to the design of simulation models for spatio-temporal mobile radio channels, which are important for the design, optimization, and test of antenna array based mobile communication systems. The proposed spatio-temporally correlated simulation model is completely deterministic and enables the emulation of the desired fading behaviour with comparably little effort. Moreover, it can be configured flexibly to simulate not only different kinds of theoretical channels with given spatial, temporal, and frequency correlation properties, but also real-world fading channels for mobile communication systems with adaptive antennas.