A Generalized Model for the Spatial Characteristics of the Cellular Mobile Channel

In this paper, we present an intensive study of the spatial characteristics of the cellular mobile channel for picocell, microcell, and macrocell environments. We review the previous physical channel models and make appropriate comments/corrections wherever needed. We find that almost all physical channel models proposed so far are specific to particular cellular environments and that no general model exists in the literature. Thus, we propose a generalized physical channel model, referred to as the eccentro-scattering model, and derive the expressions for the probability density function (pdf) in an angle of arrival (AoA) of the multipath signals at a base station (BS) for the picocell, microcell, and macrocell environments using the two most commonly used scatterers' distributions, i.e., uniform and Gaussian. The derived formulas, in closed form, can be further used in designing beamwidth and channel tracking algorithms and assessing the performance of smart antennas. We discuss the relations between the results obtained for different cellular environments in the uniform and the Gaussian scattering and investigate the effects of the standard deviation of the scatter density and size of the scattering disc on the pdf of AoA at the BS. Previous work on the AoA statistics considering either the shape of the scattering regions or the distribution of scatterers within that region can more easily be reproduced using the provided general formula. We prove that assuming the scatterers to be either uniformly or Gaussian distributed in sparsely populated areas gives almost the same distribution of AoA of multipaths at the BS.     

Complex Envelope Second-Order Statistics in High-Altitude Platforms Communication Channels

High-altitude platforms are one of the most promising alternative infrastructures for realizing next generation high data rate wireless networks. This paper presents a three-dimensional (3-D) scattering model for land mobile stratospheric multipath-fading channel with its complex faded envelope. From the scattering model and the complex envelope second-order statistics are derived for a 3-D non-isotropic scattering environment. When we discuss on the second-order statistics we refer to the level crossing rate and the average fade duration, whichare two main parameters in describing the fading severity over time and are very important in assess system characteristics such as hand off, velocities of the transmitter and receiver and fading rate. Numerical calculations have been carried out to demonstrate theoretical derivations and the utility of the proposed model.     

一种分层蜂窝网中基于用户分类的建模分析方法

随着无线网中用户需求的业务量持续增大,且用户具有不同移动性,分层蜂窝结构(HCS)被提出。该文研究一种微小区/宏小区的双层蜂窝结构的网络性能,此系统采用双向溢出策略,呼叫用户根据其速度选择合适的接入层(慢用户接入微小区,快用户接入宏小区)。该文提出一种用户分类建模分析方法(分为快用户和慢用户)来估计分层蜂窝网络性能,它不同于以往的蜂窝层分类(分为微小区层和宏小区层)建模方法。此用户分类模型包括一个快用户模型和一个慢用户模型,两个模型都是简单的一维马尔可夫过程。理论分析和仿真结果都证明了用户分类分析模型的正确性。随后利用此模型分析了为速度阈值的作用和被阻用户重复呼叫情况下的网络性能。     

基于雨衰雪衰影响的空间信道统计模型

针对某些特殊的移动通信环境中信号的到达角度( TOA)、到达时间( AOA)等信道参数估计的复杂性,提出一种基于散射体均匀分布室外统计信道模型。该模型将树木中的树冠层作为散射体呈均匀分布在移动台与基站周围的椭圆形区域内,通过树冠层在雨雪环境中的相对介电常数来分析降雨降雪量对信号传输带来的影响,可以方便地估计出此室外微小区的空时信道参数,如AOA概率密度分布函数、TOA概率密度分布函数以及到达角度/到达时间( AOA/TOA )联合概率密度分布函数。仿真结果表明,信号的到达时间TOA以及到达角度AOA随着降雨降雪量的增大而增大,尤其当降雪量增大使得树冠层相对介电常数达到4.5时,信号的传输将被阻塞。该模型的信道参数估计结果符合理论与经验,扩展了移动无线通信信道模型的研究与应用。     

Angle of Arrival Statistics for a 3-D Cylinder Model

In this paper, a three-dimensional (3-D) geometric model is considered to simultaneously describe angle of arrival (AoA) of multipath waves in the azimuth and elevation planes. The model is suitable in a macrocellular environment with a low MS antenna and an elevated base station (BS), where scatterers are distributed in a cylinder with the radius of the cell and the height of the BS. Closed-form expressions for the probability density functions in the angles are provided as seen from the mobile station (MS). Results show that the azimuth AoA depends on the ratio of the distance between the BS and the MS to the radius of the cell whereas the elevation AoA depends on the height of the BS, the radius of the cell and the distance between the BS and the MS. Monte-Carlo simulations are performed to examine the accuracy of the proposed model.     

Statistics of macrocell-synchronous femtocell-asynchronous users? delays for improved femtocell uplink receiver design

In a typical macrocell network, the mobile users are synchronized to the macrocell base station (mBS), where users further away to the mBS transmit their signals earlier. In such a network, the signals of the macrocell users arrive at a femtocell base station (fBS) asynchronously, which may yield interference problems such as inter-carrier-interference in orthogonal frequency domain multiple access (OFDMA) systems. In this letter, statistics of the arrival times of macrocell-synchronous femtocell-asynchronous mobile users' signals to an fBS is derived (conditioned on the fBS-mBS distance), and its implications on the femtocell uplink receiver design are briefly discussed.     

基于 Inverted-Parabolic 分布的空间统计信道模型

针对在非均匀散射体分布下信号到达角度、到达时间以及多普勒效应等信道参数估计的复杂性,提出一种合理的空间信道模型,并引入几何分割法导出基于散射体Inverted-Parabolic分布的空间统计信道模型。模型能方便地估计室外宏小区和微小区移动通信环境下各种重要的空时信道参数,如AOA、TOA概率分布密度函数和多普勒功率谱以及信号的空—时相关性。数值结果与均匀散射体圆模型和高斯散射体圆模型对比表明本模型的信道参数估计结果符合理论和经验,且与实测结果吻合较好。在基站设计采用指向性天线时研究了移动台MS的多普勒效应,修正了Clarke U-shaped经典模型,阐明了天线主瓣宽度 、空间模型参数D/R和MS移动参数影响信道参数的机理。     

Geometrical-based statistical macrocell channel model for mobileenvironments

We develop a statistical geometric propagation model for a macrocell mobile environment that provides the statistics of angle-of-arrival (AOA) of the multipath components, which are required to test adaptive array algorithms for cellular applications. This channel model assumes that each multipath component of the propagating signal undergoes only one bounce traveling from the transmitter to the receiver and that scattering objects are located uniformly within a circle around the mobile. This geometrically based single bounce macrocell (GBSBM) channel model provides three important parameters that characterize a channel: the power of the multipath components, the time-of-arrival (TOA) of the components, and the AOA of the components. Using the GBSBM model, we analyze the effect of directional antennas at the base station on the fading envelopes. The level crossing rate of the fading envelope is reduced and the envelope correlation increases significantly if a directional antenna is employed at the base station     

Analytically Derived Uplink/Downlink TOA and 2-D-DOA Distributions With Scatterers in a 3-D Hemispheroid Surrounding the Mobile

This paper presents the open literature's first closed-form explicit expressions of the trivariate joint and marginal distributions of a landmobile cellular wireless communication system's uplink and downlink multipaths' time of arrival and two-dimensional direction of arrival, rigorously derived via thorough mathematics based on a “geometrical” model of the three-dimensional (3-D) spatial relationships among the mobile station, the scatterers, and the base station. The scatterers are herein modeled to have a uniform 3-D spatial distribution in an aboveground hemisphere with a flat circular base (or alternatively, within a sphere) centered at the mobile.     

Angle and Time of Arrival Statistics for a 3-D Pie-Cellular-Cut Scattering Channel Model

In this paper, investigated a 3-D pie-cellular-cut (PCC) scattering channel model for microcell environments, that idealizes the mobile station (MS) located inside of a 3-D scattering semispheroid and base station (BS) employing a directional antenna at the center of the semispheroid. The joint probability density functions (PDFs) and marginal PDFs of Angle of arrival (AOA) and Time of Arrival (TOA) seen at the BS and the MS in correspondence with azimuth and elevation angles are derived. The results show that the proposed 3D scattering channel model performs better compared with previously proposed 2D models for outdoor and indoor environments, which promotes the research of the statistical channel models.     

A crossing-tier location update/paging scheme in hierarchical cellular networks

Location update/paging strategies have been widely studied in the traditional single-tier cellular networks. We propose and evaluate a novel crossing-tier location update/paging scheme that can be used in a hierarchical macrocell/microcell cellular network. Location update is proceeded only in the macrocell tier, where a location area (LA) is made up by larger macrocells. A mobile user will stay in such a LA for longer time. Therefore, the cost on location update can be reduced due to the decreased frequency of location update. To reduce the paging delay, the paged mobile user will be searched in the macrocell tier only when the paging load is not high. Otherwise, it will be searched in the microcell tier, where a sequential searching method is applied. The operation for the scheme is simple, as the macrocell/microcell cellular network has the advantage because a mobile user can receive a signal from both a microcell and the overlaid macrocell. Analytical models have been built for cost and delay evaluation. Numerical results show that, at relatively low cost, the crossing-tier scheme also achieves low paging delay.     

Three-Dimensional Modeling, Simulation, and Capacity Analysis of Space–Time Correlated Mobile-to-Mobile Channels

A 3-D reference model is proposed for multiple-input multiple-output (MIMO) mobile-to-mobile (M-to-M) multipath-fading channels. From this model, a closed-form joint space-time correlation function is derived for a 3-D nonisotropic scattering environment. Two sum-of-sinusoids-based 3-D simulation models for MIMO M-to-M multipath-fading channels are proposed. The statistics of the simulation models are verified by simulation. Finally, these simulation models are used to evaluate the effect of the space-time correlation on the outage capacity of uniform linear antenna arrays and to compare the capacities of linear, circular, and spherical antenna arrays.     

Three-Dimensional Urban EM Wave Propagation Model for Radio Network Planning and Optimization Over Large Areas

A new 3-D urban electromagnetic wave propagation model is presented. It provides fast 3-D deterministic predictions in urban radio configurations and over large areas. The various techniques to make it suitable to the network planning and optimization of large wireless networks are described. The resulting radio propagation maps exhibit seamless coverage between the various environments (dense urban, urban, and suburban). The model efficiently addresses all types of outdoor transmitter configurations (macrocells, minicells, microcells, and picocells) and all types of receiver locations (at ground level, over the rooftop, and at high building floors). It predicts the field strength as well as the dominant specular contributions of the impulse responses to build ray spectra (including delays and angles). Thus, the model may also be used to estimate the performances of new radio systems [diversity and multiple-input–multiple-output (MIMO)]. The narrowband power prediction of the model is evaluated by comparison with microcell measurements. The evaluation stresses the advantage of 3-D modeling compared with the vertical-plane approach or 2-D ray tracing. Finally, the ability of the model to simulate radio wideband characteristics in a complex environment is demonstrated by comparing delay-spread estimates to measurements collected from a high-macrocell transmitter in a hilly city and to arrival angles collected in a suburban macrocell area.      

Joint AoA and Channel Estimation for SIMO- OFDM Systems: A Compressive-Sensing Approach

Millimeter-wave (mmWave) transmission has been considered in future fifth generation (5G) communication systems. Since the pathloss in mmWave is severe, beamforming with antenna arrays, an enabling technology in the 5G era, will become a must. To conduct receive beamforming, however, we need to know the information about the angle-of-arrival (AoA). In this paper, we consider joint AoA and channel estimation for single-input-multiple-output (SIMO) OFDM systems. As known, wireless channels are sparse, and this is particularly true for mmWave environments. Conventional compressive-sensing (CS) based channel estimation methods only consider single-input-single-output systems. We propose new matching-pursuit-based CS methods for channel estimation in SIMO-OFDM systems, using frequency-domain pilots. With the estimated channels, AoA’s are then estimated by the maximum-likelihood method. Since a hidden parameter is involved in the problem, an expectation-maximization (EM) algorithm is then employed. The Cramer-Rao lower bound (CRLB) is also derived for the AoA estimation. Simulation results show that the proposed channel estimation can significantly outperform existing methods while the proposed AoA estimation attains the CRLB.     

Analysis of Non-WSSUS Fading Dispersive Channel Model

1Introduction Basically,whenthepropagationcharacteristicsofra diomobilecommunicationsarestudied[1],italways comestheWSSUSmodel,introducedbyBello[2]first ly,whichregardstheradiomobilechannelasafully stochasticchannelandassumestheuncorrelateddisper sivitybo…     

Statistical Simulation Modeling of 3-D HAP-MIMO Channels

High altitude platforms (HAPs) have been designated as an alternative wireless infrastructure for facilitating next generation high-speed mobile communications services. This paper deals with the design and performance evaluation of a three-dimensional (3-D) sum-of-sinusoids statistical simulation model for HAP multiple-input?Cmultiple-output Ricean fading channels. The performance of the simulation model is investigated with respect to the temporal and spatial correlation functions. The results indicate that the simulation model accurately and efficiently approximates the statistical properties of a recently proposed non-realizable reference model.     

Performance analysis of hierarchical cellular networks with queueing and user retrials

How to efficiently utilize the scarce radio channel resource while maintaining the desired user‐perceived quality level and improved network performance is a major challenge to a wireless network designer. As one solution to meet this challenge in cellular mobile networks, a network architecture with hierarchical layers of cells has been widely considered. In this paper, we study the performance of a hierarchical cellular network that allows the queueing of both overflow slow‐mobility calls (from the lower layer microcells) and macrocell handover fast‐mobility calls that are blocked due to lack of free resources at the macrocell. Further, to accurately represent the wireless user behaviour, the impact of call repeat phenomenon is considered in the analysis of new call blocking probability. Performance analysis of the hierarchical cellular structure with queueing and call repeat phenomenon is performed using both analytical and simulation techniques. Numerical results show that queueing of calls reduces forced call termination probability and increases resource utilization with minimal call queueing delay. It is also shown that ignoring repeat calls leads to optimistic estimates of new call blocking probability especially at high offered traffic. Copyright © 2005 John Wiley & Sons, Ltd.     

移动通信中无线信道特性的研究

从等效低通信道的时变冲激响应的相关函数和功率密度谱函数出发,研究了一些描述广义平稳非相关散射(WSSUS)的无线信道特性的统计参数,并对无线移动衰落信道的特性进行分类。分析了3种常见的小尺度多径衰落信道的统计模型,给出了在平坦衰落信道中系统传输比特误码率的一般分析方法。最后,利用这些模型和方法,给出了一些常见数字调制信号的传输误码率的数值结果。结果表明：衰落对无线移动通信系统传输性能的影响是很大的,在实际中应设法消除它。     

Mobile-to-mobile fading channels in amplify-and-forward relay systems under line-of-sight conditions: statistical modeling and analysis

This paper deals with the modeling and analysis of narrowband mobile-to-mobile (M2M) fading channels for amplify-and-forward relay links under line-of-sight (LOS) conditions. It is assumed that a LOS component exists in the direct link between the source mobile station (SMS) and the destination mobile station (DMS), as well as in the links via the mobile relay (MR). The proposed channel model is referred to as the multiple-LOS second-order scattering (MLSS) channel model. The MLSS channel model is derived from a second-order scattering process, where the received signal is modeled in the complex baseband as the sum of a single and a double scattered component. Analytical expressions are derived for the mean value, variance, probability density function (PDF), cumulative distribution function (CDF), level-crossing rate (LCR), and average duration of fades (ADF) of the received envelope of MLSS channels. The PDF of the channel phase is also investigated. It is observed that the LOS components and the relay gain have a significant influence on the statistics of MLSS channels. It is also shown that MLSS channels include various other channel models as special cases, e.g., double Rayleigh channels, double Rice channels, single-LOS double-scattering (SLDS) channels, non-line-of-sight (NLOS) second-order scattering (NLSS) channels, and single-LOS second-order scattering (SLSS) channels. The correctness of all analytical results is confirmed by simulations using a high performance channel simulator. Our novel MLSS channel model is of significant importance for the system level performance evaluation of M2M communication systems in different M2M propagation scenarios. Furthermore, our studies pertaining to the fading behavior of MLSS channels are useful for the design and development of relay-based cooperative wireless networks.