Adaptive terminal to base station assignment in BFWA systems

In point-multipoint systems the signal to interference plus noise ratio highly depends on the assignment of terminal stations (TS) to base stations (BS). The Broadband Fixed Wireless Access (BFWA) systems operate at high carrier frequencies. In this frequency range wave propagation is highly influenced by precipitation. Applying site diversity can mitigate rain attenuation effects. Present contribution provides a special site diversity method adopting genetic algorithm to adaptively optimize TS-BS assignments from point of view of the interference in BFWA service area. Rain events are generated with a Markov modeled simulation of the rain cell translations.     

On the role of future high-frequency BFWA systems in broadband communication networks

Frequencies above 25 GHz represent a great opportunity for BFWA systems because of the extraordinary bandwidths available. But standards for high-frequency BFWA published so far have not been able to unleash this potential. We believe this is due to the fact that the performance characteristics have been shaped considering these systems in isolation. This has brought on a mismatch between what these systems can offer and what is really needed. Most of today's broadband networks focus on data communication. In this article, we focus on how to make high-frequency BFWA systems fit better into the architecture required for fulfilling the "broadband for all" vision (i.e., including more video streaming and transfer). By modifying and extending the standards to fulfill the performance requirements implied, high-frequency BFWA systems can play an important role in future high-capacity broadband networks with flexible resource allocation     

Rician K-Factor Distribution in Broadband Fixed Wireless Access Channels under Rain Fades

The performance of broadband fixed wireless access (BFWA) systems operating at frequencies above 10 GHz is adversely influenced by rainfall, which introduces severe attenuation and a short-term variation to the received signal. In this letter, the fading channel of a BFWA link is modeled as Rician with a strong Rician K-factor. A novel analytical model relating the Rician K-factor with the rain fading effects is presented based on which, an analytical prediction model for the cumulative distribution of the Rician K-factor is derived. Experimental data is necessary to validate the proposed models. The presented methodology provides an efficient way to incorporate the mathematically intractable physical input of rain fading into the "easy-to-simulate" Rician channel model. The proposed models can be applied on a global scale and incorporate the impact of various crucial operational and geometrical parameters of a BFWA system on the wideband multipath behavior of the channel. Useful numerical results regarding the validity of the presented models are also provided     

Empirical analysis of a 2 x 2 MIMO channel in outdoor-indoor scenarios for BFWA applications

The unquestionable advantages of multiple-input multiple-output (MIMO) systems are having a strong influence on the development of new wireless systems, both in wireless local-area networks (WLANs), and in those designed to offer broadband fixed wireless access (BFWA) services in wireless metropolitan-area networks (WMANs). The MIMO channel characterization in different environments and for different operating frequency bands is a crucial factor in the design of new systems and standards, and for adequate planning of existing systems. This article makes two main contributions. First, the experimental characterization of a 2 times 2 MIMO channel at a frequency of 2.4 GHz in a canonical outdoor-indoor scenario is presented. The channel characterization performed includes the analysis of the spatial correlation between the MIMO system subchannels and its impact on the channel capacity. Second, on the basis of the capacity results obtained, a proposal is made for the use of a 2 times 2 MIMO system in outdoor-indoor scenarios for BFWA applications in metropolitan environments. The proposal is based on the experimentally verified hypothesis that the path loss due to building penetration can be practically compensated for by the diversity gain of 2 times 2 systems     

一种基于随机森林的LOS/NLOS基站识别方法

蜂窝移动通信环境复杂多变,在基站和移动台之间不可避免会出现电波的非视距（Non-Line-of-Sight,NLOS）传播,使基站和移动台之间的距离测量误差显著增大,导致定位性能急剧下降。为了准确识别出视距（Line-of-Sight,LOS）与非视距传播的基站信号,提出了一种基于随机森林的LOS/NLOS基站识别方法,通过分析移动台与各基站接收机测量距离与定位误差之间的相关性,选择LOS/NLOS测量距离作为特征进行分类器训练,再将分类器用于LOS/NLOS基站的识别。仿真结果表明,该方法对NLOS基站的正确识别率达到90%以上,能取得较好的定位性能。     

Channel Capacity of TDD-OFDM-MIMO for Multiple Access Points in a Wireless Single-Frequency-Network

The multiple-input-multiple-output (MIMO) technique is the most attractive candidate to improve the spectrum efficiency in the next generation wireless communication systems. However, the efficiency of MIMO techniques reduces in the line of sight (LOS) environments. In this paper, we propose a new MIMO data transmission scheme, which combines Single-Frequency-Network (SFN) with TDD-OFDM-MIMO applied for wireless LAN networks. In our proposal, we advocate to use SFN for multiple access points (MAP) MIMO data transmission. The goal of this approach is to achieve very high channel capacity in both LOS and non line of sight (NLOS) environments. The channel capacity of the proposed method is derived for the direct path environments and it confirms the effectiveness of the proposed scheme in the LOS scenario. Moreover, solid computer simulation results confirm the effectiveness of the proposed method in both, single user and multiuser scenarios.     

基于粒子滤波和交互多模型的移动定位方法

为提高非视距情况下移动辐射源的定位精度,提出一种改进的交互粒子滤波算法.该算法对目标运动多模型和信号到达时间差测量噪声分布多模型联合建模.在交互多模型状态更新中利用粒子滤波对目标时变状态以及视距/非视距混合信道参数进行估计,抑制了非视距测量误差对移动定位的影响.仿真结果表明,改进算法的性能要优于现有的视距条件运动多模型和视距/非视距条件单一运动模型的定位算法,并且定位误差接近于推导的后验克拉美劳下界.     

捷联导引头弹目视线角速率估计

捷联导引头相对于框架式导引头而言,拥有许多优势。捷联导引头技术越来越受到各国军方的重视。捷联导引头无法直接测量弹目视线角速率,实现捷联导引头的工程运用首先需要解决弹目视线角速率的提取问题。弹目视线角速率提取的方法主要有两类,第一类是利用微分网络对弹目视线角进行微分来获取弹目视线角速率,第二类是利用卡尔曼滤波器对弹目视线角进行估计。建立了基于这两类方法的模型,并进行了仿真,仿真结果表明:第二类方法比第一类更具有优势。由卡尔曼滤波器估计出的惯性系弹目视线角速率比运用微分网络得到的惯性弹目视线角速率具有更小的延迟;在相同的量测噪声水平下,第二种方案输出的惯性系弹目视线角速率信号噪声水平更低。     

光电经纬仪提高多传感器测量精度的方法

为了得到多信息进行信息融合,光电经纬仪采用多传感器的方法,即在主视轴及辅助视轴上安装了传感器。作为获得信息的多种手段,主视轴传感器获得的测量数据,分析处理数据按常规方法计算即可;辅助视轴与主视轴存在平行度,辅助视轴传感器获得的测量数据,处理时必须对结果进行修正。在精度要求不高的情况下,通常的方法是直接在辅助视轴传感器获得的方位角、高低角修不平行度。本文采用坐标变换方法推导出辅助视轴误差修正模型,直接获得目标的方位角、高低角;实验证明,在高低角〈45°时,精度可提高10%。     

Line-of-sight task-space sensing methodology for the localization of robotic end-effectors

In this paper, the implementation of a line-of-sight (LOS) task-space sensing methodology is presented for guidance-based microlocalization of robotic end-effectors. The novelty of the overall system is its applicability to cases that do not allow for the direct proximity measurement of the end-effector's pose (position and orientation). The mobility of the localization application dictates the minimum number and the type (planar or spatial) of the LOS that would be necessary to use and, consequently, the exact configuration of the sensing system. Although the main focus of the paper is the presentation of the proposed LOS sensing system, a brief discussion of a robot-guidance method, which relies on the use of this sensing system, is also included. Extensive experiments conducted for a high-precision 3-DOF (degrees of freedom) planar robotic platform utilizing the overall guidance system validated our research.     

Multibeam Selection for Indoor MIMO Systems: Two Cases of Study

The performance of multiple-input multiple-output (MIMO) systems using beam selection is investigated in this paper. Based on the results of a channel sounding campaign carried out at the University of Manitoba for line-of-sight (LOS) and non-line-of-sight (NLOS) scenarios, it was possible to contrast the results of transmitter, receiver and joint beam selection in rich scattering environments. The channel was characterized in the 1-2.4 GHz frequency band with a multipath delay resolution better than 5.8 ns. The beam selection was performed by exhaustive search method. The results led us to important conclusions regarding the beam selection procedure and its potential to improve the indoor channel capacity. In LOS, the single input single output (SISO) system that favours the maximum power direction of arrival (DOA) maximizes the capacity. Capacity improvements are observed by increasing the number of receiver beams (RBs) only at high signal-to-noise ratios (SNRs) for omnidirectional transmission. The best performance in transmitter beam selection in LOS is observed by increasing the number of transmitter beams (TBs) for high SNRs. In the case of NLOS, the capacity performance is improved when more than a single beam is used in either, transmitter or receiver side. The joint transmitter-receiver beam selection exhibits best capacity performance only for large SNRs in LOS while the SISO systems outperforms any joint beam selection alternative for low SNRs. In contrast, in NLOS environments, the use of joint beam selection shows a constant capacity performance improvement starting from lower SNR than in the LOS case     

反射镜光电平台视轴稳定技术研究

针对不同类型反射镜平台视轴运动多样性的特点,从基本的反射镜视轴运动学关系出发,采用基于虚拟整体稳定平台的视轴重建方法对反射镜平台视轴惯性角速度进行数学重建。同时,深入分析了常见的典型单反射镜平台、特殊配置单反射镜平台、极坐标多反射镜平台以及直角坐标多反射镜平台的视轴运动学关系和视轴稳定控制技术。基于典型单反射镜平台俯仰轴视轴稳定控制的数值仿真结果表明,采用虚拟整体稳定平台方法的视轴稳定控制技术用于反射镜视轴稳定控制是可行的。     

A new parameter for UWB indoor channel profile identification

This paper proposes a new parameter for identifying the room typology when the receiver is in ultra wideband (UWB) indoor environments. The method proposed does not imply any estimation process at the received signal. The proposed parameter is not only able to clearly distinguish between Line-Of-Sight (LOS) and Non-Line-Of-Sight (NLOS) conditions, but it is also capable of ordering the quality of the received signal in two different LOS or NLOS rooms, although the Signal-to-Noise-Ratio (SNR) is the same. Moreover, this parameter is able to distinguish between LOS and NLOS macro groups clearly and, at the same time, to order conditions within these two macro groups (for example, clear LOS condition from Quasi-LOS, i.e., when an object partially shadows the link, etc.). The method proposed in this paper is based on the calculation of the kurtosis index of the sampled received signal. The kurtosis index can be successfully applied to the received signal in order to identify the typology of the link between transmitter and receiver (LOS, Quasi-LOS, high-NLOS, low-NLOS, extreme-low-NLOS). Results are achieved by both real measurements and simulations with IEEE802.15.3a and 4a channel models.     

气流扰动下光电系统高精度稳像控制方法

气流随机冲击引起的姿态扰动是飞行器光电系统的主要扰动源,在系统自身转轴摩擦和质量不平衡等因素的作用下,严重影响了光电系统视轴稳定性。为了有效抑制扰动力矩的影响,建立了外俯仰、内方位两轴光电系统动力学模型,给出了扰动因素和运动耦合综合作用下的扰动传递关系。根据系统动力学模型,提出了扩展卡尔曼滤波扰动力矩估计方法,并构建扰动力矩前馈控制回路,实现了对扰动力矩的实时补偿,大大提高了光电系统的稳像控制精度。利用飞行模拟转台对某两轴光电系统进行了半实物仿真实验,结果表明:在幅值为1、频率为2 Hz的载体扰动条件下,采用前馈补偿方法系统俯仰和方位框架的视轴稳定精度均方根值分别达到0.026 4 mrad和0.029 0 mrad,相比扰动观测器控制方法分别提高了64.1%和69.6%。     

基于视轴矢量序列的目标轨迹确认方法

针对椭圆轨道红外监视系统图像畸变大,基于图像配准进行目标轨迹确认误差大的问题,提出基于视轴矢量序列的目标确认分析方法;建立了目标视轴矢量序列的状态转移模型和观测模型,利用GM-PHD(Gaussian mixture probability hypothesis density)滤波器对目标视轴矢量进行滤波实现目标确认...     

偏轴反射镜平台视轴稳定技术及建模分析

常规反射镜平台采用方位/俯仰型两框架结构形式,探测器视轴平行于外框架旋转轴。区别于常规反射镜平台,偏轴反射镜平台不再遵循探测器视轴与外框架旋转轴平行的原则,其视轴角速度具有强耦合和非线性的特点。主要研究了这类偏轴反射镜平台的运动学、动力学建模和视轴稳定机理。首先,采用虚拟整体稳定平台技术推导平台运动学方程,并确定了虚拟平台框架类型的选取原则。在此基础上推导了完整的视轴坐标系动力学模型。然后,对载体运动耦合机制进行了分析并给出了控制框图。最后,对视轴运动特性进行仿真分析。仿真结果表明,该平台在视轴指向、力矩耦合等方面具有不同于常规反射镜平台的特性,且由视轴运动非线性引起的视轴交叉耦合力矩大于惯量耦合力矩。     

Performance Analysis of RSS-Based Localization in Wireless Sensor Networks

Wireless Personal Communications - In this paper, localization error of the received signal strength (RSS)-based method in mixed LOS/NLOS conditions is analysed. In contrast to the time of arrival,...     

全捷联导引头视线角速度STCKF提取技术

传统的平台导引头可以通过物理跟踪回路直接提取导弹制导所需的视线角速度信息,采用全捷联结构后,导引头失去了直接测量视线角速度的能力,视线角速度需要通过数字计算的方法来提取。针对全捷联导引头精确制导技术工程应用中的问题,首先给出了视线角速度提取方案,推导得到视线角速度估计模型,鉴于估计模型的强非线性,采用强跟踪容积卡尔曼滤波算法对视线角速度进行估计。结合小型空面导弹的典型使用条件,通过弹道仿真对视线角速度估计算法的有效性进行了验证。仿真试验表明:导引头在末制导段捕获目标后,能迅速消除滤波初始误差,准确跟踪真实的弹目视线角和视线角速度变化。为验证将滤波输出作为制导信息的可行性,考虑激光半主动全捷联导引头的典型干扰,用蒙特卡洛打靶方法对导弹制导精度进行了考核,1 000次打靶结果显示,对静止目标的制导精度为0.58 m（CEP）,对运动目标的制导精度为0.84 m（CEP）,满足精确制导武器的制导精度要求。     

Robust Mobile Location Estimator with NLOS Mitigation using Interacting Multiple Model Algorithm

A Kalman-based interacting multiple model (IMM) smoother is proposed for mobile location estimation with the time of arrival (TOA) measurement data in cellular networks to meet the Federal Communications Commission (FCC) requirement for phase 2. In this study, the line-of-sight (LOS) and non-line-of-sight (NLOS) conditions in cellular networks are considered as a Markov process with two interactive modes. Then we propose a Kalman-based IMM smoother to accurately estimate smooth range between the corresponding base station (BS) and mobile station (MS) in cellular networks. It is shown that the proposed mobile location estimator can efficiently mitigate the NLOS effects of the measurement range error even when the corresponding BS changes the condition between LOS and NLOS. Simulation results demonstrate that the performance of the proposed Kalman-based IMM smoother is improved significantly over the FCC target in both fixed LOS/NLOS and LOS/NLOS transition conditions     

基于视线测量改进的主被动联合探测数据关联

针对主被动传感器异地配置情况,利用视线测量转换过程,对主被动联合探测的数据关联算法进行了改进:首先,计算视线垂足至主动传感器的距离,以方位测量与该距离之差(测量差)构造新的统计量,通过视线间距以及测量差两个统计量检验初选出候选关联集;接着,主被动视线交叉将不完整的被动测量补充为完整测量,用精度加权法实现多角度测量之间的融合,得到候选集的定位点估计,计算各定位点与目标的关联概率;然后,以视线间距和测量差构造测量距离,利用测量距离之和表征关联集内部各视线的紧密度,给出视线关联度;最后,用视线关联度修正关联概率,最大值搜索正确关联组合。仿真实验结果验证了算法的有效性。