MIMO-OFDM系统中一种改进的信道估计方法

信道的准确估计是提高MIMO-OFDM系统性能的关键.在最优导频时域信道估计的基础上,提出了一种较低复杂度的改进算法,利用时变信道的自回归(AR)模型构造卡尔曼滤波器对估计出的时域信道响应进行滤波,提高信道时域响应的估计精度.仿真结果表明,在慢时变信道环境下,改进方法可以进一步提高信道估计的精度,同时保持了较低的复杂度.     

UPF算法在OFDM时变信道估计中的应用

为了提高正交频分复用（OFDM）系统中时变信道估计的精度和系统性能,提出一种利 用无迹粒子滤波（UPF）算法的OFDM时变信道估计方法。该方法首先将OFDM系统时变信道建 模为具有动态特性的状态方程,然后利用UPF算法,结合接收信号动态地估计信道状态。仿 真结果表明：在高斯和非高斯环境下,所提的方法均可以获得比采用传统粒子滤波（PF）算 法的信道估计方法更高的估计精度和更好的系统性能,因此适用于实际系统。     

一种新的MIMO-OFDM系统自适应快时变信道估计算法

为了能够获得较精确的快时变信道估计,利用模糊模型拟合快时变信道,提出了一种 新的信道估计算法。算法采用自适应技术进行导频子载波频域传输函数模型参数的识别,然 后通过插值拟合全部信道的频域传输函数。仿真结果表明,在系统多普勒频移小于0.1的情 况下,信道估计的MSE性能得到改善。     

一种超宽带模拟合并转发协作通信系统

针对频率选择性衰弱信道下协作通信系统信道估计复杂的问题,提出了一种模拟合并 放大转发超宽带（UWB）协作通信方案。该方案在源节点处对发送符号进行实数分布式空时 编码并附加传输参考,在中继节点处利用传输参考对多径分量进行模拟合并,从而构建了一 种改进型非正交放大转发协作通信系统。仿真结果证明,相对于无协作通信系统,模拟合并 转发协作系统无需信道估计就可获得传输性能的有效提升。     

MIMO-OFDM系统载波间干扰的时域消除

由于载波间干扰（ICI）是影响正交频分复用（OFDM）系统性能的重要因素，一般消除ICI时作信道估计都采用辅助导频的方法，需要使用大量的离散导频，为此提出了一种对MIMO信道中ICI消除的时域均衡方法。该方法利用MIMO空时检测后的数据信息迭代回去，当作导频符号估计出时变信道的冲激响应，然后通过时域均衡消除ICI，而无需额外的导频，在改善系统误误码率的同时，提高了频谱的利用率。     

基于总体最小二乘准则的OFDM系统时变信道估计

信道估计的准确程度直接影响正交频分复用系统的性能。为了提高时变信道估计算法的精度,基于总体最小二乘准则(TLS)提出了一种时变信道的估计方法。该方法用线性模型对时变信道进行建模,不仅考虑了信道噪声,同时也兼顾了模型误差。该方法能较好地跟踪信道的变化,显著消除模型误差。仿真结果表明所提算法的均方误差介于最小二乘算法与最小均方误差算法之间,在不同归一化多普勒频移下,该算法具有较好的稳健性。     

修正Kalman滤波多带UWB信道估计改进方法

针对多带超宽带(UWB)系统中修正Kalman滤波算法复杂度高的缺陷,提出一种低复杂度的修正Kalman滤波改进方法。该方法中UWB信道采用自回归模型(AR)建模,利用导频跟踪时变信道衰减因子,通过Kalman滤波和频域分段最小均方误差(MMSE)算法同时跟踪信道的时域相关性和频域相关性,提高了系统性能,降低了计算复杂度。仿真结果表明,和修正的Kalman滤波方法相比,在估计精度损失很小的情况下,所提方法极大降低了计算复杂度,提高了系统整体的估计性能。     

基于压缩感知的大规模MIMO下行信道状态信息获取

信道状态信息（Channel State Information,CSI）对于大规模多输入多输出（Multiple-Input Multiple-Output,MIMO）发挥高性能至关重要。但在上下行传输信道不存在互易性的频分双工（Frequency Division Duplex,FDD）制式下,若采用传统的信道估计方法会给CSI的获取带来巨大的导频开销和计算量。考虑利用大规模 MIMO 信道的虚角域稀疏性来减少获取CSI所需开销,在此基础上进一步研究了大规模 MIMO 正交频分复用(Orthogonal Frequency Division Multiplexing,OFDM)系统中各子载波信道在虚角域的共同稀疏特性和稀疏支撑集的时间相关特性,达到降低信道维度的目的,则大大减少了基站对 CSI 获取所需的资源开销。同时,为了降低信道稀疏支撑集信息获取所需的导频开销和提高信息的时效性,利用压缩感知技术对支撑集进行估计。仿真结果验证了所提方案性能的优越性。     

基于梳状导频的OFDM分组自适应比特装载与功率控制

无线通信环境中信道信息(ChannelStateInformation,CSI)随时间变化明显,需要不断地更新自适应比特装载和功率控制的策略。现有的OFDM自适应比特装载方法需要大量的信令来传递当前比特装载的策略,不适用于无线通信的应用环境。为此,本文针对OFDM系统的特征提出了一种利用插入梳状导频的信道估计得到的带有误差的信道信息,来完成自适应比特装载的算法。首先把OFDM子载波进行分组,然后利用基于梳状导频的信道估计对信道时变进行跟踪,使用即时获得的CS完成自适应比特装载算法。仿真实验证明,在保证算法简单、实用及保证要求的误码率(BER)性能的情况下,信道信令的开销低于传统算法的10%。     

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。     

通用数据链组网有效性评估的建模

根据现阶段综合信息网络的发展需求,考虑到通用数据链组网的 抗干扰能力强和保密性能高等特征,结合NFE即神经网络（NN）、模糊推理（FR）、专家系 统（ES）模型和 层次分析法(AHP),提出了通用数据链组网有效性研究的N FE-AHP模型,并仿真验证了NFE-AHP模型对于通用数据链组网有效性评估的适用性,结果表 明抗干扰度、鲁棒性、兼容 能力对通用数据链组网有效性评估尤为重要,对于通用数据链组网有效性评估的工程实践具 有一定的指导意义。     

Transformative service research and service dominant logic: Quo Vaditis?

This paper takes a closer look at the emerging topic of transformative service research (TSR) and compares its facets with the more established concept of the service-dominant logic (SDL). The paper thus contributes to both theory development and practical application. This work highlights the conceptual parallels in the two approaches, for example, their holistic approach, their systems thinking, addressing entities or actors within such system(s), inclusion of the wider environment, and their focus on the co-creative and interactive nature of well-being generation and value co-creation. The paper also reveals some differences, for example TSR’s focus on eudaimonic and hedonic well-being outcomes vs. SDL’s value co-creation. The paper concludes that both perspectives have merits, but could benefit from being used integratively. By comparing the areas of theory focus, practical application, value co-creation and co-destruction, intentionality, well-being and value concepts, and TSR and SDL’s “logic”, the paper provides suggestions for future research.     

优化Hammerstein模型的电磁脉冲效应建模仿真

针对采用Hammerstein模型描述电磁脉冲效应时模型参数确定困难的问题，提出一种基于优化Hammerstein模型的非线性电磁脉冲效应建模仿真方法。该方法利用高阶累积量求解模型线性延迟阶数，采用赤池信息准则（Akaike Information Criterion,AIC）优化模型非线性阶次，两者共同确定出一个参数最少、精度较高的最优模型，并以瞬态抑制器的电磁脉冲效应建模为例验证了该方法。     

FVC方法:评估公司价值的先进方法

为了更好地评估公司价值,介绍一种最近国际上出现的通用性公司价值计算模型,它所采用的算法内核更好地把对公司价值的财务分析与计算机编程技术相结合,从而可以更加有效地进行实际操作,以提高工作效率,节省时间。     

Four decades of negative word-of-mouth and negative electronic word-of-mouth: A morphological analysis

Customers voice their negative brand experiences to their family and friends in the form of negative word-of-mouth (NWOM). Web 2.0 enables the sharing of NWOM in electronic format on various social media sites, online customer review forums, and blogs, which is known as negative electronic word-of-mouth (NeWOM). Researchers need to study the spread of NWOM/NeWOM to prevent adverse consequences for companies and suggest an optimal response for its redressal. Existing literature review studies have focused on word-of-mouth (WOM) and electronic WOM (eWOM) and have considered both positive and negative WOM and eWOM concurrently. Past literature reviews have captured the breadth of the WOM domain, ignoring the depth. This research article contains a review of 282 journal papers capturing the depth of the extant literature by focusing solely on ‘negative’ WOM and eWOM (NWOM and NeWOM), and presents a broad view of the NWOM and NeWOM domains using morphological analysis (MA). This will help to conceptualize and categorize the existing state-of-the-art literature into broad dimensions and identify future research opportunities. The MA framework helps to bifurcate this literature into the following four dimensions: (i) nomenclature of NWOM and NeWOM, (ii) antecedents of NWOM/NeWOM, (iii) impacts of NWOM/NeWOM, and (iv) prevention and recovery response to NeWOM. Further dissection of these four dimensions leads to 15 sub-dimensions and 217 variants. Combinations of the 217 variants enable the identification of 550 novel future research opportunities in the area of NWOM and NeWOM.     

The political market for immigration restrictions: Model and test

This paper addresses the important question of whether public investment spending on economic infrastructure enhances economic growth in Mexico. It estimates a Cobb-Douglas production function that includes public infrastructure capital. Using cointegration analysis, the paper estimates a vector error correction model (VECM) for the 1995?–?99 period. The results suggest that there is a long-term stable relationship among the variables included in the VECM. The evidence also indicates that both public infrastructure spending and private capital formation have a positive and highly significant effect on the rate of output growth. Finally, the impulse response functions (IRF) and the variance decompositions (VDC) of the endogenous variables in the VECM suggest that the response of private capital to public infrastructure is positive while the reverse causation is not affirmed. From a policy standpoint, the findings call into question stabilization policies that disproportionately reduce public infrastructure to meet targeted reductions in the fiscal deficit (JEL, O1, O47, O54).     

PTE,innovation capital and firm value interactions in the biotech medical industry

Unlike previous studies which only focus on the main effect between IC and FV, this research includes PTE with the gap of resource-based view. IC is a key element in creating a competitive advantage, as it has a great influence on FV. A company may put relatively less into IC if it demonstrates higher efficiency. However, previous studies have neglected the fact that relative efficiency and IC affect FV and stock returns directly and indirectly. The research period was from 2006 to 2010 and the main research methods include HRA and DEA. The main research findings include the following. (1) There is a space for improvement in terms of the total technical efficiency. (2) PTE has a significant moderating effect between IC and FV. (3) IC and PTE have a significant influence on FV. (4) Apart from PTE and stock returns, IC and FV show significant differences within the sub-industry.     

以数据挖掘提升SRM决策分析能力

传统供应商关管理(SRM)在供应商分类评价方面存在不足,将数据挖掘技术引入其中,以从大量的数据信息中发现影响供应商合作价值的潜在规律,从而提升SRM的决策分析能力。设计中综合使用了数据仓库、聚类分析、决策树方法,并在国内一大型制药企业运用实践,为SRM的深入开发和应用提供了有价值的参考。     

Multinational Enterprises’ Entry Mode Strategies in Syria and Jordan: The Impact of Ownership Advantages

This study addresses the issue of ownership advantages affecting multinational enterprises’ (MNEs) entry mode strategies in developing countries. Although a few studies have focused on such effects, very little attention has been devoted to the ownership advantages generated from the institutional environment of MNEs’ home countries. To bridge this gap, this study concentrates on three types of ownership advantages: intangible asset advantages (IAA), advantages of common governance (ACG), and home‐country‐specific advantages (HCSA). Using a sample of 303 foreign affiliates, this study empirically examines the choice of MNEs between a wholly owned subsidiary (WOS) and a joint venture (JV). The data were collected from senior executives of MNEs’ subsidiaries operating in Syria and Jordan. The findings of this study reveal that MNEs’ choice of entry mode strategies is significantly influenced by intangible asset advantages, advantages of common governance, and home‐country‐specific advantages. Hence, senior executives perceiving an increased importance of these assets will opt for a WOS rather than a JV when entering a new market in the Middle East. © 2015 Wiley Periodicals, Inc.     

LT码新型度分布及其在电力线通信中的应用

Luby变换(Luby Transform,LT)码作为信道编码应用于电力线通信(Power Line Communication,PLC)，可实现电信号的可靠传输。度分布对LT码编译码性能的影响至关重要。为了得到更优的度分布，首先调整二进制指数分布(Binary Exponential Distribution,BED)中的度数比例，获得一种译码性能更优的改进的二进制指数分布(Improved BED,IBED)。然后，根据IBED在冗余度较小时译码成功率高，而冗余度增大后鲁棒孤子分布(Robust Soliton Distribution,RSD)的译码性能表现更佳的特点，通过求和归一化的方式将IBED与RSD两种度分布的优势进行有机结合，提出一种新型二进制鲁棒孤子分布(Binary RSD,BRSD)。仿真结果表明，与其他方法及传统的RSD相比，采用新度分布进行LT编码，可明显降低译码开销，并节约编译码耗时。将新型度分布应用于基于LT码的PLC系统中，能有效地抑制PLC信道中各种噪声对电信号的干扰，并提高通信效率。