低轨卫星接入系统中基于位置信息的时隙分配协议

针对浮标卫星通信系统中卫星覆盖范围广、接入链路传播时延差异大的场景结构引起的统一延迟分配协议中端到端时延长、吞吐率低的问题,提出了一种基于位置信息的时隙分配协议。协议中卫星通过获取浮标位置信息来控制时隙分配的起点,实现时隙离散分配,增大可用传输时隙长度,同时降低传输时延。OPNET 仿真结果表明所提出的时隙分配协议可以显著提高单信道传输模式下的网络吞吐量,并有效降低单信道与双信道模式下浮标卫星通信系统接入时的端到端时延。     

一种高效可靠的无人机自组网多跳TDMA协议

设计无人机自组网媒体接入控制（Medium Access Control,MAC）协议时,需要考虑其控制开销和数据传输的可靠性。鉴于此,结合现有无线自组网多跳时分多址接入（Time Division Multiple Access,TDMA）协议和无人机自组网特点,提出了一种高效可靠的无人机自组网多跳TDMA协议。首先采用高效负载均衡的时隙请求信息上传机制,选择一个负载较小的节点转发节点时隙请求信息;然后根据相互通信的父节点删除重复节点的时隙请求信息,减少相同节点的时隙请求信息转发次数;最后通过实时更新节点时隙请求信息机制,提高节点时隙请求信息传输的可靠性。仿真结果表明,该协议在数据传输成功率、平均时延、控制开销方面优于现有协议,可较好地应用在无人机自组网中。     

采用预测算法的卫星CFDAMA MAC协议时延性能分析

提出了地面站采用预测预约算法的混合式按需／自由分配-预测预约（CFDAMA-PR）卫星媒体接入控制协议。CFDAMA-PR协议可采用预定预约时隙或轮询预约时隙发送预约请求。在文中，通过计算机仿真对预定时隙预约CFDAMA-PR、CFDAMA-PA与基本DAMA协议进行性能比较，同时还对轮询预约CFDAMA-PR和CFDAMA-RR协议进行了仿真性能比较，仿真中采用IFP突发信源，仿真结果说明CFDAMA-PR协议采用预测预约算法，实现了更好的时延／吞吐量性能。     

采用TDMA和CSMA混合MAC协议的时隙调整算法

由于车联网(VANET)拓扑动态变化,车辆高速移动以及不同服务质量要求,制定媒体接入控制(MAC)协议面临巨大挑战。在控制信道间隔内采用基于TDMA和CSMA的混合接入协议是最有效的MAC协议之一。基于TDMA和CSMA的混合MAC协议(T-C-MAC)能够依据车辆环境调整TDMA帧长度,并能有效地传输非安全消息。为了提高T-C-MAC协议的性能,提出了一种基于三跳邻居信息的时隙调整(THSA) 算法。通过有效地调整车辆传输时隙,基于THSA的MAC（THSA-MAC）协议能够有效地实施广播服务,提高了安全消息传输率。实验数据表明,THSA-MAC有效地提高了安全消息传递率。     

基于分布式时隙调度协议的战术互联网媒体访问控制技术

在分析现有移动无线网络TDMA时隙调度问题的基础上,根据战术互联网骨干网拓扑与业务需求,结合跳频电台的特点,提出了一种新的动态分布式TDMA时隙调度协议(DTSP),能够适应不同业务需求,支持单播、广播和组播.DTSP协议以无冲突的预留提高系统吞吐量,以渐增方式适应动态拓扑变化,动态调整的开销较小.最后,以DTSP时隙单播预留协议为例,进行了详细分析和复杂度计算.     

多信道车载网中基于时分多址的MAC改进算法

车载网(VANETs)需提供时延敏感的安全应用和非安全应用的通信服务。这就使得媒体接入控制（MAC）协议既要满足安全消息的时延和可靠率，又要保证非安全消息的服务信道利用率，给MAC的设计提出了挑战。为此，提出基于时分多址的MAC改进算法(I-TDMA-MAC)。I-TDMA-MAC算法在每个同步帧内给每辆车分配两个子时隙，旨在提高无碰撞信道接入率和安全消息的传递率。同时，对空闲时隙采取重分配策略，并基于最短作业优先准则(SJF)给空闲时隙设置优先级，旨在提高服务信道利用率。仿真结果表明，提出的I-TDMA-MAC算法的安全消息传递率高达99%，当车流密度到达100 vehicle/km时，服务信道利用率接近于90%。     

架构在Linux平台上的无线接入Intranet方案

本文全面系统地介绍了无线接入Ｉｎｔｅｒａｎｅｔ的协议标准一无线应用协议（ＷＡＰ），并给出了一个在Ｌｉｎｕｘ平台上开发遵循ＷＡＰ协议标准的ＷＡＰ网关实现无线接入Ｉｎ－ｔｒａｎｅｔ的具体方案。     

财经界e百科

通用分组无线服务(GPRS)技术GPRS 将信包交换模式引入到 GSM网络中,从而提高了资料利用率。GPRS可提供高达115kb/s 的传输速率,并能支持 Internet 的 IP 协议及 X.25协议。GPRS 的基本原理是使多个用户共享某些固定的信道资源。它将每个时隙的传输速率从9.6kb/s 提高到14.4kb/s。实现 GPRS 网络需要在 GSM 网中引入新的网络接口和通信协议。增加的网络节     

财经界e百科

通用分组无线服务(GPRS)技术GPRS 将信包交换模式引入到 GSM网络中,从而提高了资料利用率。GPRS可提供高达115kb/s 的传输速率,并能支持 Internet 的 IP 协议及 X.25协议。GPRS 的基本原理是使多个用户共享某些固定的信道资源。它将每个时隙的传输速率从9.6kb/s 提高到14.4kb/s。实现 GPRS 网络需要在 GSM 网中引入新的网络接口和通信协议。增加的网络节     

认知无线网络中基于业务区分的自适应MAC协议

为了提高认知用户的接入效率,同时兼顾其QoS需求,提出了一种应用于认知无线网络的基 于业务区分的自适应MAC协议。对不同业务采取 不同的最优频谱检测时间,实时业务(RT)以最小化接入时延为目的确定最优的 频谱检测时间,而非实时用户(NRT)则以最大化吞吐率为目标确定最佳的频 谱检测时间。根据所确定出的最佳频谱检测时间,结合当前的业务到达速率和调度策略,不 同业务以时隙Aloha的方式接入空闲频谱。理论分析和仿真表明,所提出的自适应MAC协议能 够自适应地为认知用户的不同业务确定最优频谱检测时间,从而有效地提高频谱使用效率, 保证不同业务的QoS需求。     

Effects of Concentrated Ownership and Owner Management on Small Business Debt Financing*

Using unique data and a new powerful Monte Carlo-based statistical tool, we examine the effects of concentrated ownership and owner–management (CO-OM) on the creditor–shareholder agency conflicts in small firms. A significant CO-OM effect from the small business owner's view, but insignificant from the commercial lenders' perspective, is found. Special features of informational asymmetry problems in small firms with CO-OM are also highlighted. Theoretical and empirical contributions are made to the small business management and corporate governance literature. Findings obtained from this research have important implications for small business practitioners as well as researchers, and this study can serve as a reference for policymakers and institutional lenders to assist small firms in successfully raising money through debt financing. In addition, a new powerful methodology is introduced to deal with various potential statistical biases and can be further applied to this line of research.     

海事卫星通信系统VoIP技术的应用分析

随着VoIP技术的发展,VoIP技术结合卫星通信网络的应用越来越广泛。Inmarsat卫星系统是地球同步轨道系统,网络传播时延大,卫星VoIP电话的语音通信是否可行值得研究。结合VoIP关键技术和海事卫星通信语音通信应用场景,探讨了基于Inmarsat卫星网络实现VoIP技术的方案,并分析出此方案下VoIP系统通话过程的单向时延为350 ms,低于ITU G.114的400 ms的要求。在实际使用环境中进行了测试和验证,结果表明,基于Inmarsat网络下实现VoIP的方案是可行的。该方案实现复杂度低,可以方便地实现Inmarsat网络与地面电话网之间的互联互通,也可以为我国自主研制的宽带卫星通信系统实现VoIP技术提供参考。     

雷达低角跟踪分析与探讨

由于多径效应影响，雷达跟踪系统对处于低仰角内的目标跟踪会出现不稳定。本文对多径效应现象进行了分析，对常用方法进行了探讨。如果将分集技术与自适应技术结合起来，将很好抑制多径干扰。     

New entrants in a mature market: An empirical study of the detergent market

An analysis of the UK and German detergent markets provides useful evidence for the development of a model to predict the share changes that occur when a new product enters the market. A simple share order effect (SOE) model based on Luce's Axiom of the Independence of Irrelevant Alternatives (IIA) is tested on four different new product launches. Of these, only the product with both a new brand name and a new product format is consistent with the model. In the remaining three cases, all line extensions, the empirical data deviate from the model's predictions. The two UK line extensions appear to be affected by product format; the German line extension cannibalizes the parent. From these studies, it is suggested that radical line extensions do not cannibalize whereas line extensions that have a close fit with the parent are more likely to take sales from the core brand.     

Testing the Selectivity Hypothesis in cause-related marketing among Generation Y: [When] Does gender matter for short- and long-term persuasion?

Cause-related marketing (CRM) can enhance corporate image and increase sales, but effects may vary depending on the audience. Findings from a national survey, Study 1, reveal that Generation Y women are more likely than Generation Y men to support CRM. Our research further demonstrates unique findings with respect to message processing and response to a CRM campaign. In an experimental setting, Study 2 shows different gendered responses to a CRM campaign over time. Results show that men's purchase intentions decrease after message exposure, but increase after a two-week delay; the opposite was true for women. In line with the Selectivity Hypothesis theory, only women integrated multiple cues into the formation of purchase intentions. Theoretical and managerial aspects of gender for CRM are discussed.     

The value of family control during political uncertainty: Evidence from Thailand's constitutional change in 2014

We examine the effect of family control on firm value and corporate decision during Thailand's constitutional change arising from the 2014 coup d'état. We find that Thai family firms perform poorly when compared to non-family firms during the period of political uncertainty. The effect is more pronounced when firms have high expected agency costs from outside investors. Further, we find that family firms delay their investments, hold less cash, pay smaller dividends and have poorer access to debt financing sources relative to non-family firms. The reductions in investment and financing activities may at least partially account for their underperformance. Our evidence is consistent with the view that family control enhances firms' survivorship by establishing political connections in times of political uncertainty at the expense of minority shareholders.     

Moving forward: Balancing the financial and emotional costs of business failure

Why do owner-managers delay business failure when it is financially costly to do so? In this paper we acknowledge that delaying business failure can be financially costly to the owner-manager and the more costly the delay, the more difficult the recovery. But we complement this financial perspective by introducing the notion of anticipatory grief as a mechanism for reducing the level of grief triggered by the failure event, which reduces the emotional costs of business failure. We propose that under some circumstances delaying business failure can help balance the financial and emotional costs of business failure to enhance an owner-manager's overall recovery — some persistence may be beneficial to recovery and promote subsequent entrepreneurial action.     

Interaction between two types of information on reactions to delays

This study examines the effects of the interaction of two types of information about delays—information about the duration of a delay (delay duration information) and information about the reason for a delay (delay reason information)—on people’s reactions to delays. In this paper, we argue and demonstrate that the two types of delay information interact to affect attribution for the delay and perceived delay duration. The results obtained from an experimental study indicated that there was a stronger effect of delay reason information on attribution for the delay when delay duration information was absent than when the information was present. When no reason was given for the delay, the subjects attributed greater control to the service provider and perceived the delay to be longer when delay duration information was absent than when the information was present.     

基于累积和的改进超宽带循环平稳检测算法

针对超宽带循环平稳检测存在的门限难以设定、低信噪比下检测延迟较大的问题，提出了基于累积和的改进超宽带循环平稳检测算法。首先将信号整个三维循环谱归一化为二维灰度图，与噪声对应的灰度图比较差异，再将两类图像放入卷积神经网络（Convolutional Neural Network,CNN）自行训练提取特征，解决门限难以确定的问题。若分析三维循环谱的时间块长过短，将导致信号灰度图特征在有无噪声情况下区别不大；若块长过长会导致检测延迟较大。为此，采用累积和算法提取网络全连接层输出的信号概率作为累积和的观测统计量，自适应检测所需采样时间长度。将所提算法与传统循环平稳检测以及结合了CNN的循环平稳检测进行对比，仿真表明所提算法在低信噪比下性能最优。     

悬置微带线的过渡设计

设计了一种新型微带-悬置微带线和波导-悬置微带线的过渡结构。此过渡模型工艺简单、尺寸紧凑、加工精度不高,在较宽的频带范围内实现了较好的过渡特性。这种过渡设计可以改善悬置微带电路的应用范围,同其它电路或系统可以更好地综合应用。通过仿真设计和样品测试,在整个Ka频段,波导-悬置微带线过渡结构插入损耗小于0.75 dB。