均衡虚拟空间会议系统的混频时延和混频器数量的技术研究

合成虚拟空间会议系统(VST)的一个需要考虑的重要因素是混频器数量和混频时延的关系，其中混频器数量影响系统的成本，而混频时延影响系统的实时性，降低系统的混频时延和降低混频器数量是一对矛盾的问题．基于VST系统的通信效率与混频器关系，提出了在保证系统通信容忍的时延情况下，选取最少的混频器数量，以及在分层结构中系统通信的最小时延策略．采用这种策略能够有效地保证VST系统提供较高质量的服务时延和较低成本的混频．     

提高虚拟空间会议系统服务质量QoS的若干技术

虚拟空间会议系统是视频会汉系统发展的最高形式．本文结合作者研究工作，通过分析与视频会议系统服务质量相关的技术，提出了基于VST系统的相关技术策略，这些策略能够有效地提高VST系统的服务质量．     

产业信息

ADI发布具有宽带性能的多频带通信混频器Analog Devices,Inc.(ADI)推出集成度极高、面向通信应用的宽带无源混频器:单通道混频器ADL5811和双通道混频器ADL5812。这两款混频器具有出色的线性度、低失真、低噪声和卓越的宽带频率性能。新器件集成     

一致性场景下的边缘网络低时延存储算法

目前主流的边缘存储策略通过协同或非协同的方式来提高存储资源的请求命中率,从而降低请求延迟以满足时间敏感型业务的需求,然而这些策略并未考虑存储节点的副本数量过多所带来的一致性开销问题。提出一种基于虚拟传播树（VST）的边缘存储算法,针对边缘存储中的一致性开销问题,设计VST生成算法和节点淘汰算法,从而在副本数量高、一致性需求大的场景下实现可控低延迟服务。实验结果表明,该算法可以在一致性场景下提供低延迟服务,在非一致性场景下同样具有稳定的性能表现,请求时延和存储开销低于CV和NCV算法。     

ADI发布具有宽带性能的多频带通信混频器

Analog Devices,Inc．（ADI）推出集成度极高、面向通信应用的宽带无源混频器：单通道混频器ADL5811和双通道混频器ADL5812。这两款混频器具有出色的线性度、低失真、低噪声和卓越的宽带频率性能。新器件集成一个宽带LO（本振）放大器、一个可编程RF巴伦、一个高线性度混频器内核、一个可编程IF滤波器和一个IF放大器,为设计多频段、单板接收机提供了可能。     

重频超宽带脉冲对混频器的干扰特征分析

重频超宽带脉冲可对多种电子设备与电子器件产生干扰。针对电子器件的干扰效应,着重从仿真分析和实验两方面研究了重频超宽带脉冲对无源混频器的干扰特征。分析了混频器对超宽带脉冲信号的响应特性,给出了不同参数条件下重频超宽带脉冲信号对混频器及混频滤波电路的干扰特征。研究表明,作为干扰信号,重频超宽带脉冲信号并不能影响混频器正常工作;当重频超宽带脉冲信号与通信信号一起注入混频器时,混频器可实现其正常的变频功能,而作为衡量混频器工作性能的重要指标,变频损耗可认为基本不变;重频超宽带脉冲信号经过混频滤波电路后变为同中频信号同样频率的连续波信号,其对混频滤波电路的干扰以及之后电路的干扰类似定频连续波信号干扰。     

通信时延下AUV集群的分群控制算法北大核心CSCD

为解决通信时延下自主水下机器人(AUV)集群系统协同分群控制问题,借鉴经典蚁群算法概率公式,利用存在通信时延的子群规模需求信息和个体与群目标的距离信息,设计了满足期望子群数量和规模的就近分群策略。然后,设计了通信时延下的协同分群控制算法,使集群系统产生子群数量、规模和速度均满足需求的分群行为。最后,理论分析和仿真结果表明了该算法的有效性和可行性。     

具有通信时延的AQM控制算法的稳定性

具有通信时延的AQM控制算法是一个复杂的动态非线性反馈系统．为了调查通信时延对Internet服务质量的影响,借助广义Nyquist判据研究了具有通信时延的AQM策略的稳定性．通过对网络系统的传递函数的分析,得到了各通信回路时延相同和时延不同条件下网络系统在平衡点的稳定性判据．这些结论表明,影响Internet性能的关键因素之一的通信时延在Internet通信过程中起着重要的作用．最后仿真验证了该判据的有效性．     

ADI新款14位转换器可对3．6GHz的RF信号进行直接数字合成

针对全球通信设备制造商对于增加宽带通信系统的可用带宽和有效动态范围的要求,ADI公司最新推出两款可对3．6GHz的信号进行直接数字合成的14位DAc——AD9739与AD9789。新款AD9739和AD9789 TxDAC采用了ADI专利的Mix—Mode（混频模式）超奈奎斯特架构,支持频率高达3．6GHz的RF信号的高保真数字合成。最佳的带宽和动态范围与直接RF内核相结合,使得宽带和下一代无线设备设计工程师采用单个发送DAC架构即可支持多个通信标准,同时免去对片外混频器和低通滤波器的需求,从而降低设计复杂性、成本、功耗,并减小尺寸。     

无线多跳网络中支持多媒体QoS的中继节点转发队列调度算法研究

随着网络应用的日益广泛,一个通信网络往往需要支持多种业务。文章针对无线多跳网络,中继节点采用FIFO队列转发数据产生的时延累计效应导致的实时性服务不可用问题,提出了按照数据类型和数据包剩余时延对转发队列中数据包重新排序的策略。此策略能够在保持非实时性应用数据包时延可容忍的情况下,有效降低多媒体数据包的平均传输时延和整个系统的丢包率。     

虚拟空间会议系统的视觉空间合成

虚拟空间会议系统是在视频会议的基础上发展起来的,与会者以替身的形式出现在计算机生成的虚拟空间中,通过替身在虚拟空间中定位、观察、操纵虚拟空间的物体、与其他用户进行“面对面”交流,与会者共享“同一个空间”,达到协同工作的目的。本文介绍VST的概念,视觉空间的合成方法以及我们研制的VST系统VST－1。     

A Comparative Study of CNN- and Transformer-Based Visual Style Transfer

Vision Transformer has shown impressive performance on the image classification tasks. Observing that most existing visual style transfer (VST) algorithms are based on the texture-biased convolution neural network (CNN), here raises the question of whether the shape-biased Vision Transformer can perform style transfer as CNN. In this work, we focus on comparing and analyzing the shape bias between CNN- and transformer-based models from the view of VST tasks. For comprehensive comparisons, we propose three kinds of transformer-based visual style transfer (Tr-VST) methods (Tr-NST for optimization-based VST, Tr-WCT for reconstruction-based VST and Tr-AdaIN for perceptual-based VST). By engaging three mainstream VST methods in the transformer pipeline, we show that transformer-based models pre-trained on ImageNet are not proper for style transfer methods. Due to the strong shape bias of the transformer-based models, these Tr-VST methods cannot render style patterns. We further analyze the shape bias by considering the influence of the learned parameters and the structure design. Results prove that with proper style supervision, the transformer can learn similar texture-biased features as CNN does. With the reduced shape bias in the transformer encoder, Tr-VST methods can generate higher-quality results compared with state-of-the-art VST methods.     

Cartesian反馈线性化技术的延时补偿设计

Cartesian反馈线性化技术是减小射频功率放大器非线性失真的一种有效方式,但信号传输延时却严重影响反馈系统的稳定性,使得Cartesian反馈线性化技术受到带宽的限制.采用Smith预估补偿方法对Cartesian环路进行延时补偿设计来降低时间延时对反馈系统稳定性的影响,并给出了理论分析.计算机仿真结果也表明采用延时补偿设计的Cartesian反馈系统可以使本来早已不稳定的系统保持稳定,而且对输出功率在不同回退级时的线性化性能都有不同程度的改善.     

大时滞系统自适应模糊Smith控制

针对大时滞对象，把史密斯（Smith）预估控制原理和模糊控制器参数的自适应调整方法结合起来，即在Smith预估控制系统中，利用自适应机制在线整定模糊控制器的参数，即根据控制系统在各个阶段呈现出的不同特点来适时调节模糊控制器的量化和比例因子，以适应对象特性的变化。仿真研究表明，所提方法能有效克服普通模糊控制算法不适应大时滞系统控制和常规Smith算法过于依赖模型精度的缺陷，提高了普通模糊控制器对大滞后系统的控制能力。同时该算法还具有很强的鲁棒性和良好的控制品质。     

时滞滤波器抑制残留振荡:理论、 方法及应用

回顾了时滞滤波器的发展背景和近年来的研究状况,介绍了对滞滤波器的各种设计方法和主要研究领域。时滞滤波器可从根本上避免激发对象的振动模态而消除残留振荡,在柔性结构系统中得到了广泛应用。最后 对时滞滤波器技术中存在的问题及未来的研究方向进行了探讨。     

Stability and control of uncertain ICPT system considering time‐varying delay and stochastic disturbance

This paper studies the problem of robust exponential stability for uncertain inductively coupled power transfer (ICPT) system considering time‐varying delay and stochastic disturbance. Firstly, the model of the system is set up via a time domain method. Secondly, based on the Newton‐Leibnitz formula and stability theory, a new stability analysis of the ICPT system with uncertain parameter and time‐varying delay or stochastic disturbance is presented respectively. The proposed approach can be applied for analyzing other similar systems, and the obtained results can be also used for estimating convergence rate and region of stability. Thirdly, based on the Lyapunov‐Krasovskii functional (LKF) approach and the stochastic stability theory, robust exponential stability criteria in the mean square are derived and the relevant controller is designed. The proposed method can further reduce conservatism. Finally, the correctness and effectiveness of the obtained results are verified by an example and simulations indicate that the larger time delay, the slower attenuation. Simultaneously, the uncertain parameter and the stochastic disturbance have a significant influence on the region of stability. In addition, in respect of reducing conservatism, the effectiveness of the proposed method is demonstrated by comparing with other papers. In addition, the designed controller shows better performance for the ICPT system with the parameter uncertainty, the time‐varying delay, and the stochastic disturbance.     

An Augmented Reality System for the Treatment of Phobia to Small Animals Viewed Via an Optical See-Through HMD: Comparison With a Similar System Viewed Via a Video See-Through HMD

This article presents an optical see-through (OST) Augmented Reality system for the treatment of phobia to small animals. The technical characteristics of the OST system are described, and a comparative study of the sense of presence and anxiety in a nonphobic population (24 participants) using the OST and an equivalent video see-though (VST) system is presented. The results indicate that if all participants are analyzed, the VST system induces greater sense of presence than the OST system. If the participants who had more fear are analyzed, the two systems induce a similar sense of presence. For the anxiety level, the two systems provoke similar and significant anxiety during the experiment.     

Consensus seeking of multi-agent systems from an iterative learning perspective

The consensus seeking problems for both discrete and continuous multi-agent networks are discussed from an iterative learning perspective. It is shown that the consensus seeking process can be viewed as an iterative learning process for agents under directed networks to improve their performances from time to time in order to achieve consensus. If a desired consensus state is specified, then the multi-agent system can be guaranteed to reach consensus through reducing the tracking error between each agent’s state and the desired consensus state monotonically to zero with respect to the increasing of time. If there is no desired consensus state, then the agents can achieve consensus through reducing their states monotonically to the minimum quantity with increasing time. Simulations illustrate the observed results.