Performance analysis and comparison of PoW,PoS and DAG based blockchains

In the blockchain, the consensus mechanism plays a key role in maintaining the security and legitimation of contents recorded in the blocks. Various blockchain consensus mechanisms have been proposed. However, there is no technical analysis and comparison as a guideline to determine which type of consensus mechanism should be adopted in a specific scenario/application. To this end, this work investigates three mainstream consensus mechanisms in the blockchain, namely, Proof of Work (PoW), Proof of Stake (PoS), and Direct Acyclic Graph (DAG), and identifies their performances in terms of the average time to generate a new block, the confirmation delay, the Transaction Per Second (TPS) and the confirmation failure probability. The results show that the consensus process is affected by both network resource (computation power/coin age, buffer size) and network load conditions. In addition, it shows that PoW and PoS are more sensitive to the change of network resource while DAG is more sensitive to network load conditions.     

A shunt active filter for compensating harmonics and unbalance in three-phase four-wire systems

ABSTRACT

This paper introduces a split-capacitor shunt Active Power Filter (SC-APF) based on Synchronous Reference Frame (SRF) theory. This topology is used in compensating the currents of 3-Ph unbalanced non-linear loads. The voltage control loop used in SRF which is only suitable in controlling Four-Leg APF (FL-APF) is modified to control Spilt-Capacitor APF (SC-APF). The proposed scheme provides compensating the 3-Ph unbalanced non-linear loads with lower number of switches, passive elements, and sensors. The performance of the SC-APF with the modified calculation algorithm is verified through simulation and experimental studies.     

A Balun-Bandpass filter with good in-band performance and wide stopband

A high performance Balun BandPass Filter (BPF) with capacitively loaded multiple coupled lines with very simple structure is proposed in this paper, this structure realizes simultaneous size reduction and superior harmonic response suppression performance in bandpass filtering meanwhile good differential performance of the Balun. The theory of this structure for unbalanced input into balanced output has been studied in this paper and a proper Balun and BPF characteristic by the symmetric feeding and skew symmetric feeding have been obtained to prove the theory. The enter frequency of the fabricated Balun-BPF is operated at 2.45 GHz with 6.93% Fractional Band Width (FBW), and this frequency is used for Bluetooth and some other communication systems. The differences between the two outputs are 180° ± 1.92° in phase and within 0.33 dB in magnitude. At f ₀, the amplitude imbalance and phase difference are within 0.25 dB and 180.86°, respectively. The measured frequency responses agree well with the simulated ones. With the theoretical analyses and practical results, it is shown that the proposed one has the advantages of simple structure, convenient analysis and good performance of both BPF and Balun.     

基于布鲁姆过滤器算法和三态内容寻址存储器的高效范围匹配方法

该文基于布鲁姆过滤器算法和三态内容寻址存储器(Ternary Content Addressable Memory, TCAM)技术提出一种高效范围匹配方法,解决了目前TCAM范围匹配方案存在的存储利用率低、功耗大的问题。设计基于最长共同前缀的分段匹配算法(Segmented Match on Longest Common Prefix, SMLCP)将范围匹配拆分为前缀匹配和特征区间比对两步,TCAM空间利用率达到100%。根据SMLCP算法设计了BF-TCAM模型,使用布鲁姆过滤器对关键字过滤,屏蔽无关项参与比较,大幅降低功耗。使用流水线缩短关键路径长度,使查找操作在一个时钟周期内完成。研究结果表明,所提方法实现了零范围扩张,工作功耗较传统TCAM降低50%以上。     

一种基于频率选择的周期噪声无模型反馈控制

使用频率选择滤波方法在频域设计反馈控制器，对每个干扰频率，仅需调节两个实系数。从频率选择滤波器输出误差信号中抽取不同的频率分量，用随机撮动方法调节控制器系数，在系统运行过程中不需次级声学路径估计。仿真结果表明，文中提出的控制方法对次级声学路经的突变具有鲁棒性。     

Fast computation of wideband RCS using characteristic basis function method and asymptotic waveform evaluation technique

The Asymptotic Waveform Evaluation (AWE) technique is an extrapolation method that provides a reduced-order model of linear system and has already been successfully used to analyze wideband electromagnetic scattering problems. As the number of unknowns increases, the size of Method Of Moments (MOM) impedance matrix grows very rapidly, so it is a prohibitive task for the computation of wideband Radar Cross Section (RCS) from electrically large object or multi-objects using the traditional AWE technique that needs to solve directly matrix inversion. In this paper, an AWE technique based on the Characteristic Basis Function (CBF) method, which can reduce the matrix size to a manageable size for direct matrix inversion, is proposed to analyze electromagnetic scattering from multi-objects over a given frequency band. Numerical examples are presented to illustrate the computational accuracy and efficiency of the proposed method.     

码移键控系统的性能分析

讨论了码移键控(CSK)基本原理、基于数字匹配滤波器(DMF)的快速捕获结构和用相关乘法器代替数字匹配滤波器的快速捕获结构,并对CSK系统的接收性能进行数学分析,得到了数据码错误率公式。     

基于粒子滤波的行人跟踪研究及其性能分析

智能监控系统中的行人跟踪功能在很大程度上能够减轻工作人员的大量眼力工作,通过智能的方式自主地跟踪用户感兴趣的目标。在视频监控环境的基础上,利用改进的粒子滤波器,设计了一个行人跟踪系统,并使其具有系统性能分析的功能。通过使用Mean Shift算法进行目标位置的预估计和多特征融合的方式使该系统在视频背景复杂的情况下能够实现对行人的稳定跟踪。并在实际应用中,分析了在遮挡情况下,行人跟踪效果差的原因,并予以改进。在Visualc＋＋集成开发环境中,基于OpenCV和MATLAB编程实现了系统,能够实时地对目标进行跟踪,并对跟踪结果进行反馈。     

双MOS门极控制的EST的开关特性和安全工作区

用二维 MEDICI商用器件模拟软件对双 MOS门极控制的发射极开关晶闸管 EST( Emitter Switched Thyristor)的正偏置安全工作区 FBSOA( Forward Biased Safe- Operation-Area)及其关断动态的电流分布进行了模拟研究 .证明该器件采用 P型转向器 ( diverter)与双MOS门极相结合的结构使得空穴电流分流从而显著地提高了 EST的开关能力 ,其 FBSOA也有明显展宽     

Performance evaluation and application of channel offset schemes inindoor channel assignments

We deal with channel offset schemes and their application in three-dimensional (3-D) frequency reuse environments with ideal cubic microcells. Formulas are derived to calculate channel reuse distances (CRDs) and interchannel usage distances (IUDs) for a given offset degree. For an indoor personal communication network (PCN), an algorithm is proposed for fixed channel assignment with channel offset. The spectral efficiency of channel offset schemes is discussed and the results show that compared to the channel offsetless scheme, channel offset schemes make more efficient use of limited spectrum resources     

PERFORMANCE COMPARISON OF CELL－BASED AND PACKET－BASED SWITCHING SCHEMES FOR SHARED MEMORY SWITCHES

Shared Memory (SM) switches are widely used for its high throughput,low delay and efficient use of memory.This paper compares the performance of two prominent switching schemes of SM packet switches:Cell-Based Switching (CBS) and Packet-Based Switching (PBS).Theoretical analysis is carried out to draw qualitative conclusion on the memory requirement,throughput and packet delay of the two schemes.Furthermore,simulations are carried out to get quantitative results of the performance comparison under various system load,traffic patterns,and memory sizes.Simulation results show that PBS has the advantage of shorter time delay while CBS has lower memory requirement and outperforms in throughput when the memory size is limited.The comparison can be used for tradeoff between performance and complexity in switch design.     

DWDM光纤通信网络中光发射单元的智能化监控

实现了密集波分复用 (DWDM)光纤通信网络中光发射单元 (OTU)的智能化监控 ,设计了以80 C5 5 2单片微机为核心的盘控 (MCU)部分 ,实现了激光器输出波长、光功率、偏置电流等重要参数的随时监控 ,并能在激光器工作状态异常时 ,及时上报网管、控制告警灯并自动调节激光器 ,以保证通信系统的顺利进行。成功地完成了 16× 10 Gb/ s的系统实验 ,各波长信道的传输功率代价均小于 2 d B(误码率 =10 - 1 0 )     

改进的传输参考型超宽带系统抗NBI性能

为研究带有有限长脉冲响应陷波滤波器(NF)的传输参考型超宽带系统(TR-UWB)的抗窄带干扰性能,在IEEE 802.15.3a建议的标准超宽带信道下,分析比较了在不同参数设置下,该系统自相关接收机的误比特性能。仿真结果表明,带有陷波滤波器的传输参考型超宽带系统能够有效降低窄带干扰,并且系统接收机结构简单,无需信道估计,大大降低了计算量和系统复杂度。     

常见分集合并系统的性能分析

在移动通信中,分集技术是一种最有效的抗衰落技术。本文对3种常见的线性合并分集技术进行简要分析,给出它们的基带表示和合并器输出信噪比的概率密度函数(pdf),由此给出它们的合并增益。针对系统采用MPSK调制的情况,对瑞利衰落信道的3种合并分集系统的比特误码率(BER)性能进行理论研究,分别给出选择性合并(SC)和最大比率合并(MRC)系统的理论比特误码率表达式;对于等增益合并(EGC)分集,给出了一种近似的EGC系统的输出信噪比的pdf,由此导出EGC的一种近似的BER表达式,由蒙特卡罗仿真结果可以看出此近似的BER数值结果是准确的。数值结果显示:MRC性能最好,EGC性能稍差,而SC性能较差。文中给出的分析方法对于实际分集系统的理论研究具有普遍的指导意义。     

DGT与DCT在图像编码中的性能比较

介绍了二维实值离散Gabor变换（RDGT）的快速算法,并着重探讨了二维实值离散Gabor变换与二维离散余弦变换在图像编码中的性能及差异。     

Performance evaluation of preemptive polling schemes and ARQtechniques for indoor wireless networks

This paper examines a radio-based indoor communication network with a single radio channel shared by several data terminals. By enabling the terminals to communicate with each other and access the resources of a wired network, the system is a potential provider of in-building LAN-like services. In this indoor fading environment, a base-station approach is assumed. In the analysis, a two-state Markov chain model is used to model the nonstationary transmission channel. Two preemptive polling multiple-access schemes combine with ARQ error-control schemes to counteract the effects of a nonstationary transmission channel. The main idea devised is that of making the service interruption dependent on the propagation conditions of the transmission channel by monitoring the outcomes of the data packet transmission attempts. A performance comparison reveals the superiority of the preemptive polling systems with respect to a classical TDMA scheme     

基于三维特征和结构相似度的图像质量评价方法

分析了人眼视觉特性、双眼视差异信息等三维特征,将立体视觉与图像的结构相似度(SSIM)相结合,提出了一种新的立体图像质量评价方法。该方法考虑了立体图像的亮度、纹理细节和空间位置等因素对人感知立体效果的影响,利用加权平均结构相似性(WMSS)联合统计学方法得到评价初值,用包含三维景物深度信息的双眼视差信息进行修正,作为立体图像质量的评价结果。实验表明,该方法符合人眼视觉特性,与主观评价(MOS)的一致性较好。     

RPR三种优先级业务的时延吞吐量性能分析

弹性分组环(ResilientPacketRing,RPR)是IEEE802.17正在进行标准化主要用于城域网的新型MAC层协议,也是宽带IP光城域网技术的重要发展方向。RPR在结构上从属寄存器插入环,其时延性能为业界所关注。本文根据RPR包含3个传输缓存的完整模型,利用排队论,对两种转发缓存结构下RPR3种优先级业务的排队时延吞吐量性能进行深入分析并比较,得到最大吞吐量和节点数目的关系、单转发缓存和双转发缓存结构下RPR的3种优先级业务的排队时延吞吐量性能及其对比、排队时延和节点数目的关系等一系列极具参考价值的结果。     

MIMO-OFDM系统中信道估计技术的性能评估

本文给出了MIMO-OFDM系统中的三种信道估计算法,详细的分析与比较了这几种算法在估计均方误差、实现复杂度、跟踪速度以及频带效率等方面的性能,最后通过MATLAB仿真试验对其进行了验证.     

Performance analysis and comparison of burst transmission schemes in unsaturated 802.11e WLANs

Contention free bursting (CFB) and block acknowledgement (BACK) are two innovative burst transmission schemes specified in the IEEE 802.11e standard for reducing the contention overheads and further improving the channel utilization of wireless local area networks (WLANs). Existing studies on performance analysis of the CFB and BACK schemes have been primarily focused on the system throughput and have not taken into account the realistic factors, such as unsaturated traffic loads and finite buffer capacity. To fill this gap, this paper proposes a new and comprehensive analytical model for evaluating the Quality‐of‐Service (QoS) metrics including throughput, end‐to‐end delay, and frame loss probability of both burst transmission schemes under unsaturated traffic conditions. The proposed model is validated through extensive simulation experiments and then is used to conduct performance analysis and comparison of the burst transmission schemes under various working conditions. The analytical results reveal that (1) both CFB and BACK schemes can substantially improve the QoS performance; (2) BACK scheme outperforms the CFB scheme when the transmission opportunity (TXOP) limit exceeds a threshold; (3) the analytical model can be used to identify the optimal configuration of system parameters for the burst transmission schemes subject to QoS constraints. Copyright © 2010 John Wiley & Sons, Ltd.