Effective bandwidth estimation and testing for Markov sources

This work addresses the resource sharing problem in broadband communication networks that can guarantee some quality of service (QoS), and develops some results about data source and traffic modelling, especially in aspects of model testing and parameter estimation. The multiplexing of variable bit rate (VBR) sources poses a mathematical and statistical problem: the estimation of the resource requirements of a source or set of sources. The estimation method shall be simple enough to be practically implemented in the connection acceptance control (CAC) function.

In this paper, the VBR video sources are taken as a typical case of variable rate, with real-time constraints. This association of requirements makes the case especially interesting. A Markov model is assumed for the VBR sources. The validity of such models is under research; they seem to be appropriate at least in certain time scales. The model is tested against real video traces. In order to estimate the resource allocation or “channel occupation” of each source, the concept of equivalent bandwidth proposed by Kelly [Notes on effective bandwidth, in: F.P. Kelly, S. Zachary, I.B. Ziedins (Eds.), Stochastic Networks: Theory and Applications, Oxford University Press, Oxford, 1996, pp. 141] is used; it is based on a consistent mathematical theory, and has proven to be robust and useful for technical applications.

A calculation of the equivalent bandwidth of a Markov source, given its parameters, can be found in the literature [IEEE ACM Trans. Networking 1 (4) (1993) 424]. But in fact, one can only estimate model and parameters. In this work, an estimation of the equivalent bandwidth is given, which can be obtained from real data. The convergence and the consistency of the estimation are studied, and practical bounds are found. Illustrative calculations are performed from real video traces that were obtained using a software MPEG coder, developed by the authors. The mathematical and statistical results are valid for whatever phenomenon that can be modelled as a Markov process.     

全光纤马赫-曾德尔干涉仪型不等带宽梳状滤波器

提出了由2个3×3和1个3×3单模光纤耦合器级联组成的全光纤Mach-Zehnder干涉仪(MZI)型不等带宽交错(梳状)滤波器。分析结果表明:两对光纤干涉臂长度差相等时,各耦合器的耦合系数选取适当值,器件实现了奇偶信道上不等带宽输出,分别用于10和40Gb/s传输,信道间隔为0.8nm,信道隔离度大于25dB。与其它不等带宽梳状滤波器相比,该器件基于MZI型梳状滤波器,且在实际制作时可以对每个耦合器的分光比进行准确监测和控制,大大降低了制作困难。实验所得结果与理论分析相吻合。     

Compact planar substrate‐integrated waveguide diplexers with wide‐stopband characteristics

Compact planar substrate‐integrated waveguide (SIW) diplexers with wide‐stopband characteristics are presented for the first time based on collaborative multispurious mode suppression techniques including the harmonic staggered technique, centered coupling windows, and offset‐centered output ports. The coupling scheme using common dual‐mode resonator coupled with multiple single‐mode resonators is adopted here to eliminate the T‐junctions for size and loss reduction, and the dual‐mode coupling controlling technique we previously proposed is also employed to allocate the fractional bandwidths (FBWs) of the two channels flexibly based on the FBW design graph. Additionally, by combining the harmonic staggered technique, centered coupling windows, and offset‐centered output ports, good out‐of‐band rejections can be achieved and excellent wide‐stopband characteristics have been implemented intrinsically. Two prototypes including second‐order and third‐order SIW diplexers are synthesized, designed, fabricated, and tested as demonstrations, extending the stopbands to 1.78f₁ and 2.04f₁ with the rejection levels better than 17.5 and 20 dB, respectively.     

Adaptive notch filter design under multiple identical bandwidths

Digital notch filters are applied to remove or suppress the narrow-band interferences in digital signals, while preserving other components unchanged. Under the condition of the identical notch bandwidths, a novel design method is put forward in this paper to realize the adaptive notch filter with infinite-impulse response (IIR). Firstly, a specially simplified all-pass filter is introduced to construct an IIR non-adaptive notch filter, which serves as the core part in the adaptive one. Secondly, the criterion of least-mean-square (LMS) is applied to design the desired adaptive notch filter (ANF). The designed ANF can track and suppress multiple non-harmonic interference components simultaneously. Finally, the effectiveness and practicability of the proposed design method are verified by a set of experimental results.     

Partial Discharge Measurement of OCP-Tapes in Rotating Electrical Machines

Nowadays, PD （partial discharge） measurements are a crucial part of the preventive maintenance of electrical equipment within high voltage engineering. Especially for electrical machines, both the supplier and the user are interested in the results of PD measurements. However, PDs hardly represent the cause of the failure, more likely they are claimed as the outcome of a failure. This paper deals with the insulation of a 6 kV electrical machine, whereas PD measurements were carried out at a single stator from wound coils. During manufacturing, these coils were equipped with different materials for the OCP （outer corona protection）. Using different PD measurement systems and different bandwidths, investigations of the PD behavior of the coils were carried out. Additionally, the surface resistivity of the corona protection was determined. As a result, conclusions for the correlations between the resistance of the OCP as well as the PD behavior are stated. Furthermore, the influence of using different measurement systems, different measuring circuits, and different bandwidths is shown.     

Dual‐band band pass filter using stub‐loaded open‐loop resonators with wide controllable bandwidths

Two dual‐band band pass filters (BPF) using stub‐loaded open‐loop (SLOL) resonator are presented in this article. A novel coupling tuning method by changing the relative coupling position of the resonators is proposed to control the bandwidth of each passband in a wide range. Transmission zeros are created to improve the selectivity by source‐load coupling. Because of the large ratio of two bandwidths, a novel dual‐band matching method is proposed to match the different load impedances at two passband frequencies to the same source impedance. Hence, relax the fabrication requirement of gap. The proposed dual‐band band pass filter is designed and fabricated. The measured 3 dB fractional bandwidths (FBWs) of two 2.45/5.25 GHz dual‐band BPFs are 6.5%/14.5% and 9.8%/5.5%, respectively. The results are in good agreement with the simulation. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE 24:367–374, 2014.     

Banding of MAR-aging steel

MAR-aging steels have gained a respectable position among design engineers who demand ultra-high strength, reasonable ductility, and good fracture toughness, especially where outerspace and aerospace applications are concerned. This specialty steel category of MAR-aging alloys owes its unique properties to a complex hardening reaction, which involves precipitation of uniform intragranular ribbons (Ni₃Mo phase) on dislocations during the treatment cycle. Like any other metallurgical process, MAR-aging treatment cycles can become quite difficult, if not impossible. When that condition does exist, the end result is often called a dead heat by MAR-aging technologists. This paper examines a dead heat and makes appropriate comparisons to other live heats. Salient differences and interactive similarities are both studied in terms of microstructure, serial sections, chemical composition, and selected mechanical properties. The intent of this paper is to shed more light on the previously indistinct subject of banding.     

双质量弹簧基准问题自抗扰控制研究

本文研究了自抗扰控制(ADRC)方法在双质量弹簧基准问题的应用.传统的自抗扰控制方法倾向于使用高增益控制来抑制扰动和模型不确定性,但是对于双质量弹簧基准问题,高增益在评分中受到较大惩罚,而且对于模型参数变化没有足够的鲁棒性.为解决这一问题,本文对ADRC设计提出了两种改进方案.首先,为了减小控制信号的幅度,将扩张状态观测器(ESO)的一个极点配置在原点.其次,采用阻尼比来调整带宽.结果表明,所提出的ADRC设计可以很好地解决双质量弹簧基准系统的控制问题.     

Performance Optimization of Optically Preamplified Receivers for Return-to-zero and Non Return-to-zero Coding

We determine optimum bandwidths for optical and electrical filters in optically preamplified receivers, both for NRZ coding and RZ coding. Our simulations clearly reveal the trade-offs to be made when optimizing bandwidths: NRZ is typically limited by intersymbol interference, while RZ is limited by energy truncation. Thus, RZ allows for tighter filtering, leading to near quantum limited performance. Further, RZ systems are less susceptible to suboptimum filtering. We also show that the use of RZ with duty cycles below 33% only leads to minor additional receiver sensitivity improvements at the expense of impractically higher receiver bandwidths. Employing an RZ duty cycle of 33%, we achieved a receiver sensitivity of 52 ppb at a data rate of 10 Gbit/s, which is only 1.4 dB off the quantum limit.     

静电放电试验中示波器的选择与使用

介绍了数字示波器测量带宽及采样速率方面的有关知识,分析了示波器对静电放电试验中上升时间测量的影响,提出了解决的具体措施,对其它领域快速非重复信号的测量有一定的指导意义。