应用业务预测的动态带宽分配算法

当前以太无源光网络中动态带宽分配算法主要是基于轮询机制.其中限制带宽分配算法根据各个ONU发送的队列长度能够动态分配带宽,但是这种算法不能实时获得各个ONU的队列长度.因此,利用维纳滤波的方法对自相似业务流量进行预测,预测的结果应用于限制动态带宽分配,得出一种改进的动态带宽分配算法.这种改进算法通过预测ONU的队列长度,更确切地反映了其状态信息,有利于OLT进行准确地带宽分配.对这种算法进行了仿真分析,在业务负载介于0.1～0.5的情况下,平均包时延比较接近0.1ms,达到了改进目的.     

一种轮询周期受限的EPON双级动态带宽分配算法

提出一种新的EPON上行带宽分配算法——轮询周期受限的双级动态带宽分配算法。这种算法结合用户等级协定和DiffServ的特点,采用周期受限的轮询方法和双级的带宽分配方式,在OLT端根据ONUi提供的业务队列情况对业务量进行估算,并授权带宽给ONUi,ONUi根据实际的业务量进行再分配。仿真结果表明,这种算法实现了高的带宽利用率,与DBAM相比有效地提高了EPON的QoS。     

EPON中一种改进的DBA算法

动态带宽分配是EPON系统的关键技术之一。由于多个ONU共享同一上行信道,对上行数据流的控制显得尤为重要。EPON系统使用请求/应答机制对ONU进行带宽分配。在ETRI算法的基础上,提出了一种改进的算法,它支持队列优先级和ONU之间的公平性。通过仿真结果可以看出,改进的算法与ETRI相比,大大减少了平均队列长度。     

EPON的性能分析及优化

本文研究了以太无源光网络(EPON)的动态带宽算法,提出了基于轮询-呼叫方式的优化DBA算法.本文以合理地利用和分配带宽,确保系统得到QoS保证为目标,对上行通道剩余带宽的利用提出了相应的优化方法和调度机制,并进行了性能分析和比较.同时在研究了人们往往容易忽略的ONU的退出和启动基础上,进一步对EPON运行过程中ONU的接入和退出时带宽的利用进行了优化,并提出了解决方案.     

EPON上行链路动态带宽分配算法(DBA)分析

介绍和分析EPON的特点,侧重分析动态带宽分配算法的原理和相应类别的优缺点。主要分析3种DBA算法——间插轮询(IPACT)带宽分配算法算法、BGP算法和基于比例分配的支持服务等级区分带宽分配算法,分析其原理、上行通道的利用率及对不同业务等级之间公平性的影响,得出各自优缺点的结论。     

基于QoS升降级的无线异构网动态带宽分配策略研究

利用异构无线网络环境下实时多媒体业务传输带宽可变的特点,提出一种基于服务质量(QoS)升降级的动态带宽分配策略。该策略针对系统带宽资源不足的情况,给出基于信道容量对多媒体用户进行平缓QoS升降级的方法,使系统在用户可接受的降级程度内接入更多的呼叫,进一步,为得到满意的服务等级(GoS),设置一个限制新呼叫接入的带宽阈值,并基于Markov模型给出该阈值的计算方法。与固定划分降质水平的带宽分配策略比较的结果表明,上述带宽分配策略能有效降低新呼叫阻塞率(CBP)与切换呼叫中断率(HDP),同时能明显提高带宽资源利用率。     

基于FDMA系统的两跳中继网络的资源分配

首先介绍了一种可用于两跳中继网络的时分模式帧结构,然后基于该帧结构提出了一种资源分配算法.该算法包括两个步骤:第一个步骤是第一个时隙上的动态资源分配,第二个步骤是基站与中继站之间的最优化功率分配.两跳中继网络中下行存在三种链路:"基站-中继"链路、"基站-用户"链路和"中继-用户"链路,在系统资源有限的条件下,通过所提算法为这三种链路分配相应的带宽和功率,可以使得系统的吞吐量最大.仿真结果表明所提算法能够有效地提高系统的吞吐量.     

EPON上行接入动态带宽分配算法的研究

以太无源光网络的上行方向需要一种多址接入技术来防止以太数据包的碰撞。时分多址技术应用广泛,而波分多址技术极具潜力,是发展的方向。基于时分多址技术,提出了一种改进的动态带宽分配算法,结合了轮询机制和申请的优先级。通过建模仿真,证明了该算法可以取得较小的平均包延时和较高的带宽利用率。     

自适应光学系统时间带宽和空间带宽的匹配

自适应光学系统存在的时间带宽和空间带宽。为了有效地利用自适应光学系统的系统资源，必须使这两种带宽匹配。本文通过经系统校正后的剩余波前扰动相位的均方差与系统时间带宽和空间带宽的关系，研究了在不同条件下系统时间带宽和空间带宽的匹配问题。     

M小区EPON网络割接技术探析

EPON通信系统由光纤线路终端(OLT)、光分配网络(ODN)和光网络单元(ONU)组成。EPON组网采用树形拓扑结构,光信号通过分光器把OLT一根光纤下行的信号分成多路给每一个ONU,每个ONU上行的信号通过分光器合成在一根光纤里给OLT。     

Allocation of bandwidth and storage

We consider two allocation problems in this paper, namely, allocation of bandwidth and storage. In these problems, we face a number of independent requests, respectively, for reservation of bandwidth of a communication channel of fixed capacity and for storage of items into a space of fixed size. In both problems, a request is characterized by: (i) its required period of allocation; (ii) its required bandwidth (item width, respectively)and (iii)the profit of accepting the request. The problem is to decide which requests to accept so as to maximize the total profit. These problems in general are NP-hard. In this paper we provide polynomial-time algorithms for solving various special cases, and develop polynomial-time approximation algorithms for very general NP-hard cases with good performance guarantees.     

High bandwidth underwater optical communication

We report error-free underwater optical transmission measurements at 1 Gbit/s (10(9) bits/s) over a 2 m path in a laboratory water pipe with up to 36 dB of extinction. The source at 532 nm was derived from a 1064 nm continuous-wave laser diode that was intensity modulated, amplified, and frequency doubled in periodically poled lithium niobate. Measurements were made over a range of extinction by the addition of a Mg(OH)(2) and Al(OH)(3) suspension to the water path, and we were not able to observe any evidence of temporal pulse broadening. Results of Monte Carlo simulations over ocean water paths of several tens of meters indicate that optical communication data rates >1 Gbit/s can be supported and are compatible with high-capacity data transfer applications that require no physical contact.     

Angle-insensitive flow measurement using Doppler bandwidth

The ability to measure the velocity of blood flow independent of the orientation of the blood vessel could aid in evaluation of many disease processes, such as coronary lesions. Conventional ultrasonic Doppler techniques require knowledge of the beam-to-flow angle, and the Doppler effect vanishes when this angle is 90 degrees . By employing a spherically symmetrical range cell and the Doppler bandwidth instead of the Doppler shift, preliminary results show that flow measurement of ideal uniform flow that has a blunt velocity profile can be made without knowledge of tile orientation of the vessel, even when the angle of orientation is around 90 degrees . But when the technique is applied to a real how that has a parabolic velocity profile, the Doppler bandwidth decreases as the beam-to-flow angle increases. Although the Doppler bandwidth is sensitive to the transducer angle in this situation, the error in determining flow velocity might be acceptable if the transducer angle can be estimated to be within a small range. For this method to be regarded as practical for clinical use, however, a consistent relationship between bandwidth and flow velocity must be demonstrated over some set of clinically relevant conditions. The experimental techniques and results for how measurements of both the ideal uniform flow and the real flow are presented in this paper.     

Experimental proof of Doppler bandwidth invariance

A line flow of scatterers crossing the sound field produced by a focused circular transducer at uniform velocity originates a quasi-triangular Doppler spectrum. It is known that the spectrum shape and width depend on the line flow to beam axis angle, as well as on the transducer geometry. It has recently been theoretically predicted that this spectrum width is independent of the flow line location in the sound field. Experimental verification of the new theorem, based on the use of a thread phantom operated at various orientations, ranges, and offsets, with respect to the ultrasound transducer, is presented. The tests were made with a computerized pulsed Doppler system designed to perform optimal real-time spectral analysis of data obtained in this application. The prototype system and the experimental procedure adopted for demonstrating in vitro the invariance of the Doppler spectral bandwidth are described.     

Simple and effective bandwidth reduction algorithm

An automatic algorithm is presented for reducing the bandwidth of symmetric interconnectivity matrices. The technique takes an arbitrary input scheme and reorders the nodes so as to reduce the bandwidth. A large number of examples is presented to illustrate the reliability and cost-effectiveness of the method.     

A hybrid algorithm for reducing matrix bandwidth

A hybrid algorithm for reducing the bandwidth of symmetric matrices is described in terms of a finite element grid. The new algorithm produces significantly lower bandwidths than either the commonly-used Gibbs–Poole-Stockmeyer (GPS) or Cuthill–McKee (CM) algorithms, with run times comparable to the original CM algorithm. The new hybrid algorithm uses the GPS algorithm as a preprocessor to provide a good initial node numbering for the author's node-shuffling algorithm, which accounts for variable degrees-of-freedom per node (DOF/node). The hybrid algorithm was tested on the 30 benchmark problems that were compiled by Everstine, and on 10 supplemental problems with variable DOF/node. Bandwidths and CPU times are presented for all problems.     

A novel Mu-negative metamaterial with broad bandwidth

A novel polarization-independent Mu-negative metamaterial with broad bandwidth named fan-shaped structure, composed of periodically arranged capacity-loaded fan-shaped patches symmetrically printed on the both side of a FR4 substrate, is theoretically and numerically investigated in this paper. First, the effective constitutive parameters are retrieved from the computed scattering parameters and are found having a negative permeability characteristic in the frequency range of 6.86–9.46 GHz, which is much wider than conventional split-ring resonator. Second, simplified equivalent LC models based on detailed study of field and surface current distribution, which can account for the characteristics of its electromagnetic behaviour, are introduced. Expressions of magnetic and electric resonance frequencies, deduced from the LC models, are presented as well. Finally, the dependence of the negative permeability characteristic on the system’s geometrical parameters is analysed through a parametric investigation. This study offers a potentially simpler approach to building optimized left-handed metamaterials with a broad bandwidth.     

Rainbow holographic aberrations and the bandwidth requirements

Rainbow holographic image resolution, primary aberrations, and bandwidth requirements are presented. The results obtained for the rainbow holographic process are rather general, for which the conventional holographic image resolution, aberrations, and bandwidth requirements, can be derived. The conditions for the elimination of the five primary rainbow holographic aberrations are also given. These conditions may be useful for the application of obtaining a high-quality rainbow hologram image. In terms of bandwidth requirements, we have shown that the bandwidth requirement for a rainbow holographic construction is usually several orders lower than that of a conventional holographic process. Therefore, a lower-resolution recording medium can generally be used for most of the rainbow holographic constructions.