On variations of queue response for inputs with the same mean andautocorrelation function

This paper explores the variations in mean queue length for stationary arrival processes with the same mean and autocorrelation functions, or equivalently, the same mean and power spectrum. Three types of processes, namely, two-state Markov-modulated Poisson processes, periodic-sequence modulated Poisson processes and processes generated by randomly filtering a white noise process, are investigated. Results show that the mean queue length can vary substantially for the first type of process, and can vary moderately for the second type of process, as the parameters of the processes are varied, subject to a specified mean and autocorrelation function. However, the mean queue lengths for the third type of arrival processes are determined by the input mean and autocorrelation functions. The results suggest that the queueing performance can be hard to predict from spectral data alone when the power in low frequencies is large     

Adaptive estimation of latency change in evoked potentials bydirect least mean p-norm time-delay estimation

Evoked potentials (EP) have been widely used to quantify neurological system properties. Changes in EP latency may indicate impending neurological injury. Traditional EP analyses are developed under the condition that the background noise in EP analysis are Gaussian distributed. This paper proposes a latency change detection and estimation algorithm under α-stable noise condition, a generalization of Gaussian noise assumption. An analysis shows that the α-stable model fits the noises found in the impact acceleration experiment under study better than the Gaussian model. The robustness of the proposed algorithm is demonstrated through computer simulations and experimental data analysis under both Gaussian and α-stable noise environments     

A duality model of TCP and queue management algorithms

We propose a duality model of end-to-end congestion control and apply it to understanding the equilibrium properties of TCP and active queue management schemes. The basic idea is to regard source rates as primal variables and congestion measures as dual variables, and congestion control as a distributed primal-dual algorithm over the Internet to maximize aggregate utility subject to capacity constraints. The primal iteration is carried out by TCP algorithms such as Reno or Vegas, and the dual iteration is carried out by queue management algorithms such as DropTail, RED or REM. We present these algorithms and their generalizations, derive their utility functions, and study their interaction.     

Robustness of real and virtual queue-based active queue management schemes

In this paper, we evaluate the performance of both real and virtual queue-based marking schemes designed for use at routers in the Internet. Using fluid flow models, we show via analysis and simulations that Virtual Queue (VQ)-based marking schemes outperform Real Queue (RQ)-based marking schemes in terms of robustness to disturbances and the ability to maintain low queueing delays. In fact, we prove that a linearized model of RQ-based marking schemes exhibit a lack of robustness to constant but otherwise unknown levels of disturbances. The analytical results we present are applicable to combinations of proportionally fair and TCP-type congestion controllers at the source, and Random Exponential Marking (REM) and Proportional Control (PC) schemes at the router. The behavior of Random Early Discard (RED) and Proportional-Integral (PI) control schemes at the router are also studied via simulations.     

Frequency-hopped spread-spectrum random access with retransmissioncutoff and code rate adjustment

A transmission policy for frequency-hopped spread-spectrum random-access communication systems in which the retransmission of a blocked packet at each station is determined as a function of that station's own collision experience is examined. For stability considerations and for channel throughput increase, the information packet is encoded by a Reed-Solomon code. An equilibrium analysis is used to show that undesirable bistable behaviour can be avoided if packets are rejected after a certain number of transmission attempts and the code rate is adjusted accordingly. The region of code rate and number of transmission attempt pairs that guarantees the network stability are investigated. The packet rejection probability, average packet delay, and maximum stable throughput are evaluated     

Adaptive downlink scheduling and rate selection: a cross-layer design

In this paper, we discuss a cross-layer design for joint user scheduling and adaptive rate control for downlink wireless transmission. We take a stochastic learning-based approach to achieve this. The scheduling is performed at the medium access control (MAC) layer, whereas the rate selection takes place at the physical/link (PHY/LINK) layer. These two components residing in the two layers exchange information to ensure that user defined rate requests are satisfied by the right combination of transmission schedules and rate selections. The method is highly efficient for low mobility applications with mobile speeds in the order of a few kilometers per hour. While simple to implement, this technique requires no explicit channel estimation phase. The only feedback used are the single bit ACK/NACK signal indicating the correct reception/failure of the packet. As shown in the convergence theorems, the algorithm achieves optimal performance in "stationary" channels. With slowly varying channels, the rate selection algorithm sees a "quasi-stationary" channel and adaptively converges to an optimal solution. Simulations performed using a third-generation wireless system, namely, high-speed downlink packet access (HSDPA) validate the theoretical results.     

变速率分组SAMA系统性能研究

以扩频ALOHA(SAMA)多址访问技术为研究对象,研究了变速率方式对分组无线通信系统性能的影响,提出自适应变速率分组算法,提高了系统性能。     

Bayesian prediction for the range with a burr distribution and a random sample size

This paper is concerned with the problem of predicting the future range with the two-parameter Burr distribution, given a sample of a random size and using the Bayesian approach. We consider two possible distributions of the random sample size and the results so obtained have been illustrated numerically, using iterative techniques and computer facilities.     

CA:引导企业安全管理变革

IT业高水平的技术创新不断地为用户带来了新的、更好的产品。但同时,也使IT应用的复杂性进入一个全新层次。冠群电脑(中国)有限公司总经理兼副总裁吴沛殷女士就不止一次表示:在中国,快速发展的信息安全市场和国内企业对IT管理解决方案的需求,对信息安全厂商提出了更高的要求。她分析,由于IT供应商们不需要互相配合,而且他们之间也不经常沟通,因此情况正在越变越复杂。这导致的结果就是:没有哪些产品能够轻松的集成,消费者不得不在众多的平台、应用和标准间挣扎。另外,造成IT环境日益复杂的原因不仅有主要产品的推陈出新,还有每年发布的…     

变阶自适应滤波器及其算法研究

提出了变阶自适应滤波器和一种变步长变阶自适应LMS算法。通过仿真证明适选取参数，该算法比单一变步长算法要优越，变步长变阶自适应滤波器同时具有变步长定低阶滤波器和变步长定高阶滤波器的优点。     

Mean arrival time and mean pulsewidth of signals propagating through a dispersive and random medium

An electromagnetic pulse propagating through the ionosphere can be modified owing to dispersion as well as random scattering from electron density irregularities. As a result, the pulse arrival time and the pulsewidth are altered. In this paper we show how such quantities can be computed and related to the medium parameters. In this connection the two-frequency mutual intensity function enters in the formulation naturally. The results show that the mean arrival time is dominated by a term which indicates that the pulse is traveling at the group velocity corresponding to the carrier frequency. But there are also small but important corrections resulting from random scattering and higher order dispersion. Our results also show the importance of scattering and dispersion in lengthening the pulse. These results have important implications in satellite based navigational and communication systems.     

Spectral efficiency and cutoff rate of random spreading BICM-based CDMA signals with MMSE multiuser receivers

We analyze the spectral efficiency and cutoff rate of random spreading bit-interleaved coded-modulation based synchronous code-division multiple-access signals with minimum mean-square error multiuser receivers. Both additive white Gaussian noise and frequency nonselective Rayleigh fading channels are considered. The spectral efficiency and cutoff rate are characterized as functions of the system load, modulation schemes, and signal-to-noise ratio.     

Mean residual life and its association with failure rate

The life time distributions having decreasing, increasing, or upside-down bathtub shaped MRL (mean residual life) are used as models in many applications. Mi (1995) has shown that if a component has a bathtub shape failure rate function, then the MRL is unimodal but the converse does not hold. This paper develops sufficient conditions for the unimodal MRL to imply that the failure rate function has a bathtub shape     

Bayesian prediction of the jth order statistic with burr distribution and a random sample size

This work is concerned with the Bayesian prediction problem of the j order statistic when the size of the future sample is a random variable and the samples are drawn from a generalized Burr distribution (GBD). A numerical illustration is also given.     

无线传感器网络中结合丢包率和RSSI的自适应区域定位算法

首先分析无线传感器网络(WSN)中基于RSSI(接收信号强度指示)的现有定位算法存在的不足,然后在不同时间和空间的大量实验数据基础上,结合丢包率和RSSI提出了针对实际环境的距离评估模型和建立在此模型基础上的无线传感器网络定位算法,以此作为对无线定位研究的一种新的探索.通过实验对算法性能进行评估,证明使用该算法的WSN能够正常定位并具有较高的定位精度和稳定性.     

Decay rate (ER) modelling of G/D/1 queue, and results for ATMtelecommunications

The authors present a new formula for calculating the decay rate in the queueing system G/D/1. This queueing model has potential for application in cell-based telecommunication systems, such as ATM, since it allows generally distributed inter-cell arrival times, while keeping the cell transmission time constant. The results presented here show that considerable improvements in accuracy are now available     

Analysis of an M/G/1/N queue with vacations and its iterativeapplication to FDDI timed-token rings

We present the analysis of an M/G/1/N queueing system with vacations under a dynamic time-limited service policy. This method is used to develop a procedure for performance analysis of a fiber distributed data interface (FDDI) network serving buffer-limited stations under asynchronous service. An efficient iteration procedure is employed to evaluate the limiting state distribution of the embedded Markov chain representing the system state process. Using supplementary variables and sample biasing techniques, we derive the queue size distribution at an arbitrary instant of time as well as the packet blocking probability and the mean packet delay. By exploiting the subtle structure of conditional supplementary variables and the recursive property of the conditional residual delay, the Laplace-Stieltjes transform of the packet delay distribution and a time-domain approximation of the packet delay distribution are obtained. For the analysis of a heterogeneous multi-station FDDI network, an iterative procedure which uses repeatedly the M/G/1/N vacation model described above is presented. This procedure provides for a numerically efficient analysis method by employing constructions of the approximate vacation time distributions. We illustrate the application of our analytical techniques to both symmetric and nonsymmetric FDDI network systems     

Inference of raindrop size distribution from attenuation and rain rate measurements

A method to infer the raindrop size distribution from the measurements of point rain rate and rain attenuation at a frequency in centimeter or millimeter wave bands is proposed. This method is applied to the results of field propagation experiments at 81.8, 34.5, and 11.5 GHz through natural rain. It is shown that, if an appropriate frequency is employed, this method is effective as a frequency-scaling method for short terrestrial propagation paths.     

电源产品变更点的管理及质量控制

电源产品周期短的特性造成了其设计变更迅速、实际生产变更频繁的特点。而在产品生产中的变更有发生品质事故的隐患或者造成停产或呆料。在此介绍了变更点的管理流程,分析生产中变更可能对品质及成本的影响,总结不同变更点的管理重点,提前预防变更后可能发生的品质事故,避免发生因变更导致的浪费,确保最终产品能满足客户的需求。