一类多速率传感器动态系统的建模与估计

研究了一类时变线性动态系统的多速率多传感器数据融合状态估计问题.首先,在不同传感器以不同采样率对同一目标进行观测的情况下,提出了一种多速率建模方法,该方法可将多采样率的融合估计问题转化为同采样率的状态估计问题.随后,利用Kalman滤波对目标状态进行了在线估计,并利用有反馈分布式融合结构对上述估计进行了有机融合,从而获得了目标状态的最优融合估计值.该方法不需要对状态或观测进行扩维,计算量适当,保证了算法的实时性.以景象匹配辅助GPS/INS组合导航为例,在两种采样关系下,分别做了仿真,仿真结果验证了算法的有效性.     

Solving some overflow traffic models with changed serving intensities

This paper investigates specific systems with overflow traffic. A primary group with two Poisson traffics is considered whereupon the rejected calls from one traffic are directed to the alternative group with changed serving intensities. The generating function technique is used for analytical solving the model with secondary and ternary groups and the model that separately treated the channels in alternative groups. The obtained analytical solutions essentially reduce the constraints concerning the equation system size, convergence, and calculation time, which arise when numerically solving the steady-state system equations. For the case with single channels in the ternary group, explicit solutions for traffic parameters are obtained. Also, comparison with the model that has a unique serving intensity of overflow traffic is made.     

Approximation for mean of overflow traffic with discrete time-dependent input

Real-life arrival traffic pattern can be approximated by a sequence of step functions with durations of about a quarter-hour. For this interval, a stationary arrival rate will be assumed, and transience will be present. An approximation to the mean of the traffic overflowing from a loss system when the arrival traffic consists of such a sequence of step functions will be given.     

Blind channel estimation in multi-rate CDMA systems

Multi-rate CDMA is a potentially attractive multiple access method for future broad-band multimedia wireless networks that must support integrated voice/data traffic. The primary impairment for such multi-rate systems is the multipath nature of radio channels that results in intra-user inter-chip interference (ICI) and multi-user interference (MUI) between different users' symbols. Explicit knowledge of the channel is typically needed for high performance detectors (such as coherent demodulation). We propose a subspace method for channel estimation in multi-rate CDMA systems. A unified signal model that applies to three multi-rate CDMA schemes proposed in the literature is developed. The computational complexity for multi-rate scenarios is large and variable-accordingly, a modified approach is devised that offers performance/complexity trade-offs. Performance analysis is conducted based on a close-form expression for the mean square error of the estimator, supported by simulation results that investigate the effectiveness of our method     

Analysis of a model of two overflow traffic components with different serving intensities

This paper seeks to provide the analysis of a model of two overflow traffic components that originated from several Poisson traffics served by a common primary trunk group. Overflow parts of two of them are served in a secondary trunk group, but with changed and different serving intensities. The general solution of the system was obtained by generating function techniques, and call losses, time losses and traffic losses were defined based on state probability and solved numerically. In order to illustrate specific characteristics of the analyzed model, loss values were compared with the losses in a corresponding system with averaged serving intensity for which there is a much simpler explicit solution.     

Modeling of HTTP traffic

In this letter, the authors show that the behavior of Web users strongly affects the dynamics of TCP connections in the Internet. Analyzing actual and systematically generated HTTP traces, it is proved that the time between the downloads of two pages is critical to determine the re-utilization of connections. On the other hand, the use of the 1.1 version of the HTTP standard does not significantly affect the traffic generated by HTTP 1.0 browsers. In this sense, the heavy-tailed nature of the size of HTTP connections can be considered an invariant property     

Transient mean and variance of overflow traffic in a loss system

Simple techniques to approximate the mean and variance of the overflow traffic in a telephone system are outlined. The mean is first approximated, and by using the peakedness value obtained via the interrupted Poisson process, the variance is then approximated.     

TELNET的客户端流量模型

本文针对英特网上的一个常用协议－远程登录（ＴＥＬＮＥＴ）协议分析了它的客户端数据包产生的时间间隔分布,发现泊松模型的指数分布不能很好地刻画它的特性。本文依据Ｔｃｐｌｉｂ提供的经验分布曲线,认为Ｐａｒｅｔｏ分布在很大时间范围内能较好地描述ＴＥＬＮＥＴ的客户端流量特性,并对其突发序列的特性进行了分析。本文最后指出在描述网络流量时自相似模型要比泊松模型有效和精确得多,并给出了Ｐａｒｅｔｏ分布在建立自相似     

Modeling multiple IP traffic streams with rate limits

We start with the premise, and provide evidence that it is valid, that a Markov-modulated Poisson process (MMPP) is a good model for Internet traffic at the packet/byte level. We present an algorithm to estimate the parameters and size of a discrete MMPP (D-MMPP) from a data trace. This algorithm requires only two passes through the data. In tandem-network queueing models, the input to a downstream queue is the output from an upstream queue, so the arrival rate is limited by the rate of the upstream queue. We show how to modify the MMPP describing the arrivals to the upstream queue to approximate this effect. To extend this idea to networks that are not tandem, we show how to approximate the superposition of MMPPs without encountering the state-space explosion that occurs in exact computations. Numerical examples that demonstrate the accuracy of these methods are given. We also present a method to convert our estimated D-MMPP to a continuous-time MMPP, which is used as the arrival process in a matrix-analytic queueing model.     

高效直达电路的设置及溢出话务的计算

介绍ＣＣＩＴＴ兰皮书Ｅ．５２２建议高效直达电路的设置和溢出话务量的一种简易计算法——话务变动等价置换法。     

Modeling video traffic using wavelets

In this letter we establish a wavelet model for video traffic. Different from the existing methods which model the video traffic in the time domain, we model the wavelet coefficients in the wavelet domain. The strength of the wavelet model includes: (1) an unified approach to model both the long-range and the short-range dependence in the video traffic simultaneously; (2) a computationally efficient method for developing the model and generating high quality video traffic; and (3) feasibility of performance analysis using the model     

Modeling of split traffic under probabilistic routing

Using a general input traffic class rather than confining it to a specific input traffic model, this letter investigates the split traffic for such a general input traffic class under a probabilistic routing algorithm. Thus the obtained result is applicable for a broad range of input traffic. By way of characterizing the split traffic on each routing path, it is shown that the resultant traffic on each routing path is still the same traffic class with suitable parameter modification.     

Modeling heterogeneous network traffic in wavelet domain

Heterogeneous network traffic possesses diverse statistical properties which include complex temporal correlation and non-Gaussian distributions. A challenge to modeling heterogeneous traffic is to develop a traffic model which can accurately characterize these statistical properties, which is computationally efficient, and which is feasible for analysis. This work develops wavelet traffic models for tackling these issues. We model the wavelet coefficients rather than the original traffic. Our approach is motivated by a discovery that although heterogeneous network traffic has the complicated short- and long-range temporal dependence, the corresponding wavelet coefficients are all “short-range” dependent. Therefore, a simple wavelet model may be able to accurately characterize complex network traffic. We first investigate what short-range dependence is important among the wavelet coefficients. We then develop the simplest wavelet model, i.e., the independent wavelet model for Gaussian traffic. We define and evaluate the (average) autocorrelation function and the buffer loss probability of the independent wavelet model for fractional Gaussian noise (FGN) traffic. This assesses the performance of the independent wavelet model, and the use of which for analysis. We also develop (low-order) Markov wavelet models to capture additional dependence among the wavelet coefficients. We show that an independent wavelet model is sufficiently accurate, and a Markov wavelet model only improves the performance marginally. We further extend the wavelet models to non-Gaussian traffic through developing a novel time-scale shaping algorithm. The algorithm is tested using real network traffic and shown to outperform FARIMA in both efficiency and accuracy. Specifically, the wavelet models are parsimonious, and have a computational complexity O(N) in developing a model from a training sequence of length N, and O(M) in generating a synthetic traffic trace of length M     

Optimal admission control in cellular DS-CDMA systems with multimedia traffic

The problem of jointly controlling the data rates and transmit powers of users, so as to maximize throughput in cellular direct-sequence code-division multiple-access (CDMA) networks is addressed. The multicode (MC)-CDMA system, where the processing gain of each code is fixed and high-rate users use multiple codes for transmission, and the variable gain (VG)-CDMA architectures are considered. The throughout maximization problem is formulated as a classical optimization problem, modeling the constraints arising from the data rate requirements and power budgets. Optimal strategies to maximize throughput in both systems are derived. While the MC-CDMA system has a simple optimal rate-power allocation algorithm, the VG-CDMA system has a more complex solution.     

Hot-spot traffic relief in cellular systems

By analyzing mathematical models, it is shown that combining channel borrowing with a coordinated sectoring or overlying scheme provides effective ways to handle hot-spots in the system. Blocking probabilities with these arrangements are derived, and the dynamic sharing with bias (DSB) rule is suggested for increasing the trunking efficiency. A simple handoff model is formulated and analyzed for comparing the probabilities of additional handoffs due to sectoring and overlaying of cells. With the nominal allocation of 60 channels per cell and a donor cell having a load of 30 Erlangs, numerical results show that at a blocking requirement of 1%, the traffic load in the hot-spot cell can be increased from 47 to 63 Erlangs with the use of the channel borrowing with the cell sectoring scheme: while with the use of the DSB rule, the load can be increased further to 71 Erlangs. A slightly higher load can be carried in the hot-spot cell with the use of cell overlaying arrangement     

Modeling Internet backbone traffic at the flow level

Our goal is to design a traffic model for noncongested Internet backbone links, which is simple enough to be used in network operation, while being as general as possible. The proposed solution is to model the traffic at the flow level by a Poisson shot-noise process. In our model, a flow is a generic notion that must be able to capture the characteristics of any kind of data stream. We analyze the accuracy of the model with real traffic traces collected on the Sprint Internet protocol (IP) backbone network. Despite its simplicity, our model provides a good approximation of the real traffic observed in the backbone and of its variation. Finally, we discuss the application of our model to network design and dimensioning.     

多媒体CDMA系统在功率约束条件下的业务容量分析

码分多址接入（CDMA）技术可以灵活地支持无线多媒体业务传输。该文分析了多小区环境下CDMA系统上行链路的多媒体业务容量，主要讨论了用户最大发射功率约束条件在不同用户激活因子情况下对系统容量的影响。分析和计算结果表明用户最大发射功率约束使系统的容量有所降低。     

Efficient buffer sharing in shared memory ATM systems with spacepriority traffic

In this letter we study the problem of the optimal design of buffer management policies within the class of pushout and expelling policies for a shared memory asynchronous transfer mode (ATM) switch or demultiplexer fed by traffic containing two different space priorities. A numerical study of the optimal policies for small buffer sizes is used to help design heuristics applicable to large buffer sizes. Simulation studies for large buffer systems are then presented