A model for teletraffic performance and channel holding timecharacterization in wireless cellular communication with general sessionand dwell time distributions

Channel holding times and user mobility are important topics in the study of wireless cellular communications. We present an approach to modeling user mobility and session time which enables both the calculation of teletraffic performance characteristics and a characterization of holding time which agrees with published reports. The model allows both the dwell time and unencumbered session time to have general distributions. A derivation of the channel holding time distribution is given. We then show how the model's parameters can be chosen to fit empirical data including observations of channel holding time     

Mathematical analysis of the multi-server queueing model for dynamic channel reservation in wireless networks

We consider a multi-server queueing model with two types of customers offered in Y. C. Kim et al. (1999) for modeling dynamic channel reservation based on mobility in wireless networks. Mathematical analysis given contains essential errors what makes some results negligible. We provide a correct analysis of the model     

Aging renewal process characterizations of exponential distributions

We consider some characterizations of exponentials among distributions driving certain aging renewal processes. The necessary and sufficient conditions so considered are in terms of the operating characteristics of perfect repair (renewal) and minimal repair strategies for equipments with NBU and NBUE aging life distributions.     

The role of teletraffic modeling in the new communicationsparadigms

Teletraffic engineers provide models allowing communications networks to be planned and systems to be designed to meet the performance needs of users within a reasonable cost. The successful modeler combines analytical or simulation skills with a deep understanding of the technology. In the emerging information networking environment comprising new technologies such as ATM, Internet, wireless, etc., and new services such as video, multimedia, data and personal communications services, the old paradigms of circuit-switched calls and Erlang distributions have been severely challenged. The confluence of the shifts in technologies and services along with the convergence of computing, telecommunications, consumer electronics, and electronic media industries, and the shift from a monopolistic to competitive business paradigm, has created a tremendously rich lode of fundamental problems that need to be addressed by teletraffic engineers. In this article the author describes the historical role of the teletraffic engineer, reviews several of the major paradigm shifts, and discusses some of the challenges facing the teletraffic community with an emphasis on modeling wireless communications systems     

A teletraffic model for the Physical Downlink Control Channel in LTE

Recent advances in mobile handsets have led to new trends in mobile broadband data consumption, with a huge increase of signaling traffic generated by always-connected devices. Thus, a proper planning of control channels in mobile networks is necessary to avoid network capacity problems and provide an appropriate quality of service to the end user. A key issue in network planning is the availability of a complete and accurate system model. In this paper, an analytical performance model for the Long Term Evolution (LTE) Physical Downlink Control Channel (PDCCH) is constructed based on queuing theory. Unlike previous works, the proposed model considers important network features, such as link adaptation, and can be tuned with available network performance statistics. Model assessment is carried out by comparing performance estimates with request-level simulations and real performance measurements taken from a live LTE network. Results show that the proposed model can predict the PDCCH load distribution in a live network accurately.     

On the teletraffic capacity of CDMA cellular networks

The aim of this paper is to contribute to the understanding of the teletraffic behavior of code-division multiple-access (CDMA) cellular networks. In particular, we examine a technique to assess the reverse link traffic capacity and its sensitivity to various propagation and system parameters. We begin by discussing methods of characterizing interference from other users in the network. These methods are extremely important in the development of the traffic models. We begin with a review of several existing approaches to the problem of handling other-cell interference before presenting a novel characterization of the interference in the form of an analytic expression for the interference distribution function in the deterministic propagation environment. We then look at extending the capacity analyses that assume a fixed and equal number of users in every cell to handle the random nature of call arrivals and departures. The simplest way to do this is by modeling each cell of the network as an independent M/G/x∞ queue. This allows us to replace the deterministic number of users in each cell by an independent Poisson random variable for each cell. The resulting compound Poisson sums have some very nice properties that allow us to calculate an outage probability by analyzing a single random sum. This leads to a very efficient technique for assessing the reverse link traffic capacity of CDMA cellular networks     

Online social network model with renewal and accelerated growth

Based on observation of the growing mechanism in Twitter-like online social networks, an online social network （OSN） evolution model was proposed, a renewal mechanism for the old nodes and an accelerated growth mechanism was introduced for the new nodes, comparing with the native copying model. Topological characteristics of the generated networks, such as degree distribution, average shortest-path length and clustering coefficient, are analyzed and numerized. These properties are validated with some crawled datasets of real online social networks.     

Increasing the efficiency of roulette simulation of teletraffic

A simple modification of the roulette method of teletraffic simulation is presented. At low traffic levels it may result in a reduction, by a factor of ten or more, of the computer time required to simulate a specified number of calls.     

The time‐dependent Erlang loss model with retrials

We consider a generalization of the classical Erlang loss model with both retrials of blocked calls and a time‐dependent arrival rate. We make exponential‐distribution assumptions so that the number of calls in progress and the number of calls in retry mode form a nonstationary, two‐dimensional, continuous‐time Markov chain. We then approximate the behavior of this Markov chain by two coupled nonstationary, one‐dimensional Markov chains, which we solve numerically. We also develop an efficient method for simulating the two‐dimensional Markov chain based on performing many replications within a single run. Finally, we evaluate the approximation by comparing it to the simulation. Numerical experience indicates that the approximation does very well in predicting the time‐dependent mean number of calls in progress and the times of peak blocking. The approximation of the time‐dependent blocking probability also is sufficiently accurate to predict the number of lines needed to satisfy blocking probability requirements. This revised version was published online in June 2006 with corrections to the Cover Date.     

THE ANALYSIS OF CELL LOSS RATES IN AN ATM MUX WITH LOSS PRIORITIES

The analysis of cell loss rates in an ATM Mux with loss priorities is an important problem in the-study of traffic control in ATM networks. In this paper, the loss rates of the cells with different priorities in an ATM Mux are analyzed by approximating the actual input process with two-state MMDP and fluid flow technique, and the analytical expressions of the relation between the loss rates and the buffer size are obtained. Simulation shows that the approach is sulliciently accurate for applications.     

A certain model of reliability diagnostic of renewal objects

In the paper the model of reliability diagnostic of renewal objects which exploitation process can be described as the interrupting renewal process with the finite time of repair is discussed. The essential relationships between reliability of object and diagnostic parameters are presented.     

基于大数据分析的电能损耗预测模型的仿真分析

对电能损耗进行预测的过程中,传统的预测方法,由于影响电能损耗的因素之间具有非常复杂的非线性与强相关性,导致很难得到高精度的预测结果。提出一种基于大数据分析的电能损耗预测模型,建立电能损耗预测单元模型,分析发电器模型、变电器模型和输电器模型建立的过程,引入灰色综合关联度对大数据进行分析,对各个组成区域序列累加得到整体区域电能损耗情况,并进行微分处理,通过GM(1,1)的转换实现对整体电能损耗预测模型的构建。仿真实验结果表明,所提模型具有较高的预测精度,能够很好地避免非线性因素对模型的干扰,为电力企业制定合理的电能损耗计划提供可靠依据。     

Impact of transmission impairments on the teletraffic performanceof wavelength-routed optical networks

In a wavelength-routed optical network, a transmitted signal remains in the optical domain over the entire route (lightpath) assigned to it between its source and destination nodes. The optical signal may have to traverse a number of crossconnect switches (XCSs), fiber segments, and optical amplifiers, e.g., erbium-doped fiber amplifiers (EDFAs). Thus, while propagating through the network, the signal may degrade in quality as it encounters crosstalk at the XCSs and also picks up amplified spontaneous emission (ASE) noise at the EDFAs. Since these impairments continue to degrade the signal quality as it progresses toward its destination, the received bit error rate (BER) at the destination node might become unacceptably high. Previous work on the lightpath routing and wavelength assignment (RWA) problem assumed an ideal physical layer and ignored these transmission impairments. The main contribution of our work is to incorporate the role of the physical layer in setting up lightpaths by employing appropriate models of multiwavelength optical devices (XCSs and EDFAs) such that the BER of a candidate lightpath can be computed, in advance, to determine if this lightpath should be used for the call. Features from existing RWA algorithms are integrated with our on-line BER calculation mechanism. Our simulation studies indicate that employing BER-based call-admission algorithms has a significant impact on the performance of realistic networks     

移动通信信道损耗模型研究及仿真分析

针对导弹控制信道特点研究了信道传输损耗模型,提出利用 Longley-Rice模型建立该类通信信道模型,并推导了Longley-Rice模型的具体仿真算法,最后进行了数值仿真分析,实测数据验证了利用Longley-Rice模型建立该类信道的有效性.     

On the use of renewal theory in the analysis of ARQ protocols

An automatic-repeat-request (ARQ) Go-Back-N (GBN) protocol with unreliable feedback and time-out mechanism is studied, using renewal theory. Transmissions on both the forward and the reverse channels are assumed to experience Markovian errors. The exact throughput of the protocol is evaluated, and simulation results, that confirm the analysis, are presented. A detailed comparison of the proposed method and the commonly used transfer function method reveals that the proposed approach is simple and potentially more powerful     

基于PSASP的甘南电网网损分析

甘南小水电上网后给地方配电系统的经济运行带来了一定的影响,为了创建节能、经济的甘南电网,提高电网规划设计水平,利用PSASP对甘南电网进行了潮流仿真分析。在确定的有功潮流分布的基础上,根据给定的电网结构、参数以及实际运行中的典型24 h负荷水平进行了网损分析计算。仿真和实验结果为进行其他分析计算工作及电网重大方式变化提供了数据支持,对及时有效地发现电能损耗问题和探讨降低网损的主要措施具有重要意义。     

Stationary distributions for the random waypoint mobility model

In simulations of mobile ad hoc networks, the probability distribution governing the movement of the nodes typically varies over time and converges to a "steady-state" distribution, known in the probability literature as the stationary distribution. Some published simulation results ignore this initialization discrepancy. For those results that attempt to account for this discrepancy, the practice is to discard an initial sequence of observations from a simulation in the hope that the remaining values will closely represent the stationary distribution. This approach is inefficient and not always reliable. However, if the initial locations and speeds of the nodes are chosen from the stationary distribution, convergence is immediate and no data need be discarded. We derive the stationary distributions for location, speed, and pause time for the random waypoint mobility model. We then show how to implement the random waypoint mobility model in order to construct more efficient and reliable simulations for mobile ad hoc networks. Simulation results, which verify the correctness of our method, are included. In addition, implementation of our method for the NS-2 simulator is available.     

A teletraffic performance study of mobile LEO-Satellite cellular networks with gamma distributed call duration

In this paper, the authors develop an analytical model to study the performance of a mobile low earth orbiting (LEO) satellite cellular network. The model assumes that the call duration has a gamma distribution and considers the effect of system parameters such as the number of channels per cell, the number of channels reserved for the handoff, and the cell residence time, on the teletraffic performance of the system. The quality of service (QoS) measures studied in this paper include new call blocking probability, handoff failure probability, premature call-termination probability (CTP), and call dropping probability (CDP). Based on the causal central limit theorem, the authors use a two-parameter gamma distribution to approximate the distribution of the sum of the residence times in the cells. The analytical model presented in this paper may be used with any call-holding-time distribution. The analytical results are validated by a computer simulation.     

基于科恩分布的地球物理信号的时频分析

在简要讨论几种科恩类广义双线性时频分布的基础上,探讨双线性时频分布的算法实现与仿真流程,进而模拟出地磁脉动信号的几种时频分布,同时还对Pc脉动的几种双线性时频分布进行了比较,给出了相应的交叉项抑制和参数选取的方法。结果表明,在核函数参数选取适当的情况下,广义双线性时频表示是分析地球物理信号的有力工具。