Performance analysis of Finite-User slotted aloha in wireless networks with multiple packet reception and random traffic

In this paper, we propose an analytical approach for evaluating the performance of finite-user slotted Aloha in wireless networks with multiple packet reception and random traffic. We derive the exact values of the throughput, the average system size, the packet blocking probability, and the average system delay. Our analysis is based on probability theory. We show that our numerical results are identical to simulation results.     

A New Method for Blocking Probability Evaluation in OBS/OPS Networks With Deflection Routing

In this paper, we present a new method for the estimation of blocking probabilities in bufferless optical burst or packet switched networks. In such networks, deflection routing is used to reduce blocking probability. However, it requires certain wastage due to trunk reservation that must be used to avoid instability. We provide a wide range of simulation and numerical results to validate our new approximation method and demonstrate various effects on blocking probability and utilization, such as network size, trunk size, the maximal number of allowable deflections, and burst/packet length.     

Admission policies for integrated voice and data traffic in CDMApacket radio networks

The authors derive optimal admission policies for integrated voice and data traffic in packet radio networks employing code division multiple access (CDMA) with direct-sequence spread spectrum (DS/SS) signaling. The network performance is measured in terms of the average blocking probability of voice calls and the average delay and packet loss probability of data messages. The admission scheme determines the number of newly arrived voice users that are accepted in the network so that the long-term blocking probability of voice calls is minimized. In addition, new data arrivals are rejected if the mean delay or the packet loss probability of data exceeds a desirable prespecified level. A semi-Markov decision process (SMDP) is used to model the system operation. Then, a value iteration algorithm is used to derive the optimal admission control. Two models for the other-user interference of the CDMA system are considered: one based on thresholds and another based on the graceful degradation of the CDMA system performance, and their performance is compared. These admission policies find application in emerging commercial CDMA packet radio networks including cellular networks, personal communication networks, and networks of LEO satellites for global communications     

Impact of tuning delay on the performance of bandwidth-limitedoptical broadcast networks with uniform traffic

This paper studies the effects of tuning delay of transmitters in packet-based optical broadcast networks. We consider scheduling of random traffic with tunable transmitters and fixed-tuned receivers and obtain the degradation imposed by tuning delay using several performance criteria, such as schedule completion time, average packet delay, and session blocking rates. We show that for off-line scheduling the effects of tuning delay are small even if the tuning time is as large as the packet duration. We provide a lower bound to the expected completion time of any off-line schedule with an arbitrary number of wavelengths. We then describe a near-optimal schedule which is based on the principle of having idle transmitters tune to wavelengths just-in-time to start their transmissions. Stability and capacity issues in the transmission of real-time traffic are considered and a queueing-theoretic analysis of average packet delay is given. The packet delay is found to be insensitive to tuning delay under near-optimal transmission scheduling. Finally we extend the model to connection-oriented networks and evaluate the session blocking performance for scheduled circuit connections     

On spatially disjoint lightpaths in optical networks

Within the communication networks, a delayed constrained data packet is the one that will be dropped if not being served before a certain deadline time, which causes data packet loss affecting the quality of service (QoS). In this paper, we study the blocking probability and the mean delay of such delay constrained packets in an asynchronous single-wavelength optical buffer in optical packet switching networks, where the packet arrival process follows the Poisson process and the packet-length distribution is assumed to be general. We obtain the integral equations of the modeled system and the exact expressions of blocking probabilities and the mean delays. Numerical examples are provided to validate the results with interesting observations being highlighted.     

基于小波包分析和Elman神经网的故障诊断方法研究

由非线性电力电子装置组成的电路发生故障时,故障特征信息不易提取和识别。对此提出一种基于小波包分析和Elman神经网的电力电子装置故障诊断的方法,先运用小波包分析法提取电路在不同故障状态下电压及电流信号的特征信息,然后对数据进行归一化处理并作为Elman神经网的输入,由具有智能学习功能的神经元故障分类器完成故障识别和定位。以12脉冲整流电路为例,在Matlab软件下建立电路模型进行仿真实验,结果表明该方法能快速、准确的完成故障诊断。     

WDM光网络中一种优先共享通路保护算法

为了提高波分复用光网络的可靠性,常采用分段共享通路保护算法,该方法通常要求保护通路要均匀分段并且应满足共享风险链路组约束,网络业务的阻塞率也就比较高,因此提出了用优先共享通路保护算法来降低业务阻塞率。通过计算机仿真进行了理论分析和实验验证,取得了两种保护算法下的业务阻塞率和资源预留比的数据。结果表明,优先共享保护通路算法能够有效地融合分段共享通路保护算法的优点,同时在业务的阻塞率和资源预留比方面优于分段共享保护通路算法。     

Capacity of Slotted ALOHA in Rayleigh-Fading Channels

Fading channels may improve the capacity of slottedALOHA networks. Rayleigh fading and spatially distributed packet transmitters diminish mutual packet interference and thus reduce the average blocking probability of a shared receiver. A transmission model, combining Poisson statistics of the offered data traffic with Rayleigh statistics for the fading channel, is developed. Analytical and numerical results are presented, indicating significant improvements to signaling in cellular mobile networks and in packet radio systems with fading radio channels.     

Evaluating blocking probability in generalized connectors

Generalized connectors provide the capability to connect a single input to one or more outputs. Such networks play an important role in supporting any application that involves the distribution of information from one source to many destinations or many sources to many destinations. The authors present the first analytic model for evaluating blocking probability in generalized connectors. The model allows flexibility in specifying traffic fanout characteristics and network routing algorithms. Equations are derived for computing blocking probability for the important class of series-parallel networks. The authors investigate the accuracy of the equations by comparing the blocking probability computed using the equations to results from simulation     

Minimising the size of voids in optical packet switching using a novel packet scheduling algorithm

In this paper, we propose a new packet scheduling algorithm to minimise the size of voids in optical packet switching. The effects of excess load, output utilisation, and packet loss probability are closely studied. Other contributing factors to the packet loss probability, which include the buffer depth and the numbers of wavelength channels, are also investigated. The proposed algorithm is of importance to next generation networks where broadband capabilities with end-to-end quality of service over all-IP optical networks is envisaged.     

Predictive multicast polling for wireless networks with multipacket reception and queuing

In this paper, we propose the predictive multicast polling scheme for medium access control in wireless networks with multipacket reception capability. We concentrate on the case in which the packet arrival process is general and the maximum queue size is finite but larger than one. We derive both analytical results and simulation results. We use the theory of discrete-time Markov chain to analyze the evolution of the system state. In addition, we propose to use Markov reward processes to calculate the exact value of the network throughput. Furthermore, we obtain the average system size, the packet blocking probability, and the average packet delay. We show that our numerical results are consistent with simulation results. We also use simulation results to justify the usage of the proposed approach. Our study shows that the system performance can be significantly improved with a few additional buffers in the queues.     

Optimum arrival-time distribution for delay capture inspread-spectrum packet radio networks

The optimum arrival-time distribution that maximizes the delay-capture probability in spread-spectrum packet radio networks is derived. It is shown that when the optimum arrival-time distribution is employed, the capture probability converges to a finite value as the number of contending packets increases. Normalized throughput and average number of packet retransmissions are computed for slotted ALOHA multipoint-to-point packet radio networks employing direct-sequence spread-spectrum modulation. It is shown that large performance improvement is obtained by optimizing the arrival-time distribution compared to the uniform arrival-time distribution assumed by Davis and Gronemeyer (1980), especially when error-correction coding is employed. Two practical modifications are derived which are shown to provide performance close to the optimum along with an adaptive network load control scheme     

部分共享波长转换光网络动态路由的改进算法

提出了一种应用于部分共享波长转换（PWC）的波长路由光网络（WRON）中的基于节点阻塞的动态路由算法,它不需要共享复杂的波长转换信息,而是将各节点的阻塞特性考虑到路由过程中。为评价算法性能,在14节点的国家科学基金网（NSFNET）拓扑中进行了仿真。结果表明,新的路由算法显著改善了网络的阻塞性能和建路失败的概率,尤其是随着网络负载的降低,网络性能的改善更显著。     

Performance analysis of integrating voice and data services over PACS systems in a multicarrier environment

The purpose of this paper is to study the performance of integrating voice and data services over PACS systems in a multicarrier environment. Several time‐slot allocation schemes are proposed. With continuous‐time Markov model, the performance can be evaluated. The results show that while using one system broadcast channel (SBC), the blocking rate of circuit mode services and system throughput are improved, at the sacrifice of increasing the blocking probability of packet mode services. Copyright © 2002 John Wiley & Sons, Ltd.     

iDEN无线网络规划及优化探讨

文章介绍了iDEN数字集群系统的网络组成及性能特点,通过一个iDEN数字集群网的规划和优化实例,探讨了iDEN网络规划和优化的方法.由于常用的规划工具不支持iDEN系统仿真和分析,但考虑到iDEN与GSM网络的相似性,可以采用GSM仿真规划工具,通过修改相关参数,实现对iDEN系统的仿真.     

Voice/Data Integration Using Circuit Switched Networks

This paper assesses the impact of integrating voice and data over circuit switched networks. Three main types of circuit switching are considered: 1) traditional circuit switching, 2)fast circuit switchingemploying advanced switching speeds, and 3) enhanced circuit switchingemploying time assigned speech interpolation (TASI) and adaptive data multiplexing (ADM) techniques. The circuit switching networks are evaluated in terms of two main network performance parameters: transmission efficiency and delay. In addition, an evaluation is made of such things as protocol and error control, precedence and preemption, routing and flow control, synchronization, voice continuity, probability of error or loss, and classmarking flexibility. One of the main conclusions of this paper is that circuit switching technologies have several deficiencies associated with providing integrated voice/data service and that the future lies in the effective use of packet and hybrid (circuit/packet) switching technologies.     

Performance analysis of cellular networks

Dynamic channel allocation can reduce the probability of blocking in cellular telephone networks. However, more is needed to achieve optimal performance. The author aims at estimating the minimal blocking probability for some simple cellular networks. Some dynamic channel allocation strategies are analyzed, the optimal performance (obtained by dynamic allocation and flow control) of some very simple networks is computed, and simple bounds on optimal performance are presented. These results lead to a better understanding of cellular networks and can be used to evaluate new control algorithms     

Common packet data channel (CPDC) for integrated wireless DS-CDMAnetworks

A common packet data channel (CPDC) architecture is proposed to support bursty, packet-based services in direct sequence code-division multiple-access (DS-CDMA) integrated wireless access networks. The architecture employs an asynchronous transfer mode (ATM) strategy in the forward CPDC link and a spread ALOHA-type random access strategy in the reverse CPDC link. A congestion control algorithm using base station broadcast and portable terminal random delay call reattempt is described. A performance analysis of the CPDC architecture and algorithms is carried out, and formulas for the bit error rate, blocking probability, system delay time, transmission time, and waiting time for packet data calls are derived. The interference caused by a CPDC to stream services in the network is determined, and the capacity of a CPDC is evaluated in terms of the number of packet data subscribers that can be served with a specified grade of service (GOS)     

静电感应晶闸管静态特性的仿真模拟

引入了一种SITH仿真模型.结合实验数据,利用PSPICE模拟软件,从等效电路的角度对静电感应晶闸管(SITH)进行了正向导通,类三极管正向阻断、负阻转折特性的仿真模拟.     

The impact of MAC parameters on the performance of 802.15.4 PAN

The operation of a personal area network, operating under the IEEE Standard 802.15.4 in the beacon enabled mode, is analyzed using the theory of discrete time Markov chains and M/G/1/K queues. The model includes the impact of different parameters such as packet arrival rate, number of stations, station’s buffer size, packet size, and inactive period between the beacons. We have derived several important performance parameters such as probability of access, probability that medium is idle, queue length distribution in the device, and probability distribution of the packet service time. Some important conclusions regarding the implementation of 802.15.4 networks and compatible network devices are outlined.