一种FDDI局域网性能的数值分析方法

仿真方法在考查一个复杂且造价昂贵系统的运行和性能方面是非常有效的,因为它无须建立实际的物理模型,仅仅用高级语言编写仿真程序即可实现。本文提出一种ＦＤＤＩ （光纤分布数据接口）局域网在一定负载情况下确定平均接入时延的仿真方法,并以包含短的数据报文和长的视频报文的多媒体环境作为实验模型,实验结果表明本仿真方法的有效性。仿真程序使用Ｍａｔｈｅｍａｔｉｃａ语言,能够快速得到带有完美图形的数值仿真结果。     

一种FDDI局域网性能的数值分析方法

仿真方法在老查一个复杂且造价昂贵系统的运行和性能方面是非常有效的,因为它无须建立实际的物理模型,仅仅用高级语言编写仿真程序即可实现。本文提出一种FDDI（光纤分布数据接口）局域网在一定负载情况下确定平均接入时延的仿真方法,并以包含短的数据报文和长的视频报文的多媒体环境作为实验模型,实验结果表明本仿真方法的有效性。仿真程序使用Mathematica语言,能够快速得到带有完美图形的数值仿真结果。     

Proteus仿真技术在8051C语言程序设计教学中的应用

在分析Proteus仿真方法的基础上,构建了一个8051C语言程序设计基础实验仿真系统,设计了一个典型的实例程序,表明了用Proteus进行8051C语言程序设计的仿真,实验系统搭建简单容易,仿真过程形象直观,为8051C语言程序设计教学提供了一个很好的实验手段。     

VHDL元件的Simulink／Modelsim功能测试方法

由于VHDL语言注重硬件行为描述,VHDL程序的测试方法与传统高级设计语言程序和汇编语言程序的测试方法不同。VHDL程序测试向量的自动生成方法和覆盖率测试是其功能测试中的难点。基于Matlab／Simulink的方法,将VHDL程序作为整个模型系统中的一个元件来考察,就其硬件环境进行建模,和Modelsim进行协同仿真。该方法简化了测试流程,无需采用复杂的testbench编写方法,提高了测试的完整性。     

基于移动4G网络C语言课程研究——以C程序实验仿真平台建设与研究为例

C语言是在计算机中得到广泛应用的语言,利用其编写出的很多实际程序为人们的生活提供了极大便利。为了使C程序实验仿真平台的应用更加广泛,文章将对C程序实验仿真平台的建设进行研究。C程序实验仿真平台的建设可分为基础仿真平台的建设与研究以及综合性实验仿真平台的建设与研究,最终应用于实际。     

基于C语言的二维细胞结构蒙特卡罗法仿真

本文介绍了二维肥皂泡的计算机仿真方法，并引进蒙特卡罗法研究此类系统。采用BorlandC＋＋语言编写了仿真程序，使输出结果更加直观。     

Matlab语言在控制系统仿真中的应用

本文简要介绍了Matlab软件及其主要特点以及Matlab在信号与系统课程中的应用,重点介绍了利用Matlab语言编写时域卷积的动态程序应用,并利用MATLAB对其进行仿真实验研究,给出了仿真与实验结果。     

无速度传感器雷达交流伺服系统设计

利用DSP芯片TMS320X24X，采用模型参考自适应控制策略进行交流电机速度估算，构成雷达交流伺服系统速度内回路，并给出了原理框图和程序设计。仿真实验证明了该系统具有良好性能。     

基于VC++的战术数据链通信仿真系统设计与实现

为了实现战术数据链通信仿真系统,在分析与研究联合战术信息分发系统(JTIDS)关键技术的基础上,构建了战术数据链链路层仿真模型。依据仿真模型中各模块的划分,以VC++语言为编程实现平台,采用面向对象的程序设计方法,设计并实现了Reed-Solomon码(RS码)编译码类、循环码移位键控类、最小移频键控类。最后在高斯白噪声信道下对仿真系统进行了验证和性能分析。结果表明,设计的各个类模块功能满足系统指标,基于各个类模块构建的仿真系统符合设计要求,为下一步研究JTIDS系统干扰与抗干扰性能奠定了基础。     

基于Java的物流配送中心系统仿真模块研究与设计

本文选取物流工程中的配送中心作为研究对象,根据实际需要建立了离散事件系统模型,并按照事件安排和时间推进的机制采用Java程序设计语言设计仿真模块。     

Data aggregation in sensor networks using learning automata

One way to reduce energy consumption in wireless sensor networks is to reduce the number of packets being transmitted in the network. As sensor networks are usually deployed with a number of redundant nodes (to overcome the problem of node failures which is common in such networks), many nodes may have almost the same information which can be aggregated in intermediate nodes, and hence reduce the number of transmitted packets. Aggregation ratio is maximized if data packets of all nodes having almost the same information are aggregated together. For this to occur, each node should forward its packets along a path on which maximum number of nodes with almost the same information as the information of the sending node exist. In many real scenarios, such a path has not been remained the same for the overall network lifetime and is changed from time to time. These changes may result from changes occurred in the environment in which the sensor network resides and usually cannot be predicted beforehand. In this paper, a learning automata-based data aggregation method in sensor networks when the environment’s changes cannot be predicted beforehand will be proposed. In the proposed method, each node in the network is equipped with a learning automaton. These learning automata in the network collectively learn the path of aggregation with maximum aggregation ratio for each node for transmitting its packets toward the sink. To evaluate the performance of the proposed method computer simulations have been conducted and the results are compared with the results of three existing methods. The results have shown that the proposed method outperforms all these methods, especially when the environment is highly dynamic.     

Prevention of deadlocks and livelocks in lossless backpressured packet networks

No packets will be dropped inside a packet network, even when congestion builds up, if congested nodes send backpressure feedback to neighboring nodes, informing them of unavailability of buffering capacity-stopping them from forwarding more packets until enough buffer becomes available. While there are potential advantages in backpressured networks that do not allow packet dropping, such networks are susceptible to a condition known as deadlock in which throughput of the network or part of the network goes to zero (i.e., no packets are transmitted). In this paper, we describe a simple, lossless method of preventing deadlocks and livelocks in backpressured packet networks. In contrast with prior approaches, our proposed technique does not introduce any packet losses, does not corrupt packet sequence, and does not require any changes to packet headers. It represents a new networking paradigm in which internal network losses are avoided (thereby simplifying the design of other network protocols) and internal network delays are bounded.     

Loss estimation and control mechanism in bufferless optical packet-switched networks based on multilayer perceptron

Artificial neural networks (ANNs) are well-known estimators for the output of broad range of complex systems and functions. In this paper, a common ANN architecture called multilayer perceptron (MLP) is used as a fast optical packet loss rate (OPLR) estimator for bufferless optical packet-switched (OPS) networks. Considering average loads at the ingress switches of an OPS network, the proposed estimator estimates total OPLR as well as ingress OPLRs (the OPLR of optical packets sent from individual ingress switches). Moreover, a traffic policing algorithm called OPLRC is proposed to control ingress OPLRs in bufferless slotted OPS networks with asymmetric loads. OPLRC is a centralized greedy algorithm which uses estimated ingress OPLRs of a trained MLP to tag some optical packets at the ingress switches as eligible for drop at the core switches in case of contention. This will control ingress OPLRs of un-tagged optical packets within the specified limits while giving some chance for tagged optical packets to reach their destinations. Eventually, the accuracy of the proposed estimator along with the performance of the proposed algorithm is evaluated by extensive simulations. In terms of the algorithm, the results show that OPLRC is capable of controlling ingress OPLRs of un-tagged optical packets with an acceptable accuracy.     

Contention-based MAC protocols with erasure coding for wireless data networks

Contention-based medium access control (MAC) protocol is a key component for the success of wireless data networks. Conventional random access protocols like ALOHA and Carrier Sense Multiple Access (CSMA) suffer from packet collision which leads to low throughput. Aimed at improving the throughput performance, we propose to integrate erasure coding with contention-based MAC protocols for recovering collided packets. To demonstrate the effectiveness of this approach, we focus on combining erasure coding with slotted ALOHA and slotted non-persistent CSMA in this paper. The performances of the resulting protocols are evaluated by both analytical model and simulation. Simulation results match very well with analytical results and show that the system throughput is increased for low to medium traffic loading. Packet loss ratio is also improved considerably with our scheme when the maximum number of packet retransmission times is limited. However, the delay for our scheme is higher due to the longer waiting time in our scheme for recovering collided packets. It is also shown that delay can be significantly reduced if we choose appropriate coding parameters though throughput will be sacrificed.     

Scalable Routing Protocol for Ad Hoc Networks

In this paper we present a scalable routing protocol for ad hoc networks. The protocol is based on a geographic location management strategy that keeps the overhead of routing packets relatively small. Nodes are assigned home regions and all nodes within a home region know the approximate location of the registered nodes. As nodes travel, they send location update messages to their home regions and this information is used to route data packets. In this paper, we derive theoretical performance results for the protocol and prove that the control packet overhead scales linearly with node speed and as N ^3/2 with increasing number of nodes. These results indicate that our protocol is well suited to relatively large ad hoc networks where nodes travel at high speed. Finally, we use simulations to validate our analytical model.     

广播网络中基于补丁流的丢包恢复机制研究

现有的数字广播网络由于没有回传通道,发送端无法知悉传输过程中的丢包状况。接收端处在广播网络的不同位置,常常因处于小区边缘或受障碍物遮挡等原因造成信号减弱,从而导致丢包率提高。该文提出了一种基于pFEC (patching Forward Error Correction,补丁FEC)的丢包恢复机制,来解决单向广播网络的丢包问题。该方法利用蜂窝移动网络的双向信道来传输补丁流,提供自适应的FEC来降低丢包率。这种方式可以在广播业务中为不同位置的用户提供不同的丢包恢复能力。理论建模及仿真结果显示,在蜂窝移动网络丢包率不高的情况下,pFEC机制能够有效应对个别用户突发的丢包,从而提高广播业务整体的可靠性和服务质量。     

Adding sense of spatial locality to routing protocols for mobile ad hoc networks

Recently, there has been an increasing interest in mobile ad hoc networks. In a mobile ad hoc network, each mobile node can freely move around and the network is dynamically constructed by collections of mobile nodes without using any existing network infrastructure. Compared to static networks, it faces many problems such as the inefficiency of routing algorithms. Also, the number of control packets in any routing algorithm increases as the mobile speed or the number of mobile nodes increases. Most of the current routing protocols in ad hoc networks broadcast the control packets to the entire network. Therefore, by reducing the number of control packets, the efficiency of the network routing will be improved. If we know where the destination is, we can beam our search toward that direction. However, without using global positioning systems, how can we do this? Define the range nodes as the 1‐hop or 2‐hop neighbors of the destination node. In this paper, we propose using the range nodes to direct our searches for the destination. It can be combined with the existing routing protocols to reduce the control overhead. We show through simulations that AODV and DSR combined with the range node method outperforms the original AODV and DSR routing protocols in terms of control packets overhead. We also show that the delay introduced in find range nodes is insignificant. Copyright © 2006 John Wiley & Sons, Ltd.     

A fuzzy logic and game theory based adaptive approach for securing opportunistic networks against black hole attacks

Opportunistic networks (OppNets) are networks that can be used in situations of sparse network connectivity. Strategies for implementing secure transmission of messages in OppNets offer complex and distinctive problems that are wholly different from traditional networks using TCP/IP protocols for data transmission. In this paper, a security protocol named FuzzyPT is proposed which combats black hole attacks in OppNets. The defense mechanism is based on the information extracted from messages in the buffer, potential threat (PT) messages, and fuzzy logic. Fuzziness aids the system in being adaptive by modeling the character of nodes as either benign or malicious. It provides the network with the ability to judge the character of nodes based on relationships between different parameters instead of basing this decision on fixed conditions. FuzzyPT is observed to reduce erroneous decision‐making and decrease the number of false positives and false negatives in the system. An evolutionary game theoretic model is applied, which analyzes the decision‐making ability of relays in choosing varied strategies while forwarding messages. The evolutionary stable state is computed for the protocol, which verifies the proposition that a majority of the relays will cooperate by forwarding messages. The efficiency of the protocol is judged on various grounds such as delivery probability, network overhead ratio, packets dropped, and transmission latency. It is observed that the proposed game theoretic protocol outperforms an existing acknowledge and evolutionary game theory–based security protocol in terms of all the aforementioned performance characteristics.     

Burst transmission algorithm to improve packet level performance in contention-free slotted OBS networks

In contention-free slotted optical burst switching (SOBS) networks, controllers are utilized in order to manage the time-slot assignment, avoiding congestions among multiple burst transmissions. In this network, bursts are never lost at intermediate nodes but packets are lost at an ingress edge node due to a burst transmission algorithm. In addition, packet transmission delay increases depending on the algorithm. In order to improve packet level performance, in this paper, we propose a new burst transmission algorithm. In this method, two different thresholds are used; one is used to send a control packet to a controller and the other is used to assemble a burst. With these thresholds, a time slot can be assigned to a burst in advance and packet level performance can be improved. In order to evaluate its packet level performance and investigate the impact of thresholds, we also propose a queueing model of a finite buffer where a batch of packets are served in a slot of a constant length. Numerical results show that our proposed method can decrease packet loss probability and transmission delay with two thresholds. In addition, we show that our analysis results are effective to investigate the performance of the proposed method when the number of wavelengths is large.