On the design of self-organized cellular wireless networks

It has been observed that complex networks such as the Internet, World Wide Web, social networks, and biological systems are self-organizing in nature and exhibit some common properties such as the power law degree distribution. Recently, two models (i.e., small world and scale-free network models) have been proposed and successfully used to describe the nature of such networks. In this article we investigate whether these concepts can also be applied to cellular wireless networks, which typically do not exhibit self-organizing or scalability properties due to the limited range of the wireless nodes. Our ultimate goal is to design robust, reliable, scalable, and efficiently utilized wireless networks via self-organizing mechanisms.     

Intégration ďarchitectures à base de réseaux de neurones formels : un défi pour les technologies submicroniques

Connexionist architectures, using the formal neuron concept, may exhibit properties reminding of some simple cognitive functions. They may thus lead to new signal processing machines, implementing classification and generalization functionalities, or associative memories, for instance. Integration of these functions in silicon can be beneficial, if it is possible to solve connectivity issues and synaptic coefficients realisation, whether using analog or digital technologies. With coming submicrometer technologies, it will be possible to make progress towards networks more important than those which are integrated nowadays, but it is probably only through association of independant networks, cooperating within hierarchized architectures, that it will be possible to implement higher level functions, having a strong parallelism.     

Time-limited and band-limited environment: Signals and systems

Of concern is an environment made up of signals and systems tightly confined both in time and frequency. Such an environment is often encountered in transmission line circuits, radar, sonar, and optical circuits, and when the principal signals are well-defined sharp pulses. It will be seen that once this environment is achieved, the signals and systems possess some attractive properties. A conventional system may preserve the symmetry of a propagating signal or change its symmetry from even to odd or from odd to even. Another system may be used to predict the arrival of an incoming pulse with a high degree of accuracy. Electrical networks may also be associated with these properties. Approximation problems, existence theorems, and realization schemes will be addressed and developed.     

Complex networks: small-world, scale-free and beyond

In the past few years, the discovery of small-world and scale-free properties of many natural and artificial complex networks has stimulated a great deal of interest in studying the underlying organizing principles of various complex networks, which has led to dramatic advances in this emerging and active field of research. The present article reviews some basic concepts, important progress, and significant results in the current studies of various complex networks, with emphasis on the relationship between the topology and the dynamics of such complex networks. Some fundamental properties and typical complex network models are described; and, as an example, epidemic dynamics are analyzed and discussed in some detail. Finally, the important issue of robustness versus fragility of dynamical synchronization in complex networks is introduced and discussed.     

A new generalized energy criterion for the passivity of digitalnetworks

A general passivity criterion for digital networks is introduced. Digital networks that meet this criterion form a stable and useful class of networks. The networks in this class have properties similar to passive analog networks. These networks are all stable, and some networks, including all linear networks, are shown to have restricted gain. The gain restriction can be used to design filters that are insensitive to changes in multiplier values at frequencies of maximum gain. Emerging directly from this criterion is a procedure for interconnecting simple networks to form a complex passive network. These networks remain stable after the introduction of rounding following multiplications so that these networks do not exhibit limit cycle oscillations     

基于流量攻击和边失效的复杂网络脆弱特性

基于流量的攻击可能对复杂网络造成严重破坏,现有研究主要针对节点攻击。该文分析了部分边失效时,复杂网络的脆弱特性。此外,分析了时机策略和网络规模对边失效的影响。通过研究节点负载和度分布特点,发现复杂网络的脆弱特性源于其幂率度分布引起的节点负载的极度非均匀分布。仿真实验表明,复杂网络对随机的边失效具有较强的耐受力,但在一定条件下,攻击极少量重要边就可能引发连锁的节点过载失效,而导致网络溃散。     

Toward a theory of in-network computation in wireless sensor networks

Sensor networks are not just data networks with sensors being the sources of data. Rather, they are often developed and deployed for a specific application, and the entire network operation is accordingly geared toward satisfying this application. For overall system efficiency, it may be necessary for nodes to perform computations on data, as opposed to simply originating or forwarding data. Thus, the entire network can be viewed as performing an application-specific distributed computation. The topic of this article is to survey some lines of research that may be useful in developing a theory of in-network computation, which aims to elucidate how a wireless sensor network should efficiently perform such distributed computation. We review several existing approaches to computation problems in network settings, with a particular emphasis on the communication aspect of computation. We begin by studying the basic two-party communication complexity model and how to optimally compute functions of distributed inputs in this setting. We proceed to larger multihop networks, and study how block computation and function structure can be exploited to provide greater computational throughput. We then consider distributed computation problems in networks subject to noise. Finally, we review some randomized gossip-based approaches to computing aggregate functions in networks. These are diverse approaches spanning many different research communities, but together may find a role in the development of a more substantial theoretical foundation for sensor networks.     

The analog local loop: a growing revolution in optical transmission

To provide an economic justification for the widespread deployment of optical fiber in the local loop, it may be necessary in some situations to install networks which will carry only telephony but can be upgraded to provide broadband services. Methods by which this may be achieved using analog carrier techniques are discussed. Passive optical networks (PONs) are considered, and the application of plain old telephone service (POTS) and broadband services over PONs is considered. Frequency planning and future trends are summarized     

The impact of multicast layering on network fairness

Many definitions of fairness for multicast networks assume that sessions are single rate, requiring that each multicast session transmits data to all of its receivers at the same rate. These definitions do not account for multirate approaches, such as layering, that permit receiving rates within a session to be chosen independently. We identify four desirable fairness properties for multicast networks, derived from properties that hold within the max-min fair allocations of unicast networks. We extend the definition of multicast max-min fairness to networks that contain multirate sessions, and show that all four fairness properties hold in a multirate max-min fair allocation, but need not hold in a single-rate max-min fair allocation. We then show that multirate max-min fair rate allocations can be achieved via intra-session coordinated joins and leaves of multicast groups. However, in the absence of coordination, the resulting max-min fair rate allocation uses link bandwidth inefficiently, and does not exhibit some of the desirable fairness properties. We evaluate this inefficiency for several layered multirate congestion control schemes, and find that, in a protocol where the sender coordinates joins, this inefficiency has minimal impact on desirable fairness properties. Our results indicate that sender-coordinated layered protocols show promise for achieving desirable fairness properties for allocations in large-scale multicast networks     

Qualitative analysis for recurrent neural networks with linear threshold transfer functions

Multistable networks have attracted much interest in recent years, since multistability is of primary importance for some applications of recurrent neural networks where monostability exhibits some restrictions. This paper focuses on the analysis of dynamical property for a class of additive recurrent neural networks with nonsaturating linear threshold transfer functions. A milder condition is derived to guarantee the boundedness and global attractivity of the networks. Dynamical properties of the equilibria of two-dimensional networks are analyzed theoretically, and the relationships between the equilibria features and network parameters (synaptic weights and external inputs) are revealed. In addition, the sufficient and necessary conditions for coexistence of multiple equilibria are obtained, which confirmed the observations in with a cortex-inspired silicon circuit. The results obtained in this paper are applicable to both symmetric and nonsymmetric networks. Simulation examples are used to illustrate the theory developed in this paper.     

Global convergence of Lotka-Volterra recurrent neural networks with delays

Recurrent neural networks of the Lotka-Volterra model have been proven to possess characteristics which are desirable in some neural computations. A clear understanding of the dynamical properties of a recurrent neural network is necessary for efficient applications of the network. This paper studies the global convergence of general Lotka-Volterra recurrent neural networks with variable delays. The contributions of this paper are: 1) sufficient conditions are established for lower positive boundedness of the networks; 2) global exponential stability conditions are obtained for the networks. These conditions are totally independent of the variable delays which are therefore allowed to be uncertain; 3) novel Lyapunov functionals are constructed to establish delays dependent conditions for global asymptotic stability, and 4) simulation results and examples are provided to supplement and illustrate the theoretical contributions presented.     

循环神经网络的语音识别算法

通常采用具有前向连接权的连接网络便可实现静态输入输出模式对的联想,但是为了使网络记忆序列信息状态,必须考虑引入反馈连接权。本文构造一个具有动态神经元的多层网络结构,动态神经元带有多时延的局部反馈。此网络结构用于记忆时间序列信息,同时,相应地我们推导一种更有效、更便于实现的网络学习算法。最后,为了测试所提出网络学习动态时变数据的能力,选择几个不同参数的动态神经元模型,进行了一系列实验。     

Multihour engineering and traffic routing optimization in hierarchical telephone networks

Classical hierarchical routing in telephone networks is extended to a wider class called out-of-chain routing in such a way that some useful properties of hierarchical routing are retained. This new routing pattern offers more potential paths than the fixed hierarchical one and can be introduced as a dynamic routing where the fixed alternate sequences change at some predetermined instants during the day. The effect of this new routing pattern on the network performances is examined. The main topic of this paper is to present heuristic methods used to optimise such routings in large networks. We show on artificial networks that the throughput of a given network can be significantly improved by suitable routing choices. We demonstrate that the integration of routing changes within a multihour dimensioning process is possible but the lack of realistic data does not permit at this time to quantify the value of routing optimization on real networks.     

The distributed-lumped-active network Its application to filtering problems

The development of modern integrated circuit techniques has added a new and important network element to the list of those usually considered by the filter designer?the distributed RC network. This article discusses the properties of such networks and shows how they can be combined with lumped passive elements and active elements to produce a class of distributed-lumped-active (DLA) networks. Such networks can be applied to a wide range of filter requirements and have many advantages. For example, DLA realizations usually require fewer components than comparable realizations using lumped elements. Because partial differential equations are required to model distributed components, many new techniques of analysis and synthesis must be used in the design of DLA networks. A discussion of these techniques, including many that may be implemented on the digital computer, is presented and examples of some typical DLA realizations are given.     

Secure neighbor discovery and wormhole localization in mobile ad hoc networks

Neighbor discovery is an important part of many protocols for wireless adhoc networks, including localization and routing. When neighbor discovery fails, communications and protocols performance deteriorate. In networks affected by relay attacks, also known as wormholes, the failure may be more subtle. The wormhole may selectively deny or degrade communications. In this article we present Mobile Secure Neighbor Discovery (MSND), which offers a measure of protection against wormholes by allowing participating mobile nodes to securely determine if they are neighbors, and a wormhole localization protocol, which allows nodes that detected the presence of a wormhole to determine wormhole’s location. To the best of our knowledge, this work is the first to secure neighbor discovery in mobile adhoc networks and to localize a wormhole. MSND leverages concepts of graph rigidity for wormhole detection. We prove security properties of our protocols, and demonstrate their effectiveness through extensive simulations and a real system evaluation employing Epic motes and iRobot robots.     

A Framework for Evaluating the Performance of Cluster Algorithms for Hierarchical Networks

Table-driven routing algorithms in flat networks have the scalability problem due to the need for global topology updates. To reduce update cost, networks are hierarchically organized. Clustering algorithms organize flat networks into hierarchical networks. One important problem, which has not been adequately addressed so far, is to evaluate how good a clustering algorithm is. In other words, it is useful to know what the desired properties of hierarchical networks are. In this paper, we address this issue by considering the routing update cost, which can be measured by the total routing table size and the variance of cluster size distribution. We provide a set of desired properties of clustering algorithms. Applying these properties to the cluster structure generated by an algorithm, we can determine how good a clustering algorithm is. Specifically, we discuss how to choose appropriate number of hierarchy levels, number of clusters, and cluster size distribution, such that the topology update cost is minimized. The desired properties obtained from the analysis can be used as guidelines in the design of clustering algorithms for table-driven hierarchical networks. We apply the idea developed in this paper to evaluate three routing algorithms, namely the lowest ID algorithm, the maximum degree algorithm, and the variable degree clustering algorithm. We show how the variable degree clustering algorithm, which takes into account these desired properties, improves routing performance.     

FB-banyans and FB-delta networks: Fault-tolerant networks for broadband packet switching

Many fast packet switches for the broadband integrated services digital network (BISDN) in the literature are based on banyan networks. Although banyan networks possess nice properties such as a simple control and a low hardware cost, they are unique-path networks. Since there is a unique path from an input to an output in a banyan network, a single component failure may disrupt services of some nodes connected to such a network. Moreover, banyan networks are also blocking networks; packets can be lost within the networks. To reduce the packet loss, buffered banyan networks can be used. In an earlier work we have proposed the addition of backward links to otherwise unidirectional banyan networks to create B-banyans (and B-delta networks). Backward links not only function as implicit buffers for blocked packets, but also provide multiple paths for each input-output connection. However, the multiple paths in B-banyans may not be disjoint. In this paper, we enhance B-banyans and B-delta networks in such a way that the resulting networks can provide disjoint multiple paths for each input-output pair. The existence of disjoint multiple paths has a significant effect on the network fault-tolerance. The new networks, called FB-banyans and FB-delta networks, are k fault-tolerant, where k is the number of backward links per switch and is less than the switch size. They are also robust to more than k faults, depending on the locations of faults. The maximal fault-tolerance is achieved when k is the switch size minus 1. The performance of the new networks is analysed and compared to that of other networks of interest. FB-banyans and FB-delta networks can be used as a switch fabric for fast packet switches to provide performance comparable to that of buffered banyan networks and good fault tolerance.     

Traffic Capacity of UMTS System in Reverse Link

UMTS can be connected to data networks. So Internet traffic services such as WWW browsing, email, ftp, SMTP, etc should be handled by UMTS. Each of the traffic services has some specific properties but all of them obey a basic ON/OFF model. For a traffic service there is some unused (OFF) times between their transmitted packets which we may use them for other services to increase the traffic capacity of the network. In this paper we propose a new method on the Internet traffic evaluation in an interference limited UMTS-WCDMA system. In this method first we calculate ON and OFF time durations of the above traffic services based on the model presented in 3GPP then their activity factors. Secondly we introduce new capacity curves such as The Number of Web browsing users/Email users/ftp users/Telnet users and Fax users versus voice users. These are applicable in traffic planning for wireless systems.     

粉末电致发光的新应用—一种光神经器件

近年来，人工神经风格与神经网络计算机的研究在世界范围内已形成一个热点，本文通过对电致发光材料的各种特性的讨论，分析了固体化平板电致发光作为一种光神经器件的一些特点，指出它在神经网络实现中有很好的应用前景。     

Call admission control for capacity-varying networks

Many networks, such as Non-Geostationary Orbit Satellite (NGOS) networks and networks providing multi-priority service using advance reservations, have capacities which vary over time for some or all types of calls carried on these networks. For connection-oriented networks, Call Admission Control (CAC) policies which only use current capacity information may lead to excessive and intolerable dropping of admitted calls whenever the network capacity decreases. Thus, novel CAC policies are required for these networks. Three such CAC policies are discussed, two for calls with exponentially distributed call holding times and one for calls whose holding time distributions have Increasing Failure Rate (IFR) functions. The Admission Limit Curve (ALC) is discussed and shown to be a constraint limiting the conditions under which any causal CAC policy may admit calls and still meet call dropping guarantees on an individual call basis. We demonstrate how these CAC policies and ALC represent progressive steps in developing optimal CAC policies for calls with exponentially distributed call holding times, and extend this process to the more general case of calls with IFR call holding times.