Power Efficient Range Assignment for Symmetric Connectivity in Static Ad Hoc Wireless Networks

In this paper we study the problem of assigning transmission ranges to the nodes of a static ad hoc wireless network so as to minimize the total power consumed under the constraint that enough power is provided to the nodes to ensure that the network is connected. We focus on the Min-Power Symmetric Connectivity problem, in which the bidirectional links established by the transmission ranges are required to form a connected graph. Implicit in previous work on transmission range assignment under asymmetric connectivity requirements is the proof that Min-Power Symmetric Connectivity is NP-hard and that the MST algorithm has a performance ratio of 2. In this paper we make the following contributions: (1) we show that the related Min-Power Symmetric Unicast problem can be solved efficiently by a shortest-path computation in an appropriately constructed auxiliary graph; (2) we give an exact branch and cut algorithm based on a new integer linear program formulation solving instances with up to 35–40 nodes in 1 hour; (3) we establish the similarity between Min-Power Symmetric Connectivity and the classic Steiner Tree problem in graphs, and use this similarity to give a polynomial-time approximation scheme with performance ratio approaching 5/3 as well as a more practical approximation algorithm with approximation factor 11/6; and (4) we give the results of a comprehensive experimental study comparing new and previously proposed heuristics with the above exact and approximation algorithms.     

Enumerating catastrophic fault patterns in VLSI arrays with both uni- and bidirectional links

Characterization of catastrophic fault patterns (CFPs) and their enumeration have been studied by several authors. Given a linear array with a set of bypass links, an important problem is how to count the number of CFPs. Enumeration of CFPs for two link redundancy G={1,g} has been solved for both unidirectional and bidirectional link cases. In this paper, we consider the more general case of link redundancy G={1,2,…,k,g}, 2k<g. Using random walk as a tool, we enumerate CFPs for both unidirectional and bidirectional cases.     

Routing in the bidirectional shufflenet

We study the bidirectional shufflenet topology, which is obtained from the well-known (unidirectional) shufflenet by considering bidirectional links. More specifically, we define a shortest path routing algorithm, and derive the diameter and the average distance of the topology. The bidirectional shufflenet is then compared, in terms of average distance, with other variations of the perfect shuffle. Bidirectional links are very common in real networks. Possible applications of bidirectional shufflenets are wormhole routing electronic networks with back-pressure flow control, and wavelength routing optical networks. The former class of networks is considered, when virtual channels are used to prevent deadlocks. We show that four virtual channels are sufficient to avoid deadlocks in the bidirectional shufflenet, regardless of the number of nodes in the topology     

Joint processing of topology control and channel assignment in wireless ad hoc networks

Network topology construction and its channel assignment for each node in the constructed network topology are two main problems in the initialization of topology building. Topology control is an effective way to solve the problem of topology building. To investigate the joint effect of topology control and channel assignment, we propose a joint processing scheme composed of a k‐Neighbor topology control algorithm and a greedy channel assignment (GCA) algorithm in this paper. Based on this joint processing scheme, the relationships between the energy consumption, the total required channel number and the network connectivity are discussed. We also discuss the impact of some parameters on the performance of networks in terms of the path loss factor, node density, maximum node degree, etc. Our main contributions in this paper is that we find that topology control has a good effect on improving the performance of channel assignment, and the proposed joint processing scheme can reduce the required channel number effectively, compared with its theoretical upper bound. In particular, if the node degree in a network is not more than k, various simulations indicate that the required channel number is not more than 2k + 1. Copyright © 2008 John Wiley & Sons, Ltd.     

Equilibria in Topology Control Games for Ad Hoc Networks

We study topology control problems in ad hoc networks where network nodes get to choose their power levels in order to ensure desired connectivity properties. Unlike most other work on this topic, we assume that the network nodes are owned by different entities, whose only goal is to maximize their own utility that they get out of the network without considering the overall performance of the network. Game theory is the appropriate tool to study such selfish nodes: we define several topology control games in which the nodes need to choose power levels in order to connect to other nodes in the network to reach their communication partners while at the same time minimizing their costs. We study Nash equilibria and show that—among the games we define—these can only be guaranteed to exist if each network node is required to be connected to all other nodes (we call this the Strong Connectivity Game). For a variation called Connectivity Game, where each node is only required to be connected (possibly via intermediate nodes) to a given set of nodes, we show that Nash equilibria do not necessarily exist. We further study how to find Nash equilibria with incentive-compatible algorithms and compare the cost of Nash equilibria to the cost of a social optimum, which is a radius assignment that minimizes the total cost in a network where nodes cooperate. We also study variations of the games; one where nodes not only have to be connected, but k-connected, and one that we call the Reachability Game, where nodes have to reach as many other nodes as possible, while keeping costs low. We extend our study of the Strong Connectivity Game and the Connectivity Game to wireless networks with directional antennas and wireline networks, where nodes need to choose neighbors to which they will pay a link. Our work is a first step towards game-theoretic analyses of topology control in wireless and wireline networks. A preliminary version of this paper appeared in DIALM-POMC ’03 [8]. Stephan Eidenbenz is a technical staff member in Discrete Simulation Sciences (CCS-5) at Los Alamos National Laboraotry. He received his Ph.D. in Computer Science from the Swiss Federal Institute of Technology, Zurich, Switzerland in 2000. Stephan’s research covers areas in approximability, algorithms, computational geometry, computational biology, large-scale discrete simulation, selfish networking, efficient networking, protocol design and optimization. V. S. Anil Kumar is currently an Assistant Professor in the Dept. of Computer Science and a Senior Research Associate at Virginia Bioinformatics Institute, Virginia Tech. Prior to this, he was a technical staff member in Los Alamos National Laboratory. He received a Ph.D. in Computer Science from the Indian Institute of Science in 1999. His research interests include approximation algorithms, mobile computing, combinatorial optimization and simulation of large socio-technical systems. Sibylle Zust received her Masters degree in mathematics from ETH Zurich in Switzerland in 2002. She wrote her diploma thesis at the University of Copenhagen in Denmark. Sibylle Zust spent two and a half years (2002–2005) as a graduate research assistant at the Los Alamos National Laboratory in New Mexico, USA, where she worked on algorithmic aspects of game theory and scheduling problems. She now works for an insurance company in Zurich, Switzerland.     

Restoration performance study of k-shortest disjoint paths in WDM optical networks

Many researchers have proposed restoration techniques incorporating the concept of k-shortest disjoint paths in survivable WDM (Wavelength Division Multiplexing) optical networks, but without considering network performance and network costs simultaneously. In this paper we need to carefully look into how well the concept of shortest disjoint paths is incorporated for given objective functions. Seven objective functions and four algorithms are presented to evaluate the concept of k-shortest disjoint paths for the design of a robust WDM optical network. A case study based on simulation experiments is conducted to illustrate the application and efficiency of k-shortest disjoint paths in terms of following objective goals: minimal wavelengths, minimal wavelength link distance, minimal wavelength mileage costs, even distribution of traffic flows, average restoration time of backup lightpaths, and physical topology constraints. Sungwoo Takis an assistant professor in the Department of Computer Science and Engineering at Pusan National University. He is also a research member at Research Institute of Computer Information and Communication at Pusan National University. He received a Ph.D. degree in Computer Science from the University of Missouri Kansas City. He has served as a TPC member for the IEEE ICCCN (International Conference on Computer Communications and Networks) since 2004. His research interests include Computer Networks, Wireless Networks, Software Architecture, WDM Optical Networks, Real-time Systems, and SoC (System on Chips) based Communication Chip Design. E. K. Park is a Professor of Computer Science at the University of Missouri at Kansas City. He received a Ph.D. degree in Computer Science from the Northwestern University. His research interests include software engineering, software architectures, software agents, distributed systems, object-oriented methodology, software tolerance and reliability, computer networks and management, optical networks, database/data mining, and information/knowledge management.     

On minimizing the total power of <Emphasis Type="Italic">k</Emphasis>-strongly connected wireless networks

Given a wireless network, we want to assign each node a transmission power, which will enable transmission between any two nodes (via other nodes). Moreover, due to possible faults, we want to have at least k vertex-disjoint paths from any node to any other, where k is some fixed integer, depending on the reliability of the nodes. The goal is to achieve this directed k-strong connectivity with a minimal overall power assignment. The problem is NP-Hard for any k ≥ 1 already for planar networks. Here we first present an optimal power assignment for uniformly spaced nodes on a line for any k ≥ 1. We also prove a number of useful properties of power assignment which are also of independent interest. Based on it, we design an approximation algorithm for linear radio networks with factor min{2,(\frac \Updelta d)^a },\hbox{min}\left\{2,\left(\frac {\Updelta} {\delta}\right)^\alpha \right\}, where Δ and δ are the maximal and minimal distances between adjacent nodes respectively and parameter α ≥ 1 being the distance-power gradient. We then extend it to the weighted version. Finally, we develop an approximation algorithm with factor O(k ²), for planar case, which is, to the best of our knowledge, the first non-trivial result for this problem.     

Control of unidirectional oscillation in semiconductor orbiterlasers

Unidirectional oscillation in a ring-resonator-type semiconductor laser was demonstrated in a square-shaped orbiter laser using an optical feedback mechanism. The bistable switching phenomenon between the unidirectional and bidirectional oscillation was observed synchronized with the switching of the longitudinal lasing mode. A longitudinal-mode bistability results from the compound cavity system formed by the orbiter laser and output waveguide. The feedback light from the output waveguide end interferes with the orbiter lasing light. Switching between the unidirectional and bidirectional oscillation was controlled by injecting a current into the output waveguide, which varies the phase condition of the feedback light     

Distributed fault-tolerant topology control in wireless multi-hop networks

In wireless multi-hop and ad-hoc networks, minimizing power consumption and at the same time maintaining desired properties of the network topology is of prime importance. In this work, we present a distributed algorithm for assigning minimum possible power to all the nodes in a static wireless network such that the resultant network topology is k-connected. In this algorithm, a node collects the location and maximum power information from all nodes in its vicinity, and then adjusts the power of these nodes in such a way that it can reach all of them through k optimal vertex-disjoint paths. The algorithm ensures k-connectivity in the final topology provided the topology induced when all nodes transmit with their maximum power is k-connected. We extend our topology control algorithm from static networks to networks having mobile nodes. We present proof of correctness for our algorithm for both static and mobile scenarios, and through extensive simulation we present its behavior.     

Bidirectional optical fiber transmission systems using Ramanamplification

Bidirectional optical fiber transmission systems using Raman amplification are discussed. Analytical expressions for signals amplified by both forward and backward Raman scattering are presented. It is found that there exists an optimal pump power for the maximum unrepeated transmission length in a bidirectional system and that the maximum length is about 450 km, which is about the same as that of the unidirectional system     

Design of logical topology with K‐connected constraints and channel assignment for multi‐radio wireless mesh networks

In multi‐radio multi‐channel wireless mesh networks, the design of logical topology is different from that in single channel wireless mesh networks. The same channel assignment algorithm used for various logical topologies will lead to diverse network performance. In this paper, we study the relationship between k ‐connected logical topology and the maximum number of assigned channels. Meanwhile, we analyze the issues affecting channel assignment performance, and present the lower and upper bounds of the maximum allowable number of assigned channels for k ‐connected logical topology. We then develop a k ‐connected logical topology design algorithm based on shortest disjoint paths and minimum interference disjoint paths for each node‐pair. In addition, we propose a static channel assignment algorithm according to minimum spanning tree search. Extensive simulations show that our proposed algorithm achieves higher throughput and lower end‐to‐end delay than fault tolerant topology control algorithms, which validates the involved trade‐off between path length and nodal interference. Moreover, numerical results demonstrate that our proposed channel assignment further improves network performance under the context of limited radio interfaces. Copyright © 2014 John Wiley & Sons, Ltd.     

A Routing Algorithm for Wireless Ad Hoc Networks with Unidirectional Links

Most of the routing algorithms for ad hoc networks assume that all wireless links are bidirectional. In reality, some links may be unidirectional. In this paper we show that the presence of such links can jeopardize the performance of the existing distance vector routing algorithms. We also present modifications to distance vector based routing algorithms to make them work in ad hoc networks with unidirectional links. For a network of n nodes, neighbors exchange n×n matrices to propagate routing information. This results in loop-free routes.     

Fault-Tolerant and 3-Dimensional Distributed Topology Control Algorithms in Wireless Multi-hop Networks

The topology of a multi-hop wireless network can be controlled by varying the transmission power at each node. The life-time of such networks depends on battery power at each node. This paper presents a distributed fault-tolerant topology control algorithm for minimum energy consumption in multi-hop wireless networks. This algorithm is an extension of cone-based topology control algorithm [19, 12]. The main advantage of this algorithm is that each node decides on its power based on local information about the relative angle of its neighbors and as a result of these local decisions, a fault-tolerant connected network is formed on the nodes. It is done by preserving the connectivity of a network upon failing of, at most, k nodes (k is a constant) and simultaneously minimize the transmission power at each node to some extent. In addition, simulations are studied to support the effectiveness of this algorithm. Finally, it is shown how to extend this algorithm to 3-dimensions. An extended abstract version of this paper appeared in the 11th IEEE International Conference on Computer Communications and Networks(ICCCN02). Mohsen Bahramgiri born in 1979, recieved the Bachelor's degree in Mathematical Sciences from Sharif University of Technology, Tehran, Iran in 2000. He is now a PhD candidate in Mathematics Department at Massachusetts Institute of Technology. His research interests include Symplectic Hodge Theory on Higher dimentional Geometry, Kahler Geometry, Mathematical Physics and Geometric Analysis on one hand, and algorithmic Graph Theory and Combinatorics on the other hand. MohammadTaghi Hajiaghayi received the Bachelor's degree in computer engineering from Sharif University of Technology in 2000. He received the Master's degree in Computer Science from the University of Waterloo in 2001. Since 2001, he is a Ph.D. candidate in Computer Science and Artificial Intelligence Laboratory at the Massachusetts Institute of Technology. During his Ph.D. studies, he also worked at the IBM T.J. Watson Research Center (Department of Mathematical Sciences) and at the Microsoft Research (Theory group). His research interests are algorithmic graph theory, combinatorial optimizations, distributed and mobile computing, computational geometry and embeddings, game theory and combinatorial auctions, and random structures and algorithms. Vahab S. Mirrokni received the Bachelor's degree in computer engineering from Sharif University of Technology, Tehran, Iran in 2001. Since 2001, he is a Ph.D. candidate in Computer Science and Artificial Intelligence Laboratory at the Massachusetts Institute of Technology. During his Ph.D. studies, he also worked at the Bell-Laboratories (Networking Center and Department of Fundamental Mathematics). His research interests include approximation algorithms, combinatorial optimization, computational game theory, mobile computing, network mannagement, and algorithmic graph theory.     

The Coverage Problem in a Wireless Sensor Network

One of the fundamental issues in sensor networks is the coverage problem, which reflects how well a sensor network is monitored or tracked by sensors. In this paper, we formulate this problem as a decision problem, whose goal is to determine whether every point in the service area of the sensor network is covered by at least k sensors, where k is a given parameter. The sensing ranges of sensors can be unit disks or non-unit disks. We present polynomial-time algorithms, in terms of the number of sensors, that can be easily translated to distributed protocols. The result is a generalization of some earlier results where only k = 1 is assumed. Applications of the result include determining insufficiently covered areas in a sensor network, enhancing fault-tolerant capability in hostile regions, and conserving energies of redundant sensors in a randomly deployed network. Our solutions can be easily translated to distributed protocols to solve the coverage problem.A preliminary version of this paper has appeared in the Workshop on Wireless Sensor Networks and Applications, 2003, San Diego, CA, USA. Chi-Fu Huang received his B.S. and M.S. degrees both in Computer Science and Information Engineering from the Feng-Chia University and the National Central University in 1999 and 2001, respectively. He obtained his Ph.D. in the Department of Computer Science and Information Engineering from the National Chiao-Tung University in September of 2004. He is currently a Research Assistant Professor at the Department of Computer Science and Information Engineering, National Chiao-Tung University, Taiwan. His research interests include wireless communication and mobile computing, especially in ad hoc and sensor networks. Yu-Chee Tseng received his B.S. and M.S. degrees in Computer Science from the National Taiwan University and the National Tsing-Hua University in 1985 and 1987, respectively. He worked for the D-LINK Inc. as an engineer in 1990. He obtained his Ph.D. in Computer and Information Science from the Ohio State University in January of 1994. He was an Associate Professor at the Chung-Hua University (1994–1996) and at the National Central University (1996–1999), and a Full Professor at the National Central University (1999–2000). Since 2000, he has been a Full Professor at the Department of Computer Science and Information Engineering, National Chiao-Tung University, Taiwan. Dr. Tseng served as a Program Chair in the Wireless Networks and Mobile Computing Workshop, 2000 and 2001, as a Vice Program Chair in the Int’l Conf. on Distributed Computing Systems (ICDCS), 2004, as a Vice Program Chair in the IEEE Int’l Conf. on Mobile Ad-hoc and Sensor Systems (MASS), 2004, as an Associate Editor for The Computer Journal, as a Guest Editor for ACM Wireless Networks special issue on “Advances in Mobile and Wireless Systems”, as a Guest Editor for IEEE Transactions on Computers special on “Wireless Internet”, as a Guest Editor for Journal of Internet Technology special issue on “Wireless Internet: Applications and Systems”, as a Guest Editor for Wireless Communications and Mobile Computing special issue on “Research in Ad Hoc Networking, Smart Sensing, and Pervasive Computing”, as an Editor for Journal of Information Science and Engineering, as a Guest Editor for Telecommunication Systems special issue on “Wireless Sensor Networks”, and as a Guest Editor for Journal of Information Science and Engineering special issue on “Mobile Computing”. He is a two-time recipient of the Outstanding Research Award, National Science Council, ROC, in 2001–2002 and 2003–2005, and a recipient of the Best Paper Award in Int’l Conf. on Parallel Processing, 2003. Several of his papers have been chosen as Selected/Distinguished Papers in international conferences. He has guided students to participate in several national programming contests and received several awards. His research interests include mobile computing, wireless communication, network security, and parallel and distributed computing. Dr. Tseng is a member of ACM and a Senior Member of IEEE.This revised version was published online in August 2005 with a corrected cover date.     

Fault‐tolerant deployment with k‐connectivity and partial k‐connectivity in sensor networks

Wireless sensor networks are prone to failure, so prolonging their lifetime and preventing loss of connectivity are significant. A simple but efficient strategy is to place redundant sensor nodes to establish multi‐connectivity. This paper explores how to add as few as possible nodes (called Steiner nodes) to a sensor network such that the resulting network is k‐connected or partially k‐connected. k‐connectivity means that each pair of the nodes, whether Steiner or original, is connected by at least k node‐disjoint paths, while partial k‐connectivity only requires such connectivity among original nodes. The contribution lies in two aspects. First, the approximation ratio of an existing k‐connectivity repair algorithm is decreased from O(k⁴α) to O(k³α), where α is the approximation ratio of any algorithm that finds a minimum‐weight k‐connected spanning subgraph of a weighted complete graph. This is the best result ever obtained. Second, the first generic partial k‐connectivity repair algorithm is proposed. It is proved that the approximation ratio of this algorithm is at most O(k³α). Copyright © 2008 John Wiley & Sons, Ltd.     

Exploiting multi-interface networks: Connectivity and Cheapest Paths

Let G = (V,E) be a graph which models a set of wireless devices (nodes V) that can communicate by means of multiple radio interfaces, according to proximity and common interfaces (edges E). The problem of switching on (activating) the minimum cost set of interfaces at the nodes in order to guarantee the coverage of G was recently studied. A connection is covered (activated) when the endpoints of the corresponding edge share at least one active interface. In general, every node holds a subset of all the possible k interfaces. Such networks are known as multi-interface networks. In this setting, we study two basic problems: Connectivity and Cheapest Path. The Connectivity problem corresponds to the well-known Minimum Spanning Tree problem in graph theory. In practice, we need to cover a subgraph of G of minimum cost which contains a spanning tree of G. The problem turns out to be APX-hard in general and for many restricted graph classes, however it is possible to provide approximation algorithms: a 2-approximation in general and a (2-\frac1 k)(2-\frac{1}{ k})-approximation for the unit cost interface case, i.e. when the cost of activating an interface is unitary for any interface. We also consider the problem in special graph classes, such as graphs of bounded degree, planar graphs, graphs of bounded treewidth, complete graphs. The Cheapest Path problem corresponds to the well-known Shortest Path problem in graph theory. In the multi-interface setting this problem is still polynomially solvable, and we point out a simple Dijsktra-based algorithm with O(k|E|+k|V|log(k+|V|))O(k|E|+k|V|\log (k+|V|)) runtime in general and O(k(|E| + |V|)) runtime for the unit cost interface case.     

双向Buck/Boost变换器的教学探析

本文针对现有“电力电子技术”相关教材中存在的对双向变换器的分析不完善和各知识点之间缺乏联系等问题,探析了双向Buck/Boost变换器的拓扑生成原理,并且详细分析了变换器运行于电感电流过零模式下实现零电压开关的具体过程,并推导出了软开关的实现条件。本文有助于学生理解并加深双向变换器与基本Buck和Boost变换器之间的联系和差别,并了解软开关技术在基本变换器中的应用,具有一定的教学指导意义。     

Identification of nonminimum phase FIR systems via fourth-order cumulants and genetic algorithm

In this paper, the problem of estimating the parameters of an FIR system from only the fourth-order cumulants of the noisy system output is considered. The FIR system is driven by a symmetric, independent, and identically distributed (i.i.d) non-Gaussian sequence. We propose a new formula called Weighted Overdetermined C(q, k) (WOC(q, k)) by extending the conventional C(q, k) formula. The optimal selection of the weights in WOC(q, k) is performed by using the Genetic Algorithm (GA) optimization method which minimizes a nonlinear error function based on the fourth-order cumulants alone. Simulations are provided to reveal the effectiveness and the superiority of this novel technique over the C(q, k) and other existing techniques.     

A cost effective approach for survivable multicast traffic grooming in bidirectional multiwavelength ring networks

In this paper, we address the problem of survivable multicast traffic grooming in WDM bidirectional ring networks. The rapid growth of multicast applications such as video conferencing, distance learning, and online auction, has initiated the need for cost-effective solutions to realize multicasting in WDM optical networks. Many of these applications, being time critical and delay sensitive, demand robust and fault-tolerant means of data communication. The end user traffic demands in metro environment are in fractional bandwidth as compared to the wavelength channel capacity. Providing survivability at connection level is resource intensive. Hence cost-effective solutions that require minimum resources for realizing survivable multicasting are in great demand. In order to realize multicast traffic grooming in bidirectional ring networks, we propose a node architecture based on Bidirectional Add Drop Multiplexers (BADM) to support bidirectional add/drop functionality along with traffic duplication at each node. We also propose two traffic grooming algorithms, namely Survivable Grooming with Maximum Overlap of Sessions (SGMOS) and Survivable Grooming with Rerouting of Sessions (SGRS). Extensive simulation studies reveal that the proposed algorithms consume minimum resources measured in terms of BADM grooming ports, backup cost, and wavelengths.     

Two fast algorithms for computing point scalar multiplications on elliptic curves

The key operation in Elliptic Curve Cryptosystems(ECC) is point scalar multiplication. Making use of Frobenius endomorphism, Mfiller and Smart proposed two efficient algorithms for point scalar multiplications over even or odd finite fields respectively. This paper reduces thec orresponding multiplier by modulo τ^k-1 … τ 1 and improves the above algorithms. Implementation of our Algorithm 1 in Maple for a given elliptic curve shows that it is at least as twice fast as binary method. By setting up a precomputation table, Algorithm 2, an improved version of Algorithm 1, is proposed. Since the time for the precomputation table can be considered free, Algorithm 2 is about (3/2) log2 q - 1 times faster than binary method for an elliptic curve over Fq.