Link Assignment Research Articles

A novel cross-layer mesh router placement scheme for wireless mesh networks

Wireless mesh networks (WMNs) offer a great promise in supporting ubiquitous multimedia Internet access for mobile or fixed mesh clients (MCs). In WMNs, Internet traffic from MCs is aggregated by serving mesh router (MR) and forwarded hop-by-hop by MRs to an internet gateway (IGW) or vice versa. While deploying MRs and IGWs, intricate relationships among antenna types, wireless links with adaptive modulation and coding, MAC scheduling, routing, and equipment cost render the network planning an extremely complex problem. This article presents a novel cross-layer MR placement (CMRP) scheme that can cope up with this issue. CMRP encapsulates the cross-layer metrics into three underlying attributes: Local Coverage (LC), Backbone Residual Capacity (BRC), and Deployment Cost (DC), and are used to minimize the network deployment cost. Coupled with our proposed novel tree-based minimal cost routing scheme and weight-based link assignment for user coverage, we are able to plan the design of WMNs efficiently. Extensive simulations have been performed to examine the performance and feasibility of CMRP and compared with existing design schemes based on coverage, connectivity, and combination of the two. The result demonstrates that our approach outperforms existing schemes both in the cost performance ratio and potential implementation feasibility.

Capacity and interference aware link scheduling with channel assignment in wireless mesh networks

Wireless mesh networks (WMNs) are receiving lot of attention in recent years due to the unique features such as low cost and easy deployment. The optimal routing in these networks depends on the link capacities determined by link scheduling. To increase the throughput and network capacity, use of multiple channels and interfaces has been introduced in these networks. But the presence of interference limits the use of link and channel assignment in these types of networks. In this paper, we present a novel approach for link scheduling and channel assignment (CA) to improve the overall capacity and throughput of WMNs. The problem of link scheduling and CA is formulated as a Linear Programming (LP) problem with associated constraints. Links are sorted and placed in a particular group based upon link cost metric (LCM). The LCM value is used to group the links together and placed in appropriate group for CA. As the links are sorted and placed in appropriate groups the corresponding entries are made in Link Assignment Matrix (LAM). Once the links are grouped using LCM, then CA for these links is done and corresponding entries are made in Channel Assignment Matrix (CAM). Two algorithms, one for link scheduling and other for CA, are proposed. Simulation results show that proposed scheme outperforms the earlier approaches with respect to packet delivery fraction, end-to-end delay, aggregate throughput, fairness index and packet loss rate.

The dynamic frequency assignment problem

In this paper, we consider a frequency assignment problem occurring in a military context. The main originality of the problem pertains to its dynamic dimension: new communications requiring frequency assignments need to be established throughout a deployment. The problem decomposes in three phases: assignment of an initial kernel of communications, dynamic assignment of new communication links and reparation when no assignment is possible. Different solution methods are proposed and many computational tests are carried out on realistic instances.

Autonomous reconfiguration and control in directional mobile ad hoc networks

Requirements for increasingly complex, scalable, and dynamic wireless networks, which provide assured end-to-end broadband connectivity in a wide range of scenarios, have been emerging. In this context, we have been investigating wireless technologies that provide extremely high data rates through the use of narrow-beam free space optical (FSO) and/or radio-frequency (RF) point-to-point links. The use of directional wireless communications to form flexible backbone networks, which provide broadband connectivity to capacity- limited wireless networks or hosts using omnidirectional transmission, promises to circumvent the scalability limitations of traditional flat wireless networks. We have been investigating backbones of base stations, in which topologies and mobility can be controlled for purposes of assured communications. We refer to these as Directional Mobile Ad Hoc Networks (DMANET). Our work considers the use of topology control to assure robust end-to-end broadband connectivity in heterogeneous and dynamic environments. Topology control is defined as the autonomous network capability to dynamically reconfigure its physical topology. In the case of directional wireless backbone (DWB) networks, the physical topology can be reconfigured through: Autonomous 1) Topology Reconfiguration (ATR): dynamic redirection of point-to-point links using heuristic algorithms for creating new topologies and pointing, acquisition and tracking of links. Topology reconfiguration algorithms, which compute minimum energy configurations by determining optimal link assignments between backbone nodes, are presented. The pointing, acquisition and tracking (PAT) process needed to physically redirect point-to-point links is also addressed. 2) Mobility Control (MC): dynamic reposition and "morphing" of backbone nodes. In this model, communication links define physical interactions between network nodes. Control mechanisms are designed to mimic physical systems' natural reaction to external excitations, which drive the network topology to minimum energy configurations Using both ATR and MC, networks are completely selforganizing. They can autonomously adapt their physical topology to maximize coverage to terminals or hosts while maintaining robust backbone connectivity. In this paper, we present the design, implementation and evaluation of our novel approaches to autonomous reconfiguration and control.

Rain-Induced Bistatic Scattering at 60 GHz

The 60 GHz oxygen absorption band has been of particular interest in recent years for short-hop links between buildings in dense urban environments. The high oxygen attenuation in this band, typically in the range 12–16 dB km{−1}, limits its practical use for longer links and for Earth-space communications. However, the high attenuation results in very short frequency-reuse distances making these systems extremely well suited for high link-density deployments. However when rain falls on a link it may act as a coupling mechanism causing interference on adjacent line-of-sight links. In this paper we study the effects of rain-induced bistatic scattering on 60 GHz links and its potential impact on link planning and assignment.

A Near-Optimal Optimization Algorithm for Link Assignment in Wireless Ad-Hoc Networks

Over the past few years, wireless networking technologies have made vast forays in our daily lives. In wireless ad-hoc networks, links are set up by a number of units without any permanent infrastructures. In this paper, the resource optimization is considered to maximize the network throughput by efficiently using the network capacity, where multi-hop functionality and spatial TDMA (STDMA) access scheme are used. The objective is to find the minimum frame length with given traffic distributions and corresponding routing information. Because of the complex structure of the underlying mathematical problem, previous work and analysis become intractable for networks of realistic sizes. The problem is addressed through mathematical programming approach, the linear integer formulation is developed for optimizing the network throughput, and then the similarity between the original problem and the graph edge coloring problem is shown through the conflict graph concept. A column generation solution is proposed and several enhancements are made in order to fasten its convergence. Numerical results demonstrate that the theoretical limit of the throughput can be efficiently computed for networks of realistic sizes.

Novel Assignment Strategies for Spatial Reuse TDMA in Wireless Ad hoc Networks

Spatial reuse TDMA has been proposed as an access scheme for multi-hop radio networks where real-time service guarantees are important. The idea is to increase capacity by letting several radio terminals use the same time slot when possible. A time slot can be shared when the radio units are geographically separated such that small interference is obtained. In reuse scheduling, there are several alternative assignment methods. Traditionally, transmission rights are given to nodes or to links, i.e., transmitter/receiver pairs. We present a comparison of these two approaches and show that both have undesirable properties in certain cases, e.g. link assignment gives a higher delay for low traffic loads but can achieve much higher throughput than node assignment. Furthermore, we propose a novel assignment strategy, achieving the advantages of both methods. Simulation results show that the proposed method can achieve the throughput of link assignment for high traffic loads as well as the lower delay characteristics of node assignment for low traffic loads.

Environmentally conscious long-range planning and design of supply chain networks

In this paper, a mathematical programming-based methodology is presented for the explicit inclusion of life cycle assessment (LCA) criteria as part of the strategic investment decisions related to the design and planning of supply chain networks. By considering the multiple environmental concerns together with the traditional economic criteria, the planning task is formulated as a multi-objective optimization problem. Over a long-range planning horizon, the methodology utilizes mixed integer modelling techniques to address strategic decisions involving the selection, allocation and capacity expansion of processing technologies and assignment of transportation links required to satisfy the demands at the markets. At the operational level, optimal production profiles and flows of material between various components within the supply chain are determined. As such, the formulation presented here combines the elements of the classical plant location and capacity expansion problems with the principles of LCA to develop a quantitative decision-support tool for environmentally conscious strategic investment planning.

LEO satellite communication networks—a routing approach

AbstractIn the modern world of telecommunications, the concept of wireless global coverage is of the utmost importance. However, real global coverage can only be achieved by satellite systems. Until recently, the satellites were in geostationary orbit and their high altitude could not allow real‐time communication such as cellular networks. The development of LEO satellite networks seems to overcome this limit. However, LEO satellite systems have specific characteristics that need to be taken into account. In the same manner, the TCP/IP standard was developed for terrestrial network. The need is then to come up with a solution that would permit the use of TCP/IP on LEO satellite networks without losing too many packets.The idea is to develop a routing algorithm that maximizes the RTT delays compared to the TCP timer granularity. For that matter, we use an FSA‐based link assignment that simulates the satellite constellation as a fixed network for a predetermined time interval. In this configuration, the problem becomes a static routing problem where an algorithm can find the best solution. Copyright © 2003 John Wiley & Sons, Ltd.

Construction of a Chinese–English Verb Lexicon for Machine Translation and Embedded Multilingual Applications

This paper addresses the problem of automatic acquisition of lexical knowledge for rapid construction of engines for machine translation and embedded multilingual applications. We describe new techniques for large-scale construction of a Chinese–English verb lexicon and we evaluate the coverage and effectiveness of the resulting lexicon. Leveraging off an existing Chinese conceptual database called HowNet and a large, semantically rich English verb database, we use thematic-role information to create links between Chinese concepts and English classes. We apply the metrics of recall and precision to evaluate the coverage and effectiveness of the linguistic resources. The results of this work indicate that: (a) we are able to obtain reliable Chinese–English entries both with and without pre-existing semantic links between the two languages; (b) if we have pre-existing semantic links, we are able to produce a more robust lexical resource by merging these with our semantically rich English database; (c) in our comparisons with manual lexicon creation, our automatic techniques were shown to achieve 62% precision, compared to a much lower precision of 10% for arbitrary assignment of semantic links.

Design and Configuration of Reconfigurable ATM Networks with Unreliable Links

This paper considers a problem of configuring both physical backbone and logical virtual path (VP) networks in a reconfigurable asynchronous transfer mode (ATM) network where links are subject to failures. The objective is to determine jointly the VP assignment, the capacity assignment of physical links and the bandwidth allocation of VPs, and the routing assignment of traffic demand at least cost. The network cost includes backbone link capacity expansion cost and penalty cost for not satisfying the maximum throughput of the traffic due to link failures or insufficient link capacities. The problem is formulated as a zero-one non-linear mixed integer programming problem, for which an effective solution procedure is developed by using a Lagrangean relaxation technique for finding a lower bound and a heuristic method exploited for improving the upper bound of any intermediate solution. The solution procedure is tested for its effectiveness with various numerical examples.

Performance analysis of mean internodal distance and network connectivity for multihop network combined with unidirected ring networks

In this paper, we propose a multihop network combined with unidirected ring networks. Our proposed network has large connectivity, small internodal distance, and high efficiency of link assignment. We theoretically analyze the mean internodal distance and the network connectivity of the proposed network. It is shown by numerical calculation and computer simulation that the proposed network achieves smaller mean internodal distance than the conventional connective semirandom network and the same network connective probability as the regular networks. © 1998 Scripta Technica, Electron Comm Jpn Pt 1, 82(4): 14–22, 1999

A unified framework and algorithm for channel assignment in wireless networks

Channel assignment problems in the time, frequency and code domains have thus far been studied separately. Exploiting the similarity of constraints that characterize assignments within and across these domains, we introduce the first unified framework for the study of assignment problems. Our framework identifies eleven atomic constraints underlying most current and potential assignment problems, and characterizes a problem as a combination of these constraints. Based on this framework, we present a unified algorithm for efficient (T/F/C)DMA channel assignments to network nodes or to inter-nodal links in a (multihop) wireless network. The algorithm is parametrized to allow for tradeoff-selectable use as three different variants called RAND, MNF, and PMNF. We provide comprehensive theoretical analysis characterizing the worst-case performance of our algorithm for several classes of problems. In particular, we show that the assignments produced by the PMNF variant are proportional to the thickness of the network. For most typical multihop networks, the thickness can be bounded by a small constant, and hence this represents a significant theoretical result. We also experimentally study the relative performance of the variants for one node and one link assignment problem. We observe that the PMNF variant performs the best, and that a large percentage of unidirectional links is detrimental to the performance in general.

FSA-based link assignment and routing in low-earth orbit satellite networks

We propose a new framework for the link assignment (i.e., topological design) problem that arises from the use of intersatellite links (ISL's) in low-earth orbit (LEO) satellite networks. In the proposed framework, we model an LEO satellite network as a finite state automaton (FSA), where each state corresponds to an equal-length interval in the system period of the LEO satellite network. This FSA-based framework allows the link assignment problem in LEO satellite networks to be treated as a set of link assignment problems in fixed topology networks. Within this framework, we study various link assignment and routing schemes. In particular, both regular link assignment and link assignment optimized by simulated annealing are considered. For each link assignment, both static and dynamic routing schemes are considered. Our simulation results show that the optimized link assignment combined with static routing achieves the best performance in terms of both newly initiated call blocking probability and ongoing call blocking probability. The results also show that when the link assignment is the same, static routing gives better performance than dynamic routing since the latter requires a substantial amount of time to stabilize its routing table after a state transition.

Minimum Assignment of Test Links for Hypercubes with Lower Fault Bounds

In ann-dimensional hypercube multiprocessor system, to correctly diagnose faulty processors among themselves, the maximum allowed number of faulty processors isnunder the well-known PMC diagnostic model. When thenfault bound is adopted, all links between processors will be used in the diagnosis. However, if the fault bound is lower thann, many links can be freed from the task of performing diagnosis. In this paper, we show that each drop of the fault bound by 1 will free 2n-1links from diagnosis. We will present an algorithm that selects, in a symmetric manner, the to-be-freed links, so that only a minimum number of links will be used to perform diagnosis. A rigorous proof for the algorithm's correctness is given. The freed links will never be used for the purpose of diagnosis, so that the diagnosis and some conventional computations may be carried out simultaneously, improving the performance of the system as a whole.

ON THE CREATION OF HYPERTEXT LINKS IN FULL‐TEXT DOCUMENTS: MEASUREMENT OF INTER‐LINKER CONSISTENCY

An important stage in the process of retrieval of objects from a hypertext database is the creation of a set of inter‐nodal links that are intended to represent the relationships existing between objects; this operation is often undertaken manually, just as index terms are often manually assigned to documents in a conventional retrieval system. Studies of conventional systems have suggested that a degree of consistency in the terms assigned to documents by indexers is positively associated with retrieval effectiveness. It is thus of interest to investigate the consistency of assignment of links in separate hypertext versions of the same full‐text document, since a measure of agreement may be related to the subsequent utility of the resulting hypertext databases. The calculation of values indicating the degree of similarity between objects is a technique that has been widely used in the fields of textual and chemical information retrieval; in this paper, we describe the application of arithmetic coefficients and topological indices to the measurement of the degree of similarity between the sets of inter‐nodal links in hypertext databases. We publish the results of a study in which several different sets of links are inserted, by different people, between the paragraphs of each of a number of full‐text documents. Our results show little similarity between the sets of links identified by different people; this finding is comparable with those of studies of inter‐indexer consistency, where it has been found that there is generally only a low level of agreement between the sets of index terms assigned to a document by different indexers.

An adaptive link assignment algorithm for dynamically changing topologies

An adaptive link assignment algorithm for the distributed optimization of dynamically changing network topologies is presented. The algorithm is responsible for determining the network connectivity by controlling the selection of links to be established and disconnected. This algorithm is designed to recover from predictable link outages as well as massive unpredictable failures. To minimize computational time complexity as well as to improve transient response. Some known graph-theoretic algorithms are utilized.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Heuristic technique for processor and link assignment in multicomputers

A graph-based solution to the mapping problem using the simulated annealing optimization heuristic is developed. An automated two-phase mapping strategy is formulated: process annealing assigns parallel processes to processing nodes, and connection annealing schedules traffic connections on network data links so that interprocess communication conflicts are minimized. To evaluate the quality of generated mappings. cost functions suitable for simulated annealing that accurately quantify communications overhead are derived. Communication efficiency is formulated to measure the quality of assignments when the optimal mapping is unknown. The mapping scheme is implemented using the hypercube as a host architecture, and results for several image graphs are presented. >

Topological analysis of satellite-based distributed sensor networks

A method for evaluating the topological quality of networks for distributed sensor applications is presented. The criteria for evaluation are network survivability and delay. Nodal connectivity is used to characterize survivability, and mean path length is used to characterize delay. To calculate these two quantities, an algorithm is developed to find k shortest node-disjoint paths between a pair of nodes when each link has unit distance. The effects of nodal losses in a multiple-node satellite network consisting of a Walker low-orbit sphere and a geosynchronous constellation are examined. The example demonstrates how topological analysis on the basis of connectivity and mean path length may be used to detect, and subsequently to address, potential flaws in a network design. The results show that the geosynchronous/low-orbit link assignment protocol should be a primary concern in the design of this network. They also show that the nodal degree of a failed node, and the distribution of links between the Walker sphere and the geosynchronous constellation, are the fundamental determinants of mean path length. >

Solving Equations of Motion on a Virtual Tree Machine

The dynamic equations of motion for rigid links connected at hinges to form a tree are amenable to a parallel solution. Such a solution can potentially provide a real-time simulation of the dynamic behavior of a broad class of objects used in animation and robotics even when the number of links is large. However, the design of a parallel algorithm poses problems not encountered in the sequential, one-processor case, such as assignment of links to processes, allocation of processes to physical processors, synchronization of processes, and the reduction of communication losses. The computation time using a parallel algorithm and an unlimited number of processors is shown to grow with the height of the tree rather than with its number of links. Increased communication costs degrade performance by a factor at most equal to the fanout. The facility used to investigate these problems is a Virtual Tree Machine (VTM) multi-computer implemented on a network of autonomous VAX-11/780 computers and SUN-2 workstations...