Yuhang Yang

A hybrid load balancing strategy of sequential tasks for grid computing environments

Load balancing is of paramount importance in grid computing. Generally, load balancing can be categorised into two classes of activity based on the type of information on which the corresponding decisions are made, namely averages-based and instantaneous measures-based classes. Either class has certain flaws which confine themselves to limited performance improvement when being employed separately. It is therefore advantageous to combine both to form a hybrid one in order to make most of the strong points of each. In this paper, we address the load balancing problem by presenting a hybrid approach to the load balancing of sequential tasks under grid computing environments. Our main objective is to arrive at task assignments that could achieve minimum execution time, maximum node utilisation and a well-balanced load across all the nodes involved in a grid. A first-come-first-served and a carefully designed genetic algorithm are selected as representatives of both classes to work together to accomplish our goal. The simulation results show that our algorithm can achieve a better load balancing performance as compared to its pure counterparts.

Network lifetime maximization with cross-layer design in wireless sensor networks

This paper investigates a cross-layer design approach for minimizing energy consumption and maximizing network lifetime (NL) of a multiple-source and single-sink (MSSS) WSN with energy constraints. The optimization problem for MSSS WSN can be formulated as a mixed integer convex optimization problem with the adoption of time division multiple access (TDMA) in medium access control (MAC) layer, and it becomes a convex problem by relaxing the integer constraint on time slots. Impacts of data rate, link access and routing are jointly taken into account in the optimization problem formulation. Both linear and planar network topologies are considered for NL maximization (NLM). With linear MSSS and planar single-source and single-sink (SSSS) topologies, we successfully use Karush-Kuhn-Tucker (KKT) optimality conditions to derive analytical expressions of the optimal NL when all nodes are exhausted simultaneously. The problem for planar MSSS topology is more complicated, and a decomposition and combination (D&C) approach is proposed to compute suboptimal solutions. An analytical expression of the suboptimal NL is derived for a small scale planar network. To deal with larger scale planar network, an iterative algorithm is proposed for the D&C approach. Numerical results show that the upper-bounds of the network lifetime obtained by our proposed optimization models are tight. Important insights into the NL and benefits of cross-layer design for WSN NLM are obtained.

Narrowband Interference Mitigation in DS-UWB Systems

Interference suppression is important for ultra-wideband (UWB) systems to operate over spectrum occupied by pre-existing narrowband systems. In this letter, we first extend the code-aided interference suppression technique to a direct sequence (DS) UWB system which has been proposed for narrowband interference (NBI) suppression in direct sequence spread spectrum (DSSS) systems. Then, we introduce a new type of spreading sequence, which significantly improves the NBI suppression capability of the code-aided technique. We also discuss a preamble-aided synchronization scheme for utilizing the new type of spreading sequence.

A Hybrid Load Balancing Strategy of Sequential Tasks for Computational Grids

Load balancing is crucial to computational grids. Based on the typeof information on which corresponding decisions are made, loadbalancing approaches can be generally categorized into two classes:average-based and instantaneous approaches. Both these two classeshave merits and demerits. Its therefore advantageous to combineboth of them to work in tandem to form a hybrid approach that makesthe best of the strong points of each. In this paper, we present ahybrid load balancing strategy for sequential tasks in computationalgrids with the purpose to improve the performance by a joint effort.The simulation results show that our algorithm can achieve a betterload balancing performance than its counterparts provided insimulation.

Network Lifetime Optimization by Duality Approach for Single-Source and Single-Sink Topology in Wireless Sensor Networks

The single-source and single-sink (SSSS) topology, in wireless sensor networks, is defined as the network topology, where every node behaves as a relaying node except the single source and the single sink. We consider the problem of finding a joint optimal scheme with consideration of physical, medium access control (MAC), and network layers to maximize the network lifetime (NL) for the SSSS topology in energy-constrained wireless sensor networks (WSNs). The optimization problem, when the communication link are restricted to an interference-free time division multiple access (TDMA) scheme, can be formulated as a mixed integer-convex programming and relaxed to the convex programming. In particular, this paper focuses on utilizing the Karush-Kuhn-Tucker (KKT) optimization conditions to analytically solve this convex problem for the SSSS linear topology. An analytical expression of upper bound on NL for cross-layer optimization is derived as a function of the initial energy and quantities of data held by the sources, taking the influence of data rates, link access method and routing into account. The result agrees well with numerical result of optimization solver, and can be applied to algorithms in WSNs aiming at maximizing NL.

Network Lifetime Global Optimization by Duality Approach in Wireless Sensor Networks

The multi-source and single-sink (MSSS) topology of wireless sensor networks (WSNs) is defined as the network topology, where all of nodes can gather, receive and transmit data to the sink. We study the issue of finding the joint optimal scheme with consideration of physical, medium access control (MAC), and network layers to maximize the network lifetime (NL) for such topology in the energy-constrained WSNs. This paper presents a duality approach by utilizing the Karush-Kuhn- Tucker (KKT) optimality conditions to analytically provide a solution to this optimization problem. Analytical expression of the globally optimal NL is derived as a function of the amount of nodes, the initial energy and the data rate arrived at the nodes, taking the influence of data rates, link access and routing method into account. The analytical result agrees well with numerical result of the optimization solver and can be applied to algorithms in WSNs aiming at maximizing NL.

A Problem-Specific Genetic Algorithm for Multiprocessor Real-Time Task Scheduling

Real-time task scheduling for multiprocessor systems is generally a NP-complete problem and thus genetic algorithms (GAs) are extensively used. However, since GAs aim to be one kind of universal algorithm across a variety of problem types, they hardly use problem-specific search techniques which might help speed up the search process or lead to a better solution under certain scenarios. That partly prevents GAs from performing more effectively and efficiently. To overcome this, a problem-specific genetic algorithm is proposed to handle multiprocessor real-time task scheduling in this paper. The simulation results show that the performance of the GA are greatly improved with the assistance of certain problem-specific knowledge.

Network Lifetime Optimization by Duality Approach for Multi-Source and Single-Sink Topology in Wireless Sensor Networks

The multi-source and single-sink (MSSS) topology, in wireless sensor networks, is defined as the network topology, where all of nodes can gather, receive and transmit data to the sink. We consider the problem of finding the joint optimal scheme with consideration of physical, medium access control (MAC), and network layers to maximize the network lifetime (NL) for the MSSS topology in the energy-constrained wireless sensor networks (WSNs). The optimization problem, when the link access is an interference-free time division multiple access (TDMA) scheme, can be formulated as a mixed integer-convex programming and relaxed to the convex programming. According to the transcendental equations in programming model, we take two rather different approaches to maximize the NL in such network. First, based on the result of the SSSS network, we decompose the MSSS problem into the various SSSS issues. Another approach is to utilize the Karush-Kuhn-Tucker (KKT) optimization conditions to analytically solve this convex problem. Analytical expression of the optimal NL is a function of the initial energy and quantities of data held by the sources, taking the influence of data rates, link access and routing method into account. Although some dual gaps exist, the analytical result agrees well with numerical result of optimization solver, and can be applied to algorithms in WSNs aiming at maximizing NL.

QoS Issues in IEEE 802.16 Mesh Network

The IEEE 802.16 mesh network is a promising next generation wireless backbone network. One fundamental issue in IEEE 802.16 mesh networks is QoS provisioning. Although IEEE 802.16 standard has made certain efforts to address this issue, many technical problems still exist in this field. In this article, we present a detailed investigation of QoS issues in IEEE 802.16 mesh networks in order to provide a better understanding of the research challenges of QoS provisioning under Mesh mode. We also try to provide a rudimentary overview of several key proposals in the relevant literature.

A Novel Admission Control Algorithm for VOD Service in ADSL P2P Networks

Network video on demand is one kind of favorite VOD services nowadays. P2P technology is adopted to improve system capacity without increasing infrastructure cost. However, the limitation of upstream bandwidth in ADSL networks deteriorates P2P networks extensible capability. The traditional P2P admission control schemes become inapplicable for network VOD service in ADSL networks. The paper presents a novel admission control scheme for VOD service in ADSL P2P networks. In our scheme, a buffer will be reserved in every client. Our scheme indicates that media server can insure clients playing without interruption in case they are admitted initially. At the same time, the response latency is reduced and the efficiency of utilizing bandwidth is increased. Foremost, the buffer space in client improves P2P extensible capability for ADSL networks. System capacity is increased remarkably than without buffer and it will be infinite in theory if waiting coefficient beta is no less than 1. With waiting coefficient beta increases blocking probability decreases. The new scheme significantly improves the system performance in ADSL P2P networks. The detailed admission control policy is described in the paper