Wail Mardini

Modified WRR Scheduling Algorithm for WiMAX Networks

Worldwide Interoperability for Microwave Access (WiMAX), which is also known as 802.16 standard, supports last-mile broadband access wireless networks. WiMAX has many advantages including wide coverage area and high bandwidth. These advantages enable WiMAX to support long transmission range and high data rate compared to cellular and WiFi network. WiMAX technology uses a number of scheduling techniques in the Medium Access Control (MAC) layer, which is responsible for the utilization of available resources in the networks and distribute them among users in order to ensure the desired quality of service. In this study, we propose a Modified Weighted Round Robin (MWRR) scheduler in order to decrease the average end-to-end delay and improve the average throughput. The proposed scheduling technique has been designed and simulated using the QualNet 5.0.2 network simulator. In order to evaluate the performance of our proposed approach, we compared our results to the results of well-known scheduling techniques (weighted Round Robin (WRR), Strict Priority (SP), and Weighted Fair Queuing (WFQ)). The average percentage of improvement was around 4%.

Enhanced Fibonacci Backoff Algorithm for Mobile Ad-Hoc Network

The most known drawback of IEEE 802.11 MAC is the low performance in terms of throughput in case of congested networks. Backoff time is one of the most important factors that govern the collision probability in Ad-Hoc network. Using backoff algorithm could push the performance up and decrease collision rate. This study presents an enhanced fibonacci backoff Algorithm (EFB) for Ad-Hoc Network in which contention window size is selected from two choices: linear and Fibonacci. Simulation results show high performance and less average of end to end delay especially at high number of nodes compared to Binary Exponential Backoff algorithm (BEB).

Fibonacci Backoff Algorithm for IEEE 802.15.4/ZigBee

The IEEE 802.15.4 is a standard proposed for Wireless Personal Area Network (PAN) and supports low data rate, low cost, low complexity and low power consumption applications. In IEEE 802.15.4 MAC layer, the CSMA/CA algorithm follows the Binary Exponential Backoff (BEB) scheme in order to determine the backoff delay each node shall wait as they need to access the channel. This paper investigate a weakness concerning BEB scheme, that is, the possibility of more than two nodes choose the same backoff exponent value and consequently increasing collision and network contention level which will degrade the overall network performance. To overcome this problem, a new Fibonacci Backoff (FIB) scheme is proposed through which nodes shall wait for an incremental backoff periods as they need to access the channel. Performance of FIB algorithm will be compared to that of BEB after simulating both on two scenarios of a star topology.

Smart homes automation using Z-wave protocol

The rapid development of information technology and computer networks make them part of almost everything in our daily life and it became impossible to abandon their use. One of the main and important applications of technology in homes is home automation including controlling and automation of electronic and electrical machines remotely. Wireless Home Automation Networks (WHANs) are used in homes to connect the different devices together and to the Internet. In order to control home devices remotely, there are many popular protocols such as INSTEON, ZigBee, and Home Plug. In this paper, we focus on the relatively new protocol called Z-Wave protocol and we discuss it development and applications in smart homes. This wireless protocol has many advantages over the popular and widely used ZigBee protocol as it provides better reliability, low radio rebirth, easy usage, and easy Interoperability.

Improving Vertical Handoffs Using Mobility Prediction

The recent advances in wireless communications require integration of multiple network technologies in order to satisfy the increasing demand of mobile users. Mobility in such a heterogeneous environment entails that users keep moving between the coverage regions of different networks, which means that a non-trivial vertical handoff scheme is required in order to maintain a seamless transition from one network technology to another. A good vertical handoff scheme must provide the users with the best possible connection while keeping connection dropping probability to the minimum. In this paper, we propose a handoff scheme which employs the Markov model to predict the users’ future locations in order to make better handoff decisions with reduced connection dropping probability and number of unnecessary handoffs. Through simulation, the proposed scheme is compared with the SINR-based scheme, which was shown to outperform other vertical handoff schemes. The experiments show that the proposed scheme achieves significant improvements over the SINR-based scheme that can reach 51% in terms of the number of failed handoffs and 44% in terms of the number of handoffs.

Improved Appliance Coordination Scheme with Waiting Time in Smart Grids

Smart grids aim to merge the advances in communications and information technologies with traditional power grids. In smart grids, users can generate energy and sell it to the local utility supplier. The users can reduce energy consumption by shifting appliances’ start time to off-peak hours. Many researchers have proposed techniques to reduce the previous issue for home appliances, such as the Appliances Coordination (ACORD) scheme and Appliances Coordination with Feed In (ACORD-FI) scheme. The goal of this work is to introduce an efficient scheme to reduce the total cost of energy bills by utilizing the ACORD-FI scheme to obtain an effective solution. In this work three scheduling schemes are proposed: the Appliances Coordination by Giving Waiting Time (ACORD-WT), the Appliances Coordination by Giving Priority (ACORD-P), and using photovoltaic (PV) with priority and waiting time scheduling algorithms. A simulator written in C++ is used to test the performance of the proposed schemes using. The performance metric used is the total savings in the cost of the energy bill in dollars. The first comparison for the proposed schemes with the ACORD-FI, and the results show that the efficiency of the proposed ACORD-WT is better than the ACORD-FI, regardless of the number of appliances. Moreover, the proposed ACORD-P, is also better than the standard ACORD-FI.

Intelligent Paging Backoff Algorithm for IEEE 802.11 MAC Protocol

Backoff algorithms have been introduced to improve network performance by reducing collisions over networks, especially in large ones. The Binary Exponential Backoff used in the standard IEEE 802.11 Medium Access Control makes exponential increments to contention window sizes. The large contention window gaps produced can significantly reduce the network performance. Therefore, a new increment behavior is introduced in this paper in order to avoid failure transmissions. The Results show that shifting the contention window to the right place based on previous transmissions outperforms each of the Binary Exponential Backoff Algorithm, the Smart Adaptive Backoff Algorithm and Pessimistic Linear Exponential Backoff Algorithm, up to 7.1%, 16.5% and 19% respectively in term of data delivery ratio.

Effects of Allocation Request Shape Changes on Performance in 2D Mesh-Connected Multicomputers

Contiguous allocation in multicomputers is useful for security and accounting reasons. In mesh-connected systems, it allocates each job an exclusive submesh of processors, and the allocated submesh has the same shape and size as that requested by the job. Because of this size and shape constraint, contiguous allocation typically suffers from high processor fragmentation. Processor fragmentation can be reduced by considering contiguous allocation to all possible request shapes, while maintaining contiguity. However, request shape modification can influence communication overhead. In this paper, we study the effect of request shape modification on communication overhead and performance in two-dimensional mesh-connected multicomputers, where several common communication patterns are simulated in detail. The simulation results show that permitting all request shape changes can improve system performance substantially. For example, it improves the performance of first-fit allocation by up to 46% in terms of average job turnaround time.

Modelling with queues: an empirical study

We review the principles of computer performance modelling with queues, and validate the models using the empirical data. We focus on modelling a special configuration of two computers working in tandem: a mirroring system. Distributed system under investigation has implemented as a series of Java applets communicating using the functions of java net.* package. The mirroring aspect of the system is modelled analytically with a difference queue. The difference queue is defined for a network of two queues in parallel, as the queue consisting of elements present in one queue and absent from the other queue. The queueing models under investigation are M/M/1, and M/D/1 queues. In our study we have observed that the service times were not completely random on a typical server and could not be approximated well by exponential distribution. Our results have shown that the service was almost (i.e. with a very small variance) deterministic. We have also found that the d-queue model approximates well the behaviour of the mirroring system under low load conditions, and also provides an upper bound on the delays under high load conditions.

Mining Internet of Things for intelligent objects using genetic algorithm

Abstract The Internet of Things (IoT) is overpopulated by a large number of objects and millions of services and interactions. Therefore, the ability to search for the right object to provide a specific service is important. The merger of the IoT and social networking, the Social Internet of Things (SIoT), has made this possible. The main idea in the SIoT is that every object in the IoT can use its friends’ or friends-of-friends’ relationships to search for a specific service. However, this is usually a slow process because each node (object) is required to manage a large number of friends. This paper addresses the issue of link selection of friends and analyzes five strategies in the literature. Then it proposes a link selection strategy using the Genetic Algorithm (GA) to find the near optimal solution. The results show an improvement over the examined strategies in terms of several parameters.