Techniques are described for efficiently estimating and compensating for the effects of a communication channel in a multi-carrier wireless communication system. The techniques exploit the fact that the transmitted symbols are drawn from a finite-alphabet to efficiently estimate the propagation channel for multi-carrier communication systems, such systems using OFDM modulation. A transmitter transmits data through a communication channel according to the modulation format. A receiver includes a demodulator to demodulate the data and an estimator to estimate the channel based on the demodulated data. The channel estimator applies a power-law operation to the demodulated data to identify the channel. The techniques can be used in both blind and semi-blind modes of channel estimation.

Channel estimation for wireless ofdm systems

Computer Controlled Systems: Theory and Design

New architectural and design approaches for radio access networks have appeared with the introduction of network virtualization in the wireless domain. One of these approaches splits the wireless network infrastructure into isolated virtual slices under their own management, requirements, and characteristics. Despite the advances in wireless virtualization, there are still many open issues regarding the resource allocation and isolation of wireless slices. Because of the dynamics and shared nature of the wireless medium, guaranteeing that the traffic on one slice will not affect the traffic on the others has proven to be difficult. In this paper, we focus on the detailed definition of the problem, discussing its challenges. We also provide a review of existing works that deal with the problem, analyzing how new trends such as software defined networking and network function virtualization can assist in the slicing. We will finally describe some research challenges on this topic.

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Resource Slicing in Virtual Wireless Networks: A Survey

The contribution of this paper is on the study of packet delays for the IEEE 802.11 wireless local area network DCF MAC protocol. A method is presented capable of taking into account retransmission delays with or without retry limits. We present an analytical model based on a Markov chain which allows us to derive closed form expressions for the packet delays, the probability of a packet being discarded when it reaches the maximum retransmission limit and the average time to drop such a packet for the basic and RTS/CTS access mechanisms. The results presented are for standard protocol parameters versus the number of contention stations. Finally, the accuracy of the analytical model is verified by simulations.

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IEEE 802.11 packet delay-a finite retry limit analysis

everal protocols for routing and forwarding in Wireless Mesh Networks (WMN) have been proposed, such as AODV, OLSR or B.A.T.M.A.N. However, providing support for e.g. flow-based routing where flows of one source take different paths through the network is hard to implement in a unified way using traditional routing protocols. OpenFlow is an emerging technology which makes network elements such as routers or switches programmable via a standardized interface. By using virtualization and flow-based routing, OpenFlow enables a rapid deployment of novel packet forwarding and routing algorithms, focusing on fixed networks. We propose an architecture that integrates OpenFlow with WMNs and provides such flow-based routing and forwarding capabilities. To demonstrate the feasibility of our OpenFlow based approach, we have implemented a simple solution to solve the problem of client mobility in a WMN which handles the fast migration of client addresses (e.g. IP addresses) between Mesh Access Points and the interaction with re-routing without the need for tunneling. Measurements from a real mesh testbed (KAUMesh) demonstrate the feasibility of our approach based on the evaluation of forwarding performance, control traffic and rule activation time.

OpenFlow for Wireless Mesh Networks

This paper presents a simulation analysis of the backoff mechanism presented in the IEEE 802.11 standard. The obtained simulations allow us to determine the effective throughput and the mean packet delay versus offered load for different values of the contention window parameter and the number of contending stations. The choice of the CWmin and CWmax parameters was analyzed. In particular, the choice of CWmin value in dependence of the number of transmitting stations was presented. The simulation results show that the proper choice of the CW parameters has a substantial influence on the network performance.

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An analysis of the backoff mechanism used in IEEE 802.11 networks

In this survey we attempt to describe the Quality of Service (QoS) mechanisms employed by Medium Access Control (MAC) protocols designed for ad-hoc networks. We begin with background information: an overview of the related work, the definition of QoS and QoS-related metrics, a general description of contention-free and contention-based protocols for wireless networks, a discussion of issues affecting QoS provisioning in ad-hoc networks, as well as a novel classification of the QoS mechanisms. Then, each mechanism is briefly explained and implementation examples from different protocols are provided. Furthermore, a separate section is devoted to the completed and ongoing standardization work in the field. Afterwards, an extensive comparison of salient features, advantages and disadvantages of all described MAC mechanisms is given in order to guide future protocol designers. Finally, we comment on the most probable future research directions. Based on the presented survey, we observe that QoS provisioning is not only challenging but also a significant contemporary research problem. The protocol designs presented in the literature usually involve trade-offs between certain metrics, and currently there is no ideal solution which deals with all the issues affecting ad-hoc networks. Therefore, we trust that this survey will be of great help to designers of future QoS-aware protocols.

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A Survey of Medium Access Mechanisms for Providing QoS in Ad-Hoc Networks

A simple but accurate throughput model for IEEE 802.11 EDCA in saturation and non-saturation conditions

IP is the protocol of choice in most corporate networks today. As those networks grow larger and their operation becomes vital for the enterprise, there is a strong need to design.or redesign them in a manner that will allow for their expansion while simultaneously maintaining smooth and stable operation. CCIE Professional Development: Advanced.IP Network Design presents the principles of good IP network design and is focused on planning corporate networks from the routing point of view. Choice of transport technologies, dimensioning of the network links, choice of routers, and routing problems specific to carrier networks are outside the scope of this book, The hook is targeted at network enpineers seeking solutions to grow and stabilize their networks. A general knowledge of IP networking and routing is required for understanding the presented material. It is, however, possible to gain basic understanding of routing protocols operation from the appendices. The book consists of four parts. Part One (Chapters 1 4 ) deals with network design principles, Part Two (Chapters 5-7) deals with interior routing, and Part Three (Chapters 8 and 9) deals with exterior routing. Part Four contains appendices. A consistent example network is used throughout this book to illustrate different design choices. Also, each chapter contains case studies, which either serve as a design example or present problems that may arise in particular circumstances. Each chapter ends with a summary and review questions. Chapter 1 introduces the main network design goal, which is stability, and discusses fadtbrs that affect stability in real networks. The authors suggest a threelayer network topology, consisting of core, distribution, and access layers, and present the design goals for each layer. Chapter 2 begins with general information necessary for understanding the IP address summarization followed by a discussion of the effect of summarizing at different places in the network. The remaining part of Chapter 2 deals with addressing. Four different address allocation strategies are discussed, allowing the reader to choose the most appropri.ate strategy depending on needs. Two case studies end Chapter 2. The first one deals with the problems that arise when a default route is set to an interBOOK REVIEWS/EDITED BY ANDRZEJ JAISZCZYK U I

Wireless OFDM Systems: How to Make Them Work?

Current Internet use is evolving, users are becoming mobile and are expecting data services on the go. This fact presents big challenges and opportunities to operators, which see the increase in data services as a big market still to be exploited. However, current cellular technologies cannot accommodate the demand that will arise when the true mobile Internet evolves. Addressing these challenges, we present the CARMEN project, the vision of which is to extend operatorspsila infrastructure by providing carrier grade services through a heterogeneous wireless mesh. The CARMEN architecture will provide enough bandwidth to cope with userspsila expectations at a reduced cost, thereby generating major benefits to operators and users.

/pdf/carmen-delivering-carrier-grade-services-over-wireless-mesh-2us3muxlfd.pdf

Marek Natkaniec

Papers

An analysis of the backoff mechanism used in IEEE 802.11 networks

A Survey of Medium Access Mechanisms for Providing QoS in Ad-Hoc Networks

A simple but accurate throughput model for IEEE 802.11 EDCA in saturation and non-saturation conditions

Wireless OFDM Systems: How to Make Them Work?

CARMEN: Delivering carrier grade services over wireless mesh networks