Elsevier

Ad Hoc Networks

Volume 8, Issue 6, August 2010, Pages 614-625
Ad Hoc Networks

Topology optimization for hybrid optical/wireless access networks

https://doi.org/10.1016/j.adhoc.2009.12.001Get rights and content

Abstract

Hybrid Wireless–Optical Broadband Access Networks (WOBANs) are gauging momentum as flexible, bandwidth-effective, and cost-effective solutions for providing connectivity to residential users in metropolitan areas. In this work, we address the issue of designing the topology of deployed WOBANs. Namely, we consider the case where the coverage of a Ethernet-based Passive Optical Network (EPON) is extended by an additional wireless segment which features multi-hop wireless links operated either according to the IEEE 802.11 standard, or to the IEEE 802.16 one. We propose a mathematical programming model which optimizes the overall WOBAN topology in terms of deployment cost, while accounting for the specific traffic requirements of the residential users, and the specific features of the technological components. The potentials of the proposed model are showcased by deriving and commenting numerical results obtained when planning realistic WOBAN scenarios.

Introduction

The issue of providing effective access solutions to residential users is attracting increasing attention from different actors like service providers, commonalities, and academia. Indeed, in the last ten years, the quality of experience requested by residential users has incredibly increased (think of the quadruple play services), thus challenging the architectures of the deployed metropolitan access networks. To this extent, even if most of current access networks are mainly based on copper, optical technology is gauging momentum as an effective way to bring bandwidth to the final users. Among optical network architectures, Passive Optical Networks (PONs) are currently being deployed in many metropolitan environment, due to their favorable features in terms of offered bandwidth, robustness and maintainability.

On the other side, in many cases it is not possible or cost effective for the operator to reach every single residential user with the fiber, and consequently some type of connectivity extension must be provided through other communication technologies. In this scenario, the recent progresses in the field of wireless technologies have boosted the adoption of wireless access networks to reach the final residential users with cost effective, flexible and ubiquitous network deployments. As a consequence, it is straightforward to envision the use of Hybrid Wireless–Optical Broadband Access Networks (WOBANs) for “covering” metropolitan-scale areas, having desirable features in terms of provided bandwidth, deployment and maintenance costs.

To fully unleash the potentials of WOBAN architectures, several technical challenges have to be addressed and resolved, including the QoS management across the wireless/optical boundary [1], [2], the routing in the hybrid architecture [3] and the overall network management. Several testbeds have been recently developed to evaluate proposed algorithms and protocols [4], [5], [6]. Moreover, effective methods are needed to plan and optimize the WOBAN topology for two main reasons: first, the topology itself may have a huge impact on the overall “quality” of the network (both on the end user’s side, quality of service, and on the operator’s side, deployment cost); second, network deployments can involve hundreds of devices (optical and wireless), thus manual tuning is very unpractical and automatic topology planning and optimization tools are required.

In this work, we address the issue of designing the topology of a WOBAN composed by a Ethernet-based Passive Optical Networks (EPONs), which can be extended through a Wireless Mesh Network (WMN) operated by IEEE 802.11 and/or IEEE 802.16 standards. In details, we develop a complete mathematical programming model for the automatic planning of the entire WOBAN topology with the objective of minimizing the overall deployment costs, while accounting for the specific traffic requirements of the residential users, and the specific features of the technological components.

The main contributions of this work are:

  • A complete optimization framework for planning and dimensioning WOBANs. Solved to the optimality, it selects the best network devices to be installed, their positions and the configuration of the entire network.

  • The inclusion of a multi-hop network paradigm in the wireless domain.

  • The possibility of selecting between IEEE 802.11 and IEEE 802.16 devices for the wireless domain. The outcome shows which is the best technology to deploy in each part of the network according to technical characteristics, traffic distribution and device costs.

To the best of our knowledge, this is the first work on WOBAN planning accounting for multi-hop wireless extensions to the optical segment, further considering the choice between different wireless technologies with different features and constraints (IEEE 802.11 vs. IEEE 802.16).

The remainder of the paper is structured as follows: Section 2 overviews the related work in the field, Section 3 overviews the main building blocks of the reference WOBAN architecture, and provides the problem statement. In Section 4, we introduce the optimization model for WOBAN planning and comment on the corresponding formulation. Section 5 reports on the performance evaluation carried out to assess the quality and the utility of the proposed optimization model. Finally, concluding remarks are given in Section 6.

Section snippets

Related works

Previous work on Hybrid Optical/Wireless Access Networks can be categorized into three main areas: contributions on the general architecture of hybrid optical/wireless networks, contributions on protocol-oriented aspects of routing and channel assignment, and contributions on hybrid network planning and optimization.

Referring to the first class, architecture papers aims at analyzing the challenges to be faced when deploying such hybrid networks, deriving general guidelines on the best type of

Background and problem statement

The problem addressed in this paper is the planning of a WOBAN considering both optical and wireless realms, where the former consists of a EPON and the latter can be managed via IEEE 802.11 or IEEE 802.16 devices. Given a traffic demand distributed over a deployment area, we want to design the whole backbone infrastructure delegated to collect traffic. The backbone consists of a metropolitan Central Office (CO) from where optical fibers depart in order to feed wireless access points, both IEEE

Problem formulation

We consider a deployment area where traffic source points, named test points, are placed. Each test point can represent a single residential user or a centroid of a discrete/continuous traffic distribution according to the desired planning scenario. The set of test points is denoted by P. Similarly, IEEE 802.11 devices (MRs) and IEEE 802.16 devices (RSs) can be installed in discrete sets of candidate sites S11 and S16, respectively. Due to wiring issues, ONUs can be placed only in a limited

Numerical results

We analyzed solutions obtained by solving to optimality the proposed formulations. This allows us to highlight the effects on the solutions when some important design parameters change, as we show in Section 5.1, or when more OLT site locations are available, as reported in Section 5.2. Then, we give some commented snapshots of planned networks for a couple of interesting scenarios under different traffic conditions in Section 5.3.

Instances are solved running the state-of-the-art solver CPLEX

Conclusion and future work

In this work, we have addressed the issue of designing the topology of hybrid optical/wireless access networks, which are increasingly deployed to provide residential coverage to metropolitan areas. Mathematical programming formulations have been proposed to automatically plan the topology of hybrid network architectures based on Ethernet-Passive Optical Networks (EPONs) and Wireless Mesh Networks (WMNs) operated according to the IEEE 802.11 and IEEE 802.16 standards. The proposed formulation

Acknowledgments

This work has been partially supported by the European Network of Excellence EuroNF, in the framework of the specific joint research project FI-WI – Future Integrated Access Architecture Based on Optical and Broadband Wireless Technologies.

Ilario Filippini received the B.S. and M.S. degrees in Telecommunication Engineering from the Politecnico di Milano, Italy, in 2003 and 2005, and a Ph.D in Information Engineering in April 2009 from the Politecnico di Milano. From February 2008 to August 2008 he has been working as a visiting researcher at the Department of Electrical and Computer Engineering of The Ohio State University in Columbus (OH). He is currently a PostDoc researcher of the Electronics and Information Department of the

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    Ilario Filippini received the B.S. and M.S. degrees in Telecommunication Engineering from the Politecnico di Milano, Italy, in 2003 and 2005, and a Ph.D in Information Engineering in April 2009 from the Politecnico di Milano. From February 2008 to August 2008 he has been working as a visiting researcher at the Department of Electrical and Computer Engineering of The Ohio State University in Columbus (OH). He is currently a PostDoc researcher of the Electronics and Information Department of the Politecnico di Milano. His research activities include networking and optimization issues, in particular wireless multi-hop network planning, optimization and protocol design. He is a regular reviewer of the main journals in the networking area. He is a member of the IEEE Communication and Computer Societies.

    Matteo Cesana received his MS degree in Telecommunications Engineering and his Ph.D. degree in Information Engineering from the Politecnico di Milano in July 2000 and in September 2004, respectively. From September 2002 to March 2003 he has been working as a visiting researcher at the Computer Science Department of the University of California in Los Angeles (UCLA). He is now an Assistant Professor of the Electronics and Information Department of the Politecnico di Milano. His research activities are in the field of performance evaluation of cellular systems, ad hoc networks protocol design and evaluation and wireless networks optimization. He is an editor of Ad Hoc Networks Journal (Elsevier), and he has served in the technical program committee of several international conferences. He is a regular reviewer of the main journals in the networking area. He is a member of IEEE Communication and Computer societies.

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