The increasing demand of mobile Internet and the Internet of Things poses challenging requirements for 5G wireless communications, such as high spectral efficiency and massive connectivity. In this article, a promising technology, non-orthogonal multiple access (NOMA), is discussed, which can address some of these challenges for 5G. Different from conventional orthogonal multiple access technologies, NOMA can accommodate much more users via nonorthogonal resource allocation. We divide existing dominant NOMA schemes into two categories: power-domain multiplexing and code-domain multiplexing, and the corresponding schemes include power-domain NOMA, multiple access with low-density spreading, sparse code multiple access, multi-user shared access, pattern division multiple access, and so on. We discuss their principles, key features, and pros/cons, and then provide a comprehensive comparison of these solutions from the perspective of spectral efficiency, system performance, receiver complexity, and so on. In addition, challenges, opportunities, and future research trends for NOMA design are highlighted to provide some insight on the potential future work for researchers in this field. Finally, to leverage different multiple access schemes including both conventional OMA and new NOMA, we propose the concept of software defined multiple access (SoDeMA), which enables adaptive configuration of available multiple access schemes to support diverse services and applications in future 5G networks.

Non-orthogonal multiple access for 5G: solutions, challenges, opportunities, and future research trends

This study focuses on the routing and WavelengthAssignment (RWA) problem in wavelength-routed optical WDM networks. Most of the attention is devoted to such networks operating under the wavelength-continuity constraint, in which lightpaths are set up for connection requests between node pairs, and a single lightpath must occupy the same wavelength on all of the links that it spans. In setting up a lightpath, a route must be selected and a wavelength must be assigned to the lightpath. If no wavelength is available for this lightpath on the selected route, then the connection request is blocked. We examine the RWA problem and review various routing approaches and wavelengthassignment approaches proposed in the literature. We also briefly consider the characteristics of wavelength-converted networks (which do not have the wavelength-continuity constraint), and we examine the associated research problems and challenges. Finally, we propose a new wavelengthassignment scheme, called Distributed Relative Capacity Loss (DRCL), which works well in distributed-controlled networks, and we demonstrate the performance of DRCL through simulation.

A Review of Routing and Wavelength Assignment Approaches for Wavelength- Routed Optical WDM Networks

Optical networks are undergoing significant changes, fueled by the exponential growth of traffic due to multimedia services and by the increased uncertainty in predicting the sources of this traffic due to the ever changing models of content providers over the Internet. The change has already begun: simple on-off modulation of signals, which was adequate for bit rates up to 10 Gb/s, has given way to much more sophisticated modulation schemes for 100 Gb/s and beyond. The next bottleneck is the 10-year-old division of the optical spectrum into a fixed "wavelength grid," which will no longer work for 400 Gb/s and above, heralding the need for a more flexible grid. Once both transceivers and switches become flexible, a whole new elastic optical networking paradigm is born. In this article we describe the drivers, building blocks, architecture, and enabling technologies for this new paradigm, as well as early standardization efforts.

Elastic optical networking: a new dawn for the optical layer?

In network design, the gap between theory and practice is woefully broad. This book narrows it, comprehensively and critically examining current network design models and methods. You will learn where mathematical modeling and algorithmic optimization have been under-utilized. At the opposite extreme, you will learn where they tend to fail to contribute to the twin goals of network efficiency and cost-savings. Most of all, you will learn precisely how to tailor theoretical models to make them as useful as possible in practice. Throughout, the authors focus on the traffic demands encountered in the real world of network design. Their generic approach, however, allows problem formulations and solutions to be applied across the board to virtually any type of backbone communication or computer network. For beginners, this book is an excellent introduction. For seasoned professionals, it provides immediate solutions and a strong foundation for further advances in the use of mathematical modeling for network design. (Less)

Routing, Flow, And Capacity Design In Communication And Computer Networks

The Wiener index W is the sum of distances between all pairs of vertices of a (connected) graph. The paper outlines the results known for W of trees: methods for computation of W and combinatorial expressions for W for various classes of trees, the isomorphism–discriminating power of W, connections between W and the center and centroid of a tree, as well as between W and the Laplacian eigenvalues, results on the Wiener indices of the line graphs of trees, on trees extremal w.r.t. W, and on integers which cannot be Wiener indices of trees. A few conjectures and open problems are mentioned, as well as the applications of W in chemistry, communication theory and elsewhere.

Wiener Index of Trees: Theory and Applications

We explain why distributed control lacks the ability to optimally control networks with multiple transport domains or both IP and optical layers. We then propose a practical architecture to fix these issues and experimentally demonstrate it over commercial IP/transport gear.

The need for SDN in orchestration of IP over optical multi-vendor networks

Availability in connection-oriented service in networks has traditionally been "all-or-nothing," i.e., when a failure occurs, a connection either is unprotected or fully protected. The differences in availability and cost between these two extremes can be quite high. A general framework for service availability will be presented that fills the gap. It is shown how network resources and cost are related to service parameters of the framework for networks that are bandwidth-efficient. In addition, a simple revenue model is presented and characterized, revealing when nontraditional service agreements may be attractive.

A general framework for service availability for bandwidth-efficient connection-oriented networks

In dynamic networks with diverse application requirements, Software Defined Networking (SDN) principles enable application-aware in-operation planning. Project ACINO built a network orchestrator as the connecting component between network applications and the underlying network infrastructure.

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Application Aware Multilayer Control and Optimization of Elastic WDM Switched Optical Networks

A new characterization of tree medians is presented: we show that a vertex m is a median of a tree T with n vertices iff there exists a partition of the vertex set into ⌊n/2⌋ disjoint pairs (excluding m when n is odd), such that all the paths connecting the two vertices in any of the pairs pass through m. We show that in this case the sum of the distances between these pairs of vertices is the largest possible among all such partitions, and we use this fact to discuss lower bounds on the message complexity of the distributed sorting problem. We show that, given a network of a tree topology, choosing a median and then routing all the information through it is the best possible strategy, in terms of worst-case number of messages sent during any execution of any distributed sorting algorithm. We also discuss the implications for networks of a general topology and for the distributed ranking problem.

A New Characterization of Tree Medians with Applications to Distributed Algorithms

Elastic Optical Networking (EON) supports Bandwidth Variable Transponders (BVTs) that can tune their bit-rate and bandwidth dynamically with a trade-off between reach and capacity. However, when BVTs need to transmit at low bit-rates, part of their capacity is wasted. This issue can be solved by adding elastic multi-flow performance according to the Sliceable Bandwidth Variable Transponder (S-BVT) approach. S-BVTs enable transmitting from one point to multiple destinations, changing the traffic rate to each destination and the number of destinations on demand. This chapter presents architectures to support the S-BVT and its techno-economic impact from a Capital Expenditures (CAPEX) and Operational Expenditures (OPEX) point of view.

Ori Gerstel

Papers

The need for SDN in orchestration of IP over optical multi-vendor networks

A general framework for service availability for bandwidth-efficient connection-oriented networks

Application Aware Multilayer Control and Optimization of Elastic WDM Switched Optical Networks

A New Characterization of Tree Medians with Applications to Distributed Algorithms

Sliceable Bandwidth Variable Transponders