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

Fiber-optic communication systems form the high-capacity transport infrastructure that enables global broadband data services and advanced Internet applications. The desire for higher per-fiber transport capacities and, at the same time, the drive for lower costs per end-to-end transmitted information bit has led to optically routed networks with high spectral efficiencies. Among other enabling technologies, advanced optical modulation formats have become key to the design of modern wavelength division multiplexed (WDM) fiber systems. In this paper, we review optical modulation formats in the broader context of optically routed WDM networks. We discuss the generation and detection of multigigabit/s intensity- and phase-modulated formats, and highlight their resilience to key impairments found in optical networking, such as optical amplifier noise, multipath interference, chromatic dispersion, polarization-mode dispersion, WDM crosstalk, concatenated optical filtering, and fiber nonlinearity

Advanced Optical Modulation Formats

Flexgrid technology is now considered to be a promising solution for future high-speed network design. In this context, we need a tutorial that covers the key aspects of elastic optical networks. This tutorial paper starts with a brief introduction of the elastic optical network and its unique characteristics. The paper then moves to the architecture of the elastic optical network and its operation principle. To complete the discussion of network architecture, this paper focuses on the different node architectures, and compares their performance in terms of scalability and flexibility. Thereafter, this paper reviews and classifies routing and spectrum allocation (RSA) approaches including their pros and cons. Furthermore, various aspects, namely, fragmentation, modulation, quality-of-transmission, traffic grooming, survivability, energy saving, and networking cost related to RSA, are presented. Finally, the paper explores the experimental demonstrations that have tested the functionality of the elastic optical network, and follows that with the research challenges and open issues posed by flexible networks.

Routing and Spectrum Allocation in Elastic Optical Networks: A Tutorial

Advanced optical modulation formats have become a key ingredient to the design of modern wavelength-division-multiplexed (WDM) optically routed networks. In this paper, we review the generation and detection of multigigabit/second intensity- and phase-modulated formats and highlight their resilience to key impairments found in optical networking, such as optical amplifier noise, chromatic dispersion, polarization-mode dispersion, WDM crosstalk, concatenated optical filtering, and fiber nonlinearity

Advanced Modulation Formats for High-Capacity Optical Transport Networks

Preface. 1. Introduction. 2. Optical Fiber. 3. Photodetectors. 4. Receiver Fundamentals. 5. Transimpledance Amplifiers. 6. Main Amplifiers. 7. Optical Transmitters. 8. Laser and Modulator Drivers. Appendix A: Eye Diagrams. Appendix B: Differential Circuits. Appendix C: S Parameters. Appendix D: Transistors and Technologies. Appendix E: Answers to the Problems. Appendix F: Notation. Appendix G: Symbols. Appendix H: Acronyms. References. Index.

Broadband Circuits for Optical Fiber Communication

Growing concerns regarding the scalability of current optical networks as well as IP-based networks are driving two important trends. One trend is a shift from the current rigid optical networks to spectrally efficient elastic optical networks with a flexible bandwidth and adaptive channel spacing. The other trend is IP traffic offloading to a lower layer yielding benefits that are potentially cost-effective and power-efficient. This article presents a novel multiflow optical transponder (OTP) that enables more efficient IP optical networking. A multiflow OTP allows client data flows that arrive from a single client interface to be mapped to multiple optical flows. In cooperation with the emerging spectrally efficient elastic optical path networking technology, multiflow OTPs can provide multiple optical connections from a single OTP to multiple OTPs. IP traffic offloading to an elastic optical path layer architecture and the effect of introducing multiflow OTPs (i.e., the potential reduction in the number of router interfaces and considerable potential for cost savings) are discussed. These benefits are brought about by increasing the number of directly connected router pairs while keeping router-to-optical-node interconnections simple. A novel optical virtual private line service based on multiflow OTPs that supports multiple optical connections from a single customer site to multiple customer sites with capacity adjustment is also discussed.

Multiflow optical transponder for efficient multilayer optical networking

We propose a dispersion-tolerant optical duobinary transmission system which uses a binary intensity modulation direct detection (IM-DD) receiver. The proposed system also relaxes the fiber input power limitation due to stimulated Brillouin scattering (SBS). Tolerance to chromatic dispersion in the proposed system is estimated by a simulation. A 10 Gb/s optical duobinary signal can be transmitted over 200 km of standard single-mode fiber (SMF) with 1 dB dispersion penalty. The advantages of the proposed system are confirmed experimentally. The optical duobinary signal was successfully received by the binary IM-DD receiver at the same sensitivity as a binary IM signal. Power penalty due to chromatic dispersion over a 164-km standard SMF was about 1.8 dB at 10 Gb/s. The SBS threshold of the 10 Gb/s optical duobinary modulated light was more than +20 dBm.

Dispersion-tolerant optical transmission system using duobinary transmitter and binary receiver

This Letter proposes a novel optical duobinary transmission system with no receiver sensitivity degradation. The transmitter yields a narrowband optical signal, and the receiver configuration is as simple as a binary IM-DD receiver. The feasibility of the proposed system is experimentally confirmed at 2.5, 5 and 10 Gbit/s.

Optical duobinary transmission system with no receiver sensitivity degradation

A novel optical duobinary transmission system with no receiver sensitivity degradation

The repeaterless transmission of an optical duobinary modulated signal at 10 Gbit/s is reported. The power penalty due to the fibre chromatic dispersion is effectively reduced in comparison with conventional binary intensity modulated (IM) signals. In the case of a 164 km standard singlemode fibre, the power penalty is <1.8 dB.

K. Yonenaga

Papers

Multiflow optical transponder for efficient multilayer optical networking

Dispersion-tolerant optical transmission system using duobinary transmitter and binary receiver

Optical duobinary transmission system with no receiver sensitivity degradation

A novel optical duobinary transmission system with no receiver sensitivity degradation

10Gbit/s repeaterless transmission experiment of optical duobinary modulated signal