Orthogonal frequency-division multiplexing (OFDM) is a modulation technology that has been widely adopted in many new and emerging broadband wireless and wireline communication systems. Due to its capability to transmit a high-speed data stream using multiple spectral-overlapped lower-speed subcarriers, OFDM technology offers superior advantages of high spectrum efficiency, robustness against inter-carrier and inter-symbol interference, adaptability to server channel conditions, etc. In recent years, there have been intensive studies on optical OFDM (O-OFDM) transmission technologies, and it is considered a promising technology for future ultra-high-speed optical transmission. Based on O-OFDM technology, a novel elastic optical network architecture with immense flexibility and scalability in spectrum allocation and data rate accommodation could be built to support diverse services and the rapid growth of Internet traffic in the future. In this paper, we present a comprehensive survey on OFDM-based elastic optical network technologies, including basic principles of OFDM, O-OFDM technologies, the architectures of OFDM-based elastic core optical networks, and related key enabling technologies. The main advantages and issues of OFDM-based elastic core optical networks that are under research are also discussed.

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A Survey on OFDM-Based Elastic Core Optical Networking

This paper describes coherent optical orthogonal frequency division multiplexing (CO-OFDM) techniques for the long-haul transmission of 100-Gb/s-class channels. First, we discuss the configurations of the transmitter and receiver that implement the optical multiplexing/demultiplexing techniques for high-speed CO-OFDM transmission. Next, we review the no-guard-interval (No-GI) CO-OFDM transmission scheme which utilizes optical multiplexing for OFDM signal generation and the intradyne receiver configuration with digital signal processing (DSP). We examine the transmission characteristics of the proposed scheme, and show that No-GI CO-OFDM offers compact signal spectra and superior performance with regard to tolerance against optical amplifier noise and polarization-mode dispersion (PMD). We then introduce long-haul high-capacity transmission experiments employing No-GI CO-OFDM; 13.4 Tb/s (134 times 111 Gb/s) transmission is successfully demonstrated over 3600 km of ITU-T G.652 single-mode fiber without using optical dispersion compensation.

No-Guard-Interval Coherent Optical OFDM for 100-Gb/s Long-Haul WDM Transmission

Fast advancing silicon technology underpinned by Moore's law is creating a major transformation in optical fiber communications. The recent upsurge of interests in optical orthogonal frequency-division multiplexing (OFDM) as an efficient modulation and multiplexing scheme is merely a manifestation of this unmistakable trend. Since the formulation of the fundamental concept of OFDM by Chang in 1966 and many landmark works by others thereafter, OFDM has been triumphant in almost all the major RF communication standards. Nevertheless, its application to optical communications is rather nascent and its potential success in the optical domain remains an open question. This tutorial provides a review of optical OFDM slanted towards emerging optical fiber networks. The objective of the tutorial is two-fold: (i) to review OFDM fundamentals from its basic mathematical formation to its salient disadvantages and advantages, and (ii) to reveal the unique characteristics of the fiber optical channel and identify the challenges and opportunities in the application of optical OFDM.

OFDM for Flexible High-Speed Optical Networks

Just like Ethernet before, IEEE 802.11 is now transcending the borders of its usage from the office environment toward real-time communication on the factory floor. However, similar to Ethernet, the availability of synchronized clocks to coordinate and control communication and distributed real-time services is not a built-in feature in WLAN. Over the years, this has led to the design and use of a wide variety of customized protocols with varying complexity and precision, both for wired and wireless networks, in accordance with the increasingly demanding requirements from real-time applications. This survey looks into the details of synchronization over IEEE 802.11 with a particular focus on the infrastructure mode which is most relevant for industrial use cases. It highlights the different parameters which affect the performance of clock synchronization over WLAN and compares the performance of existing synchronization methods to analyze their shortcomings. Finally, it identifies new trends and directions for future research as well as features for wireless clock synchronization which will be required by the applications in the near future.

Clock Synchronization Over IEEE 802.11—A Survey of Methodologies and Protocols

All-optical OFDM uses optical techniques to multiplex together several modulated lightsources, to form a band of subcarriers that can be considered as one wavelength channel. The subcarriers have a frequency separation equal to their modulation rate. This means that they can be demultiplexed without any cross-talk between them, usually with a Discrete Fourier Transform (DFT), implemented optically or electronically. Previous work has proposed networks of optical couplers to implement the DFT. This work shows that the topology of an Arrayed Grating Waveguide Router (AWGR) can be used to perform the demultiplexing, and that the AWGR can be considered as a serial-to-parallel converter followed by a DFT. The simulations show that the electrical bandwidths of the transmitter and receiver are critical to orthogonal demultiplexing, and give insight into how crosstalk occurs in all-optical OFDM and coherent-WDM systems using waveforms and spectra along the system. Design specifications for the AWGR are developed, and show that non-uniformity will lead to crosstalk. The compensation of dispersion and the applications of these techniques to ‘coherent WDM’ systems using Non-Return to Zero modulation is discussed.

Design of Arrayed-Waveguide Grating Routers for use as optical OFDM demultiplexers.

Optical orthogonal frequency division multiplex (OFDM) symbol generation by all-optical discrete Fourier transform (DFT) is proposed and investigated for 100-Gbps transmission performance. We discuss a design example for a 4x25Gbps OFDM transmission system and its performance comparison with that for a 100-Gbps single-channel return-to-zero data transmission in an optically amplified system.

All optical discrete Fourier transform processor for 100 Gbps OFDM transmission

Ethernet ring protection (ERP) is an emerging solution for carrier-grade optical Ethernet networking developed as an ITU-T recommendation The most recent development of the ERP technique provides multi-ring protection in a mesh packet transport network The ERP configuration and capacity planning in a ring mesh topology can be optimized in the selection of the interconnected ring hierarchy and logical loop prevention block positions This paper reports the first investigation to understand the designing principles of protected Ethernet ring mesh networks and proposes an optimized design scheme for cost-effective and reliable ERP networking

Efficient Ethernet Ring Mesh Network Design

When a single source of multimedia contents is distributed to multiple reproduction devices, the audio and video contents require synchronous play for multi-channel stereo sound and lip-synchronization. This paper investigates capability of IEEE 802.11n wireless LANs for providing synchronized services of real-time multimedia traffic. We implement IEEE 1588 Precision Time Protocol in wireless LAN devices to characterize delay jitter and clock synchronization accuracy. The results indicate a strong potential to provide a high fidelity real-time multi-channel multimedia networking service within 430-microsecond synchronization accuracy at an approximately 80 Mbps streaming rate.

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Wireless network synchronization for multichannel multimedia services

A Novel Design Optimization For Reliable Networking Is Investigated In Ethernet Ring Mesh Networks With The Itu-T G.8032 Ethernet Ring Protection Recommendation. Designing An Ethernet Ring Mesh Consisting Of Multiple Rings To Achieve The Maximum Network Availability Is An Np-Complete Problem. We Show That A Graph With Vertex Connectivity Equal To Or Greater Than Two Is A Sufficient Condition For Designing An Ethernet Ring Mesh. A Novel Design Rule With An Efficient Heuristic Algorithm Is Proposed To Find A Design Close To An Optimal Ethernet Ring Mesh In Terms Of Maximum Network Availability. Compared With An Optimal Network Design Algorithm With An Exponential Enumeration Search Cost, The Heuristic Algorithm Achieves Network Availability Nearly As High As That Of An Optimal Design At A Polynomial Cost.

Reliable Network Design for Ethernet Ring Mesh Networks

A timestamping apparatus and method are provided. The timestamping apparatus implements timestamping on a synchronization message at a physical layer when the synchronization message is transmitted to the physical layer. At an application layer of the timestamping apparatus, a bit stream including a start indicator bit informing a start of a pseudo random number sequence, the pseudo random number sequence, and an end indicator bit informing an end of the pseudo random number sequence is generated to check whether or not a message received from the physical layer is the synchronization message, and is inserted as signature information of the synchronization message. At the physical layer of the timestamping apparatus, the signature information included in the synchronization message is detected, and timestamping information is generated when the signature information is detected.

Kyusang Lee

Papers

All optical discrete Fourier transform processor for 100 Gbps OFDM transmission

Efficient Ethernet Ring Mesh Network Design

Wireless network synchronization for multichannel multimedia services

Reliable Network Design for Ethernet Ring Mesh Networks

Timestamping apparatus and method