A Survey on
OFDM-Based Elastic Core Optical
Networking
Guoying Zhang
12
, Marc De Leenheer
13
, Annalisa Morea
4
, and Biswanath Mukherjee
1
1
University of California - Davis, USA
2
China Academy of Telecom Research, China
3
Ghent University - IBBT, Belgium
4
Alcatel-Lucent Bell Labs, France
Email: {zguoying, mleenheer,bmukherjee}@ucdavis.edu
zhangguoying@catr.cn
annalisa.morea@alcatel-lucent.com
November 2011
批注 [gyzhang1]: Reviewer1/Comme
nt4: The title should clearly state the
focus of optical core networks (as it is,
see e.g. page 10).
[Authors’ Response] Thank you for
pointing this issue out. We have
modified the title to emphasis the
scope of this paper.
Contents
Abstract ............................................................................................................................................. 1
1. Introduction ............................................................................................................................... 1
2. Theoretical Fundamentals of OFDM ........................................................................................ 2
2.1. OFDM Principle ........................................................................................................ 2
2.2. Building Blocks of OFDM Systems .......................................................................... 4
2.3. OFDM Technology Description ............................................................................... 5
2.3.1. Guard Interval and Cyclic Prefix....................................................................... 5
2.3.2. Channel Estimation ........................................................................................... 6
2.3.3. Link Adaption .................................................................................................... 6
2.4. Advantages and Disadvantages of OFDM ................................................................ 7
3. Optical OFDM Transmission Technology ................................................................................ 7
3.1. O-OFDM Signal Synthesis Types ............................................................................. 8
3.1.1. FFT-Based Approach ......................................................................................... 8
3.1.2. Optical Approach ............................................................................................ 10
3.2. O-OFDM Signal Detection Types ........................................................................... 12
3.2.1. Direct Detection .............................................................................................. 12
3.2.2. Coherent Detection (CO-OFDM) .................................................................... 12
3.3. MIMO O-OFDM ..................................................................................................... 12
3.4. Modulation Formats and Adaptive Modulation ...................................................... 15
4. OFDM-Based Elastic Core Optical Network .......................................................................... 17
4.1. Elastic Optical Network Concept ............................................................................ 17
4.2. OFDM-Based Elastic Optical Network Architecture .............................................. 19
4.3. Key Enabling Technologies ..................................................................................... 20
4.3.1. Node-Level Technologies ................................................................................ 20
4.3.1.1. Data-Rate/Bandwidth-Variable Transponder ................................... 20
4.3.1.2.
Bandwidth-Variable Optical Switching ........................................... 23
4.3.2. Network-Level Technologies .......................................................................... 25
4.3.2.1. Flexible Spectrum Slot Specification .............................................. 26
4.3.2.2. Routing and Spectrum Allocation Algorithm .................................. 27
4.3.2.2.1. Static RSA with ILP (Integer Linear Programing) .......................... 27
4.3.2.2.2. Heuristic Algorithms for Static and Dynamic RSA ......................... 28
4.3.2.2.3. RSA for Survivable Networks ......................................................... 29
4.3.2.2.4. Distance-Adaptive RSA .................................................................. 29
4.3.2.2.5. RSA for Time-Varying Traffic ......................................................... 31
4.3.2.2.6. Network Defragmentation RSA ...................................................... 31
4.3.2.3. Traffic Grooming ............................................................................. 32
4.3.2.4. Survivability Strategies ................................................................... 32
4.3.2.5. Optical Network Virtualization ....................................................... 33
4.3.2.6. Energy Efficiency ............................................................................ 34
4.3.2.7. Network Control and Management Scheme .................................... 34
5. Conclusion .............................................................................................................................. 34
6. References ............................................................................................................................... 35
7. Acronyms ................................................................................................................................ 43
A Survey on OFDM-Based Elastic Core Optical Networking
1
Abstract
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.
Keywords: Optical Orthogonal Frequency-Division Multiplexing (O-OFDM), Elastic Optical
Network, Data Rate/Bandwidth-Variable Transponder, Bandwidth-Variable Wavelength Cross-
Connect (BV-WXC), Routing and Spectrum Allocation (RSA), Traffic Grooming, Survivability,
Network Virtualization.
1. Introduction
In recent years, Internet traffic in the core network has been doubling almost every two years,
and predictions indicate that it will continue to exhibit exponential growth due to emerging
applications such as high-definition and real-time video communications [1][2]. As a result of this
rapid increase in traffic demands, large-capacity and cost-effective optical fiber transmission systems
are required for realizing future optical networks. So far, Wavelength-Division Multiplexing (WDM)
systems with up to 40 Gb/s capacity per channel have been deployed in backbone networks, while 100
Gb/s interfaces are now commercially available and 100 Gb/s deployment are expected soon.
Moreover, it is foreseen that optical networks will be required to support Tb/s class transmission in the
near future [2][3]. However, scaling to the growing traffic demands is challenging for conventional
optical transmission technology as it suffers from the electrical bandwidth bottleneck limitation, and
the physical impairments become more severe as the transmission speed increases [3].
On the other hand, emerging Internet applications such as Internet Protocol television (IPTV),
video on demand, and cloud and grid computing applications demonstrate unpredictable changes in
bandwidth and geographical traffic patterns [4]. This calls for a more data- rate flexible, agile,
reconfigurable, and resource-efficient optical network, while the fixed and coarse granularity of
current WDM technology will restrict the optical network to stranded bandwidth provisioning,
inefficient capacity utilization, and high cost.
To meet the needs of the future Internet, the optical transmission and networking technologies are
moving forward to a more efficient, flexible, and scalable direction. Solutions such as optical packet
switching (OPS) and optical burst switching (OBS) that meet these requirements have been studied in
the past few years, but cannot be considered as a near-term solution due to their immaturity [5].
批注 [gyzhang2]: [Authors’
Comments] We have modified this
sentence to emphasis the scope of
this paper.
批注 [gyzhang3]: Reviewer1/Com
ment 6a) Page 1: 40 Gb/ => up to 40
Gb/s.
[Authors’ Response:] We have
updated it.
A Survey on OFDM-Based Elastic Core Optical Networking
2
Recently, OFDM (Orthogonal Frequency-Division Multiplexing) has been considered a
promising candidate for future high-speed optical transmission technology. OFDM is a multi-carrier
transmission technology that transmits a high-speed data stream by splitting it into multiple parallel
low-speed data channels. OFDM first emerged as a leading physical-layer technology in wireless
communications, as it provides an effective solution to inter-symbol interference (ISI) caused by the
delay spread of wireless channels. It is now widely adopted in broadband wireless and wireline
networking standards, such as 802.11a/g Wi-Fi, 802.16 WiMAX, LTE (Long-Term Evolution), DAB
and DVB (Digital Audio and Video Broadcasting), and
DSL (Digital Subscriber Loop) around the
world [3].
Because of the great success of OFDM in wireless and wireline systems, it is currently being
considered for optical transmission and networking. With the intrinsic flexibility and scalability
characteristics of optical OFDM technology (which will be described in Section 4.1 in more detail), a
novel elastic optical network architecture, possessing the capability to manage signals with different
data rate and variable bandwidth, can be built to meet the requirements of future optical networks [6].
In this paper, we present a comprehensive survey of OFDM-based optical high-speed
transmission and networking technologies, with a specific focus on core optical network scenarios. We
start with basic OFDM principles in Section 2, and introduce various kinds of optical OFDM
transmission schemes and technologies in Section 3. Next, we address the OFDM-based elastic optical
network, detailing its architecture and enabling technologies in Section 4. Finally, we present our
concluding remarks in Section 5.
2. Theoretical Fundamentals of OFDM
2.1. OFDM Principle
OFDM is a special class of the Multi-Carrier Modulation (MCM) scheme that transmits a high-
speed data stream by dividing it into a number of orthogonal channels, referred to as subcarriers, each
carrying a relatively-low data rate [3]. Compared to WDM systems, where a fixed channel spacing
between the wavelengths is usually needed to eliminate crosstalk, OFDM allows the spectrum of
individual subcarriers to overlap because of its orthogonality, as depicted in Figure 1. Furthermore, the
inter-symbol interference (ISI) of the OFDM signal can be mitigated as the per-subcarrier symbol
duration is significantly longer than that of a single-carrier system of the same total data rate.
Figure 1 Spectrum of WDM signals and OFDM signal [7].
From the spectrum perspective, the orthogonal condition between multiple subcarriers is satisfied
when their central frequencies are spaced n/T
s
apart, where n is an integer and T
s
is the symbol
duration. It can be seen in Figure 2(a) that the peak point of a subcarrier's spectrum corresponds to the
批注 [gyzhang4]: Reviewer1/Com
ment 6b) Page 2: Is [1] a good
reference for DSL?
[Authors’ Response:] This is a
mistake. We have changed the
reference to be [3], and that is the
reference for the whole sentence.
![Figure 14 Concept of bandwidth-variable WSS [6].](/figures/figure-14-concept-of-bandwidth-variable-wss-6-h7eq7oym.webp)
![Figure 8 Schematic diagram of the all-optical OFDM [36][42]: a) Transmitter configuration; b) Receiver configuration.](/figures/figure-8-schematic-diagram-of-the-all-optical-ofdm-36-42-a-12d9ook0.webp)
