672 IEEE COMMUNICATIONS LETTERS, VOL. 18, NO. 4, APRIL 2014
Influence of Physical Layer Configuration on
Performance of Elastic Optical OFDM Networks
Guanjun Gao, Jie Zhang, Lei Wang, Wanyi Gu, and Yuefeng Ji
Abstract—We study how the physical layer characteristics
and novel digital impairment mitigation techniques impact the
performance of elastic optical OFDM networks. The relationship
between bandwidth blocking ratio (BBR) and fiber type, span
length, dispersion management, FEC and intra-channel nonlin-
earity compensation are evaluated through cross-layer network
simulations, which integrate closed-form expressions of quality
of transmission into routing, modulation level and spectrum
allocation (RMSA). An adaptive FEC assisted RMSA is proposed
and proved to improve the network performance by optimizing
the FEC overhead assignment for individual paths. Numerical
simulations also show considerable performance improvement
by deploying shorter span-length fiber links without dispersion
management, and imperceptible influence of intra-channel non-
linearity compensation for flexible grid networks under very
heavy traffic. These results provide valuable suggestions for phys-
ical layer fiber deployment and application of novel impairment
mitigation techniques on elastic optical networks, such as intra-
channel nonlinearity compensation as well as soft-decision FEC.
Index Terms—Elastic optical network, orthogonal frequency-
division multiplexing (OFDM), forward error correction (FEC),
nonlinearity compensation.
I. INTRODUCTION
E
NABLED by flexible bandwidth transceivers and spec-
trum selective switches, elastic optical network (EON)
with flexible modulation and spectrum allocation emerges as
an inevitable trend in future network evolution [1]-[2]. A
key feature of EON is the modulation format and spectrum
can be adaptively allocated and adjusted according to the
distance and capacity requirements [1]-[3]. Thus it improves
the network performance significantly compared to traditional
waveleng th switched op tical networks (WSON) with the fixed
modulation format and wavelength grid [3]-[6]. By exploiting
this feature, efficient resource provisioning in the elastic
network is receiving sustained attention, which incorporate
quality of transmission (Qo T) or transmission reach awareness
into planning, designing and operation stages of EON [3]-[7].
Recent studies on EON employ the QoT relations obtained by
simulations or based on simple transmission reach assump-
tions for homogeneous standard single-mode fiber (SSMF)
Manuscript received November 26, 2013. The associate editor coordinating
the re view of this letter and approving it for publication was I. Djordjevic.
G. Gao, J. Zhang, W. Gu, and Y. Ji are with the State Ke y Laboratory
of Information Photonics and Optical Communications, Beijing University
of Posts and Telecommunications, Beijing 100876, China (e-mail: champi-
ongao@gmail.com).
L. Wang is with the ZTE Cooporations, Beijing China.
This work was supported in part by National Basic Research Program
of China under Grant 2010CB328204, in part by National High-tech R&D
Program of China under Grant 2012AA011301, in part by National Natural
Science Foundation of China under Grant 61302085, in part by China
Postdoctoral Science Foundation under Grant 2012M520207, and in part by
a ZTE cooperation foundation.
Digital Object Identifier 10.1109/LCOMM.2014.021214.132628
spans, neglecting the varieties of physical span configura-
tions and n ovel impairments m itigation techniques [4]-[7].
Because of its high dependency on QoT, the performance
of EON is closely related to the physical layer configura-
tion (PLC) and influenced by novel impairments mitigation
techniques such as digital back propagation (DBP) based
nonlinearity com pensation and soft-decision FEC (SD-FEC)
[8]-[9]. Moreover, although the impacts of PLC have been
analyzed for metropolitan networks with 10-Gbit/s on-off-
keying (OOK) signals considering the linear impairments with
different values of span length and dispersion parameter [10],
such cross-layer influences and r elations are not investigated
for nationa l size elastic optical OFDM networks with various
span configurations, advanced software d efined transmitters,
as well as coherent detection based impairments mitigation
techniques such as SD-FEC and DBP.
In this paper, we present a comprehensive study on how the
physical layer specification and novel impairments mitigation
techniques impact the EON performance, by incorporating a
fast and accurate closed-form expression for nonlinear trans-
mission performance of CO-OFDM systems, and considering
varieties of fiber type, span length, channel spacing, dispersion
management, FEC and DBP based intra-channel nonlinearity
compensation. The benefits of using novel fiber type, SD-
FEC and nonlinearity compensations are evaluated, providing
insightful guidance for physical layer deployment of EON. An
adaptive FEC allocation scheme is also presented to improve
the EON performance by optimizing the coding gain and
overhead of various FEC schemes.
II. T
RANSMISSION PERFORMANCE MODELING
The closed-form expression for transmission performance
of CO-OFDM systems are first derived for densely spaced
systems without frequency guard band (GB), considering a
variety of span length, fiber type and dispersion management
strategy [11]. Further extensions are derived and substantiated
considering the influence of GB [12], or using DBP based
nonlinearity compensations with or without non-deterministic
nonlinear effects [13]. In this paper we focus on the intra-
channel nonlin earity compensated systems either with or with-
out the influence of GB. For polarization-division-multiplexed
(PDM) systems, the performance indicators including signal-
to-noise ratio (SNR), maximum SNR (SNR
m
)andQ
2
factor
are generalized as [12]-[13]
I
0
= I
2/3
/I
1/2
NL
,SNR
m
= I
3/2
0
/(3n
2/3
0
),
Q
2
=
√
2erfc
−1
2
1 −
1
V
log
2
V
erfc
3log
2
V
V
2
− 1
SNR
V
(1)
1089-7798/14$31.00
c
2014 IEEE