COL 12(12), 120603(2014) CHINESE OPTICS LETTERS December 10, 2014
1671-7694/2014/120603(5) 120603-1 © 2014 Chinese Optics Letters
Novel iteration-free blind phase noise estimation
for coherent optical OFDM
Hongliang Ren (任宏亮)
1,2*
, Jiaxing Cai (蔡嘉兴)
1
, Jin Lu (卢 瑾)
1
,
Hao Wen (
温 浩)
1
, Linlin Xue (薛林林)
1
, Yali Qin (覃亚丽)
1
,
Shuqin Guo (
郭淑琴)
1
, Shouli Zhou (周守利)
1
, and Weisheng Hu (胡卫生)
2
1
College of Information Engineering, Zhejiang University of Technology,
Hangzhou 310023, China
2
State Key Laboratories of Advanced Optical Communication Systems and Networks,
Shanghai Jiao Tong University, Shanghai 200240, China
*
Corresponding author: hlren@zjut.edu.cn
Received May 27, 2014; accepted October 11, 2014; posted online November 14, 2014
We propose a novel iteration-free blind phase noise estimation scheme for coherent optical orthogonal
frequency division multiplexing (CO-OFDM) systems. In the new algorithm, the cost function is selected as
the similar expression with real and imaginary parts as that in the modied constant modulus algorithm,
and the new cost function is derived under some assumptions, where it is innitely approximated by the
sine and cosine functions. By means of the analytical formula of the cost function, the initial coarse common
phase error can be obtained with only some samples, where the algorithm avoids computational complexity
of conventional blind phase noise compensation scheme. In CO-OFDM systems with high-order modulation
format (32 quadrature amplitude modulation) and narrow linewidth lasers, it is proved by the simulation
results that the phase noise can be eectively compensated with the proposed blind estimation method.
OCIS codes: 060.2330, 060.1660, 060.4080.
doi: 10.3788/COL201412.120603.
Coherent optical orthogonal frequency division
multiplexing (CO-OFDM) has been considered as a
promising candidate for high-speed long-haul optical
communications due to its high chromatic dispersion
and polarization mode dispersion (PMD) tolerance
[1–8]
.
As is known to all, the coherent system performance
suers seriously from laser phase noise, because it intro-
duces both common phase error (CPE) and inter-carrier
interference (ICI).
Many research studies have focused on the phase
noise mitigation for CO-OFDM system. The digital
pilot-aided scheme is a conventional solution to the
problem
[9]
, where frequent pilot symbols are required,
and it leads to low bandwidth eiciency. In order to
enhance the spectral eiciency, an improved algorithm
with the pseudo-pilots is used to reduce the original
digital pilot overhead
[10]
. At the same time, blind phase
noise compensation method has also been proposed
in CO-OFDM system
[11]
; however, the computational
complexity is signicantly increased due to the utiliza-
tion of orthogonal basis expansion-based algorithms.
In Refs. [12,13], a complete blind phase noise correc-
tion scheme has been presented, and the decision-
directed phase equalizer (DDPE) has been proposed
in the non-data-aided scheme. The DDPE has the
similar eective performance with conventional equal-
izer (CE) for low-order modulation formats in the
CO-OFDM systems, but the system performance will
be degraded greatly by the decision errors for high-
order modulation formats. To achieve the good phase
noise correction capability, dispersion minimization
(DM) algorithm has been utilized before the DDPE
for the CO-OFDM systems with high-order modula-
tion formats in Ref. [13], where the cost function used
in the constant modulus algorithm (CMA) is cho-
sen with the same expression as the OFDM wireless
systems
[14–16]
. Although the system performance can
benet greatly from the introduction of DM algorithm
before DDPE, the algorithm with iteration operations
is often wrongly converged due to the severe distor-
tion of cost function aected by the considerable noise
in the CO-OFDM systems with high-order modula-
tion formats. Next, the wrong convergence result fur-
ther resists in the improper CPE compensation in the
subsequent DDPE.
In this letter, we propose an eective IFB phase noise
compensation method in the CO-OFDM systems with
high-order modulation formats. Based on the blind
phase noise suppression scheme
[13]
, the cost function in
the new DM algorithm has the similar form with real
and imaginary parts as that used in the modied CMA
(MCMA). The novel cost function is experimentally in
close proximity to the sine and cosine functions. Then,
the initial CPE can be easily calculated with only some
samples instead of the iterative operation because the
initial CPE is located on an extreme point of the cost
function. Subsequently, the conventional DDPE scheme
is used to remove the residual CPE. It is proved by
the simulation results that the new phase estimation
scheme has the advantages of both high bandwidth ei-
ciency and low computational complexity for high-order
modulation formats CO-OFDM systems.