Dual-Polarization OFDM/OQAM-PON with Efficient
Channel Equalization Methods
Bangjiang Lin
1
, Xuan Tang
1
, Yiwei Li
1
, Shihao Zhang
1
, Zabih Ghassemlooy
2
1
Quanzhou Institute of Equipment Manufacturing, Haixi Institutes, Chinese Academy of Sciences, Fujian, China
2
Faculty of Engineering and Environment, Northumbria University, U.K.
linbangjiang@163.com
Abstract—We present dual-polarization OFDM/OQAM
transmission for passive optical network. The ISFA and MMSE
with the full loaded and half loaded preamble structures are
used to mitigate the intrinsic imaginary interference.
Keywords—Orthogonal frequency division multiplexing
(OFDM), Offset quadrature amplitude modulation (OQAM),
Passive optical network (PON)
I.
I
NTRODUCTION
Due to its high spectral efficiency, high tolerance against
various fiber dispersion effects and extreme flexibility on both
multiple services access and dynamic bandwidth allocation, the
digital signal processing (DSP) based OFDM-PON has been
intensively investigated. Polarization dimension has also been
carried out to transmit more information for OFDM-PON [1-4]
with multiple inputs multiple outputs (MIMO) processing.
Compared with the polarization division multiplexing (PDM)
scheme [2], the polarization interleaving (PI) scheme has much
less computation complexity and more flexible hardware
implementation [3-4]. The dual-polarization OFDM-PON with
cyclic prefix (CP) has high tolerance against the chromatic
dispersion (CD) induced inter-symbol interference (ISI) and
the polarization mode dispersion (PMD) induced crosstalk
between polarizations. However, the insertion of CP will lead
to reduced spectral efficiency.
For the virtue of higher spectrum efficiency brought by the
elimination of CP and lower out of band radiation using
specially designed filter bank, OFDM/offset quadrature
amplitude modulation (OFDM/OQAM) has been considered as
an attractive alternative to conventional OFDM [5]. To date
OFDM/OQAM systems have already been introduced in the
digital ratio technical standards, wireless regional area network
(WRAN IEEE 802.22) , coherent optical communications [6-7]
and IM/DD transmission system [8].
In this paper, we introduce the OFDM/OQAM system in
the dual-polarization PON. The complete channel transmission
responses and the CD and PMD induced intrinsic imaginary
interference (IMI) effect are systemically deduced for
OFDM/OQAM-PON based on PI. As we have known,
interference approximation method (IAM) has the advantage of
requiring low computational complexity and promising
robustness against ISI by boosting the power of the “pseudo
pilot” [9]. Thus we extend the IAM method proposed in [9] to
PI-OFDM/OQAM-PON system. The half loaded and full
loaded (FL) preamble structures are used to de-multiplex the
two polarizations. To further increase the accuracy of channel
estimation (CE), intra-symbol frequency-domain averaging
(ISFA) and minimum mean squared error (MMSE) are
combined with IAM. Both ISFA and MMSE perform channel
estimation based on the channel frequency response (CFR)
calculated from IAM. In ISFA estimator, averaging is carried
out over the estimated matrix for multiple adjacent frequency
subcarriers (SCs). In MMSE estimator, additional information
such as the signal to noise ratio (SNR) and statistical
characteristics of the channel are required. As shown in our
simulation, compared with IAM method, ISFA and MMSE
with the HL method offer improved receiver sensitivity by
about 1 dB and 2 dB respectively in the case of back to back
(BTB), while the improvement are about 0.5 dB and 1.5 dB
with the FL method. For channel estimation, the FL method is
more powerful than the HL method in mitigating the IMI effect
and optical noise.
II. P
ROPOSED CHANNEL ESTIMATION METHODS
Fig. 1 shows the schematic block diagram of the proposed
PI-OFDM/OQAM-PON. After fiber transmission, the received
PI OFDM/OQAM symbols (i.e.,
,,
mn
r and
,,ymn
r ) can be
written as:
Fig. 1. Schematic diagram of (a) transmitter and (b) receiver for PI
OFDM/OQAM-PON. (S/P: serial-to-parallel conversion, P/S: parallel-to-
serial conversion, FIR: finite impulse response)