Application of Kramers–Kronig receiver in
SSB-OFDM-RoF link
Yuancheng Cai (蔡沅成), Yun Ling (凌 云)*, Xiang Gao (高 翔), Bo Xu (许 渤),
and Kun Qiu (邱 昆)
Key Laboratory of Optical Fiber Sensing and Communications, Ministry of Education, University of Electronic
Science and Technology of China, Chengdu 611731, China
*Corresponding author: yling@uestc.edu.cn
Received September 21, 2018; accepted November 23, 2018; posted online December 28, 2018
We propose and investigate the use of a Kramers–Kronig (KK) receiver in a single sideband orthogonal fre-
quency division multiplexing radio over fiber (SSB-OFDM-RoF) link based on an optical remote heterodyne
solution. This scheme is effective in eliminating the signal-to-signal beating interference introduced by
square-law detection of a photo-detector in an SSB-OFDM-RoF link. We extensively study the influences of
different carrier-to-signal power ratios (CSPRs), laser linewidths, and transmission distances on our proposed
scheme. It is proved that the KK-based receiver can reduce optimal CSPR by more than 5 dB and provide
about 1.1 dB gain over the conventional mixer-based receiver scheme with CSPR of 11 dB after 75 km fiber
transmission.
OCIS codes: 060.5625, 060.2330, 060.2840.
doi: 10.3788/COL201917.010605.
Radio over fiber (RoF) technology has been extensively
studied due to its numerous advantages, such as broad
bandwidth, low attenuation, and flexibility for wireless
links in recent years. RoF combined with optical remote
heterodyne technology
[1–3]
, where the modulated signal
light is coupled with an optical carrier generated by a local
oscillator (LO) at the central station (CS), and no LO is
required at the base station (BS), further simplifies the BS
and greatly reduces the overall cost of the system. Among
different modulation schemes, orthogonal frequency divi-
sion multiplexing (OFDM), especially the single sideband
(SSB) OFDM, has attracted much attention in RoF sys-
tems because of its high spectral efficiency, good tolerance
to dispersion effects and multipath fading
[4,5]
.
In OFDM-RoF systems, as is well known, heterodyne
detection has a simpler structure and lower cost than co-
herent detection based on a balanced photo-detector (PD)
because it requires only one single-ended PD. However,
the signal-to-signal beating interference (SSBI) will be in-
troduced by square-law detection of the PD. Without
SSBI cancellation processing, the SSBI may deteriorate
the system performanc e considerably. Generally, there
are two common methods to obtain intermediate fre-
quency or baseband from the RF signal; one is using a
power detector, such as a Schottky diode
[6,7]
, and the other
is employing an electric mixer
[8]
. For the mixer scheme, an
extra high-power LO is necessary, which makes the receiver
more complex and expensive. On the other hand, a power
detector scheme does not need the LO, but an electric RF
tone (usually produced at the transmitter) along with the
information-bearing signal is needed for square-law detec-
tion, which increases the transmitter complexity and de-
creases the power efficiency. Furthermore, none of the
two methods can remove the SSBI term if no additional
measures are used. Solutions to SSBI elimination include
a guard-band between the carrier and signal bands so that
the SSBI term falls into a separate frequency range to the
signal–carrier beat term
[6]
, the iterative SSBI estimation
and cancellation technique
[9,10]
, Volterra nonlinear equal-
izer
[11,12]
, and selective subcarrier encoding in OFDM sys-
tems
[8,13]
. For these approaches, either spectral efficiency
is reduced or system complexity is increased. Instead of de-
pending on extra techniques to eliminate SSBI, the recently
proposed approach named the Kramers–Kronig (KK) algo-
rithm can fully reconstruct the complex signal from the de-
tected amplitude of the photocurrent and is able to alleviate
the SSBI very well
[14–17]
. In the previous report, the KK-
based receiver was mainly used for a data center intercon-
nection system. We believe that it is also advantageous to
use a KK receiver in the RoF link for wireless and optical
access networks.
In this Letter, we propose and investigate the applica-
tion of the KK receiver in an SSB-OFDM-RoF link based
on optical remote heterodyne solution. This scheme can
accurately reconstruct the complex baseband signal in
the digital domain from the RF signal, while effectively
removing the SSBI term. Since the perturbation to the sig-
nal introduced by the nonlinear SSBI term is eliminated
by KK operation, further signal processing, like electrical
chromatic dispersion compensation (ECDC), can be per-
formed at the receiver. The key advantages of the pro-
posed KK receiver-based SSB-OFDM-RoF scheme are
listed in the following: (1) simplify the system structure
and reduce the complexity of transceiver, since some hard-
ware devices, such as power detector, electric mixer, and
microwave LO, are avoided; (2) significantly improve the
system performance and effectively eliminate the SSBI
term introduced by square-law detection of the PD.
COL 17(1), 010605(2019) CHINESE OPTICS LETTERS January 10, 2019
1671-7694/2018/010605(5) 010605-1 © 2019 Chinese Optics Letters