Volterra-based Nonlinear Equalization for
Nonlinearity Mitigation in Organic VLC
Xiangyu Li
1
, Hanjie Chen
1
, Shangbin Li
1
, Qian Gao
1
, Chen Gong
1
, and Zhengyuan Xu
1,2
1
Key Laboratory of Wireless-Optical Communications, Chinese Academy of Sciences
University of Science and Technology of China, Hefei, Anhui 230026, China
2
Shenzhen Graduate School, Tsinghua University, Shenzhen 518055, China
Email: lxy93@mail.ustc.edu.cn, xuzy@ustc.edu.cn
Abstract—Organic light emitting diodes (OLEDs) show
promising applications due to their unique advantages compared
with conventional commercial LEDs. In OLED-base visible light
communication (VLC), the nonlinearity may severely degrade
the system performance, especially for modulation format with
high peak to average power ratio (PAPR) such as orthogonal
frequency-division multiplexing (OFDM). We experimentally an-
alyze the OLED nonlinearity by Volterra series and apply the
Volterra-based nonlinear equalizer to demodulate the signal. It is
shown that the proposed system achieves transmission distance
of 3 meters, which exceeds the longest reported in the organic
VLC literature. It can mitigate both inter-symbol interference
(ISI) and nonlinearity more effectively than other equalizers.
Experimental results at different distance and driving voltage
are also reported.
Index Terms—Visible light communication, organic light emit-
ting diode, Volterra series, nonlinear equalizer.
I. INTRODUCTION
Nowadays, organic light emitting diodes (OLEDs) have
attracted increasing attention for their potential applications in
display and lighting [1], [2]. Compared to conventional LEDs,
OLEDs can offer several advantages such as transparency,
flexibility, high-quality color rendering, long lifetime, and low
production cost. In addition to illumination, these devices can
also be used for data communication as a subset of visible
light communication (VLC).
For VLC, data are transmitted by modulating the intensity
of LEDs. The intensity variation is beyond the human eyes
perception threshold such that it can not be perceived by
human eyes. Therefore, VLC can provide illumination and
information transmission at the same time. Compared with a
conventional radio frequency (RF) system, VLC has several
advantages, such as almost unlimited potential bandwidth,
license-free operation, and higher security [3], [4], [5]. How-
ever, for OLEDs the small bandwidth (BW) compared to
conventional LEDs is a key disadvantage, typically in the order
of several hundreds of kHz, which inevitably decreases the
transmission rate, or distance for a given data rate. To increase
the transmission bandwidth, equalization techniques have been
exploited [6].
It is well known that the finite bandwidth will cause inter-
symbol interference (ISI). In addition, OLEDs suffer from
intrinsic nonlinearity, which will severely degrade the commu-
nication performance. In order to achieve a high data trans-
mission rate, an orthogonal frequency-division multiplexing
(OFDM) technique has been introduced into VLC [7], where
modulating a conventional LED with OFDM technique does
not degrade the emitted light quality [8]. However, due to
the high peak-to-average power ratio (PARR) of the OFDM
signals, the OLED nonlinearity will significantly degrade the
overall system performance. The LED nonlinearity mainly
comes from the electro-opto power conversation. It can be
categorized into dynamic or static as well as memory-less
or memory types [9]. Some methods have been proposed to
compensate the LED nonlinearity [10], [11], [12], [13], [14].
However, the OLED nonlinearity has never been addressed
in the literature. Moreover, the transmission distance of an
organic VLC system in existing works is only in the order
of centimeters. To make the device more applicable for com-
mercial use, the long distance performance and corresponding
techniques need to be investigated.
In this paper, we experimentally demonstrate the application
of Volterra based nonlinear equalization for an organic VLC
system. We adopt the Volterra series to model the OLED’s
nonlinearity, and the nonlinear equalizer to recover the data
symbols. In the experiments, the end-to-end transmission
distance is 3 meters, which significantly exceeds the trans-
mission distances reported in the existing literature. Using the
time domain equalizer (TDE) of order K =2, the system
can achieve BER=2.9e-3, which is below the forward error
correction (FEC) limit. Due to the extremely low bandwidth,
the effective data rate is about 80 kb/s. The performance at
different distance and driving voltage V
dc
is also demonstrated.
Experimental results show that the nonlinear equalizers based
on Volterra series can significantly outperform the linear
equalizers.
The rest of the paper is organized as follows. Section II
introduces the nonlinear model and the modulation scheme
of system, and then illustrates the basic principle of the
Volterra-based nonlinear equalizer. Section III describes the
experimental setup and validates the effectiveness of nonlinear
equalizer in mitigating the nonlinearity of OLED. Finally,
conclusions are drawn in section IV.
II. P
RINCIPLE
A. Nonlinear Model
OLED is the major nonlinear source in an organic VLC
system. The OLED nonlinearity mainly stems from the electro-
opto power conversation, which is a static nonlinear function.
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