Experimental verification of performance improvement
for a gigabit wavelength division multiplexing visible
light communication system utilizing asymmetrically
clipped optical orthogonal frequency
division multiplexing
Yiguang Wang, Yuanquan Wang, and Nan Chi*
Department of Communication Science and Engineering, and Key Laboratory for Information Science of Electromagnetic
Waves (MoE), Fudan University, Shanghai 200433, China
*Corresponding author: nanchi@fudan.edu.cn
Received May 2, 2014; revised July 7, 2014; accepted August 16, 2014;
posted August 18, 2014 (Doc. ID 210591); published September 19, 2014
Asymmetrically clipped optical orthogonal frequency division multiplexing (ACO-OFDM) has been a promising
candidate in visible light communications (VLC) due to its improvement in power efficiency and reduction of
nonlinearity based on previous simulation analysis. In this paper, for the first time as far as we know, we
experimentally verify that ACO-OFDM would be an efficient scheme to improve the performance of a gigabit
wavelength division multiplexing VLC system. Our theoretical investigations reveal that the advantages of
ACO-OFDM can be attributed to the reduction of inter-carrier interference caused by signal–signal beating noise.
An aggregate data rate of 1.05 Gb∕s is successfully achieved over 30 cm transmission below the 7% forward-
error-correction threshold of 3.8 × 10
−3
. The experimental results show that ACO-OFDM can outperform DC-biased
optical OFDM by BER performance of 1.5 dB at the same data rate and 4 dB at the same bandwidth, which clearly
demonstrates the benefit and feasibility of ACO-OFDM. © 2014 Chinese Laser Press
OCIS codes: (060.2605) Free-space optical communication; (060.4510) Optical communications; (230.3670)
Light-emitting diodes.
http://dx.doi.org/10.1364/PRJ.2.000138
1. INTRODUCTION
In recent years, visible light communication (VLC) based on
light emitting diodes (LEDs) has been garnering increasing at-
tention for short-range wireless communication as LEDs are
considered to be major candidates for future illumination [
1].
Compared to traditional short-range wireless communication
at radio frequency (RF), VLC offers several advantages, such
as being such as cost effective, license-free, and immune to
electromagnetic interference, and having high security. RGB
LEDs, compared with white LEDs, have become better solu-
tions to high-speed VLC systems as they offer the possibility of
wavelength division multiplexing (WDM) technology.
In VLC systems, spectrally efficient modulation formats
have been widely used to increase the transmission data rate.
Due to the inherent robustness against multipath effects, high
signal-to-noise ratio (SNR), and high spectral efficiency,
orthogonal frequency division multiplexing (OFDM) modula-
tion has become an excellent choice for high-speed VLC sys-
tems [
2–4]. However, the time-domain OFDM signal envelope
is utilized to modulate the intensity of the LED. For this pur-
pose, the signal needs to be nonnegative in the intensity-
modulated system. Therefore, a large DC bias has to be used
to make OFDM signals non-negative, i.e., DC-biased OFDM
(DCO-OFDM), which results in low power efficiency and
low modulation depth. In order to overcome this disadvant-
age, asymmetrically clipped optical OFDM (ACO-OFDM)
has been proposed. For ACO-OFDM, the time-domain signal
is made unipolar by simply clipping the negative part, which
does not need a large DC bias. Only odd subcarriers are modu-
lated by signals, while even subcarriers are vacant, and all of
the clipping distortion products fall on the even subcarriers.
A number of investigations on ACO-OFDM-based VLC systems
have been conducted recently [
5–10]. In Ref. [5], the author
makes a comparison between ACO- and DCO-OFDM in a si-
mulated VLC system and attributes the performance improve-
ment of ACO-OFDM to the increased modulation depth and
power efficiency. In Refs. [
6] and [7], the clipping noise
and capacity of ACO-OFDM-based VLC systems are analyzed.
Three different receiver designs are theoretically discussed in
[
8]. Reference [11] has proposed a novel modulation scheme
called asymmetrically clipped DC-biased optical OFDM (ADO-
OFDM), which transmits ACO-OFDM on the odd subcarriers
and DCO-OFDM on the even subcarriers. Compared to ACO-
OFDM, ADO-OFDM uses all the subcarriers to carry data, so
the spectral efficiency is higher. However, this research is all
based on theoretical analysis and simulations, and lacks
experimental demonstration.
In this paper, for the first time as far as we know, we ex-
perimentally verify the performance improvement for a giga-
bit WDM VLC system using ACO-OFDM. We theoretically
analyze ACO-OFDM at first. Our investigation reveals that,
compared to DCO-OFDM, the advantages of ACO-OFDM
138 Photon. Res. / Vol. 2, No. 5 / October 2014 Wang et al.
2327-9125/14/050138-05 © 2014 Chinese Laser Press