Experimental demonstration of an adaptive orthogonal
frequency division multiplexing visible light
communication system
Xinyue Guo (郭心悦)* and Xin Li (李 鑫)
Shanghai Key Lab of Modern Optical Systems, School of Optical-Electrical and Computing Engineering,
University of Shanghai for Science and Technology, Shanghai 200093, China
*Corresponding author: guoxinyue21@163.com
Received July 17, 2016; accepted September 23, 2016; posted online October 26, 2016
We propose and experimentally demonstrate a simple visible light communication system by combining an adap-
tive transmission technique with orthogonal frequency division multiplexing. In the adaptive transmission
scheme, power allocation is performed in such a way as to maximize the channel capacity under electric power
constraints, and adaptive modulation is then introduced to achieve the maximum data rate given a target bit
error rate. Experimental results show that spectrum efficiency can be greatly improved through this adaptive
transmission technique.
OCIS codes: 060.2605, 060.4080.
doi: 10.3788/COL201614.110604.
Recently, visible light communication (VLC) based on
white light-emitting diodes (LEDs) is garnering increasing
attention in both academia and industry
[1–4]
. With the ben-
efits of being cost effe ctive, license free, electromagnetic
interference free, and highly secure, it is one of the most
compelling technologies for supplementing traditional ra-
dio frequency communication, especially in areas such as
hospital, aircraft, and high-security environments
[5,6]
; how-
ever, the data rate of the VLC link is limited by the modu-
lation bandwidth of the high-brightness LEDs used in
light fixtures and lamps. Due to the power–bandwidth
trade-off of LEDs and various parasitic impedances in
the LED packaging, signals modulated at high frequencies
are strongly attenuated
[2]
. As a result, the frequency re-
sponse of the LED is not flat, which causes serious inter-
symbol interference (ISI) for high-speed transmissions.
The orthogonal frequency division multiplexing (O FDM)
scheme has been proposed to improve the data rate, and
has proved particularly convenient for VLC systems
because it decomposes the channel into multiple parallel
frequency-flat subchannels to eliminate ISI
[7–10]
.
Adaptive transmission techniques have also been
recently introduced to improve spectrum efficiency.
Wu et al. provide an in-depth theoretical analysis of adap-
tive modulation for high-speed VLC
[11]
. Park et al. propose
a VLC transmission power optimization scheme that min-
imizes the bit error rate (BER)
[12]
. A framework for trans-
mission power and rate optimization is built under certain
lighting constraints in Ref. [
13]. All these works prove that
high data rates can theoretically be achieved over such
limited bandwidths by using adaptive transmission tech-
niques; however, adaptive VLC system design and the ex-
perimental demonstration are not referenced. Chow et al.
propose and demonstrate an adaptive control of the OFDM
modulation order to maintain the VLC transmission
performance
[14]
, where the modulation order is adapted ac-
cording to the received signal-to-noise ratio (SNR) and the
same modulation order is used in all the subcarriers. After-
ward, Yeh et al. provide an adaptive OFDM scheme where
the bit loading is introduced to obtain the optimal SNR
of each subcarrier
[15]
. Both schemes are practical and the
system performance can be greatly improved; however,
the maximum spectrum efficiency is not achieved.
In this Letter, we propose and experimentally demon-
strate a simple VLC system by combining an adaptive
transmission technique with OFDM. A realizable adaptive
transmission technique is proposed for an OFDM-based
VLC system that is aimed at spectrum efficiency maximi-
zation under the constraints of power and the target BER.
The adaptive OFDM scheme is implemented by two steps.
The first step is power allocation. Power is allocated
to each frequency-flat subchannel based on the idea of
maximizing the channel capacity under electric power
constraints. The second step is adaptive modulation.
Maximum spectrum efficiency under certain BER con-
straints is achieved by adaptive modulation. Different
modulation orders are determined for each subchannel
according to a target BER and SNR. Then an experimen-
tal demonstration is set up to verify the effectiveness of the
proposed adaptive VLC system. Experimental results
show that the adaptive transmission scheme can greatly
improve the spectrum efficiency as compared to the sys-
tem without adaptive transmission.
A block diagram of the OFDM-based VLC system using
the adaptive transmission technique is presented in Fig.
1.
In the system, OFDM modulation is employed to elimi-
nate the ISI and increase the data rate. An adaptive trans-
mission scheme containing power allocation, adaptive
modulation, and power control is proposed to increase
the data rate further.
COL 14(11), 110604(2016) CHINESE OPTICS LETTERS November 10, 2016
1671-7694/2016/110604(5) 110604-1 © 2016 Chinese Optics Letters