02-03-2013, 04:21 PM
1.1-Gb/s White-LED-Based Visible Light Communication Employing Carrier-Less Amplitude and Phase Modulation
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Abstract
We demonstrate 1.1-Gb/s visible light communication
(VLC) employing carrier-less amplitude and phase
modulation (CAP) and a commercially available phosphorescent
white light emitting diode (LED). Optical blue filtering, precompensation,
and decision feedback equalization are used to
compensate the frequency response of the phosphor-based white
LED. Various modulation orders of CAP signals are investigated
to maximize the capacity of the VLC system. The record data rate
of 1.1 Gb/s with the bit error rate performance below the FEC
limit of 10−3 is successfully achieved >23-cm air-transmission
via a 220-MBaud 32-CAP signal.
INTRODUCTION
WHITE light emitting diodes (LEDs) have attracted lots
of attention for next generation illumination due to
advantages such as long lifetime, high efficiency, cost effectiveness,
small size and low power consumption, compared
with incandescent or fluorescent lamp. Hence, LEDs have
been widely used in traffic application, flat panel displays, and
illumination application. To add the value to LED illumination,
visible light communications (VLC) with white LEDs have
attracted considerable interests in next generation short range
wireless access because of the advantages of worldwide availability,
high security, immunity to radio frequency interference,
unlicensed spectrum, and spatial reuse of the modulation
bandwidth in adjacent communication cells [1]–[3].
PRINCIPLE OF THE CAP TRANSCEIVER SYSTEM
Since a directly-modulated LED is an intensity modulator,
complex vector signals, such as QAM, must be up-converted
to an RF frequency at the transmitter in the traditional scheme
[10]. However, it is not ideal for direct-detection systems with
very limited bandwidth, such as VLC systems. Alternatively,
spectrally-efficient CAP is closely related to the well-known
QAM, and they have the same spectral characteristics and
theoretical performance [11]. The CAP modulation, however,
is carrier-less, and as a consequence, it is more suitable for a
band-limited intensity-modulated SC system. The block diagram
of the digital CAP transmitter is shown in Fig. 1(a). The
bit stream s[n] is passed through an encoder, and mapped into
two uncorrelated multi-level digital data, i [n] and q[n], which
denote the in-phase and the quadrature signals, respectively.
EXPERIMENTAL SETUP
Fig. 2(a) shows the experimental setup of the VLC system.
The CAP signal is generated by an arbitrary waveform
generator (AWG) with an off-line Matlab program [10]. The
roll-off parameter is set to zero. The sampling rate and the
DAC resolution are 1 GSample/s and 8 bit, respectively. A
phosphorescent white LED module (OSTAR LE CWE3B) is
adopted as the VLC transmitter. This LED consists of six
chips, and the viewing angle is 130° (full opening angle at
50% maximum intensity). The separating distance between the
transmitter and receiver is 23 cm.
CONCLUSION
In this letter, we experimentally demonstrate a VLC
system based on the CAP modulation with a commerciallyavailable
phosphorescent white LED. Optical blue filter, precompensation,
and DFE are utilized to improve the frequency
response of the VLC system. The maximum symbol rates to
achieve the BER of < 10−3 are measured under different
modulation orders, and they are 110-MBaud, 170-MBaud
and 220-MBaud for 128-CAP, 64-CAP and 32-CAP signals,
respectively. In addition, the record data rate of 1.1 Gbps is
successfully demonstrated.