24-12-2012, 02:57 PM
10m/500Mbps WDM visible light communication systems
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Abstract:
A wavelength-division-multiplexing (WDM) visible light
communiction (VLC) system employing red and green laser pointer lasers
(LPLs) with directly modulating data signals is proposed and
experimentally demonstrated. With the assistance of preamplifier and
adaptive filter at the receiving sites, low bit error rate (BER) at
10m/500Mbps operation is obtained for each wavelength. The use of
preamplifier and adaptive filter offer significant improvements for freespace
transmission performance. Improved performance of BER of <10−9,
as well as better and clear eye diagram were achieved in our proposed
WDM VLC systems. LPL features create a new category of good
performance with high-speed data rate, long transmission length (>5m), as
well as easy handling and installation. This proposed WDM VLC system
reveals a prominent one to present its advancement in simplicity and
convenience to be installed.
Introduction
Visible light communication (VLC) systems are presently being developed by researchers
seeking to create high-speed, high security, and friendly communication networks using large bandwidth visible light instead of radio-frequency (RF) and microwave signals. It has many
attractive features, such as worldwide available and unlicensed bandwidth, non-interference
with radio bands, and the potential of spatial reuse of operating frequencies in adjacent
communication cells. Moreover, VLC systems can provide many benefits, like: providing
communication link in specific areas in which RF communication is prohibited, such as in a
hospital or in an aircraft; providing a secure link channel since the light beam is visible and
directional [1–6]. VLC systems use modulated light wavelengths emitted and received by a
variety of suitably adapted standard sources, such as indoor and outdoor lighting, display,
illuminated sign, television, computer screen, digital camera and digital camera on mobile
phone for communication purposes, primarily through the use of light emitting diode (LED).
With the rapid progress of VLC systems, the increasing requirements raise the needs for highspeed
transmission rate. LED VLC systems are recognized as creating a possible valuable
addition to future generations of technology, which have the potential to use light for the
purposes of advanced technical communication at high-speed surpassing that of current
wireless communication systems. In the previous studies, high-brightness LED (HB-LED) is
employed not only as the lighting devices but also as the light sources for LED VLC systems
[7, 8].
Experimental setup
The experimental configuration of our proposed WDM VLC systems employing red and
green LPLs with directly modulating data signals over a 10-m free-space link is shown in the
Fig. 1. The LPLs, with wavelength/color/power of 671nm/red/5mW and 532nm/green/5mW,
were directly modulated by a 500 Mbps pseudorandom binary sequence (PRBS) of 210-1
generated by a Tektronix arbitrary waveform generator (AWG) with a 1 × 2 splitter. The
modulated red and green lights were transmitted over a distance of 10 m, and then reached to
the PIN-photodiodes (PIN-PDs). The PIN-PD has the detection wavelength range of 350-
1100 nm, with a responsivity of 0.65 mA/mW. The received signals were then amplified by
the preamplifiers with low noise figure of around 4.5 dB, and passed through the adaptive
filters for errors corrections. The performance and accuracy of the adaptive filter depends on
the data length. In this experiment, we use 210-1 PRBS length (not 215-1 or 223-1); for the
same number of filter taps, lower data length results in better performance and accuracy. The
two 500 Mbps data signals were multiplexed together by a 2 × 1 multiplexer. Finally, the data
signals were fed into a BER tester (BERT) for BER analysis and an oscilloscope for eye
diagram evaluation.
Conclusions
We proposed and demonstrated a WDM VLC system using red and green LPLs with directly
modulating data signals. With the help of preamplifier and adaptive filter t the receiving sites,
low BER of <10−9 at 10m/500Mbps operation is obtained for each wavelength. The use of
preamplifier and adaptive filter offer significant improvements for free-space transmission
performance. Improved performance of BER of <10−9, as well as better and clear eye diagram
were achieved in our proposed WDM VLC systems. Employing LPLs in VLC systems is a
promising option, an attractive feature that could accelerate the VLC deployment. This
proposed that such a WDM VLC system has been successfully demonstrated, which can interoperate
with free-space lightwave transport applications.