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ABSTRACT: We investigate the performance of visible light communication (VLC) system with a pulse width modulation (PWM) dimming control scheme. Under this scheme, the communication quality in terms of number of transmitted bits and bit error rate (BER) of less than 10<sup>-3</sup> should be guaranteed. However, for on-off-keying (OOK) signal, the required data rate becomes 10 times as high as the original data rate when the duty cycle of dimming control signal is 0.1. To make the dimming control scheme easy to be implemented in VLC system, we propose the variable M-QAM OFDM VLC system, where M is adjusted according to the brightness of LED light in terms of duty cycle. The results show that with different duty cycles the required data rates are not higher than the original value and less LED lamp power is required to guarantee the communication quality, which makes the dimming control system that satisfies both communication and illumination requirements easy to be implemented and power-saving.
Optics Express 08/2012; 20(17):18861-8. · 3.59 Impact Factor
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ABSTRACT: This paper investigates the performance of our recently proposed LED lamp arrangement to reduce the SNR fluctuation from different locations in the room for multi-user visible light communications. The LED lamp arrangement consists of 4 LED lamps positioned in the corners and 12 LED lamps spread evenly on a circle. Our studies show that the SNR fluctuation under such a LED lamp arrangement is reduced from 14.5 dB to 0.9 dB, which guarantees that users can obtain almost identical communication quality, regardless of their locations. After time domain zero-forcing (ZF) equalization, the BER performances and channel capacities of 100-Mbit/s and 200-Mbit/s bipolar on-off-keying (OOK) signal with most significant inter-symbol interference (ISI) are very close to that of the channel without any ISI caused by this LED lamp arrangement.
Optics Express 02/2012; 20(4):4564-73. · 3.59 Impact Factor
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ABSTRACT: We propose a scheme to improve the SNR distribution as well as the spectral efficiency of M-QAM OFDM signal for indoor visible light communication by tilting the receiver plane. Newton method is employed for the photo-detector to receive maximum power by finding the optimal tilting angle. This method is a fast algorithm that only three searching steps are needed. The simulation results show that in the case of one LED source, the maximum spectral efficiency improvement is 0.44bit/s/Hz when the launching power of LED source is 12W; while in the case of four LED sources, the maximum spectral efficiency improvement is 0.21bit/s/Hz when the total launching power of the four LED sources is 12W.
Optics Express 07/2011; 19(14):13418-27. · 3.59 Impact Factor
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ABSTRACT: The bit-error rate (BER) expressions of 16- phase-shift keying (PSK) and 16- quadrature amplitude modulation (QAM) are analytically obtained in the presence of a phase error. By averaging over the statistics of the phase error, the performance penalty can be analytically examined as a function of the phase error variance. The phase error variances leading to a 1-dB signal-to-noise ratio per bit penalty at BER=10(-4) have been found to be 8.7 x 10(-2) rad(2), 1.2 x 10(-2) rad(2), 2.4 x 10(-3) rad(2), 6.0 x 10(-4) rad(2) and 2.3 x 10(-3) rad(2) for binary, quadrature, 8-, and 16-PSK and 16QAM, respectively. With the knowledge of the allowable phase error variance, the corresponding laser linewidth tolerance can be predicted. We extend the phase error variance analysis of decision-aided maximum likelihood carrier phase estimation in M-ary PSK to 16QAM, and successfully predict the laser linewidth tolerance in different modulation formats, which agrees well with the Monte Carlo simulations. Finally, approximate BER expressions for different modulation formats are introduced to allow a quick estimation of the BER performance as a function of the phase error variance. Further, the BER approximations give a lower bound on the laser linewidth requirements in M-ary PSK and 16QAM. It is shown that as far as laser linewidth tolerance is concerned, 16QAM outperforms 16PSK which has the same spectral efficiency (SE), and has nearly the same performance as 8PSK which has lower SE. Thus, 16-QAM is a promising modulation format for high SE coherent optical communications.
Optics Express 06/2010; 18(12):12088-103. · 3.59 Impact Factor
