Shangbin Li

Power and Rate Optimization for Visible Light Communication System With Lighting Constraints

Visible-light communication (VLC) will be deployed in various indoor environments, including those requiring different lighting colors, which imposes the needs for transmission optimization under certain lighting constraints. This work establishes a framework for the transmission power and rate optimization, for light emitting diode (LED)-based VLC systems under lighting constraints. We describe the system model of LED-based color-division VLC system, which incorporates the transmission power spectral density, the receiving optical filters, the human eye perception, and the lighting constraints. Then, we formulate the corresponding power and rate optimization problems, for both point-to-point communication system and broadcast communication system. More specifically, for a point-to-point communication system, it maximizes the transmission rate subject to the transmission power constraint and the lighting constraint; and for a broadcast system, it minimizes the total transmission power subject to some quality of service (QoS) constraint across all receivers. Various convex optimization problems have been formulated and solved analytically or using standard convex optimization solutions. It is obsesrved that the optimal symbol modulation power allocation scheme significantly outperforms the equal power allocation scheme.

DD-informative modulation for visible light communications under lighting constraints

Visible light communication employs low-cost intensity modulation and direct detection, where positive time-domain baseband signals are generated to drive LEDs through addition of a DC bias. However, the non-informative bias in this straightforward and easy-to-implement approach significantly reduces the system energy efficiency. In this article, new energy-efficient modulation schemes leveraging informative DC-bias are introduced. Under some lighting constraints, a convex optimization problem is formulated. Optimal constellations are constructed in either the time domain or frequency domain by compact sphere packing. Several DC-informative system architectures are then discussed. Finally, technical implementation challenges are investigated.

Signal Characterization and Receiver Design for Visible Light Communication Under Weak Illuminance

We characterize the received signals and propose corresponding detection methods for the visible light communication under weak illuminance. Photo-multiplier tube is employed as the receiver, which can amplify weak photon-level signal down to a series of electrons. It is observed that under the extremely low transmission power, the received signals can be characterized by the discontinuous pulses. As the received power increases, the density of the pulses increases, and finally, the received signals form continuous waveforms. We provide the sampling-based and pulse counting-based transmitted symbol detection methods for the continuous signal waveform and the discontinuous pulses, respectively. We further improve the symbol detection performance by combining the two types of detection schemes. Numerical results show that the pulse counting detection can outperform the sampling-based detection with lower sampling rate, and the combined detection can improve the detection performance.

A 51.6 Mb/s Experimental VLC System Using a Monochromic Organic LED

An organic light emitting diode (OLED) shows characteristics different from a traditional semiconductor LED when both are applied to visible light communication (VLC). This paper first experimentally characterizes its static and dynamic communication properties with varying input signals. This band-limited and power-limited light source leads to unique communication channel and noise models. Accordingly, the orthogonal frequency-division multiplexing in conjunction with offset quadrature amplitude modulation (OFDM-OQAM) is applied, and its performance is compared against the traditional dc-biased optical OFDM. To further enhance the communication performance, a bit and power loading algorithm and a proper equalization algorithm are jointly implemented to combat the channel frequency selectivity and increase the data rate. A bit-rate of 51.6 Mb/s based on a monochromic OLED is experimentally achieved through the proposed design. The rate is comparable to the multicolor OLEDs-based VLC link in the literature.

Visible light communication performance in weak illumination environment

We consider the visible light communication in extremely weak illumination environment. The system consists of an LED transmitter and a photomultiplier tube (PMT) receiver. We also show the bit-error rate (BER) of the signal detection.

Power and rate optimization for visible light communication system with lighting constraints

Visible-light communication (VLC) will be deployed in various indoor environments, including those requiring different lighting colors, which imposes the needs for transmission optimization under certain lighting constraints. This work establishes a framework for the transmission power and rate optimization, for light emitting diode (LED)-based VLC systems under lighting constraints. We describe the system model of LED-based color-division VLC system, which incorporates the transmission power spectral density, the receiving optical filters, the human eye perception, and the lighting constraints. Then, we formulate the corresponding power and rate optimization problems, for both point-to-point communication system and broadcast communication system. More specifically, for a point-to-point communication system, it maximizes the transmission rate subject to the transmission power constraint and the lighting constraint; and for a broadcast system, it minimizes the total transmission power subject to some quality of service (QoS) constraint across all receivers. Various convex optimization problems have been formulated and solved analytically or using standard convex optimization solutions. It is obsesrved that the optimal symbol modulation power allocation scheme significantly outperforms the equal power allocation scheme.

Volterra-based nonlinear equalization for nonlinearity mitigation in organic VLC

Organic light emitting diodes (OLEDs) show promising applications due to their unique advantages compared with conventional commercial LEDs. In OLED-base visible light communication (VLC), the nonlinearity may severely degrade the system performance, especially for modulation format with high peak to average power ratio (PAPR) such as orthogonal frequency-division multiplexing (OFDM). We experimentally analyze the OLED nonlinearity by Volterra series and apply the Volterra-based nonlinear equalizer to demodulate the signal. It is shown that the proposed system achieves transmission distance of 3 meters, which exceeds the longest reported in the organic VLC literature. It can mitigate both inter-symbol interference (ISI) and nonlinearity more effectively than other equalizers. Experimental results at different distance and driving voltage are also reported.

Hidden Markov Model-Based Signal Characterization for Visible Light Communication under Weak Illuminance

Weak illumination by light emitting diode (LED) can be realized by either peak-power transmission at a low duty cycle or low-power transmission at a regular duty cycle. In this paper, we address the signal characterization and transmission rate of visible light communication for the latter case. We first characterize the LED nonlinear effect via a state transition model based on the experimental measurements. Then, we adopt hidden Markov model (HMM) to characterize the LED transmission under weak illumination. Based on the HMM, we propose a Monte Carlo method to compute the achievable transmission rate and apply Viterbi algorithm to detect the signals. The achievable transmission rates and detection performance of the HMM-based model are evaluated by simulation results. Moreover, both numerical and experimental results show lower bit error rate of the Viterbi algorithm compared with the per symbol detection.

Visible light communication optimization under lighting constraints

A framework for the transmission power and rate optimization is established for light emitting diode (LED)-based visible light communication systems under lighting constraints.