Qian Gao

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.

User Grouping and Power Allocation for NOMA Visible Light Communication Multi-Cell Networks

To design an efficient multiple access scheme for visible light communication (VLC) multi-cell networks, this letter leverages the non-orthogonal multiple access (NOMA), which has received significant attention in the 5th generation wireless communication. A user grouping based on user locations is proposed to reduce interference for VLC multi-cell networks. With the residual interference from the successive interference cancellation in NOMA taken into account, we optimize the power allocation within each cell to improve the achievable user rate under user quality of service constraint. The performance of the proposed approaches is evaluated by the numerical results.

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.

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.

Analysis and design of amplitude modulation for optical wireless communication with shot noise

This paper addresses the analysis and design of amplitude modulation in optical wireless scattering communication with Poisson channel and shot noise. We show that the detection error probability of the receiver with photoelectric conversion and post-processing circuits cannot be lower than that of the photon-counting receiver. We also provide an upper bound on the error detection probability, based on the Chebyshevs inequality. According to the proposed upper bound, we provide the modulation signal constellation, with equal space between the squared roots of the signal power levels, instead of between the signal power levels. We prove that the upper bound can approach zero as the transmission power approaches infinity. In numerical evaluations, under the same peak power constraint, the proposed signal constellation shows smaller detection error probability and larger capacity compared with the signal constellation with equal space between the signal power levels. Numerical results also show that the modulation with 4 power levels suffice except for high transmission power and small path loss in the optical wireless scattering communication.

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.

Joint Transceiver and Offset Design for Visible Light Communications With Input-Dependent Shot Noise

In this paper, we investigate the problem of the joint transceiver and offset design for point-to-point multiple-input–multiple-output (MIMO) and multiple user multiple-input–single-output visible light communication (VLC) systems. Both uplink and downlink multi-user scenarios are considered. The shot noise induced by the incoming signals is considered, leading to a more realistic MIMO VLC channel model. Under key lighting constraints, we formulate non-convex optimization problems aimed at minimizing the sum mean squared error. To optimize the transceiver and the offset jointly, a gradient projection-based procedure is resorted to. When only imperfect channel state information is available, a semidefinite programming-based scheme is proposed to obtain robust transceiver and offset. The proposed method is shown to non-trivially outperform the conventional scaled zero forcing and singular. value decomposition-based equalization methods. The robust scheme works particularly well when the signal is much stronger than the noise.

Joint Transceiver and Offset Design for Visible Light Communications with Input-Dependent Noise

In this paper, we investigate the problem of the joint transceiver and offset design for point-to-point multiple-input–multiple-output (MIMO) and multiple user multiple-input–single-output visible light communication (VLC) systems. Both uplink and downlink multi-user scenarios are considered. The shot noise induced by the incoming signals is considered, leading to a more realistic MIMO VLC channel model. Under key lighting constraints, we formulate non-convex optimization problems aimed at minimizing the sum mean squared error. To optimize the transceiver and the offset jointly, a gradient projection-based procedure is resorted to. When only imperfect channel state information is available, a semidefinite programming-based scheme is proposed to obtain robust transceiver and offset. The proposed method is shown to non-trivially outperform the conventional scaled zero forcing and singular. value decomposition-based equalization methods. The robust scheme works particularly well when the signal is much stronger than the noise.

Optical interference alignment for an indoor visible light communication X-channel

In visible light communication (VLC) networks, signals from densely deployed light sources strongly interfere with each other. Proper interference management is expected to improve the VLC system performance. In this article, we propose an optical interference alignment (OIA) approach to minimize mutual interference, where the conventional decoding-as-noise scheme is not applicable. A concrete algorithm is provided under lighting constraints with guaranteed decoding error probability. Numerical results demonstrate the significant performance gain offered by this scheme.