Dimmable Visible Light Communication Research Articles

Capacity Results for Range-Limited SISO and MISO Dimmable VLC Channels

This paper investigates the capacity results of dimmable visible light communications (VLCs) channel under practical range-limited constraints. Upper and lower bounds for both single-input single-output (SISO) and multiple-input single-output (MISO) scenarios which are valid in all signal-to-noise (SNR) region are derived. We reveal that the SISO capacity is a symmetrical function of the dimming target, and is strictly increasing at its left half. Tight MISO upper bounds are obtained by solving non-convex problems, and alternating optimization method is employed with constraint transformations.

Dimmable Visible Light Communication Scheme Based on Punctured Polar Codes

Dimmable Visible Light Communication Scheme Based on Punctured Polar Codes

On Signal Quality Measures in Dimmable Visible Light Communications: Definitions and Conversions

This letter suggests the use of signal quality measures that accommodate various signaling configurations in dimmable visible light communications. Although a popular measure of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$E_{b} /N_{0}$ </tex-math></inline-formula> has still been used in the performance analysis of optical transmission techniques, it fails not only to capture essential physical characteristics in optical signals but also to reflect the dimming adjustment feature properly. This letter assesses various alternatives of the quality measure that have been used for optical communication signals and suggests to use a new measure of the ratio of bit peak signal level to noise standard deviation denoted by <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$A_{b} /\sigma $ </tex-math></inline-formula> . The proposed measure allows for the joint consideration of code rates and optical channel properties, such as dimming support and signal transmission based on intensity modulation and direct detection.

Bit Error Probability Performance of Binary Dimmable Visible Light Communication Systems

This paper evaluates the practically achievable best error performance obtained from a dimmable visible light communication (VLC) system that conveys information using binary modulations, such as on-off keying (OOK). As compared to previous studies that address the ideal performance of dimmable VLC systems only over reliable channels with arbitrarily small error probability, this paper presents the best achievable error probability of various configurations with the dimming targets, signal quality, and data rate. The numerical results establish the ultimate decoding error performance targeted for dimmable VLC systems and are expected to provide a practical guideline for the enhanced VLC system design.

Shaped polar codes for dimmable visible light communication

In this paper, the shaped polar codes scheme for dimmable visible light communication (VLC) is proposed for the first time. A precoder of shaped polar codes is used to realize dimming control by changing the probability of 1s in a codeword, which is equal to the dimming value in on–off keying (OOK) modulation VLC systems. Simulation results show that our shaped polar codes scheme can achieve about 2.5 dB and 2.8 dB higher coding gains compared to the low-density parity-check (LDPC) codes with compensation symbols scheme and the polar codes with compensation symbols scheme, respectively. Furthermore, the proposed scheme can still maintain satisfactory performance at higher information rates.

Joint multi-LED dimming control scheme based on the additively uniquely decomposable constellation group

As a novel mode of wireless communication, visible light communication (VLC) considers both communication and illumination. Dimming control is one of the essential functions of the systems. IEEE 802.15.7 group has proposed some dimming control schemes for point-to-point communication. However, there are few schemes designed for joint multi-LED dimmable VLC systems. In this thesis, a dimming control scheme has been proposed for joint multi-LED dimmable VLC systems by utilizing the channel state information (CSI) and data rates. By maximizing the minimum Euclidean distance (MED) of the received signal constellation, we design the optimal additively uniquely decomposable constellation group (AUDCG) under the dimming control constraint. Finally, we can conclude that the AUDCG scheme, which we introduced in this thesis, has better error performance than the scheme that combines time division multiplexing (TDM) and variable on–off keying (VOOK) for joint multi-LED dimmable VLC systems.

Dimming-Based Modulation Schemes for Visible Light Communication: Spectral Analysis and ISI Mitigation

Visible light communication (VLC) is being envisioned as an enabling technology to provide the much-needed spectral relief for the ever-increasing demand for Internet connectivity and data consumption. Since VLC uses illumination sources for lighting as well as communication, it is required to provide dimming control for proper lighting and enhanced error performance for reliable data communication. In this paper, we address both these issues holistically. We formulate and study the power spectral densities of dimming-based modulation schemes, namely variable on-off keying (VOOK) and variable pulse position modulation (VPPM), and hence, derive their bandwidth requirements and spectral efficiencies. Moreover, the capacity of VLC systems is severely limited by the inter-symbol interference (ISI) occurring as a result of the multipath propagation of light signals in VLC. We propose to ameliorate the error performance of VLC systems by using channel equalization for ISI mitigation, thereby enhancing the system capacity. We develop the analytical model of a dimmable VLC system employing channel equalization and use this model to study the effect of dimming and data rate on the error performance of VOOK and VPPM schemes. We present simulation and analytical results to show that the performance of dimming-based modulation schemes is significantly improved using channel equalization.

Dimming control scheme based on hybrid LACO-SCFDM for visible light communications

This paper proposes a hybrid layered asymmetrically clipped optical (HLACO) single-carrier frequency-division multiplexing (SCFDM) scheme for dimmable visible light communication. It designs a signal structure that combines layered asymmetrically clipped optical (LACO)-SCFDM and negative LACO-SCFDM in proportion for improving the inherent weaknesses of orthogonal frequency-division multiplexing (OFDM)-based dimmable schemes and further enhancing the system performance. Compared to the HLACO-OFDM-based dimming scheme, it obtains a lower bit error ratio and enables efficient communication over broader dimming range. Its spectral efficiency realizes 2.875 bit·s−1·Hz−1 within the dimming range of 30%–70%, and the attainable average spectral efficiency gains exceed at least 19.21% compared to other traditional dimmable schemes.

Constant Weight Space-Time Codes for Dimmable MIMO-VLC Systems

Visible light communication(VLC), which combines communication and illumination, is regarded as a potential wireless communication. For illumination requirements of VLC systems, dimming control is a significant function. Many schemes have been proposed for multi-input multi-output (MIMO) VLC systems or dimmable VLC systems, but few schemes combine the two. The dimming control scheme that has been proposed for MIMO-VLC systems in the reference still has a probability for improvement in spectral efficiency and error performance. This paper proposes a dimming control scheme that utilizes the constant weight space-time codes (CWSTC) to improve spectral efficiency and error performance for MIMO-VLC systems. Simultaneously, we also present the codeword structure and a low implementation complexity detection algorithm for the scheme. Finally, performance analysis and simulation results provide comparisons between the proposed scheme and other existing dimming control schemes.

Spectral-Efficient L/E-ACO-SCFDM-Based Dimmable Visible Light Communication System

In this paper, we propose a dimmable visible light communication (VLC) system based on spectral-efficient layered/enhanced asymmetrically clipped optical single-carrier frequency-division multiplexing (L/E-ACO-SCFDM). L/E-ACO-SCFDM superimposes multi-layer ACO-SCFDMs occupying different subcarriers for enhancing the spectral efficiency of the system. Both the adjustable layer polarities and the low peak-to-average-power ratio property of ACO-SCFDM make it better suited to the linearity-limited VLC system. Meanwhile, L/E-ACO-SCFDM has the signal-to-noise ratio averaging advantage, which can effectively resist the high-frequency distortion caused by the bandwidth limitation of the VLC system. Based on the maximization of spectral efficiency of the system, the layer amplitudes, layer spectral efficiencies, and bias voltage are jointly optimized for providing the efficient communication under different illumination requirements. Benefiting from the numerous strengths, the proposed L/E-ACO-SCFDM-based dimming scheme can achieve at least 22.0% average spectral efficiency gain compared with several state-of-the-art OFDM-based dimming schemes within the same dimming range, which shows the great superiority for future practical applications of VLC.

Binary signaling design for visible light communication: a deep learning framework.

This paper develops a deep learning framework for the design of on-off keying (OOK) based binary signaling transceiver in dimmable visible light communication (VLC) systems. The dimming support for the OOK optical signal is achieved by adjusting the number of ones in a binary codeword, which boils down to a combinatorial design problem for the codebook of a constant weight code (CWC) over signal-dependent noise channels. To tackle this challenge, we employ an autoencoder (AE) approach to learn a neural network of the encoder-decoder pair that reconstructs the output identical to an input. In addition, optical channel layers and binarization techniques are introduced to reflect the physical and discrete nature of the OOK-based VLC systems. The VLC transceiver is designed and optimized via the end-to-end training procedure for the AE. Numerical results verify that the proposed transceiver performs better than baseline CWC schemes.

Enhanced Multiple Pulse Position Modulation Aided Reverse Polarity Optical OFDM System With Extended Dimming Control

In this paper, we propose a multiple pulse position modulation (MPPM) aided reverse polarity optical orthogonal frequency division multiplexing scheme that aims to enhance the spectral efficiency (SE) for dimmable visible light communication (VLC) systems. In this scheme, we exploit the MPPM patterns to transmit the extra information bits without the increase of the signal bandwidth and, thus, improving the SE. Specifically, for each frame, the binary information stream is divided into two parallel groups, where the first group is used to select the patterns of MPPM symbols, while the other is modulated by optical OFDM. Then, the time-domain OFDM signal is accommodated by both the “on” and “off” slots of MPPM symbols for transmissions over the VLC channel. With the aid of a forward error correction aided decision feedback approach, the system performance can be further improved. Theoretical analyses on the dimming level, the average power consumption and the frame error probability are provided and verified by simulation results. It is shown that the proposed system with extended dimming control can achieve the highest effective spectral efficiency in most scenarios without substantially increasing the computational complexity, while still maintaining a power consumption level similar to those of the reference systems.

Fractional Reverse Polarity Optical OFDM for High Speed Dimmable Visible Light Communications

In this paper, fractional reverse polarity optical orthogonal frequency division multiplexing (FRPO-OFDM) is studied to enable dimming compatible visible light communications. The scheme combines a layered asymmetrically clipped optical OFDM (ACO-OFDM) sequence with an information-carrying brightness control sequence (BCS) in the form of $M$ -ary pulse position modulation. We derive the expressions of the FRPO-OFDM signal and its achievable brightness level, and develop an effective detector which can recover information from both sequences based on maximum likelihood detection. We show that when the detector is to be implemented, the use of multi-layer ACO-OFDM imposes strong periodicity on the BCS, which leads to a trade-off between spectral efficiency and brightness resolution for dimming control. It is shown that high spectral efficiency can be achieved with practical dimming requirements. Simulation results show that the extra information carried by the BCS can be decoded with extremely low bit error rate and thus has negligible impacts on the demodulation of the ACO-OFDM signal, when the system nonlinearity is not dominating.

On Optimal Non-Equally Spaced M-PAM in Dimmable Visible Light Communication

In this letter, channel capacity of dimmable visible light communication systems with M-ary pulse amplitude modulation (M-PAM) channel input alphabets is investigated. Mutual information is maximized considering both the probability input distribution and the M-PAM levels simultaneously. Schemes with non-equally spaced M-PAM levels are obtained as a result of this maximization process and they lead to gains in capacity when compared with previous schemes proposed in the literature.

A Spectral-Efficient Transmission Scheme for Dimmable Visible Light Communication Systems

Dimming control is of vital importance for visible light communication (VLC) systems. Conventional dimmable transmission schemes based on compensation are spectrally inefficient. In this paper, we propose the use of two techniques, i.e., time-sharing and superposition, to construct spectral-efficient dimmable transmission schemes. For VLC systems with on–off keying (OOK) signaling, we present a general framework to construct dimmable transmission scheme by time-sharing among different dimming control codes. Arbitrary dimming target is achieved by adjusting the proportion of each dimming control code. We, then, give a practical construction of dimming control codes with semi-constant weight codes. We obtain optimal proportions of the semi-constant weight codes, which maximize the asymptotic spectral efficiency using linear programming. We also compute achievable rates of the proposed scheme under different dimming targets and different signal-intensity-to-noise-amplitude ratios. To achieve higher spectral efficiency ( $>$ 1.0 (b/s)/Hz), we present a dimmable multilevel transmission scheme based on superposition. In the proposed scheme, the first $\ell$ $-1$ levels adopt traditional OOK modulation, whereas the $\ell$ th level adopts the dimmable transmission scheme for OOK modulation. The transmitted signal is formed by superimposing modulated signals of the $\ell$ levels. Analysis shows that the proposed scheme achieves a higher spectral efficiency than the state-of-the-art schemes. Hence, it provides an attractive candidate for dimmable VLC systems with demanding spectral efficiency.

PAM sequence design for dimmable visible light communication

In current visible light communication (VLC) systems employing intensity modulation and direct detection (IM/DD), the transmitted optical intensity signal must satisfy the nonnegativity, peak optical intensity and illumination constraints. By taking into account the three constraints, we first present the signal space for the pulse amplitude modulated (PAM) sequences in the maximum flickering time period (MFTP). Then, to minimize the error probability of the VLC systems, we seek to find the PAM sequences providing the largest minimum Euclidean distance. Since the objective function is nonconvex and nondifferentiable, it is difficult to solve the original optimization problem directly. Thus, two methods corresponding to the joint design and greedy algorithm, are proposed to design the PAM sequences in VLC. The two methods offer a tradeoff between the symbol error rate (SER) performance and design complexity.

A Serial Concatenation-Based Coding Scheme for Dimmable Visible Light Communication Systems

Dimming control is desirable for visible light communication (VLC) systems to provide different levels of brightness. In this letter, we propose a new coding scheme for dimmable VLC systems based on serial concatenation of column-scaled (CS) low-density parity-check (LDPC) codes and constant weight codes (CWCs). In the proposed scheme, the cardinality of the finite field on which the CS LDPC code is defined varies adaptively according to the CWC. Hence, transformation between symbol metrics and bit metrics is avoided. Other advantages of the proposed scheme are described as follows: 1) its coding rates are not constrained by the dimming range as error control and dimming control are decoupled; 2) it can be easily configured to support a wide range of dimming targets; and 3) it requires essentially the same hardware architecture to implement the encoder/decoder pair. Hence, the proposed coding scheme provides an attractive candidate for VLC systems with both error and dimming control.

An Efficient Flicker-Free FEC Coding Scheme for Dimmable Visible Light Communication Based on Polar Codes

Visible light communication (VLC) could provide short-range optical wireless communication together with illumination using LED lighting. However, conventional forward error correction (FEC) codes for reliable communication do not have the features for dimming support and flicker mitigation which are required in VLC for the main functionality of lighting. Therefore, auxiliary coding techniques are usually needed, which eventually reduce the coding efficiency and increase the complexity. In this paper, a polar codes-based FEC coding scheme for dimmable VLC is proposed to increase the coding efficiency and simplify the coding structure. Experimental results show that the proposed scheme has the following advantages: 1) equal probability of 1's and 0's in codewords, which is inherently supporting 50% dimming balance; 2) short run length property (about 90% bits have runs shorter than 5) which can avoid flickers and additional run-length limited line coding; 3) higher coding efficiency about twofold than that of other coding schemes; 4) capacity achieving error correction performance with low-complexity encoding and decoding, which is about 3 dB higher coding gain than that of RS(64,32) in IEEE standard for dimming ratio 50% and about 1 dB higher coding gain than that of LDPC codes for dimming ratio 25% (or 75%).

Convex Optimization Approach to Multi-Level Modulation for Dimmable Visible Light Communications under LED Efficiency Droop

This paper deals with a design method and capacity loss of an efficient multi-level modulation scheme for dimmable visible light communications (VLC) systems that use light-emitting diodes (LEDs) with efficiency droop. To this end, the impact of such an impairment on dimmable VLC is addressed with respect to multi-level modulations based on pulse-amplitude modulation (PAM) via data-rate optimization formulation.

Asymmetrical Hybrid Optical OFDM for Visible Light Communications With Dimming Control

This letter proposes an asymmetrical hybrid optical orthogonal frequency division multiplexing (AHO-OFDM) scheme for dimmable visible light communication systems. In the proposed scheme, either asymmetrically clipped optical OFDM (ACO-OFDM) or pulse-amplitude-modulated discrete multitone (PAM-DMT) signal is inverted and then both the signals are combined for transmission, where pulsewidth modulation is no longer required for dimming control. The power of ACO-OFDM and PAM-DMT signals is adjusted so that the amplitude of the combined AHO-OFDM signal is asymmetrical, which could utilize all the available subcarriers as well as the entire dynamic range of light-emitting diodes with various dimming levels. Simulation results show that the proposed scheme could achieve a wide dimming range with a small throughput fluctuation.