Visible Light Communication Modulation Research Articles

Enhanced Modulation Bandwidth by Integrating 2D Semiconductor and Quantum Dots for Visible Light Communication

Light‐emitting devices present a tremendous potential for visible light communication (VLC) due to their dual functionality as both communication and lighting devices. Herein this study, the significant enhancement in VLC modulation bandwidth by integrating two‐dimensional (2D) semiconductor and quantum dots (QDs) emitter is reported. Generally, the modulation bandwidth of CdSe‐based QDs is limited to only less than 25 MHz; however, with the proposed hybrid emitter, a maximum modulation bandwidth of 130 MHz for CdSe/ZnS QDs emitter is able to be achieved. The WSe2 monolayer is integrated into an Au–nanorod–decorated CdSe/ZnS QDs emitter to achieve high modulation performance. The modulation bandwidth of the hybrid QD–Au–WSe2 emitter (130 MHz) is found to be higher than those of the pristine QDs and QD–WSe2 heterostructure without Au nanorods (79 and 91 MHz, respectively). A significant increase is observed in the transition rate of QDs excitons when they are integrated with Au nanorods and WSe2 monolayer, which is substantiated by a reduction in average carrier lifetime from time‐resolved photoluminescence analysis. This approach and the findings open an opportunity to apply 2D semiconductors into the next‐generation miniature VLC devices, for high‐speed optical communications.

3D indoor positioning with spatial modulation for visible light communications

In this paper, a novel three-dimensional (3D) indoor visible light positioning (VLP) algorithm is proposed based on the spatial modulation (SM) and its error performance assessed as compared to the conventional received signal strength (RSS)-based 3D VLP systems. As contrasted to the traditional VLP system, the proposed SM-based 3D VLP system first estimates the optical channel gain between the transmitting light-emitting diodes (LEDs) and the two photo detectors (PDs) attached to the user by a pilot-based channel estimation technique. Then, unknown 3D positions of the receiver are determined by the trilateration algorithm with distances computed from the estimates of the channel gains. Consequently, the 3D VLP system achieves an interference-free transmission with increased spectral efficiency and without the need for a demultiplexing process at the receiving end. The algorithm’s performance is evaluated regarding positioning error by applying the SM over four LEDs and the number of pilots selected as a function of the environmental signal-to-noise ratios (SNRs). The computer simulation results show that the positioning errors are obtained in an order of magnitude smaller than RSS-based techniques in an indoor industrial environment. This is mainly because the distances involved in determining the 3D positions can be determined more precisely by the pilot-aided channel estimation method without creating any data rate problem in transmission due to the higher spectral efficiency of the SM.

A survey on the integration of visible light communication with power line communication: Conception, applications and research challenges

The extensive enhancement of wireless communication industry over the last decade revolutionized the change of our daily life. In this scenario, it becomes utmost difficult for the network providers to cater the needs of the end users. Consequently, this mandates the necessity to rely on alternative communication-based technologies. Therefore, one such communication is visible light communication (VLC) which is regarded as a promising complement to radio frequency (RF) based wireless communication. The renowned nature of VLC is that it renders simultaneous illumination and communication by utilizing light emitting diodes (LEDs). However, VLC by itself cannot be employed directly as an information source. Therefore, this necessitates for VLC to be connected to a backhaul network to furnish communication. Based upon these grounds, power line communication (PLC) turns out to be the most feasible communication technology which reinforces as an excellent communication backbone for VLC systems. Predominantly, the inherent benefit offered by the integrated PLC–VLC systems is that the existing power line infrastructure can be leveraged to supply power to the LED, while the energy-efficient LED-based illumination systems render wireless support. Accordingly, this paper presents a comprehensive review of the integrated PLC–VLC systems, physical layer aspects which includes detailed study on PLC–VLC channel modeling and modulation techniques. In addition, this survey focuses in detail on the multiple access techniques and clearly discusses several technical aspects that are associated with the cascaded PLC–VLC systems as well as highlights the current state-of-the-art research aspects in the directions of hybrid PLC-VLC-RF systems. Additionally, this survey outlines the societal applications of PLC–VLC systems which includes the applications of PLC–VLC in hospitals, aircrafts, military, Internet of Things (IoT) devices, etc., as well as summarizes the challenges that are of paramount important while designing high speed integrated PLC–VLC systems.

Spectral-Efficient PAM Modulations for Dimmable Visible Light Communication Systems

In visible light communications (VLC), the bulbs are used to provide communication and illumination simultaneously. Therefore, it is important to design modulation schemes, which are capable of adjusting the illumination level. The simplest approach to achieve this is compensating an all-one or an all-zero sequence, which however is spectrally inefficient. In this paper, we propose to use the constant sum codes to construct spectral-efficient dimmable pulse amplitude modulation (PAM) for VLC. We also present an efficient algorithm based on graph expanding to design the mapping for the proposed dimmable PAM. Numerical results show that the spectral efficiencies of the proposed dimmable PAM are higher than those of the state-of-the-arts. Numerical results also show that the proposed dimmable PAM performs better than the state-of-the-arts in coded VLC. These results show the potential advantages of the proposed dimmable PAM.

Visible Light Communication Based Vehicle Localization for Collision Avoidance and Platooning

Collision avoidance and platooning applications require vehicle localization at cm-level accuracy and at least 50 Hz rate for full autonomy. The RADAR/LIDAR and camera based methods currently used for vehicle localization do not satisfy these requirements, necessitating complementary technologies. Visible light positioning (VLP) is a highly suitable complementary technology due to its high accuracy and high rate, exploiting the line-of-sight propagation feature of the visible light communication (VLC) signals from LED head/tail lights. However, existing vehicular VLP algorithms impose restrictive requirements, e.g., use of high-bandwidth circuits, road-side lights and certain VLC modulation strategies, and work for limited relative vehicle orientations, thus, are not feasible for general use. This paper proposes a VLC-based vehicle localization method that eliminates these restrictive requirements by a novel VLC receiver design and associated vehicular VLP algorithm. The VLC receiver, named QRX, is low-cost/size, and enables high-rate VLC and high-accuracy angle-of-arrival (AoA) measurement, simultaneously, via the usage of a quadrant photodiode. The VLP algorithm estimates the positions of two head/tail light VLC transmitters (TX) on a neighbouring vehicle by using AoA measurements from two QRXs for localization. The algorithm is theoretically analyzed by deriving its Cramer-Rao lower bound on positioning accuracy, and simulated localization performance is evaluated under realistic platooning and collision avoidance scenarios. Results demonstrate that the proposed method performs at cm-level accuracy and up to 250 Hz rate within a 10 m range under realistic harsh road and channel conditions, demonstrating its eligibility for collision avoidance and safe platooning.

Flexible Generalized Spatial Modulation for Visible Light Communications

Adaptive spatial modulation (ASM) varies the modulation size across the transmit light-emitting diodes (LEDs) to improve the overall spectral efficiency of visible light communication (VLC) systems. This article proposes a novel ASM scheme, referred to as flexible generalized spatial modulation (FGSM), for VLC systems. The proposed FGSM system changes the modulation sizes over the LEDs and the number of active LEDs, to improve the average symbol error rate (SER) and spectral efficiency compared to ASM with a fixed overall number of LEDs. The modulation sizes are selected in order to optimize the average SER under a predefined spectral efficiency value. A closed-form expression of approximate SER is derived along with decoding complexity calculations for the proposed system. Numerical results are provided to confirm the superiority of the proposed system and to support theoretical derivations.

Optical Energy-Constrained Slot-Amplitude Modulation for Dimmable VLC: Suboptimal Detection and Performance Evaluation

Energy-constrained slot-amplitude modulation (ECSAM) enables light dimming, eliminates light flicker and constrains the peak optical power while providing robust communication links. However, the complexity of the maximum-likelihood (ML) based ECSAM receiver increases exponentially with required spectral efficiency. This paper provides a comprehensive performance evaluation of ECSAM for the indoor visible light communication (VLC) channel with multipath propagation under realistic illumination constraints and imperfect channel estimation. A sub-optimal receiver that employs a slot-by-slot detection algorithm followed by a slot-correction mechanism for reducing the receiver complexity is proposed. Additionally, the method for optimal selection of parameters when designing the signal waveform is presented. The analytical upper bound on the symbol error rate of ECSAM is derived using the union-bound technique. The results show that the error performance of the sub-optimal receiver are comparable to that of the optimal ML receiver. Compared with conventional power or bandwidth efficient VLC modulation techniques such as multiple pulse position modulation (MPPM) and pulse amplitude modulation (PAM), ECSAM provides complete flexibility in modifying the signal constellation for a desired dimming level to maximise the spectral efficiency and provide a robust bit error rate performance especially in the multipath propagation channel induced intersymbol interference.

Design and performance analysis of indoor cooperative IHDAF protocol-based spatial modulation-index modulation visible light communication system.

Spatial modulation (SM) has been employed in indoor visible light communication (VLC) systems because of its high data rate and low complexity transmission. However, the activated LED may have poor channel conditions in conventional SM VLC systems, which leads to significant performance degradation. In this paper, a cooperative incremental hybrid decode-amplify-forward (IHDAF) protocol-based SM-index modulation (SM-IM) VLC system is proposed. For the SM-IM scheme, the spatial information and the modulated information are jointly transmitted in one symbol via the optimal VLC channel. The system model and the theoretical outage probability of the proposed IHDAF protocol-based SM-IM VLC system are presented. Numerical results show that the outage probability of the IHDAF protocol-based SM-IM VLC system can be significantly improved compared with the traditional amplify-and-forward and decode-and-forward protocol-based SM VLC systems. Additionally, the power allocation of the proposed scheme is also studied.

Nonlinear predistortion scheme based on Gaussian kernel-aided deep neural networks channel estimator for visible light communication system

A scheme for Gaussian kernel-aided deep neural networks nonlinear predistortion (GK-DNNPD), which could effectively reduce the computational complexity of the receivers, is experimentally demonstrated. Compared with lookup table (LUT) PD, the GK-DNNPD could increase the Q -factor of 8 pulse amplitude modulation visible light communication (VLC) system by 1.56 dB at 1.335 Gbps. We experimentally proved that GK-DNNPD could increase the bitrate under hard-decision forward error correction from 1.335 to 1.385 Gbps. This is the first time that GK-DNNs are utilized for PD in the field of VLC systems. Meanwhile, GK-DNNPD requires less data for training than LUT, and the space complexity of the model is lower than LUT as well, which provides GK-DNNPD with the potential to be applied in practical VLC systems.

Enhanced Performance of CAP-Modulated Visible Light Communication System Utilizing Geometric Shaping and Rotation Coding

Aiming to improve the performance of free space visible light communication (VLC) system, we combined the use of rotation coding together with geometric shaping (GS) technology in carrierless-amplitude-and-phase (CAP) modulation visible light communication system. In this paper, we designed a new GS-16QAM constellation named Triangular. Triangular GS-16QAM has a better noise resistance due to its larger value of the minimum Euclidean distance. Based on the excellent new 16QAM constellation, we further improve the performance of VLC system utilizing a proposed new coding technology named rotation coding after the quadrature-amplitude-modulation (QAM) mapping. The rotation coding can reduce the overlapping problem of the outer constellation points induced by non-linear impairment. Finally, the upper gain about 1 dB is achieved with rotation coding in 1.2 m free space VLC communication when the transmission speed is relatively low about 80 Mb/s. While the transmission speed is relatively high around 2 Gb/s in CAP-VLC system, Triangular constellation with rotation coding still has positive effect for transmission quality with about 1 dB enhancement than the square 16QAM. All of these results are verified by simulations and experiments.

1.7 to 2.3 Gbps OOK LED VLC Transmission Based on 4 × 4 Color-Polarization-Multiplexing at Extremely Low Illumination

To achieve the high traffic rate of a GaN LED-based visible light communication (VLC), a 4 × 4 color-polarization-multiplexing system is demonstrated by using two blue and two green LEDs. In the measurement, an available bandwidth of blue and green LEDs can be greater than 465 MHz for VLC modulation traffic by using the suitable analogy front end circuit. Hence, the proposed VLC system can deliver 1.7 to 2.3 Gbit/s on – off keying traffic rates in the free space transmission length of 1–4 m under the extremely low illumination of 6.9–136.1 lux for the indoor application. Moreover, the measured BER of each LED is less than the forward error correction target of 3.8 × 10−3 to maintain the better signal performance.

Visible light communications: multi-band super-Nyquist CAP modulation.

In this paper, we experimentally demonstrate the performance of a non-orthogonal multi-band super-Nyquist carrier-less amplitude and phase (m-SCAP) modulation for visible light communications (VLC). We break the orthogonality between sub-bands in the frequency domain by compressing the spectrum, purposely overlapping them, and introducing inter-band interference (IBI). We demonstrate that our proposed system can tolerate IBI, and hence spectral efficiency can be increased without introducing additional complexity to the receiver. We show that m-SCAP can tolerate up to 30% and 20% compression for 4- and 16-level quadrature amplitude modulation, respectively, thus leading to an improvement in spectral efficiencies up to 40% and 25%, respectively, at the cost of bit error rate performance, which however remains below the 7% forward error correction limit. Moreover, the experimental results are supported by numerical simulations.

Smart μLED Display-VLC System With a PD-Based/Camera-Based Receiver for NFC Applications

This paper presents a smart micro-light-emitting-diode (μLED) display system employing visible light communication (VLC) as the near-field communication technology for portable devices equipped with μLED displays. In the transmitter, a VLC modulator is integrated into a 400 × 240 gallium nitride (GaN) μLED display with a pixel size of 30 × 30 μm2 to enable simultaneous display and VLC functions. In the receiver, two different configurations are implemented, including a photodiode (PD)-based and a smartphone camera-based receiver. The smart μLED display-VLC system with the two different receivers is characterized by varying the distance and the angle between the transmitter and the receiver. Experimental results show that the PD-based system can achieve a bit rate of 2 Mb/s and a maximum overall data rate of 550 kb/s beyond 10 cm, but it is sensitive to angular misalignment. In contrast, the camera-based system is more suitable for the transmission of short pieces of information at a bit rate of 16.6 kb/s, and the maximum overall data rate is 5 kb/s at a distance of 5 cm (and 2.5 kb/s when the distance is extended to 10 cm). Moreover, the camera-based system is less sensitive to angular misalignment.

Chaos-Based Multicarrier VLC Modulator With Compensation of LED Nonlinearity

The massive deployment of light-emitting diode (LED) lightning infrastructure has opened the opportunity to reuse it as visible light communication (VLC) to leverage the current RF spectrum crisis in indoor scenarios. One of the main problems in VLC is the limited dynamic range of LEDs and their nonlinear response, which may lead to a severe degradation in the communication, and more specifically in the bit error rate (BER). This is aggravated by the extensive usage of multicarrier multiplexing, based on optical orthogonal frequency division multiplexing (O-OFDM), characterized by a high peak-to-average power ratio. Here, we present a chaos-based coded modulation (CCM) setup specifically adapted to the LED nonlinearities. It replaces the usual modulation, while keeping the multicarrier O-OFDM structure unchanged. First, we obtain a semi-analytical bound for the bit error probability, taking into account the LED nonlinear response. The bound results particularly tight for the range of signal-to-noise ratio of interest. Then, we propose a method to design the modulator based on optimization techniques. The objective function is the semi-analytical bound, and the optimization is applied to a parameterization of the CCM conjugation function. This appropriately shapes the chaotic waveform and leads to BER improvements that outperform classical counterparts under ideal predistortion.

Enhanced performance of a multiband super-Nyquist CAP16 VLC system employing a joint MIMO equalizer.

In this paper, we have experimentally demonstrated the feasibility of a LMS-Volterra based joint MIMO equalizer in multiband super-Nyquist carrierless amplitude phase modulation visible light communication system. To obtain higher spectrum efficiency, overlapping between different sub-bands is introduced in this experiment. By using joint MIMO equalizer, an aggregate data rate of 1.26 Gb/s is successfully achieved in 1-m indoor free space transmission with the BER below the 7% FEC limit of 3.8 × 10-3. To our best knowledge, this is the first time that our proposed joint MIMO equalizer is used to equalize multiband super-Nyquist data in VLC system.

Adaptive Spatial Modulation for Visible Light Communications With an Arbitrary Number of Transmitters

As a power and bandwidth efficient modulation scheme, the optical spatial modulation (SM) technique has recently drawn increased attention in the field of visible light communications (VLC). To guarantee the number of bits mapped by the transmitter's index at each timeslot is an integer, the number of transmitters (i.e., light-emitting diodes) in the SM based VLC system is often set be a power of two. To break the limitation on the required number of transmitters and provide more design flexibility, this paper investigates the SM based VLC with an arbitrary number of transmitters. Initially, a channel adaptive bit mapping (CABM) scheme is proposed, which includes three steps: bit mapping in space domain, bit mapping in signal domain, and the channel adaptive mapping. The proposed CABM scheme allows operation with an arbitrary number of transmitters, and is verified to be an efficient scheme through numerical results. Based on the CABM scheme, the information-theoretical aspects of the SM based VLC are analyzed. The theoretical expression of the mutual information is first analyzed. However, it is very hard to evaluate system performance. To obtain more insights, a lower bound of the mutual information is derived, which is in closedform. Both theoretical analysis and numerical results show that the gap between the mutual information and its lower bound is small. Finally, to further improve the system performance, the precoding scheme is proposed for the SM based VLC. Numerical results show that the system performance improves dramatically when using the proposed precoding scheme.

Non-Uniform Time Slot Based Modulation for Visible Light Communication System

Recently, visible light communication (VLC) has got increasing attention in the field of indoor wireless communications. VLC has the obligation of lighting besides data communications. The IEEE 802.15.7 task group proposed a VLC modulation format named color shift keying in which data symbols are defined based on the diffused light wavelength. This paper presents a new modulation scheme for indoor wireless visible light communication system named non-uniform time slot modulation (NUTS). The NUTS modulation scheme defines the feeder signals of red, green and blue LEDs as rectangular pulses with appropriate width and their positions. In this method, the time axes of all the three light sources (channels) are slotted to some non-uniform durations that all symbols are spanned over these slots as orthogonal dimensions. The proposed scheme has some advantages with respect to other approaches such as low bit error rate and high bit rate. Furthermore, it provides appropriate synchronization capability. Besides, in the design of NUTS modulation scheme it has been tried to deliberate all practical constraints, as far as possible.

Hadamard-Coded Modulation for Visible Light Communications

Visible light communication (VLC) systems using the indoor lighting system to also provide downlink communications require high-average optical powers to satisfy the illumination needs. This can cause high-amplitude signals common in higher-order modulation schemes to be clipped by the peak power constraint of the light emitting diode (LED) and lead to high-signal distortion. In this paper, we introduce Hadamard coded modulation (HCM) to achieve low error probabilities in LED-based VLC systems needing high-average optical powers. This technique uses a fast Walsh–Hadamard transform (FWHT) to modulate the data as an alternative modulation technique to orthogonal frequency division multiplexing (OFDM). HCM achieves a better performance for high-illumination levels because of its small peak to average power ratio (PAPR). The power efficiency of HCM can be improved by reducing the DC part of the transmitted signals. The resulting so-called DC-reduced HCM (DCR-HCM) is well suited to environments requiring dimmer lighting.

A Fully Integrated IEEE 802.15.7 Visible Light Communication Transmitter With On-Chip 8-W 85% Efficiency Boost LED Driver

This paper presents an IEEE 802.15.7 Physical Layer I (PHY-I) standard compliant visible light communication (VLC) transmitter system-on-a-chip (SoC), enabling the use of ordinary white LED lights as beacons or broadcasters for location-based applications. The mixed-signal SoC integrates a baseband digital signal processing (DSP) unit, a VLC modulator, and a switching boost LED driver with an on-chip power MOSFET. The DSP unit supports various coding schemes as well as both the on-off keying (OOK) modulation and the variable pulse-position modulation specified in the aforementioned standard. The boost LED driver is designed to power a matrix of 4 × 5 LEDs using Li-ion batteries for portable applications. The SoC simultaneously supports VLC and LED illumination with nine dimming levels. Implemented in a 0.35-μm CMOS process with 20-V devices, the SoC achieves a measured VLC data rate of up to 266 kb/s at a package error rate (PER) < 10% using a 211 −1 PRBS (pseudo random binary sequence) input. The communication distance measured is more than 2 m using no optical lens with the link efficiency of 5 nJ/bit. From an input at 3–5 V, the boost converter generates an output at 6–20 V with a 92% peak efficiency and an 8-W rating.

DC-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.