Multiple-input Multiple-output Visible Light Communication Research Articles

Energy Efficiency Optimization for MIMO Visible Light Communication Systems

Multiple-input multiple-output (MIMO) visible light communication (VLC) systems can support high data rates for indoor communications. In this letter, we focus on maximizing the energy efficiency (EE) of MIMO VLC systems, where the non-negativeness of the transmit signal, the optical and electrical power constraints, and the data rate and bit error rate (BER) requirements are taken into account. The formulated problem is a difficult nonlinear fractional program. We exploit the Dinkelbach’s algorithm and Lagrangian analysis to obtain a semi-closed form solution. The performance advantage of the proposed design is verified by simulation results.

MBER Combining for MIMO VLC With User Mobility and Imperfect CSI

Visible light communication (VLC) has emerged as a green, low-cost, and secure supplement for existing radio frequency (RF) based systems. Although promising, the performance of VLC based systems is limited by several impairments, which degrade the achievable bit error-rate (BER) performance, viz. variations in channel-gain due to user-mobility, and channel-estimation error. Hence, in this letter, the bit error rate (BER) of maximal ratio combining is quantified over a multiple-input multiple-output (MIMO) VLC system, while considering the aforementioned impairments. Next, using the derived expressions, exact and asymptotic combiners based on the minimum bit error-rate (MBER) criterion are formulated for MIMO VLC systems impaired by user-mobility, and channel-estimation error. The accuracy of the contributed expressions for BER, and the performance of the proposed MBER combiner (MBERC) are corroborated by simulations performed over realistic MIMO VLC channels. Additionally, it is found that the proposed MBERC delivers improved BER performance in presence of channel-estimation error and user-mobility, which makes the proposed methodology viable.

FFDNet-Based Channel Estimation for Massive MIMO Visible Light Communication Systems

Channel estimation is of crucial importance in massive multiple-input multiple-output (m-MIMO) visible light communication (VLC) systems. In order to tackle this problem, a fast and flexible denoising convolutional neural network (FFDNet)-based channel estimation scheme for m-MIMO VLC systems was proposed. The channel matrix of the m-MIMO VLC channel is identified as a two-dimensional natural image since the channel has the characteristic of sparsity. A deep learning-enabled image denoising network FFDNet is exploited to learn from a large number of training data and to estimate the m-MIMO VLC channel. Simulation results demonstrate that our proposed channel estimation based on the FFDNet significantly outperforms the benchmark scheme based on minimum mean square error.

Pairwise Coding for MIMO-OFDM Visible Light Communication

This work proposes a dual pairwise coding (DPWC) technique for multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) based visible light communication (VLC) systems. DPWC is a technique designed to mitigate the signal-to-noise ratio (SNR) imbalance created in the received information symbols due to the light emitting diodes’ bandwidth limitations and the strong correlation of typical indoor VLC MIMO channels. With singular value decomposition precoding, the MIMO VLC channel is decomposed into independent parallel sub-channels. The DPWC technique is then applied to further improve the system performance by pairing and interleaving OFDM subcarriers and MIMO sub-channels with imbalanced SNR. The error performance of the proposed DPWC technique is investigated in detail via simulation and experimental demonstration. Its effectiveness with different degrees of bandwidth-limitation (data rate) and channel correlation is presented, and the results are compared with other variants of the pairwise coding technique. DPWC provides performance improvement with a significant reduction in the SNR required to achieve a specific bit error rate (BER).

Effective Receiver Design for MIMO Visible Light Communication with Quadrichromatic LEDs

In this paper, we propose a receiver designing principle for the multiple-input multiple-output (MIMO) visible light communication (VLC) systems with quadrichromatic light emitting diodes (QLEDs). To simultaneously transmit multiple data streams, the system consists of multiple QLEDs and multiple receivers; each includes four photodiodes (PDs). We optimize the Euclidean distance of the received signal over some constraints by considering the normal vectors of the receivers. The numerical results show that our proposed receiver design has a better bit error rate (BER) performance in comparison with the conventional receiver.

Quadrature spatial modulation sub-carrier intensity modulation (QSM-SIM) for VLC

In this paper, a new spectrally efficient modulation scheme called quadrature spatial modulation sub-carrier intensity modulation (QSM-SIM) is proposed for multiple-input multiple-output (MIMO) visible light communication (VLC) systems. In QSM-SIM, in addition to the digital modulation symbols, two LED indices are used simultaneously for transmission of data bits with the help of a sinusoidal signal pair. Then, spatial modulation quad-LED complex modulation (SM-QCM), which is based on quad-LED complex modulation (QCM), is enhanced such that the number of LEDs is greater than four. Bit error rate (BER) performances of the considered modulation schemes are analyzed for different MIMO plans. The upper bound on BER performances of the QSM-SIM and SM-QCM schemes are derived analytically in order to validate the simulation results. In this work, pulse amplitude modulation (PAM), QCM, and SIM are used as benchmarks. In addition, for the purpose of reducing channel correlation, the power imbalance (PI) method is applied to the VLC-MIMO system. Best power imbalance factors are obtained for the considered modulation schemes and benchmarks under fixed signal to noise ratio (SNR) values. The results show that the proposed schemes outperform the benchmarks with PI communication scenarios.

Channel estimation by tensor-based noise compensation for relay-assisted multiple-input multiple-output and orthogonal frequency division multiplexing indoor visible light communication system

For channel estimation in the relay-assisted multiple-input multiple-output and orthogonal frequency division multiplexing indoor visible light communication (VLC) system affected by light source, there is a problem that the received signal cannot be separated by simple filtering. To solve this problem, a channel estimation by PARATUCK2-PARAFAC-based noise compensation which introduces tensors to construct the suitable model of VLC is proposed. First, the transmitting pilots for channel estimation and noise estimation are constructed separately with the Hermitian symmetry structure. Then the tensor-based transmission model of the indoor VLC system is established, and the signals for channel and noise estimations are received. Finally, an asymptotic estimation for separating signals from different sources and noise is proposed by PARATUCK2-PARAFAC. Simulation results show that the proposed algorithm provides a more effective scheme for channel estimation comparing with the state-of-the-art algorithms.

Filter-Bank Modulation Based Signal Design and Transmission Techniques for Intensity Modulated MIMO Visible Light Communication Systems

Current research in wireless communication undoubtedly points towards the tremendous advantages of using visible light as a spectrum for significantly boosting the capacities and capabilities of communication systems. The intensity of light can be rapidly modulated to obtain a communication scheme which can transport much larger volumes of data at higher rates and lesser latency compared to current radio frequency methods. In this paper, we have developed two novel filter bank based multicarrier techniques for communication using visible light. We propose a new signal design that employs pulse shaping with square root raised cosine filtering and frequency translation to generate orthogonal multicarrier signals. Based on this, we propose a filter bank modulation technique for multiple-input–multiple-output visible light communication. Further, we develop another filter bank modulation method using spatial indexing which further improves the data rate and spectral efficiency. The advantages of the proposed methods are thoroughly investigated through exhaustive simulation studies. The methods are found to yield very good bit error rate performance and high data rates.

Secrecy Performance of the MIMO VLC Wiretap Channel With Randomly Located Eavesdropper

We study in this paper the secrecy performance of the multiple-input multiple-output (MIMO) visible light communication (VLC) wiretap channel. The underlying system model comprises three nodes: one transmitter, equipped with multiple fixtures of LEDs, one legitimate receiver and one eavesdropper, each equipped with multiple photo-diodes (PDs). The VLC channel is modeled as a real-valued amplitude-constrained Gaussian channel and the eavesdropper is assumed to be randomly located in the coverage area. We propose a low-complexity precoding scheme that aims at enhancing the secrecy performance of the system. Specifically, assuming discrete input signaling, we derive an average achievable secrecy rate for the underlying system in a closed-form, and the derived expression is a function of the precoding matrix and the input distribution using stochastic geometry. Then, we propose a low-complexity design of the precoding matrix based on the generalized singular value decomposition (GSVD) of the channel matrices of the system. We examine the resulting average achievable secrecy rate using the truncated discrete generalized normal (TDGN) distribution, which is the best-known discrete distribution available in the literature. Finally, we validate the proposed scheme through extensive simulations and we demonstrate its superiority when compared to other schemes reported in the literature.

Performance enhancement for indoor visible light communication system with an improved inter-symbol interference model using optimized hemispherical optical-angle-diversity-receivers

Several hemispherical optical receivers based on angle diversity technology are optimized to achieve better reception for multiple-input multiple-output (MIMO) visible light communication (VLC) system with an improved inter-symbol interference (ISI) model. The optimal parameters are obtained via analyzing the performances under different diversity dimensions, spatial distances between adjacent photodiodes (PDs) and inclination angles. The simulation results reveal that under the condition of optical angle diversity receiver (OADR) with 4 PDs, the optimal spatial distance between adjacent PDs is 0.1 m and the inclination angle is 50∘, respectively. Compared with common plane model of 4 PDs, the average SNR has increased by 15.2%. It is no doubt that the OADR is a kind of promising alternative for indoor visible light communications.

Enhancing power allocation efficiency of NOMA aided-MIMO downlink VLC networks

In order to enhance the achievable sum rate of indoor non-orthogonal multiple access (NOMA) aided multiple-input multiple-output (MIMO) visible light communication (VLC) downlink networks, in this paper, an efficient low computational complexity power allocation strategy termed as normalized logarithmic gain ratio power allocation (NLGRPA) is proposed, in which the optical channel information of all transmitter light-emitting diodes (LEDs) are exploited and properly ordered to ensure efficient power allocation Numerical results depict that our proposed NLGRPA method exhibits significant improvement in terms of achievable sum rate of NOMA aided MIMO-VLC networks when compared with other conventional power allocation approaches. Specifically, the proposed NLGRPA algorithm attains an achievable sum rate improvement of more than 55% and 33% compared with the gain ratio power allocation (GRPA) method and normalized gain difference power allocation (NGDPA) method in the 4 × 2 MIMO-VLC networks with nine randomly distributed users.

Görünür Işık Haberleşmesi için Çift Dördün Uzaysal Yoğunluk Modülasyonu

In this paper, a new spectrally efficient space modulation technique, which is called double quadrature spatial intensity modulation (DQSIM), is proposed for multiple-input multiple-output (MIMO) visible light communication (VLC) systems. Sub-carrier intensity modulation (SIM), which ensures the use of in-phase/quadrature (I/Q) signals in intensity modulation direct detection (IM/DD) systems, is used as a digital modulation scheme. In RF, quadrature spatial modulation (QSM) transmits the I/Q signals through single or multiple antennas selected independently from each other. Furthermore, the orthogonality between I and Q components is provided for the half period of sinusoids. DQSIM utilizes these two features and transmits four fold more bits than spatial modulation (SM) via spatial constellation. SIM uses two-fold bandwidth compared to on-off keying (OOK), while DQSIM uses three fold. DQSIM outperforms benchmark modulation schemes, which are SIM-SM and PAM-SM, at the BER value of 10 -4 . Furthermore, DQSIM performance has increased with increasing number of LEDs.

Chromaticity-Adaptive Generalized Spatial Modulation for MIMO VLC With Multi-Color LEDs

In this paper, we propose a chromaticity-adaptive generalized spatial modulation (CA-GSM) method for multiple-input multiple-output (MIMO) visible light communication (VLC) systems with quadrichromatic LEDs (QLEDs). After the MIMO-VLC system model is constructed, the CA-GSM method based on chromaticity-adaptive constellation optimization is brought forward accounting for the correlated MIMO channel with multi-color crosstalk and quadrangle chromaticity region. This work mainly investigates the optimal active QLED selection pattern in CA-GSM aiming at maximizing the minimum Euclidean distance of received multi-color constellation. Considering power, amplitude and chromaticity constraints, the optimization problem of chromaticity-adaptive constellation is transformed and solved by the linear approximation of Taylor series. Therefore, the design algorithm of CA-GSM is derived with the optimal QLED selection pattern. Simulation results verify that our proposed CA-GSM can achieve performance improvement compared to the multi-stream spatial modulation and the conventional design method without considering channel.

Robust MUI Suppression for MIMO Visible Light Communication System With Location-Aided Chaotically Rotating Orthogonal Scheme

In practical multiple-input multiple-output (MIMO) visible light communication (VLC) systems, the imperfect channel state information brings the issue that the precoding scheme may not well suppress multi-user interferences (MUIs). In this letter, with the objective of suppressing MUIs more effectively, we utilize the location information of users obtained from positioning systems, and present a real domain location-based chaotically rotating orthogonal scheme. In our design, we first develop a range-variable chaotic mapping method and embed users’ location information into the chaotic sequences. Then, we exploit the chaotic rotation to construct orthogonal matrices with the aim to orthogonalize transmitted signals. At the receiver, with the aid of the known location information and the chaotically rotating orthogonalization structure, the information can be retrieved from received signals, hence achieving robust MUI suppressions. Simulations are performed and the results demonstrate that our proposed scheme can effectively combat the MUI and improve the reliability performances for VLC systems.

Modeling of Multipath Channel and Performance Analysis of MIMO‐DCO‐OFDM System in Visible Light Communications

When a big path di.erence exists between the multiple transmitter-receiver links, time dispersion is inevitable. A multipath channel model is proposed for Multiple-input multiple-output (MIMO) Visible light communications (VLC). To combat Intersymbol interference (ISI) as well as increase the channel capacity, a combination of MIMO and Direct-currentbiased Optical orthogonal frequency division multiplexing (DCO-OFDM) is studied. The performance analysis of MIMO-DCO-OFDM taking into account the limitation of the forward current of the o.-the-shelf LED is derived. The accuracy of the theoretical results is veri.ed by comparison with the Monte Carlo Bit error ratio (BER) simulation results under di.erent DC bias and di.erent clipping levels.

Precoder Design for MIMO Visible Light Communications With Decision-Feedback Receivers

Decision-feedback equalization is considered for point-to-point multiple-input multiple-output visible light communication systems. Based on the geometric mean decomposition (GMD) and uniform channel decomposition (UCD), two precoders under the signal non-negativity and total average power constraints are designed for such systems. The GMD scheme can decompose the channel into multiple parallel sub-channels with equal gains. The UCD scheme further improves performance through power allocation. Simulation results of bit-error-rate and capacity are presented. It is shown that the proposed schemes can outperform conventional linear designs and the UCD scheme performs better than the GMD scheme.

Fast-adaptive color-collaborative constellation designs for multicolor multiple-input multiple-output visible light communications systems.

A fast-adaptive color-collaborative signal constellation (CCSC) is proposed for chromaticity-changeable multicolor multiple-input multiple-output (MIMO) visible light communications (VLC) systems. The design of CCSC aims at developing the constellation to minimize the average optical power with shaping-based lattice code. For multicolor VLC signals, we arrive at the fact that the optimum shape of the constellation bounding region is an inequilateral N-D simplex. With the densest lattice-packing structure, detailed design steps of CCSC are fully elaborated by lattice construction, effective point selection, and chromaticity adjustment. As CCSC has a low complexity, its constellation structure can adapt quickly to changeable chromaticity demands. Simulation results show that the performance of CCSC is better than enhanced standard color shift keying (CSK) and is close to iterative CSK modulation based on numerical search.

Angular Diversity Aperture (ADA) Receivers for Indoor Multiple-Input Multiple-Output (MIMO) Visible Light Communications (VLC)

The angular diversity aperture (ADA) receiver is a new form of optical wireless receiver which is made up of a number of receiving elements (REs) each consisting of a photodiode (PD) located below an aperture in an opaque screen. Previous work on the use of ADA receivers for visible light communication (VLC) analyzes only REs with round apertures and photodiodes with a limited range of parameters. This paper extends the analysis to calculate the channel gains for REs with for both round and square apertures and PDs and for more parameters. Graphs show how the gain varies as a function of the relative orientation of the transmitter and receiver for ten different designs. It is shown that the directionality of an RE depends on the offset of the PD from the aperture and that the field of view depends on the distance between the aperture and the PD. Detailed theoretical analysis and extensive simulation results demonstrate the bit error rate (BER) performance of receivers based on these ten designs in a multiple-input multiple-output (MIMO) VLC application. The round and square designs are found to have very similar BERs. It is shown that, even with high levels of shot noise, good BER results can be achieved throughout a typical scenario.

Effect of Wiring and Cabling Topologies on the Performance of Distributed MIMO OFDM VLC Systems

Since most indoor spaces have multiple luminaires for illumination, for visible light communication (VLC) systems, multiple-input multiple-output (MIMO) communication emerges as a natural solution to improve the data rates and/or the link reliability. The existing works on MIMO VLC systems, however, overlook the characteristics of the lighting infrastructure and the luminaire design, which might have implications for the VLC system design. A luminaire typically consists of multiple LED chips. The wiring topology refers to how the LED chips are connected within the luminaire. The cabling topology, on the other hand, refers to how the luminaires are connected to the communication access point (AP). Based on the type and length of cabling and wiring, significant delays can be introduced, which should be taken into account in channel modeling. In this paper, we adopt the non-sequential ray tracing to model the distributed MIMO VLC channels for various practical wiring and cabling topologies. Based on the developed channel models, we provide a comparative performance analysis of repetition coding (RC), spatial multiplexing (SMUX), and spatial modulation (SMOD) MIMO modes. Our results quantify the effect of wiring/cabling delays and provide insights into the optimized design of lighting infrastructure and luminaires for the support of VLC as an add-on service.

Joint data transmission and dimming control optimization for MIMO–VLC systems with channel-adaptive spatial constellation design

In the field of indoor wireless communications, visible light communications (VLCs) have attracted great attention for synergistically providing both illumination and data transmission. Meanwhile, multiple-input multiple-output (MIMO) technique has been applied in VLC systems to boost data rate by utilizing spatial resources. However, different geometrical locations of transceivers provide distinct optical channels which may effect the performance of the conventional MIMO–VLC techniques severely. In this paper, we propose the channel-adaptive spatial constellation (CASC) design for the MIMO–VLC systems by fully taking advantage of the channel state information (CSI), where the optimal transmitted signal constellation can be constructed via maximizing the minimum Euclidean distance (MED) of the received signal constellation. Meanwhile, the practical lighting constraints are taken into consideration with the non-linearity characteristic of light-emitting diode (LED) and the dimming requirements to maintain a specific indoor illumination level. Finally, simulations results indicate that the proposed CASC design can achieve significant improvement of error performance compared with the conventional MIMO–VLC schemes.