Optical MIMO Research Articles

Adaptive TLS-OQSM technology of a wireless optical MIMO communication system over an oceanic vertical turbulence channel

Adaptive TLS-OQSM technology of a wireless optical MIMO communication system over an oceanic vertical turbulence channel

Analysis of Optical Wireless MIMO Communication in Underwater Medium

Analysis of Optical Wireless MIMO Communication in Underwater Medium

OFDM-based time-domain optical MIMO with general-numbered LED configurations

OFDM-based time-domain optical MIMO with general-numbered LED configurations

Towards an optical MIMO system performance improvement using MGDM multiplexing and EDFA optical amplification

This paper proposes a creative (3 × 3) MIMO transmission system employing multimode fibers MMF and MGDM spatial multiplexing technology. Based on spatial injection and spatial detection of light beams, the MGDM approach allows the MMF fiber to benefit from its entire bandwidth and increase its transmission capacity. To increase the quality and transmission capacity, the injection and detection parameters have been optimized. The transmission and reception conditions on the optical fiber are adjusted to ensure the transfer of high-speed services. Thus, ideal injection and detection conditions increase the quality of signals received on an MMF fiber. The proposed transmission chain decreases the modal and chromatic dispersions during transmission, for this reason, three subsystems interconnected by spatial connectors are created. To decrease interference between the modes of the same groups and to correct for attenuation of the signal on a 1200 m cable, two EDFA optical amplifiers were integrated. The simulation of the proposed chain (3 × 3) MIMO of distance 1.2 Km is realized to transmit data with a total rate of about 4.5 Gb/s (1.5 Gb/s for each user). Then, the comparison between the BER and quality factor Q performance was done for a system with and without optical amplifier.

Channel Model and Signal-Detection Algorithm for the Combined Effects of Turbulence and Link Misalignment in Underwater Optical Massive MIMO Systems

In recent years, underwater wireless optical communication (UWOC) has become a potential wireless carrier candidate for signal transmission in water mediums such as oceans. Underwater signal transmission is impaired by several challenges such as turbulence, scattering, attenuation, and misalignment. In this paper, we propose an improved-order successive interference cancellation (I-OSIC) algorithm based on partition space–time block coding (STBC) technology to solve the sub-channel correlation enhancement problem, which is caused by the combined effects of turbulence and link misalignment in the underwater optical massive multiple-input multiple-output (massive MIMO) systems. The partition STBC technology can make the encoded symbols orthogonality of space and time resist random fading under turbulence environments and fully use the communication link of the massive MIMO system. Under link misalignment conditions, the receiver detector will receive multiple beams. The proposed I-OSIC algorithm based on partition STBC can precisely track the degree of link misalignment error and reorder receiver signals based on the minimum interference criterion. It can use the channel matrix to estimate the interference magnitude of the link misalignment, and then eliminate the interference successively by demodulating the least interfered signal first. When the link misalignment error is large, the I-OSIC algorithm can provide a signal-to-noise ratio (SNR) gain of about 3 dB and provides the same error performance compared with the successive interference cancellation algorithm based on the received signal power.

DeepGOMIMO: Deep Learning-Aided Generalized Optical MIMO with CSI-Free Detection

Generalized optical multiple-input multiple-output (GOMIMO) techniques have been recently shown to be promising for high-speed optical wireless communication (OWC) systems. In this paper, we propose a novel deep learning-aided GOMIMO (DeepGOMIMO) framework for GOMIMO systems, wherein channel state information (CSI)-free detection can be enabled by employing a specially designed deep neural network (DNN)-based MIMO detector. The CSI-free DNN detector mainly consists of two modules: one is the preprocessing module, which is designed to address both the path loss and channel crosstalk issues caused by MIMO transmission, and the other is the feedforward DNN module, which is used for joint detection of spatial and constellation information by learning the statistics of both the input signal and the additive noise. Our simulation results clearly verify that, in a typical indoor 4 × 4 MIMO-OWC system using both generalized optical spatial modulation (GOSM) and generalized optical spatial multiplexing (GOSMP) with unipolar nonzero 4-level pulse-amplitude modulation (4-PAM) modulation, the proposed CSI-free DNN detector achieves near the same bit error rate (BER) performance as the optimal joint maximum-likelihood (ML) detector, but with much-reduced computational complexity. Moreover, because the CSI-free DNN detector does not require instantaneous channel estimation to obtain accurate CSI, it enjoys the unique advantages of improved achievable data rate and reduced communication time delay in comparison to the CSI-based zero-forcing DNN (ZF-DNN) detector.

Robust Power Allocation in Optical Satellite MIMO Links With Pointing Jitter

In this letter, an optical satellite system is considered comprised of a geostationary satellite with multiple transmitters on-board and an optical ground station with multiple receiving telescopes. <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mathbf {\mathrm {A}}$ </tex-math></inline-formula> robust power allocation strategy for the downlink is investigated incorporating the effects of the atmospheric impairments as well as the optical beam pointing jitter. Firstly, a theoretical analysis for the optical satellite system under pointing jitter is given and a maximin optimization problem is formulated maximizing the worst-case network capacity. The power allocation is carried out under peak and total power constraints using standard convex techniques. The lower bound of the ergodic network capacity for independent log-normal optical channels over variable jitter variance is derived. The proposed methodologies are evaluated via simulations using experimental channel measurements from the ARTEMIS-optical satellite campaign and their performances are compared to baseline power allocation strategies. The presented results show the effects of jitter on the network capacity and confirm the superiority of the proposed allocation scheme.

On the Joint Effects of HPA Nonlinearities and IQ Imbalance on Mixed RF/FSO Cooperative Systems

In this work, we provide a framework analysis of dual-hop hybrid Millimeter Wave Radio Frequency (RF)/Free Space Optical (FSO) MIMO relaying system. The source is equipped with multiple antennas and employs conjugate beamforming while the destination consists of multiple apertures with selection combining. The system also consists of a relay operating at amplify-and-forward mode. The RF channels are subject to Nakagami-m fading while the optical links experience the Málaga distribution. In addition, we introduce the impairments to the relay and receiver. In fact, the relay is impaired by the High Power Amplifier (HPA) nonlinearities while the receiver suffers from the In phase and Quadrature Imbalance. Moreover, we assume two types of HPA nonlinearities impairments called Soft Envelope Limiter (SEL) and Traveling Wave Tube Amplifier (TWTA). Closed-forms of the outage probability, the bit error probability, and the ergodic capacity are derived. Capitalizing on these performances, we derive the high SNR asymptotes to unpack insightful metrics such as the diversity gain. We also address the impacts of some key factors on the system performance such as the impairments, the interferers, the number of antennas and apertures and the pointing errors, etc. Finally, the analytical expressions are confirmed by Monte Carlo simulation.

Experimental Evaluation of Indoor Optical Wireless MIMO Systems With Square and Linear Array Constellations

In this article, we investigate the performance of the newly designed 4 × 4 optical wireless multiple-input-multiple-output (MIMO-OWC) system based on a linearly-shaped arrangement of transmitters and receivers, to achieve long-distance and high data rate transmission. To highlight the importance of selecting an appropriate arrangement for the optical elements, we carried on a comparative study, considering both the conventional square and the proposed horizontal linear constellation of optical modems. The performance of the bit error rate (BER) is experimentally evaluated at distances up to 65 m, using two important metrics inherent to the MIMO transmission channel matrix, i.e., the Frobenius norm and the condition number. The results show that the channel matrix shape characterized by the condition number dominates the BER if the Frobenius norm is smaller than 1. Furthermore, the proposed MIMO-OWC system employing a linearly-shaped arrangement of transmitters and receivers, shows to be more immune to the calibration error rather than the conventional square constellation optical modems. Moreover, the transmission of 100 Mbps data-rate and a BER lower than 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-4</sup> could be successfully achieved at a 65 m communication range.

Nonlinearities effects on optical MIMO systems

Multimode fibers (MMF) are enjoying a renewed attention boosted by recent advances in multimode complex nonlinear optics. Reason behind nonlinearity is occurred either due to intensity dependence of the medium refractive index or to inelastic-scattering phenomenon. The most commonly occurred non-linear effects in optical Multiple Input Multiple Output (O-MIMO) are the Kerr, Stimulated Brillouin Scattering (SBS) and Stimulated Raman Scattering (SRS) effects. The impact of Kerr, SBS and SRS instigate distortions to the optical signal transmission over MIMO transmission system. In this work, we focus on the impact of the optical Kerr, SBS and SRS effects on the overall performance of a MIMO transmission system. It is observed that in O-MIMO system, nonlinear effects degrade the system performance since many channels propagate simultaneously. They can result in pulse distortion and crosstalk between channels. Here, a comparative study between MIMO communication system with and without nonlinearities allows an accurate performance evaluation. The comparison is performed using Q-factor and Bit Error Rate (BER). The outcome is analyzed using OptiSystem software tool.

Evolution and Impact of Wi-Fi Technology and Applications: A Historical Perspective

The IEEE 802.11 standard for wireless local area networking (WLAN), commercially known as Wi-Fi, has become a necessity in our day-to-day life. Over a billion Wi-Fi access points connect close to hundred billion of IoT devices, smart phones, tablets, laptops, desktops, smart TVs, video cameras, monitors, printers, and other consumer devices to the Internet to enable millions of applications to reach everyone, everywhere. The evolution of Wi-Fi technology also resulted in the first commercial piloting of spread spectrum, high speed optical communications, OFDM, MIMO and mmWave pulse transmission technologies, which then became more broadly adopted by cellular phone and wireless sensor networking industries. The popularity and widespread Wi-Fi deployment in indoor areas further motivated innovation in opportunistic cyberspace applications that exploit the ubiquitous Wi-Fi signals. The RF signal radiated from Wi-Fi access points creates an “RF cloud” accessible to any Wi-Fi equipped device hosting or supporting these opportunistic applications. Wi-Fi positioning and location intelligence were the first popular opportunistic applications of Wi-Fi’s RF cloud. Today, researchers are investigating opportunistic applications of Wi-Fi signals for gesture and motion detection as well as authentication and security. This paper provides a holistic overview of the evolution of Wi-Fi technology and its applications as the authors experienced it in the last few decades.

Study of the Valuation of Multimode Optical Fibers by Translation of Transmission Techniques of Optical Fiber and High Speed Mimo Radio Frequency in Local Area Network.

— In this paper, we focused on making a study of the valuation of multimode optical fiber which is used a lot in local networks and yet that we talk less in this last decade which knows an increase of new technologies using an enormous speed. To do so, we made a translation between radio frequency MIMO and optical MIMO; a study which has already been carried out in a framework of comparison of two technologies and in the literature, this convergence is already possible. Note that this is done in terms of transfer functions and of which we have made a very explicit analytical study compared to other studies already carried out in the literature for an educational and didactic objective for future studies in this context. Then we focused on doing our valuation study of multimode optical fiber, through optical MIMO technology, and our thinking was based on the quality of the signal at reception, for this, a study of modulation formats was made, because with the rise of technologies, this of course leads to an increase in speeds, so that certain formats tend to almost total disappearance. During this study, the RZ (Return to zero) format is much better in a larger local network, in terms of its Q factor and NRZ (None Return to Zero), for a smaller network, depending on its bit error rate (BER) and their eye diagrams which have a very large aperture and this is extended for the RZ format.

The Hermitian Jacobi Process: A Simplified Formula for the Moments and Application to Optical Fiber MIMO Channels

The Hermitian Jacobi Process: A Simplified Formula for the Moments and Application to Optical Fiber MIMO Channels

Performance Evaluation of MPPM-Coded Wireless Optical MIMO System with Combined Effects over Correlated Fading Channel

The performance of wireless optical MIMO system with multiple pulse position modulation (MPPM) over correlated fading channel is investigated. The combined effects of atmospheric attenuation, atmospheric turbulence, and pointing error are taken into consideration. The bit error rate (BER) and the ergodic channel capacity are analyzed by utilizing the Poisson counting model and the exponential correlation model. Moreover, their approximate expressions are derived. The simulation results demonstrate that the pointing error is the most prominent influence factor over weak correlated channel. The performance degradation caused by a high channel correlation coefficient is more than that of pointing error in strong correlated channel. Therefore, the use of pointing, acquisition, and tracking (PAT) system and reasonable arrangement of the number and spacing of antennas at the transceiver are the keys to improve system performance.

Efficient Optical MIMO–OFDM Channel Estimation Based on Correntropy Compressive Sensing

The compressive sensing (CS) technique is widely used in the field of radio-frequency channel estimation. However, in optical wireless channel (OWC) estimation, CS needed to be adapted to cope with the nonlinear distortion resultant from the electrical-to-optical and optical-to-electrical conversion process of the OWC. Therefore, a robust CS channel estimation technique is proposed for the optical MIMO–OFDM system. The proposed CS channel estimation technique is based on higher-order statistics (HOS). In which, the correntropy is exploited as a HOS similarity measurement instead of the second-order statistics euclidean distance (ED) used with the conventional CS to handle the OWC nonlinear distortion. Herein, the ED is the most popular iterative CS algorithms such as orthogonal matching pursuits, sparsity adaptive matching pursuit, and self-aware step size sparsity adaptive matching pursuit is efficiently replaced by the HOS correntropy based CS to show the effectiveness of the proposed algorithm. Moreover, the most recent visible light communication system GLIM-OFDM is considered here to test the proposed technique. However, the pre-estimated channel state information (CSI) obtained from the previous OFDM frame is exploited as initial information in estimating the CSI of the current OFDM frame, which improves overall system performance. A comparison with the conventional CS reconstruction algorithms is conducted via extensive simulation analysis. The simulation results show the superiority of the bit error rate of the proposed correntropy based CS channel estimation scheme compared to the conventional CS-based channel estimation algorithms.

Networked multiple-input-multiple-output for optical wireless communication systems.

With the escalation of heterogeneous data traffic, the research on optical wireless communication (OWC) has attracted much attention, owing to its advantages such as wide spectrum, low power consumption and high security. Ubiquitous optical devices, e.g. light-emitting diodes (LEDs) and cameras, are employed to support optical wireless links. Since the distribution of these optical devices is usually dense, multiple-input-multiple-output (MIMO) can be naturally adopted to attain spatial diversity gain or spatial multiplexing gain. As the scale of OWC networks enlarges, optical MIMO can also collaborate with network-level operations, like user/AP grouping, to enhance the network throughput. Since OWC is preferred for short-range communications and is sensitive to the directions/rotations of transceivers, optical MIMO links vary frequently and sharply in outdoor scenarios when considering the mobility of optical devices, raising new challenges to network design. In this work, we present an overview of optical MIMO techniques, as well as the cooperation of MIMO and user/AP grouping in OWC networks. In consideration of the challenges for outdoor OWC, key technologies are then proposed to facilitate the adoption of optical MIMO in outdoor scenarios, especially in vehicular ad hoc networks. Lastly, future applications of MIMO in OWC networks are discussed. This article is part of the theme issue 'Optical wireless communication'.

The Hermitian Jacobi Process: A Simplified Formula for the Moments and Application to Optical Fiber MIMO Channels

С помощью замены базиса в алгебре симметрических функций мы вычисляем моменты эрмитова процесса Якоби. Расставив члены в строго определенном порядке и подсчитав определитель «почти верхнетреугольной» матрицы, мы получаем формулу моментов, которая значительно проще формулы, выведенной в [L. Deleaval, N. Demni, J. Theoret. Probab., 31:3 (2018), 1759-1778]. В качестве приложения мы рассматриваем эрмитов процесс Якоби как динамическую модель оптоволоконных каналов MIMO и вычисляем его пропускную способность (по Шеннону) для достаточно малых мощностей передатчика. В случае, когда размер эрмитова процесса Якоби больше порядка момента, нашу формулу моментов можно записать как линейную комбинацию сбалансированных обрывающихся $ _4F_3$-рядов в единице.

Neural Network-Based Joint Spatial and Temporal Equalization for MIMO-VLC System

The limited bandwidth of white light-emitting diode (LED) limits the achievable data rate in a visible light communication (VLC) system. A number of techniques, including multiple-input-multiple-output (MIMO) system, are investigated to increase the data rate. The high-speed optical MIMO system suffers from both spatial and temporal cross talks. The spatial cross-talk is often compensated by the MIMO decoding algorithm, while the temporal cross talk is mitigated using an equalizer. However, the LEDs have a non-linear transfer function and the performance of linear equalizers are limited. In this letter, we propose a joint spatial and temporal equalization using an artificial neural network (ANN) for an MIMO-VLC system. We demonstrate using a practical imaging/non-imaging optical MIMO link that the ANN-based joint equalization outperforms the joint equalization using a traditional decision feedback as ANN is able to compensate the non-linear transfer function as well as cross talk.

Progress report on visible light communication in intelligent transportation environment

With the continuous and rapid development of modernization and motorization, the number of cars in China has maintained a high growth, which leads to problems such as increased traffic congestion and frequent accidents. The emergence of intelligent transportation system can effectively solve problems and contradictions between people, vehicles and roads in real time. In recent years, the development of visible light communication in the intelligent transportation environment has been more and more rapid. This paper briefly summarizes the research and development of visible light communication in the intelligent transportation environment. First of all, the main interference factors of outdoor visible light communication are summarized: background light and atmospheric turbulence. Then, some methods and techniques to suppress or weaken them, such as the average aperture and channel coding mainly reduce the influence of atmospheric turbulence on outdoor optical communication, and the error rate of the outdoor environment experiment system is 10-3-10-7. Adaptive optical MIMO technology mainly inhibits the communication interference caused by background light. In the outdoor background light environment, the communication distance can reach 15m and the bit error rate is 10-4. Finally, the research direction of outdoor visible light communication technology and its application in the field of intelligent transportation are prospected.

Demonstration of Compact Free-Space Optical MIMO Transmitter and Receiver Using Tri-Wavelength VCSELs and Silicon APDs

The use of multi-wavelength optical tests can be found in many applications including industrial manufacturing, food testing, and hospitals. This effort was targeted at making compact devices that could emit multiple wavelengths and detect multiple wavelengths simultaneously. Multiple approaches were considered. The chosen design accomplishes multiple input and multiple output spectral measurements through a direct-sequence spread spectrum (DSSS) technique. The devices demonstrated within this paper are novel in that they allow simultaneous operation of multiple wavelengths and multiple detectors using readily available components in a compact arrangement.