Indoor optical wireless localization system with height estimation for high-speed wireless communications in personal areas

Beam-steering-based optical wireless technologies are being widely investigated due to the capability of providing high-speed wireless connectivity in indoor applications. However, high-speed indoor optical wireless systems are traditionally realized with discrete bulky components, significantly limiting their practical applications. In this Letter, we demonstrate an infrared optical wireless communication system employing a miniaturized silicon integrated photonic circuit for beam steering for the first time. Experimental results show that up to 12.5Gb/s optical wireless communication can be achieved with error-free performance over a free-space range of 140cm, and limited mobility of users can be realized. The experimental results of this Letter open the way for realizing integrated high-speed optical wireless communications.

High-speed optical wireless communication (OWC) systems based on light-emitting diode (LED), such as Li-Fi, are promising solutions for the looming spectrum crisis in 6G wireless communications. OWCs typically extend the RF spectrum by harnessing the visible light and infrared spectra, but the recent advancements in deep-ultraviolet (DUV) LED device technology allow us to further extend the OWC spectrum down to the DUV range, namely the solar-blind band. This talk reviews the recent progress of the high-speed OWCs based on DUV-LEDs including Gbps-class transmission demonstrations in direct sunlight and analyses on the microscopic structural and optical characteristics of high-speed AlGaN-based LEDs.

In this paper, we experimentally illustrate the effectiveness of neural networks (NNs) as non-linear equalisers for multilevel pulse amplitude modulation (PAM-M) transmission over an optical wireless communication (OWC) link. In our study, we compare the bit-error-rate (BER) performances of two decision feedback equalisers (DFEs)—a multilayer-perceptron-based DFE (MLPDFE), which is the NN equaliser, and a transversal DFE (TRDFE)—under two degrees of non-linear distortion using an eye-safe 850 nm single-mode vertical-cavity surface-emitting laser (SM-VCSEL). Our results consistently show that the MLPDFE delivers superior performance in comparison to the TRDFE, particularly in scenarios involving high non-linear distortion and PAM constellations with eight or more levels. At a forward error correction (FEC) threshold BER of 0.0038, we achieve bit rates of ~28 Gbps, ~29 Gbps, ~22.5 Gbps, and ~5 Gbps using PAM schemes with 2, 4, 8, and 16 levels, respectively, with the MLPDFE. Comparably, the TRDFE yields bit rates of ~28 Gbps and ~29 Gbps with PAM-2 and PAM-4, respectively. Higher PAM levels with the TRDFE result in BERs greater than 0.0038 for bit rates above 2 Gbps. These results highlight the effectiveness of the MLPDFE in optimising the performance of SM-VCSEL-based OWC systems across different modulation schemes and non-linear distortion levels.

Optical wireless technology has been considered as a promising candidate to provide high-speed wireless connectivity in personal work/living spaces. Previously we proposed and demonstrated a high-speed indoor communication system by incorporating limited mobility with localization function. Furthermore, we showed that by using a novel single channel imaging receiver, better system performance can be achieved and the demonstration was based on single-mode fiber due to its low transmission loss feature. However, in most already installed inbuilding optical fiber distribution networks, multi-mode fiber was deployed since it is low-cost and easy to handle. In this paper, we experimentally demonstrate the feasibility of the proposed optical wireless personal area communication system with single channel imaging receiver based on multi-mode fiber. In addition, the wavelength-division-multiplexing (WDM) technology is also incorporated to realize an ultra-broadband connectivity in wireless personal area networks. The results show that a simultaneous operation of a 4 × 10 Gbps down-link and a 400 Mbps up-link can be realized simultaneously and the beam footprint is larger than 1 m even when a channel selecting optical bandpass filter with ~77% transmission efficiency was used.

The combination of orthogonal frequency division multiplexing (OFDM) and spatial modulation (SM) can enhance the capacity of optical wireless communication (OWC) systems with low complexity. In this paper, we propose a novel SM scheme for intensity modulation/direct detection (IM/DD) OWC systems by employing discrete Hartley transform based OFDM (DHT-OFDM). Due to the use of DHT with one-dimensional constellations, the Hermitian symmetry constraint, which is generally imposed in conventional discrete Fourier transform based OFDM (DFT-OFDM) to obtain a real-valued output signal, is not required in DHT-OFDM. As a result, DHT-OFDM based SM can achieve much higher spectral efficiency than that of DFT-OFDM based SM in OWC systems. Simulation results show that, for an indoor 4×4 SM-OWC system with a spectral efficiency of 6 bits/s/Hz, DHT-OFDM achieves a remarkable 4.5-dB transmit signal-to-noise ratio reduction for an overall bit error rate of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> in comparison to conventional DFT-OFDM.

We proposed a 940-nm VCSEL-based QAM-OFDM optical wireless communication (OWC) system using adaptive bit-power loading strategy over 12 meters which achieved 4.46-Gbps data rate below forward error correction (FEC) criterion of 3.8 × 10-3.

Time-coordinated SPAD-based receiver for high-speed optical wireless communication

Multihop relaying is a potential technique to mitigate channel impairments in optical wireless communications (OWC). In this paper, multiple fixed-gain amplify-and-forward (AF) relays are employed to enhance the OWC performance under the combined effect of atmospheric turbulence, pointing errors, and fog. We consider a long-range OWC link by modeling the atmospheric turbulence by the Fisher-Snedecor <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${\mathcal {F}}$</tex-math></inline-formula> distribution, pointing errors by the generalized non-zero boresight model, and random path loss due to fog. We also consider a short-range OWC system by ignoring the impact of atmospheric turbulence. We derive novel upper bounds on the probability density function (PDF) and cumulative distribution function (CDF) of the end-to-end signal-to-noise ratio (SNR) for both short and long-range multihop OWC systems by developing exact statistical results for a single-hop OWC system under the combined effect of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${\mathcal {F}}$</tex-math></inline-formula> -turbulence channels, non-zero boresight pointing errors, and fog-induced fading. Based on these expressions, we present analytical expressions of outage probability (OP) and average bit-error-rate (ABER) performance for the considered OWC systems involving single-variate Fox's H and Meijer's G functions. Moreover, asymptotic expressions of the outage probability in high SNR region are developed using simpler Gamma functions to provide insights on the effect of channel and system parameters. The derived analytical expressions are validated through Monte-Carlo simulations, and the scaling of the OWC performance with the number of relay nodes is demonstrated with a comparison to the single-hop transmission.

When the optical signal is transmitted in atmospheric channel in the wireless optical communication (WOC) systems, the inter-symbol interference (ISI) will be caused by the atmospheric motion and the fading characteristics of the atmospheric channel. In addition, device noises such as photodetectors noises can also affect the signal in the real communication systems. It is difficult to eliminate both types of interference by the single equalization algorithm at the same time, therefore, a cascaded equalization algorithm is proposed. First of all, we use the MATLAB to simulate the cascaded equalization algorithm, the convergence performance of the algorithm is analyzed, the bit error rate (BER) under different signal-to-noise ratios (SNR) are also compared. Then, the algorithm is verified under laboratory conditions, we calculate the BER of the receiving signal, which is processed by the cascade equalization algorithm. The simulation analysis and experiments results show that, the convergence performance of the cascaded equalization algorithm is improved effectively, the ISI is decrease, the BER can reduce to about 10-8 , decreased by 4 orders of magnitude than without equalization. It can improve the communication performance of the WOC systems, the validation of the cascaded equalization algorithm is verified.

This paper is an overview of indoor OFDM (orthogonal frequency division multiplexing)/DMT (discrete multitone) optical wireless (OW) communication systems. Indoor OW OFDM/DMT systems can be classified into two groups. One group produces half-wave symmetry time signal at the output of the OFDM modulator by special assignment of subcarriers. Thus, allowing signal clipping at the zero level and avoiding the need of DC bias at the expense of data rate reduction. ACOOFDM (asymmetrically clipped OFDM system) and PAM (pulse amplitude modulation)-DMT are two techniques from the first group. The second group assigns data to all possible subcarriers to increase the data rate. However, half-wave symmetry signals cannot be achieved and DC bias is needed to convert the bipolar signal to a unipolar signal before modulating the LED (light emitting diode) intensity. DC-biased OFDM and a novel technique, proposed in this paper, called orthogonal PAM-DMT (OPAM-DMT) that is an extension of the proposed PAM-DMT by using discrete sine transform and discrete cosine transform to transmit two orthogonal signals at the same time, are two techniques from the second group. This paper considerers a practical LED model and studies the performance of all these systems in terms of average electrical OFDM signal power versus bit-error-ratio (BER) in the presence of additive white Gaussian noise channel (AWGN). It is shown that LED clipping has significant impact on the performance of all these systems and the performance of these systems substantially depends on the considered modulation order.

The wireless optical communication is a kind of broadband access technology, it can be said that it properly combined with the optical fiber and wireless communication technology. More to say, it is a powerful supplement of modern optical fiber communication. In this paper, based on the advantages of wireless optical communication technology, this paper introduces the wireless optical communication technology in the application of 2G network, 3G network and extends the application in backbone network, and analyzes the common problems and solutions in the wireless optical communication. With the advance of technology, the wireless optical communications technology development prospects will be more and more broad, is worthy of popularization and application.

In this paper, a multipoint-to-point system consisting K users and a central node over wireless optical communication (WOC) channel is analyzed. The scenario focused on is that there is simultaneous communication from a number of users to the central node. As a powerful solution, we utilize non-orthogonal multiple access (NOMA) technique in the system. Although the superiority of NOMA in radio frequency (RF) system has been greatly considered, the NOMA in WOC still needs further research due to the special features of WOC, especially the non-broadcast nature of optical beam and the vulnerable turbulence channel. With the special features of WOC in mind, system is evaluated in terms of outage probability, bit error rate and ergodic sum rate. In addition, we theoretically prove that NOMA outperforms orthogonal multiple access (OMA), and the performance gain increases with the increase of turbulence strength. Hence, NOMA is more suitable for WOC, especially in strong turbulence channel. Moreover, we also analyze the user pairing scheme. Monte Carlo simulations have been done, which match quite well with the theoretical analysis.

In this paper we experimentally investigate the impact of polarization state on our recently proposed indoor gigabit optical wireless communication system. Our findings indicate that ~0.7 dB variation in the receiver sensitivity will be introduced.

The rapid developments of the image sensor technology have made them an important tool in different areas. Many applications utilizing image sensors were proposed. In recent years, there is a tendency to utilize light-emitting diodes (LED) as a light source replacing normal lamps due to its obvious advantages over incandescent light sources, which including lower energy consumption, longer lifetime, improved robustness, smaller size, faster switching, and greater reliability. It is also being used as a transmitter of optical wireless communication (OWC). Therefore, application using LED and image sensor as transmitter and receiver respectively becomes an attractive option for the imaging system. Wireless communication utilizing image sensor is an intercross research of imaging technology and communication technology, few researches have been conducted to implement image sensors in OWC systems. In this paper, we systematically introduce the image sensor communication (ISC) technology and provide important theoretical analysis on the proposed system. A new method of region detection using size, shape matching is proposed. Furthermore the communication signal recovering algorithms for OWC utilizing image sensor is presented

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