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Non-orthogonal multiple access (NOMA) is a promising scheme to improve the spectral efficiency, user fairness, and overall throughput in visible light communication (VLC) systems. However, the error propagation (EP) problem together with linear and nonlinear distortions induced by multipath, limited modulation bandwidth and nonlinearity of light emitting diode significantly limit the transmission performance of NOMA-VLC systems. In addition, having accurate channel state information, which is important in the recovery of NOMA signal, in mobile wireless VLC systems is challenging. In this work, we propose a convolutional neural network (CNN) based demodulator for NOMA-VLC, in which signal compensation and recovery are jointly realized. Both simulation and experiment results show that, the proposed CNN based demodulator can effectively compensate for both the linear and nonlinear distortions, thus achieving improved bit error ratio (BER) performances compared with the successive interference cancellation (SIC) and joint detection based receivers. Compared to SIC, the performance gains are 1.9, 2.7 and 2.7 dB for User1 for power allocation ratios (PARs) of 0.16, 0.25 and 0.36, respectively, which are 4, 4 and 2.6 dB for User2 for PARs of 0.16, 0.25 and 0.36, respectively.

In this paper, we propose a non-line of sight (NLOS) visible light positioning (VLP) system using a binocular camera and a single light emitting diode (LED) for the realization of 3D positioning of an arbitrary posture. The proposed system overcomes the challenges of the shadowing/blocking of the line of sight (LOS) transmission paths between transmitters and receivers (Rxs) and the need for a sufficient number of LEDs that can be captured within the limited field of view of the camera-based Rx. We have developed an experimental testbed to evaluate the performance of the proposed system with results showing that the lowest average error and the root mean square error (RMSE) are 26.10 and 31.02 cm following an error compensation algorithm. In addition, a label-based enhanced VLP scheme is proposed for the first time, which has a great improvement on the system performance with the average error and RMSE values of 7.31 and 7.74 cm and a 90 th percentile accuracies of < 11 cm.

We propose an optical power domain non-orthogonal multiple access (OPD-NOMA) scheme for visible light communications. OPD-NOMA superposes user messages in the optical power domain based on a light-emitting diode (LED) array. The maximum driven current for respective circuits is reduced compared to that of conventional NOMA, in which the LED-array-module is driven by a single circuit. OPD-NOMA reduces the gain and bandwidth requirements for the driver circuit of light source. The nonlinear power-current response of LED largely restricts its usable dynamic range and thus the transmit power. In OPD-NOMA, signals with lower powers suffer from reduced nonlinear distortion. The experimental results show that, OPD-NOMA offers improved transmission performance compared to conventional NOMA using the same driver circuit, since it can make a better use of the linear dynamic range of the LED’s power-current response.

We propose a non-orthogonal multiple access (NOMA) scheme for visible light communications (VLC) based on single carrier (SC) transmission and frequency-domain successive interference cancellation. The scheme can achieve low peak-to-average power ratio (PAPR), a good balance between throughput and fairness, and a higher system capacity for a larger number of users. We show by experiment that SC with a lower PAPR offers improved bit error rate (BER) performance compared with the orthogonal frequency division multiplexing.

We experimentally demonstrate a hybrid non-orthogonal multiple access (NOMA) and single carrier division multiplexing (SCFDM) transmission scheme for visible light communications, which offers higher spectral efficiency, improved tolerance against multi-path and a good balance between the data throughput and fairness. Compared with the orthogonal frequency division multiplexing based NOMA, NOMA-SCFDM with lower peak to average power ratio offers enhanced tolerance to the light emitting diode nonlinearity and improved bit error rate performance.

Asymmetrically clipped optical orthogonal frequency division multiplexing (ACO-OFDM) has been proposed in visible light communication (VLC) systems to overcome the dc-biased optical OFDM power consumption issue at the cost of the available electrical spectral efficiency. Due to the implementation of inverse fast Fourier transform, all the optical OFDM schemes including ACO-OFDM suffer from large peak-to-average power ratio (PAPR), which degrades the performance in VLC systems as the light-emitting diodes used as the transmitter have a limited optical power-current linear range. To address the PAPR issue in ACO-OFDM, we introduce a unipolar-pulse amplitude modulation frequency division multiplexing by adopting the single carrier frequency division multiple access (SC-FDMA). This is achieved by considering a PAM as an SC-FDMA data symbol and inserting a conjugate copy of the middle and first SC-FDMA FFT output subcarriers after the middle and last subcarriers, respectively. Simulation results show that, for the proposed scheme, the PAPR is 3.6 dB lower compared with ACO-OFDM. The PAPR improvement is further analyzed with the simulation results demonstrating that the proposed scheme offers 2.5 dB more average transmitted power compared to ACO-OFDM.

Non-orthogonal multiple access (NOMA) is a promising scheme for flexible passive optical networks (PONs), which provides high throughput and overall improved system performance. NOMA with the successive interference cancellation (SIC)-based receiver, which is used to detect the multiplexed signal in a sequential fashion, requires perfect channel state information and suffers from the error propagation problem. In this paper, we propose a convolutional neural network (CNN) based signal demodulation method for NOMA-PON, which performs channel estimation and signal detection in a joint manner. The CNN is first trained offline using the captured data for a given received optical power and then used to recover the data stream directly in the online mode. We show by experimental demonstration that, the proposed CNN-based receiver (Rx) outperforms the conventional SIC-based Rx and is more robust to the nonlinear distortion. We show that for the CNN-based system with 20 km optical fiber, the required received optical power levels at a bit error rate (BER) of 1×10−3 are lower by 4, 3 and 2.5 dB for power allocation ratios of 0.16, 0.25, 0.36, respectively compared with SIC-based system. In addition, the BER performance of CNN deteriorates considerably less with non-linear distortion compared with SIC.

Advanced modulation and multiple access schemes with high spectral efficiencies are desirable to overcome the bandwidth limitation in low-cost optical and electrical devices to fulfill the high-data rate requirements in passive optical networks (PONs). We propose a non-orthogonal multiple access (NOMA) scheme, known as power-code division NOMA (PCD-NOMA), for the next-generation PON, where the optical network units (ONUs) are divided into several groups with similar path losses. The ONUs per groups are allocated in the same power domain multiplexing layer with different codebooks. We show by experimental demonstration that the proposed PCD-NOMA with a high spectral efficiency offers improved overall system performance and reduced required transmission power in the next-generation PON, particularly in flexible PON where ONUs have different path losses. For PON with a power difference loss of 14 dB, the reduced required transmission powers are 5 and 11 dB for downstream and upstream, respectively, compared with orthogonal frequency division multiple access.

We propose an experimental demonstration of sparse code multiple access (SCMA) based visible light communications (VLC) system, in which the multi-dimensional codewords selected from a predefined codebook set are used to encode the transmitted data and a message passing algorithm (MPA) based multi-user receiver is used to detect the multiplexed codewords. Compared with the orthogonal frequency-division multiple access scheme, the SCMA scheme offers 150% overloading gain in the number of supported users at the cost of slightly decreased transmission performance.

We experimentally demonstrate a discrete wavelet multitone (DWMT) modulation scheme based on pulse amplitude modulation (PAM) for next generation passive optical network (PON), which offers high tolerance against chromatic dispersion, high spectral efficiency, low peak to average power ratio (PAPR) and low side lobes. The experimental results show the chromatic dispersion induced power penalties are negligible after 20km fiber transmission. Compared with orthogonal frequency division multiplexing (OFDM), DWMT offers a better receiver sensitivity.

A PE-ACO-OFDM (Position-Encoded Asymmetrically Clipped Optical Orthogonal Frequency Division Multiplexing) signaling scheme for intensity modulation and direct detection is introduced in this paper, where the antiasymmetry characteristics of ACO-OFDM are exploited to improve the rate of data transmission. This is achieved by reducing the symbol duration of the ACO-OFDM signal, where only the first half of ACO-OFDM is used to transmit the ACO-OFDM data symbol after inverting its negative samples to positive ones. In addition, encoded ACO-OFDM samples are combined with every ACO-OFDM symbol to allow the receiver to identify the position of the inverted samples. Simulation results are introduced, and it is shown that the data rates of PE-ACO-OFDM improve by 33% compared with ACO-OFDM, when a 256-quadrature amplitude modulation scheme is considered as the encoded constellation order. It is also shown that the signal to noise ratio of the proposed PE-ACO-OFDM is higher by almost 1 dB compared with the traditional ACO-OFDM.

Orthogonal frequency division multiplexing/offset quadrature amplitude modulation (OFDM/OQAM) is a promising modulation candidate for passive optical network (PON) due to its high flexibility, better time–frequency focusing characteristic, great resistance to the inter symbol and inter carrier interferences and higher spectrum efficiency compared to OFDM. However, the intrinsic imaginary interference together with linear and nonlinear distortions make it more difficult to recover the transmitted OFDM/OQAM signal at the receiver side. To mitigate the transmission impairments, a modified convolutional neural network (CNN) is utilized to learn the channel state information and the constellation demapping mechanism for OFDM/OQAM-PON. The distorted received signals are equalized implicitly to obtain the transmitted binary bits directly. The simulation results show that the CNN based receiver (Rx) can compensate the linear and nonlinear distortions more effectively compared to traditional pilot-based Rx, especially for the high order modulation long-reach PON.

We present interleave division multiple access (IDMA) scheme combined with orthogonal frequency division multiplexing (OFDM) for passive optical network, which offers improved transmission performance and good chromatic dispersion tolerance. The interleavers are employed to separate different users and the generated chips are modulated on OFDM subcarriers. The feasibility of IDMA-OFDM-PON is experimentally verified with a bitrate of 3.3 Gb/s per user. Compared with OFDMA, IDMA-OFDM offers 8 and 6 dB gains in term of receiver sensitivity in the cases of 2 and 4 users, respectively.

We experimentally demonstrate a non-orthogonal multiple access (NOMA) scheme for optical multiple inputs multiple outputs (MIMO) visible light communications (VLC) with single carrier transmission and frequency domain successive interference cancellation, which offers low peak to average power ratio, a good balance between throughput and fairness, and a higher system capacity for a larger number of users. The MIMO demultiplexing and the inter-user interference mitigation are realized with efficient channel equalization. The optimum power allocation ratio is about 0.29 in the case of four users.

A dye@metal–organic framework (MOF) hybrid was used as a fluorophore in a white-light-emitting diode (WLED) for fast visible-light communication (VLC). The white light was generated from a combination of blue emission of the 9,10-dibenzoate anthracene (DBA) linkers and yellow emission of the encapsulated Rhodamine B molecules. The MOF structure not only prevents dye molecules from aggregation-induced quenching but also efficiently transfers energy to the dye for dual emission. This light-emitting material shows emission lifetimes of 1.8 and 5.3 ns for the blue and yellow components, respectively, which are significantly shorter than the 200 ns lifetime of Y3Al5O12:Ce3+ in commercial WLEDs. The MOF-WLED device exhibited a modulating frequency of 3.6 MHz for VLC, six times that of commercial WLEDs.

We introduce a non-orthogonal multiple access (NOMA) scheme for next generation passive optical network (PON) with single carrier transmission and frequency domain successive interference cancellation (FD-SIC), which offers low peak to average power ratio, a good balance between throughput and fairness, and a higher system capacity for a larger number of users. The feasibility of the proposed scheme is verified with 6.6 Gbps bidirectional NOMA-PON transmission. The effect of power allocation on the bit error rate performance is investigated.

We experimentally demonstrate optical multiple inputs and multiple outputs (MIMO) transmission for non-orthogonal multiple access (NOMA) based passive optical network (PON) using polarization interleaving, which offers a higher system capacity for a larger number of users. The MIMO demultiplexing and the inter-user interference mitigation are realized with efficient channel equalization. The optimum power allocation ratio is about 0.42 in the case of four users.

We experimentally demonstrate an indoor visible light positioning system based on optical camera communications, in which the transmitted coordinate data are spatially separated and demodulated by a camera. The receiver’s position is calculated based on the coordinates of light-emitting diodes in the real word and in the image. The experimental results show that the proposed system with under-sampled phase shift keying modulation offers an error free data transmission and mean positioning errors of 5.0 and 6.6 cm for $h$ of 120 and 180 cm, respectively.

We propose an indoor visible light communication (VLC) and positioning system using the orthogonal frequency division multiplexing access (OFDMA) scheme, which can provide both indoor positioning and communications. Three subcarriers with the maximum received signal intensity with respect to three light-emitting diodes (LEDs) are selected for indoor positioning based on the trilateration algorithm. The experiment results show that the proposed system with quadrature phase shift keying (QPSK) mapping offers a mean positioning error and an error vector magnitude of 1.68 cm and more than 15 dB, respectively.

In this study, the authors present efficient frequency-domain channel estimation (CE) methods based on the adjacent subcarriers frequency-domain averaging (ASFA) and minimum mean squared error (MMSE) schemes for the orthogonal frequency division multiplexing/offset quadrature amplitude modulation (OFDM/OQAM) passive optical network (PON) system. The complete channel transmission response for OFDM/OQAM-PON with the chromatic dispersion induced intrinsic imaginary interference effect is systemically derived. Compared with the conventional interference approximation CE method, ASFA and MMSE offer improved receiver sensitivity.

The authors present efficient frequency-domain channel estimation methods based on the intra-symbol frequency-domain averaging (ISFA), minimum mean squared error (MMSE) and weighted inter-frame averaging (WIFA) schemes for the orthogonal frequency division multiplexing (OFDM) visible light communications (VLC) system. OFDM-VLC with quadrature phase shift keying, 16- and 64-quadrature amplitude modulation mapping is experimentally demonstrated. Compared with the conventional least square channel estimation method, ISFA, MMSE and WIFA offer improved performance with MMSE offering the best performance in terms of the error vector magnitude but at the cost of high complexity. The authors show that the WIFA can improve the estimation accuracy of time-varying VLC optical channel.

The data rate of optical camera communication (OCC) systems is limited by the low sampling rate of a camera. The screen-to-camera (SC) based OCC systems offer higher data rate by employing the optical multiple inputs multiple outputs scheme. However, the spatial intersymbol interference and image blurring is an issue especially when the link distance grows and the receiver is in mobility. In this paper, we propose a blur equalization method based on Wiener filtering which has the advantages of low complexity and easy modeling. The experimental results show that the BER performance of SC based OCC system can be improved using the proposed equalizer.

Satellite communication is one of the pioneer technologies to provide seamless communication across the globe. With large number of satellites deployed in the space, inter-satellite communication has become an important phenomenon for researchers to establish communication link between satellites. In this work, a cost-effective inter-satellite communication system is proposed by using spectral amplitude coding based on optical code division multiplex access technique and polarization division multiplexing scheme. Ten channels, each carrying 10 Gbps non-return to zero encoded data, are transmitted over 25,000 km inter-satellite optical wireless communication (Is-OWC) link. Furthermore, Is-OWC is subjected to space turbulences such as transmitting and pointing errors. The reported results show the successful transmission of 100 Gbps data over Is-OWC link.

Radio over visible light communications (Ro-VLC) can be a pioneering technology to provide ubiquitous radio services particularly in the radio network-permitted locations. In this work, three channels, each up-converted to a 50 MHz radio signal carrying 25 Mbps data, is transmitted over a 0.5 m visible light communications link by using the cost effective on-off key (OOK) modulation format. Three red, green and blue light emitting diodes are adopted for parallel transmission. We show simulation results, carried out using OptiSystem™ software, for the bit error rates for the proposed diffuse system for both nonreturn to zero and return to zero data formats.

We compare the bit error rate (BER) performances of discrete Fourier transform (DFT), discrete cosine transform (DCT) and discrete wavelet modulation (DWT) based orthogonal frequency division multiplexing (OFDM) schemes for visible light communications (VLC). The experiment results show that DWT-OFDM-VLC system with low peak to average power ratio (PAPR) offers better BER performance compared to DFT-OFDM-VLC and DCT-OFDMVLC systems.

In this paper, we propose Li-Tect, an algorithm to detect the shape of an object located in an indoor environment using low cost optical elements through sensing the environment's light. The algorithm analyzes, relying on the predictability of optical propagation paths, how much light is expected to propagate in the absence of obstructions caused by the presence of an object. Then, based on the received light when the object is in the room, the algorithm infers the shape of the object. In addition, the algorithm considers the reflected paths from surfaces in order to determine the object's estimated shape. We study five different scenarios characterized by different levels of complexity, room sizes, and a range of reflection nodes. The algorithm is also tested in a real prototype where several experiments are carried out in two scenarios to demonstrate the capabilities of Li-Tect in 2-D and 3-D monitoring and shape detection cases. Finally, the results show that the shape and the detection of objects in the scenarios can be easily acquired with high accuracy, even if the number of transceivers is reduced. This work was supported in part by the Spanish Government under the National Projects “ELISA” and “TERESA-ADA” with ID TEC2014-59255-C3-3-R and TEC2017-90093-C3-2-R, respectively and in part by the European project called VisIoN. This work has been finalized under the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie Grant Agreement 764461. Publicado

Discrete multi-tone (DMT) based passive optical network (PON) is a subject of great interest for recent research works, due to its high spectral efficiency, high flexibility and high tolerance to the fiber chromatic dispersion. In this paper, we investigate the transmission performance of DMT transmission for next generation PON, including the optimization of modulation index and the power fading of double sideband (DSB) induced by chromatic dispersion. A new single sideband (SSB) DMT modulation based on a dual-driver Mach-Zehnder modulator (DDMZM) is also presented, which can eliminate the power fading. The simulation results show that 4 × 25 Gb/s DSB DMT-PON combining with wavelength division multiplexing (WDM) and the single wavelength 100 Gb/s SSB-DMT are both promising candidates for future access network.

We propose and experimentally demonstrate an asymmetrical time wavelength division multiplexing passive optical network (TWDM-PON) scheme with 100-Gb/s downstream and 40-Gb/s upstream capacity using four pairs of wavelengths. Double sideband (DSB) orthogonal frequency division multiplexing (OFDM) with 16-QAM mapping is used for downstream transmission, while on–off keying (OOK) modulation is used for upstream transmission. The experimental results show that the power budget for bidirectional transmission is more than 35.5-dB. This scheme can be a promising solution for 100-Gb/s TWDM-PON with high power budget.

Orthogonal frequency division multiplexing (OFDM) based on intensity modulation and direct detection (IM/DD) is a promising candidate for future passive optical network (PON). As the IM/DD system requires the output to be unipolar, a direct current (DC) is required but with a reduced energy efficiency. Asymmetrically clipped optical OFDM (ACO-OFDM) has been proposed to improve the energy efficiency at the cost of a lower spectral efficiency. With infinite layers’ superimposition, layered ACO-OFDM (LACO-OFDM) can significantly improve the spectral efficiency while the computation complexity is very high. In this paper, we propose a triple-layer hybrid optical OFDM (THO-OFDM) scheme for PON, which combines N-point ACO-OFDM, N/2-point ACO-OFDM and N/2-point PAM-DMT signals for simultaneously transmission. Compared with LACO-OFDM, the proposed THO-OFDM offers better spectral and energy efficiency, reduced peak-to-average power ratio and computation complexity. The simulation results show that the transmitted THO-OFDM-PON can attain a ∼ 1.2 dB power gain compared with the LACO-OFDM-PON over 20 km fiber link.

The combination of optical multiple inputs multiple outputs (MIMO) and orthogonal frequency division multiplexing (OFDM) is a viable option to overcome the bandwidth limitation and increase the transmission data rate in visible light communications (VLC). In MIMO-VLC systems with pre-coders and equalizers it is essential to know the perfect channel state information. Traditional channel estimation (CE) techniques such as least square (LS) are widely used in MIMO-VLC systems. However, the LS algorithm is subject to noise enhancement, which results in lower estimation accuracy. Besides, the pilot tones between different transmitters should be orthogonal either in time or frequency domains, which increase the overhead. Since the physical VLC channel model exhibits strong sparsity, we propose a CE method based on compressive sensing (CS) for MIMO-OFDM VLC systems. The feasibility of the proposed CS-CE method is verified by experimental demonstration of a $2\times 2$ MIMO-OFDM VLC system. The experimental results show that, the proposed method offers improved bit error rate performance with reduced overhead compared with the LS-CE scheme.

We experimentally demonstrate a multicarrier interleave division multiple access (IDMA) scheme for bidirectional visible light communications using orthogonal frequency division multiplexing (OFDM), which has the advantages of good tolerance against multi-path, high spectral efficiency and excellent transmission performance. The generated IDMA signals are modulated on OFDM subcarriers and the different users are separated by the interleavers. When compared with orthogonal frequency domain multiple access, IDMA-OFDM offers increased transmission spans of 30 and 50 cm at a bit error rate (BER) of 10 -3 in the cases of two and four users, respectively.

We propose a visible light positioning system based on an artificial neural network (ANN) and optical camera communications. The receiver’s position is approximately and precisely estimated based on the decoded block coordinate and a typical back propagation ANN, respectively. The experimental results show that the proposed scheme offers a mean positioning error of 1.49 cm, which is required in many indoor positioning scenarios where high accuracy is essential.

We experimentally demonstrate a 2 × 2 optical MIMO-VLC system based on the modified OFDM/OQAM scheme. The ASFA preamble structure is proposed to mitigate theIMI effect.