This article presents a novel scheme based on underwater optical wireless communication and positioning (UOWC-UOWP) for an underwater wireless sensor network (UWSN). A dual-hop system is adopted to extend the limited coverage area of the UWSN with mobile nodes, consisting of a grade-index plastic optical fiber (GI-POF) link and a wireless link. Specifically, the mini-LED offers high-speed and flexible uplink transmission and the high-power LED enables both downlink transmission and positioning. The time frame design and code division multiplexing access (CDMA) support multi-user signal transmission. Proof-of-concept experiments with GI-POF and wireless link demonstrate the feasibility of the proposed scheme, which offers full-duplex communication, high-precise positioning and extended distance. To the best of our knowledge, the UOWC-UOWP convergent system is proposed for the first time. It has great potential to support high-capacity transmission between mobile nodes for future underwater transmission scenarios.

Visible light communication (VLC) based on a light-emitting diode (LED) suffers from a limited bandwidth of commercial LED, device nonlinearity, channel distortion, and transmitted power caused by a complex free-space channel, power amplifier, and illuminant devices resulting in a limited data rate. In this Letter, to provide an alternative high-speed solution, we first designed and fabricated three 175 µm tricolor mini-LEDs with various wavelengths. They are used to set up a spatial division multiplexing-wavelength division multiplexing VLC system over a 2 m link. Then we utilize a neural network receiver to replace the traditional channel estimation, equalization, and demodulation at the offline digital signal processing of the receiver. The experiment showed that the data rates of 2.65, 7, and 7 Gbps were achieved in three respective links using quadrature phase shift keying-optical orthogonal frequency division multiplexing. The three data rates have bit-error rates below the forward error correction limit, whose data rate sum of 16.6 Gbps is the highest mini/micro-LED-based VLC, to the best of our knowledge.

As an important supplement to radio frequency (RF) communication in a crowded indoor environment, high-speed multi-user visible light communication (VLC) is a promising candidate for practical application compared with point-to-point architecture. In this work, an area division concept is proposed based on the multi-directional low-cost array transmitter. For the first time, a series of parallel mini/micro-LEDs transmitters with various chip sizes are designed, fabricated and packaged, which are used to build a multi-user VLC link. The size-dependent characteristics of the parallel mini/micro-LEDs transmitters for VLC are systematically analyzed, including the linearity, electroluminescence, impedance, achievable bandwidth and data rate. The proposed transmitters with active regions of 75 μm, 100 μm, 125 μm, 150 μm, and 175 μm can provide access bandwidths of 278 MHz, 190 MHz, 133 MHz, 104 MHz and 85 MHz at 50-mA driving current for two independent users over a 3-m link, accordingly. The VLC system based on the parallel 75-μm micro-LED transmitter can simultaneously support two independent users at different positions with a summing data rate of 2.6 Gbps by implementing pulse-amplitude modulation 4-level (PAM4) schemes with Volterra equalizer. The maximum distance-rate product of 7.8 Gbps·m exhibits superiority to accelerate the practical deployment of high-speed multi-user VLC.

Visible light communication (VLC) beyond 10 Gbps is an important characteristic that can support the future 6 G high-capacity requirements. On the one hand, in order to break the electro-optics (E-O) bandwidth limitation of the light-emitting diodes (LEDs), we fabricated two high-bandwidth ( > g i g a h e r t z ) single wetting layer micro-LEDs with 50 and 75 µm active regions. On the other hand, for mitigating the nonlinear effects of the VLC system, an artificial neural network equalizer is designed and implemented in offline digital signal processing. Both efforts lead to a breakthrough of data rates at a single VLC link. Using quadrature phase shift keying orthogonal frequency division multiplexing, the data rate of a 1.025 GHz VLC link based on a 75 µm micro-LED can reach 8.75 Gbps with a bit-error-ratio (BER) of 2.73 × 10 − 3 . In addition, the E-O characteristics and communication performances of micro-LED with two diameters are compared and discussed. To the best of our knowledge, the data rate of 8.75 Gbps is the highest record of the VLC link based on a single-pixel blue micro-LED with a BER within the forward error correction citation of 3.8 × 10 − 3 .

Visible light communication and positioning (VLCP) is a promising candidate for constructing a multi-functional wireless network with large-scale connectivity and centimeter-level positioning. However, there is still a lack of effective methods to offer simultaneous visible light communication (VLC) and visible light positioning (VLP) functions for multiple users. Thus, we propose a multi-user VLCP system based on a dual-domain multiplexing (DDM) scheme, where both the time and code resources are multiplexed to transmit VLCP signals for multiple users simultaneously. In the proposed system, the data of different users are distinguished by using code division multiplexing technology, while the VLCP signals transmitted from different LEDs are separated by adopting time division multiplexing technology. The performances, including bit-error rate and positioning error, are evaluated through both simulation and experimentation to verify the feasibility of the proposed multi-user VLCP system. In the experiment, a VLCP system with four LED transmitters was able to simultaneously support low-speed VLC with free error and accurate VLP with a 2 cm precision for eight users. This offers an effective solution to support a large number of users with simultaneous VLC and VLP functions in the future multi-functional wireless network.

In this paper, vertical cavity surface emitting laser (VCSEL) array is used to establish gigabits/second (Gbps) optical uplink, device-to-device (D2D), and Internet-of-thing (IoT) links, as a supplementary for visible light communication (VLC) and ultra-low latency near-field communication in a typical indoor scenario. The mathematical model based on a modified Monte-Carlo ray-tracing (MMCR) algorithm for VCSEL-based optical wireless communication (OWC) is presented, which takes into account both accuracy and time complexity for the calculation of the channel characteristics including power distribution, impulse response, error analysis, and signal-to-noise ratio (SNR). Simulation firstly takes a global approach to the optical uplink lens design method, compared between Lambertian and Gaussian sources, and then extended six typical line-of-sight (LOS) or non-line-of-sight (NLOS) VCSEL-based OWC models. For demonstration, we adopted a 940-nm VCSEL array and 850-nm single-pixel VCSEL to establish LOS and NLOS systems after measuring the optics-electronics and bandwidth characteristics, respectively. Furthermore, multiple multi-carrier schemes are adopted to improve the OWC performance system based on a 940-nm VCSEL array including uniform-loading orthogonal frequency division multiplexing (OFDM), channel-coded OFDM, bit-loading/ power-allocation OFDM, and OFDM access (OFDMA). Results show that OFDM can effectively decrease the inter-symbol interference (ISI) of the indoor channel and increase the data rate, and the bit/ power-loading method achieves the highest 7.2 Gbps transmission with the bit error rate (BER) within the forward error correction (FEC). All the theoretical and experimental results, for the first time, provide a comprehensive design and optimizing process of VCSEL-based indoor high-capacity OWC systems for future optical uplink, D2D, and IoT applications.