Omnidirectional optical communication system designed for underwater swarm robotics.

In this paper, an omnidirectional underwater wireless optical communication (UWOC) system is proposed, including six lens-free transceivers. An omnidirectional communication with a data rate of 5 Mbps in a 7-m underwater channel is experimentally demonstrated. The optical communication system is integrated into a self-designed robotic fish, and the signal is processed real-time through an integrated micro-control unit (MCU). In addition, it is experimentally demonstrated that the proposed system could establish a stable communication link between two nodes, regardless of the nodes' locomotion and attitude, with a data rate of 2 Mbps and a communication range up to 7 m. In particular, the optical communication system features small footprint and low power consumption, which is suitable for integration in autonomous underwater vehicle (AUV) swarms to achieve an omnidirectional information transmission with low latency, high security, and high data rate compared with its acoustic counterpart.

Fisheye lens-based UWOC system with an FOV of ±90°.

The link alignment is a challenge in underwater wireless optical communication (UWOC). This paper proposes a UWOC system adopting a fisheye lens with a field of view (FOV) of ±90° at the receiver to alleviate alignment requirement, and a mobile scanning device (MSD) is exploited to track the variation of the imaging position generated by the fisheye lens due to different incidence angles. In a 7-m tap water channel, a transmission with a data rate of 400 Mbps and an FOV of ±90° is realized with 16-quadrature amplitude modulating-orthogonal frequency division multiplexing (16-QAM-OFDM) modulation and orthogonal matching pursuit (OMP) channel estimation algorithm.

Underwater quasi-omnidirectional wireless optical communication based on perovskite quantum dots.

In this paper, a quasi-omnidirectional transmitter is proposed and demonstrated for underwater wireless optical communication (UWOC) using the photoluminescence of perovskite quantum dots (QDs). The proposed transmitter, without complex driving circuits, is compact and reliable thanks to the lens-free design. The system performance is tested in a 50-m swimming pool with a water attenuation coefficient of 0.38 dB/m. The maximum data rates of on-off-keying (OOK) signals over 10-m and 20-m transmission distances can reach 60 Mbps and 40 Mbps, respectively. When four clients are adopted in a code division multiple access (CDMA) based UWOC network, the maximum data rates of each client can reach 10 Mbps and 7.5 Mbps over 10-m and 20-m underwater channels, respectively. The system can meet the requirements of the last meter end-user access in the Internet of underwater things (IoUT) and underwater optical cellular network systems.

9.14-Mbps 64-PPM UWOC system based on a directly modulated MOPA with pre-pulse shaping and a high-sensitivity PMT with analog demodulation.

A pulsed fiber master oscillator power amplifier (MOPA), which is combined with second harmonic generation (SHG) and modulated by directly changing the current of the low-power seed laser, is designed in this paper to overcome the 'green gap' of semiconductor lasers and the difficulty of obtaining high-power and wide-bandwidth driving circuits. To decrease the guard slot and increase the data rate of a high-order pulse position modulation (PPM) system, pre-pulse shaping (PPS) is utilized to decrease the fluctuation of pulse power, which is caused by the gain dynamics of multi-order amplification of the MOPA, from 55.6% to 27.5% for 25-ns pulses and from 22.4% to 16.7% for 10-ns pulses, respectively. Moreover, an analog PPM demodulation method is proposed to mitigate the nonlinear effect caused by space charge limitations at dynodes of a photomultiplier tube (PMT) and increase the robustness of the system. In an optical darkroom, a 99-m 64-PPM UWOC transmission, of which the measured link loss is around 13.16 attenuation length (AL), is realized in a water tank with a data rate of 9.14 Mbps. The average received optical power ranges from -60.87 to -52.51 dBm, corresponding to a bit error rate (BER) range of 1.93 × 10-4 to 2.3 × 10-3. To further prove the reliability of the proposed system, we implement a 65-m UWOC experiment with the same data rate at a BER of 3.42 × 10-4 in a 50-m standard swimming pool. The maximum link loss is measured to be 15 AL.

Series-connected solar array for high-speed underwater wireless optical links.

Solar panels are being increasingly used as detectors in underwater wireless optical communication (UWOC) systems, as the large detection area can significantly simplify the link alignment. However, the greatest problem in such a scheme is the limited bandwidth of the solar panel, which was originally optimized for energy harvesting rather than communication. In this Letter, we propose series-connected solar arrays for high-speed underwater detection, by taking a deep dive into the fundamentals of the solar array. As the size of the solar array increases from 1×1 to 3×3, the -20-dB bandwidth increases from 4.7 MHz to 24.2 MHz. To further improve the frequency response, a reverse bias is applied on the array. With a reverse bias voltage of 90 V, the -20-dB bandwidth of the proposed 3×3 solar array is extended to 63.4 MHz. To the best of our knowledge, it is the highest bandwidth achieved among the reported solar panel-based optical communication systems with a large detection area. Using the proposed series-connected solar array, a data rate of 150 Mbps is achieved over a 35-m underwater channel with a frequency domain equalizer. The proposed system shows that off-the-shelf solar cells have great potential in high data rate UWOC systems.

Demonstration of a 2 × 2 MIMO-UWOC system with large spot against air bubbles.

In order to reduce turbulence-induced scintillation and deal with alignment problems, a 2×2 multiple-input multiple-output (MIMO) underwater wireless optical communication (UWOC) system is proposed and experimentally demonstrated. With help of the large divergence angle of light beams and large field of view (FOV) of the detectors, the effect of high-density air bubbles is greatly eliminated. Simulation and experimental results confirm that, in most intensity-modulation/direct-detection (IM/DD) MIMO-UWOC systems, the repetition coding (RC) scheme performs better than the space-time block coding (STBC) scheme. In a 50 m swimming pool, the maximum horizontal offset can reach 97.9 cm, which is 421% and 192% higher than that of STBC multiple-input single-output (MISO) and RC-MISO/STBC-MIMO schemes, respectively. With a data rate of 233 Mbps and a transmission distance of 50 m, the large detection range can meet a variety of underwater wireless communication requirements. The experiment indicates that, when the difference in the transmission distance between the two optical signals is higher than 1 m, the bit error rate (BER) of the RC scheme increases sharply, while the BER of the STBC scheme is stable. The MIMO coding scheme needs to be selected according to the actual application environment.

GsRSS3L, a Candidate Gene Underlying Soybean Resistance to Seedcoat Mottling Derived from Wild Soybean (Glycine soja Sieb. and Zucc).

Soybeans are a major crop that produce the best vegetable oil and protein for use in food and beverage products worldwide. However, one of the most well-known viral infections affecting soybeans is the Soybean Mosaic Virus (SMV), a member of the Potyviridae family. A crucial method for preventing SMV damage is the breeding of resistant soybean cultivars. Adult resistance and resistance of seedcoat mottling are two types of resistance to SMV. Most studies have focused on adult-plant resistance but not on the resistance to seedcoat mottling. In this study, chromosome segment-substituted lines derived from a cross between Suinong14 (cultivated soybean) and ZYD00006 (wild soybean) were used to identify the chromosome region and candidate genes underlying soybean resistance to seed coat mottling. Herein, two quantitative trait loci (QTLs) were found on chromosome 17, and eighteen genes were found in the QTL region. RNA-seq was used to evaluate the differentially expressed genes (DEGs) among the eighteen genes located in the QTLs. According to the obtained data, variations were observed in the expression of five genes following SMV infection. Furthermore, Nicotiana benthamiana was subjected to an Agrobacterium-mediated transient expression assay to investigate the role of the five candidate genes in SMV resistance. It has also been revealed that Glyma.17g238900 encoding a RICE SALT SENSITIVE 3-like protein (RSS3L) can inhibit the multiplication of SMV in N.benthamiana. Moreover, two nonsynonymous single-nucleotide polymorphisms (SNPs) were found in the coding sequence of Glyma.17g238900 derived from the wild soybean ZYD00006 (GsRSS3L), and the two amino acid mutants may be associated with SMV resistance. Hence, it has been suggested that GsRSS3L confers seedcoat mottling resistance, shedding light on the mechanism of soybean resistance to SMV.

Quasi-omnidirectional transmitter for underwater wireless optical communication systems using a prismatic array of three high-power blue LED modules.

In this study, a quasi-omnidirectional underwater wireless optical communication (UWOC) system is implemented with a prismatic array consisting of three uniformly distributed high-power LED modules as the transmitter. Over a 10-m underwater channel in a 50-m standard swimming pool, a data rate of 22 Mbps is achieved without adopting any digital signal processing algorithm. With zero forcing (ZF) based frequency domain equalization (FDE) and a maximum ratio combining (MRC) algorithm, the maximum net data rates achieved are 69.65 Mbps, 39.8 Mbps and 29.85 Mbps over 10-m, 30-m, and 40-m underwater channels, respectively. In the proposed UWOC system, the receiver could successfully capture optical signals at different directions from the transmitter and the bit error rates (BERs) measured in different directions show small fluctuations. The proposed system could meet the demands of high-speed data transmission among units in a swarm-robot system and last meter user access in an underwater optical cellular network system.

200-m/500-Mbps underwater wireless optical communication system utilizing a sparse nonlinear equalizer with a variable step size generalized orthogonal matching pursuit.

Linear and nonlinear impairments in underwater wireless optical communication (UWOC) systems caused by the limited bandwidth and nonlinearity of devices severely degrade the system performance. In this paper, we propose a sparse Volterra series model-based nonlinear post equalizer with greedy algorithms to mitigate the nonlinear impairments and the inter-symbol interference (ISI) in a UWOC system. A variable step size generalized orthogonal matching pursuit (VSgOMP) algorithm that combines generalized orthogonal matching pursuit (gOMP) and adaptive step size method is proposed and employed to compress the Volterra equalizer with low computational cost. A maximum data rate of 500 Mbps is realized with the received optical power of -32.5 dBm in a 7-m water tank. In a 50-m swimming pool, a data rate of 500 Mbps over 200-m underwater transmission is achieved with a BER lower than the forward error correction (FEC) threshold of 3.8 × 10-3. The number of kernels of the sparse Volterra equalizer is reduced to 70% of that of the traditional Volterra equalizer without significant BER performance degradation. Compared with orthogonal matching pursuit (OMP) scheme and regularized orthogonal match pursuit (ROMP) scheme, the VSgOMP scheme reduces the running time by 68.6% and 29.2%, respectively. To the best of our knowledge, this is the first time that a sparse Volterra equalizer combined with VSgOMP algorithm is employed for the nonlinear equalization in a long-distance high-speed UWOC system.

Experimental demonstration of an underwater wireless optical communication employing spread spectrum technology.

For some industrial underwater wireless optical communication (UWOC) applications, the transmission distance matters more than the communication rate. Attenuation length (AL) is an important distance indicator of UWOC system. In this paper, to the best of our knowledge, the spread spectrum (SS) technology is firstly applied in a UWOC system and the capability to extend transmission distance or AL is demonstrated. A 42-m UWOC is experimentally demonstrated with 6.68 ALs. Compared with the conventional not-return-to-zero on-off-keying (NRZ-OOK) modulation scheme, the proposed SS scheme with a spread spectrum gain (SSG) of 5 achieves an AL extension by 0.51 and 0.81, respectively, with the same data rate and bandwidth. And the minimum required signal-to-noise ratio (SNR) is reduced by 9 dB to as low as -0.8 dB. Besides, the feature of the SS scheme that could work in a bandwidth-limited long-reach underwater channel without the equalization process is experimentally demonstrated.

Blue-laser-diode-based high CRI lighting and high-speed visible light communication using narrowband green-/red-emitting composite phosphor film.

We experimentally demonstrate high-speed visible light communication (VLC) and high-quality solid-state lighting (SSL) using polymethyl-methacrylate-doped phosphor film based on cesium lead bromide quantum dot (CsPbBr3-QD) and potassium fluorosilicate K2SiF6:Mn4+, which is excited by a blue gallium nitride laser diode. A 1.6 Gbps data rate is achieved by employing a non-return-to-zero on-off keying modulation scheme. The measured bit error rate of 2.7×10-3 adheres to the standard threshold (3.8×10-3) of forward error correction. Moreover, the generated white-light source has a high color rendering index of 93.8 and a correlated color temperature of 4435 K, and it exhibits a Commission Internationale de l'Eclairage (CIE) 1931 chromaticity coordinate at (0.3556, 0.3520), which is close to the ideal CIE value of white light (0.3333, 0.3333). This work opens up exciting possibilities for future high-speed indoor VLC and high-quality SSL.

Linking the chemical nature of soil organic carbon and biological binding agent in aggregates to soil aggregate stability following biochar amendment in a rice paddy.

Changes in soil aggregation with biochar amendment have been investigated extensively, but how biochar affects the chemical composition of organic carbon (C) and biological binding agents in aggregates and their linkage with soil aggregate stability remains unclear. Soil samples were collected in a rice paddy treated with 0 (C0, control), 10 t ha-1 (C10), 20 t ha-1 (C20) and 40 t ha-1 (C40) biochar for twenty months. The amount and chemical composition of soil organic C (SOC), microbial abundances and glomalin-related soil protein (GRSP) were determined in bulk soil and four fractions: large macroaggregates (>2000 µm), small macroaggregates (250-2000 µm), microaggregates (53-250 µm), and silt + clay (<53 µm). Our results showed that the proportion of >250 µm water-stable aggregates and mean weight diameter were gradually increased with increasing biochar addition rate. The concentrations of SOC, readily oxidizable C and microbial biomass C increased most in the small macroaggregates, followed by microaggregates under biochar amendment. Increasing biochar addition rate gradually decreased the relative contents of alkyl C, O-alkyl C and carbonyl C, but increased those of aromatic C across the aggregates, resulting in a higher aromaticity and hydrophobicity of SOC with respect to the control. The abundances of bacteria, fungi and archaea and the content of GRSP were significantly enhanced in the large and small macroaggregates under the C40 treatment. The proportion of >250 µm aggregates was significantly correlated with the contents of soil organic C fractions, GRSP and microbial abundance. Structural equation modeling further revealed that changes in SOC hydrophobicity and GRSP content under biochar amendment had significant and direct effects on the soil aggregate size distribution. In summary, our findings suggest that biochar amendment in rice paddy could improve soil aggregation through altering the chemical composition of soil organic C and the abundance of biological binding agents.

Studies on the developmental potentiality of cultured cell nuclei of fish.

By means of the serial nuclear transplantation technique, the authors obtained a nuclear transplant fish from subcultured cell originated from the blastula cells of the crucian carp (Carassius auratus Linnaeus). This nuclear transplant fish survived for three years, but its sexual glands were undifferentiated. The authors have also obtained a sexually mature adult fish from short-term cultured kidney cell nucleus of an adult crucian carp. Results of the experiment implied that the subcultured cell nuclei of fish blastula cells and the specialized somatic cell nuclei of adult fish still retained their developmental totipotency, and thus, it indicated that there is a possibility of fish somatic cell breeding through the use of nuclear transplantation.