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).

Theoretical analysis and experimental demonstration of gain switching for a PPM based UWOC system with picosecond pulses.

Shortening pulse width can improve the power efficiency and data rate of a pulse position modulation (PPM) based underwater wireless optical communication (UWOC) system at a fixed average optical power, which is more suitable for the energy-limited underwater environment. As a common method to generate short pulses, gain switching has the advantages of a tunable switching frequency and simple structure, facilitating the generation of high-order PPM signals. However, the output characteristics of electrical gain switching seriously affect the demodulation of PPM signals and limit the data rate.

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.

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.

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.

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.

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.

Long-reach underwater wireless optical communication with relaxed link alignment enabled by optical combination and arrayed sensitive receivers.

To extend the transmission distance and relax the strict alignment requirement of underwater wireless optical communication ((UWOC), we design and implement a UWOC system using a 3×1 fiber combiner and a high-sensitive multi-pixel photon counter (MPPC). The 50-m and 100-m transmission distances (corresponding to 24 attenuation lengths) are experimentally achieved with the data rates of 16.78 Mbps and 8.

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.

Towards power-efficient long-reach underwater wireless optical communication using a multi-pixel photon counter.

The transmission distance of underwater wireless optical communication (UWOC) is severely limited by the rapid decay of light intensity in water. Power-efficient pulse position modulation (PPM) and ultra-sensitive multi-pixel photon counter (MPPC) open the door toward designing long-reach UWOC systems. In this paper, a 46-m UWOC system based on PPM and MPPC was proposed and experimentally demonstrated with ultra-low transmitting power into the underwater channel.