Orthogonal waveform-based backscattering interference suppression technique for underwater optical wireless communication.

The backscattering effects degrade the detection performance in a full-duplex underwater optical wireless communication (UOWC) system when the power of received backscattering interference is comparable to that of a target signal. In this paper, the orthogonal waveforms with the Hermite-Gaussian function and prolate spheroidal wave function are first introduced for a pulse position modulation based dynamic UOWC system to alleviate the backscattering effects. Then, a joint maximum likelihood detection scheme is proposed accordingly.

Spread spectrum for covert communication in ultra-violet communication system.

In this paper, we propose a covert communication scheme based on a spread spectrum for ultra-violet communication. We first characterize the system model of the communication system, where Warden is adopted to monitor the legitimated user transmission based on the binary hypothesis test and Kolmogorov-Smirnov test. To avoid periodic transmission of the pilot sequence which potentially degrades covertness, we propose a blind synchronization approach, such that the pilot sequence does not need to be transmitted.

Experimental investigation on backscattering interference cancellation for full-duplex UOWC based on time-reversal preprocessing.

A co-frequency and full-duplex (FD) underwater optical wireless communication (UOWC) system has the potential to significantly enhance spectral efficiency, reduce complexity, and further facilitate UOWC networking. However, the inevitable performance degradation due to self-interference introduced by backscattering presents a significant challenge. In this paper, we first experimentally explore the inherent characteristics of the underwater backscattering channel.

Experimental saturation characteristics of the PMT and adaptive compensation algorithm for OWC.

Orthogonal frequency division multiplexing (OFDM) utilizes numerous sub-carriers to achieve high transmission data rates. The frequency selectivity of the channel becomes a crucial factor influencing the communication performance of OFDM-based systems. In optical wireless communication (OWC) systems, the photomultiplier tube (PMT) may experience saturation when the incident optical power approaches its saturation threshold.

Resource-efficient channel estimation for DCO-OFDM based VLC systems.

We consider a resource-efficient pilot design for visible light communication (VLC) system employing direct-current offset orthogonal frequency division multiplexing (DCO-OFDM). Firstly, we experimentally verify that the normalized channel gain vectors remain approximately the same at different locations under a line-of-sight (LOS) path between the transmitter and the receiver. Then, under the constant normalized subcarrier gain assumption, it is proved that a single pilot subcarrier is optimal to maximize the achievable rate without signal clipping.

Intraspecific variations of leaf hydraulic, economic, and anatomical traits in Cinnamomum camphora along an urban-rural gradient.

Urbanization brings numerous benefits to residents, but it also introduces complex, variable, and heterogeneous habitat conditions to urban plants, resulting in an arid and hot urban environment that decreases tree growth and the ecological service capacity of trees. In this study, we evaluated leaf hydraulic, economic, and anatomical traits and their covariations of Cinnamomum camphora along an urban-rural gradient in Hefei, Eastern China. We found that Cinnamomum camphora in urban adopted a conservative hydraulic strategy with low leaf turgor loss point (Tlp), leaf hydraulic conductance (K), and leaf water potential resulting in 50 % loss of hydraulic conductance (P), as well as a quick investment-return economic strategy with low unit leaf dry matter content (LMA) and high leaf nitrogen content (Leaf N).

Wide dynamic range signal detection for underwater optical wireless communication using a PMT detector.

In the underwater optical wireless communication (UOWC) scenario, a photomultiplier tube (PMT) with higher sensitivity, lower noise, and a larger receiver area is employed as the photon detector to further extend the transmission distance. Due to the complex underwater environment, the high directionality of the light beam, and the vibration of a transceiver, the incident optical power usually spans a very wide dynamic range, and the PMT may operate in any one of the three regimes: pulse, transition, and waveform. While it is difficult to obtain the analytical characterization of the output electric signals across these regimes, this paper resorts to experimental measurements of the upsampled discrete samples within a training symbol duration.

Multilevel polarization shift keying modulation for turbulence-robust underwater optical wireless communication.

Turbulence is an intractable issue for underwater optical wireless communication (UOWC). Most literature has been mainly focused on the modeling of turbulence channels and performance analysis rather than mitigation of the turbulence effect, especially from the experimental aspects. In this paper, a multilevel polarization shift keying (PolSK) modulation based UOWC system is established utilizing a 15 m-long water tank, and the system performance is investigated under specific temperature gradient-induced turbulence and various transmitted optical powers.

RSS-based visible light positioning with unknown receiver tilting angle: robust design and experimental demonstration.

In this paper, we consider the received signal strength (RSS)-based indoor visible light positioning (VLP) with unknown receiving angle. A novel VLP scheme is proposed by joint estimation of the receiver coordinate and receiver characteristic vector. We equivalently convert the original estimation problem into the problem that maximizes the projection of the RSS vector on the column space spanned by the measurement matrix.

Anti error and erasure coding for water-to-air visible light communication through wavy water surface with wave height up to 0.6 meters.

Considering large dynamic optical intensity range in a water-to-air (W2A) channel, we propose two promising channel coding schemes, namely the concatenated Reed Solomon-Low Density Parity Check (RS-LDPC) code and Raptor code, for W2A visible light communication (VLC). We establish a W2A-VLC link to verify the performance under different wavy water environments and different water depths with a green light emitting diode (LED). A wave generator is adopted to emulate the wavy water surface with wave height up to 0.

Coordination of leaf hydraulic and economic traits in Cinnamomum camphora under impervious pavement.

Background: Paved urban environments can pose great threats to the physiological functioning and ecological services of street trees. In this context, assessment of leaf phenotypic plasticity is crucial for understanding the ecological strategy of tree species under impervious pavements.

Results: In this study, we measured a set of leaf economic traits, hydraulic traits of Cinnamomum camphora, and surrounding environmental factors in a street site (the soil was covered by the impervious pavement) and a park site (the soil was covered by grass) in Hefei, eastern China.

Capacity analysis for pulse amplitude modulated visible light communications with dimming control.

This paper focuses on the capacity-approaching, nonuniform signaling for the pulse amplitude modulated (PAM) visible light communications under the non-negativity, peak power, and dimmable average power constraints. The input distribution is characterized by three parameters, i.e.