Non-line-of-sight optical wireless sensor network operating in multiscattering channel

The Investigation of Underwater Wireless Optical Communication Links Using the Total Reflection at the Air-Water Interface in the Presence of Waves

With the development of underwater exploration, underwater networking is in urgent demand. At present, underwater wireless optical communication (UWOC) is primarily based on line-of-sight (LOS) communication links. However, the underwater environment is so complicated that LOS communication links are easily affected by a couple of factors such as air bubbles, turbidity, oceanic turbulence, and so on. We put forward novel UWOC links using the total reflection at the air-water interface, which can mitigate those phenomena. This paper aims to investigate a UWOC link based on the total reflection at the air-water interface. In our work, we achieved the maximum data rate of 300 Mb/s and a bit error rate (BER) of 3.10 × 10−3 under the forward error correction (FEC) with the total reflection angle of 7°. Furthermore, we verified the performance of the total reflection-based UWOC links at the air-water interface in the presence of waves and evaluated the impact on the UWOC links when the frequency and amplitude of the waves varied.

71-Mbit/s ultraviolet-B LED communication link based on 8-QAM-OFDM modulation

A demonstration of ultraviolet-B (UVB) communication link is implemented utilizing quadrature amplitude modulation (QAM) orthogonal frequency-division multiplexing (OFDM). The demonstration is based on a 294-nm UVB-light-emitting-diode (UVB-LED) with a full-width at half-maximum (FWHM) of 9 nm and light output power of 190 μW, at 7 V, with a special silica gel lens on top of it. A -3-dB bandwidth of 29 MHz was measured and a high-speed near-solar-blind communication link with a data rate of 71 Mbit/s was achieved using 8-QAM-OFDM at perfect alignment. 23.6 Mbit/s using 2-QAM-OFDM when the angle subtended by the pointing directions of the UVB-LED and photodetector (PD) is 12 degrees, thus establishing a diffuse-line-of-sight (LOS) link. The measured bit-error rate (BER) of 2.8 ×10^-4 and 2.4 ×10^-4, respectively, are well below the forward error correction (FEC) criterion of 3.8 ×10^-3. The demonstrated high data-rate OFDM-based UVB communication link paves the way for realizing high-speed non-line-of-sight free-space optical communications.

Performance evaluation of modulation and multiple access schemes in ultraviolet optical wireless connections for two atmosphere thickness cases

The exploitation of optical wireless communication channels in a non-line-of-sight regime is studied for point-to-point and networking configurations considering the use of light-emitting diodes. Two environments with different scattering center densities are considered, assuming operation at 265 nm. The bit error rate performance of both pulsed and multicarrier modulation schemes is examined, using numerical approaches. In the networking scenario, a central node only receives data, one node transmits useful data, and the rest of them act as interferers. The performance of the desirable node's transmissions is evaluated. The access to the medium is controlled by a code division multiple access scheme.

Research on multiple-scattering channel with Monte Carlo model in UV atmosphere communication

A non-line-of-sight (NLOS) ultraviolet (UV) communication channel model is established by using a Monte Carlo simulation method based on photon tracing. This method considers the multiple-scattering effects of UV signal propagation in the atmosphere, and simulates the condition of dual receivers for diversity reception. The channel characteristics of the UV communication are obtained by simulating the photon arrival probabilities. The model is employed to study the characteristics of NLOS UV scattering channels for a variety of scattering conditions, including the separation distance between transmitter and receiver, transmit/receive elevation angle, beam divergence, and field of view. The model has advantages in reliable prediction of UV communication for the dual-receiver condition, as validated by outdoor experiments at fixed elevation angles.

Theoretical and experimental research on diversity reception technology in NLOS UV communication system

Diversity reception technology is introduced into ultraviolet communication area in this article with theory analysis and practical experiment. The idea of diversity reception was known as a critical effective method in wireless communication area that improves the Gain significantly especially for the multi-scattering channel. A theoretical modeling and simulation method are proposed to depict the principle and feasibility of diversity reception adopted in UV communication. Besides, an experimental test-bed using ultraviolet LED and dual receiver of photomultiplier tube is setup to characterize the effects of diversity receiving in non-line-of-sight (NLOS) ultraviolet communication system. The experiment results are compared with the theoretical ones to verify the accuracy of theoretical modeling and the effect of diversity reception. Equal gain combining (EGC) method was adopted as the diversity mechanism in this paper. The research results of theory and experiment provide insight into the channel characteristics and achievable capabilities of ultraviolet communication system with diversity receiving method.

Impact of finite receiver-aperture size in a non-line-of-sight single-scatter propagation model

In this paper, a single-scatter propagation model is developed that expands the classical model by considering a finite receiver-aperture size for non-line-of-sight communication. The expanded model overcomes some of the difficulties with the classical model, most notably, inaccuracies in scenarios with short range and low elevation angle where significant scattering takes place near the receiver. The developed model does not approximate the receiver aperture as a point, but uses its dimensions for both field-of-view and solid-angle computations. To verify the model, a Monte Carlo simulation of photon transport in a turbid medium is applied. Simulation results for temporal responses and path losses are presented at a wavelength of 260 nm that lies in the solar-blind ultraviolet region.

On connectivity of wireless ultraviolet networks

Non-line-of-sight optical communication can be enabled by modulating signals into an UV carrier and then transmitting them through an atmospheric scattering channel. This paper investigates some connectivity issues for such UV communication networks. We discuss k-connectivity in a multiuser interference environment. Compared with the studied case without considering multiuser interference in which more users bring higher probability of k-connectivity, a large number of noncoordinated users cause higher interference and limit the network performance. Thus, node density should be carefully designed in accordance with network configurations. Four typical scenarios are discussed, depending on whether each node transmitter is capable of adjusting its pointing angle and tracking a target receiver. They lead to different link losses and consequently the network k-connectivity properties. One of the cases simplifying the transceiver design for adjustable pointing is also illustrated, where each node is equipped with multiple transmitters to be activated via electronic on/off switching. The number of transmitters on a single node then becomes another critical parameter whose effect on k-connectivity is studied. These results will provide a guideline for system and network designers.

An approximate closed-form link loss model for non-line-of-sight ultraviolet communication in noncoplanar geometry

Non-line-of-sight UV communication link path loss models have been explored for both coplanar and noncoplanar geometries, and these typically require numerical evaluation. In this Letter, we propose a closed-form and easily applied model to describe link behavior, applicable to noncoplanar geometry. The model is compared with a recently reported analytical model and shows good agreement.

UV communications channel modeling incorporating multiple scattering interactions

In large part because of advancements in the design and fabrication of UV LEDs, photodetectors, and filters, significant research interest has recently been focused on non-line-of-sight UV communication systems. This research in, for example, system design and performance prediction, can be greatly aided by accurate channel models that allow for the reproducibility of results, thus facilitating the fair and consistent comparison of different communication approaches. In this paper, we provide a comprehensive derivation of a multiple-scattering Monte Carlo UV channel model, addressing weaknesses in previous treatments. The resulting model can be used to study the contribution of different orders of scattering to the path loss and impulse response functions associated with general UV communication system geometries. Simulation results are provided that demonstrate the benefit of this approach.

Experimental demonstration of ultraviolet pulse broadening in short-range non-line-of-sight communication channels

An experimental test-bed using a narrow-pulsed ultraviolet (UV) laser and high-bandwidth photomultiplier tube was set up to characterize pulse broadening effects in short-range non-line-of-sight (NLOS) scattering communication channels. Pulse broadening is reported as a function of the transmitter elevation angle, transmitter beam angle, receiver elevation angle, receiver field-of-view, and transmitter-receiver distance. The results provide insight into the channel bandwidth and achievable communication data rate.

Non-line-of-sight ultraviolet link loss in noncoplanar geometry

Various path loss models have been developed for solar blind non-line-of-sight UV communication links under an assumption of coplanar source beam axis and receiver pointing direction. This work further extends an existing single-scattering coplanar analytical model to noncoplanar geometry. The model is derived as a function of geometric parameters and atmospheric characteristics. Its behavior is numerically studied in different noncoplanar geometric settings.

Non-line-of-sight underwater optical wireless communication network

The growing need for ocean observation systems has stimulated considerable interest within the research community in advancing the enabling technologies of underwater wireless communication and underwater sensor networks. Sensors and ad hoc sensor networks are the emerging tools for performing extensive data-gathering operations on land, and solutions in the subsea setting are being sought. Efficient communication from the sensors and within the network is critical, but the underwater environment is extremely challenging. Addressing the special features of underwater wireless communication in sensor networks, we propose a novel non-line-of-sight network concept in which the link is implemented by means of back-reflection of the propagating optic signal at the ocean-air interface and derive a mathematical model of the channel. Point-to-multipoint links can be achieved in an energy efficient manner and broadcast broadband communications, such as video transmissions, can be executed. We show achievable bit error rates as a function of sensor node separation and demonstrate the feasibility of this concept using state-of-the-art silicon photomultiplier detectors.