The characteristics of non-line-of-sight (NLOS) ultraviolet (UV) overwater communication channels under shore-to-vessel conditions and multiple scattering effects is modeled using Monte Carlo simulations. The field experiment measured received photon distribution, and calculated path loss at distances of up to 164 meters with the support of a GPSsynchronized accelerometer. Key parameters, such as transceiver elevation angles, water surface reflection index, airborne humidity, pollution, and temperature, were considered and analyzed in path loss simulations to more accurately compare with measured data. These channel modeling and experimental results will serve as the foundation for further study of the NLOS UV overwater and maritime communication system.
In this report, the characteristics of non-line-of-sight (NLOS) ultraviolet (UV) overwater communication channels which includes scattering and turbulence effects are modeled using Monte Carlo multiple scattering simulation. The overwater field experimental measurements of turbulence effect and path loss at the distances of up to 1700 meters were reported and analyzed by considering key parameters such as communication distance, transceiver angles, water surface reflection index, along with airborne humidity, and temperature. These channel modeling and experimental results will serve as the foundation for further study of the NLOS UV overwater communication system in shore-to-shore (STS), shore-to-vessel (STV), and vessel-to-vessel (VTV) communication link configurations.
In this study, the characteristics of overwater non-line-of-sight (NLOS) ultraviolet (UV) communication channel which include scattering and turbulence effect are modeled using single scattering and Monte Carlo multiple scattering simulation. In addition, simulation results of turbulence effect and path loss at a short separation distance are reported and analyzed where, transmitting angles, along with airborne humidity and temperature were taken into considerations as key parameters which affect the distribution of the receiving signals. Overwater NLOS UV communication channel measurement test bed is proposed with field testing plan. These channel modeling results will be valuable for studying overwater NLOS UV communication performance and the development of unique overwater NLOS UV communication system.
Optical beam propagation through the turbulent media such as the vehicle exhaust plumes need to be studied in order to estimate the communication performance degradations on vehicular visible light communication (V2LC) networks. When the optical transceiver is close to the exhaust plumes, the optical waves may be distorted in both phase and amplitude, by perturbations on the air's refractive index spatially and temporally. In this paper, the authors present the measurements performed on V2LC communication link using two different vehicles. In particular, several different transceiver configurations with respect to the position of exhaust nozzle have been tested and compared, and the turbulence strength is evaluated by scintillation index (SI). Since the V2LC applications are mainly based on intensity modulated, direct detection method, only the receiving optical power fluctuation (scintillation) will be discussed. Finally, the error rate performance under different log intensity variances is analyzed, demonstrating that scintillation effects introduced by the vehicle exhaust can be negligible in V2LC applications.
Multiple-input multiple-output (MIMO) technique is now used in most new broadband communication system, and orthogonal frequency division multiplexing (OFDM) is also utilized within current 4th generation (4G) of mobile telecommunication technology. With MIMO and OFDM combined, visible light communication (VLC) system’s diversity gain is increase, yet system capacity for dispersive channels is also enhanced. Moreover, with the emerging massive MIMO-OFDM VLC system, there are significant advantages than smaller systems’ such as channel hardening, further increasing of energy efficiency (EE) and spectral efficiency (SE) based on law of large number. This paper addresses one of the major technological challenges, system architecture design, which was solved by semispherical beehive structure (SBS) receiver and so that diversity gain can be identified and applied in Massive MIMO VLC system. Simulation results shows that the proposed design clearly presents a spatial diversity over conventional VLC systems.
Short range non-line-of-sight (NLOS) ultraviolet (UV) communication, with its solar blind and Non-Line-of- Sight characteristic, received grant interest. However as the communication range increases, the communication performance deteriotes due to NLOS UV turbulence, even with special UV turbulence mitigation. In this work, we conducted a series of outdoor experiments to investigate the received signal energy distribution, which is the product of the complex interaction of transmitted UV radiation, by utlizing both a UV LED array and a UV laser, with the atmosphere. Separation distance, pointing angles and UV light source were taken into considerate as key parameters to affect the distribution. These experimental results will be valuable for studying NLOS UV communication performance.
This paper describes an optical ranging and communication method based on all-phase fast fourier transform (FFT). This kind of system is mainly designed for vehicle safety application. Particularly, the phase shift of the reflecting orthogonal frequency division multiplexing (OFDM) symbol is measured to determine the signal time of flight. Then the distance is calculated according to the time of flight. Several key factors affecting the phase measurement accuracy are studied. The all-phase FFT, which can reduce the effects of frequency offset, phase noise and the inter-carrier interference (ICI), is applied to measure the OFDM symbol phase shift.
Advances in ultraviolet (UV) source, detector, and solar-blind filtering technologies have recently spurred significant research interest in non-line-of-sight (NLOS) UV communications. Although this research has primarily focused on short-range applications, the achievable range of a NLOS UV system can be extended (e.g., up to a few kilometers) with the use of a pulsed UV laser transmitter. However, the short-duration high-intensity pulses of such a laser have the potential to overwhelm the response time of photomultiplier detectors, which are often employed by a receiver to implement high-sensitivity photon-counting detection. In particular, after the detection of a photon, there exists a period of time, called dead time, during which the detector is unable to detect subsequently impinging photons, resulting in missed photon detections and, hence, altered received signal statistics relative to an ideal photon counter. In this paper, we examine the effect of receiver dead time on a NLOS UV system. We extend an existing UV NLOS channel model to account for nonzero dead time at the receiver and then use this extended model to examine the significance of dead-time effects for various representative system configurations. The results suggest the importance of accounting for dead time when designing practical UV communication systems.
Recently, Ultraviolet communication is paid more and more attention, with its solar blind and Non-Line-of-Sight characteristic. However, it is hard to capture and recover the transmitted signal outdoor without synchronized signal. In this work, we integrate Universal Software Radio Peripheral (USRP) into UV communication system and employ GPS as synchronized signal. At receive side, photon counting and adaptive threshold method are used to recover original signal. Through experiments, we test path loss and BER of the system under di erent con guration geometries. Some results are compared to the previous proposed path loss and BER models.
In this paper, we consider the problem of precoder design for an optical intensity modulation (IM) system with multiple redgreen- blue (RGB) light emitting diodes (LEDs) as transmitters and imaging lens with color filters as receivers. The purpose of using a precoder is to optimally allocate power for each LED based on the current channel condition to minimize the detection error rate. To achieve the goal, an non-convex optimization problem due to a nonconvex constraint is formulated first taking into account several crucial lighting constraints, such as flicker-free, color rendering index (CRI), and luminous efficacy rate (LER) as well as the average optical intensity constraint and non-negative transmitter-side signal constraint. By manipulations we transform the problem into a semi-definite programming (SDP) and by approximation we relaxed the non-convex constraint into a convex one. The resulting convex problem is iteratively solved by CVX, an add-in to MATLAB, which jointly optimizes the precoder and DC-biases driving each LED. We assume that M-PAM signal constellation is used as input to the precoder and an MMSE receiver is applied to recover the input signals in this paper, while our method is not restrict to the specific choice.
Free space optical (FSO) communication has attracted tremendous research interest in the recent year. Most existing
works focus only on the line-of-sight (LOS) transmission by infrared (IR) or visible light lasers/LEDs, while this article
suggested a framework of non-line-of-sight (NLOS) FSO, motivated by our recent experimental results on the successful
transmission of NLOS ultraviolet (UV) beams for up to kilometers, which is comparable to the typical distance a LOS
FSO transmission. The NLOS provides an alternate path when the LOS path is shadowed or is highly attenuated. In order
to mitigate the multipath dispersion of the NLOS FSO, a baseband orthogonal frequency division multiplexing (OFDM)
modulation scheme was proposed, based on Discrete Hartley Transform (DHT) and asymmetric clipping to guarantee
the positive-realness of the transmitted optical intensity. The proposed system could reduce the hardware complexity
of transmitter and receiver. Minimum mean square error (MMSE) precoder was applied before the DHT to remove the
crosstalk between subcarriers, i.e. the frequency domain orthogonality of OFDM was preserved. Performance of the BPSK
modulated communication system was given under lognormal atmospheric turbulence for demonstration of the feasibility
of the proposed method.
Recently ultraviolet (UV) scattering channels have received renewed interest for non-line-of-sight (NLOS)
communication. Monte Carlo simulations and field experiments have yielded valuable results to predict channel path
loss and impulse response at relatively short ranges, critical for communication link analysis. However, as
communication range increases, the effect of turbulence becomes pronounced and inevitably induces additional
impairments to system performance. This paper suggests a turbulence modeling method for NLOS UV channels
incorporating the effects of scattering and absorption. The modeling results can be applied to study communication
performance.
We report some latest experimental results on non-line-of-sight (NLOS) ultraviolet (UV) scattering communication
channel characteristics. Those results include both channel path losses and impulse responses, critical for UV
communication system design. Path losses were measured using a UV light-emitting-diodes (LEDs) based test-bed,
while impulse responses by a UV laser based test-bed. The effects of transmitter and receiver pointing angles, separation
distance and transmit beam angle are demonstrated.
Fundamental characteristics of non-directed line-of-sight links for indoor wireless optical communication systems have
been widely discussed. In this paper, we present experimental visible light channel characterization results, including
impulse response and path loss, and further predict the fundamental communication system performance trade-offs
among transmitted optical power, range, data rate and bit-error rate. These results provide guidelines to system design.
Non-line-of-sight (NLOS) ultraviolet (UV) scattering channel impulse response in the deep UV solar-blind spectrum
band is investigated. Taking into account a light source power angular distribution and applying a photon tracing
technique, Monte Carlo simulation is performed to obtain the channel impulse response and associated path loss. Some
comparisons are carried out with an existing single scattering channel model, as well as field measurements in both the
impulse response model and path loss, to demonstrate modeling accuracy. The importance of considering multiple
versus single-scattering in the analysis is shown. The results provide guidelines for study of limitations to data rate and
communication range in NLOS UV communications.
Visible light communication in conjunction with solid state lighting has become an emerging area of interest to achieve
lighting and wireless communication simultaneously in an indoor environment. It is anticipated to be a low cost
supplement to existing wireless communication technologies. Most existing work has primarily focused on a
unidirectional downlink using visible light spectra. The appropriate choice of an uplink to achieve bidirectional
communication is a big challenge. In this paper, candidate options of the uplink are compared in terms of device
performance, light safety, background interference, and path loss. In visible light communication, white light emitting
diodes as optical transmitters are also characterized in terms of impulse response and electrical spectrum. A digital preequalization
idea to increase their bandwidth is proposed. Performance of the downlink visible light communication
system is also experimentally studied in order to demonstrate the feasibility of the proposed design.
Recent advances in ultraviolet (UV) semiconductor sources and detectors have inspired significant research activities in
short-range UV communications, particularly in non-line-of-sight (NLOS) channel conditions due to atmospheric
scattering. However, a scattering channel involves complex interactions of photons with atmospheric particles. This
paper presents a parametric channel model that greatly simplifies channel characterization. For a short range link, single
scattering may dominate in some scenarios. We model the channel impulse response with a gamma function as well as
its variants to better fit the prediction by a widely adopted analytical single scattering model. Normalized mean square
fitting error is adopted to validate our parametric model. Path losses and channel bandwidths are subsequently studied
under different geometrical link configurations.
Motivated by rapid advances in solar blind ultraviolet (UV) light emitting diodes (LEDs), filters and photomultiplier
tubes (PMTs), together with unique UV atmospheric propagation characteristics, a non-line-of-sight (NLOS) UV
communication test-bed has been recently built and utilized for extensive experimental evaluation of performance of
NLOS UV links in outdoor environments. Towards this end, key link components are first characterized and their
limitations are identified. The tradeoffs among communication range, received number of photons, and bit-error-rate are
revealed via field measurement results. Wavelength diversity is achieved by utilizing combinations of sources and
detectors centered at different wavelengths in the solar blind band. It is demonstrated that signals can be reliably
transmitted to their destinations of dozens of meters away through an NLOS channel. Although all reported results in
this paper are based on open field experiments, it is found that reflections from surrounding objects such as trees and
buildings can enhance the received signal strength, up to an order of magnitude increase in the received number of
photons in some cases, thus significantly improving link performance.
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