Non-line-of-sight Communication Research Articles

Non-line-of-sight ultraviolet transmission coverage in non-precipitating, foggy, and rainy weather.

Sensitivity to weather conditions is the principal limitation of free-space optical communication. However, for the scattering based ultraviolet (UV) non-line-of-sight (NLOS) communication, the atmospheric scattering effect functions as an attenuation factor and potentially as a performance enhancer. To investigate the UV NLOS transmission coverage under different weather conditions, we employ the Mie Theory in conjunction with classical aerosol and hydrometeor particle models to estimate the absorption coefficient, the scattering coefficient, and the scattering phase function. We then use these atmospheric parameters combined with a range estimation model to determine the coverage of the UV NLOS communication for specified path loss. Simulation results reveal that in non-precipitating weather, poorer visibility correlates with broader coverage. In foggy conditions, the coverage range in light fog exceeds that in fog-free environments; however, as fog intensity increases, the coverage range decreases. Rain enhances the coverage range; and heavier precipitation results in a larger coverage area.

Reconfigurable Intelligent Surface-Aided Orthogonal Time Frequency Space and Its Deep Learning-Based Signal Detection

Orthogonal time frequency space (OTFS) has emerged as a promising modulation for next-generation wireless systems. This two-dimensional (2D) modulation has the inherent capability of providing uninterrupted connectivity and improved performance in a high-mobility doubly-selective channel by mapping the information symbols to the delay-Doppler (DD) domain. In order to improve the directivity of OTFS signals, this paper considers a reconfigurable intelligent surface (RIS)-aided OTFS transmission for a high-speed environment. While OTFS mitigates the dispersion due to the highly mobile wireless channels by mapping the transmit symbols to the DD domain, RIS improves the directivity by appropriately shifting the phase of the signal in non-line-of-sight (NLOS) communication channels. We provide a concrete matrix-based mathematical model of the RIS-aided OTFS communication system. Capitalizing on the simple matrix multiplication-based model, a number of detectors can be used. These include the usual zero-forcing (ZF) and the minimum mean-squared error (MMSE) linear detectors, and a low-complexity message passing algorithm (MPA)-assisted detector. We evaluate the performance of these detectors for RIS-based OTFS systems. A deep learning (DL)-based signal detector is also proposed for the RIS-aided OTFS system. A significant improvement in bit-error-rate (BER) performance is achieved using the system considered, while the RIS-induced computational burden is not high. Furthermore, in NLOS communication, our system can ensure seamless connectivity with a reduced number of base stations (BS).

The LOS/NLOS Classification Method Based on Deep Learning for the UWB Localization System in Coal Mines

A localization system is one of the basic requirements for coal mines. Ultra-wideband (UWB), as a technology with broad application prospects, is considered to have great potential in the absence of satellite signals, especially in the underground mine environment, as it can provide rescue assistance. However, state-of-the-art UWB position systems in coal mines cannot efficiently differ the line-of-sight from all communication links, which results in deterioration of the localization accuracy. In this paper, we propose a LOS/NLOS classification method based on a deep learning algorithm. Specifically, we utilize the Generative Adversarial Networks (GAN) to generate diagnostic data for frame transmission under non-line-of-sight (NLOS) condition. Then, a Convolutional Neural Network (CNN) is adopted to identify the NLOS communication. Finally, the trilateral centroid positioning algorithm (TCPA) based on ranging data is used to verify the effect of our method for a localization system in coal mines. Field experiments show that our method can accurately differ the LOS/NLOS with the accuracy of 91.19%. The TCPA algorithm with our method can obtain 3.11% improvement compared with the scenario without using our method.

Characterization of Blue-Green Light Non-Line-of-Sight Transmission in Seawater

The blue-green light in the 450 nm to 550 nm band is usually used in underwater wireless optical communication (UWOC). The blue-green light transmission in seawater is scattered by the seawater effect and can achieve communication in non-line-of-sight (NLOS) transmission mode. Compared to line-of-sight (LOS) transmission, NLOS transmission does not require alignment and can be adapted to various underwater environments. The scattering coefficients of seawater at different depths are different, which makes the scattering of light in different depths of seawater different. In this paper, the received optical power and bit error rate (BER) of the photodetector (PD) were calculated when the scattering coefficients of blue-green light in seawater vary from large to small with increasing depth for NLOS transmission. The results show that blue-green light in different depths of seawater in the same way NLOS communication at the same distance, the received optical power and BER at the receiver are different, and the received optical power of green light is greater than that of blue light. Increasing the forward scattering coverage of the laser will suppress the received optical power of the PD, so when performing NLOS communication, appropriate trade-offs should be made between the forward scattering coverage of the laser and the received optical power.

The Impact of Vertical Salinity Gradient on Non-Line-of-Sight Underwater Optical Wireless Communication

The non-line-of-sight (NLOS) underwater communication can offer a viable route in signal propagation and coverage, thus mitigating the pointing, acquisition, and tracking difficulties in line-of-sight optical communication. However, implementing the NLOS link is non-trivial. While the NLOS technique relies on light scattering, i.e., channel turbulence can facilitate NLOS communication, the associated path-loss (PL) can be significant. Signal fading can degrade link robustness, which arises due to ocean water temperature and salinity fluctuation and gradients. To evaluate the robustness of NLOS in natural waters, we systematically measure the link metrics, such as the bit error ratio, PL, and signal-to-noise ratio (SNR), of water bodies of uniform and nonuniform vertical salinity ranging from 30–40‰ (part-per-thousand). We found that salinity-induced turbulence can establish NLOS communication with PL reduction of 2.35 dB/m and SNR increase by 32.5 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\%$</tex-math></inline-formula> for dynamic water. Furthermore, a strong correlation was obtained between the strength of signal fluctuations and the received SNR. Finally, we obtained a Gaussian distribution of the statistical scintillation behavior. These results demonstrated the benefit of using the NLOS regime for underwater wireless sensor networks for aiding designers and engineers.

Non-line-of-sight optical communication based on orbital angular momentum.

Optical non-line-of-sight (NLOS) communication can exploit the indirect light path to provide free-space communications around obstacles that occlude the field of view. Here we propose and demonstrate an orbital angular momentum (OAM)-based NLOS communication scheme that can greatly improve its channel dimensionality. To verify the feasibility for extending the amount of multiplexed OAM channel dimensionality, the effects of bit accuracy versus the number of channels in measuring OAM modes are quantified. Moreover, to show the ability for broadcast NLOS tasks, we report a multi-receiver experiment where the transmitted information from scattered light can be robustly decoded by multiple neuron-network-based OAM decoders. Our results present a faithful verification of OAM-based NLOS communication for real-time applications in dynamic NLOS environments, regardless of the limit of wavelength, light intensity, or turbulence.

Visible light communication for intelligent transportation systems: A review of the latest technologies

In seeking to improve traffic congestion and safety on roads and highways, there has been an increased interest in intelligent transportation systems (ITS). The emerging visible light communication (VLC) technology is a new candidate to enable wireless access in ITS. The purpose of this study is to present a comprehensive review of the current studies related to VLC. Since VLC facilitates illumination and data communication simultaneously, it reduces energy consumption significantly. Additionally, VLC is immune to electromagnetic interference, provides high data security, and utilizes unregulated visible light spectrum, showing promise as a potentially cheaper alternative to existing radio frequency (RF) based technology. Moreover, recent advances in semiconductor materials and solid-state technologies have enabled the development of efficient light-emitting diodes (LEDs) and laser diodes (LDs) which are used as transmitters in a VLC system. Although 10 s of Gbits/s data rate has been demonstrated in indoor VLC links, successful implementation of it in outdoor environments requires further research to overcome the challenges presented by environmental factors, unwanted lights, non-line of sight communication, directional radiation pattern, frequent fragmentation, and so on. Besides, in recent years, semiconductor LDs have been garnering more attention since they can transmit more data over longer distances due to their high quantum efficiency and modulation bandwidth compared to LEDs. As a result, urban planners, policy-makers, transportation engineers, and vehicle manufacturers are considering LD-based VLC to facilitate vehicle-to-vehicle and vehicle-to-infrastructure communication. Thus, this paper reviews and compares the most recent developments in VLC technologies, identifies their benefits and potential use in ITS applications, discusses the probable barriers for their implementation in our existing transportation infrastructure, and suggests future research directions and recommendations to overcome these challenges. • Recent developments in visible light communication (VLC) technology and its potential use in ITS applications are reviewed. • Light-emitting diodes (LEDs) and laser diodes (LDs) can be used as transmitters in VLC systems. • The overall performance of LDs is superior to that of the LEDs. • LDs can transmit more data over longer distances due to their high quantum efficiency and modulation bandwidth. • It is recommended to focus more on LD-based illumination in V2V and V2I communications.

Directive mmWave radio channel modeling in a ship hull

AbstractWireless connectivity has been realized for multiple environments and different frequency bands. However, little research exists about mmWave communication in industrial environments. This paper presents the 60 GHz double-directional radio channel for mmWave communication in a ship hull for Line-of-Sight (LOS) and non-Line-of-Sight (NLOS) conditions. We performed channel measurements using the Terragraph channel sounder at different locations in the ship hull and fitted LOS path loss to a one-slope path loss model. Path loss and root-mean-square delay spread of the LOS path is compared to the reflected path with lowest path loss. NLOS communication via this first-order reflected path is modeled by calculating the path distance and determining the reflection loss. The reflection losses have a considerable contribution to the signal attenuation of the reflected path. The channel models are implemented in an indoor coverage prediction tool, which was extended with a ray launching algorithm and validated by comparison with an analytical electromagnetic solver. The results show that the mmWave radio channel allows high-throughput communication within a ship hull compartment, even when no LOS path between the transmitter and receiver is present.

LaUV: A Physics-Based UV Light Simulator for Disinfection and Communication Applications

The sterilization properties of the C-band of the ultraviolet (UV) light have been well-known for many years; however, their application has become more vital and widespread today due to the Covid-19 pandemic. Nevertheless, minimal work has been devoted to simulating UV-C propagation for surface disinfection in indoor environments. UV light has also been proposed for non-line-of-sight (NLOS) outdoor communication applications, where a number of simulators have been developed, but with several simplifications. The current work presents a fully-featured simulator for UV light propagation, called LaUV, designed mainly for indoor settings, capable of calculating measurable parameters that can be used for indoor surface disinfection and communication applications. LaUV considers atmospheric absorption and scattering according to Rayleigh and Mie theory, and reflections from rough surfaces. The scattering cross-section and probability density function of the scattering angles (phase function) are calculated accurately for any wavelength, concentration, and diameter distribution of spherical scattering particles (aerosols and droplets). Examples are presented for indoor environments, including empty rooms and rooms with furniture, for different environmental conditions and surface albedos. Interesting initial conclusions can be drawn, considering the spatial distribution of UV exposure for surface disinfection applications and channel modeling for line-of-sight (LOS) and NLOS communication, demonstrating the versatility and the potential applications of the proposed simulator.

Performance analysis of MIMO communication system with NLOS UV channel

Performance analysis is carried out, of a multiple input, multiple output (MIMO) ultraviolet (UV) communication system with a non-line-of-sight (NLOS) UV channel. The achievable bit error coefficient is calculated using three spatial multiplexing methods for different bitrate values, azimuthal deviation between the directional diagrams of an optical transmitter and an optical receiver, and different noise levels. Full Text: PDF ReferencesZ. Xu, B. Sadler, "Ultraviolet communications: potential and state-of-the-art", IEEE Commun. Mag. 4667-73 (2009). CrossRef D. Han, Y. Liu, K. Zhang et al., "Theoretical and experimental research on diversity reception technology in NLOS UV communication system", Opt. Expr. 20(14), 15833 (2012). CrossRef Q. Guo, N. He, Z. He, "Research on the channel performances and transmission in UV-LED scatter communications", Study Opt. Comm. 3, 64 (2013). DirectLink G. Chen, L. Liao, Z. Li et al., "Experimental and simulated evaluation of long distance NLOS UV communication", Communication Systems, Networks and Digital Signal Processing (CSND-SP), 9th Int. Symp. on IEEE, 904-909 (2014). CrossRef M.A. El-Shimy, S. Hranilovic, "Spatial-Diversity Imaging Receivers for Non-Line-of-Sight Solar-Blind UV Communications", J. Lightwave Techn. 33(11), 2246 (2015). CrossRef G. Shaw, M. Nischan, M. Iyengar, S. Kaushik, M. Griffin, NLOS UV communication for distributed sensor systems, Proc. SPIE 412683, 96 (2000). CrossRef I.S. Konstantinov, G.S. Vasyliev, O.R. Kuzichkin, D.I. Surzhik, I.A. Kurilov, S.A. Lazarev, "AUV Link Mobile Ad-Hoc Network Examination", J. Eng. Adv. Techn. 8(5S) July 2019 CrossRef I.S. Konstantinov, G.S. Vasilyev, O.R. Kuzichkin, I.A. Kurilov, S.A. Lazarev, "Modeling and Analysis of the Characteristics of Ultraviolet Channels under Different Conditions of Radiation Propagation for the Organization of Wireless AD-HOC Network", J. Adv. Res. Dynam. Contr. Syst. 07, 1853 (2018) DirectLink I.S. Konstantinov, G.S. Vasyliev, O.R. Kuzichkin, D.I. Surzhik, I.A. Kurilov, S.A. Lazarev, "Development Of Uv Communication Channels Characteristics Modeling Algorithm In A Mobile Ad-Hoc Network", J. Adv. Res. Dynam. Contr. Syst. 11(08), 1920 (2019). CrossRef G. Chen, F. Abou-Galala, Z. Xu, B.M. Sadler, "Experimental evaluation of LED-based solar blind NLOS communication links", Opt. Expr. 16(19), 15059 (2008). CrossRef

NLOS Communication: Theory and Experiments in the Atmosphere and Underwater

In this paper, we present investigations of non-line-of-sight (NLOS) communication carried out in Russia and in collaboration with researchers in Israel. The theories of radiative transfer and linear systems provide the theoretical basis for this joint research, and experimental results demonstrate that maximal ranges for NLOS communication through atmospheric channels can reach hundreds of kilometers in the visible range and tens of kilometers in the ultraviolet (UV) range of the spectrum. Finally, we predict the range of bistatic underwater communication systems can reach hundreds of meters.

Superior Deep-Ultraviolet Source Pumped by an Electron Beam for NLOS Communication

Deep-ultraviolet (DUV) light ranging from 200 to 280 nm, that is, a solar-blind region, has been widely applied to water purification, sterilization, and integrated biosensors. As the light source for nonline-of-sight (NLOS) communication, DUV light has the natural advantage of a negligible background due to strong ozone absorption. However, the existing DUV sources suffer from either low power or low modulation frequency. Here, we demonstrate a DUV source pumped by an electron beam (EB) at 246 nm with a record-high performance for NLOS communication, that is, a simultaneous continuous-wave output power of 430 mW and a modulation frequency of 5 MHz. Significantly, both the output power and the modulation frequency can be further improved when the horsepower of EBs is fully released. Not only does the proposed DUV source show great capability for NLOS communication and other potential applications, but the EB pumping approach can also be extended to various emission processes.

Broadcast Performance Analysis and Improvements of the LTE-V2V Autonomous Mode at Road Intersection

An autonomous V2V communication mode (also known as side-link mode 4), which facilitates V2V communication in out of eNB coverage areas, has recently been introduced into the Long term evolution (LTE) standard. Recent research has studied the performance of this LTE-V2V autonomous mode for a highway use case. However, performance analysis for a highway use case cannot be easily applied to an intersection use case as it may contain non-line-of-sight (NLOS) communication links. In this paper, we analyze and evaluate the safety message broadcasting performance of LTE-V2V autonomous mode in an urban intersection scenario. Considering practical path loss models, we present the impact of NLOS communication link on the overall message dissemination performance. Through the analytical and simulation results, we show that the overall message dissemination performance degrades drastically with increasing vehicle density and increasing distance of the transmitting vehicle from the intersection. To improve the performance, we propose a vehicle-assisted relaying scheme in which the relaying vehicle is selected in an autonomous manner. We also present two resource allocation strategies for the relaying vehicle. For low to medium vehicle density along the street, we observe significant improvement in message dissemination through relaying compared to the scheme without relaying.

Research on relay selection of armored formations wireless UV covert communication

In view of the end-to-end communication interruption problem of armored formations in complex battlefield environments, relay-assisted methods are often used to establish cooperative communications links, and the choice of relay is a key issue. In order to improve the communication coordination ability among formations, an optimal relay selection algorithm for armored formations based on wireless ultraviolet (UV) covert communication is proposed on the premise of decode-and-forward protocol, combined with the threshold decision idea. The algorithm combines the advantages of UV NLOS(non-line-of-sight) communication. The optimal relay selection is made for the formations according to the signal-to-noise ratio (SNR) threshold and channel characteristics selection strategy, and the bit error rate (BER) performance is analyzed under Gaussian noise model. The simulation results show that the optimal relay link can be obtained by selecting the appropriate cooperation threshold according to different SNR environments and relay number. Furthermore, adjusting the receiving and transmitting status of the relay, when the cooperative communications link changes dynamically, can effectively improve the communication quality of the cooperative relay link.

Оптическая связь на рассеянном или отражённом лазерном излучении

Results of theoretical and experimental research of NLOS (NonLine of Sight) communication systems in the atmosphere, under water, and in mixed media based on publications of authors from China, Canada, Greece, the USA, Great Britain, Russia, and other countries are discussed in the present work. The theory of radiation transfer and the linear systems theory provide the basis for theoretical research. The radiation transfer equation is solved by the Monte–Carlo method in the singlescattering approximation. It is demonstrated that approximate methods are applicable when the average scattering multiplicity in open communication channels does not exceed 1. The Monte Carlo method is used to study the influence of opticalgeometric parameters of schemes of communication channels on the probabilities of communication errors, signal/noise ratios, limiting base lengths, attenuation of informationcarrying signals, and their superposition leading to communication errors. Examples of communications in the atmosphere in the UV range at distances up to 1300 m, in the visible range up to70 km, and under water up to 20 m are given. Search for optimal methods of signal modulation, development of software and hardware complexes for numerical simulation of the transfer properties of communication channels, refinement of analytical models of impulse transfer characteristics of noncoplanar schemes of bistatic optoelectronic communication systems (OECS), and research of the effect of winddriven sea waves and processes of radiation scattering in water are planned to study the efficiency of operation of the communication systems and to expand ranges of variations of the input NLOS and OECS parameters in the experiments carried out in natural water reservoirs.

Performance analysis of downlink mmWave networks under LoS/NLoS propagation with blockage and directional beamforming

Due to the spectrum scarcity in conventional celluar frequency bands, millimeter wave (mmWave) frequency bands are attracting increasing attention as a promising candidate for future wireless cellular communication networks. The performance analysis in terms of coverage and rate of mmWave network is a crucial aspect and has been received an increasing interest in recent literature. However, the impact of LoS/NLoS propagation and outage on the coverage probability and rate of the mmWave network is yet to be completely understood. In this paper, we analyze the performance of mmWave networks considering (a) only Non Line-of-Sight (NLoS) environment and (b) both NLoS and LoS propagation. In particular, we compare the coverage and rate performances of mmWave networks with a more practical blockage model that encompasses an outage state, standard path loss function,and directional beamforming which is implemented using number of antennas and scanning angle at the transmitter and receiver. Further, for more practical and precise analysis, we assume that channel amplitudes are Nakgami-m distributed with different fading parameters for NLoS and LoS communication links. Also, different from existing works, the user association with a BS is assumed with a LoS/NLoS path with the smallest pathloss. Our numerical results depict that the presence of an outage state in blockage model decreases the performance of mmWave network. Also, we show the presence of LoS propagation increases the performance of network at the small average cell radius. Further, the impact of variable number of transmit antennas, scanning angle, and antenna radiation efficiency on the network performance is also addressed.

Performance Analysis of IEEE 802.15.4 in Different NLOS Environments of Smart Grids

Background: In smart grids mainly there are two types of communications based on the paths travelled by the received signals. These are line of sight (LOS) communication and non-line of sight (NLOS) communication. These communication models are formed because of different harsh environments like 500 kV outdoor substations, main power control room and underground transformer vaults which are very difficult to access and monitor for a human being during an operational power grid. In the recent research, the network lifetime has been evaluated with respect to the arrival rate, distance and duty cycle for LOS and NLOS communication. Methods:The systematic analysis is performed to characterize the aptness of the cluster tree topology of ZigBee based wireless sensor networks in the monitoring of non-line of sight regions having different shadowing channel properties in the smart grids. Results: The performance is evaluated by thoroughly analyzing the average end-to-end delay with respect to the packet interval, throughput, energy consumption, packet reception rate and network lifetime with respect to the packet size. The simulations are performed on QualNet 6.1 simulator. The objective of this work is to determine the influence of packet interval, packet size and different NLOS environments on the performance of ZigBee based wireless sensor network deployed in smart grids and to give prominence to this field for further exploration. Conclusion: The simulation results illustrate that huge errors in packet reception and variable link capacity in complex environments of the smart grid spectrum gives rise to many challenges in the reliability of ZigBee based wireless communications in smart grids. The design and implementation of efficient algorithms and protocols to reduce the collisions and interference can be considered for the future work. Keywords: Smart grid, Wireless sensor network, Shadowing parameters, Cluster tree topology, QualNet 6.1.

A 60GHz Wireless Cooperative Communication System Based on Switching Beamforming

The challenge of penetrating obstacles along with impact from weak multipath effects makes 60GHz signal very difficult to be transmitted in non-line of sight (NLOS) channel. So 60GHz system is vulnerable to obstructions and thus likely results in link interruption. While the application of cooperative technology to solve link blockage problemin 60GHz system should consider the characteristic of directional transmission for 60GHz signal. Therefore in this paper a system is proposed to solve the link blockage problem in 60GHz NLOS communication environment based on the concept of cooperation and also the beamforming technology, which is the basis of directional transmission for 60GHz communication system. The process of anti-blockage solution with cooperative communication is presented in detail, and the fast switching and recovery schemes are well designed. The theoretical values of symbol error rate (SER) using decode and forward (DF) cooperation and amplify and forward (AF) cooperation are presented respectively when the common channel interference exists. Simulation results demonstrate that the performance based on DF cooperation is better than the performance based on AF cooperation when directional transmission is used.

ToA Node Distance Estimation Enhancement in MANET Localization Algorithm Based on Cooperative Trilateration

This paper provides a brief survey of the Time of Arrival (ToA) ranging method often used in the Range-based localization for node distance estimation. It is focused especially on the Non Line-of-Sight (NLoS) channel identification – one of the dominant factors that negative affect the location accuracy. It deals with the improvement of the received signal arrival time determination in the case of NLoS communication with undetected direct path. The low complexity NLoS mitigation method is proposed in this paper that estimates the time of arrival of the missing direct path as a mean of the time delays of reflected paths. This method is implemented in the cooperative positioning algorithm based on the circular trilateration. The IEEE 802.15.4a statistical channel model is used to simulate the mobile node communication.

A Path Loss Model for Non-Line-of-Sight Ultraviolet Multiple Scattering Channels

An ultraviolet (UV) signal transmission undergoes rich scattering and strong absorption by atmospheric particulates. We develop a path loss model for a Non-Line-of-Sight (NLOS) link. The model is built upon probability theory governing random migration of photons in free space, undergoing scattering, in terms of angular direction and distance. The model analytically captures the contributions of different scattering orders. Thus it relaxes the assumptions of single scattering theory and provides more realistic results. This allows us to assess the importance of high-order scattering, such as in a thick atmosphere environment, where short range NLOS UV communication is enhanced by hazy or foggy weather. By simulation, it is shown that the model coincides with a previously developed Monte Carlo model. Additional numerical examples are presented to demonstrate the effects of link geometry and atmospheric conditions. The results indicate the inherent tradeoffs in beamwidth, pointing angles, range, absorption, and scattering and so are valuable for NLOS communication system design.