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This paper studies the maximum reliability of multi-hop relay UAVs, in which UAVs provide wireless services for remote users as a coded cooperative relay without an end-to-end direct communication link. In this paper, the analytical expressions of the total power loss and total bit error rate are derived as reliability measures. First, based on the environmental statistical parameters, a LOS probability model is proposed. Then, the problem of minimizing the bit error rate of static and mobile UAVs is studied. The goal is to minimize the total bit error rate by jointly optimizing the height, elevation, power and path loss and introducing the maximum allowable path loss constraints, transmission power allocation constraints, and UAV height and elevation constraints. At the same time, the total path loss is minimized to achieve maximum ground communication coverage. However, the formulated joint optimization problem is nonconvex and generally difficult to solve. Therefore, we decomposed the problem into two subproblems and proposed an effective joint optimization iteration algorithm. Finally, the simulation results are given, and the analysis shows that the optimal height of different reliability measures is slightly different; thus, using the mobility of UAVs can improve the reliability of communication performance. [ABSTRACT FROM AUTHOR]

In this paper, a detailed analysis has been carried out related to body-to-body communication links in an indoor office environment using compact ultra-wideband wearable antennas. The links have been analysed on the basis of path loss magnitude variation and statistical information which are dependent on the orientation and distance. Four orientations of the transmitter and receiver are chosen, namely facing front, back, side right, and side left. The distance between the links is varied up to 5 m to consider the effect of separation between the Tx and Rx. The path loss magnitude has been classified into three ranges, which mainly represent direct path propagation (R1:40–55 dB), partially obstructed/high multipath links (R2:55–60 dB), and totally obstructed links (R3 > 60 dB). The presence of path loss in the range R1 is highest (35%) for the case when the Tx is facing front for B-to-B links due to the high chance of direct line-of-sight propagation between the Tx and Rx. The percentage of occurrence of PL (>60 dB) is highest (95 %) for the scenario in which the Tx is facing back for B-to-B links which is due to the obstruction caused for all the orientations of the receiver. The difference in PL statistics and modelling is observed for various B-to-B links that are attributed to the fact of the presence of two human subjects and the corresponding orientations. This leads to variation in the antenna radiation pattern which in turn affects the propagation characteristics and the channel parameters. [ABSTRACT FROM AUTHOR]

Existing intervisibility analysis methods suffer from computational inefficiency due to redundant sampling points. To address this issue, we propose a new approximate method called line-of-sight (LoS) zoning, which leverages continuous terrain relief to identify potentially obscuring zones (POZ) of LoS. By limiting the sampling range to a much smaller POZ, the number of sampling points is significantly reduced. The optimal sampling interval of 6 is determined by striking a balance between computational efficiency and accuracy. Through experiments in both mountainous and plain areas, regardless of the height range and resolution conditions, we demonstrate the high efficiency of the LoS zoning method, especially in scenarios with a high proportion of visible LoS. To account for potential visibility errors caused by sharp peaks in the terrain, we conducted experiments under fixed time intervals to assess the calculation quality of different methods. The results show that in mountainous and plain areas, the improvement in detection rate compared to the hopping strategy method is around 4–6 times in most scenarios. This significant performance enhancement highlights the superiority of the LoS zoning method, and shows great promise in terrain avoidance, path planning in the military, and detection of dangerous targets. [ABSTRACT FROM AUTHOR]

Essential for improving the accuracy and reliability of bowel cancer screening, three-dimensional (3D) surface reconstruction using capsule endoscopy (CE) images remains challenging due to CE hardware and software limitations. This report generally focuses on challenges associated with 3D visualization and specifically investigates the impact of the indeterminate selection of the angle of the line–of–sight on 3D surfaces. Furthermore, it demonstrates that impact through 3D surfaces viewed at the same azimuth angles and different elevation angles of the line–of–sight. The report concludes that 3D printing of reconstructed 3D surfaces can potentially overcome line–of–sight indeterminate selection and 2D screen visual restriction-related errors. [ABSTRACT FROM AUTHOR]

The research studies hyper-Rayleigh behavior of a wireless communication system functioning in the presence of the generalized multipath fading. Although the initial metric (hyper-Rayleigh mode (HRM)) is quite informative, it is defined only asymptotically (i.e., for the infinitely increasing SNR). In spite of mathematical simplifications brought by such a definition (i.e., in this case most of the performance characteristics defining the HRM can be easily evaluated), it sufficiently limits its applications since, evidently, the real-life systems function in the presence of a finite (and usually not very high) SNR. The study presents a novel approach to the fading channel analysis (i.e., finite signal-to-noise ratio hyper-Rayleigh mode (fHRM)). The proposed metric (fHRM) is studied on the newly presented channel model-fluctuating double-Rayleigh with Line-of-Sight (fdRLoS) fading model. To accomplish this, the novel expressions for two channel-dependent system characteristics (i.e., the Amount of Fading (AoF) and the Outage Probability (OP)) were derived in exact form valid for arbitrary fading parameters. Based on the derived expressions, the finite SNR hyper-Rayleigh map is obtained, which helps to identify the parameters' values corresponding to the specific propagation scenarios, which were further deployed to analyze the problem of the communication link physical layer security quantified in terms of the probability of strictly positive secrecy capacity (SPSC). Numerical verification of the derived closed-form expressions was performed. Several peculiarities of the system performance are observed and discussed. [ABSTRACT FROM AUTHOR]

In this paper, the path following of underactuated unmanned surface vehicles (USVs) is solved under the circumstance of external environment disturbances, uncertain model parameters, and limited thrust. First, a preset performance line-of-sight guidance law based on the adaptive extended state observer (ESO) is proposed to ensure that the USV can follow the path safely and quickly while restricting the position errors of the desired path. Then, in the dynamic control subsystem, a fixed-time ESO is proposed to improve the convergence rate of the estimated correlated perturbations and unknown state quantities. Finally, a finite-time saturation compensation system is introduced to improve the saturation compensation speed of the actuator when the thrust is finite. The effectiveness of the proposed performance control strategy is verified by path following simulation. [ABSTRACT FROM AUTHOR]

On account of the external disturbances and difficult maneuverability of a hovercraft, this paper devises a safety-guaranteed, robust, nonlinear, path-following control strategy of a hovercraft targeted for unknown dynamics, unavailable velocity, and unknown external ocean disturbances. Firstly, for the sake of accurately observing unavailable lumped disturbances and unavailable velocity measurements, a finite-time extended state observer (FTESO) is proposed. Secondly, a line-of-sight (LOS) guidance law constructed with a bounded-gain-forgetting (BGF) adaptive estimator is devised to follow the desired path while considering external environmental disturbances accurately, in which the tracking errors and the parameter estimation are both proven to be bounded. In addition, for the sake of safety, a safety-guaranteed auxiliary system that can constrain the drift angle during the hovercraft's navigation is proposed. Thirdly, the robust, nonlinear, path-following controllers achieved high tracking performance with the constructed safety-guaranteed compensation backstepping method. Finally, according to the Lyapunov and homogeneous theories, the observation error can be guaranteed to zero and the tracking error can converge to an arbitrarily small region near zero in finite time. Numerical simulations illustrate the effectiveness for the proposed robust, nonlinear, path-following scheme. [ABSTRACT FROM AUTHOR]

With the tremendous increase in wireless user traffic, investigation on the end-to-end reliability of wireless networks in practical conditions such as non-homogeneous fading channel conditions is becoming increasingly widespread. Because they fit well to the experimental data, generalized channel fading distributions like κ–μ are well suited for modeling diverse fading channels. This paper analyzes the symbol error rate (SER) and outage probability (OP) performance of multiple-input multiple-output (MIMO) space-time block-code (STBC) selective decode and forward (S-DF) network over κ–μ fading channel conditions considering the additive white Gaussian noise (AWGN). First, the closed-form (CF) analytical expressions for the probability density function (PDF) and the cumulative distribution function (CDF) of the received signal-to-noise ratio (SNR) as well as its moment generating function (MGF) are derived. Second, the OP performance is then investigated for various values of the channel fading parameter and SNR regimes. The simulation findings show an increase in SER performance with an improved line-of-sight (LOS) component. Furthermore, the results show that the S-DF relaying systems can function properly even when there is no fading or LOS component. The OP has been increasing with the increase in the value of μ and κ. In medium and high SNR regimes, simulation results exactly match with analytical results. [ABSTRACT FROM AUTHOR]

Concentrating on a surface vessel with input saturation, model uncertainties and unknown disturbances, a path following the adaptive backstepping control method based on prescribed performance line-of-sight (PPLOS) guidance is proposed. First, a prescribed performance asymmetric modified barrier Lyapunov function (PPAMBLF) is used to design the PPLOS and the heading controller, which make the path following position and heading errors meet the prescribed performance requirements. Furthermore, the backstepping and dynamic surface technique (DSC) are used to design the path following controller and the adaptive assistant systems are constructed to compensate the influence of input saturation. In addition, neural networks are introduced to approximate model uncertainties, and the adaptive laws are designed to estimate the bounds of the neural network approximation errors and unknown disturbances. According to the Lyapunov stability theory, all signals are semi-globally uniformly ultimately bounded. Finally, a 76 $\,{\cdot }\,$ 2 m supply surface vessel is used for simulation experiments. The experimental results show that although the control inputs are limited, the control system can still converge quickly, and both position and heading errors can be limited to the prescribed performance requirements. [ABSTRACT FROM AUTHOR]

The performance of millimeter wave (mmWave) line-of-sight multiple input multiple output (LOS MIMO) systems using hybrid arrays of planar subarrays was studied. We characterized the achievable maximum spatial multiplexing gain for such LOS MIMO systems by the measures of spectral efficiency and effective degree of freedom (EDoF). By proposing a joint plane-wave and spherical-wave-based general 3D channel model, we derived the optimal design parameters in the analog domain, i.e., the optimal subarray separation products, and analyzed their sensitivity on the system performance. We also gave analytical eigenvalue expressions of the equivalent LOS MIMO channel matrix, which are applicable to the case of a non-optimal design, as well as the upper and lower bounds of the EDoF for system performance evaluation. A piecewise uniform quantization codebook was further designed for quantizing phase shifter values in practical applications. The numerical and simulation results show that planar subarrays are superior to traditional arrays in terms of spectral efficiency and EDoF in Ricean fading channels because they are more robust to the change in the communication distance and the deviation from the optimal design. The use of hybrid arrays of planar subarrays effectively removes the limitation of mmWave LOS MIMO systems using traditional arrays, through which, the conventional Rayleigh distance criterion has to be satisfied to achieve the optimal performance. [ABSTRACT FROM AUTHOR]

The use of mmWaves for achieving 5G networks is increasingly being seen as a necessity due to the vastly improved bandwidth and data rates at these frequencies. These waves suffer from severe attenuation and their use may, however, be restricted, in the immediate future, to short-range networks, such as personal area networks (IEEE 802.11ad) or vehicular and mobile adhoc networks operating in proximity. MmWaves require directional antennas which have the added advantage of allowing spatial reuse. Even though the high gain in a given direction in such antennas allows us to extend the range, there are several factors, such as error in antenna orientation, fading, blockage which show that an optimum beamwidth can be obtained to maximize the network throughput. The treatment of transmissions, during Line-of-Sight transmission conditions and during Non-Line-of-Sight, is completely different. The paper has evaluated the optimum beamwidth for successful mmWave transmissions in mmWave adhoc networks at 60 Ghz in short-range mmWave networks (IEEE 802.11ad). [ABSTRACT FROM AUTHOR]

Traditional back propagation neural networks (BPNNs) for ultrawideband (UWB) indoor localization can effectively improve localization accuracy, although there is high likelihood of becoming trapped in nearby minima. To solve this problem, the random weights and thresholds of the BPNN are optimized using the Harris Hawks optimization algorithm (HHO) to obtain the optimal global solution to enhance the UWB indoor positioning accuracy and NLOS resistance. The results show that the predicted trajectory of the HHO and BPNN hybrid algorithm (HHO-BP) matches the actual position in the two-dimensional localization scenario with four base stations; the optimized average positioning error is effectively reduced in both indoor LOS and NLOS environments. In the LOS environment, the total mean error of the traditional BPNN algorithm is 6.52 cm, which is 26.99% better than the UWB measurement error; in the NLOS environment, the total mean error of the conventional BPNN is 14.82 cm, which is 50.08% better than the UWB measurement error. The HHO–BP algorithm is further optimized on this basis, and the total mean error in the LOS environment is 4.50 cm, which is 22.57% better than the conventional BPNN algorithm; in the NLOS environment, the total mean error is 9.56 cm, which is 17.54% better than the conventional BPNN algorithm. The experimental findings suggest that the approach has greater calibration accuracy and stability than BPNN, making it a viable choice for scenarios requiring high positional precision.

We studied the boundary layer effects on flame temperature measurements using line-of-sight (LOS) absorption spectroscopy. The primary objective is to quantify the measurement uncertainty of the LOS-determined temperature, which is influenced by the thermal and species boundary layers existing in standard laminar premixed flames. The boundary layer thickness (δ), central flame temperature (Tc) and species concentration (Xc) are the major factors investigated in this work. Typical absorption lines of H2O in the wavelength range of 1.4–2.9 μm were examined under different boundary layer conditions (δ/L = 0–50%, L is the optical path length above the flame; Tc = 1400–2200 K; and Xc = 14–20%). As a result, the thermal boundary layer is observed to contribute mainly to the temperature deviation of the LOS measurement, which increases with δ and Tc. In comparison, the variation of Xc between 14% and 20% has a negligible effect on the temperature measurement in the presence of both thermal and species boundary layers. A systematical investigation of all the selected line pairs reveals that a properly selected line pair reduces the temperature deviation by a maximum of 16.8% under typical laminar flame conditions. The particular line pair centered at 4029.52 cm−1 and 4030.73 cm−1, which could be detected by a single tunable semiconductor laser, is recommended for the LOS temperature measurement over a temperature range of 1400–2200 K. Finally, we performed a case study of five representative temperature measurements in laminar flames and successfully corrected the LOS-determined temperature by taking into account the boundary layer effects. [ABSTRACT FROM AUTHOR]

In this paper, a guidance and control system for multi-satellite assembly missions in proximity operations is proposed. Utilizing the Tschauner-Hempel relative motion equations, the system is developed within the framework of model predictive control. Linear inequality constraints are employed to handle control input saturation of thrusters and to ensure collision avoidance between satellites. Additionally, a new line-of-sight constraint method is introduced to facilitate smooth docking while simplifying the optimization problem. The proposed algorithm aims to minimize a predefined cost function, which is a weighted sum of state errors and control efforts. At each sampling time, an online quadratic optimization problem is solved to determine the optimal control action that satisfies all mission constraints. Nonlinear numerical simulations in MATLAB are used to demonstrate that the proposed guidance and control system achieves the desired performance. The algorithm is tested for various multi-satellite assembly configurations (cubic and hexagonal) in elliptic orbits of arbitrary eccentricity. A comparative study is conducted between the proposed algorithm and a linear model predictive control algorithm based on the Clohessy-Wiltshire linear model. The results show that the proposed algorithm achieves superior performance in terms of constraint satisfaction and control efforts. [ABSTRACT FROM AUTHOR]

The research studies hyper-Rayleigh behavior of a wireless communication system functioning in the presence of the generalized multipath fading. Although the initial metric (hyper-Rayleigh mode (HRM)) is quite informative, it is defined only asymptotically (i.e., for the infinitely increasing SNR). In spite of mathematical simplifications brought by such a definition (i.e., in this case most of the performance characteristics defining the HRM can be easily evaluated), it sufficiently limits its applications since, evidently, the real-life systems function in the presence of a finite (and usually not very high) SNR. The study presents a novel approach to the fading channel analysis (i.e., finite signal-to-noise ratio hyper-Rayleigh mode (fHRM)). The proposed metric (fHRM) is studied on the newly presented channel model-fluctuating double-Rayleigh with Line-of-Sight (fdRLoS) fading model. To accomplish this, the novel expressions for two channel-dependent system characteristics (i.e., the Amount of Fading (AoF) and the Outage Probability (OP)) were derived in exact form valid for arbitrary fading parameters. Based on the derived expressions, the finite SNR hyper-Rayleigh map is obtained, which helps to identify the parameters’ values corresponding to the specific propagation scenarios, which were further deployed to analyze the problem of the communication link physical layer security quantified in terms of the probability of strictly positive secrecy capacity (SPSC). Numerical verification of the derived closed-form expressions was performed. Several peculiarities of the system performance are observed and discussed.

Essential for improving the accuracy and reliability of bowel cancer screening, three-dimensional (3D) surface reconstruction using capsule endoscopy (CE) images remains challenging due to CE hardware and software limitations. This report generally focuses on challenges associated with 3D visualization and specifically investigates the impact of the indeterminate selection of the angle of the line–of–sight on 3D surfaces. Furthermore, it demonstrates that impact through 3D surfaces viewed at the same azimuth angles and different elevation angles of the line–of–sight. The report concludes that 3D printing of reconstructed 3D surfaces can potentially overcome line–of–sight indeterminate selection and 2D screen visual restriction-related errors.

This treatise presents a framework for the optimisation of a colour-based optical spatial modulation for visible light communication (VLC). The focus is particularly on the conflicting interests between illuminance and signal transmission. The system under consideration is configured with a non-line-of-sight (NLoS) model, based on the joint use of colour shift keying (CSK) and optical spatial modulation (OSM) with intensity modulation and direct detection (IM/DD). With the adaptation of the aforementioned optical techniques and convex optimisation, the design and development of a colour-based optical wireless system is carried out. Firstly, an optimisation problem with the intention of minimising the total luminous intensities of the light emitting diode (LED) arrays subject to the transmitting LED array’s optical power budget, minimum required illuminance level, LED-user channel conditions and latency intolerant users’ (LITUs) quality-of-service (QoS) target constraints is defined. Secondly, a coordinated algorithm for the selection of a transmitting LED array, maintenance of a particular illuminance and signal-to-interference-plus noise ratio (SINR) levels during symbol transmission is designed. Lastly, through computer simulations, a numerical analysis is carried out to demonstrate and evaluate the performance of the algorithm. During the transmission of all symbols, the proposed framework is capable of satisfying the SINR target for LITUs while reducing the optical power by approximately 20% to 25% and 20% to 75% for transmitting and non-transmitting LED arrays, respectively. Additionally, provided that the required illuminance level is specified within the standardised levels of 300 lux to 1500 lux, the proposed system can provide adequate illuminance as per the users’ requirement at all points where either a LITU or a latency tolerant user (LTU) is located at any given instance. However, fair SINR levels are not guaranteed at the points where the LTUs are positioned. On the other hand, the algorithm disposes low illuminance levels ranging from 100 lux to 250 lux at locations towards the room boundaries where there are no users. The proposed system is able to achieve data rates of 5 Mbps to 25 Mbps using commercially-off-the-shelf LEDs.

Underwater optical wireless communication (UOWC) systems have been widely studied to achieve high-speed wireless communications. To investigate and design UOWC systems, a mathematical model to characterize the accurate performance of UOWC systems is important. However, the previous mathematical models of UOWC systems have limitations, which mainly focused on the line-of-sight (LOS) link, and only considered the vertical incident background light or optical filters with constant transmittance for simplicity. To overcome these limitations, we establish an accurate UOWC system model, incorporating the previously overlooked impact of signal and sun lights incident angles and including both LOS and non-line-of-sight (NLOS) channels. Our proposed accurate UOWC system model is validated by Monte Carlo (MC) simulations. Results show that our proposed model can capture the changes of received powers of both signal and background lights with various transmitter and receiver alignments and orientations in both LOS and NLOS channels, which typically affect the signal-noise-ratio (SNR) and bit-error-rate (BER) performance of UOWC systems. Furthermore, we show that the incident angles of both signal and sun lights have significant impact on the system performance, and our proposed model can be used to optimize the PD rotation angle to improve the SNR performance. Therefore, the more accurate UOWC channel model established in this paper provides a fundamental framework for future UOWC system design and optimization.

In this paper, a novel event-triggered composite learning finite-time control scheme is presented for underactuated marine surface vehicles (MSVs) trajectory tracking under unknown dynamics and unknown time-varying disturbances. Line-of-sight (LOS) tracking control method is employed to address the underactuation problem of MSVs. The neural networks (NNs) are untilized to approximate unknown dynamics. The serial-parallel estimation model is employed to construct the prediction error, and the prediction errors and tracking errors are fused with construct the NN weights updating. Combining the result of approximation information, the disturbances observers can be created to achieve disturbance estimation. Fractional power technology is artistically introduced to realize the finite-time trajectory tracking control of MSVs based on composite learning. The proposed control scheme ensures the simultaneous realization of high precision tracking performance and unknown information approximation. Moreover, an event-triggered mechanism is introduced to reduce the transmission load and the execution rate of actuators. It is proved that the proposed control scheme ensures all error signals of the MSVs trajectory tracking control system can converge to the neighborhood of zero within a finite time. Finally, the simulation results on an MSV verify the effectiveness and superiority of the proposed control scheme.

Spatial modulation (SM) as a multiple-input multiple-output (MIMO) technique is a solution suitable which offers, with low system complexity and cost, improved spectral efficiency compared to single-input-single-output (SISO) systems. Moreover, the transmission chain is simplified which decreases energy consumption. This paper aims to analyze the SM system transmission under different line-of-sight/non-line-of-sight (LOS/NLOS) propagation scenarios. The analysis of the SM system performance is based on both simulations and experimental results and the bit error rate (BER) is tackled. Concerning the experimental results, two strategies are considered in order to configure the propagation channel. One method consists in constructing a controlled propagation environment. More precisely, the multipath channel’s Rician K-factor is imposed by configuring the power levels of the LOS and of the NLOS components. The second method consists in performing over-the-air transmissions on a realistic propagation channel. A channel sounding method allows us to measure the channel characteristics. The experimental results are confronted with the system-level simulation results, good agreement between experimental and simulation results are obtained. The results show that the SM system can maintain the performance in multipath propagation in the presence of indirect paths for both two proposed propagation environments.

Next-generation satellite systems targeting multi-Terabit-per-second throughput require surmounting layers of design challenges. For feeder links, extremely high frequency (EHF) band is desired to overcome spectrum limitations and reduce equipment size. Multiple gateways are utilized to aggregate their bandwidths and serve as site diversity, mitigating the increased susceptibility of the EHF band to atmospheric attenuation. Toward this, multiple-input multiple-output (MIMO) technology is well suited for feeder links that share the same time, frequency, and polarization resources. This paper provides novel extension of MIMO-enabled feeder links when clustering more than two gateways and mounting more than two antennas onboard geostationary multibeam satellite, exploiting line-of-sight MIMO on uplinks and downlinks. Arsenal of countermeasures against inter-antenna interference and weather impairments is designed to maximize gains in signal-to-noise ratio, spatial multiplexing, and spatial diversity. Comparisons between offered sum rates and theoretical MIMO capacity are provided when gateway clusters form linear versus circular patterns. Methodology for gateway diversity is developed and analyzed when deploying redundant MIMO feeder links that handle rerouted traffic. Algorithms for ground-based channel state information (CSI) acquisition are designed and implemented in receiver architecture that tackles strong practical impairments. Numerical studies reveal that MIMO-enabled feeder links offer greatly enhanced overall network availability compared with state-of-the-art single-input single-output (SISO) solutions. [ABSTRACT FROM AUTHOR]

In spite of several promising attributes that motivate industry players to adopt visible light communication (VLC), its strong coverage limitation is a major disincentive. A reasonable way to overcome this bottleneck in indoor environments is to capitalize on the prevailing wireless local area network (WLAN) to boost reliable mobile access. To this end, a vertical handover (VHO) scheme is required to smoothly merge VLC networks and WLANs. Thus, this article presents an adaptive VHO scheme which considers the cause of a VLC link disruption and the types of applications running in a user device (UD) to make appropriate handover decisions. The proposed hybrid application-aware VHO (HA-VHO) technique combines three approaches (immediate handover, static dwell timing and dynamic dwell timing), in order to improve the overall handover outcome. Performance comparisons with other VHO designs (immediate VHO, dwell VHO and channel adaptive dwell VHO) reveal that the HA-VHO scheme provides higher data rates in most cases, while adaptively reducing the total signaling cost of inter-network handovers. What is more, it can provide relatively high quality of experience (QoE) for real-time applications. [ABSTRACT FROM AUTHOR]

This paper introduces a prescribed-time extended state observer (PTESO) guidance law specifically developed for the path tracking of underactuated unmanned surface vehicles (USVs) navigating under time-varying ocean current conditions. The PTESO is utilized for accurate determination of the sideslip angle of the USV, particular during maneuvering along curved trajectories or in the presence of time-varying ocean disturbances. This process guarantees a prompt and accurate calculation of the sideslip angle, thus enabling more accurate path tracking in the presence of external disturbances caused by wind, waves, and currents. The stability of the closed-loop system's input-state is established using cascade theory. Furthermore, in order to improve the accuracy of USV positioning, the paper suggests utilizing ultra-wideband (UWB) technology for USV localization. A layout scheme has been developed for the placement of UWB devices on the vessel, and an equation has been derived for calculating the heading angle. The proposed approach's effectiveness is substantiated through the validation of simulation results, while the feasibility of the method is confirmed by experimental results. • The prescribed-time extended state observer is employed for the estimation of sideslip angle. • It effectively suppresses the initial peak phenomenon of the extended state observer (ESO). • Ultra-Wideband (UWB) technology is applied to ship positioning. [ABSTRACT FROM AUTHOR]

On account of the external disturbances and difficult maneuverability of a hovercraft, this paper devises a safety-guaranteed, robust, nonlinear, path-following control strategy of a hovercraft targeted for unknown dynamics, unavailable velocity, and unknown external ocean disturbances. Firstly, for the sake of accurately observing unavailable lumped disturbances and unavailable velocity measurements, a finite-time extended state observer (FTESO) is proposed. Secondly, a line-of-sight (LOS) guidance law constructed with a bounded-gain-forgetting (BGF) adaptive estimator is devised to follow the desired path while considering external environmental disturbances accurately, in which the tracking errors and the parameter estimation are both proven to be bounded. In addition, for the sake of safety, a safety-guaranteed auxiliary system that can constrain the drift angle during the hovercraft’s navigation is proposed. Thirdly, the robust, nonlinear, path-following controllers achieved high tracking performance with the constructed safety-guaranteed compensation backstepping method. Finally, according to the Lyapunov and homogeneous theories, the observation error can be guaranteed to zero and the tracking error can converge to an arbitrarily small region near zero in finite time. Numerical simulations illustrate the effectiveness for the proposed robust, nonlinear, path-following scheme.

In this paper, we investigate the optimal line-of-sight (LoS) coverage problem for multiple access point (multi-AP) mmWave wireless LANs in indoor scenarios. Due to the weak diffraction ability of mmWave signals at 60 GHz, maintaining LoS communications between APs and client devices is critical to achieve ultra-high data rates with mmWave communications. We focus on the use of multiple APs deployed to maximize LoS coverage in a target area, and we develop multi-AP placements that maximize LoS coverage by means of both analytical and algorithmic methods. We consider two main scenarios, which differ in their assumptions about knowledge of obstacles and clients. In a random-obstacle, random-client scenario, we derive the LoS-optimal positions of APs by solving a thinnest covering problem. For a fixed-obstacle, random-client scenario, we propose an efficient algorithm that produces a multi-AP placement, which is shown through simulation to provide near-optimal LoS coverage. Finally, through extensive ns-3 simulations based on the IEEE 802.11ad protocol and mmWave-specific channel models, we show that our multi-AP placements are significantly better than existing placement approaches, both in terms of LoS coverage and aggregate throughput. [ABSTRACT FROM AUTHOR]

Cell-free systems are characterized by the absence of a cell-based spatial subdivision. In these systems a large number of access points may serve each user, which contribute to improve signal transmission conditions. In this context, it is important to obtain equations that describe the behavior of the system, as a function of its main parameters. Such equations become more complete when more effects are taken into account. One of these effects is the loss of channel reciprocity due to radiofrequency (RF) mismatch. This paper proposes the introduction of a multiplicative model for the reciprocity errors resulting from RF mismatch in all devices of a cell-free model. Additionally, it also proposes the use of different levels of mismatch for each device. The main contribution of this work is an analytical expression for the downlink achievable rates in the presence of multiplicative reciprocity errors due to RF mismatch. Based on it, one can compute the approximate value of the achievable rates. The analytical expression is used in scenarios with and without line-of-sight. It is shown that the analytical expression is very close when there is line-of-sight, as it provides achievable rate values closer to that obtained by using Monte Carlo simulation.

The performance of millimeter wave (mmWave) line-of-sight multiple input multiple output (LOS MIMO) systems using hybrid arrays of planar subarrays was studied. We characterized the achievable maximum spatial multiplexing gain for such LOS MIMO systems by the measures of spectral efficiency and effective degree of freedom (EDoF). By proposing a joint plane-wave and spherical-wave-based general 3D channel model, we derived the optimal design parameters in the analog domain, i.e., the optimal subarray separation products, and analyzed their sensitivity on the system performance. We also gave analytical eigenvalue expressions of the equivalent LOS MIMO channel matrix, which are applicable to the case of a non-optimal design, as well as the upper and lower bounds of the EDoF for system performance evaluation. A piecewise uniform quantization codebook was further designed for quantizing phase shifter values in practical applications. The numerical and simulation results show that planar subarrays are superior to traditional arrays in terms of spectral efficiency and EDoF in Ricean fading channels because they are more robust to the change in the communication distance and the deviation from the optimal design. The use of hybrid arrays of planar subarrays effectively removes the limitation of mmWave LOS MIMO systems using traditional arrays, through which, the conventional Rayleigh distance criterion has to be satisfied to achieve the optimal performance.

This paper aims to present a systematic approach to evaluate the parameters affecting the vessel's performances in the target tracking motion control scenario and, for this reason, three guidance laws have been formalised. Such scenario consists of reaching and following a target of which it is only possible to know the instantaneous position and velocity, hence when the future motion is unknown. The standard Line-Of-Sight, Pure Pursuit, and Constant Bearing have been modified and deeply tested. The target tracking scenario has been divided into two parts: the target approach and following strategies. The increase in system complexity needs advanced tools to predict the vehicle response in both standard and non-standard conditions. Simulation can support the designer's effort for the transition from a traditional to an autonomous ship in the whole ship design; hence, all the guidance laws have been virtually tested and a sensitivity analysis is carried out to understand each parameter effect. Several manoeuvres have been performed and the results are shown to highlight benefits and drawbacks for each law. Eventually, key performance indicators are outlined and some suggestions are given to the proper settings of the guidance law parameters in the function of the specific mission. [ABSTRACT FROM AUTHOR]

This research paper presents the Physical (PHY) layer analysis of multiple input multiple output (MIMO) systems in line-of-sight environments between a user equipment (UE) and a base station when an information data is transmitted. The data transmission in wireless networks often takes place in non-line-of-sight in urban environments and Line-of-Sight (LoS) in rural environments depending on the bandwidth, power constraints. Using MIMO technology, the data transmission takes place with increased number of transmit and receive antennas which results in reduced signal to noise ratio (SNR) requirement. In this research work, simulation for PHY layer metric of probability of error, mean square error (MSE) for data transmission in MIMO wireless networks is obtained Matrix Laboratory (MATLAB) for LoS environment which follows Rician distribution. Probability of error reduces to a significant extent when the Rician factor increases as the line-of-sight component prevails which also takes lesser power in the lower SNR limits. Further, in MIMO systems also the probability of error and MSE reduces in concatenation with single antenna terminals thereby exploring power control a significant possibility for implementation in massive MIMO and millimeter wave communication systems for 5G and 6G systems. [ABSTRACT FROM AUTHOR]

In this paper, a composite learning control scheme was proposed for underactuated marine surface vessels (MSVs) subject to unknown dynamics, time-varying external disturbances and output constraints. Based on the line-of-sight (LOS) approach, the underactuation problem of the MSVs was addressed. To deal with the problem of output constraint, the barrier Lyapunov function-based method was utilized to ensure that the output error will never violate the constraint. The composite neural networks (NNs) are employed to approximate unknown dynamics. The prediction errors can be obtained using the serial-parallel estimation model (SPEM). Both the prediction errors and the tracking errors were employed to construct the NN weight updating. Using approximation information, the disturbance observers were designed to estimate unknown time-varying disturbances. The stability analysis via the Lyapunov approach indicates that all signals of unmanned marine surface vessels are uniformly ultimate boundedness. The simulation results verify the effectiveness of the proposed control scheme.

This paper focuses on horizontal path following control with prescribed performance for an autonomous underwater vehicle (AUV) with input saturation nonlinearity and dead-zone nonlinearity. The proposed control scheme consists of two functional parts, namely prescribed-performance line-of-sight with extended state observer (PELOS) based guidance and nonlinear model predictive control (MPC) based attitude control. Firstly, PELOS guidance is derived with an error transformed function such that the path following errors are restricted in the prescribed maximum overshoot and converge at a rate not lower than the prescribed convergence rate bound. Subsequently, the dedicated MPC with a smooth inverse dead-zone model is designed to remove the chattering phenomenon caused by dead-zone nonlinearity. It is illustrated that with the help of the designed controller, required transient and steady constraints of path following errors are never violated and the control input is chattering-free and smooth despite of the influence of saturation and dead-zone of actuators. Finally, three comparative numerical simulation results are carried out to demonstrate the effectiveness and advantages of the proposed path following control method. • A path following controller composed of PELOS guidance and MPC method is proposed for AUV. • The PELOS guidance introduces PPC to ensure the prescribed performance of tracking errors. • The dedicated MPC can well deal with the input saturation and dead-zone. • Comparative simulations verify transient and steady-state performance of the controller. [ABSTRACT FROM AUTHOR]

This paper proposes a formation control method for two underactuated unmanned surface vessels (USVs) to follow curved paths in the presence of ocean currents. By uniting a line-of-sight (LOS) guidance law and the null-space-based behavioral control (NSB) framework, we achieve curved path following of the barycenter, while maintaining the desired vessel formation. The closed-loop dynamics are investigated using cascaded systems theory, and it is shown that the closed-loop system is USGES and UGAS, while the underactuated sway dynamics remain bounded. Simulations show that the barycenter task errors converge to zero, validating the theoretical results, while a small cross-track error is observed in the experiments. [ABSTRACT FROM AUTHOR]

This paper describes a tool created to simulate the effects of evaporation ducts on wireless communication networks which are close to the sea surface. The tool is an extension of the ns-3 network simulator and implements two propagation loss models: Two Ray, which models reflection effects; and Three Ray, which models the effects of both reflection and refraction. As the Three Ray model has the evaporation duct height as one of its parameters, a model to estimate this height based on weather conditions (meteorological measurements) was also implemented. The tool allows us to show how signal is weakened with the distance from the transmitter to the receiver, under different evaporation duct heights. It has been of increading interest to model these effects due to the importance of wireless networks located over the sea surface for supporting different types of applications, such as surveillance, security and ecological monitoring. Extending ns-3 is of particular importance, as it is one of the most largely used simulators for designing and evaluating communication networks. [ABSTRACT FROM AUTHOR]

In line-of-sight massive MIMO, there are use cases where the channel vectors of some users become highly correlated. Highly correlated users lead to a large reduction in the sum-rate of linear and nonlinear precoders with max-min power control. To alleviate the loss in the sum-rate, some users can be dropped and rescheduled. The optimal dropping strategy can be found by an exhaustive search. In this letter, a successive filter-based dropping algorithm (SFDA) is proposed, which improves upon the existing dropping algorithms in the literature. At each step, the user with the highest filter norm is dropped. By comparing the sum-rate of all the steps, the best set of dropped users is found. In contrast to previous threshold-based algorithms in the literature, SFDA does not require a predefined threshold for the spatial correlation of users. Compared to an exhaustive search, the complexity of SFDA is reduced. Simulations results show when a 100 antennas base station serves 10 users, SFDA improves the 5th percentile sum-rate compared to previous algorithms in the literature up to 6 bits/channel use. [ABSTRACT FROM AUTHOR]

The ability to find the location of a mobile object and track it in two-dimensional (2D) and three-dimensional (3D) space is an indispensable feature of wireless communication systems. In particular, the increase in demand for using self-navigation technology in unmanned vehicles is attracting additional attention to this area of research. The methods and techniques developed for these systems compete in terms of simplicity, performance, and accuracy. However, the majority of solutions focus on only one of these performance metrics and are not applicable to the projected systems. In this study, a new location estimation solution that satisfies all three performance metrics (simplicity, accuracy, and efficiency) is achieved. The developed algorithms can be executed on a mobile object to allow it to learn its position in space. Furthermore, the simplicity of the mathematical operations used, namely binary shift and add operations, makes our algorithm hardware-friendly. Accelerated coordinate rotation digital computer (CORDIC) algorithms are used for the first time with line-of-sight (LOS) and single-bounced-scattering non-line-of-sight (SBS NLOS) signal arriving approaches for mobile object self-positioning. This study also introduces a newly developed 'vector-breaking' method (VBM) to estimate the location of a mobile object using the arriving signals from scatters with unknown locations. Test results using the developed algorithm show that the projected level of accuracy has been achieved. Furthermore, the developed algorithm performs better than the solutions currently available in the field. [ABSTRACT FROM AUTHOR]

Ultra-dense networks (UDNs) are widely considered as an effective solution to greatly improve coverage by shortening the communication distance between user equipments (UEs) and base stations (BSs). The reality of UDN is that line-of-sight (LOS) communication becomes more likely to occur but this desirable result also complicates the performance analysis of random UDNs and puts an obstacle on the design and optimization of UDNs. The aim of this paper is to derive analytical results that take into account the phenomenon of having mixed LOS and non line-of-sight (NLOS) links in UDNs. In particular, the use of an arbitrary shaped thinning process to model the LOS wireless links allowed us to investigate a wide set of scenarios for what concerns the desired and interfering power levels. Our contribution is an accurate approximation in closed form for the success content delivery probability (SCDP) that decouples the contribution from LOS and NLOS links. Simulation results corroborate the accuracy of the proposed approximation.

For the next generation wireless networks, backhaul links with data rates of several Gbit/s are required. Line-of-Sight-MIMO with optimally arranged antennas can exploit the full multiplexing gain of orthogonal MIMO streams to achieve high throughput, as shown in recent works utilizing the 60 GHz mm wave band. In contrast, conventional MIMO systems operating at sub-6 GHz carrier frequencies, as utilized in modern WLAN networks, rely on rich scattering channels to enable reliable transmissions. In this work, we explore the feasibility of applying the LoS-MIMO concept to wireless single-carrier links operating at sub-6 GHz frequencies. For this, we investigate the sub-6 GHz LoS-MIMO channel in a 4 × 4 MIMO configuration by performing measurements in an anechoic chamber and an outdoor backhaul-like environment. In addition, different adaptive equalizers are evaluated. The results show, that the LoS-MIMO concept holds for sub-6 GHz frequencies both in pure LoS and in outdoor environments. It provides high multiplexing gain; however, the multipath propagation limits the potential performance of the equalizers in terms of achievable BER. [ABSTRACT FROM AUTHOR]

This article focuses on the problem of path following for underactuated unmanned surface vehicles (USVs) considering model uncertainties and time-varying ocean currents. An extended state observer (ESO)-based integral line-of-sight (ILOS) with an integral sliding mode adaptive fuzzy control scheme is proposed as the main control framework. First, a novel ESO is employed to estimate the surge and sway velocities based on the kinetic model, which are difficult to measure directly. Then, the adaptive ILOS guidance law is proposed, in which the integral vector is incorporated into the adaptive method to estimate the current velocities. Meanwhile, an improved fuzzy algorithm is introduced to optimize the look-ahead distance. Second, the controller is extended to deal with the USV yaw and surge velocity signal tracking using the integral sliding mode technique. The uncertainties of the USV are approximated via the adaptive fuzzy method, and an auxiliary dynamic system is presented to solve the problem of actuator saturation. Then, it is proved that all of the error signals in the closed-loop control system are uniformly ultimately bounded. Finally, a comparative simulation substantiates the availability and superiority of the proposed method for ESO-based ILOS path following of USV. [ABSTRACT FROM AUTHOR]

Cell-free systems are characterized by the absence of a cell-based spatial subdivision. In these systems a large number of access points may serve each user, which contribute to improve signal transmission conditions. In this context, it is important to obtain equations that describe the behavior of the system, as a function of its main parameters. Such equations become more complete when more effects are taken into account. One of these effects is the loss of channel reciprocity due to radiofrequency (RF) mismatch. This paper proposes the introduction of a multiplicative model for the reciprocity errors resulting from RF mismatch in all devices of a cell-free model. Additionally, it also proposes the use of different levels of mismatch for each device. The main contribution of this work is an analytical expression for the downlink achievable rates in the presence of multiplicative reciprocity errors due to RF mismatch. Based on it, one can compute the approximate value of the achievable rates. The analytical expression is used in scenarios with and without line-of-sight. It is shown that the analytical expression is very close when there is line-of-sight, as it provides achievable rate values closer to that obtained by using Monte Carlo simulation. [ABSTRACT FROM AUTHOR]