Receiver Pair Research Articles

W-band Scalable 2×2 Phased-Array Transmitter and Receiver Chipsets in SiGe BiCMOS for High Data-Rate Communication

This article presents a pair of W-band phased-array transmitter (TX) and receiver (RX) chipsets in a 0.13- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> SiGe BiCMOS process for high data-rate wireless communication. Both the chips integrate four compact front-end channels in 2 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> 2 distribution, and the distance between the adjacent RF pads is less than 1.8 mm ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.56\lambda $ </tex-math></inline-formula> at 90 GHz) to fit for the tight antenna array and enable array scaling by tiling multiple unit cells. A 6-bit active phase shifter based on the improved phase-inverting variable gain amplifiers is leveraged to achieve high phase-shift precision and bandwidth concurrently. A noise reduction technique using a parallel inductor to resonate with the parasitic capacitors of the cascode transistors is adopted in the low-noise amplifier design. A novel miniature power combiner, which occupies a much more compact area than the Wilkinson power combiner while delivering great RF performance, is proposed and elaborately analyzed. System-level calibration for local oscillator (LO) leakage and dc-offset suppression is enabled by introducing digitally controlled current sources into the up-conversion and down-conversion mixers. On-wafer measurements for the TX chip exhibit a single-channel IF-to-RF conversion gain (CG) of 26 dB, a competitively high output 1-dB compression point (OP <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\mathrm {1\,dB}}$ </tex-math></inline-formula> ) of 11 dBm. The RX chip achieves an RF-to-IF CG of 19.5 dB with 9-/14-GHz IF/RF 3-dB bandwidth, a noise figure of 7.7 dB, and an input 1-dB compression point of −28 dBm. The phase-shift characteristics are verified by the TX/RX front-end measurements, achieving a 6-bit phase resolution with minimum rms phase/gain error smaller than 0.83°/0.45 dB and a large phase-shift bandwidth higher than 20 GHz. Preliminary wireless transmission test using a low-cost die-on-printed circuit board (PCB) prototype demonstrates wireless data rates of 1.6 and 0.8 gigabits per second (Gb/s) at distances of 0.4 and 1 m with 256-quadratic-amplitude modulation (QAM) and 16-QAM modulated signals, respectively.

Surface-wave tomography using SeisLib: a Python package for multiscale seismic imaging

Summary To improve our understanding of the Earth’s interior, seismologists often have to deal with enormous amounts of data, requiring automatic tools for their analyses. It is the purpose of this study to present SeisLib, an open-source Python package for multiscale seismic imaging. At present, SeisLib includes routines for carrying out surface-wave tomography tasks based on seismic ambient noise and teleseismic earthquakes. We illustrate here these functionalities, both from the theoretical and algorithmic point of view and by application of our library to seismic data from North America. We first show how SeisLib retrieves surface-wave phase velocities from the ambient noise recorded at pairs of receivers, based on the zero crossings of their normalized cross-spectrum. We then present our implementation of the two-station method, to measure phase velocities from pairs of receivers approximately lying on the same great-circle path as the epicentre of distant earthquakes. We apply these methods to calculate dispersion curves across the conterminous United States, using continuous seismograms from the transportable component of USArray and earthquake recordings from the permanent networks. Overall, we measure 144 272 ambient-noise and 2055 earthquake-based dispersion curves, that we invert for Rayleigh-wave phase-velocity maps. To map the lateral variations in surface-wave velocity, SeisLib exploits a least-squares inversion algorithm based on ray theory. Our implementation supports both equal-area and adaptive parametrizations, with the latter allowing for a finer resolution in the areas characterized by high density of measurements. In the broad period range 4–100 s, the retrieved velocity maps of North America are highly correlated (on average, 96 per cent) and present very small average differences (0.14 ± 0.1 per cent) with those reported in the literature. This points to the robustness of our algorithms. We also produce a global phase-velocity map at the period of 40 s, combining our dispersion measurements with those collected at global scale in previous studies. This allows us to demonstrate the reliability and optimized computational speed of SeisLib, even in presence of very large seismic inverse problems and strong variability in the data coverage. The last part of the manuscript deals with the attenuation of Rayleigh waves, which can be estimated through SeisLib based on the seismic ambient noise recorded at dense arrays of receivers. We apply our algorithm to produce an attenuation map of the United States at the period of 4 s, which we find consistent with the relevant literature.

Vehicle Over Speeding Detection

Our proposed project aims to develop a system that detects cars driving at speeds over specified limit and inform concerned authorities immediately. Road accidents occurrences have increased recently so there needs to be a system that allows to detect over-speeding cars. Current speed detection systems are handheld guns held by police personnel that allow them to check car speed and then manually inform authorities about the vehicle. Whereas this proposed system does not need any human interception and records car speed as well as wirelessly informs authorities of over-speeding detections. The system first calculates the time required by the specific car for moving from first point to the second. Based on this data it calculates the car speed. This data is gathered and then transmitted by the system wirelessly to concerned authorities at a remote location. The mechanism consists of IT transmitter- receiver pair that work in combination for vehicle detection purpose. The microcontroller is now used to process this data and calculate the time required by vehicle to travel from one point to the other. Depending upon this time it now calculates vehicle speed as well as displays this on an LCD display. The system also sends this data wirelessly. It sounds a buzzer alarm if an over speed vehicle is detected. Over speeding of vehicles is the major cause of accidents in recent times. Monitoring of such over speeding vehicles especially on highways is of prime importance. Many manual methods are being used to detect the over speeding vehicles by traffic control team. However, these methods require lot of man power and continuous monitoring by traffic personnel. In this study, an attempt is made to develop an automatic speed monitoring system, which provides a simple way to monitoring speeds of all the vehicles from a centralized control room. This system calculates the instantaneous speed of vehicle with help of sensors and the over speeding vehicle is detected using an image processing technique using Python programming language. The developed model is validated with real world traffic data and comparative analysis of speeds obtained by manual method and developed model shows that model truly represents the field condition.

Optimal relaying in molecular communications

Molecular communication via diffusion (MCvD) schemes are limited to short distances between the nanomachines due to the transmitted signal becoming rapidly weaker as the distance increases. Additionally, these schemes are very often affected by high inter-symbol interference, which makes them prone to errors, thus leading to unreliability. In this paper, a novel system is proposed, which aims to enhance the received signal shape and the overall performance of MCvD schemes over longer distances. A relay nanomachine is introduced between the transmitter–receiver pair, which collects the first portion of the molecules emitted from the transmitter and keeps them for some delay time τ, then releases them towards the receiver, such that the delayed and non-delayed portions of the molecules arrive almost at the same time. In this way, the signal’s strength is enhanced by pointing more molecules towards the intended direction, that is, the receiver node. An analytical model for the optimal relaying scheme is proposed, alongside with an optimization problem to find the most advantageous τ value. Comparison between the proposed scheme and the conventional single-input single-output scenario is provided by means of analytical and computer simulation results, showing a promising improvement in error rates when the relay is introduced.

Hadamard Aperiodic Interval Codes for Parallel-Transmission 2D and 3D Synthetic Aperture Ultrasound Imaging

We present a new set of near orthogonal codes which we call Hadamard Aperiodic Interval (HAPI) codes and demonstrate their utility for parallel multi-transmitter synthetic aperture imaging. The codes are tri-state and sparse. Locations of non-zero bits are based on marks in a sequence of aperiodic intervals, also known as a Golomb ruler. The values of non-zero bits are selected from Hadamard sequences that are mutually orthogonal. This ensures that cross-correlation sidelobe magnitudes between differing codes are bounded by unity while the autocorrelation approaches a delta function with mainlobe-to-sidelobe levels scaling with the number of non-zero bits. We use simulations to demonstrate the potential of the codes for synthetic aperture imaging. A multiplicity of transmitter elements is used to transmit codes simultaneously, with a different code for each element. Echo signals are received from a multiplicity of transducer elements in parallel. Channel data from each receiver element are cross-correlated with respective HAPI codes to estimate the transmit–receive signature associated with each transmitter–receiver pair while minimizing crosstalk. This estimate of the full transmit–receive synthetic aperture dataset is then used to form high-quality images demonstrating image quality and signal-to-noise ratio improvements over multiple flash angle imaging and synthetic aperture imaging methods for linear arrays. We also demonstrate simulated full volume synthetic aperture imaging with random sparse arrays, possible with one extended HAPI code-set transmit event.

Active Millimeter Wave Imaging Using Leaky-Wave Focusing Antenna

In this article, an active millimeter-wave imaging system using two rectangular waveguide leaky-wave focusing antennas deployed in a quasi-monostatic transmitter and receiver pair is proposed. The broadband design method of the focusing antenna is presented, where the phase constant is derived from the radiation direction of a rectangular waveguide leaky-wave antenna. To eliminate the effect of mutual coupling between the transmitting and receiving antennas and scattering from the surrounding environment, the scattered field from the object is obtained by subtracting the incident field from the total field. The 1-D detection of conducting sphere, conducting and dielectric cylinders, and a conducting plate is performed by experiment to validate the imaging capability of the proposed system. The 2-D imaging of a conducting cylinder in free space and positioned in front of a human body phantom representing the human body is finally performed to simulate the practical application of the system.

Consistent individual variation in plant communication: do plants have personalities?

Animal biologists have recently focused on individual variation in behavioral traits and have found that individuals of many species have personalities. These are defined as consistent intraspecific differences in behaviors that are repeatable across different situations and stable over time. When animals sense danger, some individuals will alert neighbors with alarm calls and both calling and responding vary consistently among individuals. Plants, including sagebrush, emit volatile cues when they are attacked by herbivores and neighbors perceive these cues and reduce their own damage. We experimentally transferred volatiles between pairs of sagebrush plants to evaluate whether individuals showed consistent variation in their effectiveness as emitters and as receivers of cues, measured in terms of reduced herbivore damage. We found that 64% of the variance in chewing damage to branches over the growing season was attributable to the identity of the individual receiving the cues. This variation could have been caused by inherent differences in the plants as well as by differences in the environments where they grew and their histories. We found that 5% of the variance in chewing damage was attributable to the identity of the emitter that provided the cue. This fraction of variation was statistically significant and could not be attributed to the environmental conditions of the receiver. Effective receivers were also relatively effective emitters, indicating consistency across different situations. Pairs of receivers and emitters that were effective communicators in 2018 were again relatively effective in 2019, indicating consistency over time. These results suggest that plants have repeatable individual personalities with respect to alarm calls.

Anomalous Areas Detection in Rocks Using Time-Difference Adjoint Tomography

Detecting anomalous areas (such as caves, faults, and weathered layers) in rocks is essential for the safety of facilities and personnel in subsurface engineering. Seismic tomography has been proved to be an effective exploration technology in engineering geophysics. However, the complexity, anisotropy, and uncertainty in rock environments pose challenges to the resolution and robustness of tomography methods. Traditional tomography methods have difficulty balancing reliability and efficiency. Therefore, we developed a time-difference adjoint tomography method combining the arrival-time difference and the adjoint state method. The effectiveness was verified by numerical experiments and a laboratory-scale acoustic experiment. The effectiveness of the proposed method was demonstrated by the experimental results. The adjoint scheme avoids additional ray tracing and improves the efficiency of the inversion, which allows the use of finer forward grids in practice. By considering the differential arrivals of receiver pairs, the proposed method is robust in the face of systematic errors and relatively stable against large random noises. Moreover, the velocity contrast obtained by the proposed method is sharper than for first-arrival tomography in the areas where the rays are not dense, resulting in a clearer indication of the anomalous areas in the tomographic image.

Performance Analysis of an IRS-Aided Wireless Communication System With Spatially Correlated Channels

An intelligent reflecting surface (IRS) assisted wireless communication system, with statistically correlated channels between the transmitter and the IRS pair and between the IRS and the receiver pair, is studied in the absence of channel state information (CSI). Assuming the phases added by IRS elements to be deterministic, the closed-form analytical expression for the symbol error probability (SEP) and the upper bound on the channel capacity are derived, with the transmitter employing binary phase-shift keying (BPSK) modulation for data transmission. The asymptotic SEP expression is derived and the achievable diversity order of the system is shown to be independent of the number of IRS elements. A search based algorithm is proposed to obtain the optimal phase at IRS minimizing the average SEP, as a equal phase configuration. The optimal equal phase is also found to maximize the average channel capacity. Numerical results are presented for the case of channels following a practical IRS correlation model.

Active-Source Interferometry in Marine and Terrestrial Environments: Importance of Directionality and Stationary Phase

ABSTRACT We utilize active-source seismic interferometry with dense seismic arrays both offshore and onland to explore the utility of this method to create virtual sources and reveal body-wave reflections in these two different environments. We first utilize data from an ocean-bottom cable (OBC) array in the Gulf of Mexico with equal numbers of sources (160 airgun shots) and receivers (160 ocean-bottom four-component sensors). We next use data from a geophone array across the Bighorn Mountains of Wyoming with many receivers (1300 vertical-component geophones) but a small number of sources (14 borehole active-source shots). We find that the OBC virtual source results, which produce strong reflections from sub-seafloor structures, are far superior to the onland results which lack usable reflections, and we explore reasons for these differences through a set of selective stacking approaches. We present techniques to account for the direction the seismic waves travel (directionality) and stationary phase and show that improvements can be made when incorporating these corrections. Although interferometric methods are based on assumptions of large numbers of widely distributed actual sources, we find that selective exclusion of potentially problematic source–receiver pairs can yield improved results. These geometric adjustments to active-source interferometry methods have utility for dense-nodal-array surveys that are now common in academic studies, but that often suffer from sparse source geometry.

Pre-Heart Attack Alarm System

Heart beat is a unit of computing or counting extremity of heart function, whose unit is beat per minute (bpm). Heart has pacemaker cells that creates electrical waves, these cells cause heart rhythm for right atrium with its spread throughout the heart, blood pumping occurs. The human heart naturally break about 60 to 100 bpm, which can vary from condition to condition. Any disorder in heartbeat will lead to heart attack. Which can be detect by human beings by measuring beats. I present a heart rate measuring system which will be first microcontroller system that continuously tracking the beats and wide awake human few months before heart attack. Infrared sensor (RX sensor) will send infrared lights to the body. This sensor has a pair of transmitter and receiver. Using Photodiode (RX sensor) we will detect reflective lights from the body and this signal is sent to the microcontroller which is embedded in the casual wearable (i.e. ring or bracelet etc.) to detect hearth beat. Using this device will generate an alert to the person having increasing cholesterol after before reaching threshold specified for heart attack.

On CSI and Passive Wi-Fi Radar for Opportunistic Physical Activity Recognition

The use of Wi-Fi signals for human sensing has gained significant interest over the past decade. Such techniques provide affordable and reliable solutions for healthcare-focused events such as vital sign detection, prevention of falls and long-term monitoring of chronic diseases, among others. Currently, there are two major approaches for Wi-Fi sensing: (1) passive Wi-Fi radar (PWR) which uses well established techniques from bistatic radar, and channel state information (CSI) based wireless sensing (SENS) which exploits human-induced variations in the communication channel between a pair of transmitter and receiver. However, there has not been a comprehensive study to understand and compare the differences in terms of effectiveness and limitations in real-world deployment. In this paper, we present the fundamentals of the two systems with associated methodologies and signal processing. A thorough measurement campaign was carried out to evaluate the human activity detection performance of both systems. Experimental results show that SENS system provides better detection performance in a line-of-sight (LoS) condition, whereas PWR system performs better in a non-LoS (NLoS) setting. Furthermore, based on our findings, we recommend that future Wi-Fi sensing applications should leverage the advantages from both PWR and SENS systems.

Spatiotemporal variations in seismic attenuation during hydraulic fracturing: A case study in a tight oil reservoir in the Ordos Basin, China

During hydraulic fracturing (HF) stimulation for unconventional reservoir development, seismic attenuation has a significant influence on high-frequency microseismic data. Attenuation also provides important information for characterizing reservoir structure and changes to it due to HF injections. However, the attenuation effect is typically not considered in microseismic analysis. We have adopted the spectral ratio and centroid-frequency shift methods to estimate the subsurface attenuation (the factor [Formula: see text]) in a tight oil reservoir in the Ordos Basin, China. The P- and S-wave attenuations are calculated using the 3C waveform data recorded by a single-well downhole geophone array during a 12-stage HF stimulation. Both methods provide similar results (with differences in [Formula: see text] of absolute values less than 0.010 for P- and S-waves). For individual events, their median [Formula: see text] values calculated from different geophones are selected to represent the average attenuation. Spatiotemporal variations in attenuation are obtained by investigating [Formula: see text] values along propagating rays linking different source–receiver pairs. The [Formula: see text] values derived at different HF stages reveal significant attenuation in the targeted tight sandstone layer (0.030–0.062 for [Formula: see text] and 0.026−0.058 for [Formula: see text]), and the attenuation is apparently increased by fluid injection activities. We explain the sudden decrease in attenuation near the geophone array as a result of high shale content using log data from a horizontal treatment well. The consistency between the [Formula: see text] values and horizontal well-log data, as well as the HF process, indicates the reliability and robustness of the attenuation results. By studying spatiotemporal variations in attenuation, the changes in subsurface structures may be quantitatively characterized, thereby creating a reliable basis for microseismic modeling and data processing and providing additional information on monitoring the HF process.

Optimized NFC Circuit and Coil Design for Wireless Power Transfer with 2D Free-Positioning and Low Load Sensibility.

This paper proposes a method for optimizing and designing a wireless power transfer system operating at . It can be used as guidelines for designing coils for the new-trending technology that enables NFC devices to not only to communicate but also to charge. Since NFC wireless charging is an emerging technology, it is of interest to propose optimizations and a dedicated circuit design for such systems. This work proposes an optimization procedure to calculate the dimensions of a transmitter and receiver pair that assures the highest efficiency while considering all possible positions of a receiver that is placed on a desired surface. This procedure seeks to facilitate and automate the design of rectangular-shaped coils, whereas the literature proposes mainly square-shaped coils. Afterwards, a circuit analysis was conducted, and the series-parallel compensation network is proposed as the most promising topology of the receiver to assure a low efficiency sensibility to load variations for wireless power transfer systems. A pair of optimized transmitter and receiver coils is prototyped, and the experimental results are tested against the theory. The transmitter of and receiver of are separated by . The receiver can move on a surface of and the load can vary from to while assuring a minimum and maximum efficiency of and , respectively.

Intelligent Reflecting Surface assisted millimeter wave communication for achievable rate and coverage enhancement

In a wireless terrain, the presence of various obstacles leads to compliance of non-Line-of-sight (NLOS) norms between transmitter and receiver, which renders severe degradation in the service quality of the communication link and thereby limits the anticipated performance. The expected achievable rate is primarily affected by the location of the mobile receiver as well as the characteristics of the obstacles surrounding it for any wireless terrain. The achievable rate can be improved by deploying Intelligent Reflecting Surface (IRS) panels at properly identified locations. The presence of IRS panels stimulates a supplementary wireless channel that enhances reliable end-to-end connectivity between transmitter and receiver, especially when the direct path (Line-of-sight, LOS) is either experiences severe signal degradation or completely missing in shorter epochs. Using IRS, the performance of the wireless network can be improved by smartly re-configuring the passive reflecting elements which are embedded on a planar surface. In this paper, due to inherent geographical terrain specific attributes and the mobility aspects of a receiver, the end-to-end characterization of the wireless channel between a pair of transmitter and receiver is modeled using cascade arrangements of Time-Invariant (TI) and Time-Variant (TV) channel's impulse response. Further, the overall performance of wireless links is evaluated in terms of the key performance measures, namely, achievable rate and the span of network coverage. Obtained simulation results for two distinct geographical terrains validate the enhanced status of performance measures in IRS-assisted wireless terrains while regulating the system parameters, namely, IRS panel specifications, transmit power, and the velocity of the mobile receiver.

Damage identification in aluminum plates based on iterative partition algorithm using waveform centroid

In the field of structural damage monitoring, sensor arrays are often used to detect damage sites. However, the use of a large number of sensors increases the required amount of data processing, which imposes severe restrictions on effective online monitoring of industrial applications. In this study, an area-division method based on a waveform centroid algorithm is proposed to locate damage sites accurately using a limited number of sensors. Experiments are conducted on a 600 mm × 600 mm × 1.5 mm aluminum alloy plate to evaluate the performance of the proposed method. Four piezoceramics, acting as exciters and receivers, are arranged on the central region of the plate, dividing the entire detection area into eight portions. In order to scan the plate structure, Lamb waves are generated from each of the piezoceramics while the others function as receivers. By performing three successive comparisons after processing the data corresponding to each exciter–receiver​ pair via the waveform centroid algorithm, the specific portion containing the damage site can be identified. Subsequently, two ellipses are drawn using the three piezoceramics neighboring the identified portion, to visually locate the damaged site. The technique is applicable under conditions with low signal-to-noise ratios with an error of 1.5% in this study. It has the potential to be useful in industrial applications, in the context of real-time structural health monitoring.

An Observational Study of GPS-Derived Integrated Water Vapor over India

This study describes the process of deriving integrated water vapor (IWV) from (a) a set of 18 GPS receivers that were installed at different airports across India and (b) a pair of GPS receivers located in Ahmedabad situated around 8 km apart. The Zenith Tropospheric Delay was estimated from the GPS observations using the GAMIT software. Further, IWV was estimated from the ZTD values using surface temperature and pressure from ERA-I reanalysis as additional inputs. The IWV estimates for 1 year—March 2013 to February 2014—were compared with ECMWF Reanalysis Interim (ERA-I) reanalysis as well as radiosonde soundings. The Root Mean Squared Error (RMSE) was ≈6 mm or better for most stations. The IWV estimates for July 2013 were assimilated into the WRF model and had a positive impact on model analysis of IWV. The forecasted rain improved by up to 3–4 mm/day in some regions as a result of GPS-derived IWV estimates. For the Ahmedabad receivers, the GPS-derived IWV was compared with IWV from ERA-I reanalysis and was found to have a RMSE of ≈7.7 mm which is &lt;20% of the mean value. The study demonstrates that the observed IWV variation is consistent with rainfall patterns over Ahmedabad. The rise and dips in the IWV correlate well with the active-break cycle in the monsoon rain. The study demonstrates the value of local measurements of IWV with high temporal frequency, as they are more likely to respond to fast-moving weather phenomena such as rainfall. Thus, the GPS-derived IWV measurements are likely to have significant value in the short-term forecasts of precipitation.

Road sinkhole detection with 2D ambient noise tomography

Seismic methods are often used for detection of precollapsed sinkholes (voids) under roadways for remediation to minimize risks to the safety of the traveling public. Although active-source seismic methods can provide accurate subsurface profiles, they require closing the traffic flow for hours during testing and may potentially cause sinkhole collapse due to ground perturbation by source excitation. To address these issues, we have developed a new 2D ambient noise tomography (2D ANT) method for imaging voids under roadways. Instead of using the approximated Green’s function, whose required assumption of energy balance at both sides of each receiver pair is rarely satisfied, the crosscorrelation function of traffic noise recordings is inverted directly to obtain velocity structures. To adopt the concepts of seismic interferometry and derive the model structural kernel, passing-by vehicles are assumed to be moving sources along the receiver array. The source power-spectrum density is determined via the reverse time imaging approach to approximate the source distribution. The 2D ANT method is first demonstrated on a realistic synthetic model with the accurate recovery of the model variable layers and a buried void. To demonstrate its effectiveness on real-world problems, we successfully apply it to field data for assessment of a repaired sinkhole under U.S. Route 441, Florida, USA. The field experimental result finds that the method is capable of resolving the subsurface S-wave velocity ([Formula: see text]) structure and detecting a low-velocity anomaly. The inverted [Formula: see text] profile from 2D ANT generally agrees with that of 2D active-source full-waveform inversion, including the [Formula: see text] value and depth of the anomaly. To our best knowledge, this is the first study to directly invert the waveform crosscorrelation of traffic noise recordings to extract material property at the engineering meter scale (&lt;30 m depth).

EMR: A new metric to assess the resilience of directional mmWave channels to blockages

Millimeter-wave (mmWave) communication systems require narrow beams to compensate for high path loss and to increase the communication range. If an obstacle blocks the dominant communication direction, alternative paths (directions) should be quickly identified to maintain reliable connectivity. In this paper, we introduce a new metric to quantify the Effective Multipath Richness (EMR) of a directional communication channel in the angular domain. In particular, the proposed metric takes into account the strength and spatial diversity of the resolved Multipath Components (MPCs), while also considering the beamwidth of the communication link and the blockage characteristics. The metric is defined as a weighted sum of the number of distinct MPC clusters in the angular domain, where the clustering of the MPCs is performed based on the cosine-distance between the dominant MPCs.&#x0D; For a given transmitter (TX) and receiver (RX) pair, the EMR is a single scalar value that characterizes the robustness of the communication link against blockages, as it captures the number of unique communication directions that can be utilized. It is also possible to characterize the blockage robustness for the whole environment by evaluating the spatial distribution of the EMR metric considering various different TX/RX locations. Using our proposed metric, one can assess the scattering richness of different environments to achieve a particular service quality. We evaluate the proposed metric using our 28 GHz channel measurements in a library environment for Line-of-Sight (LOS) and NLOS scenarios, and compare it with some other commonly used propagation metrics. We argue that EMR is especially informative at higher frequencies, e.g., mmWave and terahertz (THz), where the propagation attenuation is high, and directional Non-Light-of-Sight (NLOS) communication is critical for the success of the network.

The Spoofing Detection of Dynamic Underwater Positioning Systems (DUPS) Based on Vehicles Retrofitted with Acoustic Speakers

The need of precision for underwater positioning and navigation should be considered as strict as those present at the sea surface. GNSS provides 4D positioning (XYZT). Each satellite contains two rubidium and two cesium atomic clocks. They are monitored by an atomic clock on the ground, and the entire system is constantly calibrated to a universal time standard, Coordinated Universal Time (UTC). GNSS receivers determine the time T to within 100 billionths of a second without the cost of owning, operating and maintaining an atomic clock. Of particular importance is the measurement of XYZT underwater. We assume that some surface vehicles are additionally equipped with an Acoustic Speaker, which transmits the XY coordinates of the vessel with an indication of accuracy and the time T of the vessel. Submarine vehicles determine their position by help of acoustic signals from several surface acoustic sources using the Time of Arrival (ToA) algorithm. Detection of Spoofing for the Dynamic Underwater Positioning Systems (DUPS) based on vehicles retrofitted with acoustic speakers is very actual problem. Underwater spoofing works as follows: N acoustic speaker on N ships transmit the coordinates {xi,yi,ti}, i=1,N¯. GNSS signals are susceptible to interference due to their very low power (−130 dBm) and can be easily jammed by other sources, which may be accidental or intentional. The spoofer, like an underwater vehicle, receives these signals from N vessels, distorts them and transmits with increased acoustic power. All receivers into the spoofed area will calculate the same coordinates, so the indication of the coincidence of coordinates from a pair of diversity receivers is an indication of spoofing detection.