Effects Of Multipath Interference Research Articles

Optimizing V2V communication in ITS: The benefits of silver-coated DSRC

The silver-coated DSRC of antennas are used for short-range communication between vehicles (V2V) in intelligent transportation systems (ITS), including DSRC (Dedicated Short-Range Communication). It has silver as a conducting material for the antennas and offers several benefits including higher data rates, increased range, and improved reliability for V2V communication. Using multiple antennas in a silver-coated DSRC provides spatial diversity, reducing the effects of multipath fading and interference. The radiation pattern can also be focused in a specific direction to increase the signal strength. The integration of artificial intelligence (AI) and autonomous drivers into ITS is becoming increasingly important, and V2V communication is a crucial aspect of these systems. The use of a silver-coated DSRC can provide a reliable and efficient solution for DSRC communication in V2V communication, which is essential for the success of ITS. The increased data rates, range, and reliability facilitate the exchange of information between autonomous vehicles, enabling them to make more informed decisions and operate more safely on roads.

Throughput Maximization Using Deep Complex Networks for Industrial Internet of Things

The high-density Industrial Internet of Things needs to meet the requirements of high-density device access and massive data transmission, which requires the support of multiple-input multiple-output (MIMO) antenna cognitive systems to keep high throughput. In such a system, spectral efficiency (SE) optimization based on dynamic power allocation is an effective way to enhance the network throughput as the channel quality variations significantly affect the spectral efficiency performance. Deep learning methods have illustrated the ability to efficiently solve the non-convexity of resource allocation problems induced by the channel multi-path and inter-user interference effects. However, current real-valued deep-learning-based power allocation methods have failed to utilize the representational capacity of complex-valued data as they regard the complex-valued channel data as two parts: real and imaginary data. In this paper, we propose a complex-valued power allocation network (AttCVNN) with cross-channel and in-channel attention mechanisms to improve the model performance where the former considers the relationship between cognitive users and the primary user, i.e., inter-network users, while the latter focuses on the relationship among cognitive users, i.e., intra-network users. Comparison experiments indicate that the proposed AttCVNN notably outperforms both the equal power allocation method (EPM) and the real-valued and the complex-valued fully connected network (FNN, CVFNN) and shows a better convergence rate in the training phase than the real-valued convolutional neural network (AttCNN).

Array Scheduling With Power and Bandwidth Allocation for Simultaneous Multibeam Tracking Low-Angle Targets in a VHF-MIMO Radar

The very high frequency (VHF) radar suffers from the multipath interference and false alarms when tracking low-angle targets. The co-located multiple-input multiple-output (MIMO) radar technique can mitigate these adverse effects with waveform diversity. However, the limited resources restrict the potential of the VHF-MIMO radar. In this paper, an array scheduling with power and bandwidth allocation (ASPBA) strategy is proposed for the VHF-MIMO radar tracking low-angle targets. The predicted posterior Cramér-Rao lower bound (PCRLB) under the multipath interference and measurement origin uncertainty (MOU) effects is derived to serve as the optimization metric. The measurement amplitude information (AI) is incorporated into the PCRLB to facilitate target detection and tracking. It is shown that the ASPBA problem is a mixed integer programming and NP-hard problem, where the array, power, and bandwidth allocation variables are both coupled in the objective and constraints. An efficient three-stage-based solution is proposed for problem-solving. The approximated relationship among three variables is derived using Hölder's inequality, and an auxiliary variable is introduced to describe the array contribution. Thereby, the array scheduling is determined by a heuristic rounding algorithm, and the power and bandwidth allocation are achieved using the approximated relationship. Simulation results confirm the effectiveness and efficiency of the proposed ASPBA strategy, compared with state-of-the-art algorithms. It is also shown that the target height is a main factor that influences the resource allocation results in the low-angle tracking scenario.

저고도 해상표적 추적에서 다중경로 영향 억제를 위한 다중 주파수 모노펄스 방향 탐지 방법

This paper proposed a monopulse method using multiple frequencies to overcome multipath interference in the tracking of low-altitude sea targets. The method determines target elevation candidates by comparing the difference between the measured complex monopulse ratios and those calculated considering multipath interference at three adjacent frequencies. The final target elevation is determined among the candidates by using a cost function set based on the characteristics of the results considering multipath interference. Because the proposed method requires solely the measured target distance and monopulse ratios, it can be applied to the existing monopulse radar system without additional configuration. The suppression effect of multipath interference was verified by a simulation conducted for tracking low-altitude targets in a multipath environment.

Wireless Battery-Free Harmonic Communication System for Pressure Sensing.

In this paper, an efficient passive wireless harmonic communication system is proposed for the real-time monitoring of the pressurized pipelines. A pressure sensor is fabricated using the additive manufacturing technique and a harmonic radio frequency (RF) tag is designed to operate at the fundamental frequency (f) of 2 GHz that shifts the phase of the back reflected RF signal according to the applied pressure ranging from 0 to 20 psi. A power efficient phase modulation with virtually no losses is achieved using a hybrid coupler-based phase shifter that efficiently reflect back the incoming signal using an end coupled reactive impedance element/sensor. The phase delay introduced by the reactive element gets doubled with the second harmonic communication, which increases the sensitivity by a factor of two. The concept of harmonic backscattering is exploited to reduce the effects of multi-path interference and self jamming, as well as improving the signal-to-noise ratio (SNR).

Real-Time Indoor Geolocation Tracking for Assisted Healthcare Facilities.

A leading cause of physical injury sustained by elderly persons is the event of unintentionally falling. A delay between the time of fall and the time of medical attention can exacerbate injury if the fall resulted in a concussion, traumatic brain injury, or bone fracture. The authors present a solution capable of finding and tracking, in real-time, the location of an elderly person within an indoor facility, using only existing Wi-Fi infrastructure. This paper discusses the development of an open source software framework capable of finding the location of an individual within 3m accuracy using 802.11 Wi-Fi in good coverage areas. This framework is comprised of an embedded software layer, a Web Services layer, and a mobile application for monitoring the location of individuals, calculated using trilateration, with Kalman filtering employed to reduce the effect of multipath interference. The solution provides a real-time, low cost, extendible solution to the problem of indoor geolocation to mitigate potential harm to elderly persons who have fallen and require immediate medical help.

Target Localization in High-Coherence Multipath Environment Based on Low-Rank Decomposition and Sparse Representation

In a multipath propagation environment, prevalent target localization methods are mainly based on the classical two-ray propagation model without considering other reflected waves. Because the received target echoes are considerably corrupted by multipath reflections in the case of complex terrain, these prevalent methods might fail to work or achieve poor performance. To solve this problem, we first consider a practical multipath propagation scenario to reveal the dynamic structural relationship of the spatial paths based on the spherical earth model. Subsequently, a target localization algorithm based on low-rank decomposition (LRD) and sparse representation (SR) framework is proposed. The proposed algorithm can effectively mitigate the effects of complex multipath interference without using any prior knowledge on the illuminated terrain and the reflecting paths. Experiments on synthetic data and real data validate the effectiveness of the proposed algorithm.

Design of an Embedded Communication System for Underwater Asynchronous Localization

Most applications of underwater acoustic sensor networks (UASNs) rely on reliable location information. In this letter, we present an embedded communication system for underwater asynchronous localization. An asynchronous localization protocol is developed and encoded for the actual implementation on an embedded communication system. Particularly, the embedded communication system is composed of four transducers, one control center and four acoustic modems. In order to reduce the effect of multipath interference, the direct-sequence spread-spectrum (DSSS) technology is applied to the design of modem. Meanwhile, the iterative least squares method is implemented to estimate the position. Finally, experimental results are given to verify the effectiveness of the proposed system. It is demonstrated that the influences of asynchronous clock can be well eliminated.

Highly Directional Multipath Free High Data-Rate Communications With a Reconfigurable Modem

This paper presents a high data-rate underwater acoustic communication system that does not rely on large, powerful, and computationally complex modems. Our small size, weight, and power system is a reconfigurable acoustic modem platform (RAMP) that exploits transducer directivity to reduce the effects of multipath and mutual interference, thus eliminating the need for a traditional channel equalizer. Experimental results are shown to demonstrate the feasibility of RAMP in a shallow-water ocean environment to deliver real-time data transfer.

Evaluation of effects of multipath and co-channel interference on time reversal multiple-input/multiple-output in underwater acoustic channel

The relationship between the performance of time-reversal-based multiple-input/multiple-output (MIMO) communication technique and the changes in the multipath environment is investigated quantitatively. In this study, the performance of adaptive time reversal (ATR)-MIMO is investigated by a parametric study approach. The ATR-MIMO communication technique is applied to the multipath-rich synthetic shallow sea acoustic dataset. We focused on discussing about the relationship among the changes in the multipath environment, the number of transmissions, the capability of ATR-MIMO to remove cochannel interference (CCI), and the efficiency of utilization of the energy of the multipath. The results reveal which characteristic of an acousticwavefield affects the performance of ATR-MIMO and how the performance saturates when the multipath environment changes. It is also demonstrated that ATR-MIMO can utilize the energy of the multipath as effectively as the passive-time-reversal-based single-input/multiple-output communication technique in a Gaussian-noise-dominant environment.

Lowering the Spectral Detection Threshold for Molecular Impurities in Gas Mixtures by Interference Multiplexing

We consider the most feasible ways to significantly improve the sensitivity of spectroscopic methods for detection and measurement of trace concentrations of greenhouse gas molecules in the atmosphere. The proposed methods are based on combining light fluxes from a number of spectral components of the specified molecule on the same photodetector, taking into account the characteristic features of the transmission spectrum of devices utilizing multipath interference effects.

Minimizing the Number of Spans for Terrestrial Fiber-Optic Systems Using Quasi-Single-Mode Transmission

We show that quasi-single-mode transmission in few-mode fibers (FMFs) can reduce the number of spans for a fixed transmission distance and, consequently, the cost per bit for terrestrial transmission systems by minimizing both the Capex and Opex. The Gaussian-noise model is employed to estimate the nonlinear noise power spectral density both, which depends on the effective area of the FMF and span length, for Er-doped fiber amplifier (EDFA) and hybrid Raman/EDFA systems. Together with amplified spontaneous emission noise, an optical signal-to-noise ratio (OSNR) for a fixed transmission distance as a function of the effective area of the FMF and span length can be obtained. Given a target OSNR for a particular modulation format, we determine the maximum span length or the minimum number of spans as the effective area of the FMF varies both analytically and through numerical simulations. The effect of multipath interference in the FMF on the minimum number of span has also been investigated.

Performance of GPS sidereal filters during a satellite outage

Abstract Sidereal filtering is the name of a technique used to reduce the effect of multipath interference on a GPS position time series associated with a static or quasi-static antenna. This article assesses the impact of a GPS satellite outage on the performance of a sidereal filter. Two different types of sidereal filter are tested: a position-domain sidereal filter (PDSF) and an observation-domain sidereal filter (ODSF). A satellite outage is simulated at two static receivers with contrasting antenna types and multipath environments. At both stations, the ODSF is more effective than a PDSF at removing multipath error over averaging intervals under around 200 seconds in length whether there is an outage or not. However, difference in the performance of the two types of sidereal filter was much more significant at the station more prone to multipath interference. The results are particularly relevant for applications where high-rate precise point positioning (PPP) is used for monitoring: If a PDSF is applied, then errors due to highfrequency multipath interference may still alias into the resulting position time series if a satellite outage occurs and possibly increasing the false alarm rate. In contrast, an ODSF is likely to perform better in such circumstances.

Modeling shock formation and propagation in high-performance jet aircraft noise

Nonlinear propagation can play an important role in both time and frequency-domain features of far-field supersonic jet noise. Many aspects of nonlinear propagation, such as waveform steepening and greater-than-expected high-frequency spectral levels, have been previously predicted for select angles and engine conditions. This paper builds on previous successes and presents a comparison of nonlinear and linear predictions for the F-35B aircraft. Results are shown over a wide spatial and angular range and over varying engine power conditions, including showing evidence of nonlinear propagation in the forward direction at the highest engine conditions. In addition, specific features, such as individual shocks, are compared between numerically propagated and measured waveforms, highlighting the successes and deficiencies of current propagation models. Weather and multi-path interference effects are also addressed and corrected using an empirical model. [Work supported by USAFRL through ORISE. Distribution A: Approved for public release; distribution unlimited; Cleared 07/10/2017; JSF17-714.]

Performance analysis of passive time reversal communication technique for multipath interference in shallow sea acoustic channel

In this study, the performance of passive time reversal (PTR) communication techniques in multipath rich underwater acoustic environments is investigated. It is recognized empirically and qualitatively that a large number of multipath arrivals could generally raise the demodulation result of PTR. However, the relationship between multipath and the demodulation result is hardly evaluated quantitatively. In this study, the efficiency of the PTR acoustic communication techniques for multipath interference cancelation was investigated quantitatively by applying a PTR-DFE (decision feed-back filter) scheme to a synthetic dataset of a horizontal underwater acoustic channel. Mainly, in this study, we focused on the relationship between the signal-to-interference ratio (SIR) of datasets and the output signal-to-noise ratio (OSNR) of demodulation results by a parametric study approach. As a result, a proportional relation between SIR and OSNR is confirmed in low-SNR datasets. It was also found that PTR has a performance limitation, that is OSNR converges to a typical value depending on the number of receivers. In conclusion, results indicate that PTR could utilize the multipath efficiently and also withstand the negative effects of multipath interference at a given limitation.

Testing gravity with pulsar scintillation measurements

We propose to use pulsar scintillation measurements to test predictions of alternative theories of gravity. Comparing to single-path pulsar timing measurements, the scintillation measurements can achieve a factor of 10^5 improvement in timing accuracy, due to the effect of multi-path interference. Previous scintillation measurements of PSR B0834+06 have data acquisition for hours, making this approach sensitive to mHz gravitational waves. Therefore it has unique advantages in measuring gravitational effect or other mechanisms (at mHz and above frequencies) on light propagation. We illustrate its application in constraining scalar gravitational-wave background, in which case the sensitivities can be greatly improved with respect to previous limits. We expect much broader applications in testing gravity with existing and future pulsar scintillation observations.

Vehicle Localization Based on Global Navigation Satellite System Aided by Three-Dimensional Map

Accurate vehicle localization technologies are significant for current onboard navigation systems and future autonomous vehicles. More specifically, positioning accuracy is expected at the submeter level. This paper presents an accurate vehicle self-localization system and evaluates the proposed system in different classes of urban environments. The developed system adopts an innovative global navigation satellite system (GNSS) positioning method as the key technique. The GNSS positioning method can improve the positioning error by reducing the effects of multipath interference and non-line-of-sight errors with the aid of a three-dimensional map. To improve positioning accuracy further, the vehicle localization system integrates the GNSS positioning technique with inertial sensors and vision sensors by considering the characteristics of each sensor. The inertial sensors represent vehicle movement with heading direction and vehicle speed. The vision sensor is used to recognize the position change relative to lane markings on the road surface. Those techniques and sensors collaborate to provide an accurate position in the global coordinate system. To verify the effectiveness and stability of the proposed system, a series of tests was conducted in one of the most challenging urban cities, Tokyo. The experiment results demonstrate that the proposed system can achieve submeter accuracy for the positioning error mean and has a 90% correct lane rate in the localization.

Suppressing Multipath Interference by Using Smart Antenna for Passive UHF RFID System

Since the effect of multipath interference under indoor environment, some tags cannot be activated without sufficient power in detection area for the passive UHF RFID system, which decreases the tag recognition rate greatly. It is proposed in this paper that the smart antenna is used to overcome multipath interference. The influence of using the smart antenna on the tag received power is analyzed based on multipath channel modeling. Simulation results show that the tag received power tends to be more stable when using the smart antenna than using the traditional single antenna under multipath environment for the passive UHF RFID system, which improves tag recognition rate.

Azimuth-dependent elevation threshold (ADET) masks to reduce multipath errors in ionospheric studies using GNSS

Physical structures found in the vicinity of GNSS receivers can introduce multipath interference effects when a signal arrives at the receiver by different routes. Multipath effects are well recognized as one of the most significant sources of error that degrade the accuracy of GNSS signals for navigation and positioning applications. These effects also reduce the quality of GNSS data used for ionospheric studies. The principal cause of multipath effects is proximity of the antenna to reflecting structures and it is more pronounced when the signal comes from a satellite with low elevation. Typically, conservative fixed-elevation thresholds of 20–40° are used to filter out signals from low elevation angles, but this leads to the exclusion of a significant quantity of useable data. In this paper we present a series of azimuth-dependent elevation thresholds that were developed by characterizing the multipath environment of the GPS Ionospheric Scintillation and TEC (Total Electron Content) Monitor (GISTM) receivers installed by SANSA (South African National Space Agency) at Mauritius (20.14°S and 57°E), Marion Island (46.87°S and 37.86°E) and SANAE IV in Antarctica (71.73°S and 2.2°W). The threshold masks were developed from azimuth-elevation maps of the S4 index, σϕ index, the Code-Carrier Divergence Standard Deviation (CC-STDDEV) and the L1 Carrier-to-Noise Density (L1 CNo) from 1-min scintillation data taken over a period of 10–12months at each location to identify signals that are distorted by multipath effects. Using the azimuth-dependent elevation threshold (ADET) mask typically gives 22–28% more useful data than using a fixed-elevation threshold at the sites studied in this paper.

Azimuthal coherence of the sound field in the vicinity of a high performance military aircraft

Mixing noise from a jet engine originates from an extended spatial region downstream of the nozzle and is partially correlated both spatially and temporally. Previously, the coherence properties in the downstream (axial) direction of the sound field of a tethered military aircraft were investigated, resulting in the identification of different spatial regions based on coherence length [B. M. Harker et al., AIAA J. 54, 1551-1566 (2016)]. In this study, a vertical array of microphones to the side of the jet plume is used to obtain the azimuthal coherence of the sound field. Although multipath interference effects and a limited angular aperture make coherence length calculation impossible, information about upper and lower bounds can be extracted. The measured azimuthal coherence as a function of downstream distance and frequency is then compared to that predicted by sound field reconstructions using multisource, statistically optimized near-field acoustical holography (M-SONAH) [A. T. Wall et al., J. Acoust. Soc. Am., 139, 1938-1950 (2016)]. This comparison helps to benchmark the performance of a reduced-order M-SONAH algorithm that employs only axisymmetric cylindrical basis functions to represent the direct and image sound fields. [Work supported by USAFRL through ORISE (2016).]