Echo Interference Research Articles

Analysis of passive interference on radio station from AC UHV power

The problems of Electromagnetic Interference in Airborne Intelligence Radar Stations near the AC UHV Transmission Lines is researched in this paper, which is mainly passive interference. And then analyzed the passive interference of AC UHV lines. It mainly studied the influence of the tower and line on the distance detection performance of the air-to-air intelligence radar of the UHV transmission lines. and integrated the influence of the surface reflection surface, the shadowing effect and the secondary radiation echo interference, Proposed a passive interference protection distance for UHV transmission lines and airborne intelligence radar stations

Tongue-driven sonar beam steering by a lingual-echolocating fruit bat.

Animals enhance sensory acquisition from a specific direction by movements of head, ears, or eyes. As active sensing animals, echolocating bats also aim their directional sonar beam to selectively “illuminate” a confined volume of space, facilitating efficient information processing by reducing echo interference and clutter. Such sonar beam control is generally achieved by head movements or shape changes of the sound-emitting mouth or nose. However, lingual-echolocating Egyptian fruit bats, Rousettus aegyptiacus, which produce sound by clicking their tongue, can dramatically change beam direction at very short temporal intervals without visible morphological changes. The mechanism supporting this capability has remained a mystery. Here, we measured signals from free-flying Egyptian fruit bats and discovered a systematic angular sweep of beam focus across increasing frequency. This unusual signal structure has not been observed in other animals and cannot be explained by the conventional and widely-used “piston model” that describes the emission pattern of other bat species. Through modeling, we show that the observed beam features can be captured by an array of tongue-driven sound sources located along the side of the mouth, and that the sonar beam direction can be steered parsimoniously by inducing changes to the pattern of phase differences through moving tongue location. The effects are broadly similar to those found in a phased array—an engineering design widely found in human-made sonar systems that enables beam direction changes without changes in the physical transducer assembly. Our study reveals an intriguing parallel between biology and human engineering in solving problems in fundamentally similar ways.

BDS/GPS INTEGRATED POSITIONING METHOD RESEARCH BASED ON NONLINEAR KALMAN FILTERING

Abstract. In order to realize fast and accurate BDS/GPS integrated positioning, it is necessary to overcome the adverse effects of signal attenuation, multipath effect and echo interference to ensure the result of continuous and accurate navigation and positioning. In this paper, pseudo-range positioning is used as the mathematical model. In the stage of data preprocessing, using precise and smooth carrier phase measurement value to promote the rough pseudo-range measurement value without ambiguity. At last, the Extended Kalman Filter(EKF), the Unscented Kalman Filter(UKF) and the Particle Filter(PF) algorithm are applied in the integrated positioning method for higher positioning accuracy. The experimental results show that the positioning accuracy of PF is the highest, and UKF is better than EKF.

Massive MIMO full-duplex relaying with hardware impairments

Massive multiple-input-multiple-output full-duplex relaying (MM-FDR), which exploits both the benefits of large-scale antenna arrays and full-duplex transmission, is considered as a promising technology to achieve very high spectral efficiency in the future wireless network. Despite the inevitable presence of transceiver impairments due to the use of low-cost hardware components, most of the prior works on MM-FDR assume perfect transceiver hardware which is unrealistic in practice. This paper investigates the impact of hardware impairments on the MM-FDR. Based on the recent experimental results, the effect of hardware impairments is modeled using transmit and receive distortion noises. The end-to-end achievable rate is derived and the scaling behaviors of echo interference due to the full-duplex operation, multi-user interference and effective distortions caused by hardware impairments are obtained. The scaling results show that the achievable rate of MM-FDR is limited by the hardware impairments at the sources and destinations, instead of that at the relay or other interferences, as the number of relay antenna tends to infinity. A low-complexity power control scheme is proposed to further improve the energy efficiency of MM-FDR with hardware impairments. Simulation results show that the proposed scheme can improve the spectral-energy efficiency tradeoff significantly.

Variation in frequency-modulated call type for different flight densities in Mexican Free-tailed bats

Mexican free-tailed bats (Tadarida brasiliensis) adapt their call type depending on multiple factors. These bats have two general types of echolocation sounds, frequency-modulated (FM) and constant frequency (CF). CF calls are generally produced during the search phase of foraging, and FM calls are used during approach, prey capture, and roost emergence. In this study, we examined how Mexican free-tailed bats adapt their calls during emergence to avoid echo interference. We extracted individual calls from within a 500-ms sample that corresponded to five different emergence density categories. We found that these bats produce eight different FM call types during emergence. For each call within the sample, we characterized the call shape and calculated different parameters (duration, start frequency, peak frequency, end frequency). We compared the acoustic parameters across density categories and call shape, and compared the distribution of call shape across density categories. The results indicate that the call parameters and call shape vary from bat to bat, but there is no clear trend that this variance is due to the bat density. Therefore, these bats are likely changing their call shape and frequency characteristics to distinguish their own echoes from those of other bats.

Who shall I say is calling? Validation of a caller recognition procedure in Bornean flanged male orangutan (Pongo pygmaeus wurmbii) long calls

Acoustic individual discrimination has been demonstrated for a wide range of animal taxa. However, there has been far less scientific effort to demonstrate the effectiveness of automatic individual identification, which could greatly facilitate research, especially when data are collected via an acoustic localization system (ALS). In this study, we examine the accuracy of acoustic caller recognition in long calls (LCs) emitted by Bornean male orangutans (Pongo pygmaeus wurmbii) derived from two data-sets: the first consists of high-quality recordings taken during individual focal follows (N = 224 LCs by 14 males) and the second consists of LC recordings with variable microphone-caller distances stemming from ALS (N = 123 LCs by 10 males). The LC is a long-distance vocalization. We therefore expect that even the low-quality test-set should yield caller recognition results significantly better than by chance. Automatic individual identification was accomplished using software originally developed for human speaker recognition (i.e. the MSR identity toolbox). We obtained a 93.3% correct identification rate with high-quality recordings, and 72.23% with recordings stemming from the ALS with variable microphone-caller distances (20–420 m). These results show that automatic individual identification is possible even though the accuracy declines compared with the results of high-quality recordings due to severe signal degradations (e.g. sound attenuation, environmental noise contamination, and echo interference) with increasing distance. We therefore suggest that acoustic individual identification with speaker recognition software can be a valuable tool to apply to data obtained through an ALS, thereby facilitating field research on vocal communication.

Full-Duplex Massive MIMO AF Relaying With Semiblind Gain Control

This paper proposes an amplify-and-forward-based massive multiple-input–multiple-output full-duplex relaying (AF-MM-FDR) protocol, where multiple source–destination pairs communicate simultaneously with a common full-duplex relay. A zero-forcing (ZF)-based relay transceiver design with semiblind gain control is presented, considering the problem of relay oscillation. The asymptotic expression of end-to-end signal-to-interference-plus-noise power (SINR) is derived under the general power scaling scheme. The scaling behaviors of echo interference (EI) and effective channel estimation error are determined. Scaling results show that the deployment of very large antenna arrays at the relay has the potential to eliminate the effect of EI due to the full-duplex operation, if the power scaling scheme is selected properly. Moreover, based on the asymptotic analysis, a low-complexity power control scheme is proposed to optimize the spectral efficiency of AF-MM-FDR. Simulation results show that the proposed power control scheme improves the spectral–energy efficiency tradeoff of AF-MM-FDR significantly.

Shear wave arrival time estimates correlate with local speckle pattern.

We present simulation and phantom studies demonstrating a strong correlation between errors in shear wave arrival time estimates and the lateral position of the local speckle pattern in targets with fully developed speckle. We hypothesize that the observed arrival time variations are largely due to the underlying speckle pattern, and call the effect speckle bias. Arrival time estimation is a key step in quantitative shear wave elastography, performed by tracking tissue motion via cross-correlation of RF ultrasound echoes or similar methods. Variations in scatterer strength and interference of echoes from scatterers within the tracking beam result in an echo that does not necessarily describe the average motion within the beam, but one favoring areas of constructive interference and strong scattering. A swept-receive image, formed by fixing the transmit beam and sweeping the receive aperture over the region of interest, is used to estimate the local speckle pattern. Metrics for the lateral position of the speckle are found to correlate strongly (r > 0.7) with the estimated shear wave arrival times both in simulations and in phantoms. Lateral weighting of the swept-receive pattern improved the correlation between arrival time estimates and speckle position. The simulations indicate that high RF echo correlation does not equate to an accurate shear wave arrival time estimate-a high correlation coefficient indicates that motion is being tracked with high precision, but the location tracked is uncertain within the tracking beam width. The presence of a strong on-axis speckle is seen to imply high RF correlation and low bias. The converse does not appear to be true-highly correlated RF echoes can still produce biased arrival time estimates. The shear wave arrival time bias is relatively stable with variations in shear wave amplitude and sign (-20 μm to 20 μm simulated) compared with the variation with different speckle realizations obtained along a given tracking vector. We show that the arrival time bias is weakly dependent on shear wave amplitude compared with the variation with axial position/ local speckle pattern. Apertures of f/3 to f/8 on transmit and f/2 and f/4 on receive were simulated. Arrival time error and correlation with speckle pattern are most strongly determined by the receive aperture.

Echo Interference Suppression Approach for Doppler Through-Wall Radar

Because of the particularity of through-wall radar (TWR) applications, TWR often operates in a complicated environment, which can lead to severe interferences in the received echo and thus hamper the accurate target detection. To solve the issue, in this paper, an echo interference suppression approach, which combines hardware and algorithm process, is proposed for Doppler TWR. Compared with the traditional methods, which mainly based on the fixed filter parameters, the proposed approach takes advantage of feedback structure and microcontroller to intelligently adjust the filter parameters according to the real-time interference variation and thus achieves not only more effective, but also more stable interference suppression performance even in a dynamic environment. Series of experimental measurements are presented to illustrate the performance of the proposed techniques.

Full-Duplex Massive MIMO Relaying: An Energy Efficiency Perspective

This paper investigates the multi-pair full-duplex massive MIMO relaying, where multiple source-destination pairs communicate simultaneously with the help of a common full-duplex decode-and-forward relay. It is assumed that the sources and destinations are equipped with single antenna while the relay is equipped with very large antenna arrays. The asymptotic end-to-end signal-to-interference-plus-noise ratio (SINR) is analyzed under the general power scaling scheme, when maximal ratio combining/maximal ratio transmission scheme or zero-forcing reception/zero-forcing transmission scheme is employed at the relay. Theoretical results show that the effect of echo interference due to full-duplex operation can be eliminated by the large antenna arrays of the relay, if the power scaling scheme is selected properly. On the basis of the SINR expressions, the energy efficiency scaling law is derived. Furthermore, we present the power control scheme at the sources and relay to maximize the energy efficiency, subject to the required spectral efficiency and maximum power constraints. We show that the power control problem can be approximated as a geometric program problem and solved efficiently by the convex optimization tools. Numerical results are presented to validate the asymptotic analysis as well as the proposed power control scheme. The results demonstrate that the deployment of full-duplex relay is beneficial to achieve energy efficient transmission in massive MIMO relaying network.

Practical opportunistic full‐/half‐duplex relaying

The opportunistic full-/half-duplex relaying schemes are studied where the effects of imperfect channel state information (CSI) and transmit imperfection are taken into account. The opportunistic schemes with different levels of channel knowledge, that is, the scheme with CSI at the transmitter (CSIT), the scheme with CSI at the receiver (CSIR) and the scheme with only statistical CSI, are proposed. Power adaption (PA) schemes with different levels of channel knowledge are presented and combined with the opportunistic schemes to further improve the system performance. The opportunistic schemes are evaluated in the term of average capacity. The author's results show that the opportunistic scheme with CSIR achieves comparative performance to the scheme with CSIT when the PA is not used. Moreover, it is shown that the choice of full-duplex relaying becomes more attractive when the quality of estimation for desired channels degrades. However, the converse is true as the quality of estimation for echo interference channel degrading or the power of transmit noise increasing.

Support Vector Machine을 이용한 선에코 특성 분석 및 탐지 방법

SVM은 학습 데이터를 두 개의 집단으로 분리시키는 최적의 초평면을 찾는 이진 분류기로서 우수한 성능 때문에 다양한 분야에서 귀납 추론, 이진 분류, 예측 등을 목적으로 사용되는 알고리즘이다. 또한 대표적인 블랙박스 모델 중 하나이기 때문에 학습 후 생성되는 SVM의 해석에 대한 연구도 활발히 진행되고 있다. 본 논문에서는 SVM 알고리즘을 이용하여 기상 레이더의 데이터 내에 비교적 높은 빈도로 발생하여 기상 예보의 정확도를 감소시키는 비강수에코 중 하나인 선에코를 자동으로 탐지하는 방법에 대한 연구를 수행하였다. 학습 데이터로는 평균 반사도, 크기, 발생 형태, 중심 고도 등과 같은 특성을 활용하였는데, 이는 기상 레이더 데이터에 저장된 다양한 데이터 중 반사도 값을 선택한 후 클러스터링 기법을 통해 추출한 것이다. 이와 같이 학습된 SVM 분류기를 실제 사례를 바탕으로 하여 검증하였으며, Decision Tree 알고리즘을 적용하여 생성한 분류기의 해석을 수행하였다. A SVM is a kind of binary classifier in order to find optimal hyperplane which separates training data into two groups. Due to its remarkable performance, the SVM is applied in various fields such as inductive inference, binary classification or making predictions. Also it is a representative black box model; there are plenty of actively discussed researches about analyzing trained SVM classifier. This paper conducts a study on a method that is automatically detecting the line-shaped echoes, sun strobe echo and radial interference echo, using the SVM algorithm because the line-shaped echoes appear relatively often and disturb weather forecasting process. Using a spatial clustering method and corrected reflectivity data in the weather radar, the training data is made up with mean reflectivity, size, appearance, centroid altitude and so forth. With actual occurrence cases of the line-shaped echoes, the trained SVM classifier is verified, and analyzed its characteristics using the decision tree method.

Effect of subaperture beamforming on phase coherence imaging.

High-frame-rate echocardiography using unfocused transmit beams and parallel receive beamforming is a promising method for evaluation of cardiac function, such as imaging of rapid propagation of vibration of the heart wall resulting from electrical stimulation of the myocardium. In this technique, high temporal resolution is realized at the expense of spatial resolution and contrast. The phase coherence factor has been developed to improve spatial resolution and contrast in ultrasonography. It evaluates the variance in phases of echo signals received by individual transducer elements after delay compensation, as in the conventional delay-andsum beamforming process. However, the phase coherence factor suppresses speckle echoes because phases of speckle echoes fluctuate as a result of interference of echoes. In the present study, the receiving aperture was divided into several subapertures, and conventional delay-and-sum beamforming was performed with respect to each subaperture to suppress echoes from scatterers except for that at a focal point. After subaperture beamforming, the phase coherence factor was obtained from beamformed RF signals from respective subapertures. By means of this procedure, undesirable echoes, which can interfere with the echo from a focal point, can be suppressed by subaperture beamforming, and the suppression of the phase coherence factor resulting from phase fluctuation caused by such interference can be avoided. In the present study, the effect of subaperture beamforming in high-frame-rate echocardiography with the phase coherence factor was evaluated using a phantom. By applying subaperture beamforming, the average intensity of speckle echoes from a diffuse scattering medium was significantly higher (-39.9 dB) than that obtained without subaperture beamforming (-48.7 dB). As for spatial resolution, the width at half-maximum of the lateral echo amplitude profile obtained without the phase coherence factor was 1.06 mm. By using the phase coherence factor, spatial resolution was improved significantly, and subaperture beamforming achieved a better spatial resolution of 0.75 mm than that of 0.78 mm obtained without subaperture beamforming.

Full Duplex Relay Based Cognitive Radio System with Physical Layer Network Coding

In this paper, a full duplex relay (FDR) based cognitive radio (CR) system is proposed with two secondary source nodes and two secondary destination nodes. The concept of physical layer network coding (PLNC) is applied on decode and forward (DF) FDR to ensure that both source nodes can transmit data to both destination nodes. Further, the availability of multiple spectrum bands enables CR system to decode source symbols at destination nodes. The major advantage of the proposed system with FDR and PLNC is that it requires only one time slot to send the data from both the source nodes to both the destination nodes. If FDR is replaced with half duplex relay (HDR), 2 time slots are required for the CR system. If PLNC is not applied at the DF relay, the CR system would require 2 or 4 time slots when FDR or HDR is employed, respectively. In Nakagami-$$m$$m fading channels environment, analytical expressions are derived for end-to-end outage performance of the proposed PLNC based system in the presence of echo interference at the FDR and with HDR in the place of FDR. The outage performance of the proposed CR system is analyzed for various scaling and shape parameters of Nakagami-$$m$$m fading channels.

Outage Analysis of Multihop Full Duplex Relaying

We consider a multihop full duplex relaying (FDR) system, where multiple full duplex decode-and-forward relays are connected in cascade so as to forward the information from a source terminal to a destination terminal. Since FDR causes additional echo interference at the relay, we introduce a parameter that captures the ability of the relays to isolate transmission from reception. This parameter is defined as the ratio of the received desired signal power to the received interference power, when the transmit power is the same for the useful and the interfering signals, and dubbed as quotedblleft path-loss-to-interference ratioquotedblright (PLIR). For given values of the PLIR, we investigate the number of full duplex relays that lead to the minimum outage probability. The performance of multihop half duplex relaying (HDR) is also studied as a benchmark, showing that FDR outperforms HDR, in terms of the outage probability, for sufficiently large values of PLIR.

Research on the Interference Cancellation Based on Adaptive Algorithms

The adaptive interference cancellation algorithms(AICA) is proposed in this paper. The Matlab simulation results of the performance of six different kinds of AICA are presented. According to the comparison of the simulation results, especially the usage of resource, convergence rate and effects of cancellation, the NLMS adaptive interference cancellation algorithm and frequency-domain block LMS algorithm are selected, which are suitable for the further design on FPGA. By simulating the functions by Modelsim, and analyzing the PSD curve and the constellation of output signals, the adaptive interference cancellation algorithm system based on frequency-domain block LMS have achieved expected effect. The frequency-domain block LMS adaptive echo interference cancellation system has better flatness on the in-band PSD curve and better convergence effect on the constellation. Therefore, frequency-domain block LMS adaptive interference cancellation algorithm is chosen as the design with high performance-price ratio. The more points there are, the more obvious advantages it will perform.

Ultrasound temperature estimation based on probability variation of backscatter data

In recent years, ultrasound imaging has become an attractive modality for noninvasive temperature monitoring. Temperature variations that occur during tissue heating could induce changes in various acoustic parameters that may affect the echo interference so as to make ultrasound backscattering a random process. In this study, we assumed that the degree of variation in the probability distribution of the backscattered signals is temperature dependent. The feasibility of using the variation in the backscatter statistics for ultrasound temperature estimation was investigated in this study. We tested this hypothesis by carrying out experiments on agar phantoms and tissue samples using a temperature-regulated water tank and a microwave ablation system. During heating, raw images of the backscattered-signal envelope of each phantom and tissue at temperatures ranging between 37 °C and 45 °C were acquired to construct the parametric matrix based on the ratio of the change in the Nakagami parameter (RCN), which was used as a quantitative measure of the backscatter statistics. The absolute value of the RCN (ARCN) matrix was obtained, to which a polynomial approximation was applied to obtain the ARCN(pa) image. The results showed that the RCN matrix locally increased or decreased with increasing temperature, indicating bidirectional changes in the backscatter statistics. We also found that the ARCN significantly increased with the temperature, demonstrating that the magnitude of the variation in the probability distribution of the backscattered-signal envelope is a monotonic function of temperature. Unlike the phantom, tissues tended to exhibit a nonlinear dependency of the ARCN on the temperature that may be attributable to tissue denaturation. Especially, the ARCN(pa) image is highly suitable for visualizing the contour of the temperature distribution during microwave ablation of tissue samples. This study has demonstrated that temperature changes are reflected in variations in the envelope statistics. This novel approach makes it possible to develop an ultrasound temperature imaging method for simultaneously estimating the thermal dose and the tissue properties.

Ultrasound guided spinal procedures

Ultrasound (US) is an increasingly used imaging technique in interventional pain therapy allowing identification of soft tissues, vessels and nerves, without exposing patients or personnel to radiation. Imaging is performed continuously and the spread of the injected fluid can be visualized in real time. Spinal procedures which may be performed with US imaging are lumbar or cervical facet joint blocks, sacroiliac joint injections, caudal epidural injections and extraforaminal cervical or lumbar nerve root blocks. Limitations are the poor resolution of narrow-gauge needles, the loss of resolution with increasing working depth and possible interference of echoes from overlying structures with the image of the target area.

VSB-Based Digital On-Channel Repeater with Interference Cancellation System

This paper investigates the design and performance of a digital on-channel repeater (DOCR) for use in Advanced Television Systems Committee (ATSC) digital television (DTV) broadcasting. The main drawback of a DOCR is the echo interference caused by coupling between transmitter and receiver antennas, which induces system instability and performance degradation. In order to overcome this problem, an echo canceller based on the adaptive echo channel estimation (ECE) technique has been researched and applied for a DOCR. However, in the case of ATSC, the pilot signal, which is used for carrier synchronization, may cause a DC offset error and reduce the isolation performance of the echo canceller for a DOCR in an ATSC network. Moreover, since the multipath fading effect of a radio channel usually occurs in a real environment, it should be minimized to improve the overall performance of a DOCR. Therefore, due to the limited isolation performance of echo canceller and the multipath fading effect, an interference cancellation system (ICS) is proposed for a DOCR in an ATSC network. The performance of the proposed DOCR with an ICS is evaluated by software simulation and hardware test results.

Anti-Radiation-Missile detection based on parameterized time-frequency analysis

Based on the characteristics of Anti-Radiation-Missile (ARM) echo wave, 3 parameters Chirplet Transform (CT) was proposed from the perspective of parameterized Time-Frequency (TF) analysis, which combining 3 kinds of affine TF transform to be a kind of TF atom. What's more, based on the time-shift feature of ARM and aircraft echo wave's 3 parameters CT, a new method of ARM detection which can be implemented fast by Fast Fourier Transform (FFT) algorithm was proposed, considering the difference of the 3 parameters CT's modulus between the received signal and its delay signal as the detectable quantity. Aircraft echo interference could be counteracted effectively, while ARM echo energy could be saved without much attenuation. Therefore, the detection system was simplified. Computer simulation results show that ARM can be detected fast and precisely by this way in the surrounding of high aircraft echo interference and low Signal to Noise Ratio (SNR), so that a reliable early warning of ARM launching can be achieved.