Estimating acoustic flow parameters for multiple echoes within a biologically motivated signal processing framework

Frequency-agile(FA) radars allow flexible changes in carrier frequency between adjacent pulses, offering significant advantages in anti-jamming performance. However, the discontinuity in echo phase renders the Fast Fourier Transform (FFT) unsuitable, resulting in a high computational burden for coherent integration.To address this challenge, this paper proposes a Frequency-Pulse Repetition Time(PRT) Coupled Agile (FPCA) waveform design scheme, wherein the velocity-induced phase within a coherent processing interval (CPI) is constrained to be an integer multiple of a constant, thereby facilitating subsequent coherent integration. We first derive the analytical relationship between carrier frequency and PRT in FPCA, and then propose two FPCA design approaches: one with a constrained lower PRT bound, and another with both upper and lower PRT bounds.Furthermore, a fast signal processing method tailored for the proposed waveform in multi-target scenarios is developed.After phase cancellation of the echoes, the Velocity Spectrum Profile (VSP) is obtained via FFT, and multiple VSPs are non-coherently accumulated to suppress cross-terms arising from phase compensation, enabling robust estimation of strong target velocities.Velocity compensation and IFFT are then applied to obtain range estimates for strong targets, followed by weak target imaging based on the CLEAN algorithm.Simulation results are provided to validate the effectiveness of the proposed scheme. Compared with existing coherent processing methods for frequency-agile radars, the proposed approach significantly reduces computational complexity, requiring only several to a dozen FFTs to obtain target parameter estimates, thus offering a practical frequency-agile solution for radar platforms with limited computational resources and stringent real-time requirements.

Acoustic technology is an accepted and important component of aquatic research and resource management. Despite the widespread use of echosounders, few guidelines aid in the choice of appropriate sonar system parameters for acoustic surveys. Choice of acoustic carrier frequency is analogous to the choice of spotlight colour used to illuminate a painting. Three primary biological factors influence the scattering of sound by aquatic organisms: swimbladder presence, organism length, and organism behaviour. We illustrate the influence of these factors on the amplitude of backscattered echoes using a Kirchhoff-ray mode scattering model to quantify fish and zooplankton backscatter as a function of carrier frequency, fish length, and swimbladder aspect. Model results illustrate that echo amplitudes from aquatic organisms are largely dependent on the presence or absence of a swimbladder. Target strengths generally increase with increasing carrier frequency and organism length. Swimbladder angle relative to the incident sound wave affects scattering amplitudes at all frequencies. Measurements of backscatter from swimbladdered fish are relatively robust when the ratio of fish length to acoustic frequency wavelength ranges between 2 and 10. As fish length to frequency wavelength ratios increase, echo amplitudes become more dependent on aspect and peak when the swimbladder is perpendicular to the acoustic wavefront.

The traditional probe–pass integration system embeds communication information into a radar waveform, which leads to a high level of waveform autocorrelation sidelobes and a poor false symbol rate at low signal-to-noise ratios. This article proposes a three-dimensional indexed modulation-based design method for probe–pass integration waveforms. This method realises communication information modulation and demodulation by simultaneously indexing orthogonal waveform selection, transmitting pulse PRI changes and carrier frequency changes in three dimensions, and applying compressed perception technology to solve the problems of PRI shortcuts and carrier frequency, resulting in a velocity term in the received waveform that cannot be accumulated by phase reference to realise velocity super-resolution. Finally, the radar detection performance and communication performance are simulated and analysed, and the simulation results reveal that the method proposed in this paper can not only satisfy the radar detection performance requirements but also achieve a lower unsigned rate on the basis of an improved communication rate.

<p indent=0mm>Compared with urban application scenarios, Global Navigation Satellite System (GNSS) navigation receivers that are mounted on high-speed aircraft must handle a higher carrier frequency dynamic and output the measured result at a higher frequency. Both these factors adversely affect the accuracy of the carrier frequency measurement. Herein, we propose an adaptive carrier-tracking algorithm to measure the radial velocity by introducing a fuzzy logic controller in the carrier-tracking loop. The proposed algorithm adaptively adjusts the loop bandwidth as the carrier frequency changes, improving the velocity measurement accuracy while ensuring dynamic adaptability. Herein, the measured result of the loop is used to calculate the input variables of the fuzzy controller, and the output of the fuzzy controller is used to adjust the loop bandwidth. The fuzzy controller adopts a single input and single output Takagi-Sugeno model, which is easy to implement. The analysis and simulation are performed under fixed-, linear-, and sine-shaped Doppler frequency scenarios. The radial velocity between the aircraft and the receiver is set in the range of <sc>±10 km/s,</sc> and the radial acceleration is set in the range of <sc>±30<italic>g</italic>.</sc> To ensure the validity of the measurement results, we output the measurement results at a frequency of 1000 points per second. Simulation results demonstrate that when the input carrier-to-noise ratio is <sc>40 dB Hz,</sc> the velocity accuracy of the proposed algorithm is better than <sc>0.3 m/s</sc> (1<italic>σ</italic>).

peer reviewed

Extracorporeal shock wave therapy (ESWT) achieves its therapeutic purpose mainly through the biological effects produced by the interaction of shock waves with tissues, and the accurate measurement and calculation of the mechanical parameters of shock waves in tissues are of great significance in formulating the therapeutic strategy and evaluating the therapeutic effect. This study utilizes the approach of implanting flexible polyvinylidene fluoride (PVDF) vibration sensors inside the tissue-mimicking phantom of various thicknesses to capture waveforms at different depths during the impact process in real time. Parameters including positive and negative pressure changes (P+, P-), pulse wave rise time ([Formula: see text]), and energy flux density (EFD) are calculated, and frequency spectrum analysis of the waveforms is conducted. The dynamic response, propagation process, and attenuation law of the shock wave in the phantom under different impact intensities were analyzed. Results showed that flexible PVDF sensors could precisely acquire the characteristics of pulse waveform propagating within the phantom. At the same depth, as the driving pressure increases, P+ and P- increase linearly, and [Formula: see text] remains constant. At the same driving pressure, P+, P-, and EFD decay exponentially with increasing propagation depth. At the same depth, the spectra of pulse waveforms are similar, and the increasing driving pressure does not cause significant changes in carrier frequency and modulation frequency. The research findings could provide a reference for developing ESWT devices, improving treatment strategies, and enhancing the safety of clinical applications.

A frequency-hopping communication receiver based on Rydberg atoms, whose carrier frequency changes in accordance with a predetermined sequence, is proposed for what we believe to be the first time and experimentally verified. Based on the coherent population trapping (CPT) effect of atoms, a five-level system is built under the assumption of a constant laser wavelength, where the carrier is the resonance band corresponding to different separated quantum states. Pseudo-random binary sequence (PRBS) and complex image signals undergo keying modulation to achieve frequency-domain hopping reception. In the experiment, a dynamic range of 62 dB is demonstrated. The digital transmission with a data rate of 1 Mbps is performed reliably, within a tunable bandwidth of 50 MHz, an instantaneous bandwidth of 700 kHz and a max hopping rate of 20000 hop/s. The proposed atom-based frequency-hopping receiver is suitable for secure communications, satellite uplinks, quantum cryptography, and high-precision scientific research.

This work aims to design and implement a secure frequency hopping spread spectrum system (FHSS) on an FPGA. Design is modelled using the Verilog HDL module. In this work, Xilinx ISE Design suite 14.4 software is used along with the ModelSim simulator and XST synthesizer. The core of the FHSS transmitter is a Direct Digital Synthesizer (DDS) which generate desired frequency signal. This is a very secure communication system because its carrier frequency changes at every fixed interval in a Pseudo-Random manner. In this work, the simulation and synthesis procedure of a frequency hopping binary frequency shift keying (FH/BFSK) spread spectrum system is designed and described.

The frequency and signal design of the American global positioning system (GPS) is currently in a modernization period. The baseline configuration of GPS only consists of two signals on two carrier frequencies (C/A and P(Y) code). At present the existing satellites (IIA, IIR) are replaced by new modernized satellites (IIR-M, IIF) which are capable of transmitting additional signals. The modernization of GPS includes the extension of the frequency plan by a third frequency band (L5). We will evaluate the theoretical potential performance of the baseline signals and the new modernized signals of GPS in terms of positioning accuracy. This includes a discussion of the main error sources and the signal characteristics (signal modulation, carrier frequency and receiver bandwidth). Based on the contributions of the individual error sources we will give estimations of the typical performance of GPS for single-frequency and double-frequency receivers.

A prominent feature predicted for the backscattering of tone bursts by thin spherical shells is an enhancement of a guided wave contribution in the midfrequency range [L. G. Zhang et al., J. Acoust. Soc. Am. 91, 1862–1874 (1992)]. This feature may be useful for certain inverse problems and is associated with a strongly coupled slightly subsonic wave denoted by some authors as the a0− wave. The present research gives a comparison between a ray approximation and experiments in which tone bursts having carrier frequencies in the range 35&amp;lt;ka&amp;lt;70 were incident on an empty stainless steel shell in water of radius a. The sphere’s radius to thickness ratio is a/h=43.8. Time records of echoes provided a means for measuring the guided wave contribution distinct from that of the specular reflection. As predicted, the guided wave echo can be over three times the amplitude of the specular echo and the ka dependence generally follows the predicted hump. Echoes manifest structures similar to those calculated by a time domain Fourier synthesis from the partial wave series.

In this work, a biomimetic sonarhead mounted on a mobile robot is used as a platform with which to test the type of acoustic flow in cf-bats considered by Muller [R. Muller and H.-U. Schnitzler, J. Acoust. Soc. Am. (submitted)]. Such acoustic flow, based on changes in Doppler shift and echo amplitude, provides crude localization information which suffices for tasks like obstacle avoidance in which high accuracy is not needed. Previous results with the biomimetic sonarhead [V. A. Walker, H. Peremans, and J. C. T. Hallam, J. Acoust. Soc. Am. 104, 569–579 (1998)] showed the availability of dynamic cues in the form of frequency and amplitude modulations obtained by pinnae motion. Kuc’s sensorimotor model for the fm bat [R. Kuc, J. Acoust. Soc. Am. 94, 1965–1978 (1994)] has been adapted to the cf bat and implemented in the robot. Appropriate experiments, composed of a prey capture task during which obstacle avoidance by means of acoustic flow is performed, have been designed to exclude trivial static cues such as the echo delay correspondent to the closest reflector. The results of this on-going work will be included in the final abstract if accepted.

In this thesis, we cope with the fundamental mathematical and physical problems of the space-time-Doppler UWB system design for fading channels: multi-input multi-output (MIMO) wireless communication with adaptive filtering. The estimation algorithm from equalizer providing an accurate parameters estimate is investigated. UWB radio is a fast emerging technology with uniquely attractively features inviting major advances in wireless communications, networking, radar, imaging, and positioning systems. By its rule-making proposal in 2002, the Federal Communications Commission (FCC) in the United States essentially unleashed huge new bandwidth (3.6-10.6 GHz) at the noise floor, where UWB radios overlaying coexistence RF systems cerate using low-power ultra-short information bearing pulses. Right now, there are three basic types of UWB: multiband OFDM UWB (MB-OFDM UWB), impulse-UWB (I-UWB), and direct sequence UWB (DS-UWB). We focus on I-UWB and MB-OFDM-UWB, and compare their performance. A simple means for spreading the spectrum of low duty cycle pulse trains is time hopping (TH), with pulse position modulation (PPM) for data modulation at the rate of many pulses per data bit. The main contribution of this thesis for I-UWB is the design of leading edge detectors, coherent correlation detector (CCD), and pilot performance enhancement compared with different Rayleigh and Ricean fading conditions. For MB-OFDM UWB, we have considered the performance analysis and design criteria of MIMO OFDM UWB systems for high data-rate wireless transmission. The signal processing of frame detection, time synchronization, frequency synchronization, channel estimation, synchronization tracking using pilot subcarriers and 2-D MIMO detection algorithms is discussed. The main contributions of this thesis are 1) Compared with receiver employing the Maximum Likelihood (ML) detector, the receiver employing a low-complexity linear Minimum Mean Square Error (MMSE) demodulator can perform a limited performance loss in spatially uncorrelated channels. 2) Due to the operations of spreading and dispreading combined with MMSE-based frequency domain equalization, the adverse effects of the low-SNR subcarriers on the average BER performance are potentially improved. This is a direct consequence of spreading, because even if the signal corresponding to a specific chip is obliterated by a deep frequency domain channel fade, after dispreading these effects are spread over the Walsh-Hadamard Transform (WHT) length. Hence there is a high chance of still recovering all the partially affected subcarrier symbols without errors. 3) As a test case, the OFDM-based 200 Mb/s MB-UWB network (IEEE 802.15.3a) are considered, but the simulation results are shown above section. 4) The simulation channel can be easily applied to NOS and NLOS situation with WHT transformation from Simulink model. The fading channels of UWB with low/high signal to noise ratio (SNR), multipath effects, and multiuser interference may introduce large errors in location. The location engine performs the following tasks: █ Data fusion techniques: Different data fusion techniques are implemented using Time Of Arrival (TOA), Angle Of Arrival (AOA), or a combination of both. █ Channel modeling: A multipath, multiuser channel environment is created that models path loss, shadowing, Rayleigh fading, and Doppler frequency effects. █ Parameter estimation: TOA and AOA estimation algorithms are implemented as part of the location finding engine. Different variations of algorithms are implemented for performance and comparison purposes. █ Configuring the physical layer for different wireless networks. Among the programmable parameters are spreading factor, packet size, training length, constellation type, modulation technique, carrier frequency, level of transmitted signal power, and the number of antennas at the transmitter for both sides. █ Configuring the mobile user conditions. The wireless channel models depend on the Doppler frequencies present in the environment. The Doppler frequency depends on the mobile speed and carrier frequencies as input and generates a Rayleigh fading channel with the U-shape Doppler spectrum. █ Configuring the environmental parameters and network geographical structure. One of the factors affecting the performance of the wireless location system is the environment type (e.g., bad urban, urban, suburban, or rural area). For example, in a bad urban area with many blocking objects and buildings, non-line of sight (NLOS) effects plays an important role in the estimation accuracy.

The narrow-band portions of the echolocation pulses seen in cf-bats are a hypothetical substrate for target localization. This localization could be based on estimates of echo envelope amplitude and carrier frequency together with their derivatives. Evaluation of these parameters is referred to as "acoustic flow" in loose analogy to optic flow. It is assessed whether the requirements for this task may be reconciled with known principles of auditory function. For the evaluation of a single echo, this seems to be the case: auditory filter shapes provide sufficient frequency resolution; at the same time envelopes are preserved well and some noise removal is achieved. Nevertheless, should bats not be endowed with additional capabilities for noise removal, analysis of acoustic flow would be limited to favorable signal-to-noise ratios. Multiple, temporally overlapping echoes are probable in any realistic echolocation scenario. In this case, additional auditory processing steps have to be postulated, which allow simultaneous estimation of multiple carrier frequencies and reduction of demodulation distortions.

With China's exploration of the sea, unmanned boats on the water are receiving more and more attention. Due to the complex situation on the water, unmanned boat obstacle avoidance still has defects. To address the above problems, this paper designs unmanned fish-finding and obstacle avoidance based on Pixhawk. The Kalman filter algorithm is used for sensor information fusion, which realizes the state estimation of the fish-finding unmanned ship. The BUG2 obstacle avoidance algorithm is used for obstacle avoidance, that optimizes the automatic obstacle avoidance function of the fish-finding unmanned ship. The fish finder is used to detect the position information of the fish, that realizes the function of the fish-finding unmanned ship tracking the fish. The PID control algorithm is used to control the driving of the ship, which makes the fish-finding unmanned ship converge to the desired course quickly and accurately. The lateral error of the vessel is within 1m. The simulation results verify the feasibility of the system, and the sea trial experiments of the unmanned fish-finding vessel prove the reliability and stability of the system.

Using frequency-modulated echolocation, bats can discriminate the range of objects with an accuracy of less than a millimeter. However, the echolocation mechanism is not well understood. The delay separation of three or more closely spaced objects can be determined through analysis of the echo spectrum. However, delay times cannot be properly correlated with objects using only the echo spectrum because the sequence of delay separations cannot be determined without information on temporal changes in the interference pattern of the echoes. To illustrate this, Gaussian chirplets with a carrier frequency compatible with bat emission sweep rates were used. The delay time for object 1, T1, can be estimated from the echo spectrum around the onset time. The delay time for object 2 is obtained by adding T1 to the delay separation between objects 1 and 2 (extracted from the first appearance of interference effects). Further objects can be located in sequence by this same procedure. This model can determine delay times for multiple closely spaced objects with an accuracy of about 1 microsecond, when all the objects are located within 30 microseconds of delay separation. This accuracy is possible even with objects having different reflected intensities and in a noisy environment.