Receive Beam Patterns Research Articles

Synergistic optimization strategy for beamforming and power allocation in dual-functional radar-communication systems

The dual-functional radar-communication (DFRC) integrated system presents an ideal solution to address the challenge of spectrum resource congestion in future networks. This paper explores an adaptive power allocation technique based on beamforming to enhance the word error probability (WEP) performance of the DFRC system. Initially, a joint optimization model is developed to minimize the WEP while adhering to constraints on radar signal-to-interference-noise ratio (SINR), peak-to-average-power ratio, sidelobe level, and total transmit power. This model incorporates dual-function transmit beam, radar, and communication receive beam patterns. Subsequently, the proposed subproblem convex relaxation alternating update (SCRAU) algorithm is introduced to achieve a locally optimal solution for multi-carrier power allocation. This algorithm decomposes the original non-convex optimization problem into three sub-problems with lower complexity and iteratively optimizes them. Simulation experiments validate that the SCRAU algorithm can simultaneously fulfill radar and communication functions. The SCRAU algorithm demonstrates superior WEP performance compared to current advanced algorithms.

Time-Invariant and Localized Secure Reception With Sequential Multicarrier Receive-FDA

Secure communication in the physical layer (PHY) using frequency diverse array (FDA) antennas has become a prominent research topic in recent years due to the unique range-angle dependent beam pattern exhibited by FDAs. However, the time-varying and periodic nature of the FDA beam pattern prevents the achievement of a time-invariant range-angle focused beam pattern. Consequently, a range-angle focused beam is only achieved at a specific time instant. Therefore, it is not yet possible to focus a beam to a specific point or area in space permanently in a time-invariant manner, due to both natural propagation mechanisms and the independent time parameter. Once a wave is transmitted, time variation cannot be altered. Thus, for the FDA beam pattern, it continues to propagate over time indefinitely. However, in the case of receiving, the time parameter is under the control of the receiver. The receiver can set the time at which the incoming wave is sampled or acquired. In this study, a cross-linear array structure called the Sequential Multi-Carrier Receiver FDA (SMCR-FDA) and a relevant methodology are proposed to obtain a three-dimensionally localized time-invariant range-angle focused receive beam pattern. Additionally, several novel concepts, including the cross-linear array structure, the secure reception concept, and the Positional Modulation Technique are introduced.

Scalable Phase-Coherent Beam-Training for Dense Millimeter-Wave Networks

Millimeter wave (mm-wave) communications use analog beamforming techniques, which steer the signal energy in a desired direction, to overcome the high path-loss at such frequencies. To determine the direction in which to steer, mm-wave standards such as IEEE 802.11ad specify beam training mechanisms for both access points as well as client stations. However, the overhead of the beam training limits scalability as the density of network deployments increases and mobile devices that require constant re-training are supported. We design SPIDER, a low-overhead beam-training mechanism where only access points actively participate in the training and stations perform passive compressive estimation of the angle-of-arrival. To this end, stations carry out phase-coherent measurements by switching through multiple receive beam patterns on a time-scale of tens of nanoseconds when receiving a packet preamble. Since no suitable testbed platforms exist that support such fast antenna reconfiguration, we design a high-performance, full-bandwidth FPGA-based testbed platform for flexible mm-wave experimentation, that we make available as open source. The performance analysis with this testbed shows that our algorithm achieves highly accurate angle estimation used to drive the beam steering decisions and reduces overhead by an order of magnitude compared to IEEE 802.11ad beam training.

Heptuna: The most outstanding subject

One of the best experimental collaborators I have ever worked with was HEP, a bottlenose dolphin (Tursiops truncatus). HEP was instrumental in leading the way for subsequent dolphin investigations. In the first study on dolphin sound localization, HEP was the willing subject [D. L. Renaud and A. N. Popper, “Sound localization by the bottlenose porpoise Tursiops truncatus,” J. Exp. Biol. 63, 569–585(1975)]. Thus began a series of critical experiments that set the foundations of cetacean hearing and echolocation. I had the pleasure to partner with Whit Au and HEP to explore the many aspects of dolphin hearing and echolocation. HEP carried the experience of his training and testing to new experiments. If he saw just one response manipulandum, he seemed to know it was a go/no go response requirement, or if two, a forced choice response. HEP was the first animal to use “jaw phones” to test hearing, and interaural time and intensity differences. He demonstrated he could control his echolocation clicks, he provided measures of his transmitting and receiving beam patterns, and much more. Unfortunately, we lost HEP in 2010 after a 40-year history with the U.S. Navy Marine Mammal Program.

A Novel Real-Time Echo Separation Processing Architecture for Space–Time Waveform-Encoding SAR Based on Elevation Digital Beamforming

Space–time waveform-encoding (STWE) SAR can receive echoes from multiple sub-swaths simultaneously with a single receive window. The echoes overlap each other in the time domain. To separate the echoes from different directions, traditional schemes adapt single-null steering techniques for digital receive beam patterns. However, the problems of spaceborne DBF-SAR, in practice, such as null extension loss, terrain undulation, elevation angle of arrival extension, and spaceborne antenna beam control, make the conventional scheme unable to effectively separate the echoes from different sub-swaths, which overlap each other in the time domain.A novel multi-null constrained echo separation scheme is proposed to overcome the shortcomings of the conventional scheme. The proposed algorithm can flexibly adjust the width of the notch to track the time-varying pulse extension angle with less resource consumption. Moreover, the hardware implementation details of the corresponding real-time processing architecture are discussed. The two-dimensional simulation results indicate that the proposed scheme can effectively improve the performance of echo separation. The effectiveness of the proposed method is verified by raw data processing instance of an X-band 16-channel DBF-SAR airborne system.

Suppression of Range Ambiguity in Spaceborne SAR With Elevation Beam Pattern Mask Design

In this letter, we present a method to design an elevation beam pattern mask for spaceborne synthetic aperture radar (SAR) to reduce the range ambiguity. The proposed two-way elevation beam pattern mask, which requires relatively low sidelobe levels only in the direction of strong range ambiguous echoes, can be highly suitable for enhancing the range ambiguity to signal ratio (RASR). The power levels of the different ambiguous echoes are estimated based on the backscattering coefficient model and satellite geometry. To meet the two-way beam pattern mask, both transmit and receive beam patterns are synthesized simultaneously through the minimax algorithm. To confirm the effectiveness of this mask design method, the RASR performance is evaluated by using various swaths.

Seabed sediment classification using multibeam backscatter data based on the selecting optimal random forest model

Seabed sediment classification using acoustic remote sensing technique is an attractive approach due to its high coverage capabilities and limited costs compared to taking samples of the seafloor. This paper focuses on backscatter intensity correction, sonar image quality improvement, and classifier construction, which aims to improve the accuracy of seabed sediment classification. The details are as follows. 1) A series of multibeam echosounder backscatter intensity correction model is constructed, including time-varying gains (TVG), transmission loss, actual area of insonification, source level, transmitting and receiving beam patterns, specular area correction, etc., to obtain accurate intensity values that accurately reflect seabed sediment types. 2) The pulse coupled neural network (PCNN) image enhancement model is established to improve the quality of sonar images, and 40 dimensional features are included to enrich the intensity description. 3) Selecting optimal random forest (SORF) seabed sediment automatic classification models that can select the input feature vectors and optimize the model parameters automatically are established. 4) Taking multibeam backscatter intensity data collected in Jiaozhou Bay as an example, the effectiveness and advantages of SORF are verified by comparing with support vector machine (SVM) and random forest (RF) classifiers.

Directional hearing sensitivity for 2-30 kHz sounds in the bottlenose dolphin (Tursiops truncatus).

Bottlenose dolphins (Tursiops truncatus) depend on sounds at frequencies lower than 30 kHz for social communication, but little information on the directional dependence of hearing thresholds for these frequencies exists. This study measured underwater behavioral hearing thresholds for 2, 10, 20, and 30 kHz sounds projected from eight different positions around dolphins in both the horizontal and vertical planes. The results showed that the sound source direction relative to the dolphin affected hearing threshold, and that directional characteristics of the receiving beam pattern were frequency dependent. Hearing thresholds obtained from two adult dolphins demonstrated a positive relationship between directivity of hearing and stimulus frequency, with asymmetric receiving beam patterns in both the horizontal and vertical planes. Projecting sound from directly behind the dolphin resulted in frequency-dependent increases in hearing threshold up to 18.5 dB compared to when sound was projected in front. When the projector was situated above the dolphin thresholds were approximately 8 dB higher as compared to below. This study demonstrates that directional hearing exists for lower frequencies than previously expected.

Time-Invariant Joint Transmit and Receive Beampattern Optimization for Polarization-Subarray Based Frequency Diverse Array Radar

We propose a polarization-subarray based frequency diverse array (FDA) radar with the subarray-based FDA as the transmit (Tx) array and the polarization-sensitive subarray-based FDA (PSFDA) as the receive (Rx) array. The subarray-based FDA has the capability to achieve a single maximum beampattern at the target location, while the PSFDA can provide an extra degree of freedom to further suppress the interference and, thus, to improve the radar's signal-to-interference-plus-noise ratio (SINR). The time-dependent frequency offsets are designed for the proposed radar to realize the time-invariant beampattern at the desired target location over the whole pulse duration. To further improve the target detection performance, the time-invariant joint Tx–Rx beampattern design is considered based on the output SINR maximization. To effectively solve the nonconvex output SINR maximization problem, a suboptimal alternating optimization algorithm is proposed to iteratively optimize the FDA Tx beamforming, the PSFDA spatial pointings, and the PSFDA Rx beamforming. Numerical experiments illustrate that the time-invariant and single-maximum joint Tx–Rx beampattern at the target location is achieved. Moreover, compared to the basic FDA and logarithmic frequency offset FDA as well as conventional phased array radars, the proposed polarization-subarray based FDA radar achieves a significant SINR improvement, particularly when the desired target and the interferences are spatially indistinguishable.

Methods for Grating Lobe Suppression in Ultrasound Plane Wave Imaging

Plane wave imaging has been proven to provide transmit beams with a narrow and uniform beam width throughout the imaging depth. The transmit beam pattern, however, exhibits strong grating lobes that have to be suppressed by a tightly focused receive beam pattern. In this paper, we present the conditions of grating lobe occurrence by analyzing the synthetic transmit beam pattern. Based on the analysis, the threshold of the angle interval is presented to completely eliminate grating lobe problems when using uniformly distributed plane wave angles. However, this threshold requires a very small angle interval (or, equivalently, too many angles). We propose the use of non-uniform plane wave angles to disperse the grating lobes in the spatial domain. In this paper, we present an approach using two uniform angle sets with different intervals to generate a non-uniform angle set. The proposed methods were verified by continuous-wave transmit beam patterns and broad-band 2D point spread functions obtained by computer simulations.

Radar wideband digital beamforming based on time delay and phase compensation

ABSTRACTIn conventional phased array radars, analogue time delay devices and phase shifters have been used for wideband beamforming. These methods suffer from insertion losses, gain mismatches and delay variations, and they occupy a large chip area. To solve these problems, a compact architecture of digital array antennas based on subarrays was considered. In this study, the receiving beam patterns of wideband linear frequency modulation (LFM) signals were constructed by applying analogue stretch processing via mixing with delayed reference signals at the subarray level. Subsequently, narrowband digital time delaying and phase compensation of the tone signals were implemented with reduced arithmetic complexity. Due to the differences in amplitudes, phases and time delays between channels, severe performance degradation of the beam patterns occurred without corrections. To achieve good beamforming performance, array calibration was performed in each channel to adjust the amplitude, frequency and phase of the tone signal. Using a field-programmable gate array, wideband LFM signals and finite impulse response filters with continuously adjustable time delays were implemented in a polyphase structure. Simulations and experiments verified the feasibility and effectiveness of the proposed digital beamformer.

Nested Array Sensor With Grating Lobe Suppression and Arbitrary Transmit–Receive Beampattern Synthesis

Sparse arrays have potential advantages over their regularly spaced counterparts, but they will generate undesired grating lobes. This paper investigates a sparse linear phased-array for grating lobe suppression and arbitrary transmit–receive beampattern synthesis. To achieve these aims, a modified two-level nested-array is developed, which provides increased degrees-of-freedom than a standard uniform linear array with the same number of elements via the difference co-array processing algorithm in the receiver. A least squares and iterative algorithm is also devised for linear array arbitrary transmit–receive beampattern design with minimum number of antenna elements. Moreover, the nested-array design is exploited for minimum variance distortionless response adaptive beamforming and direction finding. The effectiveness of the proposed approach is verified through extensive numerical results.

Classroom demonstration of synthetic aperture and array concepts

Although often time consuming to develop and present, classroom demonstrations are an effective tool used in physics education. This talk walks through a demonstration of the basic concepts of array processing and synthetic aperture sonar. An emphasis has been placed on limiting equipment and setup time required to implement this demonstration, while allowing the presenter break the discussion into several conceptual topic areas. Primary topics include pulse compression and temporal/range resolution, array aperture footprint and azimuthal/range resolution, influence of transmitter and receiver beampatterns, and the importance of temporal coherence and measurement platform motion. Hardware require for this demonstration can be made as simple as a speaker and a single electret microphone used with a common PC soundcard.

Single-RF MIMO-OFDM system with beam switching antenna

In this paper, we investigate the replica interference problem of a multiple input multiple output (MIMO) receiver with a beam switching antenna (BSA) within the orthogonal frequency division multiplexing (OFDM) framework. Our frequency-domain analysis has revealed the following important findings: (i) without co-existing system, replica interference in the system can be completely avoided as long as the beam pattern switching rate of the BSA receiver is an integer multiple of the product of the OFDM sampling rate and the number of receiving beam patterns and (ii) with co-existing systems, replica interference cannot always be avoided because co-existing systems may induce replicas in the operating frequency bands of the system. We present a replica interference criterion that depends on the co-existing status and users’ beam switching capabilities. Based on our findings, we propose various replica interference avoidance (RINA) strategies for different co-existing and cooperating network scenarios. In addition, the overall network operation principles of the proposed RINA strategy are presented. Simulation results verify that the proposed MIMO-OFDM system with a BSA successfully provides both MIMO and OFDM benefits, thereby resolving replica interference issues.

A theoretical model of linearly filtered reverberation for pulsed active sonar in shallow water.

This paper presents a statistical model useful for characterizing pulsed active sonar reverberation in shallow water. The model is based on the fundamental assumption that reverberation consists of echoes from point scatterers having random positions, strengths, and Doppler dilations. Receive array beam patterns, simple propagation losses, and planar bistatic geometry are included. The probability distribution of uniformly dense scatterers as a function of echo delay and bearing is explicitly related to the change in the area from which scatterer echoes contribute to the reverberation, and is presented in closed form. The cross Q-function of the transmitted waveform and the linear filter applied to the received signal arises naturally from the development. This function, along with environmental spreading, determines the shape of the reverberation along the Doppler axis. The assumptions and simplifications under which the reverberation decouples into independent spatial (delay and bearing) and Doppler terms are presented.

Encoding phase information is critical for high resolution spatial imaging in biosonar

The auditory system is responsible for translating acoustic information into a robust neural representation. In echolocating mammals, precise timing of neural onset-responses is critical to reconstruct complex acoustic scenes. Phase is often ignored in transmit and receive beam patterns, but it holds significance when considering broadband signals. A beam pattern's phase alternates outside of the main lobe, which leads to a frequency-dependent structure that is useful for spatial localization. For imaging in azimuth, binaural spectral patterns and time delay between the ears encode angular position. Imaging in elevation relies principally on specific spectral patterns encoded by each ear. The additional phase information decorrelates broadband echoes arriving from off-axis. This decorrelation only occurs on the order of a single wave period; however, the pattern of dispersion across frequency is sufficient to defocus echoes arriving from off-axis in the peripheral region, while accepting echoes arriving from the focal area of attention. We propose that acoustic spectral pattern matching by echolocating animals includes both magnitude and phase components of beams in the form of timing the onset response. Computational modeling results are presented showing how encoding phase information leads to high-resolution images despite dynamic environments and variability in the target strength of objects.

Effects of transmitting correlated waveforms for co‐located multi‐input multi‐output radar with target detection and localisation

Space time coding plays quite an important role in the design of multi-input multi-output (MIMO) radar. It has been shown that the correlation characteristics of waveform set have a great impact on the performance of target detection and localisation for MIMO radar. In this study, the target detection and localisation performance of co-located MIMO radar is analysed theoretically and experimentally, when correlated (not ideally orthogonal or fully coherent) waveforms are transmitted. The relationship between transmit–receive beam pattern improvement and correlation coefficients of transmitted waveforms is investigated. The signal to interference and noise ratio varying with correlation coefficients in range-Doppler matched processing is defined and analysed. Furthermore, Cramer–Rao bound for target direction of arrival estimation and target detection probability in the Neyman–Pearson criteria are derived when transmitting correlated waveforms. It is shown that the MIMO radar detection and localisation performance is much dependent with the correlation level of transmitted waveforms, which can be quite useful for MIMO radar orthogonal waveform design. Numerical simulation validates the theoretical analysis.

Effects on beam pattern performance for colocated multi‐input multi‐output radar transmitting correlated waveforms

The authors investigate the role of correlated waveforms in transmit–receive beam pattern performance of colocated multi-input multi-output (MIMO) radar, which presents many advantages by waveform diversity. The mutual orthogonality among the transmitted waveforms is often assumed but cannot be achieved in practice due to the limitation of signal duration and hardware precision. The authors introduce a common model considering the waveform correlation and propose a matched processing structure for the next estimation of parameters. The sufficient statistic for direction estimation is derived, and the transmit–receive beam pattern related to the waveform correlation matrix is obtained. This work mainly studies the effects of transmitting correlated waveforms with all kinds of correlation forms on beam pattern level. By employing these theoretical results, four numerical examples are performed further to obtain both qualitative and quantificational analyses of MIMO radar transmit–receive beam pattern performance with respect to the changing of the cross-correlation levels of the transmitted waveforms, which can provide a good guidance for orthogonal waveform design when considering MIMO radar beam patterns.

In situ calibration of seafloor acoustic backscatter data from swath mapping sonars

Geometric and radiometric corrections are necessary to convert raw seafloor acoustic backscatter data to imagery in which the intensity variations are due to the geoacoustical properties of the bottom and the angular dependence of the backscattering process. Radiometric corrections include removal of the combined effects of the sonar's transmit and receive beam patterns, and removal of the area ensonified. To this end, a method is presented to estimate the transmit/receive beam pattern of a multibeam swath mapping sonar using seafloor acoustic backscatter data collected over an entire survey area. This involves estimating the scattering area at each sounding based on local seafloor slopes. For a given sonar installation, results show that such beam pattern estimates remain stable to within ± 0.5 dB over different survey areas.

Optimal Sensor Placement for a Constellation of Multistatic Narrowband Pixelated Sensors

This paper presents a novel approach to selecting the location of a constellation of multistatic RF sensors to optimize system detection and tracking. The method works by computing the posterior Cramer-Rao lower bound on localization error as a function of sensor positions, and then selecting sensor locations to minimize the bound. One important contribution of this study is the derivation of the bound for a non-Gaussian, nonlinear pixelated sensor model which includes transmit and receive beam patterns, direct path energy, and target impulse response. A second contribution is a report on the results of two field collections which illustrate the efficacy of the method.