Ambiguity Function Analysis Research Articles

Generalized Ambiguity Function Analysis and Geometry Parameter Optimization for Flexible Conformal Array-MIMO Radar

Generalized Ambiguity Function Analysis and Geometry Parameter Optimization for Flexible Conformal Array-MIMO Radar

Ambiguity Function Analysis and Optimization of Coherent FDA Radar

Ambiguity Function Analysis and Optimization of Coherent FDA Radar

Ambiguity Function Analysis and Side Peaks Suppression of Link16 Signal Based Passive Radar

Ambiguity Function Analysis and Side Peaks Suppression of Link16 Signal Based Passive Radar

Ambiguity function analysis of iridium burst transmissions for opportunistic navigation

AbstractThe objective of this work is to investigate the Ambiguity Function (AF) characterization of the Iridium L‐band downlink burst transmissions under single burst and multiband multi‐burst mode to demonstrate its suitability and capability as Signal of OPportunity (SoOP) for navigation. The Iridium bursts are collected and examined by demodulating without any prior knowledge for frame verification. The comprehensive analysis and theoretical model of the two mode AFs are presented and verified to evaluate the waveform properties with resolution and sidelobes in both the Doppler and delay domains. Degradation in AF resulting from signal model and multiband channel combination is characterized to exploit the trade‐offs for selection and utilization of the Iridium burst. It has been found that the single burst even with maximum length of 20.32 ms appears available but far from excellent for navigation, while the multiband mode produces significant improvements over the time delay and Doppler resolution as well as a certain degradation on the AF sidelobes. Issues relating to the Iridium bursts utilization have been identified.

SASA: Super-Resolution and Ambiguity-Free Sparse Array Geometry Optimization With Aperture Size Constraints for MIMO Radar

To improve the performance of multiple-input-multiple-output (MIMO) radar, various sparse arrays have been employed. However, the angular resolution of existing non-uniform arrays optimized by either combinatorial algorithms or heuristic ones is limited by the Rayleigh criterion, which is strictly related to the aperture size. Based on the angular ambiguity function (AAF) analysis, two new models are established in this work for directly optimizing the sidelobe level (SLL) or the main lobe width (MLW) with the constraints of aperture size and element spacing. The aforementioned designs result in non-convex and nonlinear optimization problems, and solutions are derived via the alternating direction multiplier method (ADMM). Furthermore, considering a parametric trade-off between SLL and MLW, a hybrid algorithm is proposed to search for the SLL-MLW Pareto front boundary. Finally, simulations are provided to demonstrate the high angular resolution and ambiguity-free properties of the optimized sparse arrays.

A Transmitter Design for the Multi-beam CC-OFDM Azimuth Scanning MIMO Radar

A conventional phased array radar provides a high gain by transmitting coherent signals over a large number of antenna elements. However, it does not provide a full time-on-target because it produces beams that scan the whole angular view of the radar. This paper describes an implementation of circulating codes (CC) in azimuth scanning MIMO radar that adopts OFDM waveform. The CC MIMO technique can produce a beam toward a certain angle by applying an appropriate delay difference between the MIMO antennas that transmit the same waveform across the azimuth. The adoption of OFDM waveform in the CC MIMO radar, gives the possibility to apply the phase difference for beamforming in the frequency domain of the OFDM signals. CC-OFDM MIMO with spectrum division into sub-bands and use of orthogonal codes, allow for simultaneous transmission of orthogonal OFDM symbols that generate orthogonal beams toward different angles. This strategy makes it possible for the radar system to have multiple and simultaneous beamforming to provide a full-time coverage. Furthermore, the transmission of a series of orthogonal OFDM symbols in each beam enables the detection of long-range targets. By taking as an example the design of long-range surveillance radar, the paper discusses further issues pertinent to the implementation of the CC OFDM MIMO radar, including the beam squinting problem and its remedy, arrangement of the multiple beams, the radar system structure, use of Golay codes for orthogonalization and PAPR mitigation, use of software-defined radar that eliminates the need of amplitude and phase control in each transmitter, transmit scheduling for multi-beam long-range target detection, and multidimensional ambiguity function analysis. The latter indicates that the CC OFDM MIMO radar can achieve a high resolution in angle, range, and velocity, with beam isolation of -30 dB for neighboring beams and co-channel beams.

Ambiguity Function Analysis for Orthogonal-LFM Waveform Based Multistatic Radar

Over the last decade, research on multistatic radar waveform design has attracted significant consideration among the radar system designers.Among the waveform design techniques, linear frequency modulated waveforms are widely used, but the problem associated with it is range Doppler coupling and complexity in achieving adequate pulse-to-pulse diversity. In this letter, an orthogonal linear frequency modulated (OLFM) waveform has been used as the transmitted waveforms, which has good correlation properties and large time bandwidth product. The ambiguity function (AF), which is the output of the matched filter, is used to analyze the target resolution capabilities of the OLFM waveforms. The mathematical expressions of the AF with OLFM waveforms for the multistatic architecture are represented based on the target fluctuations observed at the receiver. These expressions allow the ambiguity in resolving target position and velocity vectors for any transmitted waveform in the multistatic topology. The normalized cross-correlation value of the LFM waveforms is compared with the OLFM waveforms, which signify the isolation factor between two transmitted waveforms at the receiver. A performance comparison has been made based on the probability of target detection for various multistatic scenarios under numerous signal-to-noise ratio (SNR) conditions.

Determination of the Appropriate Kernel Structure in Electroencephalography Analysis of Alcoholic Subjects

Alcoholism is one of the major health problems in the world. The organ most affected by alcohol is the brain. It has been shown that alcohol causes neuronal loss in the brain and reduces brain blood flow and oxygen use. Electroencephalography is a method that measures the instantaneous electrical activity of the brain. It is known that valuable information can be obtained by observing the biological effects of alcohol through EEG. As their methods of signal processing and analysis have evolved, Electroencephalography signals have attracted the attention of researchers in this field. In this study, methods of the time-frequency analysis were applied to Electroencephalography signals obtained from normal and alcoholic subjects. For this purpose, the Cohen’s class distribution was examined. Ambiguity function analysis, which was in the structure of the distribution, was applied to the signals. Then, from the kernel structure inside the distribution, the Wigner-Ville distribution, which was very common, was reached and this distribution was examined. The inadequacy of the distribution resolution was seen and analysis of the new time-frequency distributions, which were obtained by making convolution with 4 types of kernel functions (nonseparable, separable, Doppler independent, lag independent), was performed. As a result, it was shown that the resolution of time-frequency distributions could be improved with proper kernel functions. Thus, at the end of these analyses, changes that alcohol caused in brain functions were revealed.

Ambiguity Function Analysis of Random Frequency and PRI Agile Signals

Random frequency and pulse repetition interval (PRI) agile (RFPA) signals bring excellent performance of electronic counter-countermeasures to radar systems and have been received considerable attention in recent years. However, the research on their ambiguity function (AF) is not comprehensive. In this article, the analytical expressions of the AF expectation and variance are given. According to the expressions, the direct relationships between the key metrics of the AF and the waveform parameters of RFPA signals are specified. The results in this article are verified by Monte Carlo simulations and provide some insights into RFPA waveform design.

SVD-Based Ambiguity Function Analysis for Nonlinear Trajectory SAR

A nonlinear trajectory of a radar platform in synthetic aperture radar (SAR) may lead to severe coupling between the range and the azimuth, which may make the ambiguity function (AF) analysis complicated. The numerical algorithm-based AF analysis may be computationally expensive, while the existing analytical algorithm-based AF analysis may cause large errors because it does not consider the coupling between the range and the azimuth. By observing that the singular value decomposition (SVD) is good to deal with the coupling problem, in this article, we propose an effective AF analysis based on SVD. The key idea is to first use a small amount of sampling points for SVD of the coupled term in the AF and then the decoupled vectors are fitted to high-order polynomials for the analytical AF calculation. It converts the double integral into the product of two single integrals in the calculation. From the proposed SVD-based AF analysis, three parameters, namely, 3-dB resolution, peak sidelobe ratio (PSLR), and integrated sidelobe ratio (ISLR), are then effectively computed. The simulated results verify the good performance of the proposed SVD-based AF analysis.

Analysis and Optimization of Ambiguity Function in Radar-Communication Integrated Systems Using MPSK-DSSS

With increasingly sophisticated electromagnetic environment of combat platforms, radar communication integration has attracted wide interests. In this letter, instead of designing a new integrated signal, we employ multiple-phase shift keying direct sequence spread spectrum (MPSK-DSSS) signal as radar communication integrated signal due to its advantage of outstanding correlation. On the one hand, the closed form expression of average ambiguity function is obtained, by which we can analyze the relationship between parameters of integrated signal and radar range resolution. On the other hand, to improve radar peak sidelobe level (PSL) influenced by random communication signals, we propose a joint optimization method based on sequence mapping at the transmitter and sidelobe suppression at the radar receiver. Simulation results show that the sidelobe levels of the optimized integrated signal is effectively suppressed at the cost of slight communication rate loss.

Ambiguity function analysis of human echolocator waveform by using gammatone filter processing

Human echolocation is a technique used by small group of people (normally blind persons) to observe their surrounding via emitting an active signal (usually tongue click) and analyse the return echo. This skill allows them to navigate safely by ‘seeing through sound’. Remarkable performances upon echolocating have attracted scholars’ attention from multidiscipline field including psychophysical and engineering. Study of waveform diversity has reported the signal is wideband, consisting of multiple frequency components with exponential decay factor that probably made up the entire unique signal. As such, wideband perspective is considered during ambiguity function analysis using wide-band ambiguity function method. The waveform analysis continues and reported optimum autocorrelation function is achieved by adopting a bio-inspired technique, which incorporated gammatone-filter processing. It will be interesting to synthesise the waveform using gammatone-filter approaches prior to relay it into ambiguity function process for analysis. Therefore, it is worth to explore its output results in this paper, which hold new findings that may help to understand how these humans achieve an optimum performance upon echolocating including ambiguity function characteristic. Thus, the new knowledge explored in this paper could be beneficial in emerging concept for new development in radar and sonar system application in near future.

Weight Matrix-Based Least Mean Square Algorithm for Target Detection in Passive Radars

Ambiguity function analysis is the most expensive process for target detection in passive radars. The computational cost is attributed to the extensive range-Doppler field required to evaluate the cross-correlation function. Some tools like fast Fourier transform or batching algorithm are employed to partially reduce the computational effort. In this paper a different generalization of least mean square algorithm is utilized for target detection. The basic idea is to employ the properties of the computed weight matrix to extract target coordinates. The algorithm performance is investigated by computer simulation using some practical simulated FM stereo signal. The results reveal the lower computational complexity of the presented procedure compared to existing methods..

Generalised ambiguity function analysis of distributed MIMO synthetic aperture radar

The abundant space, time, frequency and code resources of distributed multiple-input multiple-output (MIMO) synthetic aperture radar (SAR) enables it to bring various applications. The generalised ambiguity function (GAF) of distributed MIMO SAR is analysed. By equating the bistatic SAR to equivalent phase centre (EPC), the GAF can be expressed as sum of that of mostatic SAR. The influence of EPC's position on GAF is analysed, including its effects on amplitude items in range direction, in azimuth direction and phase item, and the boundary conditions of formation scale within which the envelope items are not affected are deduced. Furthermore, the phase in GAF is expressed as linear combinations of EPC position related to formation centre. The simulation results verify the negligibility of formation scale and show that the linear combination expression is accurate enough to evaluate the resolution.

Passive Radar Imaging by Filling Gaps Between ISDB Digital TV Channels

Integrated Services Digital Broadcasting-Terrestrial/Satellite (ISDB-T/S) signal, used in Japan as the digital television (TV) broadcasting standard, is exploited in this paper for passive bistatic radar two-dimensional imaging of stationary targets. A multifunctional system is developed with commercial-off-the-shelf antennas, low-noise block downconverters, and amplifiers. Several practical issues of using ISDB-T/S signals for imaging are highlighted. Ambiguity function analysis, accurate time delay estimation, inverse filtering, and local frequency correction are carried out. Multiple TV channels are combined to improve the range resolution. In order to reduce the artifacts caused by the frequency gaps among multiple TV channels, two low-rank matrix-completion-based algorithms are proposed. Experiment results with different targets validate the performance of the designed system and the proposed algorithms.

Ambiguity Function and Cram $\acute{\text{e}}$ r–Rao Lower Bound Calculation for CommSense System

In our previous work, we have shown that the channel equalization blocks of telecommunication systems can be used to sense the environment, a scheme which we call communication-based sensing (CommSense). The current work presents the ambiguity function analysis for different waveform in passive forward-looking radar geometry for CommSense system. Cram $\acute{{\bf e}}$ r–Rao lower bound (CRLB) for a two path receive signal model is also calculated for the time delay in the scattered path when there is direct path interference.

Ambiguity Function Analysis for OFDM-Based LDACS Passive Multistatic Radar

The ambiguity function analysis is central to investigating the resolution capabilities of a radar system. It is particularly important for passive radar scenarios, where the signals of opportunity have not been originally designed for radar purposes. This paper focuses on studying the achievable resolution capabilities for a noncoherent orthogonal frequency division-multiplexing (OFDM)-based passive multistatic radar for L-band digital aeronautical communication system (LDACS) signals. For this purpose, the ambiguity function obtained when employing the OFDM-based LDACS communications signals as signals of opportunity is studied. A generic bistatic link is considered and closed-form expressions for the expectation of the corresponding ambiguity function when accounting for the different signal contributions are derived. The resulting expressions are then used to evaluate and analyze the overall multistatic radar ambiguity function for two sample radar scenarios. The results highlight the impact of the geometry on the shape of the ambiguity function, allowing therefore for a better understanding of the effect that the geometry has on the range and velocity resolution capabilities of the studied system.

Novel Adaptive Filter Design for Filter Bank Multicarrier System Under Doubly Dispersive Channel Conditions

ABSTRACTFilter bank multicarrier (FBMC) has emerged as the favourite multicarrier communication technique since it meets the demands of the next-generation standards, especially for communication under doubly dispersive channels. In order to combat the undesirable channel effects like inter symbol interference and inter carrier interference, the prototype filters used in FBMC systems must satisfy orthogonality conditions and be well localized simultaneously in both time and frequency domains. Even though conventional doubly localized filters are optimum in the absence of channel, they fail to satisfy orthogonality and localization criteria under doubly dispersive channels. In the present study, an adaptive filter design method is proposed in which the prototype filter is designed as the weighted sum of a time-limited Nyquist filter, a band-limited Nyquist filter, and doubly localized Gaussian filter based on the analysis of discrete ambiguity function (DAF). The filter is designed to vary its characteristics according to the maximum time and frequency domain dispersions of the channel, so that signal-to-interference ratio is maximized. In order to ensure distortion-less transmission, the perfect reconstruction criterion for distortion-less transmission is mapped to specific conditions for DAF according to two-dimensional channel scattering function. The superiority in performance of the proposed adaptive filter is analysed in terms of signal-to-interference ratio and bit error rate, and is compared with the conventional filters for various channel scattering conditions.

Study of the influence of time-varying plasma sheath on radar echo signal

The time-varying plasma sheath surrounding a reentry spacecraft (or object) can influence the radar detection of the spacecraft seriously, causing detection error or even track loss. To study the influence of plasma sheath on radar detection, a time-varying plasma sheath model based on scattering matrix method is constructed. In the model, the surface media of reentry object is considered, together with some algorithm adjustments to avoid computational singularity, and the time-varying characteristics of plasma sheath are taken into account based on available measured data. By the model, the reflection coefficient of plasma sheath and the radar echo reflected by plasma-covered object are both calculated. And then a processing method of time-varying echo signal based on ambiguity function are put forward, by which the time delay and Doppler frequency of echo signal are analyzed. In the simulation, the rules of a series of time-varying parameters of plasma affecting the reflection coefficient are analyzed. Then, by ambiguity function analysis, the influence rules of plasma sheath on radar echo are revealed, accompanied by some qualitative and quantitative results. The proposed model, method, and simulation results are thought to be helpful for the radar detection of plasma-covered reentry objects.

Performance Analysis of Phased Array and Frequency Diverse Array Radar Ambiguity Functions

Performance Analysis of Phased Array and Frequency Diverse Array Radar Ambiguity Functions