Sharif Digital Repository

One non-cooperative illuminator recently considered for passive radar applications is the DVB-T (Digital Video Broadcasting-Terrestrial) signal. The thumbtack ambiguity function of the DVB-T signal, in addition to being stationary over time, makes such a signal a good candidate for such applications. However, certain ambiguities in its ambiguity function necessitates certain issues to be carefully considered when the DVB-T signal is to be utilized in these scenarios. Methods have been already proposed to resolve them. In this paper, after studying the origins of these ambiguities, we propose special processing schemes to reduce the complexity of the parts associated with resolving these... 

Accurate modeling of sea clutter and detection of low observable targets within sea clutter are the major goals of radar signal processing applications. Recently, fractal geometry has been applied to the analysis of high range resolution radar sea clutters. The box-counting method is widely used to estimate fractal dimension but it has some drawbacks. We explain the drawbacks and propose a new fractal dimension based detector to increase detection performance in comparison with traditional detectors. Both statistically generated and real data samples are used to compare detector performance  

Pulse compression is an active research topic in radar systems. A problem in pulse compression is masking of small targets by the range sidelobes of large nearby targets. A new filter structure is introduced here to suppress the sidelobes of radar signals that result from standard matched filtering. The proposed filter is applicable for any type of binary coding signals. Several techniques are used to calculate the filter coefficients such as Wiener filter technique, Lagrange multiplier method, and linear programming (LP) algorithm. Also, a weighting function is utilized to shape the sidelobe energy in an iterative manner that will yield more sidelobe reduction. Comparison of the proposed... 

In noise radars, measuring the cross-correlation between transmitted and received signals is known as a common method of signal processing. However, it brings a lot of unwelcome sidelobes which can lean to masking weak echoes of far targets. There are many classical and modern methods of masking effect removal which are based on signal processing in the receiver side. A method of waveform design for decreasing this effect is presented and its efficiency is compared to purely random waveform generation method and CLEAN algorithm. Moreover, performance of collaborative using of receiver-based and transmitter-based techniques is considered  

The problem of estimating pulse repetition interval (PRI) of an interleaved pulse train which consist of several independent radar signals, is the main issue of signal processing in electronic support systems. PRI Transform algorithm is one of the well known and effective methods of PRI detection which is capable of detecting several close jittered signals and surpassing subharmonics, but have some drawbacks especially because of small PRI dynamic range and heavy computations. In this paper a modified PRI transform is introduced which manage wide range of PRIs simultaneously, and speed up the algorithm by significantly reducing the computations. Moreover an efficient threshold is set for... 

Waveform design for target identification and classification in multiple-input multiple-output (MIMO) radar systems has been studied in several recent works. In previous works, optimal signals for an estimation algorithm are found assuming that only signal- independent noise exists. This work extends previous research by studying the case where clutter is also present. We develop a procedure to design the optimal waveform which minimizes estimation error at the output of the minimum mean squared error (MMSE) estimators in two scenarios. In the first one different transmit antennas see uncorrelated aspects of the target, and we consider the correlated target aspects in the second one.... 

In this study, a detector/estimator is proposed for compressed sensing radars, which does not need to reconstruct the radar signal, and which works directly from compressive measurements. More precisely, through direct processing of the measurements, and without the need for reconstructing the original radar signal, the system performs target detection, and then estimates range, Doppler frequency shift and radar cross section in the presence of a Gaussian clutter. It can be seen that for large compression ratios, the detection performance and estimation quality is comparable with a common radar system while having a much lower data rate and with less computational load  

The authors deal with the robust design of multiple-input-multiple-output (MIMO) space-time transmit code (STTC) and space-time receive filter (STRF) for a point-like target embedded in signal-dependent interference. Specifically, they assume that the radar exploits knowledge provided by dynamic environmental database, to roughly predict the actual scattering scenario. Then, they devise an iterative method to optimise the (constrained) STTC and the (constrained) STRF which sequentially improves the worst-case (over interfering scatterers statistics) signal-to-interference-plus-noise ratio (SINR). Each iteration of the algorithm is handled via solving two (hidden) convex optimisation... 

Sea clutter refers to the radar returns from the sea surface. Accurate modelling of sea clutter and detection of low observable targets within sea clutter are major problems in remote sensing and radar signal processing applications. Recently fractal geometry is applied to the analysis of high range resolution radar sea clutters. The box-counting method is widely used to estimate fractal dimension but it has some drawbacks rarely considered in literature. We explain the problem of box size range and present a novel method to select an appropriate range  

one of the main problems of radar identification in electronic warfare support system is analysis of pulse repetition interval (PRI) modulation. In this paper a robust method of recognizing the PRI modulation type of radar signals is proposed to improve robustness of previous recognition methods as well as to reduce the complexity. Simulation results show that the proposed method achieves much better error recognition rate in case of missing and spurious pulses than other methods such as autocorrelation based techniques and the Noone method  

Waveform design for target identification and classification in MIMO radar systems has been studied in several recent works. While the previous works assumed that the noise was independent of the transmission signals, here we extend the results to the signal dependent noise (clutter). We consider two scenarios. In the first scenario it is assumed that different transmit antennas see uncorrelated aspects of the target. In the second scenario, we consider the correlated target. As clutter is dependent to signal, target estimation error cannot vanish only by increasing the transmission power. It can be shown that in the second scenario, MIMO radar receiver can nullify the clutter subspace.... 

Some periodic and quasi-periodic pulse trains are emitted by different sources in the environment and a number of sensors receive them through a single channel simultaneously. We are often interested in separating these pulse trains for source identification at sensors. This identification process is termed as deinterleaving pulse trains. Deinterleaving pulse trains has wide applications in communications, radar systems, neural systems, biomedical engineering, and so on. This paper studies the deinterleaving problem with the assumption that both sources and sensors are fixed. In this study, the problem of deinterleaving pulse trains is modeled as a blind source separation (BSS) problem. To... 

A novel information theoretic code design approach for cognitive multiple-input multiple-output (MIMO) radars is proposed in the current paper. In the suggested solution, we consider an agile multi-antenna radar with spectral cognition and design optimized transmission codes considering practical limitations such as peak-to-average power ratio (PAR) and spectral coexistence in a spectrally crowded environment. As exact performance expressions for the detector is not analytically tractable in this case, an information theoretic approach is taken into account to design the transmission codes. Simulation results illustrate the efficiency of the proposed method  

One of the important obstacles in MIMO (Multiple Input Multiple Output) radars is the issue of designing proper transmit signals. Indeed, the capability of signal design is a significant advantage in MIMO radars, through which, the system can achieve much better performance. Many different aspects of this performance improvement have been considered yet, and the transmit signals have been designed to attain such goal, e.g., getting higher SNR or better detector's performance at the receiver. However, an important tool for evaluating the radar's performance is its ambiguity function. In this paper, we consider the problem of transmit signal design, in order to optimize the ambiguity function... 

For the target parameter estimation in MIMO radars in the presence of strong clutter, non-adaptive compressive sensing methods have a poor performance. On the other hand, the adaptive ones usually need higher data acquisition time. In this paper, we propose an adaptive compressive sensing method called L-BGT that has tolerable data acquisition time. furthermore, we have presented the essential changes in a distributed MIMO radar to exploit an adaptive group testing compressive sensing method  

In this paper, the problem of the waveform design for colocated multiple-input multiple-output (MIMO) radars is considered in two parts. In the first part, we design transmit waveform in order to approximate the desired beampattern with low number of samples in the transmitter. Unlike the traditional waveform design methods, in our solution, waveforms are designed for a specific number of samples. Also, the constant envelope constraint that is an important practical constraint is considered. In the second part, we jointly design the transmit waveform and receive filter by a sequential algorithm, considering a priori information of target and interference angle locations. We have evaluated... 

By employing the MIMO (multiple-input-multiple-output) technology in radar, some new problems emerged, that, in order to benefit the MIMO gains in radar, it was necessary to solve them suitably. One of such obstacles is determining the positions of receive antennas in a MIMO radar system with widely separated antennas (WS MIMO radar), since it is shown that the antennas' positions affect the whole system's performance considerably. In this study, a proper receivers' positioning procedure is proposed. To do this end, four criteria are developed based on the proposed MIMO detector and the MIMO ambiguity function. The simulations verify that the proposed positioning procedure improves the... 

High resolution range profile (HRRP) is a widely noted tool in radar target recognition. However, its high sensitivity to the target's aspect angle makes it necessary to seek solutions for this problem. One alternative is to assume consecutive samples of HRRP identically and independently distributed in small frames of aspect angles, an assumption which is not true in reality. Based on this simplifying assumption, some models, such as the hidden Markov model, have been developed to characterise the sequential information contained in multi-aspect radar echoes. As a result, these models consider only the short dependency between consecutive samples. Considering such issues, in this study, the... 

Compressive sensing (CS) is a widely used technique for (multiple) target detection in multiple input multiple output (MIMO) radars. In this paper, our goal is to enhance the quality of CS-based detection techniques for a colocated MIMO radar with given location of transmit and receive nodes. Our approach is to design the transmit waveforms based on the given antenna locations and optimally allocate the total power budget among the transmitters. The design criterion in this paper is the coherence of the resulting sensing matrix. Based on this criterion, we derive and solve a convex optimization problem for power allocation. For waveform design, however, the direct method studied is...