Highly squinted synthetic aperture radar (SAR) data focusing is a challenging problem with difficulty to correct the severe range-azimuth coupling and motion errors. Squint minimization processing with the range-walk correction is widely adapted to simplify the decoupling processing, while it destructs the azimuth-shift invariance of conventional SAR transfer function. In this paper, a two-stage focusing algorithm (TSFA) is proposed to generate a focused imagery for the highly squinted airborne SAR. In the proposed algorithm, conventional range cell migration correction and azimuth matched filtering are performed and a fine focusing stage is established to correct the azimuth variance. In the fine focusing procedure, the coarse-focused image is divided into azimuth blocks to accommodate the correction of azimuth-variant residual range migration and phase terms. Moreover, precise motion compensation is embedded into the TSFA procedure to form an accurate airborne SAR imagery, which may be called the extended TSFA. In order to balance the processing precision and computational load, optimal selection of block size is investigated in detail. Both simulated and real measured airborne SAR data sets are used to validate the proposed approaches.

Synthetic aperture radar (SAR) systems mounted on unmanned aerial vehicles (UAVs) are usually sensitive to trajectory deviations that cause serious motion error in the recorded data. In this letter, a novel range-dependent map-drift algorithm (RDMDA) is developed to accommodate the range-variant characteristics of severe motion errors. Utilizing the algorithm as a core estimate, we come up with a robust motion compensation strategy for the UAV SAR imagery. RDMDA outperforms the conventional MDA in both accuracy and robustness while it keeps similar efficiency. Real data experiment shows that the proposed approach is appropriate for precise imaging of UAV SAR systems equipped with only a low-accuracy inertial navigation system.

Due to the skew data support region (DSR) of the 2-D wavenumber spectrum for high-squint synthetic aperture radar (HS-SAR), the conventional w-k algorithm cannot fully utilize the DSR and thus degrades the resolution if simply taking a rectangle region. Meanwhile, for the small-aperture data, direct azimuth imaging in the distance domain will lead to serious aliasing. A modified ω-k algorithm is derived in this paper to solve these problems. The maximum usage of DSR is achieved by the coordinate rotation. As for the azimuth dependence, the method of azimuth resampling is used to get the uniform focusing. Different from the traditional w-k method, the modified w-k algorithm focuses the small-aperture data in the azimuth wavenumber domain by SPECAN processing, which avoids padding a large number of zeros when imaging in the azimuth distance domain. Simulated and real-data results show the validity and effectiveness of the presented algorithm.

ABSTRACT Correlation power analysis (CPA) has been a powerful and thoroughly studied threat for implementations of block ciphers and public key algorithms but not yet for stream ciphers. This paper proposes a novel CPA attack on the hardware‐oriented stream cipher Trivium, one of the finally chosen ciphers by the eSTREAM project. Based on the Hamming distance model, the proposed attack exploits the resynchronization phase of Trivium. By choosing proper initial value vectors, the algorithmic noise of the device is completely eliminated. Furthermore, a novel concept of modified correlation coefficients is introduced, which can be used to describe the relation between the hypothetical power consumption values and the measured power consumption values. Through the calculation of modified correlation coefficients, the effect of the electronic noise is significantly decreased and values of the hypotheses can be discriminated uniquely by the highest modified correlation coefficient. According to the recovered hypotheses, many equations on the secret key bits can be obtained, which will be sequentially solved to extract the secret key of Trivium. Compared with Fischer's differential power analysis attack on Trivium, the proposed algorithm is more efficient and robust. Finally, a simulation attack is mounted to confirm the efficiency of the algorithm. Copyright © 2011 John Wiley & Sons, Ltd.

Based on compressive sampling theory, a novel method for high-resolution inverse synthetic aperture radar (ISAR) imaging is presented in this letter by transmitting sparse probing frequencies. In this method, only a few measurements in the range frequency and cross-range time domains are needed to reconstruct the target scene by solving an inverse problem through either a linear program or a greedy pursuit. By transmitting merely a few probe frequencies instead of wideband signals, the proposed method can obtain an unambiguous ISAR image with superresolution. The validity of the proposed approach is also confirmed using numerical simulations and real data.

In this letter, a novel single-range image fusion method for radar imaging of spinning space debris with dimensions smaller than the radar range resolution is proposed. On the assumption that the target consists of isolated isotropic scattering centers, a 2-D image can be obtained using single-range unit cross-range echo data, which have a theoretical resolution of a quarter of a wavelength. The proposed approach is computationally efficient particularly for smaller sized targets, as the total rotational angle is divided into four small sections, allowing for easier processing of each region. Moreover, the proposed method can be used to directly obtain an image in Cartesian coordinates, unlike current algorithms where images are obtained in a polar format, requiring reformatting to the Cartesian grid. The validity of the proposed approach is confirmed using numerical simulations.