Li-hua Zhong

Strong Echo Cancellation Based on Adaptive Block Notch Filter in Passive Radar

In passive radar, the waveform is not controlled by the system, so strong echoes usually produce high sidelobes in the correlation function. Since the sidelobes can mask the weak targets, strong echo cancellation methods are required. The generalized adaptive notch filter (GANF) is an efficient method compared with the extensive cancellation algorithm. However, the GANF estimates different frequencies separately (in parallel or series), and a point-by-point iterative operation is adopted, which leads to heavy computational burden. This letter presents a multifrequency estimation notch filter which is a simplified GANF based on the signal model. Furthermore, an adaptive block notch filter is proposed to reduce the processing time. The efficiency of the block notch filter is verified by simulations.

The GF-3 SAR Data Processor

The Gaofen-3 (GF-3) data processor was developed as a workstation-based GF-3 synthetic aperture radar (SAR) data processing system. The processor consists of two vital subsystems of the GF-3 ground segment, which are referred to as data ingesting subsystem (DIS) and product generation subsystem (PGS). The primary purpose of DIS is to record and catalogue GF-3 raw data with a transferring format, and PGS is to produce slant range or geocoded imagery from the signal data. This paper presents a brief introduction of the GF-3 data processor, including descriptions of the system architecture, the processing algorithms and its output format.

Adaptive direct signal and clutter cancellation based on phase-offset block least mean square filter in passive radar

The direct signal and clutter heavily degrade the performance of the target detection in passive radar. Therefore a reference antenna is necessary in order to acquire the direct signal, which is used to perform the adaptive filtering in order to cancel the direct signal and the clutter received on the surveillance antenna. However there may be distance between the two antennas, leading to reduced relativity between the reference signal and the surveillance signal. Consequently the reduced relativity results in decreased cancellation performance. In this paper a phase-offset block least mean square (BLMS) filter is designed to compensate the distance and perform the adaptive cancellation. Simulations and experiments based on real-life data is carried out to verify the effectiveness and efficiency of the proposed method.

Medium-Earth-orbit SAR imaging based on keystone transform and azimuth perturbation

Due to the significant azimuth variance property in medium-Earth-orbit (MEO) synthetic aperture radar (SAR) echo, it is difficult for the conventional SAR algorithms to achieve a good compromise between accuracy and efficiency. A novel algorithm based on Keystone transform (KT) and azimuth perturbation (AP) is introduced in this paper to handle this problem. The function of KT is to correct the range walk and thus to mitigate the azimuth variance effect on range processing. The function of AP is to equalize the Doppler histories in each range gate and thus to mitigate the azimuth variance effect on azimuth compressing. Simulation results of an L-band MEO SAR with 5 m resolution at 10,000 km altitude demonstrate the capability of our algorithm.

An extended processing scheme for coherent integration and parameter estimation based on matched filtering in passive radar

In passive radars, coherent integration is an essential method to achieve processing gain for target detection. The cross ambiguity function (CAF) and the method based on matched filtering are the most common approaches. The method based on matched filtering is an approximation to CAF and the procedure is: (1) divide the signal into snapshots; (2) perform matched filtering on each snapshot; (3) perform fast Fourier transform (FFT) across the snapshots. The matched filtering method is computationally affordable and can offer savings of an order of 1000 times in execution speed over that of CAF. However, matched filtering suffers from severe energy loss for high speed targets. In this paper we concentrate mainly on the matched filtering method and we use keystone transform to rectify range migration. Several factors affecting the performance of coherent integration are discussed based on the matched filtering method and keystone transform. Modified methods are introduced to improve the performance by analyzing the impacts of mismatching, precision of the keystone transform, and discretization. The modified discrete chirp Fourier transform (MDCFT) is adopted to rectify the Doppler expansion in a multi-target scenario. A novel velocity estimation method is proposed, and an extended processing scheme presented. Simulations show that the proposed algorithms improve the performance of matched filtering for high speed targets.

Doppler walk rectification based on KWT in passive radar

Doppler walk is introduced by high speed motion of targets in passive radar, which decreases the signal-to-noise ratio. In this paper, a Doppler walk rectification method based on keystone-Wigner-Ville transform (KWT) is proposed, and the interference, weights and noise impact are analyzed. No prior information and parameters searching are unnecessary.

Threshold determination for dynamic programming based track-before-detect in passive bistatic radar

Track-before-detect (TBD) is effective on weak target detection in passive bistatic radar (PBR). The probability of false alarm (PFA) and the probability of detection (PD) in TBD based on dynamic programming algorithm (DPA) are determined by threshold. The extreme value theory and generalized Pareto distribution are usually used to obtain the relationship between PD, PFA and threshold. However, DPA must be performed several times to estimate parameters resulting in much processing time. An iterative method based on Gaussian distribution is another solution but is not suitable for the Chi-square distribution in PBR. Therefore fast threshold determination methods without Gaussian assumption are proposed in this paper. First, a data simulation method is presented. Then an approximation of PD is introduced to further reduce the complexity. Moreover, empirical formulas based on the hypothesis of Chi-square distribution are developed for real-time processing. Simulations verify that the methods are more suitable for real-time processing.

Combined analysis of probability of missed detection and positioning accuracy for receiver selection in SFN based passive radar systems

Multistatic passive radar systems provide higher positioning accuracy comparing with the bistatic ones. However, the positioning performance of the multistatic passive radar systems is largely dependent on the geometry. Especially, it is difficult to designate transmitters from the given ones in a single frequency network (SFN) based passive radar system. Therefore the receiver location is of crucial importance. In this paper, the influence of different receiver positions for the probability of missed detection and the target positioning accuracy are analyzed. Then a performance function for selecting the optimal receiver is proposed. Finally, a simulation with three transmitters and one receiver is presented.