| 1. |
- Ankel, Martin, 1996, et al.
(författare)
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Bistatic noise radar: Demonstration of correlation noise suppression
- 2023
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Ingår i: IET Radar, Sonar and Navigation. - : Institution of Engineering and Technology (IET). - 1751-8792 .- 1751-8784. ; 17:3, s. 351-361
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Tidskriftsartikel (refereegranskat)abstract
- In this study, spatial separation of the radar transmitter and receiver units is considered, as a means of reducing the masking effect in noise radars. A bistatic radar system is constructed, with emphasis on a lightweight transmitter unit that can be mounted on a commercial Unmanned Aerial Vehicle (UAV). The system uses pseudo-random noise, generated digitally at the receiver and transmitter units. Correlation losses, due to non-linearities in the transmitter and receiver units, are measured to 0.1 dB. This study shows that by separating the transmitter and receiver unit the masking effect is significantly reduced, compared to a monostatic setup. This reduction is enough for the system to detect a slow flying UAV. Thus, bistatic separation should be considered as a practical tool to reduce the masking effect. By processing clutter with an extended CLEAN algorithm, the correlation noise floor is further suppressed.
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| 2. |
- Ankel, Martin, 1996, et al.
(författare)
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Implementation of a coherent real‐time noise radar system
- 2023
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Ingår i: IET radar, sonar & navigation. - : Institution of Engineering and Technology (IET). - 1751-8784 .- 1751-8792.
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Tidskriftsartikel (refereegranskat)abstract
- The utilisation of continuous random waveforms for radar, that is, noise radar, has been extensively studied as a candidate for low probability of intercept operation. However, compared with the more traditional pulse-Doppler radar, noise radar systems are significantly more complicated to implement, which is likely why few systems exist. If noise radar systems are to see the light of day, system design, implementation, limitations etc., must be investigated. Therefore, the authors examine and detail the implementation of a real-time noise radar system on a field programmable gate array. The system is capable of operating with 100% duty cycle, 200 MHz bandwidth, and 268 ms integration time while processing a range of about 8.5 km. Additionally, the system can perform real-time moving target compensation to reduce cell migration. System performance is primarily limited by the memory bandwidth of the off-chip dynamic random access memory.
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| 3. |
- Ata'a, A.W. 1978-, et al.
(författare)
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Deinterleaving of radar signals and PRF identification algorithms
- 2007
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Ingår i: IET radar, sonar & navigation. - : Institution of Engineering and Technology (IET). - 1751-8784 .- 1751-8792. ; 1:5, s. 340-347
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Tidskriftsartikel (refereegranskat)abstract
- Electronic warfare (EW) receivers are passive receivers which receive emissions from other platforms, and do certain analysis on these emissions. Some EW receivers receive radar pulses, measure the parameter of each pulse received and group the pulses that belongs to the same emitter together to determine the radar parameters for each emitter. These parameters are then compared with values stored for known radar types, to identify the emitter type. Two parts are focused, emitters deinterleaving and PRF-type identification. The deinterleaving is done through parameters clustering. Two parameters are selected for clustering direction of arrival and radio frequency. A self-organising neural network called Fuzzy ART is proposed for clustering. This algorithm has a very good clustering quality and can run in real-time applications. The PRF-type identification is done through time-of-arrival (TOA) analysis. Three previously presented algorithms are combined in new scheme to do the TOA analysis (or PRF-type identification). These algorithms are difference TOA histogram, TOA folding histogram and sequence search algorithm. The complete proposed system has been tested using three different tests. These tests are simple PRI test, jittered PRI test and staggered PRI test. The proposed system identifies up to 90 simple emitters, 20 jittered emitters and 20 staggered emitters. In all tests, the data were simulated and generated using software.
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| 4. |
- Bjorklund, Svante, et al.
(författare)
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Features for micro-Doppler based activity classification
- 2015
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Ingår i: IET radar, sonar & navigation. - : Institution of Engineering and Technology (IET). - 1751-8784 .- 1751-8792. ; 9:9, s. 1181-1187
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Tidskriftsartikel (refereegranskat)abstract
- Safety and security applications benefit from better situational awareness. Radar micro-Doppler signatures from an observed target carry information about the target's activity, and have potential to improve situational awareness. This article describes, compares, and discusses two methods to classify human activity based on radar micro-Doppler data. The first method extracts physically interpretable features from the time-velocity domain such as the main cycle time and properties of the envelope of the micro-Doppler spectra and use these in the classification. The second method derives its features based on the components with the most energy in the cadence-velocity domain (obtained as the Fourier transform of the time-velocity domain). Measurements from a field trial show that the two methods have similar activity classification performance. It is suggested that target base velocity and main limb cadence frequency are indirect features of both methods, and that they do often alone suffice to discriminate between the studied activities. This is corroborated by experiments with a reduced feature set. This opens up for designing new more compact feature sets. Moreover, weaknesses of the methods and the impact of non-radial motion are discussed.
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| 5. |
- Björklund, Svante, et al.
(författare)
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Auxiliary beam terrain-scattered interference suppression : reflection system and radar performance
- 2013
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Ingår i: IET Radar, Sonar & Navigation. - : The Institution of Engineering and Technology (IET). - 1751-8784 .- 1751-8792. ; 7:8, s. 836-847
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Tidskriftsartikel (refereegranskat)abstract
- Terrain-scattered interference (TSI), that is, jammer signals reflected on the earth's surface, is a significant problem to military airborne radar. In auxiliary beam TSI suppression, the TSI in the main radar beam is estimated by a single or several auxiliary beams and is subtracted from the main beam channel. The signal to subtract is the auxiliary beam signals fed through an estimate of the ‘reflection system’, which describes scattering on the surface. The authors first present results on the structure of this TSI suppression, on the estimation of the reflection system and on the quality of the estimate. Then the authors derive theoretical expressions for the signal-to-interference plus noise ratio (SINR) and the remaining TSI power for a single auxiliary beam. Since the SINR is directly connected to the radar performance, it can be seen what factors affect the performance and how. It was noted that when the estimated reflection system is missing one or more delays of the true system, the TSI filter cannot suppress the TSI signal completely. This phenomenon, which is called ‘TSI leakage’, has a very large impact on the performance. The SINR cannot be kept constant. Instead, an ‘SINR improvement’ can be defined.
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| 6. |
- Haglund, Anders, 1965, et al.
(författare)
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Recovery of missing samples in Orthogonal Frequency Division Multiplexing signals with optimisation using data carriers
- 2024
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Ingår i: IET Radar, Sonar and Navigation. - 1751-8792 .- 1751-8784. ; In Press
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Tidskriftsartikel (refereegranskat)abstract
- A method is proposed for reconstructing an Orthogonal Frequency Division Multiplexing (OFDM) signal that contains data gaps, with the aim to improve demodulation. The main objective is to use the method in a passive radar application with missing data samples and to improve target detection. The OFDM signal is assumed to comply with the Digital Video Broadcasting Terrestrial standard. The proposed recovery method is based on optimisation of a novel objective function, which consists of two parts. The first part is a function of the energy in the out-of-band frequencies, whereas the second, and novel part, uses the location of data carriers in the constellation diagram. The method is evaluated using both simulations and real data. The authors show that the proposed method significantly improves the OFDM signal in just a few iteration steps. The proposed method improved the condition number more than a factor ten thousand millions compared to using the least square method on the out-of-band frequencies only. The authors also decode the symbols with the Viterbi decoding algorithm and show how the required number of iterations with the proposed algorithm depends on the amount of missing samples and on the Signal-to-Noise Ratio in order to achieve a Bit Error Rate of less than one in one hundred thousand millions.
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| 7. |
- Lei, Shiwen, et al.
(författare)
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Analyses of the performance of adaptive subspace detector on fluctuating target detection in system-dependent clutter background
- 2016
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Ingår i: IET Radar, Sonar and Navigation. - : Institution of Engineering and Technology (IET). - 1751-8784 .- 1751-8792. ; 10:9, s. 1635-1642
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Tidskriftsartikel (refereegranskat)abstract
- The adaptive subspace detector in system-dependent clutter background (SDC-ASD) is proved to be able to improve the detection performance for deterministic target detection in the authors' previous study. However, the exact performance of the SDC-ASD for fluctuating target detection is still unknown. In this study, with the aid of matrix decomposition theory, the analytical performance of the SDC-ASD for detecting fluctuating target is considered and assessed. At the design stage, the rigorous mathematical derivation processes for the exact theoretical detection performance of the SDC-ASD for fluctuating target detection is derived. The theoretical results, which have explicitly expressions for both the false alarm probability and the detection probability, not only provide an effective mathematical method to analyse the fluctuating target detection performance, but also can further simplify the deterministic target detection assessments. At the analysis stage, Monte Carlo simulations are resorted to validate the analytical results. Numerical experiments are conducted to assess the effectiveness of the SDC-ASD for fluctuating target detection. Results show that the SDC-ASD, by dealing separately with the clutter and the noise, performs the best in comparison with its published counterparts, i.e. the generalised likelihood ratio detectors, the adaptive matched filters, the adaptive subspace detectors and the low-rank detectors based on sample covariance matrix.
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| 8. |
- Li, Haipeng, et al.
(författare)
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Underwater source localization in the presence of strong interference
- 2021
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Ingår i: IET Radar, Sonar and Navigation. - : Institution of Engineering and Technology (IET). - 1751-8784 .- 1751-8792. ; 15:3, s. 226-239
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Tidskriftsartikel (refereegranskat)abstract
- The underwater localization of a broadband target in the presence of strong interference and noise has been widely investigated. A novel clutter suppression approach based on oblique projections is proposed, exploiting the prior information of the expected target response. The method uses a generalised likelihood ratio formulation to select the oblique projection best matching the measured data. The performance of the proposed method is verified through numerical examples and measured sonar data. The results indicate that the method provides good performance for time difference of arrival estimation and target localization under low signal to clutter ratio as compared to existing methods.
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| 9. |
- Peng, Dongdong, et al.
(författare)
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Robust Particle Filter Based on Huber Function for Underwater Terrain Aided Navigation
- 2019
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Ingår i: IET radar, sonar & navigation. - : Institution of Engineering and Technology (IET). - 1751-8784 .- 1751-8792.
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Tidskriftsartikel (refereegranskat)abstract
- Terrain aided navigation is a promising technique to determine the location of underwater vehicle by matching terrain measurement against a known map. The particle filter is a natural choice for terrain aided navigation because of its ability to handle nonlinear, multimodal problems. However, the terrain measurements are vulnerable to outliers, which will cause the particle filter to degrade or even diverge. Modification of the Gaussian likelihood function by using robust cost functions is a way to reduce the effect of outliers on an estimate. We propose to use the Huber function to modify the measurement model used to set importance weights in a particle filter. We verify our method in simulations of multi-beam sonar in a real underwater digital map. The results demonstrate that the proposed method is more robust to outliers than the standard particle filter.
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| 10. |
- Vu, Viet Thuy, 1977-, et al.
(författare)
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Changing flight heading during pass to enhance SAR change detection performance
- 2021
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Ingår i: IET radar, sonar & navigation. - : John Wiley and Sons Inc. - 1751-8784 .- 1751-8792. ; 15:8, s. 817-826
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Tidskriftsartikel (refereegranskat)abstract
- Due to the wavelength-resolution characteristics, wavelength-resolution synthetic aperture radar (SAR) is considered for the change detection application aiming to achieve high detection probability and low false alarm rate. However, wavelength-resolution SAR change detection suffers from the problems caused by specular reflection of the elongated structure in the SAR scene, the dependency of radar cross-section on incident angle of electromagnetic wave, the interference due to antenna backlobe and so forth. Hardware and software solutions are therefore desired to deal with these problems. The authors propose to change flight heading during passes as a natural solution. The proposed solution is tested with the CARABAS data using a typical SAR change detection method. The achieved change detection results show the good performance of the proposed solution, for example, the detection probability is up to 100% with the false alarm rate of 0.5 per square kilometre. © 2021 The Authors. IET Radar, Sonar & Navigation published by John Wiley & Sons Ltd on behalf of The Institution of Engineering and Technology.
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