Medium Pulse Repetition Frequency Research Articles

A novel multi-pulse repetition frequency set selection method based on the clear area evaluation matrix

Since the traditional multiple pulse repetition frequency (PRF) selection methods do not consider the influence of measurement errors and granularity division, this paper introduces a novel medium pulse repetition frequency (MPRF) set selection method for the ground-based pulsed-Doppler radar system. Specifically, we define the clear area evaluation matrix (CAEM) and derive the analytic expression of the objective function using the truth table. Compared with the traditional method based on the blind zone map (BZM), the CAEM based method preliminarily selects the measurement data considering the influence of measurement errors. To keep in line with practical processing, the CAEM solves the ambiguity of some measurement points and uses the deviation tolerance to select the results again. The genetic algorithm (GA) is utilized to maximize the objective function. The experiments show that CAEM improves computational efficiency by about 38 times and the accuracy by about 7% compared with the BZM method.

Comparative histological evaluation of two PRF formulations (PRF High and PRF Medium) on quality of life and healing outcome of apicomarginal defects: A randomized clinical trial

The objective of this randomized clinical trial was to investigate the effects of two PRF formulations (PRF High and PRF Medium) on quality of life and healing outcome (2D and 3D) of apicomarginal defects.Patients presenting with endodontic lesions and concomitant periodontal communication were randomly allocated to PRF High and PRF Medium groups. The treatment protocol in each group included a periapical surgical procedure with placement of PRF clot and membrane in the bony defect and on the denuded root surface, respectively. Quality of life was assessed for 1 week after surgery following a modified version of the patient's perception questionnaire. Postoperative pain was assessed using a visual analog scale. Clinical and radiographic evaluations were performed using Rud and Molven 2D criteria and Modified PENN 3D criteria. Buccal bone formation was assessed using sagittal and corresponding axial sections in CBCT. Histological analysis was performed using hematoxylin and eosin (H and E) staining and attaching primary antibodies to tissue sections.In total, 40 patients were enrolled in the trial (N = 20 per group). PRF Medium group patients reported significantly less swelling on the 1st (p = 0.036), 2nd (p = 0.034), and 3rd (p = 0.023) days, and average pain on the 2nd (p = 0.031), 3rd (p = 0.03), and 4th (p = 0.04) days postoperatively. The difference in success rate for periapical healing was non-significant between the PRF Medium group (89.5%) and PRF High group (90%), in both 2D and 3D imaging (p = 0.957). The formation of buccal bone was observed in five cases (26.3%) and four cases (20%) in the PRF Medium and PRF High groups, respectively, with a non-significant difference (p = 0.575). PRF Medium clots had a loose fibrin structure with a significantly higher number of neutrophils (473.79 ± 82.89 per mm2) than PRF High clots, which had a dense structure and fewer neutrophils (253.15 ± 63.86 per mm2) (p = 0.001). Autologous platelet concentrates (APCs) promoted satisfactory periapical healing, with no significant difference between the groups.Within the limitations of the study, it seems that PRF Medium should be preferred over PRF High when the patients’ quality of life is the priority.

Improving the accuracy of measurement range and speed air target radar mode medium pulse repetition frequency by estimation the signal level of background returns

Improving the accuracy of measurement range and speed air target radar mode medium pulse repetition frequency by estimation the signal level of background returns

Enhanced Pre-STAP Beamforming for Range Ambiguous Clutter Separation with Vertical FDA Radar

Medium pulse repetition frequency (MPRF) is an important mode in airborne radar system. Since MPRF mode brings both Doppler and range ambiguities, it causes difficulty for the airborne radar to suppress ground or sea clutter. In recent years, it has been pointed out that the frequency diverse array (FDA) radar is capable of separating the range ambiguous clutter, which is helpful for the airborne radar in detecting weak moving targets originally buried in ambiguous clutter. To further improve the ambiguous clutter separation performance, an enhanced pre-STAP beamforming for range ambiguous clutter suppression is proposed for the vertical FDA planar array in this paper. With consideration of range dependence of the vertical spatial frequency, a series of pre-STAP beamformers are designed using a priori knowledge of platform and radar parameters. The notches of the beamformers are aligned with the ambiguous clutter to extract echoes from desired range region while suppressing clutter from ambiguous range regions. The notches can be widened by using covariance matrix tapering technique and the proposed method can improve the performance of range ambiguous clutter separation with limited degrees-of-freedom (DOFs). Simulation examples show the effectiveness of the proposed method.

Mono-pulse radar angle estimation algorithm under low signal-to-noise ratio

In the case of low signal-to-noise ratio (SNR), in order to improve the angle measurement accuracy of the mono-pulse radar seeker, a target angle estimation algorithm is proposed. The algorithm takes the target angle as a state variable under the Bayesian framework, expands it to the state vector, performs state modeling and observation modeling on it, and builds a particle-based eye angle estimator, which improves the target angle estimation performance. The effectiveness of the algorithm is verified by the simulation data of the medium pulse repetition frequency radar seeker.

Multi‐frame track‐before‐detect algorithm for disambiguation

In practice, medium pulse repetition frequency (PRF) radar system is widely used as it takes both the advantages of low and high PRF radars. However, range and Doppler ambiguities appear in such a complicated system. Traditional target tracking algorithms first threshold raw measurements and obtain points from different PRF, then perform ambiguity resolutions over them to obtain the unambiguous measurements. It leads to a rather poor performance when target signal-to-noise ratio is low. While multi-frame track-before-detect (MF-TBD) is an advantageous method to track weak targets, but it fails to be applied in multiple PRF radar system directly. In this study, two algorithms based on MF-TBD are proposed. Classical ambiguity resolution (CAR) TBD first resolves ambiguities by means of a robust Chinese Remainder Theorem, where the first detection threshold is below the normal threshold, and then MF-TBD is applied for further tracking. The simulation shows that the proposed method significantly outperforms the CAR detect-before-track algorithm.

A Novel Waveform Design Method for Shift-Frequency Jamming Confirmation

Shift-frequency jamming is generally used to form range false targets for ground-based early-warning radar systems; the frequency shift value of such interference is larger than the Doppler shift value of the moving target, and the key element to suppress the shift-frequency jamming is the frequency shift value estimation. However, in the low- or medium-pulse repetition frequency (PRF) mode, it is challenging to estimate the accurate frequency shift due to the velocity ambiguity. To solve this problem, a novel sparse Doppler-sensitive waveform is designed based on the ambiguity function theory, where the basic idea is to design a waveform sensitive to a specific Doppler but insensitive to other Dopplers; therefore, this waveform can recognize the specific Doppler of the target unambiguously. To apply the designed waveform in practice, the detection and estimation processing flow is provided based on the waveform diversity technique and the family of the sparse Doppler-sensitive waveforms. Simulation experiments are presented to validate the efficiency of the proposed method, and we conclude that the advantage of this method is that it can be used to confirm the specific Doppler of the target unambiguously with few pulses even under the condition of a low PRF.

Fusion of radar sensing and wireless communications by embedding communication signals into the radar transmit waveform

A joint radar-communication (JRC) system with both radar sensing and communication abilities is proposed to improve spectrum utilisation efficiency. The transmitter of the JRC consists of multiple antenna subarrays transmitting orthogonal waveforms. If the communication receivers are in radar sidelobe directions, the communication data symbols are embedded in the magnitude ratio as well as the phase shift between transmit waveform pairs. In the case of the communication receivers in radar main lobe direction, the data symbols are embedded in the phase shift between transmit waveform pairs only to preserve optimum radar target detection performance. Novel symbol mapping constellation scheme is designed to achieve a high data transmission rate while maintaining a relatively low symbol error rate. The simulation results show that with medium pulse repetition frequency radar waveforms used, the data transmission rate of the proposed JRC system is in the range of Mbits/s.

MPRF(Medium Pulse Repetition Frequency) 모드의 추적 PRF 선택

This paper is a study on PRF selection method to accurately detect the target in the target tracking mode of airborne radar. The proposed methods are an ‘optimization’ method to select the closest to the center of the allowable zone considering the uncertainty of the target distance and velocity prediction and a ‘quasi-optimization’ method to improve the real time performance. In addition, the characteristics of the proposed methods are compared and analyzed through cost function and calculation time.

Bernoulli filter for range and Doppler ambiguous radar

A pulse Doppler radar worked in medium or high pulse repetition frequency (PRF) may suffer from range and Doppler ambiguities. The common method to solve ambiguities is to use multiple PRFs and do correlation between them. The ghosting problem may be caused by the false alarms in the correlation. When the signal-to-noise ratio is low, a low detection threshold is needed to guarantee the probability of detection, which may create a large amount of false alarms that are intractable for existing techniques. This study uses a Bayesian method to detect and track a single target in a range and Doppler ambiguous radar. The authors’ method is formulated based on the finite set representation of the target state and the recently developed Bernoulli filter. Besides, a sequential Monte Carlo implementation of the Bernoulli filter is proposed for the problem of range and Doppler ambiguous measurement. Simulation results show that the proposed filter can simultaneously detect and track the target using the ambiguous measurements in the presence of dense false alarms.

Clutter suppression approach for non‐sidelooking airborne radar with medium pulse repetition frequency

For non-sidelooking airborne radar operating in medium pulse repetition frequency mode, the space–time adaptive processing (STAP) technique suffers from a significant performance loss due to the range dependence of clutter. Here, an efficient clutter suppression approach is presented to improve STAP performance. Utilising the characteristics of clutter, the near-range clutter, the major reason for the performance degradation, is extracted from raw returns using a specially designed oblique projector firstly, and then is mitigated by an adaptive beamformer estimated from the extracted components. Subsequently, an azimuth-Doppler STAP beamformer is employed to further suppress the residual clutter. To enhance the robustness of the approach, a simple steering vector calibration technique is taken into account. The proposed approach can eliminate the near-range clutter effectively, and therefore alleviate the clutter range dependence greatly. The STAP performance can be improved significantly. Simulation results demonstrate the effectiveness of the presented method.

MPRF 파형을 사용하는 항공기 레이더에서 탐색/추적을 위한 실시간 PRF 선택

항공기 레이더는 하방 또는 사방의 공대공 표적을 탐지/추적하기 위하여 보통 MPRF 파형을 사용한다. 항공기용 레이더가 MPRF 파형을 운용하기 위하여, 거리/속도에서 존재하는 모호성을 해결하면서 클러터를 회피하여 하방 공대공 표적을 탐지할 수 있는 최적의 PRF들을 선택하여 운용할 수 있어야 한다. 이 논문은 실시간 환경변화 상황에서 표적을 탐지/추적하기 위한 최적의 PRF들을 실시간으로 찾는 방법을 제시한다. Airborne radar usually use MPRF(medium PRF) waveforms to detect and track look-down or all-directions air-to-air targets. To use MPRF waveforms, airborne radar have to operate optimal PRF schedules and select optimal PRFs able to detect look-down air-to-air targets, overcoming look-down clutter and resolving range/velocity ambiguities. In this paper, we propose a real-time search method for the optimal(and sub-optimal) PRFs able to detect and track targets in real-time change of situation for MPRF pulsed-Doppler airborne radars.

Real-Time Selection of Pulse Repetition Frequency (PRF) Set for a Triple 2-of-3 PRF Scheme

A triple 2-of-3 pulse repetition frequency (PRF) scheme is presented for medium PRF pulsed-Doppler airborne radars, and a real-time method is developed that searches for optimal or sub-optimal PRF sets according to momentary battle situations. The effectiveness of the real-time search method of PRF sets is demonstrated by the experimental results obtained using simulated data.

Research on Medium PRF Selection of Airborne Pulsed Doppler Radar by Simulated Annealing Algorithm

Research on Medium PRF Selection of Airborne Pulsed Doppler Radar by Simulated Annealing Algorithm

Examination of the Effect of Array Weighting Function on Radar Target Detectability

A methodology is described to assess the detectability of targets by an airborne fire control radar (FCR) operating in a medium pulse-repetition frequency (PRF) mode in the presence of strong ground clutter as a function of the transmitting and receiving antenna array weighting functions and proportion of failed array elements. It describes the radar, antenna, and clutter modelling processes and the method by which target detectability is quantified. The detectability of targets in clutter is described using a detectability map, which provides a useful means of comparing target detectability as clutter conditions change. It concludes that the best target detectability is to be achieved using those weighting functions on transmit and receive which result in the lowest average sidelobe levels but that the margins between the more highly tapered weighting functions were small. Furthermore, it concludes that target detectability degrades as the proportion of failed elements increases. A failure of 5% of the elements gave modest, though meaningful, degradations in target detectability and would therefore form a suitable upper limit.

Performance comparison of PRF schedules for medium PRF radar

Previous work has shown how evolutionary algorithms (EAs) are an effective tool in optimising the selection of pulse repetition frequency (PRF) values of medium PRF schedules in an airborne fire control radar (FCR) application requiring target data in three PRFs. The optimisation is driven by the requirement to minimise range/Doppler blindness whilst maintaining full decodability. In this paper we detail work in which the optimisation process is applied to design novel short medium PRF schedules requiring target data in just two PRFs. The paper reports on the testing of a variety of near-optimum schedules to compare their blindness, decoding, and ghosting performances. The results show that in many situations, the 2 of N schedules are a practical alternative to conventional 3 of N processing.

Medium PRF radar PRF selection using evolutionary algorithms

Evolutionary algorithms are applied to the optimization of pulse repetition frequency (PRF), for both eight-and nine PRFs, in medium PRF radar while considering the detailed effects of sidelobe clutter and many other technical factors. The algorithm presented also ensures that all the solutions produced are fully decodable and have no blind velocities. The evolutionary algorithm was able to identify near-optimum PRF sets for a realistic radar system with only a modest computational effort.

Medium PRF set selection using evolutionary algorithms

This paper presents a new and novel method of selecting multiple pulse repetition frequency (PRF) sets for use in medium PRF pulsed-Doppler radars. Evolutionary algorithms are used to minimise the blind areas in the range/Doppler space. The evolutionary algorithm allows optimal solutions to be generated quickly, far faster than with exhaustive searches, and is fully automatic, unlike existing techniques. The evolved solutions compare very favorably against the results of both an exhaustive search and existing published PRF set selection methods. This evolutionary approach to generation of PRF sets is a major advance in medium PRF radar design.

Ground clutter model for airborne MPRF radars in look-down search mode

The performances of a medium pulse repetition frequency (MPRF) radar operating in air-to-air look-down mode are strongly influenced by the presence of ground clutter. The clutter echo received both on the antenna main beam and side lobes can increase the number of false alarms. To correctly account for the effects of ground clutter, one has to develop a model capable of reproducing clutter characteristics as a function of range and frequency. The authors propose a model to estimate range/Doppler distribution of ground clutter mean power. The proposed discrete model permits an easy development of simulation packages which quantify the effects of ground clutter in MPRF systems and which allow the evaluation of MPRF radars performances in most typical operating conditions. Three-dimensional plots of the range/Doppler distribution of mean ground clutter power, obtained by a FORTRAN code that implements the model, are presented. Moreover, the dependence of ground clutter power on important mission and radar parameters is discussed.

New approach for Doppler ambiguities resolution in medium pulse repetition frequency radars

MPRF radars exhibit both range and Doppler ambiguities. An algorithm is proposed to resolve Doppler ambiguities which has been tested through a computer-based simulation both for fixed radiofrequency and radiofrequency hopping.