The mobile channel is slow fading and time selective, thus the multiplicative and additive noise of the channel will smear the spectral line, or arouse Doppler spread. This spread will make the parameters estimation a...The mobile channel is slow fading and time selective, thus the multiplicative and additive noise of the channel will smear the spectral line, or arouse Doppler spread. This spread will make the parameters estimation accuracy degrade. The goal of this paper is to analytically assess this degradation when Carrier Frequency Offset (CFO) and Doppler shift exist jointly. Then the finite-sample Cramer-Rao Lower Bound (CRLB) is derived and close-form asymptotical expression is given for large-sample CRLB. These expressions give insights into the performance room for frequency estimation. Also the variance of Doppler shift estimator is simulated to illustrate the theoretical results.展开更多
The optimal imaging time selection of ship targets for shore-based inverse synthetic aperture radar （ISAR） in high sea conditions is investigated. The optimal imaging time includes opti- mal imaging instants and opt...The optimal imaging time selection of ship targets for shore-based inverse synthetic aperture radar （ISAR） in high sea conditions is investigated. The optimal imaging time includes opti- mal imaging instants and optimal imaging duration. A novel method for optimal imaging instants selection based on the estimation of the Doppler centroid frequencies （DCFs） of a series of images obtained over continuous short durations is proposed. Combined with the optimal imaging duration selection scheme using the image contrast maximization criteria, this method can provide the ship images with the highest focus. Simulated and real data pro- cessing results verify the effectiveness of the proposed imaging method.展开更多
Given the capabilities of modern high-performance missiles,efficient evasion maneuver strategies are crucial for enhancing UAV survivability.This paper addresses the integration of evasion strategies and maneuver timi...Given the capabilities of modern high-performance missiles,efficient evasion maneuver strategies are crucial for enhancing UAV survivability.This paper addresses the integration of evasion strategies and maneuver timing for targeted UAVs.First,a three-dimensional engagement scenario is modeled using the relative motion mechanism.Subsequently,a fundamental evasion strategy focusing on large roll maneuvers and two-phase acceleration is developed.With the initiation timing of direct force control designated as the control variable,the formulation of a constrained optimization problem to maximize miss distance is fully articulated.While preserving the high fidelity of the established switching model,the feasible timing intervals and the optimal timing are determined through numerical optimization.Finally,simulation experiments are conducted focusing on omnidirectional attacks from the upper hemisphere.The results demonstrate that by implementing specific evasion maneuvers at optimal timing,the target successfully escapes the effective range of the proximity fuse,thus confirming the feasibility of the proposed evasion maneuver and timing strategy.展开更多
文摘The mobile channel is slow fading and time selective, thus the multiplicative and additive noise of the channel will smear the spectral line, or arouse Doppler spread. This spread will make the parameters estimation accuracy degrade. The goal of this paper is to analytically assess this degradation when Carrier Frequency Offset (CFO) and Doppler shift exist jointly. Then the finite-sample Cramer-Rao Lower Bound (CRLB) is derived and close-form asymptotical expression is given for large-sample CRLB. These expressions give insights into the performance room for frequency estimation. Also the variance of Doppler shift estimator is simulated to illustrate the theoretical results.
基金supported by the Innovation Foundation for Scientific Research Base(NJ20140008NJ20150018)+1 种基金the Aeronautical Science Foundation of China(20132052035)the National Defense Basic Scientific Research(B2520110008)
文摘The optimal imaging time selection of ship targets for shore-based inverse synthetic aperture radar （ISAR） in high sea conditions is investigated. The optimal imaging time includes opti- mal imaging instants and optimal imaging duration. A novel method for optimal imaging instants selection based on the estimation of the Doppler centroid frequencies （DCFs） of a series of images obtained over continuous short durations is proposed. Combined with the optimal imaging duration selection scheme using the image contrast maximization criteria, this method can provide the ship images with the highest focus. Simulated and real data pro- cessing results verify the effectiveness of the proposed imaging method.
文摘Given the capabilities of modern high-performance missiles,efficient evasion maneuver strategies are crucial for enhancing UAV survivability.This paper addresses the integration of evasion strategies and maneuver timing for targeted UAVs.First,a three-dimensional engagement scenario is modeled using the relative motion mechanism.Subsequently,a fundamental evasion strategy focusing on large roll maneuvers and two-phase acceleration is developed.With the initiation timing of direct force control designated as the control variable,the formulation of a constrained optimization problem to maximize miss distance is fully articulated.While preserving the high fidelity of the established switching model,the feasible timing intervals and the optimal timing are determined through numerical optimization.Finally,simulation experiments are conducted focusing on omnidirectional attacks from the upper hemisphere.The results demonstrate that by implementing specific evasion maneuvers at optimal timing,the target successfully escapes the effective range of the proximity fuse,thus confirming the feasibility of the proposed evasion maneuver and timing strategy.
