Underwater acoustic (UA) communication channel in the shallow water is fast time-varying and selective fading. Proper de-spreading method is needed for the orthogonal frequency division multiplexing spread spectrum UA...
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Underwater acoustic (UA) communication channel in the shallow water is fast time-varying and selective fading. Proper de-spreading method is needed for the orthogonal frequency division multiplexing spread spectrum UA communication system to reconstruct the information. The conventional de-spreading algorithm decrease the communication rate due to the using of the pilot for channel estimation. To accurately estimate the channel response without much loss in communication efficiency, an improved pilot-free spread spectrum de-spreading (IPSSD) method is proposed in this paper. This algorithm first recognizes the spread spectrum signal in frequency domain using the sparseness of the underwater acoustic channel. Then a decision feedback estimation of the channel impulse response is achieved according to the recognition results. The least square method is utilized to decrease the estimation complexity, and channel puncturing technique is exploited to correct the estimation error, thus realizing the robust performance of the communication system. The results obtained by Monte Carlo simulation and lake-trial are provided, demonstrating that the new pilot-free algorithm can significantly improve the performance of de-spreading algorithm under the circumstance of limited spreading length, and hence, increase the communication efficiency.
In this paper, we present a novel high-gain multiband surface-wave antenna base on extraordinary optical transmission. In order to make the performance of antenna more better we introduced metal wall structure, it can...
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ISBN:
(数字)9781728153049
ISBN:
(纸本)9781728153056
In this paper, we present a novel high-gain multiband surface-wave antenna base on extraordinary optical transmission. In order to make the performance of antenna more better we introduced metal wall structure, it can improve the gain of antenna and the half-power beamwidth also have a good embodiment in the E-plane and H-plane. Simulation results show that the gain of proposed antenna can reach more than 12 dB.
Tracking with multistatic sonar measurements is challenging due to the fact that the measurements are nonlinear functions of the Cartesian state. To obtain a global estimation of the target position, the existing appr...
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Tracking with multistatic sonar measurements is challenging due to the fact that the measurements are nonlinear functions of the Cartesian state. To obtain a global estimation of the target position, the existing approaches are to fuse local estimations of the target position or expand the measurement vector to be global. But those methods may cause large amounts of calculations due to the need for many Kalman filters or a high dimension of the measurement vector. The paper converted measurements from measurement coordinates to Cartesian coordinates to obtain the global estimation of the target position based on a Kalman filter and avoiding the high dimension problem, which means a low calculation cost. The performance of the proposed method is demonstrated by different simulated scenarios.
Main results of theoretical and experimental investigations since the 1980s of 20th century that led to the formation and developing of new fundamental science discipline: 'Fractal Radio Physics and Fractal Radio ...
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As a special bistatic configuration, space-missile borne bistatic synthetic aperture radar (SMB-BiSAR) is proposed, which has many potential applications in precision detection and guidance. Compared with traditional ...
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As a special bistatic configuration, space-missile borne bistatic synthetic aperture radar (SMB-BiSAR) is proposed, which has many potential applications in precision detection and guidance. Compared with traditional bistatic SAR, SMB bistatic SAR has complicated structure, and the imaging performance should be analyzed. In this paper, the geometric model of SMB-BiSAR is constructed in the reference target local (RTL) coordinate system firstly. Then, the range history is introduced with the vector notation. According to the range history, the Doppler properties and 2-D resolution are derived by using gradient method, and the forward-looking ability is demonstrated, which would guide the subsequent research. The simulations verify the validity of the analysis method.
An optimum strategy of reference emitter placement for dual-satellite time difference of arrival (TDOA) and frequency difference of arrival (FDOA) localization based on particle swarm optimization is proposed to impro...
ISBN:
(数字)9781538682463
ISBN:
(纸本)9781538682470
An optimum strategy of reference emitter placement for dual-satellite time difference of arrival (TDOA) and frequency difference of arrival (FDOA) localization based on particle swarm optimization is proposed to improve localization accuracy. Firstly Cramer-Rao lower bound (CRLR) of dual-satellite TDOA and FDOA localization system with ephemeris error and system error is derived. Then, the optimum strategy of reference emitter placement is transformed to multidimensional constraint optimization problem by using CRLB as the criterion for performance of dual-satellite TDOA and FDOA localization system. Finally, optimum strategy of reference emitter placement is obtained by using particle swarm optimization (PSO) to solve the target function. Simulation results demonstrate that the proposed method can derive optimum strategy of reference emitter placement validly. Besides, when the optimum strategy of reference emitter placement is applied, only two reference emitters are demanded to eliminate the effect of ephemeris error and system error on localization accuracy.
Here, a multi-beam TEM-horn antenna with beam direction is proposed. Presented construction allows obtaining scanning beam and complicated antenna patterns, thus it can be used as substitute of ultra-wideband phased a...
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The low altitude, slow speed and small size object which we call LSS-object for short, such as small UAV (unmanned aerial vehicles) have become a hot issue of air defense security, which is difficult to detect and ide...
The low altitude, slow speed and small size object which we call LSS-object for short, such as small UAV (unmanned aerial vehicles) have become a hot issue of air defense security, which is difficult to detect and identify accurately from the image. In this paper, aiming at the problem of LSS-object detection under noise environment, the detection method based on deep learning is proposed. Firstly, a standard training dataset consisting 5 classes of typical objects is constructed. Then, the standard dataset is augmented with noise of different intensity. Finally, YOLO v3 algorithm is used to form a LSS-object detection system which can adapt to environment noise. The training and detection experiments were carried out on the GPU server. After only using the noise-free dataset for training, the mAP(mean Average Precision) of the noise-free test set detection reached 81.07%, but the mAP decreased to 20.68% when the noise variance was *** adopting the mixed training strategy of the dataset with noise variance of 0.01 and noise-free data, the mAP for the test set detection with noise variance of 0.03 was increased to 70.61%, and the mAP still reached 79.85% in noise-free test set detection. The experiment results show that the mixed training strategy can greatly improve the accuracy in the noisy images detection while maintaining a higher accuracy in noise-free images.
The problem of stationary target location by multiple passive radar sensors that using unknown and non-cooperative opportunity illuminator is considered. Traditional two-step approach which estimating the time differe...
The problem of stationary target location by multiple passive radar sensors that using unknown and non-cooperative opportunity illuminator is considered. Traditional two-step approach which estimating the time difference of arrival (TDOA) and angle of arrival (AOA) firstly and locating using those parameters secondly. We explore the direct location with multiple passive radar sensors without estimating the intermediate parameters. As the reference path from the transmitter to receivers may be blocked in practice, we discuss the both cases that location without and with reference path. Two maximum likelihood algorithms of direct location are proposed for multiple passive radar sensors without and with reference. Monte Carlo simulations indicate that the direct location algorithm is superior to two-step approach with TDOA and AOA at low SNR for multiple passive radar sensors.
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