Search

Signal enhancement has always been one of the important fields of acoustic signal processing. The purpose of signal enhancement is to eliminate noise as far as possible from noisy signal, and to improve signal to noise ratio (SNR) for later signal processing. Some traditional algorithms can reduce the background noise, but the effect is not significant and also cause a lot of damage to the pure signal. With statistical theory, this paper proposes a signal enhancement algorithm based on Short-time magnitude spectrum estimation-Minimum mean square error estimation (MMSE), It can realize the signal enhancement by introducing the prior SNR and the posterior SNR in the calculation of the gain function. The results show that this method can suppress noise effectively, improve SNR and reduce the damage to the expected signal. At the same time, the algorithm has small calculation and can be processed in real time, which has important practical significance in engineering application.

Warship systems which belong to cyber-physical systems (CPSs) are facing severe cyber security challenges with the adoption of large amount of Information Technology. Security events happened in warship systems can cause serious consequences, such as death of person, destruction of warship and even the failure of the war, which are quite different from IT systems. This paper proposes a comprehensive resilient security protection framework which combines static security protection and dynamic security protection after analyzing warship systems security situation. In the framework, some prevention and isolation techniques are used for static protection to reinforce the security, and a close-loop based security protection with ability of intrusion tolerance is achieved for dynamic protection to realize active defense. This framework contributes to warship security design for designers and promote warship cyber security against cyber attacks.

Channel estimation is an important procedure of coherent demodulation of OFDM system for underwater acoustic communications, by which the system performance is largely restricted. In this paper, the performance of three pilot patterns and their own application conditions are analyzed and compared. According to the simulation and experiment results, it is concluded that scatter pilot pattern is very suitable for OFDM system for underwater acoustic communications. In addition, vector hydrophone is also can be used to improve communication performance via joint processing of pressure and particle velocity.

Vector hydrophone has natural dipole beam-pattern, and can also simultaneously and colocatedly measure the scalar and vector information of ocean acoustic field, which makes it convenient to determine the direction of arrival (DOA) and represent the stable interference structure of vector acoustic field. Utilizing the DOA and interference structure information together acquired by single vector hydrophone, it is able to position the target of interest. Firstly, bearing-time course for passing-by target is obtained by using the line or continuous spectrum imbedded in the received signal of vector hydrophone. Then, CPA ratio between the CPA range and speed of target as well as CPA instant are estimated on the basis on LMS criteria. Finally, the speed of target can be determined through the theoretically predicted interference range and the real interference time interval to fulfill target positioning including DOA and range. The idea was effectively validated during the experiment that took place in October of 2010 in South China Sea nearly 100m depth. Moreover, the idea presented here can be easily extended for further application such as combining the waveguide invariant. [Work supported by the National 863 Project (No. 2011AA090502) and National Defense Foundation Project (B2420132004).]