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Wireless sensor network is an emerging network technology in the 21 st century. Its emergence brings a new phase in the development of network. Lately, there are more and more investigations on wireless sensor network MAC protocols. The research results on MAC protocol is summarized, some typical MAC protocols are analyzed, such as S-MAC, T-MAC, -MAC, and etc. A new power controlled sensor MAC protocol(PC-MAC) is introduced for wireless sensor networks, which can provide an effective mechanism for improving energy efficiencies for decreasing the transmitting power directly and avoiding collision. The simulation results show that energy can be saved up to 50%-96% by it.

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Studies on the direction distribution of laser beam intensity reflected from the sea surface is important for engineering practice in the area of optoelectronic confrontation on the sea surface. In the traditional theory of electromagnetic scattering from rough surfaces, the scattered field from the sea surface can be obtained by solving the Maxwell's equations. As is well known, it is difficult to solve the Maxwell's equations. Therefore, the numerical calculation method and approximate analytical method are used to obtain the scattered field from the sea surface. However, for the numerical calculation method, it is difficult to meet the computing requirements of large electrically targets such as the sea surface. Meanwhile the approximate analytical method has certain restrictions on the parameters of rough surface in physical approximation. What is more, the inherent error is also caused by the physical approximation. In this paper, we investigate the laser beam reflection from rough sea surface with Monte Carlo method and principles of geometric optics. The rough sea surface which is simulated with the fractal method is divided into a lot of small planes, and the mathematical equations to describe the geometric characteristics of the planes are established in the sea reference coordinate system. After that, based on the simulation of Gaussian beam with Monte Carlo method, the laser beam is divided into a great number of rays and the statistical properties of the rays satisfy the propagation characteristics of Gaussian beam. Then, the laser beam reflection model from the sea surface is derived in the reference coordinate system. The direction distribution of the laser beam intensity reflected from the sea surface is simulated under a certain experiment condition with this model. The results show that the simulation results of laser beam reflection from the sea surface fit the experimental results well.