Due to the diversity of underwater environments, it is difficult to test the underwater optical communication systems in actual seawater. This letter uses the Monte Carlo model to study channel capacity of underwater optical communications. Matlab is used to analyze the transmission of laser of various wavelengths in different water and the influence of changes in water quality. Furthermore, the influences of seawater type, divergence Angle, transmission distance and beam type on the power received by the receiver are analyzed when blue-green laser is used as the light source. The experiment shows that in the same water quality, with the increase of divergence Angle and transmission distance, the light intensity received by the receiver becomes smaller and smaller and the photon distribution becomes more and more dispersed. Compared with the Gaussian beam, when the attenuation coefficient is small, the energy of the receiving end is more concentrated when flat-top beam is used as the light source.
Due to increasing demand for high-speed and large capacity of data transmission, seamless connection between space network and Internet becomes one of the current trends of space communication. Under this background, this paper proposes an IPv6 over AOS gateway system based on FPGA to integrate the Internet and the space network. The system achieves protocol conversion to transmit IPv6 packets through the packet service in the AOS spatial data link protocol, and also has the function of address resolution and label switching. The main contents of this paper are as follows: 1. The IPv6 protocol, NDP protocol, MPLS technology and the conversion mechanism of IP over AOS protocol are studied. 2. The system test environment was set up to simulate the datagram transmission of spatial link between different node, the system performance and link stability were carried out by using logic analyzer and network packet capture tools. 3. The results of the function verification and performance test were analyzed and summarized according to packet loss rate and bandwidth availability ratio. The system achieves a variety of data types and large capacity information data transmission, it can also reduce networking costs while improving the transmission efficiency.
The digital micromirror device DMD is widely used in visible light projection, special-purpose spatial light modulation, and infrared scene simulation, due to its high resolution, uniformity and energy concentration. In some applications that require high frame rate scene image display, it is necessary to ensure that the DMD displays high gray level images at a high frame rate. However, the display frame rate of the pulse width modulation (PWM) method is limited by the minimum time required for DMD loading data, unable to achieve high frame rate display. Although the DMD binary display mode can meet the requirements of high frame rate display, it cannot meet the requirements of high gray level. The paper proposes an image display method that uses light source and DMD to synchronize modulation. Decompose the high-order gray image into bit planes according to the gray threshold, and the DMD displays each bit plane in binary mode under the trigger of an sync pulse. The intensity of the illumination laser source is modulated by an acousto-optic modulator to match the bit plane and the radiated laser power. This method makes use of the function of high frame rate display in DMD binary mode cooperate with light intensity modulation of illumination laser source, and realizes high frame rate and high dynamic range image display. With this method, the maximum frame rate of 8-bit gray level image with 1920 ×1080 resolution can reach 2KHz. The experimental system has realized 200Hz frame rate display of 8-bit gray level image with 1920 ×1080 resolution.
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