Anti error and erasure coding for water-to-air visible light communication through wavy water surface with wave height up to 0.6 meters.

Considering large dynamic optical intensity range in a water-to-air (W2A) channel, we propose two promising channel coding schemes, namely the concatenated Reed Solomon-Low Density Parity Check (RS-LDPC) code and Raptor code, for W2A visible light communication (VLC). We establish a W2A-VLC link to verify the performance under different wavy water environments and different water depths with a green light emitting diode (LED). A wave generator is adopted to emulate the wavy water surface with wave height up to 0.6 m. The receiver is fixed 3.2 m above the water, and the transmitter varies from 2.5 m to 4.0 m under the water through a up-down-moveable platform. We test the coding schemes with different code lengths and code rates under 5 MSym/s air-interface symbol rate. Experimental results show that both schemes can reduce the bit error ratio (BER) and frame error rate (FER) of a W2A-VLC system, and thus can improve the reliability. Via comparing the two codes with the same overhead and approximately the same code length, it is demonstrated that Raptor code can generally outperform the concatenated RS-LDPC code. Our research provides promising channel coding methods without feedback for a W2A-VLC system.

A simple strategy for converting starch to novel compressible carbonaceous foam: mechanism, enlightenment and potential application.

Preparation of new materials from biomass is good for sustainable development. Carbon/carbonaceous foams (CFs), as important materials widely applied in both military and civil use, are usually made from nonrenewable materials at high temperature (usually over 1000 °C) and high pressure (at MPa magnitude). Although some biomass raw materials have been used, there is still a fascinating issue waiting to be discussed. That is, what kind of biomass would be suitable for making CFs, or what the biggest challenge might be if these raw materials are used. Herein, a CF with advanced compressibility was made from starch with a simple and energy efficient strategy. The product can be made at much lower temperature (below 500 °C) and pressure (∼190 Pa) than conventional strategies. The understanding of the conversion mechanism provides inspiration for the conversion of other biomass into value-added carbonaceous materials. Due to the presence of reactive groups on the surface of the as-prepared CF, the product can be further modified or used as a substrate to prepare composites for catalysis, phase change energy storage, sensors, water purification, and so on. In this work, its potential application in oil/water separation was demonstrated.