Direct-adaptation based bidirectional turbo equalization for underwater acoustic communications: Algorithm and undersea experimental results.

The direct-adaptation based turbo equalizer (DA-TEQ) has been widely studied for underwater acoustic communications due to its decent performance and simple implementation. However, there are still some inherent problems that limit its practical application, such as slow convergence rate and error propagation effect. In this paper, a direct-adaptation based bidirectional turbo equalizer (DA-BTEQ) is proposed for underwater acoustic communications. The proposed scheme incorporates a forward DA-TEQ with a backward DA-TEQ to exploit bidirectional diversity gain and combat error propagation, thereby enabling faster convergence rate and better symbol detection performance. A general symbol combining scheme, which is suitable for turbo equalizers with high-order modulations, is derived by using the minimum mean square error criterion. The proposed scheme has been tested by the undersea trial data collected in an experiment conducted at the coast of Jiaozhou Bay in March 2017. The results demonstrate that the DA-BTEQ is effective against error propagation and clearly outperforms the traditional single-direction DA-TEQ for both single-input multiple-output and single-input single-output systems.

A Review of Research on Mechanical Properties and Durability of Concrete Mixed with Wastewater from Ready-Mixed Concrete Plant.

The wastewater from ready-mixed concrete plants is currently being recycled as concrete mixing water. It has attracted significant attention from the construction industry and researchers since it promotes sustainable development through environmental protection, energy-saving, and emissions reduction. This article review first introduces the nature of wastewater in ready-mixed concrete plants in different regions. Then the effects of solid content in water on various properties of concrete, including working performance, durability and microscopic properties, are reviewed, respectively, when concrete is mixed with wastewater instead of tap water. Furthermore, the microscopic mechanism of action in concrete mixing with wastewater is discussed, and future work is recommended. This review provides fundamentals on the study of the properties of concrete after wastewater is mixed into concrete.