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With the large resources invested by many countries in the world, the networks of quantum communication have been developed. However, with the increase of communication distance, the losses on the communication line will greatly limit the distance of quantum communication. On the other hand, the no-cloning theorem that protects the security of quantum communication also restricts the application of classical repeater stations through amplifying the attenuated signal in quantum communication. To resolve this problem, the concept of quantum repeater (QR) protocol was proposed. The protocol uses the unique characteristics of quantum mechanics such as entanglement swapping (ES) to further distribute quantum correlations, entangle the nodes that have never interacted, and even resist losses caused by the transmission lines to achieve long-distance quantum communication. In this article, we discuss the difficulties encountered by quantum communications over long-distance transmissions and explain the solution: QR protocol. With the different architectures of QR protocol, their protocols can be divided into memory-based and all-optical types. We will introduce the physical principles of the two different types of QR and the process of the protocol. We also report on some recent progresses of QR. In addition, we also discuss the twin-fi eld quantum key distribution (TFQKD) scheme, recently proposed for long-distance quantum communication. We believe that this report will help the readers to understand the architecture of long-distance quantum communication and the technical challenges that it faces. [ABSTRACT FROM AUTHOR]

For the motion law of automatic inspection equipment for repeater station on rigid pavement, the kinematics model of automatic inspection equipment is established, and the dynamic analysis of wheel-ground contact force is carried out, on this basis, the slip ration is estimated by use of Burckhardt model. The simulation experimental data and theoretical experimental data of the automatic inspection equipment were obtained by using ADAMS and MATLAB respectively. The data analysis shows that the error mainly comes from the friction vibration between the tire and the ground. The displacement error between theoretical data and simulation data is less than 0.0154m under the experimental conditions of dry concrete pavement and turning radius of 1.192m. The result indicates that the kinematics model can be used for the prediction of trajectory of skid steering for inspection equipment under rigid pavement conditions. [ABSTRACT FROM AUTHOR]