Abstract-Cloud Radio Access Network (C-RAN) is a novel mobile network architecture which can address a number of challenges the operators face while trying to support growing end-user's needs. The main idea behind C-RAN is to pool the Baseband Units (BBUs) from multiple base stations into centralized BBU Pool for statistical multiplexing gain, while shifting the burden to the high-speed wireline transmission of In-phase and Quadrature (IQ) data. C-RAN enables energy efficient network operation and possible cost savings on baseband resources. Furthermore, it improves network capacity by performing load balancing and cooperative processing of signals originating from several base stations. This article surveys the state-of-the-art literature on C-RAN. It can serve as a starting point for anyone willing to understand C-RAN architecture and advance the research on C-RAN.

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Inspirited by the wide range of applications of graphene and the similarity between boron and carbon, 2D boron sheets have gained extensive research interest. In this work, using first-principles combined with a nonequilibrium Green's function method, thermal conductance of fully hydrogenated borophene, named borophane, is studied. Interestingly and in contrast to widely perceived sense, at 300 K, it is found that the thermal conductance of borophane in the armchair direction is remarkably larger than that of graphene. More interesting, a dimensionality crossover is observed in phonon transmission where low-frequency phonons exhibit 2D characteristic, while high-frequency phonons behave like a 1D system, oriented along armchair direction, which results in the ultrahigh thermal conductance. An anomalous increase of thermal conductance with uniaxial tensile strain is observed, which is well explained by the unique puckered structure and chemical bonding in borophane. The excellent in-plane stiffness and flexibility together with the high thermal conductance suggest that borophane is promising for soft thermal channel. Moreover, this unique dimensionality crossover in phonon transmission offers a perfect platform for studying the effect of phonon population in mode space, which is of primary importance for thermal transport in low-dimensional systems.

Heat energy in solids is carried by phonons and electrons. However, in most two-dimensional (2D) materials, the contribution from electrons to total thermal conduction is much lower than that for phonons. In this work, through first-principles calculations combined with non-equilibrium Green's function theory, we studied electron and phonon thermal conductance in recently synthesized 2D hydrogen boride. The hexagonal boron network with bridging hydrogen atoms is suggested to exhibit comparable lattice thermal conductance (4.07 nWK −1 nm −2) as graphene (4.1 nWK −1 nm −2), and similar electron thermal conductance (3.6 nWK −1 nm −2), which is almost ten times that of graphene. As a result, total thermal conductance of 2D hydrogen boride is about twofold of graphene, being the highest value in all known 2D materials. Moreover, tensile strain along the armchair direction leads to an increase in carrier density, significantly increasing electron thermal conductance. The increase in electron thermal conductance offsets the reduction in phonon thermal conductance, contributing to an abnormal increase in thermal conductance. We demonstrate that the high electron density governs extraordinarily high thermal conductance in 2D hydrogen boride, distinctive among 2D materials.

The direct torque controlled permanent magnet synchronous motor (PMSM) drive has become competitive compared with other types of drive systems because of its simple and sensorless control algorithm. The application of the system, however, is handicapped by the difficulty of starting under full load due to the unknown initial rotor position. This paper presents a nonlinear model of PMSMs which incorporates both the structural and saturation saliencies to enable the numerical simulation of rotor position detection algorithms. In this model, the phase inductances are expressed by Fourier series as the functions of the stator current and rotor position. The measurement of the inductances on a surface mounted PMSM is outlined. The simulation of direct torque control (DTC) on PMSM is conducted by using the proposed model, and the results are compared with that obtained by the PMSM model in the Simulink library. The performance of an initial rotor position estimation scheme with the model is simulated. Experiment is carried out based on the same algorithm to verify its validity. The effectiveness of the scheme to estimate the initial rotor position for an SPMSM is discussed and verified by numerical simulation.