A Rate-Splitting Based Bound-Approaching Transmission Scheme for the Two-User Symmetric Gaussian Interference Channel with Common Messages

This paper is concerned with a rate-splitting based transmission strategy for the two-user symmetric Gaussian interference channel that contains common messages only. Each transmitter encodes its common message into multiple layers by multiple codebooks that drawn from one separate code book, and transmits the superposition of the messages corresponding to these layers; each receiver decodes the messages from all layers of the two users successively. Two schemes are proposed for decoding order and optimal power allocation among layers respectively. With the proposed decoding order scheme, the sum-rate can be increased by rate-splitting, especially at the optimal number of rate-splitting, using average power allocation in moderate and weak interference regime. With the two proposed schemes at the receiver and the transmitter respectively, the sum-rate achieves the inner bound of HK without time-sharing. Numerical results show that the proposed optimal power allocation scheme with the proposed decoding order can achieve significant improvement of the performance over equal power allocation, and achieve the sum-rate within two bits per channel use (bits/channel use) of the sum capacity

Novel double-layer DC/AC railway traction power supply system with renewable integration

Back-to-back converter based railway traction power supply system (TPSS) can eliminate neutral sections in the traction side and improve power quality in the grid side, but it still has some drawbacks such as low reliability, difficulty in accepting large-capacity renewable energy, and power mismatches. In this study, a double-layer DC/AC TPSS with renewable integration is proposed to address these challenges and to improve system performance. The proposed topology breaks the limit of back-to-back structure and enables more flexible free energy flow. A top-down system design method is proposed in this study. Firstly, the characteristics of the proposed TPSS for integration with renewable power are described and compared with the traditional back-to-back topology. Secondly, a DC droop controller and a AC droop controller are designed for DC layer grid and AC layer grid, respectively, to control the power flow in each layer. The traditional AC droop control is based on the inductive transmission impedance, but the resistance of traction transmission line cannot be ignored. Thus, a modified droop control strategy with the consideration of line resistance is also proposed in this study. Subsequently, the voltage control strategy for the single modular multilevel converter is designed to track the reference signal from the upper droop controller. Finally, a general double-layer DC/AC TPSS is designed from bottom to top, and the simulation results confirm that the proposed TPSS with renewable integration is capable of delivering desirable performance

Inflationary magnetogenesis with a self-consistent coupling function

In this paper, we discuss the inflationary magnetogenesis scenario, in which the coupling function is introduced to break the conformal invariance of electromagnetic action. Unlike in conventional models, we deduce the Maxwell's equations under the perturbed FRW metric. We found that, the self-consistency of the action depends on the form of the coupling function when the scalar mode perturbations have been considered. Therefore, this self-consistency can be seen as a restriction on the coupling function. In this paper, we give the restrictive equation for coupling function then obtain the specific form of the coupling function in a simple model. We found that the coupling function depends on the potential of the inflaton and thus is model dependent. We obtain the power spectrum of electric field and magnetic field in large-field inflation model. We also found that the coupling function is a incresing function of time during slow-roll era as most of inflationary magnetogenesis models, it will lead to strong coupling problem. This issue is discussed qualitatively by introducing a correction function during the preheating