Optimal Multicell Coordinated Beamforming for Downlink High-Speed Railway Communications

Abstract

This paper investigates the multicell coordinated beamforming (MCBF) design for high-speed railway communications, where a high-mobility train goes through a multicell multiuser system in urban areas. All passengers in the train are aggregated to be a high-mobility “big user.” In order to explore the downlink system performance limit, we formulate an optimization problem to maximize the information rate from the serving base station to the high-mobility train while guaranteeing the minimal required achievable information rates of all low-mobility users outside the train by optimizing MCBF vectors. The interchannel interference (caused by Doppler effect to the train), the intercell interference and the interuser interference are jointly considered. Since the problem is nonconvex and cannot be solved directly, we first introduce an auxiliary variable (AV), and for a given AV, we find the optimal MCBF vectors via solving a second-order cone programming. Then, by updating the AV with the bisection method, the corresponding global optimal MCBF vectors are numerically obtained. Simulation results show that our proposed MCBF design greatly enhances the information throughput of the high-mobility train without degrading the required data rates of low-mobility users.