Location-Fair Beamforming for High Speed Railway Communication Systems

In this paper, transmission scheme for the base station with a large number of antennas in the high-speed train (HST) networks in the presence of Doppler shift is considered. A location-fair transmission scheme based on sectorized beams, in which the received signal-to-noise ratio or signal-to-interference-plus-noise ratio (SINR) inside the beam range varies little, is first proposed to counter the effect of high Doppler shift. An optimization problem for the beam design is formulated to maximize the expected average power within the beam coverage range with limited variation in the instantaneous received power in different locations. Subsequently, the two HSTs encountering scenario is considered. An optimization problem to maximize the sum transmission rate with suppressed average interference and limited variation in the instantaneous received SINR for each HST is formulated, which is nonlinear and cannot be solved directly. Alternatively, the objective function is shifted to minimizing the power consumption, for which an iterative algorithm to derive the optimal solution is designed. Through numerical results, the tradeoff between fairness and cumulated mobile service is demonstrated. Overall, a location-fair solution for the HST networks in the presence of Doppler shift is provided.