An mmWave-Based Adaptive Multi-Beamforming Scheme for High Speed Railway Communications

Focusing on the increasingly growing demands for tremendous data rate and reliable mobile services in the high speed railway (HSR) communication systems, it is essential to explore an effective solution to enhancing the system capacity. The directional beamforming combined with millimeter wave (mmWave) technology remains to be one of the most potential ways to increase the throughput in the future HSR networks. Therefore, an mmWave-based adaptive multi-beamforming scheme for HSR communications is proposed in this paper. In the proposed scheme, multiple beams with different beamwidth are formed by the base station (BS) simultaneously to improve the system capacity. The mobile relays (MRs) are provided with the ability to adjust the receiver (RX) beams automatically during a transmitter (TX) beam to enhance the received signal-to-noise ratio (SNR). The outage probability could be decreased dramatically in this scheme because that the connection drop occurs only if the multiple beams miss the communication at the same time. Unfortunately, when the train moves to the edge region of the cell, the increasing inter beam interference (IBI) will degrade the system performance. Thus, a novel adaptive algorithm adjusting the activated beams in real time is presented in this scheme to mitigate the IBI and maintain an optimal capacity. Theoretical analysis and simulations are conducted to verify that the proposed scheme can improve the throughput with a lower outage probability in HSR scenarios.