Low-Complexity Beam Selection Scheme for High Speed Railway Communications

Large-scale multiple input multiple output (MIMO) assisted beamforming based on millimeter waves is an effective way to increase system capacity and data transmission rate for high speed railway (HSR) communication systems. To reduce the number of handovers and improve system throughput, multi-stream beamforming with different beamwidths is used as the transmit beam at the base station (BS). However, when the train moves toward the cell edge, the inter-beam ambiguity (IBA) between multiple beams becomes more and more serious, and the performance of the system will decrease significantly if multiple beams are still activated simultaneously. In order to overcome such difficulty, a low-complexity beam selection scheme based on multi-stream beamforming is proposed in this paper. With this methodology, when the train is in the vicinity of the BS, all beams are activated to achieve the performance of high throughput. Neverthless, when the train moves at the cell edge, only one beam is activated due to the insupportable IBA. The optimal beam switching position could be calculated according to the requirements of the angular resolution. Observing from the theoretical analysis and the simulation results, the proposed scheme can achieve low complementation complexity with high throughput performance.