To provide high speed mobile data to the passengers of HSR for infotainment services, the best option is LTE or LTE-R. High-speed railway (HSR) is one of the most important modes of passenger transport with many advantages, such as safety, high capacity, short intervals, and comfort. Experimental validation results reveal that providing multi-Gbps backhaul transmission is possible and worthwhile for both train and car scenarios. We then validate the proposed vehicular communication system by implementing an experimental testbed consisting of baseband modem, RF frontend, and array antenna units, and by performing field trials in an actual subway tunnel and urban road environments. Based on that, we provide a set of fundamental design elements including numerology, frame structure, reference signal, multi-antenna scheme, and handover. In order to support a very high data rate with such a high carrier frequency while guaranteeing sufficient robustness against high mobility-related behaviors such as fast channel variation and unstable handover, we employ a relaying network architecture consisting of a backhaul link to a vehicle UE and an in-vehicle access link. Employing a millimeter wave (mmWave) frequency band around 25 GHz, the proposed system provides mobile backhaul connectivity for vehicle user equipments (UEs). This paper proposes a vehicular communication system that can achieve multi-Gbps data rate transmission for train and car applications. Observing from the theoretical analysis and the simulation results, the proposed scheme can achieve low complementation complexity with high throughput performance. The optimal beam switching position could be calculated according to the requirements of the angular resolution. Neverthless, when the train moves at the cell edge, only one beam is activated due to the insupportable IBA. With this methodology, when the train is in the vicinity of the BS, all beams are activated to achieve the performance of high throughput. In order to overcome such difficulty, a low-complexity beam selection scheme based on multi-stream beamforming is proposed in this paper. 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. 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). 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.

In conclusion, both theoretical and simulation results show that the proposed scheme can efficiently perform seamless handover for high-speed rail with low implementation overhead. The simulation results show that in the proposed scheme, the communication interruption probability is smaller than 1% when the handover location is properly selected and the system throughput is not affected by handover. It can be seen from analytical results that the handover failure probability decreases as cell overlap increases and the communication interruption probability decreases with the decrease of train handover location and the increase of cell overlap. A complete handover protocol is designed and the performance of the proposed scheme is analyzed. Moreover, bi-casting is adopted to eliminate the data forwarding delay between the serving BS and target BS. In the proposed scheme, the front antenna executes handover while the rear antenna is still communicating with BS, so that the communication can keep non-interruptive throughout the handover. Aiming to reduce the interruption time, this paper proposes a seamless handover scheme based on a dual-layer and dual-link system architecture, where a Train Relay Station is employed to execute handover for all users in a train and two antennas are mounted at the front and rear of a train.

Due to frequent handovers in broadband wireless communications in high-speed rail, communication interruption during handover could seriously degrade the experiences of passengers on the train.

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