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Seamless handover for high mobility environments

As a major 5G scenario, high mobility up to 500km/h is an important feature to be supported and will pose conspicuous challenges to wireless communication systems. But compared with other features, provisioning highly reliable services for users or devices in high mobility environments has not received enough attention. Especially, handovers in mobile communication systems for high-speed railways (HSR) were treated with overly simplified assumptions, which may lead to ineffective designs and undermine railway safety or users' experience. This paper attempts to analyze the phenomenon of variant Doppler effects in typical high mobility environments and its impacts on wireless transmission. A general soft handover scheme using dual-link structure and beamforming is proposed based on a brief survey of previous studies. Finally, an effort is made to extract some guidelines for constructing soft handovers to achieve seamless transmission in high mobility environments.