A Multifrequency Seamless Dual-Link Handover Scheme Based on Beamforming for High-Speed Railway

Algorithm 1

A multifrequency seamless dual-link handover algorithm based on beamforming.

	Initialization: The train position is x, the train speed is  = 360 km/h, the cell radius is R, the overlap area length is Doverlap, and the distance between adjacent base stations is D. The front and rear antennas of the train receive signals. The positions of the front and rear antennas for the source BS are x + L, x respectively; the positions of the front and rear antennas for the target BS are D − x − L, D − x, respectively. The RSS of the front and rear antennas are calculated by equations (2) and (3), namely: SIRf,i(x + L), SIRf,j(2R − D − x − L), SIRr,i(x + L), SIRr,j(2R − D − x).
	Step 1 Handover preparation
(1)	The front antenna periodically sends a signal measurement report to the source BS
(2)	if
	Then, the front antenna is selected to communicate with the source base station.
	else Select the rear antenna.
(3)	if
	The target BS assigns a beam with a gain of GBF to the overlap region, and a gain of size GBF is obtained for the received signal of the target BS, which is as follows:
	end
	Step 2 Handover Execution
	while {0 < x < R}
	If
	&
	The front antenna triggers the handover.
	if
	the first phase of communication was interrupted.
	if
	The first antenna fails to handover.
	if N < m
	The front antenna continues to handover.
	else Front antenna fails to handover, which is expressed as  = 1. The rear antenna disconnects the communication link for switching. Now, . The second phase of communication is interrupted.
	else Successful handover
	if
	The rear antenna fails to handover,
	if M < n
	The antenna continues to handover.
	else (The entire handover process fails, continue to wait for judgment.)
	else the antenna is switched successfully.
	end
	end while
	Step 3 Handover Completion
	If any antenna is switched successfully, the other antenna can convert its communication frequency, and the entire handover is completed.