A base station includes an obtaining unit and an instructing unit. The obtaining unit obtains, from another base station that communicates with a mobile device, a propagation delay amount between the other base station and the mobile device. When a propagation delay amount between the base station and the mobile device which is based on the propagation delay amount obtained by the obtaining unit is present within a predetermined range from a boundary of a detecting window that is used in detecting a preamble sequence transmitted from the mobile device, the instructing unit instructs the mobile device to stop the transmission of the preamble sequence corresponding to another detecting window that lies adjacent across the boundary.