Patent 8942117 was granted and assigned to Hitachi, Ltd. on January, 2015 by the United States Patent and Trademark Office.
A frame time having a certain period of time is divided into: a time period (for inter-base-station time division multiplex communication) in which one of the base stations has a transmission right in the simultaneous transmission and carries out inter-base-station time division multiplex communication so as to avoid interference between the base stations; and a time period (for inter-base-station simultaneous communication) for communication which is simultaneously carried out between the plurality of base stations. Furthermore, the time periods are switched for the communication.