According to the general mobile radio communication technology, there has been realized a radio access system having radio cells (or cells) with which a bas station can communicate in an area defined around the base station, the radio access system accommodating a plurality of mobile terminals. The overall communication capacity of the radio access system is increased by using different frequencies and spreading codes between adjacent cells for reusing frequencies.
One example of a radio communication system which employs adaptive antennas in conventional mobile communications is disclosed in Japanese laid-open patent publication No. 7-87011. FIG. 1 of the accompanying drawings shows a pattern of beams radiated from a base station in an antenna device of the radio communication system disclosed in the above publication. As shown in FIG. 1, predetermined angularly narrow beams are generated in desired directions under directivity control to cover all bearings. The radio communication system disclosed in the above publication inspects a change in the intensity of received electric power which occurs as a communicating mobile unit (also referred to as “terminal station” in the present specification) moves and adapts itself to the movement of the mobile unit under directivity control.
Japanese laid-open patent publication No. 2000-22618 discloses a base station in a radio access system which changes the direction of an antenna and a beam angle based on the positional information of mobile terminals to minimize interferences between radio links to increase the number of mobile terminals that can be accommodated by cells of the base station. While the systems disclosed in Japanese laid-open patent publications Nos. 7-87011 and 2000-22618 predict positions and control beam directions and beam widths, they select beams of predetermined beam characteristics, and do not adaptively control beam characteristics to form nulls in the directions of given interference signals by adapting themselves to radio wave environments.
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