In a CSMA wireless LAN, a sector antenna power detectors detects the power received
by antenna elements of a sector antenna. A reference power generator generates
a reference power, and a comparator compares the detected power with the reference
power. A controller unit, based on the comparison result, determines whether there
is a hidden terminal station. If a hidden terminal station is determined to exist,
the controller outputs control signals so as to direct the terminal station to
increase the transmission power. The terminal station in turn will increase the
transmission power in response to the control signals to widen the communication area.