To reduce the power consumption of a slave unit in an unconnected state denoting that the slave unit is not connected to a master unit.
At least one link channel is prepared to establish a wireless link between the slave unit and the master unit, the slave unit in an unconnected state broadcasts a connection request signal including the information of the slave unit and making a request connected to the master unit via one selected free link channel, awaits a connection request response signal including connection admission information transmitted from the master unit for receiving the connection request signal, and establishes the wireless link when the slave unit receives the connection request response signal within a prescribed time Taw after the transmission of the connection request signal. Further, when no free link channel is detected or no connection request response signal is received within the prescribed time Taw, the slave unit reaches a power-down state for a prescribed time Tpd wherein the power consumption level of the slave unit is lowered, and thereafter the slave unit restores from a power-down state to a free link channel selection state. The slave unit in the unconnected state denoting that the slave unit is not connected to the master unit accesses one or more link channels at random, then the probability of finding out the free link channel is increased and the time until the slave unit is connected to the link channel can considerably be reduced.
KAWAI KENJI
OTERU AKIKO
ICHINO HARUHIKO
