Patent ID: 7224980

Claim:
A radio system comprising: a portable device; and a stationary device for wirelessly communicating with said portable device, wherein said portable device operates such that when said portable device receives first signals from said stationary device, said portable device sends second signals representative of reception intensity data of the first signals back to said stationary device, and said stationary device sends the first signals from a plurality of stationary-device side antennae located at different positions respectively, and when said stationary device receives the second signals from said portable device through the respective stationary-device side antennae, said stationary device determines a position of said portable device by using the reception intensity data of the first signals included in the respective second signals, wherein said stationary device varies the setting of the relation of the amplitudes between transmission output powers of the first signals from said respective stationary-device side antennae and sends the first signals, and said stationary device determines the position of said portable device by using the reception intensity data obtained for each said setting, said stationary device is arranged to vary the setting of the relation between transmission output powers of the first signals among a plurality of conditions including at least a first condition, a second condition and a third condition, wherein in the first condition the transmission output power of one of the plurality of stationary-device side antennae is larger than an other of the plurality of stationary-device side antennae, in the second condition the transmission output power of the one of the plurality of stationary-device side antennae is equal to the other, and in the third condition the transmission output power of the one of the plurality of stationary-device side antennae is less than the other, the first signals include an identification code of each antenna and a condition code specifying which of said first condition, second condition or third condition is being used, the second signals, in addition to the reception intensity data, contain said antenna identification code and said condition code.