Patent ID: 7353391

Claim:
An authenticating method for portable radio devices, comprising data communicating means for performing radio communication over a first coverage area and authenticating means for performing authentication of said portable radio devices over a second coverage area, comprising the steps of: switching coverage area of two or more of said portable radio devices, prior to initiating authentication between the portable radio devices, from the first coverage area to the second coverage area, the second coverage area being smaller than the first coverage area; bringing, prior to initiating authentication between the portable radio devices, the two or more portable radio devices having the second coverage area to within a proximity of one another so that the coverage areas of the two or more portable radio devices overlap; initiating mutual authentication by establishing communication between the two or more portable radio devices based only on the bringing of the two or more portable radio devices to within the proximity; and performing mutual authentication between the two or more portable radio devices by said authenticating means automatically when the coverage area of the two or more portable radio devices overlap.