Patent ID: 8208928

Claim:
A mobile communication method in which a mobile station performs a handover from a handover source radio base station to a handover target radio base station via an inter-radio base station interface, the mobile communication method comprising the steps of: (A) acquiring, at the handover target radio base station, from the handover source radio base station, a first key for generating a certain key used in a communication between the handover target radio base station and the mobile station; (B) acquiring, at the handover target radio base station, from the switching center, a second key for generating a certain key used in a communication between a next handover target radio base station and the mobile station; and (C) updating, at the mobile station, upon receiving a handover command signal from the handover source radio base station, a first key for generating a certain key used in a communication between the handover source radio base station and the mobile station, to the first key for generating the certain key used in the communication between the handover target radio base station and the mobile station, wherein, in step (C), the mobile station updates the first key for generating the certain key used in the communication between the handover source radio base station and the mobile station, to the first key for generating the certain key used in the communication between the handover target radio base station and the mobile station, based on a parameter included in the handover command signal, and wherein step (C) further comprises the steps of: (C1) generating, at the mobile station, the first key for generating the certain key used in the communication between the handover target radio base station and the mobile station based on the parameter included in the handover command signal, when the parameter is incremented; and (C2) generating, at the mobile station, the first key for generating the certain key used in the communication between the handover target radio base station and the mobile station based on the first key for generating the certain key used in the communication between the handover source radio base station and the mobile station, when the parameter included in the handover command signal is not incremented.