Patent ID: 7298729
Filing Date: 2007-11-20
Classification: G04R,H04W

Abstract:
1. A radio communication system comprising: first and second portable terminals each of which is assigned a unique identifier and has a display for displaying time information and time difference information and a timepiece for measuring current time; and a first switching network having first and second base stations which are assigned unique identifiers and perform radio communication with said first and second portable terminals, a first switching unit connected to said first and second base stations, a first database which stores positions of said first and second portable terminals in association with positions of said first and second base stations, and a second database which stores pieces of time difference information of said first and second base stations, wherein said first portable terminal comprises time difference acquisition request means for adding the identifier of said second portable terminal and issuing a time difference acquisition request for said second portable terminal to said first base station when said second portable terminal connected to said second base station is to be called via said first base station, and current time calculation means for calculating current time of said second portable terminal on the basis of time difference information sent from said first base station in response to the time difference acquisition request from said time difference acquisition request means and time information from said timepiece, and outputting the current time of said second portable terminal to said display, said first base station adds the identifier of said first base station to the time difference acquisition request containing a terminal identifier received from said first portable terminal, and transmits the time difference acquisition request to said first switching unit, said first switching unit comprises first time difference acquisition means for acquiring the time difference information of said first base station from said second database on the basis of the identifier of said first base station contained in the time difference acquisition request received from said first base station, position information acquisition means for acquiring position information of said second base station containing a base station identifier from said first database on the basis of the identifier of said second portable terminal contained in the time difference acquisition request received from said first base station, second time difference acquisition means for acquiring the time difference information of said second base station from said second database on the basis of the base station identifier contained in the position information of said second base station output from said position information acquisition means, and time difference calculation means for calculating a time difference between said first and second base stations by using pieces of time difference information output from said first and second time difference acquisition means, and transmitting a calculation result to said first portable terminal via said first base station.