Patent ID: 7505428

Claim:
A time difference information supply system, comprising: a terminal unit for receiving satellite signals as signals from positioning satellites; and a plurality of communication base stations asynchronous with one another, which can communicate with the terminal unit and include base station time measuring means for measuring time of the communication base stations, transmission information producing means for producing transmission information containing transmission time, and transmission information transmitting means for transmitting the transmission information to the terminal unit on transmission radio waves, the terminal unit including distance information storing means for storing distance information indicating distances between the terminal unit and the communication base stations with which the terminal unit can communicate, satellite time synchronizing means for maintaining synchronicity with time of the positioning satellites based on the satellite signals from the plural positioning satellites, transmission radio wave receiving means for receiving the transmission radio waves from the plural communication base stations simultaneously or sequentially, reception time information producing means for producing reception time information indicating reception time of the transmission radio waves, communication base station distance acquiring means for acquiring distances between the terminal unit and the communication base stations from the distance information storing means, estimated reception time information producing means for producing estimated reception time information indicating estimated reception time of the transmission radio waves based on the transmission time contained in the transmission information and the distances between the terminal unit and the communication base stations, transmission time difference information producing means for producing transmission time difference information indicating differences of the transmission time based on the reception time information and the estimated reception time information, transmission time difference information storing means for storing the transmission time difference information of the plural communication base stations, time difference change rate information producing means for producing time difference change rate information indicating change rates of differences of the transmission time based on the plural transmission time difference information and the reception time information of the transmission radio waves on which the transmission information that the transmission time difference information is based upon is transmitted, and time difference change rate information storing means for storing the time difference change rate information.