| 摘要 |
PROBLEM TO BE SOLVED: To avoid retrial of speech or transmission even when it is required to make speech or transmission in the case that the equipment passes through a location of a weak reception electric field strength by increasing a data transfer rate prior to entry to an obstacle. SOLUTION: A navigation system 3 retrieves an obstacle for radio wave transmission such as a tunnel or a skyscraper around a vehicle and provides the retrieval result to an obstacle arrival time estimate section 2. The obstacle arrival time estimate section 2 estimates a time of a radio wave reaching a transmission obstacle from a current vehicle position based on the distance between the vehicle and the obstacle for radio wave transmission such as a tunnel or a skyscraper and on the speed of the vehicle and provides the result of estimate to a transmission control section 1A. Then the transmission control section 1A uses a protocol to control the data transmission rate so as to increase it when the residual data amount during transmission is small in the case that the vehicle approaches the obstacle for radio wave transmission such as a tunnel or a skyscraper. |
