| 摘要 |
PROBLEM TO BE SOLVED: To reduce the communication expenses of a terminal by making the communication with and data reception from external equipment only when the reception sensitivity is low. SOLUTION: A headquarters server 2 receives GPS signals from a reception antenna 3 and calculates Doppler data and GPS navigation data after discriminating the propriety of the S/N of the signals. On the other hand, a terminal 4 detects the intensity of the reception electric field through another reception antenna 6 and, when the electric field is good, extracts the navigation data and Doppler data on the terminal 4 side. When the electric field is bad, the terminal 4 extracts the navigation data and Doppler data from the server 2. Then the terminal 4 decides a memory section and a calculated section in accordance with the detected intensity of the reception electric field and stores the received GPS signals in a memory. Thereafter, the terminal 4 performs Doppler correction on the received GPS signals, divides the corrected data into sections with the navigation data, and obtains a pseudo range by finding the point at which the correlative value becomes the maximum by means of a correlative peak position detecting section. The terminal 4 calculates its position by using the pseudo range and extracted navigation data. |
