| 摘要 |
PURPOSE:To make it possible to perform data communication positively between a mobile station and a fixed station by specifying the fixed station whose frequency becomes the maximum strength of an electric field among the received field strengths from other fixed station when the received field strength becomes less than a judging reference value. CONSTITUTION:A fork lift 1B performs data communication with a radio apparatus 9B of a fixed station. The fork lift 1B is moved to the position of a fork lift 1D. When the radio waves of frequencies f1-f3 are transmitted from fixed stations 9A-9C at the same time for judging the positions, respectively, the lift 1B receives only the frequency f2. The received field strength is compared with a judging reference level. When the strength becomes less than the level, the lift 1B sequentially finds the received field strengths of the received frequencies f1 and f3 and specifies the frequency where the field strength becomes the maximum value, i.e., f3 at this time. The lift 1B transmits the frequency f3 as the position data. In a host computer 14, it is judged that the position of the lift 1B is the position close to the radio apparatus 9C. Thereafter, the communication is performed with the radio apparatus 9C. |
