| 摘要 |
In a location monitoring system for monitoring the location of a plurality of mobile units operating on preestablished routes from a centrally located control station, and where each mobile unit (14) communicates partly with a base station (10), partly with signposts (15, 16) located in specific positions along the known routes, from which the mobile units (14) receive position-specific information during passage, the transmitters (12, 15) in both the base station (10) and in each individual signpost (15, 16) are arranged to have the same operating frequency (F1). This saves an extra receiver in each of the mobile units (14) while minimizing the need for transmission channels. Moreover, the antenna (16) of the signpost has been given a signal emission in a narrow range around it and with such signal strength that the message acceptance to the signals of a signpost (15, 16) during the passage thereof is reasonably good (50%), and at the same time the probability that a message from the base station (10) is not received is very low (=0.1). |
