MOBILE DATA COMMUNICATION SYSTEM

摘要

A mobile data communication system in which a fixed station consecutively interrogates a fleet of vehicles to receive and send messages thereto. A receiver of the fixed station effects for each vehicle in turn synchronism with the reply message transmitted by the relevant vehicle. To do this the bit phase error between the reply message signal and a clock signal produced by the fixed station is measured in the latter by means of a phase discriminator 22 and corrected in a control loop comprising also an integrator 23 an adder 21 and a divider 18 as shown in FIG. 2. A store 26 stores information relating to the position of the vehicles, and control means use this information to produce a control signal corresponding to the bit phase error caused by the time delay of the message from the fixed station to the vehicle and vice versa. A switch 24 is operated at the beginning of each message sequence to feed the control signal into the control loop to practically correct the bit phase error.