Radiotelephone system with central office having individual processors assignable to respective mobile units aboard communicating vehicles

Abstract

Abstract A central office, designed for short-wave radiocommunication with mobile units aboard several vehicles in its area, has a plurality of fixed processing units operating on different frequency channels to communicate with various vehicle-borne mobile units in the area. Each processing unit includes a programmer (PG) which measures the response periods of a mobile unit to calling and switching signals transmitted by the central office and terminates the connection in the case of excessive delays. Each mobile unit has a transceiver tunable to any of these channels under the control of a ring counter (CA) which, on being started by an alert signal from the central office (in response to an incoming call) or by actuation of a hook switch aboard the vehicle (to initiate an outgoing call), drives the transceiver through all or part of a scanning cycle until a free channel has been found or until the search is halted by a concurrently actuated delay counter (CR). In either case, the ring counter locks the transceiver to the channel last explored until the next call is initiated. Each channel comprises two carrier waves modulated by a selected pair of audio frequencies out of a total of six such frequencies (f1 - f6) available for the transmission of numerical information in either direction; a seventh frequency (f7) is used in combination with two of the others (f5, f6) to pass switching or supervisory signals from the central office to the vehicle. If the call number of the mobile unit and/or of a station called from the vehicle includes two or more like digits in immediate succession, a repetition code (R) is substituted for the second, fourth etc., iterative digit to facilitate recognition of transition from one digit to the next.

Inventors

• 👤 L Sarati
• 👤 V Intini

Bibliographic Details