Supervising system for use in radio transmission

A phase shift monitoring system for a mobile communication system having a central station, one or more base stations coupled with said central station through a wired communication link, and a plurality of mobile radio stations linked with said base stations through radio communication links;

• said base stations, responsive to a command signal supplied from said central station, transmitting from time to time a specific signal common to said mobile radio stations through carrier waves of a common frequency, together with ordinary information signals for communication between said mobile radio stations and said central station, said specific signal having a predetermined repetition rate, characterized in that each of said base stations comprises:
• means for detecting said specific signal;
• means for providing a time reference pulse in timed relationship with said information signals;
• means responsive to said time reference pulse and said specific signal for determining whether the fluctuation in the timing of said specific signal is within a preset tolerable limit;
• means responsive to said determining means for generating an alarm signal when said preset tolerable limit is exceeded;
• and means for transmitting said alarm signal to said central station, and means for readjusting the transmission timing of said command signal to compensate for said fluctuation;
• whereby the specific signals are rendered in phase when transmitted at said base stations through said radio communication so that the interference caused at said mobile radio stations may be minimized.