Two-way paging system and apparatus

A wireless paging unit capable of receiving alert messages transmitted thereto from a paging network and capable of transmitting an acknowledgment of receipt thereof, comprising:

• antenna means for receiving and transmitting signals;
• a receiver connected to said antenna means for receiving a signal and converting said signal to numerical samples when indicated by a timing control means;
• memory means for storing said numerical samples in time order of reception;
• processing means for processing said stored numerical samples to determine a location in said memory means of a predetermined signal pattern and to generate a time-of-arrival indication based on said location;
• and
• timing control means for receiving said time-of-arrival indication and for activating a transmitter to transmit a digitally coded reply with a predetermined timing related to said indicated time-of-arrival.

A wireless paging unit capable of receiving alert messages transmitted from a paging network and of transmitting a reply in response to receipt thereof, comprising:

• a first oscillator means for determining a receiver power down period based on a calibration count value;
• a second oscillator means for determining operating channel frequencies of said receiver and of a transmitter;
• said receiver being activated by a signal controlled by said first oscillator means to receive and process a signal received on a receive operating channel frequency and to produce a time-of-arrival and frequency error indication from said received signal;
• frequency correction means for using said frequency error indication to correct said second oscillator means and to use said corrected second oscillator means to perform a calibration measurement to determine said calibration count value;
• and
• timing control means for receiving said time of arrival indication and in response thereto for activating a transmitter to transmit a digitally coded reply having a predetermined timing related to said indicated time-of-arrival and at an operating channel frequency derived from said second oscillator means and compensated for said frequency error.