# US 5,708,971 A · Two-way paging system and apparatus > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 5,708,971 A - Document ID: US5708971A - Status: Granted - Kind: A - Application number: 08/402,947 - Filed: 1995-03-13 - Granted: 1998-01-13 - Earliest claimed: 1994-01-11 - Assignees: Ericsson Inc. - Inventors: Paul W. Dent - Web page: https://patentgrep.com/patent/US5708971A ## CPC - H04W 84/025: {with acknowledge back capability} - G08B 3/1008: {Personal calling arrangements or devices, i.e. paging systems (selective calling systems and call receivers H04W84/00, H04W68/00)} - H01Q 1/246: {specially adapted for base stations} - H01Q 21/08: the units being spaced along or adjacent to a rectilinear path {(waveguide fed H01Q21/0037)} - H01Q 21/28: Combinations of substantially independent non-interacting antenna units or systems {(multiple beam H01Q25/00)} - H04B 7/0851: {using training sequences or error signal (minimizing error signal H04B7/0854)} - H04B 7/10: Polarisation diversity; Directional diversity - H04B 7/18513: {Transmission in a satellite or space-based system} - H04B 7/18515: {Transmission equipment in satellites or space-based relays} - H04B 7/18532: {Arrangements for managing transmission, i.e. for transporting data or a signalling message} - H04B 7/18567: {Arrangements for providing additional services to the basic mobile satellite telephony service} - H04L 1/0069: {Puncturing patterns} - H04L 1/0071: {Use of interleaving (interleaving per se H03M13/27)} - H04L 1/06: using space diversity - H04L 25/03331: {Arrangements for the joint estimation of multiple sequences} - H04W 16/28: using beam steering - H04B 7/0837: {using pre-detection combining (H04B7/0868 takes precedence)} - H04L 2001/0098: {Unequal error protection} - H04W 88/022: {Selective call receivers} - H04W 88/185: {Selective call encoders for paging networks, e.g. paging centre devices} - H04W: WIRELESS COMMUNICATION NETWORKS (broadcast communication H04H; communication systems using wireless links for non-selective communication, e.g. wireless extensions H04M1/72) - G08B: SIGNALLING SYSTEMS, e.g. PERSONAL CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS - H01Q: ANTENNAS, i.e. RADIO AERIALS (radiators or antennas for microwave heating H05B6/72) - H04B: TRANSMISSION - H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M) ## Abstract Paging systems typically include a network of ground stations or orbiting satellites equipped with transmitters and antennas for transmitting paging messages to small, battery-operated paging receivers that are worn about the person, known as pagers. Conventional pagers are receive-only devices and the network receives no confirmation that paging has been successful. The present invention includes the provision of two-way pagers that contain a transmitter for transmitting an acknowledgment confirming reception of a paging message, and a network of receiving stations able to receive said acknowledgments. The network makes use of advanced phased-array antenna signal processing techniques to render the return link operable with much less transmitter power in the portable unit than employed by the base station. ## Claims ### Claim 1 A wireless paging unit for receiving alert messages addressed thereto transmitted by a paging network and for transmitting an acknowledgment in response to receipt thereof, comprising: antenna means for receiving and transmitting signals; antenna coupling means coupled to said antenna means and controlled by a control means to adapt said antenna means for one of reception and transmission; a receiver connected via said antenna coupling means to said antenna means for receiving a signal and generating a time-of-arrival indication upon detecting a predetermined signal pattern; said control means also for receiving said time of arrival indication and in response thereto for adapting said antenna means for transmission and for activating a transmitter at a time based on said indicated time-of-arrival; and wherein said transmitter is coupled via said antenna coupling means to said antenna means and activated by said control means to transmit a digitally coded acknowledgment signal at said time. ### Claim 2 (depends on 1) A paging unit according to claim 1 in which said control means further comprises: high-frequency crystal reference oscillator and counter means for determining an operating frequency of said receiver and said transmitter; and low-frequency oscillator and counter means for determining a power-down period for said receiver and said high frequency crystal reference oscillator. ### Claim 3 (depends on 2) A paging unit according to claim 2 in which said high-frequency crystal reference oscillator and counter means is controlled during power-on periods to calibrate said low frequency oscillator and counter means. ### Claim 4 (depends on 2) A paging unit according to claim 2 in which said operating frequency determination is performed using a frequency synthesizer programmed by said control means to adaptively generate either a transmit or a receive frequency. ### Claim 5 (depends on 4) A paging unit according to claim 4 in which said transmit frequency is the same as said receive operating frequency and said receive frequency is a receive local oscillator frequency. ### Claim 6 (depends on 5) A paging unit according to claim 5 in which said receive local oscillator frequency is the same as said receive operating channel frequency. ### Claim 7 (depends on 1) A paging unit according to claim 1 in which said receiver is a homodyne receiver. ### Claim 8 (depends on 1) The wireless paging unit of claim 1, wherein said control means determines said time for activating said transmitter using said indicated time-of-arrival and a predetermined delay. ### Claim 9 (depends on 8) The wireless paging unit of claim 8, wherein said predetermined delay is 2-10 milliseconds. ### Claim 10 (depends on 1) The wireless paging unit of claim 1, wherein said control means includes a counter which is continuously incrementing to generate count values and said control means adds said indicated time of arrival, a starting state of said counter and a predetermined delay to identify a particular count value as said time for activating said transmitter. ### Claim 11 (depends on 10) The wireless paging unit of claim 10, wherein said predetermined delay is 2-10 milliseconds. ### Claim 12 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. ### Claim 13 (depends on 12) A paging unit according to claim 12 in which said timing control means, prior to activating said transmitter, adapts said antenna means from a receive state to a transmit state. ### Claim 14 (depends on 12) A paging unit according to claim 12 in which said processing means further processes said stored numerical samples to produce a frequency error indication. ### Claim 15 (depends on 14) The paging unit according to claim 14 in which said timing control means uses said frequency error indication in activating said transmitter at a desired frequency. ### Claim 16 (depends on 15) The paging unit according to claim 15 in which said frequency error indication is used by said timing control means to adjust a frequency synthesizer to generate transmit frequency which has been compensated for said frequency error. ### Claim 17 (depends on 14) The paging unit according to claim 14 in which said frequency error indication is used to correct a frequency of a crystal reference oscillator. ### Claim 18 (depends on 17) The paging unit according to claim 17 in which said crystal reference oscillator is used to control the operating channel frequency of said transmitter. ### Claim 19 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.