United States Patent [19] [11] Patent Number: 4,713,808 Gaskill Et Al

United States Patent [19] [11] Patent Number: 4,713,808 Gaskill et al. [45] Date of Patent: Dec. 15, 1987

[54] WATCH PAGER SYSTEM AND 4,569,598 2/1986 Jacobs ...... 368/47 COMMUNICATION PROTOCOL 4,641,304 2/1987 Raychaudhun ...... 370/93 [75] Inventors: Garold B. Gaskill, Portland; Daniel J. Primary Examiner-Donate W- Olms Pal-k; Robert G_ Ruuman, both of Assistant Examiner-Melvm Marcelo Beaverton; Donald T. Rose, Portland; Attorney, 1489f!’ 0' FirmfKlal'quisti Sparkmatli Joseph F. Stiley, III; Lewis w. , Campbell, Lelgh & Whmsron Barnum, both of Tigard, all of Greg; [57] ABSTRACT Don G. Hoff, Tiburon, Calif. _ . _ _ _ _ _ ' ‘ _ A wide area pagmg system 1s dlsclosed 1n wh1ch pagmg [73] Asslgnee: A 8‘ E Corporation’ San Franclsco’ messages input to the system in one local area can be Cahf' broadcast to a receiver in any other local area without [21] APPL No_; 302,344 necessarily broadcasting the message in all areas. A . local area clearinghouse in each area stores resident [22] F?ed' Nov‘ 27’ 1985 subscriber data including current location and receiver [51] Int. Cl.‘ ...... H04J 3/24; H04] 3/26 serial number. This data is used to transfer messages [52] US. Cl...... 370/94; 370/93 over a data network to the correct clearinghouse. The [58] Field of Search ...... 370/94, 60, 93; system uses a TDM data protocol. The data is encoded 340/825-52 and transmitted at a very high rate (e.g., 19,000 band) in [561 References Cited short packets (256 bits/l3 milliseconds) via stereo FM sidebands. Receivers are assigned to receive sequen U'S' PATENT DOCUMENTS tially numbered time slots matching a portion of their 3,532,985 10/1970 Glomb et a1...... 375/115 address. The addresses of intended receivers are in 3,628,147 12/1971 Makimo ...... 325/4 cluded in the data packets. Battery-powered receivers gills fatal-1 are deactivated between packets and reactivated in v 9 a 011 E - .. , . . _ 4,131,855 12/1978 Harnagawa ...... 328/129 acwrdance with m? seqllemlal “me 51°‘ number 4 315 332 2/1982 Sakami et al 455/181 scheme to receive an incoming packet. Messages longer 413171220 2/1982 Martin ...... 455/53 than a Packet are Segmented and transmitted in two 0r 4,337,463 6/1982 Vangen ...... 340/8253 more packets, linked together by data contained in the 4,358,836 11/1982 Tohyama et al...... 368/47 packets. A watch pager used in the system employs a 4,369,443 V1933 Gtallanza et a1- - 340/32547 wristband antenna which electromagnetically couples 3:332:21‘ a1- ' to the user’s body. The watch pager displays time, tele 4:419:765 ‘12/1983 Wycoff et al ...... 455/36 ph°ne.numbers and icons representing c°mm°n types 4,437,095 3/1984 Akaho’ri et al. 340/825.44 °f Pagmg messages 4,518,961 5/1985 Davis et al. 340/825 44 4,519,068 5/1985 Krebs et al...... 370/82 20 Claims, 30 Drawing Figures

602

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\ I\ I / \ CONTROL SLOTS TIME SLOTS Y 3 \r 604 606 604 US, Patent Dec. 15,1987 Sheet 1 of 17 4,713,808

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39 24c 38 REGIONAL REGIONAL DATACOMM. TELECOMM. SUBSCR'BERS <1 6 NETWORK NETWORK 36 I \ \ LOCAL LOCAL LOCAL <1 H CLEARINGI-IOuSE CLEARINGI-IOUSE CLEARINGHOUSE 32 24 LOCAL LOCAL SUBSCRIBERS 62 DATACOMM. TELECOMM. REQUESTORS NETWORK OI ; vOICE MAIL \24b 45L RECEIVER f I ‘ 20d \,\ TRANSMITTER TRANSINITTER m TRANSMITTER LINK '- K 5 QJ LINK \ w BROADCAST - 44° {IA/4% NETWORK 44 44a 44b REPEATER TRANSMITTER TRANSMITTER TRANSMITTE\R\ OK 20'\--RECEIvER ZOQLRECEIVER ZObT-RECEIVER RECEIVER \ SUBSCRIBER 240 20c

US. Patent Dec. 15, 1987 Sheet 6 of 17 4,713,808

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260 US. Patent Dec. 15, 1987 Sheet 8 of 17 4,713,808

PROCESS AND REASSEMBLE PACKETS

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US. Patent Dec. 15,1987 Sheet 10 0f 17 4,713,808

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US, Patent Dec. 15,1987 Sheet 13 of 17 4,713,808

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10/ Ohm mCmOmEOU 4,713,808 1 2 slot in which data for the particular page receiver is WATCH PAGER SYSTEM AND transmitted. The drawbacks of this approach, however, COMMUNICATION PROTOCOL have been several. First, it is dif?cult to synchronize accurately the page receiver to the transmitter. Second, RELATED APPLICATION DATA long messages that cannot be transmitted in a single The application is related to US. patent application time slot require an inordinate amount of time to be Ser. No. 06/678,603, ?led Dec. 5, 1984, by Don G. completely transmitted to a page receiver. Third, page Hoff, entitled PAGER WATCH SYSTEM UTILIZ receivers using this approach have largely relied on a ING TIME SLOT COMMUNICATION, assigned to single communications channel, which may not be AT&E Systems Incorporated, a wholly-owned subsid strong enough in a particular area to transmit success iary of the assignee of this application. fully to the page receiver. Finally, it has so far proven BACKGROUND OF THE INVENTION impractical to implement pagers with miniature batter ies because previous pagers do not have low enough Technical Field power consumption to avoid frequent battery replace This invention relates to communication systems and ment or recharging. receivers and more particularly to wide area paging One such prior art paging system is disclosed in US. systems and portable paging receivers with low power Pat. No. 3,937,004 to Natori et al. The Natori et al. consumption and method of data transmission to many patent describes a page receiver in the form of wrist receivers on a common channel. Description of Prior Art 20 watch that activates its receiver circuitry periodically Prior paging systems generally provide two catego for a given time interval to detect a paging signal that ries of coverage. Local area coverage is typically pro may be directed to it. In the particular embodiment vided by transmitting a page simultaneously from one given, the receiver is activated ?ve minutes out of a or more transmitters operating on a single frequency, ?fteen minute transmission cycle. Although this tech covering all or a portion of a metropolitan area, to a nique does reduce power consumption, it still requires recipient within the local area. Such coverage is obvi receiving circuitry to be on one-third of the time. ously limited to the broadcast range of a local transmit A battery-saving arrangement for pagers is also dis ter. Wide area coverage, encompassing several overlap closed in U.S. Pat. No. 4,398,192 to Moore et al. Page ping areas of a large metropolitan area or a number of receivers are assigned to groups, and the receivers of non-overlapping metropolitan areas, is typically pro 30 each group are activated during a time segment of a vided by transmitting a paging request to several trans transmission cycle set aside for the group. Each re mitters via telecommunications and broadcasting the ceiver within a particular group then is active during paging message from all transmitters to an intended the entire group time segment to detect any individually recipient who may be anywhere within the wide cover addressed messages for it. The Moore system requires age area. The foregoing approach to providing a wide 35 the receiver to be on or energized much longer than is area coverage is expensive and limited to a relatively actually necessary to receive a message. small number 'of paging users. As paging traf?c in The paging system of US. Pat. No. 4,437,095 to creases, the local and wide area coverage users begin to Akahori et al. is similar in operation to Moore et al. The compete for paging channel space. Each wide area user Akahori et al. page receiver requires its receiving cir occupies a portion 'of the available paging channel space 40 cuitry to power up periodically to detect a synchroniza for all of the page transmitters within the wide coverage tion signal and then again a predetermined time later for area, displacing local coverage users of the same chan group messages. With this approach, the Akahori et al. nel portion from each transmitter. It would be prefera receiver is able to reduce its power consumption only ble to be able to provide wide area paging coverage by about half over continuously-powered receivers. without displacing local area coverage users of the same 45 US. Pat. No. 4,383,257 to Giallanza et al. discloses a channel portion from all transmitters in the wide area. variation of the previous approach. The receiving cir Another problem with present paging systems is their cuitry in Giallanza et al. is sequentially activated and incompatibility. Local area coverage users may use one type of paging message encoding scheme-for broadcast deactivated in a periodic duty cycle. It is activated in time to detect a synchronization signal that is transmit ing a page to a page receiver and wide area coverage 50 users may use a second type. A user who travels fre ted by a transmitter whenever a message isto be sent to quently must carry different page receivers to receive a receiver. If a synchronization signal is detected, the both types of messages. One solution to the incompati receiver remains activated beyond its duty cycle to bility is disclosed in US. Pat. No. 4,518,961 to Davis et determine if succeeding address signals identify such al. Davis et al. describes a single page receiver that receiver to continue receiving messages. This approach stores the encoding schemes for a number of paging also requires the receiving circuitry to be on at least a systems, encoding schemes such as POCSAG, the pag ?xed amount of the time regardless of whether mes ing protocol for the British Post Of?ce, and GGC, a sages are being sent to it. In most cases, this on-time is paging protocol designed by Motorola, Inc. This is only much longer than is necessary to actually receive the a partial solution, however, because the number of en 60 transmitted message. coding schemes greatly exceeds the number the Davis Synchronizing a receiver to a transmitter by use of a et al. receiver can store. real time signal is known in the prior art, but such appa~ Prior paging systems have also used various methods ratus requires the receiver to be continuously on. For for reducing the power consumption of battery example, US. Pat. No. 4,358,836 to Tohyama et al. operated portable page receivers to minimize their 65 discloses an electronic watch that receives a real time overall size and to extend their battery life. One ap signal from a transmitter to synchronize its internal proach involves supplying power to receiver circuitry clock. Similarly, US. Pat. No. 4,337,463 to Vangen in the page receiver only during a predetermined time discloses a time synchronization system for synchroniz 4,713,808 3 4 ing clocks at remote stations to a clock at a master increase the cost and complexity of the modulator unit. station. Extensive ?ltering must also be provided in the receiver US. Pat. No. 4,419,765 to Wycoff et al. discloses a circuit to separate the desired paging information, mod power-limited paging receiver that also has frequency ulated around 57 kilohertz, from the broadcast stereo scanning capability. If an incoming signal is not de audio, which ends at 53 kilohertz. This again increases tected on a present channel, the receiver can scan over the costs and complexity of the system. several channels. However, the scanning is done Accordingly, a need remains for a versatile, wide blindly. As a result, this scanning consumes power un area paging system that overcomes the foregoing and necessarily. other drawbacks of prior paging systems. Another drawback of the above devices that use dedicated time slots to receive messages is their limited SUMMARY OF THE INVENTION receiving capability, Messages that cannot be transmit One object of the invention is to improve upon prior ted in a single time slot may require several transmission paging systems through increased efficiency, greater cycles to complete. usefulness over a wider area, reduced size, lower power US. Pat. No. 4,519,068 to Krebs et al. discloses a consumption and the ability to service a large number of method for sending messages of a variable length. Krebs users. et al. transmits data messages which have several ?elds, Another object of the invention is to provide a porta including a sync ?eld to synchronize the receiver to the ble electronic paging receiver having the same size, transmitter and data blocks which follow the sync ?eld. time-keeping accuracy and battery-life characteristics The ?rst channel data block includes the station ad as a conventional electronic wristwatch. dress. The second channel data block includes an infor A further object of the invention is to enable paging mation ?eld that indicates the number of following via a common system of a virtually unlimited number of channel data blocks. Krebs et al., however, is impracti pager subscribers within any desired area, including cal for time division multiplexing because of its format. local, regional, national, continental, and worldwide In known portable paging receivers, which typically 25 communication capability. operate in the 150, 200 or 400 megahertz frequency An additional object of the invention is to provide bands, the antenna usually comprises a conductor such wide area paging coverage without displacing wrapped around a ferrite bar. This antenna, together local area access to the paging system. with the associated paging receiver, is mounted within Still another object of the invention is to enable sub a nonconducting enclosure sized to ?t in a pocket or scribers in such paging system reliably and ef?ciently to clip on a belt. Miniaturization of the enclosure beyond receive messages of unlimited length and information ‘this size is limited by the comparatively bulky ferrite content. antenna that must be contained. I One aspect of the invention provides a paging system The pager size problem is further aggravated as the including at least two local area transmitters, each cov paging frequency is lowered. Lower frequency receiv ering a local area of non-overlapping coverage, a plural ers use larger inductors, capacitors and ?lters in their ity of paging receivers assigned to and normally resid frequency dependent circuits. Lower frequency paging ing in each local area, and means for transferring paging 'is desirable, however, because of its superior radio sig requests from one local area to another area where the nal propagation characteristics. intended recipient of the paging request is currently In 'a paging system marketed by the Telecommunica located. Associated with each local area transmitting tions Group of American Diversi?ed Capital Corp., means are a subscriber storage means for storing a paging data is believed to be encoded on a 57 kilohertz unique identifying address and a current location for subcarrier in an FM broadcast signal and transmitted at each resident page receiver, means for inputting the a rate of 1200 baud. Signal modulation is believed ef identifying address for a selected one of the paging fected by phase modulating the 57 kilohertz carrier. If 45 receivers, and routing means for routing paging mes consecutive data elements are identical, the train of 57 sages to the local transmitter means serving the current kilohertz cycles repeats without interruption. If, how location of the intended recipient. The paging messages ever, the data changes state, i.e. from a O to a l or 1 to are routed through a communications network means, a 0, the phase of the 57 kilohertz subcarrier is suddenly in accordance with the stored current location of the reversed. This is believed effected by doubling the 50 selected paging receiver. Thus, a paging message for a length of the positive going or negative going cycle of paging receiver normally residing in a ?rst local area, the subcarrier, thereby introducing a brief DC compo but temporarily located in a second local area, is broad nent into the subcarrier signal. The phase of the subcar cast by the transmitting means serving the second local rier is thereafter shifted 180° relative to the previous area. This arrangement leaves the portion of the broad subcarrier phase. 55 cast channel that would otherwise be allocated to the The American Diversi?ed system suffers from a vari paging receiver temporarily located in the second local ety of drawbacks. The slow baud rate limits severely area. the number of users who can be served effectively and In another aspect of the invention, the paging re the rate at which information can be transmitted. Addi quests are transmittted from a local area transmitting tionally, it is known that to try to increase the number of 60 means to a page receiver in the form of packets, each users by increasing baud rate and shortening message packet having an address corresponding to a time dur length reduces reception reliability. This problem is ing which the packet is transmitted. This time is de?ned most apparent when usng a mobile RF receiver to re as a time slot within a predetermined number of sequen ceive very high frequencies such as FM. Furthermore, tially numbered time slots forming a subframe, and a the phase modulation technique employed generates 65 subframe within a predetermined number of sequen broadband spurious components which must be ?ltered tially numbered subframes forming a periodic time with elaborate ?ltering circuits so as to reduce interfer frame. Each page receiver has an address also corre ence with the broadcast audio. These ?ltering circuits sponding to a time slot and subframe which controls