United States Patent [191
`Zabarsky et al.
`
`[11]
`[45]
`
`Patent Number:
`Date of Patent:
`
`4,644,351
`Feb. 17, 1987
`
`[54] TWO WAY PERSONAL MESSAGE SYSTEM
`WITH EXTENDED COVERAGE
`[75] Inventors: Alan P. Zabarsky, Coral Springs,
`Fla; Suzette D. Steiger,
`Lincolnwood; Edward F. Staiano,
`Rolling Meadows, both of I11.; Jerry
`L. Sandvos, Plantation, Fla.
`[73] Assignee: Motorola, Inc., Schaumburg, I11.
`[21] Appl. No.: 608,334
`[22] Filed:
`May 8, 1984
`
`[51] Int. Cl.‘ ....................... .. H04Q 7/00; G08B 5/22;
`H04B 1/00
`[52] US. Cl. ........................ .. 340/825.44; 340/825.52;
`455/33; 455/53; 379/57
`[58] Field of Search .................... .. 340/825.44, 825.47,
`340/825.52, 825.55, 825.48; 455/33, 38, 49, 53,
`54, 56; 179/2 BB, 2 EC, 18 BF
`References Cited
`U.S. PATENT DOCUMENTS
`
`[56]
`
`4,354,252 10/1982
`Lamb et a1. .
`4,383,257 5/1983
`Giallanza et a1. .
`4,385,295 5/1983
`Willard et a1. .
`4,398,063 8/ 1983
`Hass et a1. .
`4,412,217 10/1983
`Willard et al. .
`4,438,433 3/ 1984 Smoot et al. .
`4,475,010 10/1984 Huensch et al. .
`OTHER PUBLICATIONS
`Overview of Digital Networking Products; Digital
`Equipment Corp; 1983; pp. 34 thru 3-10; 3-20 thru
`3-23, 4-6 thru 4-9.
`Systems Network Architecture-Technical Overview;
`IBM; 1982; pp. 4-13 thru 4-16.
`Systems Network Architecture-Concepts and Prod
`ucts; IBM; pp. 2-9 thru 2-11, 2-13 thru 2-19, 2-21 thru
`2-25, 4-1 thru 4-5, A-l.
`
`List Continued on next page.
`
`Primary Examiner-Ulysses Weldon
`Assistant Examiner-Ralph E. Smith
`Attorney, Agent, or Firm-—Raymond A. Jenski; Donald
`B. Southard
`
`3,478,877 11/1969 Schwitzgebel et a1. .
`3,557,312 l/1971 Vogelman et a1. . ’
`3,641,276 2/1972 Keller et a]. .
`3,678,391 7/1972 Gough .
`3,694,579 9/ 1972 McMurray .
`3,714,375 l/ 1973 Stover .
`3,742,481 6/1973 Nickerson .
`3,772,597 11/1973 Stover .
`3,783,384 l/1974 Wycoff .
`3,846,783 11/ 1974 Apsell et a1. .
`3,906,166 9/1975 Copper et al. .
`3,906,445 9/ 1975 Beckmann et a1. .
`3,976,995 8/ 1976 Sebestyen ..................... .. 340/825.44
`3,984,775 10/1976 Cariel et al. .
`4,010,460 3/ 1977 De Rosa .
`4,010,461 3/1977 Stodolski .
`4,152,647 5/ 1979 Gladden et a1. .
`4,156,867 5/ 1979 Bench et al. .
`4,172,969 10/1979 Levine et a1. .
`4,178,476 12/1979 Frost ............................ .. 340/825.44
`4,187,398 2/1980 Stark .
`4,197,526 4/ 1980 Levine et al. .
`4,233,473 11/ 1980 Frost .
`4,263,480 4/ 1981 Levine .
`4,336,524 6/1982 Levine ........................... .. 179/2 EC
`
`ABSTRACT
`[57]
`A communications system for carrying messages via a
`radio channel between one central site of a plurality of
`central sites and a plurality of two-way remote data
`units is disclosed. Each central site has a radio coverage
`area and each remote unit has a unique address and ‘
`association with one of the central sites. When a mes
`sage addressed to one of the remote units is received in
`a central site, a ?le of remote unit addresses is searched
`to ?nd the location and central site association of the
`' remote unit to which the message is addressed. If an
`address match is found indicating that the remote trans
`ceiver is in the coverage area of the message-receiving
`central site, the addressed message is stored and trans
`mitted in that site. If an address match is found indicat
`ing that the remote transceiver is in another central site,
`the addressed message is conveyed to that site for trans
`mission.
`
`29 Claims, 13 Drawing Figures
`
`Microsoft Ex. 1005
`Page 1 of 25
`
`

`
`4,644,351 " "
`
`‘Page 2
`
`OTHER PUBLICATIONS
`Computer Network and Distributed Processing; James
`Martin; 1981; pp. 341 thru 343, 418 thru 421, 431.
`Metro-Page 200, Automatic Radio Paging Exchange,
`System Manager Guide; Motorola; 1983; pp. 1-3 and
`1-6.
`Nordic System Description, Instruction Manual; Mo
`torola; 4/83; pp. 10 and 13, FIG. 10, (Manual
`#68P81150E03).
`Dyna T—A—C System Description, Instruction Man
`ual; Motorola; 6/83, pp. 10 and 11, (Manual
`#68P81l50EO1-A).
`Experience Gathered During the Development, and
`Operation, of a Nationwide Mobile Digital Communi
`cations System; Riidiger C. Lodde; 32nd IEEE Vehicu
`
`lar Technology Conference; May 1982; pp. 384-391.
`Advanced Mobile Phone System; Instruction Manual
`No. 68P81039E25-A; Motorola, Inc. 1979; pp. ii, 1-5.
`“BPR-ZOOO”, Display Radio Pager; Sales Brochure
`No. RB--05—05, Motorola Inc., 1983.
`Optrx Visual Display Pager; Radio Communications
`Report; Feb. 13, 1984.
`Marketing a New System Entails Some Trial and Error,
`and Changes; Charles E. Priddy; Telephony; Aug. 8,
`1983.
`Millicom Inc., Prospectus; pp. 12-19; Landenburg,
`Thalmann & Co., Inc.; Reinheimer Nordberg, Inc.
`RDX 1000, Portable RF Data Terminals; Instruction
`Manual No. 68P8l014C65-A; Motorola, Inc. 1978.
`
`Microsoft Ex. 1005
`Page 2 of 25
`
`

`
`U.S. Patent
`
`Feb. 17,.1987
`
`Sheet 1 of 13
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`4,644,35 1
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`Page 3 of 25
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`Microsoft Ex. 1005
`Page 3 of 25
`
`
`
`

`
`US. Patent Feb. 17,1987
`
`_Sheet20fl3
`
`4,644,351
`
`959,. 2
`
`BASE
`TRANSCENER
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`202
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`TRANSCEIVER
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`CENTRAL SITES
`
`Microsoft Ex. 1005
`Page 4 of 25
`
`

`
`US Patent Feb. 17,1987
`
`Sheet3ofl3 ' 4,644,351
`
`Microsoft Ex. 1005
`Page 5 of 25
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`

`
`US, Patent Feb. 17,1987
`
`Sheet 4 of 13
`
`4,644,351
`
`Microsoft Ex. 1005
`Page 6 of 25
`
`

`
`US. Patent Feb. 17,1987
`
`Sheet5of13
`
`4,644,351
`
`3
`SERIAL
`DATA 0————/-—
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`SIGNALS
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`INPUT
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`Microsoft Ex. 1005
`Page 7 of 25
`
`

`
`U.S. Patent Feb. 17,1987
`
`Sheet6ofl3
`
`4,644,351
`
`PROCESSOR
`
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`EXECUTIVE
`
`TRANSCENER
`
`BASE
`TRANSCEIVER
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`CONTROL
`PROCESSOR
`
`Microsoft Ex. 1005
`Page 8 of 25
`
`

`
`U.S. Patent Feb. 17,1987
`
`~Sheet70fl3
`
`4,644,351
`
`PERFORMANCE
`MONITOR
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`
`Microsoft Ex. 1005
`Page 9 of 25
`
`

`
`U.S. Patent, Feb. 17,1987
`
`Sheet 8 of 13
`
`4,644,35 l
`
`‘ PAGER QDDRESS
`I
`I
`
`MESSAGE. POINTER 808
`
`__ROAMER POINTER
`
`NEXT PAGER
`ADDRESS
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`Microsoft Ex. 1005
`Page 10 of 25
`
`

`
`US. Patent Feb. 17,1987
`
`Sheet90fl3
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`4,644,351
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`Microsoft Ex. 1005
`Page 11 of 25
`
`

`
`US. Patent Feb. 17,1987
`
`Sheet 10 of 13 4,644,351
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`Microsoft Ex. 1005
`Page 12 of 25
`
`

`
`US. Patent Feb. 17,1987 '
`
`Sheetll ofl3 4,644,351
`
`INITIALIZATION
`SEQUENCE
`
`1%,?’ . ' 1 1
`
`TO RECENE
`FUNCTIONS
`
`MESSAGE OR
`SPECIAL
`F UNg'l'lON
`
`1106
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`
`COMPOSE
`MESSAGE
`
`1104
`GENERATE
`PREDETERMINED
`
`RECALL
`MESSAGE
`
`TRANSMIT MESSAGE
`
`Microsoft Ex. 1005
`Page 13 of 25
`
`

`
`U.S. Patent Feb. 17,1987
`
`Sheet 12 ofl3 4,644,351
`
`USER
`(KEYPAD)
`
`ON '? TRANSMIT ON 1202
`MESSAGE TO SITE
`INITIALIZATION
`
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`1212
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`NUMBER
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`TO SITE
`
`[1224
`PLACE IN
`PROTECTED MEMORY
`
`Microsoft Ex. 1005
`Page 14 of 25
`
`

`
`U.S. Patent Feb. 17,1987
`Sheetl3 ofl3 4,644,351
`ANOTHER PEX
`RF MODEM/PAGER
`VALUE ADDED
`v
`TELEPHONE NETWORK
`DATA WORK m
`
`DATE TIME
`1 3 STAMP |
`» NEEDED
`
`1502
`
`YES
`
`THIS MESSAGE
`FROM ANOTHER PEX
`
`1304
`
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`
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`
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`TO ROAM PEX
`
`1512
`
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`ADDRESS PEX
`LOCATION
`ALGORITUM
`
`‘ SEND MESSAGE
`TO HOME PEX
`
`1 328
`
`1326
`
`Microsoft Ex. 1005
`Page 15 of 25
`
`

`
`1
`
`TWO WAY PERSONAL MESSAGE SYSTEM WITH
`EXTENDED COVERAGE
`
`5
`
`15
`
`20
`
`25
`
`BACKGROUND OF THE INVENTION
`This invention relates generally to radio paging sys
`tems and more particularly to a two-way radio personal
`data message system in which a miniature transceiver is
`carried by an individual for presentation of messages to
`that individual and for transmission of messages to a
`central site for relay to another individual or to a data
`base. Several central sites may coordinate their opera
`tion such that messages may be relayed between sites
`and follow a particular pager from one central site to
`another. Interconnection between the central sites and
`data communications networks enable the exchange of
`messages between the remote pager units and external
`data message generators and data bases.
`‘
`In a desire to satisfy the need of individuals who must
`be away from their base of operations to communicate
`with their base, several types of radio communications
`systems have been developed. A traditional form of
`radio communication utilizes a base station transceiver
`located at a site of favorable radio propagation and a
`number of transceivers mounted in vehicles for commu
`nications in a manner such as the familiar two-way radio
`police communications. Another form of radio commu
`nications is a mobile telephone service, which allows
`interconnection with the extensive public switched
`telephone network (PSTN) and affords the availability
`of the mobile telephone user to everyone who has a
`telephone. Mobile telephone and two-way radio equip
`ment, however, is generally large, heavy, and unlikely
`to be carried with the user at all times. Because of this,
`the advantages of mobile telephone and two-way radio
`are diminished.
`Portable cellular radiotelephones offer excellent two
`_way communications services which exceed the needs
`of pager users at a higher cost commensurate with the
`services. Real time voice (or data) is not always desir
`able to an individual who wishes only to have a message
`taken without having a current activity disturbed.
`Pagers have been and continue to be, in their simplest
`form, miniature receivers which are well known by the
`general public and those skilled in the art. These devices
`are generally tuned to a particular radio frequency
`which is shared with many other pager users and which
`is typically modulated with tones or data bits. A partic
`ular sequence of tones or data bits is used as an address
`or identi?cation for one particular pager or a group of
`pagers of the many monitoring the radio frequency.'
`Reception of the particular sequence activates an acous
`tic, visible, or tactile alert thereby indicating a call has
`been made to that pager (generally from a telephone
`connected to the PSTN). Depending upon the equip
`ment and system complexity, the pager may receive a
`voice or data message following the alert or the alert
`alone may simply indicate to the user that a call was
`made and a prearranged action, such as to telephone a
`speci?c telephone number, should be taken. More re
`cent developments have allowed data messages to be
`stored in a memory within the pager and recalled at the
`user’s convenience.
`Pagers have also evolved into devices which can
`transmit in addition to receiving. Complex telephone
`answering devices have demonstrated the ability to
`answer a telephone call, alert a user via a pager, collect
`a message from the telephone caller, and relay it to the
`
`4,644,351
`2
`pager. Advanced forms of telephone-answering device
`pagers offer the user the ability to transmit an acknowl
`edge from the pager to the answering device thereby
`causing the device to take a particular action such as to
`return a tone to the telephone caller indicating recep
`tion of the call. This predetermined response, however,
`offers a limited repertoire of responses over a limited
`geographic distance.
`Most pager users, however, wish to move about
`freely and have their pager respond to messages and
`generate messages without regard for radio coverage
`areas or distance from the base station. Telephone an
`swering devices provide coverage ranging to a hundred
`meters or so while a commercial shared paging service
`with an optimum transmitting site may provide cover
`age as much as 100 kilometers from the site. More exten
`sive networks of simulcast transmission provide shared
`service users an even greater area of coverage than a
`single transmission site can provide. The advent of sat
`ellite communications makes possible a nationwide link
`ing of shared service systems into a national paging
`network. It has also been proposed to angle modulate
`high power AM broadcast stations with paging infor
`mation and conceivably signal pagers 1000 kilometers
`from the station.
`Data communication systems, networked with each
`other and covering large areas and many terminals, are
`well known and extensively described in the literature.
`One highly prevalent system couples messages gener
`ated at one terminal through a local mode, or local data
`controller for a number of terminals, which routes the
`message to another local mode for distribution to a
`second terminal using an address embedded in the mes
`sage for routing instructions. A more sophisticated sys
`tem utilizes one or more central message processors to
`control the routing of the message and may be repro
`grammed to allow the terminals to be moved about the
`system. The problems faced when the terminals are
`highly mobile and connect to the local mode or central
`site via a radio channel compound the complexity of the
`location algorithm and require data transmission tech
`niques different than those used in traditional data net
`works.
`Electronic mail services provide message services for
`terminal users who may log on to a timesharing system
`and request messages which have been stored at the
`timesharing computer site from any place which has a
`telephone or other means of connecting to the timeshar
`ing system. The disadvantage of this technique is that
`there is no indication to the user that a message is being
`held. The delivery of the message must wait until the
`user logs on at some location and receives a message
`held indication from some central site.
`A dynamic communications system roaming user
`location technique has been described for mobile tele
`phone systems and in particular for cellular radiotele
`phone systems which may provide country-wide radio
`telephone service. In these systems, the radiotelephone
`user may preregister in a radiotelephone area other than
`the “home” area (normal service and billing area) for
`service to be provided in the other or “roam” area.
`When the user arrives in the roam area, the radiotele
`phone is quali?ed to make radiotelephone calls and has
`calls which are received in his home area forwarded to
`the roam area for transmission to the user. If sufficient
`data links are available, the roaming quali?cation may
`be automatically performed when the roaming radio
`
`40
`
`45
`
`65
`
`Microsoft Ex. 1005
`Page 16 of 25
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`

`
`4,644,351
`
`3
`telephone appears in the roaming area and the user
`initiates a ?rst telephone call. The roaming radiotele
`phone identi?cation is entered into a list of roamers in
`the home area so that incoming calls to the radiotele
`phone are forwarded to the roaming area. If, however,
`the roaming radiotelephone is out of range or turned off
`or if the user is not close to the radiotelephone, the user
`cannot receive a call and generally has no notion that a
`call was attempted.
`Thus it has been shown that it is possible to create a
`nationwide service for sending messages to individuals.
`Ideally such a service should make every effort to con
`vey the message to the user and provide the user every
`possibility of generating and transmitting a message.
`Pagers, because of their physical dimensions, tend to
`remain with their users more often than other communi
`cations devices and can be used for generating and
`transmitting messages in the more advanced devices. It
`has not been feasible, until the present invention, to
`coordinate the radio pager and the supporting system
`into a nationwide network which can ensure a convey
`ance of a message to the radio pager and accept mes
`sages and acknowledgements from a radio pager wher
`ever in the system the pager might be located.
`
`SUMMARY OF THE INVENTION
`Therefore, it is an object of the present invention to
`provide a paging system capable of relaying messages
`over a wide area.
`It is a further object of the present invention to enable
`the delivery of a message to a particular pager unit
`wherever in the system it may be located.
`It is a further object of the present invention to enable
`a two-way pager to generate messages and convey these
`messages to their predetermined destination.
`,
`It is a further object of the present invention to pro
`vide a system capable of accepting an acknowledge
`I-ment and a veri?cation transmitted by a message
`receiving two-way pager unit.
`Accordingly, these and other objects are achieved in
`the present invention which is a communications system
`for transmitting messages via a radio channel from one
`of a plurality of ?xed central sites having essentially
`different coverage areas to a plurality of remote units.
`Each remote unit is assigned a unique address and is
`associated with one of the central sites. When a message
`for a selected one of the remote units is accepted in a
`central site, it is stored in the paging site associated with
`the selected remote unit. A ?le of the remote unit ad
`dresses and the locations of those remote units not in the
`radio coverage area of their associated central sites is
`searched to discover the location of the selected remote
`unit. If the selected remote unit is in the radio coverage
`area of its associated control site which is also the site in
`which the message was accepted, the message and ad
`dress are transmitted in the radio coverage area most
`likely to contain the selected remote unit of that central
`site. If the remote unit is not in the radio coverage area
`of its associated central site, the message and address are
`conveyed to the central site indicated in the address ?le.
`When the selected remote unit receives the message it
`stores the message and returns a message received ac
`knowledgement to the central site which subsequently
`deletes the message ‘from its storage. Thus, the remote
`unit‘will receive messages addressed to it regardless of
`the central site radio coverage area in which it is lo
`cated.
`
`4
`BRIEF DESCRIPTION OF THE DRAWINGS
`FIG. 1 depicts a single paging system which has been
`cont-ructed in accordance with the present invention
`with four of a possible plurality of remote units shown.
`FIG. 2 shows a block diagram of the preferred em
`bodiment of a central site of FIG. 1.
`FIG. 3 is a diagram of the radio coverage area that is
`divided into a number of zones.
`FIG. 4 is a diagram of the format of the transmitted
`message.
`FIG. 5 is a block diagram of the Network Control
`Processor of FIG. 2.
`FIG. 6 shows a block diagram of three central sites
`linked for site to site communication.
`FIG. 7 is a diagram of the paging executive of FIG.
`6.
`FIG. 8 is a diagram of the local and roamer ?les of the
`paging executive of the preferred embodiment.
`FIG. 9 is a perspective diagram of the preferred
`pager embodiment of FIG. 1.
`FIG. 10 is a block diagram of the pager.
`FIG. 11 is a flowchart of the pager transmission pro
`cess.
`FIG. 12 is a ?owchart of the pager message reception
`process.
`~
`FIG. 13 is a flowchart of the central site roaming
`pager algorithm.
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENT
`A single site paging system, which has been con
`structed in accordance with the present invention and
`which typically is connected to a system of other pag
`ing sites, can be depicted generally as shown in FIG. 1
`wherein a central site 100 may be accessed by the public
`switched telephone network (PSTN) 101, another value
`added network (VAN) interface 102 (such as that of
`fered by Telenet or other carriers), another message
`encoding pager or dedicated line 103. The central site
`100 may be dialed like any other telephone number in
`the PSTN and an interconnect external terminal 104
`may be used to create a data message designated by a
`unique identi?cation address for each one of the many
`pagers 106 in the radio coverage area of the paging site.
`The external terminal 104, which may encode a data
`message may be similar to the terminals described in
`U.S. Pat. No. 3,906,445 to Beckmann et al., issued Sept.
`16, 1975 (Alphanumeric Terminal for a Communica
`tions System) and in U.S. Pat. No. 4,354,252 to Lamb, et
`al., issued Oct. 12, 1982 (Programmable Digital Data
`Terminal for Mobile Radio Transceivers), both as
`signed to the assignee of the present invention. A dedi
`cated line 103 may likewise be used to connect an exter
`nal terminal 108 to the central site 100.
`A value added network (VAN) 102 (such as that
`offered by Tymnet, Inc.) may switchably connect the
`central site 100 to one or more public service data bases
`110 (such as The Source) or to data backbone networks
`112 such as Digital Equipment Corporation’s DECnet
`or IBM’s SNA. A pager may become a remote terminal
`for these types of services, sending and receiving data
`messages and information such as stock quotations or
`news services information.
`It should be realized that although the pager as de
`?ned in the preferred embodiment is a self-contained
`data terminal capable of sending and receiving data
`messages, it need not be so intelligent as described and
`
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`into seven zones, Zl-Z7, and that includes the three
`base transceivers 200, 201 and 202 associated with NCP
`204.
`Transmitter T1 of base transceiver 200 has a coverage
`area within circle 300, transmitter T2 of base trans
`ceiver 201 within circle 301, and transmitter T3 of base
`transceiver 202 within circle 302. Each time a pager unit
`transmits, signal strength readings are taken by receiv
`ers R1, R2 and R3. These readings can be expressed by
`the following signal strength indicator (SSI) matrix:
`
`20
`
`30
`
`The signal strength readings taken by receivers R1,
`R2 and R3 are used to compute an adjusted signal
`strength for each zone Zl-Z7 by adjusting the mea
`sured signal strength for each receiver R1, R2 and R3
`by corresponding predetermined factors associated
`with the particular zone and then combining the ad
`justed signal strengths. The predetermined factors used
`to compute the adjusted signal strength depend on a
`number of factors such as the terrain, the height and
`gain of the antennas, and the sensitivity of the receivers.
`These predetermined factors associated with each zone
`are most often empirically determined and depend upon
`the characteristics of the equipment and terrain in each
`data communications system. The predetermined fac
`tors can be arranged in a zone selection matrix, such as,
`for example the matrix ZSEL:
`
`[ZSEL] =
`
`15.5
`0
`0
`
`0
`15.3
`0
`
`0
`0
`15.7
`
`10.7
`0
`10
`
`10.4
`9.8
`' 0
`
`0
`10.2
`11
`
`7.7
`7.5
`7.4
`
`An adjusted signal strength matrix for each of the
`zones Z1-Z7 may then be computed according to the
`following matrix formula to obtain the adjusted signal
`strength matrix ZADJ:
`
`5
`may be merely a remote radio modem unit to be con
`nected to a computer or other data terminal to provide
`the radio system interface. Nevertheless, in the descrip
`tion provided herein the term pager refers to a human
`transportable two-way radio device which interfaces
`with a communications network for the reception and
`transmission of data messages and may or may not have
`integral capability of message generation and presenta
`tion. Messages may also originate with one pager for
`transmission to another pager. After composition, the
`message is transmitted to the central site 100, stored,
`and retransmitted to a designated pager.
`A block diagram of the paging site of FIG. 1 is shown
`in FIG. 2 in which several base station radio transceiv
`ers, such as those depicted at 200, 201, 202 which are
`manufactured by Motorola Inc. as model number
`C55WNB0l07A, may be connected to and controlled
`by a network control processor (NCP) 204 which will
`be described subsequently. Additional base transceivers
`206, 207, 208 of a similar variety may be connected to
`NCP 210 which may be located at a convenient location
`separate from NCP 204. These transceivers are gener
`ally arranged such that continuous radio coverage may
`be obtained over a relatively large and essentially con
`tiguous geographic area due to the separate location of
`25
`each base transceiver. This extended coverage area may
`be considered to be part of one paging central site. The
`paging service may be employed as part of a larger
`system using compatable signalling.
`The NCPs 204, 210 are connected with a microcom
`puter based paging executive (PEX) 212 (to be de
`scribed later) via a high speed data link which enables
`the entities to exchange handshakes and messages in a
`brief amount of time. The PEX 212 interfaces with
`35
`other paging sites and external networks via a common
`data packet switch 214 using an X.25 protocol, for ex
`ample, which can be integral to or external to the PBX
`212.
`.
`The RF communications channel between the base
`transceiver and a pager is preferably comprised of ?rst
`and second carrier signals which may be modulated
`with the message signals. The transmitters of the base
`transceivers 200, 201, 202 may each operate on unique
`?rst carrier signals in discrete radio coverage zones
`while the receivers of the transceivers may each operate
`on unique second but associated carrier signals in associ
`ated zones. The transmitters and receivers of the base
`transceivers 206, 207, 208 also utilize the unique but
`associated carrier signals which comprise a set of du- .
`plex radio channels enabling simultaneous transmission
`50
`and reception of messages. Although the carrier signals
`of base transceivers 200, 201, and 202 in their respective
`zones may be the same as the carrier signals of trans
`ceivers 206, 207, and 208 in their respective zones in
`order to conserve radio spectrum, it is not intended that
`transmissions from the base transceivers contain identi
`cal message modulations such as might be expected in
`simulcast transmission systems.
`Since the messages are not transmitted simulta
`neously on each radio channel, it is necessary for each
`NCP to have a reasonably accurate determination of the
`location of each pager in the radio coverage area of its
`associated base transceivers. This location determina
`tion enables the NCP to select the base transceiver
`transmitter best covering the zone in which the pager is
`located.
`Referring to FIG. 3, there is illustrated a geographi
`cal area of a data communications system that is divided
`
`40
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`45
`
`60
`
`65
`
`Then, using the ZADJ matrix, NCP 204 can select the
`zone which has the largest adjusted signal strength for a
`particular transmission from a pager. The selected zone
`can be stored together with other data in a location of
`the short term memory of NCP 204 associated with that
`portable pager radio.
`Thus, the microprocessor based NCP 204 maintains a
`continuously updated routing list of most-likely loca
`tions where each pager in the paging site may be found.
`This continuously updated memory is maintained in the
`preferred embodiment for a short period of time which
`may be on the order of 30 minutes. A long term location
`memory storage is maintained at the PBX for the entire
`paging site and designations for a selected NCP and for
`a particular base transceiver are included in the memory
`of the PBX.
`Whenever a message is to be transmitted to a particu
`lar pager, the PBX 212 (see FIG. 2) selects the NCP 204
`or 210 and base transceiver to route the message. The
`selected NCP, in this case, 204 causes the transmission
`of the message signal on the carrier signal of the trans
`mitter that covers the zone which had the largest ad
`justed signal strength for the last transmission from the
`particular pager.
`If the pager does not acknowledge the transmission of
`the message signal from the NCP 204, NCP 204 may
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`attempt one or more retransmissions of the message
`signal by means of that selected transmitter. If the re
`transmissions likewise are not acknowledged by the
`pager, NCP 204 may then transmit the message signal
`via the transmitter covering the zone which had the
`second largest adjusted signal strength for the last trans
`mission from that pager. Again, if the pager does not
`acknowledge the transmission from NCP 204, NCP 204
`may ‘resend the message signal one or more times by
`means of that selected transmitter.
`If an acknowledge is not received in the zone with
`the second largest signal strength, the zone with the
`third largest adjusted signal strength from the last trans
`mission is caused to receive a message transmission.
`This message searching continues until all the base
`transceiver zones associated with NCP 204 are tried. At
`this time a no-acknowledge signal is returned to PEX
`212 which initiates a polling sequence in which the
`selected pager is polled in every zone in the paging
`central site starting with the pager’s “home” zone and
`20
`continuing with the zone of every NCP associated with
`PEX 212. If no acknowledge is received, the message is
`stored as will be described later.
`Message protocols are transformed in each NCP
`from that received by the NCP from its PBX to a proto
`col compatible with a fading radio channel. The data
`transmission protocol used in the preferred embodiment
`is a 4800 bits per second (bps) direct frequency shift
`~ keying (FSK) modulation of the transmitter. This speed
`' and type of modulation allows standard 25 KHz chan
`lnel spacings to be employed without interference.
`The message protocol of the present invention uses a
`' random delay contention system on the inbound radio
`. channel from the pagers and a continuous data stream
`on the outbound radio channel to communicate mes
`sages to the pager. The data message blocking is shown
`in FIG. 4 and is of incrementally variable length de
`r pending upon the length of the message. A bit sync, 400,
`~ of 20 bits of alternating l’s and O’s may preceed all
`v transmissions of a 40 bit message sync, 402 plus message
`.- information, acknowledgements, or system controls.
`-The remainder of the data message is divided into a
`number of channel data blocks (one of which is shown
`as channel data block 1, 404). The channel data blocks
`are divided into a basic information unit, 406, which is
`a 48 bit sequence of user data, a pager address, or gen
`eral system control; a parity sequence, 408, which is
`formed from the basic information unit, 406, by a rate
`§K=7 convolutional encoding; and a channel status
`sequence, 410, which is used to indicate the status of the
`inbound radio channel. A suf?cient number of channel
`data blocks are included in the transmission to convey
`the message.
`Transmission protocols similar to that used in the
`present invention are disclosed in application Ser. No.
`512,800, ?led on July 11, 1983 on behalf of Freeburg et
`al. (Method and Apparatus for Coding Messages Be
`tween a Primary Station and Remote Stations of a Data
`Communications System) and in