United States Patent 119]
`
`[11] Patent Number:
`
`4,875,038
`
`
`Siwiak et al.
`[45] Date of Patent:
`Oct. 17, 1989
`
`340/325.47
`340/825.44
`
`3-1-O/825.44
`
`3
`
`‘I
`2 0”
`
`4,466,001
`
`s/1934 Moore et a1.
`D
`Entire
`
`.
`
`.
`
`.
`
`1/1931
`4.,535_741
`2/1987 Engel
`4,646,082
`t al.
`4554.882 3/1937
`Ikeda ?
`713,303 12 1987 G kill
`4'
`”
`”
`‘T “I
`Primary E.xtlmI'ner'—Gerald Bngauce
`Attorney, Agent. or.F?rm—Wil1iam E. Zitelli; Vincent B.
`Ingrassia
`ABSTRAC1‘
`[57]
`An acknowledge back (acbback) paging system is pro.
`vided which includes a central station which transmits a
`g'°."p °fm°mg° Signals mam"? °f acbback Page“
`which are addressed as a group. The users of the group
`of addressed ack-back pagers indicate a response to
`their respective pagers thus providing ack-beck data.
`The pagers in the group of addressed ack-back pagers
`then simultaneously transmit back to the central station
`their ack-back data on different frequency sub—bands, a
`different frequency sub-band being allocated to each of
`the pagers in the group.
`
`[75]
`
`[543 FREQUENCY DIVISION MUI.Tl1’LEXED
`ACKNOVQLEDGE BACK pA(',-ING SYSTEM
`Invtors: Knzimierzsiwiak, Coral Springs;
`Leon Jasinsld, Fort Lauderdale;
`Francis R. Steel, Parkland, all of Fla.
`I73] Assignee: Motoroh, Inc., Schaumburg, 111.
`
`[211 A991‘ N°" 141554
`[221 Filed:
`Jan. 1, 1930
`H040 9/00
`[51]
`Int. Cl.4
`340/825.44; 340/825.4-7;
`[52] US. CL
`m/3*8725;/3:: ggggfi
`H I
`f
`E3113/aS2?ft§h§i"i'i'-"§§5?5i 93 94 50 3591 '73’
`'
`’
`'7}? 31,9/5% 5:7_ 435/31
`95
`’
`’
`’
`’
`’
`References Cited
`U.S. PATENT DOCUMENTS
`
`[58]
`
`[56]
`
`3,573,379 4/1971 Schmitz
`3,973,200 8/1976 Akerberg ..
`4,194,153
`3/1930 Masakietal
`4,208,630
`5/1930 Martinez
`4,352,955 10/1932 Knietal.
`4,392,242 7/1933 Km .
`
`370/75
`340/325.44
`
`455/31
`379/57
`
`
`
`21 Claims, 9 Drawing Sheets
`
`
`F-‘AGER P
`
`
`ACK BACK
`
`‘ GOOGLE 1026
`
`GOOGLE 1026
`
`1
`
`

`
`U.S. Patent
`
`Oct. 17, 1939
`
`Sheet 1 of9
`
`4,875,038
`
`FIG. 1
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`2
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`

`
`U.S. Patent
`
`Oct.17, 1939
`
`Sheet 2 of9
`
`4,875,038
`
`FIC.2
`
`
`
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`
`CENTRAL
`STATION
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`US. Patent
`
`Oct. 17, 1939
`
`Sheet 4 of 9
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`
`U.S. Patent
`
`Oct. 17, 1939
`
`Sheet 5 of 9
`
`4,875,038
`
`FIG. 5
`
`500
`
`INPUT MESSAGE
`
`STORE MESSAGE IN RAM
`
`COUNT MESSAGES I=1+ 1
`
`
`
`a 540
`
`TRANSMIT PREAMBLE
`
`545
`
`
`
` N
`
`560
`
`57°
`580
`
`
`
`LOOK UP AND RI-:rR1EvE ADDRESSES
`CORRESPONDING TO M PAGERS FROM MEMORY
`
`RESET I = 1
`
`RETRIEVE ADR I
`
`TRANSMIT ADR I
`
`®Y
`
` 800
`
`TRANSMFT REFERENCE CARRIER FR
`
`RESET I = 1
`
`REFRIEVE MESSAGE I
`
`610
`
`62°
`
`55°
`
`540
`
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`
`TRANSMIT MESSAGE I
`
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`
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`
`RECEIVE ACK BACK SIGNALS FROM
`
`THE GROUP 0'‘ M M55550 PMS
`
`7
`
`

`
`U.S. Patent
`
`Oct. 17, 1939
`
`Sheet 7 of9
`
`4,875,038
`
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`
`

`
`US. Patent
`
`Oct. 17, 1989
`
`Sheet 3 of 9
`
`4,875,038
`
`AB PAGER
`‘__ Ea
`
`SUB-—BAND #
`
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`AB-11
`
`AB-12
`
`AB-13
`
`AB—14
`
`AB--15
`
`AB--16
`
`AB-17
`
`AB-18
`
`158-19
`
`AB—20
`
`149.9905
`
`149.9915
`
`149.9925
`
`149.9935
`
`149.9945
`
`149.9955
`
`149.99 65
`
`149.9975
`
`149.9985
`
`149.9995
`
`150.0005
`
`150.0015
`
`150.0025
`
`150.0035
`
`150.0045
`
`150.0055
`
`150.0065
`
`150.0075
`
`150.0085
`
`150.0095
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`
`FIG.7
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`9
`
`

`
`“US. Patent
`
`Oct.
`
`1939
`
`Sheet 9 of 9
`
`4,875,038
`
`1110
`
`Fla 8
`
`
`
`COUNT PACER ADDRESSES
`ADR COUNT =
`ADR COUNT + 1
`
`
`
`
`
`"[5
`
`11
`
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`
`— M
`
`ADR
`
`ENTER
`BATTERY
`
`1130
`
`H90
`
`1200
`
`1210
`
`1220
`
`WAKE-UP PAGER
`
`ADRCOUNT = 0/ADR MAX = M
`
`
`
`LISTEN FOR
`VAUD ADDRESS
`
`
`
`
`
`Y
`
`COUNT FAGER ADDRESSES
`ADR COUNT = ADR COUNT + 1
`
`COUNT FREQUENCY OF REFERENCE
`CARRIER Fe AND STORE Fc
`
`MEASURE AND STORE SIGNAL
`STRENGTH or CARRIER Fe
`
`MSG GGUNT = o
`
`REGENE NEXT MESSAGE
`
`MSG COUNT = MSG COUNT + 1
`
`
`
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`DUPUCATE IIESSAGE
`
`WAIT FOR ACK BACK FIELD
`
`SELECT ONE or In! SUB—BANcI'5IgUrIf[(_i‘r_R
`“CK HACK BASED 0” “DR
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`LOOK UP FREQUENCY OFFSET
`FD CORRESPONDING To THE
`55130753 5u3..BANn
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`
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`
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`
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`
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`
`1400
`
`
`
`TURN TRANSMITTER CIRCUITS ON
`
`DATA AT LOW POWER
`
`TURN TRANSMITTER c1RcurTs ON
`
`
`
`TRANSMTF ACK BACK
`DATA AT HIGH POWER
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`

`
`1
`
`4,875,038
`
`FREQUENCY DIVISION MULTIPLEXED
`ACKNOWLEDGE BACK PAGING SYSTEM
`
`5
`
`10
`
`20
`
`25
`
`30
`
`35
`
`BACKGROUND OF THE INVENTION
`
`This invention relates in general to radio communica-
`tions systems. More particularly, the invention relates
`to radio paging systems.
`In the past several years, radio paging technology has
`advanced from the rather simple tone-only pager (tone
`alert only, no voice), to the tone and voice pager (tone
`alert with a voice message) and more recently to the
`alphanumeric display pager. In a typical conventional
`alphanumeric display paging system such as that shown
`as system 10 in FIG. 1, a central transmitter or paging
`terminal 20 is used to generate the radio pages which
`are transmitted via a radio link to a fleet of paging re-
`ceivers 1, 2, 3 .
`.
`. N, wherein N is the total number of
`pagers in system 10. A unique digital address is associ-
`ated with each of paging receivers 1, 2, 3 .
`.
`. N. A page
`which is transmitted by paging terminal 20 consists of
`the unique digitally encoded address of the particular
`pager to which the page is targeted, immediately fol-
`lowed by a corresponding digitally encoded numeric or
`alphanumeric page message which is intended for dis-
`play on the target pager.
`Typically, the numeric or alphanumeric page mes-
`sage is stored in a memory within the paging receiver
`for later recall and display by the pager user. Paging
`receivers are available with a wide range of message
`storage capabilities which range from the ability to
`store just a few rather short numeric page messages to
`the ability to store a relatively large number of longer
`alphanumeric page messages.
`However, conventional display paging systems are
`generally one way systems. That is, the user receives a
`paging message from the central terminal but has no
`way of responding to that message with his or her
`pager. Instead, the pager user must seek out a telephone
`or other means of responding to the originator of the
`pacing message-
`BRIEF SUMMARY or 'I'l-IE INVENTION
`
`Accordingly, it is one object of the present invention
`is to provide a paging system in which the radio pager
`is capable of responding hack to the paging terminal and
`the caller.
`Another object of the present invention is to provide
`a radio paging system in which a group of addressed
`pagers are capable of simultaneously transmitting ac-
`knowledge back signals on a plurality of respective
`predetermined sub-band frequencies.
`In one embodiment of the invention, an acknowledge
`back pager is provided which has a unique address
`associated therewith. The pager includes a receiver for
`receiving paging signals from a central station. Such
`paging signals include a batch of M pager addresses
`transmitted in a sequential order during a first time
`frame, wherein M is the number of pager addresses in
`the batch. The pager further includes a decoder, cou-
`pled to the receiver. for detecting the presence of the‘
`pager's address within the batch of M addresses. An
`address order determining apparatus is coupled to the
`decoder for determining the order of the pager’s ad-
`dress within the batch of M addresses. The pager fur-
`ther includes a sub-band transmitter for transmitting an
`acknowledge back signal on a selected one of a plurality
`of M predetermined frequency sub-bands, the selected
`
`45
`
`50
`
`55
`
`65
`
`11
`
`2
`one of the sub-bands exhibiting a predetermined rela-
`tionship to the order of the address of the pager within
`the batch of M addresses.
`The features of the invention believed to be novel are
`specifically set forth in the appended claims. However,
`the invention itself, both as to its structure and method
`of operation, may best be understood by referring to the
`following description and the accompanying drawings.
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a block diagram of a conventional display
`type radio paging system.
`FIG. 2 is a block diagram of the ack-back paging
`system of the present invention.
`FIG. 3 is a block diagram of the central station em-
`ployed iu the paging system of FIG. 2.
`FIG. 4A is a time vs. event representation of the
`transmissions from the central station of the system of
`the invention.
`FIG. 4B is a representation of an address block used
`in the paging protocol of the paging system of the in-
`vention.
`
`FIG. 4C is a representation ofa message block used in
`the paging protocol of the paging system of the inven-
`tion.
`FIG. 4D is a time vs. event representation of the
`receiver portion of the central station.
`FIG. 4-E is a time vs. event representation of the
`activity of aclt-back pager AB-1.
`FIG. 4F is a time vs. event representation of the
`activity of ack-back pager AB-2.
`FIG. 4G is a time vs. event representation of the
`activity of ack-back pager AB—M.
`FIG.
`ll-I-I
`is a time vs. event representation of the
`activity of a non aclt-back pager in the paging system of
`the invention.
`FIG. III is a time vs. event representation of the activ-
`ity of an unpaged ack-back pager in the paging system
`of the invention.
`FIG. 5.is a flowchart depicting the operation of the
`central station in the paging system of the invention.
`FIG. 6 is a block diagram of one of the aclt-back
`pagers employed in the paging system of the invention.
`FIG. 7 is subchannel frequency look-up table em-
`ployed by the aclt-back pagers in the system of the
`invention.
`FIG. 8 is a flowchart of the operation of the ack-back
`pagers of the paging system of the invention.
`DETAILED DESCRIPTION OF THE
`INVENTION
`
`FIG. 2 is a simplified block diagram of the acknowl-
`edge baclt paging system 100 of the present invention.
`Paging system 100 includes a central station or paging
`terminal 110 which is capable of both transmitting out-
`going paging signals and of receiving acknowledge
`back (ack-back) paging signals. Paging system 100 in-
`cludes a plurality of ack-back pagers 121, 122 .
`.
`. P,
`wherein P is die total number of ack-back pagers in the
`pager population of system 100. Each of ack-back pag-
`ers 121, 122 .
`.
`. P has the capability of receiving paging
`signals from central station 110 and of permitting the
`pager user to respond to such paging signals. That is,
`pagers 121, 122 .
`.
`. P permit the user to reply or ac-
`knowledge back to a page from central station 110. It is
`noted that conventional non aclt-back pagers such as
`pager 130 are also includable in system 100. In FIG. 2,
`
`11
`
`

`
`4,875,038
`
`3
`double arrows between central station 110 and each of
`ack-back pagers 121, 122 .
`.
`. P are used to denote that
`two way communication exists between central station
`110 and such ack-back pagers. A single arrow denotes
`that only one way communication exists between sta-
`tion 111] and pager 130.
`FIG. 3 is a more detailed block diagram of central
`station or paging terminal 110. Central station 110 in-
`cludes a conventional telephone interface 14-0 of the
`type generally used for central paging terminals. Tele-
`phone interface 140 couples outside telephone lines 141,
`14-2, etc. to an input 150A of a microcomputer 150.
`Telephone interface 140 converts message signals from
`lines 141, 142, etc. to digital signals which microcom-
`puter 150 can process. For example, a caller wishing to
`send an alphanumeric page to an ack-back pager user
`uses dual tone multi frequency (DTMF) to key in a
`desired message. Telephone interface 140 then converts
`such analog DTMF alphanumeric message to its digital
`equivalent which microcomputer 150 processes as dis-
`cussed later in more detail. Central station 110 further
`includes a keyboard 160 coupled to a data input 15013 of
`microcomputer 150. Keyboard 160 permits an operator
`to directly input messages into microcomputer 150 for
`transmission to pagers within the pager population.
`A read only memory (ROM) 170 is coupled to a
`memory port 150C of‘ microcomputer 15!). ROM 170
`includes a. control program which controls the opera-
`tion of microcomputer 150 and the circuits coupled
`thereto. A random access memory (RAM) 180 is cou-
`pled to a memory port 150D microcomputer 150. RAM
`180 provides temporary storage space for microcom-
`puter 150 as it carries out the instructions of the control
`program within ROM 17!}.
`When a paging message and the identity of the partic-
`ular pager to be addressed are provided to microcom-
`puter 150, the control program causes microcomputer
`150 to generate digital paging signals at its output 150E
`according to the protocol later described. Microcom-
`puter output 150E is coupled via a level shifter 190 to
`the input of a transmitter 200. The output of transmitter
`200 is coupled to an antenna 219 having dimensions and
`characteristics appropriate to the particular paging fre-
`quncy channel selected for the operation of central
`station 110. Level shifter 19!} serves to adjust the signal
`level of the paging signals generated at microcomputer
`output 150E to a level appropriate for the input of trans-
`mitter 2.00.
`For purposes of this example, it will be assumed that
`ack-back pagers 121, 122-? are acknowledging back via
`phase shift keyed (PSK) digital modulation. Those
`skilled in the art will appreciate that other forms of
`modulation as well may be employed by acknowledge
`back pagers 121. 122-P to respond to the paging signals
`transmitted by central station 110. In such a PSK em-
`bodiment, central station 1l0 includes a receive antenna
`220 for receiving the ackback signals transmitted by
`ack-back pagers 121, 122-P. In actual practice, antenna
`210 may also be employed as antenna 220. Receive
`antenna 220 is coupled to the input of a PSK receiver
`230 which includes an in-phase (1) output 230A and a
`quadrature (Q) output 23-BB. Receiver outputs 230A
`and 23013 are respectively connected to inputs 240A and
`24013 of digital signal processor 24-0. One digital signal
`processor which may be employed as processor 240 is
`the model DSPSGOOO manufactured by Motorola, Inc.
`Digital signal processor 240 includes a control input
`240C which is coupled to a control output l50F of
`
`10
`
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`
`20
`
`25
`
`30
`
`35
`
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`
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`
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`
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`
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`microcomputer 150 to permit microcomputer 150 to
`control processor 240. Digital signal processor 240 fur-
`ther includes a data output 240D which is coupled to
`the data input 150G of microcomputer 150. Thus, it is
`seen that digital signal processor 24-0 decodes the digital
`data received at the I and Q inputs 240A and 24013
`thereof and transforms such information into digital
`data which is provided to microcomputer data input
`‘ISBG.
`FIG.’s 4-A—6I are timing diagrams which show the
`signaling protocol employed by central station 110 and
`ack-back pagers 121. 122-1’. More specifically, FIG. 4A
`is a simplified timing diagram of the paging protocol
`transmitted by central station 110. In FIG. 4A, time is
`represented on the horizontal axis and respective events
`are denoted as they occur at designated points ir1 time
`along such time axis. Central station 110 first transmits
`a preamble signal 300 during a time interval T1. In one
`bodirnent, preamble symbol 30!) consists of a plural-
`ity of alternating 0'3 and 1’s transmitted for a duration of
`time T1. For example, preamble symbol is a 01010] . . .
`signal.
`invention, central
`In accordance with the present
`station 110 groups paging addresses into groups of M
`wherein M is the number of paging addresses in a partic-
`ular group. For purposes of this example, and not by
`way of limitation, the number of paging addresses and
`thus the number of messages corresponding to such
`addresses is selected to be 2|] (that is, M=20). That is, as
`messages are called into central station 110 via tele-
`phone interface M0 or keyboard 160, such paging mes-
`sages and corresponding address information are held
`or stored in RAM 180 until a group of up to M=20
`messages has been provided to station 110. In alterna-
`tive embodiments of the invention, non ack-back pages
`may be interspersed with ack-back pages to increase the
`efficient throughput of the paging system if desired as
`will be discussed later. The group of M=20 ack-back
`pagers is a subgroup of the overall population of P
`pagers. Once station 110 has received 20 or M paging
`messages, microcomputer 150 sequentially transmits the
`20 corresponding addresses as a group 310 during a time
`interval T2 subsequent to time interval T1 as shown in
`FIG. 4A.
`FIG. 4B shows the sequential relationship of each of
`the addresses within group 310. The addess of the first
`pager of the group of M pagers to be addressed is desig-
`nated address I and is transmitted first in group 310 as
`shown. The pager to which address 1 corresponds is -
`designated AB-1 for reference. The address of second
`pager of the group of M selected acl:-back pagers is
`designated address 2 and is transmitted immediately
`following address 1. The pager to which address 2 cor-
`responds is designated pager AB-2. This process of
`address transmission continues sequentially in the same
`fashion until all of the addresses of the group of M
`pagers are transmitted ending with address M, the ad-
`dress of the last or M'th pager. in group 310. The pager
`to which address M corresponds ss designated pager
`AB-M. A non-ack back pager AB-3 is shown addressed
`in the block of M pages as will be described later in the
`discussion of FIG. 4H.
`In one embodiment of the invention, the duration of
`time during which preamble signal 300 is transmitted,
`namely T1, is approximately equal to 10 msec. Those
`skilled in the art will appreciate that T1 may have val-
`ues greater than or less than I0 msec providing T1 is
`sufficiently long to permit the ackback receivers 121,
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`. P to synchronize to the paging signals transmit-
`.
`122 .
`ted by central station 110. Apparatus for synchronizing
`paging receivers to paging signals is well known to
`those skilled in the art and is included in ack-back pag-
`ers 121, 122 .
`.
`. P.
`For purposes of example, the time duration T2 of the
`group 310 of addresses is selected to be approximately
`equal to 1 sec. Those skilled in the art will appreciate
`that T2 may actually be greater or less than 1 sec de-
`pending upon the number of paging addresses M se-
`lected to be in the group 310 and the frequency of trans-
`mission of the digital data comprising such paging ad-
`dresses. The selection of the time period T2 in this ex-
`ample should not be taken as in any way limiting the
`invention. To reiterate,
`the particular pagers of the
`population P which are addressed in address block 310
`are dignated as pagers AB-1 (the first pager to be
`addressed), pager AB-2 (the second pager to be ad-
`dressed). . . pager AB-M (the last pager addressed of the
`group of M pagers).
`After transmission of the group of M addresses, cen-
`tral station 1l0 transmits a reference carrier signal at a
`frequency Fgxat 320 during a time interval T3 follow-
`ing time interval T2. Subsequent
`to transmission of
`reference carrier 320, central station 110 sequentially 25
`transmits the 20 paging messages corresponding to the
`20 paging addresses of address group or block 310.
`More specifically, these M or 20 data messages are sent
`as a group or block 330 of messages. Each of the M
`messages in block 330 bears a predetermined relation- 30
`ship to the order of the pager addresses in block 310.
`For example, in one embodiment of the invention and as
`shown more clearly in FIG. 4C, message block 330
`includes message 1 data followed in time by an end of
`message (EOM) field. The EOM field of message 1 is 35
`followed sequentially in time by the message 2 data
`which is in turn followed by another EOM field. The
`process of sending the respective messages 3, 4, etc.
`within message block 330 continues until message M is
`transmitted followed by a respective EOM field as 40
`shown in FIG. 4C.
`In the embodiment of the invention described above,
`the predetermined relationship between the sequence of
`messages transmitted in message block 330 and the se-
`quence of pager of addresses transmitted in address
`block 310, is conveniently selected such that address 1 is
`first transmitted in block 310 and the message 1 corre-
`sponding to such address 1 is transmitted first in the
`later following message block 330 occurring during
`time slot T4. To illustrate this predetermined relation-
`ship further, address 2 is transmitted second, that is
`immediately after address 1 in address block 310. Corre-
`spondingly, in the later following time slot T4, message
`2 is transmitted second, that is, immediately following
`message 1’s EOM field. The same relationship exists
`between the remaining addresses in block 310 and mes-
`sages in block 330.
`The invention, however, is not limited to the particu-
`lar predetermined relationship described above be-
`tween the sequence of pager addresses in address block
`310 and corresponding messages in message block 339.
`For example, in another embodiment of the invention,
`the sequence of pager addresses would remain as illus-
`trated in FIG. 413 with address 1 being sent frst fol-
`lowed by address 2 and so forth until address M is trans-
`mitted completing the block. However, the sequential
`order in which the messages in message block 330 are
`transmitted in such embodiment may cornrnence with
`
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`6
`transmission of message M first followed by message
`M-1 (or message 19) followed by message M-2 (18) and
`so forth until message 1 is fuially transmitted at the end
`of message block 310. (EOM fields are still situated
`between messages.) What is important here is that a
`predetermined relationship exists between the order in
`which the paging addresses are transmitted in address
`block 310 to the order in which the paging messages are
`transmitted in message block 330 so as to permit ac-
`knowledge back pagers AB-1, AB-2,
`.
`.
`. AB-M to
`match a particular message within block 330 to a re-
`spective paging address of block 310. This enables a
`particular pager to determine which of the 20 paging
`messages in block 330 is intended for it, as will be dis-
`cussed subsequently in more detail. Although examples
`have been discussed above wherein the predetermined
`relationship between the order of the pager addresses of
`address block 319 and the paging messages of message
`block 330 are both ascending, and in the other example
`ascending/descending, those skilled in the art will ap-
`preciate that an arbitrary relationship between the pag-
`ing addresses on block 310 and the paging messages of
`block 330 may also be selected as long as this predeter-
`mined known relationship is programmed into acknowl-
`edge back pagers 121, 122 .
`.
`. P.
`A reference carrier exhibiting a frequency of PM is
`generated during a period of time T3 subsequent to the
`end of transmission of the pager addresses in address
`block 310. In one embodiment of the invention, T3 is
`equal to approximately 70 msec. Those skilled in the art
`will appreciate that T3 may be longer or shorter than 70
`msec providing the reference carrier shown at 32!] ex-
`hibits a time duration sufficiently long to enable fre-
`quency determining circuitry, later described, in ac]:-
`back pagers 121, 122 .
`.
`. P to determine the frequency
`of reference carrier 320.
`FIG. 4D is a time vs. evt diagram of the status of
`receiver 230 in central station 110. Subsequent to time
`period T4, receiver 230 at central station 110 is turned
`on to receive aclt-back signals from the 20 pagers in the
`group of M during a time period T5. Each of the group
`of M ack-back message signals transmitted by the re-
`spective ack-back pagers in the group of M are on a
`different respective frequency sub-band within a com-
`mon frequency channel as will be discussed in more
`detail subsequently. Receiver 230 is thus capable of
`distinguishing and decoding message signals on each of
`the 20 or M different sub-band frequencies. The config-
`uration and operation of receiver 230 is discussed in
`more detail later.
`FIG. IIE is a time versus event diagram for the status
`of ack-back pager AB-1, that is, the first addressed
`pager of the group of M pagers. FIG. 4B is drawn to the
`same time scale as FIG. 4A. During the T1 time inter-
`val, pager AB~l receives the preamble at 340. During
`the following time period T2, pager AB-1 receives and
`decodes address 1, which in this example is the address
`of pager AB-1. It is noted that prior to reception of the
`preamble at 340, pager AB-1 is in a "sleep” or “battery
`saver” state. That is, prior to such T1 time period, pager
`AB-1 and the other pagers of the population of P pag-
`ers, have several of their power consuming circuits
`turned off or placed in low power consumption states.
`Those skilled in the art are already familiar with the
`powering down of radio pager circuits in order to
`achieve battery saving and thus exactly which circuits
`in the pager are powered down, and the degree to
`which they are powered down, are not discussed here
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`in detail. What is important, however, is that the ack-
`back pagers of the population of P pagers are placed in
`a “battery saving" state or “sleep state” during pre-
`scribed periods of time such as that mentioned above
`and which will be later specified.
`When pager AB-1 receives the preamble 340 during
`time period Tl. pager AB-1 is switched from a battery
`saving state to a fully operational state such that pager
`AB-1 is capable of receiving information transmitted
`thereto. That is, subsequent to reception of the pream-
`ble at 34-0, pager A134 is fully turned on such that pager
`AB-1 receives and decodes its address at 350 at the
`beginning of the T2 time period. In one embodiment of
`the invention, pager AB-1 conveniently returns to the
`“sleep state" for the remainder of the T2 time period
`during which pager addresses are transmitted. Prior to
`receiving the reference carrier Fgx at time period T3,
`pager AB—1 is returned from the “sleep state” to the
`fully operational state. Upon reception of the reference
`carrier, FR at 360, pager AB-1 determines the fre-
`quency of such carrier in a manner described in more
`detail subsequently.
`Referring to FIG. 4E, in conjunction with 4C, it is
`seen that the message 1 transmitted during time period
`T4 at 370 is received by pager AIM at 300 as shown in
`FIG. 4B. Pager AB-1 receives message 1 at 380 and
`matches message 1 to address 1. That is, by means later
`described in more detail, pager AB-I is programmed to
`determine that message 1 is the particular message of
`the group of M messages which is intended for pager
`2113-}. Subsequent to reception and display of message 1
`at 380 as shown in FIG. 4B, the user of pager AB-1
`indicates his or her response to message 1 during a time
`period T6 at 385. Time period T6 is not drawn to scale
`with respect to the other time periods discussed. Time
`period T6 is sufficiently long to permit indication of a
`response by the pager user. Subsequent to time period
`T6, pagers AB-1, AB-2 .
`.
`. AB-M simultaneously trans-
`mit acknowledge back signals on respective frequency
`subbantis (subchannels) back to central station 110 as at
`390 during a time period T5. Subsequent to the ack-back
`transmission at 390. pagers AB-1, AB-2 .
`.
`. AB-M are
`placed in the “sleep state" until awakened again by a
`preamble as at 340. In an alternative embodimt of the
`invention. ack—back pagers AB-1 .
`.
`. AB-20 reply back
`automatically without action by the pager user. In such
`an embodiment, prior to being paged, the user prese-
`lects a reply already stored in the pager or keys into the
`pager a predetermined message which the pager uses as
`the ack back reply when it is later addressed by central
`station 110. For example, the ack-back pager user se-
`lects a “not available” response or otherwise keys into
`the pager a “not available" response when the pager
`user wishes to inform callers into central station 11!] that
`the pager user is not taking any calls currently. Clearly,
`the reply data may be provided to the ack-back pagers
`in many different ways. In the case of a user selectable
`response already programmed into the pager, time per-
`iod T6 can be arbitrarily short, that is just sufficiently
`long enough to permit transmission of such a selectable
`response whose length is predetermined and known to
`the microcomputer 150 in central station 110.
`FIG. 4-F is a time versus event diagram of the status
`of ack-back pager AB-2, that is, the second pager ad-
`dressed of the group of M ack-back pagers. Pager AB-2
`receives the preamble at 340 and then switches from a
`“sleep state” to a fully turned on state. Pager AB-2
`receives address I (the address of pager AB-1) at 350.
`
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`Pager AB-2 decodes such address I at 350 and deter-
`mines that the decoded address is not its own address.
`At 400, pager AB-2 receives its own address, namely
`address 2. Pager AB-2 decodes and determines that
`address 2 is its own address. As with pager AB-1 of
`FIG. 4B. pager AB-2 of FIG. 4F goes to the “sleep
`state” for the remainder of the T2 time period. Pager
`AB-2 “wakes up" in time for reception of the reference
`carrier F“ at 360 during time period T3. As seen by
`examining" FIG. 4-F _ir1 conjunction with FIG. 4C, pager
`AB-2 receives the AB-1 page data transmitted at 370
`within time period T4. As explained in more detail
`subsequently, pager AB-2 determines that the AB-1
`message data is not a match. That is, pager AB-2 deter-
`mines that the pager AB-1 message data (message 1) is
`not intended for pager AB-2. After the end of message
`(EOM) marker following message 1, pager AB-2 re-
`ceives the AB-2 message data (message 2) at 410 within
`time period T4. Pager AB-2 determines that the mes-
`sage 2 data at 410 is a match and that such message 2
`data is intended for AB-2. The message 2 data is then
`displayed to the user of pager AB-2 who indicates an
`acknowledge back response to pager AB-2 during time
`period T6 at 415. During the subsequent time period T5,
`hhe acknowledge back message is sent to central station
`119 on a second frequency sub-band different from the
`first frequency sub—band on which pager AB-1 trans-
`mits. Subsequent to transmission of the acknowledge
`back response at time period T5, pager AB-2 is caused
`to go to sleep.
`FIG. 4G is a time versus event diagram of the status
`of ack-back pager AB-M, the last of the group of M
`pagers to be addressed. Pager AB-M receives the pre-
`amble at 340 to switch it from a “battery saver state" to
`a fully operational state. Pager AB-M then receives the
`19 addresses of the other pagers in the group of M, such
`as at 350 and 409 until finally pager AB-M receives and
`decodes its own address at 420. Pager AB-M is thus
`signaled that a message for it will be transmitted mo-
`mentarily. Pager AB-M receives the reference carrier
`signal Fgx at 360. Referring to FIG. 4G in conjunction
`with FIG. 4C, it is seen that pager AB-M receives mes-
`sage L message 2 .
`.
`. message M-1 and determines that
`all of these messages are not matches. That is, such page
`data messages are not intended for AB-M. Pager AB-M
`receives the page data message M transmitted at 430
`(FIG. 4C) and received at 440 (FIG. 40) within time
`period T4. Pager AB-M determines that such message
`M at 440 is intended for pager AB-M and displays the
`contents as such message M to the pager user. During
`time period T6 at 415, the pager user