.
`Umted States Patent
`
`[19]
`
`USDOS365569A
`[11] Pateut Number:
`
`5,365,569
`
`Witsamnn et a].
`
`[45] Date of Patent:
`
`Nov. 15, 1994
`
`15‘] Egg? smm WION
`
`[7'5]
`
`FOREIGN PATENT DOCUMENTS
`0228237
`9/1989 Japan
`04-70027
`3/1992 Japan
`
`31'5”!)7
`375/107
`
`Inventors: Mark I... Wits-nan; Roger E. Bum
`David W. Gleaner; Joe] R.
`Crowley-Diem, an of Quincy, 111.
`.
`.
`[73] Assignee: Gleam Emma. Ltd
`Vancouver, Canada
`
`“
`
`mm” Emm‘"”—C“"‘S Km“
`Assistant Examiner—Michael B. Chernoi’f
`Attorney. Agent, or FEm—ChdnetisemO'Connor,
`.
`Johnson&Kmdness
`ansrmcr
`[57]
`A simulcast system for broadcasting the same signal for
`a number of Spaced—apart broadcast sites is disclosed.
`The system (20) of this invention includes a hub (28)
`[22] Filed;
`A“ 17‘ 1992
`5
`adapted to receive the signal to be simulcast and a num-
`her of Stations (30> that «=wa broadest the signal-
`Eli 3’5 “3. :31::::::::::::::::.If???‘143?5¥?5§}§°3
`The ““5 1’1““ "1° “19"“ Sign” PM“ ”rm“! ‘° ”‘5
`[53] Field of Searcha 3155/16. 31-2. 56.1,
`PDBs (36). As part of the signal packetization process,
`.
`.
`455/72, 12.1, 13.2, 13.1; 379/56. 5?, l, 9. 27,
`the hub evaluates the rate at which the 513211an should be
`”1* 279; 340/321“; 3751'107. 33, In};
`broadcast and assigns a start time at which the signals
`should be broadcast; this information is attached to the
`37065.1. 95'3’ 94’1' 94'2' 84
`PDBs. After :1 PER is created it is forwarded to the
`.
`References
`Stations over a link channel. Each station includes a
`Cited
`station controller (32) and a station transmitter (31-). The
`11-5 PATENT DOCUMENTS
`station controller. upon receiving a PDB. forwards the
`£709,402 sums-1 arm;
`455/51;
`4.849.993
`7/1989 Johnsoneta!
`signal therein to the transmitter at the start time indi-
`375/103
`
`catod and at the appropriate broadcast rate. All of the
`4,350,032 7/1939 Freeburg .....
`455/512
`
`stations transmitting the signals contained within a sin-
`4.968.966 11/1990 Jas‘mld ct al.
`340/325-44
`gle PDB do so based on the start time and broadcast
`g-ggrgg 1323i T9903 5‘ “1.1“
`Wit-1535?;5:
`
`rate information contained in that PDB. Consequently.
`-
`.
`am a '
`-
`each station 1,1,0“qu same signals at the me time
`5.077.759 12/1991 lelharn .........
`345/10?
`
`and at the same rate so as to ensure their simultaneous
`i'fig'gi 1323: Kohno let-.31 ‘
`”'sggi’g
`
`455/16 Mini-“ion-
`5.162.790 11/1992 1m
`
`.. 455113.:
`5,220,516 6/1993 LoGano eta].
`
`5,257,404 10/1993 Goreham et a1.
`455151.:
`
`[21] Appl. No; 931,789
`
`56
`
`]
`
`[
`
`47 Claims, 21 Drawing Sheets
`
`
` 3!]
`STA ”0N m so new
`
`
`‘20
`J
`
`V
`
`39
`
`'I
`STATION
`
`I
`
`STATION
`30
`
`'
`
`
`
`
` STA 7'.
`
`cwram.
`
`33
`
`30
`
`1
`
`APPLE 1010
`
`APPLE 1010
`
`1
`
`

`

`US. Patent
`
`4my15,lV.oN
`
`whS
`
`120.m
`
`5,365,569
`
`tuzBSm
`1QSEEEE
`
`953$
`
`:NEEEE
`
`>3:Em
`
`N6E
`
`>3:x3413%
`
`>5:5%
`
`an>3:Em.
`
`JG?
`
`fig,
`
`>5:Em
`
`2
`
`
`
`
`

`

`US. Patent
`
`1v.
`
`991
`
`12f02teehS
`
`5,365,569
`
`>8:Em
`
`>
`
`4msezuE::53
`
`
`
`5,2.i225.
`
`o>N_222%Te8
`Igslal
`
`
`
`/\A/
`
`.I(
`
`>
`
`>8:Emem.
`
`gr
`
`
`
`>32Em.cm.
`
`Ammass35:we;
`SE.5//\l¥\1%\\\
`
`
`//
`
`>5:Em.an
`
`H‘smza
`
`\
`
`\
`
`\\\\l/
`
`>
`
`as:Em.
`
`on
`
`53.
`
`HEM.
`
`«.523
`
`>
`
`anan:Em
`
`,ieiEm
`
`
`
`mmNassau.5::33
`
`mmESEE»:53
`
`NSt
`
`3
`
`
`

`

`US. Patent
`
`Nov. 15, 1994
`
`Sheet 3 of 21
`
`5,365,569
`
`34
`
`V
`
`‘3
`
`4.~:3192'
`
`45
`
`32
`
`
`STAT10NCONTROLLER
`
`
`
`(‘3:
`<2
`LL
`
`
`
`
`
`28
`
`HUB
`
`
`FACINGTERMINAL
`
`42
`
`4
`
`

`

`US. Patent
`
`Nov. 15, 1994
`
`Sheet 4 of 21
`
`5,365,569
`
`
`
`a£22«SEQ
`
`VES:3SS
`
`wE22335:
`
`Swag:55
`
`ShainaE:
`
`£23REE
`
`mm
`
`1—7a NE53:5,:
`
`EHHUHHIa
`
`REVESQMQ
`
`sawas
`
`—1
`
`5355.
`
`$252.5
`
`.92:
`
`as:
`
`mm
`
`VN
`
`xbz—SZDEE
`
`zmqqexszeb
`
`923E
`
`gussega
`
`:Eéfifi
`
`NN
`
`5
`
`
`
`
`

`

`U.S. Patent
`
`Nov. 15, 1994
`
`Sheet 5 of 21
`
`5,365,569
`
`80
`
`FLAG ADDRESS CONTROL
`
`
`
`
`
`OPCODE
`
`INFORMA TION
`
`
`
`
`
`
`
`LENGTH
`
`CONTROL
`
`STATION
`
`
`
`MESSAGE MESSAGE
`CHANNEL
`NUMBER
`PRIORITY
`NUMBER
`
`
`
`
`FIG. 5.
`
`98
`
`100
`
`MODE
`
`FREQ
`
`TIME
`
`ZONE
`
`740
`
`142
`
`144
`
`146
`
`ST. TIME
`
`LENGTH
`
`BA TA
`
`150
`
`152
`
`154
`
`i56
`
`6
`
`

`

`US. Patent
`
`4m5s
`
`nf06amS
`
`5,365,569
`
`
`
`
`
`1.#252,:m25E
` EEzEE3:EEE25E
`
`.m6E
`
`N3
`
`7
`
`
`
`

`

`US. Patent
`
`Nov. 15, 1994
`
`Sheet 7 of 21
`
`5,365,569
`
`CHECK FOR
`BIT TRANSITION
`
`ISO
`
`
`TRANSITION
`
`DETECTED
`?
`
`
`
`SITVSEE figs?"
`BIT TRANS.
`
`9
`
`- YES
`
`
`
`RECORD
`CURRENT BIT
`
`STATE AND TIME
`
`
`
`RECORD CURRENT
`BIT STATE AND
`TRANSITION TIME
`
`232
`
`FILTER
`TRANSITION
`TIME
`
`comm BIT
`DURATION
`
`I 6' 6
`
`168
`
`YES
`
`I70
`
`BIT
`DURATION
`
`
`TIME 32 TIMES
`
`GREATER OR SMALLER
`
`
`THEN N.T.L. BIT
`
`DURATION
`9
`
`
`
`
`
`
`
`NO
`
`FIG. 9A.
`
`8
`
`

`

`US. Patent
`
`Nov. 15, 1994
`
`Sheet 3 of 21
`
`5,365,569
`
`172
`
`1.94
`
`
`
`
`BIT
`
`DURA TIDN
`
`N0
`EVEN MUL TIPLE
`
`
`0F N.T.L. BIT
`
`
`DURATION
`
`9
`YES
`
`ngggggg 33:3
`
`:74
`
`ADD BITS
`T0 PDB BUFFER
`
`”'6
`
`
`
`
`
`
`
`B!T
`
`DURATION
`
`NO
`EVEN nmsog
`
`OF N.T.L. BIT
`
`DUMPTION
`
`.
`YES 0
`
`CONVERT ALL BITS
`IN PDB BUFFER T0
`NEW BIT DURATION
`
`41m NEW an"
`TO PDB BUFFER
`
`SET LAST BIT
`
`DURATION TO NEW BIT
`
`DURATION
`
`:93
`
`’33
`
`'99
`
`{90
`
`
`
`THAN 640 BITS
`
`
`IN PDB BUFFER OR
`TOTAL DURATION
`GREATER THAN
`
`300m
`9
`
`YES
`
`FLUSH BITS IN
`PDB BUFFER
`UREA TE PDB
`
`I
`
`192
`
`FIG. QB.
`
`9
`
`

`

`US. Patent
`
`Nov. 15, 1994
`
`Sheet 9 of 21
`
`5,365,569
`
`206'
`
`FIND COMMON
`DIVISOR BETWEEN
`LAST AND NIT.
`BIT DURATIONS
`
`207
`
`
`
`
`COMMON
`DIVISOR
`?
`
`NO
`
`YES
`
`CONVERT BITS IN
`PDB BUFFER TO
`
`NEW BIT DURATION
`
`208
`
`FLUSH ALL BITS
`FROM BUFFER
`
`
`
`CREATE PUB
`
`220
`
`COMPUTER CAPTURED
`BITS TO NEW
`BIT DURATION
`
`2m
`
`.401) CAPTUREB BIT
`TO PDB BUFFER
`
`222
`
`ADD CAPTURED BITS
`T0 PDB BUFFER
`
`2 ’2
`
`
`
`SA VE LAST BIT
`TRANSITION TIME
`AS NEW
`DURATION
`
`SET BIT DURATION
`T0 THAT 0F
`COMMON DIVISOR
`
`FIG-3.90.
`
`10
`
`10
`
`

`

`US. Patent
`
`Nov. 15, 1994
`
`Sheet 10 of 21
`
`5,365,569
`
`T73
`
`130
`
`
`
`333,11. SEC.
`
`2500,12. SEC.
`
`FIG. 10A.
`
`FIG. 100.
`
`11
`
`11
`
`

`

`US. Patent
`
`Nov. 15, 1994
`
`Sheet 11 of 21
`
`5,365,569
`
`FIG 11A
`
`7“:
`3333p. SEC. 1666;; SEC
`
`I i
`
`a I
`
`FIG. 17D.
`
`12
`
`12
`
`

`

`US. Patent
`
`Nov. 15, 1994
`
`Sheet 12 of 21
`
`5,365,569
`
`’7"U
`
`9—;
`
`LP” F/G.72A.
`
`J
`
`IOODuSEC.
`
`666;; SEC.
`
`
`
`13
`
`13
`
`

`

`US. Patent
`
`Nov. 15, 1994
`
`Sheet 13 of 21
`
`5,365,569
`
`
`
`CENTRAL
`
`l- PROgErISYSING fl
`
`
`
`
`MEMORY
`4%.!
`
`LNK. CHNL.5
`LNK. CHNL.5
`
`STA T. PNTR
`
`LNK. CHNL.4
`
`LNK. CHNL.3
`
`LNK. CHNL.2
`
`LNK. CHNL.,
`
`PDB PNTR
`
`PDB PNTR — 282
`P33 PNTR
`
`PRM LNK.
`
`3m). LNK.
`
`LNK. PNTR
`
`FIG. 14.
`
`300
`
`\
`
`30!
`
`302
`
`304
`
`306
`
`
`
`ADDR.
`
`
`
`FIG. 15.
`
`14
`
`14
`
`

`

`US. Patent
`
`Nov. 15, 1994
`
`Sheet 14 of 21
`
`5,365,569
`
`\ES:3ES
`
`NE:EuE:
`
`Im\ll.
`ammwmié
`
`435%.
`
`53%
`
`8.3m:
`
`REE
`
`A:qua
`
`oumfifi
`
`.SEK
`
`as3.3
`
`subs:
`
`53%
`
`th.<.3\k-
`
`8.395
`
`km?»
`
`~5me
`
`.SEE
`
`.9Gt
`
`SEE:ES
`
`mm
`
`’
`
`l
`
`15
`
`15
`
`
`
`
`
`
`
`
`

`

`US. Patent
`
`Nov. 15, 1994
`
`Sheet 15 of 21
`
`5,365,569
`
`
`
`
`mmrfiamwxix—5ia>233EbwzbbwmmF595:mmmmqex
`3%wmmvmm.Nmmownm3“mvm3%
`
`
`Emammagt33dxmqwmhMEVS‘MEEEQNE
`gm.Nvmmmmmmmmmm
`
`6me
`
`N“GE
`
`16
`
`

`

`US. Patent
`
`Nov. 15, 1994
`
`Sheet 16 of 21
`
`5,365,569
`
`280.
`
`28!)
`
`
`
` ALAIN HUB
`
`REBUNDANT
`
`
`REDUNDANC Y
`CONTROLLER
`
`
`
`
`
`
`PA SING
`TO LINK
`TERMINAL
`CHANNELS
`
`
`Z2
`24
`
`RED UNDANCY
`CONTROLLER
`
`1/0
`
`362
`
`17
`
`17
`
`

`

`US. Patent
`
`Nov. 15, 1994
`
`Sheet 17 of 21
`
`5,365,569
`
`t2.“x3.
`
`
`
`mam.mamwmuctmcxus.
`
`mhuuemssseu
`
`hath!
`
`mam.
`
`3&225m2:~§§§SE
`
`18
`
`18
`
`

`

`5,365,569
`
`NN6E
`
`US. Patent
`
`11v.0N
`
`4m
`
`mS
`
`2f0
`
`mSE8aVE235E:
`
`11N6
`
`s,5ENE:
`
`an»
`
`zemmEeEEgE
`
`Na».
`
`
`
`i;1;u>:u§-
`
`maimumz
`
`$5,235E:
`
`555%22::
`
`
`
`«SEES.55..
`
`ms:BEBE
`
`19
`
`19
`
`
`
`
`
`

`

`US. Patent
`
`m.
`
`4
`
`9m
`
`5,365,569
`
`n>33in
`
`.m323:5me
`
`“m.
`
`NV03:max:
`
`>5:Em>5:x5.
`
`«4ax4.
`
`>5:Em.3«
`
`No3:
`
`no.“
`4‘
`
`223.5%
`
`53:
`
`m3S
`
`cm
`
`em
`
`20
`
`20
`
`
`

`

`US. Patent
`
`Nov. 15, 1994
`
`Sheet 20 of 21
`
`5,365,569
`
`450
`
`452
`
`454
`
`456
`
`458
`
`\. BROADCAST
`
`LENGTH
`
`TIME
`
`FIG.23.
`
`21
`
`21
`
`

`

`US. Patent
`
`Nov. 15, 1994
`
`Sheet 21 of 21
`
`5,365,569
`
`22.2%
`
`$33.28
`
`
`
`9%
`
`
`
`memMMuozm
`
`emote
`
`NZSEME
`
`mam
`
`.VNGE
`
`”@2235ES
`
`_522::E:_
`
`22
`
`22
`
`
`

`

`1
`
`5,365,569
`
`5
`
`10
`
`IS
`
`20
`
`25
`
`35
`
`2
`received signals are to be rebroadcast. Collectively, the
`individual delay circuits are set to ensure that the trans-
`mitter sites associated therewith all broadcast the same
`signal at the same time.
`While analog systems have proved useful for simul-
`cast applications. they are not without disadvantages.
`Some analog simulcast
`systems
`require significant
`amounts of air time to constantly send new delay rate
`instructions to the individual mmincr sites to ensure
`that they all transmit the same signal. This “overhead"
`air time may significantly depreciate the amount of air
`time that is available to forward signals containing use-
`ful data, such as paging signals, to the transmitter sites
`for rebroadcast. Furthermore, the actual transmission
`delay time for any transmit station is a function of the
`link prepagation time, the time it takes the signals to
`travel from the central station to the transmit station. If
`this link should change, as may happen because of an
`intermediate component failure, or due to a change in
`the day-to-day economics of running particular links,
`then the link propagation time will change. For exam-
`ple, the satellite receiver at one transmitter station may
`be taken out of service for maintenance, in order to
`maintain the transmission of simulcast data to the site. a
`link over the publicly switched telephone network may
`be temporarily established. Until a new link propagation
`time is forwarded to a transmitter site, that site will
`broadcast the page at a time out of phase with those
`broadcast by the surrounding sites. Still another disad-
`vantage cf many simulcast transmission systems is that
`they require maintenance receivers to continually moni-
`tor the delay between the time a signal is first forwarded
`by a central unit and the time it is finally broadcast by a
`transmitter site; this information is then used by the
`system's control circuitry to regularly adjust the trans-
`mission delay times for the individual transmitting sites.
`A further limitation associated with analog linking
`networks is that in each step of the central station-to-
`transmittcr site signal mnsfer. there is degradation of
`the signal. This happens as a result of the normal signal
`loss that occurs when an analog signal is processed by
`an amplifier and that occurs as a consequence of the
`broadcast and transmission of a radio signal. Usually,
`the longer the link between the central station and the
`transmitter site and/or the more times the signal is sub-
`jected to intermediate processing, the greater the degra-
`dation from the original signal. As a consequence of this
`degradation.
`the final signal that is received by the
`transmitter site for simultaneous broadcast may be so
`changed that the actual broadcast signal is unintelligible
`by the receivers for which it was intended.
`SUMMARY OF THE INVENTION
`
`DIGITAL SIMUUZAST TRANSMSSION SYSTEM
`
`FIELD OF THE INVENTION
`
`This invention relates generally to aimulcasttransmis~
`sion systems and, more particularly. to asimulcast mans-
`mis-on system for broadcasting signals that are for-
`warded to transmitting sites over one or more digital
`signal communication networks.
`BACKGROUND OF THE INVENTION
`
`Shnulcasting is the practice of broadcasting a single
`radio-frequency signal from multiple locations at the
`same time. Simulcast transmission networks are estab-
`lished when it is desirable to maximize the area over
`which receivers tuned to the network’s broadcast fre-
`quency are able to pick up and process the broadcast
`signal. A paging system is one type of radio system that
`is operated as a simulcast system. In a paging system.
`system subscribers are provided with small radio re-
`ceivers, called pagers. The paging system further in-
`cludes one or more paging terminals and a number of
`transmitter sites. The paging terminals are connected to
`the publicly switched telephone network and receive
`calls for the individual system subscribers In response
`to receiving an incoming call, a paging terminal will
`generate a message, a page. The page is forwarded to
`the transmitter sites. which broadcast the page for re-
`ceipt by the subscriber’s pager. When a page is received
`by a pager for the subscriber to whom the pager is
`assigned, an annunciator or display integral with the
`pager is actuated to inform the subscriber of the call.
`Paging systems are provided with multiple, spaced-
`aparr transmitter sites to maximize the coverage area in
`which a pager can function.
`The individual transmitter sites of a paging system
`and of other simulcast networks must operate in concert
`soas totransmit thesamesignalattheexactsamein-
`scant. This is important because pagers or other receiv-
`ers in areas where signals from two or more transmit-
`ting sites can be received will receive signals from each
`transmitter site. If the signals are out of phase, their sum
`produces a single signal that frequently cannot be pro-
`cessed by the receiver. Thus, paging systems and like
`broadcast systems are typically constructed so that each
`transmitter site broadcasts the same signal simulta-
`neously. This ensures that in overlap areas the signals
`from multiple transmitter sites will be in phase and
`combine to produce a single signal that can readily be
`processed by the intended receiver.
`Many simulcast systems have some type of analog
`signal link network between the central station. from
`which the signal to be broadcast originates, and the
`individual transmitter sites from which the signal
`is
`finally broadcast. A link network may take the form of
`a telephone or fiber-optic signal link between the cen-
`tral station and one or more particular transmitter sites.
`A link may alternatively take the form of a radio link
`between the central station and the transmitter site over
`a carrier frequency different from that over which the
`transmitter sites actually broadcast the simulcast signals
`Thelinkstosometransmittersitesmayacruallybea
`multi—link connection. For example, it is not uncommon
`for a central station to first forward the signal to be
`simulcmt to a satellite transmitter. The signal is sent up
`to a satellite, which retransmits it to one or more trans-
`mitter sites. In some of these systems each transmitter
`site includes a delay circuit that regulates when the
`
`55
`
`60
`
`65
`
`This invention relates generally to a new simulcast
`system for linking remote transmitter sites to a central
`site and for ensuring that the transmitter sites all broad-
`cast the same signal at the same time. More particularly,
`this invention is related to a simulcast transmission sys-
`tem that transmits data in digital format to the system
`transmitter sites and wherein integral with the data are
`instructions that direct all the transmitter sites to broad-
`cast the data at a specific time and in a specific format.
`The simulcast transmission system of this invention
`includes a central unit. called a hub. that in a paging
`system environment is configured to accept the pages
`formed by one or more paging terminals. There are also
`a number of transmitter sites, called stations, that accept
`
`23
`
`23
`
`

`

`5,365,569
`
`3
`pages from the hub and rebroadcast them for general
`reception by the pagers. The hub receives, or captures.
`paging signals generated by the paging terminals. Based
`on ancillary information generated with the paging
`signalsandonthe characterisfitzsofthepsging signals
`themselves, the hub determines lthe particular format of
`the paging signals that are generated by the paging
`terminal Specifically, the hub determines if the signals
`areinanalogordigital format. Ifthesignalsareiudigi-
`tal format, the hub determines the time period of each to
`signal, which is referred to as its bit duration. Regard-
`lessoftbeformoftbepagesuponleavingthepaging
`terminal. the hub repackage: the pages into a digital
`signal form wherein all of the signals have the same bit
`duration. The signals are placed in a packet called a 15
`paging data block (PDB). At the head of each PDB, the
`hub places a block of control instructions indicating the
`start time at which the signals therein should be broad-
`cast and data from which the rate of broadcast of the
`signals can be determined. The PDBs are then sent to 20
`me individual stations over one or more link channels.
`which serve as the hulHo—station signal pathways The
`P985 are sent over the link channels to the stations at a
`rate faster than the rate at which the signals therein are
`broadcast
`The stations each include a station controller that is
`adapted to receive the PDBs over the link channels and
`a transmitter for broadcasting the signals contained in
`the PDBs. When a station receives a PDB. the station
`controller strips away the control information and for- so
`wards the paging signals to the transmitter. Based on
`the control information. the station controller then reg-
`ulates the mode in which the signals are broadcast.
`when the transmitter broadcasts the paging signals. and
`the rate at which they are broadcast.
`In the simulcast system of this invention. each station
`controller receives the same PDB. Each station con-
`trols the broadcast of data from the associated transmit-
`ter based on a common start time and baud rate informa-
`tion. Consequently, all the stations will broadcast the 40
`same information at the same time. This ensures that
`receivers, the pagers, in areas where signals from multi-
`ple stations are piCkcd up, will not receive overlapping
`signals that produce an unintelligible composite signal.
`There are a number of advantages to the simulcast 45
`system ofthis invention The start time for each PDH is
`established by the hub and nmd be for only a time later
`than tlI: time the last station will receive PDBS. Other
`tbantlrisreqtfiremenethestantimeisindepeodentof
`therime‘rttakestbePDBstOpropagatetothestations 50
`over the link channels. Consequently. a change in hub-
`to-station PDB propagation time for any single station
`will not affect that station's ability to broadcast informa-
`tion simultaneously with the other stations. Moreover,
`the PDBs are sent to the stations over the link channels 55
`at a rate faster than the rate at which the pages therein
`are to bebroadcast. Thismakesitposaible to use thelink
`channels as a medium for other communication, such as
`the sending of commands and configuration information
`to the stations, without infringing on the time needed to 6!)
`forward the page: to the stations for broadcast.
`The system of this invention also operates indepen-
`dently of the characteristics of the signals it is used to
`broadcast. For example, whenever the data rate of the
`signals to be broadcast changes, or the nature changes 65
`from digital to analog format, the system automatically
`sends the signals'in a PDB with appropriate transmis-
`sion connol information. On receipt by the station con
`
`4
`trailers. the data are automatically simulcast at the ap-
`propriate time. and in the appropriate format based on
`that control information. Thus, this system is well suited
`to simulcast signals from paging terminals and like units
`that generate signals having widely varying characteris-
`tics, sucb as changing baud rates. and/or that may
`change from analog to digital format.
`This simulcast system further allows PDBs to be
`forwarded to the individual stations over two or more
`link channels. Processing equipment at the individual
`station controllers can then Selectively transmit the data
`from the first error-free PDB received, or from the
`packet that has the fewest errors. Link spreading can be
`employed to forward PDBs from the hub to a particular
`station so that the station will receive some PDBs over
`a first link channel and the remainder of its PDBs over
`
`one or more additional link channels. Link Spreading is
`useful if. for example. economics or other factors make
`it difficult to send all the PDBs to a particular station
`over a single link channel. Still another advantage of
`this feature of the invention is that it allows the system
`to be configured so that there is always one or more
`secondary link channels over which PDBs can be for-
`warded to the individual stations in the event that the
`primary link channels fail. Should such failure occur,
`the station controllers will receive PDBs over the sec-
`ondary link channel to ensure the uninterrupted broad-
`cast of pages.
`Another feature of this invention is that it does not
`require the use of maintenance receivers to constantly
`monitor the signals broadcast by the various stations to
`ensure that the signals are broadcast in synchronization
`Also, commands to the stations can be interleaved with
`the transmission of PDBs to the stations to keep the loss
`oflink transmission time to a minimum.
`Furthermore, error correction material is added to
`the PDBs prior to their transmission Otter the link chan-
`nels. The station controllers use this error correction
`material to correct errors that develop in PDBs during
`the transmission to the stations. This ensures that the
`control information acted upon by the station controller
`and the paging signals that are broadcast by the trans-
`mitter are as similar as possible to the information and
`paging signals that were first generated by the hub.
`Still another feature of this invention is that signals
`other than signals for rei'trttadcarit1 the PDBs, can be
`broadcast over the link channels. The link channels can
`be used as the communications medium for broadcast-
`ing software instructions for downloading to the station
`controllers. This reduces the frequency with which
`personnel have to make site visits to the stations to
`perform hands-on maintenance or system-updating
`tasks. Also. some link channels may be configured as
`duplex links over which signals can be transmitted by
`the stations back to the hub. This allows the link chan-
`nels to beuseduotonlyaspaths over which PDBa and
`station instructions are transmitted. but also as the me—
`dium through which the stations transmit information
`back to the hub regarding their operational status. This
`featureofthe systemserveatominimize theneedtoset
`up ancillary station-to-hub links to reduce the overall
`costs associated with operating a simulcast system.
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`The invention is pointed out with particularity in the
`appended claims. The above and further advantages of
`the invention may be better understood by referring to
`
`5
`
`25
`
`35
`
`24
`
`24
`
`

`

`5,365,569
`
`6
`
`GLOSSARY
`
`5
`the following description, taken in conjunction with the
`accompanying drawings, in which:
`FIG. 1 is a bloolt diagram of the basic elements of the
`paging system of this invention;-
`FIG. 2 is a block diagram illustrating how a plurality
`of local area groups of stations comprise a single wide
`area group of paging stations;
`FIG. 3 is a diagrammatic view of the publicly
`switched telephone net-work-to-station interconnec-
`tions established by the broadcast system of this inven-
`lion;
`FIG. 4 is a block diagram view of the major compo-
`nents of the hub of the system of this invention;
`FIG. 5 depicts the elements of an HDLC frame;
`FIG. 6 illustrates in block diagram form a paging
`terminal interface;
`FIG. 7 illustrates a control-type paging data block;
`FIG. 8 illustrates a data-type paging data block;
`FIGS. 9A-9C represent in block diagram form the
`processing steps performed by the paging terminal in«
`terface to analyze, or capture, digital paging signals;
`FIG.
`lllA illustrates the profile of one particular
`digital paging signal captured by the paging terminal
`interface;
`FIGS. 1013 and 10C illustrate the contents of the PDB
`buffer before and after the capture of the digital paging
`signal of FIG. 10A;
`FIG. 11A illustrates the profile of another digital
`paging signal captured by the paging terminal interface;
`FIGS. llB—IID illustrate the contents of the PDB
`bufi'er before, during. and after the capture of the digital
`paging signal of FIG. 11A,-
`F'IG. 11A illustrates the profile of another digital
`paging signal captured by the paging terminal interface;
`FIGS. 12B-12D illustrate the contents of the PDB
`bufi'er before, during. and after the capture of the digital
`paging signal of FIG. 12A;
`FIG. 13 depicts in block diagram form the hub cen-
`tral processing unit;
`FIG. It depicts the link tables and link channel
`queues that are stored in the memory of the hub central
`processing unit;
`FIG. 15 depicts the structure of a station packet;
`FIG. 16 depicts in block diagram form a link modem;
`FIG. 17 depicts the structure of a link flame;
`FIG. 18 is a block diagram depicting the relationship
`between the redundancy controller and the other con»
`trad-station elements of this invention. the main hub, the
`redundant hub. the paging terminals. and the link chan-
`nels;
`FIG. 19 depicts in block diagram form a trantnnitting
`station including the system controller through which
`paging signals are forwarded to a. station transmitter for
`broadcast;
`FIG. 20 depicts in block diagram form primary com-
`ponents of a converter uplink repeater,
`FIG. 2]. depicts the primary components ofa mainte-
`nance Operating point;
`FIG. 2 depicts hOw a system of this invention de-
`signed to simulcast multiple signals in a single geo»
`graphic area can be provided with a spare. or redun—
`dant, transmitting station;
`FIG. 23 illustrates an alternative form of a data-type
`paging black: and
`FIG. ”depicts in block diagram form an alternative
`transmitting station including the system control that
`regenerates the signals for broadcast by the station's
`transmitter.
`
`5
`
`ll}
`
`15
`
`25
`
`30
`
`35
`
`45
`
`55
`
`65
`
`The following are definitions of frequently appearing
`terms and acronyms that appear in the Detailed De-
`scription. Terms that have a subscript suffix “g” are
`those wherein the system of this invention has multiple
`numbers of those units. which are distinguished from
`each other in the Detailed Description.
`CURE Convener Uplink Repeater. A. unit in a hub-
`to-station link channel that serves as the interface
`
`between segments of the channel.
`GPIO General Purpose Input-Output board. An in-
`terface device connected between the hub. a sta-
`tion, a CURE or MOP. and the TNPP link.
`HDLC bus/frame High-level Data Link Control bus.
`The intra-hub bus over which signals are ex-
`changed between the hub central processor and the
`PTIs and the LMs. Signals are transferred over the
`HDLC bus in packets lmowu as I-[DLC frames.
`Hub The central unit of the system that receives
`paging signals from a paging terminal and that
`forward s the paging signals to the stations for
`broadcast by the stations.
`Link frame The packet in which station packets are
`sent over a link channel from the hub to the sta-
`dons.
`LAG Local Area Group. A subset of stations in a
`wide area group.
`Link channel, A communications network over
`which PDBS are transmitted from the hub to one or
`more stations.
`LM; Link Modern. The interface unit between the
`hub and a link channel over which PDBs are for-
`ward to the link channel. Each link modem serves
`as the interface to two separate link channels.
`MOP Maintenance Operating Point. A. receiver posi-
`tioned to monitor the signals broadcast by one or
`more stations and that provides status reports on
`the operating state of the associated stations back
`to the hub on the basis of those signals.
`Paging terminal A unit that generates paging signals
`for simulcast by the system of this invention.
`I'VI‘Ix Paging Terminal Interface. The interface unit of
`the hub that receives paging signals from the pag-
`ing terminal and converts them into PDBs.
`PDB Paging Data Block. The basic signal packet in
`which paging signals and the control information
`for regulating the broadcast of same are broadcast
`from the hub to the stations.
`Station A transmitter site distal from the hub from
`which signals are broadcast. Signals are broadcast
`from a number of stations simultaneously.
`Station packet A packet of data that is sent to the
`stations from the hub central processing unit
`through a link modem and a link channel. A station
`packet may contain a paging data block or mate-
`rial, such as operating instructions, that the station
`should act upon-
`TNPP link Telocator Network Paging Protocol link.
`A communications network, separate from the link
`channels, over which the system state information
`is exchanged between the hub and the other ele-
`ments of the system. the stations. the MOPS, and
`the CURES.
`WAG Wide Area Group. A large set of stations
`through which pages are broadcast.
`
`25
`
`25
`
`

`

`7
`
`5,365,569
`
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENT
`
`I. System overview
`FIG. 1 illustrates a simulcast broadcast system 20 of 5
`this invention. The system 20 broadcasts pages that are
`generated by a set of paging terminals 22 and 24 con-
`nected to a publicly switched telephone network
`(PSTN)26. The system 20 includes a hub 28 that re-
`ceives the pages from the paging terminals 22 and 24 to
`and a set of stations 30 that broadcast
`the pages
`throughout the area in which the system operates. The
`pages broadcast by the stations 30 are monitored by
`receivers. known as pagers 29, assigned to individual
`systemsubscribers. Thehubflreceivestbepagesfrom 15
`the paging terminals 22 and 24 in the form of paging
`signalsandbundlesthepagingsignalsintopacltetsre
`ferred to as paging data blocks (PDBs) 36. Integral with
`each P133 36 is control information that indicates the
`start time at which the pages therein should be broad- 20
`cast and the rate at which they should be broadcast. The
`hub 28 forwards the PDBs 36 to the stations 30 over any
`convenient communications link. Each station 30 in-
`cludes a station controller 32. that processes the infor-
`mation contained in the PDBs 36. and a transmitter 34 25
`capable of broadcasting the pages over a frequency on
`which they can be monitored by the pagers 29. The
`various copies of a P133 36 sent to a number of stations
`anallcontainthesamestartlimeandbaudrate informa-
`tion. Accordingly. the station controllers 32 integral 30
`with those stations/{onward the pages contained in the
`P09 36 to their associated transmitters 34 at the same
`time and at the same speed. Thus, the individual stations
`30 will all broadcast the same paging signal at the same
`time. Consequently. pagers 29 located in areas where 35
`paging signals from two or more stations 30 can be
`received, as represented by overlapping circles 35. will
`receivesigualsthatarehtphascandthatcanbepro—
`ceased as a single. coherent signal.
`The system 20 of this invention is capable of forward- 40
`ingpagesfor simulcast to theatationswlocated inane
`or more wide area groups (WAGs) 37 ofstations, one of
`which is illustrated in bloc]: form by FIG. 2. Each
`WAG 3'! includes a number of stations located in a
`par-ocular. relatively large geographic area. Depending as
`on the availability of paging frequencies. there may be
`multiple WAGs 3‘7 in a single geographic area. The
`stations as within each WAG 3'1 are further broken
`down into small geographic subgroups called Local
`Area Groups (LAGs) 33. Some individual stations 30 50
`may belong to two or more LAG-s 38. Individual sta-
`tions 30. though. do not normally belong to multiple
`WAG! 3?.
`Each station 30 is provided with at least one transmits
`ter 31.. When the system 30 of this invention is employed 55
`asapaging system. onetypeoftransmitter thatmaybe
`employed is a (QT-7995 transmitter manufactured by
`Glenayre Electronics of Quincy. 111.. which broadcasts
`signals that have a carrier frequency of approximately
`900MHz.Transmitter3-iiscapableofbroadcasnng60
`signalsinany formathiwhich theycanbeprocessedby
`the complementary pagers 29. For example. some trans-
`mitters are capable of broadcasting analog signals, two-
`level frequency shift digital signals.
`four-level
`fre-
`quency shift signals. and/or ERMIES-format signals. 65
`Also, as represented diagrammatically by station 30:2,
`some stations may have two or more transmitters 34.
`These stations 300 are able to transmit signals over two
`
`distinct. non-interfering carrier frequencies simulta-
`neously. Station 300 is thus capable of receiving and
`broadcasting pages that are to be transmitted simulta-
`neously through the stations associated with two sepav
`rate WAGs 37.
`Also depicted by FIG. 2 are two maintenance operat-
`ing points (MOPS) 40. Each M0? Ml is adapted to re-
`ceive radio signals from one or more stations 30 over
`the frequency over which the pages are broadcast and-
`lor a frequency distinct from that over which paging
`signals are broadcast The MOPS Ml monitor the perfor-
`malice of the individual stations 30 and further receive
`status information from the stations regarding the oper-
`ating state of the stations. The MOPS so, in turn1 for.
`ward the information about the performance and oper-
`ating states of the associated stations 30 back to the hub
`28, which responds as is appropriate.
`The PSTN 26-to-station 30 interconnections to one
`particular station transmitter 34 are illustrated diagram-
`matically by FIG 3 Paging terminal 24'ts connected to
`the PSTN 26 by a set of one or more trunk lines 33. The
`paging terminal 24 receives calls for paging system
`subscribers and in response to those calls generates
`pages. Each page is a set of signals that includes an
`addresscodeto ensure thatit isonly processedbythe
`pager 29 assigned to the subscriber for whom the pag