llllllllllllllIllllllllllllllllLllllJglllll/Ellllllllllllllllllllllllll
`
`United States Patent [19]
`Thompson et al.
`
`[11] Patent Number:
`[45] Date of Patent:
`
`5,594,726
`Jan. 14, 1997
`
`[54] FREQUENCY AGILE BROADBAND
`COMMUNICATIONS SYSTEM
`
`['75] Inventors: Leo J- Thompson’ Lilbum; Gregory T-
`Dubberly, Atlanta; John A. Ritchie,
`Jr., Duluth, allof Ga.
`
`[73] Assignee: Scienti?c-Atlanta, Inc., Atlanta, Ga.
`
`3/1990 Allison, III et al. ................... .. 358/84
`4,912,552
`5/1990 Von Kohorn ...... ..
`.. 358/84
`4,926,255
`8/1990 Iwamura et a1. .
`. 379/53
`4,955,048
`4,961,109 10/1990 Tanaka .................................... .. 358/84
`(List continued on next page)
`
`FOREIGN PATENT DOCUMENTS
`Wow/13956 11,1990 WIPO.
`
`[21] Appl. No.: 219,848
`-
`_
`[22] Wed‘
`
`Mar‘ 30’ 1994
`Related US. Application Data
`
`[63] Continuation-in-part of Ser.No. 123,363, Sepv 17, 1993, Pat.
`No‘ 5’499’241‘
`[51] Int. Cl.6 ...................................................... .. H041 1/00
`[52] US. Cl. ......................... .. 370/485; 370/524; 455/51;
`455/6-1; 348/12
`[58] Field of Search ................................ .. 348/12, 11, 14,
`348/15; 370/691, 71, 73, 110.1, 112; 375/219,
`222, 202; 455/5.1, 6.10, 4.1, 6.3, 6.2, 3.1
`
`[56]
`
`References Cited
`
`U‘S- PATENT DOCUMENTS
`4,1941 Goldsmith
`272367501
`9/1966 Beltmmi,
`3,275,746
`9/1970 Hauer ...................................... .. 370/76
`3,529,088
`3,992,589 11/1976 Kuegler ....... ..
`370/120
`4,099,202 7/1978 Cavanaugh - - - - - - - -
`- - - -- 358/35
`
`OTHER PUBLICATIONS
`A Passive Optical/Coax Hybrid Network Architecture for
`Delivery of CATV, Telephony and Data Services; 1993. by
`M‘ Meslya’ pp‘ 358-364‘
`Primary Examiner_—-Benedict V. Safourek
`Assistant Examiner_AJ-it Patel
`Attorney, Agent, or Firm—Jones & Askew
`
`ABSTRACT
`[57]
`A broadband communications system for coupling tele
`phony or other digital networks to a CATV network. The
`system transmits a multiplex of telephony signals in the
`forward band of the CATV network. Each forward channel
`is QPR modulated on a carrier and contains multiple sub
`scriber telephony signals. The forward telephony channels
`are demodulated and demultiplexed by a plurality of sub
`scriber terminals into the individual telephony signals
`directed to an addressed subscriber. Audio
`control
`signals returning from the subscnber are digltized into
`standard telephony signals and QPSK modulated on a carrier
`onto the reverse band of the CATV network. The multiplic
`ity of reverse band telephony channels are demodulated and
`multiplexed into a standard telephony signal which is
`guegtly igterfaced to ;he telephonylnetwgrk. Eh? reverlse
`an I“? ‘1 ators are requ‘incy .ag‘ e a“ m0 “ ate te 6'
`hon signals from a subscnber 1n a selected one or more
`P
`y
`_
`_
`_
`frequency subbands Hi the reverse
`Of thC SUbSCI'lptlCH
`network, so as to provide selectably changeable frequencies
`and selectably variable bandwidth in the reverse band com
`mensurate with a selected subscriber communication fea
`ture. e.g. a single voice line, multiple voice lines, ISDN
`service, data communications services, security monitoring
`Services etc
`
`-
`
`-
`
`.
`
`370/951
`455/612
`
`370/1041
`370/941
`_ _ _ __ 358/34
`370/581
`358/133
`358/143
`- ' - -- 358/84
`379/53
`
`,
`
`,
`
`eme son e
`
`.
`
`5996119111 ‘1231
`1%;
`4,633,462 12/1986 Shine et all‘ n
`4709 418 11/1987 Fox etal. ........ ..
`’
`’
`-
`4,742,512
`5/1988 Akashi et al.
`4,748,618
`5/1988 Brown et a1. .
`4,761,634
`g/lggg Clark et a1_ _ _ ' _ _ _ _
`4,763,317
`8/1988 Lehman et al.
`4,849,811
`7/1989 Kleinerman .... ..
`4,887,158 12/1989 Guichard et al- -
`4,888,638 12/1939 Bob" - - - - - - - - - ~ - - -
`4,888,795 12/1989 Ando et al.
`
`4,891,694
`
`l/1990 Way . . . . . . . . . . . . . . . . .
`
`. . . .. 358/86
`
`’
`
`-
`
`4,905,080
`4,907,079
`
`358/84
`2/1990 Watanabe et al.
`3/1990 Turner et a1. ........................... .. 358/84
`
`113 Claims, 15 Drawing Sheets
`
`TELEPHONY
`TELEPHO
`NETWOR i’ NETWORK L?
`
`Flask
`NEDE
`
`crv
`,zz NETWORK !~'
`
`1
`
`INPUI ,
`INYEHFACE!
`'- 1;
`
`:
`
`HONY
`‘IE
`NE 7058 '9
`
`EMISE
`SERVKNG
`
`SUESCNEEH
`PREMISES
`
`ARRIS883IPRI0001020
`
`

`
`5,594,726
`Page 2
`
`us. PATENT DOCUMENTS
`
`4,974,252 11/1990 Osborne .................................. .. 379/92
`4,975,902 12/1990 Damany
`.370/62
`4995 071
`2/1991 Weber et al
`379/53
`5003384 3,1991 Burden ml
`358,84
`
`5,008,926
`5,014,125
`5,029,333
`
`. . . .. 379/54
`4/1991 Misholi . . . . . . . . . .
`_
`5/1991 Pocock et a1, __
`358/86
`7/1991 Graves et a1. ....................... ..m370/58.1
`
`5,063,587 11/1991 Semasa et a1. .......................... .. 379/53
`75,77
`1 H h‘
`.............................. ._
`4
`5’0
`1 12/199
`as mm
`358/8
`5,084,903
`1/1992 McNamara m1. .................... .. 375/18
`5,088,111
`2/1992 McNamara e181.
`375/18
`5,124,980
`6/1992 Maki ....... ..
`370/77
`370/50
`9/1994 Beierle er a1
`5,351,234
`8/1995 Beveridge ............................... .. 348/13
`5,440,335
`5,469,495 11/1995 Beveridge ............................... ._ 379/56
`
`ARRIS883IPRI0001021
`
`

`
`US. Patent
`
`Jan. 14, 1997
`
`Sheet 1 of 15
`
`5,594,726
`
`TELEPHONY1 0 TELEPHONY
`NETWORK N NETWORK l9
`
`1
`
`FIBER
`
`CW
`22 NETWORK L?
`
`22
`
`INTERFACE
`
`TELEPHONY
`NETWORK 1;?
`
`32
`
`::
`TELEPHONY
`NETWORK l9
`FIG. 1
`
`26 \24
`
`28
`
`SERVING
`AREA 29
`
`41
`
`39
`CLASSS
`T SWITCH
`
`_
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`245,55]
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`14'
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`FOR
`
`FIG. 2
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`32
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`(-43
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`:
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`. FOT
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`INTERFACE
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`_,
`PREMISES
`_°
`53
`—@
`3
`Ed
`
`ARRIS883IPRI0001022
`
`

`
`U.S. Patent
`
`Jan. 14, 1997
`
`Sheet 2 of 15
`
`5,594,726
`
`/—REVERSE BAND
`/
`DIPLEx CROSSOvER REGION
`
`CATv
`AELE8CJ§II8N
`
`1
`
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`
`I
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`FREQUENCY
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`ALLOCATION ~>| I<—50kHz
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`480 089'
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`
`2
`
`5
`4
`3
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`)
`
`550 MHz
`
`II
`
`5248 TELEPHONY
`5.12
`MHz MHZ UPSTREAM
`/
`388 DS¢
`
`TELEPHONY
`29.824 MHz DOWNSTREAM
`/
`480 DS¢
`
`\mH I<-128kHz
`/
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`
`UP1 UP2 UPS "-UP194 SOMHz
`
`H I<~3MHz
`'I_III_I H H III
`
`<- 15.84 MHz ->\
`
`UPSTREAM
`CHANNELS
`UP194
`UP1,UP2
`DSO-I .DSO-2
`BSD-388
`OPSK
`
`DOWNSTREAM CHANNELS
`DN1,DN2
`DN48O
`(EACH 3 MHz BAND TO
`CARRY D52 (96 B808)
`lN OPR - INCLUDING DIRECTORY
`CHANNEL AND SIGNALING CHANNEL
`
`FIG. 3C
`
`ARRIS883IPRI0001023
`
`

`
`US. Patent
`
`Jan. 14, 1997
`
`Sheet 3 0f 15
`
`5,594,726
`
`41g D
`
`
`
`"rim ............................ 1 2 mm
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`G |
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`
`4
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`FIG. 4
`
`ARRIS883IPRI0001024
`
`

`
`US. Patent
`
`Jan. 14, 1997
`
`Sheet 4 of 15
`
`5,594,726
`
`II
`DEMOD1ULATOR
`- _..____.I
`I
`DS¢
`03-0 Ii
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`TRANSMITTER :
`
`--______________-_.6"-- (P
`
`.................................... .
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`TELEPHONY TERMINAL (CIU) /— 82
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`
`CATV
`TERMINAL
`
`SUBSCRIBER 30
`PREMISES w
`
`ARRIS883IPRI0001025
`
`

`
`U.S. Patent
`
`Jan. 14, 1997
`
`Sheet 5 of 15
`
`5,594,726
`
`51
`
`D31
`
`CH1
`
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`V
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`
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`
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`FIG. 7A
`
`COM DATA
`ALARM
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`SCRAMBLER
`1/ 2 8-1
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`EN2
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`CR BIT LOC
`
`CR BIT TYPE
`
`SUBFRAME
`FIG. 7B
`
`ARRIS883IPRI0001026
`
`

`
`U.S. Patent
`
`Jan. 14, 1997
`
`Sheet 6 of 15
`
`5,594,726
`
`e
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`ARRIS883IPRI0001027
`
`

`
`U.S. Patent
`
`Jan. 14, 1997
`
`Sheet 7 0f 15
`
`5,594,726
`
`.
`
`Multiframe definition
`
`16 data bytes
`1
`O 1
`1
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`16 data bytes
`subframe1
`0 1 DL DL AL A B C
`16 data bytes
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`subframe7
`0 1 DL DL AL A B C 16 data bytes
`
`I --------------- -- total of 17 bytes per subframe --------------- --|
`2 ms subframe period
`68 kb/s data rate
`
`SUBFRAME
`1
`I__I_=__B | aDsD DATA BYTES | DL [Rose DATA BYTESI DL | sDsD DATA BYTESW
`FRAMING R'ié' ________________________________________________________________________________ "
`(7 bits SYNC
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`DATABYTES
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`4 SUBFRAMES = 1 SUPERFRAME
`
`|
`
`FIG. 9B
`
`DIRECTORY SIGNALING
`CHANNEL CHANNEL
`
`
`
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`
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`
`FIG. 9C
`
`ARRIS883IPRI0001028
`
`

`
`U.S. Patent
`
`J
`
`14, 1997
`
`,m8tM...hS
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`51
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`ARRIS883IPRI0001029
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`

`
`U.S. Patent
`
`Jan. 14, 1997
`
`Sheet 9 of 15
`
`5,594,726
`
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`
`U.S. Patent
`
`Jan. 14, 1997
`
`Sheet 10 of 15
`
`5,594,726
`
`
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`ARRIS883IPRI0001031
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`

`
`U.S. Patent
`
`Jan. 14, 1997
`
`Sheet 11 of 15
`
`5,594,726
`
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`

`
`U.S. Patent
`
`Jan. 14, 1997
`
`Sheet 12 of 15
`
`5,594,726
`
`
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`
`

`
`U.S. Patent
`
`Jan. 14, 1997
`
`Sheet 13 0f 15
`
`5,594,726
`
`128 kHz
`CHANNEL
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`UP4 (5.504 MHz) s3
`
`ISDN (0)
`
`use-144
`
`(1/4 D80)
`
`20
`
`25s
`
`UNUSED
`
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`
`T1
`
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`
`OFF HOOK 260 256
`
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`
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`
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`
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`
`15
`
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`UP130 (21.632 MHz) 85 SECURITY
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`
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`
`ALARM
`
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`
`SIGNALLING
`
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`
`(EACH 128 kHz CHANNEL CARRIES TWO 64 kbps DSO'S, ONE 16 kbps DIGITAL
`OVERHEAD CHANNEL, QPSK MODULATED, IN ONE 108 kHz BAND WITH 20 kHz
`GUARD BAND)
`
`FIG. 15
`
`ARRIS883IPRI0001034
`
`

`
`US. Patent
`
`Jan. 14, 1997
`
`Sheet 14 of 15
`
`5,594,726
`
`f CALLING SUBSCRIBER
`60’
`INITIATES TELEPHONE /
`CALL
`
`V<
`LINE CARD 9s
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`
`625
`/
`
`630
`
`632
`
`INCREMENT ERROR
`COUNT FOR
`DESIGNATED CARRIER
`
`FIG. 16
`
`ARRIS883IPRI0001035
`
`

`
`US. Patent
`
`Jan. 14, 1997
`
`Sheet 15 0f 15
`
`5,594,726
`
`CALLING
`SUBSCRIBER
`INITIATES
`CALL
`
`701
`
`I
`‘I
`II
`I
`
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`FOR SUBSCRIBER
`(ON PARTICULAR
`INCOMING DSO
`LINE)
`
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`
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`IDENTITY OF
`/_\ CUSTOMER
`705
`
`\
`ASCERTAIN REQUESTED
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`
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`
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`
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`
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`UNUSED D80 8 8‘ REVERSE IN REvERsE CI-IANNEL
`CHANNELS uPn
`
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`
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`LEVEL TABLE)
`
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`TRANSMIT SELECTED REVERSE
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`AND
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`DSO FOR INCOMING SIGNALS
`IN FORWARD DIRECTORY CHANNEL
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`
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`
`FIG. 17
`
`ARRIS883IPRI0001036
`
`

`
`5,594,726
`
`1
`FREQUENCY AGILE BROADBAND
`COMMUNICATIONS SYSTEM
`
`CROSS REFERENCE TO RELATED
`APPLICATION
`
`This application is a continuation-in-part of application
`Ser. No. 08/123,363, ?led Sep. 17, 1993, now US. Pat. No.
`5,499,241, entitled “Broadband Communications System”.
`
`FIELD OF THE INVENTION
`
`The system pertains generally to broadband communica
`tions systems, such as cable or community antenna televi
`sion (CATV) networks, and is more particularly directed to
`communicating telephony signals, and other or similar sig
`nals, over CATV and equivalent networks.
`
`BACKGROUND OF THE INVENTION
`
`2
`trunk system typically comprises of a combination of
`coaxial cable and optical ?bers with trunk ampli?ers peri
`odically spaced to compensate for attenuation of the signals
`along the line. Such modern trunk systems utilizing ?ber
`optics and coaxial cable are often referred to as “?ber/coax”
`systems.
`The “distribution systems” utilize a combination of opti
`cal ?bers and coaxial cable to deliver signals from the trunk
`system into individual neighborhoods for distribution to
`subscribers. In order to compensate for various losses and
`distortions inherent in the transmission of signals along the
`cable network, line-extender ampli?ers are placed at certain
`intervals along the length of the cable. Each ampli?er is
`given just enough gain to overcome the attenuation loss of
`the section of the cable that precedes it. A distribution
`network is also called the “feeder”.
`There is a strong desire in the CATV and telecommuni
`cations industry to push optical ?ber as deeply as possible
`into communities, since optical ?ber communications can
`carry more signals than conventional networks. Due to
`technological and economic limitations, it has not yet
`proved feasible to provide ?ber to the subscriber’s home.
`Present day “?ber deep” CATV distribution systems includ
`ing optical ?bers and coaxial cable are often called “?ber
`To-the-Serving-Area” or “FFSA” systems.
`“Subscriber drops” are taps in the distribution system that
`feed individual 75 .Q coaxial cable lines into subscribers’
`television sets or subscriber terminals, often referred to as
`“subscriber premises equipment” or “customer premises
`equipment” (“CPE”). Since the tap is the ?nal service point
`immediately prior to the subscriber premises, channel autho
`rization circuitry is often placed in the tap to control access
`to scrambled or premium programming.
`Cable distribution systems were originally designed to
`distribute television and radio signals in the “downstream”
`direction only (i.e., from a central headend location to
`multiple subscriber locations, also referred to as the “for
`ward” path). Therefore, the component equipment of many
`older cable systems, which includes ampli?ers and compen
`sation networks, is typically adapted to deliver signals in the
`forward direction only. For downstream transmissions, typi
`cal CATV systems provide a series of video channels, each
`6 MHz in bandwidth, which are frequency division multi
`plexed across the forward band, in the 50 MHz to 550 MHZ
`region of the frequency spectrum. As ?ber is moved more
`deeply into the serving areas in ?ber/coax and Fl‘SA con
`?gurations, the bandwidth of the coax portion is expected to
`increase to over 1 GHz.
`The advent of pay-per-view services and other interactive
`television applications has fueled the development of bidi
`rectional or “two-way” cable systems that also provide for
`the transmission of signals from the subscriber locations
`back to the headend. This is often referred to as the
`“upstream” direction or the “reverse” path. This technology
`has allowed cable operators to provide many new interactive
`subscriber services on the network, such as impulse-pay
`per-view (IPPV). In many CATV systems, the band of
`signals from 5 MHz to 30 MHz is used for reverse path
`signals.
`However, the topology of a typical CATV system, which
`looks like a “tree and branch” with the headend at the base
`and branching outwardly to the subscriber’s, creates tech
`nical di?iculties in transmitting signals in the upstream
`direction back to the headend. In the traditional tree and
`branch cable network, a common set of downstream signals
`are distributed to every subscriber home in the network.
`Upstream signals ?owing from a single subscriber toward
`
`20
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`25
`
`30
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`35
`
`40
`
`In order to introduce the present invention and the prob
`lems that it solves, it is useful to overview a conventional
`CATV broadband communication system, and then examine
`certain prior approaches to problems encountered when
`attempting to introduce telephony signals into the broadband
`environment.
`Conventional Cable Television Systems (CATV)
`Cable television systems, sometimes referred to as com
`munity-antenna television (CATV) systems, are broadband
`communications networks of coaxial cable and optical ?ber
`that distribute television, audio, and data signals to sub
`scriber homes or businesses. In a typical CATV system, a
`single advantageously located antenna array feeding a cable
`network supplies each individual subscriber with a usable
`television signal.
`'
`Since the pioneer days, cable networks have experienced
`enormous growth and expansion in the United States, par
`ticularly in urban networks. It is estimated that CATV
`networks currently pass approximately 90% of the popula
`tion in the United States, with approximately 60—65% of all
`households actually being connected. While cable systems
`originally had very simple architectures and provided a
`limited number of different television signals, the increase in
`the number of television broadcasters and television owners
`over the last several decades has resulted in much more
`complex and costly modern cable distribution systems.
`A typical CATV system comprises four main elements: a
`headend, a trunk system, a distribution system, and sub
`scriber drops.
`The “headend” is a signal reception and processing center
`that collects, organizes and distributes signals. The headend
`receives satellite-delivered video and audio programming,
`over-the-air broadcast TV station signals, and network feeds
`delivered by terrestrial microwave and other communication
`systems. In addition, headends may inject local broadcasting
`into the package of signals sent to subscribers such as
`commercials and live programming created in a studio.
`The headend contains signal-processing equipment that
`controls the output level of the signals, regulates the signal
`to-noise ratio, and suppresses undesired out-of-band signals.
`Typical signal-processing equipment includes a heterodyne
`processor or a demodulator-modulator pair. The headend
`then modulates received signals onto separate radio fre
`quency (RF) carriers and combines them for transmission
`over the cable system.
`The “trunk system” is the main artery of the CATV
`65
`network that canies the signals from the headend to a
`number of distribution points in the community. A modem
`
`45
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`ARRIS883IPRI0001037
`
`

`
`3
`the headend pass by all the other upstream subscriber homes
`on the segment of distribution cable that serves the neigh
`borhood.
`The standard tree and branch topology has not proven to
`be well suited for sending signals from each subscriber
`location back to the headend, as is required for bidirectional
`communication services. Tree and branch cable distribution
`systems are the most ef?cient in terms of cable and distri
`bution usage when signals have to be distributed in only the
`downstream direction. A cable distribution system is gener
`ally a very noisy environment, especially in the reverse path.
`Interfering signals may originate from a number of common
`sources, such as airplanes passing overhead or from Citizens
`Band (CB) radios that operate at a common frequency of 27
`MHz, which is within the typical reverse channel bandwidth
`of CATV networks. Since the reverse direction of a tree and
`branch con?guration appears as an inverted tree, noise is
`propagated from multiple distribution points to a single
`point, the headend. Therefore, all of the individual noise
`contributions collectively add together to produce a very
`noisy environment and a communications problem at the
`headend.
`Present day FFSA systems facilitate the communication
`of signals in the reverse direction by dividing the subscriber
`base of a cable network into manageable serving areas of
`approximately 400-2500 subscribers. This allows for the
`reuse of limited reverse band frequency ranges for smaller
`groups of subscribers. The headend serves as the central hub
`of a star con?guration to which each serving area is coupled
`by an optical communications path ending in a ?ber node.
`The ?ber node is connected to the serving area subscribers
`over a coaxial cable distribution sub-network of feeders and
`drops in each serving area. In the FTSA con?guration, some
`of the signals in the forward direction (e.g., television
`program signals) are identical for each serving area so that
`the same subscriber service is provided to all subscribers. In
`the reverse direction, the con?guration provides an indepen
`dent spectrum of frequencies con?ned to the particular
`serving area. The FTSA architecture thus provides the
`advantage of multiplying the bandwidth of the reverse
`portions of the frequency spectrum times the number of
`serving areas.
`The Desire for Telephony Service
`The ever-expanding deployment of ?ber optic technology
`in CATV systems across the country has cable operators
`looking to provide a whole new range of interactive services
`on the cable network. One area that is of particular interest
`is telephony service. Because of recent advances in tech
`nology as well as the loosening of regulations, the once
`distinct lines between the cable television network and the
`telephone network have blurred considerably. Currently
`there is a great demand for a broadband communication
`system that can e?iciently provide telephone service over
`the existing cable distribution network.
`Moreover, there is substantial interest expressed by tele
`phone system operating companies in the idea of increased
`bandwidth for provision of new services to telephone sub
`scribers, such as television; interactive computing, shop
`ping, and entertainment; videoconferencing, etc. Present day
`“copper” based telephony service (so called because of the
`use of copper wires for telephone lines) is very bandwidth
`limited—about 3 kHz-—and cannot provide for such
`enhanced services by the telephone companies without
`massive changes to the telephone networks infrastructure.
`Existing communications systems, however, have not
`proven to be well suited for the transmission of telephony
`signals on the cable network. A system for transmitting
`
`35
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`40
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`50
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`60
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`65
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`5,594,726
`
`15
`
`20
`
`4
`telephony signals must be con?gured to allow single point to
`single point distribution (i.e., from a single subscriber to a
`single subscriber). However, unlike the telephone compa
`nies with their well-established national two-way networks,
`the cable industry is fragmented into thousands of individual
`systems that are generally incapable of communicating with
`one another. The cable network is instead ideally con?gured
`for single point to multiple point signal transmission (i.e.,
`from a single headend downstream to multiple subscriber
`locations).
`Moreover, CATV systems do not have the switching
`capabilities necessary to provide point to point communi
`cations. A communications system for the transmission of
`telephone signals must therefore be compatible with the
`public switched telephone networks (“PSTN”) operated by
`the telephone operating companies. To be useful in the
`carriage of telephony signals, a CATV network must be able
`to seamlessly interface to a telephony network at a point
`where it is commercially viable to carry telephony signals.
`It must also provide signals that can pass to other parts of the
`interconnected telephone systems without extensive modu
`lation or protocol changes to thereby become part of the
`international telephone system.
`Telephony on Data Communications Network
`One approach taken to provide a bidirectional broadband
`communications system is shown in U.S. Pat. No. 5,084,903
`of McNamara et al., assigned to First Paci?c Networks
`(hereinafter referred to as “FPN”). This patent describes an
`approach to the communication of telephony signals that
`appears primarily designed to operate in an o?ice-type data
`communications network environment (e.g., Ethernet). Data
`communications networks are typically bandwidth sym
`metrical, that is, the forward and reverse signal paths con
`sume equal amounts of bandwidth, and the topology is star
`or serial, not tree and branch. In contrast, CATV networks
`are bandwidth asymmetrical, with heavy allocation of band
`width for use in the downstream direction and limited
`upstream bandwidth. As the present inventors have discov
`ered, the noise problem in the upstream direction is di?icult
`in a broadband bandwidth-asymmetrical, tree and branch
`topology, as contrasted with a symmetrical of?ce-type data
`communications network.
`The system described in the FPN patent employs two
`different modulation schemes for communicating informa
`tion between a central headend and a plurality of subscriber
`nodes. For downstream communications, the FPN system
`transmits signals continuously in a plurality of 6 MHZ
`bandwidth charmels. In a preferred embodiment, an AM
`PSK modulator is used in the downstream path. For
`upstream communications, the FPN system transmits pack
`ets of information in bursts to a headend using an offset
`quadrature phase shift keyed (OQPSK) modulator.
`While the FPN communications system may be suitable
`for communicating telephony signals on a data communi
`cations network such as Ethernet, it does not solve certain
`problems that occur in the carriage of telephony signals on
`a broadband cable network. Due to the single point to
`multiple point con?guration (tree and branch) of the CATV
`network, upstream transmissions of telephony signals have
`to contend with multiple noise sources as the branch signals
`from each subscriber are merged together toward the head
`end. It is believed, however, that the burst mode approach
`used in the reverse path of the FPN system is particularly
`susceptible to these noise issues. Speci?cally, it is believed
`that the framing bits and sequencing of the data streams are
`susceptible to interruption when an interference signal is
`sustained for any signi?cant length of time (i.e., for longer
`
`ARRIS883IPRI0001038
`
`

`
`5
`than the length of a data frame) anywhere within one of the
`6 MHz bandwidth channels used to carry telephony signals.
`It is further believed that the interruption of the framing
`bits may result in the loss of content in all telephone
`conversations represented within the data frame interrupted.
`In a data communications environment, this signal interrup
`tion may only be noticeable as a slowdown on the network,
`and, though inconvenient, may be considered acceptable.
`However, such degradation of signal quality in a cable and
`telephony environment is undesirable and may be unaccept
`able.
`There is no discussion in the FPN patent of any means for
`insertion or removal of telephony signals from and to the
`public switched telephone network (PSTN). The FPN sys
`tem appears to provide only a local area telephone network
`designed primarily for inter-office communications (such as
`o?ice to o?ice intercom), as only limited access to the PSTN
`is suggested. There are a number of diiferent locations in the
`FPN equipment where telephony signal insertion and
`removal could occur, but the patent does not describe any
`means for signal insertion or removal, or discuss any of the
`issues associated with signal insertion and removal. At best,
`it appears that telephony signals would be inserted and
`removed at nodes directly connected to the broadband media
`(e.g., the coaxial cable), as suggested at col. 3, line 30. The
`patent does not indicate how such insertion and removal
`directly from the broadband medium should best be effected,
`and is silent on issues involving multiple telephony chan
`nels.
`Therefore, there is a need for a broadband communica
`tions system that is compatible with the existing public
`switched telephone networks and that is not sensitive to
`noise or other interference issues, particularly in the reverse
`path. There is also a need for a broadband communications
`system that is bandwidth ef?cient and provides a higher
`spectral e?iciency than present systems, thereby increasing
`the number of subscribers that may be served by each
`broadband network with telephony and enhanced services
`offered by CATV system operators, telephone company
`operating companies, and others.
`
`20
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`35
`
`SUMMARY OF THE INVENTION
`
`The invention includes methods and apparatus for pro
`viding broadband communications, including bidirectional
`telephony communications, over a cable distribution net
`work. In particular, the present invention provides an inte
`grated CATV/telephony system that is compatible with
`today’s public switched telephone networks and can also
`deliver video, data, security monitoring, and other services
`without affecting current in-home wiring or equipment.
`In one embodiment, the method includes communicating
`telephony signals from a telephony network to the CATV
`subscribers in the forward band of the cable network and
`communicating telephony signals from the CATV subscrib
`ers to the telephony network in the reverse band of the cable
`network.
`In another preferred embodiment, the method includes the
`digitizing of individual subscriber telephony signals into a
`multiplexed signal that is carried on a frequency division
`multiplexed (FDM) carrier in the forward band of the cable
`network. The digital multiplexed signal is quadrature partial
`response (QPR) modulated on a carrier which is positioned
`in an otherwise unused portion of the CATV network
`forward band. In the illustrated embodiment, the QPR signal
`is preferably approximately 3 MHz in bandwidth and easily
`?ts in a standard 6 MHz video channel. In another preferred
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`5,594,726
`
`6
`embodiment, a pair of the QPR signals can be placed in an
`otherwise unused channel in the cable line to utilize approxi
`mately 6 MHZ of bandwidth. By making a system which
`uses a robust digital signal, the b