O Umted States Patent [191
`McMullan, Jr. et a1.
`
`IlllllllllillllllIllllIllliIlllllllll1111111111111llllllllllllllllll
`
`US005255
`1111 Patent Number:
`[45] Date of Patent:
`
`5 255 086
`9
`9
`Oct. 19, 1993
`
`[54] METHOD AND APPARATUS FOR RF DATA
`TRANSFER IN A CATV SYSTEM
`
`_
`[73] A$S1gt1ee=
`
`[75] Inventors: Jay C. McMullan, Jr.; David J.
`Naddor, both of Doraville; Robert J.
`Beyers, II, Snellville, all of Ga,
`_
`_
`Scienti?c-Atlanta, Inc., Norcross,
`63-
`1211 Appl No.1 562,675
`[22] Filed:
`Aug 3’ 1990
`
`[60]
`
`-
`-
`Related US. Application Data
`Division of Ser. No. 503,422, Apr. 2, 1990, Pat. No.
`5,142,690, which is a continuation-in-part of Ser. No.
`498,084, Mar. 20, 1990, Pat. No. 5,155,590, and a con-
`tinuation-in-part of Ser. No. 498,083, Mar. 20, 1990.
`
`Int. C105 . . . . . . - . . . . . . . . . . . . . .
`
`- . . . 4 . . .
`
`4,538,174 8/1985 Gargini et a1. ...................... .. 358/86
`4,553,161 11/1985 cam ........... ..
`.. 358/86
`4,633,462 12/1986 Sti?e et a1.
`.... .. 370/85
`4,648,123 3/1987 Schrock . . . . . . .
`. . . . .. 455/67
`4,686,564 8/1987 Masuko et a1.
`.. 358/86
`4,754,426 1/ 1988 Rast et a1. ............. ..
`.. 358/86
`4,860,379 8/1989 Schoencberger et a1
`455/5
`4,920,533 4/1990 Dufresne et a1. ..... ..
`370/852
`5,010,329 4/1991 Nagakura ...... ..
`340/825.08
`Primary Examiner-Reinhard J. Eisenzopf
`Assistant Examiner-Chi H. Pham
`Attorney, Agent, or Firm-William A. Marvin;
`Frederick W. Powers, 111
`
`[57]
`ABSTRACT
`1
`-
`-
`Afme‘hct’d “.wmmnmg ‘1;:- a11l.°°at‘f°“ °f a p°tPulan°n
`0 561,510 8 wins among a p um lty_o gmuPs _0 {6mm}:
`units 15 provided. Each remote un1t has a digital 1dent1
`?er respectively associated therewith‘ A maximum and
`
`C]. - . . . . . . . . . . . . .
`
`. . . . . . . ..
`
`86;
`
`a minimum average number of fcmote units p61‘ group is
`
`.... .. 353/84, 36; 455/ 2'61
`....
`[58] P1611150; ielarzh
`825 68' @5147 ' s'zg'sg 6'812’53
`
`'
`
`’
`
`'
`
`’
`
`‘
`
`’
`
`‘
`
`’
`
`‘
`
`’
`
`[56]
`
`References Cited
`U_s_ PATENT DOCUMENTS
`
`'
`
`3’924’187 12/1975 Dormans '
`3,943,447 3/1976 Shorno, III et a1. .
`4,454,538 6/1984 Toriumi .............................. .. 358/86
`4,477,799 ‘0/1984 Rocci et aL _
`4,477,800 10/1984 O'Brien ............................. .. 340/533
`4,486,773 12/1984 Okubo . . . . . .
`. . . . .. 358/84
`Islam 6‘ a1- --
`-
`358/86
`4,509,073 4/1985 Ban“ 6‘ a1
`455/2
`4,512,033 4/1985 Schrock
`370/94
`4,528,663 7/1985 Citta ........ ..
`4,533,948 8/1985 McNamara ....................... .. 358/122
`
`imp . . . . . . . . . .
`
`. . . ..
`
`,
`
`,
`
`?xed. The remote units are assigned to the groups of
`remote units in accordance with the respective digital
`
`identi?ers. The average number of remote units per
`group is then determined as remote units are assigned
`thereto. Next, the average number of remote units per
`group is compared to the ?xed maximum number of
`remote units per group. The above steps are repeated
`while the average number of remote units per group is
`l
`.
`655 than °r equal t° the ?xed max‘mum m‘mbcr °f
`remote units per group. The number of groups is
`changed such that the average number of remote units
`per group is between the ?xed maximum and minimum
`number of remote units per group if the average number
`0; remote units per group exceeds the maximum number
`0 remote “"5 Per group'
`
`-
`
`-
`
`18 Claims, 18 Drawing Sheets
`
`"w
`
`1'
`
`HEADEND
`
`P110
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`153
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`1“ 160
`
`&15‘ §
`
`I
`
`181
`
`RF 0411 RETURN
`mmswrran
`CATV TERMINAL
`1
`
`[:1
`
`TELEVISION
`
`200
`120
`
`ARRIS883IPRI0001199
`
`

`
`US. Patent
`
`Oct. 19, 1993
`
`Sheet 1 of 18
`
`5,255,086
`
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`ARRIS883IPRI0001200
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`
`US. Patent
`
`Oct. 19, 1993
`
`Sheet 2 of 18
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`5,255,086
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`ARRIS883IPRI0001201
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`

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`U.S. Patent
`
`39919..1«L.C0
`
`Sheet 3 of 18
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`5,255,086
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`ARRIS883IPRI0001202
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`U.S. Patent
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`81£104LlemS
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`5,255,035
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`ARRIS883IPRI0001203
`
`

`
`US. Patent
`
`Oct. 19, 1993
`
`Sheet 5 of 18
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`5,255,086
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`ARRIS883IPRI0001204
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`

`
`U.S. Patent
`
`Oct. 19, 1993
`
`Sheet 6 of 18
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`5,255,086
`
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`ARRIS883IPRI0001205
`
`

`
`US. Patent
`
`Oct. 19, 1993
`
`Sheet 7 of 18
`
`‘5,255,086
`
`CYCLE1
`i, I
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`CYCLE 2
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`GROUP 1 PERIOD
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`
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`
`FIG. 7
`
`1200
`
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`m
`
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`AMP
`
`LEVEL
`DETECTOR
`
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`[-1204
`
`TEMP
`COMP
`
`FIG. 12
`
`1203
`
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`
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`
`‘low
`
`ARRIS883IPRI0001206
`
`

`
`Sheet 3 of 18
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`5,255,086
`
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`ARRIS883IPRI0001207
`
`

`
`US. Patent
`
`Oct. 19, 1993
`
`Sheet 9 of 18
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`5,255,086
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`ARRIS883IPRI0001208
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`

`
`U.S. Patent
`
`Sheet 10 of 18
`
`5,255,086
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`Sheet 11 of 18
`
`5,255,086
`
`ARRIS883IPRI0001210
`
`

`
`U.S. Patent
`
`Oct. 19, 1993
`
`8If0214|.8e..nS
`
`5,255,086
`
`ARRIS883IPRI0001211
`
`

`
`U.S. Patent
`
`Oct. 19, 1993
`
`Sheet 13 of 18
`
`5,255,086
`
`om$>oomm
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`ARRIS883IPRI0001212
`
`

`
`US. Patent
`
`Oct. 19, 1993
`
`“ Sheet 14 of 1s
`
`5,255,086
`
`RF-IPPv PROOEssOR
`OONTROLLER MODULE
`9506
`[-1350
`8250 4 f BAUD
`uART M8232
`
`FIG. 13
`
`1
`
`ASYSTEM
`' MANAGER
`
`$4300
`
`80188
`
`CHANNEL D “340
`283%
`I
`A, sYNTHEsIzER
`1390v
`RAXM
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`m 1341/ 1K 8
`1360
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`1342/ 2H8‘
`128K
`1343@ ANALYZER
`CHANNEL C y1330
`DUAL 8
`PORT 1
`/ 1I;I(AXIIII8
`1331
`
`8097
`
`INTEL
`
`-
`
`8097
`
`, SYNTHESIZER
`RF REcEIvER
`
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`
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`
`RF REcEIvER
`
`> SYNTHESIZER
`RF REcEIvER
`
`ARRIS883IPRI0001213
`
`

`
`US. Patent
`
`0a. 19, 1993
`
`Sheet 15 of 18
`
`5,255,086
`
`MONITOR
`
`SETUP
`
`-—-— MAIN MENU -——
`
`MONITOR < BERT
`
`8 UP ET
`CALIBRATE
`
`f1401
`
`——- MAIN MENU -—
`
`MONITOR BERT
`SETUP <
`CALIBRATE
`
`-— MONITOR MENU —
`
`SUMMARY< DUPLICATE J14")
`FREQUENCY ACTIVITY
`UNIQUE
`SIGNAL
`
`— SUMMARY -——
`
`BUFFER 1000<TIMER J14“
`SENT
`500
`3:02
`UNIQUE 1500
`
`-—-— FREQUENCY -—
`
`A 11.8 < C 13.8
`C 12.8 D 14.8
`
`J1412
`
`-—— UNIQUE TOTAL -
`
`A
`B
`
`250 < C
`230
`D
`
`270
`250
`
`-— DUPLICATE TOTAL -
`
`A
`B
`
`311 < C
`421
`D
`
`389
`267
`
`_-_ ACTIVITY -_
`
`11415
`
`(IN PERCENT)
`10<% C 20%
`13% D 21%
`
`A
`B
`
`—— MONITOR SSA --
`
`STTADDR 180F4CA1 <
`THIS 0A AT 3.5 HI
`BEST 06 AT 2.5 OK
`
`—— MONITOR RSSI ——
`
`A 2.4 < OK
`5 2.5
`HI
`
`C 2.3 OK
`D 2.2 LOW
`
`FIG. 14a
`
`—— SETUP MENU -—
`f1420
`
`PASSWORD < RSSI
`VERSION
`SSA
`SETFREO
`MISC
`
`—— PASSWORD ——
`
`PASSWORD
`
`1234 <
`
`—— SOFTWR VERSION - 11422
`MAIN
`0309 <
`A
`14 C 14
`B
`14 D 14
`
`— FREQUENCY (CAT1)
`
`CURRENT CATEGORY 1
`A 11.8 < C 13.8
`B 12.8
`D 14.8
`
`I1423
`
`—- FREQUENCY (CAT2)
`
`CURRENT CATEGORY 2 <
`A11.8
`C 13.8
`B 12.8
`D 14.8
`
`—--— SETUP RSSI -——- 11425
`
`DELAY
`MEAS.
`
`0 < LO - 4dB
`9 HI +4dB
`
`—- SETUP SSA -— 1142s
`
`FREQ. 11.8< #BADBITS
`ALLOW 5
`DELAY
`0
`1
`MEAS. 125
`COUNT
`
`—- MISCELLANEOUS -— _f1427
`
`LCD ANGLE MED <
`LCD TIME
`5
`LOCK TIME
`5
`
`ARRIS883IPRI0001214
`
`

`
`US. Patent
`
`Oct. 19, 1993
`
`Sheet 16 of 18
`
`5,255,086
`
`CALIBRATION
`
`—-—— MAIN MENU -—
`MONITOR BERT
`SETUP
`CALIBRATE <
`
`11401
`
`- CALIBRATION MENU -
`DATEIPASS< RSSI - B
`ssA
`RSSI - c 11430
`ass: - A
`ass: - o
`
`BERT
`
`-— MAIN MENU
`
`MONITOR BERT <
`SETUP
`CALIBRATE
`
`_f1401
`
`—-—- BERT MENU —
`PASSWORD MISSED J14“)
`FREQ
`CROSSED
`GOOD
`RSSI
`
`-- DATE/PASSWORD —
`PASSWORD 1234<
`DATE
`309
`FREQUENCY 1 1.8
`
`pm
`
`_- EEPROM STATUS - J 1432
`
`EEPROM STATUS OK <
`
`——- CALIBR ssA —
`SET -3dB<
`—3dB 1.5 114333
`NOM 1.5
`+3dB 3.5
`
`VALUE 1.5
`
`-— CALIBR RSSI (A) —
`SET -10dB<
`~10dB 0.8 j1434a
`—8dB 1.0
`- SdB 1.2
`
`VALUE 2.5
`
`— SET RSSI (A) ——
`J1435a
`
`-- CALIBR RSSI (B) — j1434b
`SEE CALIBR RSSI (A)
`
`—— SET RSSI (B) — J1435b
`SEE SET RSSI (A)
`
`-—- CALIBR RSSI (C) -— I143“;
`SEE CALIBR RSSI (A)
`
`-— SET RSSI (C) —-— J-1435c
`SEE SET RSSI (A)
`
`-- CALIBR RSSI (D) —- j1434d
`SEE CALIBR RSSI (A)
`
`_- SET RSSI (0) -_ 11435‘)
`SEE SET RSSI (A)
`
`- PASSWORD CONTROL
`PASSWORD 1234
`RESTART
`NO
`
`-— FREQUENCY (CAT1) —
`CURRENT CATEGORY 1
`A 11.8 <
`C 13.8
`B128
`014.8
`
`-- BERT GOOD TOTALS - j 1443
`C 9999999
`A 9999999
`D 9999999
`8 9999999
`
`~— BERT MISSED TOTAL - J 1444
`A0
`C0
`B0
`D0
`
`—- BERT CROSS TOTAL - I 1445
`A0
`C0
`80
`D0
`
`-— BERT ACTIVITY — j 1446
`(IN PERCENT)
`C 75%
`A 75%
`D 75%
`s 15%
`
`---—' BERT RSSI — J 1447
`(AVERAGE)
`C 2.0 LOW
`A2.4 OK
`D 2.4 OK
`82.8 HI
`
`FIG. 14b
`
`ARRIS883IPRI0001215
`
`

`
`US. Patent
`
`Oct. 19, 1993
`
`Sheet 17 of 13
`
`5,255,086
`
`XMITDATA
`
`5w 5v CTL
`
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`FIG. 15
`
`ARRIS883IPRI0001216
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`US. Patent
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`Oct. 19, 1993
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`Sheet 18 of 18
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`5,255,086
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`26E
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`ARRIS883IPRI0001217
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`1
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`METHOD AND APPARATUS FOR RF DATA
`TRANSFER IN A CATV SYSTEM
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`5
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`20
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`40
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`5,255,086
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`noise and the funneling effect; ingress or unwanted
`external signals; common mode distortion resulting
`from defective distribution apparatus; impulse noise
`from power line interference and other influences; and
`ampli?er non-linearities.
`White noise and Gaussian noise are terms often used
`to describe random noise characteristics. White noise
`describes a uniform distribution of noise power versus
`frequency, i.e., a constant power spectral density in the
`band of interest, here, 5-30 megahertz. Components of
`random noise include thermal noise related to tempera
`ture, shot noise created by active devices, and l/f or
`low frequency noise which decreases with increased
`frequency. The term noise floor is used to describe the
`constant power level of such white noise across the
`band of interest.
`This noise is carried through each return distribution
`ampli?er which adds its own noise and is bridged to the
`noise from all branches to a line to the headend. This
`addition of noise from each branch of a distribution tree
`'in a direction toward a headend is known as noise fun
`neling or the funneling effect. The constant noise floor
`power level de?nes a noise level which a data carrier
`power level should exceed.
`The present invention is especially concerned with
`interference noise which causes peaks in the noise spec
`tral density distribution in the band of interest. Interfer
`ence noise destroys effective data transmission when
`known data transmission coding techniques such as
`frequency or phase shift keying are practiced over a
`single data transmission channel. In particular, interfer
`ence noise especially relates to the four characteristics
`of return plant introduced above: ingress, common
`mode distortion, impulse noise and amplifier non
`linearities.
`Ingress is unwanted intended external signals enter
`ing the cable plant at weak points in the cable such as
`shield discontinuities, improper grounding and bonding
`of cable sheaths, and faulty connectors. At these weak
`points, radio frequency carriers may enter caused by
`broadcasts in, for example, the local AM band, citizen’s
`band, ham operator band, or local or international
`shortwave band. Consequently, interference noise
`peaks at particular carrier frequencies may be seen in
`noise spectral density measurements taken on cable
`distribution plant susceptible to ingress.
`Common mode distortion is the result of non-lineari
`ties in the cable plant caused by connector corrosion
`creating point contact diodes. The effect of these diodes
`in the return plant is that difference products of driving
`signals consistently appear as noise power peaks at mul
`tiples of 6 megahertz, i.e., 6, 12, 18, 24 and 30 megahertz
`in the band of interest.
`55.
`Impulse noise is de?ned as noise consisting of im
`pulses of high power level and short duration. Corona
`and gap impulse noise are created by power line dis
`charge. Temperature and humidity are especially in?u
`ential in determining the degree of corona noise, while
`gap noise is a direct result of a power system fault, for
`example, a bad or cracked insulator. The resultant im
`pulse noise spectrum can extend into the tens of mega
`hertz with a sin x/x distribution.
`Ampli?er nonlinearities or oscillations relate to pulse
`regenerative oscillations caused by marginally stable or
`improperly terminated ampli?ers. The result is a comb
`of frequency peaks within the return plant band whose
`
`CROSS-REFERENCE TO RELATED
`APPLICATIONS
`This application is a divisional application of U.S.
`application Ser. No. 07/503,422 ?led on Apr. 2, 1990
`and entitled “Cable Television Radio Frequency Data
`Processor.” U.S. Pat. No. 5,142,690 application Ser. No.
`07/503,422 is a continuation-in-part application of com
`monly assigned copending application Ser. No. 498,084
`entitled “Cable Television Radio Frequency Subscriber
`Data Transmission Apparatus and Calibration Method”
`U.S. Pat. No. 5,155,590 and commonly assigned co
`pending application Ser. No. 498,083 entitled “Cable
`Television Radio Frequency Subscriber Data Transmis
`sion Apparatus and RF Return Method”, both ?led
`Mar. 20, 1990.
`BACKGROUND OF THE INVENTION
`1. Technical Field
`The present invention generally relates to a technique
`for recovering data from a plurality of remote units and,
`more particularly, to a data return protocol for recover
`ing data from a plurality of set-top terminals in a cable
`television system.
`2. Description of the Prior Art
`The development of cable television systems has
`reached the stage where the provision of two way infor
`mation flow is not only desirable but is practically re
`quired by the implementation of new services. For ex
`ample, in the implementation of impulse pay-per-view
`service where the subscriber may impulsively select an
`event for viewing and assume a charge, at least one data
`channel such as a telephone communication channel or
`an RF channel is required in an upstream (reverse)
`direction from a cable television subscriber to a cable
`television headend to report service usage data. Other
`uses for a return path include power meter reading,
`alarm services, subscriber polling and voting, collecting
`subscriber viewing statistics, and home shopping. While
`not every cable television system operator provides for
`two way transmission, manufacturers of cable television
`equipment have tended to provide for upstream trans
`mission in the direction from the subscriber toward the
`headend. Practically all such manufacturers provide
`so-called split or two way systems having a spectrum of
`frequencies for upstream transmission which at least
`includes a band from 5 to 30 megahertz. This band of
`interest comprises cable television channel T7
`(5.75-1l.75 megahertz), T8 (11.75-17.75 megahertz),
`T9 (17.75-23.75 megahertz) and T10 (23.75-29.75
`megahertz). These return path channels, each having
`television signal bandwidth, may be used, for example,
`for video conferencing. Whether a so-called “sub-split",
`“mid-split” or “high-split” system is applied for two
`way transmission by a headend operator, all three types
`of split transmission systems typically involve an up
`stream transmission in the 5-30 megahertz band of inter
`est.
`An article entitled “Two-Way Cable Plant Charac
`teristics” by Richard Citta and Dennis Mutzbaugh pub
`lished in the 1984 National Cable Television Associa
`tion conference papers demonstrates the results of an
`examination of typical cable television (CATV) return
`plants. Five major characteristics in the 5-30 megahertz
`upstream band were analyzed. These include white
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`spacing is related to the distance between the mistermi-
`nation and the amplifier.
`From examining typical cable distribution plants,
`Citta et al. concluded that “holes” exist in valleys be-
`tween peaks in the noise spectrum they plotted between
`0 and 30 megahertz. They proposed that these valleys
`may be used to advantage by carefully choosing return
`carriers “slotted” in these valleys.
`In follow-up articles published at the 1987 National
`Cable Television Conference and in U.S. Pat. No.
`4,586,078, Citta et al. conclude that a 45 kilobit data
`signal may be alternately transmitted by a coherent
`phase shift keying (CPSK) technique over carriers at
`5.5 megahertz and 11.0 megahertz or in the vicinity of
`the T7 and T8 cable television channels respectively. A 15
`switch at the subscriber terminal alternately selects the
`5.5 MHz carrier or the harmonically related 11 MHZ
`carrier for transmission. This form of alternating carrier
`transmission of messages is continued until the data is
`successfully received. In other words, alternating trans-
`mission on the two carriers occurs until an acknowl-
`edgement signal indicating successful receipt of a mes-
`sage is received at a terminal. While the choice of these
`carrier frequencies is claimed to avoid the noise distri-
`bution peaks caused by interference noise, there is con-
`siderable concern that such a modulated phase shift
`keyed data stream will run into noise peaks in cable
`television distribution network outside of the investiga-
`tions of Citta et al. Referring to FIG. 2 republished here
`from U.S. allowed application Ser. No. 07/188,478 filed
`Apr. 29, 1988, U.S. Pat. No. 4,912,721, transmission at
`5.5 MHz should be practically impossible. Noise peaks
`have been known to appear and disappear based on
`time-of-day, season, and other considerations.
`Other return path or upstream data transmission
`schemes have been tried. These schemes include, for
`example, the telephone system, described as “ubiqui-
`tous” by Citta et al. In other words, the return data path
`to a cable television headend is not provided over the
`cable television distribution plant at all. The serving
`cable is intentionally avoided either because of the inter-
`ference noise problem in a split system or because the
`system is a one way downstream system. Instead, the
`subscriber’s telephone line is used for data transmission.
`In this instance, however, there is concern that local
`telephone data tariffs may require the payment of the
`line conditioning surcharges if the telephone line to a
`subscriber’s home is used for data transmission in addi-
`tion to normal “plain old” telephone service. Further-
`more, the telephone line is only available when the
`subscriber is not using it, requiring an unscheduled or
`periodic data flow.
`Another known return data transmission scheme
`involves the application of a separate data channel at a
`carrier frequency that avoids the troublesome 5-30
`megahertz band. This scheme, of avoiding the noisy
`5-30 megahertz band, is only possible in midsplit and
`high split systems.
`So-called spread spectrum transmission of data is a
`technology which evolved for military requirements
`from the need to communicate with underwater subma-
`rines in a secure manner. Spread spectrum derives its
`name from spreading a data signal having a compara-
`tively narrow bandwidth over a much larger spectrum
`than would be normally required for transmitting the
`narrow band data signal.
`More recently the security advantages provided by
`spread spectrum transmission have been disregarded in
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`favor of its capability of application in an environment
`of interference. For example, communications systems
`operating over a power line where impulse noise levels
`due to the power line are high have been attempted in
`the past but found to be only marginally acceptable, for
`example, power line plug-in intercom systems commer-
`cially available from Tandy Radio Shack. The Japanese
`N.E.C Home Electronics Group, however, has demon-
`strated a spread spectrum home bus operating at 9600
`baud over an AC line in a home that is practical up to
`distances of 200 meters of power line. The NEC system
`has been characterized as the missing link between a
`coaxial cable (for example, a cable television cable) and
`an AC power line common to the majority of homes.
`U.S. Pat. No. 4,635,274 to Kabota et al. describes a
`bidirectional digital signal communication system in
`which spread spectrum transmission is applied for up-
`stream data transmission in a cable television system.
`Such technology is very expensive, however, when
`compared with telephone data return.
`Consequently, despite the development of spread
`spectrum and other RF data return, the requirement
`remains in the cable television art for an upstream data
`transmission having high data throughout from a plural-
`ity of subscriber premises to a cable television headend
`utilizing the cable television distribution plant and
`which is relatively impervious to interference noise.
`The concept of Impulse Pay Per View (IPPV) is well
`understood in the art, but is described briefly here for
`completeness. Essentially it is a sales method by which
`a pay (cable) television subscriber may purchase spe-
`cific program events on an individual basis. Further-
`more, the purchase may be contracted on an “impulse”
`basis solely by interacting with the subscriber’s in-home
`set-top terminal (STT). Although it is not a requirement
`that the event being purchased be “in progress", it is a
`requirement that the system support the purchase of
`events that are in progress. The purchase must be han-
`dled in a manner that does not incur any appreciable
`delay in the subscriber’s ability to view the event imme-
`diately (i.e. instant gratification).
`Although several
`techniques of implementing the
`above sales method exist, all techniques have common
`requirements. Some part of the system must make a
`decision whether or not to allow the purchase and sub-
`sequent viewing of the event. If allowed, the purchase
`of the specific event must be recorded and reported to
`what is typically known as the “billing system” so that
`the program vendor eventually receives revenue from
`the transaction.
`Ti accomplish purchased event reporting, a so-called
`“store and forward” technique is used. In the store and
`forward method, the set-top terminal assumes that if the
`subscriber is pre-enabled for IPPV capability, then an
`event purchase is allowed. When the subscriber per-
`‘forms the necessary steps to purchase an event, the
`set-top terminal -allows the event to be viewed (typi-
`cally by de-scrambling a video signal on a particular
`channel) and records the purchase of the event. The
`record is typically stored in a secure, nonvolatile mem-
`ory, as it represents revenue to the program vendor.
`Obviously, in order to_ realize the revenue, the ven-
`dor’s billing system must obtain the purchase record
`data stored in all of the subscriber’s set-top terminals in
`a timely manner. To accomplish this, the system control
`computer (hereafter called the system manager) period-
`ically request that the set-top terminals return the IPPV
`purchase data stored in memory. When the system man-
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`ager receives the data from a set-top terminal, it typi-
`cally then acknowledges the receipt to the terminal (i.e.,
`as does Citta et al.) and the data is cleared from memory
`to make room for additional purchase data. The system
`manager then forwards this data to the billing system,
`and the IPPV purchase cycle is completed.
`While IPPV return data considerations are important
`to the determination of an RF data return technique,
`such IPPV return data considerations are not the only
`consideration, but admittedly are the most critical be-
`cause of the high data throughput requirements. Other
`requirements such as using the return data path for
`subscriber polling, burglar alarm, meter reading, home
`shopping, energy management and the like are additive
`to the data throughput requirements of IPPV service.
`Consequently, there remains a requirement in the art
`for RF data return apparatus having high data through-
`put to the degree of supporting a full range of services
`including IPPV service.
`SUMMARY OF THE INVENTION
`
`The present invention relates to radio frequency data
`return apparatus for the periodic and prompt recovery
`of set-top tenninal purchase record and other informa-
`tion via reverse cable RF communication. The present
`invention is primarily related to modifications to so-
`called system manager apparatus at a headend for re-
`ceiving data returned over an RF data return path, a
`frequency diverse RF receiver apparatus for receiving
`data modulated and transmitted over a plurality of data 30
`channels from all the subscriber terminals or modules of
`a system, and the subscriber terminal or module itself.
`It is one object of the present invention that imple-
`menting RF subscriber data return not require any sig-
`nificant changes to the billing system. Furthermore, the
`RF subscriber data return process should operate inde-
`pendently of telephone line return; i.e., they should
`operate side by side. Also, RF subscriber data return
`apparatus should be compatible with any headend or
`terminal apparatus used for forward or downstream
`transmission. A familarity with the system apparatus
`and terms may be obtained from the following over-
`view:
`
`SYSTEM MANAGER. This is the primary control
`computer for the cable television system. The system
`manager accepts input commands from both human
`operators and the billing computer. It generates appro-
`priate control transactions that are sent over the for-
`ward (downstream) cable path to the set-top terminals
`via a control transmitter. It accepts return data from a
`frequency diverse data receiver and processor (also
`called herein the RF-IPPV processor) and forwards the
`return data to the billing computer.
`CONTROL TRANSMITTERS. These are devices
`for converting standard RS-232 serial data from the
`system manager to a modulated RF signal for transmis-
`sion over the cable to a set-top terminal or IPPV mod-
`ule. In a known cable system available from the assign-
`ees of the present invention, the control transmitter may
`be an Addressable Transmitter (ATX) or a Headend
`Controller and Scrambler, or a combination of both.
`For the purposes of the present invention, the control
`transmitter is primarily a pass-through device and is
`described for completeness.
`BIDIRECTIONAL AMPLIFIER. These trunk dis-
`tribution amplifiers and line extenders amplify and pass
`a certain portion of the RF spectrum in the forward
`(downstream) direction and a different portion of the
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`RF spectrum in the reverse direction. This makes bidi-
`rectional communication possible over a single coaxial
`cable. The bidirectional amplifiers are also passthrough
`devices and are described only for completeness.
`SET TOP TERMINAL. These devices are the inter-
`face between the cable system and a subscriber and
`his/her television set. Among other functions, the set-
`top terminals perform tuning, frequency down conver-
`sion, and de-scrambling of the cable video signals on a
`selective basis. They accept both global and addressed
`control transactions (i.e. transactions directed to either
`all or individual terminals) from the control transmitter
`to configure and control the services they deliver. In
`addition, the set-top terminal may be equipped with an
`internal radio frequency return module or be provided
`with an interface to an adjunct external data return
`module so that a secure memory device of either the
`terminal or the external module may be provided for
`storing purchased event or other data to be returned.
`Furthermore, either the set-top terminal or an associ-
`ated module includes a frequency deiverse reverse path
`data transmitter in accordance with the present inven-
`tion. Such a set-top terminal either equipped or associ-
`ated with an RF-IPPV module will be referred to
`herein as an RF-STT.
`RF IPPV MODULE. The RF IPPV module is a
`module associated with the set top terminal if the set top
`terminal is not provided with an internal frequency
`diverse reverse path RF data transmitter.
`RF IPPV PROCESSOR. The RF IPPV processor is
`primarily a frequency diverse RF data receiver for the
`reverse path data transmitters of the terminals or mod-
`ules. It simultaneously recovers data from modulated
`RF signals on up to four (or more) distinct reverse data
`channels. It then filters out redundant data messages,
`assembles the data into packets, and forwards the pack-
`ets to the system manager on a standard RS-232 data
`link. A minimum of one processor is required for each
`cable television system headend.
`It is an overall object of the present invention that the
`radio frequency subscriber data return apparatus must
`be easy to use, work reliably and have high data
`throughput, integrity and security. In addition, the pres-
`ent invention is designed to meet three specific perfor-
`mance goals:
`I. The RF data transmission apparatus must be ex-
`tremely tolerant of relatively high levels of discrete
`interference sources typical in reverse channels of cable
`distribution plants. The interference is due to ingress of
`external RF sources into the cable piant, all of which
`are “funneled” to the data receiver.
`2. The data return method must be fast enough so that
`an operator can obtain data from all set-top terminals, in
`even a large, two hundred thousand tenninal per hea-
`dend cable television system, every 24 hours or less.
`'
`3. Any frequency or level adjustment of the individ-
`ual set-top terminals or associated modules required at
`installation in a subscriber location must be virtually
`automatic.
`
`The present invention is particularly concerned with
`the second of these objectives. In accordance with the
`present invention, a method of controlling the alloca-
`tion of a population of remote units among a plurality of
`groups of remote units is provided. Each remote unit
`has a digital identifier respectively associated therewith.
`A maximum and a minimum average number of remote
`units per group is fixed. The remote units are assigned to
`the groups of remote units in accordance with the re-
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`spective digital identifiers. The average number of re-
`mote units per group is then determined as remote units
`are assigned thereto. Next, the average number of re-
`mote units per group is compared to the fixed maximum
`number of remote units per group. The above steps are
`repeated while the average number of remote units per
`group is less than or equal to the fixed maximum num-
`ber of remote units per group. The number of groups is
`changed such that the average number of remote units
`per group is between the fixed maximum and minimum
`number of remote units per group if the average number
`of remote units per group exceeds the maximum number
`of remote units per group.
`Also in accordanc