Note: Descriptions are shown in the official language in which they were submitted.
it
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SU33SCRIBER CONTROL System
BACKGROUND OF THE INVENTION
_ _
This invention relates to communications in general and,
more particularly, to a subscriber control system for
communicating with subscriber terminals at remote toga-
lions via cable
This application is a divisional of an application filed
on September 28, 1983 under No. 437,750-8.
In the table T.V. area, a customer buys separate
services separately. For example, in one particular
cable system there is available 2 basic cable service, a
movie channel, an entertainment channel, sod a sports
channel. The subscriber pays or each separately. It
is thus necessary thaw the cable service be able to con-
trot which of the services the customer receives. In
the past, it has been the common practice to accomplish
this in Dyne Do two ways. One way of doing this is to
place at the subscriber multi tap i.e., at a location
outside the home from which a number of homes are fed,
negative traps. These negative traps are filters which
are put in place and which trap or filter out the chant
nets to which the subscriber is nut subscribing. This
requires, each time a subscriber changes his subscript
lion, that a serviceman be sent out to remove or insert
the nighttime trap. the other manner Do insuring that
52
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only those who subscribe receive a channel is through
the use of scrambling. The channels fox which one must
pay extra are scrambled and the subscriber is provided
with a descrambler. This, of course, increases the
overall C05t and requires additional equipment which
must be maintained Furthermore, in either of these
instances, it is difficult to selectively supply to
subscribers an individual event for which they pay
separately (per view), for example a major prize tight
or other sporting event, concert or the like.
Thus, there is a need for an improved system which per-
mitt addressing subscribers in a cable system to, in
effect, enable and disable tiers of service which are
paid for separately.
SUMMARY OF THE INVENTION
The present invention provides such a system. A key
element of the system is a tuned trap in combination
with switching means for switching the tuned trap in and
Quit of the circuit. The tuned trap, which utilizes a
varactor diode for tuning contains two sections which
provide a two pole filter. One of the poles is fixed
and the other pole is tuned back and forth through the
first pole at a predetermined rate. What this results
in is a scramble which is not recoverable wince in the
system of the present invention it is not intended to be
decoded. Rather, with the addressable system of the
present invention, when the ~ubsciber subscribes, that
trap is simply bypassed or disconnected. Thus, unlike
present ramble systems which Jan be avoided wince, as
a practical matter, crumble which is too difficult
cannot be used, subscriber with the system of the
present invention cannot other than by getting into the
.
~L22~3~5;~
-3-
equipment and modifying it, this equipment being outside
of his house on a pole, defeat the scramble
In the system of the present invention, in addition to
transmitting T.V. signals over the cable, subscribers
are addressed by means of an FISK [Frequency Shift
Key] modulated 103.8 MHz Carrier. The system can ad-
dress 10,000 subscribers per minute for per view son-
vice. feedback is provided to indicate the status of
the addressed subscribers.
this system also can provide alarm services and it
capable of addressing alarm customers at a rate of 2200
subscribers per minute for continuously readdressing
subscriber terminals with tier latch commands and inter-
rotating the subscriber terminal as to the status of its
tier latches. The tier latches are the switches which
witch in and out the tuned traps and can also be
switches relating to an alarm system. The data it no-
turned to the central computer location on 24.3 MHz FISK
carrier. The two-way system is, of course, not
absolutely necessary. The system will work simply by
sending out the addresses and command information The
replies, however, help to pinpoint failures in the soys-
them so that prompt service calls can be made.
The present system is designed such that each subscriber
terminal must receive its correct address in the same
command twice in succession before it will execute the
command. this double valid data requirement has the
effect of reducing the error ratio
The subscriber terminal, one of which is provided for
each one to four subscribers, is housed in a high recur-
fly housing about the size of a line extender amplifier
Co-ax wiring is provided between the outputs of this
multi tap and the subscriber drops.
.,.. ,~... I..... . . .... ..
~8~5~
In accordance with the present invention, the terminal
is powered through subscriber drop by means of a
calculator-type low voltage power supply on the us-
scriber's premises. Thus, normally each subscriber will
S be supplying power to the common terminal, although the
design is such that the terminal will operate properly
with at fleas two power supplies connected out of the
four possible. Included within the subscriber terminal
is a housing or common printed circuit board and
subscriber printed circuit boards, one for each
subscriber. The common board contains an RF doomed-
later, 9 bit address decoder and a scramble generator.
Each of the subscriber boards contains a 5 bit address,
4 bit data decoder, an 8 bit addressable latch, tuned
traps pin diode switch drivers, a 9 bit data encoder and
8 pin diode switches. Each housing is assigned an ad-
dress prior to installation using computer which blows
address fuses on the housing PC board and prints the
housing serial number which is the same as the address.
The subscriber printed circuit board is unaddressed and
received its address on being plugged into the housing.
The system is such that the installers need have no
knowledge of binary or urinary addressing and incorrect
and duplicate addresses are avoided. Furthermore, the
subscriber boards are interchangeable.
As noted above, the tuned traps of the present invention
provide a type of scramble which cannot be decoded. The,
scramble generator includes means for generating a
scramble square-wave voltage which is fed to a varactor
ED which tunes the one pole of the trap. It varies in
tuned frequency at the scramble frequency rate. When
the pole is tuned to the same frequency as the other
pole of trap, the trap will be tuned to its maximum
depth of bout 60 dub. when the varactor tuned pole it
out of tune with the other poles the trap will be as
minimum attenuation of about 30 dub. This scheme has the
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5Z
effect of attenuating the visual carrier by 30 dub plus
adding a 97~ AM scramble modulation to the visual
carrier. in addition to destroying the sync modulation,
it also destroys the video modulation resulting in a
hard scramble regardless of fine tuning adjustment to
the Two jet. In addition to the video scramble, an
audio scramble occurs due to the phase modulation which
toe trap induces on the visual carrier This phase
modulation of the visual carrier appears on the 4.5 MHz
audio inter carrier and has the same effect as FM mod-
lotion of the audio carrier. The amount of FM deviation
equivalent caused by the phase modulation is somewhat
dependent on the T.V. receiver.
The frequency of the scramble is obtained from the data
pulse stream in order to establish a stable and uniform
scramble frequency throughout the CAPTIVE. liable T.V.
system since the frequency for the lest scramble" is
critical. To prevent the loss of scramble signal in the
event that the data stream is interrupted, a free-
running scramble oscillator is included in the sub-
scriber terminal. This oscillator is normally lQsked to
the data frequency, but should the data stream be
interrupted, the oscillator will continue to run close
to the ideal scramble frequency.
At the central location, the equipment for controlling
the subscriber terminals includes five basic parts:
1. A self-c~ntained subscriber controller which
it capable of operating independently and con-
twins memory and battery backup this unit
continually addresses the subscriber terminals
with data which has been fettered in its memory;
2. A mini-computer;
3. A hard disk drive with cassette copy control;
.~. Intelligent terminals, e.g., microcomputers
end
5. At least one printer
S Other than the subscriber controller, the rest of the
equipment is standard off the shelf hardware. For
example, the mini-computer could be a DEC*mini-computer
or possibly an IBM*Per~onal Computer. The intelligent
terminals can also ye Impersonal Computers. The
mini-computer end the intelligent terminals are used so,
first of all, provide the data to the memory in the
subscriber-controller and to change and monitor data.
This memory indicates the services to which each sub-
scriber has scribed This controller is optically
isolated from the system and designed for a higher MTRF
than the rest of the system for continuous service.
through the use of battery backup, along with a real
time clock, the subscriber controller, which Jan store
up Jo 4 days of per view turn on information will con
tinge to operate, even if disconnected from the rest of
the equipment, thereby preventing disaster in the case
of a computer failure or power failure just before a per
view program turn-on time, e.g., just before a big prize
fight. In the event of a failure of the controller,
fiubscriber terminal will maintain their Emory index
finitely us long as they are towered.
The purpose of the minicomputer end the Ward disk are
to tore subscriber statistic end contain numerous
programs such US customer 6t~tistics, per view program
guide, billing, mailing libels, printer control, con-
troller control 9 trouble reporting, ~elf-~o~itoring,
maintenance programs, etc. The intelligent terminal
interact with the minicomputer nod the subscriber
* denotes trade mark
,, .... ' .' '''' ,'''' ''. " ',"' ' '
~2~5~2
controller to update information, ire., customer tier
commands, per view turn-on, billing date start, etc.
The terminals, since they are preferably computers can
also be used in a local mode as word-processors for
S doing accounts payable, general ledger payroll income
tax, etch It is also possible to provide programs on
these computers that use the subscriber data-base but
which cannot change it.
The system of the present invention also allows the pro-
vision of a subscriber alarm system. The subscriber
alarm terminal is located on the subscriber premises and
connected to the subscriber drop. Alarm subscribers are
interrogated five times more often than non-alarm sub-
scribers resulting in a rate of Lydia per minute. In a
5y5tem with 333 alarm customers, each alarm terminal
would be polled every two seconds. The alarm system can
send eight different alarm codes on a priority bases.
In addition, its data encoder has six spare bits for
future data [36 = ~29,000] different codes, the system
being a urinary system.
the system has the capacity for serving from 5,000 to
100,000 subscribers, dependent only on the number of
memory integrated circuits added and the size of the
hard disk memory used. The subscriber terminals are
addressed with a combination of binary and urinary bits
that allows for a maximum of 629,856 subscribers per
system.
BRIEF DESCRIPTION OF TIE DRAWINGS
FIG. 1 is an overall block diagram of the system of the
present invention
FIG. PA i block diagram of the ~ubseriber terminal
S aec~rding to the prevent invention.
FIG. us is a block diagram of the equipment located at
the business office.
FIG. 2C a block diagram of equipment located at the CAT
head end.
JIG. 3 is circuit diagram of the varactor tuned trip
according to the present invention.
FIG. 4 illustrates the lay-out of the trap of FIG. 3.
FIGS. PA, I 5C and SD are spectrum analysis diagrams
showing the of f cat of the trap of Fit . 3 .
DETAILED DESCRIPTION
FOG. 1 is a very basic block diagram of the system of
the preserlt invention. the basic elements include the
office equipment indicated generally as 11, in which
the mean piece of equipment it the controller, Also
included, however, is the mini-computer, do k drive and
intelligent terminals. Information from the off 11
is eta to the head end 13 where it it added to the
incoming T.V. signal which a transmitted over the
line 17 Jo plurality of terminals 19 etch of which
have up to four customer drops 21. Mach customer drop
21 Jay then be bonneted to customer equipment 23
including converter end television jet. The
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controller in the office addresses each of thy terminals
enabling the various tiers of service, depending on the
customer ! S desires,,
FIG. PA is a more detailed lock diagram of the equip-
mint at an individual terminal. The incoming signal on
line 17 is fed over a line 31 to couple video and audio
to the output 33 at which point a cable can be connected
providing the customer drop 21. The line 31 is coupled
into a first pair of switches aye and 35b which are
closed Jo provide basic service. If these switches are
open, then the customer receives nothing. A plurality
of additional pairs of switches, such as switches aye,
3~b, aye, 39b, aye and 41b are used to provide the van-
out tiers of service. It is contemplated that tiers A
through E may be provided, one of these being a per view
tier, i.e., tier which is selected only for viewing a
particular event. As used here, a tier may be a single
channel or a group of channels. More conventionally it
is used to refer to a group of channels. Thus, in more
general terms, the pairs of switches control the
reception of a portion of the T.V. frequency spectrum
which Jay include one or more channels. The incoming
signal on line 31 is coupled in serial through all of
these pairs of witches Jo the output 33. There is a
capacitor 43 in the output for isolation of a DC voltage
which is fed back from the subscriber over the cable
through input 33, through a filter comprising a choke 45
nod capacitor 47, Jo the power supply unit 49 which
includes a zoner diode 51 to clamp the voltage to 12
volts, a capacitor 53 and a resistor 55 for current
limiting purposes. Coupled to the resistor 55 Are four
diodes 57 to isolate the power supplies of the different
subscribers from each other. The power supply with it
12 volt output on line 59 provides all of the power for
the unit of FIG. PA.
.... . . . . ..
The switches are used to coupled in tuned traps to trap
one of the tiers of service. Thus with all traps in
place the trapped tiers are crumbled Those ire-
quenches not trapped pass through unaffected. This is
shown by spectrum and layer traces of FIGS. PA and us.
JIG. PA shows reference lines for two channels of a
coaxial switch The center line is 225 MHz, frequency
divisions 5 MHz~diY. As shown by FIG. PA from the point
of zero frequency, at which high attenuation is
indicated by a dip 501 through 450 MHz coveting all of
the cable spectrum the two traces 503 and S05 are
identical and show essentially no attenuation
FIG. 5B shows the effect of placing a trap to tuned to
Shea at 55.25 MHz in one channel of the switch. The
reference channel trace 5~3 is as before. Now, however,
the trace 505 of the channel with the trap exhibits a
sharp dip thigh attenuation) at the Shea frequency. All
other frequencies pass essentially untainted. This
corresponds, for example, to a case where switches AYE
and 37B of JIG. PA are connected to trap 61 (a Shea
trap) and all other switches are bypassing their no-
spective traps.
The switches aye and b, aye end b, and aye and b will be
in a position shunting a tuned trap 61, as shown in con-
notion with witches aye and 37b or coupling through
tuned trap 63 or 65 as shown in connection with switches
aye and b, and aye and b. Each of the tuned traps will
be tuned lo a particular channel, for example the mid-
band channels A-I. When the trap is in place it will
filter out that particular channel. If one assumes, for
example what the tiers correspond to channels and ore in
the position shown, channel A would pass through without
being filtered out by a trap 61. however, since the
wakes aye and b, and aye and b are in the position
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connecting in the trap, channels end E would be
filtered out and could not be received by that
particular custom. '
the remainder of the circuitry comprises irk s or
controlling the setting of these switches and for
feeding beck information eoncernirlg the state of the
various switches. As indicated previously, the informal
lion is transmitted on a 103.B I carrier. This signal
is provided on a line 71 through capacitor 73 Jo a
lo 103.8 MHz band pays jilter 75, the output of the jilter
being on input to a mixer 77 receiving on input from
97.3 MHz voltage-controlled ocular. The output of
the mixer at 6.5 MHz is coupled through a 6.5 MHz band
pass filter 81 into FM receiver By which receives the
information end provides output data on line BY. The
data enters decoder 87 where the terminal address it
decode. The decoder By may be a Motorola MY 145028
which receives nine bit eerily word and decodes it end
compares it with the Address set in by address fuses 89.
If the received address corresponds to that jet in on
the fuses valid transmission output it generated on
line 88. Address fuses 89 also supply address inputs to
decoders 91 in the individual subscriber boards. A
valid address signal from decoder 87 triggers moo-
stable multi vibrator 93 which enables an AND gate it to
couple additional date which defines the elected tiers
over line 97 Jo the decoders 91 (only one of four of
which us shown). These decoders may be I 15027 which
interpret the first five bits us address end the lust
your bits us data. The decoder 91 when a proper address
is recognized, provides an output on lines 92 which has
three address bit and one status bit, providing owe-
Rand. This data us coupled issue on eight bit drowsy-
Allah lath lOl,upon generation of the valid address
inlay from decoder 91, which, in turn, operates
wrier 103. The driver outputs control the various
.. ....
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I
pairs of witches, the first output, or example, con-
trolling witches aye and 35b. In succession, the
decoder 91 provides information for setting each of the
eight latches in addressable latch 101. This permits
controlling seven Shari of service the eighth address
being a signal to tart transmission or feedback.
Feedback is accomplished through Lowe use of a nine bit
encoder 105~ this may be an MY 145C26. Encoder 105 no-
ponds to a transmit start sunnily which is the eighth
output of toe latch 101, through striver 103. The data
encoded onto line 12 is the state, as provided on lines
104, of the outputs of driver 103. It also prcvid~s on
output on line 107 indicating that transmit is on. This
mutes the FM receiver 83. it also closes White 109
coupling a sisal through a capacitor 111 to 24.33 M~lz
band pass filter 113 and when through a choke 115 onto
line 71 from which it will be provided to line 17 and
back to the head end. Necessary frequencies both for
receiving and transmitting are generated using a cry-
tat 121 which oscillates at 3.579545 MHz. This it a
very conventional crystal wince it is used in essenti-
ally all color television jets. This crystal is used
along with a phase locket loop frequency synthesizer 123
to provide a control voltage output on line 125. The
~ntrol voltage is coupled through filter wormed by
resistors 127 and 129 with capacitor it 131 to ground
at their genuine, into the voltage controlled oscil-
later 79. Output from the voltage controller oscillator
it coupled back through A divide by your stage 133 and
divide by sixteen stage 135 to divide by 434 input of
- the synthesizer 123. This loop maintains the frequency
during receiving, it 97.3 By It Lowe Montana a eon-
ton frequency of 97.3 MHz while being frequency shirt
keyed by data coupled on line 141 from the nine bit en-
coder through resistor 143 to provide a frequency shift
keyed 24..3 MHz return signal. Bemuse the filter come
prosing capacitor 131 end resistor 127 and 1~9 has
.. ..... . . . .. . ..
13
long time constant, the control voltage supplied by
capacitor 131 sways at that providing the center ire-
quench while the actual frequency is modulated about
this center frequency by the voltage through resistor
143. If only a one way system is required mixer 77 can
be supplied simply from g7.3 MHz crystal controlled
oscillator. The remainder of the circuits of FIG. PA
are for gyrating the guano wave signal which is us
iced o tune the varactors in the traps 61, 63, and 65.
This circuit includes an actable multi vibrator 151 which
is synchronized to clock signal on line 153, the cluck
signal being obtained prom the decoder 87 end at the
data frequency. One output ox the mul~ivibrator it
coupled through a resistor divider comprising resistors
162 and 163 to ground the junction of these two which is
the line coupled to traps 61, 63 end 65 to modulate
them. this has on it a square wave varying between
15 volts and ground. The other output of the multi vibrator
is coupled into a binary ripple counter 155 which has a
divide by 32, a divide by 64 and divide by 4096
output. These outputs are combined in Rand gates 157
and lS9 and ~nverter 169 to provide further modulator
fiignal output on line 161. This is used to further
modulate the final output. the outputs from gates 157
and 159 ore coupled through resistors 15B end 160 to the
junction of resistors 162 and 163. These gates when on
pull the signal toward ground. The resulting modulation
causes in the aforementioned video and audio scrambling.
FIG. 2B shows the head end portion of the system. The
39 output of the head end is coupled through plurality of
bi-dire~ional line amplifiers 171 in the line 17.
Included in the head end unit are head end processor
173 generating video information,. This. video inform-
lion is coupled through a filter 175 Jo the output line
17~ Also received within this unit is the address no
control information this information comes in on line
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17 on a carrier of 18 MHz which is frequency shift keyed
with the information. In the head end, the 18 MHz
information, aver pa sing through filter 175, which
includes a high pass section and a low pays section, is
converted in a converter 177 to 103.8 My which is then
amplified inane amplifier 179 and coupled back to the
output through filter 175. The information now at 103.B
MHz is transmitted to the various ~erminalsg Returning
information it 24 I is received and converted in
converter 181 to 104 MHz. The 104 MHz signal it
amplified in amplifier 183 and transmitted back to the
business office at this frequency.
FIG. 2C shows the equipment at the business office.
Visible is another line amplifier 171 in the line 17.
15 . The equipment includes a mini-computer 201 which is
coupled to hard disk 203 for memory purposes along
with a printer 205. Also provided are one or more in-
telligent terminals 207. The key part of the system is
the controller 209 which includes its own battery back-
up power ~upply211. Within the controller is contained
A ~ommunicstions controller 213 which handles c~mmunica-
lions with external devices such as the intelligent ton-
finals 207, the minicomputer 201, the printer 205, etc.
Communications controller also receives an input from a
time clock 215 which establishes the system frequencies.
Communication controller and time clock 215 couple into
CPU 217 which is provided with a static memory 219 and,
program Emory 221. The static memory 219 stores all
of the witch or latch status change or all oonsumer6
for period of four days. This information is then,
under control ox the communications controller end CPU
provided as an output through a data encoder 222 which
convert it to urinary date an frequency shift keying
transmitter 223 which provides thy output it lo MHz on
line 225 which is then coupled through or 227. This
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I
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is the information, then, which is provided to the head
end.
. .
The received information from the head end at 154 My is
coupled through filter 227 Jo a 104 to 10.7 MHz con-
venter 229 and FISK receiver 231 and thence to a data de-
coder 233 whereupon the data is fed back into the CPU.
This information can then be coupled through the come
monkeyshines control 213 to the mini-computer 201 where
it is available for interrogation from the intelligent
terminal 207 and cay also be used to generate alarms,
etc. or provide outputs on printer 205 to indicate
malfunctions in the system.
FIG. 3 is a circuit diagram of one of the varactor tuned
traps such as the trap 61. The trap includes an upper
section 301 and a lower section 303. The upper section
301 includes an input terminal 304 and an output ton-
final 305. In one parallel branch are coils LEA and Lo
In another parallel branch is a variable coil or
inductor Lo in series with a capacitor C2. The lower
portion 303 of the filter, which is the voltage tuned
portion, includes three branches. The middle branch has
capacitor Of to ground, the left hand branch, in par-
allot with capacitor Of, contains a capacitor C3 and
varac~or diode Curl in series and, the third branch, also
in parallel with Of a variable inductor Lo. The control
input for the varactor diode Curl is at an input terminal
307 which is coupled through a resistor Al to the junk- -
lion between diode Curl and Al. A appeaser C5, is
coupled between input terminal 304 and output terminal
305 to improve operation. The circuit of JIG. 3 has two
poles. One pole is tuned Jo the frequency of the chant
not to be filtered out. The other pole is caused, by
means of a square wave modulation input on terminal 307,
to iffy back and forth cross the first pole. The no-
35 cult of this is Winnie by the waveforms of FIGS. PA and
. I
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SUB which represent outputs obtained from the screen of a
spectrum analyzer. FIG. SC shows both sections tuned to
the same frequency and JIG. ED, the one pole retuned.
In effect, when both sections are tuned to the same
S exact frequency phase cancellation, i.e. theoretically
infinite dub of attenuation result. Only by tuning
through this point is phase cancellation insured.
The physical arrangement of the parts of Fig. 3 are if-
lust rated in Pig. 4. All of the components are mounted
on an elongate printed circuit board 309. The copper
pattern 311 on the other side of the board is shown in
dotted lines. As illustrated, coils Lo and Lo which are
variable are contained within cans 313 and 315 and
include a screwdriver adjustable core 319.
