CA1228152A - Subscriber control system - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

An addressable control system which includes an address generator at a head end, generating address control signals fox each of a plurality of remote subscribers, a modulator for modulating a carrier with the address and control sig-nal and coupling it onto cables, circuits at receiving ter-minals for receiving and demodulating the modulated carrier to recover the address signals, address decoding means for each subscriber to decode the address and control signals and circuits responsive to the decoding means to select the channels which each subscriber will receive, and may in-clude a filter including one pole which is fixed at the center frequency to be tuned out and a second variable pole responsive to an input voltage, the second pole adapted to vary in frequency about the first pole. The system also has an encoder for encoding the status of the received sig-nals and a modulator for modulating a return carrier with the encoded states and putting this on the cable so that the signals may be demodulated at the head end. To carry out the demodulating and also to modulate the return sig-nals, a local oscillator and mixer is used which generates both an intermediate frequency for the mixer and a carrier frequency for the return signal.

Description

it 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

-2-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 .

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-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.

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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 , . ' :, ' '' ' .

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 .- , - ' . ' ' ' ' ' .

- 9 l 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 .

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 .. ....
. I, .

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 .. ..... . . . .. . ..

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 so 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 .

I
.

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

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.

Claims (6)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. An addressable control system for a cable television system which includes a head end from which televi-sion signals are transmitted on a plurality of channels, a plurality of receiving terminals each of which supply a group of subscribers via subscriber drops and cables interconnecting said head end with said terminals comprising:

a) means at said head end for generating address and control signals for each subscriber;

b) means at said head end for modulating a carrier with said address and control signal and for coupling said modulated carrier onto said cables;

c) means at said receiving terminals for receiving said modulated carrier and demodulating it to recover said address and control signals;

d) address decoding means for each terminal and each subscriber within a terminal coupled to decode said address and control signals;

e) means at said terminal responsive to said address decoding means and said control signals to select the channels which each subscriber will receive;

f) means to encode the status of receive commands at said terminal;

g) means to modulate a return carrier with coded states and couple said modulated return carrier onto said cables; and h) means at said head end for receiving said modu-lated return carrier and recovering encoded states, means for demodulating including a local oscillator and mixer, said local oscilla-tor comprising an oscillator adapted to genera-te an intermediate frequency for said mixer and a carrier signal for said return signal.

2. Appararatus according to claim 1 wherein said means to select, comprise negative traps and means to alternately switch in or bypass said negative traps.

3. Apparatus according to claim 2 wherein said negative traps comprise two poles filters having a first pole tuned to the frequency to be filtered out and a second pole which is variable in response to an input signal about said first pole and further including means at said terminal for providing a periodic wave signal to said filter trap to vary the frequency of said second pole.

4. Apparatus according to claim 3 wherein said means to supply said periodic wave signal is synchronized to the address and control signal frequency.

5. Apparatus according to claim 1 and further including means to compare said encoded states with corres-ponding command data.

6. Apparatus according to claim 1 wherein said local oscillator includes:

a) a phase locked loop frequency synthesizer;

b) a crystal coupled to said synthesizer;

c) a voltage controlled oscillator receiving a control voltage from said synthesizer;

d) a filter having long time constant disposed between said synthesizer and said voltage controlled oscillator;

e) a divide by n circuit coupled to the output to said voltage controlled oscillator.