CA1171165A

CA1171165A - Fail-safe catv system center facility

Info

Publication number: CA1171165A
Application number: CA000392141A
Authority: CA
Inventors: Akihiko Naito
Original assignee: Pioneer Electronic Corp
Current assignee: Pioneer Corp
Priority date: 1980-12-22
Filing date: 1981-12-11
Publication date: 1984-07-17
Also published as: JPS57106289A; FR2497048A1; FR2497048B1; GB2090108B; DE3150515A1; DE3150515C2; GB2090108A; JPS6351595B2; US4427995A

Abstract

FAIL-SAFE CATV SYSTEM CENTER FACILITY

ABSTRACT OF THE INVENTION

A fail-safe CATV system center facility in which abnormalities in a normal down-data signal transmitter are automatically corrected for so that there is no loss of reception at the terminal units. FM and AM
detectors detect the presence ox absence of the normal FSK data signal. The outputs of the FM and detectors are AND'ed together then delayed to control the switch state of a switch which selects between the outputs of the normal down data signal transmitter and a back-up transmitter for coupling through to the table system. The back-up transmitter produces a clock signal which is obtained by modulating a carrier signal having the same frequency as that of the normal down data signal, preferably a frequency shift keyed signal.

Description

-- 1 -- , The presen-t invention relates to a CATV system in which a single central facility (hereinaEter referred to as "a center" when applicable) is used to transmit video signals to a number of terminal units and two-way data communication is effected therebetween. More particular-ly, the invention relates to a CAT~ system in which trans-mitter difficulties in the center do not prevent normal reception at the terminal units, specifically, when a primary transmitter in the center which transmits a "down"
data signal (which is a data signal transmitted from the center) is in an abnormal state, a back-up signal trans-mitter is operated so that the system can operate normally at all times.
In a CATV system, a center is coupled through cables to terminal units. The center outputs a "down"
data signal, while each terminal unit outputs an "upl' data signal. That is, two-way data communication is carried out between the center and the terminal units/
besides the normal video signal which carries the tele-vision programs.
A computer, a transmitter~receiver unlt, etc. are provided in the center. The center carries out polling of the terminal units at various times and transmits a "down" data signal, for example as an FSK (frequency shift keying) signal, to control various functions at the terminal units and to detect the operating conditions of the terminal units. Data representative of channels which are utilized by subscribers are reported to the center from the terminal units via "up" data signals. When a subscriber views a chargeable program, an appropriate charge is made. However, if a dishonest subscriber connects a filter ' ~, ,.~':~

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I which eliminates the d~ta signals between the center and the terminal unit in his home, then it is ~o longer possible to calculate a charge for a chargeable program.
In order to eliminate this drawback, the system miay be designed that, when a terminal unit does not receive a "do~n" data signal for a predetermined period of time (for instance three minutes), the detector circuit in ~he tenminal unit detects this 10 condition and then stops the operation of the video signal receiving circuit. Alternatively, if the center receives no "upi' data signal (representing the : fact that a subscri~er is viewing a chargeable program) for a predetermined period of time, that is, when the terminal unit does not answer the center for a particular period of time, the center transmits an instruction slgnal to the terminal unit to stop the operation of the video signal receiving circuit so that the subscriber can no longer use the tenminal unit~
I, in this system, the "down" data signaï
transmittin g section in Ehe center becomes ~ut of order ~nd cannot transmit the "down" data signal normally or correctly, ~h~n a serious dificul~y occurs in that all of ~he terminal units ca~ot receive video signals. This trouble m~y be eliminated ~, by employing a techni~ue whereby a plurality o~
and ~ .}~ ~ e~e ~ systems are provided in the center, and if one system becomes out of order, ~hen ano~her system is used. ~owever, this technique is disadvantageous in ~hat it is considerably expe~sive. .
A typical example of a ~ATV system will be described with reference to Fig. 1. In this system, ter~inal units are provided, for i~stance, in se~eral te~ ~housands of home~ 2 for a single center _ _ __ . _ . _ .. .. : , ., , . , _ , ,~

.. , ,: ... ., . . . , , . . ............. ,-, - , 1 facility 1. The center 1 and the terminal units form one set or group. The center 1 is connec-ted through coaxial cables to the terminal units in the homes 2.
A main cable 3 extends from the center 1. Main cable amplifiers 4 and branching units 5 are provided along the main cable 3 at predetermined points. Plural branch cables 6 extend from each branching unit $.
Extension cable amplifiers 7 and taps 8 are provided along each branch cable 6 at pxedetermined positions.
Plural auxiliary branch cables 9 extend from each tap 8 with the auxiliary branch cables 9 leadlng into the homes 2. Provided in each home 2 is a terminal unit 28 including a converter lO, a television set 11 and a control box 12. The end of the auxiliary branch cable 9 is connected to the converter 10 which is in turn connected to the television set 11 and the control box 12. In this fashion, the main cable from the center l spreads branches repeatedly connecting the center 1 to the terminal units in the homes 2.
A signal receiving antenna 13 is installed outside the center 1. The antenna 13 is connected to a demodulator 15 in a source group 14. The source group 14 includes a video disc player 16, a video tape recorder 17, a studio 18 and other such eguipment as desired. Signals from the ~ource group 14 are applied to a modulation and transmission section 19. The section 19 includes two systems. One of the two systems includes an IF modulation circuit 20, a scrambling circuit 21, and an up-converter circuit 22 - 30 while the other includes an IF modulation circuit 23 and an up-c`onverter ~. The outputs~ of the up~
converter circuits 22 and 24 are connected to the main cable 3~ The main cable 3 is connected to a transmitter-receiver 25 which communicates with the converters 10. Th transmitter receiver 25 is-connected to a~ computer 26 which is connected -to .
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1 peripheral equipment 27 such as a printer and a display unit.
The opexation of ~he CATV system thus constructed will now be described. First, the switch of the television set is turned on and ~he television set is se~ to a predetermined designated channel which is preferably not used by local overthe~air stations.
The control box 12 is then operated so that the freguency of a desired channel to be received is 10 conver~ed into that of the designated channel by th~
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con~e~ 10. The channels which can be selected by the control box can be classified into a group A
channels of which television signals are received over the air and retransmitted without modification, a group B of channeis of independent programs provided free of charge and a group C of channels of chargeable programs. Each group has several corresponding channels. Typically, selection can be made ~rom about twenty to thirty channels.
For the group A, a television signal received by - the signal receiving antenna is demodulaked by the demodul~tor 15 a~d then;applied;to the modulation and .. ~ ., . . .. . . ~ . ~ . ...
transmission section 19. The signal is modulated by the IF modulation circuit 23. The ~requency of the signal thus modulated is increased to a predetermined value by the up-convexter circuit 24. Thus, the kelevision signal receIved is changed into a signal upo~ a desired channel which i5 then transmitted through the main cable 3, the branch cables 6 and the auxiliary branch cable 9 to th~ television sets 11.
. The independen~ pro~rams~ of group B are for '-m stance wea~her forecast programs and news programs.
A telev.ision signal provide~ by the video disc player 16 or the video :tape recorder 17 or a '-.television signal from a live program produced in the 6tudio 18 is modulated ard frequency-multiplied by ~he - !
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1 IF modulation circuit 23 and the up~con~erter circuit 24 into a television signal upon the desired chanrel which is applied to the main cable 3. I'he independent progra~s are free of charge irrespective of the number of times of television signal reception or the period of time of television signal reception.
Each subscriber can receive the television signals for a basic monthly charge.
The chargeable programs of group C are typically lo new movie programs, special programs, or the like. A
television si~nal provided by the video disc player 16 or ~he video tape recorder 17, or a television signal from a live program produced in the studio 18 is modulated by the IF modulation circuit 20. ~
scrambling synchronizing signal of predetermined form is added to the video signal in the televisïon signal by the scrambling circuit 21. Because of this .signal, if the television signal is receiYed only as it.is by the television set, it is impossible to reproduce normal pictures on the television set. The television signal thus treated is applied to the up-con~erter 22 ; where lts frequency is increased to ~he requency of a designated channel. The television signal thus processed is supplied to the main cable 3.
Upon receiving the television signal of the chargeable program by the television set in each home Z, ~he scrambled television signal .is converted into a normal video signal by the converter 10 so ~hat noxmal pictures can be observed on the television set 11~ Whenever a chargeablP program is received, a predetermined fee is charged to the subscriber~ The -sum of the monthly basic charge and the special use fee is billed to the subscriber.
In order to determine Whether received progxams are free of charge or ~ot, it is ~ecessa~y to detect what subscribers have used what channel~ for .
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1 par~icular periods of time. For this purpose, th~
transmitter-receiver 25 outputs a retrieving signal at predetermined time intervals to address the converter 10 in each terminal unit with an address num~er assigned to that particular terminal unit to determine if a group C channel is being used at the retrieval time. In response to this, the converter 10 sends to the txansmitter-receiver 25 an answering siynal representative of the channel which is in use at thP retrieval time. The charge data transmitted and xec~ived by the transmitter-receiver 25 is arranged and stored by Ehe computer 26 and displayed or printed out by the peripheral equipment 27. As the - retrieving signal is transmitted at fixed predetermlned time intervals of typical;ly several seconds tc several tens of seconds, audience ratings can also be immediately calculated.
A subs~riber can choose which programs he wishes to view ~y operating his control bo~ 12 while watching ~he television set 11. The subscriber's choice or answer is encoded and sent thxough the coaxial cables to ~e center 1.
SU~MARY OF THE INVENTION
-- ~, In view o~ the above-described dificulties, the in~ention provides a CATV system having an improved l.
reliability in which a back-up signal transmitter fo.r outputting a clock signal, which is obtained by .-.
modula`.ting a carxier signal having the same ~re~uency as that of a "do~m" data signal according to the sarlle ~ i modulation tech~i~ue as tha~ of ~h~Q "down" data signal, is provided in the ce~ter. When the "down"
data signal is abnormal, the back-up signal ~.-transmitter transmits the clock signal instead of the "down" data signal to the terminal units so that the t~rminal units ca~ recaive video signals at all× ~r.~:, BRIEF DESCRIPTION OF THE DRAWINGS
FIG~ 1 is an explanatory diagram outlining the if-~
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1 arrangement of a known CATV system; and FIC.. 2 is a block diagram of a preferred embodiment of a CA~I system center of the invention.
DESCRIPTION OF THE PREFEXP~ED EMBODIMENTS
FIG. 2 shows a preferred embodiment o~ the invention, specifically, improved portions of the centerO A video transmission section 19 is here connected to the main cable 3 through a coupler unit 31 in order to transmi~ video signals to the aforementioned terminal units 28. A computer 26 and a transmitter-receiver 25 are connected to each other, also as in the prior art system. -The transmitter-re~eiver ~5 is connected through a sig~al splittex 35 to a terminal a of a switch circuit 36.
The coupler 31 has one input connected to a terminal c of the switch circuit 36. An armature d connected to the terminal c can be set to either the terminal a or ~he terminal b of thi~ swit~h circuit 36.
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In practice, the a~nature d is operated by means of a coaxial relay or the like.
A bandpass filter 37 for transmitting a '1down"
- - data ignal is~ connected to one output o the ~pli~ter 35. A detection circuit 39 is c~nnected through an ~nplifier 38 to the bandpass fil-ter 37.
The detection circuit 39 outputs an ~M detection - output signal e, which i~ obtained by subjecting a carrier signal to AM detection, and a clock signal f which is obtained by subjecti~g an FSK signal to FM detection. The two si~nals e and f are applied to an AND gate 40. The output o~ the ~ND gate 40 is appiled through a delay circuit 41 to a driver circuit 42. The operation o the switch circuit 36 is controlled by the driver cixcuit 42. A clock signal generating circuit 43 for generating a clock si~nal having a predetermined period is connected to a modulator 44 which modulates the clock signal as an :

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1 FSIC signal. The terminal b o~ the switch circui-t 36 is connected -to the output of the modulator 4~.
The operation of the above-described ~ATV system will be described.
When the computer 36 and the transmitter-receiver 25 operate normall~ and output the normal "down" ~ata signal, the "down" data signal is passed through the splitter 35.
The "down~' data signal thus generated is applied through the bandpass filter 37 to the amplifier 38 where i-t is amplified.
The detection circuit 3~ includes both an AM
detector 39a ~or detecting the presence or absence of the carrier signal of the "down" data signal and an FM
detection circuit 39b ~or detecting the presence or absence of the clock signal. These two detectors thus provide the AM detection output signal e and the clock signal f. The signals e and f are applied to the AND
gate ~0, the output of which is applied to the delay circuit ~1. When both of the signals e and ~ are present, the delay circuit ~1 outputs no signal. Accordingly, the armature d of the switch circuit 36 is maintained at the terminal ar and therefore the "down" data signal from the transmitter-receiver 25 is transmi-tted through the splitter 35, the switch circuit 36 and the coupler 31 to the main cable 3 and to the terminal units 28. ~lso, an "up" data signal from each terminal unit 2~ can then be transmitted to the transmitter-receiver 25 and from there to the computer 26 taking the above-described path in the opposite direction. Thus, two-way data communi-cations are carried out.
If the "down" data signal is abnormal because the computer 26 and the transmitter-receiver 25 are out of order for instance, at least one of the AM detection output signal e and the clock signal f are not outputted by the detection circuit 39, and accordingly ~:~7~1~5 ,~ 9 .

1the AND gate 40 provides no output. One or two minutes after the provision of the output from the AND
gate 40 is suspended, the delay circuit 41 supplies a detection signal representative of the abnormal condition to the driver 42. As a result, ~he driver 42 oper~tes the switch circuit 36 so that the armature d is tripped over to the terminal b.
Therefore, the FSK signal, which is generated by sub~ecting the clock signal from the clock signal ;:
generating circui-t 43 to modulation by ~he modulator 44, is applied through the switch circuit 36 -:
and the coupler 31 to the main cable 3 so that the FSK signal is then transmitted to the terminal units 28 on a carrier signal having the same frequency ~.
as that of the "dow~" data signal. As the FSK signal is received by each terminal unit ~8, the ~erminal units 28 can continue to receive video signals from .-.
the transmission section 19. ~ :
The delay circuit 41 is provided to permit operation without operating the switch circuit 36 in the case when the "down" data signal is interrupted mom~ntarily or becomes abnormal for an extremely short time~ That is, the delay circuit 41 is pro~ided so that normal operation of the system will be ~., interrupted only when an abnormal condition continues~
for some time. ":~
When the cornputex 26 and ~he transmitter- !~,',i - receiver 25 again are capable of transmitting normal~ ~~~~~` .`.
"down" data signals, the delay circuit 41 detects the~-' fact that the computer 2~ and ~the transmitter- - ~s receiver 25 are in ~h normal condition ~nd provides s'-no output. As a resultj the dxiver ~2 causes the ~;.
switch circuit to be set back to its normal state so ~ '`
th~t the transmi~ter-receiver-2~ is coupled to the terminal units. Thus, two-way data communications are ef~ected again. ~ ... . . . ~:`

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1 With the CATV system according to the invention arranged as described above, i~ the "down" data signal ~ e_ c, ~
from the center ~e~em-s abnormal, -the back-up transmitter outputs a clock signal which is obtained by subjecting a carrier signal having the same frequency as that of the "down" data slgnal to the same modulation as that of ~he "down" data signal.
Accordingly, the terminal units can continuously receive the video signals without interruption.
It is unnecessary to provide in the center a a plurality of systems of "down" data signal transmitters each having the same function.
Therefore, the back-up system can be simple in - arrangement and can therefore be manufactured at low s~st.

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Claims

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

1. In a CATV system in which a central facility is coupled through cables to a number of terminal units and two-way data communication is effected therebetween, said central facility comprising:
normal down data signal transmitting means;
abnormality detecting means for detecting a down data signal abnormality in a down data signal produced by said down signal data transmitting means, said abnormality detecting means including an FM detector, an AM detector, and AND gate means having first and second inputs coupled, respectively, to outputs of said FM detector and said AM detector, an output of said AND gate means being coupled to control a switching position of said switching means;
back-up transmitting means for producing a clock signal by modulating a carrier signal to form a frequency shift keyed signal having the same. frequency as that of said down data signal; and switching means for stopping, when said abnormality detecting means detects that said down data signal is in an abnormal condition, transmission of said down data signal and coupling said clock signal from said back-up transmitting means to said cables, wherein when said down data signal is abnormal, clock signals for down data signals are transmitted to said terminal units by said back-up transmitting means.

2. The CATV system as claimed in claim 1 wherein said abnormality detecting means further comprises a bandpass filter receiving an input from an output of said normal down signal transmitting means and amplifier means having an input coupled to an output of said bandpass filter means and an output coupled to an input of said FM detector and said AM detector.

3. The CATV system as claimed in claim 1 or 2 wherein said abnormality detecting means further comprises a delay circuit having an input coupled to an output of said AND gate means and an output coupled to a control input of said switching means for controlling a switch position of said switching means.