CA2177163C - Data modulation arrangement for selectively distributing data - Google Patents
Data modulation arrangement for selectively distributing dataInfo
- Publication number
- CA2177163C CA2177163C CA002177163A CA2177163A CA2177163C CA 2177163 C CA2177163 C CA 2177163C CA 002177163 A CA002177163 A CA 002177163A CA 2177163 A CA2177163 A CA 2177163A CA 2177163 C CA2177163 C CA 2177163C
- Authority
- CA
- Canada
- Prior art keywords
- data
- signal
- signals
- modulator
- modulated
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
Links
Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N7/00—Television systems
- H04N7/16—Analogue secrecy systems; Analogue subscription systems
- H04N7/173—Analogue secrecy systems; Analogue subscription systems with two-way working, e.g. subscriber sending a programme selection signal
- H04N7/17309—Transmission or handling of upstream communications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N7/00—Television systems
- H04N7/16—Analogue secrecy systems; Analogue subscription systems
Abstract
A cable television distribution arrangement is supplied via optical fibers with additional digital signals which are delivered to customers via coaxial drop cables (20) modulated at frequencies above those of the conventional analog television channels. A reduction in the required number of modulators is achieved, while delivering individually selected signals to individual customers, by supplying digital signals for a group of customers to a first modulator (72) and a pseudo data signal to a second modulator (84), and selecting (78) between the outputs of the two modulators individually for each customer in the group. Switching between the outputs of the modulators is carried out during overhead information (O/H) which is additionally supplied commonly to both modulators.
Description
PCT/CA94/On67 1 ~vo 95/l8~ln 2 t 7 7 1 6 3 DATA MODULATION ARRANGEMENT FOR SELECTIVELY
DISTRIBUTING DATA
Technical Field and Tndv~trial Application This invention relates to data m~dul~tion a~T~nge ~ c, and is particularly 5 concern~1 with a data mod~ tion arr~ngçment for selectively distributing data. A
particular eY~mple of the use of such an alT~ng~-ment is to f~ilit~t~ selective distribution of broadcast digital television signals to subscribers in a television distribution network.
B~ck~round Art Cable television distribution alT~nge~ ~ ~r~ are well known. In such arrange.
10 analog television signals are carried to cuctomtors via a bl~lched coaxial cable which includes bridger amplifiers, line extenders, and cUstQm~r taps. Each television signal occupies a 6 MHz channel at a fi~lucllcy from about 50 MHz to about 550 MHz or more.
The upper frequency is limited by the bandwidth of the bridger amplifiers and line extenders and the attenuation of the coaxial cable, which as is well known increases with 15 increasing frequency.
There is an increasing desire for additional capacity in cable television distribution ~rr~n~ r~ This ~lem~nrl includes a desire for additional broadcast television signals in analog or co,~lcssed digital form, additional facilities in~lu-ling for example video-on-dem~n-l (VOD) and near-VOD services (e.g. movies broadcast with stepped starting20 times), and a desire for tr~n~mi~ion of control and possibly other information in the opposite, u~sL~ca"~, direction via the network.
To meet this desire, various ways have been pluposed for supplying additional signals via a cable television distribution arr~ngem~nt~ typically involving the supply of such signals via optical fibers to a~,ùpliate points in the coaxial cable system with 25 delivery of the signals to the customer premises via the coaxial cable, referred to as the drop cable, which already exists from the cUstom~r tap to the customer pl~,ll~ises.
It is desired to supply to each customer only those services or television signals for which the customer has agreed to pay. As dirr~ t cn~tom~rs have dirr~
pl~ ,nces, there is a need to provide, at each cUstomer tap, eq-lirment which extracts 30 from all of the signals which are available on the network only those which are allocated for each particular customer. Only these signals are then delivered in modlll~t~d form for tr~n~mi~sion to the ~;u~o~ r via the l~s~ec~ e drop cable.
One way of doing this is to provide an individual modulator for each cu~tom~r.
However, this l~UUcS a large number of mod~ tors, each of which is powered via the 35 coaxial cable, with consequent disadvantages of high compleYity, costs, and power consumption and dissipatiûn. An ~ltern~tive is to provide a mod~ tor which is common to a group of cU~tom~rs; however, this fails to meet the above desire in that it delivers to all ~;uslo"~ in the group the signals for which only one ~ olll~,~ in that group may have 2 2~77163 agreed to pay, thus involving a risk of other customers in the group receiving signals to which they are not entitled.
In International Standard Electric Corporation's EP 0 158 548 dated October 16, 1985, entitled "Cable Television Network", there is proposed a network in which an 5 exchange 3 includes a modulator 13 to which subscribers can be connected via a switching matrix 12 for receiving a modulated television signal. Other subscribers are connected via the switching matrix 12 to a second modulator 15 which is supplied with a filtered television signal comprising only synchronization pulses and a black level signal. This document does not further discuss the nature of the switching in the switching matrix or 10 from one modem to the other. In addition, the signals are analog television signals, and not digital data signals.
An object of this invention is to provide an improved data modulation arrangement for selectively distributing data.
Disclosure of the Invention According to one aspect of this invention there is provided a data modulation arrangement for selectively distributing data to a plurality of outputs, comprising: a first modulator responsive to a digital data signal to produce a first modulated signal; a second modulator responsive to a digital pseudo data signal to produce a second modulated signal;
a plurality of multiplexers each for supplying a modulated signal to a respective one of 20 said plurality of outputs, each multiplexer having first and second inputs to which the first and second modulated signals, respectively, are supplied; and a control unit for controlling each multiplexer to supply the f1rst and the second modulated signals selectively to the respective output; wherein the control unit is arranged to supply additional information simultaneously in both the data signal and the pseudo data signal, and to control each 25 multiplexer to switch between the first and second modulated signals at its inputs only during said additional information. This facilitates continuity of the RF spectrum of the signal produced at each output. The additional information can conveniently comprise overhead information to accompany the data.
In an embodiment of the invention described below, the outputs comprise coaxial 30 drop cables of a cable television distribution arrangement, the first and second modulators modulate the data signal and the pseudo data signal, respectively, to frequencies greater than 550 MHz, and each of the first and second modulators comprises a binary phase shift keyed modulator and an up-converter.
The invention also provides a television signal distribution network including drop 35 cables each to a respective customer for supplying analog television signals in a predetermined frequency range, the network further including a drop unit for supplying to a plurality of drop cables digital signals modulated at frequencies above said frequency range, the drop unit comprising: a plurality of multiplexers each having first and second ,A
inputs and an output coupled to a respective one of said plurality of drop cables; a first modulator, for mod~ ting digital signals for customers associated with said plurality of drop cables to frequencies above said predetermined frequency range, having an output coupled to the first input of each of the plurality of multiplexers; a second modulator for 5 modlll~ting a pseudo data signal to said frequencies above said predetermined frequency range, having an output coupled to the second input of each of the plurality of multiplexers; and a control unit for controlling each of the plurality of multiplexers to couple its first or its second input selectively to its output; wherein the first modulator is arranged to modulate additional information with the digital signals, the second modulator 10 is arranged simultaneously to modulate the additional information with the pseudo data signal, and the control unit is arranged to control each multiplexer to switch between its f1rst and second inputs only during the additional information.
~vo 9sll8sln 2 :~ 7 7 1 6 3 PCT/CA94/00671 The invention also provides a method of supplying digital signals selectively toeach of a plurality of cUstom~rs~ comprising the steps of: supplying digital signals for one or more custom~rs in a group of c--ctomçrs from a source of digital signals to a modnl~tor to produce a data mo~lnl~ted signal; producing a pseudo data modlll~ted signal having S similar spectral characterictic~ to those of the data modul~t~l signal; and selectively supplying the data modlll~ted signal and the pseudo data mo-llll~ted signal to each ~;u~L~""~,l in said group so that each cUctom~r in said group is supplied with the data modulated signal in respect of digital signals for that C~-!'10-~ and otherwise is supplied with the pseudo data modlll~ted signal; wll~leill parts of the pseudo data modlllate(l signal are subst~nti~lly identical to cimult~neously occurring parts of the data modul~te~ signal, and ~wi~ching between the data modulated signal and the pseudo data modulated signal for each cUctomer is carried out only during said parts of the modlll~te l signals. Said parts of the modulated signals can conveniently comprise overhead information for the customers.
Conveniently the step of producing the pseudo data mo(lnl~t~d signal comprises the step of supplying a source of pseudo data to a second modulator.
Brief Description of the Drawingc The invention will be further understood from the following description with reference to the accompanying drawings, in which:
Fig. 1 schem~ti~lly illu~ es a network col l ll,. ;.~ing a cable television distribution arr~ngement with an additional bidirectional tr~ncmiccion capability, to which an embodiment of this invention is applied;
Figs. 2 and 3 illustrate radio frequency spectra at different points in the network of Fig. 1;
Fig. 4 shows a block diagram of a drop unit used in the network of Fig. 1 in accordance with an embo-liment of the invention; and Fig. 5 is a more ~let~iled block diagram of a Ll~ of the drop unit of Fig. 4.
Mode(s) of Carryin~e Out the Invention Fig. 1 illustrates parts of a conventional cable television distribution arr~ng~mf nt, shown above a broken line 10, which is supple.l.~ .-lecl with an additional bidirectional tr~ncmicsion capability, shown below the broken line 10. As is well known, the conventional cable television distribution arr~ngement co~ ises a bridger amplifier 12, coaxial cables 14, passive customer taps (TAP) 16, line extend~rs 18, and a coaxial drop cable 20 to a television receiver (TV) 22 in customer premises 24.
- The ~klition~l bidirectional tr~ncmiccion capability comprises optical fiber I~l"~ination units (FTUs) 26 and optical fibers 28 connected thereto. Each FTU 26 is inserted into the path of a coaxial cable 14 following a bridger arnplifier 12 or line extender 18, and serves to supply to the coaxial cable 14 in the downstream direction (from the so-called head end, not shown, to the customer premises) digital signals at wo ss/l8sl0 PCT/CAg4/00671 frçquencies above those of the analog television signals already carried by the cable 14, as further described below. The arr~ngem~nt generally also in~lu(lçs tçrmin~ion units (rI') 30 which arç inserted into the coaxial cable 14 precçding the line extenders 18 and serve subst~nti~lly to çlimin~te the high fi~u~ ;y digital signals from bçing supplied to the line 5 extenders and from being reflectçd back to the taps 16. However, if the coaxial cable 14 is sufficiendy long, so that the high frequency digital signals are sufficiently ~ttenll~te~l, and the bandwidth of the line ext~nders 18 is sufficiently restricted (for example to 550 MHz), then tçrmin~tion units 30 can bç omittçd The high fi~u~n~;y digital signals are carried from the head end via the opticalfibers 28 to each FTU 26. As illustrated in Fig. 1, dirre~ FTUs can be coupled individually to a lespe~ /e fiber 28, or a plurality of FTUs 26 can be coupled via an optical splitter 32 to a common fiber 28 extending from the head end. In either case, the FTU 26 inserts the high frequency digital signals onto the coaxial cable 14 so that these are carried with the analog television signals as far as the next termination unit 30 or line extender 16. The analog and digital signals are then available to the customer prçmises 24 via the customer taps 16, which are supplçmentçcl with a drop unit described further below for supplying signals to set-top units (STU) 34 within the customer premises 24, via the existing cable drops 20. As this invention is not directly concerned with the FTUs 26 and the set-top units 34, these are not further described here.
In the opposite, upstream, direction of tr~n~mi~ion, a unit 34 can send control signals (for example, television program requests) and optionally other information to the head end via the coaxial cable drop 20, cUstomçr tap 16, coaxial cable 14, FTU 26, and optical fibçrs 28. DirrGrel1t wavelengths or other forms of multiplexing can conveniently bç used for the different directions of tr~n~mic~ion on the optical fibers 28.
Referring to Fig. 2, conventional analog VHF and UHF television signals and FM
radio signals are carried by the coaxial cables 14 at frequencies from 50 to 550 MHz.
Additional UHF television signals may possibly be present at higher frequenries, for eY~mrle about 33 additional signals at frequencies from 550 MHz up to about 750 MHz, depending upon the bandwidth of the bridger amplifiers 12 and line extenders 16 and the a~ n of the coaxial cables 14.
At higher frequencies, in a frequency range from 750 to 950 MHz, a first 16 QAM
(quadrature amplitude modulated) digital signal channel is supplied from the FTUs 26 to the coaxial cable 14. This can provide a data rate of 600 Mb/s, and thus can accommodate 200 colll~ ssed digital video signals each with a bit rate of 3 Mb/s. A second similar channel is provided in a rl~uel,cy range from 950 to 1150 MHz, acco.l~.lodating another 200 digital video signals, and a third similar channel can be provided in the frequency range form 550 to 750 MHz to accommo~l~tç a further 200 digital video signals, replacing a smaller number of possible analog television signals in this frequency range.
WO 95/18510 ~ 17 716 3 PCT/CA94/00671 For the upstream direction of trAncmiccion~ control signals can be carried in the relatively low frequency range from 5 to 30 MHz, but preferably control signals and possibly other data are carried in a QPSK (quadrature phase shift keyed) chAnnelproviding an upstream bit rate of 300 Mb/s in a frequency range from 1150 to 1350 MHz, 5 as shown in Fig. 2.
On the coaxial cable drops 20, the radio frequency spectrum is as shown in Fig. 3.
Up to 750 MHz, the spe ;L-~-- is the conventional analog signal s~,ecL,u~ in the frequency range from 50 to 750 MHz, with the option of low frequency u~sL~ ll control signals in the frequency range from 5 to 30 MHz as described above. The digital video signals are 10 carried downstream on the cable drops 20 to the cuctomçr premises in the form of a BPSK (binary phase shift keyed) signal providing a bit rate of 150 Mb/s in a frequency range from 750 to 950 MHz. This bit rate can accommo~lAte 50 co..-p~ssed digital video signals each with a bit rate of 3 Mb/s. Control signals and other data are preferably carried UpSLI~ll via the cable drops 20 by a multiple access BPSK signal providing the same bit rate of 150 Mb/s in a frequency range from 950 to 1150 MHz.
It should be appreciated that the high frequency digital signals are subject to the same At~çn~.Ation on the coaxial cables that analog signals at the same frequencies would be. However, although analog television signals at these frequencies are impractical in the network, it is practical to detect and lege.lcl~e the digital signals at these frequencies, and they are not condllctç~l via the bridger amplifiers 12 and line extenders 16 with their relatively restricted bandwidths.
Fig. 4 illustrates a drop unit which, as intlicAteA above, is provided at a cuct- m~r tap 16 and is provided for a group of, for example 8, customers. The drop unit includes a directional coupler 40 and protection unit 42 via which signals are derived from the coaxial cable 14 in conventional manner, and a power supply unit 44 via which power for the drop unit is derived from the coaxial cable 14 in known manner. Up~ n control signals are also supplied to the cable 14 via the protection unit 42 and the coupler 40. For simplicity it is AC~ l~ in the following description that low frequency upsL-~dm control signals are not present.
The drop unit includes a diplexing filter 46 which sep~ ÇS the downstream analog television signals onto a path 48 which may optionally include an amplifier 50, shown in broken lines. Do~ sL~ digital signals at the higher frequencies as described above are supplied from the diplexing filter 46 to a 16 QAM receiver (Rx) unit 52 via a directional coupler 54, and up~l,ea~.. control signals are supplied via the directional coupler 54 to the diplexing filter 46 from a QPSK trAncmit~r (Tx) 56. A control unit 58 derives the u~ a.ll control signals from the group of customers via their coaxial cable drops 20, diplexing filters 60, and a BPSK receiver unit 62. The control unit 58 also supplies downstream digital signals, as selected by the cu~omcl:~, and overhead ~ .. .. . . ..
wo ss/lssln 21 7 71 6 3 PCT/CAg4/00671 i,~l.n&Lion to a BPSK tr~ncmitter unit 64 as is further described below. The tr~ncmittf r unit 64 is controlled by the control unit 58 via control paths l~lese.l~ed by a line 66 to supply to each c~lctomçr only those signals to which the customer is entitled, as described further below. The tr~ncmittf~r unit 64 is also supplied with the down~Ll~a,.. analog video S signals from the path 48, and combines these with the dow--sLl~anl BPSK digital signals for supply to the coaxial cable drops 20 via the diplexing filters 60.
As can be appreciated, the units 52,56, and 58 serve to provide co.,~ ..nications with an FTU 26 and the head end of the network, for supply of desired digital signals to the group of customers served by the drop unit. Thus the receiver unit 52 can comprise a plurality of receivers for receiving the downstream digital signals in the frequency ranges as described above with lcf~ ,.lce to Fig. 2, and the Ll",~ . 56 Op~l~Les in theul,sLI.,~ll frequency range also as described above with reference to Fig. 2. The control unit 58 can derive the selected downstream digital signals for supply to the customers in any desired manner. For example, the signals may be co~ ic~tç d using ATM
(asynchronous transfer mode) techniques, with the data of each digital video signal ch~nnçl being i(1~ntifif~d by the label in each ATM cell carrying that data, and the control unit 58 using the cell label to determine whether or not to supply the cell data to the tr~ncmit~ç r unit 64. ATM cells can also be sent from the head end to the drop unit to inform the control unit 58 of the signal entitlement of each customer served by the drop unit. As this invention is not directly concerned with the details of the units 52,56, and 58, these are not further described here.
Referring to Fig. 5, the BPSK tr~ncmittf r unit 64 includes a dowl,~L,e~" data path including a buffer 70, a BPSK mod~ tor 72, an up-converter 74, a b~ndp~cs filter (BPF) 76, and, for each customer in the group of cUstomçrs supplied via this tr~ncmittçr unit, a respective analog multiplexer (MUX) 78 and analog mixer 80. The t~n~ unit 64 also includes a pseudo data path comprising a buffer 82, a BPSK modulator 84, anup-converter 86, and a b~n-lpacs filter (BPF) 88. Overhead information (O/H) is supplied from the control unit 58 to both of the buffers 70 and 82, and hence to both the data path and the pseudo data path.
Under the control of the control unit 58, the data of each digital signal which is to be supplied to any one or more of the customers in the group is derived from the receiver unit 52 and supplied to the buffer 70, together with the overhead information which for example serves for polling difr"~nl cu~Lo"~ premises units 34 for information to be Ll,ln!~llliLI~ upstream in a mllltiple access manner. The data and overhead il~l",ation are read out from the buffer 70 under the control of the control unit 58 to mod~ te an IF
(inlf,. Inetl;s~tf, frequency) signal supplied to the BPSK mod~ tor 72. The reslllt;ng modulated IF signal is converted to the RF (radio frequency) ~ecL~ w" described above with reference to Fig. 3 by the up-converter 74 to which an RF signal is supplied, and the , .
~vo gS/18510 2 17 7 1 6 3 PCT/CAg4/00671 resulting RF signal is filtered in the b~n-lp~cs filter 76. The resulting data mo~lnl~t~ RF
signal is supplied from the output of the b~n-lp~cs filter 76 to a first input of each of the multiplexers 78.
The control unit 58 simlllt~neously controls the buffer 82 to store the overheadinformation when this is stored in the buffer 70, and to store pseudo data, recycled from the output of the buffer 82, when real digital signal data is stored in the buffer 70. The res-llting pseudo data and overhead ulfolll~lion is supplied in a similar l,lanl-e~ under the control of the control unit 58 to modulate the IF signal in the modlll~tor 84, the resulting modlll~t~,d signal similarly being converted to the same RF range in the up-converter 86 and filtered in the b~ntlp~cs filter 88. The resulting pseudo data modulated RF signal is supplied to a second input of each of the multiplexers 78.
For each customer, the control unit 58 supplies to a control input of the rc~ecL-ve multiplexer 78 a control signal to select, and pass on to the respective mixer 80, either the data modulated RF signal at its first input or the pseudo data modulated RF signal at its second input. The control signal is produced by the control unit 58 to select the data modulated RF signal at the first input only for digital signals to which the respective cllctQmer is entitl~cl, and otherwise to select the pseudo data modlll~te~l RF signal at the second input so that the cUctomer is not supplied with other digital signals being supplied only to other customers in the same group.
Each control signal is produced by the control unit 58 so that swik;hil~g in the~;s~;L~-~e multiplexer 78 between the signals at the two inputs of the mlllti~lexer occurs only during the overhead information, and hence only at times when the same infollllalion is simnlt~neously present at both multiplexer inputs. This ensures that the RF spectral characteristics of the mod~ ted signal supplied to each customer are continuously 25 preserved, this being an important re~luil.,l~nl.
The filters 76 and 88 may be impl~ ed using digital signal procescing techniques and hence may give rise to a memory effect in the inrol.llalion supplied to the multiplexer inputs; in other words, although the overhead information supplied on both the data path and the pseudo data path is the same, the data and pseudo data are dirr~ t and so produce dirr.,.e,~l lingering effects on the overhead inrollllalion as this is supplied to the multiplexers 78. The duration of each sequence of overhead information (for example, several ~ucces~ive bytes) can be selected to be sufficient to accommod~te this memory effect, thereby to ...~ i.l the l~uil~ conlilluily of RF spectral characteristics during ~wilching of the multiplexers.
The output of each multiplexer 78 is supplied to the l~,i,p~tive mixer 80, where it is combined with the conventional analog video signals (from the path 48 in Fig. 4) for supply to the l.,s~ec~ e customer via the fes~cli~e di~lcAu~g filter 60 and coaxial cable drop 20. As shown in Fig. 5, the output signal from each mixer 80 can optionally be .. . . . . ... ....
wo 95/l8sln 2 ~ 7 7 1 6 3 PcT/cAg4mn67l inhibits~ by a further control signal from the control unit 58, to prevent delivery of any signals to a customer.
It should be appreciated that this arrangement of the BPSK tr~ncmin~or unit 64 enables only two modulators (or, more exactly, two sets of units 72, 74, 76 and 84, 86, 5 88, each set conci~ting of a modulator, an up-converter, and a b~n-lp~cs filter) to serve a group of for example 8 or more CUSLu~ , in contrast to the prior art which would require one modulator for each ~;U:i10111~,l in order to achieve the same selective supply of signals to each customer. Thus there is a subst~nti~l saving in costs and power re4uil~nlellts. As discussed above, the downstream BPSK specLI um on the coaxial cable drops provides a bit rate of 150 Mb/s and can accommo~te 50 conl~,essed digital video channels, which is ample to meet the total ~ uire.ll~ for 8 or more cu~LOIll~
Although a particular embo-lim~ont of the invention has been described in detail, it should be appreciated that numerous modifications, variations, and adaptations may be made without departing from the scope of the invention as defined in the claims.In particular, it should be appreciated that the particular bit rates, RF spectra, modulation methods, and so on described above are given purely by way of example, and the invention is not in any way limited thereto. Furth~,.lllo,~, the particular manner described above for producing the pseudo data signal is given by way of example, and other methods of producing a pseudo data modulated RF signal may ~ltern~tively be used.
20 Instead of switching each multiplexer be~n its inputs during the overhead information, other additional information may be supplied cim~llt~neously in both the data and pseudo data paths and switching may be carried out during such other additional infolllla~ion. In addition, the invention is not limited to the particular form of the network as described above, this again being given purely by way of example and explanation.
DISTRIBUTING DATA
Technical Field and Tndv~trial Application This invention relates to data m~dul~tion a~T~nge ~ c, and is particularly 5 concern~1 with a data mod~ tion arr~ngçment for selectively distributing data. A
particular eY~mple of the use of such an alT~ng~-ment is to f~ilit~t~ selective distribution of broadcast digital television signals to subscribers in a television distribution network.
B~ck~round Art Cable television distribution alT~nge~ ~ ~r~ are well known. In such arrange.
10 analog television signals are carried to cuctomtors via a bl~lched coaxial cable which includes bridger amplifiers, line extenders, and cUstQm~r taps. Each television signal occupies a 6 MHz channel at a fi~lucllcy from about 50 MHz to about 550 MHz or more.
The upper frequency is limited by the bandwidth of the bridger amplifiers and line extenders and the attenuation of the coaxial cable, which as is well known increases with 15 increasing frequency.
There is an increasing desire for additional capacity in cable television distribution ~rr~n~ r~ This ~lem~nrl includes a desire for additional broadcast television signals in analog or co,~lcssed digital form, additional facilities in~lu-ling for example video-on-dem~n-l (VOD) and near-VOD services (e.g. movies broadcast with stepped starting20 times), and a desire for tr~n~mi~ion of control and possibly other information in the opposite, u~sL~ca"~, direction via the network.
To meet this desire, various ways have been pluposed for supplying additional signals via a cable television distribution arr~ngem~nt~ typically involving the supply of such signals via optical fibers to a~,ùpliate points in the coaxial cable system with 25 delivery of the signals to the customer premises via the coaxial cable, referred to as the drop cable, which already exists from the cUstom~r tap to the customer pl~,ll~ises.
It is desired to supply to each customer only those services or television signals for which the customer has agreed to pay. As dirr~ t cn~tom~rs have dirr~
pl~ ,nces, there is a need to provide, at each cUstomer tap, eq-lirment which extracts 30 from all of the signals which are available on the network only those which are allocated for each particular customer. Only these signals are then delivered in modlll~t~d form for tr~n~mi~sion to the ~;u~o~ r via the l~s~ec~ e drop cable.
One way of doing this is to provide an individual modulator for each cu~tom~r.
However, this l~UUcS a large number of mod~ tors, each of which is powered via the 35 coaxial cable, with consequent disadvantages of high compleYity, costs, and power consumption and dissipatiûn. An ~ltern~tive is to provide a mod~ tor which is common to a group of cU~tom~rs; however, this fails to meet the above desire in that it delivers to all ~;uslo"~ in the group the signals for which only one ~ olll~,~ in that group may have 2 2~77163 agreed to pay, thus involving a risk of other customers in the group receiving signals to which they are not entitled.
In International Standard Electric Corporation's EP 0 158 548 dated October 16, 1985, entitled "Cable Television Network", there is proposed a network in which an 5 exchange 3 includes a modulator 13 to which subscribers can be connected via a switching matrix 12 for receiving a modulated television signal. Other subscribers are connected via the switching matrix 12 to a second modulator 15 which is supplied with a filtered television signal comprising only synchronization pulses and a black level signal. This document does not further discuss the nature of the switching in the switching matrix or 10 from one modem to the other. In addition, the signals are analog television signals, and not digital data signals.
An object of this invention is to provide an improved data modulation arrangement for selectively distributing data.
Disclosure of the Invention According to one aspect of this invention there is provided a data modulation arrangement for selectively distributing data to a plurality of outputs, comprising: a first modulator responsive to a digital data signal to produce a first modulated signal; a second modulator responsive to a digital pseudo data signal to produce a second modulated signal;
a plurality of multiplexers each for supplying a modulated signal to a respective one of 20 said plurality of outputs, each multiplexer having first and second inputs to which the first and second modulated signals, respectively, are supplied; and a control unit for controlling each multiplexer to supply the f1rst and the second modulated signals selectively to the respective output; wherein the control unit is arranged to supply additional information simultaneously in both the data signal and the pseudo data signal, and to control each 25 multiplexer to switch between the first and second modulated signals at its inputs only during said additional information. This facilitates continuity of the RF spectrum of the signal produced at each output. The additional information can conveniently comprise overhead information to accompany the data.
In an embodiment of the invention described below, the outputs comprise coaxial 30 drop cables of a cable television distribution arrangement, the first and second modulators modulate the data signal and the pseudo data signal, respectively, to frequencies greater than 550 MHz, and each of the first and second modulators comprises a binary phase shift keyed modulator and an up-converter.
The invention also provides a television signal distribution network including drop 35 cables each to a respective customer for supplying analog television signals in a predetermined frequency range, the network further including a drop unit for supplying to a plurality of drop cables digital signals modulated at frequencies above said frequency range, the drop unit comprising: a plurality of multiplexers each having first and second ,A
inputs and an output coupled to a respective one of said plurality of drop cables; a first modulator, for mod~ ting digital signals for customers associated with said plurality of drop cables to frequencies above said predetermined frequency range, having an output coupled to the first input of each of the plurality of multiplexers; a second modulator for 5 modlll~ting a pseudo data signal to said frequencies above said predetermined frequency range, having an output coupled to the second input of each of the plurality of multiplexers; and a control unit for controlling each of the plurality of multiplexers to couple its first or its second input selectively to its output; wherein the first modulator is arranged to modulate additional information with the digital signals, the second modulator 10 is arranged simultaneously to modulate the additional information with the pseudo data signal, and the control unit is arranged to control each multiplexer to switch between its f1rst and second inputs only during the additional information.
~vo 9sll8sln 2 :~ 7 7 1 6 3 PCT/CA94/00671 The invention also provides a method of supplying digital signals selectively toeach of a plurality of cUstom~rs~ comprising the steps of: supplying digital signals for one or more custom~rs in a group of c--ctomçrs from a source of digital signals to a modnl~tor to produce a data mo~lnl~ted signal; producing a pseudo data modlll~ted signal having S similar spectral characterictic~ to those of the data modul~t~l signal; and selectively supplying the data modlll~ted signal and the pseudo data mo-llll~ted signal to each ~;u~L~""~,l in said group so that each cUctom~r in said group is supplied with the data modulated signal in respect of digital signals for that C~-!'10-~ and otherwise is supplied with the pseudo data modlll~ted signal; wll~leill parts of the pseudo data modlllate(l signal are subst~nti~lly identical to cimult~neously occurring parts of the data modul~te~ signal, and ~wi~ching between the data modulated signal and the pseudo data modulated signal for each cUctomer is carried out only during said parts of the modlll~te l signals. Said parts of the modulated signals can conveniently comprise overhead information for the customers.
Conveniently the step of producing the pseudo data mo(lnl~t~d signal comprises the step of supplying a source of pseudo data to a second modulator.
Brief Description of the Drawingc The invention will be further understood from the following description with reference to the accompanying drawings, in which:
Fig. 1 schem~ti~lly illu~ es a network col l ll,. ;.~ing a cable television distribution arr~ngement with an additional bidirectional tr~ncmiccion capability, to which an embodiment of this invention is applied;
Figs. 2 and 3 illustrate radio frequency spectra at different points in the network of Fig. 1;
Fig. 4 shows a block diagram of a drop unit used in the network of Fig. 1 in accordance with an embo-liment of the invention; and Fig. 5 is a more ~let~iled block diagram of a Ll~ of the drop unit of Fig. 4.
Mode(s) of Carryin~e Out the Invention Fig. 1 illustrates parts of a conventional cable television distribution arr~ng~mf nt, shown above a broken line 10, which is supple.l.~ .-lecl with an additional bidirectional tr~ncmicsion capability, shown below the broken line 10. As is well known, the conventional cable television distribution arr~ngement co~ ises a bridger amplifier 12, coaxial cables 14, passive customer taps (TAP) 16, line extend~rs 18, and a coaxial drop cable 20 to a television receiver (TV) 22 in customer premises 24.
- The ~klition~l bidirectional tr~ncmiccion capability comprises optical fiber I~l"~ination units (FTUs) 26 and optical fibers 28 connected thereto. Each FTU 26 is inserted into the path of a coaxial cable 14 following a bridger arnplifier 12 or line extender 18, and serves to supply to the coaxial cable 14 in the downstream direction (from the so-called head end, not shown, to the customer premises) digital signals at wo ss/l8sl0 PCT/CAg4/00671 frçquencies above those of the analog television signals already carried by the cable 14, as further described below. The arr~ngem~nt generally also in~lu(lçs tçrmin~ion units (rI') 30 which arç inserted into the coaxial cable 14 precçding the line extenders 18 and serve subst~nti~lly to çlimin~te the high fi~u~ ;y digital signals from bçing supplied to the line 5 extenders and from being reflectçd back to the taps 16. However, if the coaxial cable 14 is sufficiendy long, so that the high frequency digital signals are sufficiently ~ttenll~te~l, and the bandwidth of the line ext~nders 18 is sufficiently restricted (for example to 550 MHz), then tçrmin~tion units 30 can bç omittçd The high fi~u~n~;y digital signals are carried from the head end via the opticalfibers 28 to each FTU 26. As illustrated in Fig. 1, dirre~ FTUs can be coupled individually to a lespe~ /e fiber 28, or a plurality of FTUs 26 can be coupled via an optical splitter 32 to a common fiber 28 extending from the head end. In either case, the FTU 26 inserts the high frequency digital signals onto the coaxial cable 14 so that these are carried with the analog television signals as far as the next termination unit 30 or line extender 16. The analog and digital signals are then available to the customer prçmises 24 via the customer taps 16, which are supplçmentçcl with a drop unit described further below for supplying signals to set-top units (STU) 34 within the customer premises 24, via the existing cable drops 20. As this invention is not directly concerned with the FTUs 26 and the set-top units 34, these are not further described here.
In the opposite, upstream, direction of tr~n~mi~ion, a unit 34 can send control signals (for example, television program requests) and optionally other information to the head end via the coaxial cable drop 20, cUstomçr tap 16, coaxial cable 14, FTU 26, and optical fibçrs 28. DirrGrel1t wavelengths or other forms of multiplexing can conveniently bç used for the different directions of tr~n~mic~ion on the optical fibers 28.
Referring to Fig. 2, conventional analog VHF and UHF television signals and FM
radio signals are carried by the coaxial cables 14 at frequencies from 50 to 550 MHz.
Additional UHF television signals may possibly be present at higher frequenries, for eY~mrle about 33 additional signals at frequencies from 550 MHz up to about 750 MHz, depending upon the bandwidth of the bridger amplifiers 12 and line extenders 16 and the a~ n of the coaxial cables 14.
At higher frequencies, in a frequency range from 750 to 950 MHz, a first 16 QAM
(quadrature amplitude modulated) digital signal channel is supplied from the FTUs 26 to the coaxial cable 14. This can provide a data rate of 600 Mb/s, and thus can accommodate 200 colll~ ssed digital video signals each with a bit rate of 3 Mb/s. A second similar channel is provided in a rl~uel,cy range from 950 to 1150 MHz, acco.l~.lodating another 200 digital video signals, and a third similar channel can be provided in the frequency range form 550 to 750 MHz to accommo~l~tç a further 200 digital video signals, replacing a smaller number of possible analog television signals in this frequency range.
WO 95/18510 ~ 17 716 3 PCT/CA94/00671 For the upstream direction of trAncmiccion~ control signals can be carried in the relatively low frequency range from 5 to 30 MHz, but preferably control signals and possibly other data are carried in a QPSK (quadrature phase shift keyed) chAnnelproviding an upstream bit rate of 300 Mb/s in a frequency range from 1150 to 1350 MHz, 5 as shown in Fig. 2.
On the coaxial cable drops 20, the radio frequency spectrum is as shown in Fig. 3.
Up to 750 MHz, the spe ;L-~-- is the conventional analog signal s~,ecL,u~ in the frequency range from 50 to 750 MHz, with the option of low frequency u~sL~ ll control signals in the frequency range from 5 to 30 MHz as described above. The digital video signals are 10 carried downstream on the cable drops 20 to the cuctomçr premises in the form of a BPSK (binary phase shift keyed) signal providing a bit rate of 150 Mb/s in a frequency range from 750 to 950 MHz. This bit rate can accommo~lAte 50 co..-p~ssed digital video signals each with a bit rate of 3 Mb/s. Control signals and other data are preferably carried UpSLI~ll via the cable drops 20 by a multiple access BPSK signal providing the same bit rate of 150 Mb/s in a frequency range from 950 to 1150 MHz.
It should be appreciated that the high frequency digital signals are subject to the same At~çn~.Ation on the coaxial cables that analog signals at the same frequencies would be. However, although analog television signals at these frequencies are impractical in the network, it is practical to detect and lege.lcl~e the digital signals at these frequencies, and they are not condllctç~l via the bridger amplifiers 12 and line extenders 16 with their relatively restricted bandwidths.
Fig. 4 illustrates a drop unit which, as intlicAteA above, is provided at a cuct- m~r tap 16 and is provided for a group of, for example 8, customers. The drop unit includes a directional coupler 40 and protection unit 42 via which signals are derived from the coaxial cable 14 in conventional manner, and a power supply unit 44 via which power for the drop unit is derived from the coaxial cable 14 in known manner. Up~ n control signals are also supplied to the cable 14 via the protection unit 42 and the coupler 40. For simplicity it is AC~ l~ in the following description that low frequency upsL-~dm control signals are not present.
The drop unit includes a diplexing filter 46 which sep~ ÇS the downstream analog television signals onto a path 48 which may optionally include an amplifier 50, shown in broken lines. Do~ sL~ digital signals at the higher frequencies as described above are supplied from the diplexing filter 46 to a 16 QAM receiver (Rx) unit 52 via a directional coupler 54, and up~l,ea~.. control signals are supplied via the directional coupler 54 to the diplexing filter 46 from a QPSK trAncmit~r (Tx) 56. A control unit 58 derives the u~ a.ll control signals from the group of customers via their coaxial cable drops 20, diplexing filters 60, and a BPSK receiver unit 62. The control unit 58 also supplies downstream digital signals, as selected by the cu~omcl:~, and overhead ~ .. .. . . ..
wo ss/lssln 21 7 71 6 3 PCT/CAg4/00671 i,~l.n&Lion to a BPSK tr~ncmitter unit 64 as is further described below. The tr~ncmittf r unit 64 is controlled by the control unit 58 via control paths l~lese.l~ed by a line 66 to supply to each c~lctomçr only those signals to which the customer is entitled, as described further below. The tr~ncmittf~r unit 64 is also supplied with the down~Ll~a,.. analog video S signals from the path 48, and combines these with the dow--sLl~anl BPSK digital signals for supply to the coaxial cable drops 20 via the diplexing filters 60.
As can be appreciated, the units 52,56, and 58 serve to provide co.,~ ..nications with an FTU 26 and the head end of the network, for supply of desired digital signals to the group of customers served by the drop unit. Thus the receiver unit 52 can comprise a plurality of receivers for receiving the downstream digital signals in the frequency ranges as described above with lcf~ ,.lce to Fig. 2, and the Ll",~ . 56 Op~l~Les in theul,sLI.,~ll frequency range also as described above with reference to Fig. 2. The control unit 58 can derive the selected downstream digital signals for supply to the customers in any desired manner. For example, the signals may be co~ ic~tç d using ATM
(asynchronous transfer mode) techniques, with the data of each digital video signal ch~nnçl being i(1~ntifif~d by the label in each ATM cell carrying that data, and the control unit 58 using the cell label to determine whether or not to supply the cell data to the tr~ncmit~ç r unit 64. ATM cells can also be sent from the head end to the drop unit to inform the control unit 58 of the signal entitlement of each customer served by the drop unit. As this invention is not directly concerned with the details of the units 52,56, and 58, these are not further described here.
Referring to Fig. 5, the BPSK tr~ncmittf r unit 64 includes a dowl,~L,e~" data path including a buffer 70, a BPSK mod~ tor 72, an up-converter 74, a b~ndp~cs filter (BPF) 76, and, for each customer in the group of cUstomçrs supplied via this tr~ncmittçr unit, a respective analog multiplexer (MUX) 78 and analog mixer 80. The t~n~ unit 64 also includes a pseudo data path comprising a buffer 82, a BPSK modulator 84, anup-converter 86, and a b~n-lpacs filter (BPF) 88. Overhead information (O/H) is supplied from the control unit 58 to both of the buffers 70 and 82, and hence to both the data path and the pseudo data path.
Under the control of the control unit 58, the data of each digital signal which is to be supplied to any one or more of the customers in the group is derived from the receiver unit 52 and supplied to the buffer 70, together with the overhead information which for example serves for polling difr"~nl cu~Lo"~ premises units 34 for information to be Ll,ln!~llliLI~ upstream in a mllltiple access manner. The data and overhead il~l",ation are read out from the buffer 70 under the control of the control unit 58 to mod~ te an IF
(inlf,. Inetl;s~tf, frequency) signal supplied to the BPSK mod~ tor 72. The reslllt;ng modulated IF signal is converted to the RF (radio frequency) ~ecL~ w" described above with reference to Fig. 3 by the up-converter 74 to which an RF signal is supplied, and the , .
~vo gS/18510 2 17 7 1 6 3 PCT/CAg4/00671 resulting RF signal is filtered in the b~n-lp~cs filter 76. The resulting data mo~lnl~t~ RF
signal is supplied from the output of the b~n-lp~cs filter 76 to a first input of each of the multiplexers 78.
The control unit 58 simlllt~neously controls the buffer 82 to store the overheadinformation when this is stored in the buffer 70, and to store pseudo data, recycled from the output of the buffer 82, when real digital signal data is stored in the buffer 70. The res-llting pseudo data and overhead ulfolll~lion is supplied in a similar l,lanl-e~ under the control of the control unit 58 to modulate the IF signal in the modlll~tor 84, the resulting modlll~t~,d signal similarly being converted to the same RF range in the up-converter 86 and filtered in the b~ntlp~cs filter 88. The resulting pseudo data modulated RF signal is supplied to a second input of each of the multiplexers 78.
For each customer, the control unit 58 supplies to a control input of the rc~ecL-ve multiplexer 78 a control signal to select, and pass on to the respective mixer 80, either the data modulated RF signal at its first input or the pseudo data modulated RF signal at its second input. The control signal is produced by the control unit 58 to select the data modulated RF signal at the first input only for digital signals to which the respective cllctQmer is entitl~cl, and otherwise to select the pseudo data modlll~te~l RF signal at the second input so that the cUctomer is not supplied with other digital signals being supplied only to other customers in the same group.
Each control signal is produced by the control unit 58 so that swik;hil~g in the~;s~;L~-~e multiplexer 78 between the signals at the two inputs of the mlllti~lexer occurs only during the overhead information, and hence only at times when the same infollllalion is simnlt~neously present at both multiplexer inputs. This ensures that the RF spectral characteristics of the mod~ ted signal supplied to each customer are continuously 25 preserved, this being an important re~luil.,l~nl.
The filters 76 and 88 may be impl~ ed using digital signal procescing techniques and hence may give rise to a memory effect in the inrol.llalion supplied to the multiplexer inputs; in other words, although the overhead information supplied on both the data path and the pseudo data path is the same, the data and pseudo data are dirr~ t and so produce dirr.,.e,~l lingering effects on the overhead inrollllalion as this is supplied to the multiplexers 78. The duration of each sequence of overhead information (for example, several ~ucces~ive bytes) can be selected to be sufficient to accommod~te this memory effect, thereby to ...~ i.l the l~uil~ conlilluily of RF spectral characteristics during ~wilching of the multiplexers.
The output of each multiplexer 78 is supplied to the l~,i,p~tive mixer 80, where it is combined with the conventional analog video signals (from the path 48 in Fig. 4) for supply to the l.,s~ec~ e customer via the fes~cli~e di~lcAu~g filter 60 and coaxial cable drop 20. As shown in Fig. 5, the output signal from each mixer 80 can optionally be .. . . . . ... ....
wo 95/l8sln 2 ~ 7 7 1 6 3 PcT/cAg4mn67l inhibits~ by a further control signal from the control unit 58, to prevent delivery of any signals to a customer.
It should be appreciated that this arrangement of the BPSK tr~ncmin~or unit 64 enables only two modulators (or, more exactly, two sets of units 72, 74, 76 and 84, 86, 5 88, each set conci~ting of a modulator, an up-converter, and a b~n-lp~cs filter) to serve a group of for example 8 or more CUSLu~ , in contrast to the prior art which would require one modulator for each ~;U:i10111~,l in order to achieve the same selective supply of signals to each customer. Thus there is a subst~nti~l saving in costs and power re4uil~nlellts. As discussed above, the downstream BPSK specLI um on the coaxial cable drops provides a bit rate of 150 Mb/s and can accommo~te 50 conl~,essed digital video channels, which is ample to meet the total ~ uire.ll~ for 8 or more cu~LOIll~
Although a particular embo-lim~ont of the invention has been described in detail, it should be appreciated that numerous modifications, variations, and adaptations may be made without departing from the scope of the invention as defined in the claims.In particular, it should be appreciated that the particular bit rates, RF spectra, modulation methods, and so on described above are given purely by way of example, and the invention is not in any way limited thereto. Furth~,.lllo,~, the particular manner described above for producing the pseudo data signal is given by way of example, and other methods of producing a pseudo data modulated RF signal may ~ltern~tively be used.
20 Instead of switching each multiplexer be~n its inputs during the overhead information, other additional information may be supplied cim~llt~neously in both the data and pseudo data paths and switching may be carried out during such other additional infolllla~ion. In addition, the invention is not limited to the particular form of the network as described above, this again being given purely by way of example and explanation.
Claims (11)
1. A data modulation arrangement for selectively distributing data to a plurality of outputs (20), comprising a first modulator (72) responsive to a digital data signal to produce a first modulated signal; characterized by:
a second modulator (74) responsive to a digital pseudo data signal to produce a second modulated signal;
a plurality of multiplexers (78) each for supplying a modulated signal to a respective one of said plurality of outputs (20), each multiplexer having first and second inputs to which the first and second modulated signals, respectively, are supplied; and a control unit (58) for controlling each multiplexer to supply the first and thesecond modulated signals selectively to the respective output;
wherein the control unit (58) is arranged to supply additional information (O/H)simultaneously in both the digital data signal and the digital pseudo data signal, and to control each multiplexer (78) to switch between the first and second modulated signals at its inputs only during said additional information.
a second modulator (74) responsive to a digital pseudo data signal to produce a second modulated signal;
a plurality of multiplexers (78) each for supplying a modulated signal to a respective one of said plurality of outputs (20), each multiplexer having first and second inputs to which the first and second modulated signals, respectively, are supplied; and a control unit (58) for controlling each multiplexer to supply the first and thesecond modulated signals selectively to the respective output;
wherein the control unit (58) is arranged to supply additional information (O/H)simultaneously in both the digital data signal and the digital pseudo data signal, and to control each multiplexer (78) to switch between the first and second modulated signals at its inputs only during said additional information.
2. A data modulation arrangement as claimed in claim 1 wherein the outputs (20) comprise coaxial drop cables of a cable television distribution arrangement.
3. A data modulation arrangement as claimed in claim 1 or 2 wherein the first and second modulators modulate the data signal and the pseudo data signal, respectively, to frequencies greater than 550 MHz.
4. A data modulation arrangement as claimed in claim 1, 2, or 3 wherein each of the first and second modulators comprises a binary phase shift keyed modulator (72, 84), an up-converter (74, 86), and a bandpass filter (76, 88).
5. A television signal distribution network including drop cables each to a respective customer for supplying analog television signals in a predetermined frequency range, the network further including a drop unit for supplying to a plurality of drop cables digital signals modulated at frequencies above said frequency range, the drop unit comprising:
a plurality of multiplexers each having first and second inputs and an output coupled to a respective one of said plurality of drop cables;
a first modulator, for modulating digital signals for customers associated with said plurality of drop cables to frequencies above said predetermined frequency range, having an output coupled to the first input of each of the plurality of multiplexers;
a second modulator for modulating a pseudo data signal to said frequencies abovesaid predetermined frequency range, having an output coupled to the second input of each of the plurality of multiplexers; and a control unit for controlling each of the plurality of multiplexers to couple its first or its second input selectively to its output;
wherein the first modulator is arranged to modulate additional information with the digital signals, the second modulator is arranged simultaneously to modulate the additional information with the pseudo data signal, and the control unit is arranged to control each multiplexer to switch between its first and second inputs only during the additional information.
a plurality of multiplexers each having first and second inputs and an output coupled to a respective one of said plurality of drop cables;
a first modulator, for modulating digital signals for customers associated with said plurality of drop cables to frequencies above said predetermined frequency range, having an output coupled to the first input of each of the plurality of multiplexers;
a second modulator for modulating a pseudo data signal to said frequencies abovesaid predetermined frequency range, having an output coupled to the second input of each of the plurality of multiplexers; and a control unit for controlling each of the plurality of multiplexers to couple its first or its second input selectively to its output;
wherein the first modulator is arranged to modulate additional information with the digital signals, the second modulator is arranged simultaneously to modulate the additional information with the pseudo data signal, and the control unit is arranged to control each multiplexer to switch between its first and second inputs only during the additional information.
6. A network as claimed in claim 5 wherein the frequencies above said frequency range are greater than 550 MHz.
7. A network as claimed in claim 5 or 6 wherein each of the first and second modulators comprises a binary phase shift keyed modulator, an up-converter, and a bandpass filter.
8. A method of supplying digital signals selectively to each of a plurality of customers, comprising supplying digital signals for one or more customers in a group of customers from a source of digital signals to a modulator (72) to produce a data modulated signal; characterized by the steps of:
producing a pseudo data modulated signal having similar spectral characteristics to those of the data modulated signal, parts of the pseudo data modulated signal being substantially identical to simultaneously occurring parts of the data modulated signal;
selectively supplying the data modulated signal and the pseudo data modulated signal to each customer in said group so that each customer in said group is supplied with the data modulated signal in respect of digital signals for that customer and otherwise is supplied with the pseudo data modulated signal; and switching between the data modulated signal and the pseudo data modulated signalfor each customer only during said parts of the modulated signals.
producing a pseudo data modulated signal having similar spectral characteristics to those of the data modulated signal, parts of the pseudo data modulated signal being substantially identical to simultaneously occurring parts of the data modulated signal;
selectively supplying the data modulated signal and the pseudo data modulated signal to each customer in said group so that each customer in said group is supplied with the data modulated signal in respect of digital signals for that customer and otherwise is supplied with the pseudo data modulated signal; and switching between the data modulated signal and the pseudo data modulated signalfor each customer only during said parts of the modulated signals.
9. A method as claimed in claim 8 wherein the selectively supplied data modulated and pseudo data modulated signals are supplied to each customer in said group atfrequencies greater than 550 MHz via a coaxial drop cable (20) of a cable television distribution arrangement.
10. A method as claimed in claim 8 or 9 wherein said parts of the modulated signals comprise overhead information for the customers.
11. A method as claimed in claim 8, 9, or 10 wherein the step of producing the pseudo data modulated signal comprises the step of supplying a source of pseudo data to a second modulator.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US08/175,455 US5408259A (en) | 1993-12-30 | 1993-12-30 | Data modulation arrangement for selectively distributing data |
| US08/175,455 | 1993-12-30 | ||
| PCT/CA1994/000671 WO1995018510A1 (en) | 1993-12-30 | 1994-12-07 | Data modulation arrangement for selectively distributing data |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2177163A1 CA2177163A1 (en) | 1995-07-06 |
| CA2177163C true CA2177163C (en) | 1999-07-27 |
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ID=22640278
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002136603A Expired - Fee Related CA2136603C (en) | 1993-12-30 | 1994-11-24 | Television signal distribution network |
| CA002177163A Expired - Fee Related CA2177163C (en) | 1993-12-30 | 1994-12-07 | Data modulation arrangement for selectively distributing data |
Family Applications Before (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002136603A Expired - Fee Related CA2136603C (en) | 1993-12-30 | 1994-11-24 | Television signal distribution network |
Country Status (6)
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|---|---|
| US (2) | US5408259A (en) |
| EP (1) | EP0737403B1 (en) |
| JP (1) | JP2844019B2 (en) |
| CA (2) | CA2136603C (en) |
| DE (1) | DE69416429T2 (en) |
| WO (1) | WO1995018510A1 (en) |
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-
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- 1993-12-30 US US08/175,455 patent/US5408259A/en not_active Expired - Fee Related
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- 1994-11-24 CA CA002136603A patent/CA2136603C/en not_active Expired - Fee Related
- 1994-11-28 US US08/348,850 patent/US5499047A/en not_active Expired - Lifetime
- 1994-12-07 DE DE69416429T patent/DE69416429T2/en not_active Expired - Fee Related
- 1994-12-07 JP JP7517693A patent/JP2844019B2/en not_active Expired - Lifetime
- 1994-12-07 EP EP95902019A patent/EP0737403B1/en not_active Expired - Lifetime
- 1994-12-07 WO PCT/CA1994/000671 patent/WO1995018510A1/en active IP Right Grant
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| WO1995018510A1 (en) | 1995-07-06 |
| JPH09500511A (en) | 1997-01-14 |
| CA2177163A1 (en) | 1995-07-06 |
| US5499047A (en) | 1996-03-12 |
| CA2136603C (en) | 1999-08-03 |
| EP0737403A1 (en) | 1996-10-16 |
| EP0737403B1 (en) | 1999-02-03 |
| DE69416429T2 (en) | 1999-06-10 |
| JP2844019B2 (en) | 1999-01-06 |
| US5408259A (en) | 1995-04-18 |
| DE69416429D1 (en) | 1999-03-18 |
| CA2136603A1 (en) | 1995-07-01 |
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