CA1252169A - Method and apparatus for transmitting base-band data in a conductor carrying an rf signal - Google Patents

Abstract

METHOD AND APPARATUS FOR
TRANSMITTING BASE-BAND DATA IN
A CONDUCTOR CARRYING AN RF SIGNAL

Abstract of the Disclosure Base-band data is supplied to the coaxial cable of a cable television distribution system which also carries an RF signal. The data has a frequency below the lowest frequency component of the RF signal. The data and RF signals in the cable are separated at a remote location. The separated RF signal is supplied to a television, while the separated data signal is supplied to a remote receiver/transmitter. Data may be transmitted bidirectionally along the cable without interfering with the RF
signal.

Description

- lZ52~69 , , , Background of the Invention Field of the Invention The present invention relates generally to the field of base-band data transmission, and, more particularly, to an improved method and apparatus for transmitting such data along a conductor which also carries an RF signal.

Description of the Prior Art:
In a cable television system, an R~ signal is typically distributed along a coaxial cable to a pluralit-y of televisions. In some systems, notably those in hospitals, motels and hotels, it may also be desirable to transmit data between a "main" station and a number of "remote" stations. Such data might, for example, include patient monitoring or environmental information. Heretofore, upon information and belief, some cable television systems have also supplied 60 Hz power along the coaxial cable.
Such power was needed to operate amplifiers, and avoided the need for an external power source at each amplifier. However, such internal power supply is believed to have prevented the use of the coaxial cable for base-band data transmission.

Summary of the Invent on The present invention, in one aspect, provides an improved method of transmitting base-band data between a "main" station and a plurality of "remote"
stations via a conductor, such as a coaxial cable, which also carries an RF signal. This improved method minimally includes the steps of: selectively generating at the "main"
station a main data signal }-aving a frequency (e.g., 0-7 Mhz) less than the lowest lZSZ~69 frequency component of the RF signal; supplying the main data signal to the conductor;
separating the main data signal from the RF signal in the conductor at a distant location;
and supplying such separated main data signal to at least one of the plurality of 1'remote"
stations. If desired, this method may, optionally include the further steps of: selectively generating at ]east one of the "remote" stations, a remote data signal at such base-band frequency; supplying this remote data signal to the conductor; separating the remote data signal from the RF signal in the conductor; and supplying the separated remote data signal to the main station or other "remote" station. Thus, such data transmission may be either unidirectional or bidirectional with networking capab~lities.
The invention also provides, in another aspect, improved apparatus for use in a cable television system having a coaxial cable carrying an RF signal, an RF network directional coupler in series with the cable, a television, and a conductor operatively arranged between the coupler and television. Such improved apparatus comprises:
a "rcmote" station capable of receiving and selectively generating base-band data at a frequency less than the lowest frequency of the RF signal; a first RF choke operatively arranged between the data generator and a mode of the condl~ctor; a first data choke arranged between the television and thc mode; a second data choke arranged between the coupler and the mode; and a secol~nd RF choke arrangcd bctween the cable and the mode; whereby data may be transmitted betwccn the "rcrnotc" station and the cable without intcrfcring with thc provision of thc l~l signnl to the Iclcvision.
Accord;ngly, t1~e gencral objcct of tllc invcntion is to providc an improvcd method of, and appalatus for, trnns1nitting basc~ d data betwccn a "main" station and a plurality (i.e., onc or morc) of "relnote" stations, or "rcmote"-to-"l emote" stations, vin a condl1ctor whicl~ nlso calries an 1~1~ s;gnnl.

" ~LZSZ~69 .

Another object is to provide an improved method of transmitting unmodulated data, either unidirectionally or bidirectionally, on the eoaxial eable of a eable television distribution network, without the need for modems and without interfering with the distribution of an RF signal to the television on the network.
These and other objects and advantages will beeome apparent from the foregoing and ongoing written specification, the drawings, and the appended claims.

Brief Description of the Drawings Fig. 1 is a sehematie bloek diagram of a portion of a prior art cable television distribution system.
Fig. 2 is a sehematie block diagram of a portion of an improved system in whieh a base-band signal and an RF signal may be simultaneously transmitted in a eoaxial eable.
Fig. 3 is a schematic block diagram of the RF/data coupler, the television, and the remote station.
Fig. 4 illustrates the typical rrcquency spectrum of the prior art system shown in Fig. 1.
Fig. 5 illustrates the frequency spectrll'm of the improved system snown in Fig. 2.

l~escription of the Prcferrcd rmbo(3imcnts At the outsct, it shollld be clcarly lln(lelstood thrlt lil;e refclence nulllerals are inten(led to refer to the snlTle elerments or struetllre eollsistcntly throughollt -`-" 1252~69 the several drawing figures, as the description or ope~ation of said e]ements or structure may be further described or explained by the entire written specification of which this detailed description is an integral part.
The present invention provides an improved method and apparatus for transmitting data via a conductor which also carries an RF ti.e., radio frequency) signal.
In short, an unmodulated base-band data signal and a modulated RF signal may be carried simultaneously in the same conductor, and subsequently separated from one another.
The invention is uniquely suited for use with hospital television systems, and to similar distribution systems where an electrical conductor, typically a coaxial cable, is employed to distribute and supply an RF signal to a large number of televisions.
However, the invention could with like ease be applied to similar distribution systems in hotels, motels, and the ]ike, and to other systems. ~lence, the hospital television environment is exemp]ary only, and should not be viewed as a limitation in construing the scope of the appended claims.
In the hospital environment, there is typically a television in each patient room, whether private or semi-pr ivate. These televisions are usually wall mounted, aad operated by means of a remote handset because of possib]e patient immobility.
The handset may be directly connected to the television by means of a control cnb1e.
An incoming RF signal is supplied to a distribution system, which, in turn, supplies the signal to the various putient televisions. The distriblltion sys~em commonly employs a coaxial cable, and a plurality of RF directional couplers, each of which provides a tap for an individunl telovision.
The l~ signal C3istl ibution by tl1e coaxial cnble typiclllly hflS a frequency spectrulll of from nbout 50 1\~ to nbout 300 + 1\1h~ 'ithin this brond frequency spectrum, the fl ccjuencies of the various televixion ch~r1l1els occupy bnnd widths of , about 6 Mhz each. The range of from about 30 Mhz to about Sû Mhz is normally reserved for filter cross-over in two-way RF distribution systems. Some cable systems may transmit electrical power on the coaxial cable at a relatively low frequency of about 60 Hz. This is typically used to power various RF amplifiers along the line, thereby obviating the need for an external power supply at each amplifier.
The present invention modifies this existing distribution network by: (1) removing the internal 60 Hz power supply; and (2) by using a low frequency range of from 0 up to 7 Mhz as a direct data path between a "main" station and a plurality of 'rremote" stations. This improvement permits bidirectional transmission (i.e., ~rom the "main" station to each "remote" station, and vice versa, or "remote-to-remote"
stations,) of base-band data while the RF signal is simultaneously supplied to each television. The "main" anq "remote" stations are preferably data transmittcr/receivers.
Some of the remote stations may be associated with patient televisions; others may be associated with various transducers which are capable of converting a sensed parameter (e.g., the "open" or "closed" condition of a door, temperature, opcration of a particular electrical or mechanical device, and the like) into an electrical data signal. Some of the "remote" stations may be associated with means for controlling the telcvision by overriding the patient-controlled operation of same. Other "remote"
stations may, in response to an addrcssed quaere generated by the "mnin" stntion, be stimlllated into gcnernting a dnta "rcport" Or tllc scrlscd pal nmcter b~ck to tl~e "rnain" station. This data "report" may bc cncodcd with appl opriate data indicating ~or identifying the pnrticl~lar "rcmote" stntion from which it was scnt. Tlle "main"
station may inc]lJdc mcans for gcncrnting vidco nnd audio infortnntion on a pnlticular tclevi~;ion chnnncl rcscrvcd for tl~is pnlpose; nnd n complltcr for receiving nnd storing the data "rcports".

i2SZl~;9 At this point, an example may best il]ustrate one particular application.
In many hospitals, patients are given the opportunity of making meal selections within, of course, the confines of their treatment. Typically, a selection card for the following meal is distributed with each meal. The patient indicates his preference by marking the selection card, and these are returned when the dirty dishes are collected. Such cards are then forwarded to the kitchen and, ideally, each patient will receive his selection at the subsequent meal.
With the improved system, the computer generates an appropriate main data signal which instructs each "remote" station to turn the associated television "on", and then to tune to a particular channel. These instructions are in the form of command data which override the patient's command and control the television.
Thus, all televisions are simultaneously turned "on", and turned to the same channel.
The "main" station then generates an appropriate audio/video signal on the frequency of this channel, which signal is transmitted to each patient television. For example, such signal might say "The selections for lunch are: A, B or C", and then instruct each patient to indicate his particular selcction. Each "remote" station contains a means for permitting the patient to rcspond. For example, the handset by which the patient controls the operation of his television, might be modified to have one or more push-button switches thereon for permitting patient rcsponse. Indced, one or more of the "relnote" stations could, if dcsircd, be providcd Witll a ful] hcyboard for generating whatcver responscs migllt be neccssal y. At nny r ntc, ench paticnt indicates his selcction by pllshing the approprinte button on his h.llldset, nnd this data, encoded with the nddress of the "rclnote" stntion from wllich it was scnt, is then translnitted brlck nlong tlle conxi~il cnblc to thc "mnin" stntion, ~hcl c it is rcccivcd nnd stored. Thcrcnf~er, SIICIl 1lltn iS provi(lcd to thc l;itchcn. Vpoll receipt .

iZ52~69 of this information, the computer then returns control of the various televisions to the individual patients, who are then free to tune to the channels of their choice.
lt is important to note that the normal RF signal, and the data signals being transmitted between the "main" and "remote" stations, coexist simultaneously in the same coaxial cable without interference.
Thus, a patient in one room may watch the channel of his choice, while data is transmitted to or from the same room, or some other "remote" station. For example, a "remote" station may include one or more patient monitoring transducers (e.g., heartbeat), and this data may be transmitted to the "main" station while the monitored patient watches the television channel of his choice. Indeed, such data may be transmitted even if the patient opts to turn his television "off". If desired, an appropriate transducer in the handset may be used to sense the ambient temperature in the patient's room, and this data can be transmitted back to the computer for subsequent control of heating, cooling or air handling equipment, as appropriate. While these are only a few examples, they are believed to illustrate the advantages of being able to transmit data bidirectionally on an cxisting coaxial cable used to distribute an RF signal.
Turning now to the drawings, Fig. l illustrates the prior art manner by which an RF signal has been distributed throughout a cable network. An RF signal, such as illustrnted in Fig. 4, was supplicd viu a corlxirll cnble 10 ul)d n powcr-blocking capacitor 11 to a power col~pler 12. Powcr at GO llz frorn n source 13 wus supplied throlJgh an RF choke 14 to the cable in tllc power couplcr. The supplied powcr nnd RF signal wcrc thcl cnftcr supplicd to a plurality of dircctional powcr-pnssing Rl;
couplcrs, scvcrnlly in(licntc(3 nt 15. I~ach of coupicrs 15 wrls connectcd to a television sct I G throlJgh a powcr-blocking cnpacitor 18. Persons skillcd in this urt will " 12~Z~f~i9 .

appreciate that capacitor 11 permitted passage of the RF signal, but prevented power from source 13 from passing back toward the source of the RF signal. The RF choke 14 permitted passage oi power from source 13 to cable 10, but prevented passage of the RF signal to the- power source. Each of capacitors 18 permitted passage of the RF signal, but not power, to the associated television set. As previously noted, the system provided 60 Hz power along the coaxial cable to obviate the need for an external power source at each RF amplifier. Such power was needed to operate various RF
amplifiers (not shown), which were needed to prevent diminution of the RF signal along the distribution system.
Fig. 4 illustrates the typical frequency spectr~lm of such prior art systems.
Power îrom source 13 was supplied at about 60 Hz; the band from about 30-50 Mhz was reserved for cross-over filters; and the range from about 50-300 Mhz was occupied by a large number of television channels, each having a band width of about 6 Mhz.
Thus, each television on this distribution system could independently watch the channel of the patient's choice merely by tuning his tclevision to the channel frequency of his choice.
An improved system incorporating the inventive apparatus is shown in Fig.

2. Initially, it is pointed out that the 60 llz power supply 13 has been replaced by a computer 19 associated with a suitable video/audio ~enerator 20. Power for ttle vurious RF amplifiers along the line is supplied by nn e~;ternal powel SOUICC (not sllown). This poses no substr3ntial inconvcnience since G0 ll:~ power is avnilable at comrnon wall out]ets, and is, in fact used to power each individunl television. I~l!nce, such power source mny commonly be a wall outlct itself, or the powcr ~nlpply ]ine ]cadirlg to cach individual television.
In tllc improvcd system, tlle power coupler 12 is dcrlominatcd n datn coup]er 21. Ilowcver, the data collp]er i.s, in rnct, the sarne e]ement as the power coup1er, i~521~9 albeit it is put to a new use. As with the earlier system (Fig. 1), an RF signal is supplied through a coaxial conductor 22 and power-blocking capacitor 23 to the data coupler.
Base-band data, within the frequency component range of O to a maximum of about 7 Mhz, is supplied from computer 19 via an RF choke 24 to conductor 22. The superimposed RF-data signals are, in turn, supplied to a plurality of series-connected RF/data couplers, severally indicated at 25, there being one coupler for each television set 26. A data receiver/transmitter 29 is operatively associated with each television set.
Referring now to Fig. 3, each RF/data coupler 25 is shown as incll~ding an RF coupler 15 associated with coaxial cable 22. A central node 28 is connected to the RF coupler 15 through a data-choking capacitor 30, and is connected to the associated television through data-choking capacitor 31. Node 28 is connected to cable 22 through an RF choke 32, and is further connected to the "remote" data receiver/transmitter via another RF choke 33. As previously noted, an RF choke will permit passage o~ the data signal, but will block passage of the RF signal. Conversely, a data choke or a power-block will permit passage of the RF signal, but will block passage of the data signal. Thus, the data signal path between coa~cial cnble 22 and the "remote" station, includes RF choke 32, node 28, and RF choke 33. A data signal in node 28 is prevented from entering RF coup]cr 15 by data choke 30~ and is prcvcntcd from entering tc1evision 26 by data c11okc 31. Tlle RI; sit~nnl patll bct~vccn tlle RF
couplcr 15 and the telcvision includcs data choke 30, node 28, and data choke 31. RF
choke 33 prevents tl-e RF signal rrom entcring the "rcmote" stntion 29. RF chokc 32 [)crmits dnta gcncratcd by "rcmotc'l station 29 to bc trarls~rlitted to conxinl cnble 22. Thus~ tlle improvcd apparat~ls scpflraics tllc RI; and data siL~nals. The sepnrnted RF si~nnl is sllpplied to the telcvision, while thc sel>arntcd dntn signal is sul)plicd to thc "rcmotc" data r cccivcr/transmittcr. It sl)ould bc clcnrly undcrstood that thc dnta c~ .

i2S;~9 signal has a direct path between the coaxial cable 22 and the "remote" station 29 via ~F choke 329 node 28, and RF choke 33. Hence, data may be transmitted from or to the "remoteT' station independently of the operation of the associated television.
Fig. 5 illustrates the frequency spectrum of the combined RF/data signal in tl~e coaxial cable. From 7 Mhz upwards, the RF signal portion is as previously descri~ed with respect to Fig. 4. ~owever, the low frequency range of 0-7 Mhz is reserved for transmission of unmodulated base-band data. However, the spectrum for data transmission is not limited to 7 Mhz and may extend higher in frequency with an appropriate change in the data and RF filters, and RF signal frequency allocation.
lt should also be noted that the 60 Hz internal power supply of the prior art system, has been rep]aced by the provision of the external power source.
Thus, the invention broadly pro~tides an improved method of transmitting data between a "main" station and a plurality of "remote" stations, and between "remote"
stations themselves, via a conductor (preferably of the existing in situ coaxial type) which also carries an RF signal. The improved method includes the steps of: selectively generating at the "main" station a main data signal having a frequency less than the lowest frequency component of the RF signal; supplying this main data signal to the conductor; separating the main data signal from the RF signal in the conductor; and supplying the separated main data signal to at least some of the "remote" stations.
lf desired, the improved method rnay include the f~lrther stcps of: selc!ctivc!ly generating at ]cast one Or the "remote" stntions n relnote clnta signal llnving a frequency less than the lou~est freqllcncy cornponcnt of the RF signal; supplying the remote data signal to the conductor; scparating the rcrnote data sign~l froln the 1~ signnl in the condnctor; nnd snpplying such scpnl ated r crnotc dnta signnl to the ~main~ stntion. In efrect, thc impl oved mcthod contempl.ltes the trnnsmission of lZ~Z~;9 base-band data bidirectionally between main and remote stations, or "remote"-to-"remote" stations along a conductor which simultaneously carries an unidirectional RF signal.
In another aspect, the ;nvention provides improved apparatus for use in a cable television system having a coaxial cable carrying an RF signal, an RF network directional coupler in series with the cable, and a conductor operatively arranged between the coupler and a televsion. This improved apparatus includes: a remote data station capable of receiving (and, preferably, capable of also selectively generating) base-band data at a frequency less than the ]owest frequency of the RF signal; a first RF choke arranged between the remote station and a node of the conductor; a first data choke arranged between the televison and the node; a second data choke arranged between the coupler and the node; and a second RF choke arranged between the cable and the node.
The remote station need not necessarily be invariably associated with a television, albeit this arrangement is preferred because the coaxial cable may well be in place. If desired, suitable data couplers may connect the cable with a suitable remote station, such as to sense a door "open" or "closed" condition, to monitor ambient temperature at a location r emoved from a televison, as for some other purpose.
Therefore, while the presently preferred ernbodiment of the ;mploved rnethod and appartus has been shown nnd described, nnd severnl modiricntions t31elcof discussed, persons skilled in tl)is art will readily appreciate îllat vnl iO~IS additiollnl cllanges and modifications can be made without departing from tlle spirit of tllc invcntion, as derined and differentiated by the following claims.

Claims (8)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. The method of transmitting unmodulated data between a main station and a remote station via a conductor also carrying an RF signal, said conductor having a plurality of electrically-powered amplifiers spaced therealong to prevent diminution of said RF signal, which comprises the steps of: supplying electri-cal power to each of said amplifiers via a path other than along said conductor; selectively generating at said main station an unmodulated main data signal without the use of carriers having its frequency components occupying a base-band frequency spectrum of from zero to a maximum frequency less than the lowest frequency component of said RF signal; supplying said main data signal to said conductor; separating said main data signal from the RF signal in said conductor; and supplying such separated main data signal to said remote station.

2. The method as set forth in claim 1 and further compris-ing the step of: encoding said main data signal with the identity of the remote station which is to receive said main data signal.

3. The method as set forth in claim 1 and further compris-ing the steps of: selectively generating at said remote station, an unmodulated remote data signal having its frequency components occupying said base-band frequency spectrum; supplying said remote data signal to said conductor when said main data signal is not supplied to said conductor; separating said remote data signal from the RF signal in said conductor; and supplying such separated remote data signal to said main station.

4. The method as set forth in claim 3 wherein said remote data signal is encoded with the identity of the remote station from which it was generated.

5. The method as set forth in claim 1 and comprising the further steps of: separating the RF signal from said main data signal in said conductor; and supplying such separated RF signal to a television.

6. The method as set forth in claim 5 and comprising the further steps of: controlling the operation of said television in response to said main data signal.

7. The method as set forth in claim l and comprising the further step of: controlling the operation of an appliance at said remote station in response to said main data signal.

8. The method as set forth in claim 3 wherein said remote data signal is generated in response to said main data signal.