GB2256115A - Switched cable television networks. - Google Patents

Abstract

In a switched cable television network where at least one channel is supplied to a subscriber at a dedicated frequency, the particular channel VHF1-4 being determined by an off-premise switch or converter SW1-4 in response to dynamic subscriber selections, the subscriber is enabled to control the selected channel from any of a plurality of spatially separated locations at his premises. This is done using a single home control unit 10 in association either with infra red receiver/ multiplexer units 15 connected to outlets 1-6 at each of the spatially separated locations (the outlets being connected to the home control unit by a coaxial cable 13), or with a mobile unit which communicates directly with the home control unit at radio frequencies. A plurality of independent selections may be made of channels to be supplied to the subscriber at a plurality of dedicated frequencies, (Figs. 5, 6, not shown), this selection facility also being exercisable at a plurality of spatially separated locations. <IMAGE>

Description

TITLE OF THE INVENTION CABLE TELEVISION BACKGROUND TO THE INVENTION FIELD OF THE INVENTION The present invention relates to the field of cable television (giving that term its current broad definition to include cabled broadcasting of television, radio and data services as well as cabled provision of interactive services such as teleshopping). In particular, the invention relates to switched cable networks in which the subscriber has an element of choice in the channels physically provided to his home at a given time.

As is well known there are two main types of final distribution network (secondary network) used in delivery of cable television to subscribers. In "tree and branch" networks each individual subscriber has a drop cable tapped off from a feeder cable that passes the house (see Fig.la). In "switched star" networks a switching/control node is provided, common to a group of subscribers, housing switches or frequency agile convertors for each subscriber. Each switch serves to select a particular channel from those provided on the trunk cable and to feed only the selected channel along the individual drop cable to a subscriber (see Fig.1b).

A variant of the above two proposals has been made ("distributed switching"). In this variant the switching nodes are made small (maybe even covering only a single subscriber) and separate control nodes are provided each controlling a plurality of switching nodes (see Fig.1c).

A feature of switched networks (whether switched star or distributed) is that at a given time the full set of channels available on the network is not supplied on the subscriber drop cable but instead a suhset of channels is supplied, at least some of which are selected in response to dynamic subscriber requests (others, such as free channels, may be provided continuously).

In a switched network the selection of a channel which the subscriber has indicated he wishes to view is physically performed hy equipment located in a street cabinet. As a result only one or two switched channels need to be delivered to the home, this results in very efficient use of the frequency spectrum in the final distribution network. The philosophy behind this method of distribution is that, in any household, only a few of the 60 or more channels available on the main distribution network are required for viewing or recording at any one time and thus it is much more efficient to carry only these channels into the home.

In conventional switched networks the circuitry controlling the switch mechanism/frequency agile convertor in the street cabinet is provided at least in part via a home control unit, HCU, operated by the subscriber (some control functions, such as checking entitlement of a subscriber to view a given channel, may be performed in the switchpoint itself or, in a distributed system, in a control node).

DESCRIPTION OF THE PRIOR ART A conventional channel selection mechanism in a switched star network will now be described with reference to Fig.2.

In the example shown in fig.2 , the subscriber -eceives a number of free channels as well as a group of premium channels. Only a selected one of the premium channels at a time is provided on the subsciber's drop cable.

At the local switchpoint the television channels supplied on the incoming trunk cable are accessed and amplified. A polling signal is generated and transmitted sequentially to each of the subscribers connected to the switchpoint. At a subscriber's home the home control unit, HCU, responds to a polling signal by transmitting back to the local switchpoint data on the currently selected premium channel, SPC (this data is held in a memory in the HCU and is updated on selection of a new premium channel by the subscriber via a keypad or infrared remote control).

In the switchpoint there is a frequency agile convertor in respect of each subscriber. This frequency agile convertor acts to convert the selected premium channel from a VHF frequency at which it was present on the incoming trunk cable to a UHF frequency, UHF1, specific to that subscriber. The converted signal is output on the subscriber drop cable and is used by appliances in the subscriber's home which are tuned to frequency UHF1.

Additional signals may also be transmitted from the switchpoint to the subscriber, for example to provide power to the subscriber's HCU.

In any cable television distribution network the final unit to be installed in the subscriber's home has to cater for a wide variety of "in-home" equipment configurations. Some households may have only a single television receiver, whereas others may have several television receivers and video recorders in various locations around the house (although usually these will not all be in use at the same time).

A problem arises for a subscriber who has appliances in a number of different rooms when it comes to changing the selected premium channel. If the subscriber only has a single HCU then even though all of his appliances may be tuned to UHF1 this only means that all of the appliances may view the premium channel currently selected at the HCU. If the HCU is located in room A then a subscriber who is viewing the premium channel in room B will be obliged to go into room A in order to change the selected premium channel. Clearly this will be inconvenient.

Alternatively, if the subscriber wants to be able at a number of different locations to independently select which premium channel he is viewing then he must obtain a number of home control units, one for each location. The ability to independently select a premium channel may be considered to be a "level of service" and so if a subscriber can independently select premium channels at two different locations within his home it may be said that he has two levels of service.

A system in which the subscriber has two or three locations at which he can independently change selected premium channels is described in a paper "Innovative Aspects of a Switched Star Cabled Television Distribution System" by Daniel H. Smart, 1987 NCTA Technical Papers, pages 27 to 35. The subscriber installation in such a system is illustrated in Fig.3.

In this prior art system a plurality of UHF channels are assigned to the subscriber, one for each level of service. The subscriber has two home control units, one at each of the locations at which the subscriber wishes to be able to independently select the premium channel . Each of the HCUs controls the selection of the particular premium channel to he sent to the subscriber at one of the assigned UHF frequencies, i.e. HCU 1 controls the selection of the channel received at UHF1 and HCU 2 controls the selection of the channel received at UHF2. The lodal switchpoint polls each of the HCUs separately in order to check which channels to provide at frequencies UHF1 and UHF2.

Normally one HCU would be required for each independently controllable outlet in the home. Since each HCU contains complex and costly electronic systems the cost of the HCUs required escalates dramatically as the number of outlets grows with increased "in-home" equipment useage.

SUMMARY OF THE INVENTION The problems associated with the prior art may be overcome by envisageing the ability to independently select a desired channel as a mobile facility. In other words the ability to independently select a particular channel should be treated as a facility to be exercised at any location within the subscriber's home, rather than as a facility associated with a fixed HCU.

According to one preferred embodiment of the invention this may be achieved by providing the subscriber with one infrared remote control for each level of service that the subscriber desires, each remote control being adapted to control selection of the channel to he supplied at one of the subscriber's UHF or VHF switched delivery channel frequencies.

This embodiment of the invention allows a subscriber to walk from room to room and use a remote control 201 in any suitably equipped room to change the selected channel at VHF1. Similarly, another member of the subscriber's family may have an additional remote control 202 enabling that person to control selection of the channel received at VHF2. Each room is suitably equipped to operate the invention by providing it with circuitry for receiving channel selections from a remote control and for transmitting to a central HCU the selections being made by a remote control in that room.

The central HCU receives data on the channel selections being made by each remote control and conveys this data to the local switchpoint where it is used to control the relevant frequency agile convertors/switches.

In this way the subscriber has great flexibility in viewing and changing selected premium channels at a variety of locations within his home and, where the subscriber receives a number of "levels of service", the complex electronics in one HCU can be shared by a number of very simple infrared receivers associated with each of a very large number of independent outlets.

BRIEF DESCRIPTION OF THE DRAWINGS Further features and advantages of the present invention will become clear from the following description of embodiments thereof, given by way of example, and illustrated hy the accompanying drawings, in which: Fig.1 illustrates diagrammatically the different types of final distribution network proposed for delivery of cable television services to subscribers, in which: Fig.1a shows a "tree and branch" network; Fig.1b. shows a "switched star" network; and Fig.1c shows a "distributed switching" network; Fig.2 is a diagram to illustrate a conventional process for channel selection in a switched network; Fig.3 shows a prior art system in which channel selections may be made independently at a number of different locations; Fig.4 shows in diagrammatic form a first embodiment of the invention; Fig.5 shows in block diagrammatic form a home control unit according to a second embodiment of the invention; and Fig.6 shows in block diagrammatic form an outlet useable with the HCU of Fig.5.

DESCRIPTION OF SPECIFIC EMBODIMENTS OF THE INVENTION A first embodiment of the invention is illustrated diagramatically in Fig.4.

In this embodiment of the invention the subscriber is connected via a drop cable to a switchpoint in a street cabinet. The subscriber has four levels of service, in other words the subscriber has the capacity to make four independent selections of premium channels, and so there are four switches/frequency agile convertors for the subscriber in the switchpoint. The four selected channels will be transmitted along the subscriber's drop cable at frequencies VHF1, VHF2, VHF3 and VHF4. Each of these signals can carry any of the 60 or more premium channels available on the main trunk network.

Additionally the subscriber may receive a group of fixed "bypass" channels. These channels are not under the control of the switches in the street cabinet but are extracted from the trunk cable using a suitable filter and are delivered to the subscriber "en bloc". They are often used to carry a basic tier of programmes and provide a useful service in relation to video recorders. A single home control unit, HCU 10, is installed in the subscriber's home, close to the point of entry of the subscriber drop cable. From the HCU 10 a coaxial cable 13 carries the received cable television signals to other locations in the home where outlets are provided for access to the cabled services.This cable carries the switched delivery channels VHF1, VHF2, VHF3 and VHF4, together with the bypass channels and other signals provided by the cable network, such as frequency modulated radio services, to all outlets.

In order to be able to exercise the mobile channel change facility according to the present invention in the vicinity of any of the outlets 1-6, each of those outlets is provided with an infrared receiver/multiplexer unit 15. Each unit 15 is adapted to receive infrared signals from a mobile remote control unit 20 and to diplex those signals onto the coaxial cable 13. The received infrared signals identify not just the new premium channel which it is desired to select but also the delivery channel on which that premium channel is to be delivered to the home. These signals are transmitted to the HCU 10 via the coaxial cable 13 for use in controlling the switches/frequency agile convertors in the local switchpoint.

The H.C.U. 10 may include an associated power unit through which it generates signals for providing power to the switches/frequency agile convertors in the local switchpoint and for providing power to the infrared receivers/multiplexers 15, and, if necessary, to amplifiers required to extend the home installation.

One infrared remote control unit 20 is supplied to the subscriber for each "level of service" that he requires. In the present example, where the subscriber can independently control the premium channel supplied to him on each of four switched delivery channels, he has four levels of service and thus is provided with four infrared remote control units 20.

Each of the infrared remote control units 20 is factory preset so as to control the operation of a particular one of the switches/frequency agile convertors SW1, SW2, SW3 or SW4, dedicated to the subscriber in his local switchpoint.

In the present embodiment the group of infrared remote control units supplied to a particular subscriber are equipped with different identification codes. When a subscriber uses a particular one, 202, of the remote control units 20 to make a selection of a premium channel to be received on a given switched delivery channel, VHF2, then the remote control 202 transmits, to a nearby infrared receiver/multiplexer unit 15 a signal containing, preferably in digital form, the channel number of the desired premium channel and the identification code of that handset 202. This channel number and identification code data is passed along the coaxial cable 13 to the HCU 10 by the infrared receiver/multiplexer unit 15.

The infrared receiver/multiplexer units 15 may each diplex their channel selection signals onto the coaxial cable 13 as soon as they receive a respective channel selection signal from a remote control unit 20.

Alternatively they may store the channel selection data and release it to the HCU 10 on receipt of a polling signal from the HCU.

In other embodiments of the invention different methods may be used in order to identify to the H.C.U. the particular switched delivery channel that a given remote control unit 20 is to control. For example, in a second embodiment of the invention each receiver/multiplexer unit 15 may be adapted to cause channel selection signals to be diplexed on to the coaxial cables at a different subcarrier frequency depending on which of the subcarrier's remote control units originated the channel selection.

In such circumstances the infrared receiver/multiplexer units 15 may identify which remote control is originating a given received channel selection signal by recognition of an identification code transmitted by the remote control 20, or by the recognition of the frequency at which the remote control is transmitting (in a system where each remote control transmits channel selection signals at a different, characteristic frequency). In the latter case, since it is preferable to keep the complexity of the infrared receiver multiplexer units 15 low, the infrared receiver/multiplexer units 15 may be adapted to diplex the received signals onto the coaxial cable 13 at a frequency related to that used by the remote control 20.

Figs.5 and 6 show in block diagrammatic form an HCU and an outlet suitable for use in such a second embodiment of the invention.

In this second embodiment of the invention the remote control unit 201 used to control the switched delivery channel at VHF1 is adapted to cause data transmissions to the HCU, via the coaxial cable 13, at a subcarrier frequency 4.5 MHz. Similarly the control 202 causes data transmissions at a subcarrier frequency of 5.5 MHz, control 203 causes data transmissions at a subcarrier frequency of 6.0 MHz and control 204 causes data transmissions at 10.7 MHz. These data channel frequencies have been selected because of the ready availability of cheap mass-produced filters at these frequencies (these frequencies are the TV sound frequencies used in various parts of the world).

The general mode of operation of HCU units according to the invention is, as follows. The HCU 10 has been programmed to associate the identification code (or frequency) of a particular remote control unit, e.g.

202, with a particular one of the switched delivery channels, VHF2, and has an area of memory reserved in respect of each remote control unit. On receipt of a channel selection data signal on the coaxial cable 13 the HCU 10 identifies the remote control originating the channel selection, 202, extracts the data representing the channel number of the desired premium channel and stores that data in the area of memory assigned to that remote control unit 202. The HCU 10 transmits the channel number data to the local switchpoint in response to a polling signal transmitted on the subscriber drop by the local switchpoint.

In an HCU unit according to the second embodiment of the invention, as illustrated by Fig.5, channel selection signals for the switched delivery channels are extracted from the coaxial cable 13 by a diplexer 30. The data signals for the individual switched delivery channels are separated out by a splitter 32 and a group of band-pass filters & detectors 33. A microprocessor 35 in the HCU receives the individual data signals at communications ports 1 to 4.

The channel selections for given switched delivery channels are processed by the microprocessor 35.

Communications port 5 of the microprocessor is reserved for communications with the local switchpoint (carried on the subscriber drop cable via a MODEM 36 and diplexer 37).

In order to check which premium channels are required by a subscriber on each of his switched delivery channels the local switchpoint may generate a polling signal in respect of each switched delivery channel and transmit each of these polling signals sequentially on the subscriber drop, awaiting channel number data in respect of the first switched delivery channel before transmitting the polling signal in respect of the second delivery channel.

Alternatively, the switchpoint may be configured so as to transmit only a single polling signal to each subscriber and to receive back from the subscriber's HCU 10 a longer data message containing the channel numbers of the selected premium channels for all of the switched delivery channels. Each channel number may have associated with it a code identifying the switched delivery channel for which that channel number is selected, or the channel number data may be arranged in the data message in a predetermined order such that the switchpoint looks at a particular location in the data message in order to find the channel number selected for a given switched delivery channel.

It will be readily apparent to a person skilled in the art that the polling signals may be generated using known circuitry generally used and proposed for that purpose in switched networks and, once the channel number data has been obtained in respect of a particular switched delivery channel, known methods and apparatus may be used for extracting the desired premium channel from the trunk network, converting the signal to the appropriate switched delivery channel frequency, e.g. VHF2, and delivering that signal to the subscriber via his drop cable. Such known methods and apparatus are described, for example, in the D.H. Smart article mentioned above, the technical disclosure of which is incorporated herein by reference.

In operation the distribution system within the home can be considered to be a loop through system feeding as many outlets as desired. Various appliances may be connected at each outlet in order to make use of the provided cabled services. In the Fig.4 example there are six outlets; in practice it is likely that each outlet will be in a different room. Televisions are connected at outlets 1,5 and 6, a video recorder is connected at outlet 3, and outlets 2 and 4 do not have video appliances connected thereto. Radio receivers may be connected to the f.m. socket of any of these outlets.

Each video appliance is tuned to receive one or more of the bypass channels and switched delivery channels VHF1, VHF2, VHF3 and VHF4, as well as any desired off-air broadcast channels.

In order to be able to fully appreciate the mobile facility offered by the present invention of being able to select from any location the premium channel to be delivered on a particular switched delivery channel, e.g. VHF2, every appliance should be tuned so as to be able to receive that switched delivery channel VHF2. In that way a subscriber equipped with the remote control 202 which controls selection of the premium channel to be provided at VHF2 can wander from room to room, use his remote control to select any premium channel he wishes to view (which will be provided at VHF2), and view that selected channel on any appliance.

If only some of the appliances (e.g. TV1 and TV2) were tuned to VHF2 then the situation could arise where the subscriber was in a room (housing outlet 6) at which he could change the premium channel provided on VHF2 but he would not be able to view his selection in that room. This may be acceptable in some applications.

In summary, a remote control 201 adapted to control selection of the channel to be provided at VHF1 may be used in conjunction with the infrared receiver/multiplexer unit 15 at any outlet to change the selected channel on VHF1 but the selection can only be viewed on televisions/video recorders tuned to VHF1.

It can be useful for the subscriber if each of the infrared receiver/multiplexer units 15 possesses a display showing the identifying number of the premium channel last selected via that unit 15. In this example the units 15 are shown as having two-digit liquid crystal displays. Alternatively, "on-screen" display of channel selection may be used by means of text inserters in the switchpoint.

The specific embodiments described above are only examples of how the invention may be implemented.

A large number of alternative embodiments are possible differing from those described above in major and minor details. Some of the available variations have been mentioned above but examples of further alternatives are given below.

Firstly, the mobile units 20 used for making channel selections need not be infrared remote control units. The mobile units may operate in a different portion of the frequency spectrum. Clearly the receiver/multiplexer units 15 would be tailored to receive channel selection signals at the appropriate frequencies. However by departing from the infrared remote control units the possibility is opened up of adopting a system resembling cordless telephone technology so as to dispense with receiver/multiplexer units 15 entirely. In other words the mobile units 20 would be adapted to transmit their channel selection signals over distances of tens or hundreds of metres directly to a central HCU equipped with appropriate receiver circuitry.

Also, the mobile units 20 need not be remote control units but may be adapted for mechanical coupling to/uncoupling from the receiver/multiplexer units 15, or indeed for coupling/uncoupling directly with the outlets (in which case the mobile unit includes the circuitry for multiplexing channel selection signals onto the coaxial cable 13). The slight loss in convenience for the subscriber would be offset in the latter case by reduction in the amount of circuitry required in the subcarrier's installation.

In other embodiments of the invention specially adapted televisions and video recorders may be used which incorporate the functions of the receiver/multiplexer units 15.

In further embodiments of the invention it is the mobile units 20 themselves that may be dispensed with. Instead of using mobile units each of the receiver/multiplexer units 15 may be equipped with a keypad or other means for manual entry of channel selections on the switched delivery channels. In its basic version such a system relies on the subscriber inputting details not only of the desired channel but also of the switched delivery channel to be used for provision of the selected programme. Unless the subscriber and his family are very disciplined this may give rise to pranks whereby for example family member B who is supposed to control VHF2 uses the receiver/multiplexer at outlet 3 to alter the channels selected on VHF1, VHF3 and VHF4 currently being viewed by other family members in other parts of the home.

This problem may be avoided by assigning codes, or PIN numbers, to each of the switched delivery channels, known only to the person intended to control that delivery channel.

An additional advantage provided by embodiments of the invention lies in the area of "parental control" of viewing. If a subscriber wishes to prevent his children from having access to particular premium channels available via the switched delivery channels then he can do so in a number of ways. He can withhold from them entirely the ability to make independent channel selections (e.g. by failing to give them a mobile unit 20 or a switched delivery channel PIN number). Alternatively he can give them the ability to control particular switched delivery channels (e.g. VHF2 and VHF3) and condition the system so as not to output the vetoed premium channels on those switched delivery channels VHF2 and VHF3.This may be done by providing a memory at the HCU, or at the local switchpoint, storing details of the premium channels that are allowed to be output via the subscriber drop cable on particular switched delivery channels. Channel selection requests are then vetted with reference to this stored information before operating the relevant frequency agile convertor at the local switchpoint.

Alternatively, the subscriber may allocate to his children independent control of switched delivery channel VHF2 and himself hold a master control (or set of master control codes) capable of controlling VHF2 as well as one or more other switched delivery channels.

Thus the subscriber may check and alter his children's viewing selections.

In order to avoid a "battle of the remote controls" with the subscriber and his children alternately switching away from and switching back to, respectively, a vetoed channel, the subscriber may also be furnished with buttons/codes indicating that his selections for viewing at VHF2 are to be temporarily locked, ie. only changeable in response to a further channel selection signal from the subscriber or in response to a "release" signal from the subscriber.

Claims (14)

THAIS:

1. A subscriber installation in a cable television network of the switched type wherein a subscriber receives cable television via a subscriber drop cable, at least one channel being output on the subscriber drop cable at a frequency f1 dedicated to the subscriber and the particular channel to be output at said dedicated frequency f1 being determined by an offpremise switch or frequency agile convertor in response to dynamic subscriber selections, the subscriber installation comprising: outlets, at a plurality of spatially separated locations, at which the signals provided on the drop cable at the dedicated frequency may be accessed for viewing; selection means, operable in the vicinity of any of said outlets, for selecting the particular channel to be output at the dedicated frequency on the subscriber drop cable; and a home control unit for processing the selections made by the selection means and conveying them to the off-premise switch/converter.

2. A subscriber installation according to claim 1, wherein the selection means comprises a mobile unit adapted to transmit channel selection signals directly to the home control unit at radio frequencies.

3. A subscriber installation according to claim 1, wherein each of the outlets is connected to the home control unit and there is further provided a receiver/multiplexer unit at each of the outlets, said receiver/multiplexer units each being adapted to receive channel selection data from the selection means and to convey said data to the home control unit.

4. A subscriber installation according to claim 3, wherein the selection means comprises a mobile unit adapted to transmit channel selection signals to said receiver/multiplexer units.

5. A subscriber installation according to the claim 3, wherein the selection means comprises a keypad or other manually actuable means for entering channel selections directly into said receiver/multiplexer units.

6. A subscriber installation according to claim 1, wherein a plurality of channels are output on the subscriber drop cable at frequencies dedicated to the subscriber and the particular channel to be output at each of said dedicated frequencies is determined by a respective switch or frequency agile converter in response to dynamic subscriber selections, and wherein the outlets are adapted to provide access for viewing the signals provided on the drop cable to be had at any of the dedicated frequencies and the selection means is adapted for selecting the particular channel to be output at each of said dedicated frequencies.

7. A subscriber installation according to claim 6, wherein the selection means comprises a plurality of mobile units each adapted to control channel selection for one of the dedicated frequencies and each adapted to transmit channel selection signals directly to the home control unit, said channel selection signals indicating the dedicated frequency to which the channel selection signal relates.

8. A subscriber installation according to claim 6, wherein each of the outlets is connected to the home control unit, and there is further provided a receiver/multiplexer unit at each of the outlets, said receiver/multiplexer units each being adapted to receive from the selection means channel selection data and an indication of the dedicated frequency to which a given channel selection signal relates.

9. A subscriber installation according to claim 8, wherein the selection means comprises a plurality of mobile units each adapted to control channel selection for one of the dedicated frequencies and each adapted to transmit to the receiver/multiplexer units channel selection signals indicating the dedicated frequency to which the channel selection signal relates.

10. A subscriber installation according to claim 9, wherein each of said mobile units has an identification code and is adapted to include said identification code in the channel selection signals generated thereby.

11. A subscriber installation according to claim 9, wherein each of said mobile units has a different subcarrier frequency associated therewith such that receiver/multiplexer units receiving channel selection signals from said mobile unit convey the channel selection to the home control unit via a data channel at said subcarrier frequency.

12. A subscriber installation according to claim 11, wherein said subcarrier frequencies are at radio frequencies.

13. A subscriber installation according to claim 8, wherein the selection means comprises a keypad or other manually actuatable means for entering directly to said receiver/multiplexer units channel selections and an indication of the dedicated frequencies to which the respective channel selections relate.

14. A subcarrier installation according to any of claims 6 to 13, wherein the home control unit stores information on vetoed channels which are not to be supplied on the subscriber drop cable at a particular dedicated frequency and vets channel selections so as to identify selection of a vetoed channel for said particular dedicated frequency and prevent said selection from being put into effect.