GB2501111A - Method of, and transmitter apparatus for, local UHF television broadcasting - Google Patents

Abstract

A method of broadcasting local digital terrestrial television (DTT) in the UHF band comprises: providing at least one single frequency network, each single frequency network comprising at least one local UHF transmitter (micro-transmitter, 302), the or each local UHF transmitter including a local data storage device, 312; receiving, from a remote data source (e.g., satellite gateway) 108, a data stream comprising data packets including broadcast content data; storing, on the local data store, the broadcast content data; and broadcasting, from the local UHF transmitter, broadcast content as a local UHF band digital terrestrial television transmission. Also claimed for example, with or without requiring that the local transmitter has such integral storage or receives remote source data are similar methods wherein: broadcast UHF frequencies are selected, or broadcast content formatted, based on received metadata; content is transmitted specifically in COFDM (coded orthogonal frequency division multiplexing) format; and transmission is timed so that UHF transmitters are substantially synchronised. Broadcast content may be selectively stored based on data stream metadata. Local UHF transmitters may provide geographical location information.

Description

Method of, and Apparatus for. Localised Television Broadcasting The present invention relates to a method of, and apparatus for, localised television broadcasting. More particularly, the present invention relates to a method of and apparatus for, localised television broadcasting using a network of low power transmifters.

A number of approaches to audio-visual content distribution are known in the art.

Terrestrial television is broadcast in both analogue and, increasingly, Digital Terrestrial Television (DTT) formats. In addition, distribution of audio-visual content by direct-to-home satellite is an established approach which, generally, provides additional channels and content on a pay-per-view or subscription basis.

However, due to the need for specific receiving equipment for satellite television services, the majority of television viewers tend to rely on DTT, particularly for public service broadcasts. Viewers with older televisions can also receive DTT via a low-cost set-top-box.

Current DTT broadcasting techniques use a number of widely-spaced, high power transmitters, each of which covers a large geographic area. This approach is acceptable for national or county-level DTT broadcasting where the same audio-visual content is to be broadcast across a wide geographic area.

However, increasingly, advertisers and content providers wish to provide more localised services to tailor advertising or content provision to a particular town, city or local region. Local television has, by definition, inherently small audiences. Therefore, whilst there is a recognised demand for such services, a commercially-sustainable local TV service model and associated content provision network has yet to emerge.

A recent mandate from the Department for Culture Media and Sport (DCMS) has specified a new countrywide local TV service for the United Kingdom to be carried on thc cxisting UHF digital terrestrial TV (DTT) network. One of thc kcy barricrs to cntry for ncw digital TV channels is thc cost of crcating new contcnt and thc nccd for acccss to large audiences to be able to recover this cost through advertising. In addition, research has shown that it may be difficult for any sustainable local TV service to operate other than in a few large cities.

At present, the current model utilised by the Department for Culture, Media and Sport (DCMS) relates to the use of existing UHF transmitter sites for local broadcasting.

Figure 1 shows an idealised coverage plot for a conventional DTT transmitter, in this case Emley Moor mat in Yorkshire.

The coverage region is centred to the South West of Leeds, but covers other towns and cities such a York and Harrogate within a radius of about 30 miles. Even if the power output is lowered, the same broadcast frequency cannot be utilised for different services in York or Harrogate. Therefore, there is a limit on how localised services can be using existing bmadcasting technology. Any advertising material broadcast on a particular frequency will be seen by any of the approximately 500,000 people in the coverage area.

Statistically, only a few people may actually watch the local TV channel and only a small proportion of those may see the advert. This makes it difficult to charge a premium for local advertising and is the main rca on that local TV is considered to be unsustainable for any community under 500,000. In contrast, normal print media can be commercially successful with circulation of only 150,000. Print media are able to charge a premium for advertising because it is known who has received the local paper and, as a result, the advertising can be precisely targeted.

In addition, conventional high power transmitters with wide coverage areas have a further problem that certain areas will not receive coverage, despite theoretically being within range.

Figure 2 shows the actual TV coverage for the Leeds area and Figure 3 shows the actual covcragc for a region of North Yorkshire. Thcsc two covcragc arcas ovcrlap such that viewers in thc city of York can receive cithcr scrvicc.

As shown, cvcn utilising a rcduccd powcr lcvel for local TV, a service in Lccds could still intcrfcrc with a local service in, for example, Sheffield (approximately 30 miles away) if the same broadcast frequency is used. This limits the number of services which could be provided using only certain frequencies. In addition, the coverage is not complete and therc are gaps in the covcrage, even relatively close to the transmittcr.

Therefore, existing or proposed solutions for local TV broadcasting suffer from a technical problem regarding the localisation ofthe broadcasting content. The interference between different broadcasts limits either the number of local TV broadcasts that can be provided in a given area or demands a large number of frequencies for transmission. The present invention seeks to address these issues.

According to a first aspect of the present invention, there is provided a method of broadcasting local digital terrestrial television in the UHF band, the method comprising: providing at least one single frequency network, each single frequency network comprising at least one local UHF transmitter, the or each local UHF transmitter including a local data storage device; receiving, from a remote data source, at least one data stream comprising data packets including broadcast content data; storing, on said local data storage device of the or each UHF transmitter, at least some of said broadcast content data; and broadcasting, from said at least one local UHF transmitter, said broadcast content data as a local digital terrestrial television transmission in the UHF band.

In one embodiment, at least one data stream comprises or further comprises metadata, and said step of storing comprises: selectively storing broadcast content data in dependence upon said metadata.

In one embodiment, said step of selectively storing comprises identizing data packets based on content schedule metadata.

In one embodiment, said data steam is received from a single source.

In one embodiment, said single source comprises a satellite downlink or a fibre channel network.

According to a second aspect of the present invention, there is provided a method of controlling the operating frequency of a local digital television broadcast in the UHF band, the method comprising: providing at least one single frequency network, each single frequency network comprising at least one local UHF transmifter operable to broadcast at a selected UHF frequency; receiving, from a remote data source, at least one data stream comprising data packets including broadcast content data and/or metadata; selecting, locally on said UHF transmifter, the broadcast UHF frequency in dependence upon the metadata; and broadcasting, from said at least one local UHF transmifter, said broadcast content data as a local digital television transmission in the UHF band at said selected UHF frequency.

In one embodiment, said broadcast frequency is specified in said metadata.

In one embodiment, the or each device within a single frequency network is operable to switch to said selected frequency.

In one embodiment, a controller is operable to supply control metadata to said remote data source.

In one embodiment, said broadcast frequency is selected by said controller in dependence upon the geographic location of the or each local UHF transmitter.

In one embodiment, the or each local UHF transmitter is configured to provide said controller with the geographic location of said particular local UHF transmifter.

In onc embodiment, thc or cach local UHF transmittcr is configured to provide said controller with the geographic location of said particular local UHF transmitter via said remote data sourcc.

In one embodiment, said remote data source comprises a satellite or a network server.

According to a third aspect of the present invention, there is provided a method of broadcasting local digital television in the UHF band, the method comprising: providing at least one single frequency network, each single frequency network comprising at least onc local UHF transmitter; storing, locally on said UHF transmitter, broadcast content; and broadcasting, said at least one local UHF transmitter, in a COFDM format as a local digital terrestrial television transmission in the UHF band.

In one embodiment, said step of storing comprises storing broadcast content data on a local storage device.

In one embodiment, the method thither comprises the step of prior to said step of storing: receiving, from a remote data source, at least one data stream comprising said broadcast content data.

In one embodiment, said data stream comprising data packets including broadcast content data and data packets comprising metadata.

In one embodiment, the or each data stream is received from a single common source.

In one embodiment, said single source comprises a satellite downlink or a fibre channel network.

According to a fourth aspcct of thc present invcntion, thcre is provided a method of controlling external dcviccs utilising a local digital television broadcast in the UHF band, the method comprising: providing at least one single frequency network, each single frequcncy network comprising at least one local UHF transmitter operable to broadcast at a sclccted UHF frequency; rccciving, from a rcmotc data sourcc, at least onc data stream comprising data packets including broadcast content data and/or metadata; formatting, locally on said UHF transmitter, the broadcast content data for transmission in dependence upon the metadata to control external devices; and broadcasting, from said at least one local UHF transmitter, said broadcast content data as a local digital television transmission in the UHF band in order to control said external devices.

In one embodiment, said external devices comprise street lamps.

In one embodiment, said step of formatting comprises: formatting said data content into DYB format; and adding control data for controlling said external devices to the service channel of said DVB format data.

In one embodiment, said at least one single frequency network comprises a plurality of local UHF transmitters.

In one embodiment, each local UHF transmitter within a single frequency network broadcasts on the same frequency channel.

In one embodiment, the local UHF transmitters are spaced apart by less than about3.5Icm.

In one embodiment, the or each local UHF transmitter has a power output of less than 5W.

In one embodiment, the or each local UHF transmitter has a power output of less than 1W.

In onc cmbodiment, said broadcast contcnt is broadcast in thc DVB-T or thc DVB-T2 format.

In onc embodiment, said broadcast contcnt data compriscs audiovisual contcnt.

In one embodiment, said audio-visual content data comprises programmes, adverts or programme information.

According to a fiflh aspect ofthe present invention, there is provided a method of coordinating the transmission of a local digital television broadcast in the UHF band, the method comprising: providing at least one single frequency network, each single frequency network comprising a plurality of local UHF transmitters operable to broadcast at a selected UHF frequency; storing, locally on each UHF transmitter, broadcast content data; timing transmission of said broadcast content data between said UHF transmitters such that transmission of broadcast content data from said UHF transmitters is substantially synchronised; and broadcasting, from said local UHF transmitters, said broadcast content data as a local digital television transmission in the UHF band.

In one embodiment, said local UHF transmitters comprise GPS timing devices.

According to a sixth aspect of the present invention, there is provided a local UHF transmitter comprising a local storage device operable to store broadcast content data and a transmission device operable to broadcast said broadcast content data as a local digital television transmission in the UHF band at said selected UHF frequency.

In one embodiment, the transmitter is further operable to carry out the method of the third aspect.

In one embodiment, the transmitter further comprises a receiver for receiving data content for storage on said storage device.

In one embodiment, the transmitter is further operable to carry out the method of the first to fifth aspects.

According to a seventh aspect of the present invention, there is provided a computer program product executable by a programmed or programmable processing apparatus, comprising one or more software portions for performing the steps of the first to third aspects.

According to an eighth aspect of the present invention, there is provided a computer usable storage medium having a computer program product according to the sixth aspect stored thereon.

Embodiments of the present invention will now be described in detail with reference to the accompanying drawings, in which: Figure 1 is a schematic illustration of the broadcast radius of a typical conventional high-power transmitter; Figure 2 is a plot of the actual TV coverage for a region of West Yorkshire; Figure 3 is a plot of the actual TV coverage for a region of North Yorkshire; Figure 4 is a schematic showing the micro-transmitter approach of an embodiment of the present invention; Figure 5 is a further schematic showing the micro-transmitter approach of an embodiment of the present invention; Figure 6 is a schematic showing the different power outputs from a conventional transmitter and from a micro-transmitter of an embodiment of the present invention; Figure 7 is a schematic diagram of the content delivery network according to an embodiment of the present invention; Figure 8 is a thither diagram showing the content delivery network according to an embodiment ofthe present invention; Figure 9 is a schematic diagram showing the data components of the content delivery network according to an embodiment of the present invention; and Figure 10 is a schematic diagram showing the broadcast frequency range for Digital TclTestrial Television in the United Kingdom.

The present method and apparatus provides a micro-transmitter approach to a national local TV network in which low-power, loealised transmitters provide audio-visual content to a local region. The transmitters receive and store data to be transmitted at a specific time.

The general principle of the present invention is shown in Figure 4. As shown in Figure 4, the micro-transmitters are grouped into single frequency networks (SFN) 10 comprising one or more micro-transmitters. In each SFN 10 the one or more micro-transmitters are operable to broadcasts at a specified single frequency.

As shown in this example, SFNs 10 can cover cities such as Leeds, York, Sheffield and Hull using multiple transmitters within one SFN. An SFN comprising only a single transmitter can be used for smaller towns such as Harrogate, Ripon or Scarborough.

Due to the low power output of the micro-transmitters, different content can be broadcast on each SFN 10 utilising the same frequency without risk of interference between different SFNs 10.

Figure 5 shows multiple clusters of 7 micro-transmitters grouped together to form a plurality of SENs 10-ito 10-4 to cover different areas. Each SFN 10-1 to 10-4 can be used to transmit different, locally-focussed content.

In terms of output power, Figure 6 illustrates a comparison between a conventional high-power transmitter and the micro-transmitter approach of the present invention. As shown, a lot of the high-power transmitter signal is wasted providing signal to uninhabited areas. However, the micro-transmitter approach enables efficient use of available frequencies and power to provide locally-focussed content.

In terms of energy efficiency, it can be sccn clearly that the micro-transmitter approach has significant benefits. It also enables the same frequencies to be reused more often as the masts are widely separated. Where overlap is unavoidable and different content is required to be delivered from adjacent masts then a rotating frequency reuse scheme could be used -this could be achieved with three frequencies if appropriately distributed. The high power transmitters in the UK have greater scope to interfere with each other and have to operate on an eleven frequency reuse scheme, which is less efficient in terms of available bandwidth.

An embodiment of the present invention will now be described with reference to Figures 7 to 10.

The arrangement of the present invention comprises an audio-visual content delivery network 50. The network 50 is shown in Figures 7 and 8. Figure 7 shows a general schematic of the elements comprising the network 50. Figure 8 shows a more detailed breakdown of the network components.

The network 50 comprises a content generation section 100, a content distribution section 200 and a broadcast section 300.

The content generation section 100 comprises a content server 102 and a service information server 104. The content server 102 is operable to receive and collate content (e.g. television programmes, adverts etc.) The service information server 104 is operable to receive programme information and metadata related to the content received by the content server 102.

The data from the content server 102 and service information server 104 is then formatted into the DVB-S2 (Digital Video Broadcasting -Satellite -Second Generation) format in a format converter 106. DVB-S2 is a digital television broadcast standard that has been designed to succeed the DVB-S system. It was ratified by ETSI (EN 302307) in March 2005. DVB-S2 is based on, and improves upon DVB-S and the electronic news-gathering (or Digital Satellite News Gathering) system.

Once the data has been prepared in the correct format, the data packets are sent via a satellite gateway 108 to the content distribution section 200 via a data uplink. In this embodiment, the content distribution section 200 comprises a satellite 202. However, this need not be the case and the content distribution section 200 may comprise alternative forms; for example, a fibre network or microwave link. The satellite 202 is operable to receive the data from the satellite gateway 108 and then send the data to the broadcast section 300 via a data downlink.

The broadcast section 300 comprises a plurality of micro-transmitters 302 grouped into single frequency networks (SFNs) 304. Each SFN 304 may comprise one or more micro-transmitters 302. The micro-transmitters receive the data from the satellite 200 and store appropriate data content locally for subsequent broadcasting. Each micro- transmitter 302 has a smart cache and a low-power DTT transmitter. Each micro-transmitter 302 cooperates with its peers to form either a Single Frequency Network (SFN) 304 as described (e.g. when the peer transmitters 302 are serving the same community) or to minimise interference when they are serving a different community.

The form and content of the data transmission from the content generation section to thc broadcast scction 200 will now bc dcscribcd with rcfcrcncc to Figurc 9. Figurc 9 shows a schematic of thc satellite gateway 208, satellite 202 and a micro-transmitter 302. The micro-transmitter 302 may form part of a collection of micro-transmitters 302.

Thc micro-transmitter 302 comprises a receiver scction 310, a data storc 312, a controller 314, a combiner 316 and atransmitter scction 318.

Data 400 is prepared for transmission in the gateway 208. The Data 400 compriscs contcnt data 402 and metadata 404. As shown in Figurn 9, thc content data 402 comprises video, audio, teletext and electronic programme guide (EPG) data. The metadata 404 is in the form of XML files.

Thc contcnt data 402 is transmitted as files. In one embodiment, transmission is in accordance with Internet Protocols such as FTP over TCP/W. With regard to the content data 402, each file comprises a programme, advert, link or logo with visual effects.

Although the transport stream can handle multiple programmes, only one programme is foreseen per transport system file to maintain schedule flexibility at play-out.

The content data 402 (in the form of video and/or audio content such as programmes, adverts etc.) is sent to the micro-transmitter 302 over the content distribution section 200 as MPEG-2 Transport Stream (TS) files. The content data 402 is streamed in a format which can be viewed directly on a television (with decoding) in a conventional manner but which can also be stored as a file (extensions *ts t.mpg or *.mp4).

Each content file will have a name to reflect content, release date and file type.

The MPEG-2 TS is divided into 188 byte packets. Each packet has a Packet Identifier (PID) which refers to video (PID w), audio (RID x), EPU (PID y) and teletext (PID z). In addition there are tables for signalling (Service Information or SI which have well-known PIDs. The MPEG-2 TS data files are encapsulated within a DVB-T, DVB-T2, DVB-S, DVB-S2, DVB-C or DVB-H packet format. The DVB packet format enables forward error correction to be applied to guarantee faithful delivery of the TS.

Thc content data 402 is transmitted across a data transmission channcl 406 and is received by the receiver section 310 oft micro-transmitter 302. The content data 402 can then bc saved locally on thc micro-transmitter 302 to the data cache 312. Thc data cachc 312 compriscs a local data storage systcm non-cxhaustive cxamples of which may comprise: a hard disk drive, a RAIl) network of drives; a flash drive; or any other suitable local storage device operable to receive and store data content 402 for later playback.

A key aspect of provision of local TV services is that particular content (e.g. adverts) can be targeted at particular regions. For example, a SFN 304 covering the Leeds area might broadcast specific advertising content applicable to the Leeds area which would be of little benefit to those living in other towns or regions. Specificity and localisation is expected to be of great interest to advertisers and enables TV broadcasting to ibilow a publishing style model which is expected to generate greater revenue due to the targeted nature thereof The content data 402 transmitted by the sateffite 202 is a constant data stream received from a single satellite. Each SEN 304 (which may comprise one or more micro-transmitters 302) may be operable to broadcast different content based on the location of that SEN 304; for example, advertising targeted to a specific region. In order to broadcast this media content, it must first receive the correct content from the satellite.

Tn order to achieve this, the packet identifiers identifr the nature of the data content and include information thereon. These metadata tags can be utilised, in this implementation, to identii' which content should be stored by which micro-transmitter 302.

Thereibre, in operation, the satellite will transmit a stream of data packets at a constant load. This is beneficial for the operation and efficiency of the satellite because a substantially constant data rate can be established and maintained.

The micro-transmitter 302 will receive the same data stream from the satellite 202 as any other micro-transmitter 302. However, the packet identifier in each data packet may identify which packets are destined for which micro-transmitters 302 in a given SFN 304. Therefore, the micro-transmitter 302, which comprises the data cache 312 (an internal storage device such as a hard drive or a flash drive), will selectively store content that is destined for the SFN 304 to which the micro-transmitter 304 is associated based upon the metadata for each packet. Alternatively, which data is stored locally on a micro-transmitter 302 may be determined by the mctadata 404 received by the transmitter 302 as will be described below.

Concomitantly, any packets which, based upon the data or metadata, are destined for other SFNs 304 will bc ignored by the micro-transmitter 302 and not stored.

Numerous approaches to the implementation of this procedure may be used. Specific packet identifiers may be used for particular SFNs 304. Alternatively, metadata 404 may be used for content selection as will be described later.

An advantage of storing audio-visual content at the transmitter 302 is that the satellite link 200 can be operated at constant capacity throughput. This minimises the satellite bandwidth required to carry a particular local TV channel, which directly reduces the cost of access for a channel operator.

The present invention enables the play-out timing of video sequences to be no longer directly linked to their time of arrival at the transmitter. Tn addition, the playback may be controlled directly by the channel operator by means ofmetadata 404 that is also delivered via the satellite link.

Thus each micro-transmitter 302 (or group of transmitters) can broadcast its own sequence of national or locally specific content, including the insertion of national or locally specific advertisements. This method of permitting the channel operator to control play-out obviates the need for an expensive facility that is normally required to aggregate the inputs from different channel operators and form the video feeds for DTT transmitters.

Once stored, the data can then be retrieved from the data cache 312 by the controller 314 as and when it is required for playback. The data can then be combined with any necessary metadata in the combiner 316 for transmission by the transmission section 318.

Metadata 404 is also sent from the gateway 108, across the content distribution section 200 to the micro-transmitter 302. In the context of this application, the metadata 404 does not comprise electronic progranune data or teletext data and refers to micro-transmitter control data.

The metadata 404 is again sent as files using, for example, an XML format and schema. A number of different metadata files may be used as discussed below: 1) Configuration files for micro-transmitter installation and commissioning Each micro-transmitter 302 has a unique identifier as well as a unique Single Frequency Network (SFN) 304 identifier with which it is associated. When there is only one micro-transmitter 302 in a coverage area, a unique SFN identifier is assigned to cater for expansion.

The metadata 404 transmitted by the gateway 108 comprises a configuration file to set up each micro-transmitter 302 before it is commissioned. The values which may be specified by the file include one or more of the following parameters: Antenna gain (dBi); PA output power (dBm); Broadcasting channel number; DTT profile (e.g. 16 QAM, FEC, guard time); Polarisation.

The metadata 404 is transmitted at installation and is updated as necessary. The metadata 404 channel can be used at any time to command a micro-transmitter 302 to perform an update, for example, to change frequency of operation.

2) Multiplex configuration files The metadata 404 may also comprise a configuration file to be sent to each micro-transmitter 302 to specify the multiplex it will transmit. This file may, for example, spcci: Number and type of video/audio TV channels (standard or high definition, and bit rates); channel icons; format of the service information (SI) channel.

The rnctadata 404 is transmitted at installation and is updated as necessary. Thc metadata 404, howevcr, can be used at any time to command a micro-transmitter 302 to perform an update, for example, to changc frequency of operation.

The transmission of mctadata 404 as outlincd in items 1) and 2) above has multiple applications. Each SFN 304 (which may comprisc one or more micro-transmittcrs 302) may bc operable to broadcast different contcnt based on the location of that SFN 304. Evcn though the SFN 304 is relatively confined and short range, there is still a risk that if the SFNs 304 arc operating on thc same broadcast frequcncy, they could interferc with one another. Such a situation may occur, for example, in local villages which are served by different SFNs 304.

Therefore, it is desirable to be able to set and to modify automatically the broadcast frequency of a particular micro-transmitter 302 or transmitters 302 forming an SFN 304. This may be especially important if a new network is installed near to an existing network and manually modifying all neighbouring transmitters is time consuming and impractical.

The use of a centralised transmission system to remote micro-transmitters 302, with each micro-transmitter 302 being responsive to particular metadata 404, can be used in this instance. The metadata 404 can be used to modiI' transmission parameters of particular micro-transmitters 302. For example, a controller (such as the regulatory body Ofcom) may sct a particular transmission frcqucncy which is thcn transmittcd as metadata 404 to the micro-transmifters 302. The metadata 404 may be targeted at specific micro-transmitters 302 and may switch ccrtain groups of micro-transmittcrs 302 to ccrtain frcqucncics and othcr groups to othcr operating frcqucncics as rcquircd.

Therefore, a body such as the channel operator or Ofcom could set the frequencies for a particular region or SFN 304 remotely, or using the location of the transmitters 302 as will be described below.

In addition, the ability to control individual transmitters using metadata 404 could provide the facility to shut down particular transmitters if desired. For example, if one transmitter 302 is playing illegal or inappropriate content, it could be disabled or prevented from broadcasting by the regulator via an XML metadata command 404.

3) Content Scheduling files The metadata 404 will also comprise data relating to a daily content schedule file for each SFN 304. This should ideally be received no later than 2355hrs for the following day's content play-out. The metadata 404 in this instance may specify the following: -the day's content for each stream within the multiplex, -the start-time and stop-time for each content file to be transmitted by the MT, -the start and stop times of each break for advertisements, -the file names for each advertisement and the play-out sequence during the break, -the category of content (programme, advertisement, wipe, trailer), -the start and stop times of each new content file to be transmitted on the satellite, -the location of content files within the directory structure of the data cache 312.

Table 1 below provides an example of a typical content schedule.

Time \:fode C:overage 0100:00 TeSt Card -Services wifl start at 06(30 as. National for BBC3 and BBC4. with differew tiniei 060000 Cached regional news Regional 0700:00 Cached local news (magazine) Local 0900:00 Cached regional news (repeat) Regional 1000:00 National Feed Na.tio.aal 120C00 Cached reaional news Regional 1300:00 Cached local news (maaazine) Local 1500:00 National Feed National 170000 Regional news (new) Regional 1800:00 Cached local news frepeat) Local 2000:0 0 National Feed National 0059:59 Close down National

Table 1.

In addition, the content scheduling files sent via the metadata channel 408 may, in an embodiment, specil which data packets are to be stored by the data cache 312 and which are to be ignored.

4) Files to be purged The metadata 404 may also comprise data which indicates which data is to be purged from the data cache 3 I 2.

Once the data 402 and metadata 404 have been stored, the audio-visual content can then be scheduled for transmission by the controller 314. The relevant data content 402 is then combined with any metadata or service information as required by the combiner 316 and formatted into the relevant DVB format for transmission by the transmission section 318.

A key aspect of terrestrial TV is the use of Coded Orthogonal Frequcncy Division Multiplexing (COFDM). This breaks the signal into thousands of parallel narrow band channels. Each narrow channel only carrics a fraction of thc vidco information.

COFDM is particularly well matched to video applications because it is very tolerant of the cffccts of multi-path intcrfcrcncc. In othcr words, a typical rcccivcr may rcccivc multiple signals, both direct ("line of sight") signal and signals resulting from reflections from buildings, land mass or atmospheric effects. Multi-path interference may null some channels and reinforce others, and this may change over time.

Multi-path interference could be viewed in the frequency domain as a frequency selective channel response. Another frequency-dependent effect for which COFDM offers real benefit is the presence of isolated narrow-band interfering signals within the signal bandwidth.

COFDM addresses these frequency-dependent effects as a result of the use of forward error coding. The coding and decoding is integrated in a way which is specially tailored to frequency-dependent channels and brings much better performance than might be thought based on a casual inspection. This way it is able to correct for missing information from channels that are temporarily lost.

The inventors have appreciated, for the first time, that a cellular network of low-power micro-transmitters can be used in conjunction with COFDM technology to provide efficient local coverage for provision of local television services.

The use of low power transmitters also benefits this application. To be able to operate COFDM, the transmitter power amplifiers have to be highly linear. This is, in practice, difficult to achieve at high powers but is straightforward at power levels below the 1W level. Furthermore, low power linear amplifiers are easier to design for operation over a wide band, which permits a regulator such as Ofcom to make changes to frequency allocations without the need to fit a new power amplifier at each micro-transmitter 302.

The broadcast data in DVB-T COFDM format is then transmitted by the micro-transmitter 302 in the UHF band. The micro-transmitter 302 transmits a low-power (approximately 1W) DVB-T signal on a UHF channel designated as geographically inter-leaved, that is, in spectrum freed as a result of the Digital Switchover in the United Kingdom.

The low power operation (of order 1\V) of the transmitters 302 enables small coverage areas to be defined and avoids the frequency spectrum limitations imposed on high power (of order 10kw and above) transmitters. The low power of the transmitters 302 gives a broadcast range for each transmitter 302 of approximately 1 km. The following description relates to local TV broadcasting from a United Kingdom perspective. However, the principles of the present invention could be applied to all EU States and other countries within the footprint of a relevant satellite or connected to a fibre network.

Figure 10 shows a schematic of the WF band allocated to DTT in the United Kingdom. As shown, the frequency range extends from approximately 600 -800 MHz.

Within the allocated UHF band a number of channels are defined. This will vary depending upon the region specified. For example, in London, 6 UHF channels are allocated to the 6 multiplexes that make up FreeView, namely Channels 22, 23, 25, 26, 28and30.

Each DVB-T UHF TV signal occupies an 8 MHz channel numbered from 21 to 68. Channel 21 is centred on 474 MHz and Channel 68 on 850 MHz. Each channel supports either 1705 carriers (2k mode) or 6817 carriers (8k) in COFDM. Table 2 below is taken out of the ETSI document EN 300 744 that specifies first generation DVB-T.

ReqScd CM for 2 O4-pftc V-tj trMe {MbI(z DEF str ntf 2) St flY(S CGate-Coot Gao Rion Iatkn taks Chc'i't ch4rt dtknn} 4 2 Si Vft% U AWCNI -d -. A crK A-A--.

I * t 4-- k -

c:rof-t: ;3-I 2.Ls 2-3 J.C/ S4C fl; s,tr:-rc) 0 (LFt t--"l 9&E -r -"c cot NE-:.

Table 2.

The term A/L is the fraction of the useful symbol time assigned to the guard interval. For A/T= V4 this means 118th of the symbol is repeated at the start of the symbol and 118th at the end.

The most likely constellation is QPSK rate 2/3 (recommended by Ofcom for local TV). From the table above this gives a useflil bit rate of 6.64 Mbit/s after the forward error correction decoding. Neglecting the Reed-Solomon outer code but taking account of the inner 2/3 code the symbol rate is 4.98 Msymbolis (dividing 6.64 Mbit/s by 2/3 and dividing by 2 as there are 2 bits per symbol).

Assuming approximately 2000 sub-carriers (the 8k mode would be better but Is older STBs may not be compatible) gives a symbol rate for each carrier of about 25 ksymbol/s. Thus each symbol has a duration of about 40 jts with 5 s at the star and 5 jis at the end as guard intervals. Assuming no other timing issues other than the speed of light this gives a maximum path length difference of 3.5 km. Therefore, it is desirable for the micro-transmitters 302 to be spaced apart by no further than this distance.

The DVB-T profile is set according to capacity and coverage. Currently a QPSK rate 2/3 profile is proposed. Over time the network can evolve to DVB-T2 as the number of second generation DVB receivers increases.

Each SEN 304 may comprise one or more micro-transmitters 302. In general, a plurality of micro-transmitters 302 will be provided within one SFN 304. Since each micro-transmitter 302 is an independent device comprising a data storage device 312 and broadcasting equipment 318, it is required to coordinate the transmission of the same broadcast from multiple independent sources.

As described above, COFDM is tolerant ofthe efibcts of multi-path interference.

Many oft effects ofmulti-path interibrence from, for example, different transmitters can be handled by means of a sufficient inter-symbol gap. This is provided so that interference from different transmitters (which may well be a significant distance apart) is minimised and is workable.

However, where closely-spaced and independendy transmitting micro-transmitters operate as an SEN, it is difficult to coordinate the transmission outputs of each transmitter to a sufficient degree of accuracy such that the delay does not exceed an acceptable inter-symbol gap lbr digital television transmission. Such a problem has not been encountered with conventional broadcast equipment. Neither has such an issue been encountered with conventional playback equipment because it is not usually necessary to synchmnise the outputs from multiple content playback devices.

Tn order for the transmitters 302 within an SFN 304 to transmit the same signal at the same time (within the guard intenral constraints), a OPS receiver is provided within each micro-transmitter 302. The UPS transmitter solves 4 unknowns (latitude, longitude, altitude and time). Time is locked to the atomic clocks on-board the UPS satellites.

Sincc thc satcilites transmit thcir cphemeris data, the OPS rcccivcr can recover a clock that, aftcr somc averaging, is near atomic in its accuracy. In an embodimcnt, thc UPS receiver outputs a 1 pulse per second signal. This signal can then be phase locked to a 10 MHz rcfercncc. Each micro-transmittcr 302 thcn locks to this rcferencc signal to coordinatc transmission of data within an SFN 304.

In an embodiment, the use of UPS receivers enables each micro-transmifter 302 to know its precise geographical location. This information can be utilised not only for timing transmission but also for frequency selection. In an embodiment, the micro-transmitter 302 may utilise satellite based geo-location data within the transmitters 302 to ensure they obey a predetermined service mask that is under the control of the national regulator.

The use of a centralised transmission system to remote micro-transmitters 302, with each micro-transmitter 302 being responsive to particular metadata 404, can be used in this instance. The metadata 404 return channel (shown in Figure 9) enables the micro-transmifters 302 to upload data such as geographic location information to a controller or regulatory body via the satellite 202.

21) Based on the location information received from the micro-transmitters 302, the regulator or controller can then specify modified transmission parameters of particular micro-transmitters 302. using targeted metadata 404 to switch certain groups of micro-transmitters 302 to certain frequencies and other groups to other operating frequencies as required.

In a further embodiment, the use of a centralised transmission system to remote micro-transmitters 302, with each micro-transmitter 302 being responsive to particular data, can be used to control other devices. The data packets can, in addition to targeting storage of content or control of frequency on each micro-transmitter 302, can be used to include information in the data channel of a digital terrestrial television (DTT) broadcast.

Data to, for cxamplc, opcratc strcct lights would bc carricd within thc MPEG-2 TS on its own privatc PID. Such data can span scvcral MPEG-2 packcts. Data forrnattcd as IP packets can also span several MPEG-2 packets and, indeed, this is how satellites can providc broadband scrviccs (with a rcturn link known as a Rcturn Channcl by Satcllitc giving thc tcrm DVB-S/RCS. A strcct light could thcn bc cquippcd with a simple and inexpensive decoder to enable switching on or off of street lights in the broadcast region.

The control of external hardware devices is rendered useful by the localised nature of the SFNs which enable precise control of local devices to a high degree of granularity, e.g. to control street lights in one specific village.

Methods of operation of an embodiment of the present invention will now be described with reference to Figures 11 to 13.

Figure 11 shows a method of operation of an aspect of the present invention.

Step 500: Receive content from single external source At step 500, the content is received by a micro-transmitter 302 forming part of a SFN 304 from an external source such as satellite 202. The content data 402 and metadata 404 are received by the receiver 310 of the micm-transmitter. The method proceeds to step 502.

Step 502: Store content At step 502, the content data 402 (comprising data packets including programme data, adverts, programme guide information or teletext) is stored locally on the micro-transmitter 302 in the data cache 312. The method proceeds to step 504.

Step 504: Format content At step 504, the content data 402 stored on the data cache 312 is processed and formattcd in thc DVB-T format with COFDM for broadcasting. Thc rncthod procccds to stcp 506.

Step 506: Broadcast content At step 506, the content 402 is then broadcasted in the UHF spectrum in the DVB-T format using COFDM by the transmission section 318. The content can then be received by local television receivers.

Figure 12 shows a method of operation of a further aspect of the present invention.

Step 600: Receive content from single external source At step 600, the content is received by a micro-transmitter 302 forming part of a SFN 304 from an external source such as satellite 202. The content data 402 and metadata 404 are received by the receiver 310 of the micio-transmitter. The method proceeds to step 602.

Step 602: Selectively store content At step 602, the content data 402 (comprising data packets including programme data, adverts, programme guide information or teletext) is stored locally on the micro-transmitter 302 in the data cache 312. The data to be stored is selected in dependence upon a parameter of the data or as specified by the micro-transmitter 302. Since the data stream will comprise content not necessarily destined for a particular SFN 304, the packet identifier for each packet, either alone or in conjunction with metadata 404, can be used to select which content is to be stored and which is to be ignored or immediately deleted.

The method proceeds to step 604.

Step 604: Format content At step 604, the content data 402 stored on the data cache 312 is processed and formatted in the DVB-T format with COFDM for broadcasting. The method proceeds to step 606.

Step 606: Broadcast content 1(S) At step 606, the content 402 is then broadcasted in the UHF spectrum in the DVB-T fornrnt using COFDM by the transmission section 31S. The content can thcn be received by local television receivers.

Figure 13 shows a method of operation of a further aspect of the present invention.

Step 700: Receive content from single external source At step 700, the content is received by a micro-transmitter 302 forming part of a 21) SFN 304 from an external source such as satellite 202. The content data 402 is received by the receiver 310 of the micro-transmitter. The method proceeds to step 702.

Step 702: Receive ni etadata from single external source At step 702, the metadata 404 is received by a micro-transmitter 302 forming part of a SFN 304 from an externa' source such as satellite 202. The metadata 404 are received by the receiver 310 ofthe micro-transmifter. The method proceeds to step 702.

Step 704: Store content At step 704, the content data 402 (comprising data packets including programme data, adverts, programme guide information or teletext) is storcd locally on thc micro-transmitter 302 in thc data cache 312. The method proceeds to stcp 704.

Step 706 Select UHF frequency In dependence upon the received metadata, the UHF broadcast frequency for the transmission of audio-visual content by the broadcasting section 318 is selected. The relevant hardware transmission parameters of the transmission section 318 are then set in dependence upon this metadata.

Step 708: Broadcast content At step 708, the content 402 is then broadcasted in the UHF spectrum in the DVB-T format using COFDM by the transmission section 318. The content can then be received by local television receivers.

Figure 14 shows a method of operation of a further aspect of the present invention.

Step 800: Receive content from single external source At step 800, the content is received by a micro-transmitter 302 forming part of a SFN 304 from an external source such as satellite 202. The content data 402 is received by the receiver 310 of the micro-transmitter. The method proceeds to step 802.

Step 802: Receive ni etadata from single external source At step 802, the metadata 404 is received by a micro-transmitter 302 forming part of a SFN 304 from an external source such as satellite 202. The metadata 404 are received by the receiver 310 ofthe micro-transmitter. The method proceeds to step 804.

Step 804: Store con tent At step 804, the content data 402 (comprising data packets including programme data, adverts, programme guidc information or teletext) is stored locally on the micro-transmitter 302 in the data cache 312. The method procccds to step 806.

Step 806: Format content and control content At step 806, the content data 402 stored on the data cache 312 is processed and formatted in the DVB-T format with COFDM for broadcasting. In this embodiment, the content may be formatted such that control signals for external receiving devices may be controlled. For example, the data channel forming part of the DVB-T format may be populated with control commands for operation of street lights.

The method proceeds to step 808.

Step 808: Broadcast content At step 808, the content 402 is then broadcasted in the UHF spectrum in the DVB-T format using COFDM by the transmission section 318. The content can then be received by local television receivers.

Variations of the above embodiments will be apparent to the skilled person. The precise configuration of hardware and software components may differ and still fall within the scope of the present invention. In addition, alternative or additional steps may be implemented with respect to the present invention.

In addition, it is known to provide users with the facility to SMS or call a content provider to change the content displayed on the TV. An example of this is marketing sales channels or gambling channels. However, the localised metadata feature of the Red Squirrel TV apparatus enables specific targeting of particular regions to tailor content modification to a uscr's particular village or district.

Additionally, the method of content provision to the micm-transmittets is not material to thc prcscnt invcntion. WhiLst thc above cmbodimcnts of thc invcntion rclatc to thc usc of a satellite upllnk/downllnk, othcr content provision methods may be uscd. For example, a fibre-channel network, internet connectivity or microwave transmission methods may be used. Alternatively, in particular cases, data may be loaded manually onto each micro-transmitter.

Embodiments of the present invention have been described with particular refrrence to the examples illustrated. While specific examples are shown in the drawings and are herein described in detail, it should be understood, however, that the drawings and detailed description are not intended to limit the invention to the particular Ruin disclosed. It will be appreciated that variations and modifications may be made to the examples described within the scope of the present invention.

Claims (40)

1. CLAIMS1. A method of broadcasting local digital terrestrial television in the UHF band, the method comprising: providing at least one single frequency network, each single frequency network comprising at least one local UHF transmitter, the or each local UHF transmitter including a local data storage device; receiving, from a remote data source, at least one data stream comprising data packets including broadcast content data; storing, on said local data storage device of the or each UHF transmitter, at least some of said broadcast content data; and broadcasting, from said at least one local UHF transmitter, said broadcast content data as a local digital terrestrial television transmission in the UHF band.
2. 2. A method according to claim 1, wherein at least one data stream comprises or further comprises metadata, and said step of storing comprises: selectively storing broadcast content data in dependence upon said metadata.
3. 3. A method according to claim 2, wherein said step of selectively storing comprises identifying data packets of broadcast content data based on content schedule metadata.
4. 4. A method according to claim I, 2 or 3, wherein the or each data stream is received from a single common source.
5. 5. A method according to claim 4, wherein said single source comprises a satellite downlink or a fibre channel network.
6. 6. A method of controlling the operating frequency of a local digital television broadcast in the UHF band, the method comprising: providing at least one single frequency network, each single frequency network comprising at icast onc local UHF transmittcr opcrablc to broadcast at a sclcctcd UHF frcqucncy; receiving, from a remote data source, at least one data stream comprising data packcts including broadcast contcnt data and/or mctadata; sclccting, locally on said UHF transmittcr, thc broadcast UHF frcqucncy in dependence upon the metadata; and broadcasting, from said at least one local UHF transmitter, said broadcast content data as a local digital television transmission in the UHF band at said selected UHF frequency.
7. 7. A method according to claim 6, wherein said broadcast frequency is specified in said metadata.
8. 8. A method according to claim 6 or 7, wherein the or each device within a single frequency network is operable to switch to said selected frequency.
9. 9. A method according to any one of claims 6 to 8, wherein a controller is operable to supply control metadata to said remote data source.
10. 10. A method according to claim 9, wherein said broadcast frequency is selected by said controller in dependence upon the geographic location of the or each local UHF transmitter.
11. 11. A method according to claim 10, wherein the or each local UHF transmifter is configured to provide said controller with the geographic location of said particular local UHF transmifter.
12. 12. A method according to claim 11, wherein the or each local UHF transmifter is configured to provide said controller with the geographic location of said particular local UHF transmifter via said remote data source.
13. 13. A mcthod according to any one of claims 6 to 11, whcrcin said remote data sourcc comprises a satellite or a nctwork server.
14. 14. A mcthod of broadcasting local digital television in the UHF band, the method comprising: providing at least one single frequency network, each single frequency network comprising at least one local UHF transmitter; storing, locally on said UHF transmitter, broadcast content data; and broadcasting, said at least one local UHF nansmitter, said broadcast content data in a COFDM format as a local digital terrestrial television transmission in the UHF band.
15. 15. A method according to claim 14, wherein said step of storing comprises storing broadcast content data on a local storage device.
16. 16. A method according to claim 14 or 15, further comprising the step of, prior to said step of storing: receiving, from a remote data source, at least one data stream comprising said broadcast content data.
17. 17. A method according to claim 16 wherein the or each at least one data stream comprising data packets including broadcast content data and data packets comprising metadata.
18. 18. A method according to claim 16 or 17, wherein the or each data stream is received from a single common source.
19. 19. A method according to claim 18, wherein said single source comprises a satellite downlink or a fibre channel network.
20. 20. A method of controlling external devices utilising a local digital television broadcast in the UHF band, the method comprising: providing at icast onc single frcqucncy network, cach singlc frcqucncy network comprising at icast onc local UHF transmitter operable to broadcast at a selected UHF frequency; receiving, from a rcmote data source, at icast onc data strcam comprising data packcts including broadcast contcnt data and/or mctadata; formatting, locally on said UHF transmitter, the broadca t content data for transmission in dependence upon the metadata to control external devices; and broadcasting, from said at least one local UHF transmitter, said broadcast content data as a local digital television transmission in the UHF band in order to control said external devices.
21. 21. A method according to claim 20, wherein said external devices comprise street lamps.
22. 22. A method according to claim 20 or 21, wherein said step of formatting comprises: formatting said data content into DVB format; and adding control data for controlling said external devices to the service channel of said DVB format data.
23. 23. A method of coordinating the transmission of a local digital television broadcast in the UHF band, the method comprising: providing at least one single frequency network, each single frequency network comprising a plurality of local UHF transmitters operable to broadcast at a selected UHF frequency; storing, locally on each UHF transmitter, broadcast content data; timing transmission of said broadcast content between said UHF transmitters such that transmission of broadcast content data from said UHF transmitters is substantially synchronised; and broadcasting, from said local UHF transmitters, said broadcast content data as a local digital television transmission in the UHF band.
24. 24. A mcthod according to claim 23, whcrcin said local UHF transmittcrs comprisc OPS timing dcviccs.
25. 25. A mcthod according to any onc of thc prcccding claims, whcrcm said at Icast onc singic frcqucncy nctwork compriscs a plurality of local UHF transmittcrs.
26. 26. A method according to claim 25, wherein each local UHF transmitter within a single frequency network broadcasts on the same frequency channel.
27. 27. A method according to claim 25 or 26, wherein the local UHF transmifters are spaced apart by less than about 3.5 km.
28. 28. A method according to any one of the preceding claims, wherein the or each local UHF transmifter has a power output of less than 5W.
29. 29. A method according to claim 28 wherein the or each local UHF transmitter has a power output of less than 1W.
30. 30. A method according to any one of the preceding claims, wherein said broadcast 21) content is broadcast in the DVB-T or the DVB-T2 format.
31. 31. A method according to any one of the preceding claims, wherein said broadcast content comprises audio-visual content.
32. 32. A method according to claim 31, wherein said audio-visual content comprises programmes, adverts or programme information.
33. 33. A local UHF transmitter comprising a local storage device operable to store broadcast content data and a transmission device operable to broadcast said broadcast content data as a local digital television transmission in the UHF band at said selected UHF frequency.
34. 34. A local UHF transmittcr according to claim 33, furthcr opcrablc to carry out thc method of any one of claims 14 to 19.
35. 35. A local UHF transmitter according to claim 33 or 34, further comprising a receiver for receiving data content for storage on said storage device.
36. 36. A local UHF transmitter according to claim 35, further operable to carry out the method of any one of claims ito 32.
37. 37. A computer program product executable by a programmed or programmable processing apparatus, comprising one or more software portions for performing the steps of any one of claims 1 to 32.
38. 38. A computer usable storage medium having a computer program product according to claim 37 stored thereon.
39. 39. A method substantially as shown in and/or described with reference to any one or more of Figures I to 14 of the accompanying drawings.
40. 40. A computer program product substantially as described with reference to any one or more of Figures 1 to 14 of the accompanying drawings.