GB2223899A

GB2223899A - Labelling of broadcast programmes

Info

Publication number: GB2223899A
Application number: GB8821619A
Authority: GB
Inventors: John Philip Chambers
Original assignee: British Broadcasting Corp
Current assignee: British Broadcasting Corp
Priority date: 1988-09-15
Filing date: 1988-09-15
Publication date: 1990-04-18
Anticipated expiration: 2008-09-15
Also published as: GB2223899B; GB8821619D0

Abstract

In order that a television programme may be given a secure labelling, the short programme label SPL (28) of the Television Service Data Line is varied according to a predetermined algorithm. The teletext decoder is programmed with the SPL algorithm in order that it may lock on to the changing SPL during a broadcast. Algorithms may be fed to the decoder from a conditional access unit. A bar code identifying the SPL algorithm for a given programme may be published alongside the programme listing to enable the decoder to lock on to a programme at any time during its transmission. <IMAGE>

Description

LABELLING OF BROADCAST PROGRAMMES This invention relates to the labelling of individual broadcast programmes by means of auxiliary data carried by, for example, by teletext for television or RDS (Radio Data Systems) for radio. It is particluarly relevant to the introduction of security to labelling techniques to prevent recording of broadcast material by recording mediums activated by data carried on the broadcast signal.

The UK teletext system distinguishes between magazine/page orientated teletext, such as the CEEFAX system which provides information for display on a television receiver, and services using independent data lines. An example of the latter is Datacast (RTM) data transmission service, which is a service allowing one-way transmission of general data using the teletext system as the carrier.

Another data line is the Television Service data line (TSDL) which provides for the inclusion of a Short Programme Label (SPL) unique to each programme. This data line is typically broadcast at a frequency of 1 HZ. The data line also carries a further 16 bit label known as the Network Identification (NI). The NI is a code unique to the network broadcasting the programme, e.g. BBC1. The combination of NI and SPL may be used to programme a video recorder or similar apparatus as it provides an identification for any broadcast programme that it unique over a time span of a few weeks.

The existing VPS (Video Programming System) used in West Germany is an example of such a system.

NI and SPL information can be located alongside published programme details e.g. in the form of a bar code. The codes may be read by a light pen and entered into the recording medium. When the teletext decoder associated with the recording medium identifies the stored Nl and SPL or the incoming signal it will activate the recorder. Our published application No. 2200519 describes the programming of broadcast receiving devices.

Such systems have the inherent problem that they do not give the broadcaster, who may be the copyright holder, any control over the recording of programmes for future use. Once the SPL of a particular programme is known, anyone with a suitable teletext decoder may programme a recorder to store the programme. Such considerations apply equally to other forms of programme labelling such as RDS.

We have appreciated that the problem may be overcome by varying the programme label in accordance with a known sequence. A receiver would then require knowledge of the sequence to enable a decoder to lock onto the programme.

For example, in the case of a teletext system, the short programme label could vary according to a known algorithm.

The sequence could be pseudo-random and generated by a conventional pseudo-random binary sequence generator (PSBR).

The invention is defined in the appended claims, to which reference should now be made.

The invention will now be described in greater detail with reference to the accompanying drawings, in which: Figure 1 shows the composition of a Television Service Data Line in a teletext transmission; and Figure 2 shows, in block form, a broadcasting system embodying the invention.

The invention will be more easily understood if the TSDL is first described in some detail. Figure 1 shows the composition of a TSDL which is composed of 45 eight-bit bytes. The line, as with all independent data lines, commences with two bytes of a clock runin sequence CR1 10 followed by a framing code byte FC 12. The next two bytes are the magazine and row addresses bytes MRAG 14. These bytes are Hamming coded and each carries four message bits, three of the total of eight message bits are the magazine number (from 1 to 8) and the remaining five, the row address. In TSDL MRAG is 8/30 i.e. magazine 8 row 30. In the original CCIRsystem B teletext specification rows 30 and 31 were reserved for applications unrelated to the page and magazine structure of teletext.Thus the magazine number is merely, with the row 30 and 31, an address for one of 16 independent data channels and not a page that can be displayed as a CEEFAX page.

The first byte after the MRAG 14 is the identification byte 16.

This is Hamming coded and identifies a data line with channel address 0 as a TSDL.

The next six bytes are the initial teletext page 18. These bytes are Hamming coded and specify the magazine number and sub-code of a page of the accompanying teletext service intended to be selected automatically in a decoder as an introduction to the service.

The network identification Nl, 20, occupy the next two bytes.

The NI is a 16 bit number which identifies uniquely the broadcasting network accompanying the data line. The data may be used together with a look-up table or content addressable memory to provide information in a human-readable form.

The seven bytes following the NI are devoted to time and data codes. The data is coded such that at any moment the codes are the same anywhere in the world, making it possible to adjust the information received to provide local time and date regardless of the time zone of the source. The TSDL is transmitted every second and all the information relates to the next second. The first byte is the local offset time 22 indicating the difference between local time and date and coordinated Universal Time (UTC) and Modified Julian Date (MJD). UTC is signalled in the next three bytes and MJD in the remaining three bytes.

The SPL follows the time and date bytes. The SPL is a sixteen bit number which uniquely identifies a broadcast programme.

Programmes nearby in time are given SPLs deliberately chosen to have a significant Hamming distance between them, so that a decoder searching for a particular SPL is unlikely to be misled by a similar SPL corrupted by a few bit errors.

The final 20 bytes of the TSDL carry information coded according to the UK teletext character set and intended to be displayed on the receiver screen. This information may, for example be the programme title.

The TSDL is typically transmitted at a frequency of 1 HZ. A system embodying the invention proposes that the SPL be varied repeatedly and continuously, possibly at the 1 HZ rate. The SPL is varied according to a known algorithm and so the pattern of change is deterministic. Thus, if the generating algorithm is known to the decoder, the sequence can be locked onto and followed with the same ruggedness as if it were a non-varying SPL.

Figure 2 shows a block diagram of a broadcasting system suitable for transmitting and receiving a varying SPL. The system is similar in many respects to that described in the previously mentioned application 2200519. Therefore, brief description only will be given.

The broadcast television signal is combined with teletext data 30 and this combined signal is further combined with the TSDL 32.

The composite is transmitted in conventional manner on a broadcast medium and, at a receiver, a conventional teletext decoder 34 extracts the teletext information from the selected channel. The extracted teletext data is fed to a controller 36 and the video signal is passed to a video tape recorder 38 in conventional manner.

The off-air picture signal is fed to a receiver display 40 which also acts as a teletext display. Handling of the picture signal is conventional and will not be described any further.

Channel selection may be made through a keyboard 42 or barcode reader 44 as indicated previously. Both are connected with the controller by one of many well known ways. Alternatively selection may be by a cursor on a teletext screen.

The controller 36 communicates with a multipage memory 46 which can store the currently displayed teletext page and associated page.

These pages may be initial teletext pages, the addresses of which are stored at location 18 of the TSDL. The memory also includes a programme information page which would store the initial SPL of a programme together with a schedule time and a programme name. The controller must also be supplied with a clock 48 for keeping track of MJD and UTC and a register 50 for storing the local offset, without which the controller would not be able to recognise a given programme from the UTC and MJD information contained in the TSDL. Of course, MJD and UTC information is not necessary if the controller is making an untimed open search which- monitors N1 and SPL searching for codes corresponding to stored values to actuate the recorder.

In order that the decoder can lock onto the changing SPL, it must be fed with knowledge of the SPL algorithm so that at any given time the decoder can predict the next SPL from the present SPL. Of course, the broadcast will not always be picked up at the beginning of a transmission and so the initial received SPL would not necessarily be the initial SPL of the programme. The SPL algorithm may be fed to the decoder 34 from a conditional access unit 52. Such conditional access are known and need not be described further.

Rather than publishing details of the initial SPL as is at present done with VPS systems (where, of course, the SPL is unchanging) a code identifying the SPL algorithm may be published.

As the algorithm for each programme is different, the controller can test each SPL according to the algorithm and if the succeeding SPLs match those predicted by the conditional access unit 52, the controller will remain locked onto a programme. Thus, it is not necessary to pick up the start of a transmission.

Although the invention has been described in relation to teletext, it can equally well be applied to programme labelling systems using other carriers such as RDS.

Claims

1. A method of labelling a broadcast signal comprising introducing a programme label onto the signal at periodic intervals and repeatedly varying the programme label indicative of a given programme in accordance with a predetermined sequence.

2. A method according to claim 1 wherein the broadcast signal is a television signal and the programme label is contained in a teletext data line carried on the signal.

3. A broadcast receiver for receiving data carried on a broadcast signal, comprising means for extracting the data from the signal, means for identifying from the data a programme label accompanying received programmes and including means for predicting variations in the programme label for a given broadcast programme in accordance with a predetermined sequence, and means for activating a recorder to record a received programme upon identification of a programme label varying according to the given sequence.

Amendments to the claims have been filed as follows 1. A method of labelling a broadcast signal comprising introducing a programme label onto the signal at periodic intervals and repeatedly varying the programme label indicative of a given programme in accordance with a predetermined sequence.

4. A broadcast receiver according to claim 3, comprising a memory means for storing the initial programme labels and their scheduled transmission times.

5. A broadcast receiver according to claim 3 or 4, wherein the means for predicting variations in the programme label comprises means for receiving and storing algorithms dictating the sequence of variations of the programme label of future programmes to be transmitted.

6. A method of labelling a broadcast signal substantially as herein described with reference to the accompanying drawings.

7. A broadcast receiver for receiving data carried or a broadcast signal, substantially, as herein described with reference to the accompanying drawings.