BROADCAST RECEIVER SYSTEM

Abstract: A broadcast receiver (30) separates (34) 16-bit binary programme labels from a transmitted television signal and applies the TV signal to a video recorder (36). The viewer enters on a keypad (42) short labels comprising up to three decimal digits which are converted by a mapping function processor (44), e.g. a look-up table, into full 16-bit binary codes which differ in at least two binary positions. These codes are stored (40) and compared with the received codes and when they agree the video recorder is switched to record the TV signal. The viewer thus does not have to enter long codes but can use short labels to identify the programmes. The labels are printed in the TV Guide (16).

Description: _ _ BROADCAST RECEIVER SYSTEM Background of the Invention Methods of automatic programme delivery for broadcast services are currently known from European Broadcasting Union, Brussels, "Specification of the Domestic Video Programme Delivery Control System", Tech. 3263-E, August 1990, previously published May 1989 as Annex 2, Doc. Ref: SPB 459 rev. Typically, these services use different 16-bit programme labels to provide unique identification of each programme. In one implementation, the viewer may enter, by means of a keypad, the labels of the programmes he or she wishes to be automatically recorded. When the receiver detects the presence of a desired label, the video recorder is set to "record" mode. Using such a system the desired programmes will still be correctly recorded even if their transmission is delayed or re-scheduled. There is a conflict of interests between the values chosen for programme labels by the broadcaster and those easily entered by the viewer. In the example, the broadcaster has 65,536 possible 16-bit binary numbers available. Of these, the broadcaster would be well advised to choose a subset whose bit patterns, over a period of several days, differ from each other in at least two positions. This reduces the risk of a single bit error imitating a wanted label and so causing the false triggering of a video recorder. On the other hand, if, as is common, decimal digit entry is used and leading zeros are not necessary, the use of low value numbers would be of great advantage to the viewer. Low value numbers also take up little room when printed in a television (TV) programme listing and are less susceptible to publishing error. Video recorders are known from EP-A-0 133 985 and EP-A-0 122 626 which are provided with a bar code reader which can be used by the viewer to enter programme schedule data into a memory. This data is compared with transmitted signals to determine which programmes are to be recorded and to control a recorder accordingly. This overcomes the problem of long codes because the viewer does not have to enter them, but at the expense of a bar code reader associated with each receiver. Our GB-A-2 192 743 describes a unit which recovers video recorder type commands from an off-air TV signal, and generates infra-red signals representing RECORD and STOP which mimic the signals generated by a normal remote control unit. This does not assist in the problem of entering 16-bit programme labels by the viewer. A code converter is described in GB-A-2 191 643 which receives a generalised PLAY command from a remote controller and converts it to a specific PLAY command required to activate the currently selected one of a number of video sources, all. controllable by the same remote control unit. It is of course known to add increased error protection to digital data transmissions by adding protection bits, allowing erroneous data to be detected and possibly corrected at a receiver, see e.g. GB-A-2 038 145. It has also been proposed to add bits to a digital data stream in order to label it and facilitate its subsequent identification, see e.g. GB-A-2 196 517. Summary of the Invention The invention is defined in the independent claims appended hereto, to which reference should now be made. Advantageous features are defined in the dependent claims. The problem is solved in accordance with this invention by defining a function that maps input decimal numbers at the low end of the range, such as 0 to 999, to output numbers chosen from the full range of 0 to 65,535 and having markedly different bit patterns. Thus if low order numbers from the range 0 to 999 are input to the function, the corresponding output numbers are well spaced over the range 0 to 65,535. This allows the labels to be entered by the viewer with fewer keystrokes than would otherwise be needed. However, the function preferably should also accept input numbers in the remainder of the range up to 65,535. This allows a broadcaster to publish four- or five-digit (decimal) programme labels if (in this example) the one thousand labels with three or fewer digits are insufficient to cover a particularly programme-intensive period. In this case, the corresponding output numbers must still be unique but they can no longer be guaranteed to differ from each other in at least two (binary) bit positions. In a practical system, the function would obviously need to be specified and provided in all decoders as well as being used by the broadcaster compiling the 16-bit (binary) labels for transmission. A one-to-one mapping function is used, i.e. each possible input value maps onto a unique output value, and vice versa. Such a function may be implemented as a look-up table. The input number specifies the location within the table at which the output number can be found. Alternatively, suitable mapping functions based on modulo-2 arithmetic may be found. It will be apparent that the method described provides the broadcaster with well spaced, error tolerant, 16-bit numbers and the viewer with short, easily-typed programme labels. However, the method does not restrict the broadcaster to a subset of the 65,536 possible programme labels. Indeed all 65,536 values may be used, when appropriate, at the expense of a little extra keying on behalf of the viewer. The system can be applied to any programme delivery service, (i.e. VPS, or format 1 or 2), including radio programmes to be recorded on an audio recorder. It makes the manual selection of programmes quicker, simpler, and less likely to error, and reduces the apparent complexity of keyboard entry. It is particularly applicable to subscription television. Brief Description of the Drawing The sole figure in the drawing is a diagrammatic block schematic of a broadcast transmitted together with a receiver embodying the invention. Detailed Description of the Preferred Embodiment The accompanying drawing shows a programme delivery control (PDC) system embodying the invention comprising a transmitting station 10 and a receiving station 30. The transmitting station includes a programme scheduling computer 12 which is controlled by the broadcaster 14 who assigns to each television programme an identification number called a programme label. These are short easily-typed numbers, and are printed in the TV Guide as illustrated diagrammatically at 16. The computer outputs the current short label for each programme and a mapping function processor 18 converts this to a full 16-bit binary code. This is combined in a combiner 20 with a television signal received at an input 22 and applied to the transmitter 24. Typically the programme label is continuously carried as a part of the broadcaster's teletext service data. At the receiver 30 the signal is received by an antenna 32 and processed in conventional fashion by circuits not shown. A separator circuit 34 separates the 16-bit programme label from the TV signal and applies the TV signal to a video recorder 36. The extracted programme labels are applied to a label comparison circuit 38, where they are compared with a list of wanted labels held in a store 40. So long as the current programme label matches one of the stored labels, the video recorder records the received TV signal. When the current programme label no longer matches any wanted labels, the video recorder stops recording. The wanted labels are entered into the store 40 by the user keying the short labels on a keypad 42. The keypad has ten keys 0 to 9 and an ENTER key, thus permitting codes of varying length to be entered. These are applied to a mapping function processor 44 which mirrors the operation of the processor 18 at the transmitter and converts the short labels to the full 16 bit labels. As noted above, the broadcaster assigns to each TV programme a short, easily typed ' number. It is this number which is published adjacent to the programme entry in a TV guide. When the programme is broadcast, the mapping function is used to transform the short number into a more error tolerant value suitable for transmission along with the TV programme. The mapping function is also used within the receiver to transform short, easily-typed numbers entered by the viewer into their error tolerant equivalents. These may then be compared with the currently received programme label to determine whether or not to record the current TV programme. In principle, as an alternative the received programme labels could be applied to an inverse mapping function to convert them to the short label form and the short labels then compared. In practice such comparison would mean re-conversion to binary, and the arrangement illustrated is preferred. Two specific examples of the implementation of the mapping function will now be given. I_. Example using a look-up table. Low value, user-friendly input numbers which map onto output numbers whose bit patterns differ greatly from each other may be stored in a read-only memory. A suitable look-up table is set out in Table 1. Table 1 Decimal No. Binary equivalent input Broadcaster preferred keyed by to mapping function output values for viewer transmission "0" 0000000000000000 0000000000000000 0000000000000001 1111111111111111 "2" 0000000000000010 1010101010101010 "3" ooόooduooooooon 0101010101010101 0000000000000100 1010101011111111 "5" 0000000000000101 0101010100000000 "998" 0000001111100110 1001011011110010 "999" 0000001111100111 0011011001010001 "65533" 1111111111111101 0011011001010011 "65534" 1111111111111110 0011001000010011 "65535" 1111111111111111 1011001000010011 As is seen, four and five digit numbers keyed by the viewer still result in unique output values but with less markedly different bit-patterns: II. Example using Modulo-2 Arithmetic The following Table 2 demonstrates how modulo-2 based arithmetic may be used to transform low value consecutive 16-bit binary numbers into output values whose bit patterns differ markedly from neighbouring values. The algorithm assumes a 16-bit input number with individual bit positions labelled 0 (Least Significant Bit) to 15 (Most Significant Bit). Table 2 The algorithm is followed through step by step. Each step is completed and appropriate bit inversions performed before proceeding to the following step. Some input and corresponding output values are tabulated in Table 3 below. Table 3 It will be noted that this is a one-to-one transform, in that each possible input value produces a unique output value. The function is reversible; output values may be transformed back to their input values simply by executing the steps of algorithm in reverse. Other similar transforms may be defined by assigning different bits to be inverted at each step.

Claims: CLAIMS 1. A broadcast receiver system comprising means (32) for receiving a broadcast signal and providing a programme output representative of a broadcast programme, means (34) for identifying programme labels in the received broadcast signal, means (42) for entering selected programme labels for a selective control function, -means (40) for storing the entered programme labels, and means (38) for comparing the stored and received programme labels, characterized by label conversion means (44) coupled between the entering means and the comparing means for transcoding the labels entered via the entering means. 2. A system according to claim 1, in which the conversion means comprises a look-up table. 3. A system according to claim 1, in which the conversion means comprises modulo-2 processing means. 4. A system according to claim 1, in which the control function comprises the operation of a recorder for recording the received programme. 5. A system according to claim 1, in which the conversion means is coupled between the entering means and the storing means. 6. A broadcast receiver system comprising means (32) for receiving a broadcast signal and providing a programme output representative of a broadcast programme, means (34) for identifying programme labels in the received broadcast signal, means (42) for entering selected programme labels for a selective control function, means (40) for storing the entered programme labels, and means (38) for comparing the stored and received programme labels, characterized by label conversion means for transcoding on a one-to-one basis the labels applied to one input of the comparing means. such that the selected entered programme labels may comprise less, bits than the corresponding programme labels in the received broadcast signal, which such corresponding programme labels differ from each other in at least two binary bit positions. 7. A system according to claim 6, in which the selected entered programme labels may further comprise all possible labels which can be identified by the number of bits in the received programme labels. 8. '• A method of receiving a broadcast signal provided with programme labels, comprising the steps of entering selected programme labels for a selective control function, storing the entered programme labels, identifying programme labels in the received broadcast signal, and comparing the stored and received programme labels, characterized by transcoding the entered selected programme labels for storage such that the selected entered programme labels may comprise less bits than the corresponding programme labels in the received broadcast signal. 9. A method according to claim 8, in which the control function comprises the control of a video recorder to record selected programmes. 10. A broadcast transmitter system comprising means for generating a television signal for broadcasting, means (12,14) for allocating programme labels to programmes in the television signal, and means (20) for combining programme labels with the television signal for transmission, characterized by label conversion means (18) coupled between the allocating means and the combining means for transcoding on a one-to-one basis short- code programme labels allocated by the allocating means to transmission programme labels which comprise more bits than the short-code programme labels.

Inventors: SARGINSON PETER ASHLEY, SARGINSON, PETER, ASHLEY
Applicants: BRITISH BROADCASTING CORP, BRITISH BROADCASTING CORPORATION
Application year: 1991
Main classification: H04N5
IPC codes: G11B15, H04B1, H04H1, H04N5, H04N7