GB2385473A

GB2385473A - Tuning a set-top box output to an allocated TV channel

Info

Publication number: GB2385473A
Application number: GB0202547A
Authority: GB
Inventors: Oliver Patrick Durkin
Original assignee: NOVAPAL Ltd
Current assignee: NOVAPAL Ltd
Priority date: 2002-02-04
Filing date: 2002-02-04
Publication date: 2003-08-20
Anticipated expiration: 2022-02-04
Also published as: GB2385473B; GB0202547D0

Abstract

A television signal receiving apparatus, such as a digital set-top box for transmitting an output signal for a television, video or the like, the apparatus comprising: ```receiving means (51) to receive and decode digital television signals; ```means to output (72) the decoded television signals in a form of an output signal for a standard analogue television; and ```sweeping means (72) to vary the frequency of the output signal such that the apparatus can be tuned to a television, video recorder etc. which displays the output signal.

Description

Apparatus for Receiving Broadcasts The present invention relates to the field of apparatus for receiving broadcasts and especially for receiving digitally broadcast signals such as digital television signals.

More specifically. the present invention relates to so-called digital set-top boxes which convert digital television signals for use with standard analogue televisions.

Digital broadcasting is becoming more and more popular due to the fact that it allows many more channels to be transmitted using less frequency spectrum with both high quality pictures and sound.

Currently, most televisions are analogue televisions which are configured to receive conventional analogue television signals such as NTSC. PAL or SECAM. To allow these televisions to also receive digital signals, digital set-top boxes (STBs) are provided. These STBs receive and decode digital broadcasts transmitted using a digital modulation scheme such as Quaternary Phase Shift Keying (QPSK), Quadrature amplitude modulation (QAM), Vestigial sideband (e. g. 8VSB) or coded orthogonal frequency division multiplexing (COFDM), and output them in a form suitable for reception and display by a standard analogue television. Such STBs are currently on the market and are produced by many manufacturers, for example, Pace Micro Technology PLC, Nokia etc.

When a user acquires one of these STBs, the user needs to tune a free channel of their analogue television to receive the output signal of the STB. This may be a rather awkward task as often, the user has not needed to tune the television since it was purchased, which may be many years ago. Often, the user will need to consult the original television manual which the user might have mislaid over the course of time.

The present invention seeks to address this problem and thus in a first aspect, the present invention provides a broadcast receiving apparatus comprising receiving means to receive and decode broadcast signals; output means to output the decoded broadcast

signals in a form of a standard analogue TV signal suitable for receipt by a standard analogue receiving apparatus : and tuning means to vary a frequency of the output signal.

Examples of standard analogue television signals which may be received and displayed by a standard analogue television set are PAL, NTSC. SECAM etc. These signals comprise a number of discrete frequencies carrying video luminance data. video chromiance data, mono audio data, stereo audio data, etc. with a fixed relationship to each other. The tuning means is configured to change these frequencies in order to tune the apparatus to the receiving apparatus.

When the user is installing the digital receiving apparatus, he just needs to select a free channel on the receiving analogue apparatus and then tune the output of the digital receiving apparatus to that of the free channel of the analogue receiving apparatus. The receiving apparatus may be a standard analogue television or a video recorder or the like.

The present invention is primarily intended for use with digitally broadcast signals and more specifically, television signals but may also be used with pure audio signals.

Generally, the digital receiving apparatus will be a so-called digital set-top box (STB). However, the apparatus may be provided in the form of a circuit or module to be installed directly into a television set, video recorder or other type of audio/video apparatus.

Preferably, the tuning means is controlled in response to user input provided via a user interface. A remote control may be used for providing these user inputs.

The apparatus is preferably configured so that the tuning means is configured to perform a tuning process where the frequency of the output signal is changed until a user input is received from the user interface.

This tuning process may be initiated by a user failing to provide a user input in time or by the user pressing a button. The tuning process being stopped when the user supplies the required input.

As the user may accidentally press buttons, the apparatus is preferably configured to require the user to interact with the user interface to confirm the choice of output frequency. Failure to interact sufficiently by either pressing an incorrect button or by not responding in time results in the tuning process re-commencing.

Failure to interact within a number of complete sweeps of the available frequency spectrum (e. g. in the case where the user has left the room, or the channel chosen on the receiving device is incapable of receiving the signal from the STB) will result in an error condition. This may be signalled to the user by flashing LEDs etc located on the STB.

The receiving channel may incapable of receiving the output signal if the frequency of the receiving channel is outside that of the range of frequencies which may be outputted by the set-top box. Also, the frequency of the receiving channel may be subject to bad interference, for example, the receiving frequency may be equal to the frequency of one of the received digital or analogue channels, or even the frequency of a video output if present.

The user will be able to tell when the output frequency reaches the desired frequency as at this point, the television will display a signal from the digital set-top box. Preferably, when this procedure is performed, the apparatus is in a set-up mode where the output signal carries a test signal. For example, this test signal may be a fixed image displaying a welcome message to the user or a fixed image giving further instructions to the user etc.

If the receiving channel is unsuitable and the STB signals an error condition the user can either select another channel or, in the extreme unlikely event that all channels are unsuitable, the user can re-tune one of its receiving channels so that it is suitable for receiving the output signal.

The apparatus may be configured such that the output signal is outputted as an output channel selected from a plurality of output channels, each output channel having a different frequency. The tuning means stepping through the available output channels until the user selects the correct output channel.

The tuning means may scan through the channels in ascending or descending order. Alternatively, the channels may be scanned through in order of preference. For example, if an output channel is known to be unsuitable for some reason, then this output channel is offered as a last option.

Output channels may be unsuitable for many reasons. For example, it may experience interference from a received STB channel or a VCR etc. The apparatus may itself be able to determine unsuitable channels. Alternatively, it may rely on user inputs which indicate that previous output channels have been rejected by the user as unsuitable.

In addition to or as an alternative to the apparatus driving the tuning process, the apparatus may be configured to allow the user to increase or decrease the frequency of the output channel manually in fixed frequency steps by pressing an appropriate button and thus, allowing fine tuning of the apparatus.

Preferably, the output signal is a VHF or UHF output signal which is configured to connect to the standard television aerial input of a video recorder or television.

When the STB is intended to be connected to a video recorder, the output signal may be provided via a scart lead which allows both a signal to be transmitted to the video for recording and a signal to be transmitted to the video for passing onto the television.

The apparatus will receive both analogue and digital signals. Preferably, the analogue signals are just received and sent to the television with the output signal derived from the digital signals.

In a second aspect. the present invention provides a method of operating an apparatus for receiving broadcast signals for a television, the apparatus comprising means for receiving and decoding broadcast signals and outputting the decoded signals as an output signal. the television having a plurality of channels for displaying received signals and at least one designated channel for displaying the output signal, the method comprising changing the frequency of the output signal until the frequency of the output signal tunes to that of the designated channel of the receiving device.

The broadcast may be provided via wireless terrestrial networks, satellite or cable, or any of a variety of in-house wired or wireless distribution systems.

Figure I is a schematic of a television with set-top box in accordance with an embodiment of the invention; Figure 2 is a schematic of the remote control of Figure 1 ; Figure 3 is a flow diagram of the steps performed by the STB of Figure I when it is switched on; Figure 4 is a flow diagram of the processes performed to tune the STB to the TV output; Figure 5 is a continuation of the flow diagram of Figure 4; Figure 6 is a block diagram of the main electrical components of the set-top box of Figure 1 ; Figure 7 is a block diagram of the UHF/VHF remodulator of Figure 6; and Figure 8 schematically illustrates the set-top box of Figure I connected to both a video and a television.

In Figure 1. a set-top box (STB) I is connected to aerial 3 via UHF cable 5. The STB I is connected to television 9 via UHF cable 7. UHF cable 5 is the standard aerial feed for the television 9 but is plugged into the STB 1. Output cable 7 from STB I is configured to be connected to the aerial feed port (not shown) on television 9. The output is a standard UHF/VHF output carrying a standard TV signal such as NTSC.

SECAM, PAL or the like.

The STB I may additionally be connected to the TV using a SCART (peritelevision) connector (not shown) which carries an unmodulated pure video signal and audio signal.

A remote control 11 is configured to communicate with STB 1. Details of the remote control 11 will be described with reference to Figure 2.

In operation, analogue and digital television signals are received by aerial 3 and communicated to STB 1 via UHF cable 5. STB 1 decodes received digital television signals and outputs the decoded digital television signals and analogue signals to television 9 via UHF cable 7.

The STB 1 can only output one digital channel at a time. The selected digital channel is output from STB I as a UHF analogue television output signal along with any analogue television signals which are also received by aerial 3.

The television 9, is a conventional analogue television which has a plurality of user selectable output channels which are used to display analogue television channels, on screen 10, normally received directly from aerial 3. To display an analogue channel received from aerial 3, an output channel of the television is selected and this channel is tuned to the frequency of the desired received analogue channel.

Prior to the STB I being installed, the analogue television 9 received analogue television signals direct from aerial 3 and selected output channels of the television 9 were tuned to display the various analogue television channels.

With the STB I now connected between the aerial 3 and the television 9. the television still receives the analogue channels. However, in addition. it also receives an analogue television output signal corresponding to a selected digital channel.

The television 9 can only display this digital channel if one of the free channels of the television and the STB output signal are tuned to the same frequency.

Previously, a free channel of the television had to be tuned to the frequency of the output signal of the STB. However, as will be explained in greater detail with reference to figures 3 to 5. in the present invention, the output of the STB is tuned to that of a free channel of television 9 thus avoiding the need for the user to work out how to tune the television to the STB.

The STB outputs the decoded digital signal in the form of a standard analogue television signal which can be received and displayed by a standard analogue television set. Examples of such standard analogue television signals are NTSC, PAL or SECAM etc, each of which comprise a plurality of frequencies with a fixed relationship to each other. These plurality of frequencies can be thought of as constituting an output channel. Thus, tuning the STB can be understood either in terms of varying the output frequency of the STB or varying the output channel of the STB.

In addition to outputting the received digital and analogue television signals, the STB outputs information to the analogue TV 9 to be displayed as an on-screen display (OSD) message. Examples of OSDs are channel banners which indicate the name of the selected channel, icons which indicate a status of the STB such as muted, volume etc. OSDs may also be used to display program information.

OSD messages are used to indicate user information such as, now and next program information, channel guide, the selected channel when the user changes channel, whether the output of the STB has been muted etc. Examples of OSD messages will be described with reference to the specific functions of the STB.

The channel outputted by the STB is selected using remote control 11 (which will be described in more detail with reference to figure 2).

The channels are assigned to their logical channel numbers by the STB using data embedded in the digital signals received, e. g. BBC 1 is STB channel 1. BBC2 is STB channel 2... BBC choice is STB channel 7 etc. Depressing the down channel selector allows the user to scan through the channels in descending order.

The up channel selector and down channel selector may also be used for navigation in the program guide, information for which is received by the STB. This will be described in more detail later. Also, the up and down selectors are used in the procedure to tune the STB to the television. This will be described in more detail with reference to figures 3 to 5.

The local control interface 13 comprises standby/setup button 19 which allows the set-top box 1 to be switched from an operational mode to a standby mode.

In the standby mode, STB I is in a low power mode where the tuner is held in a reset mode and there is no conversion of digital signals to audio and video signals (the tuner and decoding apparatus will be described with reference to figure 6). The standby mode can be accessed at any time during normal viewing by pressing standby/setup button 19. When the standby/setup button 19 is pressed briefly, the STB mutes both audio and video outputs. Other housekeeping functions are performed when the standby mode is entered such as checking for previously undetected digital channels.

The STB will also perform a scan for digital channels. This will be described in more detail after the discussion of figure 3.

The Standby/setup button 19 is also used to tune the STB 1 to the TV 9. This will be described in detail with reference to figures 3 to 5.

STB I also comprises display area 21 which has a red LED 23 which is lit when the set-top box is in a standby mode and a green LED 25 which is lit when the box is in

an operational mode. The LEDs may be simultaneously lit or may flash etc. to indicate other modes of operation. for example during tuning of the STB 1.

Figure 2 shows an example of a remote control which may be used to control the STB of figure 1. Remote control 11 comprises standby button 31 which allows STB 1 to be switched between a standby mode and an operational mode in the same manner as described with reference to button 19 on the box. However, standby button 31 is not used in the same manner as standby/setup button 19 to tune the STB to the TV 9 which will be explained with reference to figures 3 to 5.

Mute button 32 is provided which allows the user to mute the outputted sound from the STB 1. The mute button specifically toggles on and off of both the UHF modulator audio intercarrier and baseband audio outputs of the STB 1. When the mute button mutes the sound an appropriate icon is displayed on the screen 10 of television 9 using the OSD capability of STB 1. The mute is reset to off when the STB is switched out of standby or powered on from mains cycling.

A numerical key-pad 33 is provided which comprises 10 keys numbered from 0 to 9. Key pad 33 allows the user to input numerical values, for example, to select a particular digital channel, provide a numerical response to a prompt displayed on the screen 10 of the television 9. The STB is configured to display digits, pressed by the user, on screen 10 using its OSD. When a channel is selected, the STB 1 outputs a channel banner indicating the channel, which overlies the displayed program using the OSD facility.

The STB I is also configured to display interim channel banners when multiple digit channels are selected using the number keys. The STB is configured to wait for 1 second for a second numerical key to be pressed. For example, if"I"is pressed, the STB displays a channel banner on screen 10 with "BBC I", if another"I"is received within one second, the channel banner is changed to"BBC News 24"which is currently on channel number 11.

If an encrypted channel is selected. a blank screen will be shown and the STB outputs an OSD message on the blank screen indicating that the selected channel has become unavailable.

Some channels are audio only channels. e. g. BBC Parliament. When such channels are selected, the audio channel will be outputted from the STB and the TV screen 9 will be blank. The STB I will output an OSD message to be displayed on the blank screen indicating that the selected channel is an audio channel only.

An arrow key arrangement 35 is also provided on remote control 11. Arrow key arrangement comprises an up arrow key, a down arrow key. a right arrow key and left arrow key.

The up and down arrow keys allow the user to scan through the available digital channels in ascending order. As the STB I scans through the digital channels, the channel number and name is displayed as a channel banner using the OSD capability of STB I on the screen 10 of television 9. The up and down arrow keys are also used in the tuning processes which will be described with reference to the flow chart of figures 3 to 5.

The left and right arrow keys are used to navigate the program guide and may also be used in channel selection.

A"Back"button 39 is provided which allows the user to toggle between the currently viewed and previously viewed channel. The previously viewed channel will not be stored when the power is cycled on the STB but will be stored when the STB enters standby mode.

As well as operating in a so-called'normal viewing'mode, where the STB 1 outputs the received analogue and digital channels, the STB can also operate in other modes where it outputs information concerning the outputted digital channels. These modes are accessed by pressing the guide 43, info 45, select 47 or status 49 buttons.

Guide button 43 is provided, which when depressed during normal viewing mode causes the STB I to enter guide mode. In guide mode, the STB outputs the program guide for display on screen 10 of TV 9. Specifically, the program guide is a list of program channels with the title of the current program and the next program on each program channel.

The list of program channels comprises all free to air (FTA) channels defined on the user's list of channels. How the user defines this list will be explained with reference to figure 3. Only program channels which were not 100% encrypted when the user defined the channel list will be displayed by the program guide.

If a channel is currently unavailable, for example, if the transmitted program has been scrambled by the service provider, then the program guide will indicate that the channel is currently unavailable.

An info button 45 is provided which, when depressed during normal viewing mode, causes the STB I to enter'info'mode. In'info'mode, the STB outputs as an OSD using a detailed synopsis for the program currently being transmitted on the channel being viewed when the user entered"info"mode. The display information is taken from the broadcast service information streams received by the STB 1. Broadcast service information contains information relating to delivery system, content and scheduling/timing of broadcast streams etc.

A select button 47 is provided which, when depressed during normal viewing mode causes the STB to enter'select'mode. In'select'mode, the STB outputs as an OSD, the title and start times of the current and next programs transmitted on the selected channel and the current time, so called'now and next information'. The displayed information is summary version of that displayed when the info button 45 is depressed.

The now and next information disappears when the select button 47 is depressed again and the STB switches back to normal viewing mode. The now and next

information also disappears if the STB receives no user input in the 40 seconds after the select button has been pressed.

The select button 47 is also used during the set-up of the STB, this will be described in more detail with reference to figure 3.

The STB enters'status mode'when the status button 49 is depressed. In this mode, the STB outputs information concerning the current set-up of the STB (e. g. the selected wide mode, audio channel, output frequency and channel of the STB). information concerning the currently selected channel and data concerning the signals received by the STB I.

Cancel button 41 is used to cancel guide, info, select or status modes and to return the STB to normal viewing mode.

Previously, the functions accessible by just pressing one of the function buttons have been described. However, it is possible to press a sequence of buttons.

If the channel is changed after the select mode has been entered, by either entering another channel number via the numerical keys 33 or using up and down arrows 35, the now and next information for the newly selected channel is displayed.

Pressing the info button 45 or the guide button 43 just after pressing the select button 47 has the same effect as if the info 45 or guide 43 buttons were pressed in normal viewing mode.

Once the info button 45 has been pressed, the STB I enters an info mode and outputs extended program information for the program currently transmitted on the selected channel is displayed. Pressing either the left or the right arrow keys 35 displays extended program information for the next program to be transmitted on the selected channel. Pressing either of the left or right arrow keys 35 again causes the extended program information to be displayed for the current program. Thus, the left

and right arrow keys 35 can be used to toggle between extended program information for the current and next program transmitted on the selected channel.

Pressing the up or down arrow keys 35 on the remote control 11. or entering a different channel number using numerical key-pad 33 on the remote control I I when the STB is in info mode, causes the STB to output extended now information for the channel number selected by the arrow keys or numerical key pad.

Pressing select when the STB is in info mode causes the STB I to switch out of info mode and display the channel whose extended information was outputted when select was pressed. Normal viewing of this channel can then continue.

Pressing guide 43 when the STB is in info mode causes the STB to switch to guide mode and output the program guide. Pressing cancel 41 causes the STB to switch back into normal viewing mode where it outputs the channel which was selected when the info mode 45 was entered.

The guide mode of the STB I is accessed by pressing the guide button 43.

Pressing the up or down arrow keys 35 on the remote control l l, or entering a channel number using numerical key-pad 33 on the remote control when the STB is in the guide mode causes the newly selected channel number to be highlighted on the displayed channel guide.

The channel guide is likely to extend over more than one screen, other pages of the guide can be accessed by pressing the right or the left arrow keys 35 on the remote control 11.

Pressing select 47 when the STB I is in guide mode causes the STB I to enter normal viewing mode outputting the channel highlighted when select was pressed.

Pressing cancel 41 when the STB I is in guide mode causes the STB I to return to normal viewing mode outputting the channel which was selected when the guide mode was entered.

Pressing the info button 45 when the STB is in the guide mode causes the STB to enter the info mode and output extended program information concerning the highlighted channel.

If no response is received from the user for 20 seconds in the guide mode. then the STB will switch back to normal viewing mode.

Entering Status mode and the pressing the Info button 45 causes the STB I to output more detailed status information, for example, the quality of the received signal. the current version of the software and hardware of the STB 1 and data relating to the spare capacity of the memories of the STB 1.

Pressing the Guide button 43 while in the status mode causes the STB to output more detailed information, for example, relating to the size and quality of the signal received from the transmitters which are detected by the STB 1.

Subtitles button 44 when depressed toggles hides or shows subtitles which are broadcast with the digital channels.

Audio button 46 is provided which allows the user to step through the various alternative audio channels which may be provided for a particular digital program channel. For example, BBC I in Wales may be accompanied by both an English language audio channel and a Welsh language audio channel for certain programs. In such an example, the audio button allows the user to switch between the two audio channels.

When a user switches between audio channels, the audio language of the newly selected audio channel is displayed as a banner on the screen 10. The selected audio channel is then saved as the preferred audio channel for the currently viewed program channel.

When a user first depresses audio button 46. the language of the audio channel is displayed as a banner on screen 10, subsequent pressing of audio button 46 steps through the particular audio channels available for the currently view program channel.

The last selected audio channel for a specific program channel is then saved as the preferred audio channel for that program channel and will be outputted the next time that program channel is selected.

A wide button 48 is provided which when pressed allows the user to scan through various screen format options. Conventional analogue signals are broadcast in full format 4: 3. However, digital broadcasters tend to prefer wide screen format 16: 9 as this gives a better proportioned picture. Viewing a broadcast sent using 16 : 9 format using a 4: 3 display format causes the image to be stretched vertically. Similarly, as some broadcasts are still sent using 4: 3 format, viewing these using 16 : 9 format results in a horizontally stretched image.

In an attempt to provide a sensibly proportioned image for both viewers using 4: 3 display format and 16: 9 display format, some channels and sometimes specific programs are broadcast using 14: 9 format. Letter boxing is also used to correctly proportion the display area.

The STB will automatically select the display format by using the active format descriptor (AFD) transmitted with the digital channel and a look-up table within the STB 1.

If the user is not happy with the automatically selected display format, then the user can change the display format by pressing wide button 48. Pressing the wide button once causes the STB to output the display format as an OSD message.

Pressing the wide button 48 a second time allows the user to scan through the following display modes: Wide-16 : 9 (for use with a wide screen display)

Normal-for use with a 4: 3 display. This allows the viewer to view widescreen material in the transmitted format Centre Cut-Out-For use with 4: 3 displays (allows the viewer to view only the centre of widescreen material.

The STB is configured to store the last selected display mode and use this as the default, the next time the STB is activated.

Next, the process of installing and tuning the STB to the television will be described with reference to figures 3 to 5.

In step S 101, the user connects the STB I (STB) to the television 9 and aerial 3.

Specifically, lead 5 (Figure 1) is a standard television aerial output from aerial 3.

Instead of plugging this aerial output 5 into the back of television 9, the output is plugged into the input of STB 1. A"fly-lead"7 then runs from an output of STB I and plugs into the standard aerial port of television 9.

Once connected, the television is turned on in step S 103 and a free channel is selected. When the STB is very first turned on, it automatically enters'set-up'mode and it outputs a welcome screen with instructions to the viewer in S 105. In this set-up mode, the STB 1 may need to complete two tasks: i) scan the incoming signals to identify digital channels : and ii) tune the output signal to that of the television.

When the STB is connected to the TV and switched on for the first time, the STB will need to be tuned to the TV. However, this process will not be necessary every time the STB is switched on. Thus, in S 105, SIB I outputs instructions to the viewer to tune the STB to the TV if required, or enters normal viewing mode via S 117 if the STB has already been configured.

In this specific example, the viewer is requested to hold down the standby/setup button 19 (on the STB) to tune the STB to the TV or to press and release the Standby/setup button 19 (on the STB) if there is no need to tune the STB to the TV. If the STB is connected to the TV via a scart lead, the welcome screen is displayed on the

television when the STB and television are switched on. If the STB is connected to the television via a UHF lead, then no welcome screen will be seen until the STB is tuned to the TV. In this situation. the user refers to the manual which will carry the same instructions as the welcome screen.

If the user wishes to tune the STB to the TV in step S 107, the STB follows the processes which will be described later with reference to figures 4 and 5.

If the user does not wish to perform this tuning function or if the user has completed this tuning procedure, the STB proceeds to step S109 where it scans the received digital channels and stores information identifying the location of these channels.

Once the incoming digital channels have been stored and scanned, the user defines their channel list in step Sill. In this step, the STB outputs a list of the currently detected FTA channels. The user, by using the up and down arrow keys 33 on the remote control, can highlight a particular channel and indicate by pressing keys indicated by the STB whether they want the highlighted channel to appear in the user defined channel list which is displayed when the previously described guide mode is entered.

The viewer exits editing the channel list by pressing select and then the STB switches to normal viewing mode. This completes the set-up procedure.

The procedure for tuning the STB I to the television is entered when the user holds down the standby/setup button 19 on the STB I for five seconds in step S 119 of Figure 4 in response to S107 of Figure 3. At this point, green LED 21 flashes on STB 1 in step S121.

Once the green LED flashes, the STB outputs a further screen indicating the current STB output channel and frequency in step S 125 and requesting the user to start to scan for digital channels in step S 127.

If the user sees this message. they will press the standby/setup button 19 on the STB to scan for digital channels and start the process at S 109 of figure 3. If no response is received within 10 seconds. then the STB starts to scan its output frequencies/channel corresponding to its digit to tune to the TV 9. The STB output frequency is quantised into predefined number channels and the STB steps its output frequency. or more correctly output frequencies through these channels one at a time.

The STB steps to the next output channel in step S 131 and outputs an OSD instructing the user to stop the scan in step S133. In this specific example, the user stops the scan by pressing the standby/setup button 19 on the STB or the select button 47 on the remote control 11. If no response is received within one second in step S135. then the STB steps its output frequency to the next output channel in step S131 and this loop is repeated until the user sees the image requesting the user to stop the scan and the user stops the scan.

The user stops the scan of the output frequency by pressing standby/setup button 19 or the select button 47, the STB turns on red LED in step S 137 in response to this act of Figure 5. The STB then checks to see if the selected output channel is suitable in step S139. For example, if the selected output channel frequency corresponds to that of a digital channel received by the STB, then the output channel is unsuitable as it will suffer from poor picture quality and/or interference.

If the current output channel is not suitable, then the STB will output a request to the user in step S 143 to adjust the output channel by either pressing the up arrow or the down arrow key 35 on the remote control I I to adjust the output channel up or down by one. If no response is received in step S153, the red LED is turned off and STB 1 returns to step S131 and starts scanning the output frequency again.

If the user responds by adjusting the output channel in step S149 using the arrow keys 35, the STB 1 reverts back to step S 139 to check if the new output channel is acceptable.

If the STB determines that the selected output channel is acceptable, the process proceeds to step S 141 where the STB outputs a message requesting the user to confirm that the output channel is acceptable by pressing standby/setup button 19 or select button 47, or to press the up or down arrow keys to adjust the output channel. The user may wish to adjust the output channel if the user is not entirely happy with the picture quality.

If no response is received at step S145 within 10 seconds, then the STB switches off the red led and returns to step 131 to resume scanning of its output frequency. If the user responds by adjusting the output channel in step S149, the STB reverts back to step S139 to check if the newly selected output channel is acceptable.

If the user confirms the choice of output channel by pressing standby/setup 19 or select 47, the STB I saves the output channel information and turns off the red LED, the scan of incoming digital channels in step S109 of figure 3 is then commenced and the remainder of the steps of the flow chart of figure 3 are completed.

If the output frequency is scanned through its whole range and no welcome screen appears or if bad interference is encountered, (for example, from a VCR or other analogue channels received by the STB 1), the selected free TV channel may not be appropriate. In this situation, the viewer can select another free channel on the TV and tune the STB to this channel.

Although the STB can scan through its preferred output channels, the user may also manually step the frequency of the output of the STB by pressing the up or down buttons 35 on the remote control 11.

The STB is configured to place a previously rejected output channel frequency at the bottom of its list of preferred output channels so that there is little chance of picking this output frequency again.

The STB will indicate to the user that it is has stepped through all of its output channels using its green and/or red LED.

The above description has concentrated on the initial set up of the system.

However, some of the above functions are performed again after set up.

When the standby button is pressed in normal viewing mode, the STB I enters standby mode and performs a scan of the received digital channels. If new channels are detected, the STB outputs an OSD message the next time the STB is removed from standby to inform the user of the new channels and requests the user to re-scan to add these channels. If existing channels are no longer detected, then they are not removed from the channel list.

When the STB 1 performs this scanning routine, the standby mode can be exited by pressing either standby/setup button 19 on the STB I or standby button 31 on the remote control 11. This causes the scanning of incoming channels to stop and to output the previously selected channel.

When the STB exits standby mode, it first checks to see if the initial set-up (described with reference to figures 3 to 5) has been completed. If it has not be completed, then it enters the set-up mode automatically. If set-up has been completed, the STB I retrieves the last watched channel from the memory and displays it. If the last watched channel is unavailable, for example if it has become scrambled, the STB will either output an OSD warning that this channel is not available or it will tune to the first available channel.

Figure 6 schematically illustrates the main components of the STB I of figure 1.

The STB 1 comprises three main sections: signal receiving section 51 which receives and demodulates signals received from aerial 3; digital signal processing section 53 which receives a demodulated digital signal from the signal receiving section 51 and processes it via audio and video baseband signal outputs 55 and 57 ; and

signal output section 72 which receives the audio and video baseband signals 55 and 57 and converts them into a signal which can be received by a standard analogue television. this section also received analogue signals from the signal receiving section for output with the converted digital signal.

Aerial 3 collects both analogue and digital broadcasts and sends them via cable 5 to signal receiving section 51. Signal receiving section 51 comprises RF tuner 59, which receives the signal from aerial 3. The receiving section 51, further comprises COFDM demodulator chip 61 which receives signals from RF tuner 59.

Digital television signals are broadcast using coded orthogonal frequency division multiplexing (COFDM). The digital data is sent using either 1,705 carriers or 6,817 carriers. To carry the digital data, each carrier is modulated using QPSK (where each carrier is a 2 bit carrier), 16-QAM (where each carrier is a 4 bit carrier) or 64QAM (where each carrier is a 6 bit carrier). Analogue signals are transmitted using one of the standard analogue transmissions protocols such as NTSC. PAL or SECAM.

COFDM demodulator 61 demodulates the COFDM signal.

Before the digital signal is broadcast, it is compressed using MPEG-2. The COFDM demodulator 61 outputs an MPEG-2 encoded signal. This is outputted into MPEG transport stream 63. The MPEG-2 signal is then processed in digital signal output section 53.

In this section, the MPEG signal is first demultiplexed using MPEG demultiplexer 67. The output from the MPEG demultiplexer 67 is then fed into MPEG decoder 69 which outputs audio signal 55 and video signal 57. Audio signal 55 and video signal 57 are baseband signals (Composite video with blanking and sync-CVBS and component red, green and blue-RGB for video and simple analogue for audio) which can be displayed by an analogue television set equipped with a suitable input socket (e. g. a peritelevision or"scart"socket).

In addition to the MPEG demultiplexer 67 and the MPEG decoder 69, the digital signal output section may further comprise a descrambler 77 which allows decoding of

scrambled MPEG signals. Even free-to-view digital signals are often scrambled to prevent them from being received in non-authorised countries or even in certain regions of the broadcasting country. This is necessary because of restrictions placed on the allowed territorial extent of broadcasts due to copyright and associated legal rights.

To control the STB, a processing unit 81 is provided in digital signal output section 53. The processing unit will also control certain operations performed by the receiving unit 51. Processor 81 executes the STB application which is stored in permanent memory unit 83. Permanent memory unit 83 may be a flash type memory or be provided by a simple ROM type memory. Processor 81, MPEG demultiplexer 67 and the MPEG decoder 69 use a synchronous DRAM (SDRAM) memory 79 for data storage in the execution of their tasks. This memory may also be used to store the STB application for execution (following transfer of this from the flash or ROM memory), to gain speed and flexibility advantages over execution from flash or ROM memories.

The STB application primarily serves to allow user interaction with the STB and to ensure that the STB behaves in a predictable and reliable fashion.

Specifically, this program controls the following: I. It initiates the first service once the power is switched on; 2. It performs a channel changing operation instructed by the user via either remote control I I or local control interface 13; 3. It supports the sending of messages for displaying on the television screen 10 (figure I) for user interaction; 4. It provides partial service information. for example, digital data described in the delivery system content and schedule/timing of broadcast datastreams; and 5. It monitors the propagation of errors and sends warnings to the viewer when errors are noted.

In addition to the permanent memory 83, the system also comprises a nonvolatile programmable memory 65 which will typically be an EEPROM.

The non-volatile programmable memory 65 is used to store information which needs to be maintained when the power supply is switched off. but which will need to be frequently changed over time. or which is specific to the particular user installation.

This stores the following: I. The previously viewed digital channel, selected by the viewer using either remote control I I or local control interface 13; 2. The previously selected widescreen mode, selected using button 48 on the remote control 11 ; 3. The previously selected frequency of the output signal; 4. The channel allocation map, storing the results of the last digital channel scan performed by RF tuner 59; and 5. Factory set information such as output levels etc.

6. Flags to indicate the state of the STB during production and user installation, such as'tested OK","never installed","fully installed and working", etc.

Audio signal 55 and video signal 57 are together fed into the signal output section 72 which comprises UHF Remodulator 73. UHF remodulator 73 forms them in to a single frequency analogue Television output signal in the VHF or UHF frequency spectrum. The UHF Remodulator 73 also comprises means for varying the frequencies of the output signal to allow the STB to be tuned to the television.

If a SCART output is additionally provided, the audio signal 55 and video signal 57 are also sent to the SCART output.

In addition to the digital signals as described above, the RF tuner 59 may also receive analogue signals. Thus, in this example, the RF tuner has a second output 71 which feeds into the UHF remodulator 73. UHF remodulator 73 modulates the baseband audio and video signals 55,57 and mixes this signal with the tuner output 71, then outputs this mixture via television output 75. The UHF remodulator 73 is described in more detail with reference to figure 7.

Figure 7 schematically illustrates the main components of remodulator 73. The remodulator comprises four main sections: a BST section 81 ; a modulator section 83 : a VCO and PLL section 85; and a BUS section 87.

The video and audio baseband signals 55 and 57 are received by the modulator section 83. The modulator section converts the video 55 and audio signals into PAL style signals. The frequency, or more correctly frequencies, of the PAL output signal of the modulator section are modulated by the output from the VCO and PLL section 85 which operates under the control of signals received from BUS section 87.

The BUS section 87 receives commands from the processing unit 81 located in the digital signal processing section. Thus, when the STB receives instructions from the user to scan the output frequency of the digital output, the CPU sends the appropriate instructions via BUS section 87 to VCO and PLL section 85 which physically controls the output frequencies of the PAL signal from the modulator section 83.

The BST section 81 receives the PAL signal from the modulator section 83 and analogue signals direct from tuner 59 in the signal receiving section 51 to form a loopthrough. The analogue signals and the PAL signal from modulator section 83 are mixed together in the BST section and outputted as TV output signal 74.

The previous description described the STB 1 being directed to television 9.

However, the STB may also be connected to the television 9 via video recorder 91 as illustrated in figure 8. In such a system, the STB must be connected upstream of the video 91.

During set-up, the video recorder must be turned on (not on standby) to ensure that the selected output frequency of the STB is not interfered with by the video recorder output frequency. The frequency of the output signal from the STB may then be tuned to the video recorder as opposed to a television.

As with standard digital set-top boxes. it is not possible to record a different digital channel to the one being viewed on the television screen since the STB only outputs one digital channel at a time.

Also, while recording a digital channel, the VCR will record any information displayed on the television screen or presented to the audio channels. To overcome this problem, the set-top box may output to a VCR via a scart connector which may provide a clean AV feed.

The above specific example relates to a set-top box which detects digital signals sent over a terrestrial wireless transmission system. However, it will be appreciated by those skilled in the art that the present invention could also be adapted to receive digital signals transmitted via satellites, cable or other wired or wireless mediums. The structure of the set-top box for these uses remains similar to that described with reference to Figure 6. However, the signal receiving unit 51 would be replaced with a signal receiving unit suitable for receiving satellite, cable or other digital signals.

Claims

CLAIMS: 1. A broadcast receiving apparatus comprising: receiving means to receive and decode broadcast signals; output means to output the decoded broadcast signals in a form of a standard analogue TV output signal suitable for receipt by a standard analogue receiving apparatus; and tuning means to vary a frequency of the output signal.
2. An apparatus according to claim 1, wherein the output signal comprises a plurality of discrete frequencies with a fixed relationship to one another. and said tuning means comprises means to vary the frequencies of the output signal.
3. An apparatus according to any preceding claim, further comprising a user interface configured to control the tuning means in response to user inputs.
4. An apparatus according to claim 3, further comprising a control remote from the output means for providing user inputs.
5. An apparatus according to either of claims 3 or 4, wherein the tuning means is configured to change the output frequency of the output signal until a user input is received from the user interface to select an output frequency.
6. An apparatus according to claim 5, further comprising processor means configured to establish if an unsuitable output frequency has been selected.
7. An apparatus according to claim 6, wherein said processor means is configured to prompt said user to confirm if an the selected output frequency is suitable or unsuitable.
8. An apparatus according to either of claims 6 or 7, wherein said apparatus comprises memory means and said processor is configured to establish if an unsuitable frequency has been selected from data stored in said memory means.

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9. An apparatus according to any of claims 6 to 8. comprising memory means for storing details of previously selected unsuitable channels and/or frequencies.
10. An apparatus according to any preceding claim. wherein the output signal is selected from one of a plurality of predetermined different frequency output channels and said tuning means comprises means to change the output signal to a different one of said output channels.
11. An apparatus according to claim 10, when dependent on claim 9. wherein the tuning means is configured to scan through the predetermined output channels one by one leaving channels with unsuitable frequencies until last.
12. An apparatus according to either of claims 10 or l l, wherein the tuning means is configured to step the output signal to just the next available channel in response to a single user input, such that a user can step through the available output channels by continually providing a user response.
13. An apparatus according to any preceding claim, wherein the apparatus has a setup mode and in said set-up mode, the output signal carries a test signal.
14. An apparatus according to claim 13, wherein the apparatus is configured to be connected to a television having a plurality of receiving channels wherein at least one channel is designated to receive the output signal, said receiving channel displaying a test image when the output signal is tuned to that of the designated channel.
15. An apparatus according to any preceding claim, wherein the output signal is a VHF or UHF signal.
16. An apparatus according to claim 15, wherein the output signal is a PAL, NTSC or SECAM signal

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17. An apparatus according to any preceding claim, wherein the broadcast signals are digital signals.
18. An apparatus according to any preceding claim. further comprising an output cable to carry the output signal. wherein said output cable is configured to connect to the standard television aerial input of a video recorder or television.
19. An apparatus according to any of claims 1 to 18. further comprising a scart (peritelevision) connector for outputting audio and video signals.
20. An apparatus according to any preceding claim, configured to output both the output signal and the received broadcast signal such that both analogue and digital signals are outputted.
21. A method of operating an apparatus for receiving broadcast signals for a television, the apparatus comprising means for receiving and decoding broadcast signals and outputting the decoded signals as an output signal, the television having a plurality of channels for displaying received signals and at least one designated channel for displaying the output signal, the method comprising changing the frequency of the output signal until the frequency of the output signal tunes to that of the designated channel of the receiving device.
22. An apparatus according as substantially hereinbefore described with reference to any of the accompanying drawings.
23. A method of operating an apparatus as substantially hereinbefore described with reference to any of the accompanying figures.