Digital broadcast receiver having a time shifting function

A digital broadcast receiver for realizing functions approximately corresponding to those of a VCR by utilizing a time shifting service broadcasting the same program on a plurality of channels which are time-shifted from one another in broadcasting the program by varying periods of delay time. For example in resuming viewing after an interruption of viewing on the desired one of the channels to realize the function of pause, the channel is determined the delay time of which relative to the channel initially viewed is greater than and most approximate to the interruption period, and the initial channel is automatically changed over to the channel thus determined.

FIELD OF THE INVENTION 
The present invention relates to digital broadcast receivers, and more 
particularly to a digital broadcast receiver which is adapted for 
automatic channel change-over according to the contemplated purpose. 
BACKGROUND OF THE INVENTION 
Digital broadcasting systems are scheduled to provide a time shifting 
service to broadcast a particular program on a plurality of channels A to 
E as offset by stepwise varying periods of delay time as shown in FIG. 7. 
When the subscriber performs a viewing starting procedure for the time 
shifting service before the broadcast starting time of the channel on 
which the broadcast starts latest, the broadcast starts immediately 
thereafter on one of the channels, so that a near video on demand function 
resembling a video on demand function can be realized with respect to 
channel selection. 
The video on demand service provides the same function of pause, rewind or 
fast forward as is available with a video cassette recorder (VCR), whereas 
the near video on demand service is not adapted for such a function of the 
VCR since a plurality of subscribers watch a program on a single channel. 
On the other hand, U.S. Pat. No. 5,357,276 proposes a method of realizing 
functions nearly corresponding to the functions of pause, rewind and fast 
forward of the VCR by utilizing a time shifting broadcast service. With 
this method, however, the amounts of time shift of a plurality of channels 
are registered as fixed values in advance, so that if the time shift data 
is altered after the registration, an error is likely to occur unless the 
time shift data is updated. Further since one channel is merely changed 
over to another by a single keying action in realizing the function 
generally corresponding to rewind or fast forward, key manipulation must 
be repeated a number of times to reach the desired channel, hence a 
cumbersome procedure. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a digital broadcast 
receiver which is adapted to realize functions corresponding to those of 
pause, rewind and fast forward of the VCR free of errors and by a simple 
procedure utilizing a time shifting broadcast service. 
The present invention provides a first digital broadcast receiver for 
receiving a time shifting service broadcasting the same program on a 
plurality of channels which are time-shifted from one another in 
broadcasting the program by varying periods of delay time, to realize a 
function approximately corresponding to that of pause (interruption of 
viewing) of a VCR, the receiver comprising manipulation means for 
inputting a viewing interrupt command and a viewing resuming command, time 
measuring means for measuring the period of interrupt time after the 
viewing interrupt command is given and until the viewing resuming command 
is given, memory means for obtaining and storing the delay time of the 
plurality of channels, search means for searching the memory means in 
response to the viewing resuming command and determining the channel the 
delay time of which relative to the channel initially viewed is greater 
than and most approximate to the interrupt time, and channel change means 
for changing over the channel initially viewed to the channel determined. 
When the subscriber gives a viewing interrupt command while viewing one of 
the channels on the digital broadcast receiver described, the time 
measuring means immediately starts to measure time. When the subscriber 
thereafter gives a viewing resuming command, the time measuring means 
calculates the period of interrupt time and feeds the result to the search 
means. Upon or prior to the transmission of the viewing resuming command, 
the memory means obtains the delay time of the channels from multiplexed 
data sent forward by digital broadcasting and stores the delay time. 
The search means thereafter searches the memory means and determines the 
channel to which the channel initially viewed is to be changed over. Since 
the channel determined has relative to the initial channel a delay time 
greater than the interrupt time, no portion of the program will be missed 
despite the change of channel. Further because the delay time of the 
channel determined relative to the initial channel is most approximate to 
the interrupt time, the overlapping portion of the.program involved in 
viewing can be minimized. 
When the memory means is adapted to obtain the delay time upon the 
transmission of the viewing resuming command, the latest data as to the 
delay time of the channels is available, with the result that even if an 
alteration is made in the delay time before the viewing resuming command 
is given, an accurate pause operation can be realized based on the altered 
data. 
The present invention provides a second digital receiver for receiving a 
time shifting service broadcasting the same program on a plurality of 
channels which are time-shifted from one another in broadcasting the 
program by varying periods of delay time, to realize a function 
approximately corresponding to rewind or fast forward of a VCR, the 
receiver comprising manipulation means for inputting a time difference for 
rewind or fast forward, memory means for obtaining and storing the delay 
time of the plurality of channels, calculation means for calculating a 
target delay time upon input of the time difference by adding or 
subtracting the input time difference to or from the delay time of the 
channel currently being viewed, search means for searching for the channel 
having a delay time most approximate to the target delay time, and channel 
change means for changing over the initially viewed channel to the channel 
searched for. 
When the subscriber inputs a command for reverse corresponding to rewind of 
the VCR or a command for forward corresponding to fast forward of the VCR 
and inputs a desired time difference while viewing one of the channels on 
the digital receiver described, the input data is fed to the calculation 
means. Upon or prior to the input of the time difference, the memory means 
obtains the delay time of the channels from multiplexed data forwarded by 
digital broadcasting and stores the delay time. 
The calculation means then adds (in the case of reverse), or subtracts (in 
the case of forward) the input time difference to or from the delay time 
of the channel currently being viewed to calculate a target delay time. 
The result of calculation is fed to the search means. 
With reference to the result, the search means searches the memory means 
and determines the channel to which the initially viewed channel is to be 
changed over. Since the channel determined has a delay time most 
approximate to the target delay time relative to the initial channel, the 
desired reverse (or forward) operation will be realized. 
When the memory means is adapted to obtain the delay time upon the input of 
the desired time difference, the latest data as to the delay time of the 
channels is available, with the result that even if an alteration is made 
in the delay time before the time difference is input, an accurate reverse 
or forward operation can be realized based on the altered data. 
As described above, the digital broadcast receivers embodying the invention 
realize a function corresponding to the function of pause, reverse or fast 
forward of the VCR by utilizing a time shifting broadcast service.

DETAILED DESCRIPTION OF EMBODIMENT 
An embodiment of the invention will be described below in detail with 
reference to the drawings. 
FIG. 1 shows the construction of a digital broadcast receiver according to 
the invention. 
A digital broadcast signal received by a tuner 1 is fed to a demodulation 
circuit 2 and thereby demodulated to digital data, which is then passed 
through an error correction circuit 3 for the correction of errors and 
thereafter separated as desired into video, audio and control data by a 
data separation circuit 4. 
The video data separated is fed to a video output circuit 5, by which the 
data is decoded into a video signal and then delivered to a display device 
(not shown). The audio data separated is fed to an audio output circuit 6 
and thereby decoded into an audio signal, which is then output to a 
speaker device (not shown). The control data separated is fed to a control 
circuit 7. 
The control circuit 7 decodes the control data and manipulation data input 
from a manual input device 8 to control the overall receiver in accordance 
with the results of decoding. 
Usable as the manual input device 8 is an infrared remote controller shown 
in FIG. 2. The remote controller has common manual keys, i.e., POWER key 
10, CHANNEL UP key 11, CHANNEL DOWN key 12, VOLUME UP key 13, VOLUME DOWN 
key 14, numeric keys 15 for entering, for example, the number of channel 
to be viewed and ENTER key 16 to be manipulated after a numerical value is 
keyed in with use of numeric keys. Also arranged on the remote controller 
are manipulation keys characteristic of the invention, i.e., NVOD (near 
video on demand) key 17 to be pressed for NVOD viewing, and reverse key 
18, pause key 19 and forward key 20 to be manipulated respectively for 
reverse, pause and forward as will be described later. The numeric keys 15 
are used also for inputting time data for the reverse procedure or forward 
procedure. 
FIG. 4(a) shows the packet structure of multiplexed digital data (transport 
stream) for digital broadcasting. Each packet comprises a header portion 
and a payload portion. 
The header portion includes the first to eighth bits serving as a 
synchronization byte for effecting packet synchronization, and the twelfth 
to twenty-fourth bits serving as a packet identification number (PID). 
This value indicates the attribute of data of the payload portion. The 
data separation circuit 4 of FIG. 1 extracts the packet of specified PID 
in response to a command from the control circuit 7. 
The payload portion shown in FIG. 4(a) includes the first to eighth bits 
providing a table ID to represent the type of the data included in the 
payload portion. The attribute and type of all the data can be detected 
from the combination of the PID of the header portion and the table ID of 
the payload portion, making possible the data separation by the data 
separation circuit 4 of FIG. 1. 
According to the present embodiment, 100 is assigned to the PID, and 100 to 
the table ID, and the data portion is given the format shown in FIG. 4(b). 
Sixteen bits are used for the channel number, and eight bits for the delay 
time (in minutes). A required umber of such 24-bit groups are repeated 
from the starting end of the data portion. A channel number comprising 
bits 1 only is attached to the tail end of the data. 
FIG. 3 shows a procedure for receiving time shifting broadcast service by 
the digital broadcast receiver described. 
After the power source is turned on by pressing the POWER key 10, a channel 
providing the time shifting service is selected by pressing the CHANNEL UP 
key 11, CHANNEL DOWN key 12 or numeric key(s) 15. The NVOD key 17 is then 
pressed, whereupon a request for NVOD viewing is made in step S1 of FIG. 
3, followed by a viewing procedure including a request for charging. 
Consequently when the time comes to start the selected program, step S2 is 
executed for the subscriber to start to view the program. 
Step S3 then checks which of the pause key 19, reverse key 18 and forward 
key 20 has been pressed. Step S4 follows when the pause key is pressed, or 
step S7 follows when the reverse key is pressed, or step S8 follows if the 
forward key is pressed. The sequence advances to step S10 if none of these 
keys is pressed. 
When the pause key is pressed, program delay data as to the channel 
currently being viewed is stored along with the current time in step S4. 
FIG. 5(a) shows an example of what is stored at this time. 
Subsequently, an inquiry is made in step S5 of FIG. 3 as to whether a 
command is given to terminate the pause. When the answer is affirmative, 
step S6 follows to calculate the time elapsed from the current time stored 
as stated above, i.e., an interrupt time. Furthermore, program delay data 
as to all channels on which the same program is being broadcast is 
obtained and stored. FIG. 5(b) shows an example of which is stored at this 
time. The program was available on three channels A, B and C at the time 
when the pause was started, while the program is broadcast additionally on 
four channels D to G when the pause is terminated. 
Further in step S6 of FIG. 3, the destination channel to be accessed by 
skipping is determined based on the interrupt time and the program delay 
data. More specifically, the program delay data is checked to select the 
channel whose delay time relative to the channel initially viewed is 
greater than the interrupt time and most approximate to the interrupt 
time. 
If no corresponding channel is found, the channel whose relative delay time 
is greatest is selected. If the initially viewed channel is the final 
channel, the final channel is to be selected. 
Since the interrupt time is 40 minutes in the case of the examples of FIGS. 
5(a) and 5(b), the channel E (45 minutes in relative delay time) is 
selected the delay time of which relative to the channel B initially 
viewed is greater than 40 minutes and most approximate to 40 minutes. 
A channel change-over is thereafter made in step S9 of FIG. 3. For example, 
suppose a channel with a delay of 15 minutes is selected in the case where 
the interrupt time after the start of the pause and until the termination 
of the pause is 10 minutes as seen in FIG. 6. The channel change is then 
made upon the termination of the pause. Although this results in a 
5-minute overlapping portion in viewing the program, no portion of the 
program will be missed. 
An inquiry is made in step S10 as to whether the program has come to an 
end. The sequence returns to step S3 if the answer is negative. The NVOD 
viewing procedure is terminated when the answer is affirmative. 
When the reverse key is pressed, step S7 is performed to obtain program 
delay data and thereafter determine a target delay time by adding a 
desired reverse time to the delay time of the channel currently being 
viewed. The channel having a delay time most approximate to the target 
delay time is then selected and determined as the destination channel to 
be accessed by skipping. For example, when the controller is manipulated 
for 20-minute reverse during viewing the channel B in the example of FIG. 
5(b), 20 minutes is added to the 15-minute delay time of the channel B to 
determine a 35-minute target delay time. The channel C having a delay time 
(30 minutes) most approximate to this target delay time is then determined 
as the destination channel. 
Alternatively, it is possible to select the channel having a delay time 
greater than the target delay time and most approximate to the target 
delay time and determine this channel as the destination channel. For 
example, when a command for 20-minute reverse is given while the channel B 
is being viewed in the example of FIG. 5(b), the channel D is selected 
which has a delay time (45 minutes) greater than the target delay time of 
35 minutes and most approximate to 35 minutes. 
Step S9 then follows for a channel change-over. An inquiry is made in step 
S10 as to whether the program has come to an end. The sequence returns to 
step S3 if the answer is negative. The NVOD viewing procedure is 
terminated when the answer is affirmative. 
When the forward key is pressed, step S8 is performed to obtain program 
delay data and thereafter subtract a desired forward time from the delay 
time of the channel currently being viewed, whereby a target delay time is 
determined. The channel having a delay time most approximate to the target 
delay time is selected and determined as the destination channel to be 
accessed by skipping. 
For example, when the controller is manipulated for 20-minute forward 
during viewing the channel E in the example of FIG. 5(b), 20 minutes is 
subtracted from the 60-minute delay time of the channel E to determine a 
40-minute target delay time. The channel D having a delay time (45 
minutes) most approximate to this target delay time is then determined as 
the destination channel. 
Alternatively, it is possible to select the channel having a delay time 
smaller than the target delay time and most approximate to the target 
delay time and determine this channel as the destination channel. For 
example, when a command for 20-minute forward is given while the channel E 
is being viewed in the example of FIG. 5(b), the channel C is selected 
which has a delay time (30 minutes) smaller than the target delay time of 
40 minutes and most approximate to 40 minutes. 
Step S9 then follows for a channel change-over. An inquiry is made in step 
S10 as to whether the program has come to an end. The sequence returns to 
step S3 if the answer is negative. The NVOD viewing procedure is 
terminated when the answer is affirmative. 
As described above, the digital broadcast receiver embodying the invention 
is adapted to realize functions resembling the functions of pause, rewind 
and fast forward of a VCR. In connection with pause, especially, viewing 
can be resumed immediately after the controller is manipulated for the 
termination of pause without the likelihood of missing any portion of the 
program. Further for rewind or fast forward, the desired time difference 
is input, thereby ensuring an immediate and rapid change-over to a channel 
on which the program is available with a time difference most approximate 
to the contemplated rewind time or fast-forward time, or to a channel on 
which there is no likelihood of missing any portion of the program to be 
viewed by rewind or fast forward. 
The embodiment described above is intended to illustrate the present 
invention and should not be construed as limiting the invention defined in 
the appended claims or restricting the scope thereof. The receiver of the 
present invention is not limited to the foregoing embodiment in 
construction but can of course be modified variously without departing 
from the spirit of the invention as set forth in the claims.