U.S. patent application number 12/806456 was filed with the patent office on 2010-12-16 for robust mode staggercasting fast channel change.
Invention is credited to Jill MacDonald Boyce, Jeffrey Allen Cooper, Kumar Ramaswamy.
Application Number | 20100315561 12/806456 |
Document ID | / |
Family ID | 36568629 |
Filed Date | 2010-12-16 |
United States Patent
Application |
20100315561 |
Kind Code |
A1 |
Cooper; Jeffrey Allen ; et
al. |
December 16, 2010 |
Robust mode staggercasting fast channel change
Abstract
A method and apparatus for staggercasting a plurality of content
representative signals includes encoding a first and a
corresponding second signal representing each of the plurality of
content representative signals. A composite signal is generated
comprising the plurality of first and second encoded signals. In
the composite signal, each respective second encoded signal is
delayed with respect to the corresponding first encoded signal. The
first and second encoded signal representing a selected one of the
content representative signals is extracted to reproduce the
selected content representative signal. The extracted first encoded
signal is decoded if an error is detected in the extracted second
encoded signal, otherwise the extracted second encoded signal is
decoded. When a different content representative signal is newly
selected, the first extracted encoded signal is decoded until the
delayed second extracted encoded signal is available.
Inventors: |
Cooper; Jeffrey Allen;
(Rocky Hill, NJ) ; Boyce; Jill MacDonald;
(Manalapan, NJ) ; Ramaswamy; Kumar; (Princeton,
NJ) |
Correspondence
Address: |
ROBERT D. SHEDD;PATENT OPERATIONS
THOMSON LICENSING LLC, P. O. BOX 5312
PRINCETON
NJ
08543-5312
US
|
Family ID: |
36568629 |
Appl. No.: |
12/806456 |
Filed: |
August 13, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10543481 |
Jul 26, 2005 |
7810124 |
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PCT/US2004/001769 |
Jan 23, 2004 |
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12806456 |
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60443672 |
Jan 28, 2003 |
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Current U.S.
Class: |
348/726 ;
348/731; 348/E5.097; 348/E5.113 |
Current CPC
Class: |
H04N 21/44209 20130101;
H04N 21/4384 20130101; H04N 7/17318 20130101; H04N 21/4349
20130101; H04N 21/26275 20130101 |
Class at
Publication: |
348/726 ;
348/731; 348/E05.113; 348/E05.097 |
International
Class: |
H04N 5/455 20060101
H04N005/455; H04N 5/50 20060101 H04N005/50 |
Claims
1. A method for staggercasting a plurality of content
representative signals, comprising the steps of: for each of the
plurality of content representative signals: encoding a first
signal representing the content; and encoding a second signal
corresponding to the first encoded signal; generating a composite
signal comprising the plurality of first and second encoded signals
wherein each respective second encoded signal is delayed with
respect to the corresponding first encoded signal; extracting the
first and second encoded signal representing a selected one of the
content representative signals to reproduce the selected content
representative signal; decoding the extracted first encoded signal
if an error is detected in the extracted second encoded signal,
otherwise decoding the extracted second encoded signal; and when a
different content representative signal is newly selected, decoding
the first extracted encoded signal until the delayed second
extracted encoded signal is available.
2. (canceled)
3. (canceled)
4. (canceled)
5. (canceled)
6. (canceled)
7. (canceled)
8. A staggercasting receiver, for receiving a composite signal
comprising a plurality of first and corresponding second encoded
signals representing a corresponding plurality of content
representative signals, wherein each respective second encoded
signal is delayed with respect to the corresponding first encoded
signal, comprising: a demultiplexer, responsive to the composite
signal, for extracting the first and second encoded signals
representing a selected one of the plurality of content
representative signal and generating an error signal representing
an error in the first and second encoded signals; a decoder,
coupled to the demodulator, for: decoding the extracted first
encoded signal if an error is detected in the extracted second
encoded signal, otherwise decoding the extracted second encoded
signal; and when a different content representative signal is newly
selected, decoding the first extracted encoded signal until the
delayed second extracted encoded signal is available.
9. (canceled)
10. (canceled)
11. (canceled)
12. (canceled)
13. (canceled)
14. A method for processing a received staggercasted signal
represented by a composite signal comprising a plurality of first
and corresponding second encoded signals representing a
corresponding plurality of content representative signals, wherein
each respective second encoded signal is delayed with respect to
the corresponding first encoded signal, comprising the steps of:
extracting the first and second encoded signals representing a
selected one of the plurality of content representative signal and
generating an error signal representing an error in the first and
second encoded signals; decoding the extracted first encoded signal
if an error is detected in the extracted second encoded signal,
otherwise decoding the extracted second encoded signal; and when a
different content representative signal is newly selected, decoding
the first extracted encoded signal until the delayed second
extracted encoded signal is available.
15. (canceled)
16. (canceled)
17. (canceled)
Description
[0001] The present patent application claims priority from
provisional patent application No. 60/443,672 filed on Jan. 28,
2003.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to staggercasting methods and
apparatus.
[0004] 2. Background of the Invention
[0005] Current digital television transmission standards in the
United States, as proposed by the Advanced Television Systems
Committee (ATSC) dated Sep. 16, 1995, incorporated by reference
herein, use a single carrier modulation technique: eight level
vestigial sideband modulation (8-VSB). Because it is a single
carrier modulation technique, it is susceptible to signal
degradation in the communications channel, such as fading caused by
multipath and other signal attenuation. While some such fading may
be compensated by channel equalization techniques, if the fade is
long enough and severe enough, then the receiver will lose the
signal and the demodulator system will lose synchronization.
Reacquiring the signal, and resynchronizing the demodulator can
take several seconds and is quite objectionable to a viewer.
[0006] To overcome this problem, a first ATSC proposal permits
creation of a second communications channel by permitting use of a
more robust modulation technique for a limited period of time, e.g.
less than 10%. For example, a 2 or 4-VSB modulation technique may
be used for selected frames. A second ATSC proposal permits a more
robust encoding technique, e.g. trellis encoding, while maintaining
an 8-VSB modulation technique. Such a system permits improved
performance with compatible receivers while maintaining backwards
compatibility with existing receivers.
[0007] Another known technique for overcoming fading is
staggercasting. PCT Application No. US02/22723 filed Jul. 17, 2002,
by K. Ramaswamy, et al., and PCT Application No. US02/23032 filed
Jul. 19, 2002 by J. A. Cooper, et al., incorporated by reference
herein, disclose staggercasting communications systems.
Staggercasting communications systems transmit a composite signal
including two component content representative signals: one of
which is delayed with respect to the other. Put another way, one of
the component content representative signals is advanced with
respect to the other. The composite signal is broadcast to one or
more receivers through a communications channel. At a receiver, the
advanced-in-time component content representative signal is delayed
through a delay buffer so that it becomes resynchronized in time
with the other component content representative signal. Under
normal conditions, the undelayed received component content
representative signal is used to reproduce the content. If,
however, a signal fade occurs, then the previously received and
advanced-in-time content representative signal in the delay buffer
is used to reproduce the content until either the fade ends and the
composite signal is available again, or the delay buffer empties.
If the delay period, and the associated delay buffer, is large
enough then most probable fades may be compensated for.
[0008] PCT Application No. US02/22723 filed Jul. 17, 2002, by K.
Ramaswamy, et al., and PCT Application No. US02/23032 filed Jul.
19, 2002 by J. A. Cooper, et al. also disclose a staggercasting
system in which one of the component signals in the composite
signal represents the content at a higher quality than the other
component signal. In this arrangement, the lower quality component
signal is advanced in time relative to the higher quality component
signal. As described above, at the receiver under normal
conditions, the undelayed received component, which in this case is
the higher quality component signal, is used to reproduce the
content. If, however, a signal fade occurs, then the previously
received and advanced-in-time content representative signal, which
in this case is the lower quality component signal, in the delay
buffer is used to reproduce the content until either the fade ends
and the composite signal is available again, or the delay buffer
empties. This permits reproduction of a higher quality signal under
normal conditions, and reproduction of a lower quality signal in
the presence of a fade event. Because the lower quality signal
requires fewer bits to transmit, the overhead required to provide
fade resistance is decreased.
[0009] The systems disclosed in PCT Application No. US02/22723
filed Jul. 17, 2002, by K. Ramaswamy, et al., and PCT Application
No. US02/23032 filed Jul. 19, 2002 by J. A. Cooper, et al., may be
used to transmit a plurality of content representative signals,
each staggercasted using a first and a delayed second component
signal. When a new content representative signal is selected by a
viewer, the delay buffer in the receiver must fill before the
second component signal may be decoded. This delay period is
annoying to a viewer and therefore undesirable. A system which can
decrease the time required between when a new content
representative signal is selected and when it begins to be decoded
and displayed is desirable.
BRIEF SUMMARY OF THE INVENTION
[0010] In accordance with principles of the present invention, a
method and apparatus for staggercasting a plurality of content
representative signals includes encoding a first and a
corresponding second signal representing each of the plurality of
content representative signals. A composite signal is generated
comprising the plurality of first and second encoded signals. In
the composite signal, each respective second encoded signal is
delayed with respect to the corresponding first encoded signal. The
first and second encoded signal representing a selected one of the
content representative signals is extracted to reproduce the
selected content representative signal. The extracted first encoded
signal is decoded if an error is detected in the extracted second
encoded signal, otherwise the extracted second encoded signal is
decoded. When a different content representative signal is newly
selected, the first extracted encoded signal is decoded until the
delayed second extracted encoded signal is available.
BRIEF DESCRIPTION OF THE DRAWING
[0011] FIG. 1 is a block diagram of a portion of a staggercasting
transmitter;
[0012] FIG. 2 is a block diagram of a portion of a staggercasting
receiver;
[0013] FIG. 3 is a packet timing diagram useful in understanding
the operation of the staggercasting communications system
illustrated in FIG. 1 and FIG. 2;
[0014] FIG. 4 is a GOP timing diagram useful in understanding the
operation of an enhanced staggercasting communications system;
[0015] FIG. 5 is a block diagram of a selector which may be used in
the receiver illustrated in FIG. 2;
[0016] FIG. 6 is a block diagram of a portion of another embodiment
of a staggercasting receiver;
[0017] FIG. 7 is a video frame timing diagram useful in
understanding the operation of the staggercasting receiver
illustrated in FIG. 6;
[0018] FIG. 8 illustrates an extended syntax and semantics for the
program map table (PMT) and/or program and information systems
protocol--virtual channel table (PSIP-VCT);
[0019] FIG. 9 is a block diagram of a portion of another embodiment
of a staggercasting transmitter for transmitting multiple
resolution version of a content representative signal;
[0020] FIG. 10 is a block diagram of a portion of another
embodiment of a staggercasting receiver for receiving a transmitted
multiple resolution version of a content representative signal;
[0021] FIG. 11 is a block diagram of a portion of a transmitter for
transmitting a dual interlaced content representative signal;
[0022] FIG. 12 is a block diagram of a portion of a receiver for
receiving a dual interlaced content representative signal; and
[0023] FIG. 13 is a display diagram useful in understanding the
operation of the dual interlace transmitter illustrated in FIG. 11
and dual interlace receiver illustrated in FIG. 12.
DETAILED DESCRIPTION OF THE INVENTION
[0024] FIG. 1 is a block diagram of a portion of a staggercasting
transmitter 100 according to principles of the present invention.
One skilled in the art will understand that other elements, not
shown to simplify the figure, are needed for a complete
transmitter. One skilled in the art will further understand what
those elements are and how to select, design, implement and
interconnect those other elements with the illustrated
elements.
[0025] In FIG. 1, a source (not shown) of content, which in the
illustrated embodiment may be a video image signal, audio sound
image, program data, or any combination of these, provides a
content representative signal to an input terminal 105 of the
transmitter 100. The input terminal 105 is coupled to respective
input terminals of a robust mode encoder 110 and a normal mode
encoder 120. An output terminal of the robust mode encoder 110 is
coupled to a first input terminal of a multiplexer 140. An output
terminal of the normal mode encoder 120 is coupled to an input
terminal of a delay device 130. An output terminal of the delay
device 130 is coupled to a second input terminal of the multiplexer
140. An output terminal of the multiplexer 140 is coupled to an
input terminal of a modulator 150. An output terminal of the
modulator 150 is coupled to an output terminal 115. The output
terminal 115 is coupled to a communications channel (not
shown).
[0026] In operation, the normal mode encoder 120 encodes the
content video, audio and/or data using a source encoding technique.
In the illustrated embodiment, the source encoding technique is the
MPEG 2 encoding technique, although any such source encoding
technique may be used. The source encoding process is performed
using predetermined parameters including resolution, frame rate,
quantization level, etc. Further processing is performed in the
normal mode encoder 120 to system encode the source encoded content
representative signal. In the illustrated embodiment, the source
coded content representative signal is formed into a series of
transport packets containing the encoded video, audio and/or data.
These transport packets are formatted according to the MPEG 2
standard, although any such system encoding may be used.
[0027] The robust mode encoder 110 also encodes the content video,
audio and/or data, using a source encoding technique. The source
encoding technique used by the robust mode encoded 110 is more
robust compared with the source encoding technique of the normal
mode encoder 120. In the illustrated embodiment, the robust mode
encoding used is a video coding technique designated MPEG AVC/H.264
currently being developed by the Joint Video Team (JVT) of the
ISO/IEC MPEG and ITU-T VCEG committees, and termed JVT coding
below. However, any such source encoding technique may be used. For
example, other source coding techniques, such as enhanced trellis
coding, which provide robust encoding relative to the MPEG normal
mode encoder 120, may also be used. The robust encoding process is
also performed using predetermined parameters including resolution,
frame rate, quantization level, etc., but the values of these
parameters may be different for the robust encoding process than
those for the normal encoding process. Processing is also performed
in the robust mode encoder 110 to system encode the source encoded
content representative signal. In the illustrated embodiment, the
source coded content representative signal is formed into a series
of transport packets, also according to the MPEG 2 standard,
although, again, any such system encoding may be used.
[0028] The normal mode encoded signal is delayed by the delay
device 130 by an amount intended to allow the system to operate
through a range of expected fade periods. The value of this
parameter depends on the characteristics of the communications
channel. For example, in an urban setting, with many buildings and
moving objects, such a airplanes, fading is much more common and
can last longer than in rural flat settings. In the illustrated
embodiment, the delay may be varied from around 0.5 seconds to
several seconds.
[0029] FIG. 3 is a packet timing diagram useful in understanding
the operation of the staggercasting communications system
illustrated in FIG. 1 and FIG. 2. FIG. 3 illustrates the system
coded transport packet streams at the input terminal of the
multiplexer 140. In FIG. 3, packets from the robust mode encoder
110 are represented by a horizontal row of squares 300, labeled
using lower case letters: "a", "b", "c", and so forth. Packets from
the normal mode encoder 120 are represented by a horizontal row of
squares 310, labeled using numbers: "0", "1", . . . , and upper
case letters: "A", "B", "C", and so forth. Packets labeled by the
same letter contain data representing content from the same time.
That is, packet "a" from the robust mode encoder 110 contains data
representing content which corresponds in time to the content
represented by the data in packet "A" from the normal mode encoder
120. Each packet in the normal mode and robust mode packet streams
contains data in the header identifying them as belong to that
packet stream. The delay device 130 delays the normal mode encoder
120 packets by a time delay T.sub.adv. That is, robust mode packets
are advanced in time by T.sub.adv with respect to corresponding
normal mode packets. In the embodiment illustrated in FIG. 3,
T.sub.adv is ten packet time periods. This time period may vary
from around 0.5 seconds to several seconds, as described above.
[0030] The robust mode and delayed normal mode packet streams are
multiplexed together into a composite packet stream in the
multiplexer 140. The composite packet stream is time domain
multiplexed, meaning that a single data stream carrying successive
packets, one at a time, is produced. Additional packets containing
other data, such as identification and control data (not shown),
may also be multiplexed into the composite packet stream produced
by the multiplexer 140. In addition, other packet streams
representing other content sources (also not shown), possibly
including both normal mode and robust mode packet streams
representing one or more of the other content representative
signals, may also be multiplexed into the composite packet stream
produced by the multiplexer 140, all in a known manner. The packet
streams 300 and 310 in FIG. 3 represent the component content
representative signals in the composite packet stream. As may be
seen, packet "A" from the normal mode encoder 120 is transmitted at
the same time as packet "k" from the robust mode encoder 110.
[0031] The composite packet stream from the multiplexer 140 is then
channel coded for transmission over the communications channel. In
the illustrated embodiment, the channel coding is done by
modulating the composite packet stream in the modulator 150. The
channel coding for the normal mode packet stream is different from
the channel coding for the robust mode packet stream. More
specifically, the modulation applied to the robust mode packet
stream is more robust than that applied to the normal mode packet
stream. In the illustrated embodiment, when packets in the normal
mode packet stream are modulated, the modulation is 8-VSB
modulation according to the ATSC standard. When packets in the
robust mode packet stream are modulated, the modulation is more
robust modulation, for example 4-VSB or 2-VSB, as described
above.
[0032] In short, in the illustrated embodiment, the normal mode
packet stream is source encoded using the MPEG 2 encoding technique
and is channel encoded using 8-VSB modulation. This is fully
backward compatible with the prior ATSC standard. Also in the
illustrated embodiment, the robust mode packet stream is source
encoded using the JVT encoding technique and is channel encoded
using 4-VSB and/or 2-VSB modulation. One skilled in the art will
understand that the new ATSC standard, referred to above, refers
only to the channel encoding of the robust mode packet stream, i.e.
4-VSB and/or 2-VSB, and does not specify a source encoding
technique. Consequently, any such source encoding technique may be
used according to the standard, and the JVT encoding technique in
the illustrated embodiment is one example of such source encoding
for the robust mode packet stream. In the remainder of this
application, `normal mode packet stream` will refer to the packet
stream which is source encoded using the MPEG 2 source encoding
technique, system encoded into packets according to the MPEG 2
standard, and channel encoded using 8-VSB modulation; and `robust
mode packet stream` will refer to packets which are source encoded
using the JVT source encoding technique, system encoded into
packets according to the MPEG 2 standard, and channel encoded using
4-VSB and/or 2-VSB modulation.
[0033] The modulated composite signal is then supplied to the
communications channel (not shown), which may be a wireless RF
channel, or a wired channel, such as a cable television system. The
composite signal may be degraded by the communications channel. For
example, the signal strength of the composite signal may vary. In
particular, the composite may fade due to multipath or other signal
attenuation mechanisms. One or more receivers receive the possibly
degraded composite signal from the communications channel.
[0034] FIG. 2 is a block diagram of a portion of a staggercasting
receiver 200 according to principles of the present invention. In
FIG. 2, an input terminal 205 is connectable to the communications
channel (not shown) so that it is capable of receiving the
modulated composite signal produced by the transmitter 100 (of FIG.
1). The input terminal 205 is coupled to an input terminal of a
demodulator 207. An output terminal of the demodulator 207 is
coupled to an input terminal of a demultiplexer 210. A first output
terminal of the demultiplexer 210 is coupled to a selector 230. A
second output terminal of the demultiplexer 210 is coupled to a
delay device 220. An output terminal of the delay device 220 is
coupled to a second input terminal of the selector 230. An output
terminal of the selector 230 is coupled to a signal input terminal
of a multi-standard decoder 240. A control signal output terminal
of the demultiplexer 210 is coupled to respective corresponding
input terminals of the selector 230 and the multi-standard decoder
240. An output terminal of the multi-standard decoder 240 is
coupled to an output terminal 215 The output terminal 215 produces
a content representative signal which is supplied to utilization
circuitry (not shown) such as a television receiver with an image
reproduction device to reproduce the image represented by the video
content, a sound reproduction device to reproduce the sound
represented by the audio content, and possibly including user input
devices to allow a viewer to interact with the received data
content.
[0035] In operation, the demodulator 207 demodulates the received
modulated signal using the appropriate demodulation techniques
required to receive packets from either the normal mode packet
stream (8-VSB) or robust mode packet stream (4-VSB and/or 2-VSB).
The resulting signal is a received composite packet stream signal.
The received composite packet stream signal is demultiplexed by the
demultiplexer 210 into respective normal mode source encoded and
robust mode source encoded component packet streams according to
the identification data in the header of each received packet. The
received normal mode packet stream is supplied directly to the
selector 230. The received robust mode packet stream is passed
through the delay device 220, which delays the received robust mode
packet stream by the same time duration that, in the transmitter
100 of FIG. 1, the normal packet stream is delayed. Consequently,
the content represented by the two packet stream signals at the
input terminals of the selector 230 is time aligned.
[0036] The demultiplexer 210 also produces an error signal at the
control signal output terminal should a portion of the received
composite signal be unusable. Any of several techniques may be
used, for example, a signal-to-noise ratio detector or a bit-error
rate detector. In addition, an error in the received composite
signal may be detected by detecting missing packets. Each packet
includes in its header both data identifying which packet stream
the packet belongs to and a packet sequence number. If a sequence
number for a packet stream is missed, then a packet is missing, and
an error is detected. In this case, the packet stream from which
the packet is missing may be noted, and only that packet stream
detected as having an error. These or any other such detector may
be used, alone or in combination.
[0037] Although the control signal is illustrated as emanating from
the demultiplexer 210, one skilled in that art will understand that
different error detectors may be require signals from different
places in the receiver. Whatever arrangement is used, an error
signal E is generated which is active when a portion of the
composite signal is unusable. The selector 230 is conditioned to
pass one of the two packet streams signals to the multi-standard
decoder 240 in response to this error signal E. The multi-standard
decoder 240 is conditioned to decode that packet stream signal, in
a manner to be described in more detail below.
[0038] The multi-standard decoder 240 performs both system decoding
(depacketizing) and source decoding of whichever packet stream is
supplied to it by the selector 230. The multi-standard decoder 240
can be configured to perform source decoding of the packet stream
signals according to different coding standards. For example, when
a normal mode encoded packet stream is received from the selector
230, the multi-standard decoder 240 is configured to depacketize
and source decode these packets according to the MPEG 2 standard
and regenerate the content representative signal. Similarly, when a
robust mode encoded packet stream is received from the selector
230, the multi-standard decoder 240 is configured to depacketize
the packets according to the MPEG 2 standard and to source decode
these packets according to the JVT standard, and regenerate the
content representative signal.
[0039] The operation of the receiver 200 of FIG. 2 may be
understood by referring again to FIG. 3. Time t0 may represent the
time when the receiver is turned on, or when a user specifies a new
content source to receive. During the time, T.sub.adv, between t0
and t4, robust mode packets "a" to "j" are loaded into the delay
device 220, and normal mode packets, designated "0" though "9" are
received. At time t4, the normal mode packet "A" becomes available
from the demultiplexer 210 and delayed robust mode packet "a"
becomes available from the delay device 220. Under normal
conditions, the error signal is not active on the error signal line
E. In response, the selector 230 couples the normal mode packet
stream to the multi-standard decoder 240, and the multi-standard
decoder 240 begins to generate the content representative signal
from the normal mode packets, as described above. This is
illustrated by the cross hatching 301 in the normal mode packets
"A" through "G".
[0040] From time t1 to t2 a severe fade occurs in the
communications channel and from time t2 to t3 the receiver recovers
the modulated signal and resynchronizes to that signal. During this
time, from t1 to t3, normal mode packets "H" to "M" and robust mode
packets "r" to "w" are lost. This is indicated by the cross
hatching 302 and 303 in those packets. However, robust mode packets
"h" to "m" have been previously successfully received. Because of
the delay device 220, these robust mode packets are available at
the other input to the selector 230 from time t1 to t3.
[0041] The occurrence of the fade is detected and indicated by an
active error signal on the error signal line E. In response to the
active error signal on the error signal line E, the selector 230
couples the previously received robust mode packets "h" to "m" to
the multi-standard decoder 240. Concurrently, the multi-standard
decoder 240 is configured to depacketize and decode robust mode
packets. Consequently, from time t1 to t3, packets "h" to "m" from
the robust mode packet stream are decoded and the content
representative signal remains available to the utilization
circuitry (not shown). This is illustrated by the cross hatching
301 in the robust mode packets "h" through "m".
[0042] At time t3, the fade ends and the composite signal becomes
available again. Consequently the normal mode packets "N", "O",
"P", . . . , become available. The disappearance of the fade is
detected and indicated by an inactive error signal on the error
signal line E. In response, the selector 230 couples the normal
mode packet stream to the multi-standard decoder 240. Concurrently,
the multi-standard decoder 240 is configured to depacketize and
decode normal mode packets and continues to generate the content
representative signal.
[0043] During the fade and recovery, from time t1 to t3, robust
packets "r" through "w" were lost. Consequently, from time t6
through t7, when normal mode packets "R" through "W" are received,
there are no corresponding robust mode packets in the delay device
220. During this time, there is no protection against a fade.
However, once the delay device is refilled, fade protection becomes
available again.
[0044] As described above, the content representative signal
remains available to the utilization circuitry (not shown) despite
the occurrence of a fade from time t1 to t3. In addition, because
of the robust source coding and channel coding (modulation)
techniques, the robust mode packets are likely to survive more
severe channel degradation, and thus be available when normal mode
packets may not be. The quality of the content signal carried by
the robust mode packet stream may be different from that in the
normal mode packet stream. In particular, the quality of the
content signal in the robust mode packet stream may be lower than
that in the normal mode packet stream. A lower quality content
signal requires fewer bits to transmit than a higher quality
content signal, and such a robust mode packet stream will require a
lower throughput than the normal mode packet stream. Thus, at the
expense of a second, lower throughput packet stream, a system which
will permit a graceful degradation in the event of a fading event
is possible.
[0045] Also as described above, the content signal may include
video, audio and/or data. In particular, audio data may be carried
in both the normal mode packet stream and the robust mode packet
stream so that audio data also remains available despite the
occurrence of a fade. The audio content signal carried by the
robust mode packet stream may have a different quality,
specifically a lower quality, than that in the normal mode packet
stream. An audio signal at a lower quality may be carried by fewer
bits and fewer packets, and, thus, would make relatively low
requirements on the robust mode packet stream. This also would
permit a graceful degradation in the event of a fade event.
[0046] With a system described above, switching from the normal
mode packet stream to the robust mode packet stream may occur at
any time. If the robust packet stream carries content
representative data which is identical to that in the normal packet
stream down to the packet level, this may not present a problem.
However, if the robust packet stream carries content representative
data which is different from that in the normal packet stream, for
example, if the content is represented at a different resolution,
quantization level, frame rate, etc., then the viewer may notice a
change in the reproduced image which may be objectionable. In a
worse case, if a packet stream switch occurs in the middle of
decoding a picture, then the decoding of that picture and other
surrounding pictures may fail altogether, and the video image may
be disrupted for a much longer period of time, until the decoder
resynchronizes to an independently decodable picture.
[0047] As described above, the normal mode packet stream is carried
by a combination of source, system and channel encoding. In the
illustrated embodiment, the source and system coding is according
to the known MPEG 2 coding scheme and the channel encoding uses the
8-VSB modulation technique. The MPEG source coding scheme encodes a
video image signal as a sequence of independent decoding segments.
An independent decoding segment (IDS), also termed an elementary
stream segment, is a segment which may be decoded accurately
independent of any other independent decoding segment. In the MPEG
standard, independent decoding segments include a sequence, group
of pictures (GOP) and/or picture. These independent decoding
segments are delimited in the compressed bitstream by unique start
codes. That is, an independent decoding segment is considered to be
all the data beginning with a segment start code, up to but not
including the next segment start code. Pictures in the MPEG 2
standard are either intra-coded (I pictures), inter-prediction (P
pictures) or bi-directional prediction (B) pictures. I pictures are
encoded without reference to any other pictures. A GOP includes a
group of pictures encoded as a combination of I, P, and/or B
pictures. In a closed GOP, all pictures in the GOP may be decoded
without reference to pictures in any other GOP. The start of each
GOP is clearly identified in the MPEG 2 packet stream.
[0048] Also as described above, the robust mode packet stream is
carried by a combination of source, system and channel encoding. In
the illustrated embodiment, the source encoding is according to the
JVT encoding scheme, the system encoding is according to the MPEG 2
standard and the channel encoding uses the 2-VSB and/or 4-VSB
modulation techniques. Pictures coded using the JVT source coding
standard are made up of coded slices, and a given picture may
contain slices of different coding types. Each slice may be an
intra-coded (I) slice, an inter-predictive (P) slice, a
bi-predictive (B) slice, an SI slice in which only spatial
prediction is used, or an SP slice which may be accurately
reproduced even when different reference pictures are used. The JVT
source coding standard also includes an instantaneous decoding
refresh (IDR) picture. An IDR is a particular type of JVT encoded
picture, which contains only I slices and marks the beginning of an
IDS. An IDR indicates that the current picture, and all later
encoded pictures may be decoded without requiring reference to
previous pictures. An IDR may be encoded once for every
predetermined number of pictures, emulating a GOP in the MPEG 2
standard. In the JVT source encoding scheme, independent decoding
segments may be delimited by IDRs, which are clearly identified in
the JVT packet stream.
[0049] By imposing some constraints on the normal and robust source
encoding schemes, a system may be developed which can switch from
the normal mode packet stream to the robust mode packet stream
while minimizing objectionable artifacts. If independent decoding
segments are encoded to begin at identical content locations in
both the normal (MPEG 2) and robust (JVT) packet streams, switches
may be made between the normal and robust packet streams at
independent decoding segment locations with minimal objectionable
artifacts. In the illustrated embodiment, the independent decoding
segment used in the normal (MPEG 2) packet stream is a closed GOP
and begins with an I picture. In the corresponding robust (JVT)
packet stream, each independent decoding segment begins with an IDR
picture. The I picture in the normal (MPEG) mode packet stream and
the IDR picture in the robust (JVT) mode packet stream both encode
the same video picture from the content source (not shown). Both
source encoding schemes permit IDSs to be formed and delimited in
other manners. For example, the MPEG 2 source encoding scheme also
permits slices to be formed to represent a picture. Any such manner
may be used provided that IDSs are inserted into both packet
streams at identical content locations.
[0050] Referring again to FIG. 1, the input terminal 105 is further
coupled to an input terminal of a scene cut detector 160,
illustrated in phantom. An output terminal of the scene cut
detector 160 is coupled to respective control input terminals of
the normal mode encoder 120 and the robust mode encoder 110.
[0051] In operation, the scene cut detector 160 detects the
occurrence of a new scene in the video content. In response to
detection of a new scene, a control signal is sent to the normal
mode encoder 120 and the robust mode encoder 110. Both the normal
mode encoder 120 and the robust mode encoder 110 begin encoding a
new independent decoding segment in response to the control signal.
The normal mode encoder 120 inserts a new I picture and the robust
mode encoder 110 inserts an IDR picture into their respective
encoded packet streams. The normal mode encoder 120 and the robust
mode encoder 110 operate to generate corresponding independent
decoding segments having the same time durations. As described
above, the encoded content representative signals are system coded
into respective packet streams.
[0052] The delay device 130 is set to introduce a delay equal to
the independent decoding segment time duration. The multiplexer 140
combines the robust mode encoded packet stream and the delayed
normal mode encoded packet stream into a composite packet stream.
The composite packet stream is channel encoded (modulated) in an
appropriate manner by the modulator 150 and supplied to the
communications channel via the output terminal 115.
[0053] The operation of the transmitter in this mode of operation
may be better understood by reference to FIG. 4. FIG. 4 illustrates
the packet streams at the input to the multiplexer 140. In FIG. 4,
a sequence of independent decoding segments (IDS) from the robust
mode encoder 110 is illustrated as a series of rectangles 400, and
a sequence of independent decoding segments from the normal mode
encoder 120 is illustrated as a series of rectangles 410. As
described above, the time locations within the content, and the
durations of the independent decoding segments from the robust mode
encoder 110 and the normal mode encoder 120 are the same. Because
the delay introduced by the delay device 130 is the same as the
time duration of an IDS, IDSs from the robust mode encoder 110
align with the immediately preceding IDS from the normal mode
encoder 120.
[0054] At time t0, which may represent a change in scene, as
detected by the scene cut detector 160, the undelayed robust mode
encoded IDS N begins and the previously delayed normal mode encoded
IDS N-1 begins. Each robust mode (JVT source coded) IDS is
illustrated as a series of rectangles 440 representing respective
slices, and begins with an independent decoding refresh (IDR)
picture. The IDR picture is followed by B, P, SI, and/or SP slices.
These slices are, in turn, system coded into a sequence 450 of
transport packets "a", "b", "c", etc. Similarly, each normal mode
IDS (MPEG 2 source coded) is illustrated as a series of rectangles
420 representing a GOP which begins with an I picture. The I
picture is followed by an arrangement of P pictures and B pictures.
These I, P and B pictures are, in turn, system coded into a
sequence 430 of transport packets "A", "B", "C", etc. The
illustrated arrangements are examples only, and any appropriate
arrangement may be used.
[0055] This composite signal is received by a receiver. Referring
again to the receiver 200 in FIG. 2, at time t0, the received
robust mode IDS N is loaded into the delay device 220 during time
T.sub.adv. The delay device 230 introduces the same delay (one IDS
time period) to the received robust packet stream that in the
transmitter the delay device 130 introduced into the normal packet
stream. Consequently, the received normal packet stream and delayed
robust packet stream at the input terminals of the selector 230 are
realigned in time with respect to the content representative
signal.
[0056] Under normal conditions, the selector 230 couples the normal
mode packet stream to the multi-standard decoder 240, and the
multi-standard decoder is conditioned to decode normal mode
packets, as described in more detail above. If an error is detected
in the composite signal or a portion of it, as described above,
then switching is performed between the normal mode packet stream
and the robust mode packet stream. In this embodiment, at the
beginning of the IDS, the selector 230 couples the robust mode
packet stream to the multi-standard decoder 240, and the
multi-standard decoder 240 is conditioned to decode robust mode
packets, as described in more detail above. If no further errors
are detected in the composite signal, then at the beginning of the
next IDS, the selector 230 couples the normal mode packet stream to
the multi-standard decoder 240 and the multi-standard decoder 240
is conditioned to decode normal mode packets again.
[0057] In the receiver 200 in FIG. 2 switching from decoding the
normal mode packet stream to decoding the robust mode packet stream
and vice versa occurs at the beginning of an IDS. Each IDS is an
independent decoding segment, beginning with either an I picture
(normal mode) or an IDR picture (robust mode), which may be
successfully decoded without reference to any other picture.
Further, subsequent pictures may be decoded without reference to
pictures preceding the IDS. Thus, decoding and display of the
content representative signal may be immediately performed without
objectionable artifacts caused by the switching.
[0058] To further minimize video artifacts caused by switching from
decoding a normal mode video packet stream to a robust mode packet
stream, and vice versa, the image characteristics of the resulting
video signal may be gradually changed between those of the normal
mode video signal and those of the robust mode video signal when a
switch occurs. This is especially desirable when the robust mode
video stream is lower quality compared to the normal mode video
stream, for example, if the spatial resolution, frame rate, etc. of
the robust mode video stream is less than that of the normal mode
video stream.
[0059] FIG. 5 is a block diagram of a selector 230'' which may be
used in the receiver illustrated in FIG. 3. Such a selector 230''
may gradually change the video characteristics (e.g. resolution,
frame rate, etc.) of the resulting video signal between those of
the normal mode video signal and those of the robust mode video
signal at the time of a switch between them. FIG. 5a is a
functional diagram which illustrates the operation of selector
230'', and FIG. 5b is a structural block diagram illustrating an
embodiment of such a selector 230'' which may be used in the
receiver illustrated in FIG. 2.
[0060] In FIG. 5a, the robust mode video signal is coupled to one
end of a track 232 and the normal mode video signal is coupled to
the other end of the track 232. A slider 234 slides along the track
232 and generates a resulting video signal which is coupled to the
output terminal of the selector 230''. The resulting video signal
is coupled to the output terminal 215 of the receiver 200 (of FIG.
2). A control input terminal is coupled to receive the error signal
E from the demultiplexer 210. The control input terminal is coupled
to an input terminal of a controller circuit 231. The position of
the slider 234 along the track 232 is controlled by the controller
circuit 231, as indicated in phantom.
[0061] In operation, when the slider 234 is at the upper end of the
track 232, then a resulting video signal having the characteristics
(e.g. resolution, frame rate, etc.) of the robust mode video signal
is coupled to the output terminal of the selector 230''. When the
slider 234 is at the lower end of the track 232, then a resulting
video signal having the characteristics of the normal mode video
signal is coupled to the output terminal of the selector 230''. As
the slider 234 moves between the upper end and the lower end of the
track 232, then the characteristics of the resulting video signal
at the output terminal of the selector 230'' is adjusted to be
between those of the normal mode and robust mode video signals. The
closer the slider 234 is to the upper end of the track 232, the
closer the characteristics of the resulting video signal are those
of the robust mode video signal than to those of the normal mode
video signal. The closer the slider 234 is to the lower end of the
track 232, the closer the characteristics of the resulting video
signal are those of the normal mode video signal than to those of
the robust mode video signal.
[0062] The value of the error signal E indicates when a switch is
to occur, as described above. When a switch occurs from one video
signal (e.g. the normal mode or robust mode video signal) to the
other video signal, for a time interval of one or more video
pictures around the time when the switch occurs, the slider 234 is
gradually moved from one end of the track 232 to the other. For
example, during a switch from the normal mode video signal to the
robust mode video signal, the slider 234 begins at the bottom of
the track. For several video pictures before the switch, the slider
gradually moves from the bottom of the track 232 to the top. At the
time of the switch from the normal mode packet stream to the robust
mode packet stream, the slider is at the top of the track 232.
Consequently, the characteristics of the resulting video signal
gradually change from those of the normal video signal to those of
the robust mode video signal during several video pictures before
the switch to the robust mode packet stream occurs. Similarly, at
the time of the switch from the robust mode packet stream to the
normal mode packet stream, the slider is at the top of the track
232. For several video pictures after the switch, the slider
gradually moves from the top of the track 232 to the bottom.
Consequently, the characteristics of the resulting video signal
gradually change from those of the robust video signal to those of
the normal mode video signal during several video pictures after
the switch to the normal mode packet stream occurs.
[0063] In FIG. 5b, the video signal from the multi-standard decoder
240 (of FIG. 2) is coupled to a first input terminal of a variable
video quality filter 236 and a first input terminal of a selector
238. An output terminal of the video quality filter 236 is coupled
to a second input terminal of the selector 238. An output terminal
of the selector 238 generates the resulting video signal and is
coupled to the output terminal 215 (of FIG. 2). The error signal E
from the demultiplexer 210 is coupled to a controller circuit 231.
A first output terminal of the controller circuit 231 is coupled to
a control input terminal of the video quality filter 236 and a
second output terminal of the controller circuit 231 is coupled to
a control input terminal of the selector 238.
[0064] In operation, the video characteristics of the decoded video
signal is varied by the video quality filter 236 in response to the
control signal from the controller circuit 231. The control signal
from the controller circuit 231 conditions the video quality filter
236 to produce a video signal having a range of video
characteristics between those of the normal mode video signal and
those of the robust mode video signal. Under normal conditions,
when no switching occurs, the controller circuit 231 conditions the
selector 238 to couple the decoder video signal to the output
terminal as the resulting video signal.
[0065] In response to a change in the value of the error signal E,
indicating a switch between the normal mode video signal and the
robust mode video signal as described above, for a time interval
near the switch time the controller circuit 231 conditions the
selector 238 to couple the video signal from the video quality
filter 236 to the output terminal and conditions the quality filter
236 to gradually change the video characteristics of the resulting
video signal. More specifically, if a switch from the normal mode
video signal to the robust mode video signal occurs, for a time
interval of several video pictures before the switch occurs the
video quality filter 236 is conditioned to gradually change the
video characteristics of the resulting video signal from those of
the normal video signal to those of the robust video signal. At the
beginning of that time interval, the selector 238 is conditioned to
couple the filtered video signal to the output terminal as the
resulting video signal. When that time interval is complete, and
the decoded video signal is derived from the robust mode packet
stream, the selector 238 is conditioned to couple the decoded video
signal to the output terminal as the resulting video signal.
Similarly, if a switch from the robust mode video signal to the
normal mode video signal occurs, for a time interval of several
video pictures after the switch occurs the video quality filter 236
is conditioned to gradually change the video characteristics of the
resulting video signal from those of the robust video signal to
those of the normal video signal. At the beginning of that time
interval, the selector 238 is conditioned to couple the filtered
video signal to the output terminal as the resulting video signal.
When that time interval is complete, and the decoded video signal
is derived from the normal mode packet stream, the selector 238 is
conditioned to couple the decoded video signal to the output
terminal as the resulting video signal.
[0066] Abrupt switching between video signals having different
video quality (resolution, frame rate, etc.) may cause artifacts
which may be objectionable to a viewer. Because the video quality
of the resulting video signal is gradually reduced before switching
from the normal mode video signal to the robust mode video signal
and gradually increased after switching from the robust mode video
signal to the normal mode video signal, objectionable artifacts
resulting from the switch are minimized.
[0067] Another embodiment of a staggercasting communications system
may also provide switching while minimizing objectionable artifacts
and does not require any special placement of IDSs in the normal
and robust mode packet streams. A receiver 200' is illustrated in
FIG. 6. In FIG. 6, elements which are similar to those in the
receiver 200 in FIG. 2 are designated by the same reference number
and are not described in detail below. In FIG. 6, the first output
terminal of the demultiplexer 210 is coupled to the input terminal
of the normal mode decoder 240'. A first output terminal of the
normal mode decoder 240' is coupled to the first input terminal of
the selector 230' and a second output terminal of the normal mode
decoder 240' is coupled to a first input terminal of a normal mode
frame store 250'. The output terminal of the delay device 220 is
coupled to the input terminal of the robust mode decoder 240''. A
first output terminal of the robust mode decoder 240'' is coupled
to the second input terminal of the selector 230' and a second
output terminal of the robust mode decoder 240'' is coupled to a
first input terminal of a robust mode frame store 250''. The output
terminal of the selector 230' is coupled to respective second input
terminals of the normal mode frame store 250' and the robust mode
frame store 250''. An output terminal of the normal mode frame
store 250' is coupled to a second input terminal of the normal mode
decoder 240' and an output terminal of the robust mode frame store
250'' is coupled to a second input terminal of the robust mode
decoder 240''.
[0068] In operation, the delay device 220 introduces the same delay
into the robust mode packet stream that the delay device 130 in the
transmitter 100 (of FIG. 1) introduces into the normal mode packet
stream. Consequently, the packet stream signals at the respective
input terminals of the normal mode decoder 240' and the robust mode
decoder 240'' are time aligned with respect to the content
representative signal.
[0069] Both the normal and the delayed robust mode packet streams
are system and source decoded to produce corresponding content
representative signal streams, as described in detail above. In the
illustrated embodiment, these content representative signal streams
are respective sequences of video pictures. In both normal mode
decoding and robust mode decoding, video data representing
surrounding pictures are required to decode predictive pictures or
slices. The normal mode frame store 250' holds these surrounding
pictures for the normal mode decoder 240' and the robust mode frame
store 250'' holds these surrounding pictures for the robust mode
decoder 250''.
[0070] In the receiver illustrated in FIG. 6, switching is
performed on a picture-by-picture basis rather than on an IDS
basis. The normal mode decoder 240' decodes normal mode packets
into an associated content representative signal containing
successive video pictures. Concurrently, the robust mode decoder
240'' decodes robust mode packets into an associated content
representative signal containing successive video pictures. As
described above, the demultiplexer 210 produces an error signal on
the error signal line E indicating that the composite signal from
the demodulator 207, or at least some portion of it, is unusable.
In the embodiment illustrated in FIG. 6, this error signal may be
generated by detecting missing packets in the demultiplexed packet
streams. Thus, the error signal on the error signal line E
indicates not only that a packet is missing but also which packet
stream is missing a packet. Because the packets carry in the
payload a portion of the data forming a video picture carried by
the packet stream, and carry data in the header identifying the
packet stream to which this packet belongs, the packet stream which
is missing a packet may be marked as erroneous.
[0071] A video picture may be successfully received in both the
normal and robust mode packet streams; may be successfully received
in the normal mode packet stream but erroneously received in the
robust mode packet stream; may be erroneously received in the
normal packet stream but successfully received in the robust packet
stream; or may be erroneously received in both the normal and
robust mode packet streams.
[0072] Under normal conditions, that is, when no error is detected
in either the normal mode nor the robust mode packet streams, both
the normal mode decoder 240' and the robust mode decoder 240''
successfully decode the corresponding video picture. The selector
230' couples the content representative video picture derived from
the normal mode decoder 240' to the output terminal 215. Also,
under normal conditions, the normal mode decoder 240' supplies
video pictures to the normal mode frame store 250' and the robust
mode encoder 240'' supplies video pictures to the robust mode frame
store 250''.
[0073] If an error is detected in the robust mode packet stream but
no error is detected in the normal mode packet stream, then only
the normal mode decoder 240' successfully decodes the corresponding
video picture. The selector 230' couples the content representative
video picture derived from the normal mode decoder 240' to the
output terminal 215. Also, the normal mode decoder 240' supplies
the decoded video picture to the normal mode frame store 250'.
However, because the robust mode decoder 240'' did not successfully
decode the corresponding video picture, it doesn't supply any video
picture to the robust mode frame store 250''. Instead, the
successfully decoded video picture from the normal mode decoder
240' is routed from the selector 230' to the robust mode frame
store 250''.
[0074] If an error is detected in the normal mode packet stream but
no error is detected in the robust mode packet stream, then only
the robust mode decoder 240'' successfully decodes the
corresponding video picture. The selector 230' couples the content
representative video picture derived from the robust mode decoder
240'' to the output terminal 215. Also, the robust mode decoder
240'' supplies the decoded video picture to the robust mode frame
store 250''. However, because the normal mode decoder 240' did not
successfully decode the corresponding video picture, it doesn't
supply any video picture to the normal mode frame store 250'.
Instead, the successfully decoded video picture from the robust
mode decoder 240'' is routed from the selector 230' to the robust
mode frame store 250'.
[0075] In the above two cases, the video picture stored in the
frame store associated with the decoder which did not successfully
decode that video picture is the video picture from the other
decoder. This may degrade subsequent decoding compared to what it
would be if the correct video picture were stored in the frame
store. This is especially true should the substituted video picture
be of lower quality than the erroneous video picture. However, the
accuracy of subsequent decoding is better than if no video picture
at all were stored in the frame store.
[0076] Should an error be detected in a video picture in both the
normal mode and robust mode packet stream then no accurate video
picture is decoded and other masking techniques must be
performed.
[0077] The operation of the receiver 200' illustrated in FIG. 6 may
be better understood by reference to FIG. 7. In FIG. 7, a top set
of rectangles (MPEG) respectively represent the input 420 and
output 520 of the normal mode decoder 240'; a middle set of
rectangles (JVT) respectively represent the input 440 and output
540 of the robust mode decoder 240''; and the bottom set of
rectangles (OUTPUT) respectively represent the video pictures 460
and their source 560 at the output terminal 215. Referring to the
MPEG decoding: the upper set of rectangles 420 represent the source
coded video pictures (I, P, and/or B) at the input terminal of the
normal mode decoder 240'. The lower set of rectangles 520 represent
the resulting video pictures at the output terminal of the normal
mode decoder 240'. Similarly, referring to the JVT decoding: the
upper set of rectangles 440 represent the source coded IDR picture
(which may include a plurality of only I slices) and the following
source coded video slices (I, P, B, SI and/or SP) at the input
terminal of the robust mode decoder 240''. The lower set of
rectangles 540 represent the resulting video pictures at the output
terminal of the robust mode decoder 240''. Referring to the output
terminal 215, the upper set of rectangles 460 represent the output
video pictures and the lower set of rectangles 560 represent the
source of that particular video picture.
[0078] More specifically, in the normal mode (MPEG) packet stream,
the video pictures 6, 10 and 13 are each missing at least one
packet, as indicated by crosshatching. Similarly, in the robust
mode (JVT) packet stream, the video pictures 7 and 10 are missing
at least one packet, as indicated by the crosshatching. All the
other video pictures for both the normal mode and robust mode
packet streams include all packets and may be successfully
decoded.
[0079] For video pictures 0-5, 8, 9, 11, 12 and 14, the selector
230' couples the video pictures derived from the normal mode
decoder 240' (MPEG) to the output terminal 215, as indicated by "M"
in FIG. 7. In addition, for these video pictures, the video
pictures from the normal mode decoder 240' are supplied to the
normal mode frame store 250' and the video pictures from the robust
mode decoder 240'' are supplied to the robust mode frame store
250''.
[0080] For pictures 6 and 13, the video pictures in the normal mode
packet stream are erroneous but the corresponding video pictures in
the robust mode packet stream are complete and available. For these
pictures, the selector 230' couples the video picture from the
robust mode decoder 240'' (JVT) to the output terminal 215, as
indicated by "J" in FIG. 7. Because for these pictures there is no
normal mode video picture, the robust mode video picture from the
robust mode decoder 240'' is coupled to both the robust mode frame
store 250'' and the normal mode frame store 250'.
[0081] For picture 7, the video picture in the normal mode packet
stream is complete but the corresponding video picture in the
robust mode packet stream is erroneous. For this picture, the
selector 230' couples the video picture from the normal mode
decoder 240' to the output terminal 215, as indicated by "M" in
FIG. 7. Because for this picture there is no robust mode video
picture, the normal mode video picture from the normal mode decoder
240' is coupled to both the normal mode frame store 250' and the
robust mode frame store 250''.
[0082] For picture 10, the video picture in both the normal mode
and robust mode packet streams is erroneous. Because there is no
valid video picture, some form of error masking may be used. This
is indicated by an "XX" in FIG. 7. Because there is no valid video
picture from either the normal mode decoder 240' or the robust mode
decoder 240'', no decoded video picture may be stored in either the
normal mode frame store 250' or the robust mode frame store 250''.
The data stored in the frame stores 250' and 250'' may also be
derived from some form of error masking.
[0083] By decoding both packet streams into streams of video
pictures, and switching from one video stream to the other at the
beginning of each video picture, video artifacts resulting from
failure to properly decode a packet stream may be minimized.
Switching with a gradual change of video quality, as illustrated in
FIG. 5 may be used in a receiver as illustrated in FIG. 6. However,
because in the receiver of FIG. 6 switching occurs at each picture,
artifacts from such switching are not as objectionable as when
switching occurs at IDS boundaries, as in FIG. 2.
[0084] Degraded channel conditions may, however, result in frequent
switches between normal mode and robust mode packet streams. This
frequent switching may result in artifacts which may be
objectionable to a viewer. This is especially true if the video
quality of the robust mode video signal is substantially different
from that of the normal mode video signal.
[0085] In order to minimize artifacts caused by over-frequent
switching between the normal mode packet stream and the robust mode
packet stream, the selector 230 (of FIGS. 2) and 230' (of FIG. 6)
is configured to restrict switching at more often than a
predetermined frequency. More specifically, the selector 230 or
230' may monitor the frequency at which switching is desired, and
compare it to a predetermined threshold.
[0086] If the frequency of desired switching is over the threshold,
then the frequency at which actual switching occurs is restricted
to below some maximum frequency. This is a form of switching
hysteresis.
[0087] For example, assume that the normal mode packet stream
carries a video signal of high quality (e.g. high definition (HD))
and the robust mode packet stream carries a video signal of lower
quality (e.g. standard definition (SD)). When the normal mode HD
packet stream is unavailable, then the robust mode SD packet stream
is processed to generate the image. Upscaling an SD video signal
for display on an HD display device generates a video image of poor
quality. If the normal mode packet stream is fading in and out
frequently, but the robust mode packet stream remains available,
then frequent switches between the normal mode HD video signal and
the robust mode SD video signal occur. Frequent switches between HD
and SD packet streams, with frequent switches between high quality
and low quality images, produce artifacts which are objectionable
to a viewer.
[0088] Continuing the example, if the error signal E indicates that
switching should occur (i.e. normal mode packets are missing) e.g.
more than two times per minute, then actual switching is restricted
to minimize the switching artifacts described above. In this
example, under these conditions the selector 230 or 230' selects
the robust mode packet stream for e.g. at least one minute for
every switch. This will decrease the number of switches and, thus,
minimize the visible artifacts resulting from those switches. One
skilled in the art will understand that this is only one embodiment
implementing switching hysteresis. The thresholds for the maximum
switching frequency to invoke hysteresis and for the restricted
switching frequency may be made different than those of the
example. Such thresholds may be determined empirically to find
those which minimize objectionable visible artifacts. Further, the
thresholds may be dynamically varied during the operation of the
receiver. Finally, other hysteresis algorithms may be developed to
restrict switching in the presence of conditions which would
normally result in excessive switching.
[0089] Referring again to FIG. 3 and FIG. 4, at the beginning of
any broadcast or channel change, there is a period designated
T.sub.adv during which the normal mode packets (310, 410) are
filling the delay device 220 (of FIG. 2 and FIG. 6). In the
receivers illustrated in FIG. 2 and FIG. 6, only after the delay
circuit 220 is full does the receiver begin operation. However,
this causes undue delay when a receiver is switched on or a channel
is changed. During the time interval T.sub.adv, however, the robust
mode packet stream (300, 400) is immediately available.
[0090] In FIG. 2, the undelayed robust mode packet stream is
coupled directly from the demultiplexer 210 to a third input
terminal of the selector 230, as illustrated in phantom. When the
receiver is powered on or a new channel is selected, the selector
230 couples the undelayed robust mode packet stream to the
multi-standard decoder 240. The multi-standard decoder 240 is
conditioned to depacketize and decode the robust mode packets, as
described in detail above, and a video signal is made immediately
available to the utilization circuitry at output terminal 215. When
the normal mode packet stream becomes available, then the selector
230 will couple the normal mode packet stream signal to the
multi-standard decoder 240.
[0091] In FIG. 6, the undelayed robust mode packet stream is
coupled directly from the demultiplexer 210 to the robust mode
decoder 240''. When the receiver is powered on or a new channel is
selected, the robust mode decoder 240'' is conditioned to
depacketize and decode the robust mode packet stream from the
demultiplexer 210 and generate a robust mode video signal, as
described in more detail above. The selector 230' is conditioned to
couple the robust mode video signal from the robust mode decoder
240'' to the utilization circuitry via the output terminal 215.
When the normal mode packet stream becomes available, then the
normal mode decode 240' depacketizes and decodes it and produces a
normal mode video signal. The selector 230' is conditioned to
couple the normal mode video signal to the utilization circuitry
via the output terminal 215.
[0092] In either case, data in the normal mode and robust mode
packet streams are analyzed to determine when the normal mode
packet stream has become available and normal operation of the
receiver may be commenced. In accordance with known MPEG 2 system
(transport packet) encoding, information related to the system time
clock (STC) in the transmitter is placed in the encoded packet
streams via program clock reference (PCR) data. Further
information, termed a presentation time stamp (PTS), which
indicates when a portion (termed an access unit) of a packet stream
must be decoded, is included at least at the beginning of each such
access unit. When the normal mode and robust mode packet streams
are depacketized and decoded by the multi-standard decoder 240
(FIG. 2) or the normal mode decoder 240' and the robust mode
decoder 240'' (FIG. 6), the system time clock (STC) in the receiver
is synchronized to that in the transmitter through the PCR data.
When the value of the PTS in the normal mode packet stream is equal
to the value of the receiver STC, this indicates that the normal
mode packet stream is in synchronism with the robust mode packet
stream, and the receiver may begin normal operation by decoding the
normal mode packet stream, as described above.
[0093] Because many content representative signals may be
transmitted on one multiplexed transport packet stream, a known
means for supplying information about the different packet streams
has been developed. Each packet stream is identified by a packet
identifier (PID), which is included in the header of each packet in
that packet stream. One packet stream, having a predetermined known
PID, contains one or more data tables containing identification and
other information about all the other packet streams. This known
table structure may be used to carry information about robust mode
packet streams which are not related to any other normal mode
packet stream. However, additional information must be sent from
the transmitter to the receivers about robust packet streams which
are related to other normal mode packet streams.
[0094] An extended syntax and semantics for these existing tables
may carry the necessary data. FIG. 8 is a table which illustrates
an extended syntax and semantics for the program map table (PMT)
and/or program and information systems protocol--virtual channel
table (PSIP-VCT). Each row in FIG. 8 represents either a data item
in the extended table, or a meta-syntactical description in
pseudo-code form. The first column is either a name of a data item
or a meta-syntactical specification. The second column is a
description of the data item or syntactical specification. The
third column is an indication of the size of any data item.
[0095] The first item 802 in the extended syntax is the number of
robust packet streams used to staggercast other normal mode packet
streams. Then information for each such staggercast robust mode
packet stream is included in the table, as indicated by the
meta-syntactic specification in the next row and the last row of
the table. Some such information is required for every robust mode
packet stream. For example, data 804 represents the program
identifier (PID) for the robust mode packet stream; data 806
represents the type of data being carried by that packet stream;
data 808 represents the PID of the normal mode packet stream
associated with this packet stream; and data 810 represents the
delay being introduced into the normal mode packet stream by the
delay device 130 in the transmitter 100 (of FIG. 1).
[0096] Some such information, however, relates to robust mode
packet streams only of a particular data type. For example, if the
robust mode packet stream carries video data, then information 812
related to the compression format, frame rate, interlace format,
horizontal and vertical resolution, and bit rate is sent from the
transmitter to the receivers so that the video image represented by
the robust mode packet stream may be properly decoded and
displayed. Similarly, if the robust mode packet stream carries
audio data, the information 814 related to the compression format,
bit rate, sample rate; and audio mode (surround, stereo, or mono)
is sent from the transmitter to the receivers so that the sound
represented by the robust mode packet stream may be properly
decoded and reproduced.
[0097] One other piece of data relates to the relative quality of
the content representative signal carried by the robust mode packet
stream. As described above, the quality of the content
representative signal carried by the robust mode packet stream may
be different from that of the normal mode packet stream with which
it is associated. In the examples described above, the quality of
content representative signal carried by the robust mode packet is
specified to be lower than that of the associated normal mode
packet stream. However, under some conditions, the provider may
transmit a higher quality signal on the robust mode packet stream.
In this condition, it is preferred that receivers use the content
representative signal carried by the robust mode packet stream
instead of the associated normal mode packet stream. This is
indicated to the receivers by the data 816.
[0098] By providing information associating robust mode packet
streams to normal mode packet streams, a receiver 200 (of FIG. 2)
or 200' (of FIG. 6) may find both the normal mode and robust mode
packet streams in the multiplexed packet stream, and concurrently
process both of them as described above. Prior receivers which do
not include the capabilities of the receivers of FIG. 2 and FIG. 6
will ignore this information and process the normal mode packet
stream in the known manner.
[0099] As described above, the delay introduced between the robust
mode packet stream and the associated normal mode packet stream by
the delay device 130 in the transmitter 100 (of FIG. 1) is
transmitted as the data 810 in the table illustrated in FIG. 8.
This permits the transmitter to change the delay period and permits
the receiver to adjust its delay period accordingly. For example,
under some channel conditions fading may be more likely than
others, or the characteristics of the fading may change (i.e. the
fades may be longer). Under such conditions, the delay period may
be increased. The length of the delay is transmitted to the
receivers, which will adapt the delay devices 220 (in FIG. 2 and
FIG. 6) to the same delay period. Other conditions may also require
differing delay periods.
[0100] The staggercasting concept described above may be expanded.
Multiple versions of the same content representative signal,
encoded into video signals having different video quality (e.g.
resolution, frame rate, etc.), may be staggercasted. FIG. 9 is a
block diagram of a portion of another embodiment of a
staggercasting transmitter for transmitting multiple versions of a
content representative signal. In FIG. 9 those elements which are
the same as those in the transmitter illustrated in FIG. 1 are
designated by the same reference number and are not described in
detail below. FIG. 10 is a block diagram of a portion of a
corresponding embodiment of a staggercasting receiver. In FIG. 10,
those elements which are the same as those in the receiver
illustrated in FIG. 2 are designated by the same reference number
and are not described in detail below.
[0101] In FIG. 9a, input terminal 105 is coupled to an input
terminal of a hierarchical encoder 160. Hierarchical encoder 160
source encodes and packetizes a plurality of output packet stream
signals. A first one (0) of the plurality of output packet stream
signals is coupled to a corresponding input terminal of the
multiplexer 140'. The remainder of the plurality of output packet
stream signals, (1) to (n) are coupled to respective input
terminals of a corresponding plurality of delay devices 130(1) to
130(n). The delay period introduced by the delay device 130(2) is
greater than that introduced by delay device 130(1); the delay
period introduced by the delay device 130(3) (not shown) is greater
than that introduced by delay device 130(2); and so forth. The
delays may be specified in terms of packets, as illustrated in FIG.
3; independent decoding segments, as illustrated in FIG. 4; or
video picture periods, as illustrated in FIG. 7. Respective output
terminals of the plurality of delay devices 130(1) to 130(n) are
coupled to corresponding input terminals of the multiplexer
140'.
[0102] In operation, the first packet stream signal (0) carries a
base video signal source encoded at a lowest video quality. The
second packet stream signal (1) carries extra video information.
This extra video information, when combined with the base video
signal (0) produces a video signal with a higher video quality than
that of the base video signal (0) alone. The third packet stream
signal (2) carries further extra video information. The video
information in this signal, when combined with the base video
signal (0) and the video information in the second packet stream
signal (1) produces a video signal with a higher video quality than
that of the combination of the base signal (0) and the second
signal (1). The video information in the additional packet stream
signals, up to packet stream signal (n) from the hierarchical
encoder 160, may be combined to produce video signals of higher
video quality. The multiplexed signal is channel encoded
(modulated) and supplied to receivers via output terminal 115.
[0103] FIG. 10a is the receiver corresponding to the transmitter
illustrated in FIG. 9a. The demultiplexer 210 extracts a plurality
(0) to (n) of packet streams. Packet stream (n) is coupled to a
corresponding input terminal of a hierarchical decoder 260. The
remainder (0) to (n-1) (not shown) of the plurality of packet
streams are coupled to respective input terminals of a
corresponding plurality 220 of delay devices. The plurality 220 of
delay devices are conditioned to realign all of the plurality (0)
to (n) of packet streams in time at the input terminals of the
hierarchical decoder 260. The error signal on signal line E from
the demultiplexer 210 is coupled to a control input terminal of the
hierarchical decoder 260. An output terminal of the hierarchical
decoder 260 is coupled to the output terminal 215.
[0104] In operation, the demodulator 207 channel decodes
(demodulates) the received signal as appropriate, as described in
more detail above. The multiplexer 210 extracts the plurality, (0)
to (n), of packet streams carrying the hierarchy of video
information corresponding to the packet streams (0) to (n)
illustrated in FIG. 9a. These packet streams are aligned in time by
the plurality 220 of delay devices. The error signal from the
demultiplexer 210 indicates which packet streams are unavailable,
e.g. missing packets. The plurality of packet streams are
depacketized and the highest quality video image which may be
hierarchically decoded from the available packet streams is
produced by the hierarchical decoder 260. That is, if a fading
event has made all but the packet stream (0) carrying the base
video signal unavailable, then the hierarchical decoder 260
depacketizes and decodes only the packet stream (0). If the packet
stream (1) is also available, then the hierarchical decoder 260
depacketizes and decodes both the packet stream (0) and the packet
stream (1) and generates a video signal of higher quality, and so
forth. If all packet streams (0) to (n) are available, then the
hierarchical decoder 260 depacketizes and decodes them all and
generates a video signal of the highest video quality.
[0105] In FIG. 9b, the input terminal 105 is coupled to respective
input terminals of a plurality 170 of video encoders. The output
terminal of a first one 170(0) of the plurality 170 of video
encoders is coupled to a corresponding input terminal of the
multiplexer 140'. The output terminals of the remainder, 170(1) to
170(n), of the plurality 170 of video encoders are coupled to
respective input terminals of a plurality of delay devices 130(1)
to 130(n). The delay period introduced by the delay device 130(2)
is greater than that introduced by delay device 130(1); the delay
period introduced by the delay device 130(3) (not shown) is greater
than that introduced by delay device 130(2); and so forth. The
delays may be specified in terms of packets, as illustrated in FIG.
3; independent decoder segments, as illustrated in FIG. 4; or video
frame periods, as illustrated in FIG. 7. Respective output
terminals of the plurality of delay devices are coupled to
corresponding input terminals of the multiplexer 140'.
[0106] In operation, the first encoder 170(0) source encodes the
content representative signal and system encodes (packetizes) the
resulting source encoded signal to generate a packet stream
carrying information representing a video signal at lowest quality:
in the illustrated embodiment, a quarter-common-interface-format
(QCIF) video signal. The second encoder 170(1) similarly generates
a packet stream carrying information representing a video signal at
a higher quality than that produced by the first encoder 170(0): in
the illustrated embodiment, a common-interface-format (CIF) video
signal. Other video encoders, not shown, similarly generate packet
streams carrying video signals at successively higher video
quality. An SD video encoder 170(n-1) similarly generates a packet
stream carrying an SD quality video signal and an HD video encoder
170(n) similarly generates a packet stream carrying an HD quality
video signal. These packet streams are multiplexed by the
multiplexer 140' then channel encoded (modulated) and transmitted
to the receivers via the output terminal 115.
[0107] FIG. 10b is the receiver corresponding to the transmitter
illustrated in FIG. 9b. In FIG. 10b, the demultiplexer 210 extracts
a plurality (0) to (n) of packet streams. The packet stream (n) is
coupled to an input terminal of a HD decoder 270(n). The remainder
of the packet streams (0) to (n-1) are coupled to respective input
terminals of a plurality 220 of delay devices. Respective output
terminals of the plurality 220 of delay devices are coupled to
corresponding input terminals of a plurality 270 of video decoders.
Respective output terminals of the plurality 270 of video decoders
are coupled to corresponding input terminals of a selector. The
error signal on the error signal line E from the demultiplexer 210
is coupled to a control input terminal of the selector 280.
[0108] In operation, the demodulator 207 channel decodes
(demodulates) the received composite signal as appropriate, as
described in more detail above. The demultiplexer 210 extracts the
packet streams (0) to (n) corresponding to those generated by the
plurality 170 of video encoders illustrated in FIG. 9b. The
plurality 220 of delay devices realigns all these packet streams
(0) to (n) in time at the respective input terminals of the
plurality 270 of video decoders. Each packet stream is coupled to
the video decoder appropriate for decoding the video signal carried
by that packet stream. For example, the packet stream carrying the
QCIF quality video signal is coupled to the QCIF decoder 270(0);
the packet stream carrying the CIF quality video signal is coupled
to the CIF decoder 270(1) and so forth. Each video decoder in the
plurality 270 of video decoders depacketizes and source decodes the
signal supplied to it to generate a video signal. The error signal
E from the demultiplexer 210 indicates which of the packet streams
(0) to (n) is unavailable due to errors (e.g. missing packets). The
selector 280 is conditioned to couple the highest quality video
signal produced from available packet streams to the output
terminal 215.
[0109] One skilled in the art will understand that image scaling
may be required for some of the lower quality video image signals
in the transmitter systems illustrated in FIG. 9. The encoders,
either the hierarchical encoder 160 of FIG. 9a or the plurality 170
of encoders of FIG. 9b, include any such image scaling circuitry
which is necessary it is not shown to simply the figure.
[0110] For the communications system illustrated in FIG. 9 and FIG.
10, any of the packet streams produced by the hierarchical encoder
160 (of FIG. 9a) or any of the plurality 170 of video encoders (of
FIG. 9) may be source encoded according to the robust source
encoding scheme (JVT) and channel encoded (modulated) by the robust
modulation scheme (4-VSB and/or 2-VSB), as described in more detail
above. The corresponding demodulation and decoding of that packet
stream takes place in the receiver of FIG. 10. Also, the lowest
quality video signal is advanced the most, and consequently has the
highest fade resistance. Further, the lowest video quality signal
may be encoded with the least number of bits and thus takes a small
amount of time to transmit. As the video quality of the video
signal carried by packet streams increases, the time by which that
packet stream is advanced decreases, consequently the fade
resistance decreases. Thus, when the channel characteristic has no
fades, then the packet stream(s) carrying the highest video quality
signal remain(s) available. Mild fades leave packet stream(s)
carrying lower video quality signals available, and severe fades
leave only the packet stream carrying the lowest quality video
signal available. This gradual reduction in video quality as
channel characteristics degrade is a desirable characteristic for a
viewer.
[0111] As described above, and illustrated in FIG. 1 and FIG. 9b,
the same content representative signal may be staggercasted as a
packet stream carrying a high quality video signal and as one or
more packet streams carrying reduced video quality video signals.
In such a communications system, it is, therefore, possible for
some receivers, for example, a television receiver in a cellular
phone or personal digital assistant (PDA), to extract and decode
only a reduced quality content representative signal. In such a
receiver, the display device is lower resolution and may only be
able to display a reduced quality video signal. Further, the use of
battery power makes it advantageous to minimize the amount of data
processed. Both of these considerations suggest that such receivers
decode only the packet stream carrying a video signal of
appropriate video quality and display that image.
[0112] FIG. 10c illustrates a receiver. In FIG. 10c, the input
terminal 205 is coupled to the input terminal of the demodulator
207. An output terminal of the demodulator 207 is coupled to the
input terminal of the demultiplexer 210. An output terminal of the
demultiplexer 210 is coupled to an input terminal of a decoder 270.
An output terminal of the decoder is coupled to the output terminal
215.
[0113] In operation, the demodulator 207 demodulates the received
composite signal in the appropriate manner, as described in more
detail above. The demultiplexer 210 selects only a single packet
stream having a video signal of the desired quality. For example,
this may be a QCIF format video signal, such as produced by the
QCIF encoder 170(0) of FIG. 9b and carried on packet stream (0).
The packet stream (0) is extracted by the demultiplexer 210 and is
decoded by the decoder 270 to produce the QCIF format video signal.
Such a receiver need only receive the table illustrated in FIG. 8
to determine the PID of the desired lower quality video signal
packet stream (0). From the resolution data 812 transmitted in the
table, the mobile receiver is able to select the packet stream
carrying the reduced quality video signal desired for
processing.
[0114] The communications system illustrated in FIG. 9 and FIG. 10
may be further extended. In the systems described above, video
information carried in additional packet streams, may be used to
provide graceful degradation under worsening channel conditions.
However, such systems may also transmit additional video
information which can enhance the quality of video signals under
good channel conditions. By including a packet stream carrying
augmented video information, in addition to the packet stream
carrying the normal video signal, an augmented video image may be
transmitted.
[0115] FIG. 11 is a block diagram of a portion of a transmitter for
transmitting a dual interlaced video signal and FIG. 12 is a block
diagram of a portion of a receiver for receiving a dual interlaced
video signal. FIG. 13 is a display diagram useful in understanding
the operation of the dual interlace transmitter illustrated in FIG.
11 and the dual interlace receiver illustrated in FIG. 12. In FIG.
11, those elements which are the same as those illustrated in FIG.
1 are designated by the same reference number and are not described
in detail below. In FIG. 12, those elements which are the same as
those illustrated in FIG. 6 are designated by the same reference
number and are not described in detail below.
[0116] Referring to FIG. 13, a content source produces a
progressive scan video display, illustrated schematically at the
top of FIG. 13 as a sequence of video lines 1310 within a display
border 1320. A normal HD video image picture includes 1080 lines.
Such an HD video image is transmitted at a rate of 30 frames per
second in interlaced format. That is, an interlacer generates two
fields: a first field including only odd numbered lines and a
second field including only even numbered lines. These fields are
transmitted successively at a rate of 60 fields per second.
[0117] In FIG. 11, the input terminal 105 is coupled to a dual
output interlacer 102. A first output terminal of the dual output
interlacer 102 is coupled to the input terminal of the robust mode
encoder 110. A second output terminal of the dual output interlacer
102 is coupled to the input terminal of the normal mode encoder
120.
[0118] Referring again to FIG. 13, the frame display image 1330(A)
corresponds to the video signal A produced at the first output
terminal of the dual output interlacer 102 and the frame display
image 1330(B) corresponds to the video signal B produced at the
second output terminal of the dual output interlacer 102. In the
frame display images 1330(A) and 1330(B), solid lines are
transmitted in one field, and dotted lines are transmitted in the
following field. In the frame display image in 1330(A) solid lines
are odd lines and dotted lines are even lines; and in the frame
display image 1330(B), solid lines are even lines and dotted lines
are odd lines. This is illustrated in more detail in the field
display images 1340(A), 1340(B), 1350(A) and 1350(B) beneath the
frame display images 1330 (A) and 1330(B). In field 1, video signal
A transmits the odd lines as illustrated in field display image
1340(A), and video signal B transmits the even lines, as
illustrated in field display image 1340(B). In field 2, the video
signal A transmits the even lines as illustrated in field display
image 1350(B) and the video signal B transmits the odd lines as
illustrated in field display image 1350(B).
[0119] As described in more detail above, the video signal A is
source encoded using JVT source encoding, then system encoded
(packetized) by the robust mode encoder 110. The video signal B is
source encoded using MPEG 2 source encoding, then system encoded
(packetized) by the normal mode encoder. The modulator channel
encodes (modulates) the robust mode packet stream using 4-VSB
and/or 2-VSB modulation, and modulates the normal mode packet
stream using 8-VSB modulation.
[0120] In FIG. 12, a first output terminal of the demultiplexer 210
is coupled to the input terminal of the normal mode decoder 240'
and a second output terminal of the demultiplexer 210 is coupled to
the input terminal of the delay device 220. The output terminal of
the normal mode decoder 240' is coupled to a first signal input
terminal of a dual input deinterlacer 202 and the output terminal
of the robust mode decoder 240'' is coupled to a second signal
input terminal of the dual input deinterlacer 202. The error signal
from the demultiplexer 210 is coupled to a control input terminal
of the dual input deinterlacer 202. An output terminal of the dual
input deinterlacer 202 is coupled to the output terminal 215.
[0121] As described in more detail above, the demodulator 207
channel decodes (demodulates) the robust mode packet stream using
4-VSB and/or 2-VSB demodulation and demodulates the normal mode
packet stream using 8-VSB demodulation. The normal mode decoder
240' system decodes (depacketizes) and source decodes the normal
mode packet stream using JVT decoding to reproduce the video signal
B. The robust mode decoder 240'' depacketizes and source decodes
the robust mode packet stream using MPEG 2 decoding to reproduce
the video signal A.
[0122] The dual input deinterlacer 202 operates to combine the
interlaced scan lines of the video signal A from the robust mode
decoder 240'' with the interlaced scan lines of the video signal B
from the normal mode decoder 240' to produce a progressive scan
field. For field 1, the odd scan lines from video signal A,
illustrated in field display image 1340(A), are combined with the
even scan lines from video signal B, illustrated in field display
image 1340(B). The resulting progressive scan field is illustrated
in the field display image 1345. For field 2, the even scan lines
from video signal A, illustrated in field display image 1350(A),
are combined with the odd scan lines from video signal B,
illustrated in field display image 1350(B). The resulting
progressive scan field is illustrated in the field display image
1355. Thus, a progressive scan field may be produced at the output
terminal of the dual input deinterlacer 202 each field period. For
an HD signal, this means that a full 1080 line image is produced 60
times per second.
[0123] The dual interlaced technique described above and
illustrated in FIG. 11, FIG. 12 and FIG. 13 may also be combined
with the techniques described above to provide a wider range of
graceful degradation in the event channel conditions degrade. If
channel conditions render one of the packet streams carrying video
signals A or B unavailable, then the error signal E indicates this
to the dual input deinterlacer 202. The dual input deinterlacer 202
begins producing the standard HD interlaced video signal from the
available video signal. The display device (not shown), is
reconfigured to display the image represented by the standard
interlaced video signal until the other video signal becomes
available again. If neither of the HD video signals are available,
then the highest quality available video signal may be displayed,
as described in detail above with reference to the transmitter in
FIG. 9 and the receiver in FIG. 10.
[0124] The same technique may also be used to convert any
interlaced format video signal, for example an SD video signal, to
a progressive scan video signal at twice the frame rate. It is not
necessary for the two video signals A and B to be staggercasted, as
illustrated in FIG. 11 and FIG. 12. It is only necessary that they
be simulcasted. However, staggercasting additionally provides
graceful degradation in the presence of fade events, as described
above.
[0125] The communications system described above may be further
extended to cooperate with a recording device, such as a digital
personal video recorder (PVR). Such PVR devices are becoming
included in digital television receivers due to the decreasing
costs of such a device. In FIG. 9b, a PVR device 295 includes a
video terminal (Vid) bidirectionally coupled to the selector 280,
and a control terminal (Ctl) also bidirectionally coupled to the
selector 280, as illustrated in phantom. The selector 280 is also
coupled to a source of user control, also as illustrated in
phantom.
[0126] The selector 280 is configured to couple any desired video
signal from the plurality 270 of video detectors to the PVR 295
independently of the input video signal coupled to the output
terminal 215. The selector 280 may also be configured to couple an
input video signal from the PVR 295 to the output terminal 215 for
playback. The selector 280 may also supply control data to the PVR
295, and the PVR 295 supply status data to the selector 280 over
the bidirectional control terminal.
[0127] The PVR 295 may be controlled in several modes of operation.
In one mode of operation, the best available video signal is
coupled to the PVR 295 for recording. In this operational mode, the
selector 280 couples the same input video signal to the PVR 295 as
is coupled to the output terminal 215. This will result in the best
quality video signal being recorded, but will take the most storage
space, in the PVR 295. This will take advantage of the normal mode
and robust mode packet streams carrying the video signal and the
graceful degradation that provides. Alternatively, a lower
resolution video signal may be coupled to the PVR 295 than is
coupled to the output terminal 215. For example, while the selector
280 may couple the best available video signal to the output
terminal 215, the selector 280 may couple a video decoder 270
producing a lesser quality video signal to the PVR 295. This lesser
quality video signal may be a selected one of the available video
signals, such as the SD quality video signal from the SD decoder
270(n-1), with graceful degradation supplied by the lesser quality
video decoders. Such a signal will require less storage space in
the PVR 295 than the best available video signal. This will help to
conserve storage space in the PVR 295, and allow for longer
recording times. In the event that the selected lower quality video
signal becomes unavailable, a higher quality signal may be recorded
until the lower quality signal becomes available again. The
selection of which lesser quality video to record (i.e. SD, or CIF
or QCIF) may be directly selected by a viewer via the user input
terminal. Alternatively, the selector 280 may automatically control
this selection according to some criterion. For example, a status
signal from the PVR 295 can indicate the amount of storage
remaining in the PVR 295. As the amount of storage remaining drops,
the selector 280 may automatically couple a video decoder 270
having reduced video quality to the PVR 295. Other criteria may be
derived and used to control which video signal is coupled to the
PVR 295 by the selector 280.
[0128] Similarly, a user may desire to control the selection and
display of the television programs being broadcast by a
transmitter. In existing broadcasting systems, one of the
transmitted packet streams carries a user program guide, containing
information about all programs currently being broadcast and those
due to be broadcast in the near future. From the program guide
data, an image of a table listing all such programs, their channels
and times may be generated by an on-screen display generator (OSD)
282 as illustrated in FIG. 10b. A user may control the display of
the program guide information as an aid in finding a desired
program and selecting that program to view using a user interface.
The user interface displays images to present information to a
viewer, requests input from a viewer and accepts viewer input from
controls which may be incorporated in the receiver or in a remote
control. Existing systems allow a viewer to request additional
information about a program listing, such as a more detailed
description of the program, a rating (G, PG, R, etc.), time
duration, time remaining and so forth.
[0129] Additional information related to the staggercasting system
described above may be added to the displayed program table, or the
additional-information display. This information may be derived
from the PSIP-VCT/PMT tables illustrated in FIG. 8. For example,
additional indicators may be added to the displayed program table
and/or additional-information display indicating that: this program
is being staggercasted; what the video quality is of the video
signals being staggercasted; what the audio quality of the audio
signals being staggercasted; and so forth. By displaying this
information for a viewer, the viewer is able to base selection of a
program on it. More specifically, a viewer may select a program
that is being staggercasted; or may select a program having video
signal of a desired video quality, e.g. to match the display device
to which the signal is being supplied.
[0130] Current receivers also allow a viewer to set certain
parameters. For example, a user may wish to automatically view all
transmitted channels, or only channels to which the viewer is
subscribed, or the subscribed channels plus pay-per-view channels,
and so forth without having to manually change the
on-screen-display each time it is displayed. A user interface
presents a user with a screen image, via the OSD 282, on which this
selection may be made using the user controls. An additional screen
image may be produced, or an existing screen image modified, on
which a viewer sets choices about selection and display of video
signals which have been staggercasted, as described above. For
example, a viewer may select to have the program table display only
staggercasted programs, or to display staggercasted programs
carrying video signals at or above a minimum video quality.
* * * * *