Multiplex communications – Communication techniques for information carried in plural... – Adaptive
Reexamination Certificate
2000-05-31
2004-08-24
Nguyen, Steven (Department: 2665)
Multiplex communications
Communication techniques for information carried in plural...
Adaptive
C370S538000
Reexamination Certificate
active
06782006
ABSTRACT:
This application is based on application Nos. H11-164919 and H11-323313 filed in Japan, the content of which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a digital broadcasting apparatus, and in particular to a digital broadcasting apparatus that adjusts bitrates assigned to source data items which compose additional information and are sent along with video and audio data of a broadcast program.
2. Background Art
As digital broadcasting has become more common in recent years, more and more additional information is being multiplexed and broadcasted with broadcast programs. The bitrate necessary to send each source data item composing the additional information depends on the nature of the source data item. Note that source data in this specification refers to data that composes information transmitted in addition to broadcast programs, and includes a plurality of source data items. Japanese Laid-Open Patent Application No. H10-304325, for instance, discloses a method for calculating the bitrate of each source data item from the size of the source data item.
With conventional methods, however, once a bitrate is determined for a source data item, the bitrate cannot be changed. This causes problems if the broadcast time is extended and the number of source data items to be sent changes. More specifically, if more source data items need to be sent, all source data items may not fit into the bandwidth reserved for source data. On the other hand, when source data items are deleted, the reserved bandwidth will not be used efficiently.
SUMMARY OF THE INVENTION
In view of the stated problems, the object of the present invention is to provide a digital broadcasting apparatus that adjusts the bitrate of each source data piece to efficiently use a bandwidth reserved for source data even if the number of source data pieces to be sent changes.
The stated object is achieved by a digital broadcasting apparatus that multiplexes a plurality of source data pieces into a transport stream of video and audio data of a broadcast program and transmits the transport stream to a receiving apparatus, the digital broadcasting apparatus including: a source data storage unit for storing the plurality of source data pieces; a bitrate storage unit for storing information that shows a bitrate for each source data piece and a total bitrate available for transmitting the plurality of source data pieces; a transmission period storage unit for storing a transmission start time and transmission end time of each source data piece; a bitrate assigning unit for assigning, before the current time reaches each transmission start time and transmission end time in the transmission period storage unit, a transmission bitrate to each source data piece according to the information in the bitrate storage unit so that a sum of the transmission bitrates is no more than the total bitrate; a source data reading unit for reading, from the source data storage unit, each source data piece whose transmission start time matches the current time; a multiplexing unit for (1) holding each source data piece read by the source data reading unit between the transmission start time and transmission end time thereof, and (2) repeatedly multiplexing each held source data piece into the transport stream according to the transmission bitrate assigned to the held source data piece; and a transmission unit for transmitting the transport stream into which each held source data piece has been multiplexed by the multiplexing unit.
With this construction, the digital broadcasting apparatus of the present invention efficiently uses a bandwidth reserved for source data by flexibly adjusting the transmission bitrate of each source data piece according to the time when the source data piece is transmitted. This allows the receiving apparatus that receives digital broadcasts to efficiently receive and use the source data pieces.
Here, the bitrate assigning unit may include: a sum calculation unit for calculating a sum of the bitrates for transmission pieces, the transmission pieces being source data pieces to be simultaneously transmitted; a judging unit for judging whether the sum calculated by the sum calculation unit exceeds the total bitrate; a first calculation unit for calculating, if a judgement result by the judging unit is negative, the transmission bitrate of each transmission piece according to a first equation; and a second calculation unit for calculating, if a judgement result by the judging unit is affirmative, the transmission bitrate of each transmission piece according to a second equation.
With this construction, the digital broadcasting apparatus assigns a transmission bitrate to each source data piece so that the bandwidth reserved for transmitting source data pieces is efficiently used.
Here, according to the first equation, a certain portion of a difference between the total bitrate and the sum calculated by the sum calculation unit may be added to the bitrate for each transmission piece, according to the second equation, a certain portion of a difference between the total bitrate and the sum calculated by the sum calculation unit may be subtracted from the bitrate for each transmission piece, and the bitrate assigning unit may further include a recalculation unit for (3) setting at “0” the transmission bitrate of each transmission piece whose transmission bitrate calculated by the second calculation unit was “0” or less and (4) recalculating the transmission bitrates of the other transmission pieces.
With this construction, even if the transmission of some source data pieces has become impossible, the digital broadcasting apparatus efficiently transmits other source data pieces.
Here, instead of each transmission piece whose transmission bitrate was set at “0” by the recalculation unit, the multiplexing unit may multiplex message data, that is assigned a low transmission bitrate and shows that transmission of the transmission piece has been canceled, into the transport stream.
With this construction, the digital broadcasting apparatus informs a user that the transmission of some source data pieces has been canceled.
Here, according to the first equation, a certain portion of a difference between the total bitrate and the sum calculated by the sum calculation unit may be added to the bitrate for each transmission piece, according to the second equation, a certain portion of a difference between the total bitrate and the sum calculated by the sum calculation unit may be subtracted from the bitrate for each transmission piece, the bitrate storage unit may further store a minimum bitrate and a maximum bitrate of each source data piece, the minimum bitrate of a source data piece being the lowest bitrate at which the receiving apparatus will be able to process the source data piece with sufficient speed, and the maximum bitrate of a source data piece being a bitrate above which no significant gain in speed at processing the source data piece will be able to be achieved for the receiving apparatus, the bitrate assigning unit may further include a transmission bitrate recalculation unit that (5), if there is at least one transmission piece whose transmission bitrate calculated by the second calculation unit is below the minimum bitrate thereof, sets the transmission bitrate of the at least one transmission piece at “0” and recalculates the transmission bitrates of the other transmission pieces according to the first equation, and (6), if there is at least one transmission piece whose transmission bitrate calculated by the second calculation unit is above the maximum bitrate thereof, sets the transmission bitrate of the at least one transmission piece as the maximum bitrate and recalculates the transmission bitrates of the other transmission pieces according to the second equation, and the multiplexing unit may multiplex each transmission piece into the transport stream according to the transmission bitrates set and recalculated by the transmission bitrate reca
Hirai Junichi
Kakiuchi Takashi
Mori Toshiya
Tanaka Akihiro
Matsushita Electric - Industrial Co., Ltd.
Nguyen Steven
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