DESCRIPTION
DIGITAL RECEIVING DEVICE
TECHNICAL FIELD
The present invention relates to a digital receiving device for receiving
digital broadcast waves.
BACKGROUND ART
In digital broadcasting, such as digital multimedia broadcasting (DMB)
and integrated services digital broadcasting (ISDB) including digital radio
broadcasting and digital television broadcasting, broadcast data compressed
using highly-efficient compression algorithm, such as Moving Picture Expert
Group (MPEG), is multiplexed for terrestrial or satellite transmission.
Digital broadcast data in this digital broadcasting is divided into packets of
data, such as video data and audio data, and compressed for transmission in
multiplexed transport stream (TS). Each transport stream is combined and
decompressed by a receiving device to select a predetermined program and is
output after receive the processed audio or video data.
Fig. 6 is a block diagram of conventional digital receiving device 1A for
processing digital incoming data. Digital receiving device 1A includes
receiving processor 1, error corrector 2, and decoder 3.
In digital receiving device 1A, receiving processor 1 processes data
received from broadcast waves to reproduce transport streams that are
original packet data from multiplexed data. Then, error corrector 2 corrects
errors in all the received packet data. Error corrector 2 corrects the errors
when the number of the errors is not greater than a predetermined number

in the received packet data, and outputs the packet data. Decoder 3
decodes the packet data output from error corrector 2 to reproduce sounds
from the broadcast waves.
A conventional digital receiving device similar to digital receiving
device 1A shown in Fig. 6 is disclosed, for example, in Patent Literature 1.
Conventional digital receiving device 1A may cause a delay in
processing according to processing capability of a microcomputer as the
increase of a bit rate of incoming digital broadcast waves, consequently
outputting sound improperly.
CITATION LIST
PATENT LITERATURE
Patent Literature l: Japanese Patent Laid-Open Publication No.
2005-73235
NON-PATENT LITERATURE
Non-patent Literature l: ISO/IEC 13818-1
SUMMARY
A first bit rate calculator of a digital receiving device receives incoming
packet data including first and second packet data, and calculates a first bit
rate of the incoming packet data. If the first bit rate is not greater than a
predetermined threshold, the first bit rate calculator outputs the incoming
packet data to an error corrector, the error corrector error-corrects the
incoming packet and outputs the error-corrected incoming packet data, and
the decoder decodes the incoming packet data output from the error corrector.
If the first bit rate is greater than the predetermined threshold, the first bit
rate calculator outputs the incoming packet data to the separator, the

separator outputs residual packet data obtained by discarding the second
packet data from the incoming packet data, the error corrector error-corrects
the residual packet data and outputs the error-corrected residual packet
data, and the decoder decodes the residual packet data output from the error
corrector.
This digital receiving device can reduce occurrence of delay in
processing even if the bit rate of digital data increases.
BRIEF DESCRIPTION OF DRAWINGS
Fig. 1 is a block diagram of a digital receiving apparatus including a
digital receiving device in accordance with an exemplary embodiment.
Fig. 2 is a block diagram of a digital receiving apparatus including
another digital receiving device in accordance with the embodiment.
Fig. 3 is illustrates a format of packet data of the digital receiving
device in accordance with the embodiment.
Fig. 4 is a flow chart for illustrating an operation of the digital
receiving device in accordance with the embodiment.
Fig. 5 is a flow chart for illustrating an operation of the digital
receiving device in accordance with the embodiment.
Fig. 6 is a block diagram of a conventional digital receiving device.
DETAIL DESCRIPTION OF PREFERRED EMBODIMENT
Fig. 1 is a block diagram of digital receiving apparatus 440 including
digital receiving device 420 according to an exemplary embodiment. In the
following description, known related components not directly affect the
embodiment will not be detailed.
Digital receiving apparatus 440 includes antenna 400, receiving

processor 410 connected to antenna 400, digital receiving device 420
connected to receiving processor 410, and loudspeaker 430 connected to
digital receiving device 420.
Receiving processor 410 converts broadcast waves received via antenna
400 to packet data to obtain digital sounds, and outputs the packet data to
digital receiving device 420. The packet data includes at least first packet
data that is audio data and second packet data that is video data.
Digital receiving device 420 includes bit rate calculator 421, separator
422 connected to bit rate calculator 421, bit rate calculator 423 connected to
separator 422, error corrector 424 connected to bit rate calculators 421 and
423, and decoder 425 connected to error corrector 424.
Conventional digital receiving device 1A shown in Fig. 1A corrects
errors in all the received packet data. Since error-correction load is high,
delay in processing occurs, depending on processing capability of
microcomputer, as a bit rate of incoming digital broadcast wave increases.
This may result in improper output of sounds.
Digital processing is a rapidly advancing field, and error correction is
increasingly adopted in the form of software, so as to support changes in line
with advancement. Changes can be supported by the use of software for
correcting errors. However, processing capability of microcomputer cannot
be changed. Therefore, a high-cost microcomputer with high processing
capability needs to be selected if processing load increases. If this type of
microcomputer is not selected, update is not feasible by the use of software.
Digital receiving device 420 according to the embodiment can
efficiently obtain audio data from packet data output from receiving
processor 410 even if a microcomputer with low processing capability is used.
An operation of digital receiving device 420 will be described below.

Bit rate calculator 421 calculates a bit rate of packet data output from
receiving processor 410, and determines, based on calculated bit rate,
whether or not error corrector 424 can error-correct the packet data, i.e., can
correct errors in the packet data, within a predetermined time. If bit rate
calculator 421 determines that error corrector 424 can error-correct all the
packet data output from receiving processor 410 within the predetermined
time, bit rate calculator 421 outputs the packet data to error corrector 424
without outputting the data to separator 422. If bit rate calculator 421
determines that error corrector 424 cannot error-correct all the packet data
output from receiving processor 410 within the predetermined time, bit rate
calculator 421 outputs the packet data to separator 422 without outputting
the data to error corrector 424.
Separator 422 discards packet data including the second packet data
that is video data in the packet data output from bit rate calculator 421, and
outputs, to bit rate calculator 423, residual packet data other than the
discarded packet data. The residual packet data includes the first packet
data that is audio data.
Bit rate calculator 423 calculates a bit rate of the residual packet data
including the first packet data that is audio data, and determines, based on
the calculated bit rate, whether or not error corrector 424 can error-correct
all the residual packet data within a predetermined time. If bit rate
calculator 423 determines that error corrector 424 can error-correct all the
residual packet data, bit rate calculator 423 outputs all the residual packet
data to error corrector 424. If bit rate calculator 423 determines that not all
the residual packet data can be error-corrected within the predetermined
time, bit rate calculator 423 discards the residual packet data, and does not
output the residual packet data to error corrector 424.

Error corrector 424 error-corrects only the residual packet data not
discarded by the above processing. Then, decoder 425 converts the
error-corrected packet data to audio data for reproducing digital sounds.
The discarded residual packet data is not sent to error corrector 424, and
thus error corrector 424 does not error-correct the discarded residual packet
data. Accordingly, digital receiving device 420 can suppress a delay in
processing by error corrector 424 even if an inexpensive microcomputer with
low processing capability is used as error corrector 424.
Fig. 2 s a block diagram of digital receiving apparatus 440A including
another digital receiving device 420A according to the embodiment. In Fig.
2, components identical to those of digital receiving apparatus 440 shown in
Fig. 1 are denoted by the same reference numerals. In digital receiving
processor 420 shown in Fig. 1, bit rate calculator 423 is connected between
separator 422 and error corrector 424. Digital receiving device 420A shown
in Fig. 2 includes bit rate calculator 423 connected not between separator
422 and error corrector 424, and does not include bit rate calculator 423. If
it is estimated that throughput of error correction is not so large in the
second packet data that is audio data, digital receiving device 420A may be
used instead of digital receiving device 420 shown in Fig. 1. In digital
receiving device 420A, error corrector 424 error-corrects all the residual
packet data. This provides digital receiving device 420A with a small circuit
size, a small size and, small power consumption.
Fig. 3 illustrates a format of packet data 303 of digital receiving device
420 according to the embodiment. According to the embodiment, packet
data 303 has a format specified by MPEG-2 standard. As shown in Fig. 3,
in all types of packet data 303, packet data 303 includes header 300 and data
301 following header 300. Packet data 303 carries divided data obtained by

dividing the data to be sent. Data 301 includes the divided data. Header
300 stores information on the divided data.
Data 301 changes according to the type of the packet data. If source
data to be sent is audio data, data 301 stores divided data that is obtained by
dividing the source data into data having a predetermined data length. If
the source data to be sent is information packet data, data 301 stores a
content of this information.
Header 300 stores packet identification (PID) 302 that is an identifier
for identifying packet data 303.
Fig. 4 is a flow chart illustrating an operation of digital receiving device
420. The operation of digital receiving device 420 shown in Fig. 1 is
described with reference to Fig. 4. Bit rate calculator 421 calculates a bit
rate of the packet data output from receiving processor 410 (Step 101A). Bit
rate calculator 421 compares the calculated bit rate with predetermined
threshold TH1 (Step 101), and determines whether or not all the packet data
can be error-corrected within a predetermined time. Threshold TH1 is
determined based on an overall processing load and capability of the
microcomputer. Threshold TH1 is a reference for evaluating whether or not
the bit rate causes a delay in processing.
More specifically, if the calculated bit rate is not greater than threshold
TH1 at Step 101 ("No" at Step 101), error corrector 424 error-corrects the
packet data (Step 104). For example, Reed-Solomon code can be used for
error correction which means relatively busy processing load can be set.
Decoder 425 decodes the packet data after the error correction, and converts
the error-corrected packet data to audio data (Step 105).
If the calculated bit rate is greater than threshold TH1 in Step 101
("Yes" at Step 101), bit rate calculator 421 outputs the packet data to

separator 422, Separator 422 separates the packet data (Step 102). At
Step 102, separator 422 discards packet data which is not required for
reproducing digital sound, and outputs residual packet data required for
reproducing digital sound to bit rate calculator 423. This operation reduces
the size of the data, and reduces a load including error correction.
Bit rate calculator 423 calculates a bit rate of the residual packet data
(Sep 103A), and compares the bite rate with threshold TH1 (Step 103). If
the bit rate calculated at Step 103A is not greater than threshold TH1 ("No"
at Step 103), bit rate calculator 423 outputs the residual data to error
corrector 424. Error corrector 424 error-corrects the residual packet data
(Step 104). Decoder 425 decodes the error-corrected residual packet data,
and converts the residual data to audio data (Step 105).
If the bit rate calculated in Step 103A is greater than threshold TH1
("Yes" in Step 103), bit rate calculator 423 discards the residual packet data
and does not output the residual data to error corrector 424 (Step 106). Bit
rate calculator 423 re-evaluates the bit rate calculated at Step 103A, using
threshold TH1 used in Step 101, to determine whether or not a delay in
processing occurs. If bit rate calculator 423 determines that a delay in
processing occurs based on the evaluation results, processing ends at Step
106 without decoding the residual packet data. This operation avoids error
correction using the microcomputer that may cause a delay in processing,
thereby preventing actual delay in processing.
An operation of separator 422 for separating the packet data required
for reproducing sound will be described below. Fig. 5 is a flow chart
illustrating the operation of separator 422 of digital receiving device 420
according to the embodiment. Necessary packet data to be selected by the
separation processing includes a packetized elementary stream (PES) of

audio packet data that is a source of audio data, a program association table
(PAT) of information packet data for identifying the PES, an object descriptor
(OD), and a binary format for scenes (BIFS).
These terms are in accordance with ISO/IEC 13818-1 that is standards
for an MPEG-2 system, and their functions are described later. These types
of packet data can be identified by referring to PID 302 of packet data.
Separator 422 separates audio packet data by referring to data
transferred by the above information packet data. As shown in Fig. 5,
separator 422 determines, in the order of the data obtained, whether or not
the obtained packet data is a PAT (Step 201). The searching of the PAT is
started from the packet data first obtained. This operation enables
separator 422 to obtain audio packet data even if the PMT and PID 302
required for a range of searches are changed simultaneously.
If the packet data is the PAT at Step 201 ("Yes" in Step 201), separator
422 refers to the content of the PAT, and confirms whether or not PID 302 for
searching a PMT is changed (Step 202). To avoid updating PID 302 for
detecting unsearched PMT and a PES that is audio packet data that exist
before the PAT, separator 422 only confirms at Step 202 whether or not PID
302 is updated, and does not change PID 302. The timing for changing PID
302 for searching the PMT will be described later.
Separator 422 determines whether or not the packet data is the PMT.
More specifically, separator 422 determines whether or not PID 302 of the
packet data indicates that the packet data is the PMT (Step 203). The
searching of the PMT starts from packet data in which the PMT is not
searched, and completes at packet data before the packet data determined to
be the PAT. Alternatively, the searching of PMT completes when the last
packet data is searched within a search range is completed. This operation

enables separator 422 to detect PMT even if PID 302 of the PMT is changed
by the PAT.
If it is determined at Step 203, based on PID 302, that the packet data
is not the PMT ("No" at Step 203), separator 422 confirms whether or not the
packet data includes PID 302 indicating the PES that is audio packet data,
so as to confirm whether or not the packet data is audio packet data (Step
204A). The searching of the PES that is audio packet data starts from
packet data in which the PES that is audio packet data is not detected, and
completes at packet data before the data determined to be the PMT.
Alternatively, the searching of the PES completes when the last packet data
obtained is searched within a search range. This operation enables the
searching of the PES that is audio packet data in a range in which the PMT
is valid.
If it is determined that the packet data is the PMT at Step 203 ("Yes" at
Step 203), separator 422 refers to a content of the detected PMT, and
confirms whether or not the PMT is changed (Step 205). Since the PMT is
packet data that is sent at a constant period in accordance with the
standards, the PMT may not be changed in its content. Accordingly, if no
change is confirmed, separator 422 searches for the PES that is audio packet
data at subsequent Step 204A.
If it is determined that the PMT is changed at Step 205 ("Yes" at Step
205), PID302 of the PES that is audio packet data may change at this
moment. However, separator 422 does not update PID 302 for searching
the PES that is audio data at this moment. Separator 422 only confirms the
change.
If it is determined that the PMT is changed at Step 205 ("Yes" at Step
205), separator 422 confirms a BIFS in the packet data in order to promptly

confirm a content of the OD to be referred to for confirming PID 302 of the
PES that is audio packet data (Step 206). The BIFS is searched by referring
to the content of the PMT that is changed and by detecting applicable PID
302. The searching of the BIFS starts from packet data next to the data
including the changed PMT, and ends either when packet data before the
packet data which is determined to be the next PMT is searched or when the
last packet data obtained is searched. This operation enables to the search
for the BIFS in a range in which a PMT with PID302 for search is valid.
Next, separator 422 confirms a content of the OD in order to confirm
PID 302 of the PES that is audio packet data (Step 207). This search is
executed by referring to the content of the changed PMT and detecting
applicable PID 302, similarly to Step 206. When the change of the PMT is
found by confirming PID 302 of PES that is audio packet data, a range to
search using PID 302 before change remains in packet data where PES that
is audio packet data is not yet searched. Accordingly, at Step 207, separator
422 does not update PID 302 of the PES that is audio packet data. The
searching of the OD starts from the packet data next to the packet data with
the changed PMT, and completes at packet data before the data determined
to be the PAT or PMT. Alternatively, the searching may complete when the
last packet data obtained is searched.
After confirming PID 302 of the PES that is audio packet data at Steps
205, 206, and 207, separator 422 searches for the PES that is audio packet
data (Step 204B). After separator 422 completes the searching for the PES
that is audio packet data at Step 204B, separator 422 updates PID 302 of the
PES that is audio packet data confirmed at Steps 205 and 207 (Step 208).
After updating PID 302 at Step 203, separator 422 searches for the PMT at
Step 203.

If it is determined that the PMT is not changed at Step 205 ("No" at
Step 205), separator 422 searches for audio packet data at Step 204A.
The above steps are repeated to complete the searching of the PMT and
PES that is audio packet data up to packet data before the data having the
PAT is detected at Step 201. This changes a valid range of the PMT due to
the PAT, and thus, separator 422 updates PID 302 used for searching the
PMT at Step 203 (Step 209). At Step 209, separator 422 changes PID 302 of
the PMT to be searched next.
After updating PID 302 of the PMT at Step 209, separator 422 confirms
whether or not the searching of the PES that is audio packet data is
completed in all the packet data obtained (Step 210). If the search of PES
that is audio packet data is completed at Step 210 in all packet data obtained
("Yes" at Step 210), separator 422 ends the separation processing.
If, at Step 210, there is still packet data in which the PES that is audio
packet data is not searched ("No" at Step 210), the operation returns to Step
201, and separator 422 determines whether or not next packet data is the
PAT.
As described above, in digital receiving device 420 according to the
embodiment, separator 422 separates audio packet data for reproducing
sound and information packet data for detecting this audio packet data from
packet data received. This operation can reduce packet data error-corrected
by error corrector 424. Accordingly, digital sound can be reproduced even if
data with a high bit rate containing video images is received.
As described above, in digital receiving device 420 according to the
embodiment, attributes of packet data are separated based on a bit rate of
digital broadcast packet data in which enormous quantity of video data
exists, in addition to audio data to be output, and data accompanying the

packet data. The number of packet data is reduced to the number of data
digital receiving device 420 can process. Digital receiving device 420 can
thus appropriately process only required audio data by appropriately
separating and discarding enormous quantity of video data that is not
needed for reproducing sound. Accordingly, required processing capability
can be extremely suppressed even if a microcomputer with low processing
capability is used. Even if a bit rate of incoming data increases, digital
sound can be reproduced.
In digital receiving device 420 according to the embodiment, bit rate
calculator 423 discards packet data based on the bit rate of incoming packet
data. However, digital receiving device 420 according to the embodiment is
not limited to this operation. Error corrector 424 may calculate the number
of errors per a predetermined time in the packet data. If the calculated
number of the errors is smaller than a correction limit, error corrector 424
corrects the errors in the packet data. If the calculated number is greater
than the correction limit, error corrector 424 may not correct errors in the
packet data.
In ordinary digital broadcast receiving devices, standards specify error
correction of both video signals and audio signals. It is common sense
knowledge that errors in both signals are corrected. However, in digital
receiving device 420 according to the embodiment, unlike ordinary digital
receiving devices, video data is discarded before error correction. This can
extremely suppress required processing capability also in a microcomputer
with low processing capability. Digital sound can thus be reproduced even if
a bit rate of incoming data increases.
INDUSTRIAL APPLICABILITY

A digital receiving device according to the present invention can extract
predetermined data, such as audio data, from data even if a bit rate is high,
and is applicable to digital receiving devices using MPEG-2.
REFERENCE MARKS IN THE DRAWINGS
410 Receiving Processor
420 Digital Receiving Device
421 Bit Rate Calculator (First Bit Rate Calculator)
422 Separator
423 Bit Rate Calculator (Second Bit Rate Calculator)
424 Error Corrector
425 Decoder

We Claim:
1. A digital receiving device comprising:
a first bit rate calculator receiving incoming packet data including
first packet data and second packet data, and calculating a first bit rate of
the incoming packet data;
a separator connected to the first bit rate calculator;
an error corrector connected to the first bit rate calculator and the
separator; and
a decoder connected to the error corrector.
wherein, if the first bit rate is not greater than a predetermined
threshold, the first bit rate calculator outputs the incoming packet data to
the error corrector, the error corrector error-corrects the output incoming
packet and outputs the error-corrected incoming packet data, and the
decoder decodes the incoming packet data output from the error corrector,
and
wherein, if the first bit rate is greater than the predetermined
threshold, the first bit rate calculator outputs the incoming packet data to
the separator, the separator outputs residual packet data obtained by
discarding the second packet data from the incoming packet data, the error
corrector error-corrects the residual packet data and outputs the
error-corrected residual packet data, and the decoder decodes the residual
packet data output from the error corrector.
2. The digital receiving device of claim 1, further comprising
a second bit rate calculator connected between the separator and
the error corrector, the second bit rate calculator calculating a second bit rate
of the residual packet data output from the separator,

wherein, if the first bit rate is greater than the predetermined
threshold and the second bit rate is not greater than the predetermined
threshold, the residual packet data output from the separator is output to
the error corrector, the error corrector error-corrects the residual packet data
and outputs the error-corrected residual packet data, and the decoder
decodes the residual packet data output from the error corrector, and
wherein, if the first bit rate and the second bit rate are greater
than the predetermined threshold, the second bit rate calculator discards the
residual packet data output from the separator, and the error corrector does
not error-correct the residual packet data.
3. The digital receiving device of claim 1, wherein the error corrector is
operable to:
calculate the number of errors in packet data,
correct the errors in the packet data if the calculated number is not
greater than a correction limit, and
discard the packet data if the calculated number exceeds the
correction limit.
4. The digital receiving device of claim 1, wherein the first packet data
is an audio signal of digital broadcast, and the second packet data is a video
signal of digital broadcast.