Method and apparatus for filtering data-streams

Details Method and apparatus for filtering data-streams Method and apparatus for filtering data-streams

1999-06-14

2001-11-13

Kelley, Chris (Department: 2613)

Pulse or digital communications

Bandwidth reduction or expansion

Television or motion video signal

Reexamination Certificate

active

06317463

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates generally to information filters, and more particulary, to filters for extracting system information from HDTV transport data streams.
BACKGROUND OF THE INVENTION
Information filters are used in many applications where it is necessary to select and extract information from a data stream. The extracted information has to satisfy a predetermined pattern. For example, information filters are used to select and extract system information from a transport data stream (TS) in a HDTV (MPEG) data stream.
FIG. 1
shows a typical prior art information filter
100
. The filter requires three memory banks. A first bank
110
stores programmable values as a pattern field
111
. The pattern field can be written to the first bank by a host computer. A second bank
120
stores an enable field
121
also written by the host. The enable field indicates the locations of the enabled bits in the pattern field. A third bank
130
stores bits from the data stream
140
which will be output when bits from the data stream
140
match bits in the pattern field
111
, selected by the enable field
121
.
Only bits specified in the enable field have to be matched with the bits of the pattern field. All input bits are stored in the third memory bank so that all of the input bits may be output when matching conditions are met.
The matching is performed by a comparator
150
that compares the bits of the data stream
140
with the bit pattern
111
according to the enable field
121
. In order to minimize the size of the comparing logic, and to increase the operational speed of the filter
100
, the input data stream is usually compared serially with the pattern field, or in a serially/parallel format where suitable, i.e., the comparison is done in units of eight bits (a byte) at the time.
If the data stream includes matching patterns, then a matched signal on line
151
causes an output controller
160
to output the content of the third memory bank. The output
161
is the extracted system information. If the pattern field of the filter
100
is fully programmable with one bit resolution, then all three memory banks have to be at least equal to the size of the pattern field. This makes this type of filtering a memory-demanding application. It is desired to reduce the amount of memory used while filtering a data stream.
SUMMARY OF THE INVENTION
The invention provides a data stream filter. The filter includes a first memory bank storing a pattern field, and a second memory bank storing an enable field.
A comparator compares units of an input data stream with identically sized units of the pattern field according to corresponding units of the enable field.
An input controller, coupled to the comparator and second memory bank, writes matching units of the input data stream over the corresponding units of the pattern field.
An output controller, coupled to the comparator and the second memory bank outputs the content of the second memory bank when all units of the pattern field are matched.
In one aspect of the invention the data stream includes a system table, and the units are eight bits.


REFERENCES:
patent: 5321750 (1994-06-01), Nadan
patent: 5619501 (1997-04-01), Tamer et al.
patent: 5974501 (1999-10-01), Shaver et al.
patent: 6177922 (2001-01-01), Schiefer et al.

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