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Synchronization and error detection in a packetized data stream
| Details |
Inventors: Heegard, Chris; King, Andrew J.; Lovely, Sydney; Kolze, Thomas J.;
Assignee: General Instrument Corporation of Delaware (Chicago, IL)
Primary Examiner: Baker; Stephen M.
Assistant Examiner:
Attorney, Agent or Firm: Lipsitz; Barry R., Hoppin; Ralph F.
A method and apparatus are provided for achieving synchronization and detecting errors in a data stream such as an MPEG-2 transport packet stream. In an MPEG embodiment, the MPEG sync word is removed and replaced with a parity code that is used at the decoder for both synchronization and error detection. A syndrome calculator in the decoder can be implemented using a unique one bit in, one bit out FIR filter. Codewords used to generate the parity code can be provided by a linear block code that is a dual of a shortened cyclic code. |
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DETAILED DESCRIPTION In accordance with the present invention, a method is provided for achieving synchronization and detecting errors in a data stream carrying successive packets of k information bits and r synchronization bits.
The synchronization bits of each packet comprise a predefined, searchable pattern.
At least one synchronization pattern is located in the data stream to enable the boundaries for the k information bits of successive packets to be determined.
In one embodiment, the synchronization pattern in each packet is replaced with an r-bit parity code derived from a counterpart set of k information bits in the data stream, thereby generating a modified data stream.
The modified data stream is communicated to a decoder.
At least one of the parity codes is located in the modified data stream at the decoder to achieve synchronization.
This enables the boundaries for the k information bits of successive packets to be determined.
Once synchronization has been achieved, the parity codes are compared to checksums obtained from their counterpart k information bits at the decoder to determine when the information bits in a received packet contain an error.
The data stream can comprise an MPEG compatible data stream, e.
g.
, an MPEG-2 data stream or a similarly formatted data stream.
The parity codes can be scaled such that when decoded at the decoder, they will match MPEG synchronization patterns.
In an MPEG-2 embodiment, the number of information bits (prefix, adaptation field and payload) in a packet is k=1496.
In a preferred MPEG implementation, the synchronization pattern for each packet precedes the k information bits of that packet, whereas the counterpart set of k information bits for each parity code comprises the k information bits immediately preceding the parity code.
The parity code can be generated from a linear block code comprising a dual of a shortened cyclic code.
Communication apparatus in accordance with the present invention enables a receiver to robustly obtain synchronization and detect errors in a data stream carrying successive packets of k information bits and an r-bit parity code
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I/O Systems 
