Synchronization and error detection in a packetized data stream
AssigneeGeneral Instrument Corporation of Delaware
InventorsChris Heegard, Andrew J. King, Sydney Lovely, Thomas J. Kolze
Life of this patent
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Abstract
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.
Claims24
A method 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 comprising a predefined searchable pattern, comprising the steps of:
- locating at least one synchronization pattern in said data stream to enable the boundaries for the k information bits of successive packets to be determined;
- replacing the synchronization pattern in each packet with an r-bit parity code derived from a counterpart set of k information bits in said data stream, thereby generating a modified data stream;
- communicating said modified data stream to a decoder;
- locating at least one of said parity codes in said modified data stream at said decoder to achieve synchronization, thereby enabling the boundaries for the k information bits of successive packets to be determined;
- and
- comparing said parity codes to checksums obtained from their counterpart k information bits at said decoder to determine when the information bits in a packet contain an error.
Communication apparatus for enabling 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, the parity code of each packet comprising a predefined pattern of bits detectable at said receiver by searching for said pattern and functioning as a checksum for information bits carried in said data stream, said apparatus comprising:
- means for inserting the parity codes in said packets prior to communication to said receiver, each of said parity codes being derived from a counterpart set of k information bits in said data stream;
- means for communicating said data stream to said receiver after insertion of said parity codes;
- means for locating at least one parity code in said data stream at said receiver to achieve synchronization, thereby enabling the boundaries for the k information bits of successive packets to be determined;
- and
- means at said receiver for comparing said parity codes to checksums obtained from their counterpart k information bits to determine when the information bits in a packet contain an error.
A decoder for a packetized digital data stream in which successive packets each contain k information bits and an r-bit parity code, the parity code of each packet being derived from k bits of information carried by said data stream, comprising:
- means for searching said data stream during a signal acquisition phase to locate a parity code contained therein;
- means for establishing a synchronization condition based on one or more parity codes located by said searching means;
- means for comparing a checksum derived from the k information bits of each packet to the parity code for those k information bits during a tracking phase;
- and
- means for signalling an error in the k information bits for a packet when the checksum for those bits does not match the parity code therefor.
Apparatus for calculating syndromes for linear block coded codewords, comprising:
- a finite impulse response filter having an input for receiving a serial bit stream of codeword data, each codeword containing k information bits and r parity bits, said filter having an output for providing a serial bit stream of syndromes, said syndromes comprising a fixed linear combination of a current bit of said codeword data input to said filter and the k previous bits of said codeword data;
- wherein said filter has an impulse response h.sup.k+1 (x), where:
- ##EQU18## g(x) is a generator polynomial of degree r describing a recursion to provide an infinite impulse response, and
- a(x) and b(x) are polynomials chosen such that the polynomial h.sup.k+1 (x) will be of degree k, have a non-zero constant term h.sub.0 =1, and have a non-zero final term h.sub.k =1 to provide finite impulse responses.
Dependencies are inferred from the claim text.