WO2002067429A2 - Systeme et procede d'amelioration de correction d'erreur dans le decodage en treillis, de protection d'erreur inegale de paquets de donnees de longueur variable basee sur un codage convolutionnel systematique recursif, et de codage de protection d'erreur inegale basee sur une retroaction - Google Patents

Systeme et procede d'amelioration de correction d'erreur dans le decodage en treillis, de protection d'erreur inegale de paquets de donnees de longueur variable basee sur un codage convolutionnel systematique recursif, et de codage de protection d'erreur inegale basee sur une retroaction Download PDF

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WO2002067429A2
WO2002067429A2 PCT/IL2002/000123 IL0200123W WO02067429A2 WO 2002067429 A2 WO2002067429 A2 WO 2002067429A2 IL 0200123 W IL0200123 W IL 0200123W WO 02067429 A2 WO02067429 A2 WO 02067429A2
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Prior art keywords
data
encoding
packets
operable
paths
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PCT/IL2002/000123
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English (en)
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WO2002067429A8 (fr
WO2002067429A3 (fr
Inventor
Ofer Amrani
Meir Ariel
Jacob Goldberger
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Cute Ltd.
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Priority claimed from US09/785,489 external-priority patent/US20020157058A1/en
Priority claimed from US09/785,192 external-priority patent/US20020144209A1/en
Priority claimed from US09/785,191 external-priority patent/US20020146074A1/en
Application filed by Cute Ltd. filed Critical Cute Ltd.
Priority to AU2002232101A priority Critical patent/AU2002232101A1/en
Publication of WO2002067429A2 publication Critical patent/WO2002067429A2/fr
Publication of WO2002067429A3 publication Critical patent/WO2002067429A3/fr
Publication of WO2002067429A8 publication Critical patent/WO2002067429A8/fr

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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L1/00—Arrangements for detecting or preventing errors in the information received
    • H04L1/004—Arrangements for detecting or preventing errors in the information received by using forward error control
    • H04L1/0056—Systems characterized by the type of code used
    • H04L1/0067—Rate matching
    • H04L1/0068—Rate matching by puncturing
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
    • H03M13/00—Coding, decoding or code conversion, for error detection or error correction; Coding theory basic assumptions; Coding bounds; Error probability evaluation methods; Channel models; Simulation or testing of codes
    • H03M13/27—Coding, decoding or code conversion, for error detection or error correction; Coding theory basic assumptions; Coding bounds; Error probability evaluation methods; Channel models; Simulation or testing of codes using interleaving techniques
    • H03M13/2703—Coding, decoding or code conversion, for error detection or error correction; Coding theory basic assumptions; Coding bounds; Error probability evaluation methods; Channel models; Simulation or testing of codes using interleaving techniques the interleaver involving at least two directions
    • H03M13/2707—Simple row-column interleaver, i.e. pure block interleaving
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
    • H03M13/00—Coding, decoding or code conversion, for error detection or error correction; Coding theory basic assumptions; Coding bounds; Error probability evaluation methods; Channel models; Simulation or testing of codes
    • H03M13/29—Coding, decoding or code conversion, for error detection or error correction; Coding theory basic assumptions; Coding bounds; Error probability evaluation methods; Channel models; Simulation or testing of codes combining two or more codes or code structures, e.g. product codes, generalised product codes, concatenated codes, inner and outer codes
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
    • H03M13/00—Coding, decoding or code conversion, for error detection or error correction; Coding theory basic assumptions; Coding bounds; Error probability evaluation methods; Channel models; Simulation or testing of codes
    • H03M13/35—Unequal or adaptive error protection, e.g. by providing a different level of protection according to significance of source information or by adapting the coding according to the change of transmission channel characteristics
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
    • H03M13/00—Coding, decoding or code conversion, for error detection or error correction; Coding theory basic assumptions; Coding bounds; Error probability evaluation methods; Channel models; Simulation or testing of codes
    • H03M13/37—Decoding methods or techniques, not specific to the particular type of coding provided for in groups H03M13/03 - H03M13/35
    • H03M13/39—Sequence estimation, i.e. using statistical methods for the reconstruction of the original codes
    • H03M13/3988—Sequence estimation, i.e. using statistical methods for the reconstruction of the original codes for rate k/n convolutional codes, with k>1, obtained by convolutional encoders with k inputs and n outputs
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
    • H03M13/00—Coding, decoding or code conversion, for error detection or error correction; Coding theory basic assumptions; Coding bounds; Error probability evaluation methods; Channel models; Simulation or testing of codes
    • H03M13/37—Decoding methods or techniques, not specific to the particular type of coding provided for in groups H03M13/03 - H03M13/35
    • H03M13/39—Sequence estimation, i.e. using statistical methods for the reconstruction of the original codes
    • H03M13/41—Sequence estimation, i.e. using statistical methods for the reconstruction of the original codes using the Viterbi algorithm or Viterbi processors
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
    • H03M13/00—Coding, decoding or code conversion, for error detection or error correction; Coding theory basic assumptions; Coding bounds; Error probability evaluation methods; Channel models; Simulation or testing of codes
    • H03M13/63—Joint error correction and other techniques
    • H03M13/635—Error control coding in combination with rate matching
    • H03M13/6362—Error control coding in combination with rate matching by puncturing
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L1/00—Arrangements for detecting or preventing errors in the information received
    • H04L1/0001—Systems modifying transmission characteristics according to link quality, e.g. power backoff
    • H04L1/0009—Systems modifying transmission characteristics according to link quality, e.g. power backoff by adapting the channel coding
    • H04L1/0013—Rate matching, e.g. puncturing or repetition of code symbols
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L1/00—Arrangements for detecting or preventing errors in the information received
    • H04L1/004—Arrangements for detecting or preventing errors in the information received by using forward error control
    • H04L1/0045—Arrangements at the receiver end
    • H04L1/0054—Maximum-likelihood or sequential decoding, e.g. Viterbi, Fano, ZJ algorithms
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L1/00—Arrangements for detecting or preventing errors in the information received
    • H04L1/004—Arrangements for detecting or preventing errors in the information received by using forward error control
    • H04L1/0056—Systems characterized by the type of code used
    • H04L1/0059—Convolutional codes
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L1/00—Arrangements for detecting or preventing errors in the information received
    • H04L1/004—Arrangements for detecting or preventing errors in the information received by using forward error control
    • H04L1/0056—Systems characterized by the type of code used
    • H04L1/007—Unequal error protection
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L1/00—Arrangements for detecting or preventing errors in the information received
    • H04L1/004—Arrangements for detecting or preventing errors in the information received by using forward error control
    • H04L1/0056—Systems characterized by the type of code used
    • H04L1/0071—Use of interleaving
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L1/00—Arrangements for detecting or preventing errors in the information received
    • H04L1/12—Arrangements for detecting or preventing errors in the information received by using return channel
    • H04L1/16—Arrangements for detecting or preventing errors in the information received by using return channel in which the return channel carries supervisory signals, e.g. repetition request signals
    • H04L1/1607—Details of the supervisory signal
    • H04L1/1621—Group acknowledgement, i.e. the acknowledgement message defining a range of identifiers, e.g. of sequence numbers

Definitions

  • the present invention relates to a system and method for enhanced error correction in media communications, also reliable transmission of data using unequal error protection of variable-length data packets based on recursive systematic convolutional coding, also feedback-based unequal error protection coding
  • Long message blocks typically IP packets that enter the wireless part of the network, are split up into segments of desired length, which can be
  • wireless links suffer from severe fading, noise, and interference conditions in general, thus resulting
  • FEC coding is a well-known technique for achieving error correction and detection in data communications.
  • FEC has the disadvantage of increasing transmission overhead and hence reducing usable bandwidth for the payload data.
  • it is generally used judiciously in video services, since video services are very demanding in bandwidth but can tolerate a certain degree of loss.
  • FEC has been employed for error recovery in video communications in several standards.
  • H.261 an 18-bit error-correction code is computed and appended to 493 video bits for detection and correction of random bit errors in integrated services digital network (ISDN).
  • ISDN integrated services digital network
  • Lee et al. S. H. Lee, P. J. Lee, and R. Ansari, "Cell loss detection and recovery in variable rate video," in Proc. 3rd Int. Workshop Packet Video, Morriston, Mar. 1990, the contents of which are hereby incorporated by reference propose to combine Reed-Solomon (RS) codes with block interleaving to recover lost ATM cells.
  • RS Reed-Solomon
  • An RS (32,28,5) code is applied to every block of 28 bytes of data to form a block of 32 bytes. After applying the RS code row by row in the memory up to the forty-seventh row, the payload of 32 ATM cells is formed by reading column by column from the
  • detected cell loss at the decoder corresponds to one byte erasure in
  • each row of 32 bytes after de-interleaving Up to four lost cells out of 32 cells can be recovered.
  • the Grand-Alliance High-Definition Television broadcast system has adopted a similar technique for combating transmission errors (K. Challapali, X. Lebegue, J. S. Lim, W. H. Paik, R. Saint Girons, E. Petajan, N. Sathe, P. A. Snopko, and J. Zdepski, "The grand alliance system for US HDTV," Proc. IEEE, vol. 83, pp. 158-174, Feb. 1995, the contents of which are hereby incorporated by reference).
  • data randomization and interleaving are employed to provide further protection. As a fixed amount of video data has to be accumulated to perform the block interleaving described above, relatively long delay is however introduced.
  • FEC is used at the byte level for random bit error correction and at the ATM cell level for cell-loss recovery.
  • Such use of FEC techniques may be applied to both single-layer and two-layer MPEG data. It is shown that the two-layer coder outperforms the one-layer approach significantly, at a fairly small overhead.
  • the paper also compares direct cell-level coding with the cell- level interleaving followed by FEC. It is noted that the paper concludes that the latter introduces longer delay and bigger overhead for equivalent error- recovery performance and suggests that direct cell-level correction is preferred.
  • RTP Real Time Protocol
  • Rosenberg et al J. Rosenberg and H. Schulzrinne, "An RTP payload format for generic error correction," RFC 2733, Dec. 1999, the contents of which are hereby incorporated by reference
  • xor exclusive-or
  • the sender also applies the xor operation
  • each FEC packet contains a bitmask, called the offset mask, containing 24 bits. If bit i in the mask is set to 1, it may be concluded that the media packet with sequence number N + i has been used to generate the corresponding FEC packet. N is called the sequence number base, and is incorporated into the FEC packet as well.
  • the offset mask and payload type are sufficient to signal arbitrary parity based FEC schemes with little overhead.
  • the sender As the sender generates FEC packets, they are sent to the receivers. The sender still usually sends the original media stream, as if there were no FEC. Such a procedure allows the media stream to be used by receivers which are not FEC capable.
  • FEC codes do not require the original media to be sent; as the FEC stream is sufficient for recovery.
  • Such FEC codes have the drawback, however, that all receivers must be FEC capable. Returning to systematic codes and the FEC packets are not sent in the
  • the FEC packets When sent as a separate stream, the FEC packets have their own sequence number space. At the receiver, the FEC and original media are received. If no media packets are lost, the FEC can be ignored. In the event of loss, the FEC packets can be combined with other media and FEC packets that have been received, resulting in recovery of missing media packets. The recovery is exact; the payload is perfectly reconstructed, along with most components of the header.
  • RTP packets which contain data formatted according to such a specification (i.e., FEC packets) are signaled using dynamic RTP payload types.
  • the xor-based FEC technique presented in RFC2733 uses a function f(x,y,..) defined as the xor operator applied to the packets x,y,...
  • the output of this function is another packet, called the parity packet.
  • the parity packet is computed as the bitwise xor of the input packets. Recovery of data packets using parity codes is accomplished by generating one or more parity packets over a group of data packets.
  • Four exemplary schemes are given as follows:
  • a parity code that generates a single parity packet over two data packets is selected. If the original media packets are a,b,c,d, the packet stream generated by the sender is of the form:
  • correction code introduces a 50% overhead. If packet b is lost, a and f(a,b) may be used to recover b.
  • Scheme no. 2 is similar to Scheme no. 1. However, instead of sending packet b followed by the packet formed by f(a,b), f(a,b) is sent before b. Such an order inversion requires additional delay at the sender but has the advantage that it allows certain bursts of two consecutive packet losses to be recovered.
  • the packet stream generated by the sender is of the form:
  • the packet stream generated by the sender is of the form:
  • passive error concealment In addition to forward error correction, passive error concealment is known.
  • the objective of passive concealment techniques is to estimate missing macroblocks and motion vectors. The underlying idea is that there is still enough redundancy in the sequence to be exploited by the concealment technique.
  • Passive concealment techniques are used as part of postprocessing methods which utilize spatial data, or temporal data, or a hybrid of both (see, e.g., the papers by M. Wada, "Selective recovery of video packet loss using error concealment," IEEE J. Select. Areas Commun., vol.
  • Trellis decoding builds up possible data paths, taking advantage of redundancy introduced by the use of a codebook, and then
  • the trellis decoder is able to produce a single unambiguous selection
  • a decoding device for receiving a data stream from a data sourcean encoding device for encoding a real time data stream for transfer over a noisy channel, the data being arranged in variable length packets using unequal encoding levels for different parts of the data stream, the decoder stream comprising data bits in a succession of data packets, the system comprising: a data transmitter for sending said data bits in said packets in a utilization order,
  • a data interleaver for interleaving said data bits into an interleaved order
  • an encoder for encoding said data bits in said interleaved order to form
  • parity bits for insertion into said data stream as a parity set, such that said parity
  • bits are differentially distributed over said packets from said data bits.
  • said data distributor is operable to distribute said data bits into said interleaved order in such a way as to satisfy a uniformity criterion.
  • said uniformity criterion is such as to allow reconstruction of erased data packets from surviving data packets, wherein said erased data packets do not exceed a predetermined proportion of said surviving data packets.
  • said uniformity criterion is such that for any window w taken over said interleaved data, a proportion of interleaved bits originating from any given packet is substantially the same.
  • said data packets comprise a plurality of fields of differing importance and wherein said encoder is operable to apply unequal levels of error protection encoding to said fields.
  • the encoder is operable to apply said unequal levels of error protection encoding via a puncture matrix.
  • said encoder is operable to produce said parity bits using a recursive systematic convolutional encoding process.
  • said recursive systematic convolutional encoding process is defined by
  • D indicates a once delayed prior input
  • D m dicates a twice delayed prior input
  • D 4 indicates a four times delayed prior input
  • D indicates a five times delayed prior input
  • D 6 indicates a six times delayed prior input.
  • said data packets are variable size data packets and further comprising a parity bit distributor for distributing said parity bits across said data packets in such a way as to equalize the size of the packets.
  • said encoder is operable to apply said unequal levels of error protection encoding via a puncture matrix.
  • said data packets comprise a plurality of fields of differing importance and wherein said encoder is operable to apply unequal levels of error protection encoding to said fields.
  • said device further comprises a parity bit distributor for distributing said punctured parity bits across said data packets in such a way as to equalize the sizes of said packets.
  • said data interleaver is operable to interleave said data in accordance with a uniformity criterion and wherein said uniformity criterion is
  • said uniformity criterion is such that for any window over a
  • parameters of at least one of said unequal error protection encoding levels and said puncture matrix is included in a packet header.
  • a preferred embodiment of the present invention is operable to use any selected one of only a predetermined set of combinations of puncture matrices and unequal error protection levels and is operable to include an index of said selected combination in a packet header, thus reducing packet overhead.
  • An embodiment further comprises a feedback receiver operable to receive feedback from a receiver of said data stream and to modify an encoding scheme based on said feedback.
  • said puncture matrix is selected according to feedback received from a receiver of said data stream.
  • the feedback may typically involve an indication of noise levels in the received signal and the encoder may exchange any of its encoding parameters or may even exchange the encoder itself in response to the feedback.
  • said uniformity criterion is such as to allow reconstruction of
  • said uniformity criterion is such that for any window w taken over said interleaved data, a proportion of interleaved parity bits originating from any given packet is substantially the same.
  • a decoding device for decoding a real time transmitted data stream received from a noisy channel, the data stream comprising data bits in a utilization order and interleaved parity bits, in a succession of data packets, the system comprising: a data receiver for receiving said data stream, a data receiver for deinterleaving said data bits, a parity bit retriever for retrieving and deinterleaving said parity bits from said data stream, and a decoder for decoding said data bits with said deinterleaved parity bits, thereby to reconstruct data erased by said channel.
  • said parity bit retriever is operable to retrieve parity bits which have been distributed across said data packets in such a way as to equalize packet sizes.
  • said deinterleaver is operable to deinterleave data bits
  • said uniformity criterion according to an inverse of a uniformity criterion, said uniformity criterion
  • said uniformity criterion is such that for any window over a length w of a data stream over which parity bits from a given data packet are distributed, the proportion of data bits from said given packet is substantially identical.
  • said data packets comprise a plurality of fields of differing importance and wherein said data stream comprises unequal levels of error protection encoding to said fields.
  • said data packets comprise video data compressed using a transform combined with motion vectors of identified macroblocks.
  • said parity bits are defined by the encoding process:
  • D indicates a once delayed prior input and D 2 indicates a twice delayed prior input.
  • said parity bits are defined by the encoding process:
  • G (l +D + D 4 + D 5 + D 6 ) / (1 + D + D 2 + D 4 + D 5 ), where D indicates a once delayed prior input, D 2 indicates a twice delayed prior input, D indicates a four times delayed prior input, D 5 indicates a five times delayed prior input, and D 6 indicates a six times delayed prior input.
  • parameters of at least one of said unequal error protection encoding levels and said puncture matrix are obtained from a packet header.
  • said header comprises an index defining a combination of
  • said decoder comprises a trellis decoder operable to determine at least one most likely data path from a plurality of allowed paths using a minimum Hamming distance criterion.
  • said trellis decoder further comprises a progressive windower for use when there remains more than one most likely data path, said progressive windower being operable to progressively window said trellis to enable viewing of sections of said trellis, thereby to exclude ones of said most likely data paths exhibiting predetermined features within said window.
  • said predetermined features include data units not comprised in a predetermined codebook of allowable data units.
  • said predetermined features include data units not comprised in an encoding scheme used to encode the data.
  • said data is visual data and said predetermined features include undesirable visual artifacts.
  • said predetermined features include lack of compatibility with neighboring data units.
  • said predetermined features include improbable distributions of transform coefficients.
  • transform coefficients are discrete cosine transform coefficients.
  • a preferred embodiment further comprises a feedback delivery unit for
  • said uniformity criterion is such as to allow reconstruction of erased data packets from surviving data packets, provided that said erased data packets do not exceed a predetermined proportion of said surviving data packets.
  • said uniformity criterion is such that for any window w taken over said interleaved data, a proportion of interleaved parity bits originating from any given packet is substantially the same.
  • a system for streaming data and corresponding protective parity bits in packets over a channel comprising a recursive systematic convolutional encoder at a sending end for producing said corresponding protective parity bits and a recursive systematic convolutional decoder at a receiving end for reconstructing data lost in the channel, and a data interleaver at a sending end for interleaving data for said recursive systematic convolutional encoder according to a uniformity criterion to form parity bits therefrom, and a parity bit distributor operable to distribute said parity bits over said packets differentially from corresponding data.
  • said uniformity criterion is such as to allow reconstruction of
  • said uniformity criterion is such that for any window over a length w of a data stream over which parity bits from a given data packet are distributed, the proportion of data bits from said given packet is substantially identical.
  • said data packets comprise a plurality of fields of differing importance and wherein said encoder is operable to apply unequal levels of error protection encoding to said fields.
  • a preferred embodiment is preferably operable to apply said unequal levels of error protection encoding via a puncture matrix.
  • said recursive systematic convolutional encoder is operable to produce parity bits using a process defined by
  • D indicates a once delayed prior input and D 2 indicates a twice delayed prior input.
  • said recursive systematic convolutional encoder is operable to produce parity bits using a process defined by:
  • D 4 indicates a four times delayed prior input
  • D 5 indicates a
  • D 6 indicates a six times delayed prior input.
  • parameters of at least one of said unequal error protection are preferably, parameters of at least one of said unequal error protection
  • encoding levels and said puncture matrix are included in a packet header.
  • said encoder is operable to use any selected one of only a predetermined set of combinations of puncture matrices and unequal error protection encoding levels and which encoder is operable to include an index of said selected combination in a packet header.
  • a preferred embodiment preferably comprises a feedback path operable to receive feedback from a receiver of said data stream and to modify an encoding level based on said feedback.
  • said puncture matrix is selected according to feedback received from a receiver of said data stream.
  • said decoder comprises a trellis decoder operable to determine at least one most likely data path from a plurality of allowed paths using a minimum Hamming distance criterion.
  • said trellis decoder further comprises a progressive windower operable to view windows over said trellis, such that in a case of more than one most likely path, said trellis may be viewed progressively via said windows thereby to exclude any of said most likely data paths showing predetermined features within a current one of said windows.
  • said predetermined features include data units not comprised
  • said predetermined features include data units not comprised
  • said data is visual data and said predetermined features include undesirable visual artifacts.
  • said predetermined features include lack of compatibility with neighboring data units. For example, sharp discontinuities which are not continuations of similar discontinuities in neighboring areas could constitute such artifacts.
  • said predetermined features include improbable distributions of transform coefficients.
  • said transform coefficients are discrete cosine transform coefficients.
  • said channel includes a cellular connection.
  • said data comprises compressed video.
  • said compressed video comprises motion vector portions and transformed portions.
  • said packets are variable length packets and said parity bit distributor is operable to distribute parity bits in such a way as to equalize packet lengths.
  • a preferred embodiment preferably comprises a parity bit distributor
  • said uniformity criterion is such as to allow reconstruction of
  • said uniformity criterion is such that for any window w taken over said interleaved data, a proportion of interleaved parity bits originating from any given packet is substantially the same.
  • a method of fransferring compressed multimedia data arranged into fields of varying importance over a channel liable to erasure in variable length packets comprising: inserting said data into said packets, interleaving said data using a uniformity criterion, generating parity bits using a recursive systematic convolutional code from said interleaved data, distributing said parity bits across said packets amongst said data, transferring said packets over said channel, and reconstructing said compressed multimedia data at a receiver.
  • trellis decoder for forming a trellis of possible data paths in response to a received data stream on the basis of a codebook of permissible data codewords
  • the decoder comprising:
  • an eliminator for identifying any of said possible data paths having a lowest Hamming distance and eliminating all other possible data paths to leave said paths having a lowest Hamming distance as a surviving path
  • a multiple path determiner for determining if there is more than one surviving path
  • a progressive windower for use in the event of there being more than one surviving path, said windower operable for progressively viewing said trellis using successive windows of a given size in bits in to identify predetermined features in said surviving paths appearing in said windows and to eliminate surviving paths having said predetermined features as they appear in said window, thereby to leave a single surviving path as an output of said trellis decoder.
  • said progressive windower further comprises a window adjuster operable to increase a size in bits of said window and repeat said progressive windowing in the event that a completed progressive windowing has not resulted in a single surviving path.
  • said given bit size is selected to be sufficiently large for said predetermined feature to be identifiable therein.
  • said trellis has a first end associated with an earlier part of
  • said predetermined features comprise a syntactic violation.
  • said predetermined features comprise a semantic violation.
  • said predetermined features comprise data units not found in a predetermined codebook of allowable data units.
  • said predetermined features comprise data units not found in an encoding scheme used to encode the data.
  • said data is visual data and said predetermined features comprise unlikely visual artifacts.
  • said predetermined features comprise lack of compatibility with neighboring data units.
  • said predetermined features comprise an improbable distribution of transform coefficients.
  • said transform coefficients are discrete cosine transform coefficients.
  • said paths in said trellis have descendent paths and said eliminator is operable to eliminate a path and all descendent paths thereof.
  • said paths in said trellis have descendent paths and said
  • progressive windower is operable to eliminate a path and all descendent paths
  • a preferred embodiment preferably comprises a feedback delivery unit for feeding back information indicative of data receipt quality to a data source.
  • a system for communicating data as a data stream over a noisy channel having a transmitter comprising an encoder and a receiver comprising a decoder, wherein said encoder is operable to encode a data sequence using a convolutional code and wherein said decoder comprises a trellis decoder for decoding said convolutional code by forming a trellis of possible data paths in response to a received version of said data stream on the basis of a codebook of permissible data codewords, the trellis decoder comprising: a Hamming distancer for computing a Hamming distance from said received data stream to each one of said data paths, an eliminator for identifying any of said possible data paths having a lowest Hamming distance and eliminating all other possible data paths to leave said paths having a lowest Hamming distance as a surviving path, a multiple path determiner for determining if there is more than one surviving path, and a progressive windower for use in the event of
  • said windower operable for progressively viewing said
  • said progressive windower further comprises a window adjuster operable to increase a size in bits of said window and repeat said progressive windowing in the event that a completed progressive windowing has not resulted in a single surviving path.
  • said given bit size is selected to be sufficiently large for said predetermined feature to be identifiable therein.
  • said trellis has a first end associated with an earlier part of said received data stream and a second end associated with a later part of said received data stream and wherein said progressive windower is operable to begin said successive windowing from said second end towards said first end.
  • said predetermined features comprise a syntactic violation.
  • said predetermined features comprise a semantic violation. Additionally or alternatively, said predetermined features comprise data
  • said predetermined features comprise data
  • said data is visual data and said features comprise comprises unlikely visual artifacts.
  • said predetermined features comprise lack of compatibility with neighboring data units.
  • said predetermined features comprise an improbable distribution of transform coefficients.
  • said transform coefficients are discrete cosine transform coefficients.
  • said paths in said trellis have descendent paths and said eliminator is operable to eliminate a path and all descendent paths thereof.
  • said paths in said trellis have descendent paths and said progressive windower is operable to eliminate a path and all descendent paths thereof.
  • the system further comprises a retracer for retracing from said first end to said second end of said trellis to give said single surviving path as an output.
  • a preferred embodiment preferably comprises a feedback delivery unit for feeding back information indicative of data receipt quality to a data source.
  • the channel may include a cellular connection.
  • the data may comprise compressed video.
  • the compressed video may comprise motion vector portions and
  • a method of discriminating between equally probable trellis paths surviving in a trellis decoder to select a single output path comprising: windowing over said trellis decoder to view said surviving paths in successive windows, identifying a predetermined feature in said paths as they appear in said successive windows, and eliminating ones of said surviving paths having said predetermined feature to leave a single surviving path to form said output path.
  • said progressive windower further is further operable to increase a size in bits of each of said successive windows and repeat said windowing in the event that a completed progressive windowing over said trellis has not resulted in a single surviving path.
  • said size in bits is selected to be sufficiently large for said predetermined features to be identifiable therein.
  • windowing over said trellis is carried out from a temporally later end of said trellis to a temporally earlier end.
  • the predetermined features used to reject equiprobable paths include syntactic violations. Additionally or alternatively, said predetermined features comprise a
  • said predetermined features comprise data
  • said predetermined features comprise data units not found in an encoding scheme used to encode the data.
  • said data is visual data and said predetermined features comprise unlikely visual artifacts.
  • said predetermined features comprise indications of lack of compatibility with neighboring data units.
  • said predetermined features comprise an improbable distribution of transform coefficients.
  • said transform coefficients are discrete cosine transform coefficients.
  • said paths in said trellis have descendent paths and wherein eliminating of a path includes eliminating of all descendent paths thereof.
  • said paths in said trellis have descendent paths and said progressive windower is operable to eliminate a path and all descendent paths thereof.
  • the method further comprises retracing from said said temporally earlier end of said trellis to said temporally later end to output said single surviving path.
  • a preferred embodiment comprises feeding back information indicative
  • a decoding device for receiving a data stream from a data source over a noisy channel, the data being arranged in variable length packets using unequal encoding levels for different parts of the data stream, the decoder having a feedback transmitter for sending feedback data via a feedback channel to said data source to indicate a level of quality of data receipt at said decoder, thereby to provide dynamic adaptation to conditions in said channel.
  • a preferred embodiment is operable to decode data encoded using RSC encoding.
  • the data stream comprises data bits in a utilization order and interleaved parity bits, in a succession of data packets.
  • the device preferably comprises: a data receiver for receiving said data stream, a data receiver for deinterleaving said data bits, a parity bit retriever for retrieving and deinterleaving said parity bits from said data stream, and
  • said data packets comprise a plurality of fields of differing
  • said feedback transmitter being operable to signal to said data source to increase said unequal levels of protection in the
  • said data packets comprise video data compressed using a transform combined with motion vectors of identified macroblocks.
  • parameters of at least one of said unequal error protection encoding levels and said puncture matrix are obtained from a packet header.
  • said header comprises an index defining a combination of unequal error protection encoding level and a puncture matrix in said packet header.
  • an encoding and transmitting device for encoding a data stream and transmitting said data stream over a noisy channel to a receiver device, the encoder having: at least one encoder for encoding said data, a packetizer for arranging the encoded data into variable length encoded packets using unequal encoding levels for different parts of the packet,
  • a feedback receiver for receiving feedback data via a feedback channel from said receiving device to indicate a level of quality of data receipt at said receiving device, and an adapter for utilizing said feedback data to modify parameters used in
  • said data packets comprise a plurality of fields of differing importance and wherein said encoder is operable to apply unequal levels of error protection encoding to said fields.
  • said encoder is operable to apply said unequal levels of error protection encoding via a puncture matrix.
  • said encoder is operable to produce parity bits with a recursive systematic convolutional encoding process using parameters selectable in response to said feedback data.
  • said recursive systematic convolutional encoding process is defined by
  • G (l +D)/(1 + D + D 2 ), where D indicates a once delayed prior input and D 2 indicates a twice delayed prior input.
  • said recursive systematic convolutional encoding process is defined by
  • D indicates a once delayed prior input
  • D 2 indicates a twice delayed prior input
  • D 4 indicates a four times delayed prior input
  • D 5 indicates a five times delayed prior input
  • D 6 indicates a six times delayed prior input.
  • said encoder is operable to apply said unequal levels of error
  • said data packets comprise a plurality of fields of differing importance and wherein said encoder is operable to apply unequal levels of error protection encoding to said fields, according to parameters selectable according in accordance with said feedback data.
  • said encoder further comprises a data interleaver, being operable to interleave said data in accordance with a uniformity criterion and wherein said uniformity criterion is selected such as to allow reconstruction of erased data packets from surviving data packets, whenever said erased data packets do not exceed a predetermined proportion of said surviving data packets.
  • a uniformity criterion is selected such as to allow reconstruction of erased data packets from surviving data packets, whenever said erased data packets do not exceed a predetermined proportion of said surviving data packets.
  • said uniformity criterion is such that for any window over a length w of said interleaved data, the proportion of data bits from any given packet remains substantially constant.
  • parameters of at least one of said unequal error protection encoding levels and said puncture matrix is included in a packet header and are variable in accordance with said feedback data.
  • An embodiment of the invention is selectably operable to use any selected one of only a predetermined set of combinations of puncture matrices and differential encoding levels, which selection is influenced by said feedback data and which is operable to include an index of said selected combination in a
  • a system for streaming data and corresponding protective parity bits in packets over a channel comprising
  • a feedback channel between said sending end and said receiving end for allowing encoding parameters at said sending end to be modified by receiving conditions at said receiving end.
  • said data packets comprise a plurality of fields of differing importance and wherein said encoder is operable to apply unequal levels of error protection encoding to said fields using parameters variable in accordance with feedback from said feedback channel.
  • said system is operable to apply said unequal levels of error
  • parameters of at least one of said unequal error protection encoding levels and said puncture matrix are variable in accordance with feedback from said feedback channel and are included in a packet header.
  • said encoder is operable to use any selected one of only a predetermined set of combinations of puncture matrices and unequal error protection encoding levels, said selection being at least partially dependent on feedback from said feedback channel and which encoder is operable to include an index of said selected combination in a packet header.
  • said channel includes a cellular connection.
  • said data comprises compressed video.
  • said compressed video comprises motion vector portions and transformed portions.
  • method of transferring compressed multimedia data arranged into fields of varying importance over a channel liable to erasure in variable length packets comprising: inserting said data into said packets, interleaving said data using a uniformity criterion,
  • Fig. 1 is a generalized diagram of a video packet, showing typical packet
  • Fig. 2 is a simplified diagram of an RSC encoder for use with
  • Fig. 3 is a simplified block diagram which shows a transmission path for a data stream according to an embodiment of the present invention
  • Fig. 4 is a simplified block diagram showing the datastream protection encoder of Fig. 3 in greater detail
  • Fig. 5 is a simplified block diagram showing the datastream protection decoder of Fig.3 in greater detail
  • Fig. 6 is a trellis diagram showing windowing of the frellis to eliminate data paths
  • Fig. 7 is a simplified block diagram showing a communication system according to a preferred embodiment of the present invention with a feedback channel between the decoder and the encoder.
  • Fig. 1 is a simplified diagram showing
  • packet 10 comprises a series of fields as follows: a video packet header 12 which contains general header information relevant to MPEG-4 processing, and two more fields which contain different types of compressed image data, motion vectors 14 and DC and AC DCT data 16.
  • image data is generally encoded in three stages, a first stage being discrete cosine transform (DCT), which causes progressively higher levels of detail to migrate towards one corner of the image.
  • DCT discrete cosine transform
  • a quantization stage then leads to a certain reduction in the quantity of data and this is followed by a stage of Huffman, or variable length, encoding, to provide a high level of data compression.
  • the compressed image data obtained is placed into fields in a series of packets for streaming.
  • image data as opposed to text, a certain amount of data loss can be tolerated without the effects being particularly noticeable to the viewer and
  • the video packet header 12 is essential to correct
  • the motion vector data 14 is important but less critical than the header data 12 and the DCT information 14 is least critical of all. Thus, if the packets are being transmitted over a channel in which bandwidth is at a premium, then unequal levels of protection may be provided for the different types of data.
  • packets such as packet 10 of Fig. 1, with a form of protection against channel data loss, distortion and erasure that allows for such unequal levels of protection of parts of the packet. Furthermore, it is desirable to provide a level of protection which allows for reconstruction of the image in the event of erasure of entire packets and even bursts of packets, in the event of their erasure by the channel.
  • Convolutional coding and in particular recursive systematic convolutional coding, is a popular error correction scheme in communication systems, largely due to the compact and regular description of the code via a trellis diagram and the corresponding maximum likelihood decoding algorithm known as the Niterbi algorithm (see G. D. Forney, "The Niterbi algorithm,” Proc. IEEE, vol. 61, no. 3, pp. 268-278, Mar. 1973, the contents of which are hereby incorporated by reference).
  • An important advantage of convolutional coding is that it is easy to provide unequal coding levels as discussed above using the same convolution code by means of a technique
  • puncturing which will be described in more detail below.
  • parity check bits to be transmitted as a separate stream.
  • This has the advantage of rendering the system backwards compatible with non-FEC capable hosts, so that receivers which cannot benefit from the FEC advantages can simply ignore the parity bits.
  • NSC non-systematic convolutional
  • a recursive systematic convolutional (RSC) code combines the properties of the NSC and systematic codes, and in particular, its bit error rate (BER) performance is better than the equivalent NSC code at any signal to noise ratio for codes rates larger than 2/3.
  • a binary rate RSC code is obtained from a NSC code by
  • unequal levels of encoding may be achieved using such an encoder by puncturing, meaning excluding certain outputs produced by the encoder.
  • all the outputs may be used for the most critical parts of the data, giving maximal reconstructive ability, whereas the least critical parts of the data may use high levels of puncturing to remove most of the parity bits generated by the encoder.
  • Puncturing may be implemented by using a puncture matrix which defines a perforation pattern. For example, for
  • FIG. 3 is a simplified block diagram showing a system for managing data packet transfer according to a first
  • An MPEG encoder 40 produces a stream
  • protection encoder 42 performs the function of decreasing the sensitivity of the
  • the stream is then passed through RTP 44, UDP, 46 and IP 48 protocol layers for transfer along a channel 50.
  • the stream is subject to distortion, delay and erasure. It is noted that in the case of multimedia data needed for real time playing, delayed packets are in effect erased packets as they arrive too late.
  • the stream passes through a reversed order of protocol layers, IP 52, UDP 54 and RTP 56, to a datastream protection decoder 58, whose function is complementary to that of the encoder 42 and which will be described in greater detail below. Finally the data packets are passed to an MPEG decoder 60 with channel errors repaired as far as possible.
  • each p is obtained at the output of a media encoder, such as MPEG-4 encoder 40.
  • each p ⁇ is a video packet containing an integer number of compressed macro blocks.
  • the size of a compressed macro block is not fixed, but rather depends on the amount of information it carries and the particular compression algorithm being used by the media encoder 40. Consequently, the length of a
  • video packet is not known in advance and can vary between predefined upper and lower limits.
  • l_, ... , / k denote the lengths of p ⁇ , ..., p k ,
  • the set P is transmitted over a noisy channel 50.
  • the channel may be a wireline or wireless network or any combination of wireless and wireline, and
  • the channel 50 might comprise the RTP/UDP/IP layers of the Internet (as shown), lower layers of the Universal Mobile Telecommunication System (UMTS), and a wireless fading channel in between the physical layers of the UMTS.
  • UMTS Universal Mobile Telecommunication System
  • an objective of the present embodiment is to enable reconstruction of the entire set P from P ⁇
  • the reconstruction is based on interleaving and RSC encoding applied to the compressed data at the datastream protection encoder 42, as will be described in greater detail below.
  • the RSC encoding as will be described in greater detail below, preferably generates a set Q of parity check bits.
  • Fig. 4 is a simplified diagram showing
  • the encoder 42 is the datastream protection encoder 42 in greater detail.
  • the interleaver 70 preferably carries out interleaving only for the purpose of generating the set Q of parity bits.
  • the data itself is transmitted in a non-interleaved form.
  • the parity check bits are transmitted separately or in an Internet packet header extension (in the preferred embodiment, RTP header extension).
  • RTP header extension an Internet packet header extension
  • An advantage of the present embodiment is that the selection of any particular RSC code can be changed in real time to enable a judicious tradeoff between complexity and performance.
  • the parameters of the selected RSC encoding scheme are preferably appended to the Q set and transmitted to the receiver.
  • the parameters are at least partially set according to reception conditions reported in a feedback path by the receiver, as will be described in greater detail in relation to Fig. 7 below.
  • Another preferred feature of the present embodiment is its ability, using puncturing as discussed above, to apply unequal error protection (UEP) RSC encoding to different fields of the data according to respective significance levels of the fields.
  • UDP unequal error protection
  • Such a feature is particularly useful in audio/video applications, and enhances the overall performance of the system, as discussed above with respect to Fig. 1. For example, in MPEG-4 encoding the motion vectors are more significant for the reconstruction of the video frame at the
  • the encoding procedure is thus composed of the following four steps:
  • the data bits are interleaved prior to RSC encoding to prevent, in the event of packet loss, the occurrence of bursts of errors or erasures in the decoding procedure at the receiver.
  • the data interleaving procedure preferably satisfies a uniformity criterion as follows:
  • Uniformity means that the bits of each packet p ⁇ are distributed in a uniform manner along the data interleaved bit stream. More specifically, if W denotes a window of length w through which a portion of the data interleaved stream may be viewed, then for any window W along the interleaved bit stream, p ⁇ W) denotes the number of bits belonging to i.
  • the uniformity criterion requires that the relative proportion p_(W)/w of bits belonging to each i is approximately equal to the proportion of lengths l_/s, where
  • the algorithm selects at each time unit a packet from which the current bit is drawn, and appends the selected bit to the interleaved
  • n is the total number of bits selected thus far by the algorithm.
  • the packet p x is selected as the packet that minimizes the following expression:
  • n+1 s The algorithm continues as long as n is less than s. If the selected packet is one in which n x is already equal to l x , then a zero bit is inserted instead of a data bit. Note that if all packets have equal lengths, the algorithm is reduced to iteratively passing over all the packets in a circular manner. In the case of unequal originating packets the algorithm adds the greater number of check bits to the smaller packets, giving the advantage that overall reconstructive ability is more evenly distributed around the packets. Thus the loss of any given packet is less likely to have a disproportionately high
  • UEP RSC encoding is next preferably applied to the data interleaved bit
  • the parameters of the RSC code are:
  • the puncturing pattern serves to change the error correction capability of the RSC code according to the priority of the data in the respective field.
  • high-rate error correction coding i.e., many parity check bits being punctured
  • low-priority data such as high-frequency DCT coefficients
  • high-priority data such as addresses of blocks, motion vectors, and low-frequency DCT coefficients
  • rate Vi RSC codes obtained by computer search, give effective performance with a puncturing
  • the second exemplary RSC code is a 64-state code with generator polynomials
  • any changes therein can be followed at the receiver and thus the parameters may be changed at the encoder in real-time without any prior notification to the receiver.
  • the puncturing pattern is advantageously changed along the interleaved data bit stream according to the importance of the data protected.
  • the positions along the stream where the puncturing pattern changes are made are preferably transmitted to the receiver.
  • the RSC encoder 72 is followed by the parity bit distributor 74, whose task is to interleave and apportion the parity bit set Q (after puncturing) before transmission so as to apply the uniformity criterion and thereby to prevent the occurrence of burst errors and erasures at the receiver.
  • the interleaved set Q is preferably apportioned into k portions q ... , q k of lengths mi, ... , m__, respectively, where each q_ is transmitted in the same Internet packet containing p ⁇ .
  • the uniformity criterion preferably used in the interleaving and apportionment procedure requires that /j+mj will be approximately the same for all /.
  • the uniformity criterion preferably also requires that the missing /j+m;
  • bits are distributed in a uniform manner along the received and de-interleaved
  • the UEP RSC decoder (decoder 84 in Fig. 5). Stated otherwise, for any window of length w through which a portion of the de- interleaved bit stream may be viewed, the number of missing bits, in case of one lost packet, will be approximately w k.
  • the preferred algorithm for interleaving and apportioning Q in parity bit distributor 74 is similar to the algorithm used for interleaving the data bits in data interleaver 70.
  • the bits of Q are initially arranged according to the order of their generation by the RSC code in encoder 72. The algorithm then selects, at each time unit, a parity set q y into which a selected next bit of Q is to be placed. Denoting by z- the number of bits already in set q :
  • the set q x in which the current bit is placed is the set that minimizes the following expression
  • the parity bit distributor 74 is followed by the header 1 encoder 76 for
  • the information encoded in the header typically includes:
  • the header is encoded with a fixed predetermined error correction code, and the encoded header bits are then preferably distributed among the transmitted Internet packets.
  • the encoding of the header should be strong enough to allow perfect reconstruction of the header under conditions of severe packet loss.
  • a small number of legitimate combinations of header parameters could be determined in advance. In this case, only the index of the selected combination need be transmitted as header information.
  • the datastream protection decoder 58 is designed to receive signals that have been encoded using the datastream protection encoder 42 and preferably comprises similar sub-units thereto but
  • a header decoder 80 is preferably the first unit
  • decoding is performed on a subset of the transmitted packets as follows.
  • encoded header bits are collected from the received packets (i.e., those that have survived transmission through the channel 50).
  • the collected header bits are preferably decoded at the header decoder 80 to recover the header parameters.
  • the recovered header parameters are then used by the parity bit retriever 82 to de-interleave the received set of parity bits and to identify the positions of any erasures that may have occurred.
  • erasure bits are associated with a zero metric.
  • the header parameters may be used to construct a trellis diagram corresponding to the UEP RSC code that was employed to encode the data.
  • a conventional Niterbi decoding procedure may then be used to decode the received information and reconstruct the interleaved data.
  • the decoding procedure preferably comprises a search through the trellis for the UEP RSC codeword (i.e., bit stream) with minimum Hamming distance form the received sequence of data and parity bits, which, having been found is selected as the most probable bit stream. Then, the selected bit stream is passed to the data deinterleaver 86 for the data to be de-interleaved according to the data de-interleaving scheme (the
  • Fig. 6 shows eight steps in a
  • the trellis diagram comprises a series of paths
  • Fig. 6 thus extends the performance of a system that uses trellis coding as a means of FEC of media packets transmitted through a noisy channel.
  • a trellis code is defined as any error correcting code that has a trellis representation, and includes convolutional codes, RSC codes, and even block codes. The present embodiment is useful
  • the trellis describes an RSC code, although the skilled person will appreciate that the embodiment is applicable to any code having a trellis representation).
  • the multiplexed video bit stream generally comprises variable length code (NLC) words.
  • NLC variable length code
  • the video bit sfream is not free of redundancy, such that violations of syntactic or semantic constraints will usually occur quickly after a loss of synchronization (see, e.g., C. Chen, "Error detection and concealment with an unsupervised MPEG2 video decoder," J. Visual Commun. Image Representation, vol. 6, no. 3, pp. 265-278, Sept. 1995, and J. W. Park, J. W. Kim, and S. U. Lee, "DCT coefficients recovery-based error concealment technique and its application to the MPEG-2 bit stream," IEEE Trans. Circuits Syst. Video Technol., vol.
  • the decoder may not find a matching VLC word in the code table (a syntax violation) or may determine that the decoded motion vectors, DCT coefficients, or quantizer step sizes exceed their permissible range (semantic violations). Additionally, an accumulated run that is used to place DCT coefficients into an 8x8 block may exceed 64, or the number of
  • MB's (macro-blocks) in a group of blocks (GOB) may be too small or too large. Especially for severe errors, the detection of errors can be further
  • a soft output Viterbi algorithm (SOVA) that may be used for decoding of convolutional codes (see J. Hagenauer and P. Hoher, "A Viterbi algorithm with soft-decision output and its applications," in Proc. IEEE Global Telecommunications Conf. (GLOBECOM), Dallas, TX, Nov. 1989, pp. 47.1.1-47.1.7, the contents of which are hereby incorporated by reference).
  • SOVA Soft output Viterbi algorithm
  • a set of data packets (bit stream), which has been encoded by a frellis code at the transmitter is received at the receiver end.
  • the stream is then decoded at the datastream protection decoder 58 using a search through the trellis for the most likely bit stream. If the number of lost packets does not exceed the error correction capability of the trellis code then the conventional Viterbi algorithm may normally be expected to yield a single data path as a most likely candidate for the error-free bit stream.
  • the search through the trellis for the most likely bit stream may result in more than one candidate data path, meaning several data paths each having the same likelihood of being the correct bit stream, i.e., being at the same Hamming distance from the received bit stream.
  • a preferred way to identify the set S is by applying a minimum distance decoder (such as the Viterbi algorithm) to the trellis in the following manner: At each trellis node a comparison is made between the accumulated metrics (accumulated hamming distances) of the paths entering
  • a minimum distance decoder such as the Viterbi algorithm
  • the end of the trellis is reached.
  • the surviving paths through the trellis constitute a sub-trellis which represents the set S of candidate bit streams.
  • the set S of surviving bit streams would be too large to process by the residual redundancy methods described above.
  • a low-complexity method to eliminate candidate bit streams and reduce S into a single candidate A sliding window B of width b is used, and a portion of the sub-trellis may be viewed and processed through the window.
  • the window is shown with a width b of three nodes, purely for the purpose of simplicity of illustration. In practice it will generally be larger. The objective is to eliminate paths that are unlikely to be correct. Hence the parameter b should be taken to be large enough to enable meaningful processing of the paths through B, i.e., to enable examination of the elimination criteria described below.
  • the window W is positioned at the end of the sub-trellis and the paths through the window W are examined.
  • a path through W is eliminated if it violates a syntactic constraint (e.g., the decoder cannot find a matching VLC word in the code table), a semantic constraint (e.g., the DCT coefficients exceed their permitted range), or some other likelihood criteria as follows: D A decoded bit stream is considered not likely if it includes
  • Lam et al (Lam, E. Y. and Goodman, J. W., "A mathematical analysis of the DCT coefficient distributions for images" IEEE Trans. Image Processing, Vol. 9, No.10, October 2000, the contents of which are hereby incorporated by reference) provide a mathematical analysis of the DCT coefficient distributions in natural images. The correspondence between their model and the distribution of the decoded DCT coefficients can be used as a measure of likelihood.
  • a macroblock is not likely if it has low correlation with its neighboring macroblocks.
  • the correlation can be in the spatial and/or frequency and/or temporal domains.
  • Many appropriate correlation measures have been developed for the purpose of passive error concealment (see Section V in Wang, Y. and Zhu, Q.-F. ", Error control and concealment for video communication: A review" Proc. IEEE Vol. 86, No. 5, May 1998, the contents of which are hereby incorporated by reference).
  • temporal correlation a macroblock that is very different from the motion-compensated corresponding macroblock in the previous frame is classified as not likely.
  • spatial correlation a macroblock whose boundaries do not agree with the boundary pixels of neighboring macroblocks in the same frame is
  • the processing of the sub-trellis by the sliding window W preferably
  • Fig. 7 is a simplified block diagram of a version of the device of Fig. 3 additionally having a feedback loop. Parts that are identical to those shown above are given the same reference numerals and are not referred to again except as necessary for an understanding of the present embodiment.
  • a datastream protection encoder 42 and a datastream protection decoder are connected via a channel 50 as before, but in addition the channel furnishes a return route which serves as a feedback link 90.
  • the feedback loop allows the decoder 58 to report back to the encoder so that the encoder is able to use real time data from the decoder to set its
  • the feedback channel 90 may be used to indicate received noise levels and/or which parts of the bit stream were received intact and/or which parts of the video signal could not be decoded and had to be concealed.
  • NACK negative acknowledgment
  • ACK positive acknowledgment
  • an ACK or NACK may refer to a series of macroblocks or an entire group of blocks (GOB). NACK's require a lower bit rate than ACK's, since they are only sent when errors actually occur, while ACK's have to be sent continuously. In either case, the requirements on the bit rate are very modest compared to the video bit rate of the forward channel.
  • the feedback message is usually not part of the standard video syntax but transmitted in a layer of the protocol stack which allows for control information to be exchanged.
  • Fig. 7 a system that performs adaptive error
  • correction and concealment in media communications is based on feedback
  • the embodiment uses the UEP RSC code as described above for error correction of variable- length media packets, where the particular RSC code, the puncturing pattern, the boundaries of the different priority fields, and the data and parity interleaving schemes can be adapted in real time according to control information sent from the decoder 58.
  • the level of encoding at the encoder 42 may be reduced.
  • the level of encoding may be increased and thus there is provided a dynamic response to the conditions of the channel.
  • the feedback signal may refer to encoding in general.
  • the feedback may be specific to the individual data fields.
  • the embodiment thus preferably offers optimal utilization of bandwidth by allowing real-time adaptivity to channel conditions, real-time controlled unequal error protection, efficient exploitation of the processing power at the transmitter and receiver, and real-time adaptivity to variations in packet size.

Abstract

L'invention concerne un dispositif de codage permettant de coder un train de données en temps réel pour un transfert sur un canal bruyant, ce train de données comportant des bits de données dans une succession de paquets de données. Ce système comporte: un émetteur de données destiné à envoyer lesdits bits de données dans lesdits paquets dans un ordre d'utilisation, un entrelaceur de données destiné à entrelacer lesdits bits de données en un ordre entrelacé, ainsi qu'un codeur destiné à coder lesdits bits de données dans ledit ordre entrelacé, de sorte à former des bits de parité destinés à être insérés dans ledit train de données en tant qu'ensemble de parité, de sorte que lesdits bits de parité soient distribués de manière différentielle sur lesdits paquets à partir desdits bits de données.
PCT/IL2002/000123 2001-02-20 2002-02-17 Systeme et procede d'amelioration de correction d'erreur dans le decodage en treillis, de protection d'erreur inegale de paquets de donnees de longueur variable basee sur un codage convolutionnel systematique recursif, et de codage de protection d'erreur inegale basee sur une retroaction WO2002067429A2 (fr)

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US09/785,489 US20020157058A1 (en) 2001-02-20 2001-02-20 System and method for feedback-based unequal error protection coding
US09/785,191 2001-02-20
US09/785,192 2001-02-20
US09/785,192 US20020144209A1 (en) 2001-02-20 2001-02-20 System for enhanced error correction in trellis decoding
US09/785,191 US20020146074A1 (en) 2001-02-20 2001-02-20 Unequal error protection of variable-length data packets based on recursive systematic convolutional coding
US09/785,489 2001-02-20

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US8036131B2 (en) 2007-02-05 2011-10-11 Lg Electronics Inc. Method for transmitting channel quality information based on differential scheme
KR101208545B1 (ko) 2007-02-02 2012-12-05 엘지전자 주식회사 통신 시스템에서 송신 신호에 대한 응답 신호를 송신하는방법
KR101443624B1 (ko) * 2008-01-03 2014-09-23 엘지전자 주식회사 통신 시스템에서의 데이터 송수신 방법
CN110285806A (zh) * 2019-07-05 2019-09-27 电子科技大学 基于多次位姿校正的移动机器人快速精确定位算法
CN110999148A (zh) * 2017-08-22 2020-04-10 高通股份有限公司 用于提供实况反馈的方法和装置
US11509419B2 (en) 2019-09-25 2022-11-22 Qualcomm Incorporated Acknowledgement and retransmission techniques utilizing secondary wireless channel
CN117254885B (zh) * 2023-11-14 2024-01-19 成都航天通信设备有限责任公司 随机交织关系识别方法、装置、电子设备及数据识别方法

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WO2008093233A2 (fr) * 2007-02-02 2008-08-07 Lg Electronics Inc. Procédés de transmission et de réception de données dans un système de communication
WO2008093233A3 (fr) * 2007-02-02 2010-09-02 Lg Electronics Inc. Procédés de transmission et de réception de données dans un système de communication
US8312338B2 (en) 2007-02-02 2012-11-13 Lg Electronics Inc. Methods of transmitting and receiving data in communication system
KR101208545B1 (ko) 2007-02-02 2012-12-05 엘지전자 주식회사 통신 시스템에서 송신 신호에 대한 응답 신호를 송신하는방법
US8036131B2 (en) 2007-02-05 2011-10-11 Lg Electronics Inc. Method for transmitting channel quality information based on differential scheme
US8422393B2 (en) 2007-02-05 2013-04-16 Lg Electronics Inc. Method for transmitting channel quality information based on differential scheme
KR101443624B1 (ko) * 2008-01-03 2014-09-23 엘지전자 주식회사 통신 시스템에서의 데이터 송수신 방법
CN110999148A (zh) * 2017-08-22 2020-04-10 高通股份有限公司 用于提供实况反馈的方法和装置
CN110999148B (zh) * 2017-08-22 2022-07-15 高通股份有限公司 用于提供实况反馈的方法和装置
CN110285806A (zh) * 2019-07-05 2019-09-27 电子科技大学 基于多次位姿校正的移动机器人快速精确定位算法
US11509419B2 (en) 2019-09-25 2022-11-22 Qualcomm Incorporated Acknowledgement and retransmission techniques utilizing secondary wireless channel
CN117254885B (zh) * 2023-11-14 2024-01-19 成都航天通信设备有限责任公司 随机交织关系识别方法、装置、电子设备及数据识别方法

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