Unequal error protection for perceptual audio coders

• US 6,405,338 B1
• Filed: 02/11/1998
• Issued: 06/11/2002
• Est. Priority Date: 02/11/1998
• Status: Expired due to Term

• Current Assignee: WSOU Investments, LLC (WSOU Holdings, LLC)
• Original Assignee: Lucent Technologies, Inc. (Nokia Corporation)
• Inventors: Sundberg, Carl-Eric Wilhelm, Sinha, Deepen
• Primary Examiner(s): Decady, Albert
• Assistant Examiner(s): LAMARRE, GUY J
• Application Number:
  US09/022,114
• Time in Patent Office: 1,581 Days
• Field of Search: 714/752, 714/751, 714/753, 714/746, 714/747, 714/748, 714/749, 714/750, 714/701, 714/795, 714/755, 714/776, 714/774, 714/790, 714/786, 381/22, 381/55, 381/56, 381/59, 700/94, 388/433, 704/500-504, 704/230, 704/200, 704/209, 704/222, 386/94, 380/201, 360/60, 360/51, 360/48, 375/260, 382/236, 382/232, 382/275, 348/426.1, 348/409.1, 348/473, 370/472, 370/480, 370/484
• US Class Current: 714/752
• CPC Class Codes: G10L 19/002 Dynamic bit allocation for perceptual audio coders G10L19/032
• CPC Class Codes: H04L 1/0057 Block codes H04L1/0061, H04L1/0064 take precedence
• CPC Class Codes: H04L 1/0059 Convolutional codes
• CPC Class Codes: H04L 1/007 Unequal error protection for format H04L1/0078; for codes per se H03M13/35
• CPC Class Codes: H04L 1/0072 Error control for data other than payload data, e.g. control data

Abstract

An audio information bit stream including audio control bits and audio data bits is processed for transmission in a communication system. The audio data bits are first separated into n classes based on error sensitivity, that is, the impact of errors in particular audio data bits on perceived quality of an audio signal reconstructed from the transmission. Each of the n different classes of audio data bits is then provided with a corresponding one of n different levels of error protection, where n is greater than or equal to two. The invention thereby matches error protection for the audio data bits to source and channel error sensitivity. The audio control bits may be transmitted independently of the audio data bits, using an additional level of error protection higher than that used for any of the n classes of the audio data bits. Alternatively, the control bits may be combined with one of the n classes of audio data bits and provided with the highest of the n levels of error protection. Further protection may be provided for the control bits by repeating at least a portion of the control bits from a current packet of the audio information bit stream in a subsequent packet of the audio information bit stream. Moreover, the classification of audio data bits into n different classes can be implemented on a fixed packet-by-packet basis, or in a more flexible, adaptive implementation in which different multipacket error protection profiles are used for different multipacket segments of a source-coded audio signal.

Claims

1. A method of processing a stream of audio information bits for transmission in a communication system, the audio information bits including control bits and data its the method comprising the steps of:

separating the audio data bits into n different classes of audio data bits based on error sensitivity, where n is greater than or equal to two; and

providing a different level of error protection for each of the n different classes of audio data bits;

wherein the separating step is applied to the audio data bits after an audio coding process has been applied to the audio data bits, the audio coding process including both a quantization operation and a variable length audio coding operation, and a given level of error protection is provided for a corresponding one of the classes using a fixed channel coding rate.

2. The method of claim 1 wherein the different levels of error protection include a first level of error protection for a first class of the data bits and a second level of error protection for a second class of the data bits.

3. The method of claim 1 wherein the providing step includes coding the control bits using a level of error protection higher than that used for any of the n classes of the data bits.

4. The method of claim 1 wherein a cumulative bit rate provided as a result of the providing step is substantially equivalent to that which would result if an equal level of error protection were provided for the control bits and each of the n classes of data bits.

5. The method of claim 2 wherein the providing step includes coding the control and data bits such that the control bits and the first class of data bits are both provided with the first level of error protection.

6. The method of claim 1 wherein at least a portion of the control bits from a current packet in the audio information bit stream are repeated in a subsequent packet of the audio information bit stream.

7. The method of claim 1 wherein the separating step includes separating the audio data bits into the n classes of data bits based on the impact of the data bits on perceived quality of an audio signal reconstructed from the audio information bits.

8. The method of claim 7 wherein the separating step includes separating the data bits such that data bits corresponding to a side audio channel are assigned to a class with a lower level of error protection than that of data bits corresponding to a center audio channel.

9. The method of claim 7 wherein the separating step includes separating the data bits such that data bits corresponding to a designated frequency range are assigned to a class with a higher level of error protection than that of data bits corresponding to another frequency range.

10. The method of claim 9 wherein the designated frequency range is approximately 100 Hz to 4 kHz.

11. The method of claim 1 wherein a packet of the stream of audio information bits has a length of K bits, and a first one of the n classes having a highest level of error protection is approximately of size P*K/100, where P is a fixed percentage of bits which will be assigned to the first class for multiple packets of the audio information bit stream.

12. The method of claim 11 wherein bits of the audio information bit stream are assigned a level of error protection in accordance with the following decreasing order of priority:

(a) the control bits;

(b) data bits corresponding to a center audio channel and a frequency range of about 100 Hz to 2.5 kHz;

(c) data bits corresponding to a center audio channel and a frequency range of about 2.5 kHz to 4 kHz.

(d) data bits corresponding to a difference channel in a frequency range of about 100 Hz to 4 kHz;

(e) data bits corresponding to a frequency range of about 0 to 100 Hz;

(f) data bits corresponding to a frequency range of about 4 to 8 kHz;

(g) data bits corresponding to a difference channel and a frequency range of about 4 to 8 kHz; and

(h) data bits corresponding to frequencies greater than about 8 kHz.

13. The method of claim 1 further including the step of decoding coded classes of bits using a list Viterbi algorithm to obtain an error detection flag for use in error mitigation.

14. The method of claim 1 wherein the providing step further includes the step of inserting CRC bits periodically in the audio information bitstream, wherein the CRC bits are used to provide error detection for use in an error mitigation algorithm in a decoder.

15. The method of claim 1 wherein different levels of error protection are used for different groups of packets in the audio information bit stream.

16. An apparatus for use in processing audio information for transmission in a communication system, the apparatus comprising:

a classifier for receiving a stream of audio information bits, wherein the classifier is operative to separate the audio information bits into control bits and n different classes of data bits, where n is greater than or equal to two, and the audio data bits are separated into the classes based on error sensitivity of the audio data bits, and further wherein the separation of the audio data bits into the classes occurs after an audio coding process has been applied to the audio data bits, the audio coding process including both a quantization operation and a variable length audio coding operation; and

at least n encoders, each of the n encoders receiving the data bits of one of the n classes, and coding the nth class of data bits so as to provide a corresponding one of n levels of error protection for that class of data bits, wherein a given level of error protection is provided for a corresponding one of the classes using a fixed channel coding rate.

17. The apparatus of claim 16 wherein the n different levels of error protection include a first level of error protection for a first class of the data bits and a second level of error protection for a second class of the data bits.

18. The apparatus of claim 16 further including an additional encoder for encoding the control bits using a level of error protection higher than that used for any of the n classes of the data bits.

19. The apparatus of claim 16 wherein one of the encoders is operative to encode the control bits and a given one of the classes of data bits such that both the control bits and the given class of data bits are both provided with the same level of error protection.

20. The apparatus of claim 16 wherein at least a portion of the control bits from a current packet in the audio information bit stream are repeated in a subsequent packet of the audio information bit stream.

21. The apparatus of claim 16 wherein the classifier is operative to separate the data bits into the n classes of data bits based on the impact of the data bits on perceived quality of an audio signal reconstructed from the audio information bits.

22. The apparatus of claim 21 wherein the classifier separates the data bits such that data bits corresponding to a side audio channel are assigned to a class with a lower level of error protection than that of data bits corresponding to a center audio channel.

23. The apparatus of claim 21 wherein the classifier separates the data bits such that data bits corresponding to designated frequency range are assigned to a class with a higher level of error protection than that of data bits corresponding to another frequency range.

24. The apparatus of claim 23 wherein the designated frequency range is approximately 100 Hz to 4 kHz.

25. The apparatus of claim 16 wherein a packet of the stream of audio information bits has a length of K bits, and a first one of the n classes having a highest level of error protection is approximately of size P*K/100, where P is a fixed percentage of bits which will be assigned to the first class for multiple packets of the audio information bit stream.

26. The apparatus of claim 16 wherein different levels of error protection are used for different groups of packets in the audio information bit stream.

27. An apparatus for use in decoding audio information received in a communication system, the apparatus comprising:

at least n decoders, wherein each of the n decoders is operative to decode a portion of a received audio signal to recover a corresponding portion of an audio information bit stream including control bits and n different classes of data bits, where n is greater than or equal to two, and each of the n classes of data bits has one of n levels of error protection, and further wherein separation of the audio data bits into the classes occurs after an audio coding process has been applied to the audio data bits, the audio coding process including both a quantization operation and a variable length audio coding operation, and a given level of error protection is provided for a corresponding one of the classes using a fixed channel coding rate; and

a reconstruction unit which receives the portions of the audio information bit stream from the decoders and generates audio packets therefrom.

28. The apparatus of claim 27 further including an additional decoder for decoding a portion of the received signal corresponding to the control bits, wherein the control bits have a level of error protection higher than that used for any of the n classes of the data bits.

29. The apparatus of claim 27 wherein one of the n decoders is operative to decode a portion of the received signal corresponding to the control bits and a portion of the received signal corresponding to a given one of the classes of data bits, wherein both the control bits and the given class of data bits both have the same level of error protection.

30. A method of processing a stream of coded audio information bits for transmission in a communication system, the coded audio information bits including control bits and data bits, the method comprising the steps of:

separating the audio data bits into n different classes of audio data bits based on error sensitivity, where n is greater than or equal to two, and each of at least a subset of the classes is configured so as to include audio data bits corresponding to designated non-contiguous bands of an audio frequency spectrum; and

providing a different level of error protection for each of the n different classes of audio data bits.

31. An apparatus for use in processing audio information for transmission in a communication system, the apparatus comprising:

a classifier for receiving a stream of audio information bits, wherein the classifier is operative to separate the audio information bits into control bits and n different classes of data bits, where n is greater than or equal to two, and the data bits are separated into the classes based on error sensitivity of the data bits, and each of at least a subset of the classes is configured so as to include audio data bits corresponding to designated non-contiguous bands of an audio frequency spectrum; and

at least n encoders, each of the n encoders receiving the data bits of one of the n classes, and coding the nth class of data bits so as to provide a corresponding one of n levels of error protection for that class of data bits.

32. An apparatus for use in decoding audio information received in a communication system, the apparatus comprising:

at least n decoders, wherein each of the n decoders is operative to decode a portion of a received audio signal to recover a corresponding portion of an audio information bit stream including control bits and n different classes of data bits, where n is greater than or equal to two, and each of the n classes of data bits has one of n levels of error protection, and each of at least a subset of the classes is configured so as to include audio data bits corresponding to designated noncontiguous bands of an audio frequency spectrum; and

a reconstruction unit which receives the portions of the audio information bit stream from the decoders and generates audio packets therefrom.

33. A method of processing a stream of coded audio information bits for transmission in a communication system, the coded audio information bits including control bits and data bits, the method comprising the steps of:

separating the audio data bits into n different classes of audio data bits based on error sensitivity, where n is greater than or equal to two; and

providing a different level of error protection for each of the n different classes of audio data bits, wherein the different levels of error protection are provided for a first portion of the audio data bits in accordance with a first multipacket error protection profile and are provided for a second portion of the audio data bits in accordance with a second multipacket error protection profile different than the first error protection profile.

34. An apparatus for use in processing audio information for transmission in a communication system, the apparatus comprising:

a classifier for receiving a stream of audio information bits, wherein the classifier is operative to separate the audio information bits into control bits and n different classes of data bits, where n is greater than or equal to two, and the data bits are separated into the classes based on error sensitivity of the data bits; and

at least n encoders, each of the n encoders receiving the data bits of one of the n classes, and coding the nth class of data bits so as to provide a corresponding one of n levels of error protection for that class of data bits, wherein the different levels of error protection are provided for a first portion of the audio data bits in accordance with a first multipacket error protection profile and are provided for a second portion of the audio data bits in accordance with a second multipacket error protection profile different than the first error protection profile.

35. An apparatus for use in decoding audio information received in a communication system, the apparatus comprising:

at least n decoders, wherein each of the n decoders is operative to decode a portion of a received audio signal to recover a corresponding portion of an audio information bit stream including control bits and n different classes of data bits, where n is greater than or equal to two, and each of the n classes of data bits has one of n levels of error protection, wherein the different levels of error protection are provided for a first portion of the audio data bits in accordance with a first multipacket error protection profile and are provided for a second portion of the audio data bits in accordance with a second multipacket error protection profile different than the first error protection profile; and

a reconstruction unit which receives the portions of the audio information bit stream from the decoders and generates audio packets therefrom.