Data processing: speech signal processing – linguistics – language – Audio signal bandwidth compression or expansion
Reexamination Certificate
1998-11-12
2001-06-26
Dorvil, Richemond (Department: 2641)
Data processing: speech signal processing, linguistics, language
Audio signal bandwidth compression or expansion
C704S201000
Reexamination Certificate
active
06253185
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to multiple description transform coding (MDTC) of signals for transmission over a network or other type of communication medium, and more particularly to MDTC of audio signals.
BACKGROUND OF THE INVENTION
Multiple description transform coding (MDTC) is a type of joint source-channel coding (JSC) designed for transmission channels which are subject to failure or “erasure.” The objective of MDTC is to ensure that a decoder which receives an arbitrary subset of the channels can produce a useful reconstruction of the original signal. One type of MDTC introduces correlation between transmitted coefficients in a known, controlled manner so that lost coefficients can be statistically estimated from received coefficients. This correlation is used at the decoder at the coefficient level, as opposed to the bit level, so it is fundamentally different than techniques that use information about the transmitted data to produce likelihood information for the channel decoder. The latter is a common element in other types of JSC coding systems, as shown, for example, in P. G. Sherwood and K. Zeger, “Error Protection of Wavelet Coded Images Using Residual Source Redundancy,” Proc. of the 31
st
Asilomar Conference on Signals, Systems and Computers, November 1997. Other types of MDTC may be based on techniques such as frame expansions, as described in V. K. Goyal et al., “Multiple Description Transform Coding: Robustness to Erasures Using Tight Frame Expansions,” In Proc. IEEE Int. Symp. Inform. Theory, August 1998.
A known MDTC technique for coding pairs of independent Gaussian random variables is described in M. T. Orchard et al., “Redundancy Rate-Distortion Analysis of Multiple Description Coding Using Pairwise Correlating Transforms,” Proc. IEEE Int. Conf. Image Proc., Santa Barbara, CA, October 1997. This MDTC technique provides optimal 2×2 transforms for coding pairs of signals for transmission over two channels. However, this technique as well as other conventional techniques fail to provide optimal generalized n×m transforms for coding any n signal components for transmission over any m channels. In addition, conventional transforms such as those in the M. T. Orchard et al. reference fail to provide a sufficient number of degrees of freedom, and are therefore unduly limited in terms of design flexibility. Moreover, the optimality of the 2×2 transforms in the M. T. Orchard et al. reference requires that the channel failures be independent and have equal probabilities. The conventional techniques thus generally do not provide optimal transforms for applications in which, for example, channel failures either are dependent or have unequal probabilities, or both. These and other drawbacks of conventional MDTC prevent its effective implementation in many important applications.
SUMMARY OF THE INVENTION
The invention provides MDTC techniques which can be used to implement optimal or near-optimal n×m transforms for coding any number n of signal components for transmission over any number m of channels. A multiple description (MD) joint source-channel (JSC) encoder in accordance with an illustrative embodiment of the invention encodes n components of an audio signal for transmission over m channels of a communication medium, in applications in which, e.g., at least one of n and m may be greater than two, and in which the failure probabilities of the m channels may be non-independent and non-equivalent. The encoder in the illustrative embodiment combines a multiple description transform coder with elements of a perceptual audio coder (PAC).
In accordance with one aspect of the invention, the MD JSC encoder is configured to select one or more transform parameters for a multiple description transform, based on a characteristic of the audio signal to be encoded. For example, the transform parameters may be selected such that the resulting transformed coefficients have a variance distribution of a type expected by a subsequent entropy coding operation. The components of the audio signal may be quantized coefficients separated into a number of factor bands, and the transform parameter for a given factor band may be set to a value determined based on a transform parameter from at least one other factor band, e.g., the previous factor band. As another example, the transform parameter for one or more of the factor bands may be selected based on a determination as to whether the audio signal to be encoded is of a particular predetermined type. A desired variance distribution may also be obtained for the transformed coefficients by, e.g., pairing or otherwise grouping coefficients such that the coefficients of each pair or group are required to be in the same factor band.
In accordance with another aspect of the invention, in an embodiment in which the audio signal components are quantized coefficients separated into a number of factor bands, the quantized coefficients for at least one of the factor bands may be rescaled to equalize for the effect of quantization on the multiple description transform parameters. For example, the quantized coefficients for a given one of the factor bands may be rescaled using a factor which is a function of the quantization step size used in that factor band. One such factor, which has been determined to provide performance improvements in a MD PAC JSC, is 1 /&Dgr;
2
, where &Dgr; is the quantization step size used in the given factor band. Other factors could also be used.
An MD JSC encoder in accordance with the invention may include a series combination of N “macro” MD encoders followed by an entropy coder, and each of the N macro MD encoders includes a parallel arrangement of M “micro” MD encoders. Each of the M micro MD encoders implements one of: (i) a quantizer block followed by a transform block, (ii) a transform block followed by a quantizer block, (iii) a quantizer block with no transform block, and (iv) an identity function. In addition, a given n×m transform implemented by the MD JSC encoder may be in the form of a cascade structure of several transforms each having dimension less than n×m. This general MD JSC encoder structure allows the encoder to implement any desired n×m transform while also minimizing design complexity.
The MDTC techniques of the invention do not require independent or equivalent channel failure probabilities. As a result, the invention allows MDTC to be implemented effectively in a much wider range of applications than has heretofore been possible using conventional techniques. The MDTC techniques of the invention are suitable for use in conjunction with signal transmission over many different types of channels, including, for example, lossy packet networks such as the Internet, wireless networks, and broadband ATM networks.
REFERENCES:
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patent: 5928331 (1999-07-01), Bushmitch
patent: 5974380 (1999-10-01), Smyth et al.
patent: 0123456-A2 (2000-01-01), None
V.K. Goyal et al., “Multiple Description Transform Coding: Robustness to Erasures Using Tight Frame Expansions,” In Proc. IEEE Int. Symp. Inform. Theory, Aug. 1998.
V.K. Goyal and J Kovacevic, “Optimal Multiple Description Transform Coding of Gaussian Vectors,” In Proc. IEEE Data Compression Conf., pp. 388-397, Mar. 1998.
Arean Ramon
Goyal Vivek K.
Kovacevic Jelena
Dorvil Richemond
Lucent Technologies - Inc.
Ryan & Mason & Lewis, LLP
Wieland Susan
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