Excavating
Patent
1984-12-04
1987-04-28
Smith, Jerry
Excavating
371 2, G06F 1100
Patent
active
046619542
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to a method and apparatus of providing improved protection of the more significant bits of a linearly coded and error-protected digital signal (e.g. audio, vision, etc.) making recursive use of the coded range information.
SUMMARY OF THE INVENTION
An object of the present invention is to improve the decoding performance of a digital receiver under noisy channel conditions with little or no increase in the transmission bit rate.
The present invention provides a method of error correcting a digital signal comprising receiving an error protected digital signal which includes error correction information and further information representing a parameter of the signal in each of a plurality of blocks of digital information present in the signal, deriving the further information, decoding error protection information from the signal, deriving the protected digital information and separating it into blocks, and subjecting each block of protected digital information to error correction in response to information derived from the further information and the error protection information.
BRIEF DESCRIPTION OF THE DRAWINGS
Features and advantages of the present invention will become apparent from the following description of an embodiment thereof when taken in conjunction with the accompanying drawings, in which:
FIG. 1 shows a table of range codes and corresponding bit positions to which each error protection code refers for one embodiment of the present invention;
FIG. 2 shows a table representing a range coding scheme for 14-bit samples; and
FIG. 3 shows a block diagram of a part of a receiver according to the present invention.
DETAILED DESCRIPTION
A fixed number of digitally encoded sequentially placed samples forms a `Range Code Block`. Each of these blocks is assigned a `Range Code` which signals the amplitude of the largest sample within that block. The `Range Code` information can in most cases be buried within the original error protection coding of the digital samples without further increasing the transmission bit-rate. However, if `Range Code` is sent separately, there will be a slight increase in the transmission bit-rate.
At the receiving end, the recovery of the `Range Code` ascertains the maximum possible value of the largest digital sample within that `block`. Any transmission errors affecting bits at more significant positions in the sample than indicated by the `Range Code` value is first corrected. Digital samples are then decoded for error-correction using the coding scheme used for the samples. An error extension due to the decoding procedure introducing new errors in the more significant positions in the sample is again suppressed using `Range Code` information.
Any error detected by the use of the range code information for the second time can, for example, be dealt with by the substitution of the affected sample with a new one formed from the contributions of the nearby samples according to some pre-fixed algorithms. As an example, in the case of samples protected by single error-correcting Hamming code, the use of the range code after Hamming decoding will detect some of the multiple errors occuring within the active part of the sample concerned, thus making significant improvement to the decoder performance.
The significance of this technique is that a part of a digital sample (having higher information content) is already decoded before even the application of the actual error-protection decoding used for the sample. The result is that any subsequent error-correction decoding process for the sample will have to deal with a fewer number of information bits than was originally used in the encoding, thus resulting in an improvement of the decoding capacity.
An extension of this technique can be used to provide an error protection on a fixed number of bits per sample but the position of which can be varied according to the `Range Code`. Thus, during a period of weaker signal more of the least significant
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Amin Mohammad B.
Harding Wilfrid B.
Beausoliel, Jr. Robert W.
Independent Broadcasting Authority
Smith Jerry
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