Error detection/correction and fault detection/recovery – Pulse or data error handling – Digital data error correction
Reexamination Certificate
1999-04-23
2001-12-04
Chung, Phung M. (Department: 2784)
Error detection/correction and fault detection/recovery
Pulse or data error handling
Digital data error correction
C714S756000
Reexamination Certificate
active
06327689
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
This invention relates in general to error correction and error concealment of digital data and in particular error correction and concealment for the wireless transmission of digital audio data.
2. Description of Related Art
In a noisy environment digital audio signals transmitted by means of wireless transmission can become corrupted and produce a noticeable audible noise. When the bit error rate of the audio signals approaches 3.0E-3, the audio signals can become quite distorted by the noise. Both random noise and burst noise can corrupt a wireless transmission and a method is needed to provide a way to remove the noise from the audio signal. This could take the form of error correction, and in cases where the noise errors are too many to correct, a form of hiding or concealing of the noise is needed. When noise errors are hidden, the method used needs to be such that the area of concealment is smoothed so as not to cause distortions that result in audible perturbations.
In U.S. Pat. No. 5,745,582 (Shimpuku et al.) a method and a system is disclosed to transmit and receive a digital audio signal with ECC by means of an optical transmission. In U.S. Pat. No. 5,745,532 (Campana, Jr.) a system and method is disclosed for digital wireless data which uses dual data streams delayed in time from one another to provide replacement data to the stream which has an uncorrectable error. In U.S. Pat. No. 5,742,644 (Campana, Jr.) reconstruction and re-synchronization are done for wireless serial transmissions where fading causes uncorrectable errors beyond the correction capability of ECC. In U.S. Pat. No. 5,673,363 (Jeon et al.) a method for error concealment is described where frequency components, in the last segments of a frame where an error does not occur, are used to reconstruct the frequency components of subsequent frames that are in error. In U.S. Pat. No. 5,412,638 (Koulopoulos et al.) an error correcting scheme for a digitized audio output of a CD player is described using a finite impulse response filter.
The wireless transmission of digital audio data exposes the data to corruption by noise that is random and noise that occurs in bursts. When bit error rates of the transmitted data are low (<<3.0E-3), the need for error correction ranges from not being needed to being satisfied by well known error correction techniques. However, as the bit error rate approaches 1.0E-3 to 3.0E-3 or higher, more of the transmitted digital audio data will be found to be corrupted and will require means for concealment of the corrupted data that exceeds the limit of the capability of ECC (error correction code).
SUMMARY OF THE INVENTION
In this invention an error correction scheme is described for wireless transmission of digital audio data. The scheme encompasses interleaving the data to combat burst noise, encoding the data to produce ECC bytes, transmitting the data in a serial first in first out fashion, receiving the transmitted data, decoding the data with ECC bytes, applying error correction and concealment techniques to hide errors that cannot be corrected and re-establishing the digital audio data to its original form A subsystem is provided for transmitting wireless digital audio data including formatting the data for error correction and avoidance, encoding ECC and transmitting the data in a first in first out serial sequence. A subsystem for receiving the wireless digital audio data is provided which includes receiving the transmitted data, decoding the error correction portion of the data, error correcting the data, concealing errors which cannot be error corrected, and reformatting of the digital audio data back into its original form.
The digital audio data to be sent by the transmitting subsystem is interleaved by formatting the data into a sub-frame containing even numbered bytes and a sub-frame containing odd numbered bytes. The interleaving of data into even and odd bytes between sub-frames is done to combat burst errors and distribute the burst noise so that it may be more easily corrected or concealed. The even and odd sub-frames are further organized into least significant bytes (LSB) and most significant bytes (MSB). The MSB of each sub-frame are protected by error correction codes (ECC) using Reed-Solomon or equivalent encoders. Although, the LSB could be protected, they are left unprotected to save bandwidth because experiments have shown little effect to audible noise even at a bit error rate BER=3.0E-3. The sub-frames containing the digital audio data and including ECC bytes are transmitted wireless in a first in, first out sequence.
The wireless transmitted even and odd sub-frames of the digital audio data are received by the receiving subsystem and the MSB of both sub-frames including the ECC are fed through a Reed Solomon decoder, or equivalent. Those bytes of the data that can be error corrected are corrected using the ECC and the remainder of any erroneous bytes that cannot be corrected are hidden by concealment techniques. When a sub-frame is corrupted beyond ECC correction, the lost information can be recovered by interpolation based on the other sub-frame. If more than two frames are corrupted, soft-muting is applied. Soft-muting is an application of “windowing” which as used here is a method by which a signal in the time domain is truncated, and where the truncation produces as few ripples as possible in the frequency domain, yet maintaining as rectangular a shape as possible in the time domain. The windowing function could be Hanning, Triangle or any other type function in which the weight of the window coefficients approaches zero from the center to the end of the window. When both sub-frames of a current decoded frame cannot be corrected by ECC then the current decoded frame is muted and the previous frame is soft muted. If the next subsequent frame is error free either by no errors occurring or through an ECC correction, then the subsequent decoded frame is soft muted. Once the MSB of the data are processed through correction and concealment, the digital audio data is recombined into its original format and outputted from the receiver subsystem.
REFERENCES:
patent: 4829525 (1989-05-01), Sugiyama et al.
patent: 5412638 (1995-05-01), Koulopoulos et al.
patent: 5673363 (1997-09-01), Jeon et al.
patent: 5742644 (1998-04-01), Campana, Jr.
patent: 5745532 (1998-04-01), Campana, Jr.
patent: 5745582 (1998-04-01), Shimpuku et al.
Chung Phung M.
Cirrus Logic Inc.
Goerge O. Saile & Assoc.
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