JPH10262002A - Adpcm correction system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively correct a burst error, to reduce the possibility of erroneous correction of good voices and to reduce the deterioration of reproduced voices by producing a substitution pattern from the PCM signals, correcting the pattern in response to a specific speaker and changing adaptively the length of the pattern for its substitution. SOLUTION: An error detector 21 detects the errors of the demodulated received data, and a fading cycle detector 22 finds a fading cycle from the undemodulated received signals. An RSSI level detector 23 calculates an RSSI level. A data substitution decider 24 substitutes the data on a substitution pattern having the time interval of a fading cycle, when the received data have errors and the RSSI level is lower than the prescribed one. Meanwhile, a substitution pattern generator 28 chances the length of the substitution pattern, in response to the wrong data and the fading cycle. A data substitution device 25 substitutes an ADPCM code by the substitution pattern, in response to the number of errors and decodes the ADPCM code into a PCM code via an ADPCM decoder 26.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital cordless telephone system. Adaptive PCM (ADPC
M) A communication correction method to which the method is applied.

[0002]

2. Description of the Related Art Recent portable terminals are required to be cordless and digitized. For digitization of audio, the wired system uses the 64 Kbps PCM system, and currently uses the 32 Kbps ADPCM. The transmission path of a wireless line has a finite frequency, and the number of transmission bits is preferably small in order to use the frequency effectively.
In addition, since the terminal is shared with the wired system, the 32 Kbps ADPCM system used in the wired system tends to be used. In the 32 Kbps ADPCM system, transmission errors are unavoidable in a wireless transmission system such as a cordless telephone, and voice quality such as that of a wired system cannot be obtained.

One of the causes of such transmission errors is several Hz.
There is a degree of slow fading. The whole frame of the transmission data is affected by the slow fading, and the voice quality is degraded. Such a continuous burst error is several tens of milliseconds.
If it exceeds c, an unpleasant sensation as if an impact sound is mixed in the audio signal is given. Therefore, there is a problem that such a burst error must be corrected. When an ADPCM code string containing an error is input to an ADPCM decoder, the state inside the decoder differs from that at the encoder due to an erroneous code. As a result, a waveform different from the input voice waveform is output. For this reason, the voice quality deteriorates.

[0004]

Some measures against the above-mentioned burst error are known, but the conventional ADPCM
As the correction method, only the muting method shown in FIG. 2 or a method of replacing an error pattern has been used as a method for improving the deterioration of the voice quality. For this reason, data which is not erroneous is also corrected, and the voice quality may be rather deteriorated. Also, the characteristics of the audio signal differ depending on the specific speaker, and the degree of correction differs. Further, since the period of the burst error changes with time, the replacement effect of the replacement of the fixed pattern may be weak.

In a system including a radio circuit such as a cordless telephone, a method of adaptively correcting an error is desired. SUMMARY OF THE INVENTION It is an object of the present invention to reduce the influence of a burst error, which is a conventional problem, in a system in which wireless transmission is interposed, such as a cordless telephone, to reduce the degradation of reproduced voice, and particularly to reduce the degradation of voice of a specific speaker. An ADPCM correction method that can be reduced is provided.

[0006]

According to the present invention, there is provided an error detecting means for detecting an error from demodulated adaptive differential PCM code data and redundant data, and a fading period time based on received data. Cycle detection means for detecting the error, an RSSI level detection means for detecting a predetermined RSSI level from the received data, and judging the replacement of data from data output from the error detection means, the fading cycle detection means and the RSSI level detection means. Replacement decision means, adaptive difference PC
Data replacement means for performing data replacement for replacing data of the M code with an arbitrary length according to the number of errors;
ADPCM decoder for adaptively differential PCM decoding data of M code and outputting a decoded signal; PCM storage means for storing several frames of PCM code; replacement pattern for generating a replacement pattern used for the data replacement means from PCM code Burst errors are corrected by providing a generation unit, a replacement pattern storage unit that stores a replacement pattern, and a PCM decoder that decodes the corrected PCM code into an analog signal.

From the demodulated PCM code data, ADP
A replacement pattern for replacing the data of the CM code is generated, and the length of the replacement pattern is adaptively changed to perform the replacement, thereby preventing erroneous replacement. Replacement can be performed effectively when there are many errors. Further, by detecting the time of the fading cycle, data replacement corresponding to the burst error length is performed more faithfully. Further, in addition to correcting the burst error, the replacement of the ADPCM code is facilitated, and the replacement can be performed more faithfully. Since the replacement is performed with the generated specific pattern, it is possible to reduce the deterioration of the voice of the specific speaker and improve the sound quality of the specific speaker.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIG. Demodulated ADPCM code and CR
Redundant data such as C is input to the error detector 21 and the presence or absence of an error is output. The fading period detector 22
, The received signal before demodulation is input, and the time of the fading cycle is periodically obtained. For example, the time of the fading cycle is obtained every 20 ms, and the time of the fading cycle changes as needed. The received signal before demodulation is input to the RSSI level detector 23 for obtaining the level of the received radio wave intensity, and the RSSI level is calculated and output periodically. For example, the RSSI level is output every 20 ms.

The error detection data output from the error detector 21, the fading cycle time output from the fading cycle detector 22, and the RSSI level data output from the RSSI level detector 23 are each replaced by a data replacement determination unit 24. Is input to Data is incorrect and RS
SI level is lower than an arbitrary level, for example, 10 dBuV
If it is below, the data of the replacement pattern at the time interval of the fading cycle is replaced. As for the instruction at the time of replacement, the data replacement determination unit 24 instructs the data replacement unit 25 and the replacement pattern memory 29. The data replacement unit 25 reads the replacement pattern data in the replacement pattern memory 29 and replaces the data.

On the other hand, the error detected by the error detector 21 and the time of the fading cycle output to the fading cycle detector 22 are input to a pattern generator 28,
The length of the replacement pattern is changed according to the error data and the time of the fading cycle. At this time, when the time of the fading cycle is long, the length of the replacement pattern is increased, and when the time of the fading cycle is short, the length of the replacement pattern is shortened. For example, when the fading cycle time is 8 Hz, 20
In the replacement pattern of ms data, the replacement process is performed with the replacement pattern of 10 ms when the fading cycle time is 16 Hz, and the replacement process is not performed when there is no error.

This replacement pattern is stored in a replacement pattern memory 2
9, the ADPCM code is replaced by a replacement pattern by the data replacement unit 25 in accordance with the number of errors.

When the replaced ADPCM code is ADPC
The signal is input to the M decoder 26 and decoded into a PCM code. The decoded PCM code is stored in the PCM memory 27 at regular intervals.
And is input to the pattern generator 28, and a pattern is generated at regular intervals. The pattern generation time is determined by the above-described replacement processing based on the time of the fading cycle.

On the other hand, the PCM signal is input to the PCM decoder 30, an analog audio signal is output, and a corrected audio signal is obtained.

[0014]

As described above, according to the present invention, the replacement pattern is created from the PCM signal, that is, the replacement pattern differs for each specific speaker, the deterioration of the voice of the specific speaker is reduced, and the specific speech is reduced. To make corrections suitable for the user. In addition, by adaptively changing the length of the replacement pattern for replacement, burst errors can be corrected more efficiently than conventional correction means. Furthermore, in the past, there was a case where a good voice was corrected because replacement was performed with a specific pattern,
By creating a replacement pattern at any time, the probability of erroneously correcting good speech is reduced. Further, since the length of the replacement pattern is changed in accordance with the time of the error and the fading period, it is possible to maintain good speech even in a state where the error rate is poor.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a circuit configuration for implementing an ADPCM correction method according to the present invention.

FIG. 2 is a block diagram showing a circuit configuration of a conventional ADPCM correction method.

[Explanation of symbols]

 11: Error detector 12: Code replacement circuit 13: ADPCM decoder 14: PCM decoder 15: Attenuator 21: Error detector 22: Fading cycle detector 23: RSSI level detector 24: Data replacement determiner 25: Data replacement 26: ADPCM decoder 27: PCM data memory 28: Replacement pattern generator 29: Replacement pattern memory 30: PCM decoder

Claims (1)

[Claims] An error detecting means for detecting an error from demodulated adaptive differential PCM code data and redundant data, a fading cycle detecting means for detecting a time of a fading cycle from received data, and a predetermined RS based on received data.
RSSI level detecting means for detecting SI level, error detecting means, fading period detecting means, data replacement determining means for determining data replacement based on data output from the RSSI level detecting means, and data of the adaptive differential PCM code to the number of errors Data replacement means for performing data replacement by replacing the data with an arbitrary length by an adaptive difference PCM decoding the data of the adaptive difference PCM code and outputting a decoded signal.
PCM decoder and PC for storing several frames of PCM code
M storage means; replacement pattern generation means for generating a replacement pattern used for the data replacement means from a PCM code; replacement pattern storage means for storing a replacement pattern;
An ADPCM correction method for correcting a burst error by providing a PCM decoder that decodes a corrected PCM code into an analog signal.