JPS61227432A - Signal interpolation system - Google Patents

Abstract

PURPOSE:To prevent the deterioration in the signal quality at the missing of an input signal by storing at least one period's content of an input signal of a narrow band, reading the stored signal so as to obtain the continuity of the input signal at the missing of the input signal thereby interpolating the missing input signal. CONSTITUTION:The input signal is a low frequency signal of a narrow band extracted from a signal such as a reception sound signal by a low pass filter and a period detection section 1 detects the period by utilizing the zero cross point detection of the input signal. According to the detection signal of the period detection section 1, a waveform storage section 2 stores at least one period's content of the input signal. Further, an interpolation processing section 3 identifies the polarity and level of the input signal and when a missing detection signal is fed, the section 3 reads respectively the signal stored in the waveform storage section 2 during the missing period, gives an output in place of the missing input signal and processes the signal so that the continuity between the input signal at the start missing or end of missing and the signal read the waveform storage section 2 is obtained.

Description

[Detailed Description of the Invention] [Summary] A method for accumulating at least one period of a narrow band input signal such as a sine wave signal so that continuity of the input signal can be obtained when the input signal is missing. The signal is read out and the missing input signal is interpolated to prevent the signal quality from deteriorating when the input signal is missing.

[Industrial application field]

The present invention relates to a signal interpolation method for interpolating gaps in a narrowband input signal such as a low frequency sine wave signal.

In wireless communication systems and the like, multiplexing of propagation paths causes disturbances in received signals, resulting in a sudden drop in the received signal level. Due to such fading, the noise component becomes larger than the signal component, resulting in a significant deterioration of communication quality. Therefore, a method has been adopted in which the received signal level is monitored and when the level falls below a set level, the received signal is forcibly cut off to remove the influence of noise.

[Conventional technology]

A receiving device in a conventional mobile radio system is, for example,
As shown in FIG. 4, an antenna 21, a high frequency section 22 that performs high frequency amplification, frequency conversion, etc., an intermediate frequency section 23 that amplifies intermediate frequency signals, a low frequency section 24 that performs detection, amplification, etc., and a receiver. The high frequency section 22 is provided with a switch 26 for forcibly cutting off the received signal.

A high frequency signal such as an FM signal received by an antenna 21 is amplified by a high frequency section 22 and converted into an intermediate frequency signal by frequency conversion.The intermediate frequency signal is amplified by an intermediate frequency section 23, and detected by a low frequency section 24. This is used to amplify and drive speakers, etc. Also, the missing section monitoring section 25 monitors the received signal level in the high frequency section 22, and when it detects that it has fallen below a predetermined level, it outputs a missing section detection signal and forces the switch 26 in the high frequency section 22. Turn it off. Further, this switch 26 can also be provided in the low frequency section 24.

FIG. 5 is an explanatory diagram of the operation. When (a) is a baseband received signal, the missing section monitoring unit 25 detects a drop in the received signal level and outputs the missing detection signal shown in (b) of the same figure. This turns off the switch 26. Therefore, since the noise component in the received signal level drop section is also turned off, the influence of noise can be removed.

[Problem that the invention seeks to solve]

When the received signal level drops, the switch 26 can be turned off to forcibly cut off the received signal and prevent the reproduction of the noise component. , turning off causes signal level discontinuity and click noise. Therefore, it has been proposed to provide a low-pass filter for smoothing, but due to the transient response of this low-pass filter, a sufficient improvement effect cannot be obtained.

An object of the present invention is to improve communication quality by compensating for missing portions due to forced interruption of received signals.

Means for Solving Problem C] The signal interpolation method of Zero Invention is explained with reference to the principle block diagram shown in Fig. 1.The signal interpolation method of Zero Invention is a period detection method that detects the period of a narrow band input signal such as a sine wave. part 1 and at least one of the input signals.
Equipped with a waveform storage section 2 that accumulates a period, and an interpolation processing section 3, when a missing detection signal is applied to the interpolation processing section 3, it identifies the polarity and level of the input signal immediately before that, and The reading from the waveform storage section 2 is controlled so that the signal is continuous with the signal, and the reading from the waveform storage section 2 is repeated until the missing signal ends.
Immediately after the loss ends, the polarity and level of the input signal at that time are identified, and the signal level read from the waveform storage section 2 gradually approximates the input signal level. In this way, processing for finding an intermediate value between the two is executed, and an output signal that maintains continuity even in the case of signal loss is obtained.

[Effect]

The input signal is a narrow band low frequency signal extracted from the received audio signal etc. using a low pass filter etc., and the period detection section 1
The period is detected by detecting zero crossing point of the input signal.

According to the detection signal of the period detection section 1, the waveform storage section 2 accumulates a small amount of the input signal (one period at all).The interpolation processing section 3 identifies the polarity and level of the input signal, and the missing detection signal is added. When the input signal is lost, the signal stored in the waveform storage section 2 is repeatedly read out during the missing section and output in place of the missing input signal, and the input signal and the waveform storage section 2 are read out at the start and end of the loss. The processing is performed so that continuity with the signal obtained is obtained.

[Examples] Examples of the present invention will be described in detail below with reference to the drawings.

FIG. 2 is a block diagram of an embodiment of the present invention, in which numeral 4 is a low-pass filter, 5 is a waveform memory as a waveform storage section, 6 is a period detection section, 7 is an interpolation processing section, 8 is a low-pass filter, and 9 is a block diagram of an embodiment of the present invention. 1 is a synthesis circuit, 10 is an input terminal, 11 is a counter, 12 is a zero crossing detection circuit, 13 is an arithmetic processing circuit, 14 is a switching circuit, 1
5 is an output terminal. For example, a received audio signal is applied to the input terminal 10, a narrow band low frequency signal included in the received audio signal is extracted by the low pass filter 4, and this low frequency signal is used as an input signal to be stored in the waveform memory with a 5° period. Detection part 6
and is added to the interpolation processing section 7.

In the period detection unit 6, a zero crossing detection circuit 12 detects zero crossing points of the input signal, and a counter 11 detects the time between zero crossing points.
The period of the input signal is determined based on the count contents. This period detection signal is added to the waveform memory 5.

The waveform memory 5 stores at least one cycle of the input signal based on the cycle detection signal.

The interpolation processing section 7 includes an arithmetic processing circuit 13 and a switching circuit 14. The arithmetic processing circuit 13 identifies the polarity and level of the input signal, and when the missing detection signal is added, the waveform memory 5
, and switching control of the switching circuit 14. The output signal of the interpolation processing section 7 is applied to a synthesis circuit 9 via a low-pass filter 8, where it is synthesized with the received audio signal applied to the input terminal 10 and output from the output terminal 15.

FIG. 3 is an explanatory diagram of the operation, in which (a) shows an input signal that is forcibly cut off from time t1 to time t2, and correspondingly, the missing detection signal shown in (b) is sent to the interpolation processing unit 7. Added. Further, the period T of the input signal is detected by the period detecting section 6,
According to the period detection signal, the waveform memory 5 stores a signal for one period as shown in (d). If the capacity of the waveform memory 5 is large, signals for multiple periods can be stored.

As described above, the arithmetic processing circuit 13 identifies the polarity and level of the input signal, so the polarity and level L of the input signal immediately before time t1 when the missing detection signal is added
1, reading is started from address a1 having the same polarity and level L1 so that a continuous waveform of this input signal can be obtained from the waveform memory 5. The arithmetic processing circuit 13 then controls the switching circuit 14 to switch the switching circuit 14 to output the output signal of the arithmetic processing circuit 13. Therefore, the input signal is applied to the low-pass filter 8 as a signal having a continuous waveform, as shown in FIG. 3(C).

Also, when the omission ends at time t2, the arithmetic processing circuit 1
3, the polarity and level of the input signal immediately after the end of the dropout are identified, and the address a at time t2 is retrieved from the waveform memory 5.
The polarity and level of the signal read from 2 are identified, and it is determined whether or not these polarities and levels are the same. In the case of the signal shown in FIG. 3(C), the input signal and the waveform memory 5
The level is different from the signal read from. Therefore,
If the switching circuit 14 is switched to the input signal side in this state, a discontinuous signal will be output.

Therefore, the arithmetic processing circuit 13 performs an interpolation operation corresponding to the level difference, forms a signal whose level gradually approaches the input signal, and outputs the signal. That is, as shown by the dotted line in FIG. 3(C), the interpolated signal is output. Further, the switching circuit 14 switches to the input signal side under the control of the arithmetic processing circuit 13 when this interpolation calculation is completed.

When the received audio signal is missing, the signal from the interpolation processor 7 is output from the synthesis circuit 9 via the low-pass filter 8,
Since this signal has continuity with the input signal,
Since there is no click-like noise and the narrow band signal included in the received audio signal immediately before the dropout can be output even after the dropout, it is possible to prevent the quality of reproduced audio from deteriorating.

〔Effect of the invention〕

As explained above, the present invention detects the period of a narrowband input signal extracted from a received audio signal or the like using the period detection section 1.6, and stores at least one period of the input signal in accordance with the period detection signal in the waveform storage section. 2 (waveform memory 5), and when a missing detection signal indicating a missing input signal is applied to the interpolation processing units 3 and 7, the signal is read out from the waveform storage unit 2 so as to be continuous with the input signal, and the input signal is Instead of repeating the output,
Interpolation processing is performed so that continuity between the signal read from the waveform storage section 2 and the input signal is obtained even when the dropout ends, and even when the input signal is missing, the immediately preceding input signal can be repeatedly output. It is possible to prevent deterioration in received and reproduced sound quality due to fading and the like. Furthermore, since continuity can be maintained with respect to the input signal, there is an advantage that no noise is generated.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of the principle of the present invention, Fig. 2 is a block diagram of an embodiment of the invention, Fig. 3 is an explanatory diagram of the operation, Fig. 4 is a block diagram of the receiving device, and Fig. 5 is an explanatory diagram of the operation. be. 1.6 is a period detection section, 2 is a waveform storage section, 3.7 is an interpolation processing section, 4 and 8 are low-pass filters, 5 is a waveform memory, 9 is a synthesis circuit, 10 is an input terminal, 11 is a counter, 12 1 is a zero crossing detection circuit, 13 is an arithmetic processing circuit, 14 is a switching circuit, 1
5 is an output terminal, which is an output signal. Fig. 1 is a block diagram of the principle of the present invention.

Claims (1)

[Claims] In a signal interpolation method for interpolating a missing portion of a narrowband input signal, the period detecting section (1) detects the period of the signal before the missing portion of the input signal; a waveform storage section (2) that stores at least one period of the input signal detected by step 1); an interpolation processing unit (3) that reads out and interpolates the missing portion, the interpolation processing unit (3) identifies the polarity and level at the time when the input signal starts to be missing, and the waveform storage unit (2) Start reading from the accumulated waveform signal whose polarity and level maintain continuity with the input signal immediately before the dropout, read the accumulated waveform signal repeatedly until the dropout ends, and check the polarity and level of the input signal immediately after the dropout ends. A signal interpolation method characterized by performing processing to identify and gradually approximate the level of the accumulated waveform signal read from the waveform storage section (2) to the level of the input signal.