JP3018481B2 - Circuit for measuring reception quality of modem - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a modem, and more particularly, to a circuit for measuring the quality of a received signal in the modem.

2. Description of the Related Art As shown in FIG. 2, a conventional measurement circuit of this type includes an automatic equalizer 3 for receiving a demodulated signal 1 and outputting an equalizer output 2 and an equalizer output 2 for input. It has a decision circuit 5 that outputs the error signal 4 and a low-pass filter that inputs the error signal 4 and outputs an average error signal 6 smoothed for a predetermined number of hours.

The quality measurement of the received signal was represented only by the average error signal.

However, in the above-described conventional measurement circuit, only the error signal due to a stationary cause such as white noise is focused, and only the average error signal is measured. There is a problem that it is not possible to detect deterioration of the line quality due to an unsteady cause having a short duration such as noise or impulse noise.

The present invention has been made in view of the above-mentioned conventional circumstances, and accordingly, an object of the present invention is to provide a novel reception quality measurement circuit of a modem capable of solving the above-mentioned problems inherent in the conventional technology. Is to do.

Means for Solving the Problems In order to achieve the above object, a reception quality measuring circuit of a modem according to the present invention comprises: an automatic equalizer that inputs a received demodulated signal and outputs an equalizer output; A judgment circuit for inputting an output and outputting an error signal, a low-pass filter for inputting the error signal and outputting an average error signal smoothed by a predetermined time constant, and an average error signal for inputting the average error signal and the error signal And a comparator that outputs a pulse when the error signal continuously exceeds the threshold a predetermined number of times as a threshold value.

Next, a preferred embodiment of the present invention will be specifically described with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention.

Referring to FIG. 1, one embodiment of the present invention is an automatic equalizer 3 which receives a received demodulated signal 1 and outputs an equalizer output 2.
A decision circuit 5 which receives the equalizer output 2 and outputs an error signal 4; a low-pass filter 7 which receives the error signal 4 and outputs an average error signal 6 smoothed by a predetermined time constant; The error signal 6 and the error signal 4 are input to the average error signal 6
The threshold value is a value obtained by multiplying the threshold value by a predetermined value. The comparator 9 outputs a pulse signal 8 when the error signal 4 continuously exceeds the threshold value a predetermined number of times.

 Next, the operation of this embodiment will be described.

The received demodulated signal 1 is equalized in distortion by the automatic equalizer 3, and is output to the determination circuit 5 as an equalizer output 2. The signal point is determined by the determination circuit 5, fed back to the automatic equalizer 3 as an error signal output 4 of the difference from the ideal signal point, and input so that the error signal 4 is averaged by the low-pass filter 7. It is also input to the comparator 9. The average error signal 6 is input to a comparator 9.

Here, 9 as recommended by CCITTV.29 as a received signal
Taking the case of 600 bps as an example, the error signal is output at 2400 data / sec, and the error signal represents white noise and impulse noise components applied on the communication line. The magnitude of the white noise error signal has a Gaussian distribution, and a time constant of 20 ms to 100 ms is set in the low-pass filter to smooth and stabilize the magnitude. The error signal due to the impulse noise having a duration of 1 ms to 5 ms is compressed by the low-pass filter 7, and the variation of the average error signal is small.

In the comparator 9, the threshold is set to 5 times the average error signal, and if the error signal exceeds the threshold three times in a row, the pulse is set to be output. When an error signal increases for a short time due to noise, a pulse is output.

Effect of the Invention As described above, according to the present invention, it is possible to detect an increase in the error signal in a short time by comparing the error signal with a threshold that is a predetermined multiple of the average error signal. The effect of being able to measure the quality of non-stationary short-term fluctuations such as received impulse noise and instantaneous signal interruption can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.
The figure is a block diagram of a conventional example. 1 ... demodulated signal, 2 ... equalizer output, 3 ... automatic equalizer, 4 ... error signal, 5 ... decision circuit, 6 ... average error signal, 7 ... low-pass filter, 8 ... pulse signal,
9 ... Comparator

Claims (1)

(57) [Claims] 1. An automatic equalizer for receiving a demodulated signal and outputting an equalizer output, a decision circuit receiving the equalizer output and outputting an error signal, and a predetermined time constant receiving the error signal and receiving an error signal A low-pass filter that outputs an averaged error signal smoothed in step (a), a threshold value obtained by inputting the averaged error signal and the error signal and multiplying the averaged error signal by a predetermined number, and setting the threshold value to a predetermined number of times. And a comparator for outputting a pulse when the threshold is exceeded.