JPS6361535A - Detection method for data signal - Google Patents

Abstract

PURPOSE:To omit the readjustment of a set signal detection sensitivity and avoid a fear that the reception signal detection sensitivity is more dulled than required, by using the distribution state of the baud timing phase in a reception signal. CONSTITUTION:A reception pass band signal 11 is converted to a base band signal 12 by a demodulator 1 and is inputted to an automatic equalizer 2 and a baud timing component extracting filter 3. An output 13 of the filter 3 is inputted to a data signal detecting circuit 4. The output 13 is inputted to a phase calculating circuit 5 to calculate the timing phase of an operating reception-side MODEM. Which one of areas in the range of 0 deg.-360 deg. the calculated phase is in is discriminated by an area discriminating circuit 6, and a counter 7 corresponding to this area is counted up by one. A phase frequency graph is generated in this manner by a histogram generating circuit 8. Thereafter, the variance of an average frequency calculated by the preliminarily determined number of samples and the number of divided areas and the variance of the frequency in each area are calculated by a variance calculating circuit 9. A data signal and a noise are surely distinguished from each other by a discriminator 10 in accordance with this variance value.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for reliably distinguishing between noise and data signals on the receiving side of a modem even under conditions of poor S/N ratio.

[Conventional technology]

Conventional data signal detection is, for example, CCITTRED
The incoming call level is 126d according to the notice of v, 29113 of data communication (V series observation) in BOOIlt story line.
If it is greater than or equal to Bm, it is determined that a training signal or data < i has arrived, and after determining whether it is a training signal or not, if it is determined that it is not a training signal, it is determined that a data signal has generally arrived. A data signal detection method was used to determine that However, if the noise is 126
d[1 m or more, if the signal is detected as it is, it will be determined that it is not a training signal, and it will be erroneously determined that a data signal has arrived. In such a case,
Conventionally, the actual state of the communication transmission path was investigated and the signal arrival detection level was increased to prevent false determinations.

[Problem to be solved by the invention]

However, with the above-described conventional technology, it is necessary to investigate the actual condition of the transmission path, which adds troublesome maintenance work, and the signal detection sensitivity is fixed.

Even if the line condition improves, the sensitivity will always remain low, and there is a risk that the sensitivity will become unnecessarily low.

The purpose of the present invention is to eliminate the manual re-adjustment of the signal detection sensitivity set by − degrees, avoid the risk of unnecessarily dulling the received signal detection sensitivity, and always accurately detect data signals even when the noise level is high. An object of the present invention is to provide a data signal detection method for detecting data signals.

[Means for solving problems]

A typical synchronous modem is equipped with a baud timing synchronization circuit because it is necessary to reproduce the baud timing on the transmitting side on the receiving side and receive data at the correct baud timing. Use this circuit.

For each baud timing on the receiving side, the phase of the baud timing component of the signal being received that is equal to or higher than the received signal detection level and determined to be not a training signal at that time is calculated. When a data signal to be received arrives, the phase of its baud timing component can be determined by measuring the phase using the baud timing phase of the receiving side. Due to the regularity, the calculation results will be concentrated around a certain baud timing phase. It has the property of doing. However, in the case of only noise, even if it is assumed that there is a certain received signal and the bow timing component is extracted in the same way and the phase is calculated, there is no regularity, so
The calculation results are distributed evenly over the entire phase of °. For this purpose, we divide the phase from 0° to 360'' into several regions, determine which region the calculation result of one phase falls into, count the number, and receive the counted number ゛ to be used as a sample. When examining the magnitude of the variance from the average count number, which can be set in advance from the number of signals and the number of divided regions, there is a clear difference in the magnitude, so if an appropriate threshold is set, the signal detection sensitivity can be improved. There is no need for readjustment, and data signals can be detected correctly.

[Effect]

The data signal detection method that utilizes the distribution state of the baud timing phase in the received signal as described above can accurately distinguish noise even when the noise level is higher than the set signal detection sensitivity, so it can reduce the signal detection sensitivity. This eliminates the need for troublesome adjustments and prevents the receiving modem from malfunctioning.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. 1st
The figure is a block diagram showing a method of detecting a data signal using a demodulated signal on the receiving side of a high-speed modem.

FIG. 2 is a block diagram showing detailed functions within the data signal detection circuit.

In FIG. 1, 1 represents a demodulator, 2 represents an automatic equalizer, and 3 represents a filter for extracting bow timing components.
4 is a data signal detection circuit.

A received passband signal 11 is converted into a baseband signal 12 by a demodulator 1 and input to an automatic equalizer 2 and a baud timing component extraction filter 3. The output 13 of the bow timing component extraction filter 3 is further input to a data signal detection circuit 4.

Next, the internal functions of the data signal detection circuit will be explained according to the functional block diagram of FIG. The filtered baud timing component 13 is input to a phase calculation circuit 5 to calculate the timing phase of the receiving modem in operation. The region determination circuit 6 determines which region the calculated phase falls in, for example, in a phase divided into regions of 40 degrees within the range of 0.degree. to 360", and the counter 7 of the corresponding region is incremented by 1.

In this way, a phase frequency graph (hereinafter referred to as a histogram) is created by the histogram creation circuit 8. An example is shown in FIG. Figure a shows the state of the histogram in the case of a data signal, and Figure 3 shows the state of the histogram in the case of only noise. In other words, in a data signal, if a signal point with a phase or amplitude different from the previous signal point is selected for each modulation rate, the signal will definitely contain baud timing phase information; By extracting the components and conversely calculating the bow timing phase, the bow timing phase can be reproduced and the phases are also consistent. For this reason, the number of times that the specific phase region is determined increases, resulting in a situation as shown in figure a.

However, in the case of only noise, even if you extract the frequency of the part that contains timing phase information and calculate its phase,
Since the phase of the noise is not aligned, the number of times it is determined in any phase region is almost the same, and it becomes as shown in figure b.After creating a histogram, the predetermined number of samples and the number of divided regions are determined. The variance calculation circuit 9 calculates the variance σ''=(xt xav)'' between the average frequency calculated from the number and the frequency of each area. Here, xl is the frequency of each region, and xav is the average frequency. An example of the calculation result is shown in FIG. As shown in FIGS. 3A and 3B, in the case of a data signal, the frequency is concentrated in a specific area, so the dispersion value becomes large, and in the case of only noise, there is no large difference in the frequency, so the dispersion value becomes small. From this, if the threshold value σo2 is appropriately determined based on statistical properties as shown in FIG. This means that the data signal can be detected correctly.

After creating the histogram, the number of runs is determined by whether or not it exceeds the average frequency (2 in Figure 3 a, 6 in b)
Possible methods include a method of determining the number of runs based on the average frequency, and a method of measuring the number of runs by giving a threshold value for measuring the number of runs in addition to the average frequency.

It is also possible to combine dispersion and these techniques.

〔Effect of the invention〕

As explained above, according to the present invention, noise is not mistakenly detected as a data signal, and the data signal can be detected correctly, thereby preventing malfunction of the receiving modem and correctly selecting the mode of the receiving modem. There is an effect that can be done.

[Brief explanation of drawings]

Figure 1 is a simple block diagram of a receiving modem using a previously unknown circuit, Figure 2 is a block diagram of the data signal detection circuit of the present invention, and Figure 3 is a diagram created from the calculation results of the baud timing phase. FIG. 4 is a diagram illustrating an example of a histogram, and is a diagram illustrating a discrimination determination process for distinguishing between a data signal and noise. DESCRIPTION OF SYMBOLS 1... Demodulator, 2... Automatic equalizer, 3... Baud timing signal extraction filter, 4... Data signal detection circuit.

Claims (1)

[Claims] 1. In the receiving side device of the modem, which is equipped with a circuit that calculates the baud timing phase of the transmitting side from the received signal, the baud timing phase of the data signal is adjusted to a certain constant value. A data signal detection method characterized by making a determination based on the degree of concentration in a phase. 2. In claim 1, there is provided a discriminator for identifying the bow timing phase into a phase having an appropriate number of regions divided into phases between 0° and 360°; A counter circuit that counts how many received signals with a phase were received, and the count number of each counted area is a predetermined number that determines the total number of signals from which the phase will be calculated, and the divided phase as described above. A data signal detection method comprising: a variance calculation circuit that calculates a variance with respect to an average count number calculated from the number of regions; and a determination circuit that determines a data signal from the magnitude of the variance.