JPS58105683A - Digital multi-frequency signal receiving system - Google Patents

Abstract

PURPOSE:To change the integrated section of the Fourier conversion in accordance with an input signal and to highly accurately perform identification of a multi-frequency signal, by monitoring that the conversion output has reached a level higher than a prescribed threshold after the 1st time has passed from the starting of the discrete Fourier conversion of the input signal. CONSTITUTION:Input signals are converted into linear codes by an expander 2 and multiplied by the Cos and Sin from a sine wave generator 7 and a cosine wave generator 8 at multipliers 5 and 6. These multiplied values are at integrators 9 and 10, and the integrated values are squared at multipliers 11 and 12, and then, they are added to each other at an adder 13. This added power spectrum of an angular frequency omega is added to a signal detector 14 and an F1 detecting circuit 17 and an F2 detecting circuit 18, and the 2nd and 3rd largest spectra F1 and F2 are added to an arithmetic circuit 19 and monitored at the circuits 17 and 18. After a prescribed time has passed from the starting of the integration, spectra F1 and F2 are added to a judging circuit 20 and the circuit 20 judges whether a prescribed threshold has reached or not and changes the integrated section in accordance with the input signal by controlling the integrators 9 and 10.

Description

Detailed Description of the Invention (l) 1 Technical Field of the Invention The present invention relates to a digital multi-frequency signal receiving system, particularly to a digital multi-frequency signal receiving system in a digital multi-frequency signal receiver that performs discrete Fourier transform on an input digital signal. about.

(2) Background of the technology Within the telephone exchange network, a multi-frequency signaling system that transmits a selection signal or a monitoring signal by a combination of frequencies selected from a plurality of predetermined frequencies within the voice band is used for push-button dialing on subscriber lines. It is widely used as a signal system (PB signal) or a multi-frequency signal system (MF signal) in inter-office relay lines. On the other hand, as the communication paths of telephone exchanges and the like are time-divided, digital techniques such as discrete Fourier transform are also widely used as means for receiving the multi-frequency signals. Generally, the discrete Fourier transform is performed using the unknown signal x (nT) and the known signal exp (-j
a+nT)(-cog (a+nT)+jsin(ωn
T))

F (ω)−Σx (nT) ・W (nT)・ex
p(jωnT) (11 Where, F: Discrete Fourier transform output ω: Reference angular frequency W(nT): Sample value of @function T: Sampling period N: Total number of samples within the integration period.

(3) Prior Art and Problems FIG. 1 is a diagram showing an example of a conventional digital multi-frequency signal receiving system using this type of discrete Fourier transform.

In FIG. 1, an input signal x is input from input terminal 1, digitally encoded, and compressed by a predetermined compander.
(nT) is converted into a linear code by the decompressor 2 and further scaled, and then multiplied by the single window function value W(nT) supplied from the window function generator 14 in the multiplication 113.

The output of multiplication a3 is further input to two multipliers 5 and 6, and the kernel C03 (ωnT) supplied from cosine wave generator 87
and a kernel 5in(ωnT
) are respectively multiplied. The outputs of multipliers I5 and 6 are input to integrators 9 and 10 and are integrated over said integration period (NT).

Outputs Fc and Fs of integrators 9 and 10 are shown in equations (2) and (3).

Fc−Σx (nT) −cos (ωnT
) (21 color Fs−Σx (nT) ・s in (a+
nT) (3) Output F of integrals 19 and 10
After c and Fs are squared by multipliers 11 and 12, respectively, they are input to adder 13, and as a result of the addition, the input signal x (nT>) is the voltage at the reference angular frequency ω as shown in equation (4). A dregs vector F is output.

F' - Fc' + Fs'
(4) The electric scum vector F output from the adder 13 is detected by the signal detection circuit 14 after the integration period (NT) has elapsed after starting the discrete Fourier transform. The frequency characteristics of the electric flux vector F with respect to a predetermined reference angular frequency ω are shown in FIG. To configure a digital multi-frequency signal receiver for MF signals that displays a selection signal etc. by a combination of two frequencies among the 6wR waves of 700 Hz to 1700 Hz by utilizing such characteristics, refer to the above 6 frequencies. Discrete Fourier transform is performed sequentially with the angular frequency ω, and the output electric debris vectors F are detected by the signal detection circuit 14, and the six detected electric debris vectors F are detected by the signal detection circuit 14.
The signal determining circuit 15 determines the two largest ones among them,
By finding the corresponding frequency, the received MP flaw signal can be identified.

As is clear from the above explanation, in the conventional digital multi-frequency signal receiving system, a certain integration period (NT) is required to perform the discrete Fourier transform, and the input signal x (nT) is The integration period (NT) is required even when there is no input. In addition, in order to identify the MF multiplied signal mixed with many noise frequencies, the integration period (NT) is extended even though the integration period (NT) is insufficient to identify the two frequencies that make up the MF multiplied signal. It was impossible to do so.

(4) 1. Purpose of the Invention The purpose of the present invention is to eliminate the drawbacks of the conventional digital multi-frequency signal reception system as described above, and to make it possible to change the integration period of the discrete Fourier transform to a necessary and sufficient degree depending on the input signal. It is in doing.

(6) Structure of the Invention This object is to provide a digital multi-frequency signal receiver that performs discrete Fourier transform on an input digital signal. When the output of the discrete Fourier transform reaches a predetermined threshold or more after a period of time has elapsed, monitoring of the output is started, and as a result of the monitoring, a predetermined digital multifrequency signal is detected from the output, or This is achieved by terminating the monitoring when a predetermined second time period elapses without detecting a predetermined digital multi-frequency signal from the output.

(6) 9 Examples of the invention An embodiment of the present invention will be described below with reference to the drawings.

FIG. 3 is a diagram showing a digital multi-frequency signal receiving system according to an embodiment of the present invention. Note that the same reference numerals indicate the same objects throughout the figures. In Fig. 3, the input signal x (nT) input from the input terminal 1 is converted into a linear code by the expander 2, and further standardized. However, as shown in FIG. 1, the sample value W(nT) of the window function is input to multipliers 5 and 6 without being multiplied, and the kernel c
After being multiplied by os(ωnT) and 5in(ωnT), respectively, they are integrated by integrators 9 and 10.

After the start of the integration, the outputs Fc and F3 of the integrators 19 and 10 are sequentially input to the multipliers 11 and 12 without elapse of the integration period (NT), and after being squared,
3 and inputted to the signal detection circuit 14, F1 detection circuit 17, and F2 detection circuit 18 as the electric scum vector F at the reference angular frequency ω. The F1 detection circuit 17 and the F2 detection circuit 18 use the six frequencies constituting the MF multiplied signal as the reference angular frequency ω to detect the second and third largest electrical flux vectors F from among the six electrical flux vectors F output as the reference angular frequency ω. Vectors F1 and F2 are each selected and input to the comparison calculation circuit 19. The comparison arithmetic circuit 19 inputs the electric debris vectors F1 and F2 inputted after a predetermined first time To has elapsed after the start of integration to a determination circuit. F
1 and F2 have reached a predetermined threshold, and if they are below the threshold, it is determined that the MF multiplied signal has not been input, and the integrator 9
and 10 are returned to their initial states, the integration is started again, and the determination is repeated every time the first time TO has elapsed. As a result of the determination, when the electric scum vectors F1 and F2 reach the threshold, the determination circuit is determines that the MF multiplied signal is input, and determines the difference ΔF between the electric waste vectors F1 and F2 input to the comparison calculation circuit 19 and inputs it to the determination circuit.The zero determination circuit determines that the input difference ΔF is If it is determined that the predetermined value has been reached before the elapse of the predetermined second time T2 after the start of the integration, the signal detection circuit 14 and the signal determination circuit 15 will perform the MF multiplication signal identification to be performed as described above. Then, the integrator 9 and lO are returned to their initial states and the discrete Fourier transform is restarted. If the second time 1
If the difference ΔF between the electric waste vectors F1 and F2 does not reach the predetermined value within 2, the determination circuit determines that an input signal x (nT) other than the MF signal is input, and the signal detection circuit 14 and the signal determination circuit 15 are discarded, the integrators 9 and 10 are returned to their initial states, and the discrete Fourier transform is restarted.

As is clear from the above explanation, according to this embodiment, if the first time TO is selected to be the minimum necessary time and the second time T2 is selected to be the maximum necessary, it is possible to prevent the MF multiplied signal from being input. is detected in a short time (TO), and it is possible to multiply the MF multiplied signal mixed with noise frequency with a sufficient detection time (maximum T2).

However, the integration period of the discrete Fourier transform, which is repeatedly performed for MF signal identification, is terminated as soon as the judgment circuit determines that the MF multiplied signal identification is confirmed, so the time required for MF signal texture identification is as shown in Figure 1. The integration period (NT) is not fixed as in , but is maintained at the necessary minimum within the range of the first time TO and the second time T2.

Note that FIG. 3 is only one embodiment of the present invention, and the means for determining the MF multiplied signal input, for example, is not limited to what is shown in the figure, and many other modifications may be considered. However, in any case, the effect of the present invention remains the same, and the digital multifrequency signal to be identified is not limited to the MF multiplied signal, but may include many other digital multifrequency signals such as the PB multiplied signal. However, the effects of the present invention do not change in either case.

(7) Effects of the Invention According to the present invention, in the digital multifrequency signal receiver, the integral interval in the discrete Fourier transform can be changed according to the input signal, and the time required for multifrequency signal identification is minimized. In addition, multi-frequency signals mixed with noise frequencies can be identified over a sufficient period of time.

[Brief explanation of drawings]

Fig. 1 is a diagram showing an example of a conventional digital multi-frequency signal reception system using discrete Fourier transform, Fig. 2 is a diagram showing an example of frequency characteristics of an electric scum vector, and Fig. 3 is a diagram showing an example of the present invention. FIG. 2 is a diagram showing a digital multi-frequency signal reception method according to an embodiment. In the figure, 1 is an input terminal, 2 is an expander, 3.5.6.
11 and 12 are multipliers, 4 is a window function generator, 7 is a cosine wave generator, 8 is a sine wave generator, 9 and 10 are integrators,
13 is an adder, 14 is a signal detection circuit, 15 is a signal judgment circuit, 16 is an output terminal, 17 is a Fl detection circuit, 18 is F2
A detection circuit, 19 a comparison arithmetic circuit, and 20 a judgment side 1. Figure 2

Claims (1)

[Claims] In a digital multi-frequency signal receiver that performs discrete Fourier transform on a human-powered digital signal, the discrete Fourier transform is output after a predetermined first time has elapsed after starting the discrete Fourier transform on the input digital signal. starts monitoring the output when the output reaches a predetermined threshold, and as a result of the monitoring, when a predetermined digital multifrequency signal is detected from the output, or when a predetermined digital multifrequency signal is detected from the output. A digital multi-frequency signal receiving system characterized in that the monitoring is terminated when a predetermined second time period has elapsed without any failure.