JPS61200796A - Channel frequency detection system - Google Patents

Abstract

PURPOSE:To obtain good channel detection characteristics by providing an arithmetic operating part using a square window function, an arithmetic operating part using a Hamming window function and a selection discrimination circuit and comparing the output of two operating parts for satisfying attenuation characteristics by combining single window functions. CONSTITUTION:Digital input signals are supplied through a terminal 20 to a DFT arithmetic operating part 21-1 having a square window and to a DFT arithmetic operating part 21-2 having Hamming window characteristics. An arithmetic operation using the coefficient of the square window function is performed in the operating part 21-1 while the arithmetic operation using the coefficient of the Hamming window function is effected at the operating part 21-2 with the outputs being discriminated as to the level difference in a selecting discriminating circuit 23. If the difference between the operating parts 21-1 and 21-2 is more than 6 dB, discrimination is performed of the lesser output at the circuit 23. A selector 22 is actuated based on the result of discrimination to output the results of the arithmetic operation of the lesser output.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a channel frequency detection scheme for a digital multi-frequency receiver for audio in-band signals.

(Prior Art) Regarding signal detection methods in multi-frequency signal receivers and single-frequency signal receivers, see r Digtiil MFReei.
ver Using Discrete Fourie
r Transform (TEEE Trans Co
M-21AX 212/1973) J, filters with various characteristics are combined to allow the main signal to pass or to block the interfering signal, and the main signal that has passed is filtered. ? The presence or absence of the signal was determined by comparing the power or voltage amplitude with a reference level. Second
The figure is a block diagram showing a conventional denotal signal detection method. In the figure, 1 is an input end, 2 is a channel filter, 3 is a detection converter, 4 is a detection logic circuit, and 5 is an output end. The digital signal input from input terminal 1 is
A channel filter 2 passes only a predetermined frequency band. The output of the channel filter 2 is compared with a reference level by a detection comparator 3 to determine the presence or absence of a signal. Only when the output is higher than the reference level, it is determined that the signal is valid, and the signal is sent to the detection logic circuit 4. FIG. 3 shows a detailed configuration of the channel filter shown in FIG. 2, and this channel filter is an example of a configuration realized by discrete Fourier transform (hereinafter referred to as DFT). In the same figure, 1
0 is an input terminal, 11-1.11-2 is a multiplier, 12-1.
12-2 is an integrator, 13 is an absolute value sum calculation circuit, 14-,
．． 14-2 is a coefficient generator that determines the characteristics of the channel filter, and 15 is the output terminal of the channel filter. DFT
is generally expressed by equation (1), where x(nT):
Input sample, ω(nT): Window function sample, j: δ
=V-1-1ωy: irradiation angular frequency, T: sampling period, DFT(ωy): channel ωya DFT output. The operation of the channel filter will be explained. The tzu input signal is multiplied by the coefficient (ω(nT)casωynT) of the coefficient generator 14-1 by the multiplier 11-1, and then the integrator 12
-1. On the other hand, the multiplier 11-2 multiplies the coefficient (ω(nT)ωynT) of the coefficient generator 14-2 by t and sends it to the integrator I2-2. Absolute value sum calculation circuit 13
calculates the output C of the integrator 12-1 and the output S of the integrator 12-2 and sends it to the output end 15 as the output of the channel filter 2-1. The characteristics of this channel filter are shown in FIG. In the figure, (,) is due to a square window, (1) ω of 2
The attenuation amount when (nT) = 1 is shown, and (b) is due to the mink window, and ω (nT) = 0.54 + 0 in equation (1)
．． It shows the amount of attenuation when T' is 46w2yr-. However, T' indicates the window time.

(Problem to be Solved by the Invention) The channel filter described above must remove interfering channels or noise, and therefore has the drawback that the attenuation characteristics cannot be fully satisfied with a single window function as in the configuration described above. .

The present invention has been made to solve these drawbacks, and aims to satisfy attenuation characteristics and obtain good channel detection characteristics by combining single window functions.

(Means for Solving the Problem) The present invention provides a method for detecting a channel frequency of a digital signal in an audio band signaling system, which includes an arithmetic section using a rectangular window function, an arithmetic section using a Hamming window function, and the re-arithmetic section. and a selector so as to determine that there is no signal when the difference between the outputs is equal to or higher than a specified level, and to select the smaller arithmetic unit output when the difference in the output is within the specified level difference. This is the channel frequency detection method that operates.

(Function) A digital signal input to the DFT calculation unit having square window characteristics is subjected to calculation using the coefficients of the square window function in the calculation unit, and the DFT calculation unit having Hamming window characteristics uses the coefficients of the Hamming window function. Calculations using are performed and each is output from the DFT calculation section. The output levels of these outputs are compared by a selection determination circuit, and if the level difference is above a specified value, it is determined that there is no signal, and if the level difference is within the specified value, the smaller output is selected.

(Embodiment) FIG. 1 is a schematic diagram of a channel filter according to the present invention. In the figure, 2I-1 is a DF with square window characteristics.
21-2 is a DFT calculation unit having characteristics of a Hamming window; 22 is a selector; and 23 is a selection determination circuit. The digital input signal is connected to a DF with a square window via terminal 2Q.
The signal is sent to a T calculation unit 21-1 and a DFT calculation unit 2I-2 having Hamming window characteristics. DFT calculation unit 2 no 1 and 21-
The detailed configuration diagram of 2 is similar to the configuration shown in FIG. 3, and will be explained using this figure. First, the digital input signal input to the DFT calculation unit 2/1 is sent to the multiplier 11-1 and the multiplier 1.
1-2, the coefficients (ωc nT) = 1) of the square window function of the coefficient generator 14-1.14-2 are integrated, and the outputs of the multipliers 11-1. 12
-1.12-2 to the absolute value sum calculation circuit 13.

The absolute value sum calculation circuit I3 is the integration circuit 12-1.12.
The absolute values of the outputs C and S of -2 are calculated and used as the output of the DFT calculation section 2/No.

On the other hand, the DFT calculation unit 2 NO 2 having Hamming window characteristics calculates the coefficient (ω(nT) = 0) of the Hamming window function generated by the coefficient generator 14-1.14-2 for the digital input signal.
．． The 54th minute is extracted and used as the output of the DFT calculation section 2 no 2. The selection determination circuit 23 determines the level difference between the outputs of the DFT calculation units 2I-1 and 21-2. For example, in this embodiment, if the difference between the DFT calculation units 21-1 and 21-2 is 6 dB or more, it is determined that there is "no signal", and the selector 22
does not operate, and if the difference between the DFT calculation sections 2 no. Outputs the calculation result.

FIG. 5 is a characteristic diagram of the channel filter according to the present invention. As is clear from the figure, components other than the predetermined channel frequency components have a sufficiently large amount of attenuation, and good attenuation characteristics can be obtained.

(Effects of the Invention) As explained above, channel filters of multi-frequency signal receivers, etc. may be realized and configured with recursive digital filters, but generally channel frequency detectors rectify AC waveforms and Since the presence or absence of a signal is determined based on the level, a large number of rectifier circuits are required, but if a DFT is used, the output can be obtained at a DC level, which simplifies the circuit, so it is more advantageous to use a DFT.

Since the desired characteristics cannot be obtained with a single window DFT, the present invention obtains the desired characteristics by combining two or more types of window functions, and can be applied to various types of multi-frequency signal receivers, etc. becomes possible.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a channel filter according to the present invention,
Figure 2 is a block diagram of a conventional digital signal detection method.
FIG. 3 is a conventional channel filter (7) DFT calculation circuit, FIG. 4 is a frequency characteristic diagram of the channel filter, and FIG. 5 is a frequency characteristic diagram of the channel filter according to the present invention. 2...Channel filter, 3...Detection converter/4'lator, 4...Detection logic circuit, 11-1 r 11-2
... Multiplier, 12-, . 12-2... Integrator, 13... Absolute value sum calculation circuit,
14. ,-J. 14-2... Coefficient generator, "-1+21-2...D
FT calculation unit, 22...Selector, 23...Selection determination circuit. Patent applicant Oki Electric Industry Co., Ltd. Figure 1 Figure 2 Figure 3 Figure 4 ゛fo-4CDtOfot400 Saliva mosquito ()-1z) Figure 5fO-4ω f□ f□t400 A-sac collection (Hzl Showa year) time

Claims (1)

[Claims] In a channel frequency detection method for a digital signal in an audio band signaling system, a plurality of calculation units that perform calculations by discrete Fourier transform using window functions having different characteristics are compared with the outputs of the calculation units. It has a selection determination means, which compares and determines the output of the arithmetic unit and determines 1.
A channel frequency detection method characterized by obtaining two channel signals.