KR930006544B1 - Method of dtmf receiving in use digital signal processor - Google Patents

Abstract

The method is for receiving dual tone multi-frequency signal (DTMF) generated by push-botton phone using a digital signal processor (DSP) and DTMF signal detection program. The method comprises the steps of: (A) initializing data of DTMF signal detection program; (B) checking PCM data input and discriminating that the number of PCM data is 54; (C) discriminating that the current process is a pre-process or post-process when the number of PCM data is not 54; (D) converting input PCM data into linea data using a look-up table, scaling the linear data to prevent overflow, filtering the linea data using lowpass filter, converting the linear data into rectangular wave signal; (E) processing the step (D) for high frequency band using a high-pass filter and a high frequency limiter; and (F) repeating the step (B) to (E).

Description

DTMF Receiving Method Using Digital Signal Processor

1 is a block diagram of a DTMF signal receiving apparatus using a digital signal processor.

2 is a block diagram of a DTMF signal receiving function of the present invention.

3 is a flowchart of a DTMF receiving program in a digital signal processor to which the present invention is applied.

The present invention relates to a method for receiving a dual tone multi-frequency (DTMF) signal used for connection to a call in a call processing process in an electronic exchange.

Digital Siganl Processor (DSP), which has been able to operate at high speed thanks to the rapid development of digital signal processing technology and semiconductor technology along with digitalization of communication networks and exchanges, has been widely applied in communication and exchange fields. If you implement various signal service devices such as DTMF receiver with signal processing technology in exchange as digital signal processor, you can apply multiplexing concept, reduce volume, improve reliability, reduce price, simplify maintenance, etc. Has the advantage.

The present invention provides a DTMF signal receiving apparatus for receiving data in which a DTMF signal input from a pushbutton telephone is converted into a Pulse Code Modulation (PCM) form in an exchange, and is used to receive and detect a DTMF signal. It is an object of the present invention to provide a DTMF reception method using a digital signal processor that enables more efficient signal detection by a signal detection program that performs a digital signal processor in a DTMF receiver manufactured using a signal processor.

The present invention provides a digital signal processor, an EP ROM connected to the digital signal processor, a channel multiplexing circuit, an input / output memory, a monitor, a reset circuit and a local oscillator, a microcontroller connected to the input / output memory and a monitor, and the channel multiplexing. A DTMF signal receiving apparatus having a timing control circuit connected to a circuit and a monitor, the DTMF signal receiving apparatus comprising: a first step of initializing various data contents necessary for a DTMF signal receiving program to be executed in the digital signal processor; If the PCM data is inputted, the PCM data is continuously checked. If the PCM data number is 54, the pre-processing or post-processing process is approved if the PCM data is not 54. A third step of determining and a preprocessing step in the third step If it is determined, the received PCM data is converted into linear data by the memory lookup table method, scaling to prevent overflow, filtering using a low frequency band bandpass filter to separate the low frequency band, Subsequently, the low-frequency group information is passed through the low-frequency group limiter to a square wave signal with a uniform amplitude regardless of the power level of the input signal, and the same process is performed for the high-frequency group. Filtering is performed using a group of high pass filters, and then the high frequency group information is converted into a square wave signal having a uniform amplitude regardless of the power level of the input signal through the high frequency group limit. Navy signals are frequency-matched After the pre-treatment carried out while passing through a high-pass filter coarse, characterized in that and a fourth step of performing the first iteration from step 2.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

Among the signal service functions required for connection from the electronic exchange to the call, the DTMF signal receiving function is used to receive the DTMF signal generated from the pushbutton subscriber and detect the numeric information of the subscriber, as shown in Table 1 below. Two sine waves, one from two mutually exclusive frequency groups consisting of four frequencies in each of the high and low frequency groups of ~ 3,400 Hz), which are special digit information from 0 to 15. 16 types of dialing digits are displayed, such as #, A, B, C, and D. Table 1 below shows the main reception standard table for DTMF signals, which are detected as digit information only when the DTMF signal received by the DTMF receiver meets the specified requirements shown in FIG. Is within the reference frequency ± 1.5%, and the received power level for each constituent frequency of the combined digit information must be between -3 and -24 dBmO, and the difference in the received power level between the digit constituent frequencies included is -8. It should have a value between + 4dB and discriminate as complete digit information only when the signal duration is within 24 to 40 ms and the inter-digit duration is more than 40 ms. However, if the frequency range is 'reference frequency × 3.5% or more' or the received power level for each component frequency of the combined digit information is less than -29 dBmO, it should not be detected as digit information. It should be ignored when a signal interrupt occurs, which is a break.

TABLE 1

FIG. 1 is a block diagram of a DTMF signal receiving apparatus using a digital signal processor, wherein the EP (Erasable and Programmable) ROM (3) (4), the channel multiplexing circuit (6), It consists of input / output memory (2), timing control circuit (10), microcontroller (1), monitor (7), reset circuit (9) and local oscillator (8). The digital signal processor 5 receives the PCM data input in accordance with the clock signal CLK, detects the digital information, and informs the microcontroller 1 of the corresponding digital information through the input / output memory 2. 1) organizes this information for each received channel and sends it to the controller.

Here, the microcontroller 1 reads from the input / output memory 2 in which the digital information detected by the digital signal processor 5 is written, and organizes the received data by the received channels and transmits them to the controller and the monitor 7. The operation state of the receiving apparatus is monitored and if a failure occurs, the reset circuit 9 is driven to perform the function of reactivating the digital signal processor 5, and the input / output memory 2 is the digital signal processor 5 and the microcontroller. (1) providing a communication area for communication between the digital signal processor (5) receives the PCM data input through the channel multiplexing circuit (6) and a signal receiving program embedded in the EP ROM (3) (4) The digital oscillator detects the digit information by the digital signal and transmits the information to the input / output memory 2, and the local oscillator 8 provides the clock frequency necessary for the operation of the digital signal processor 5, 3) (4) includes a signal receiving program executed by the digital signal processor 5, and the reset circuit 9 receives a signal from the microcontroller 1 to reset the operation of the digital signal processor 5; The channel multiplexing circuit 6 receives a signal from the timing control circuit 10 and receives only the PCM data corresponding to the channel to which the digital signal processor 5 should receive the PCM data input from the time switch device. (5), the timing control circuit 10 receives the FS and CLK signal from the time switch device to generate and provide the signals required by the channel multiplexing circuit 10 and the monitor (7), the monitor (7) receives a signal from the digital signal processor 5 and the timing control circuit 10 to monitor the operation state of the receiving device and to provide the monitored result to the microcontroller (1).

FIG. 2 is a block diagram of a DTMF signal reception function according to the present invention, and shows a functional block for detecting a DTMF signal by a digital filter (DF) method. DTMF signal detection algorithms require complex techniques and are being actively studied in the field of exchanges. The reason is that the range of receiving sensitivity is increased due to the elaboration of the spacing between reference frequencies and the uneven length and quality of subscriber lines. This is because the reception standard has to be secured widely, and in particular, the reception standard such as not to be affected by a dial tone or a voice signal that can be mixed with the DTMF signal is difficult. The main algorithms that have been tried so far are Infinite Impulse Response (IIR) or Finite Impulse Response (FIR) type DF method, Discrete Fourier Transform (DFT) calculation method, horseshoe correlation There is a method for analyzing a component (PARtial CORrelation (PARRCOR)), a zero-crossing counter method, etc. In this patent, among the known DF methods, the performance realized in a receiver of a conventional analog filter method can be implemented as it is. It has the advantages of high sensitivity, high noise margin, good performance in preventing digit simulation due to voice, less memory than other methods, and faster operation. A DTMF signal is detected by this possible IIR type DF method, and a known IIR type DF using a digital signal processor 5 is used. There is a way to effectively implement its objectives.

The digital signal processor 5 receives PCM data of the DTMF signal, classifies and detects frequencies by the DF method, and converts them into corresponding digital information only when the signal reception standard shown in Table 1 is satisfied. The processing is as follows. . Since the DTMF input signal is multi-frequency compressed nonlinear PCM signal data, after converting it into linear data (11), the phenomenon that the filtering calculation result of the received signal exceeds the calculation range of the digital signal processor 5 overflows ( In order to prevent overflow, the bandpass filter (13) separates the low frequency group and the high frequency group first through a scaling process (12). ) And a high frequency group high pass filter (14), respectively, and the frequency group information through the low frequency group limiter to generate a square wave signal having a uniform amplitude regardless of the power level of the input signal. (limiter) 15 and the high frequency group limiter 16, the limiter 15, 16 is a comparator with a transfer characteristic is used to use the receiver receiving operation range As well as it gives a widened to prevent a determination error of the digit similarity caused by voice and noise. Each frequency group signal whose amplitude is limited passes through four bandpass filters 17 and 18, which are adjusted to the reference frequency for each frequency group, and is then input to the level detectors 19 and 20, for each frequency group. One frequency is detected, and one signal frequency pair is detected according to signal power, signal / noise ratio, and power difference between two frequencies with respect to the detected signal frequency component, and the timing control logic 21 In order to receive and detect a DTMF signal by checking the duration of the frequency pair and the duration between digits, and determining the result as one complete digit information only after satisfying all the specifications specified in Table 1 (22), The number of PCM input data required to detect signal components is used in consideration of frequency resolution and DTMF reception timing conditions.

In particular, the result of the signal level detectors 19 and 20 is used to efficiently detect the DTMF signal frequency pairs, and the CU (CUrrent) buffer which stores the currently detected value and the value detected immediately before are stored. In the case of a LA (LAst) buffer, a counter comparing the values stored in the CU and the LA buffer with each other and indicating the result is a CNT (CouNTer) buffer, the signal level detector 19 (for each PCM data sample that is input each time) 20) Compare the values stored in the LA buffer and the CU buffer for the pair of frequencies that passed through it, and if the values are the same, increase the value stored in the CNT buffer by one, and convert the value stored in the CU buffer to the LA buffer. If the values stored in the LA and CU buffer are not equal to each other as a result of the comparison, the signal is stored when the signal persists by reducing the value stored in the CNT buffer by one and moving the value stored in the CU buffer to the LA buffer. Pause It effectively checks signal interrupts, which are interruptions, to improve the detection performance of DTMF signal frequency pairs.

3 is a flowchart of a DTMF receiving program in the digital signal processor 5 to which the present invention is applied, and is a program flowchart implemented in the digital signal processor 5 according to the signal receiving function configuration block shown in FIG. Processor 5 executes this program to receive DTMF signals. On the other hand, the exchange network uses a sampling frequency of 8 kHz for transmitting voice and signal data. Since the configuration of the DTMF signal frequency is 2 kHz or less, the receiver sampling frequency of the DTMF signal frequency can be performed at 4 kHz by a known sampling theorem, and in the present patent, the PCM input data input at 8 kHz is applied. In the digital signal processor 5, PCM input data are received and used at intervals of 4 ms. Accordingly, the time available for DTMF signal receiver signal detection can be doubled to 250μ by using 4㎑ sampling frequency, which is 125㎲ when using 8㎑ sampling frequency. By using this, the program executed in the digital signal processor 5 is divided into pre-processing and post-processing so that PCM input data is accepted only during the preprocessing process. Is shown below.

When the power is first turned on, the program starts to be executed, and initializes various data contents necessary for the DTMF receiving program to be executed in the digital signal processor 5 (23), and checks whether PCM data has been input into the digital signal processor (5). If the PCM data is input continuously (24), then the number of PCM data entered is checked to be 54 (25), and if the number of force PCM data is not 54, it is checked whether it is pre-processing or post-processing. (26) If it is checked by the preprocessing process, it takes the input PCM data and converts it into linear data by the memory look-up-table method (27), and then performs scaling to prevent overflow (28). In order to separate the low frequency group, the low frequency group bandpass filter 13 is used for filtering (29), and then the low frequency group information is performed on the low frequency group information. Converts a square wave signal having a uniform amplitude irrespective of the power level of the input signal through the transmitter 15 (30), and performs the same process for the high frequency group, and the high frequency group high pass filter to separate the high frequency group (14) and then converting the high frequency group information through the high frequency group limiter 16 into a square wave signal having a uniform amplitude regardless of the power level of the input signal (32). ), The high frequency group signal of which the amplitude is limited passes through four high pass filters 18 that are set to the reference frequency (34), and then performs preprocessing, such as PCM data is input into the digital signal processor (5). After that, the process is repeated from step 24 for continuously checking whether the PCM data has been input into the digital signal processor 5.

However, in the step 26 of checking whether the pre-processing or post-processing process is performed, the low-frequency group signal whose amplitude is passed in the pre-processing process is limited to four band pass filters that are set to the reference frequency. 17) and then one frequency is detected by the level detection method (35) using the result obtained by passing through the bandpass filter 18 for each high frequency group (35), and similarly for each frequency of the low frequency group. After detecting one frequency by the level detection method based on the result obtained by passing through the bandpass filter 17 (36), the signal power, signal-to-noise ratio, and two of the signal frequency components detected in the high frequency group and the low frequency group, respectively, After performing post-processing such as darkening and plotting one signal frequency pair (37) according to the received power difference between frequencies, etc., the PCM data is digital. It repeats from step 24 which is continuously checking whether it has been input into the signal processor 5.

However, after checking whether the number of input PCM data is 54 (25), and if the number of input PCM data is 54, the timing control logic 21 checks the duration of the frequency pair and the duration between digits. (38) In addition, if it is detected as an effective frequency pair that satisfies the reception standard specified in Table 1 (39), it is converted into a digit form and outputted out of the digital signal processor 5 to output an input / output memory (2). (40), but if the test result is not detected as a valid frequency pair, continue to set the relevant initial value for DTMF signal detection (41), and continue whether PCM data has been entered into the digital signal processor (5). The process is repeated from step 24 of inspection.

According to the DTMF reception method using a digital signal processor performed by a signal detection program in a digital signal processor in a DTMF receiver manufactured using a digital signal processor to receive and detect a DTMF signal as described above, a more efficient signal detector is possible. However, since the DTMF reception function is implemented by the signal detection program in the digital signal processor, there is an advantage that it is easy to change the program without changing the hardware when supplementing additional functions.

Claims (4)

A digital signal processor (5), an EP ROM (3) (4) connected to the digital signal processor (5), a channel multiplexing circuit (6), an input / output memory (2), a monitor (7), a reset circuit (9), and A DTMF signal receiving apparatus having a local oscillator 8, a microcontroller 1 connected to the input / output memory 2 and a monitor 7, a timing control circuit connected to the channel multiplexing circuit 6 and a monitor 7 In; In the genital digital signal processor 5, it is continuously checked whether PCM data has been input after the first step of initializing (23) various data contents required for the DTMF signal receiving program to be executed (24). A second step of determining whether 54 pieces of PCM data are input; a third step of determining whether the PCM data is pre-processing or post-processing if the number of PCM data is not 54; and If it is determined as the preprocessing step in the third step, the input PCM data is received and converted into linear data by the memory lookup table method (27), after scaling to prevent overflow (28), and the low frequency group is separated. In order to perform filtering using the low frequency group band pass filter 13 to perform the filtering, the low frequency group limiter 15 is passed through the low frequency group information. By converting into a square wave signal having a uniform amplitude irrespective of the power level of the incoming signal (30), the same process is performed for the high frequency group, and filtering using the high frequency group high pass filter 14 to separate the high frequency group. (31), and then convert the high frequency group limiter 16 into a square wave signal having a uniform amplitude irrespective of the power level of the input signal for the high frequency group information passed through it (32). DTMF characterized in that the high frequency group signal is provided with a fourth step of repeating the second step after the preprocessing process (34) passing through the four high pass filters 18 that are set to the frequency (34) Receive method. The method according to claim 1, wherein in the second step, if the number of the input PCM data is 54, the continuous timing of the detected frequency pair is examined, and whether it is an effective frequency pair satisfying a reception standard is determined (39). If detected, it is output out of the digital signal processor 5 in digit form and sent to the input / output memory 2 (40). However, if the test result is not detected as an effective frequency pair, the associated initial value for DTMF signal detection is continued. And setting (41) and repeating from the second step of continuously checking whether the PCM data has been input into the digital signal processor (5). 2. The method of claim 1, wherein, after the post-processing process is performed in the third step, the low-frequency group signal having a limited amplitude passed through the chirping process is passed through four band pass filters 17 that are set to a reference frequency ( 34) Then, one frequency is outputted by the level detection method using the result obtained by passing through the band pass filter 18 for each frequency of the high frequency group (35), and the band pass filter for each frequency of the low frequency group 17 as well. After detecting one frequency by the level detection method based on the result obtained by passing through (36), the signal power, the signal-to-noise ratio, and the received power difference between the two frequencies for the signal frequency components respectively detected in the high frequency group and the low frequency group After the post-processing process of detecting and configuring one signal frequency pair (37), etc., the method further includes repeating the operation from the second step. How to receive a DTMF. 3. The signal level detector (19) (20) according to claim 2, wherein the signal interrupt detector (19) (20) is used to efficiently check signal interrupts, which are signals which are temporarily suspended during signal detection in order to improve the detection performance of DTMF signal frequency pairs. A CU buffer that stores the currently detected value and a LA buffer that stores the immediately detected value, and compares the values stored in the CU and the LA buffer with each other and displays a counter indicating the result. In this case, for each pair of PCM data samples inputted, a comparison is made between the values stored in the LA buffer and the CU buffer for the frequency pairs passed through the signal level detectors 19 and 20. Increase the value stored in the CNT buffer by one, move the value stored in the CU buffer to the LA buffer, and if the values stored in the LA and the CU buffer are not identical to each other, store them in the CNP buffer. Decrease the value one and, DTMF reception method according to claim 1, further comprising performing a process to transfer the value stored in the buffer to the CU LA buffer.