JPS635938B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a detection device for modulated data signals. The modulated data signal is obtained by modulating a carrier wave with a digital data signal, and one example is a voice-grade data signal that uses a voice band. This voice-grade data signal is a 4.8 kb/s or 9.6 kb/s data signal carried on, for example, a 2 KHz analog carrier wave using a modulation method such as Q _AM or 4-phase PSK. With the advancement of digital signal processing technology, digital communication is progressing, and in order to make effective use of transmission paths for economical purposes, digital voice insertion method (Digital
Speech Interpolation (DSI) is currently being adopted, and when voice-grade data signals are transmitted over regular telephone lines, the problem arises that DSI frequently freezes out. Originally, the DSI method was based on the fact that during a telephone conversation, it is necessary to listen to what the other party is saying, so the average time each caller actually speaks is about half of the call time.
It has been developed focusing on the redundancy that there are times in a call that do not need to be transmitted as voice, such as pauses between syllables, words, or phrases even while speaking. That is, if you instantaneously observe a large number of telephone lines on which calls are being made, you will find that voice signals are present on only less than half of them. Therefore, in the DSI method, the digitized audio signal of each line (input trunk) is divided into unit blocks (several ms in time), which are a predetermined number of fixed sample value groups, and each unit block is divided into A voice detector determines whether or not a voice exists in a unit block, extracts a unit block in which voice exists, and inserts only the extracted unit blocks of each input trunk into each other's empty spaces to create a predetermined number of blocks. It is then reorganized into a DSI output channel and then transmitted. By eliminating the above-mentioned redundancy in this manner, the number of DSI output channels can be reduced to less than half of the total number of input trunks, and the transmission path can be more than doubled. However, when a voice-grade data signal is transmitted over a telephone line instead of a voice signal, the voice-grade data signal is transmitted unilaterally unlike a conversation, and there are no pauses like voice, so the voice detector is It is determined that audio exists in all unit blocks throughout the transmission period. As a result, the number of active input trunks exceeds the number of DSI output channels, causing a freeze-out in which information on any active input trunk is momentarily no longer transmitted. At the time of this freeze-out, the circumstances differ greatly depending on whether the audio signal is momentarily interrupted or when the voice-grade data signal is momentarily interrupted. That is, although a momentary interruption of the audio signal causes some discomfort in terms of audio quality, the receiver can understand most of the content of the call. On the other hand, a momentary interruption of the voice-class data signal renders it useless as information. Therefore, when a voice-grade data signal is transmitted over a normal telephone line, it is necessary to either transmit it on a dedicated line without passing through DSI, or to pass it through DSI without momentary interruption. What is important in this case is to detect as accurately and quickly as possible whether the input signal is a voice-grade data signal or not. This detection can also be done by demodulating the signals of each input trunk of the DSI, but this is not practical because the modulation method of the voice-class data signal cannot be specified. The necessity of detecting voice-grade data signals has been described above in connection with the adoption of the DSI method, but it goes without saying that distinguishing between voice signals and modulated data signals is often required in the field of communications. An object of the present invention is to provide a modulated data signal detection device that meets such demands. The configuration of the present invention to achieve such an object is such that, in an apparatus for determining whether a digitized input signal is an audio signal or a spectrum-shaped modulated data signal, the input signal is divided into fixed intervals. For each unit block, there is an autocorrelator that calculates the autocorrelation value of the unit block for the first order and a predetermined higher order, and whether all the autocorrelation values of each order are within a specific area determined for each order. a power calculator that calculates the power per unit block of the input signal and compares the power per unit block of the input signal to see if it exceeds a reference value; For each block divided into blocks, there is a zero-crossing counter that counts the number of zero-crossings in the block and determines whether it is within a specific range. The input signal is determined to be a modulated data signal if the unit blocks determined by the calculator to be equal to or greater than a reference value and determined by the correlation range determiner to exist occupy a predetermined number or more of the plurality of consecutive unit blocks. The present invention is characterized by comprising a signal determiner as a condition. Hereinafter, one embodiment of the present invention will be described with reference to the drawings. In this example, both the audio signal and the modulated data signal are 8KHz/13bit linear.
It is assumed that the modulated data signal is given as a PCM signal, and the modulated data signal will be explained as a voice-grade data signal with a carrier wave of about 2 KHz. Before explaining the embodiment device, let us touch on various characteristics of the modulated data signal, which are the basis of the present invention, ie, the spectrum, the number of zero crossings, and the power within the block. (a) Since the modulated data signal is always passed through a spectrum shaping filter after modulation in order to match the spectrum to the bandwidth of the transmission path, the modulated data signal has inherent autocorrelation caused by this shaping filter. The prediction coefficient that exists between the sample values and provides the optimal prediction depends on the constant of this shaping filter. The present invention utilizes the former property. (b) The modulated data signal is transmitted over a specific carrier (e.g.
2KHz) and then passes it through the above shaping filter, so the spectrum is almost flat within the band, and unlike an audio signal, the number of zero crossings per unit block can only take values within a certain range based on the above carrier wave. I don't get it. (c) The modulated data signal is typically transmitted with a power on the order of -12 dB _n O, and the power fluctuations are relatively small. It should be noted that the power that has undergone 4-phase PSK modulation is almost completely constant, but the power that has undergone _QAM modulation has some fluctuations because amplitude modulation is included. However, the degree of this is very small compared to the audio signal. Detection performance can be improved by utilizing the properties of items (b) and (c) above. Note that FIGS. 1a, b, and c show the power spectra of a 4.8 kb/s voice-grade data signal, a 9.6 kb/s voice-grade data signal, and a voice signal, respectively. FIG. 2 is a block diagram showing an embodiment of the present invention. In the figure, 1 is an input terminal, 2 and 3 are output terminals, 4 is a zero-crossing counter, 5 is an autocorrelator, and 6 is a correlation value range. 7 is a power calculator, 8 is an observation time setter, and 9 is a signal determiner. A digital input signal S is drift-compensated and inputted to the input terminal 1 . The zero-crossing counter 4 receives the digital input signal S by 32
Divide each sample into blocks (4 ms), count the number of zero crossings Z _c for each block, and set Z as the zero crossing number judgment flag for the block when the following formula (1) holds.
- Set Flag “1”, otherwise set Z-Flag “0”
is set and sent to the signal judger 9. 7≦Z _c ≦20 (1) However, the threshold in equation (1) is when the sampling frequency is 8 KHz and the block length is 32 samples. The power calculator 7 divides the digital input signal S into unit blocks (2 ms) of every 16 samples for detailed judgment, and calculates the intra-block power P _w based on the following equation (2) or (3). For example, P-Flag "0", "1", and "2" are set as power classification flags according to the power level classification shown in Table 1, and the signal judger 9, observation time setter 8, and autocorrelator 5 Send to. However, in equations (2) and (3), N is the unit block length, in this case N=16, and x _j is the amplitude value of each sample.

[Table] The autocorrelator 5 calculates the autocorrelation of the digital input signal S from a first-order correlation to an arbitrary higher-order correlation. The autocorrelation values R within a block are calculated from the 1st to the 15th order using the following equation (4). However, n is the order of 1 to 15, N
is the sample number of 16. The operation of this autocorrelator 5 is controlled by P-Flag, and it is inactive when P-Flag is “0”.
P-Flag is “0” → “1” or “0” →
It is assumed to start when the transition is "2". The correlation value range determiner 6 determines whether the following equation (5) is satisfied for all of n=1 to 15 for each order autocorrelation value R _o for each unit block obtained by the autocorrelator 5. Assuming that the unit block has a correlation unique to the spectrum shaping filter, a correlation determination flag C-Flag "1" is set and sent to the signal determiner 9. R _TH1o ≦R _o ≦R _Th2o ...(5) However, the thresholds R _Th1o and R _Th2o in equation (5)
The value of is almost uniquely determined by the characteristics of the spectrum shaping filter through which the voice-class data signal is passed and the number of samples forming a unit block. The signal judger 9 detects Z-Flag, P-Flag and C
-Flag is input, and the temporary detection flag d-Flag "1" indicating the possibility that there is data in a unit block (2me) of 16 samples is set by the judgment logic of the following equation (6), basically. When this d-Flag "1" stands three or more times within a continuous 4-unit block (8ms), the data judgment flag D-Flag "1" is set to indicate that the input signal S is a voice-grade data signal, and the output terminal 2 Send to. However, the conditions for setting D-Flag "1" based on d-Flag "1" and "0" are not limited to the above-mentioned [3 or more times/4 unit block], but can be determined as appropriate. This is based on the fact that since speech has various spectra such as voiced and unvoiced sounds, the correlation value of a speech signal rarely remains within a specific region over several consecutive unit blocks. By the way, the signal determiner 9 of the present embodiment described above further has the following functions upon determination. The first function is to conclude data detection decisions in a short time, and is controlled by the output t of the observation time setter 8. This observation time setter 8 is a time counter, and after P-Flag "2" is set once, for example,
Count up to 20ms, i.e. 10 unit blocks,
If this is exceeded, it will not be counted. So P-
D-Flag within 20ms after Flag “2” is set.
If the condition for establishing "1" is not satisfied, V-Flag "1" is set at output terminal 3 at least until P-Flag becomes "0" or "1", and during that time the input signal S is not an audio signal. The judgment is terminated and the next judgment is waited. The second function is to improve the judgment accuracy of data detection.
Controlled by Flag “0”. In other words, at least 1 within 20ms of the rise of P-Flag “2” mentioned above.
If Z-Flag “0” exists in even one block (4ms), this will be ignored even if the condition for D-Flag “1” is met, and after that block, at least P-Flag will be “0” or “0”. V-Flag "1" is set at the output terminal 3 until it becomes "1", and during that time it is regarded as an audio signal to avoid misjudgment. By the way, the signal determiner 9 used in the present invention basically uses Z-Flag "1", P-Flag "2" and C-
Temporary detection flag d that is set by logical AND with Flag “1”
- It is sufficient to determine whether the input signal S is a modulated data signal based on the continuity of occurrence of Flag “1”, but Z-Flag “0” may be used as a priority condition for negating the data signal. By providing a function to do this, false judgments will be eliminated. In addition, in the embodiment, the autocorrelator 5
By controlling the operation (start/stop) of C-Flag according to the contents of P-Flag, the reliability of C-Flag "1" is increased. In addition,
Although the block length for zero-crossing number _Zc counting is longer than the other unit blocks, this is to improve counting accuracy, and both the block length and unit block length may be determined as appropriate. Also, the power classification flag P-
Flag is set to three values of "0", "1", and "2", but it may also be set to two values, such as combining "0" and "1". Furthermore, it goes without saying that the various thresholds and judgment conditions are not limited to the numerical values or criteria shown in the embodiments. Further, similar to the audio detector, a hangover time may be provided in which the modulated data signal continues even if detection is interrupted within a certain period of time after the modulated data signal is detected. As specifically explained above with the examples,
According to the present invention, since the detection device is configured by focusing on a spectrum shaping filter and using an autocorrelator, a zero-crossing counter, and a power calculator, the detection device can be configured in a short time of, for example, 20 ms after the start of operation, regardless of the modulation method. It is possible to detect whether the signal is a modulated data signal or not based on the time. In addition to the above-mentioned applications in the DSI system, the device of the present invention is also very useful in the field of digital communications for distinguishing modulated data signals from voice signals.

[Brief explanation of the drawing]

FIGS. 1a, b, and c are diagrams showing power spectra of various signals, and FIG. 2 is a block diagram showing an embodiment of the present invention. In the drawing, 4 is a zero-crossing number counter, 5 is an autocorrelator, 6 is a correlation range judge, 7 is a power calculator, and 9 is a signal judge.

Claims (1)

[Claims] 1. In a device that determines whether a digitized input signal is an audio signal or a spectrum-shaped modulated data signal, for each unit block in which the input signal is divided into fixed intervals, an autocorrelator that calculates correlation values for the first order and a predetermined higher order; a correlation range determiner that determines whether all the autocorrelation values of each order are within a specific region determined for each order; a power calculator that calculates the power per unit block of the input signal and compares the power per unit block to see if it exceeds a standard value; A zero-crossing number counter that counts the number of zero-crossings within and determines whether or not it is within a specific range; and a signal determiner that determines that the input signal is a modulated data signal under the condition that the unit block determined to be present by the correlation range determiner occupies a predetermined number or more of the plurality of consecutive unit blocks. A detection device for a modulated data signal, characterized in that: