JPH053776B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a method for instantly identifying when a received signal level suddenly changes, whether it is a sudden change in the level of the received signal or a momentary interruption. This invention relates to a method for instantly identifying sudden signal level changes and instantaneous interruptions in a modem that receives polyphase phase modulated signals.

[Technology background]

In data communications, multiple pieces of data are simultaneously transmitted using a polyphase modulation method in order to effectively utilize communication bands and increase transmission efficiency. In data communication using this polyphase phase modulation method, a carrier is always present when data is being transmitted, so the modem receiver uses a CDi circuit (carrier detection indication circuit) to detect the presence or absence of a carrier. The modem receiver is activated when a carrier is detected.

However, if the noise on the wired or wireless transmission line is large, the carrier frequency component contained in this noise turns on the CDi circuit. Therefore, even though no data is being transmitted, it is determined that there is a carrier and the modem receiving section is activated, resulting in an inconvenient result that the modem malfunctions.

[Conventional technology and problems]

In order to prevent the modem receiver from malfunctioning due to noise, there is a conventional method that activates the modem receiver when the reception level exceeds a certain absolute level.
With this method, it was not possible to prevent malfunctions when the noise on the line was large.

Therefore, in order to prevent malfunctions even when the noise is large, a method has been adopted in which the reception section of the modem starts operating not by detecting the absolute level but by detecting the relative level. To explain the outline of this method using Figure 1, the received signal is shown in Figure 1a.
As shown in FIG. 1b, if data transmission ends at time t ₁ and the next data transmission starts again at time t ₃ , the relative level becomes low at time t ₁ , as shown in FIG. At time t ₃ it becomes high level again. The relative level detection circuit (not shown)
A stop pulse (not shown) is generated at time _{t 1} to stop operation of the modem receiver, and a start pulse (not shown) is generated at time t ₃ to start operation of the modem receiver. The modem receiving section is operated from time t ₃ to _{t 5}
The modem is trained in between, adjusts the modem so that it can receive data, and finishes the pull-in operation.
When data transmission occurs after time _t5 , it is correctly demodulated. The carrier detection operation, which indicates the operating status of the modem receiver, has a delay characteristic as shown in Figure 1c, so even if data reception stops at t ₁ , the modem receiver will continue to operate until t ₂ . Even if data reception is resumed at , t ₃ , the normal operating state is returned at t ₄ . For this reason, this method
As shown in FIG. 1d, the reception level changes from time t ₁ to _{t 3}
If there is a sudden change in the relative level and the relative level changes as well, then the time
Since the modem receiving section does not operate between _t2 and _t4 , there is a drawback that data during this period is invalid.

[Purpose of the invention]

An object of the present invention is to eliminate malfunctions of the modem receiving section by instantly identifying whether the reception level suddenly changes and the noise level increases, whether it is a sudden change in the level of the received signal or a momentary interruption; To provide a system for identifying instantaneous interruptions in sudden changes in the level of a received signal, which prevents received data from becoming invalid.

[Structure of the invention]

In order to achieve this objective, the received signal level sudden change instantaneous interruption identification method of the present invention includes an AGC circuit that smoothes level fluctuations of a received signal subjected to multiphase phase modulation, and a reference oscillator for modulating the carrier phase of the received signal. a phase error detection device that outputs a phase error signal corresponding to the phase difference between and a relative level detection circuit that detects a relative level, and when the relative level falls below a predetermined level, the threshold values of the AGC circuit and the signal quality detection circuit are initialized to cause both circuits to be pulled in instantly. do.

[Embodiments of the invention]

An embodiment of the present invention will be described based on FIGS. 2 to 4.

FIG. 2 is a block diagram of an embodiment of the present invention, FIG. 3 is a functional block diagram of the signal quality detection circuit, and FIG. 4 is an explanatory diagram of the operation of the signal quality detection circuit.

In FIG. 2, 11 is an AGC circuit for smoothing fluctuations in the reception level of the received signal, and 12, indicated by a dotted line, is a phase error detection means. Of the circuits constituting the phase error detection means 12, 13 is a roll-off filter (hereinafter referred to as ROF) for removing inter-symbol interference, and 14 is an automatic filter for removing inter-symbol interference caused by transmission path distortion. Equalizer (hereinafter
15 is a carrier phase automatic control circuit (hereinafter referred to as CAPC) that controls the phase of an internal demodulation reference oscillator (not shown) to match the carrier phase of the received signal, and 16 is the carrier phase of the received signal. This is a determination circuit that outputs a phase error signal corresponding to the phase difference with the carrier phase of CAPC 15. 17 is a signal quality detection circuit (hereinafter referred to as SQD) that outputs an identification signal for identifying whether what is received is noise or a carrier, that is, data based on the phase error signal and a predetermined threshold;
An identification circuit that identifies whether the received signal is noise or data based on the identification signal supplied from the SQD 17.The identification circuit 19 determines the relative level of the received signal and turns on the signal when it is above a predetermined level. Relative level detection circuit that outputs an off signal, 20
21 is an initialization circuit that initializes the threshold values of the AGC circuit 11 and SQD and causes them to be pulled in instantly when the relative level becomes below a predetermined threshold and outputs an off signal; 21 is an initialization circuit that causes a sudden change in the relative level of the received signal; 22 is a carrier detection circuit that detects the carrier of the received signal.

Next, the operation shown in FIG. 2 will be explained. When a multiphase phase modulated signal is received via a transmission path (not shown), level fluctuations in the received signal are smoothed by the AGC circuit 11 and then applied to the ROF 13 of the phase error detection means 12.

The ROF 13 filters high frequency components of the received signal to prevent intersymbol interference. Continued AEQ14
corrects the equalization characteristics to remove intersymbol interference due to transmission path distortion and the like. This equalization characteristic correction is performed by the RAM 2 which stores an equalization characteristic correction program corresponding to the phase error signal detected by the determination circuit 16.
1 automatically. The CAPC 15 controls the phase of an internal demodulation reference oscillator to the carrier phase of the received signal, and supplies information on the phase difference between the two to the determination circuit 16. The determination circuit 16 outputs a phase error signal for control based on the phase difference information.

A portion of the phase error signal is applied to the CAPC 15 to automatically control the phase of the demodulation reference oscillator of the CAPC 15 to the carrier phase of the received signal applied from the AEQ 14.

When another part of the phase error signal is added to the RAM 21, the RAM 21 automatically corrects the equalization characteristics of the AEQ 14 according to the equalization characteristics correction program corresponding to the phase error signal, and corrects the equalization characteristics due to transmission line distortion, etc. Eliminate the intersymbol interference that has occurred.

Still another part of the phase error signal is applied to the SQD 17, and the operation of the SQD 17 will be explained later.

A relative level detection circuit 19 receives the output of the AGC circuit 11 and detects the relative level of the received signal and noise, and when the noise increases and the relative level becomes below a predetermined threshold, an off signal is sent to the initialization circuit 20.
Add to RAM21. The relative level detection circuit 19
A moving average is taken from the output of the AGC circuit 11, and an envelope is detected from the output of the AGC circuit 11, as shown in FIG. 5C. When the received signal contains noise as shown in FIG. 5A, the output of the AGC circuit 11 becomes as shown in FIG. 5B. Relative level detection circuit 1
9, as shown in FIG. 5C, takes a moving average of the output of the AGC circuit 11 and detects the envelope of the AGC output. If it is below the threshold, it is determined that the relative level is off.

One of the objects of the present invention is to determine whether it is a momentary interruption when there is noise above the level that turns on the carrier detection circuit, as shown in Fig. 6a, or a sudden change in level, as shown in Fig. 6b. It's about identifying. It is true that the spectra of signal data and noise overlap, but if the S/N is maintained when the level suddenly changes, modulation and demodulation can be performed again as long as the AGC is pulled in, which reduces judgment errors. , by looking at SQD17, it can be seen that the level suddenly changed.

When the RAM 21 receives the off signal, it stores and holds the status of each device in the modem (not shown).
Furthermore, the automatic equalization operation of the AEQ 14 is also stopped and held.

When the initialization circuit 20 receives the off signal, it raises the bias circuit of the AGC circuit 11,
The AGC circuit 11 is instantly pulled in and initialized.

Here, an equivalent circuit of the AGC circuit 11 is shown in FIG. When the input is small, (REF-input) becomes a positive value, a large value accumulates in the tap, C becomes a large value, and the AGC output becomes large. If the input is large, (REF - input) will be a negative value,
A small value accumulates on the tap, C becomes a small value, and the AGC output becomes small. As a result, the AGC output is the size of REF, and (REF - input = 0), so the tap value remains constant and the AGC
The output is also constant. Note that the bias circuit of the AGC circuit 11 is a feedback portion in the equivalent circuit of FIG. Increasing the height of the bias circuit increases the value of α in FIG. 7, that is, the time constant decreases, and the amount of feedback increases, so the time required to reach the final value becomes shorter.

FIG. 3 is a block diagram showing the functions of the SQD 17, in which 25 and 28 are multipliers, 26 is an adder, 27 is a delay circuit, A is a coefficient, and B is a coefficient. By the way, the coefficient A and B determine the time constant of the low pass filter (LPF) that constitutes the SQD 17. Further, since the phase error signal takes an absolute value, an absolute value circuit 29 is provided. Judgment circuit 16
When a phase error signal is added from , when the received signal is noise, the output gradually increases and reaches a certain level, and when the received signal is carrier, that is, data, the output gradually decreases and reaches a certain level. When the coefficient A is at a low level SL ₁ , the noise output SN or data output is
The period during which SD reaches the final level is long, T ₁ to T ₂ , but when the coefficient A is at a high level SL ₂ , as shown in Figure 4b, the noise output SN or data output
Since the period during which SD reaches the final level is greatly shortened to T' ₁ to T' ₂ , the pull-in is performed instantaneously.

When the relative level is below a predetermined threshold and an off signal is output, the time constant of the AGC circuit 11 is made small to cause it to pull in at high speed, and then the delay tap of the SQD 17 is initialized to the intermediate value of the on/off signal. Note that the value of the output of the SQD 17 changes depending on the deterioration state of the received signal, and the value does not change depending on the coefficients A and B. Therefore, when reproducing data from a modem, it can normally be used without problems if the error rate is better than 10 ^-5 , for example, and if it is worse than 10 ^-3 there is a problem in use. Therefore, this intermediate error rate of 10 ^-4 is used as the threshold.

When SQD17 is initialized, it is instantly pulled in and outputs an on signal when it is data SD.
When the noise is SD, an off signal is output as an identification signal.

The identification circuit 18 receives the identification signal of the SQD 17, and if it is an on signal, determines that the received signal is a carrier, that is, data, and issues a restart start signal.
The data is sent to the RAM 21 and other devices in the modem (not shown), and a reception operation is started. The state before restarting
Since it is held in the RAM 21, normal operation resumes immediately. Since the period until this restart is sufficiently carried out within t ₁ to _{t 2} (about several tens of milliseconds) in FIG. 1, a situation in which the received data becomes invalid does not occur.

When the identification signal is off, the received signal is determined to be noise, and the modem receiver does not operate again. Even when the relative level of the received signal is restored and the relative level detection circuit turns on, the identification circuit 18 does not generate a re-operation disclosure signal, and the normal reception operation shown in FIG. The operation is resumed.

〔Effect of the invention〕

As explained above, according to the present invention, even if the reception level suddenly changes, it is possible to instantly identify whether it is a sudden change in the level of the received signal or noise caused by a momentary interruption of the signal, and to detect the sudden change in level. Since the modem receiving section can restart its operation instantly, even if the reception level suddenly changes, malfunction of the modem receiving section can be eliminated and received data can be prevented from becoming invalid.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of a conventional reception method for identifying received signals and noise, Fig. 2 is a block diagram of a method for identifying instantaneous interruptions in received signal levels according to the present invention, and Fig. 3 is a signal quality detection circuit (SQD). ) functional block diagram,
Figure 4 is a diagram explaining the operation of the signal quality detection circuit, Figure 5 is a diagram explaining envelope detection of AGC output, Figure 6 is a diagram explaining instantaneous interruptions due to noise and sudden level changes, and Figure 7 is an equivalent circuit of the AGC circuit. It is. In the figure, 11 is an AGC circuit, 12 is a phase error detection means, 13 is a roll off filter (ROF),
14 is an automatic equalizer (AEQ), 15 is a carrier phase automatic control circuit (CAPC), 16 is a judgment circuit, 17
is a signal quality detection circuit (SQD), 18 is an identification circuit,
19 is a relative level detection circuit, 20 is an initialization circuit, 21 is a RAM, 22 is a carrier detection circuit, 25 and 28 are multipliers, 26 is an adder, and 27 is a delay circuit.

Claims (1)

[Claims] 1. An AGC circuit that smoothes level fluctuations of a received signal subjected to polyphase phase modulation, a phase error detection means that outputs a phase error signal corresponding to the phase difference between the carrier phase of the received signal and a reference oscillator for demodulation, and this phase A signal quality detection circuit that identifies whether a received signal is noise or data based on an error signal and a predetermined coefficient value, and a relative level detection circuit that detects the relative level of the received signal based on the output of the AGC circuit, When this relative level falls below a predetermined level, the bias circuit is set high to instantly draw in the AGC circuit, and the delay tap of the signal quality detection circuit is initialized to an intermediate level between the on and off signals. A method for identifying instantaneous interruptions in sudden changes in the level of a received signal, which is characterized by causing the signal to be pulled in.