JPS6042651B2 - Phase fluctuation compensator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a phase fluctuation compensation device that can effectively compensate for phase fluctuations such as phase jitter of a transmitted signal.

When transmitting signals at high speed through a limited frequency band transmission line such as a voice band telephone line, large intersymbol interference generally occurs in the transmitted waveform due to the amplitude and phase distortion of the line.

Furthermore, the transmitted signal has phase fluctuations that change over time, such as phase jitter due to the line, leading to code errors in the transmitted signal. However, conventional devices are equipped with an automatic equalizer to compensate for the intersymbol interference.

However, this automatic equalizer cannot even compensate for the fast phase fluctuations of the signal due to the phase jitter. Therefore, in the conventional device, a phase rotation circuit is provided after the automatic equalizer to compensate for the phase rotation (variation) due to the above-mentioned phase jitter and the like. However, since the equalizer signal that controls the tap gain of the automatic equalizer generally contains a phase fluctuation component due to phase jitter, it is not possible to satisfactorily compensate for the intersymbol interference. Furthermore, even if the phase rotation circuit compensates for the phase jitter of a signal that has not been accurately compensated in this way, there is still a drawback that good compensation cannot be achieved. Therefore, it has been considered to integrally configure the automatic equalizer and the phase rotation circuit, and to make the above-mentioned circuits interact with each other to perform good phase fluctuation compensation. However, at the initial stage of operation, the tap gain of the automatic equalizer has not yet converged and deviates significantly from the optimum value. Therefore, the output of the automatic equalizer contains large phase fluctuations and intersymbol interference. Even if such a signal is input to the phase rotation circuit, the phase rotation circuit will not correctly detect the phase fluctuation. Therefore, there was a problem that the signal deteriorated significantly and the tap gain did not converge satisfactorily. In other words, the conventional device has a problem in that it cannot effectively compensate for intersymbol interference and phase fluctuations of the transmitted signal when there is phase fluctuation in the line. This system was developed with these circumstances in mind, and its purpose is to develop a phase that can effectively compensate for phase fluctuations such as intersymbol interference and phase jitter due to the transmitted signal line. An object of the present invention is to provide a fluctuation compensation device. The gist of the present invention is that, for example, an M
Using a specified pattern signal such as a sequence pseudo-random pattern signal, the tap gain of the automatic equalizer is converged using only the automatic equalizer without operating the phase correction circuit, and then the phase rotation circuit is used. Phase changes due to phase jitter, etc. The tap gain of the automatic equalizer is controlled using the equalized residual signal generated based on the motion-compensated signal.

In other words, when the tap gain converges, the degree of coupling between the phase rotation circuit and the automatic equalizer is improved by lowering the phase fluctuation compensation effect of the phase rotation circuit. After that, the degree of coupling between the above-mentioned phase rotation circuit and automatic equalization is increased, and the synergistic effect of each of the above-mentioned circuits allows the phase fluctuations of the transmitted signal to be accurately controlled. This is an effective way to compensate. Hereinafter, one embodiment of the present invention will be explained with reference to the aspects.

FIG. 1 is a schematic diagram of the apparatus of the present invention. In the figure, 1 is an automatic equalizer, into which the transmitted signal is input. The signal automatically equalized via the automatic equalizer 1 is supplied to a phase rotation circuit 2, where the phase rotation is controlled to have a predetermined phase angle, which will be described later. The signal output from the phase rotation circuit 2 is supplied to a determination circuit 3 for sign determination, and is also supplied to a phase detection control circuit 4 and a difference calculation circuit 5. The judgment output of the judgment circuit 3 is supplied to a switch circuit 6, where it is selectively extracted with, for example, an M-sequence pseudo-random pattern signal from a pattern signal generator 7, and is output to the phase detection circuit 4 and difference calculation circuit 5. Supplied. The phase detection control circuit 4 has a phase rotation circuit 2 which receives one signal input.
and the judgment output or pattern signal selected by the switch circuit 6 which is the other signal input, detect the phase error of the transmitted signal, and generate a control signal for the phase rotation/rotation circuit. It is outputting. Similarly to the phase detection control circuit 4, the difference calculation circuit 5 also detects the equalization residual signal of the transmitted signal from the input signal. This equalized residual signal is fed back to the automatic equalizer as a tap gain correction signal. Further, the phase control signal as the output of the phase detection control circuit 4 is subjected to coefficient control via the coefficient circuit 8, and then fed back to the phase rotation circuit 2 as a phase correction signal. On the other hand, a signal detector 9 is connected to the signal input side of the automatic equalizer 1, and detects the start of transmission of, for example, an M-sequence pseudo-random pattern signal, which is transmitted prior to transmission of an information signal.

Then, the time control circuit 10 detects the start time of this signal transmission.
Activate. This time control circuit 10 is a timer circuit consisting of, for example, a clock pulse counter, etc., and after a predetermined period of time has elapsed from the start of transmission of the signal, the switch circuit 6
A switching control signal is supplied to the coefficient circuit 8, and a coefficient control signal is supplied to the coefficient circuit 8. According to the control signal from the time control circuit 10, the switch circuit 6 selectively outputs the pattern signal from the pattern signal generator 7 for the predetermined time, and the coefficient circuit 8 has a phase error of approximately zero. A phase correction signal is applied to the phase rotation circuit 2. By the way, the automatic equalizer 1 is configured as shown in FIG. 2, for example. That is, a plurality of delay circuits 11 connected in series, a tap gain circuit 12 that controls the tap gain of the output of each of these delay circuits 11, and a synthesizer that combines the signals passed through each of these tap gain circuits 12. 13. and a coefficient circuit 14 that inputs the signal output from the difference calculation circuit 5 and multiplies it by a predetermined coefficient;
a multiplication circuit 15 that multiplies the signal passed through this coefficient circuit 14 by the output of each of the delay circuits 11;
and an integrating circuit 16 that integrates the output of the circuit and supplies a tap gain control signal to the tap gain circuit 12. According to the automatic equalizer 1 configured in this way, the coefficient circuit 1
4 by the equalized residual signal input to the tap gain circuit 1.
The tap gain of 2 is adjusted, and the transmitted signal input to the delay circuit 11 is automatically equalized.

Thus, according to the present device, the pattern signal is transmitted prior to the transmission of the information signal, and upon detecting the transmission of the pattern signal, the switch circuit 6 selects the signal from the pattern generator 7 and selects the signal from the coefficient circuit 8. Due to this action, a substantially zero phase rotation control signal is applied to the phase rotation circuit 2.

Therefore, at this time, the signal automatically equalized via the automatic equalizer 1 is outputted without undergoing phase rotation by the phase rotation circuit 2. Then, based on this signal and the pattern signal from the pattern signal generator 7, the tap gain control of the automatic equalizer 1 is performed by the difference calculation circuit 5. Through this tap gain control, the tap gain of the automatic equalizer 1 is converged, and the tap gain is set to a substantially stable state. Hereinafter, tap gain control based on a previously determined fixed pattern as described above will be referred to as a preset mode of the automatic equalizer. Thereafter, as explained above, the time control circuit 10 causes the switch circuit 6 to select the judgment output from the judgment circuit 3, cancel the substantially zero coefficient setting of the coefficient circuit 8, and set a predetermined coefficient value. The phase error is then applied to the phase rotation circuit 2 as a phase correction signal.

Hereinafter, the operating state in which the device operates using the determination value of the transmitted signal without depending on the predetermined fixed pattern as described above will be referred to as an adaptive mode. According to this adaptive mode, the transmitted signal (information signal) is passed through the automatic equalizer 1 to compensate for inter-symbol interference caused by the line, and is also passed to the phase rotation circuit 2 to compensate for phase fluctuations such as phase jitter. will be output. In this adaptive mode, the tap gain of the automatic equalizer has converged to a value close to the optimum value due to the preset ● mode, so each signal of the input and output of the judgment circuit 3 is used as the automatic equalizer. When the phase variation correction circuit is operated, as described above, the automatic equalizer 1 is able to perform the correction against intersymbol interference, and the phase rotation circuit 2 is able to perform the correction against the phase fluctuation with good accuracy. That is, the tap gain of the automatic equalizer 1 is almost close to the optimum value. Therefore, when the phase fluctuation correction circuit is operated on the output signal of the automatic equalizer 1, the amount of phase fluctuation is detected as a substantially correct value. Therefore, the output of the phase fluctuation correction circuit becomes a phase compensated signal with a small amount of phase fluctuation. As a result, the automatic equalizer 1 also acts effectively against intersymbol interference, and the amount of intersymbol interference appearing at the output of the automatic equalizer 1 is reduced. Effective compensation is thus achieved and accurate operating conditions can be reached quickly. Therefore, according to the device of the present invention, in the preset mode, the tap gain is well converged without imparting phase rotation to the signal, and after the tap gain has been converged, in the adaptive mode, the phase fluctuation is It is possible to perform phase fluctuation compensation that follows.

The configuration of the device of the present invention and the outline of its operation have been explained above. The following is a further explanation using an example. Impulse response waveform in an ideal transmission path with Nyquist bandwidth w
(t) is expressed by the following formula.

Here, the real component Re(w(t)) of w(t) is a waveform directly responsible for signal transmission, and the imaginary component 1m(w(t)) is a waveform generated by SS width modulation.

FIGS. 3A and 3B show the above-mentioned signals Re(Wj(t)) and Im, respectively.
This shows the signal waveform of (w(t)). As shown in FIG. 3, Im(w(t)) is the sampling point t
=IT (where i=..., -1, 0, 1, 2...), each generates an infinite number of intersymbol interferences. Therefore, the above (
When the response during code transmission in the ternary partial response of the form 1, 0, 1) is expressed on a two-dimensional orthogonal plane of Xy, it becomes as shown in FIG.

That is, the signal point distribution (thick line) in FIG.
Judgment is made depending on which of (2) it is included in. The continuous spread of the signal point distribution in the y-axis direction is SSB or V.
This is caused by SB amplitude modulation and has no direct relationship with partial response. Now, when a phase fluctuation θ exists in the line, the signal point distribution rotates by 0 angle around the origin 0, as shown in FIG.

Furthermore, if there is intersymbol interference due to amplitude distortion, phase distortion, etc. of the line, the signal point distribution at this time will expand two-dimensionally as shown schematically in FIG. The spread of the signal point distribution seen in FIG. 6 is expressed by the real component Re(zl−Nejθ
1-1) appears as an expansion of the projection component toward the X axis.
When attempting to compensate for transmission signals with such intersymbol interference and phase fluctuations using a strongly coupled configuration of an automatic equalizer and a phase fluctuation correction circuit, the tap gain of automatic equalizer 1 is optimal. Since the signal is not converged to the value, the signal outputted through the automatic equalizer 1 has a negative effect on the operation of the phase rotation circuit 2.

Furthermore, an automatic equalizer is applied based on the signal for which phase fluctuation compensation has not been correctly performed by the phase rotation circuit 2. Since the tap gain is adjusted by 1, the automatic equalization effect of the automatic equalizer 1 is also degraded. For example, if we consider the case where there is no intersymbol interference and only phase fluctuation θ exists, the distribution of the demodulated baseband signal of the transmitted signal will be in the thick line A shown in FIG. , b, c. However, since the tap gain of automatic equalizer 1 has not converged, inter-symbol interference is not compensated for, and the distribution of the demodulated baseband signal ends up being widely distributed as shown in the shaded area in FIG. It turns out. Therefore, after intersymbol interference equalization, if a signal that should exist on line segment a exists at point P in the figure due to the residual intersymbol interference, the phase error θ will have a value and a sign. It will be detected as a different 0. Then, phase fluctuation 4 compensation is performed based on this detected phase error 0. In other words, the phase fluctuation compensation acts in the opposite direction, and instead acts to increase the phase fluctuation. Therefore, in the device of the present invention, after the tap gain of the automatic equalizer 1 has converged and the intersymbol interference has been equalized with high accuracy, the phase fluctuation compensation is performed by the phase rotation circuit 2. This eliminates the above drawbacks.

That is, in the preset mode, the time control circuit 1
No phase rotation control signal is given to the phase rotation circuit 2 due to the action of 0. (The control signal level is set to approximately zero.) For this reason,
The phase rotation circuit 2 is substantially separated from the automatic equalizer 1,
Only automatic equalizer 1 operates stably in the Pj reset mode. With this preset mode, the tap gain of the automatic equalizer 1 converges, and intersymbol interference is compensated with considerable accuracy. Therefore, the output signal of the automatic equalizer 1 is distributed only slightly in the vicinity of the line segments A, b, and c shown in FIG. 5. Thereafter, in the adaptive mode, a substantially correct phase error is detected from the signal compensated as described above, and the phase rotation circuit 2 performs effective phase fluctuation compensation. By this phase fluctuation compensation, error components due to phase fluctuations due to phase jitter etc. are reduced in the tap gain control signal fed back to the automatic equalizer 1,
Conversely, the error signal based on intersymbol interference becomes dominant and begins to control the tap gain. Therefore, in the end, the distortion due to intersymbol interference is compensated with high accuracy by the automatic equalizer 1, and the distortion due to phase fluctuation of the line is compensated with high accuracy by the phase rotation circuit 2. The pattern signal from the pattern signal generator 7 used in the preset mode has the same pattern as the specific pattern signal transmitted prior to the transmission of the information signal, and this pattern signal is used to generate the automatic equalizer 1. Convergence of tap gain is performed.

Therefore, when transmitting information signals, the automatic equalizer 1
The tap gain has been converged, and phase fluctuation compensation is performed on the information signal using the adaptive mode. According to the device of the present invention, as described above, at the initial stage of signal transmission, the coupling between the automatic equalizer 1 and the phase rotation circuit 2 is made coarse, and the tap gain of the automatic equalizer 1 is adjusted. After the above-mentioned tap gain has converged, the automatic equalizer 1 and the phase rotation circuit 2 are tightly coupled, and phase fluctuation compensation can be performed with high precision.

Therefore, it is possible to efficiently compensate for phase fluctuations such as inter-symbol interference and phase jitter in the line caused by transmission, and it is possible to eliminate the problem of the automatic equalizer and phase rotation circuit adversely affecting each other as in conventional devices. There are no shortcomings. Note that the present invention is not limited to the above embodiments.

For example, the coefficient for the detected phase error 0 by the coefficient circuit 8 may be substantially zero in the preset mode, that is, a value that does not adversely affect the operation of the automatic equalizer 1 due to phase rotation. Further, the output of the automatic equalizer 1 may bypass the phase rotation circuit 2 in the preset mode. Furthermore, in the above explanation, phase fluctuation compensation is switched in two stages: preset mode and adaptive mode.
This may be done during the preset mode, or the coupling between the automatic equalizer and the phase variation compensation circuit may be controlled in stages. Further, the operating time of the time control circuit 10 may be controlled by changing the tap gain of the automatic equalizer 1 or by extracting a control signal from the output. Furthermore, the applied signal transmission method is not limited to SSB, but may be VSB or DSB. As described above, the present invention can be implemented with various modifications without departing from the gist thereof. As described in detail above, according to the present invention, it is possible to provide a phase fluctuation compensating device that has various special advantages such as being able to effectively compensate for phase fluctuations with high accuracy.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram showing one embodiment of the device of the present invention, and FIG.
The figure is a schematic diagram of the automatic equalizer of the same embodiment, and FIGS. 3 to 6 are diagrams for explaining the operation of the apparatus of the present invention, respectively.

Claims (1)

[Claims] 1. An automatic equalizer that equalizes a transmitted signal based on a tap gain correction signal, and a phase rotation of a signal outputted via this automatic equalizer based on a phase correction signal. a phase rotation circuit; a determination circuit that determines a signal output from the phase rotation circuit; and a pattern signal generator that generates a pattern signal that is the same as a specified pattern signal that is transmitted prior to the transmitted signal; a switch circuit that selectively outputs the pattern signal output from the pattern signal generator and the determination output output from the determination circuit based on a switching signal, and each output signal of the switch circuit and the phase rotation circuit; means for generating the tap gain signal based on and supplying it to the automatic equalizer; means for generating a phase correction signal from each output signal of the switch circuit and the phase rotation circuit; means for supplying a phase correction signal to the phase rotation circuit; and means for detecting the start of transmission of the pattern signal, and driving the switch circuit for a predetermined time from the time of detection to extract an output signal from the pattern signal generator. A phase fluctuation compensating device comprising: a time control circuit for stopping phase rotation by the phase rotation circuit; 2. The phase fluctuation compensation device according to claim 1, wherein the time control circuit sets the level of the phase correction signal to approximately zero level at the specific time to stop phase rotation. 3. The phase fluctuation compensator according to claim 1, wherein the time control circuit bypasses the phase rotation circuit for the specific time to stop phase rotation of the signal.