JP7023583B2 - Carrier regenerative circuit - Google Patents

Description

The present invention relates to a carrier wave regenerative circuit that reproduces a carrier wave / received wave in digital wireless transmission.

In recent years, wireless traffic has been increasing more and more, and from the viewpoint of improving the efficiency of frequency utilization, there is an increasing demand for high-speed transmission by the high multi-value QAM (Quadrature Amplitude Modulation) method in digital wireless transmission. .. In this high multi-value QAM method, the demodulation performance may deteriorate due to the phase noise (phase error) of the carrier wave generated in the transmitting device or the receiving device. Therefore, there is known a carrier regenerative circuit that improves demodulation performance (bit error rate) based on the degree of influence of phase noise and thermal noise (see, for example, Patent Document 1).

In this carrier wave reproduction circuit, the loop filter control unit controls the bandwidth of the loop filter based on the phase error detected by the phase error detector and the amplitude error detected by the amplitude error detector, thereby causing phase noise and heat. The bandwidth is set appropriately according to the noise to improve the demodulation performance.

Japanese Unexamined Patent Publication No. 2011-101177

By the way, in a microwave wireless system, wireless transmission in a multipath fading environment is a prerequisite, so C / N (Carrier / Noise, carrier-to-noise ratio) due to waveform distortion of the received signal due to fading and level fluctuation due to fading. ) The change significantly deteriorates the estimation accuracy of the phase noise of the carrier wave. However, in the carrier wave regenerative circuit described in Patent Document 1, it is difficult to realize high demodulation performance because the influence of waveform distortion due to fading is not taken into consideration.

Therefore, an object of the present invention is to provide a carrier wave regenerative circuit capable of estimating the phase noise of a carrier wave with high accuracy and realizing high demodulation performance.

In order to solve the above problems, the invention according to claim 1 is a phase, which is a first phase rotator that rotates the phase of an input signal and an input signal whose phase is rotated by the first phase rotator. An adaptive equalizer that compensates for the frequency characteristics of the rotation signal, a phase error detector that detects the phase error included in the phase rotation signal compensated by the adaptive equalizer, and a phase rotation control signal based on the phase error. A second phase rotator that rotates the phase of the input signal based on the phase rotation control signal, and the first phase rotator includes the phase rotation control signal. It is a carrier carrier reproduction circuit characterized by rotating the phase of the input signal based on.

The invention according to claim 2 updates the tap coefficient with respect to the adaptive equalizer by an algorithm based on an error between the output signal of the adaptive equalizer and the reference signal in the carrier wave reproduction circuit according to claim 1. The first tap update unit, the second tap update unit that updates the tap coefficient for the adaptive equalizer by an algorithm that does not affect the phase rotation of the carrier wave, and the first tap update unit based on predetermined conditions. It is characterized by including a switching unit for outputting the tap coefficient of one of the tap update unit or the second tap update unit to the adaptive equalizer.

According to a third aspect of the present invention, in the carrier wave regenerative circuit according to the second aspect, the switching unit makes the one tap coefficient the adaptive equalization based on the power level of the output signal of the adaptive equalizer. It is characterized by outputting to a vessel.

According to a fourth aspect of the present invention, in the carrier wave regenerative circuit according to the second aspect, the switching unit obtains one of the tap coefficients based on the power level of the tap coefficient output to the adaptive equalizer. It is characterized by outputting to an adaptive equalizer.

According to a fifth aspect of the present invention, in the carrier wave regeneration circuit according to the second aspect, the switching unit outputs one of the tap coefficients to the adaptive equalizer based on a predetermined time interval. It is a feature.

The invention according to claim 6 is the carrier wave reproduction circuit according to claim 2, wherein the switching unit normally outputs the tap coefficient of the first tap update unit to the adaptive equalizer, and the adaptation unit. When the error between the output signal of the equalizer and the reference signal is larger than a predetermined value, the tap coefficient of the second tap update unit is output to the adaptive equalizer.

According to the first aspect of the present invention, the phase rotation control signal is generated and the phase of the input signal is rotated based on the phase error of the phase rotation signal whose frequency characteristic is compensated by the adaptive equalizer, so that the phase is faded. Even if there is waveform distortion due to the above, it is possible to estimate the phase noise of the carrier wave with high accuracy and realize high demodulation performance and carrier wave reproduction. Further, since the frequency characteristic of the phase rotation signal is compensated by the adaptive equalizer, the influence of thermal noise can be reduced.

According to the invention of claim 2, the algorithm based on the error between the output signal of the adaptive equalizer and the reference signal (determination-oriented algorithm) or the algorithm that does not affect the phase rotation of the carrier (CMA algorithm) is applied. Since it is possible to switch whether to update the tap coefficient for the equalizer based on a predetermined condition, it is possible to obtain a stable output from the adaptive equalizer. That is, there is a possibility that the judgment-oriented algorithm alone will converge to an unintended signal point arrangement, and the CMA algorithm alone may have a slow convergence speed and may not be able to converge to an accurate arrangement of signal point arrangements. By switching between them, it is possible to obtain a stable adaptive equalizer output. As a result, it is possible to realize highly accurate and stable demodulation performance and carrier wave reproduction.

According to the invention of claim 3, since the two algorithms are switched based on the power level of the output signal of the adaptive equalizer, the tap coefficient is updated with the algorithm suitable for the output power level of the adaptive equalizer. Therefore, it becomes possible to obtain a stable adaptive equalizer output.

According to the invention of claim 4, since the two algorithms are switched based on the power level of the tap coefficient output to the adaptive equalizer, the tap coefficient is updated by the algorithm suitable for the power level of the tap coefficient. Therefore, it becomes possible to obtain a stable adaptive equalizer output.

According to the invention of claim 5, since the two algorithms are switched based on a predetermined time interval, that is, the two algorithms are reliably switched periodically, a stable adaptive equalizer output is obtained. It becomes possible.

According to the invention of claim 6, since the tap coefficient is usually updated by the determination-oriented algorithm, it is possible to converge to the accurate arrangement of the signal point arrangement. On the other hand, when the error between the output signal of the adaptive equalizer and the reference signal is larger than a predetermined value, the tap coefficient is updated by the CMA algorithm, so that it is prevented from converging to an unintended signal point arrangement. be able to. In this way, it is possible to obtain a stable adaptive equalizer output.

It is a schematic block diagram which shows the carrier wave regenerative circuit which concerns on Embodiment 1 of this invention. It is a schematic block diagram which shows the microwave radio system which includes the carrier wave reproduction circuit of FIG. It is a schematic block diagram which shows the periphery of the adaptive equalizer of the carrier wave reproduction circuit of FIG. It is a conceptual diagram which shows the 1st signal state when the tap is updated only by the determination direction algorithm in the carrier wave reproduction circuit of FIG. It is a conceptual diagram which shows the 2nd signal state following FIG. It is a conceptual diagram which shows the 3rd signal state following FIG. It is a schematic block diagram which shows the periphery of the adaptive equalizer of the carrier wave regeneration circuit which concerns on Embodiment 2 of this invention. It is a schematic block diagram which shows the periphery of the adaptive equalizer of the carrier wave regeneration circuit which concerns on Embodiment 3 of this invention. It is a schematic block diagram which shows the periphery of the adaptive equalizer of the carrier wave regeneration circuit which concerns on Embodiment 4 of this invention. It is a conceptual diagram which shows the normal signal state of the adaptive equalizer output in Embodiment 4 of this invention. It is a conceptual diagram which shows the abnormal signal state of the adaptive equalizer output in Embodiment 4 of this invention.

Hereinafter, the present invention will be described based on the illustrated embodiment.

(Embodiment 1)
1 to 6 show the embodiment, and FIG. 1 is a schematic block diagram showing a carrier wave regenerative circuit 1 according to the embodiment. The carrier wave regeneration circuit 1 is a circuit that reproduces a carrier wave in digital wireless transmission, and is provided in the receiving device 102 of the microwave wireless system shown in FIG. Here, the microwave wireless system will be briefly described. First, the mapped and modulated transmission signal in the transmission device 101 is analog-converted, multiplied by the carrier wave W1, and transmitted from the antenna. Then, when it is received by the antenna of the receiving device 102 via the multipath fading environment, it is multiplied by the carrier wave W2, digitally converted, demodulated by the carrier wave reproduction circuit 1, and demapped.

The carrier wave reproduction circuit 1 mainly includes a first phase rotator 2, an adaptive equalizer 3, a phase error detector 4, an LPF 5, an NCO (rotation signal generator) 6, and a second phase rotator. 7 and an equalizer 8 are provided.

The first phase rotator 2 is a rotator / multiplier that rotates the phase of the input signal, and rotates the phase of the input signal based on the phase rotation control signal of NCO6 described later. Specifically, for each of the I-channel baseband signal and the Q-channel baseband signal converted into digital signals, phase rotation is performed based on the sine wave and cosine wave of the phase rotation control signal of NCO6. Is.

The adaptive equalizer 3 compensates for the frequency characteristics of the phase rotation signal, which is an input signal whose phase is rotated by the first phase rotation unit 2, that is, is equalized to eliminate waveform distortion and data error of the phase rotation signal. It is a vessel. Here, the adaptive equalizer 3 is composed of a determination feedback equalizer (DFE) and a linear equalizer, and as will be described later, the determination oriented algorithm and the CMA algorithm are appropriately switched to adapt. The tap coefficient of the equalizer 3 is updated.

The phase error detector 4 is a detector that detects the phase error included in the phase rotation signal compensated by the adaptive equalizer 3. A specific detection method is a well-known technique. For example, a signal point corresponding to an output signal is selected from the signal point arrangement of the modulation method used between the transmission / reception devices 101 and 102, and the coordinates of the selected signal point are selected. And the coordinates of the input signal point are compared to calculate the phase error value.

The LPF 5 is a filter that removes high frequency components of the phase error detected by the phase error detector 4 according to a predetermined bandwidth, and is composed of a low pass filter (Low Pass Filter).

The NCO 6 is a generation unit that generates a phase rotation control signal based on the phase error from which the high frequency component is removed by the LPF 5, and is composed of an NCO (Numerically Controlled Oscillator, Numerically Controlled Oscillator). Specifically, the phase rotation by the first phase rotator 2 is controlled by generating an antiphase sine wave and a cosine wave based on the phase error from the LPF 5 and outputting them to the first phase rotator 2. It is something to do. Further, the generated phase rotation control signal is output to the second phase rotation unit 7.

The second phase rotator 7 is a rotator / multiplier that rotates the phase of the input signal, and rotates the phase of the input signal based on the phase rotation control signal from the NCO 6 to compensate for the frequency characteristics. Output to the device 8. That is, the phase of the input signal is rotated based on the sine wave and the cosine wave from the NCO 6 based on the phase error detected by the frequency characteristic compensation (waveform distortion and the like are eliminated) by the adaptive equalizer 3. In this way, the adaptive equalizer 3 is mounted in the carrier wave reproduction loop (first phase rotator 2, phase error detector 4, LPF 5 and NCO 6 loop), thereby compensating for the frequency characteristics. The phase noise of the input signal is canceled based on the phase error value estimated later.

Next, a method of updating the tap coefficient for the adaptive equalizer 3 will be described. In this embodiment, as shown in FIG. 3, the first tap update unit 31, the second tap update unit 32, the power detector (switching unit) 33, and the tap are applied to the adaptive equalizer 3. A coefficient switch (switching unit) 34 is provided.

The first tap update unit 31 is an algorithm (determination-oriented algorithm) based on the error between the output signal of the adaptive equalizer 3 and the reference signal, and is an update unit that calculates and updates the tap coefficient for the adaptive equalizer 3. .. That is, the tap coefficient is calculated and updated so that the error power between the output signal and the reference signal is minimized by using a judgment-oriented algorithm based on the least mean squares error (MMSE: Minimum Mean Squared Error). As a determination-oriented algorithm, an LMS (Least Mean Square) algorithm or an RLS (Recursive Left Square) algorithm is adopted.

The second tap update unit 32 is an algorithm (CMA algorithm) that does not affect the phase rotation of the carrier wave, and is an update unit that calculates and updates the tap coefficient for the adaptive equalizer 3. That is, the CMA algorithm (blind algorithm) that does not require a replica of the desired signal calculates and updates the tap coefficient so that the power level becomes constant by using the power error, and Godard as the CMA algorithm. ) The algorithm is adopted. This Goddard algorithm is an algorithm that optimizes the output based on the premise that the transmitted signal is a constant envelope signal.

The power detector 33 and the tap coefficient switch 34 are switching units that output the tap coefficient of either the first tap update unit 31 or the second tap update unit 32 to the adaptive equalizer 3 based on predetermined conditions. In this embodiment, one of the tap coefficients is output to the adaptive equalizer 3 based on the power level of the output signal of the adaptive equalizer 3. Specifically, the power detector 33 detects the power level of the output signal of the adaptive equalizer 3, and based on the detection result, indicates which of the tap coefficients 31 and 32 is to be adopted. The "switching" signal is transmitted to the tap coefficient switch 34. In response to this, the switch is switched in the tap coefficient switch 34, and the tap coefficient of the first tap update unit 31 or the second tap update unit 32 is output to the adaptive equalizer 3.

Here, at what power level (detection result) to switch to the first tap update unit 31 or the second tap update unit 32 is based on the characteristics of the adaptive equalizer 3, the desired accuracy, and the like. Is set as appropriate. For example, in the normal state, the tap coefficient of the first tap update unit 31 is output, and when the power level reaches a predetermined threshold value or less, the tap coefficient is switched to the second tap update unit 32. The tap coefficient from the tap coefficient switch 34 is also output and stored in the tap coefficient memory 30, and the stored tap coefficient is input to the update units 31 and 32 to obtain the next tap coefficient, respectively. Calculated.

As described above, according to the carrier wave reproduction circuit 1, a phase rotation control signal is generated based on the phase error of the phase rotation signal whose frequency characteristics are compensated (the waveform distortion and the like are eliminated) by the adaptive equalizer 3. Since the phase of the input signal is rotated, even if there is waveform distortion due to fading, it is possible to estimate the phase noise of the carrier wave with high accuracy (detected by the phase error detector 4) and realize high demodulation performance and carrier wave reproduction. It will be possible. Further, since the frequency characteristic of the phase rotation signal is compensated by the adaptive equalizer 3, the influence of thermal noise can be reduced.

Further, since it is possible to switch whether to update the tap coefficient for the adaptive equalizer 3 by the determination-oriented algorithm or the CMA algorithm based on a predetermined condition, it is possible to obtain a stable output from the adaptive equalizer 3. That is, there is a possibility that the judgment-oriented algorithm alone will converge to an unintended signal point arrangement, and the CMA algorithm alone may have a slow convergence speed and may not be able to converge to an accurate arrangement of signal point arrangements. By switching between them, it is possible to obtain a stable output of the adaptive equalizer 3. As a result, it is possible to realize highly accurate and stable demodulation performance and carrier wave reproduction.

Specifically, in this embodiment, since the two algorithms are switched based on the power level of the output signal of the adaptive equalizer 3, the tap coefficient is updated with the algorithm suitable for the output power level of the adaptive equalizer 3. Therefore, it becomes possible to obtain a stable output of the adaptive equalizer 3.

Here, since the adaptive equalizer 3 is implemented in the carrier wave reproduction loop, an event that converges to an unintended signal point arrangement when the tap coefficient is updated only by the determination-oriented algorithm will be described.

First, as shown in FIG. 4, when the phase-rotated output signal point (black circle in the figure) protrudes from the frame W1 of the ideal signal point / reference signal point (white circle in the figure), the output signal point of the protruding portion P1 The tap coefficient is updated so as to enter this frame W1. As a result, as shown in FIG. 5, the output signal point group is small and converges, and the power is reduced. Then, by repeating such updating of the tap coefficient, as shown in FIG. 6, for example, the four output signal points converge so as to be aggregated around the ideal signal point (the signal point arrangement size is small). An event occurs (which falls into the optimum state in the state).

On the other hand, since the CMA algorithm is not affected by the phase rotation of the carrier wave, such convergence can be prevented by using the CMA algorithm. On the other hand, since the CMA algorithm may not converge to the accurate arrangement of the signal point arrangement, it is possible to obtain a stable output from the adaptive equalizer 3 by switching between the judgment-oriented algorithm and the CMA algorithm side by side. Is to be.

(Embodiment 2)
FIG. 7 is a schematic block diagram showing the periphery of the adaptive equalizer 3 of the carrier wave regeneration circuit 1 according to this embodiment. In this embodiment, the tap coefficient of the first tap update unit 31 or the second tap update unit 32 is output to the adaptive equalizer 3 based on the power level of the tap coefficient output to the adaptive equalizer 3. The configuration is different from that of the first embodiment, and the same components as those of the first embodiment are designated by the same reference numerals, and the description thereof will be omitted.

In this embodiment, the tap coefficient from the tap coefficient switch 34 is output to the adaptive equalizer 3 and is output to the power detector 33. Then, the power detector 33 detects the power level of the tap coefficient, and based on the detection result, the tap coefficient switcher outputs a "switching" signal indicating which of the tap update units 31 and 32 is to be adopted. It is transmitted to 34. In response to this, the switch is switched in the tap coefficient switch 34, and the tap coefficient of the first tap update unit 31 or the second tap update unit 32 is output to the adaptive equalizer 3.

Here, at what power level (detection result) to switch to the first tap update unit 31 or the second tap update unit 32 is based on the characteristics of the adaptive equalizer 3, the desired accuracy, and the like. Is set as appropriate. For example, normally, the tap coefficient of the first tap update unit 31 is output, and when the power level of the tap coefficient is equal to or higher than a predetermined threshold value (so that the power of the output signal point group does not converge), the second tap is output. Switch to the update unit 32.

As described above, according to this embodiment, since the two algorithms are switched based on the power level of the tap coefficient output to the adaptive equalizer 3, the tap coefficient is an algorithm suitable for the power level of the tap coefficient. It becomes possible to obtain a stable output of the adaptive equalizer 3 by updating.

(Embodiment 3)
FIG. 8 is a schematic block diagram showing the periphery of the adaptive equalizer 3 of the carrier wave regeneration circuit 1 according to this embodiment. In this embodiment, the configuration is different from that of the first embodiment in that the tap coefficient of the first tap update unit 31 or the second tap update unit 32 is output to the adaptive equalizer 3 based on a predetermined time interval. Differently, the same components as those in the first embodiment are designated by the same reference numerals, and the description thereof will be omitted.

In this embodiment, the tap coefficient switch 34 and the timer 35 form a switching unit, and each time the timer 35 elapses (at a predetermined time ratio), either the tap update unit 31 or 32 is sequentially used. A "switching" signal indicating whether to adopt the tap coefficient is transmitted from the timer 35 to the tap coefficient switching device 34. Here, the predetermined time for transmitting the "switching" signal is set so that it can converge to the accurate arrangement of the signal point arrangement and does not converge to the unintended signal point arrangement. For example, first, the tap coefficient of the first tap update unit 31 is output, and when the first predetermined time elapses, a "switching" signal that adopts the tap coefficient of the second tap update unit 32 is transmitted. Next, when the second predetermined time (for example, a shorter time than the first predetermined time) elapses, the switching of transmitting the "switching" signal that adopts the tap coefficient of the first tap updating unit 31 is repeated. In this way, the tap coefficient of the first tap update unit 31 and the tap coefficient of the second tap update unit 32 are output alternately at a predetermined time ratio.

Thus, according to this embodiment, the two algorithms are switched based on a predetermined time interval, that is, the two algorithms are surely switched periodically (at a fixed time rate), so that they are stable. It is possible to obtain the output of the adaptive equalizer 3.

(Embodiment 4)
FIG. 9 is a schematic block diagram showing the periphery of the adaptive equalizer 3 of the carrier wave regeneration circuit 1 according to this embodiment. In this embodiment, the tap coefficient of the first tap update unit 31 is normally output to the adaptive equalizer 3, and the error between the output signal of the adaptive equalizer 3 and the reference signal is larger than a predetermined value. The configuration is different from that of the first embodiment in that the tap coefficient of the second tap update unit 32 is output to the adaptive equalizer 3, and the same reference numerals are given to the configurations equivalent to those of the first embodiment. The explanation is omitted.

In this embodiment, the output signal (equalization output) of the adaptive equalizer 3 is input to the first tap update unit 31, and is stored in advance in the output signal of the adaptive equalizer 3 and the first tap update unit 31. When the power error from the set reference signal is larger than a predetermined value, a "switching" signal that adopts the tap coefficient of the second tap update unit 32 is transmitted from the first tap update unit 31 to the tap coefficient switch 34. To transmit. Subsequently, when the error between the output signal of the adaptive equalizer 3 and the reference signal becomes a predetermined value or less, the "switching" signal that adopts the tap coefficient of the first tap update unit 31 is set to the first tap. The switching of transmission from the update unit 31 to the tap coefficient switch 34 is repeated.

Here, the threshold value of the error between the output signal of the adaptive equalizer 3 and the reference signal is set so as not to converge to an unintended signal point arrangement by the determination-oriented algorithm. For example, as shown in FIG. 10, a threshold frame W2 of a substantially regular square centered on each ideal signal point / reference signal point (white circle in the figure) is set (the reference signal points are separated by the threshold frame W2) and output. When the signal point (black circle in the figure) is within the threshold frame W2, the output of the adaptive equalizer 3 is set to the normal state. On the other hand, if the output signal point protrudes from the threshold frame W2, as shown in FIG. 11, it becomes impossible to determine from which reference signal point the output signal point deviates (the reference signal point and the output signal point have a one-to-one correspondence). Therefore, the output of the adaptive equalizer 3 is regarded as an abnormal state, and the CMA algorithm is switched to. Here, in FIGS. 10 and 11, the boundary lines of the adjacent threshold frames W2 overlap each other, but a gap / margin is provided between the threshold frames W2, and the output signal point deviates from which reference signal point. You may make sure to switch to the CMA algorithm before it becomes impossible to determine whether or not it is present.

As described above, according to this embodiment, since the tap coefficient is normally updated by the determination-oriented algorithm, it is possible to converge to the accurate arrangement of the signal point arrangement. On the other hand, when the error between the output signal of the adaptive equalizer 3 and the reference signal is larger than a predetermined value, the tap coefficient is updated by the CMA algorithm, so that it is prevented from converging to an unintended signal point arrangement. can do. In this way, it is possible to obtain a stable output of the adaptive equalizer 3.

Although the embodiment of the present invention has been described above, the specific configuration is not limited to the above-described embodiment, and even if there is a design change or the like within a range that does not deviate from the gist of the present invention. Included in the invention. For example, in the third embodiment described above, the algorithm is switched at predetermined time intervals, but the algorithm is changed for each output count of the tap coefficient from the tap update units 31 and 32 (the output count is also included in the predetermined time interval). You may switch. Further, in the above-described fourth embodiment, the "switching" signal is transmitted from the first tap updating unit 31 to the tap coefficient switching device 34, but the "switching" signal is transmitted from the second tap updating unit 32 to the tap coefficient. It may be transmitted to the switch 34.

1 Carrier regenerative circuit 2 First phase rotator 3 Adaptation equalizer 31 First tap update unit 32 Second tap update unit 33 Power detector (switching unit)
34 Tap coefficient switch (switching unit)
35 Timer (switching unit)
4 Phase error detector 5 LPF
6 NCO (Rotation signal generator)
7 Second phase rotator 8 Equalizer

Claims (6)

A first phase rotator that rotates the phase of the input signal,
An adaptive equalizer that compensates for the frequency characteristics of the phase rotation signal, which is an input signal whose phase has been rotated by the first phase rotation device.
A phase error detector that detects the phase error included in the phase rotation signal compensated by the adaptive equalizer, and a phase error detector.
A rotation signal generator that generates a phase rotation control signal based on the phase error,
A second phase rotator that rotates the phase of the input signal based on the phase rotation control signal, and
The first phase rotator rotates the phase of the input signal based on the phase rotation control signal.
A carrier wave regenerative circuit characterized by that. A first tap update unit that updates the tap coefficient for the adaptive equalizer by an algorithm based on an error between the output signal of the adaptive equalizer and the reference signal.
A second tap updater that updates the tap coefficient for the adaptive equalizer with an algorithm that does not affect the phase rotation of the carrier wave.
A switching unit that outputs the tap coefficient of either the first tap update unit or the second tap update unit to the adaptive equalizer based on a predetermined condition.
The carrier wave regeneration circuit according to claim 1, wherein the carrier wave reproduction circuit is provided. The switching unit outputs one of the tap coefficients to the adaptive equalizer based on the power level of the output signal of the adaptive equalizer.
The carrier wave regenerative circuit according to claim 2. The switching unit outputs one of the tap coefficients to the adaptive equalizer based on the power level of the tap coefficient output to the adaptive equalizer.
The carrier wave regenerative circuit according to claim 2. The switching unit outputs one of the tap coefficients to the adaptive equalizer based on a predetermined time interval.
The carrier wave regenerative circuit according to claim 2. The switching unit normally outputs the tap coefficient of the first tap update unit to the adaptive equalizer, and when the error between the output signal of the adaptive equalizer and the reference signal is larger than a predetermined value. , The tap coefficient of the second tap update unit is output to the adaptive equalizer.
The carrier wave regenerative circuit according to claim 2.

Images