JP7080566B2 - 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, a carrier wave regenerative circuit that improves demodulation performance (bit error rate) based on the degree of influence of phase noise and thermal noise is known (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 the high multi-value modulation, the phase error detection range of the carrier wave / carrier reproduction is remarkably narrowed. That is, in the case of low multi-value, the phase error detection range is wide because the distance between adjacent ideal points is large, but in the case of high multi-value, the phase error detection range is small because the distance between adjacent ideal points is small. Becomes narrower. Since the phase error detection range is remarkably narrowed, if the phase jitter (phase fluctuation) as shown in FIG. 10 increases in a phase noise environment, the carrier wave reproduction may be out of sync.

As a result, when the tap coefficient is updated only by the judgment-oriented algorithm as in the conventional case, an event that converges to an unintended signal point arrangement occurs. That is, as shown in FIG. 11, when the phase-rotated output signal point (black circle in the figure) protrudes from the frame F1 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 F1. As a result, as shown in FIG. 12, the output signal point cloud converges small and the power is reduced. Then, by repeating such updating of the tap coefficient, for example, as shown in FIG. 13, 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, in the carrier wave reproduction circuit described in Patent Document 1, the specifications of the carrier wave reproduction loop at the time of high multi-value are switched depending on whether the reduction of thermal noise is prioritized or the reduction of phase noise is prioritized. Since unstable operation due to a decrease in the phase error detection range due to the increase in the number of values is not taken into consideration, it is difficult to realize stable operation of the demodulator in a low C / N environment.

Therefore, an object of the present invention is to provide a carrier regenerative circuit capable of realizing stable and high demodulation performance even at high multi-values.

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 the 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. An algorithm based on the error between the ideal point and the output signal of the adaptive equalizer, the rotation signal generation unit that generates the Then, a tentative ideal selected according to a predetermined rule from a first tap update unit for updating the tap coefficient for the adaptive equalizer and a plurality of tentative ideal points arranged at equal distances around the ideal point. A second tap update unit that updates the tap coefficient for the adaptive equalizer by an algorithm based on an error between the point and the output signal of the adaptive equalizer, and the first tap update based on a predetermined condition. The first phase rotator includes the unit or a switching unit that outputs the tap coefficient of one of the second tap update units to the adaptive equalizer, and the first phase rotator has the input signal based on the phase rotation control signal. It is a carrier carrier reproduction circuit characterized by rotating the phase of.

According to a second aspect of the present invention, in the carrier wave regeneration circuit according to the first aspect, the second tap update unit is located farthest from the output signal of the adaptive equalizer among the plurality of provisional ideal points. It is characterized by selecting a tentative ideal point to be used.

According to a third aspect of the present invention, in the carrier wave regeneration circuit according to the first or second aspect, the switching unit adapts one of the tap coefficients to the adaptive equalizer based on the power level of the output signal of the adaptive equalizer. It is characterized by outputting to an equalizer.

The invention according to claim 4 compensates for the frequency characteristics of a first phase rotator that rotates the phase of an input signal and a phase rotation signal that is an input signal whose phase is rotated by the first phase rotator. An adaptive equalizer, a phase error detector that detects the phase error included in the phase rotation signal compensated by the adaptive equalizer, and 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 a plurality of tentative ideal points arranged at equal distances around the ideal point. A tap update unit for updating the tap coefficient for the adaptive equalizer by an algorithm based on an error between the ideal point or the tentative ideal point selected according to a predetermined rule and the output signal of the adaptive equalizer is provided. The first phase rotator is a carrier carrier reproducing circuit characterized in that the phase of the input signal is rotated based on the phase rotation control signal.

The invention according to claim 5 is the carrier wave reproduction circuit according to claim 4, wherein the tap update unit randomly selects the ideal point or the tentative ideal point from the ideal point and the plurality of tentative ideal points. It is characterized by selecting.

According to the inventions of claims 1 and 4, a 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 characteristics are compensated by the adaptive equalizer. Even if there is waveform distortion due to fading, 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.

In addition, the tap coefficient for the adaptive equalizer is updated based on the error between not only the ideal point but also a plurality of temporary ideal points arranged equidistantly around the ideal point and the output signal of the adaptive equalizer. Therefore, it is possible to obtain a stable output from the adaptive equalizer. That is, there is a possibility that only one ideal point will converge to an unintended signal point arrangement, and there is a possibility that the tentative ideal point alone will not converge to the accurate arrangement of the signal point arrangement, but the ideal point and the tentative ideal point. By updating the tap coefficient in combination with the point, 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 second aspect of the invention, in the second tap update unit, the error between the tentative ideal point farthest from the output signal of the adaptive equalizer and the output signal of the adaptive equalizer, that is, the largest error. Since the tap coefficient is updated based on the error, it is possible to more effectively prevent convergence to an unintended signal point arrangement.

According to the invention of claim 3, it is switched whether to update the tap coefficient based on the ideal point or the tap coefficient based on the tentative ideal point based on the power level of the output signal of the adaptive equalizer. Therefore, it is possible to update the tap coefficient with an algorithm suitable for the output power level of the adaptive equalizer to obtain a stable adaptive equalizer output.

According to the invention of claim 5, since the tap coefficient is updated based on the error between the randomly selected ideal point or tentative ideal point and the output signal of the adaptive equalizer, one ideal point or By fixing to the tentative ideal point, it is possible to effectively prevent the signal point arrangement from converging to an unintended signal point arrangement with a simple configuration.

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 figure which shows the example of the positional relationship between a received signal and an ideal point in the carrier wave reproduction circuit of FIG. It is a figure which shows the arrangement relation of the ideal point and the tentative ideal point in the carrier wave reproduction circuit of FIG. It is explanatory drawing which shows the tap update method by the 2nd tap update part of the carrier wave reproduction circuit of FIG. It is a figure which shows the tap update error by the 2nd tap update part of 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 figure which shows the arrangement relation of the ideal point and the tentative ideal point in the carrier wave reproduction circuit of FIG. In the present invention, it is a conceptual diagram which shows the state which the phase jitter occurs by the high multi-valued. In the present invention, it is a conceptual diagram which shows the 1st signal state when the tap is updated based on only one ideal point. 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.

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

(Embodiment 1)
1 to 7 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, frequency-converted, digitally converted by the ADC, demodulated by the carrier wave reproduction circuit 1, and demapped. Is.

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 the tap coefficient is updated as described later.

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 tap coefficient memory 30, the first tap update unit 31, the second tap update unit 32, and the power detector (switching) are used for the adaptive equalizer 3. Section 33 and a tap coefficient switch (switching section) 34. The tap coefficient memory 30 is a memory for storing the tap coefficient from the tap coefficient switch 34, which will be described later, and inputs the stored tap coefficient to the first tap update unit 31 and the second tap update unit 32.

The first tap update unit 31 is an algorithm based on the error between the ideal point (reference signal) and the output signal of the adaptive equalizer 3 (ordinary determination-oriented algorithm), and updates the tap coefficient for the adaptive equalizer 3. It is an update unit (updates the tap coefficient input from the tap coefficient memory 30). That is, in the case of the positional relationship between the received signal (output signal) S and the ideal point R as shown in FIG. 4, a judgment-oriented algorithm based on the least mean squares error (MMSE: Minimum Mean Square Error) is used. , The tap coefficient is calculated and updated so that the error power between the output signal and the reference signal is minimized, and the LMS (Least Mean Square) algorithm and the RLS (Recursive Last Square) algorithm are adopted as the judgment-oriented algorithms. The algorithm.

The second tap update unit 32 outputs the tentative ideal point K selected according to a predetermined rule from the plurality of tentative ideal points K arranged equidistantly about the ideal point R, and the output of the adaptive equalizer 3. It is an update unit that updates the tap coefficient for the adaptive equalizer 3 by an algorithm based on an error with the signal. At this time, the tentative ideal point K located farthest from the output signal of the adaptive equalizer 3 is selected from the plurality of tentative ideal points K, and the tap coefficient is updated.

Specifically, in this embodiment, as shown in FIG. 5, four provisional ideal points K are arranged at the corners of the square so that the ideal point R is at the center of the square. Here, the tentative ideal points K are arranged so that the distances between the adjacent tentative ideal points K are the same in all the regions. Among the tentative ideal points K arranged in this way, the tentative ideal point K located farthest from the output signal (received signal) S of the adaptive equalizer 3 is selected. For example, in the case of the output signal S as shown in FIG. 6, the tentative ideal point K closest to the output signal S is the first tentative ideal point K1 and is located diagonally to the first tentative ideal point K1 ( The third tentative ideal point K3 (which is a point target centered on the ideal point R) is selected as the tentative ideal point K located at the farthest point. Such selection is made in the entire area as shown in FIG. 7, and the first tap update unit 31 and the first tap update unit 31 are based on the tap update error between the selected temporary ideal point K and the output signal S of the adaptive equalizer 3. Similarly, the tap coefficient is updated by the judgment-oriented algorithm.

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 S of the adaptive equalizer 3. Specifically, the power detector 33 detects the power level of the output signal S of the adaptive equalizer 3, and based on the detection result, which tap coefficient of the tap update unit 31 or 32 is adopted is determined. The indicated "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.

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, not only the ideal point R but also the adaptive equalizer 3 is based on an error between a plurality of temporary ideal points K arranged equidistantly about the ideal point R and the output signal S of the adaptive equalizer 3. Since the tap coefficient for is updated, it is possible to obtain a stable output from the adaptive equalizer 3. That is, there is a possibility that only one ideal point R may converge to an unintended signal point arrangement, and that only one tentative ideal point K may not converge to an accurate arrangement of signal point arrangements. However, by updating the tap coefficient by using the ideal point R and the tentative ideal point K in combination, it is possible to obtain a stable adaptive equalizer output.

Specifically, based on the power level of the output signal S of the adaptive equalizer 3, it is possible to switch between updating the tap coefficient based on the ideal point R and updating the tap coefficient based on the provisional ideal point K. , It is possible to update the tap coefficient with an algorithm suitable for the output power level of the adaptive equalizer 3 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.

Moreover, in the second tap update unit 32, the error between the provisional ideal point K farthest from the output signal S of the adaptive equalizer 3 and the output signal S of the adaptive equalizer 3, that is, the largest tap update Since the tap coefficient is updated based on the error, it is possible to more effectively prevent convergence to an unintended signal point arrangement.

(Embodiment 2)
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 tap updating unit 35 that updates the tap coefficient has a different configuration from that of the first embodiment, and the same configuration as that of the first embodiment is designated by the same reference numerals, and the description thereof will be omitted.

The tap update unit 35 determines the ideal point R or the tentative ideal point K selected according to a predetermined rule from the ideal point R and a plurality of tentative ideal points K arranged equidistantly about the ideal point R. It is an update unit that updates the tap coefficient for the adaptive equidistant 3 by an algorithm based on an error with the output signal S of the adaptive equidistant 3. At this time, the ideal point R or the tentative ideal point K is randomly selected from the ideal point R and the plurality of tentative ideal points K.

Specifically, in this embodiment, as shown in FIG. 9, six tentative ideal points K1 to K6 are arranged on the circumference so that the ideal point R is at the center of the circle. Here, the tentative ideal points K are arranged so that the distances of the tentative ideal points K1 to K6 with respect to each ideal point R are the same in all regions. Then, one ideal point R or a tentative ideal point K is randomly or randomly selected from the tentative ideal points K1 to K6 and the ideal point R arranged in this way. Next, the tap coefficient is updated by the determination-oriented algorithm based on the tap update error between the selected ideal point R or provisional ideal point K and the output signal S of the adaptive equalizer 3.

For example, when the ideal point R is selected, the tap coefficient is updated based on the tap update error between the ideal point R and the output signal S of the adaptive equalizer 3, and then the tentative ideal point K3 is selected. In this case, the tap coefficient is updated based on the tap update error between the provisional ideal point K3 and the output signal S of the adaptive equalizer 3. In this way, the ideal point R and the tentative ideal point K, which are the reference of the tap update error, change randomly each time the tap coefficient is updated.

According to such an embodiment, as in the first embodiment, since the tap coefficient is updated by using the ideal point R and the provisional ideal point K in combination, it is possible to obtain a stable adaptive equalizer output. As a result, it becomes possible to realize highly accurate and stable demodulation performance and carrier wave reproduction. Moreover, since the tap coefficient is updated based on the error between the randomly selected ideal point R or tentative ideal point K and the output signal S of the adaptive equalizer 3, one ideal point R or tentative ideal point K It is possible to effectively prevent the signal point arrangement from converging to an unintended signal point arrangement by being fixed to the above with a simple configuration.

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 first embodiment described above, the tap coefficient is updated based on the ideal point R or the tap coefficient is updated based on the tentative ideal point K based on the power level of the output signal S of the adaptive equalizer 3. However, it may be switched based on the fluctuation of the phase (phase rotation) or may be switched at predetermined time intervals.

Similarly, in the above-described second embodiment, the ideal point R or the tentative ideal point K is randomly selected, but the ideal point R or the provisional ideal point K may be selected regularly. For example, the ideal point R is selected a plurality of times, then the first tentative ideal point K1 is selected, then the ideal point R is selected a plurality of times, and then the second tentative ideal point K2 is selected, and so on. May select the ideal point R and sequentially select the provisional ideal points K1 to K6 at predetermined intervals.

1 Carrier regenerative circuit 2 1st phase rotator 3 Adaptive equalizer 30 Tap coefficient memory 31 1st tap update unit 32 2nd tap update unit 33 Power detector (switching unit)
34 Tap coefficient switch (switching unit)
35 Tap update unit 4 Phase error detector 5 LPF
6 NCO (Rotation signal generator)
7 Second phase rotator 8 Equalizer S Output signal (received signal)
R ideal point K provisional ideal point

Claims (5)

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
A first tap update unit that updates the tap coefficient for the adaptive equalizer by an algorithm based on an error between the ideal point and the output signal of the adaptive equalizer.
The adaptation is an algorithm based on the error between the provisional ideal point selected according to a predetermined rule from a plurality of provisional ideal points arranged equidistantly around the ideal point and the output signal of the adaptation equalizer. A second tap updater that updates the tap coefficient for the equalizer,
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 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. The second tap update unit selects the tentative ideal point located farthest from the output signal of the adaptive equalizer among the plurality of tentative ideal points.
The carrier wave regeneration circuit according to claim 1. 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 any one of claims 1 or 2. 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 ideal point or the tentative ideal point selected according to a predetermined rule from the ideal point and a plurality of tentative ideal points arranged equidistantly about the ideal point, and the output signal of the adaptive equalizer. The tap update unit that updates the tap coefficient for the adaptive equidistant with the algorithm based on the error of
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. The tap update unit randomly selects the ideal point or the tentative ideal point from the ideal point and the plurality of tentative ideal points.
The carrier wave regenerative circuit according to claim 4.

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