JPH10173720A - Phase comparison method and quadrate amplitude modulation signal demodulation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To conduct phase comparison for carrier recovery more accurately, even when a received signal includes a linearly/nonlinearly distorted component due to a noise component or reflection or the like. SOLUTION: Taking a 1st quadrant into consideration, error discrimination area 21-36 are set to each of symbol points so as not to cause gasps on an I-Q plane, they are divided into +, -regions by a line passing through the origin O and each symbol point, and when a received signal point resides in a + region, a + level is outputted. When a received signal point resides in a - region, a - level is outputted as a phase discrimination result. In this case, a border lien of the error discrimination area is selected, so that a distance between the border line of the error discrimination area and each symbol point is not less than a prescribed value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a phase comparison method for recovering a carrier wave when demodulating a quadrature amplitude modulation (hereinafter abbreviated as QAM) signal, and a QAM signal demodulation apparatus.

[0002]

2. Description of the Related Art FIG. 5 shows Embodiments 2, 4, 6, and 6 of the present invention.
FIG. 8 is a block diagram showing the configuration of a conventional digital demodulation device, and the present invention differs from the conventional digital demodulator in the phase comparison method of the phase comparator. Here, the case of 64-value QAM will be described.

[0005] In FIG. 5, a modulated wave 100 is converted into a digital signal by an analog-digital converter 101 (hereinafter abbreviated as an AD converter). Then, it is decomposed by the detector 102 into an in-phase signal and a quadrature signal. Each signal is spectrally shaped by the roll-off filter 103, and only the value at the timing of the signal point is taken into the register 104 and output.
The complex multiplier 105 subjects this signal to a numerically controlled oscillator (NC
O) The output signal of 109 is multiplied to control the phase of the received signal, and the 8-2 converter 106 reproduces generally easy-to-handle binary data 110 from the 8-level in-phase signal and quadrature signal.

A phase comparator 107 detects a difference between a reproduced carrier phase and a modulated wave phase output from the numerically controlled oscillator 109 from the output of the register 104. The output of the phase comparator 107 is smoothed by a loop filter (LPF) 108 and the numerical control oscillator 1
09 is added to the frequency control terminal.

The conventional phase comparator 107 detects the phase difference as follows. FIG. 6 is a diagram showing an error determination area and a determination method in a conventional example.
Only quadrants are shown. For other quadrants, this is the origin O
It is a characteristic that is rotated around. In FIG. 6, 111 to 126 are symbol points. The boundary line of the error determination area is a portion sandwiched between each circumference of the I-axis, the Q-axis and each circumference, and a vertical bisector of a line connecting each symbol point. However, the radius of each circle is the average value of the distance from the origin O to each symbol point. As shown in FIG.
46. The error determination area 131 is divided into two sections by a straight line passing through the origin O and the symbol point 111. These areas are indicated by + and-as shown in FIG. Error judgment area
132 to 146 are similarly divided into two sections.

When the received signal point is in the + area, the phase comparator 107 outputs a + level as a phase comparison result. If the signal point is in the-area,-level is output.

As described above, even in the conventional phase comparison method, the error determination area is provided as large as possible in the circumferential direction around the origin O, so that the gain control is performed in the demodulation device. Although the variation of the distance from the origin O of each signal point falls within a narrow range, it is possible to perform a phase comparison suitable for applications where the phase difference is large.

[0008]

However, in the conventional phase comparison method, when there are symbol points having slightly different distances from the origin O, such as the symbol points 111, 117 and 126 and the symbol points 112 and 122, The problem is that the distance between the symbol point and the boundary line (thick solid line) of the error determination area becomes extremely small, and there is a high possibility that an erroneous comparison result will be obtained due to linear or non-linear distortion components due to noise components or reflection. was there. This problem becomes more serious as the number of symbol points slightly different from the origin O increases as the multi-valued number of QAM increases.

An object of the present invention is to solve such a conventional problem, and an object of the present invention is to provide an excellent phase comparison method and a QAM signal demodulator capable of performing a correct phase comparison regardless of the position of a symbol point. I do.

[0010]

According to the present invention, in order to achieve the above object, a sufficient distance between a symbol point and a boundary of an error determination area can be ensured.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION
An error determination area is provided as large as possible in the circumferential direction around the origin O, and the shape of the error determination area is modified so that a sufficient distance between the symbol point and the boundary line of the error determination area can be secured. As a feature, it is possible to demodulate a received signal having a large phase difference as compared with the related art and having a linear / non-linear component due to a noise component or reflection.

According to a second aspect of the present invention, there is provided a multiplier for performing a comparison between complex numbers, a phase comparator for performing a phase comparison based on a multiplication result based on the phase comparison method according to the first aspect, and A quadrature amplitude modulation signal demodulator for performing carrier recovery comprising a loop filter for smoothing and a numerically controlled oscillator for generating a recovered carrier frequency, which has a larger phase difference than conventional ones, and also has a noise component and reflection. A received signal having a linear / non-linear component can be demodulated.

According to a third aspect of the present invention, the error determination area according to the first aspect is divided into a plurality of areas by a straight line passing through the origin O and the symbol point and a straight line rotating by a fixed angle about the origin O with respect to the straight line. By dividing, the value of the function that obtains the phase error signal increases stepwise with the increase of the variable, and the phase difference is large compared to the conventional one, and the linear and non-linear components due to noise components and reflection etc. Can be demodulated.

According to a fourth aspect of the present invention, there is provided a multiplier for performing a comparison between complex numbers, a phase comparator for performing a phase comparison based on a multiplication result based on the phase comparison method according to the third aspect, and A quadrature amplitude modulation signal demodulator for performing carrier recovery comprising a loop filter for smoothing and a numerically controlled oscillator for generating a recovered carrier frequency, which has a larger phase difference than conventional ones, and also has a noise component and reflection. A received signal having a linear / non-linear component can be demodulated.

According to a fifth aspect of the present invention, the boundary of the error determination area is sandwiched between the I-axis and the Q-axis and the respective circles, and the vertical bisectors of the line connecting the respective symbol points. And each circle has its origin at the origin O
Out of circles whose radius is the average value of the distances from the symbol points to the respective symbol points, except that circles in which the distance from each symbol point to the boundary is smaller than a certain value are compared with the conventional method. It is possible to demodulate a received signal having a large phase difference and having linear and non-linear components due to noise components and reflection.

According to a sixth aspect of the present invention, there is provided a multiplier for performing a comparison between complex numbers, a phase comparator for performing a phase comparison based on a multiplication result based on the phase comparison method according to the fifth aspect, and A quadrature amplitude modulation signal demodulator for performing carrier recovery comprising a loop filter for smoothing and a numerically controlled oscillator for generating a recovered carrier frequency, which has a larger phase difference than conventional ones, and also has a noise component and reflection. A received signal having a linear / non-linear component can be demodulated.

According to a seventh aspect of the present invention, the error judging area according to the fifth aspect is divided into a plurality of areas by a straight line passing through the origin O and the symbol point and a straight line rotating by a fixed angle about the origin O with respect to the straight line. By dividing, the value of the function for obtaining the phase error signal is characterized by the stepwise increase with the increase of the variable, and the phase difference is large compared to the conventional one, and the linear / non-linear component due to noise component and reflection etc. Can be demodulated.

According to an eighth aspect of the present invention, there is provided a multiplier for performing a comparison between complex numbers, a phase comparator for performing a phase comparison based on a multiplication result based on the phase comparison method according to the seventh aspect, and A quadrature amplitude modulation signal demodulator for performing carrier recovery comprising a loop filter for smoothing and a numerically controlled oscillator for generating a recovered carrier frequency, which has a larger phase difference than conventional ones, and also has a noise component and reflection. A received signal having a linear / non-linear component can be demodulated.

The configuration of the quadrature amplitude modulation signal demodulation device according to the second, fourth, sixth and eighth aspects is the same as that of the conventional one shown in FIG. 5, and the phase comparison method of the phase comparator is different from the conventional one.

(Embodiment 1) FIG. 1 shows characteristics of a phase comparator 107 (FIG. 5) according to Embodiment 1 of the present invention. For simplicity, only the first quadrant for 64QAM is shown. The other quadrants are rotated about the origin O. In FIG. 1, 1 to 16 are symbol points. The boundary of the error determination area is I
This is a portion sandwiched between each curve of the vertical bisector of the line connecting the axis, the Q axis, each curve, and each symbol point. However, each curve is centered on the origin O, and the origin O
, And the distance from each symbol point to the boundary line is smaller than 60% of one half of the distance between adjacent symbol points. The boundary line is deformed so as not to occur. These error determination areas are 21 to 36 as shown in FIG.

The error determination area 21 is divided into two sections by a straight line passing through the origin O and the symbol point 1. These areas are designated as + and-as shown in FIG. Error judgment area
22 to 36 are similarly divided into two sections.

The phase comparator 107 determines that the received symbol point is +
If it is a zone, a + level is output as the phase comparison result. If the symbol point is -area, -level is output.

As described above, in the first embodiment, the error determination areas 21 to as large as possible in the circumferential direction around the origin O are possible.
36, and symbol points 1 to 16 and error determination areas 22 to 36
The shape of the error determination areas 22 to 36 is modified so that the distance to the boundary line can be sufficiently ensured, so that the gain control is performed in the demodulation device and the like. However, there is an advantage that the method is suitable for use in demodulating a received signal having a large phase difference and a linear / non-linear distortion component due to a noise component or reflection.

In the first embodiment, the minimum value of the distance between the symbol point and the boundary line is set to the value of 2 which is the distance between the adjacent symbol points.
Although it is set to 60% of 1/60, it can be optimized for the transmission path and the demodulation device to be used by changing the gain control capability of the demodulation device and the magnitude of the phase error of the received signal.

The configuration of the digital demodulation apparatus according to the present embodiment is as shown in FIG. 5 described above, and the operation based on the configuration is the same as the conventional one. What is different from the conventional one is a phase comparator 107. This can be easily realized by using a read-only memory (ROM) that receives a signal point as an input and outputs a phase error signal as a phase comparison.

(Embodiment 2) FIG. 2 shows characteristics of the phase comparator 107 (FIG. 5) according to Embodiment 2 of the present invention. For simplicity, only the first quadrant for 64QAM is shown. The other quadrants are rotated about the origin O. In FIG. 2, 1 to 16 are symbol points. The boundary of the error determination area is I
This is a portion sandwiched between each curve of the vertical bisector of the line connecting the axis, the Q axis, each curve, and each symbol point. However, each curve is centered on the origin O, and the origin O
, And the distance from each symbol point to the boundary line is smaller than 60% of one half of the distance between adjacent symbol points. The boundary line is deformed so as not to occur. These error determination areas are set to 41 to 56 as shown in FIG.

The error determination area 41 is divided into four sections by a straight line passing through the origin O and the symbol point 1 and a straight line rotated by a fixed angle (± 3 °) about the origin O with respect to the straight line. These areas are shown as +, ++,
−−, −. The error determination areas 42 to 56 are similarly divided into four sections.

The phase comparator 107 (FIG. 5) outputs a level corresponding to the area where the received signal point is located, and the relationship is-<-<0 <++ <+.

Therefore, according to the second embodiment, there is an effect that an output having a level corresponding to the magnitude of the phase difference can be obtained for applications having a large phase difference.

In the second embodiment, the phase difference ± 3 ゜, 4
Although the comparison of the stages is performed, the value of the phase difference that changes the output level may be another value, or more stages may be provided to obtain a highly accurate phase comparison result. .

In the second embodiment, the minimum value of the distance between the symbol point and the boundary line is determined by the distance between the adjacent symbol points being 2
Although it is set to 60% of 1/60, it can be optimized for the transmission path and the demodulation device to be used by changing the gain control capability of the demodulation device and the magnitude of the phase error of the received signal.

The configuration of the digital demodulation apparatus according to the second embodiment is as shown in FIG. 5 described above, and the configuration and operation are the same as those of the related art. What is different from the conventional one is a phase comparator 107. This can be easily realized by using a read-only memory (ROM) that receives a signal point as an input and outputs a phase error signal as a phase comparison.

(Embodiment 3) FIG. 3 shows characteristics of the phase comparator 107 (FIG. 5) according to Embodiment 3 of the present invention. For simplicity, only the first quadrant for 64QAM is shown. The other quadrants are rotated about the origin O. In FIG. 3, 1 to 16 are symbol points. The boundary of the error determination area is I
This is a portion sandwiched between each circle of a vertical bisector of a line connecting the axis, the Q axis, each circle, and each symbol point. However, each circle has a center at the origin O and has a radius equal to the average value of the distance from the origin O to each symbol point. This excludes circles that are smaller than 50% of one half of the distance. These error determination areas are set to 61 to 76 as shown in FIG.

The error determination area 61 is divided into two sections by a straight line passing through the origin O and the symbol point 1. These areas are defined as + and-as shown in FIG. Error judgment area
62 to 76 are similarly divided into two sections.

When the received signal point is in the + area, the phase comparator 107 outputs a + level as a phase comparison result. If the signal point is in the-area,-level is output.

As described above, in the third embodiment, the error determination areas 61 to 61 are as large as possible in the circumferential direction around the origin O.
76, and symbol points 1 to 16 and error determination areas 61 to 76
The error determination areas 61 to 76 are set so as to ensure a sufficient distance from the boundary line of the symbol O. Therefore, the origin O of each symbol point is determined because the gain control is performed by the demodulator.
Although the variation in the distance from the target is within a narrow range, there is an advantage that the method is suitable for use in demodulating a received signal having a large phase difference and a linear / non-linear distortion component due to a noise component or reflection.

The configuration of the digital demodulation apparatus according to the third embodiment is as shown in FIG. 5, and the operation based on the configuration is the same as the conventional one. What is different from the conventional one is the phase comparator 10
7 This can be easily realized by using a read-only memory (ROM) that receives a signal point as an input and outputs a phase error signal as a phase comparison. Further, compared to the first embodiment, the third embodiment has an advantage in hardware design that the ROM is easy to design because the boundary of the error determination area is constituted only by the arc and the straight line. .

(Embodiment 4) FIG. 4 shows characteristics of the phase comparator 107 (FIG. 5) in Embodiment 4 of the present invention. For simplicity, only the first quadrant for 64QAM is shown. The other quadrants are rotated about the origin O. In FIG. 4, 1 to 16 are symbol points. The boundary of the error determination area is I
This is a portion sandwiched between each circle of a vertical bisector of a line connecting the axis, the Q axis, each circle, and each symbol point. However, each circle has a center at the origin O and has a radius equal to the average value of the distance from the origin O to each symbol point. This excludes circles that are smaller than 50% of one half of the distance. These error determination areas are set to 81 to 96 as shown in FIG.

The error determination area 81 is divided into four sections by a straight line passing through the origin O and the symbol point 1 and a straight line rotated by a fixed angle (± 3 °) about the origin O with respect to the straight line. These areas are indicated by +, + as shown in FIG.
+,-, And-. The error determination areas 82 to 96 are similarly divided into four sections.

The phase comparator 107 outputs a level corresponding to the area where the received signal point is located, and the relationship is − <−− <0 <++ <+.

Therefore, according to the fourth embodiment, there is an effect that an output of a level corresponding to the magnitude of the phase difference can be obtained for applications having a large phase difference.

In the fourth embodiment, the phase difference is ± 3 °,
Although the comparison is performed in four stages, the value of the phase difference for changing the output level may be another value, and it is also possible to obtain more accurate phase comparison results by providing more levels. it can.

The configuration of the digital demodulation apparatus according to the fourth embodiment is as shown in FIG. 5, and the operation based on the configuration is the same as the conventional one. What is different from the conventional one is the phase comparator 10
7 This can be easily realized by using a read-only memory (ROM) that receives a signal point as an input and outputs a phase error signal as a phase comparison. Further, compared to the second embodiment, according to the fourth embodiment, since the boundary line of the error determination area is constituted only by the arc and the straight line, there is an advantage in hardware design that ROM design is easy. Have.

In each of the above embodiments, the 64-value QAM
However, the same applies to multi-valued QAMs such as 128 and 256, and the effectiveness increases as the number of multi-values increases.

[0045]

As described above, according to the present invention, the distance between the symbol point and the boundary of the error determination area can be sufficiently ensured. Even if it has a nonlinear distortion component, correct phase comparison can be performed, and the effect that the loop gain of the carrier recovery loop can be increased.

[Brief description of the drawings]

FIG. 1 is a diagram showing an error determination area and a determination method according to Embodiment 1 of the present invention.

FIG. 2 is a diagram illustrating an error determination area and a determination method according to a second embodiment of the present invention.

FIG. 3 is a diagram illustrating an error determination area and a determination method according to a third embodiment of the present invention.

FIG. 4 is a diagram illustrating an error determination area and a determination method according to a fourth embodiment of the present invention.

FIG. 5 is a block diagram illustrating configurations of Embodiments 2, 4, 6, 8 of the present invention and a conventional digital demodulation device.

FIG. 6 is a diagram showing an error determination area and a determination method in a conventional example.

[Explanation of symbols]

1-16 ... Symbol points, 21-36, 41-56, 61-76, 81-
96: error judgment area, 101: analog-digital converter, 102: detector, 103: roll-off filter, 10
4 register, 105 complex multiplier, 106 8-2 converter, 107 phase comparator, 108 loop filter (LP
F), 109 ... Numerically controlled oscillator (NCO).

Claims (8)

[Claims] 1. An apparatus for demodulating a received quadrature amplitude modulation signal, wherein a point at which an unmodulated carrier power-to-noise power ratio of each reception point is theoretically the best on an IQ plane is represented by a symbol for carrier recovery. And a circle centered on the origin with the radius of the average value of adjacent values when the error determination area corresponding to each symbol point is arranged in ascending order of the distance from the origin to each symbol point in the ascending order, Of the symbol points on the same circumference centered on the origin, the boundary is based on the perpendicular bisector of adjacent symbol points, and the boundary is set when the distance between the boundary and the symbol point is small. An area having a boundary line deformed so as to increase the distance between the line and the symbol point is defined as a point on the IQ plane of an actually received symbol as a reception signal point. Phase error signal corresponding to the position of In the error determination area, the angle between the line segment connecting the symbol point and the origin as a reference, the clockwise direction formed by the line segment and the line segment connecting the signal point and the origin is positive, and the angle with the counterclockwise direction being negative is A phase comparison method characterized by outputting a signal obtained by a function as a variable. 2. A phase comparator for performing the phase comparison method according to claim 1 for recovering a carrier of a received quadrature amplitude modulation signal, a complex multiplier, a loop filter, and a numerically controlled oscillator, A phase difference signal is output by the phase comparator based on the in-phase component output and the anti-phase component output of the complex multiplier, smoothed by the loop filter, input to the control terminal of the numerically controlled oscillator, and output A quadrature amplitude modulation signal demodulator, wherein a carrier is reproduced by a phase locked loop for inputting a signal to the complex multiplier and controlling a phase of a received signal. 3. An apparatus for demodulating a received quadrature amplitude modulation signal, wherein a point at which an unmodulated carrier power-to-noise power ratio of each receiving point is theoretically the best on an IQ plane is represented by a symbol for carrier recovery. And a circle centered on the origin with the radius of the average value of adjacent values when the error determination area corresponding to each symbol point is arranged in ascending order of the distance from the origin to each symbol point in the ascending order, Of the symbol points on the same circumference centered on the origin, the boundary is based on the perpendicular bisector of adjacent symbol points, and the boundary is set when the distance between the boundary and the symbol point is small. An area having a boundary line deformed so as to increase the distance between the line and the symbol point is defined as a point on the IQ plane of an actually received symbol as a reception signal point. Phase error signal corresponding to the position of As described above, the error determination area is divided into a plurality of areas by a straight line passing through the origin O and the symbol point and a straight line that rotates at a fixed angle around the origin O with respect to the straight line, with a line segment connecting the symbol point and the origin as a reference, The angle obtained when the clockwise direction formed by the line segment and the line segment connecting the signal point and the origin is positive and the counterclockwise direction is negative is a variable, and the signal obtained by the function that increases stepwise with the increase of the variable is A phase comparison method characterized by outputting. 4. A phase comparator for performing a phase comparison method according to claim 3 for recovering a carrier of a received quadrature amplitude modulation signal, a complex multiplier, a loop filter, and a numerically controlled oscillator, A phase difference signal is output by the phase comparator based on the in-phase component output and the anti-phase component output of the complex multiplier, smoothed by the loop filter, input to the control terminal of the numerically controlled oscillator, and output A quadrature amplitude modulation signal demodulator, wherein a carrier is reproduced by a phase locked loop for inputting a signal to the complex multiplier and controlling a phase of a received signal. 5. An apparatus for demodulating a received quadrature amplitude modulation signal, wherein a point at which an unmodulated carrier power-to-noise power ratio at each reception point is theoretically the best on an IQ plane is used as a symbol for carrier recovery. When the error determination area corresponding to each symbol point is arranged in ascending order of the distance from the origin to each symbol point, the average value of adjacent values is defined as a radius, and the center is defined as the origin. , Except for the circle in which the distance from each symbol point to the boundary line is smaller than a certain value, and the two vertical symbols between adjacent symbol points on the same circumference centered on the origin. An area having a boundary line with an equal line is defined as an area of the symbol actually received.
A point on the Q plane is a received signal point, and a phase error signal corresponding to a position of the received signal point in the error determination area is a line connecting the symbol point and the origin in the error determination area. A phase comparison method comprising: outputting a signal obtained by a function having a variable in which a clockwise direction formed by a line connecting a minute and a signal point and an origin is a positive and a counterclockwise direction is a negative. 6. A phase comparator for performing a phase comparison method according to claim 5 for recovering a carrier of a received quadrature amplitude modulation signal, a complex multiplier, a loop filter, and a numerically controlled oscillator, A phase difference signal is output by the phase comparator based on the in-phase component output and the anti-phase component output of the complex multiplier, smoothed by the loop filter, input to the control terminal of the numerically controlled oscillator, and output A quadrature amplitude modulation signal demodulator, wherein a carrier is reproduced by a phase locked loop for inputting a signal to the complex multiplier and controlling a phase of a received signal. 7. An apparatus for demodulating a received quadrature amplitude modulation signal, wherein a point at which an unmodulated carrier power-to-noise power ratio at each reception point is theoretically the best on an IQ plane is represented by a symbol for carrier recovery. When the error determination area corresponding to each symbol point is arranged in ascending order of the distance from the origin to each symbol point, the average value of adjacent values is defined as a radius, and the center is defined as the origin. , Except for the circle in which the distance from each symbol point to the boundary line is smaller than a certain value, and the two vertical symbols between adjacent symbol points on the same circumference centered on the origin. An area having a boundary line with an equal line is defined as an area of the symbol actually received.
A point on the Q plane is a reception signal point, and a phase error signal corresponding to the position of the reception signal point in the error determination area is a line passing through the origin O and the symbol point in the error determination area and the origin relative to the straight line. It is divided into a plurality of areas by a straight line rotating at a fixed angle around O, and a clockwise direction formed by the line segment connecting the symbol point and the origin and the line segment connecting the signal point and the origin is positive, A phase comparison method, characterized in that an angle obtained by taking the counterclockwise direction as a negative variable is used as a variable, and a signal obtained by a function that increases stepwise as the variable increases is output. 8. A phase comparator for performing the phase comparison method according to claim 7 for recovering a carrier of a received quadrature amplitude modulation signal, a complex multiplier, a loop filter, and a numerically controlled oscillator, A phase difference signal is output by the phase comparator based on the in-phase component output and the anti-phase component output of the complex multiplier, smoothed by the loop filter, input to the control terminal of the numerically controlled oscillator, and output A quadrature amplitude modulation signal demodulator, wherein a carrier is reproduced by a phase locked loop for inputting a signal to the complex multiplier and controlling a phase of a received signal.