JPH0357665B2 - - Google Patents

Description

[Detailed Description of the Invention] [Summary] Depending on whether the signal point of the multilevel quadrature amplitude modulation signal is close to the I axis or the Q axis, the exclusive OR output of the polarity signal of the I and Q channels and the error signal is determined. A control voltage is selected to control the output phase of the voltage controlled oscillator, and a reference carrier wave with an accurate phase is reproduced regardless of the position of the signal point.

[Industrial application field]

The present invention relates to a reference carrier regeneration circuit that regenerates a reference carrier wave for demodulating a multilevel orthogonal amplitude modulation signal.

A reference carrier wave whose phase is synchronized with the carrier wave component of the multilevel quadrature amplitude modulation signal is regenerated by controlling a voltage controlled oscillator, and the received multilevel quadrature amplitude modulation signal is generated using a carrier wave with a 90° phase difference based on this reference carrier wave. It is required to accurately control the phase of this reference carrier wave.

[Conventional technology]

For example, as shown in FIG. 5, a conventional reference carrier regeneration circuit applies the output of a voltage-controlled oscillator 21 to a demodulator 22 as a reference carrier, and outputs a multilevel orthogonal amplitude modulation signal received as a carrier in orthogonal phase to an I channel. and Q channel, and the demodulated output signal is applied to the A/D converter 23, where it is converted into a digital signal having a plurality of bits. a polarity signal of the most significant bit of the I channel converted into a digital signal;
The error signal of the lower bit of the Q channel is added to the exclusive OR circuit 24, and the exclusive OR output signal is integrated by the integrating circuit 25 to be the control voltage of the voltage controlled oscillator 21, and the output of the voltage controlled oscillator 21 is It controls the phase.

FIG. 6 is an explanatory diagram of the operation, in which signal points in the first quadrant of the 64-value orthogonal amplitude modulation signal are indicated by x marks. When the exclusive OR circuit 24 takes the exclusive OR of the polarity signal of the I channel and the error signal of the Q channel, for example, the output signal of "0" will be in the shaded area, and the Q Above and below the axis, the positions of the hatched areas are opposite. Therefore, so that the error signal becomes 0, i.e.
If the output signals of "1" and "0" of the exclusive OR circuit 24 are integrated by the integration circuit 25 and time averaged, and the voltage controlled oscillator 21 is controlled by the output signal of the integration circuit 25, the desired result can be obtained. This means that the phase reference carrier wave can be regenerated.

[Problem that the invention seeks to solve]

In the conventional example described above, the reference carrier phase can be accurately controlled when the signal point is close to the I axis;
The further away from the axis, the more inaccurate the phase control becomes, and this becomes a problem as the number of multi-values increases, such as 64, 256, etc. That is, as shown in FIG.
At signal point a, which is close to the I-axis and far from the Q-axis, there is a change in the direction almost perpendicular to the shaded area and the non-shaded area, as shown by the arrows, but the signal point a, which is far from the I-axis and close to the Q-axis, changes in the direction shown by the arrows. At point b, as shown by the arrow,
The direction of change is almost parallel. Therefore, there is a drawback that control using signal point b, which is far from the I-axis, is inaccurate compared to control using signal point a, which is close to the I-axis.

An object of the present invention is to enable accurate control even when the signal point is far from the I-axis.

[Means for solving problems]

The reference carrier regeneration circuit of the present invention switches control by determining whether a signal point is close to or far from the I-axis, and will be described with reference to FIG.

The output of the voltage controlled oscillator 1 is applied as a reference carrier wave to a demodulator 2, the received multilevel quadrature amplitude modulation signal is demodulated by the demodulator 2, and the demodulated output signal is converted into a digital signal by an A/D converter 3. Convert. The polarity signal of the I channel and the error signal of the Q channel, which have been converted into digital signals by the A/D converter 3, are added to the first gate circuit 4, an exclusive OR is taken, and the error signal of the I channel and the error signal of the Q channel are is added to the second gate circuit 5 and exclusive ORed, and the control circuit 6 determines whether the signal point is close to the I axis or the Q axis based on the data of the I and Q channels. The output of the first gate circuit 4 is selected for signal points close to the I-axis, and the output of the second gate circuit 5 is selected for signal points close to the Q-axis, and the polarities are changed and integrated. , whose integral output is used as the control voltage of the voltage controlled oscillator 1.

[Effect]

The control circuit 6 determines whether the signal point is close to the I-axis or the Q-axis, and if the signal point is close to the I-axis,
By selecting and integrating the exclusive OR output signal of the polarity signal of the I channel, the Q channel, and the error signal, the control voltage of the voltage controlled oscillator 1 is obtained. By selecting and integrating the exclusive OR output signal of the error signal and the polarity signal of the Q channel, it is used as the control voltage of the voltage controlled oscillator 1. Also, accurate phase control is possible. Note that since both exclusive logic output signals become "1" for rotations in opposite directions, they are integrated while changing their polarities.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 2 is a block diagram of an embodiment of the present invention,
11 is a voltage controlled oscillator, 12 is a demodulator, 13 is an A/D converter, 14 and 15 are exclusive OR circuits corresponding to the first and second gate circuits and an exclusive OR circuit with inverted outputs, 16 1 is a selector, 17 is an integrating circuit, and 18 is a decoder. This embodiment shows a case where the control circuit 6 in FIG.

The received multilevel quadrature amplitude modulation signal is applied to the demodulator 12, and based on the reference carrier wave added from the voltage controlled oscillator 11, an orthogonal carrier wave is formed by a 90° phase shifter, etc. The amplitude modulated signal is demodulated, and the demodulated output signal is sent to the A/D converter 1.
Added to 3. This A/D converter 13 converts it into a digital signal with multiple bits, and the IA
Channel and Q channel data are output.

The exclusive OR circuit 14 is supplied with the polarity signal of the most significant bit of the I channel and the error signal of the lower bit of the Q channel, and the inverted output exclusive OR circuit 15 is supplied with the polarity signal of the most significant bit of the I channel. , and the polarity signal of the most significant bit of the Q channel are added.

The decoder 18 decodes the digital signals of the I channel and the Q channel, and outputs a signal indicating whether the signal point is close to the I axis or the Q axis, which is used as a control signal for the selector 16.
When the signal point is close to the I axis, the selector 16 selects the output of the exclusive OR circuit 14 and applies it to the integrating circuit 17, and the integrated output becomes the control voltage for phase control of the voltage controlled oscillator 11. . Therefore,
In this case, the phase of the reference carrier wave is accurately controlled as in the case described for the conventional example. When the signal point is close to the Q axis, the selector 16 selects the output of the exclusive OR circuit 15 with the inverted output and applies it to the integrating circuit 17, and the integrated output is used as the control voltage for phase control of the voltage controlled oscillator 11. becomes. Therefore, this corresponds to a case where the positional relationship of the signal points is rotated by 90°, and the phase of the reference carrier wave is accurately controlled.

FIG. 3 is an explanatory diagram of the operation of the embodiment of the present invention,
This is shown in correspondence with the conventional example shown in FIG.
That is, the region where the selected output of the selector 16, which is controlled by the output of the decoder 18 that determines the signal point position, is "0" is indicated by diagonal lines, and it is used to detect phase errors at signal points near the I-axis. , detection of a phase error at a signal point close to the Q axis corresponds to a case of rotation by 90°. For example, at signal point a near the I-axis, there is a change in the direction almost perpendicular to the shaded area and the non-shaded area, as shown by the arrows, and at signal point b near the Q-axis, the diagonal line is also applied. As shown by the arrows, there is a change in the direction approximately perpendicular to the area where the coating is applied and the area where the coating is not applied. Therefore, even in the case of a signal point close to the Q-axis, the phase of the reference carrier wave can be accurately controlled.

FIG. 4 is an explanatory diagram of signal point positions, in which the signal points within the shaded area are determined to be close to the I axis and the output of the exclusive OR circuit 14 is selected, and the signal points within the shaded area are selected. The signal points within are determined to be close to the Q axis, and
The output of the exclusive OR circuit 15 having an inverted output is selected, and the selected output is integrated by an integrating circuit 17 to be used as a control voltage for the voltage controlled oscillator 11.

The means for determining whether a signal point is close to the I-axis or the Q-axis can employ various logic circuits, and the present invention is not limited to the above-described embodiments. It is something that can be added and changed.

〔Effect of the invention〕

As explained above, the present invention demodulates a multilevel quadrature amplitude modulation signal based on a reproduced reference carrier wave, converts the demodulated output signal into a digital signal, determines the signal point, selects the exclusive OR output of the I channel polarity signal and the Q channel error signal, and if it is close to the Q axis, selects the exclusive OR output of the I channel error signal and the Q channel polarity signal. The control voltage of the voltage controlled oscillator 1 is obtained by integrating the selected outputs so that their polarities are opposite to each other, and controlling the phase of the reference carrier wave.Accurate phase control is possible regardless of the position of the signal point. It becomes possible. Therefore, there is an advantage that even a quadrature amplitude modulation signal having a large number of values can be accurately demodulated.

[Brief explanation of drawings]

Fig. 1 is a block diagram of the principle of the present invention, Fig. 2 is a block diagram of an embodiment of the invention, Fig. 3 is an explanatory diagram of the operation of the embodiment of the invention, Fig. 4 is an explanatory diagram of signal point positions, FIG. 5 is a block diagram of a conventional main part, and FIG. 6 is an explanatory diagram of the operation of the conventional example. 1 is voltage controlled oscillator, 2 is demodulator, 3 is A/D
Converter, 4 and 5 are first and second gate circuits, 6 is a control circuit, 11 is a voltage controlled oscillator, 12 is a demodulator, 13 is an A/D converter, 14 is an exclusive OR circuit, 15 is a 16 is a selector, 17 is an integration circuit, and 18 is a decoder.

Claims (1)

[Scope of Claims] 1. A demodulator 2 that demodulates a multilevel quadrature amplitude modulation signal received using the output of the voltage controlled oscillator 1 as a reference carrier wave, and an A/D that converts the demodulated output signal of the demodulator 2 into a digital signal. a converter 3; a first gate circuit 4 that takes the exclusive OR of the I channel polarity signal and the Q channel error signal of the output of the A/D converter 3; A second gate circuit 5 calculates the exclusive OR of the output I channel error signal and the Q channel polarity signal, and based on the data of the output I channel and Q channel of the A/D converter 3. , determine whether the signal point is close to the I-axis or the Q-axis, and output the output of the first gate circuit 4 for the signal point close to the I-axis, and output the output of the second gate circuit 4 for the signal point close to the Q-axis. 1. A reference carrier regeneration circuit comprising: a control circuit 6 which selects and integrates the outputs of the gate circuits 5 so that their polarities are reversed, and uses the integrated output as a control voltage for the voltage controlled oscillator 1.