JPH0353735A - Orthogonality control system in multilevel qam demodulator - Google Patents

Abstract

PURPOSE:To reduce the time or cost required for the orthogonality considerably by dividing kinds of signal points into two depending on the result of identification obtained from demodulation outputs by 2 channels and controlling a phase shifter based on difference information of 2 kinds of mean power caused due to the deviation of the orthogonality between local signals. CONSTITUTION:A polarity detection section 9 divides kinds of signal points into two from the result of identification obtained from a demodulation output by I, Q 2 channels, and if the signal point constellation is formed to be a parallelogram and the orthogonality between local signals is deviated, the difference information of 2 kinds of average powers resulting therefrom is calculated automatically by a comparator 107 to control a phase shifter 8. Thus, the phase of a local signal is rotated so that the output of the comparator 107 is made zero. Thus, the time or cost required for adjusting the orthogonality is remarkably reduced.

Description

[Detailed Description of the Invention] [Summary] This invention relates to a method for controlling the degree of orthogonality in a multilevel QAM demodulator, and aims to automatically control the degree of orthogonality matching between two channel signals. In a multilevel QAM demodulator that detects a signal with local signals having a phase difference of 90' from each other and obtains demodulated output for two channels, at least one of the local signals is input to the detector via a phase shifter. The type of signal point is divided into two based on the identification result obtained from the demodulated output of the two channels, and the type of signal point is divided into two based on the difference information of the two types of average power caused by the deviation of the degree of orthogonality between the local signals. It is configured to control a phase shifter.

[Industrial Application Field] The present invention is directed to multi-level QAM (Quadrature Am
(plitude Modulation) relates to a method for controlling orthogonality in a demodulator.

In recent years, with the progress of advanced modulation/demodulation technology, fading compensation technology, interference compensation technology, etc., multilevel QAM modulation/demodulation technology with excellent frequency utilization efficiency has been put into practical use.

By the way, in a multilevel QAM demodulator, an intermediate frequency signal (
below. When detecting the IF signal), 90″
'Perform synchronous detection using two local signals that are out of phase. In this case, the phase difference between the two local signals must differ by exactly 90'.

[Prior Art] Fig. 5 is a block diagram showing a conventional multilevel QAM demodulator. In Fig. 5, 1 and 2 are hybrid circuits, and the hybrid circuit 1 receives an IF signal as an input signal. The hybrid circuit 2 separates the local signal from the local oscillator 3 into signals having a phase difference of 90 degrees.

4A and 4B are detectors that detect the IF signal as a local signal, 5A and 5B are low-pass filters that filter the detection output from the detectors 4A and 4B, and 6A and 6B are the filters that filter the detection output from the low-pass filters 5A and 5B. This is a discriminator that obtains the required number of bits of discrimination results from the wave output.

7A and 7B are capacitors for adjusting the phase between the IF signals input to the detectors 4A and 4B.
is configured as a variable capacitor.

Due to this structure, this multilevel QAM demodulator has an I
The F signal is detected using local signals with a phase difference of 90' from each other to obtain demodulated output for the I and Q channels, but if the phase is exactly 90' between the I and Q channels,
'The capacitance of the capacitor 7B is adjusted differently. At this time, using standard modulation@ (with orthogonality adjusted accurately), phase adjustment is performed manually while watching the required monitor.

[Problems to be Solved by the Invention] However, in such conventional systems, the phase adjustment work is performed manually, and as QAM modulation becomes more multivalued, the above phase adjustment work requires more skill. become,
This poses a problem in that phase adjustment becomes difficult.

The present invention aims to solve these problems and provides an orthogonality control method for a multilevel QAM demodulator that can automatically control orthogonality matching between two channel signals. The purpose is

[Means to solve the problem] FIG. 1 is a block diagram of the principle of the present invention.

The multilevel QAM demodulator according to the present invention, like the conventional one, as shown in FIG. Hybrid circuit 2 that separates signals into signals with 90! different phases, detectors 4A, 4B that detect input signals with local signals, detectors 4A, 4
Low-pass filters 5A, 5 that filter the detection output from B
B and low-pass filters 5A and 5B, the present invention further includes a phase shifter 8, a polarity detector 9,
It has a phase shifter control section 10.

Here, the phase shifter 8 includes the hybrid circuit 2 and the detector 7B.
It is installed between the local signal and the local signal and rotates and adjusts the phase of the local signal. Note that this phase shifter 8 may be provided between the hybrid circuit 2 and the detector 7A.

The polarity detection unit 9 uses each polarity signal of the demodulated output of two channels to divide the signal point types into two, and the phase shifter control unit 10 uses the outputs from the low-pass filters 5A and 5B and Using the detection result of the polarity detection unit 9, the difference between two types of average power caused by a shift in the degree of orthogonality between local signals is calculated, and the phase shifter 8 is operated based on the difference information of the average power. It is something to control.

[Function] Therefore, in the orthogonality control method in the multilevel QAM demodulator of the present invention, the types of signal points are divided into two based on the identification results obtained from the demodulated output for two channels, and the orthogonality between local signals is adjusted. The phase shifter 8 is controlled based on information on the difference between the two types of average power caused by the shift.

[Example] Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 is a block diagram showing an embodiment of the present invention. The multi-level QAM demodulator according to this embodiment also has a hybrid circuit 1, a hybrid circuit 2, a detection Vessels 4A, 4B. low pass) Iruta 5A, 5
B,! ! In addition to the iD'J devices 6A and 6B, this embodiment further includes a phase shifter 8, a polarity detection section 9, and a phase shift delay control section 10.

In addition, hybrid circuit 1, hybrid circuit 2, detectors 4A, 4B, low-pass filters 5A, 5B, discriminator 6
The explanation for A and 6B will be omitted since it will overlap with the conventional one.

By the way, the phase shifter 8 includes the hybrid circuit 2 and the detector 7.
B, and rotates and adjusts the phase of the local signal.

In addition, the polarity detection unit 9 uses all the demodulated outputs for the I and -Q channels [including each polarity signal (l-th bit)] to determine the type of signal point by the signal point shown in FIG. In a constellation diagram, it is divided into two parts, whether it is in the 1.3 quadrant or the 2.4 quadrant.
The positive detection unit 9 includes a ROM 91 that stores information on phase planes covering all signal points. For example, in FIG. 3, when the ROM 91 is in the 1st and 3rd quadrants, it outputs "1", and when it is in the 2nd and 4th quadrants,
It becomes rOJ output.

Furthermore, the phase shifter control section 10 includes a low-pass filter 5A,
Using the output from 5B and the detection result at the polarity detection unit 9, 2
The phase shifter control section 10 calculates the difference in the average power of each type and controls the phase shifter 8 based on the information on the difference in the average power.
2, delay circuit 103A, LO3B, switch circuit 104
A, LO4B. It includes integrators 106A, 106B and a comparator 107.

Here, the hybrid circuit 101 receives and combines the outputs from the low-pass filters 5A and 5B, and the hybrid circuit 102 divides the signal from the hybrid circuit 101 into two.

The delay circuits 103A and 103B are the hybrid circuit 10
The switch circuit 103A delays the signal from the polarity detector 9 by the detection time at the polarity detector 9.
The switch circuit closes when the signal point belongs to the 1st and 3rd quadrants in Figure 3 and opens when the signal point belongs to the 2nd and 4th quadrants in Figure 3. 104B
is closed when the signal point belongs to the 2nd and 4th quadrants of FIG. It opens when it belongs to a quadrant.

The integrator 106A integrates the signal output when the switch circuit 104A is closed to obtain the average power of the signals in the 1st and 3rd quadrants of FIG. The average power of the signals in the second and fourth quadrants of FIG. 3 is determined by integrating the signals output when

The comparator 107 consists of a ○P amplifier, and the integrator 1
The difference between the integral data from 06A and 106B (difference between the two types of average power @l) is taken, and this is output as a control signal for the phase shifter 8.

With the above-described structure, the polarity detection unit 9 determines two types of signal points (whether they are in the 1st and 3rd quadrants or the 2nd and 4th quadrants in Fig. If the signal point constellation is in the form of a parallelogram as shown in Figure 3, and the orthogonality between the local signals is shifted, the two types of average power caused by this are Difference information is automatically calculated by the comparator 107, and based on the output of this comparator 107,
Phase shifter 8 is controlled. As a result, the phase shifter 8 causes the output of the comparator 107 to be zero (the difference between both average powers is zero).
Rotate the phase of the local signal so that Note that when the output of the comparator 107 becomes zero, the phase shifter 8
stops the phase rotation.

In this way, the types of signal points are divided into two based on the identification results obtained from the demodulated outputs of the two I and Q channels, and based on the information on the difference in the average power of the 2@ class caused by the deviation in orthogonality between local signals. Therefore, the phase shifter 8 is controlled. It becomes possible to always automatically control the adjustment of orthogonality between two channel signals, and thereby the time or cost required for orthogonality can be significantly reduced.

In the embodiment shown in FIG. 2, the polarity detection section 9 includes:
A device equipped with a ROM 91 for detecting all signal points was used, but as shown in FIG. The input is input to the OR circuit 92, and the output from the exclusive OR circuit 92 is used as the switch circuit 104.
A, 104B may be opened/closed. Further, the phase shifter 8 may be provided between the hybrid circuit 2 and the detector 7A.

[Effects of the Invention] As detailed above, according to the orthogonality control method in the multi-level QAM demodulator of the present invention, the types of signal points are divided into two based on the identification results obtained from the demodulated output of two channels. Since the phase shifter is controlled based on information on the difference in two types of average power caused by a deviation in orthogonality between local signals, the adjustment of orthogonality between two channel signals is always automatically controlled. This has the advantage of significantly reducing the time and cost required for orthogonality.

[Brief explanation of drawings]

Fig. 1 is a block diagram of the principle of the present invention, Fig. 2 is a block diagram showing an embodiment of the present invention, Fig. 3 is a signal point constellation diagram when the degree of orthogonality is shifted, and Fig. 4 is the invention of the present invention. FIG. 5 is a block diagram showing another embodiment of the present invention, and FIG. 5 is a block diagram showing a conventional example. In the figure, 1.2 is a hybrid circuit, 3 is a local oscillator, 4A, 4B are detectors, 5A, 5B are low-pass filters, 6A, 6B are discriminators, 8 is a phase shifter, 9 is a polarity detector, 10 is a Phase shifter control section, 91 is a ROM, 92 is an exclusive OR circuit, 101, 102 are hybrid circuits, 103A, 103B are delay circuits, 104A, 104B are switch circuits, 105 is an inversion circuit, 106A, 106B are integrators , 107 is a converter.

Claims (2)

[Claims] (1) Multi-value Q to obtain demodulated output for 2 channels by detecting the input signal with local signals that have a phase difference of 90° from each other
In the AM demodulator, at least one of the local signals is input to the detector (4B) via the phase shifter (8), and two types of signal points are identified from the identification results obtained from the demodulated outputs of the two channels. Orthogonality in a multilevel QAM demodulator, characterized in that the phase shifter (8) is controlled based on information on the difference between two types of average power caused by a shift in the degree of orthogonality between the local signals. degree control method. (2) The signal point is divided into two types using each polarity signal of the demodulated output of the two channels;
An orthogonality control method in a multilevel QAM demodulator according to claim 1.