JPH11154827A - Demodulator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the precision of oscillated frequency control of an oscillator, used in the case of synchronization detection in the demodulator whose object is a QPSK signal wave (modulated wave). SOLUTION: The demodulator is provided with a mean phase error calculation means (a phase error detection section 7, a memory section 8, and a mean value arithmetic section 9) that detects the phase difference of a detected output signal with respect to a regular phase in QPSK demodulation from each symbol over plural symbols and calculates a mean phase error, with a dispersion arithmetic section 10 that calculates a dispersion in the phase error using the mean phase error as a reference, based on the calculated mean phase error and the phase difference for each symbol, with a discriminating section 11 that decides number of times of calculation of the mean phase error depending on the dispersion, with a control section 12 that controls the oscillator 3 or the like. The calculation of the mean phase error is conducted for a required number of times based on the decision by the discrimination section 11, and the oscillated frequency of the oscillator 3 is controlled based on the mean phase error obtained by the calculation of the required number of times.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a demodulator and, more particularly, to an oscillation frequency control of an oscillator used for synchronously detecting a QPSK signal wave (modulated wave).

[0002]

2. Description of the Related Art FIG. 3 is a main block diagram showing an example of a conventional demodulator for demodulating a QPSK signal wave (modulated wave) obtained by frequency conversion into an IF (intermediate frequency) band. In the figure, a first synchronous detector 21, a second synchronous detector 22, a voltage-controlled oscillator (VCO) 23, and a π / 2 phase shifter 24 are synchronous detector blocks, and the input QPSK signal wave And V
Synchronous detection is performed by an oscillation signal (COS wave) from CO23 and a signal (SIN wave) whose phase is shifted by π / 2. The synchronous detection outputs from the synchronous detectors 21 and 22 pass through low-pass filters (LPFs) 25 and 26, respectively, to extract only the original signal wave components. The two detection signals from the LPFs 25 and 26 are input to a phase error detection unit 27 and a carrier correction unit 31. The phase error detection unit 27 detects a phase difference of a detection output signal with respect to a normal phase in QPSK demodulation for each symbol. Data on the detected phase difference for each symbol is stored in the memory unit 28.

A control data calculator 29 calculates the oscillation frequency control data of the VCO 23 based on the data relating to the phase difference in the memory 28. This calculation is performed a preset number of times.
Therefore, control data is generated at regular intervals. The control unit 30 controls the oscillation frequency of the VCO 23 based on the control data from the control data calculation unit 29. In addition to the control of the VCO 23, the control unit 30 controls the phase error detection unit 27,
It controls the memory unit 28 and the control data calculation unit 29, respectively. Note that the carrier correction unit 31 causes the carrier to follow the phase error generated on the communication path. Therefore, the data of the phase difference is supplied from the phase error calculator 27. The signals (I signal and Q signal) from the carrier correction unit 31 are sent to the decoder 32, where the information data Do is decoded.

[0004]

As described above, in the related art (FIG. 3), the calculation of the oscillation frequency control data is performed a preset number of times. Therefore, control data is generated at regular intervals. However, the propagation environment in the communication path fluctuates, and the C / N ratio (carrier power / noise power) on the receiving side may fluctuate. For example, there is fading. In spite of the fluctuation of the C / N ratio, the calculation of the oscillation frequency control data has been performed a predetermined number of times in the related art. For this reason,
When the C / N ratio is low, the accuracy of the control data is reduced, and when the C / N ratio is high, the number of calculations may be more than necessary. In addition, start operation of this device (when power is turned on)
In the initial state, the number of calculations needs to be increased as compared with the steady state. However, the number of calculations is constant as described above, and therefore, the accuracy of the control data in the initial state is not sufficient. The conventional oscillation frequency control has the above-described drawbacks in accuracy. The present invention has been made in view of the above-described drawbacks, and has as its object to provide a demodulation device that improves the accuracy of frequency control of an oscillator used when synchronously detecting a QPSK signal wave.

[0005]

According to the present invention, there is provided a synchronous detection circuit for synchronously detecting a QPSK modulated wave using two kinds of sine wave signals having a phase difference of π / 2 and having the same frequency. In the demodulation device, QPSK is performed based on two types of mutually orthogonal detection output signals obtained by the synchronous detection.
Average phase error calculating means for detecting a phase difference of a detection output signal with respect to a normal phase in demodulation for a predetermined number of symbols, and calculating an average phase error based on each of the detected phase differences for each symbol; Variance value calculation means for calculating a variance value of the phase error based on the average phase error based on the average phase error calculated by the error calculation means and the phase difference for each symbol; A determination unit that determines the number of times the average phase error is calculated,
The average phase error calculation means, the variance value calculation means, a determination unit, and a control means for controlling an oscillator for oscillating the sine wave signal are provided, and the average phase error is calculated a required number of times based on the determination by the determination unit. And a demodulation device for controlling the oscillation frequency of the oscillator based on the average phase error obtained by calculating the required number of times.

[0006] Further, the average phase error calculating means includes a phase error detecting section for detecting a phase difference of a detection output signal with respect to a normal phase in QPSK demodulation for each symbol based on the two types of detection output signals; A memory unit for storing data relating to a phase difference for each symbol detected by the phase error detection unit;
An average value calculation unit for calculating an average phase error based on each data relating to the phase difference for each symbol.

In addition, the variance value calculation by the variance value calculation means may be performed by using data relating to a phase difference for each symbol and an average phase error from a memory unit and an average value calculation unit provided in the average phase error calculation means. The variance value calculation unit calculates the variance value based on.

Further, the number of times of calculation of the average phase error determined by the determination section is increased as the variance value increases. In this case, the determination unit may include a lookup table in which the number of times of calculating the average phase error with respect to the variance value is stored in advance.

Alternatively, the number of times of calculation of the average phase error determined by the determination unit is set to a predetermined number N1 when the variance value exceeds a set reference variance value, and the variance value is set to the set reference variance value. In the following cases, the predetermined number of times N2 may be set to be less than N1.

Further, when a signal indicating that the power is turned on is input to the control means, the determination unit determines the number of times of calculation of the average phase error to be a predetermined number which is larger than that in the steady state.

[0011]

Embodiments of the present invention will be described below with reference to the drawings based on embodiments. FIG. 1 is a block diagram of a main part showing an embodiment of a demodulation device according to the present invention, and FIG. 2 is an explanatory diagram relating to FIG. In FIG. 1, a first synchronous detector 1, a second synchronous detector 2, and a voltage-controlled oscillator (V
The CO) 3 and the π / 2 phase shifter 4 are synchronous detection blocks, and the input QPSK signal wave, the oscillation signal (COS wave) from the VCO 3 and the signal (SI
N detection) to perform synchronous detection. The above QPS
The K signal wave is an IF (intermediate frequency) band signal obtained by frequency-converting an RF signal. The synchronous detection outputs from the synchronous detectors 1 and 2 are low-pass filters (LPF) 5 and 6 respectively.
To extract only the original signal wave component. Each LPF
The two detection signals 5 and 6 are input to the phase error detection unit 7 and the carrier correction unit 13.

A phase error detector 7 is provided for detecting a phase difference (phase error) of a detection output signal with respect to a normal phase in QPSK demodulation.
Is detected for a predetermined number of symbols for each symbol (2 bits). The details of this detection are shown in FIG. The figure shows the coordinates of the I axis and Q axis in QPSK.
It shows the relationship between the normal phase (45 °) (a) of one symbol (two bits of “00”) at a certain moment and the phase (b) of the received signal, and the phase (b) of the received signal is normal. This is an example in which the phase is shifted by θs from (a). The phase error detector 7 detects the phase difference θs for a predetermined number of symbols for each symbol. Note that FIG.
(A) shows only the area of the symbol "00", but there are also areas of the symbols "01", "11", and "10", and the phase error is detected for the symbols in these areas. Each data relating to the phase difference of a predetermined number of symbols detected by the phase error detection unit 7 is stored in the memory unit 8.

An average value calculating section 9 calculates an average value (average phase error) of these data based on the data relating to a predetermined number of phase differences in the memory section 8. 1 (B) detected in FIG.
The relationship between the phase difference for each symbol and the calculated average phase error is shown (FIGS. B1, b2). FIGS. B1 and b2 show the case where the variance value is large (FIG. B1) and the variance value is small (FIG. B2) described later. In FIG. B1, each point (sign A) indicates the phase difference for each symbol detected by the phase error detection unit 7, and a straight line (sign B) indicates the average phase error calculated by the average value calculation unit 9. The same applies to FIG. B2. The variance calculator 10 calculates a variance based on the average phase error based on the average phase error calculated by the average calculator 9 and the data relating to the phase difference in the memory 8. The variance here means a variance used in statistics or the like. When the fluctuation of the phase difference is large as shown in FIG. B1, the variance value also becomes large. On the other hand, when the fluctuation of the phase difference is small as in FIG. B2, the variance value is also small.

The magnitude of the variance indicates the quality of the reception state or the stability of the operation of the demodulator. For example, when the C / N ratio is reduced due to fading or the like in the reception state, the fluctuation of the phase difference increases and the variance value increases. Conversely, when the C / N ratio is high and the reception state is good, the fluctuation of the phase difference is small and the variance is small. Therefore, by changing the method of generating the oscillation frequency control data for the VCO 3 according to the variance value, the control accuracy can be improved. On the other hand, as the oscillation frequency control data for the VCO 3, the data of the average phase error calculated by the average value calculation unit 9 is used. In this case, the calculation is performed a plurality of times. The number of calculations is changed according to the variance value described above, and when the variance value is large, the number of calculations is increased. Thereby, the accuracy of the calculation result, that is, the oscillation frequency control data can be improved.

The number of calculations based on the variance value is determined by the determination unit 11. As a method of determination in the determination unit 11, for example, a variance value (reference variance value) serving as a reference is set in advance, and if the variance value calculated by the variance value calculation unit 10 exceeds the reference variance value, N1 Times, N2 if less than the reference variance
Times (<N1). This decision method is either N1 or N2 and is the simplest. As an alternative to this, there is a method of increasing or decreasing the number of operations for the variance value in a stepwise manner. In this case, the number of operations increases as the variance value increases. There is also a method in which the determination unit 11 is a look-up table in which the number of times of calculation of the average phase error with respect to the variance value is stored in advance.

In the initial state of the operation of the present demodulator (when the power is turned on), since the VCO 3 and the like are not sufficiently stable, there is a high possibility that the fluctuation of the phase difference becomes large. Therefore, when the signal S1 indicating that the power is turned on is input to the control unit 12, the determination unit 11 determines the number of times of calculation of the average phase error to be a predetermined number which is larger than that in the steady state.
The control unit 12 sets the number of calculations for the average value calculation unit 9 based on the above determination by the determination unit 11. The average phase error data calculated by the average value calculation unit 9 based on the above setting is
3 becomes the oscillation frequency control data. The control unit 12 controls the oscillation frequency of the VCO 3 based on the oscillation frequency control data. The control unit 12 controls the phase error detection unit 7, the memory unit 8, the average value calculation unit 9, the variance value calculation unit 10, and the determination unit 11 in addition to the control of the VCO 3. In addition,
The carrier correction unit 13 makes the carrier follow the phase error generated on the communication path. Therefore, data of the phase difference is supplied from the phase error detection unit 7. The signals (I signal and Q signal) from the carrier correction unit 13 are sent to the decoder 14, where the information data Do is decoded.

[0017]

As described above, according to the present invention, Q
The accuracy of frequency control of an oscillator used for synchronous detection of a PSK signal wave can be improved. That is, since the number of times of calculating the average phase error is changed according to the variance of the phase error, high-accuracy oscillation frequency control data can be obtained even in the reception state where the C / N ratio is lowered due to fading or the like. Also,
Since the number of average phase error calculations is set to be increased even in the initial state (when the power is turned on) when the present apparatus is started to operate, the oscillation frequency control is performed with high accuracy as in the case where the C / N ratio is lowered. Data is obtained. Thus, according to the present invention,
It is possible to improve the performance of the demodulation device for the QPSK signal wave provided with the synchronous detection circuit.

[Brief description of the drawings]

FIG. 1 is a main block diagram showing an embodiment of a demodulation device according to the present invention.

FIG. 2 is an explanatory diagram related to FIG. 1;

FIG. 3 is a main block diagram showing an example of a conventional demodulation device.

[Explanation of symbols]

 1, 21 First synchronous detector 2, 22 Second synchronous detector 3, 23 Voltage controlled oscillator 4, 24 π / 2 phase shifter 5, 6, 25, 26 LPF 7, 27 Phase error detector 8 , 28 Memory unit 9 Average value operation unit 10 Variance value operation unit 11 Judgment unit 12, 30 Control unit 13, 31 Carrier correction unit 14, 32 Decoder 29 Control data operation unit

Claims (7)

[Claims] 1. A demodulator comprising: a synchronous detection circuit for synchronously detecting a QPSK modulated wave using two kinds of sine wave signals having a phase difference of π / 2 and having the same frequency. Based on the two types of detection output signals that are orthogonal to each other, the phase difference between the detection output signal and the normal phase in QPSK demodulation is detected for a predetermined number of symbols for each symbol, and the detected predetermined number of symbols are detected. An average phase error calculating means for calculating an average phase error based on each of the symbol phase differences; and an average phase error calculated by the average phase error calculating means and the phase difference for each symbol. A variance value calculation unit that calculates a variance value of the phase error based on the phase error, a determination unit that determines the number of times of calculating the average phase error according to the variance value, and the average phase error calculation unit Dispersion value calculation means, a determination unit and a control means for controlling an oscillator that oscillates the sine wave signal are provided, and the average phase error is calculated a required number of times based on the determination by the determination unit. A demodulator, wherein the oscillation frequency of the oscillator is controlled based on the obtained average phase error. 2. A phase detecting means for detecting a phase difference of a detection output signal with respect to a normal phase in QPSK demodulation for a predetermined number of symbols for each symbol based on the two types of detection output signals. An error detection unit;
A memory unit that stores data relating to the phase difference of the predetermined number of symbols detected by the phase error detection unit, and an average based on each of the data relating to the phase difference of the predetermined number of symbols stored in the memory unit. 2. The demodulation device according to claim 1, wherein the demodulation device comprises an average value calculation unit for calculating a phase error. 3. The method according to claim 1, wherein the variance value calculation by the variance value calculation means is performed by using data relating to a phase difference for each symbol and an average phase error from a memory unit and an average value calculation unit provided in the average phase error calculation means. 3. The demodulation device according to claim 1, wherein a variance value calculation unit calculates a variance value based on the variance value. 4. The demodulation device according to claim 1, wherein the number of times of calculation of the average phase error determined by said determination unit is increased as said variance value increases. 5. The lookup table according to claim 1, wherein the determination unit comprises a look-up table in which the number of times of calculating the average phase error for the variance value is stored in advance.
The demodulator according to any of the preceding claims. 6. The number of times of calculation of the average phase error determined by the determination unit is set to a predetermined number of times N1 when the variance value exceeds a set reference variance value, and the variance value is set to the set reference variance value. 2. The demodulator according to claim 1, wherein the predetermined number of times is set to N2 times less than the N1 in the following cases. 7. When the signal indicating that the power is turned on is input to the control means, the determination unit determines the number of times of calculation of the average phase error to be a predetermined number which is larger than that in a steady state. The demodulation device according to claim 1, wherein: