JP3614540B2 - PSK modulation signal evaluation apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a PSK modulation signal evaluation apparatus for evaluating the modulation accuracy of a modulation IC for producing a PSK modulation signal, and more particularly to a reproducing means for reproducing an I signal and a Q signal from a QPSK modulated signal.
[0002]
[Prior art]
Regarding a PSK modulation signal evaluation apparatus that evaluates the modulation accuracy of a modulation IC for producing a PSK modulation signal such as a QPSK (Quadrature Phase Shift Keying) modulation signal and a DQPSK (Differential Quadrature Encoded PSK) modulation signal, Hewlett-Packard Journal, vol. 42, no. 4, pp 73-82, April. 1991, Raymond A. et al. The structure and the like are disclosed in “Birgenheier,“ Measuring the Modulation Accuracy of π / 4 DQPSK Signals for Digital Cellular Transmitters ””.
[0003]
In this PSK modulation signal evaluation apparatus, a configuration as shown in FIG. 2 is introduced as reproducing means for reproducing an I signal (in-phase component signal) and a Q signal (quadrature component signal) from a PSK-modulated signal.
[0004]
FIG. 2 is a block diagram showing the configuration of the in-phase component and quadrature component reproducing means of the conventional PSK modulation signal evaluation apparatus.
[0005]
In FIG. 2, an input signal S ₀ (PSK modulation signal) which is an IF signal is input to an A / D converter 101 and converted into digital data.
[0006]
The bandpass filter 102 removes unnecessary band noise from the input signal converted into digital data.
[0007]
When communication is performed using a TDMA (Time Division Multiple Access) method or the like, the PSK modulation signal is transmitted in bursts at predetermined intervals. The burst detector 103 detects the signal transmitted in the burst form.
[0008]
The output signal of the burst detection unit 103 is directly supplied to the first interpolation filter 106 and is also supplied to the Hilbert transformer 104. The signal (in-phase component) supplied to the first interpolation filter 106 by the Hilbert transformer 104 is supplied to the burst detection unit 103. An orthogonal component is generated and supplied to the second interpolation filter 107.
[0009]
The output signal of the burst detection unit 103 is input to the baud rate phase detection unit 105, and the baud rate phase, that is, the symbol change point of the PSK modulation signal and the phase difference of the symbol clock for determining the symbol are detected.
[0010]
The first interpolation filter 106 and the second interpolation filter 107 are inserted in order to compensate for a quantization error caused when the sampling timing of the A / D converter 101 and the timing of symbol generation of the PSK modulation signal do not necessarily match. Yes. The interpolation filter is composed of, for example, an FIR filter, and the filter coefficient is corrected based on the phase difference detected by the baud rate phase detection unit 105 according to the deviation of the impulse response with respect to the unit delay array.
[0011]
Quadrature component output phase component of the output signal, and the second interpolation filter 107 of the burst detector 103 output from the first interpolation filter 106 is offset from the origin, respectively it is corrected by the offset correction section 108 It is output as an I (k) signal and a Q (k) signal.
[0012]
The I (k) signal and the Q (k) signal are deconverted to a baseband frequency by frequency conversion means (not shown), and the I signal and the Q signal are reproduced.
[0013]
[Problems to be solved by the invention]
In the conventional PSK modulation signal evaluation apparatus as described above, the in-phase component and the quadrature component generated from the input signal S ₀ by the reproducing means are respectively passed through the interpolation filter. Since the interpolation filter is composed of an FIR filter (low-pass filter), it operates effectively when the carrier frequency of the input signal S ₀ is sufficiently higher than the baseband. However, when the carrier frequency is set to a low frequency close to the baseband, a part of the data may be lost because the cut-off frequency of the filter needs to be close to the baseband.
[0014]
Further, when decimation is performed on the I (k) signal and Q (k) signal, the signal passes through the filter, so that the signal (noise) at the aliasing frequency of the filter is output without being filtered and modulated. The accuracy could not be measured accurately.
[0015]
The present invention has been made to solve the above-described problems of the prior art, and correctly reproduces the I signal and the Q signal without being affected by the carrier frequency of the PSK modulation signal, thereby improving the modulation accuracy. An object of the present invention is to provide a PSK modulation signal evaluation apparatus capable of accurately measuring.
[0016]
[Means for Solving the Problems]
To achieve the above object, a PSK modulation signal evaluation apparatus according to the present invention comprises reproduction means for reproducing an I signal and a Q signal from a QPSK modulation signal, respectively, and modulates a modulation IC for generating the QPSK modulation signal. A PSK modulation signal evaluation apparatus for evaluating accuracy from the reproduced I signal and Q signal,
In the reproduction means,
A first local oscillator whose oscillation frequency is set in the vicinity of the baseband frequency;
A first 90 ° phase shifter for shifting the phase of the output signal of the first local oscillator by 90 °;
The first QPSK modulation signal is multiplied by the output signal of the first local oscillator to frequency-convert the QPSK modulation signal at the oscillation frequency of the first local oscillator, and the first phase component of the QPSK modulation signal is output. With a mixer,
The QPSK modulation signal is multiplied by the output signal of the first 90 ° phase shifter to frequency-convert the QPSK modulation signal at the oscillation frequency of the first local oscillator, and an orthogonal component of the QPSK modulation signal is output. A second mixer that
A first decimation filter that thins out predetermined data from the in-phase component output from the first mixer;
A second decimation filter that thins out predetermined data from orthogonal components output from the second mixer;
A second local oscillator that is set to an arbitrary oscillation frequency that can be cut off when the baseband frequency is extracted by a low-pass filter;
A second 90 ° phase shifter that shifts the phase of the output signal of the second local oscillator by 90 °;
A third decimation filter that multiplies the output signal of the first decimation filter by the output signal of the second local oscillator, and frequency-converts the output signal of the first decimation filter at the oscillation frequency of the second local oscillator; A mixer,
The fourth decimation filter multiplies the output signal of the second decimation filter by the output signal of the second phase shifter, and converts the frequency of the output signal of the second decimation filter at the oscillation frequency of the second local oscillator. With a mixer,
An adder for adding the output signal of the third mixer and the output signal of the fourth mixer;
A third local oscillator in which a frequency obtained by adding the oscillation frequency of the second local oscillator to the frequency of the difference between the oscillation frequency of the first local oscillator and the baseband frequency is set as an oscillation frequency;
A third 90 ° phase shifter that shifts the phase of the output signal of the third local oscillator by 90 °;
The output signal of the adder and the output signal of the third local oscillator are multiplied to frequency-convert the output signal of the adder with the oscillation frequency of the third local oscillator, and the in-phase of the output signal of the adder A fifth mixer for outputting the components;
The output signal of the adder and the output signal of the third 90 ° phase shifter are multiplied to frequency-convert the output signal of the adder at the oscillation frequency of the third local oscillator, and the output of the adder A sixth mixer for outputting a quadrature component of the signal;
A first root Nyquist filter that is input with an output signal from the fifth mixer and is set to a predetermined filter characteristic for extracting the I signal;
A second root Nyquist filter that is input with an output signal from the sixth mixer and is set to a predetermined filter characteristic for extracting the Q signal;
It is characterized by having.
[0017]
The PSK modulation signal evaluation apparatus configured as described above includes a frequency converter including a first local oscillator, a first 90 ° phase shifter, a first mixer, and a second mixer, and a first decimation. The filter and the second decimation filter down-convert to a frequency in the vicinity of the baseband and perform data decimation to output an in-phase component and a quadrature component.
[0018]
Further, the output signals of the first decimation filter and the second decimation filter are converted to a frequency composed of a second local oscillator, a second 90 ° phase shifter, a third mixer, a fourth mixer, and an adder. Quadrature modulation is performed by a converter, and demodulation is performed by a frequency converter including a third local oscillator, a third 90 ° phase shifter, a fifth mixer, and a sixth mixer.
[0019]
The in-phase component output from the fifth mixer is passed through the first root Nyquist filter, and the quadrature component output from the sixth mixer is passed through the second root Nyquist filter, so that the I signal and the Q signal are Played.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Next, the present invention will be described with reference to the drawings.
[0021]
FIG. 1 is a block diagram showing the configuration of the in-phase component and quadrature component reproducing means of the PSK modulation signal evaluation apparatus of the present invention.
[0022]
In FIG. 1, a PSK modulated input signal S ₀ (PSK modulated signal), which is an IF signal, is input to an A / D converter 1 and converted to digital data, and unnecessary band noise is removed by a band pass filter 2. The burst detector 3 detects a signal transmitted in a burst form.
[0023]
The output signal of the burst detector 3 is input to the first mixer 6, the second mixer 7, and the baud rate phase detector 8. Further, the output signal IFC1 of the first local oscillator 4 is directly input to the first mixer 6, and the first 90 ° phase shifter 5 that advances the phase of the output signal IFC1 by 90 ° is input to the second mixer 7. An output signal is input.
[0024]
The first mixer 6 and the second mixer 7 respectively multiply the output signal of the burst detector 3 by the oscillation frequency of the first local oscillator 4 to perform frequency conversion. Further, the first mixer 6 outputs an in-phase component of the output signal of the burst detector 3, and the second mixer 7 outputs a quadrature component.
[0025]
Next, the output signal of the first mixer 6 is input to the first decimation filter 9, and the data is thinned out by the first decimation filter 9. The output signal of the second mixer 7 is input to the second decimation filter 10, and data is thinned out by the second decimation filter 10.
[0026]
Meanwhile, the output signal of the first mixer 6 and a second mixer 7, the vector indicating the position of the symbol in the coordinate plane by phase and quadrature components, the vector of the input signal S ₀ baseband and first When the frequency of the output signal IFC1 of the local oscillator 4 is different, rotation occurs on the coordinate plane. The decimation filter is inserted to reduce the computation time and to extract the symbol from the rotating vector. Since the oscillation frequency of the first local oscillator 4 is set in the vicinity of the carrier frequency of the input signal S ₀ , the output signals of the first mixer 6 and the second mixer 7 are passed through the decimation filter. is down-converted respectively to the frequency of the near baseband input signal S ₀ in.
[0027]
On the other hand, the baud rate phase detector 8 detects the phase difference between the symbol change point of the modulation signal and the symbol clock for determining the symbol from the output signal of the burst detector 3. In the first decimation filter 9 and the second decimation filter 10, the arithmetic processing is corrected by the phase difference detected by the baud rate phase detection unit 8 to estimate an ideal symbol, and then data is thinned out. .
[0028]
Next, the output of the first decimation filter 9 is input to the third mixer 13, and the output of the second decimation filter 10 is input to the fourth mixer 14. In addition, the third mixer 13 receives the output signal IFC2 of the second local oscillator 11, and the fourth mixer 14 advances the phase of the output signal IFC2 of the second local oscillator 11 by 90 °. ° The output signal of the phase shifter 12 is input.
[0029]
The oscillation frequency of the second local oscillator 11 is set to a sufficiently high frequency with respect to the baseband frequency, and can be cut off when the I signal and the Q signal are extracted by a root Nyquist filter (low-pass filter) described later. Is set to a value.
[0030]
The third mixer 13 and the fourth mixer 14 each multiply the signal output from the decimation filter by the oscillation frequency of the second local oscillator 11 to perform frequency conversion. Then, the adder 15 adds the output signals of the third mixer 13 and the fourth mixer 14.
[0031]
The output of the adder 15 is input to the fifth mixer 18 and the sixth mixer 19, respectively. In addition, the output signal IFC3 of the third local oscillator 16 is input to the fifth mixer 18, and the sixth mixer 18 The mixer 19 receives the output signal of the third 90 ° phase shifter 17 that advances the phase of the output signal IFC3 of the third local oscillator 16 by 90 °.
[0032]
The fifth mixer 18 and the sixth mixer 19 multiply the output signal of the adder 15 by the oscillation frequency of the third local oscillator 16 to perform detection.
[0033]
Here, the oscillation frequency of the third local oscillator 16, the error of the baseband and the frequency of the output signal IFC1 of the first local oscillator 4 of an input signal _{S 0} in case of a Delta] f, the frequency of the frequency = IFC2 of IFC3 What is necessary is just to select so that it may become + (DELTA) f.
[0034]
Finally, the output signal of the fifth mixer 18 is passed through the first root Nyquist filter 20 having a frequency characteristic necessary for taking out the I signal and measuring the modulation accuracy, and the output signal of the sixth mixer 19 is passed through. The I signal and the Q signal demodulated into the baseband are respectively reproduced by passing through the second root Nyquist filter 21 having a frequency characteristic necessary for taking out the Q signal and measuring the modulation accuracy.
[0035]
Therefore, with such a configuration, the I signal and the Q signal can be reproduced from the PSK modulation signal without using the Hilbert transformer and the interpolation filter, respectively, so that it is influenced by the carrier frequency of the PSK modulation signal. Therefore, the modulation accuracy can be accurately measured.
[0036]
【The invention's effect】
Since the present invention is configured as described above, the following effects can be obtained.
[0037]
Since the I signal and the Q signal can be reproduced from the PSK modulation signal without using the Hilbert transformer and the interpolation filter, the modulation accuracy can be accurately measured without being influenced by the carrier frequency of the PSK modulation signal. it can.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of in-phase component and quadrature component reproducing means of a PSK modulation signal evaluation apparatus of the present invention.
FIG. 2 is a block diagram showing a configuration of in-phase component and quadrature component reproducing means of a conventional PSK modulation signal evaluation apparatus;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 A / D converter 2 Band pass filter 3 Burst detection part 4 1st local oscillator 5 1st 90 degree phase shifter 6 1st mixer 7 2nd mixer 8 Baud rate phase detection part 9 1st decimation filter 10 Second decimation filter 11 Second local oscillator 12 Second 90 ° phase shifter 13 Third mixer 14 Fourth mixer 15 Adder 16 Third local oscillator 17 Third 90 ° phase shifter 18 Fifth mixer 19 Sixth mixer 20 First root Nyquist filter 21 Second root Nyquist filter

Claims (1)

PSK comprising reproducing means for respectively reproducing the I signal and the Q signal from the QPSK modulated signal, and evaluating the modulation accuracy of the modulation IC for generating the QPSK modulated signal from the reproduced I signal and Q signal A modulation signal evaluation device,
In the reproduction means,
A first local oscillator whose oscillation frequency is set in the vicinity of the baseband frequency;
A first 90 ° phase shifter for shifting the phase of the output signal of the first local oscillator by 90 °;
The first QPSK modulation signal is multiplied by the output signal of the first local oscillator to frequency-convert the QPSK modulation signal at the oscillation frequency of the first local oscillator, and the first phase component of the QPSK modulation signal is output. With a mixer,
The QPSK modulation signal is multiplied by the output signal of the first 90 ° phase shifter to frequency-convert the QPSK modulation signal at the oscillation frequency of the first local oscillator, and an orthogonal component of the QPSK modulation signal is output. A second mixer that
A first decimation filter that thins out predetermined data from the in-phase component output from the first mixer;
A second decimation filter that thins out predetermined data from orthogonal components output from the second mixer;
A second local oscillator that is set to an arbitrary oscillation frequency that can be cut off when the baseband frequency is extracted by a low-pass filter;
A second 90 ° phase shifter that shifts the phase of the output signal of the second local oscillator by 90 °;
A third decimation filter that multiplies the output signal of the first decimation filter by the output signal of the second local oscillator, and frequency-converts the output signal of the first decimation filter at the oscillation frequency of the second local oscillator; A mixer,
The fourth decimation filter multiplies the output signal of the second decimation filter by the output signal of the second phase shifter, and converts the frequency of the output signal of the second decimation filter at the oscillation frequency of the second local oscillator. With a mixer,
An adder for adding the output signal of the third mixer and the output signal of the fourth mixer;
A third local oscillator in which a frequency obtained by adding the oscillation frequency of the second local oscillator to the frequency of the difference between the oscillation frequency of the first local oscillator and the baseband frequency is set as an oscillation frequency;
A third 90 ° phase shifter that shifts the phase of the output signal of the third local oscillator by 90 °;
The output signal of the adder and the output signal of the third local oscillator are multiplied to frequency-convert the output signal of the adder with the oscillation frequency of the third local oscillator, and the in-phase of the output signal of the adder A fifth mixer for outputting the components;
The output signal of the adder and the output signal of the third 90 ° phase shifter are multiplied to frequency-convert the output signal of the adder at the oscillation frequency of the third local oscillator, and the output of the adder A sixth mixer for outputting a quadrature component of the signal;
A first root Nyquist filter that is input with an output signal from the fifth mixer and is set to a predetermined filter characteristic for extracting the I signal;
A second root Nyquist filter that is input with an output signal from the sixth mixer and is set to a predetermined filter characteristic for extracting the Q signal;
A PSK modulation signal evaluation apparatus comprising:

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