JPH0837544A - Offset detector for digital modulated signal - Google Patents

Abstract

PURPOSE:To stably detect an offset position by detecting maximum peak points showing both circular edge positions on a circumference from a histogram and afterwards calculating the intermediate value of both the peak points. CONSTITUTION:A histogram arithmetic part 20 reads the data of a desired data block out of I data 61a stored in a buffer memory 60, calculates the frequency distribution of the values of respective data, namely, the histogram and supplies it to a peak detecting part 30. Similarly, the histogram is calculated on the side of Q data 62a as well and supplied to the peak detecting part 30. The peak detecting part 30 detects two maximum peak points showing the positions on the circumference and afterwards, the target offset position is calculated. The intermediate value of both the peak points is calculated as the offset position. The offset position calculated like this hardly depends on the appearing state of 0/1 information in the input digital data of a DUT 100, and the offset position can be provided with stable accuracy.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for detecting offset positions of an I signal and a Q signal which are quadrature modulated signals output from a device under test.

[0002]

2. Description of the Related Art As an example of the prior art, there is a case using an averaging means and a case using an FFT processing means in order to obtain an offset of a GMSK-modulated modulation signal. This will be described with reference to FIGS. 3, 4, and 5. First, the case of using the averaging means will be described. As shown in FIG. 3, the configuration of this device is such that the device under test (DUT) 10
0, an AD converter 50, a buffer memory 60, and an average calculator 70.

The DUT 100 is, for example, a device for quadrature conversion which receives input digital information data, converts it into a quadrature modulation signal, and supplies it to a transmitter or the like. This DUT100
Input digital information data 110 at a rate of several 100 Kb / s, and the I signal 10 converted by this is input.
The AD converter 5 converts the two analog signals of 1 and Q signal 102.
Supply 0.

The AD converter 50 is, for example, an AD converter having a 12-bit resolution, has two AD converters 51 and 52, receives two analog signals from the DUT 100, and has a number of input bit rates. After being quantized at a sampling rate more than twice and converted into a digital signal, it is continuously stored and written in the corresponding I memory 61 and Q memory 62 of the buffer memory 60.

The average calculator 70 reads out data in a desired data section from the I data 61a stored in the buffer memory 60 and calculates an average value of these data. As a result of this average value calculation, as shown in FIG.
The offset position Ioff of the signal is obtained. Similarly, the average value of the Q data 62a is also calculated, and the offset position Qof of the Q signal is calculated.
f is obtained. In the offset position detection means by this means, the obtained offset position may be biased depending on the appearance state of 0/1 information of the input digital information data of the DUT 100, and the offset position may not be obtained accurately.

Next, the case of using the FFT processing means will be described. As shown in FIG. 4, the configuration of the present apparatus includes a device under test (DUT) 100, an AD conversion unit 50, a buffer memory 60, and an FFT processing unit 80.
Except for the T processing unit 80, it is the same as the above description.

The FFT processing section 80 includes a buffer memory 60.
Data in a desired data section is read out from the I data 61a stored in the FFT (fast Fourier transfe
r) Calculate and convert time data to frequency data. Among the obtained frequency data, the data of frequency = 0 Hz is obtained as the offset position Ioff of the I signal. Similarly, the Q data 62a is also subjected to FFT operation to obtain the offset position Qoff of the Q signal. Even with this means, the offset position may not be obtained accurately depending on the appearance state of 0/1 information of the input digital information data of the DUT 100.

[0008]

As described above, in the averaging means or the FFT processing means, the offset position is biased to the offset position obtained depending on the appearance state of 0/1 information of the input digital information data of the DUT 100. However, there is a problem in that the offset position cannot be accurately obtained.

Therefore, a problem to be solved by the present invention is 0/0 which is input digital modulation information to the DUT 100.
The object is to obtain a stable and stable offset position without being affected by the appearance state of one piece of information.

[0010]

In order to solve the above problems, in the configuration of the present invention, a histogram calculation unit 20 for obtaining the distribution of the level values of the I signal or the Q signal is provided, and from the histogram of the histogram calculation unit 20, The two maximum peak points are calculated, and the midpoints thereof are set to offset values Ioff and Qo.
The constituent means is provided with the peak detection unit 30 that detects ff. As a result, the offset positions Ioff and Qoff of the digital modulation signal in the modulation form in which the quadrature-modulated I signal or Q signal is distributed on the circumference of the Cartesian coordinates are detected.

As the digital modulation signal, GMS is used.
This detection means can be applied to a digitally modulated signal in a modulation form in which an I signal or a Q signal orthogonally modulated by K modulation, FSK modulation, MSK modulation, or CPFSK modulation is distributed on the circumference of rectangular coordinates. Further, there is a means of adding an AD conversion unit 50 for converting the quadrature-modulated I signal or Q signal to a digital signal to the above configuration.

[0012]

Operation: The histogram calculation section 20 uses the I signal or Q
Obtaining the signal histogram has the effect of obtaining the distribution of the circumference of the Cartesian coordinates. The peak detection unit 30 detects stable maximum offset positions Ioff and Qoff by detecting the maximum peak points indicating both circular end portions on the circumference from the histogram and then calculating an intermediate value between the peak points. is there.

[0013]

The embodiment of the present invention is for obtaining the offset of the modulated signal by obtaining the histogram distribution of both IQ signals in order to obtain the offset of the GMSK-modulated modulated signal. This will be described with reference to FIGS. 1 and 2. As shown in FIG. 1, the structure is a device under test (DUT) 1
00, an AD converter 50, a buffer memory 60, a histogram calculator 20, and a peak detector 30. Histogram calculation unit 20 and peak detection unit 30
Other than that, the configuration is the same as the conventional configuration. In the present invention, attention is paid to the point that the quadrature-modulated data positions exist on the circumference in a substantially uniform distribution, the distribution of this data is obtained, and the median value of the two maximum peaks of this distribution is obtained. As an offset position.

The histogram calculation unit 20 reads out data in a desired data section from the I data 61a stored in the buffer memory 60, and as shown in FIG. 2, the frequency distribution of the values of each data, that is, the histogram Ihist. Seeking
It is supplied to the peak detection unit 30. Similarly, Q data 62a
The side also obtains the histogram Qhist and supplies it to the peak detection unit 30.

The peak detecting section 30 detects the two maximum peak points indicating the positions on the circumference from the histogram and then finds the target offset position. For this reason, the histogram Ihist on the I side from the histogram calculation unit 20
Peak points Pi1 and Pi2 showing the maximum value are obtained from among the above. The intermediate value between the two peak points is obtained as the offset position Ioff. Similarly, on the Q side, the histogram Qhi
The offset position Qoff is found by finding the two maximum peak points Pq1 and Pq2 from st and calculating the intermediate value of both peak points. The offset position obtained in this way is the DUT1
It becomes difficult to depend on the appearance state of 0/1 information of the input digital information data of 00, and stable offset positions Ioff and Qoff can be obtained.

In the above description of the embodiment, the case of obtaining the offset of the GMSK modulated signal has been described, but a modulation system based on FSK, for example, FSK, MSK, CPFS.
K can also be used in the same manner. Also, the quadrature signal is
The offset values Ioff and Qoff can be obtained in the same manner in the case of other signals that draw a circle locus.

In the description of the above embodiment, the buffer memory 6
Although the configuration in which 0 is provided has been described, the buffer memory 60 may be omitted if desired, and the same operation can be performed.

[0018]

Since the present invention is configured as described above, it has the following effects. The histogram calculation unit 20 has an effect of obtaining the I signal or the Q signal as a distribution on the circumference of the rectangular coordinates by obtaining the histogram of the I signal or the Q signal. The peak detection unit 30 detects two maximum peak points indicating both circle end portions on the circumference from the histogram, and then calculates an intermediate value between the two peak points to calculate 0/1 of the input digital information data of the DUT 100. It is less dependent on the appearance state of information, and there is an advantage that stable and accurate offset positions Ioff and Qoff can be obtained.

[0019]

[Brief description of drawings]

FIG. 1 is a block diagram of an offset detection device using histogram means of the present invention.

FIG. 2 is a diagram showing a graph example of a histogram Ihist and a histogram Qhist according to the present invention.

FIG. 3 is a configuration diagram of a conventional offset detection device using average calculation means.

FIG. 4 is a block diagram of a conventional offset detection device using FFT processing means.

FIG. 5 is a diagram illustrating a relationship between a quadrature-modulated signal output from the DUT 100 and an offset position.

[Explanation of symbols]

 20 histogram calculation unit 30 peak detection unit 50 AD conversion unit 51, 52 AD converter 60 buffer memory 61 I memory 61a I data (I signal) 62 Q memory (Q signal) 62a Q data 70 average calculation unit 80 FFT processing unit 100 Device under test (DUT) 101 I signal 102 Q signal 110 Input digital information data Ioff, Qoff offset value Ihist, Qhist histogram

Claims (3)

[Claims] 1. An I signal for detecting an offset position of a digital modulation signal in a modulation form in which a quadrature modulated I signal (In-phase) or a Q signal (Quadrature-phase) is distributed on the circumference of Cartesian coordinates. Alternatively, a histogram calculation unit (20) for obtaining the distribution of the signal level of the Q signal is provided, and from the histogram of the histogram calculation unit (20),
A peak detection unit (3 that finds two maximum peak points and detects the midpoint as an offset value (Ioff, Qoff)
0) is provided and the above is provided, The offset detection apparatus of the digital modulation signal characterized by the above-mentioned. 2. GMSK (Gaussian filtered minimum s)
hift keying) modulation or FSK (Frequency Shift)
Keying) modulation or MSK (MinimumShift Keyin)
g) Modulation or CPFSK (Continuas Phase Frequ
ency Shift Keying) Histogram to find the distribution of the signal level of the I signal or Q signal in the detection of the offset position of the digital modulation signal of the modulation form in which the I signal or Q signal orthogonally modulated by the modulation is distributed on the circumference of the rectangular coordinates. A calculation unit (20) is provided, and from the histogram of the histogram calculation unit (20),
A peak detection unit (3 that finds two maximum peak points and detects the midpoint as an offset value (Ioff, Qoff)
0) is provided and the above is provided, The offset detection apparatus of the digital modulation signal characterized by the above-mentioned. 3. A digital device comprising an AD conversion unit (50) for converting a quadrature-modulated I signal or Q signal into a digital signal in addition to the constituent means according to claim 1 or 2. Modulation signal offset detection device.