Receiving device, mobile terminal test apparatus provided with receiving device, and mobile terminal test method
A receiving device includes a reception unit that samples a sample signal from a DUT 2 ; an FFT processing unit 21 that performs an FFT process by multiplying the sample signal by a window function; an FFT length setting unit 34 that, when the signal length of the signal to be measured is shorter than the first FFT length conforming to the communication standard, instead of the first FFT length, sets a second FFT length shorter than the signal length of the signal to be measured, as an FFT length of the FFT process; and a window function setting unit 35 that, when the signal length of the signal to be measured is shorter than the first FFT length, instead of a first window function, sets an asymmetric second window function having a peak separated from a center of a window section, as the window function.
1. A receiving device comprising:
a reception unit that samples a signal to be measured, transmitted from a device under test, and acquires a sample signal;
an Fast Fourier Transform (FFT) processing unit that performs an FFT process by multiplying the sample signal acquired by the reception unit by a window function;
a signal length calculation unit that calculates a signal length of the signal to be measured, from the sample signal acquired by the reception unit;
a comparing unit that compares the calculated signal length of the signal to be measured with a first FFT length conforming to a communication standard;
an FFT length setting unit that when as a result of the comparison by the comparing unit, the signal length of the signal to be measured is shorter than the first FFT length, instead of the first FFT length, sets a second FFT length shorter than the signal length of the signal to be measured, as an FFT length of the FFT process by the FFT processing unit; and
a window function setting unit that when as the result of the comparison by the comparing unit, the signal length of the signal to be measured is shorter than the first FFT length, instead of a first window function which is currently set as the window function used in the FFT process, sets an asymmetric second window function having a peak separated from a center of a window section, as the window function used in the FFT process.
2. The receiving device according to claim 1 , wherein
a separation distance of the peak of the second window function from the center of the window section is the number of N samples indicated by the following expression,
N
=
WL
-
3
RBW
×
SamplingRate
where WL is a section length of the second window function, RBW is a resolution bandwidth of the second window function, and SamplingRate is a rate of the sampling by the reception unit.
3. The receiving device according to claim 1 , wherein
the FFT processing unit performs the FFT process while shifting the set window function within an FFT sweep section, and
the receiving device further comprises
an FFT sweep section setting unit that when as the result of the comparison by the comparing unit, the signal length of the signal to be measured is shorter than the first FFT length, sets a section obtained by extending a measurement section corresponding to the signal to be measured, as the FFT sweep section.
4. The receiving device according to claim 2 , wherein
the FFT processing unit performs the FFT process while shifting the set window function within an FFT sweep section, and
the receiving device further comprises
an FFT sweep section setting unit that when as the result of the comparison by the comparing unit, the signal length of the signal to be measured is shorter than the first FFT length, sets a section obtained by extending a measurement section corresponding to the signal to be measured, as the FFT sweep section.
5. The receiving device according to claim 3 , wherein
the FFT sweep section obtained by extending the measurement section is a section obtained by extending the measurement section from an end point of the measurement section, by a difference obtained by subtracting a value twice a section length from a start point to a peak point of the second window function, from a section length of the second window function.
6. The receiving device according to claim 1 , wherein
the FFT length setting unit sets the second FFT length to maximum 2 n which is the number of samples or less of one symbol at a sampling rate of the sampling performed by the reception unit, where n is a natural number.
7. The receiving device according to claim 2 , wherein
the FFT length setting unit sets the second FFT length to maximum 2 n which is the number of samples or less of one symbol at a sampling rate of the sampling performed by the reception unit, where n is a natural number.
8. The receiving device according to claim 3 , wherein
the FFT length setting unit sets the second FFT length to maximum 2 n which is the number of samples or less of one symbol at a sampling rate of the sampling performed by the reception unit, where n is a natural number.
9. The receiving device according to claim 4 , wherein
the FFT length setting unit sets the second FFT length to maximum 2 n which is the number of samples or less of one symbol at a sampling rate of the sampling performed by the reception unit, where n is a natural number.
10. A mobile terminal test apparatus comprising:
a receiving device including
a reception unit that samples a signal to be measured, transmitted from a device under test, and acquires a sample signal,
an Fast Fourier Transform (FFT) processing unit that performs an FFT process by multiplying the sample signal acquired by the reception unit by a window function,
a signal length calculation unit that calculates a signal length of the signal to be measured from the sample signal acquired by the reception unit,
a comparing unit that compares the calculated signal length of the signal to be measured with a first FFT length conforming to a communication standard,
an FFT length setting unit that when as a result of the comparison by the comparing unit, the signal length of the signal to be measured is shorter than the first FFT length, instead of the first FFT length, sets a second FFT length shorter than the signal length of the signal to be measured, as an FFT length of the FFT process by the FFT processing unit, and
a window function setting unit that when as the result of the comparison by the comparing unit, the signal length of the signal to be measured is shorter than the first FFT length, instead of a first window function which is currently set as the window function used in the FFT process, sets an asymmetric second window function having a peak separated from a center of a window section, as the window function used in the FFT process;
an analysis unit that analyzes a signal obtained by the FFT processing unit; and
a display unit that displays a result of the analysis performed by the analysis unit.
11. The mobile terminal test apparatus according to claim 10 , wherein
a separation distance of the peak of the second window function from the center of the window section is the number of N samples indicated by the following expression,
N
=
WL
-
3
RBW
×
SamplingRate
where WL is a section length of the second window function, RBW is a resolution bandwidth of the second window function, and SamplingRate is a rate of the sampling by the reception unit.
12. The mobile terminal test apparatus according to claim 10 , wherein
the FFT processing unit performs the FFT process while shifting the set window function within an FFT sweep section, and
the receiving device further comprises
an FFT sweep section setting unit that when as the result of the comparison by the comparing unit, the signal length of the signal to be measured is shorter than the first FFT length, sets a section obtained by extending a measurement section corresponding to the signal to be measured, as the FFT sweep section.
13. The mobile terminal test apparatus according to claim 12 , wherein
the FFT sweep section obtained by extending the measurement section is a section obtained by extending the measurement section from an end point of the measurement section, by a difference obtained by subtracting a value twice a section length from a start point to a peak point of the second window function, from a section length of the second window function.
14. The mobile terminal test apparatus according to claim 10 , wherein
the FFT length setting unit sets the second FFT length to maximum 2 n which is the number of samples or less of one symbol at a sampling rate of the sampling performed by the reception unit, where n is a natural number.
15. A mobile terminal test method comprising:
a reception step of sampling a signal to be measured, transmitted from a device under test, and acquiring a sample signal;
an Fast Fourier Transform (FFT) processing step of performing an FFT process by multiplying the sample signal acquired in the reception step by a window function;
a signal length calculation step of calculating a signal length of the signal to be measured from the sample signal acquired in the reception step;
a comparison step of comparing the calculated signal length of the signal to be measured with a first FFT length conforming to a communication standard as an FFT length of the FFT process;
an FFT length setting step of, when as a result of the comparison in the comparison step, the signal length of the signal to be measured is shorter than the first FFT length, instead of the first FFT length, setting a second FFT length shorter than the signal length of the signal to be measured, as the FFT length of the FFT process in the FFT processing step;
a window function setting step of, when as the result of the comparison in the comparison step, the signal length of the signal to be measured is shorter than the first FFT length, instead of a first window function which is currently set as the window function used in the FFT process, setting an asymmetric second window function having a peak separated from a center of a window section, as the window function used in the FFT process;
a sweep section setting step of, when as the result of the comparison in the comparison step, the signal length of the signal to be measured is shorter than the first FFT length, setting a section obtained by extending a measurement section corresponding to the signal to be measured, as an FFT sweep section;
an analysis step of analyzing a signal obtained in the FFT processing step; and
a display step of displaying a result of analysis in the analysis step.