Receiving device, receiving method, and mobile terminal testing device

Abstract

The present invention provides a receiving device and a mobile terminal test device capable of effectively and accurately correcting the phase error of a demodulated signal. The receiving device comprises: a demodulation unit (20) for demodulating a received OFDM modulated signal to obtain a demodulated constellation signal; an ideal constellation signal generation unit (312) for generating an ideal constellation signal from the demodulated constellation signal; a data extraction unit (313) for extracting signal data contained in a portion of a symbol interval containing a known reference symbol in the entire symbol interval from the demodulated constellation signal and the ideal constellation signal; a phase error calculation unit (314) for calculating the phase error of the demodulated constellation signal relative to the ideal constellation signal based on the extracted signal data; a phase error characteristic estimation unit (315) for estimating the frequency characteristic of the phase error; and a phase error correction unit (316) for correcting the phase error of the demodulated constellation signal based on the frequency characteristic of the phase error.

Description

Technical Field

[0001] The present invention relates to a receiving device and a receiving method for correcting a phase error of a demodulated signal, and a mobile terminal test device having the receiving device. Background Art

[0002] Conventionally, for example, a mobile terminal test device is used to perform a transmission test to analyze the signal transmitted from a device under test (DUT (Device Under Test)) such as a mobile communication terminal and check the transmission performance of the DUT. The signal transmitted from the DUT is, for example, a modulated signal modulated according to communication standards such as wireless LAN (Local Area Network), LTE (Long Term Evolution), and 5GNR (New Radio).

[0003] In wideband wireless transmission systems such as wireless LAN, LTE, and 5GNR, the OFDM (Orthogonal Frequency Division Multiplexing) method with high frequency utilization efficiency is widely used as a modulation method. The OFDM method is a block transmission method that takes synchronization according to each specified data block. Specifically, the data sequence is inversely multiplexed on the transmitting side and converted into parallel data and mapped to each subcarrier. Then, IFFT (Inverse Fast Fourier Transform) processing, D / A conversion, and orthogonal modulation are performed to set it as a transmission signal. In addition, after being converted into a signal in the time domain by IFFT processing, a part of the rear end of the signal is attached to the front of the signal as a guard interval, thereby being resistant to inter-symbol interference caused by multipath fading.

[0004] The mobile terminal test device receives and demodulates the modulated signal thus generated and performs signal analysis. Accurate demodulation is required to perform high-precision analysis. However, for example, when there is a frequency deviation between the transmission signal generated in the DUT and the demodulated signal demodulated in the receiving device, a phase error deviation (phase rotation) occurs in the demodulated signal, making it impossible to grasp the accurate transmission performance of the DUT. Therefore, it is necessary to appropriately correct the phase error generated in the demodulated signal. As a device for correcting the phase error of the demodulated signal, for example, a device described in Patent Document 1 is known.

[0005] Patent Document 1 discloses a configuration for performing phase synchronization processing by obtaining a frequency-phase characteristic from a constellation diagram of an OFDM demodulated signal, changing a phase difference, and searching for a phase difference at which the inclination of the frequency-phase characteristic approaches zero.

[0006] Patent Document 1: Japanese Patent No. 6473429

[0007] However, the conventional device described in Patent Document 1 does not consider the frequency-phase characteristic used for effectively acquiring the phase synchronization of the demodulated signal (i.e., correction of the phase error) with high accuracy. If the accuracy of the acquired frequency-phase characteristic is not high, it may be impossible to effectively synchronize the phase of the demodulated signal with high accuracy. Summary of the invention

[0008] The present invention has been made to solve the above-mentioned conventional problems, and an object of the present invention is to provide a receiving device and a receiving method capable of effectively correcting a phase error of a demodulated signal with high accuracy, and a mobile terminal test device including the receiving device.

[0009] In order to achieve the above-mentioned object, the receiving device of the present invention has a receiving unit (10) for receiving a modulation signal modulated by orthogonal frequency division multiplexing (OFDM) from a mobile communication terminal (2), and the receiving device is characterized in that it has: a demodulation unit (20) for demodulating the received modulation signal to obtain a demodulated constellation signal; an ideal constellation signal generating unit (312) for generating an ideal constellation signal from the demodulated constellation signal; a data extraction unit (313) for selecting and extracting a part of signal data from the demodulated constellation signal and the ideal constellation signal; a phase error calculation unit (314) , with respect to the extracted signal data, calculating the phase error of the demodulated constellation signal relative to the ideal constellation signal; a phase error characteristic estimation unit (315) estimating the frequency characteristic or time characteristic of the phase error based on the calculated phase error; and a phase error correction unit (316) correcting the phase error of the demodulated constellation signal based on the estimated frequency characteristic or time characteristic of the phase error, the data extraction unit extracting signal data contained in a portion of a symbol interval containing a known reference symbol in the entire symbol interval from the demodulated constellation signal and the ideal constellation signal.

[0010] As described above, in the receiving device of the present invention, the data extraction unit selects and extracts a portion of signal data that meets the prescribed conditions from the demodulated constellation signal (hereinafter, also referred to as the demodulated signal) and the ideal constellation signal. With respect to the extracted signal data, the phase error calculation unit calculates the phase error, and the phase error characteristic estimation unit estimates the frequency characteristic or time characteristic of the phase error in the section of the extracted signal data (hereinafter, also referred to as the characteristic of the phase error). Moreover, the phase error correction unit corrects the phase error of the demodulated constellation signal based on the estimated characteristic of the phase error. In this way, the characteristic of the phase error can be estimated using only a portion of the signal data with high reliability, and the phase error is corrected based on the characteristic, thereby making it possible to effectively correct the phase error of the demodulated signal with high accuracy.

[0011] When phase rotation occurs in the demodulated signal, for example, signal data included in a portion of the symbol intervals including known reference symbols such as DMRS (Demodulation Reference Signal) in the entire symbol interval within one time slot is data with higher reliability than signal data of other symbols due to the characteristics of estimating the phase error. Therefore, the phase error is estimated using only the characteristics of such signal data, and the phase error is corrected based on the characteristics, thereby being able to effectively correct the phase error of the demodulated signal with high accuracy.

[0012] Furthermore, the receiving device of the present invention has a receiving unit (10) for receiving a modulation signal modulated by orthogonal frequency division multiplexing (OFDM) from a mobile communication terminal (2), and the receiving device is characterized in that it comprises: a demodulation unit (20) for demodulating the received modulation signal to obtain a demodulated constellation signal; an ideal constellation signal generating unit (312) for generating an ideal constellation signal from the demodulated constellation signal; a data extraction unit (313) for selecting and extracting a part of signal data from the demodulated constellation signal and the ideal constellation signal; and a phase error calculation unit (314). , with respect to the extracted signal data, calculating the phase error of the demodulated constellation signal relative to the ideal constellation signal; a phase error characteristic estimation unit (315) estimating the frequency characteristic or time characteristic of the phase error based on the calculated phase error; and a phase error correction unit (316) correcting the phase error of the demodulated constellation signal based on the estimated frequency characteristic or time characteristic of the phase error, the data extraction unit extracting signal data corresponding to a specified ideal constellation point near the origin of the IQ plane from the demodulated constellation signal and the ideal constellation signal.

[0013] When phase rotation occurs in the demodulated signal, the signal data corresponding to the predetermined ideal constellation point near the origin of the IQ plane is data with higher reliability than the signal data corresponding to other ideal constellation points due to the characteristics of determining the phase error. Therefore, the phase error characteristics are estimated using only such signal data, and the phase error is corrected based on the characteristics, thereby making it possible to effectively correct the phase error of the demodulated signal with high accuracy.

[0014] Furthermore, the receiving device of the present invention has a receiving unit (10) for receiving a modulation signal modulated by orthogonal frequency division multiplexing (OFDM) from a mobile communication terminal (2), and the receiving device is characterized in that it comprises: a demodulation unit (20) for demodulating the received modulation signal to obtain a demodulated constellation signal; an ideal constellation signal generating unit (312) for generating an ideal constellation signal from the demodulated constellation signal; a data extraction unit (313) for selecting and extracting a part of signal data from the demodulated constellation signal and the ideal constellation signal; and a phase error calculation unit (314) for calculating the phase error of the received constellation signal. The extracted signal data calculates the phase error of the demodulated constellation signal relative to the ideal constellation signal; a phase error characteristic estimation unit (315) estimates the frequency characteristic or time characteristic of the phase error based on the calculated phase error; and a phase error correction unit (316) corrects the phase error of the demodulated constellation signal based on the estimated frequency characteristic or time characteristic of the phase error, and the data extraction unit extracts signal data corresponding to symbols having an error vector magnitude (EVM) less than a specified reference value from the demodulated constellation signal and the ideal constellation signal.

[0015] When phase rotation occurs in the demodulated signal, the signal data corresponding to the symbol having an EVM smaller than a predetermined reference value is data with higher reliability than the signal data corresponding to other symbols having high EVM due to the characteristics of the determined phase error. Therefore, the characteristics of the phase error are estimated using only such signal data, and the phase error is corrected based on the characteristics, thereby making it possible to effectively correct the phase error of the demodulated signal with high accuracy.

[0016] Furthermore, the receiving device of the present invention may be configured as follows, that is, further comprising a second correction unit (32) for calculating a phase error between the demodulated constellation signal whose phase error has been corrected by the phase error correction unit and an ideal constellation signal regenerated from the demodulated constellation signal whose phase error has been corrected, estimating a frequency characteristic or a time characteristic of the phase error based on the calculated phase error, and correcting the phase error of the demodulated constellation signal based on the estimated frequency characteristic or time characteristic of the phase error.

[0017] After estimating the characteristics of the phase error using only a portion of the signal data with high reliability and performing a rough correction of the phase error based on the characteristics, the second correction unit estimates the characteristics of the phase error using all the signal data contained in the entire frequency interval (the entire subcarrier interval) or the entire symbol interval, and performs a main correction of the phase error based on the characteristics, thereby being able to more effectively correct the phase error of the demodulated signal with high precision.

[0018] Furthermore, the receiving device of the present invention may be configured as follows, that is, further comprising a third correction unit (32A) for extracting signal data corresponding to a predetermined ideal constellation point near the origin of an IQ plane from the demodulated constellation signal whose phase error is corrected by the phase error correction unit and an ideal constellation signal regenerated from the demodulated constellation signal whose phase error is corrected, calculating a phase error of the demodulated constellation signal relative to the ideal constellation signal with respect to the extracted signal data, estimating a frequency characteristic or a time characteristic of the phase error based on the calculated phase error, and correcting the phase error of the demodulated constellation signal based on the estimated frequency characteristic or time characteristic of the phase error.

[0019] After estimating the characteristics of the phase error using only a portion of the signal data with high reliability and performing a rough correction of the phase error based on the characteristics, the third correction unit estimates the characteristics of the phase error using only the signal data corresponding to a predetermined ideal constellation point near the origin of the IQ plane and performs a rough correction of the phase error based on the characteristics. In this way, by performing the rough correction of the phase error in two stages using different methods, a more accurate ideal constellation signal can be obtained, thereby making it possible to more effectively correct the phase error of the demodulated signal with high accuracy.

[0020] Furthermore, the receiving device of the present invention may be configured as follows, that is, further comprising a fourth correction unit (33A) for calculating a phase error between the demodulated constellation signal whose phase error is corrected by the third correction unit and an ideal constellation signal regenerated from the demodulated constellation signal whose phase error is corrected, estimating a frequency characteristic or a time characteristic of the phase error based on the calculated phase error, and correcting the phase error of the demodulated constellation signal based on the estimated frequency characteristic or time characteristic of the phase error; and a fifth correction unit (34B) for extracting signal data corresponding to a symbol having an EVM smaller than a predetermined reference value from the demodulated constellation signal whose phase error is corrected by the fourth correction unit and the ideal constellation signal regenerated from the demodulated constellation signal whose phase error is corrected, calculating a phase error of the demodulated constellation signal relative to the ideal constellation signal with respect to the extracted signal data, estimating a frequency characteristic or a time characteristic of the phase error based on the calculated phase error, and correcting the phase error of the demodulated constellation signal based on the estimated frequency characteristic or time characteristic of the phase error.

[0021] After estimating the characteristics of the phase error using only a portion of the signal data with high reliability and performing a rough correction of the phase error based on the characteristics, the fourth correction unit estimates the characteristics of the phase error using the signal data of the entire interval and performs a main correction of the phase error based on the characteristics, and then the fifth correction unit estimates the characteristics of the phase error using only the signal data corresponding to the symbol having an EVM less than a predetermined reference value and performs a rough correction of the phase error based on the characteristics. In this way, the rough correction and the main correction of the phase error are performed in multiple stages using different methods, so that the phase error of the demodulated signal can be corrected more effectively with high accuracy.

[0022] Furthermore, the mobile terminal test device of the present invention is characterized by comprising a receiving device (100) as described in any one of the above items, an analysis unit (40) for analyzing the demodulated constellation signal after the phase error correction, and a display unit (50) for displaying the analysis result performed by the analysis unit.

[0023] According to this configuration, the mobile terminal test device of the present invention can more effectively correct the phase error of the demodulated signal with high accuracy, thereby being able to test the mobile communication terminal with high accuracy.

[0024] Furthermore, the receiving method of the present invention has a receiving step (S1) of receiving a modulated signal modulated in an orthogonal frequency division multiplexing (OFDM) manner from a mobile communication terminal (2), and the receiving method is characterized in that it includes: a demodulation step (S4, S5) of demodulating the received modulated signal to obtain a demodulated constellation signal; an ideal constellation signal generating step (S11) of generating an ideal constellation signal from the demodulated constellation signal; a data extraction step (S12) of selecting and extracting a portion of signal data from the demodulated constellation signal and the ideal constellation signal; a phase error calculation step (S13) of calculating a phase error. Based on the extracted signal data, a phase error of the demodulated constellation signal relative to the ideal constellation signal is calculated; a phase error characteristic estimation step (S14) is performed to estimate the frequency characteristic or time characteristic of the phase error based on the calculated phase error; and a phase error correction step (S15) is performed to correct the phase error of the demodulated constellation signal based on the estimated frequency characteristic or time characteristic of the phase error. In the data extraction step, signal data contained in a part of the symbol interval containing a known reference symbol in the entire symbol interval is extracted from the demodulated constellation signal and the ideal constellation signal.

[0025] As described above, in the receiving method of the present invention, in the data extraction step, a portion of signal data that meets the prescribed conditions is selected and extracted from the demodulated constellation signal and the ideal constellation signal. With respect to the extracted signal data, in the phase error calculation step, a phase error is calculated, and the frequency characteristic or time characteristic of the phase error in the entire data interval is estimated by the phase error characteristic estimation unit. Moreover, in the phase error correction, the phase error of the demodulated constellation signal is corrected according to the estimated phase error characteristic. In this way, the characteristic of the phase error can be estimated using only a portion of the signal data with high reliability, and the phase error is corrected according to the characteristic, thereby effectively correcting the phase error of the demodulated signal with high accuracy. In particular, when phase rotation occurs in the demodulated signal, for example, the signal data included in a portion of the symbol interval including a known reference symbol such as DMRS in the entire symbol interval within one time slot is data with high reliability compared to the signal data of other symbols due to the characteristic of the estimated phase error. Therefore, the characteristic of the phase error is estimated using only such signal data, and the phase error is corrected according to the characteristic, thereby effectively correcting the phase error of the demodulated signal with high accuracy.

[0026] Effects of the Invention

[0027] According to the present invention, it is possible to provide a receiving device and a receiving method capable of effectively correcting a phase error of a demodulated signal with high accuracy, and a mobile terminal test device including the receiving device. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a block diagram showing the configuration of a mobile terminal test device according to the first embodiment of the present invention.

[0029] Figure 2 In the demodulated signal with a large phase rotation, Figure 2 (a) is a graph showing EVM relative to subcarrier (frequency), Figure 2 (b) is a graph showing the phase error with respect to the subcarrier (frequency).

[0030] Figure 3 It is an explanatory diagram showing an abnormal situation in which a phase error occurs due to phase rotation.

[0031] Figure 4 This is a diagram for explaining a method of generating an ideal constellation signal from a demodulated constellation signal.

[0032] Figure 5 The graph is a diagram showing a phase error with respect to a subcarrier (frequency), and shows a set frequency interval and an approximate straight line showing the frequency characteristic of the phase error in the frequency interval.

[0033] Figure 6(a) is a diagram showing a constellation diagram when the phase error of the demodulated signal is not corrected. Figure 6 (b) is a diagram showing a constellation diagram when the phase error is corrected using signal data of the entire frequency range. Figure 6 (c) is a diagram showing a constellation diagram when the phase error is corrected using only signal data of a part of the central frequency interval.

[0034] Figure 7 This is a diagram showing a flowchart of a mobile terminal test performed using the mobile terminal test device according to the first embodiment.

[0035] Figure 8 This is a diagram showing a flowchart of a mobile terminal test performed using the mobile terminal test device according to the first embodiment.

[0036] Fig. 9 It is a diagram showing the configuration of a phase error detection unit according to the second embodiment.

[0037] Fig.10 This is a diagram for explaining a method of performing rough correction of a phase error using a reference symbol and symbols before and after it.

[0038] Fig.11 This is a diagram for explaining a method of performing rough correction of a phase error using signal data corresponding to an ideal constellation point near the origin of the IQ plane.

[0039] Fig.12 It is a diagram showing a flowchart of the phase error correction method according to the second embodiment.

[0040] Fig.13 It is a diagram showing the configuration of a phase error detection unit according to the third embodiment.

[0041] Fig.14 This is a diagram for explaining a method of correcting a phase error using signal data corresponding to a symbol having an EVM smaller than a predetermined reference value.

[0042] Fig.15 This is a diagram for explaining a method of correcting a phase error using signal data corresponding to a symbol having an EVM smaller than a predetermined reference value.

[0043] Fig.16 It is a diagram showing a flowchart of the phase error correction method according to the third embodiment. DETAILED DESCRIPTION

[0044] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0045] (First embodiment)

[0046] like Figure 1 As shown, the mobile terminal test device 1 involved in the first embodiment of the present invention tests the transmission performance of the device under test (DUT) 2 by receiving and analyzing the modulation signal a transmitted from the DUT 2, and the mobile terminal test device 1 includes a receiving unit 10, a demodulation unit 20, a phase error correction unit 30, an analysis unit 40, a display unit 50, a control unit 60 and an operation unit 70. The part including the receiving unit 10, the demodulation unit 20 and the phase error correction unit 30 is also referred to as a receiving device 100. As DUT2, there is no limitation, and examples thereof include mobile communication terminals such as smartphones, mobile phones, and tablet terminals. The modulation signal a transmitted from DUT2 is, for example, an OFDM modulation signal modulated by an orthogonal frequency division multiplexing (OFDM) method according to communication standards such as LTE and 5GNR. Below, each component is described.

[0047] (Receiving Department)

[0048] The receiving unit 10 receives a modulated signal a (OFDM modulated signal) transmitted from the DUT 2 via an antenna or wired, and includes a down converter 11 , an analog-to-digital converter (ADC) 12 , and an orthogonal demodulator 13 .

[0049] The down converter 11 includes a mixer and a local oscillator, and inputs a modulation signal a sent from the DUT 2 and a local signal generated by the local oscillator into the mixer to perform down conversion, thereby generating an intermediate frequency (IF) signal b. The intermediate frequency signal b is sent to the ADC 12.

[0050] The ADC 12 samples the intermediate frequency signal b frequency-converted by the down converter 11 to convert the analog signal into a digital signal. The obtained digital intermediate frequency signal c is sent to the orthogonal demodulation unit 13 .

[0051] The quadrature demodulation unit 13 converts the frequency of the digital intermediate frequency signal c output from the ADC 12 into a baseband signal, and quadrature demodulates the I-phase component and the Q-phase component. The obtained quadrature demodulation signal d is sent to the demodulation unit 20. The quadrature demodulation signal d is a complex signal.

[0052] In the above description, the receiving unit 10 is assumed to convert the signal into an intermediate frequency signal in the down converter 11, but the signal may be converted into a baseband signal in the down converter 11. Furthermore, a signal synchronization unit may be provided between the orthogonal demodulation unit 13 and the demodulation unit 20, and the orthogonal demodulation signal d may be synchronized in symbols and frames.

[0053] (Demodulation Unit)

[0054] The demodulation unit 20 performs OFDM demodulation on the orthogonal demodulation signal d output from the orthogonal demodulation unit 13 of the reception unit 10 , and includes a fast Fourier transform (FFT (Fast Fourier Transform)) unit 21 and a subcarrier demodulation unit 22 .

[0055] The FFT unit 21 performs a fast Fourier transform process on the orthogonal demodulation signal d output from the orthogonal demodulation unit 13, and generates a frequency domain signal e. In addition, as needed, the FFT unit 21 removes the CP (Cyclic Prefix) from each symbol of the orthogonal demodulation signal d before performing the FFT process. The generated frequency domain signal e is sent to the subcarrier demodulation unit 22.

[0056] A transmission path estimation and correction unit may be provided between the FFT unit 21 and the subcarrier demodulation unit 22. The transmission path estimation and correction unit estimates the transmission path of the frequency domain signal e output from the FFT unit 21 based on, for example, a pilot signal and corrects the transmission path. When the transmission path estimation and correction unit is provided, the corrected frequency domain signal is sent to the subcarrier demodulation unit 22.

[0057] The subcarrier demodulation unit 22 performs demodulation processing on the frequency domain signal e for each subcarrier to generate an OFDM demodulation signal f. The OFDM demodulation signal f is sent to the phase error correction unit 30.

[0058] Although described in detail later, the phase error correction unit 30 corrects the phase error of the OFDM demodulation signal f. The OFDM demodulation signal s with the corrected phase error is sent to the analysis unit 40.

[0059] (Analysis and Display)

[0060] The analysis unit 40 is configured to measure and analyze, for example, transmission power, EVM (Error Vector Magnitude), constellation diagram, and spectrum of the OFDM demodulated signal s whose phase error is corrected and output from the phase error correction unit 30, and to test the transmission performance of the DUT 2. The measurement and analysis results of the analysis unit 40 are sent to the display unit 50.

[0061] The display unit 50 displays the test results of the DUT 2 including the data of the measurement and analysis results sent from the analysis unit 40 , graphs, and the like, on a liquid crystal display or the like.

[0062] The operating unit 70 is a part operated by the user to set parameters such as measurement items, measurement conditions and judgment conditions when testing DUT2, and is composed of, for example, a touch panel, a keyboard composed of hardware keys, an input device such as a dial or a mouse, and a control circuit that controls them.

[0063] The control unit 60 receives input from the operation unit 70 to set various parameters, and controls functional units such as the receiving unit 10 , the demodulating unit 20 , the phase error correcting unit 30 , the analyzing unit 40 , and the display unit 50 .

[0064] (Data Structure)

[0065] Here, an example of the data structure of the modulation signal a transmitted from the DUT2 is described.

[0066] For example, if viewed from the time axis, the modulated signal a is composed of a plurality of consecutive frames, and one frame is composed of 10 subframes. The time length of one subframe is 1ms, so the time length of one frame is 10ms. A subframe is composed of one or more time slots, and the number of time slots contained in one subframe is determined by the subcarrier spacing. One time slot contains, for example, 14 symbols.

[0067] When viewed from the frequency direction, the modulated signal a is composed of a plurality of resource blocks, and one resource block includes, for example, 12 consecutive subcarriers.

[0068] (Phase Error)

[0069] If the OFDM demodulated signal f contains a large phase rotation, it is difficult to accurately evaluate the modulation accuracy. Figure 2 (a) is a graph showing the EVM of the demodulated signal with phase rotation with respect to the subcarrier (frequency). The EVM is small in the middle subcarrier interval, and large in the subcarrier intervals at both ends.

[0070] As an example, Figure 2 (b) is a graph showing the phase error of the demodulated signal with phase rotation relative to the subcarrier (frequency). The phase error shows a linear frequency characteristic that is inclined in the central subcarrier interval, and no linear frequency characteristic like the central one is recognized in the subcarrier intervals at both ends.

[0071] Figure 3 1 is an explanatory diagram showing an abnormal situation in which a phase error occurs due to phase rotation. If there is a frequency error in the components such as the DUT 2 and the receiving unit 10, Figure 3 As shown, phase rotation occurs in the IQ data sequence constituting the OFDM demodulated signal f. In this specification, the phenomenon that the phase error gradually increases in proportion to the elapsed time as time passes is referred to as phase rotation.

[0072] exist Figure 3, the demodulation constellation points existing around the ideal constellation point IdealConst[0] extend in an arc shape and in a strip shape with the origin of the IQ plane as the center. At this time, the distance between the demodulation constellation points existing in part A and the ideal constellation point IdealConst[1] is shorter than the distance between the demodulation constellation points existing in part A and the ideal constellation point IdealConst[0]. Furthermore, the distance between the demodulation constellation points existing in part B and the ideal constellation point IdealConst[2] is shorter than the distance between the demodulation constellation points existing in part B and the ideal constellation point IdealConst[0]. Therefore, it is erroneously recognized that the ideal constellation point corresponding to the demodulation constellation points existing in part A is located at IdealConst[1], and the ideal constellation point corresponding to the demodulation constellation points existing in part B is located at IdealConst[2].

[0073] In this way, if the corresponding ideal constellation point is misidentified, the phase error will deviate greatly from the original value, and thus the EVM will also deviate from the true value. In this embodiment, by correcting the phase error caused by the phase rotation, the information of the true phase error is obtained, and based on this, the EVM and other values ​​are obtained to test the transmission performance of DUT2.

[0074] (Phase Error Correction Section)

[0075] Next, the phase error correction unit 30 will be described.

[0076] The phase error correction unit 30 corrects the phase error of the OFDM demodulated signal f output from the demodulation unit 20, and includes a first-stage correction unit 31 and a second-stage correction unit 32. The first-stage correction unit 31 performs a rough correction of the phase error, and includes a demodulation constellation signal acquisition unit 311, a first ideal constellation signal generation unit 312, a data extraction unit 313, a first phase error calculation unit 314, a first phase error characteristic estimation unit 315, and a first phase error correction unit 316. The second-stage correction unit 32 performs a main correction of the phase error, and includes a second ideal constellation signal generation unit 322, a second phase error calculation unit 324, a second phase error characteristic estimation unit 325, and a second phase error correction unit 326. In addition, the second-stage correction unit 32 of this embodiment corresponds to the second correction unit of the present invention. Hereinafter, each component is described.

[0077] The demodulation constellation signal acquisition unit 311 of the first stage correction unit 31 acquires the OFDM demodulation signal f from the subcarrier demodulation unit 22 and stores it as a demodulation constellation signal DemodConst[n]. Here, n is a data number, n=0, 1, ..., N-1, and N is the total number of data. That is, the demodulation constellation signal is a discrete signal data sequence, and each signal data is a complex data having an I-phase component and a Q-phase component.

[0078] The first ideal constellation signal generating unit 312 generates an ideal constellation signal IdealConst[n] from the demodulated constellation signal DemodConst[n]. Figure 4 This is a diagram for explaining a method of generating an ideal constellation signal from a demodulated constellation signal. Figure 4 In the above figure, as an example, three signal data of the demodulation constellation signal, namely DemodConst[0], DemodConst[1] and DemodConst[2], are plotted on the IQ plane. The ideal constellation on the IQ plane is shown by a "+" mark.

[0079] Figure 4 In the following figure, the ideal constellation points IdealConst[0], IdealConst[1] and IdealConst[2] closest to the constellation points of the three signal data DemodConst[0], DemodConst[1] and DemodConst[2] of the demodulated constellation signal are plotted on the IQ plane. That is, it is estimated that the three signal data DemodConst[0], DemodConst[1] and DemodConst[2] of the demodulated constellation signal correspond to the ideal constellation points IdealConst[0], IdealConst[1] and IdealConst[2], respectively. In this way, the signal data IdealConst[n] of the ideal constellation signal closest to the IQ plane is generated from the signal data DemodConst[n] of the demodulated constellation signal. Here, n = 0, 1, ..., N-1, and N is the total number of data.

[0080] The data extraction unit 313 selects and extracts a portion of signal data that meets the specified conditions from the demodulated constellation signal and the ideal constellation signal. Specifically, the data extraction unit 313 extracts signal data corresponding to subcarriers included in a portion of the frequency interval in the middle or center of the entire frequency interval including all subcarriers from the demodulated constellation signal and the ideal constellation signal.

[0081] Figure 5This is a diagram showing a phase error relative to a subcarrier (frequency) when there is phase rotation in the demodulated signal. The horizontal axis is the subcarrier number, and as the subcarrier number increases, the frequency increases at every subcarrier interval, so it can be considered that the horizontal axis represents the frequency. Figure 5 2 shows the set frequency interval C and the approximate straight line D indicating the frequency characteristic of the phase error in the frequency interval C.

[0082] Figure 5 In FIG. 1 , a graph of phase errors with respect to CP-OFDM symbols (0 to 13) is also shown on the right side. The horizontal axis represents the symbol number, and as the symbol number increases, the elapsed time increases, so it can be considered that the horizontal axis represents time.

[0083] For example, in Figure 5 In the example, the data extraction unit 313 extracts the signal data corresponding to the subcarriers (s1 to s2) included in the central frequency interval C of the entire frequency interval including all subcarriers (0 to 3275). That is, the signal data DemodConst[m] and IdealConst[m] of the data number m satisfying s1≤subcarrier number≤s2 are respectively extracted.

[0084] If signal data of p data numbers m1, m2, ..., mp are extracted, the extracted signal data are expressed as follows: Demodulated constellation signal: DemodConst[mi] Ideal constellation signal: IdealConst[mi], where i=1, 2, ..., p.

[0085] The part of the frequency interval C is not limited, for example, it is set to 20% to 40% of the entire frequency interval, preferably the central 30% of the entire frequency interval, and more preferably the central 20%. In addition, the part of the frequency interval C does not have to be set in the center of the entire frequency interval, and can be set offset from the center as needed, or can be set to include one side end of the entire frequency interval.

[0086] The first phase error calculation unit 314 calculates the phase error PhaseError[mi] of the demodulated constellation signal with respect to the ideal constellation signal for the extracted signal data. Here, i=1, 2, . . . , p (p is the number of extracted data).

[0087] Specifically, the phases of signal data of data numbers m1, m2, ..., mp are expressed by the following equations.

[0088] Demodulate constellation signal: DemodPhase[mi] = arg(DemodConst[mi])(1)

[0089] Ideal constellation signal: IdealPhase[mi] = arg(IdealConst[mi])(2)

[0090] Here, i=1, 2, ..., p is the number of extracted data.

[0091] Therefore, regarding each signal data extracted from the demodulated constellation signal, the phase error of each signal data from the corresponding ideal constellation signal is expressed as follows.

[0092] PhaseError[mi]=DemodPhase[mi]-IdealPhase[mi]=arg(DemodConst[mi])-arg(IdealConst[mi])(3)

[0093] Here, i=1, 2, ..., p is the number of extracted data.

[0094] The first phase error characteristic estimation unit 315 estimates the frequency characteristic of the phase error based on the calculated phase error. Specifically, for example, Figure 5 As shown, the frequency characteristic of the phase error in the frequency interval C is approximated by a straight line D. The straight line D represented by a linear equation can be obtained by, for example, the least square method. The straight line D representing the frequency characteristic of the phase error is interpolated outside the frequency interval C as represented by the dotted line and can be applied to the entire frequency interval.

[0095] The first phase error correction unit 316 corrects the phase error of the demodulated constellation signal in the entire frequency range based on the frequency characteristics of the phase error.

[0096] Specifically, the first phase error correction unit 316 corrects the phase error by rotating the phase of the demodulated constellation signal in the entire frequency range so as to make the slope of the straight line D of the frequency characteristic of the approximate phase error zero, that is, so as to make the straight line D parallel to the frequency axis (horizontal axis). In this way, by obtaining the demodulated constellation signal with the phase error corrected, an accurate ideal constellation signal can be obtained by the second ideal constellation signal generation unit 322 described later. In other words, the first stage correction unit 31 is performed for the purpose of obtaining a more accurate ideal constellation signal.

[0097] Next, the second-stage correction unit 32 that performs the main correction of the phase error will be described.

[0098] The second correction unit 32 calculates the phase error between the demodulated constellation signal whose phase error is corrected by the first phase error correction unit 316 and the ideal constellation signal regenerated from the demodulated constellation signal whose phase error is corrected, estimates the frequency characteristic of the phase error based on the calculated phase error, and corrects the phase error of the demodulated constellation signal based on the estimated frequency characteristic of the phase error.

[0099] Specifically, the second ideal constellation signal generator 322 determines the ideal constellation point closest to each signal data on the IQ plane based on the demodulated constellation signal whose phase error has been corrected by the first phase error corrector 316, thereby generating an ideal constellation signal again.

[0100] The second phase error calculation unit 324 calculates a phase error between the demodulated constellation signal whose phase error has been corrected by the first phase error correction unit 316 and the ideal constellation signal regenerated by the second ideal constellation signal generation unit 322 .

[0101] The second phase error characteristic estimation unit 325 obtains an approximate straight line representing the frequency characteristic of the phase error in the entire frequency range from the phase error calculated by the second phase error calculation unit 324 by, for example, the least square method.

[0102] The second phase error correction unit 326 re-corrects the phase error of the demodulated constellation signal whose phase error has been corrected by the first phase error correction unit 316, based on the frequency characteristic of the phase error estimated by the second phase error characteristic estimation unit 325. The demodulated constellation signal whose phase error has been corrected by the second phase error correction unit 326 is sent to the analysis unit 40 as a phase error-corrected OFDM demodulated signal s.

[0103] In addition, the demodulated constellation signal whose phase error has been roughly corrected by the first-stage correction unit 31 can be sent to the analysis unit 40 as an OFDM demodulated signal s whose phase error has been corrected, and signal analysis can be performed.

[0104] The mobile terminal test device 1 and the receiving device 100 according to the present embodiment include, for example, a computer having a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), an input / output interface, and a storage device such as a hard disk, etc., either alone or as a whole. Thus, for example, a part or all of the functions of the receiving unit 10, the demodulating unit 20, the phase error correction unit 30, the analyzing unit 40, the display unit 50, the control unit 60, and the operating unit 70 can be realized by reading various processing programs stored in the ROM and the storage device into the RAM and executing them by the CPU. For example, the control unit 60 may be a computer.

[0105] Next, refer to Figure 1 and Figure 7 A mobile terminal testing method performed using the mobile terminal testing device 1 according to the first embodiment will be described.

[0106] DUT2 sends a modulation signal a modulated by OFDM modulation.

[0107] The receiving unit 10 receives the modulated signal a via an antenna or wired connection, and inputs the modulated signal a into the down converter 11 .

[0108] The down converter 11 down-converts the modulation signal a sent from the DUT 2 into an intermediate frequency signal b (step S1 ). The intermediate frequency signal b is sent to the ADC 12 .

[0109] The ADC 12 samples the analog intermediate frequency signal b to generate a digital intermediate frequency signal c (step S2 ). The sampling is performed, for example, 14640 times, 30720 times, or 61440 times per 14 symbols (1 time slot). The digital intermediate frequency signal c is sent to the orthogonal demodulation unit 13 .

[0110] The quadrature demodulation unit 13 quadrature-demodulates the digital intermediate frequency signal c sent from the ADC 12 into a baseband signal to generate a quadrature demodulation signal d (step S3). The quadrature demodulation signal d is a complex signal in the time domain and has an I-phase component and a Q-phase component. The quadrature demodulation signal d is sent to the FFT unit 21 of the demodulation unit 20.

[0111] The FFT unit 21 performs fast Fourier transform on the orthogonal demodulation signal d in the time domain outputted from the orthogonal demodulation unit 13 to obtain a frequency domain signal e (step S4 ). The frequency domain signal e is sent to the subcarrier demodulation unit 22 .

[0112] The subcarrier demodulation unit 22 performs demodulation processing on each subcarrier from the frequency domain signal e to obtain an OFDM demodulation signal f (step S5). The demodulation processing of each subcarrier is a demodulation processing corresponding to the modulation method performed on each subcarrier in the DUT2, for example, BPSK (Binary Phase shift Keying), QPSK (Quadrature Phase shift Keying), 8PSK (Phase Shift Keying), 16QAM (Quadrature Amplitude Modulation) and 64QAM demodulation. The OFDM demodulation signal f is sent to the phase error correction unit 30.

[0113] As will be described in detail later, the phase error correction unit 30 corrects the phase error of the OFDM demodulated signal f (step S6 ). The OFDM demodulated signal s with the corrected phase error is sent to the analysis unit 40 .

[0114] The analysis unit 40 measures and analyzes the OFDM demodulated signal s whose phase error has been corrected by the phase error correction unit 30, for example, transmission power, EVM, constellation diagram, and spectrum (step S7).

[0115] The display unit 50 displays information t such as data and graphs of the measurement and analysis results obtained by the analysis unit 40 in step S7 (step S8 ).

[0116] Next, refer to Figure 1 and Figure 8 The phase error correction process will be described.

[0117] In the phase error correction unit 30, the demodulation constellation signal acquisition unit 311 acquires the OFDM demodulation signal f from the subcarrier demodulation unit 22 of the demodulation unit 20 as a "demodulation constellation signal" and stores it (step S10). The demodulation constellation signal g is a complex digital signal having an I-phase component and a Q-phase component. The demodulation constellation signal g is sent to the first ideal constellation signal generation unit 312 and the data extraction unit 313.

[0118] The first ideal constellation signal generator 312 generates an ideal constellation signal h from the demodulated constellation signal g (step S11). Specifically, the first ideal constellation signal generator 312 obtains the ideal constellation point with the closest distance on the IQ plane for each signal data of the demodulated constellation signal, thereby generating the ideal constellation signal h. The ideal constellation signal h is sent to the data extractor 313.

[0119] The data extraction unit 313 extracts signal data corresponding to the subcarriers included in a part of the frequency interval in the center of the entire frequency interval including all subcarriers from the demodulated constellation signal and the ideal constellation signal (step S12). The frequency interval for extracting the signal data is an interval that intentionally represents the frequency characteristics of the phase error, and is, for example, an interval in the center 20% of the entire frequency interval. The frequency interval for extracting the signal data changes according to the modulation method of the subcarrier, and generally, the larger the multi-value degree, the narrower it is. The frequency interval for extracting the signal data can be set by the user via the operating unit 70, or it can be set according to a specified benchmark by measuring the EVM and phase error in the entire frequency interval and comparing their average values ​​with a specified threshold value.

[0120] The first phase error calculation unit 314 calculates a phase error with respect to the signal data extracted from the demodulated constellation signal and the ideal constellation signal by the data extraction unit 313 (step S13 ).

[0121] The first phase error characteristic estimation unit 315 estimates an approximate straight line indicating the relationship between the phase error and the frequency (ie, the frequency characteristic of the phase error) based on the phase error data calculated by the first phase error calculation unit 314 in a set part of the frequency interval (step S14).

[0122] The first phase error correction unit 316 corrects the phase error of the demodulated constellation signal in the entire frequency interval using the approximate straight line obtained by the first phase error characteristic estimation unit 315 (step S15). Specifically, the phase of each signal data of the demodulated constellation signal is rotated so that the inclination of the approximate straight line representing the frequency characteristic of the phase error becomes zero. In this way, in the first stage correction unit 31, the phase error of the demodulated signal is roughly corrected using the data signal of a part of the frequency interval in the entire frequency interval.

[0123] Next, the second ideal constellation signal generating unit 322 of the second stage correcting unit 32 generates an ideal constellation signal again from the demodulated constellation signal whose phase error has been corrected by the first phase error correcting unit 316, similarly to the first ideal constellation signal generating unit 312 (step S16).

[0124] The second phase error calculation unit 324 calculates the phase error in the entire frequency range from the demodulated constellation signal whose phase error has been corrected by the first phase error correction unit 316 and the ideal constellation signal regenerated by the second ideal constellation signal generation unit 322 (step S17).

[0125] The second phase error characteristic estimation unit 325 estimates an approximate straight line representing the frequency characteristic of the phase error in the entire frequency interval based on the phase error calculated by the second phase error calculation unit 324 (step S18 ).

[0126] The second phase error correction unit 326 corrects the phase error of the demodulated constellation signal in the entire frequency range based on the approximate straight line estimated by the second phase error characteristic estimation unit 325 (step S19). In this way, in the second stage correction unit 32, the frequency characteristics of the phase error are obtained using the data signal of the entire frequency range, and the phase error is mainly corrected based on the frequency characteristics. The demodulated constellation signal with the corrected phase error is sent to the analysis unit 40. In addition, the demodulated constellation signal with the roughly corrected phase error by the first stage correction unit 31 can be sent to the analysis unit 40 for signal analysis.

[0127] Figure 6 (a) shows a constellation diagram of a demodulated signal when the phase error is not corrected. When the phase error is not corrected, an abnormality of the phase error caused by the phase rotation appears in the constellation diagram, and thus there is a scatter in the constellation diagram. Figure 6 (b) shows the constellation diagram when the frequency characteristics of the phase error are obtained using the signal data of the entire frequency range, and the phase error is corrected based on the frequency characteristics (only the main correction is performed, without the coarse correction). Compared with the case where the phase error is not corrected, the constellation diagram is improved, but there is still scatter at the four corners of the constellation diagram. Figure 6 (c) shows the constellation diagram of the demodulated signal when a rough correction is performed before the main correction according to the first embodiment. Figure 6 Compared with the case where only the main correction is performed as shown in (b), there is no dispersion in the constellation diagram, which is a significant improvement compared with the case where only the main correction is performed.

[0128] Next, the operation and effect will be described.

[0129] As described above, in the receiving device 100 and the mobile terminal test device 1 according to the present embodiment, the data extraction unit 313 extracts signal data corresponding to subcarriers included in a portion of the frequency interval in the center of the entire frequency interval including all subcarriers from the demodulated constellation signal and the ideal constellation signal. The first phase error calculation unit 314 calculates the phase error for the extracted signal data, and the first phase error characteristic estimation unit 315 estimates the frequency characteristic of the phase error in the interval of the extracted signal data. Then, the first phase error correction unit 316 corrects the phase error of the demodulated constellation signal based on the estimated frequency characteristic of the phase error. In this way, the frequency characteristic of the phase error can be estimated using only a portion of the signal data with high reliability, and the phase error is corrected based on the characteristic, thereby making it possible to effectively correct the phase error of the demodulated signal with high accuracy.

[0130] Furthermore, in the receiving device 100 and the mobile terminal test device 1 according to the present embodiment, the frequency characteristic of the phase error is estimated using only a part of the signal data with high reliability in the first stage correction unit 31, and the phase error is roughly corrected based on the frequency characteristic. Then, the frequency characteristic of the phase error is estimated using the signal data included in the entire frequency interval (the entire subcarrier interval) in the second stage correction unit 32, and the main correction of the phase error is performed based on the frequency characteristic, thereby making it possible to more effectively correct the phase error of the demodulated signal with high accuracy. In particular, after the rough correction of the phase error, an ideal constellation signal is generated again, thereby calculating the phase error based on a more accurate ideal constellation signal, and thus making it possible to estimate the frequency characteristic of the phase error with higher accuracy.

[0131] <Variation 1>

[0132] In the first embodiment, the data extraction unit 313 may be configured to extract signal data included in a portion of the symbol interval including a known reference symbol in the entire symbol interval from the demodulated constellation signal g and the ideal constellation signal h. In this case, the first phase error characteristic estimation unit 315 estimates an approximate straight line indicating the time characteristic of the phase error based on the data of the phase error in the portion of the symbol interval calculated by the first phase error calculation unit 314. The first phase error correction unit 316 corrects the phase error for the entire symbol interval using a linear approximation extended over the entire symbol interval.

[0133] When phase rotation occurs in the demodulated signal, for example, signal data included in a portion of the symbol intervals including known reference symbols such as DMRS in the entire symbol interval within one time slot is data with higher reliability than signal data of other symbols due to the characteristics of estimating the phase error. Therefore, the phase error characteristics are estimated using only such signal data, and the phase error is corrected based on the characteristics, thereby making it possible to effectively correct the phase error of the demodulated signal with high accuracy.

[0134] <Variation 2>

[0135] In the first embodiment, the data extraction unit 313 may be configured to extract signal data corresponding to a predetermined ideal constellation point near the origin of the IQ plane from the demodulated constellation signal g and the ideal constellation signal h. In this case, the first phase error characteristic estimation unit 315 estimates an approximate straight line representing the frequency characteristic or time characteristic of the phase error based on the data of the phase error calculated by the first phase error calculation unit 314 in a portion of the interval corresponding to the extracted data. The first phase error correction unit 316 corrects the phase error for the entire interval using a linear approximation extended over the entire interval.

[0136] When phase rotation occurs in the demodulated signal, the signal data corresponding to the predetermined ideal constellation point near the origin of the IQ plane is data with higher reliability than the signal data corresponding to other ideal constellation points due to the characteristics of determining the phase error. Therefore, the phase error characteristics are estimated using only such signal data, and the phase error is corrected based on the characteristics, thereby making it possible to effectively correct the phase error of the demodulated signal with high accuracy.

[0137] <Variation 3>

[0138] In the first embodiment, the data extraction unit 313 may be configured to extract signal data corresponding to symbols having an error vector magnitude (EVM) less than a predetermined reference value from the demodulated constellation signal g and the ideal constellation signal h. In this case, the first phase error characteristic estimation unit 315 estimates an approximate straight line representing the time characteristic of the phase error based on the data of the phase error calculated by the first phase error calculation unit 314 in a portion of the symbol interval corresponding to the extracted data. The first phase error correction unit 316 corrects the phase error for the entire symbol interval using a linear approximation extended over the entire symbol interval.

[0139] When phase rotation occurs in the demodulated signal, the signal data corresponding to the symbol having an EVM smaller than a predetermined reference value is data with higher reliability than the signal data corresponding to other symbols having high EVM due to the characteristics of the determined phase error. Therefore, the characteristics of the phase error are estimated using only such signal data, and the phase error is corrected based on the characteristics, thereby making it possible to effectively correct the phase error of the demodulated signal with high accuracy.

[0140] (Second embodiment)

[0141] Next, a receiving device and a mobile terminal testing device according to a second embodiment of the present invention will be described with reference to the drawings.

[0142] like Fig. 9 As shown, in the receiving device and mobile terminal test device according to this embodiment, the configuration of the phase error correction unit 30A is different from the configuration of the phase error correction unit 30 of the first embodiment. The other configurations are the same as those of the first embodiment, and the same reference numerals are used for the same configurations, and detailed descriptions thereof are omitted as appropriate.

[0143] The phase error correction unit 30A according to the present embodiment includes a first stage correction unit 31A for performing a rough correction of the phase error, a second stage correction unit 32A for performing a rough correction of the phase error from a different point of view from the first stage correction unit 31A, and a third stage correction unit 33A for performing a main correction of the phase error. The second stage correction unit 32A of the present embodiment corresponds to the third correction unit of the present invention.

[0144] The first data extraction unit 313A of the first stage correction unit 31A extracts signal data included in a portion of the symbol interval including a known reference symbol in the entire symbol interval from the demodulated constellation signal and the ideal constellation signal.

[0145] like Fig.10 As shown, it is assumed that 14 symbols, symbol #0, symbol #1, ..., symbol #13, are used as one block (time slot). In this example, symbol #2 is a known DMRS symbol. The first data extraction unit 313A extracts the signal data existing in the interval of symbol #2 of the DMRS and the left and right adjacent symbols #1 and #3, i.e., symbols #1 to #3, in the entire symbol interval from the demodulated constellation signal and the ideal constellation signal. However, the number of symbols in the symbol interval for extracting signal data is not limited to 3, and can be 2 or 4 or more.

[0146] The first phase error calculation unit 314 calculates the phase error of each signal data in the interval of symbols #1 to #3, and calculates the average value of the phase error for each symbol. Fig.10 The average phase error in signed units is plotted.

[0147] Specifically, the first phase error calculation unit 314 calculates the average phase error for each symbol according to the following equation.

[0148] [Formula 1]

[0149]

[0150] Here, M is the total number of subcarriers included in each symbol.

[0151] The first phase error characteristic estimation unit 315 estimates an approximate straight line representing the time characteristic of the average phase error based on the data of the average phase error in the interval of symbols #1 to #3, for example, by the least square method. The linear approximation representing the approximate straight line is interpolated in the interval of other symbols (symbol #0, symbols #4 to #13) and is set to a linear approximation covering the entire symbol interval (symbol #0 to symbol #13).

[0152] The first phase error correction unit 316 corrects the phase error for the entire symbol interval using a linear approximation equation extended over the entire symbol interval.

[0153] Thus, even when phase rotation occurs, the signal data included in a portion of the symbol interval including a predetermined reference symbol such as DMRS is data with higher reliability than other symbols due to the characteristics of the estimated phase error. Therefore, by estimating the time characteristics of the phase error using only such signal data and correcting the phase error based on the characteristics, the phase error of the demodulated signal can be effectively corrected with high accuracy. Furthermore, in the second stage correction unit 32A of the next stage, a more accurate ideal constellation signal can be generated.

[0154] The second data extraction unit 323 of the second-stage correction unit 32A extracts signal data corresponding to a predetermined ideal constellation point near the origin of the IQ plane from the demodulated constellation signal and the ideal constellation signal.

[0155] For example, Fig.11 As shown in FIG. 1 , the second data extraction unit 323 extracts the signal data corresponding to the four ideal constellation points closest to the origin of the IQ plane included in the E portion of the figure. It is considered that the ideal constellation corresponding to the signal data corresponding to the ideal constellation points near the origin of the IQ plane has a high probability of being normal, and has high reliability because the frequency characteristic or time characteristic of the phase error is obtained. In this embodiment, the frequency characteristic or time characteristic of the phase error is estimated using only the signal data corresponding to the ideal constellation points near the origin of the IQ plane with high reliability, and a rough correction of the phase error is performed.

[0156] In addition, in the case other than QAM, the coarse correction by the second stage correction unit 32A can be omitted. And, in the case of 16QAM or more, the coarse correction can be skipped for the symbols without constellations at the four locations. In the present embodiment, the phase error is calculated using only the subcarriers allocated to the four locations closest to the origin of the IQ plane. However, the ideal constellation points from which signal data is extracted are not limited to the four points closest to the origin of the IQ plane, and the 12 points, 16 points, etc. close to the origin of the IQ plane may be more than four points, or may be less than four points.

[0157] Next, refer to Fig.12 The phase error correction process will be described.

[0158] In the phase error correction unit 30A, the demodulation constellation signal acquisition unit 311 acquires the OFDM demodulation signal f from the subcarrier demodulation unit 22 of the demodulation unit 20 as a “demodulation constellation signal” and stores it (step S30 ).

[0159] The first ideal constellation signal generator 312 generates an ideal constellation signal from the demodulated constellation signal (step S31 ).

[0160] The first data extraction unit 313A extracts signal data corresponding to the DMRS symbol and the symbols adjacent to the left and right thereof from the demodulated constellation signal and the ideal constellation signal (step S32).

[0161] The first phase error calculation unit 314 calculates a phase error with respect to signal data extracted from the demodulated constellation signal and the ideal constellation signal (step S33 ).

[0162] The first phase error characteristic estimation unit 315 estimates an approximate straight line representing the time characteristic of the phase error based on the phase error data of a part of the symbol interval calculated by the first phase error calculation unit 314 (step S34). The approximate straight line is a linear approximation formula that interpolates the interval outside the part of the symbol interval and defines the entire symbol interval.

[0163] The first phase error correction unit 316 corrects the phase error of the demodulated constellation signal in the entire symbol interval using a linear approximation formula representing the approximate straight line estimated by the first phase error characteristic estimation unit 315 (step S35).

[0164] Next, the second ideal constellation signal generator 322 generates an ideal constellation signal again from the corrected demodulated constellation signal (step S36).

[0165] The second data extraction unit 323 extracts signal data corresponding to four ideal constellation points near the origin of the IQ plane from the demodulated constellation signal and the ideal constellation signal (step S37).

[0166] The second phase error calculation unit 324 calculates a phase error with respect to signal data extracted from the demodulated constellation signal and the ideal constellation signal (step S38 ).

[0167] The second phase error characteristic estimation unit 325 estimates an approximate straight line indicating the frequency characteristic or time characteristic of the phase error based on the data of the phase error calculated by the second phase error calculation unit 324 (step S39). If the relationship between the signal data extracted by the second data extraction unit 323 and the subcarriers of the signal data is taken into consideration, the frequency characteristic of the phase error is obtained. Furthermore, if the relationship between the signal data extracted by the second data extraction unit 323 and the symbol to which the signal data belongs is taken into consideration, the time characteristic of the phase error is obtained. The approximate straight line is set as a first-order approximation formula with the entire interval as the definition area.

[0168] The second phase error correction unit 326 corrects the phase error of the demodulated constellation signal in the entire interval using the first-order approximation obtained by the second phase error characteristic estimation unit 325 (step S40).

[0169] Next, the third ideal constellation signal generator 332 generates an ideal constellation signal again from the corrected demodulated constellation signal (step S41 ).

[0170] The third phase error calculation unit 334 calculates the phase error from the corrected demodulated constellation signal and the ideal constellation signal in the entire interval (step S42).

[0171] The third phase error characteristic estimation unit 335 estimates an approximate straight line indicating the frequency characteristic of the phase error based on the data of the phase error calculated by the third phase error calculation unit 334 (step S43 ).

[0172] The third phase error correction unit 336 corrects the phase error of the demodulated constellation signal in the entire interval using the approximate straight line obtained by the third phase error characteristic estimation unit 335 (step S44).

[0173] The demodulated constellation signal whose phase error has been corrected by the third phase error correcting unit 336 is sent to the analyzing unit 40 as a phase error corrected OFDM demodulated signal s.

[0174] Thus, even when phase rotation occurs, the signal data corresponding to the four ideal constellation points near the origin of the IQ plane have a high probability that the ideal constellation is normal and have a higher reliability than other constellation points due to the characteristics of determining the phase error. Therefore, by estimating the frequency characteristics or time characteristics of the phase error using only such signal data and correcting the phase error based on the characteristics, the phase error of the demodulated signal can be effectively corrected with high accuracy.

[0175] Furthermore, after the first stage correction unit 31A performs rough correction of the phase error using only the signal data included in a part of the symbol interval including the known reference symbol, the second stage correction unit 32A performs rough correction of the phase error using only the signal data corresponding to the ideal constellation point near the origin of the IQ plane. In this way, by performing rough correction of the phase error in two stages using different methods, the ideal constellation point can be obtained more accurately, thereby making it possible to effectively correct the phase error of the demodulated signal with higher accuracy.

[0176] In the above description, in the first stage correction unit 31A that performs the rough correction of the phase error, the signal data included in a part of the symbol interval including the known reference symbol in the entire symbol interval is extracted from the demodulated constellation signal and the ideal constellation signal, but the present invention is not limited to this structure. In the first stage correction unit 31A, the signal data corresponding to the predetermined ideal constellation point near the origin of the IQ plane can be extracted from the demodulated constellation signal and the ideal constellation signal. In this case, in the second stage correction unit 32A that performs the rough correction of the phase error from a different point of view from the first stage correction unit 31A, the signal data included in a part of the symbol interval including the known reference symbol in the entire symbol interval can be extracted from the demodulated constellation signal and the ideal constellation signal.

[0177] Furthermore, the phase error correction unit 30A of the present embodiment includes a first-stage correction unit 31A that performs a rough correction of the phase error, a second-stage correction unit 32A that performs a rough correction of the phase error from a different point of view from the first-stage correction unit 31A, and a third-stage correction unit 33A that performs a main correction of the phase error, but the present embodiment is not limited to this configuration. The configuration may be such that either or both of the second-stage correction unit 32A and the third-stage correction unit 33A are omitted, or either or both of the first-stage correction unit 31A and the third-stage correction unit 33A are omitted.

[0178] (Third embodiment)

[0179] Next, a receiving device and a mobile terminal testing device according to a third embodiment of the present invention will be described with reference to the drawings.

[0180] like Fig.13 As shown, the receiving device and mobile terminal test device according to this embodiment differ from the second embodiment in that a fourth stage correction unit 34B is added to the phase error correction unit 30B. The same reference numerals are used for the same configurations as those in the first and second embodiments, and detailed descriptions thereof are omitted as appropriate.

[0181] Specifically, the phase error correction unit 30B according to the present embodiment includes a first-stage correction unit 31A for performing a rough correction of the phase error, a second-stage correction unit 32A for performing a rough correction of the phase error, and a third-stage correction unit 33A for performing a main correction of the phase error, and further includes a fourth-stage correction unit 34B for performing a rough correction of the phase error from another point of view. In addition, the third-stage correction unit 33A and the fourth-stage correction unit 34B of the present embodiment correspond to the fourth correction unit and the fifth correction unit of the present invention, respectively.

[0182] The fourth-segment correction section 34B includes a fourth ideal constellation signal generation section 342 , a fourth data extraction section 343 , a fourth phase error calculation section 344 , a fourth phase error characteristic estimation section 345 , and a fourth phase error correction section 346 .

[0183] The fourth ideal constellation signal generating unit 342 generates an ideal constellation signal again from the demodulated constellation signal whose phase error has been corrected by the third-stage correcting unit 33A.

[0184] The fourth data extraction unit 343 extracts signal data corresponding to a symbol having an EVM smaller than a predetermined reference value from the demodulated constellation signal whose phase error is corrected by the third phase error correction unit 336 and the ideal constellation signal generated by the fourth ideal constellation signal generation unit 342.

[0185] Specifically, the fourth data extraction unit 343 calculates the EVM of each symbol of the acquired demodulated constellation signal. Fig.14 (a) is an example of a graph showing the calculated EVM. Fig.14 (a) It can be seen that the EVM of symbols #1, #8, #10, #13, and #14 is larger than the EVM of other symbols, and it is considered that the phase error correction effect of these symbols is not good.

[0186] Fig.14 (b) A graph showing the phase error of the demodulated constellation signal. It can be seen that the time characteristics of the phase error deviate from the linear trend in symbols #1, #8, #10, #13, and #14. If the characteristics of the phase error are estimated using the signal data of these symbols, it may not be possible to obtain accurate characteristics.

[0187] Therefore, in this example, 1.0% is set as the reference value of EVM, and symbols #1, #8, #10, #13, and #14 are excluded. Specifically, the fourth data extraction unit 343 extracts signal data corresponding to symbols #2, #3, #4, #5, #6, #7, #9, #11, and #12 having EVMs less than the reference value.

[0188] Fig.14 (c) is a graph showing phase errors when signal data corresponding to symbols #2, #3, #4, #5, #6, #7, #9, #11, and #12 are used. Fig.14 Compared with (b), the linear time characteristic of the phase error becomes clear.

[0189] The fourth phase error calculation unit 344 calculates a phase error of the demodulated constellation signal with respect to the ideal constellation signal, with respect to the signal data extracted by the fourth data extraction unit 343 .

[0190] The fourth phase error characteristic estimation unit 345 estimates the time characteristic of the phase error based on the calculated phase error.

[0191] The fourth phase error correction unit 346 corrects the phase error of the demodulated constellation signal in the entire symbol interval for each symbol or each signal data according to the time characteristic of the phase error. Fig.15 : is a diagram showing the situation where the phase errors of symbols #1, #8, #10, #13, and #14 are corrected based on the approximate straight line L showing the time characteristics of the phase error. Fig.15 In the example, the phase error is corrected for symbols whose EVM is greater than the reference value, but the phase error can be corrected for all symbols according to the straight line L.

[0192] Next, refer to Fig.16 The phase error correction process will be described.

[0193] The process is the same as that of the second embodiment until the phase error of the demodulated constellation signal is corrected by the third phase error correcting unit 336. In the third embodiment, the fourth ideal constellation signal generating unit 342 generates an ideal constellation signal again from the corrected demodulated constellation signal (step S50).

[0194] Next, the fourth data extraction unit 343 calculates the EVM of each symbol from the corrected demodulated constellation signal and the ideal constellation signal. Then, the fourth data extraction unit 343 extracts signal data corresponding to symbols having an EVM smaller than a reference value from the corrected demodulated constellation signal and the ideal constellation signal (step S51).

[0195] The fourth phase error calculation unit 344 calculates a phase error for the extracted signal data (step S52). The fourth phase error calculation unit 344 may obtain an average of the phase errors (average phase error) for each symbol.

[0196] The fourth phase error characteristic estimation unit 345 obtains the time characteristic of the phase error from the phase error or the average phase error calculated by the fourth phase error calculation unit 344 (step S53). The time characteristic of the phase error is approximated by a straight line expressed by a linear equation.

[0197] Next, the fourth phase error correction unit 346 corrects the phase error of the demodulated constellation signal in the entire symbol interval for each symbol or each signal data using the first-order approximation obtained by the fourth phase error characteristic estimation unit 345 (step S54). The phase error of the demodulated constellation signal can be corrected for the symbols excluded by the fourth data extraction unit 343.

[0198] The demodulated constellation signal whose phase error has been corrected by the fourth phase error correcting unit 346 is sent to the analyzing unit 40 (C) as an OFDM demodulated signal s whose phase error has been corrected.

[0199] In this way, after the phase error correction is performed by the phase error correction unit 30A according to the second embodiment, the phase error characteristic is obtained using only the signal data corresponding to the symbol having an EVM smaller than the predetermined reference value, and the phase error is roughly corrected. In this way, the phase error correction is performed in multiple stages by different methods, so that a more accurate ideal constellation signal can be obtained, and thus the phase error of the demodulated signal can be corrected with higher accuracy. In this way, the abnormality of the phase error can be avoided.

[0200] Furthermore, in the third embodiment, a fifth correction unit having the same structure as the third correction unit 33A may be provided after the fourth correction unit 34B. In this way, after the phase error characteristic is obtained based on the EVM using only the symbols with high reliability and the phase error is roughly corrected, the phase error characteristic is obtained for the entire frequency range and the main correction of the phase error is performed, thereby making it possible to correct the phase error with high accuracy.

[0201] As described above, in the first embodiment, the correction units of (1) and (5) are used, in the second embodiment, the correction units of (2), (3), and (5) are used, and in the third embodiment, the correction units of (2), (3), (5), and (4) are used.

[0202] (1) a first stage correction unit 31 that obtains a phase error characteristic using only signal data included in a portion of the central frequency interval and applies the characteristic to the entire interval to perform a rough correction of the phase error,

[0203] (2) a first stage correction unit 31A that obtains a phase error characteristic using only signal data included in a known reference symbol and its left and right adjacent symbols, and applies the characteristic to the entire interval to perform a rough correction of the phase error,

[0204] (3) a second stage correction unit 32A that obtains a phase error characteristic using only signal data corresponding to four ideal constellation points near the origin of the IQ plane and applies the characteristic to the entire interval to perform a rough correction of the phase error,

[0205] (4) a fourth stage correction unit 34B that obtains a phase error characteristic using only signal data corresponding to a symbol having an EVM smaller than a predetermined reference value and applies the characteristic to the entire interval to perform a rough correction of the phase error,

[0206] (5) A second stage correction unit 32 that obtains a phase error characteristic using signal data of the entire interval and applies the characteristic to the entire interval to perform a main correction of the phase error. However, the present invention is not limited to the combination described in the above embodiment, and may be configured as an arbitrary combination including all or part of the correction units described in (1) to (5) above in an arbitrary order.

[0207] For example, the configuration may be as follows: the first stage correction section 31A may be used alone or in combination with other correction sections to obtain the phase error characteristic using only the signal data included in the known reference symbol and the symbols adjacent to the reference symbol, and apply the characteristic to the entire interval to perform a rough correction of the phase error. Also, the configuration may be as follows: the second stage correction section 32A may be used alone or in combination with other correction sections to obtain the phase error characteristic using only the signal data corresponding to, for example, four ideal constellation points near the origin of the IQ plane, and apply the characteristic to the entire interval to perform a rough correction of the phase error. Also, the configuration may be as follows: the fourth stage correction section 34B may be used alone or in combination with other correction sections to obtain the phase error characteristic using only the signal data corresponding to the symbol having an EVM less than a predetermined reference value, and apply the characteristic to the entire interval to perform a rough correction of the phase error.

[0208] As described above, the present invention has the effect of being able to effectively correct the phase error of a demodulated signal with high accuracy, and is useful in all receiving devices and receiving methods, and mobile terminal test devices including the receiving devices.

[0209] Explanation of symbols

[0210] 1-mobile terminal test device, 2-DUT (mobile communication terminal), 10-receiving unit, 11-down converter, 12-ADC, 13-orthogonal demodulation unit, 20-demodulation unit, 21-FFT unit, 22-subcarrier demodulation unit, 30, 30A, 30B-phase error correction unit, 31, 31A-first segment correction unit, 311-demodulation constellation signal acquisition unit, 312-first ideal constellation signal generation unit, 313-data Extraction unit, 313A-1st data extraction unit, 314-1st phase error calculation unit, 315-1st phase error characteristic estimation unit, 316-1st phase error correction unit, 32-2nd segment correction unit (2nd correction unit), 32A-2nd segment correction unit (3rd correction unit), 322-2nd ideal constellation signal generation unit, 323-2nd data extraction unit, 324-2nd phase error calculation unit, 325-2nd phase error characteristic estimation unit 326-second phase error correction unit, 33A-third segment correction unit (fourth correction unit), 332-third ideal constellation signal generation unit, 334-third phase error calculation unit, 335-third phase error characteristic estimation unit, 336-third phase error correction unit, 34B-fourth segment correction unit (fifth correction unit), 342-fourth ideal constellation signal generation unit, 343-fourth data extraction unit, 344-fourth phase error calculation unit Calculation unit, 345-the 4th phase error characteristic estimation unit, 346-the 4th phase error correction unit, 40-analysis unit, 50-display unit, 60-control unit, 70-operation unit, 100-receiving device, a-modulation signal, b-intermediate frequency signal, c-digital intermediate frequency signal, d-orthogonal demodulation signal, e-frequency domain signal, f-OFDM demodulation signal (demodulation constellation signal, demodulation signal), s-OFDM demodulation signal with corrected phase error.

Claims

1. A receiving device having a receiving unit (10) for receiving a modulated signal modulated in an orthogonal frequency division multiplexing (OFDM) manner from a mobile communication terminal (2), the receiving device comprising: A demodulation unit (20) demodulates the received modulated signal to obtain a demodulated constellation signal; An ideal constellation signal generating unit (312) generates an ideal constellation signal from the demodulated constellation signal; A data extraction unit (313) selects and extracts a portion of signal data from the demodulated constellation signal and the ideal constellation signal; A phase error calculation unit (314) calculates a phase error of the demodulated constellation signal relative to the ideal constellation signal with respect to the extracted signal data; A phase error characteristic estimation unit (315) estimates a frequency characteristic or a time characteristic of a phase error based on the calculated phase error; A phase error correction unit (316) corrects the phase error of the demodulated constellation signal according to the frequency characteristic or time characteristic of the estimated phase error; and a third correction unit (32A) for extracting signal data corresponding to a predetermined ideal constellation point near the origin of an IQ plane from the demodulated constellation signal whose phase error has been corrected by the phase error correction unit and an ideal constellation signal regenerated from the demodulated constellation signal whose phase error has been corrected, calculating a phase error of the demodulated constellation signal relative to the ideal constellation signal with respect to the extracted signal data, estimating a frequency characteristic or a time characteristic of the phase error based on the calculated phase error, and correcting the phase error of the demodulated constellation signal based on the estimated frequency characteristic or time characteristic of the phase error, The data extraction unit extracts signal data included in a portion of a symbol interval including a known reference symbol in the entire symbol interval from the demodulated constellation signal and the ideal constellation signal.

2. The receiving device according to claim 1, further comprising: A second correction unit (32) calculates a phase error between the demodulated constellation signal whose phase error has been corrected by the phase error correction unit and an ideal constellation signal regenerated from the demodulated constellation signal whose phase error has been corrected, estimates a frequency characteristic or a time characteristic of the phase error based on the calculated phase error, and corrects the phase error of the demodulated constellation signal based on the estimated frequency characteristic or time characteristic of the phase error.

3. The receiving device according to claim 1, further comprising: a fourth correction unit (33A) for calculating a phase error between the demodulated constellation signal whose phase error has been corrected by the third correction unit and an ideal constellation signal regenerated from the demodulated constellation signal whose phase error has been corrected, estimating a frequency characteristic or a time characteristic of the phase error based on the calculated phase error, and correcting the phase error of the demodulated constellation signal based on the estimated frequency characteristic or time characteristic of the phase error; and a fifth correction unit (34B) for extracting signal data corresponding to a symbol having an EVM smaller than a prescribed reference value from the demodulated constellation signal whose phase error has been corrected by the fourth correction unit and the ideal constellation signal regenerated from the demodulated constellation signal whose phase error has been corrected, calculating a phase error of the demodulated constellation signal relative to the ideal constellation signal with respect to the extracted signal data, estimating a frequency characteristic or a time characteristic of the phase error based on the calculated phase error, and correcting the phase error of the demodulated constellation signal based on the estimated frequency characteristic or time characteristic of the phase error.

4. A receiving device having a receiving unit (10) for receiving a modulated signal modulated in an orthogonal frequency division multiplexing (OFDM) manner from a mobile communication terminal (2), the receiving device comprising: A demodulation unit (20) demodulates the received modulated signal to obtain a demodulated constellation signal; An ideal constellation signal generating unit (312) generates an ideal constellation signal from the demodulated constellation signal; A data extraction unit (313) selects and extracts a portion of signal data from the demodulated constellation signal and the ideal constellation signal; A phase error calculation unit (314) calculates a phase error of the demodulated constellation signal relative to the ideal constellation signal with respect to the extracted signal data; A phase error characteristic estimation unit (315) estimates a frequency characteristic or a time characteristic of a phase error based on the calculated phase error; and A phase error correction unit (316) corrects the phase error of the demodulated constellation signal according to the estimated frequency characteristic or time characteristic of the phase error, The data extraction unit extracts signal data corresponding to a predetermined ideal constellation point near the origin of an IQ plane from the demodulated constellation signal and the ideal constellation signal.

5. A receiving device having a receiving unit (10) for receiving a modulated signal modulated by an orthogonal frequency division multiplexing (OFDM) method from a mobile communication terminal (2), the receiving device comprising: A demodulation unit (20) demodulates the received modulated signal to obtain a demodulated constellation signal; An ideal constellation signal generating unit (312) generates an ideal constellation signal from the demodulated constellation signal; A data extraction unit (313) selects and extracts a portion of signal data from the demodulated constellation signal and the ideal constellation signal; A phase error calculation unit (314) calculates a phase error of the demodulated constellation signal relative to the ideal constellation signal with respect to the extracted signal data; A phase error characteristic estimation unit (315) estimates a frequency characteristic or a time characteristic of a phase error based on the calculated phase error; and A phase error correction unit (316) corrects the phase error of the demodulated constellation signal according to the estimated frequency characteristic or time characteristic of the phase error, The data extraction unit extracts signal data corresponding to a symbol having an error vector magnitude (EVM) smaller than a predetermined reference value from the demodulated constellation signal and the ideal constellation signal.

6. A mobile terminal test device, comprising the receiving device (100) according to any one of claims 1 to 5, an analysis unit (40) for analyzing the demodulated constellation signal after the phase error correction, and a display unit (50) for displaying the analysis result performed by the analysis unit.

7. A receiving method, comprising a receiving step (S1) of receiving a modulated signal modulated in an orthogonal frequency division multiplexing (OFDM) manner from a mobile communication terminal (2), the receiving method comprising: Demodulation step (S4, S5), demodulating the received modulated signal to obtain a demodulated constellation signal; An ideal constellation signal generating step (S11), generating an ideal constellation signal from the demodulated constellation signal; A data extraction step (S12), selecting and extracting a portion of signal data from the demodulated constellation signal and the ideal constellation signal; a phase error calculation step (S13), calculating, with respect to the extracted signal data, a phase error of the demodulated constellation signal relative to the ideal constellation signal; a phase error characteristic estimation step (S14), estimating a frequency characteristic or a time characteristic of a phase error based on the calculated phase error; and a phase error correction step (S15), correcting the phase error of the demodulated constellation signal according to the estimated frequency characteristic or time characteristic of the phase error, In the data extraction step, signal data corresponding to a predetermined ideal constellation point near the origin of the IQ plane is extracted from the demodulated constellation signal and the ideal constellation signal.

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