JP2007243546A - Antenna calibration apparatus and antenna calibration method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce a circuit scale of an FFT calculation circuit in an antenna calibration apparatus in a wireless base station provided with an array antenna and using OFDM. <P>SOLUTION: Odd number (or even number) subcarriers or a part of them are used for an antenna calibration signal to reduce the circuit scale of the FFT calculation circuit. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a digital wireless communication system that transmits OFDM (Orthogonal Frequency Division Multiplexing) signals by a plurality of antenna elements, and in particular, fast Fourier transform (hereinafter referred to as FFT :) in a calibration signal receiving unit when performing antenna calibration. (Abbreviated to (Fast FourierTransform)).

  In recent years, the OFDM scheme has attracted attention as a large-capacity data transmission scheme in next-generation mobile radio communication systems and next-generation high-speed wireless LANs. OFDM is a type of multi-carrier transmission scheme that transmits information signals using a plurality of carrier waves (subcarriers), and has a feature that the subcarriers are orthogonal to each other on the frequency axis.

  In an OFDM communication system, transmission data is assigned to a plurality of subcarriers having a frequency relationship orthogonal to each other in a modulation device on the transmitter side, and subjected to fast discrete Fourier transform (IFFT). The demodulator of the receiver reproduces the original pre-transmission data by performing Fast Fourier Transform (FFT) which is the reverse process of the modulator side.

  An adaptive array antenna is an important technology for realizing a high-speed mobile communication system. This adaptive array antenna uses a plurality of antenna elements, weights the received signal appropriately and combines them to direct the main beam in the direction of arrival of the desired signal and form a directional zero in the direction of arrival of the interference signal The directivity can be controlled.

  In the adaptive array antenna as described above, in order to correctly generate a transmission / reception beam with a high-precision main beam / zero point with respect to the actual signal arrival direction of the desired wave / interference wave signal, an uplink (from the mobile station to the base station) is generated. The phase / amplitude deviation generated between the antenna elements of the RF transmission / reception circuit for the number of antennas in each of the transmission path toward the station) and the downlink (transmission path from the base station to the mobile station) It is necessary to perform calibration.

  FIG. 6 shows an antenna calibration apparatus in a conventional radio base station apparatus using an array antenna that performs OFDM transmission. The figure shows a calibration signal generator 701, an IFFT calculator 702, an antenna coefficient multiplier 703, a calibration coefficient multiplier 704, wireless transmitters 705 (1) to 705 (M) (M is an integer), a switch 706, and a combiner. 707, a wireless reception unit 708, an FFT calculation unit 711, and a calibration coefficient calculation unit 712.

  The calibration signal generation unit 701 generates an antenna calibration signal s701. The signal is a signal in which power exists only in a symbol number corresponding to a subcarrier number used for antenna calibration. The subcarriers to which power is allocated are selected so as to be distributed over a band range in which OFDM transmission is performed (so as not to be unevenly distributed in a specific frequency region). Further, the symbols to which power is allocated are subjected to modulation such as spreading / QPSK and input to IFFT calculation section 702.

  IFFT calculation section 702 performs IFFT calculation, and inputs it to antenna coefficient multiplication section 703 as signal s 702 in which power exists in the subcarrier number corresponding to the symbol number to which power is allocated by calibration signal generation section 701.

  The antenna coefficient multiplier 703 has a function of generating signals s703 (1) to s703 (M) obtained by branching the input signal s702 into M signals and then multiplying each of the M signals by the antenna coefficient. However, at the time of antenna calibration, the antenna calibration signal is set by setting 1 + j × 0 (j is an imaginary unit) only to the antenna coefficient corresponding to the number of the antenna to which the input signal is output, and setting other antenna coefficients to zero. Is selected from 705 (1) to 705 (M).

  The calibration coefficient multiplier 704 receives antenna calibration coefficients s713 (1) to s713 (M) from the calibration coefficient calculator 712, which are independent of the calibration coefficient multiplier input signals s703 (1) to s703 (M). Is multiplied by However, in the stage before the antenna calibration is performed, instead of the antenna calibration coefficients s713 (1) to s713 (M), the initial value 1 + j × 0 of the multiplication coefficient is multiplied to each of s703 (1) to s703 (M). The The multiplication results are s704 (1) to s704 (M) and transmitted to the wireless transmission units 705 (1) to 705 (M).

  The wireless transmission units 705 (1) to 705 (M) have a function of converting a baseband signal into an RF band signal for each antenna element, and output signals s705 (1) to 705 (M) of the wireless transmission unit. Is input to the switch 706. The switch 706 includes output lines s706 (i) (i is 1 to M) and s707 (i), and the input signal s705 (i) is sent to either the line s706 (i) or the line s707 (i). It has a function to switch. The switch 706 switches to send the input signal s705 (i) to the line s707 (i) when the antenna is calibrated, and switches to send the input signal s705 (i) to the line s706 (i) when not calibrating the antenna. Transmit to element i.

  The switch 706 is connected so that the output signals of the wireless transmitters 705 (1) to 705 (M) are input to the combiner 707 during antenna calibration. The combiner 707 has a function of combining M RF band input signals, and the combined signal s708 is converted into a baseband signal s711 by the wireless reception unit 708.

  The FFT calculation unit 711 receives the baseband signal s711 output from the wireless reception unit 708, performs an FFT calculation, and outputs the result as a signal s712 to the calibration coefficient calculation unit 712. The output signal s712 of the FFT calculator 711 is a reproduction of the output signal of the calibration signal generator 701. The calibration signal generation unit 712 performs despreading / demodulation corresponding to the spreading / modulation performed by the calibration signal generation unit 701, calculates the channel estimation value of each subcarrier, and performs antenna calibration coefficients s713 (1) ˜ The result is output to the calibration coefficient multiplier 704 as s713 (M).

  The above procedure is performed independently for each antenna. That is, the antenna coefficient multiplication unit 703 sequentially sets 1 + j × 0 as the antenna coefficient corresponding to each antenna so that the destination of the antenna calibration signal is the wireless transmission unit 705 (1) to 705 (M) (see above). An antenna coefficient for which no value is set is set to 0), and a channel estimation value E (i) corresponding to each of the wireless transmission units 705 (1) to 705 (M) is obtained. Thereafter, the antenna calibration coefficient s713 (i) of the antenna i is obtained by E (1) / E (i), and the antenna calibration coefficient is set to the calibration coefficient multiplier 704 as s713 (i) in FIG.

  In operation, the radio base station sets an antenna coefficient for a beam pattern to be formed on the antenna coefficient, and a calibration coefficient multiplier for the signals s703 (1) to s103 (M) after the antenna coefficient is multiplied. In 104, the antenna calibration coefficients s713 (1) to s713 (M) are multiplied.

An apparatus for transmitting / receiving an antenna calibration signal in a radio base station apparatus as described above is disclosed in, for example, Japanese Patent Application Laid-Open No. 2005-348235. This document discloses an apparatus capable of calibrating an array antenna even when OFDM is applied to a downlink modulation scheme and the uplink is not OFDM. However, in this document, there is no detailed mention of a fast Fourier transform unit (FFT unit) used when obtaining a calibration value from a reference signal.
JP 2005-348235 A

  As described above, in a system using an array antenna in a base station, it is necessary to provide means for obtaining a calibration (calibration) coefficient from a reference signal for antenna calibration in the base station. In addition, when OFDM is used as a downlink modulation scheme, it is necessary to provide FFT calculation means in the base station as means for obtaining the antenna calibration coefficient.

  However, when OFDM is used as the downlink modulation scheme, it is burdensome to prepare an FFT circuit in the base station apparatus only for antenna calibration in terms of circuit scale. The reason why this becomes a problem is that the base station already has an IFFT (inverse FFT) circuit for generating a downlink OFDM signal, and in addition, an FFT circuit for antenna calibration of the same scale is prepared. Because.

  Further, if only one to several subcarriers are performed at a time by general DFT calculation instead of parallel calculation like antenna calibration FFT, the circuit scale can be relatively small. . However, in this case, when the number of subcarriers to be transmitted is determined at the time of calibration (when the OFDM transmission band is wide and it is determined to cover the whole with an appropriate interval), the subcarriers to be calculated are sequentially set. Since the DFT results are calculated one by one while switching, the problem is that the time required for antenna calibration becomes longer. The reason why this becomes a problem is that the antenna calibration needs to be performed as short as possible because the antenna calibration is performed during the original operation time.

  The present invention has been made in view of the above problems, and the circuit scale of a base station apparatus for antenna calibration while maintaining the time required for antenna calibration with almost no deterioration in the accuracy of antenna calibration. It aims at simplifying.

In order to solve the above-described problems, the present invention provides an antenna calibration apparatus and an antenna for a radio base station apparatus using OFDM, each comprising an array antenna composed of a plurality of antenna elements. In the calibration method,
As a means for sending only a part of subcarriers used for OFDM transmission as an antenna calibration signal to each radio transmission unit and performing FFT calculation on the output signal of the radio reception unit, the subcarrier included in the antenna calibration signal is used. Only the carrier is subjected to FFT calculation.

According to claims 2 and 4 of the present invention, in the antenna calibration apparatus and the antenna calibration method,
In particular, the subcarrier included in the antenna calibration signal is an even-numbered subcarrier or a part thereof (or an odd-numbered subcarrier or a part thereof).

  The reason why the effects of the present invention can be obtained will be described below with reference to FIGS.

  Formula (1) shows the definition formula for DFT calculation.

  In the equation (1), F (n) corresponds to the baseband signal output from the wireless reception unit s711 in FIG. 6 of the prior art, and f (n) corresponds to the output signal s712 of the FFT calculation unit 711 ( n = 0,..., N). W (m) is a complex number called a twiddle factor, and F (n) is multiplied by a complex number corresponding to the rotation amount determined by m.

  Next, in the case of N = 8, FIG. 3 shows a circuit configuration of the FFT for calculating the equation (1). The FFT performs the same calculation as the DFT, but saves the number of calculations by using the periodicity of the trigonometric function when the size to be calculated (N below) is a power of 2. In FIG. 3, F (0) to F (7) arranged in the vertical direction at the left end are FFT calculation target data, and these are areas (memory) in which F (0) + W (0) F (4) etc. are written by line segments. ).

  In contrast, first, butterfly calculation is performed in the section from the start point to the end point of the arrow indicated as FFT1. For example, the line segment connecting F (0) and F (0) + W (0) F (4) in FFT1 indicates that F (0) is transmitted as it is to the right, and F (4) and F ( (0) + W (0) F (4) connecting line segments (indicated by 0) indicate that they are transmitted rightward after being multiplied by W (0).

  The two line segments merge at the left of F (0) + W (0) F (4), and the merge indicates addition. Thus, in FFT1, F (0) + W (0) F (4) -F (3) + W (4) F (7) is calculated based on F (0) -F (7) and stored in the memory. Stored. Similarly, butterfly computation is performed in the order of FFT2 and FFT3, and FFT results f (0) to f (7) shown in the following equation (2) are calculated. In FIG. 3, √N for normalization existing in the equation (1) is omitted.

  FIG. 4 is a circuit that calculates only odd-numbered FFT operation results f (n), n = 1, 3, 5, and 7 among the circuits shown in FIG. When performing an odd-number FFT calculation, the number of multiplications and additions of the twiddle factors are reduced by half in each of the butterfly operations FFT4, FFT5, and FFT6 as compared to FFT1, FFT2, and FFT3, as shown in FIG. It can be seen that the amount of memory for storing the results is also halved. Similarly, when only f (n) where n is an even number is calculated, the circuit scale is halved.

  In the antenna calibration signal, it is not always necessary to calculate channel estimation values for all subcarriers used during data transmission (during normal operation other than during antenna calibration), and in the frequency band occupied by the OFDM signal, It is considered that the subcarrier position should be selected so that the subcarrier position is not unevenly distributed. For example, it is sufficient to use only odd-numbered subcarriers.

  On the other hand, even when the result obtained as the FFT calculation result is smaller (for example, when only f (1) and f (5) are obtained in FIG. 3), the butterfly operation performs a partial multiplication and addition in FFT3. The circuit reduction effect is not great.

As described above, in the antenna calibration apparatus of the base station apparatus having an array antenna and using OFDM, the present invention limits the subcarrier used for the antenna calibration signal to a specific subcarrier, thereby reducing the circuit scale of the FFT calculation means. Can be halved.

  Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a configuration of an embodiment of a calibration apparatus in a radio base station apparatus using an array antenna for performing OFDM transmission according to the present invention.

  In the present embodiment, a calibration signal generation unit 101, an IFFT calculation unit 102, an antenna coefficient multiplication unit 103, a calibration coefficient multiplication unit 104, a wireless transmission unit 105, a distributor 106, a combiner 107, a wireless reception unit 108, and an FFT calculation unit 111 The calibration coefficient calculation unit 112 is configured. These components are the calibration signal generator 701, IFFT calculator 702, antenna coefficient multiplier 703, calibration coefficient multiplier 704, wireless transmitter 705, distributor 706, combiner 707, and wireless receiver 708 shown in FIG. , The same configuration as the FFT calculation unit 711 and the calibration coefficient calculation unit 712 may be used.

  However, the calibration signal generation unit 101 is different from the conventional example in that the antenna configuration signal s101 transmits a signal in which power exists only in odd-numbered symbols in the time domain. As a result, the output signal s102 of the IFFT calculation unit 102 is a signal in which power exists only in odd-numbered subcarriers. Other functions of the calibration signal generation unit 101, that is, spreading, modulation, and the like may be the same as those in the conventional art.

  FIG. 5 shows a signal in which power exists only in odd-numbered subcarriers. In FIG. 5, the solid line is a subcarrier in which power exists, and indicates in which position in the frequency direction each subcarrier of numbers # 1, # 3,..., # N−1 appears. FFT size). As shown in FIG. 5, if only odd-numbered subcarriers are used, subcarriers can be arranged over the entire band of the transmission signal, but a signal from which subcarriers are further deleted than this state may be used for the antenna calibration signal. Conceivable. However, as the number of subcarriers used for the calibration signal is decreased, the frequency characteristics of the wireless transmission unit within the transmission band are less likely to be reflected in the antenna calibration coefficient. It is necessary to secure a certain number.

  Further, the antenna calibration signal may be generated so that power exists in even-numbered subcarriers.

  In FIG. 1, the antenna calibration signal s <b> 102 after IFFT calculation is input to the antenna coefficient multiplier 103. The antenna coefficient multiplication unit 103 has a function of branching the input signal s102 into M and then multiplying each of the M signals by an antenna coefficient. However, at the time of antenna calibration, a wireless transmission unit that outputs an antenna calibration signal by setting 1 + j × 0 to only the antenna coefficient corresponding to the number of the antenna to which the input signal is output and setting 0 to the other antenna coefficients Are selected from 105 (1) to 105 (M).

  The calibration coefficient multiplier 104 receives antenna calibration coefficients s113 (1) to s113 (M) from the calibration coefficient calculator 112, and these are independent of the calibration coefficient multiplier input signals s113 (1) to s113 (M). Is multiplied by However, in the stage before the antenna calibration is performed, instead of the antenna calibration coefficients s113 (1) to s113 (M), the initial value 1 + j × 0 of the multiplication coefficient is multiplied to each of s113 (1) to s113 (M). The The multiplication results are s104 (1) to s104 (M) and transmitted to the wireless transmission units 105 (1) to 105 (M).

  The wireless transmission units 105 (1) to 105 (M) have a function of converting a baseband signal into an RF band signal for each antenna element, and output signals s105 (1) to 105 (M) of the wireless transmission unit. Is input to the switch 106. The switch 106 has a function of switching the input signal s105 (i) to one of the lines s106 (i) or s107 (i). The switch 106 switches so that s105 (i) is sent to the s107 (i) side at the time of antenna calibration, and transmits it toward the switching antenna element i so that s105 (i) is sent to s106 (i) at times other than the time of antenna calibration. (I = 1,..., M).

  The switch 106 is connected so that the output signals of the wireless transmission units 105 (1) to 105 (M) are input to the combiner 107. The combiner 107 has a function of combining input signals of M RF bands, and the combined signal s108 is converted into a baseband signal s111 by the wireless reception unit 108.

  The antenna coefficient multiplier 103 to the wireless receiver 108 are configured in the same manner as in the conventional example.

  The FFT calculation unit 111 has a function of performing an FFT calculation using the baseband signal s111 output from the wireless reception unit 108 as an input and outputting the calculation result s112 to the calibration coefficient calculation unit 112. The FFT calculation circuit used here is illustrated in FIG. 4, that is, a circuit that outputs only the FFT calculation result of odd-numbered subcarriers. As a result, the circuit scale and power consumption of the FFT calculation unit 111 are halved compared to the conventional FFT calculation circuit shown in FIG.

  The calibration signal generation unit 112 performs despreading / demodulation spread corresponding to the spreading / modulation performed by the calibration signal generation unit 101, and then calculates the channel estimation value of each subcarrier.

  The above procedure is performed independently for each antenna. That is, the antenna coefficient multiplier 103 sequentially switches the non-zero antenna coefficient setting position so that the destination of the antenna calibration signal is each of the wireless transmitters 105 (1) to 105 (M), and each wireless transmitter 105 (1). Channel estimation values E (1) to E (M) of signals that have passed through 105 (M) are obtained. After that, the antenna calibration coefficient s113 (i) = E (1) / E (i) of the antenna i is obtained and set to the calibration coefficient multiplication unit 104 as s113 (i) in FIG.

  When the antenna calibration is completed, the operation of the base station apparatus is switched to the operation at the time of operation. In operation at the time of operation, a transmission data signal is input to IFFT calculation section 102, and an antenna coefficient corresponding to the beam pattern to be formed is set as the antenna coefficient of antenna coefficient multiplication section 103. In the antenna coefficient multiplication unit, the transmission data signal is multiplied by the antenna coefficient for each antenna, and after multiplication, s103 (1) to s103 (M) in FIG. 1 are input to the calibration coefficient multiplication unit 104.

  The calibration coefficient multiplication unit 104 multiplies s103 (i) by the antenna calibration coefficient s113 (i) obtained at the time of antenna calibration to obtain s104 (i), which is sent to the wireless transmission unit 105 (i). When the switching unit 106 is in operation, s105 (i) is connected to s106 (i), and the wireless transmission unit output signal 105 (i) is transmitted from the antenna i (i = 1,..., M).

  Next, the operation of the apparatus of the present invention will be described with reference to FIG. 1 and FIG.

  FIG. 2 is a diagram illustrating the IFFT calculation unit output signal s101s, the setting of the antenna coefficient multiplication unit 103, the connection state of the switch 106, and the output timing of the antenna calibration coefficient s113 (i) to the calibration coefficient multiplication unit 104.

  When the antenna calibration is started at time T (1) in FIG. 2, the calibration signal generation unit 101 starts outputting the antenna calibration signal s101. At the same time, the antenna coefficient multiplier 103 sets the antenna coefficient 1 + j0 (j is an imaginary unit) only for the antenna 1, and sets 0 for the other antenna coefficients. This setting is continued for one frame (data unit length of the wireless section). The switch 106 switches the connection so that the input signal s105 (i) is connected to s107 (i) at T (1) (i = 1,..., M).

  After time T (2), the IFFT calculation unit input signal s101 repeatedly outputs the same signal with a period of one frame. The antenna coefficient multiplier sets the antenna coefficient 1 + j × 0 in order to the antenna coefficients for the antennas 2, 3,..., M in order for each frame, and sets 0 to the other antenna coefficients. As a result, the calibration coefficient calculation unit 112 immediately after the end of the antenna 1 calibration section (time from T (i) to T (i + 1)) immediately after the FFT calculation on the signal that has passed through the transmission unit of the antenna i. # 1, # 3,..., # N-1 are input (i = 2,..., M).

  The calibration coefficient calculator 112 demodulates and despreads all subcarrier signals to calculate a channel estimation value. With respect to the channel estimation value, the channel estimation value for all of the N / 2 subcarriers may be calculated, but only for the subcarriers of some frequencies selected to cover the entire transmission signal band. On the other hand, a channel estimation value obtained from the subcarrier may be calculated. Next, the calibration coefficient calculation unit 112 obtains an average for the channel estimation value of each subcarrier, and holds it as channel estimation values E (i), i = 1,. To do.

  When the calculation of channel estimation values for all antennas is completed at time T (M), the antenna calibration coefficient of antenna i is obtained by s113 (i) = E (1) / E (i). The antenna calibration coefficient is sent to the calibration coefficient multiplier 104 and set as a multiplication coefficient for s103 (i) (i = 1,..., M).

The block diagram which shows the structure of the antenna calibration apparatus by this invention. The figure which shows operation | movement of the antenna calibration apparatus in embodiment of this invention. The figure which shows the conventional FFT calculation circuit. The figure which shows the FFT calculation circuit in embodiment of this invention. The figure which shows the subcarrier of the antenna calibration signal in embodiment of this invention. The block diagram which shows the structure of the conventional antenna calibration apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Calibration signal production | generation part 102 IFFT calculation part 103 Antenna coefficient multiplication part 104 Calibration coefficient multiplication part 105 (1) -105 (M) Wireless transmission part 106 Switcher 107 Synthesizer 108 Radio reception part 111 FFT calculation part 112 Calibration coefficient calculation part

Claims (4)

In an antenna calibration apparatus comprising a radio base station apparatus comprising an array antenna composed of a plurality of antenna elements and performing communication by OFDM,
Antenna calibration signal generation means for generating an antenna calibration signal in which power exists only in the symbol number used for antenna calibration;
IFFT means for performing inverse fast Fourier transform on the antenna calibration signal;
Antenna coefficient multiplication means for branching an inverse fast Fourier transform result by the IFFT means into signals corresponding to the number of the plurality of antenna elements and multiplying each signal by an antenna coefficient;
Calibration coefficient multiplication means for outputting a signal based on the output of the antenna coefficient multiplication means to any one of the plurality of antenna elements;
A radio transmission unit that is provided corresponding to the plurality of antenna elements, and that converts the calibration coefficient multiplication means output to an RF band and transmits it to a corresponding antenna;
Signal combining means for combining all output signals of each wireless transmission unit into an antenna combined signal;
A radio receiver for converting the antenna combined signal into a baseband signal;
FFT means for performing a fast Fourier transform on the radio receiver output signal;
An antenna calibration coefficient calculation means for calculating an antenna calibration coefficient from a discrete fast Fourier transform result by the FFT means;
With
The calibration coefficient multiplying unit multiplies the antenna calibration coefficient by the inverse fast Fourier transform result by the IFFT unit and outputs the result to any one of the wireless transmission units.
The antenna calibration signal generation means transmits only some of the subcarriers that can be transmitted by the radio base station, and the FFT means performs fast Fourier transform only on the subcarriers included in the antenna calibration signal. An antenna calibration apparatus characterized by the above. The antenna calibration apparatus according to claim 1,
An antenna calibration apparatus, wherein a subcarrier included in an antenna calibration signal is an even-numbered subcarrier or a part thereof, or an odd-numbered subcarrier or a part thereof. In an antenna calibration method performed in a radio base station apparatus that includes an array antenna including a plurality of antenna elements and performs communication by OFDM,
An antenna calibration signal generating step for generating an antenna calibration signal in which power exists only in the symbol number used for antenna calibration;
IFFT step for performing inverse fast Fourier transform on the antenna calibration signal;
An antenna coefficient multiplication step of branching the inverse fast Fourier transform result by the IFFT means into signals corresponding to the number of the plurality of antenna elements and multiplying each signal by an antenna coefficient;
A calibration coefficient multiplication step for outputting a signal based on the multiplication result in the antenna coefficient multiplication step to any one of the plurality of antenna elements;
A radio transmission step of converting the baseband signal obtained by the calibration coefficient multiplication step into an RF band and transmitting it to each antenna;
A signal synthesis step of synthesizing all output signals of each wireless transmission unit into an antenna synthesized signal;
A radio reception step of converting the antenna combined signal into a baseband signal;
An FFT step of performing a fast Fourier transform on the wireless receiver output signal;
An antenna calibration coefficient calculation step for calculating an antenna calibration coefficient from a discrete fast Fourier transform result by the FFT means;
With
In the antenna selection step, an inverse fast discrete Fourier transform result in the IFFT step is multiplied by the antenna calibration coefficient,
In the calibration coefficient multiplication step, only some of the subcarriers that can be transmitted by the radio base station are transmitted, and in the FFT step, only the subcarriers included in the antenna calibration signal are subjected to discrete fast Fourier transform. An antenna calibration method characterized by the above. In the antenna calibration method according to claim 3,
An antenna calibration method, wherein the subcarrier included in the antenna calibration signal is an even-numbered subcarrier or a part thereof, or an odd-numbered subcarrier or a part thereof.

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