Patent Publication Number: US-11050495-B2

Title: Electronic device including transceiver for calibrating I/Q imbalance in millimeter wave communication system and method of operating same

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application is based on and claims priority under 35 U.S.C. § 119(e) of a U.S. Provisional application Ser. No. 62/875,616, filed on Jul. 18, 2019, in the U.S. Patent and Trademark Office, the disclosure of which is incorporated by reference herein in its entirety. 
    
    
     BACKGROUND 
     1. Field 
     The disclosure relates to a wireless communication system. More specifically, the disclosure relates to an electronic device including an ultra-wideband transceiver for calibrating I/Q imbalance in a 5th-Generation (5 G) communication system using millimeter waves (mmWave) and a method of operating the same. 
     2. Description of Related Art 
     To meet the demand for wireless data traffic having increased since deployment of 4th-Generation (4 G) communication systems, efforts have been made to develop an improved 5th-Generation (5 G) or pre-5 G communication system. Therefore, the 5 G or pre-5 G communication system is also called a ‘Beyond 4 G Network’ or a ‘Post Long Term Evolution (LTE) System’. The 5 G communication system is considered to be implemented in higher frequency (mmWave) bands, e.g., 60 gigahertz (GHz) bands, so as to accomplish higher data rates. To decrease propagation loss of the radio waves and increase the transmission distance, the beamforming, massive multiple-input multiple-output (MIMO), Full Dimensional MIMO (FD-MIMO), array antenna, an analog beam forming, large scale antenna techniques are discussed in 5 G communication systems. In addition, in 5 G communication systems, development for system network improvement is under way based on advanced small cells, cloud Radio Access Networks (RANs), ultra-dense networks, device-to-device (D2D) communication, wireless backhaul, moving network, cooperative communication, Coordinated Multi-Points (CoMP), reception-end interference cancellation and the like. In the 5 G system, Hybrid Frequency Shift Keying (FSK) and Quadrature Amplitude Modulation (QAM) (FQAM) and sliding window superposition coding (SWSC) as an advanced coding modulation (ACM), and filter bank multi carrier (FBMC), non-orthogonal multiple access (NOMA), and sparse code multiple access (SCMA) as an advanced access technology have been developed. 
     The Internet, which is a human centered connectivity network where humans generate and consume information, is now evolving to the Internet of Things (IoT) where distributed entities, such as things, exchange and process information without human intervention. The Internet of Everything (IoE), which is a combination of the IoT technology and the Big Data processing technology through connection with a cloud server, has emerged. As technology elements, such as “sensing technology”, “wired/wireless communication and network infrastructure”, “service interface technology”, and “Security technology” have been demanded for IoT implementation, a sensor network, a Machine-to-Machine (M2M) communication, Machine Type Communication (MTC), and so forth have been recently researched. Such an IoT environment may provide intelligent Internet technology services that create a new value to human life by collecting and analyzing data generated among connected things. IoT may be applied to a variety of fields including smart home, smart building, smart city, smart car or connected cars, smart grid, health care, smart appliances and advanced medical services through convergence and combination between existing Information Technology (IT) and various industrial applications. 
     In line with this, various attempts have been made to apply 5 G communication systems to IoT networks. For example, technologies, such as a sensor network, Machine Type Communication (MTC), and Machine-to-Machine (M2M) communication may be implemented by beamforming, MIMO, and array antennas. Application of a cloud Radio Access Network (RAN) as the above-described Big Data processing technology may also be considered to be as an example of convergence between the 5 G technology and the IoT technology. 
     The above information is presented as background information only to assist with an understanding of the disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the disclosure. 
     SUMMARY 
     Aspects of the disclosure are to address at least the above-mentioned problems and/or disadvantages and to provide at least the advantages described below. Accordingly, as aspect of the disclosure is to provide a transceiver having a loopback hardware structure for calibrating transceiver I/Q imbalance in a wireless communication system. 
     Another aspect of the disclosure is to provide a method of calibrating transceiver I/Q imbalance through a transceiver having a loopback hardware structure in a wireless communication system. 
     Additional aspects will be set forth in part in the description which follows and, in part, will be apparent from the description, or may be learned by practice of the presented embodiments. 
     In accordance with an aspect of the disclosure, a method of operating an electronic device in a wireless communication system is provided. The method includes inputting training signals into a first loopback route and a second loopback route, determining a loopback gain and a loopback phase, based on a first training signal passing through the first loopback route and a second training signal passing through the second loopback route, determining a frequency domain compensation filter, based on the loopback gain and the loopback phase, determining a finite impulse response (FIR) filter and a direct current (DC) offset, based on the frequency domain compensation filter, and compensating for a transmission signal and a reception signal, based on the FIR filter and the DC offset. The training signals are determined based on a phase of a first training signal and a phase of a second training signal. 
     In accordance with another aspect of the disclosure, an electronic device is provided. The electronic device includes a controller, and a radio frequency (RF) transceiver. The RF transceiver includes a transmitting side, a receiving side, and a first loopback route and a second loopback route electrically connected to the transmitting side and the receiving side. The controller inputs training signals into the first loopback route and the second loopback route, determines a loopback gain and a loopback phase, based on a first training signal passing through the first loopback route and a second training signal passing through the second loopback route, determines a frequency domain compensation filter, based on the loopback gain and the loopback phase, determines an FIR filter and a DC offset, based on the frequency domain compensation filter, and compensates for a transmission signal and a reception signal, based on the FIR filter and the DC offset. The training signals are determined based on a phase of a first training signal and a phase of a second training signal. 
     The loopback phase may include a phase of the first loopback route and a phase of the second loopback route. The training signals may be determined based on a difference between the phase of the first loopback route and the phase of the second loopback route. 
     The difference between the phase of the first loopback route and the phase of the second loopback route may be 90 degrees. 
     The training signals may be determined based on a difference between a phase of the first training signal and a phase of the second training signal. 
     The difference between the phase of the first training signal and the phase of the second training signal may be 180 degrees. 
     The training signals may be determined based on a determination function. The determination function may be determined based on the difference between the phase of the first loopback route and the phase of the second loopback route and the difference between the phase of the first training signal and the second training signal. 
     A value of the determination function may not be 0. 
     The training signals may be determined based on a maximum value of the determination function. 
     An image component of the transmission signal may be removed based on the FIR filter and the DC offset. 
     An image component of the reception signal may be removed based on the FIR filter and the DC offset. 
     According to the disclosure, there is an effect of achieving an average image rejection ratio (IRR) of 48 decibel (dB) through a transceiver having a loopback hardware structure. 
     According to the disclosure, there is another effect of suppressing image signals dependent on a frequency among noise ratio (NR) signals in a bandwidth of 100 megahertz (MHz) to a noise level over all a bandwidth of 1400 MHz through a transceiver having a loopback hardware structure. 
     Other aspects, advantages, and salient features of the disclosure will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses various embodiments of the disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects, features, and advantages of certain embodiments of the disclosure will be more apparent from the following description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a block diagram illustrating an electronic device in a wireless communication system according to an embodiment of the disclosure; 
         FIG. 2  is a conceptual diagram illustrating a communication unit in a wireless communication system according to an embodiment of the disclosure; 
         FIG. 3  is a conceptual diagram illustrating a transmitter of an electronic device in a wireless communication system according to an embodiment of the disclosure; 
         FIG. 4  is a flowchart illustrating the operation order of an electronic device in a wireless communication system according to an embodiment of the disclosure; 
         FIG. 5  is a conceptual diagram illustrating an electronic device in a wireless communication system according to an embodiment of the disclosure; 
         FIG. 6  is a conceptual diagram illustrating an RF transceiver in a wireless communication system according to an embodiment of the disclosure; 
         FIG. 7  is a flowchart illustrating the operation order of an electronic device in a wireless communication system according to an embodiment of the disclosure; 
         FIG. 8  is a conceptual diagram illustrating a training signal designed to have a specific phase relation in a frequency domain of a wireless communication system according to an embodiment of the disclosure; 
         FIG. 9  is a conceptual diagram illustrating the magnitude of a training signal in a wireless communication system according to an embodiment of the disclosure; 
         FIG. 10  is a conceptual diagram illustrating a determinant in a wireless communication system according to an embodiment of the disclosure; 
         FIG. 11  is a conceptual diagram illustrating a training signal used in a wireless communication system according to an embodiment of the disclosure; 
         FIG. 12  is a conceptual diagram illustrating a training signal used in a wireless communication system according to an embodiment of the disclosure; 
         FIG. 13  is a conceptual diagram illustrating a training signal used in a wireless communication system according to an embodiment of the disclosure; 
         FIG. 14  is a graph illustrating a power spectrum density (PSD) of a transmission signal before calibration in a wireless communication system according to an embodiment of the disclosure; 
         FIG. 15  is a graph illustrating a power spectrum density of a transmission signal after calibration in a wireless communication system according to an embodiment of the disclosure; 
         FIG. 16  is a graph illustrating a power spectrum density (PSD) of a reception signal before calibration in a wireless communication system according to an embodiment of the disclosure; 
         FIG. 17  is a graph illustrating a power spectrum density of a reception signal after calibration in a wireless communication system according to an embodiment of the disclosure; 
         FIG. 18  is a graph illustrating a left edge carrier component before calibration in a wireless communication system according to an embodiment of the disclosure; 
         FIG. 19  is a graph illustrating a left edge carrier component after calibration in a wireless communication system according to an embodiment of the disclosure; 
         FIG. 20  is a graph illustrating a right edge carrier component before calibration in a wireless communication system according to an embodiment of the disclosure; 
         FIG. 21  is a graph illustrating a right edge carrier component after calibration in a wireless communication system according to an embodiment of the disclosure; 
         FIG. 22  is a conceptual diagram illustrating a multi-tone transmission signal higher than or equal to a bandwidth of 1.4 GHz before calibration in a wireless communication system according to an embodiment of the disclosure; and 
         FIG. 23  is a conceptual diagram illustrating a multi-tone transmission signal higher than or equal to a bandwidth of 1.4 GHz after calibration in a wireless communication system according to an embodiment of the disclosure. 
     
    
    
     Throughout the drawings, it should be noted that like reference numbers are used to depict the same or similar elements, features, and structures. 
     DETAILED DESCRIPTION 
     The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of various embodiments of the disclosure as defined by the claims and their equivalents. It includes various specific details to assist in that understanding but these are to be regarded as merely exemplary. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the various embodiments described herein can be made without departing from the scope and spirit of the disclosure. In addition, descriptions of well-known functions and constructions may be omitted for clarity and conciseness. 
     The terms and words used in the following description and claims are not limited to the bibliographical meanings, but, are merely used by the inventor to enable a clear and consistent understanding of the disclosure. Accordingly, it should be apparent to those skilled in the art that the following description of various embodiments of the disclosure is provided for illustration purpose only and not for the purpose of limiting the disclosure as defined by the appended claims and their equivalents. 
     It is to be understood that the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a component surface” includes reference to one or more of such surfaces. 
     For the same reason, in the accompanying drawings, some elements may be exaggerated, omitted, or schematically illustrated. Further, the size of each element does not completely reflect the actual size. In the drawings, identical or corresponding elements are provided with identical reference numerals. 
     The advantages and features of the disclosure and ways to achieve them will be apparent by making reference to embodiments as described below in conjunction with the accompanying drawings. However, the disclosure is not limited to the embodiments set forth below, but may be implemented in various different forms. The following embodiments are provided only to completely disclose the disclosure and inform those skilled in the art of the scope of the disclosure, and the disclosure is defined only by the scope of the appended claims. Throughout the specification, the same or like reference numerals designate the same or like elements. 
     Here, it will be understood that each block of the flowchart illustrations, and combinations of blocks in the flowchart illustrations, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart block or blocks. These computer program instructions may also be stored in a computer usable or computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer usable or computer-readable memory produce an article of manufacture including instruction means that implement the function specified in the flowchart block or blocks. The computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operations to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions that execute on the computer or other programmable apparatus provide operations for implementing the functions specified in the flowchart block or blocks. 
     Further, each block of the flowchart illustrations may represent a module, segment, or portion of code, which includes one or more executable instructions for implementing the specified logical function(s). It should also be noted that in some alternative implementations, the functions noted in the blocks may occur out of the order. For example, two blocks shown in succession may in fact be executed substantially concurrently or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. 
     As used herein, the “unit” refers to a software element or a hardware element, such as a Field Programmable Gate Array (FPGA) or an Application Specific Integrated Circuit (ASIC), which performs a predetermined function. However, the “unit” does not always have a meaning limited to software or hardware. The “unit” may be constructed either to be stored in an addressable storage medium or to execute one or more processors. Therefore, the “unit” includes, for example, software elements, object-oriented software elements, class elements or task elements, processes, functions, properties, procedures, sub-routines, segments of a program code, drivers, firmware, micro-codes, circuits, data, database, data structures, tables, arrays, and parameters. The elements and functions provided by the “unit” may be either combined into a smaller number of elements, or a “unit”, or divided into a larger number of elements, or a “unit”. Moreover, the elements and “units” or may be implemented to reproduce one or more central processing units (CPUs) within a device or a security multimedia card. Further, the “unit” in the embodiments may include one or more processors. 
       FIG. 1  is a block diagram illustrating an electronic device in a wireless communication system according to an embodiment of the disclosure. 
     Referring to  FIG. 1 , an electronic device  1  may include a controller  10 , a communication unit  20 , a memory  30 , a network interface  40 , and a user interface  50 . The electronic device  1  may additionally have more elements according to an implementation scheme. In the disclosure, there is no limitation on additional elements. 
     The controller  10  may control the basic operation of the electronic device  1  and may control reception and storage of various signals to be described below. For example, the controller  10  may be implemented as at least one processor or/and program for performing the operation of the electronic device  1 . 
     The communication unit  20  may be connected to another electronic device through a radio channel and may transmit and receive signals and/or message to and from various network function devices. When the electronic device  1  communicates with a 5 G network, the communication unit  20  may be a device capable of performing transmission/reception to/from the 5 G communication network. Further, the communication unit  20  may include a communication processor as necessary. When the communication unit  20  does not include a communication processor, all signals and/or message may be processed by the controller  10 . 
     The memory  30  may store various pieces of data required for controlling the electronic device  1  and may have an area for storing signals to be described below. For example, the memory  30  may store programs and various pieces of control information required by the controller  10  and further store other pieces of information described in the disclosure. 
     The network interface  40  may communicate with another electronic device in a core network. 
     The user interface  50  may provide various interfaces for a user of the electronic device  1 . 
     In order to use new applications, a 5 G communication network providing a data rate of Gbps may be used. Millimeter wave bands of 28 GHz and 39 GHz in which broadband communication is possible may be used to meet demands for an ultra-high data rate. 
     I/Q modulation may be generally used by an analog-digital converter (ADC) and a digital-analog converter (DAC) as an actual implementation to avoid demands for a high sampling speed. However, I/Q imbalance may be generated in the up/down mixer, the low-pass filter (LPF), and the DAC/ADC. The I/Q imbalance may be frequently generated in the implementation of actual I/Q modulation. Imbalance may be generated when there is a difference between components of I and Q branches. The I/Q imbalance may be independent from or dependent on the frequency. For example, imbalance of a gain and a phase occurring in the mixer may be independent from the frequency since a frequency of a local oscillator (LO) is generally fixed. When gains of pair mixers are not the same, gain imbalance may occur. Phase imbalance may occur when a phase difference between local oscillators (LOs) for I and Q branches is not accurately 90 degrees. In a narrow band system, it may be assumed that a difference in I and Q branches is constant in a bandwidth. Further, it may be assumed that frequency-dependent imbalance is ignored and only frequency-independent imbalance is considered. Unlike this, in a wideband system, frequency-dependent I/Q imbalance may be important since transfer characteristics of LPFs are different. For example, transfer characteristics of LPFs for cut-off frequencies may be different. As a result, in an ultra-wideband system, I/Q imbalance may become more severe. The I/Q imbalance may cause mirror-frequency interference or an unwanted signal in the reversed side of the center bandwidth frequency. The I/Q imbalance may ultimately result in a severe degradation in system performance, that is, error vector magnitude (EVM). As a result, the I/Q imbalance may limit the use of high-order modulation. For example, a 5 G communication system may support 256-quadrature amplitude modulation (QAM) that requires a signal to noise ratio (SNR) higher than or equal to 30 dB. It may be preferable that an image rejection ratio (IRR) is ideally higher than or equal to 40 dB. Due to non-ideal characteristics of components, an actual circuit designed in an I/Q transceiver may generally provide an IRR lower than 30 dB. Accordingly, the I/Q imbalance should be calibrated. 
     There may be a plurality of I/Q calibration techniques. However, most calibration techniques deal with an imbalance problem of a receiver or a transmitter. This may not be practical for being applied to the 5 G communication system. There are techniques for calibrating I/Q imbalance for a joint transmitter and receiver. However, the techniques may calibrate only frequency-independent I/Q imbalance, and a reference LO exactly having a phase shift of 90 degrees is required. A method of jointly calibrating frequency-dependent transmitter and receiver I/Q imbalance needs information for frequency-independent phase imbalance that should be separately estimated in advance. 
     The method of calibrating I/Q imbalance according to an embodiment may include a method of separating frequencies of the transmitter and the receiver for joint calibration. However, the method of separating frequencies may have difficulty in hardware implementation. 
     The method of calibrating I/Q imbalance according to an embodiment may include a method using a local loopback for estimating I/Q imbalance through one direct loopback and one phase shifter loopback. In order to apply the method, information on phase shifter characteristics should be acquired. However, it requires the knowledge of frequency-independent phase imbalances which need to be estimated separately in advance. 
     The method of calibrating I/Q imbalance according to an embodiment may include a method for the frequency domain to jointly estimate and compensate for frequency-independent transmitter and receiver I/Q imbalance in a 5 G millimeter wave system. The method may calibrate I/Q imbalance on the basis of the specific loopback hardware structure and specifically designed training signals. Further, the method may evaluate I/Q calibration performance through simulation and measurement. 
     Calibration of I/Q imbalance may be necessary for protecting the performance of the 5 G millimeter wave communication system. The disclosure provides a new apparatus and a new method for calibrating joint frequency-dependent I/Q imbalance for an ultra-wideband transceiver through the loopback hardware structure. 
     First, frequency-dependent I/Q imbalance of the transmitter and the receiver may be formulated as a function for an input of a loopback response to a training signal and an output of a reception signal. Further, a compensation filter may be analytically generalized as a solution of four linear equations. The loopback hardware structure and training signals may be specifically designed to have a specific phase relation for solving compensation filters. For example, the loopback hardware structure and the training signals may be implemented by complex finite impulse response (FIR) filters. 
     The calibration method according to the disclosure may provide an average IRR of 48 dB. Ultimately, a frequency-dependent image of an NR signal in a 100 MHz bandwidth is suppressed to a noise level over all a 1400 MHz bandwidth. 
       FIG. 2  is a conceptual diagram illustrating a communication unit in a wireless communication system according to an embodiment of the disclosure. 
     Referring to  FIG. 2 , the communication unit  20  may include a radio frequency (RF) transceiver  200 , a power amplifier (PA)  310 , a low-noise amplifier (LNA)  320 , and a plurality of antennas  410  and  420 . The communication unit  20  may be the same as or similar to the communication unit  20  of  FIG. 1 . 
     The RF transceiver  200  may include a plurality of low-pass filters  211  to  214 , an up mixer  220 , a loopback route  230 , and a down mixer  240 . The up mixer  220  may include a first up mixer  221  and a second up mixer  222 . The down mixer  240  may include a first down mixer  241  and a second down mixer  242 . 
     The first low-pass filter  211  may receive an output signal according to the control of the controller  10 . For example, the first low-pass filter  211  may receive a signal through one end of the first low-pass filter  211 . The first low-pass filter  211  may output an I signal by filtering the received signal. The other end of the first low-pass filter  211  may be electrically connected to one end of the first up mixer  221 . The first low-pass filter  211  may transfer the I signal to the first up mixer  221 . 
     The second low-pass filter  212  may receive an output signal according to the control of the controller  10 . For example, the second low-pass filter  212  may receive a signal through one end of the second low-pass filter  212 . The second low-pass filter  212  may output a Q signal by filtering the received signal. The other end of the second low-pass filter  212  may be electrically connected to one end of the second up mixer  222 . The second low-pass filter  212  may transfer the Q signal to the second up mixer  222 . 
     The up mixer  220  may be electrically connected to the power amplifier  310 . For example, the other end of the first up mixer  221  may be electrically connected to one end of the power amplifier  310 . The first up mixer  221  may up convert a frequency of the filtered I signal. The other end of the second up mixer  222  may be electrically connected to one end of the power amplifier  310 . The second up mixer  222  may up convert a frequency of the filtered Q signal. The up mixer  220  may transfer the up-converted I/Q signal to the power amplifier  310 . 
     The power amplifier  310  may amplify the I/Q signal received from the up mixer  220 . The power amplifier  310  may be electrically connected to a first antenna  410 . The power amplifier  310  may transfer the amplified I/Q signal to the first antenna  410 . The first antenna  410  may radiate the amplified I/Q signal to the air. 
     A second antenna  420  may receive a radio signal transmitted through the air. The second antenna  420  may be electrically connected to the low-noise amplifier  320 . The second antenna  420  may transfer the received signal to the low-noise amplifier  320 . 
     The low-noise amplifier  320  may amplify the received signal. The low-noise amplifier  320  may be electrically connected to the down mixer  240 . 
     The down mixer  240  may be electrically connected to the low-noise amplifier  320 . Further, the down mixer  240  may be electrically connected to the up mixer  220  through the loopback route  230 . The loopback route  230  may include a first switch (SW 1 )  231  and a second switch (SW 2 )  232 . For example, the down mixer  240  may be electrically connected to the up mixer  220  through at least one of the first switch (SW 1 )  231  and the second switch (SW 2 )  232 . 
     The down mixer  240  may down convert a frequency of the signal transmitted from the low-noise amplifier  320  or the up mixer  220 . For example, the first down mixer  241  may down convert the frequency of the transmitted signal. The first down mixer  241  may transfer the down-converted signal to the third low-pass filter  213 . The second down mixer  242  may down convert a frequency of the transmitted signal. The second down mixer  242  may transfer the down-converted signal to the fourth low-pass filter  214 . 
     The third low-pass filter  213  may receive the down-converted signal from the first down mixer  241 . The third low-pass filter  213  may output an I signal by filtering the down-converted signal. The fourth low-pass filter  214  may receive the down-converted signal from the second down mixer  242 . The fourth low-pass filter  214  may output a Q signal by filtering the down-converted signal. 
       FIG. 3  is a conceptual diagram illustrating a transmitter of an electronic device in a wireless communication system according to an embodiment of the disclosure. 
     Referring to  FIG. 3 , a transmitter  21  of the electronic device  1  may include the first low-pass filter  211 , the second low-pass filter  212 , the first up mixer  221 , the second up mixer  222 , an I/Q converter  223 , a local oscillator  260 , a high power amplifier (HPA)  310 , and the first antenna  410 . 
       FIG. 4  is a flowchart illustrating the operation order of an electronic device in a wireless communication system according to an embodiment of the disclosure. 
     Referring to  FIG. 4 , the controller  10  of the electronic device  1  may transmit and receive a training signal in operation S 401 . The controller  10  of the electronic device  1  may transmit and receive the training signal to calibrate I/Q imbalance. 
     The controller  10  of the electronic device  1  may estimate imbalance for a transmission signal and a reception signal in operation S 402 . For example, I/Q imbalance may include phase imbalance  0  generated by the I/Q converter  223  and amplitude imbalance dependent on a frequency by the first low-pass filter  211  of an I branch and the second low-pass filter  212  of a Q branch. X(f) is an input signal in a frequency domain. Y(f) is an output signal in a frequency domain. The output signal Y(f) or an imbalanced signal may be expressed as a sum of an original signal and a conjugate.
 
 Y ( f )= G   t ( f ) X ( f )+ C   t ( f ) X (− f )  Equation 1
 
     In Equation 1, G t (f) and G r (f) denotes an imbalance coefficient, and generally corresponds to a function of the phase θ and the amplitude imbalance defined as 
     
       
         
           
             
               
                 
                   H 
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                   ( 
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                   H 
                   Q 
                 
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                   ( 
                   f 
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             . 
           
         
       
     
     The purpose of I/Q calibration is to remove the conjugate from Equation 1. That is, the controller  10  of the electronic device  1  may compensate for the original signal X(f) in a similar form as shown in Equation 2.
 
 X   C ( f )= X ( f )− W   t ( f ) X *(− f )  Equation 2
 
     The compensated output signal may be indicated by Equation 3.
 
 Y =[ G   t ( f )− C   t ( f ) W   t *(− f )] X ( f )+[ G   t ( f )− C   t ( f ) W   t ( f )] X *(− f )  Equation 3
 
     In order to remove the image or the conjugate, a factor W t (f) referred to as a compensation filter should satisfy Equation 4.
 
 G   t ( f )− C   t ( f ) W   t ( f )=0  Equation 4
 
     Equation 4 may be expressed as shown in Equation 5. 
     
       
         
           
             
               
                 
                   
                     
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                   5 
                 
               
             
           
         
       
     
     G r (f) and C r (f) are defined as imbalance coefficients of an I/Q down-conversion reception signal (Rx). In order to remove the image, the compensation filter of the reception signal defined as W r (f) may be determined through Equation 6. 
     
       
         
           
             
               
                 
                   
                     
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                   6 
                 
               
             
           
         
       
     
     The controller  10  of the electronic device  1  may calibrate the transmission signal and the reception signal in operation S 403 . For example, the controller  10  may calibrate the transmission signal and the reception signal on the basis of the determined compensation filter. 
       FIG. 5  is a conceptual diagram illustrating an electronic device in a wireless communication system according to an embodiment of the disclosure. 
     Referring to  FIG. 5 , the communication unit  20  of the electronic device  1  may include an RF transceiver  200 , a plurality of beamformer  300 , an antenna array  400 , and a signal generator  500 . 
     The RF transceiver  200  may be the same as or similar to the RF transceiver  200  of  FIG. 2 . The plurality of beamformers  300  may be millimeter wave beamformers operating in a frequency band of 28 GHz. The plurality of beamformers  300  may be electrically connected to the RF transceiver  200 . Further, the plurality of beamformers  300  may be electrically connected to the antenna array  400 . 
     For example, a first beamformer  301  may include an up mixer  311 , a first power switch (PS)  312 , a high-power amplifier  313 , a low-noise amplifier  314 , a second power switch  315 , a down mixer  316 , and an X3 interface  317 . 
     A first end of the up mixer  311  may be electrically connected to the up mixer  220  of the RF transceiver  200  through the loopback route  230 . A second end of the up mixer  311  may be electrically connected to one end of the first power switch  312 . A third end of the up mixer  311  may be electrically connected to a second end of the X3 interface  317 . 
     The one end of the first power switch  312  may be electrically connected to a second end of the up mixer  311 . The other end of the first power switch  312  may be electrically connected to one end of the high-power amplifier  313 . 
     The one end of the high-power amplifier  313  may be electrically connected to the other end of the first power switch  312 . The other end of the high-power amplifier  313  may be electrically connected to the antenna array  400 . 
     One end of the low-noise amplifier  314  may be electrically connected to the other end of the second power switch  316 . The other end of the low-noise amplifier  314  may be electrically connected to the antenna array  400 . 
     One end of the second power switch  316  may be electrically connected to the other end of the down mixer  316 . The other end of the second power switch  316  may be electrically connected to the one end of the low-noise amplifier  314 . 
     A first end of the down mixer  316  may be electrically connected to the down mixer  240  of the RF transceiver  200  through the loopback route  230 . A second end of the down mixer  316  may be electrically connected to one end of the second power switch  316 . A third end of the down mixer  316  may be electrically connected to a third end of the X3 interface  317 . 
     A first end of the X3 interface  317  may be electrically connected to the end of the signal generator  500 . A second end of the X3 interface  317  may be electrically connected to the third end of the up mixer  311 . A third end of the X3 interface  317  may be electrically connected to a third end of the down mixer  316 . 
     One end of the signal generator  500  may be electrically connected to a third end of the X2 interface  270 . The other end of the signal generator  500  may be electrically connected to the first end of the X3 interface  317 . 
     A first end of the X2 interface  270  may be electrically connected to the up mixer  220 . A second end of the X2 interface  270  may be electrically connected to the down mixer  240 . The third end of the X2 interface  270  may be electrically connected to one end of the signal generator  500 . 
     The electronic device  1  according to an embodiment may extract compensation filters, W t (f), and W r (f). Referring to  FIG. 4 , the RF transceiver  200  may transfer a signal in a bandwidth of 1.4 GHz based on 11.2 GHz to the plurality of beamformers  300 . The RF transceiver  200  may have a loopback structure including two separated loopback routes  230 . The controller  10  may activate a transmission mode or a calibration mode by controlling the first switch  231  and the second switch  232  of the RF transceiver  200 . For example, the controller  100  may activate the transmission mode or the calibration mode by controlling on/off of the first switch  231  and the second switch  232 . 
       FIG. 6  is a conceptual diagram illustrating an RF transceiver in a wireless communication system according to an embodiment of the disclosure. 
     Referring to  FIG. 6 , the loopback route  230  of the RF transceiver  200  may be modeled by a phase shifter. 
       FIG. 7  is a flowchart illustrating an operation order of an electronic device according to an embodiment of the disclosure. 
     Referring to  FIG. 7 , the controller  10  of the electronic device  1  may perform an initialization operation S 701  for calibrating I/Q imbalance. 
     The controller  10  of the electronic device  1  may transmit and capture a training signal, and estimate a loopback gain and a phase in operation S 702 . For example, the controller  10  of the electronic device  1  may model a transfer function as shown in Equation 7.
 
 P ( f )= g ( f ) e   jϕ(f)   Equation 7
 
     In Equation 7, g(f) denotes a gain response. ϕ(f) denotes a phase response. 
     A change in the phase and the gain for a bandwidth may be ignored. At this time, the loopback response may be indicated by Equation 8.
 
 P=ge   jϕ   Equation 8
 
     The output signal Z(f) may be indicated by Equation 9.
 
( f )= ge   jϕ   G   r ( f )( G   t ( f ) X ( f )+ C   t ( f ) X *(− f ))+ ge   −jϕ   C   r ( f )( G   t *(− f ) X *(− f )+ C   r *(− f ) X ( f ))  Equation 9
 
     Equation 9 may be expressed as Equation 10.
 
 Z ( f )= ge   jϕ   X ( f ) G   r ( f ) G   t ( f )+ ge   −jϕ   X ( f ) C   r ( f ) C   r *(− f )+ ge   jϕ   X *(− f ) G   r ( f ) C   t ( f )+ ge   −jϕ   X *(− f ) C   r ( f ) G   t *(− f )  Equation 10
 
     The variables x 1˜4  are defined as Equation 11. 
     
       
         
           
             
               
                 
                   { 
                   
                     
                       
                         
                           
                             x 
                             1 
                           
                           = 
                           
                             
                               
                                 G 
                                 r 
                               
                               ⁡ 
                               
                                 ( 
                                 f 
                                 ) 
                               
                             
                             ⁢ 
                             
                               
                                 G 
                                 t 
                               
                               ⁡ 
                               
                                 ( 
                                 f 
                                 ) 
                               
                             
                           
                         
                       
                     
                     
                       
                         
                           
                             x 
                             2 
                           
                           = 
                           
                             
                               
                                 C 
                                 r 
                               
                               ⁡ 
                               
                                 ( 
                                 f 
                                 ) 
                               
                             
                             ⁢ 
                             
                               
                                 C 
                                 r 
                                 * 
                               
                               ⁡ 
                               
                                 ( 
                                 
                                   - 
                                   f 
                                 
                                 ) 
                               
                             
                           
                         
                       
                     
                     
                       
                         
                           
                             x 
                             3 
                           
                           = 
                           
                             
                               
                                 G 
                                 r 
                               
                               ⁡ 
                               
                                 ( 
                                 f 
                                 ) 
                               
                             
                             ⁢ 
                             
                               
                                 C 
                                 t 
                               
                               ⁡ 
                               
                                 ( 
                                 f 
                                 ) 
                               
                             
                           
                         
                       
                     
                     
                       
                         
                           
                             x 
                             4 
                           
                           = 
                           
                             
                               
                                 C 
                                 r 
                               
                               ⁡ 
                               
                                 ( 
                                 f 
                                 ) 
                               
                             
                             ⁢ 
                             
                               
                                 G 
                                 t 
                                 * 
                               
                               ⁡ 
                               
                                 ( 
                                 
                                   - 
                                   f 
                                 
                                 ) 
                               
                             
                           
                         
                       
                     
                   
                 
               
               
                 
                   Equation 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   11 
                 
               
             
           
         
       
     
     The output signal may be expressed as functions of four variables as shown in Equation 12.
 
 Z ( f )= ge   jϕ   X ( f ) x   1   +ge   −jϕ   X ( f ) x   2   +ge   jϕ   X *(− f ) x   3   +ge   −jϕ   X *(− f ) x   4   Equation 12
 
     The controller  10  of the electronic device  1  may estimate a compensation filter in operation S 703 . For example, the controller  10  may determine a compensation filter for a transmission signal and a compensation filter for a reception signal in a frequency domain. 
     For example, in order to remove an image part from the output signal, the controller  10  may control training signals to be transmitted and received through the loopback route  230  so as to determine a compensation filter (W t ) for a transmission signal and a compensation filter (W r ) for a reception signal in a frequency domain. 
     For example, the controller  10  may determine the compensation filter (W t ) for the transmission signal and the compensation filter (W r ) for the reception signal on the basis of training signals designed through Equation 13 and Equation 14. 
     For example, when values corresponding to x 1˜4  in Equation 11 and Equation 12 exist, the controller  10  may determine compensation filters through Equation 13 and Equation 14. 
     
       
         
           
             
               
                 
                   
                     
                       W 
                       t 
                     
                     ⁡ 
                     
                       ( 
                       f 
                       ) 
                     
                   
                   = 
                   
                     
                       
                         
                           C 
                           t 
                         
                         ⁡ 
                         
                           ( 
                           f 
                           ) 
                         
                       
                       
                         
                           G 
                           t 
                         
                         ⁡ 
                         
                           ( 
                           f 
                           ) 
                         
                       
                     
                     = 
                     
                       
                         x 
                         3 
                       
                       
                         x 
                         1 
                       
                     
                   
                 
               
               
                 
                   Equation 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   13 
                 
               
             
             
               
                 
                   
                     
                       W 
                       r 
                     
                     ⁡ 
                     
                       ( 
                       f 
                       ) 
                     
                   
                   = 
                   
                     
                       
                         
                           C 
                           r 
                         
                         ⁡ 
                         
                           ( 
                           f 
                           ) 
                         
                       
                       
                         
                           G 
                           r 
                           * 
                         
                         ⁡ 
                         
                           ( 
                           
                             - 
                             f 
                           
                           ) 
                         
                       
                     
                     = 
                     
                       
                         x 
                         4 
                       
                       
                         x 
                         1 
                         * 
                       
                     
                   
                 
               
               
                 
                   Equation 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   14 
                 
               
             
           
         
       
     
     x 1 , x 2 , x 3 , x 4 , denote G r (f)G t (f), C r (f)C r *(−f), G r (f)C t (f) and C r (f)G t *(−f). G r , C r , G t  and C t  denote imbalance coefficients in a transmitter and a receiver. 
     In order to solve four variables in Equation 11, equations that can be obtained through transmission of two different training signals X A (f) and X B (f) through two different characteristic loopback routes  230 , that is, g 1 e jϕ     1    and g 2 e jϕ     2    may be considered. For example, Equation 15 may be considered.
 
 Z=Ax   Equation 15
 
     In Equation 15, Z denotes a received signal vector and may be expressed by Equation 16. A denotes a matrix and may be expressed by Equation 17. x denotes a variable vector and may be expressed by Equation 18. 
     
       
         
           
             
               
                 
                   
                       
                   
                   ⁢ 
                   
                     Z 
                     = 
                     
                       
                         [ 
                         
                           
                             
                               
                                 Z 
                                 1 
                               
                             
                             
                               
                                 Z 
                                 2 
                               
                             
                             
                               
                                 Z 
                                 3 
                               
                             
                             
                               
                                 Z 
                                 4 
                               
                             
                           
                         
                         ] 
                       
                       T 
                     
                   
                 
               
               
                 
                   Equation 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   16 
                 
               
             
             
               
                 
                   
                       
                   
                   ⁢ 
                   
                     x 
                     = 
                     
                       
                         [ 
                         
                           
                             
                               
                                 x 
                                 1 
                               
                             
                             
                               
                                 x 
                                 2 
                               
                             
                             
                               
                                 x 
                                 3 
                               
                             
                             
                               
                                 x 
                                 4 
                               
                             
                           
                         
                         ] 
                       
                       T 
                     
                   
                 
               
               
                 
                   Equation 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   17 
                 
               
             
             
               
                 
                   
                     A 
                     = 
                     
                       [ 
                       
                         
                           
                             
                               
                                 g 
                                 1 
                               
                               ⁢ 
                               
                                 e 
                                 
                                   j 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   
                                     ϕ 
                                     1 
                                   
                                 
                               
                               ⁢ 
                               
                                 X 
                                 A 
                               
                             
                           
                           
                             
                               
                                 g 
                                 1 
                               
                               ⁢ 
                               
                                 e 
                                 
                                   
                                     - 
                                     j 
                                   
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   
                                     ϕ 
                                     1 
                                   
                                 
                               
                               ⁢ 
                               
                                 X 
                                 A 
                               
                             
                           
                           
                             
                               
                                 g 
                                 1 
                               
                               ⁢ 
                               
                                 e 
                                 
                                   j 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   
                                     ϕ 
                                     1 
                                   
                                 
                               
                               ⁢ 
                               
                                 X 
                                 A 
                                 * 
                               
                             
                           
                           
                             
                               
                                 g 
                                 1 
                               
                               ⁢ 
                               
                                 e 
                                 
                                   
                                     - 
                                     j 
                                   
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   
                                     ϕ 
                                     1 
                                   
                                 
                               
                               ⁢ 
                               
                                 X 
                                 A 
                                 * 
                               
                             
                           
                         
                         
                           
                             
                               
                                 g 
                                 1 
                               
                               ⁢ 
                               
                                 e 
                                 
                                   j 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   
                                     ϕ 
                                     1 
                                   
                                 
                               
                               ⁢ 
                               
                                 X 
                                 B 
                               
                             
                           
                           
                             
                               
                                 g 
                                 1 
                               
                               ⁢ 
                               
                                 e 
                                 
                                   
                                     - 
                                     j 
                                   
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   
                                     ϕ 
                                     1 
                                   
                                 
                               
                               ⁢ 
                               
                                 X 
                                 B 
                               
                             
                           
                           
                             
                               
                                 g 
                                 1 
                               
                               ⁢ 
                               
                                 e 
                                 
                                   j 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   
                                     ϕ 
                                     1 
                                   
                                 
                               
                               ⁢ 
                               
                                 X 
                                 B 
                                 * 
                               
                             
                           
                           
                             
                               
                                 g 
                                 1 
                               
                               ⁢ 
                               
                                 e 
                                 
                                   
                                     - 
                                     j 
                                   
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   
                                     ϕ 
                                     1 
                                   
                                 
                               
                               ⁢ 
                               
                                 X 
                                 B 
                                 * 
                               
                             
                           
                         
                         
                           
                             
                               
                                 g 
                                 2 
                               
                               ⁢ 
                               
                                 e 
                                 
                                   j 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   
                                     ϕ 
                                     2 
                                   
                                 
                               
                               ⁢ 
                               
                                 X 
                                 A 
                               
                             
                           
                           
                             
                               
                                 g 
                                 2 
                               
                               ⁢ 
                               
                                 e 
                                 
                                   j 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   
                                     ϕ 
                                     2 
                                   
                                 
                               
                               ⁢ 
                               
                                 X 
                                 A 
                               
                             
                           
                           
                             
                               
                                 g 
                                 2 
                               
                               ⁢ 
                               
                                 e 
                                 
                                   j 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   
                                     ϕ 
                                     2 
                                   
                                 
                               
                               ⁢ 
                               
                                 X 
                                 A 
                               
                             
                           
                           
                             
                               
                                 g 
                                 2 
                               
                               ⁢ 
                               
                                 e 
                                 
                                   
                                     - 
                                     j 
                                   
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   
                                     ϕ 
                                     2 
                                   
                                 
                               
                               ⁢ 
                               
                                 X 
                                 A 
                               
                             
                           
                         
                         
                           
                             
                               
                                 g 
                                 2 
                               
                               ⁢ 
                               
                                 e 
                                 
                                   j 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   
                                     ϕ 
                                     2 
                                   
                                 
                               
                               ⁢ 
                               
                                 X 
                                 B 
                               
                             
                           
                           
                             
                               
                                 g 
                                 2 
                               
                               ⁢ 
                               
                                 e 
                                 
                                   j 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   
                                     ϕ 
                                     2 
                                   
                                 
                               
                               ⁢ 
                               
                                 X 
                                 B 
                               
                             
                           
                           
                             
                               
                                 g 
                                 2 
                               
                               ⁢ 
                               
                                 e 
                                 
                                   j 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   
                                     ϕ 
                                     2 
                                   
                                 
                               
                               ⁢ 
                               
                                 X 
                                 B 
                               
                             
                           
                           
                             
                               
                                 g 
                                 2 
                               
                               ⁢ 
                               
                                 e 
                                 
                                   
                                     - 
                                     j 
                                   
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   
                                     ϕ 
                                     2 
                                   
                                 
                               
                               ⁢ 
                               
                                 X 
                                 B 
                               
                             
                           
                         
                       
                       ] 
                     
                   
                   , 
                 
               
               
                 
                   Equation 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   18 
                 
               
             
           
         
       
     
     X A (f) is expressed as X A . X A *(−f) is expressed as X A *. 
     The controller  10  may determine a variable vector x through Equation 13 by designing detailed training signals. 
       FIG. 8  is a conceptual diagram illustrating a training signal designed to have a specific phase relation in a frequency domain of a wireless communication system according to an embodiment of the disclosure. 
       FIG. 9  is a conceptual diagram illustrating the magnitude of a training signal in a wireless communication system according to an embodiment of the disclosure. 
     Referring to  FIG. 8 , in the assumption of g 1 =g 2 =1, a determinant of the matrix A indicated by det(A) may be converted to Equation 19.
 
det( A )=( X   A ( f ) X   B *(− f )− X   A *(− f ) 2  (2 −e   j(2Δ     LB     )   −e   −j(2Δ     LB     ) )  Equation 19
 
     In Equation 19, Δ LB =ϕ 1 −ϕ 2  is a phase difference between two loopback routes. X A  and X B  are training signals through two different loopback routes. Further, the controller  10  may design training signals by evaluating the determinant of the matrix A in Equation 19. The controller  10  may design and control entries of the training signals in detail 
     Training signals may be designed such that det(A) satisfies the conditions as Equation 20. 
     
       
         
           
             
               
                 
                   { 
                   
                     
                       
                         
                           
                             det 
                             ⁡ 
                             
                               ( 
                               A 
                               ) 
                             
                           
                           ≠ 
                           0 
                         
                       
                     
                     
                       
                         
                           
                              
                             
                               det 
                               ⁡ 
                               
                                 ( 
                                 A 
                                 ) 
                               
                             
                              
                           
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           as 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           high 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           as 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           possible 
                         
                       
                     
                   
                 
               
               
                 
                   Equation 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   20 
                 
               
             
           
         
       
     
     Two vector training signals may be defined as X A (f) and X B (f). Referring to  FIG. 8 , two frequency components f 1   a =−f −1   a ; f 1   b =−f −1   b  that are mutual images of the vector training signals may exist. Further, all components may have the same magnitude r and predetermined phases. The training signals may be expressed as Equation 21 and Equation 22.
 
 X   A ( f   1   a   ,f   −1   a )=[ re   jϕ     1       a     ,re   jϕ     −1       a   ]  Equation 21
 
 X   B ( f   1   b   ,f   −1   b )=[ re   jϕ     1       b     ,re   jϕ     −1       b   ]  Equation 22
 
     A difference between phase terms may be expressed as Equation 23 and Equation 24.
 
ϕ 1   b −ϕ −1   a =θ 1   Equation 23
 
ϕ 1   a −ϕ −1   b =θ 2   Equation 24
 
     A difference between phase terms may be expressed as Equation 25.
 
θ 2 −θ 1 =Δ  Equation 25
 
     The determinant of Equation 19 may be an intuitive function of the loopback phase difference Δ LB  and the phase difference Δ between training signals. 
       FIG. 9  is a conceptual diagram illustrating a determinant in a wireless communication system according to an embodiment of the disclosure. 
     Referring to  FIG. 9 , the determinant may vary depending on Δ and Δ LB . When a condition of Equation 26 is satisfied, the determinant of A may have a maximum value. 
     
       
         
           
             
               
                 
                   { 
                   
                     
                       
                         
                           
                              
                             
                               
                                 Δ 
                                 ⁢ 
                                 
                                     
                                 
                               
                               LB 
                             
                              
                           
                           = 
                           
                             90 
                             ⁢ 
                             ° 
                           
                         
                       
                     
                     
                       
                         
                           
                             
                                
                               Δ 
                                
                             
                             = 
                             
                               180 
                               ⁢ 
                               ° 
                             
                           
                           ⁢ 
                           
                               
                           
                         
                       
                     
                   
                 
               
               
                 
                   Equation 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   26 
                 
               
             
           
         
       
     
     It is assumed to design a loopback route such that |Δ LB | approaches 90° and the phase difference Δ between training signals can be selected to provide the determinant A. 
       FIG. 10  is a conceptual diagram illustrating a training signal used in a wireless communication system according to an embodiment of the disclosure. 
     Referring to  FIG. 10 , in the case of Δ=180°, a component f 1   b  of the training signal may have a phase larger by 45° from f −1   a . Further, a component f −1   b  of the training signal may have a phase smaller by 225° from f 1   a . 
       FIG. 11  is a conceptual diagram illustrating a training signal used in a wireless communication system according to an embodiment of the disclosure. 
     Referring to  FIG. 11 , the component f 1   b  of the training signal of Δ=180° may have a phase larger by 115° from f −1   a . Further, the component f −1   b  of the training signal may have a phase smaller by 315° from f 1   a . 
     For example, the controller  10  may determine the variable vector x using designed training signals through Equation 17. The controller  10  may determine compensation filters through Equation 13 and Equation 14. 
     Referring back to  FIG. 7 , the controller  10  of the electronic device  1  may estimate a Finite Impulse Response (FIR) filter and a DC offset in operation S 704 . For example, the FIR filter may be used to covert a signal in a frequency domain to a signal in a time domain. 
     A length of the FIR filter w may be M. M may be an odd number. Frequency response compensation filters for a transmission signal or a reception signal sampled in the given frequency ω n  may be expressed as Equation 3. 
     For example, when the length of the FIR filter w is M (M being an odd number), frequency response compensation filters for the transmission signal or the reception signal that is sampled in the given frequency ω n  and determined through Equation 13 and Equation 14 may be expressed as Equation 27.
 
 W (ω n )=Σ k=−(M−1)/ 2 (M−1)/ 2 w   k   e   −jω     n     k   Equation 27
 
     N point frequency sampling ω n  (n=1˜N) may be expressed as Equation 27. For example, Equation 28 to Equation 30 may be derived from N frequency points sampled through a bandwidth ω n (n=1˜N). 
     
       
         
           
             
               
                 
                   W 
                   = 
                   Aw 
                 
               
               
                 
                   Equation 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   28 
                 
               
             
             
               
                 
                   
                     A 
                     
                       N 
                       × 
                       M 
                     
                   
                   = 
                   
                     [ 
                     
                       
                         
                           
                             e 
                             
                               
                                 - 
                                 j 
                               
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               
                                 
                                   ω 
                                   1 
                                 
                                 ⁡ 
                                 
                                   ( 
                                   
                                     - 
                                     
                                       
                                         M 
                                         - 
                                         1 
                                       
                                       2 
                                     
                                   
                                   ) 
                                 
                               
                             
                           
                         
                         
                           … 
                         
                         
                           
                             e 
                             
                               
                                 - 
                                 j 
                               
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               
                                 
                                   ω 
                                   1 
                                 
                                 ⁡ 
                                 
                                   ( 
                                   
                                     
                                       M 
                                       - 
                                       1 
                                     
                                     2 
                                   
                                   ) 
                                 
                               
                             
                           
                         
                       
                       
                         
                           ⋮ 
                         
                         
                           ⋱ 
                         
                         
                           ⋮ 
                         
                       
                       
                         
                           
                             e 
                             
                               
                                 - 
                                 j 
                               
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               
                                 
                                   ω 
                                   n 
                                 
                                 ⁡ 
                                 
                                   ( 
                                   
                                     - 
                                     
                                       
                                         M 
                                         - 
                                         1 
                                       
                                       2 
                                     
                                   
                                   ) 
                                 
                               
                             
                           
                         
                         
                           … 
                         
                         
                           
                             e 
                             
                               
                                 - 
                                 j 
                               
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               
                                 
                                   ω 
                                   n 
                                 
                                 ⁡ 
                                 
                                   ( 
                                   
                                     
                                       M 
                                       - 
                                       1 
                                     
                                     2 
                                   
                                   ) 
                                 
                               
                             
                           
                         
                       
                     
                     ] 
                   
                 
               
               
                 
                   Equation 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   29 
                 
               
             
             
               
                 
                   
                     W 
                     
                       N 
                       × 
                       1 
                     
                   
                   = 
                   
                     [ 
                     
                       
                         
                           
                             W 
                             ⁡ 
                             
                               ( 
                               
                                 ω 
                                 1 
                               
                               ) 
                             
                           
                         
                       
                       
                         
                           … 
                         
                       
                       
                         
                           
                             W 
                             ⁡ 
                             
                               ( 
                               
                                 ω 
                                 N 
                               
                               ) 
                             
                           
                         
                       
                     
                     ] 
                   
                 
               
               
                 
                   Equation 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   30 
                 
               
             
           
         
       
     
     The controller  10  may estimate the FIR filter w using the least square method as shown in Equation 31.
 
 ŵ =argmin ∥ Aw−W∥   2   Equation 31
 
     Equation 31 may be expressed by Equation 32.
 
 ŵ =[( A   T   A ) −1   A   T ] W   Equation 32
 
     The controller  10  of the electronic device  1  may determine whether a residual of FIR filters approach  0  in operation S 705 . The controller  10  of the electronic device  1  may terminate the operation when the residual of FIR filters approach  0 . 
     The controller  10  of the electronic device  1  may update the FIR filters and the DC offset when the FIR filters do not approach  0  in operation S 706 . The controller  10  may calibrate the transmission signal (Tx) and the reception signal (Rx) in common by updating the FIR filters and the DC offset. The controller  10  of the electronic device  1  may repeatedly perform operations S 702  to S 705  by returning to operation S 702  after updating the FIR filters and the DC offset. 
       FIG. 12  is a conceptual diagram illustrating a training signal used in a wireless communication system according to an embodiment of the disclosure. 
     Referring to  FIG. 12 , a bandwidth BW of a wireless communication system may be 1.4 GHz. The bandwidth may aggregate  14  carrier components having a bandwidth of 100 MHz. A sampling frequency may be F S =1.96608 GHz. The magnitude of Fast Fourier Transform (FFT) and Inverse Fast Fourier Transform (IFFT) may be selected NFFT=512. Each of training signals X A  and X B  may include  512  frequency components. Frequencies within the band of the wireless communication system may be uniformly distributed over the entire bandwidth. Each frequency component may be divided by 15.36 MHz for the required SNR and may become a frequency component within a total of 92 bands. Training signals in the frequency domain are converted to training signals in the time domain using IFFT, concatenated, and doubled to form 2048 samples, or equivalent to 1.04 μs time duration. Imbalance independent from the frequency may be selected as follows. Phase imbalance may be θ t =5° and θ r =5° in a transmitter and a receiver, respectively. Imbalance dependent on the frequency may be simulated by Butterworth low-pass filters for selecting different cut-off frequencies. In the case of the transmitter, LPF cut-off frequencies of I and Q branches may be selected as f I   Tx 700 MHz and f Q   Tx =703 MHz. In the case of the receiver, LPF cut-off frequencies of I and Q branches may be selected as f I   Rx =704 MHz and f q   Tx =700 MHz. Loopback phases of two routes may be selected to have a difference of Δ LB =90°. 2048 samples of the training signals may be input through two different loopback routes. Signals received thereafter may be used to determine compensation filters as shown in Equation 18 and Equation 19. The FIR filter w may be estimated through Equation 37 to match a required frequency response, that is, W t  or W r . The method of calibrating I/Q imbalance according to an embodiment may remove an image through a modulated signal in a bandwidth of 100 MHz. 
       FIG. 13  is a conceptual diagram illustrating a training signal used in a wireless communication system according to an embodiment of the disclosure. 
       FIG. 14  is a graph illustrating a power spectrum density (PSD) of a transmission signal before calibration in a wireless communication system according to an embodiment of the disclosure. 
       FIG. 15  is a graph illustrating a power spectrum density of a transmission signal after calibration in a wireless communication system according to an embodiment of the disclosure. 
       FIG. 16  is a graph illustrating a power spectrum density (PSD) of a reception signal before calibration in a wireless communication system according to an embodiment of the disclosure. 
       FIG. 17  is a graph illustrating a power spectrum density of a reception signal after calibration in a wireless communication system according to an embodiment of the disclosure. 
     Referring to  FIGS. 14 and 16 , IRR of the transmission signal and the reception signal before calibration may be about 30 dB. 
     Referring to  FIGS. 15 and 17 , after calibration, images may be all suppressed to a noise level. 
       FIG. 18  is a graph illustrating a left edge carrier component before calibration in a wireless communication system according to an embodiment of the disclosure. 
       FIG. 19  is a graph illustrating a left edge carrier component after calibration in a wireless communication system according to an embodiment of the disclosure. 
       FIG. 20  is a graph illustrating a right edge carrier component before calibration in a wireless communication system according to an embodiment of the disclosure. 
       FIG. 21  is a graph illustrating a right edge carrier component after calibration in a wireless communication system according to an embodiment of the disclosure. 
     Referring to  FIGS. 18 and 20 , uncompensated spectrum of a 5 G-NR signal in a bandwidth of 10 MHz placed in 650.13 MHz and −650.13 MHz or a left edge carrier component are illustrated. The left and right edge carrier components may clearly appear in the opposite side of the center frequency with IRR of about 19 dB and 32 dB, respectively, or difference of 13 dB. This means that imbalance significantly depends on the frequency. 
     Referring to  FIGS. 19 and 21 , calibrated signals are illustrated. It is shown that images of the calibrated signals are suppressed to the noise level, and the performance of the I/Q calibration method according to an embodiment may be identified. 
       FIG. 22  is a conceptual diagram illustrating a multi-tone transmission signal in a bandwidth higher than or equal to 1.4 GHz bandwidth before calibration in a wireless communication system according to an embodiment of the disclosure. 
     Referring to  FIG. 22 , the multi-tone signal may be generated through separation of spectrum tones and images of the spectrum tones. For example, an image signal may significantly vary in a left bandwidth at a highest level or −72 dBm and a right lowest level or −80 dBm. 
       FIG. 23  is a conceptual diagram illustrating a multi-tone transmission signal in a bandwidth higher than or equal to 1.4 GHz bandwidth after calibration in a wireless communication system according to an embodiment of the disclosure. 
     Referring to  FIG. 23 , the worst IRR may be 40 dB, and the average IRR in a bandwidth 1.4 GHz may be 48 dB. The result of  FIG. 21  may correspond to  FIGS. 19 and 21  in which the image of the modulated signal in bandwidth 100 MHz is suppressed to the noise level. That is, the method of calibrating the I/Q signal according to an embodiment in the wireless communication system in which the average SNR is lower than 40 dB may provide the robust performance. 
     The disclosure provides a calibration method of estimating and compensating for frequency-dependent imbalance of the transmitter and the receiver. The method may be based on a design of specific training signals related to the loopback hardware structure for acquiring analysis solutions of compensation filters. Simulation and measurement with a commercial 5 G transceiver chipset may show that the proposed technique can accurately estimate the frequency-dependent imbalance and ultimately suppress the image of the 5 G NR signal to the noise level. Accordingly, the method according to the disclosure may be a robot self-calibration technique for ultra-wideband 5 G transceivers for millimeter wave communication. 
     The method according to the disclosure may be more innovative than most of the existing techniques in the sense that the derivation can be extended to other types of feedback or hardware structure. 
     While the disclosure has been shown and described with reference to various embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the disclosure as defined by the appended claims and their equivalents.