Patent Publication Number: US-11381272-B2

Title: Apparatus and method for controlling transmission power

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority under 35 U.S.C. § 119 to Korean Patent Application No. 10-2019-0108941, filed on Sep. 3, 2019 in the Korean Intellectual Property Office, the disclosure of which is incorporated by reference herein in its entirety. 
     TECHNICAL FIELD 
     Exemplary embodiments of the present inventive concept relate to wireless communications, and more particularly, to an apparatus and method for controlling transmission power. 
     DISCUSSION OF RELATED ART 
     Signal transmission in a wireless communications system may be affected by path loss, shadow fading, and the like, and thus sufficient power should be used to maintain quality of service (QoS). In particular, for wireless communications using easily attenuated high-frequency electromagnetic signals such as millimeter-wave (mmWave) signals, relatively high transmission power may be required to overcome such losses. However, when transmission power is increased, heat generated by a wireless communications device may be increased and/or high-density electromagnetic waves may be generated in a transmission process. As such, heat and energy absorbed by a user of a wireless communications device may be undesirably elevated due to the electromagnetic waves. 
     SUMMARY 
     Exemplary embodiments of the present inventive concept provide a method and apparatus for maintaining quality of service (QoS) in wireless communications and efficiently reducing exposure of a user to electromagnetic waves. 
     According to an exemplary embodiment of the inventive concept, a method is provided for controlling a transmission power of a wireless communications device to comply with an output energy limit during a measurement period, the method including calculating a target output energy based on a communications channel; obtaining a first average output energy corresponding to a previous period having a duration substantially equal to the measurement period; calculating a second average output energy by low-pass-filtering the target output energy and the first average output energy; and limiting the transmission power of the wireless communications device based on an energy margin between the output energy limit and the second average output energy. 
     According to an exemplary embodiment of the inventive concept, a method is provided for controlling a transmission power of a wireless communications device to comply with an output energy limit during a measurement period, the method including calculating a target output energy for at least one of the plurality of windows based on a communications channel; obtaining a first remaining output energy for a first of the plurality of windows based on the output energy limit and the target output energy; calculating a second remaining output energy for a remainder of the plurality of windows based on the target output energy and the first remaining output energy; and limiting the transmission power based on the output energy limit and the second remaining output energy. 
     According to an exemplary embodiment of the inventive concept, a wireless communications device is provided for controlling a transmission power to comply with an output energy limit during a measurement period divided into a plurality of windows, the wireless communications device including at least one antenna module comprising an antenna, a power detector, and a temperature sensor; a back-end module configured to provide, to the at least one antenna module, a high-frequency signal generated by processing a baseband signal in a transmission mode; and a signal processing unit configured to generate the baseband signal in the transmission mode, wherein the signal processing unit is further configured to adjust target output energy for a current one of the plurality of windows based on measurement information provided from the power detector and the temperature sensor, calculate an energy margin based on output energy output during a previous at least one of the plurality of windows, the adjusted target output energy and the output energy limit, and limit the transmission power based on the energy margin. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the inventive concept will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a schematic block diagram of a wireless communications system according to an exemplary embodiment of the inventive concept; 
         FIG. 2  is a flowchart of a method for controlling transmission power according to an exemplary embodiment of the inventive concept; 
         FIG. 3  is a graphical diagram for describing an operation of calculating target transmission power according to an exemplary embodiment of the inventive concept; 
         FIG. 4  is a schematic block diagram of a wireless communications device according to an exemplary embodiment of the inventive concept; 
         FIG. 5  is a flowchart of a method for controlling transmission power according to an exemplary embodiment of the inventive concept; 
         FIG. 6  is a flowchart of a method for controlling transmission power according to an exemplary embodiment of the inventive concept; 
         FIG. 7  is a graphical diagram for describing an operation of obtaining an output energy limit according to an exemplary embodiment of the inventive concept; 
         FIG. 8  is a flowchart of a method for controlling transmission power according to an exemplary embodiment of the inventive concept; 
         FIG. 9  is a flowchart of a method for controlling transmission power according to an exemplary embodiment of the inventive concept; 
         FIG. 10  is a tabular diagram that shows an example of a lookup table usable to limit transmission power according to an exemplary embodiment of the inventive concept; 
         FIG. 11  is a flowchart of a method for controlling transmission power according to an exemplary embodiment of the inventive concept; 
         FIG. 12  is a flowchart of a method for controlling transmission power according to an exemplary embodiment of the inventive concept; 
         FIG. 13  is a flowchart of method for controlling transmission power according to an exemplary embodiment of the inventive concept; 
         FIG. 14  is a timewise graphical diagram for describing an operation of calculating remaining output energy according to an exemplary embodiment of the inventive concept; 
         FIG. 15  is a flowchart of a method for controlling transmission power according to an exemplary embodiment of the inventive concept; 
         FIG. 16  includes a sequence of timewise graphical diagrams for describing an operation of limiting transmission power according to an exemplary embodiment of the inventive concept; and 
         FIG. 17  is a schematic block diagram of a communications apparatus according to an exemplary embodiment of the inventive concept. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a wireless communications system  5  according to an exemplary embodiment of the inventive concept. The wireless communications system  5  may include, but is not limited to, a wireless communications system using a cellular network such as, for example, a 5 th -generation (5G) new radio (NR) system, a long term evolution (LTE) system, an LTE-advanced (LTE-A) system, a code-division multiple access (CDMA) system, a global system for mobile communications (GSM) system, a wireless personal area network (WPAN) system, or another arbitrary wireless communications system. The wireless communications system  5  will be described below on the basis of a 5G NR system as a wireless communications system using a cellular network, but embodiments of the inventive concept are not limited thereto. 
     A base station (BS)  1  may generally refer to a fixed station communicating with user equipment (UE) devices and/or other base stations, to communicate and exchange data and control information with the UEs and/or the other BSs. For example, the BS  1  may be called a Node B, an evolved Node B (eNB), a next generation Node B (gNB), a sector, a site, a base transceiver system (BTS), an access point (AP), a relay node, a remote radio head (RRH), a radio unit (RU), or a small cell. In this specification, a BS or a cell may be comprehensively understood as a partial area covered by or the function of a BS controller (BSC) of CDMA, a Node-B of wideband CDMA (WCDMA), an eNB of LTE, a gNB of 5G, or a sector (or a site), and may have various coverage areas such as megacell, macrocell, microcell, picocell, femtocell, relay node, RRH, RU, small cell coverage areas, and the like. 
     A UE  10  may refer to any of arbitrary stationary or mobile devices capable of communicating with and transmitting and receiving data and/or control information to and from a BS, such as the BS  1 . For example, the UE  10  may be called a terminal, terminal equipment, a mobile station (MS), a mobile terminal (MT), a user terminal (UT), a subscriber station (SS), a wireless device, or a handheld device. Exemplary embodiments of the inventive concept will be described below on the basis of the UE  10  as a wireless communications device, but are not limited thereto. 
     A wireless communications network between the UE  10  and the BS  1  may support communications between a plurality of users by sharing available network resources. For example, in the wireless communications network, information may be transmitted using various multiple access methods such as code-division multiple access (CDMA), frequency-division multiple access (FDMA), time-division multiple access (TDMA), orthogonal frequency-division multiple access (OFDMA), single-carrier frequency-division multiple access (SC-FDMA), orthogonal frequency-division multiplexing (OFDM)-FDMA, OFDM-TDMA, and OFDM-CDMA or the like. As illustrated in  FIG. 1 , the UE  10  may communicate with the BS  1  through an uplink (UL) from the UE to the BS and a downlink (DL) from the BS to the UE. In some embodiments, as in device-to-device (D2D) communication, UEs may communicate with each other through one or more sidelinks. 
     As illustrated in  FIG. 1 , the UE  10  may include first to fourth antenna modules  11  to  14 , a back-end module  15 , at least one proximity sensor  16 , and a data processor  17 . In some embodiments, the first to fourth antenna modules  11  to  14  may be spaced apart from each other and be packaged independently. In some embodiments, the back-end module  15  and the data processor  17  may be packaged independently or together. 
     Each of the first to fourth antenna modules  11  to  14  may include at least one antenna and process signals received and to be transmitted through the antenna. In some embodiments, the first to fourth antenna modules  11  to  14  may generate or process first to fourth intermediate-frequency (IF) signals S_IF 1  to S_IF 4 . For example, the first antenna module  11  may generate the first IF signal S_IF 1  by using a radio-frequency (RF) signal received through the antenna, or the first antenna module may output through the antenna an RF signal generated by processing the first IF signal S_IF 1  provided from the back-end module  15 . In some embodiments, each of the first to fourth antenna modules  11  to  14  may be called a front-end module or an RF module. The structure of the exemplary first to fourth antenna modules  11  to  14  will be described below with reference to  FIG. 4 . 
     Short-wavelength signals may have strong directionality in a high-frequency band such as a millimeter-wave (mmWave) band, and thus quality of service (QoS) may be affected by obstructions and/or antenna directions. As such, in a wireless communications system that uses a high-frequency band to increase a data rate, a transmitter may use high transmission power such that a user of the UE  10  might be exposed to electromagnetic waves generated by the first to fourth antenna modules  11  to  14 . When each of the first to fourth antenna modules  11  to  14  includes a plurality of antennas for beamforming, spatial diversity, polarization diversity, spatial multiplexing, or the like, total radiated power output from the UE  10  may be increased over a unit having fewer antenna modules. When the UE  10  supports multiple connectivity to two or more wireless communications systems, e.g., dual connectivity, the Total Power Radiometer (TPR) radiated power measurement may also be increased. 
     Metrics such as a specific absorption rate (SAR) and a maximum permissible exposure (MPE) may be regulated to limit energy absorbed by a human body due to non-ionizing electromagnetic waves. Wireless communications devices need to comply with these or like metrics regulated by government agencies such as the US Federal Communications Commission (FCC). For example, the average energy measured from the UE  10  during a certain measurement period may be limited, and the measurement period may differ depending on a frequency band. As such, although the UE  10  may be allowed to use a relatively high transmission power over a relatively short period, the average of output energy during the measurement period may be more limited by the applicable regulations. In the following description, exemplary embodiments of the inventive concept will be described on the basis of a SAR, and metrics that the UE  10  needs to comply with will be referred to as SAR regulations. 
     The back-end module  15  may process or generate a baseband signal S_BB. For example, the back-end module  15  may generate at least one of the first to fourth IF signals S_IF 1  to S_IF 4  by processing the baseband signal S_BB provided from the data processor  17 , or generate the baseband signal S_BB by processing at least one of the first to fourth IF signals S_IF 1  to S_IF 4  received from the antenna modules. In some embodiments different from the illustration of  FIG. 1 , the first to fourth antenna modules  11  to  14  may separately generate baseband signals and provide the baseband signals to the data processor  17  and, in this case, the back-end module  15  may be omitted. 
     The data processor  17  may extract information provided by the BS  1 , such as payload data from the BS  1 , from the baseband signal S_BB received from the back-end module  15 , or the data processor  17  may generate the baseband signal S_BB including information to be provided to the BS  1 , such as payload data from the UE  10 . The data processor  17  may include a hardware block designed through logic synthesis, or include a software module including a series of instructions and a processing block including a processor for executing the instructions. The data processor  17  may be called a communications processor, a baseband processor, or a modem and, in this specification, the data processor  17  may be called a signal processing unit. 
     As illustrated in  FIG. 1 , the data processor  17  may receive first to fourth measurement signals MEA 1  to MEA 4 , respectively, from the first to fourth antenna modules  11  to  14 . For example, as further described below with reference to  FIG. 4 , the first antenna module  11 , which may include a power detector and/or a temperature sensor, may provide to the data processor  17  the first measurement signal MEA 1  including measurement information indicating detected transmission power and/or sensed temperature. The data processor  17  may accurately recognize power or energy output from the first to fourth antenna modules  11  to  14  based on the first to fourth measurement signals MEA 1  to MEA 4 , and thus transmission power may be controlled based on the actual output power, energy or temperatures of the UE  10 . 
     The at least one proximity sensor  16  may detect an external object or being in contact with or in the proximity of the UE  10 . The at least one proximity sensor  16  may detect the external object in an arbitrary manner and may include, but is not limited to, for example, a capacitive sensor, a temperature sensor, a grip sensor, and a time of flight (ToF) sensor. As illustrated in  FIG. 1 , the data processor  17  may obtain proximity information PRX from the at least one proximity sensor  16 . The data processor  17  may receive the proximity information PRX directly from the at least one proximity sensor  16  or from another element communicating with the at least one proximity sensor  16 , such as, for example, from a main processor  48  of  FIG. 4 . In some embodiments, the data processor  17  may directly generate the proximity information PRX by using the first to fourth antenna modules  11  to  14 . For example, the data processor  17  may detect the external object in the proximity of the first to fourth antenna modules  11  to  14  or detect a distance to the external object by measuring reflection coefficients of the antennas included in the first to fourth antenna modules  11  to  14 , or by analyzing correlations between signals provided to the first to fourth antenna modules  11  to  14  and signals received from the first to fourth antenna modules  11  to  14 . The data processor  17  may adjust transmission power for any or all of the antenna modules based on the proximity information PRX, and thus the UE  10  may limit the transmission power for any or all of the antenna modules when the external object or being is in the proximity of the UE  10  or a given antenna module, or provide improved QoS when the external object is not in the proximity of the UE  10  or the given antenna module. 
       FIG. 2  shows a method for controlling transmission power, according to an exemplary embodiment of the inventive concept. As illustrated in  FIG. 2 , the method for controlling transmission power may include a plurality of operations S 120 , S 140 , S 160 , and S 180 . In some embodiments, the method of  FIG. 2  may be performed by the data processor  17  of  FIG. 1 , and  FIG. 2  will now be described in conjunction with  FIG. 1 . 
     Referring to  FIG. 2 , in the operation S 120 , a target output energy may be calculated. In some embodiments, the data processor  17  may calculate the target output energy based on a communications channel with the BS  1 . For example, the data processor  17  may determine target transmission power based on a radio resource control (RRC) message, a medium access control (MAC) control element (CE) message, or downlink control information (DCI), and the target output energy may be calculated based on the target transmission power and a period in which the target transmission power is output. In some embodiments, the data processor  17  may more accurately calculate the target output energy by adjusting the target output energy based on measurement information. Examples of the operation S 120  will be further described below with reference to  FIGS. 3 and 5 . 
     In the next operation S 140 , an output energy limit may be obtained. The output energy limit may be determined according to SAR regulations. For example, a relationship between energy output from the UE  10  and a SAR measured from the UE  10  may be obtained through tests and/or simulations, and the output energy limit may be determined as output energy corresponding to a value of a SAR that the UE  10  needs to comply with during a measurement period. As such, when energy output from the UE  10  during the measurement period is controlled to be less than the output energy limit, the UE  10  may comply with the SAR regulations. In some embodiments, the UE  10  may include a non-volatile memory storing the output energy limit and, as further described below with reference to  FIG. 6 , the data processor  17  may adjust the output energy limit based on the proximity information PRX. 
     In the next operation S 160 , an average output energy may be calculated. The average output energy may refer to an average of an output energy predicted during the measurement period due to the target output energy calculated in operation S 120 . As further described below with reference to  FIG. 8 , the data processor  17  may calculate the average output energy through low-pass filtering. 
     In the next operation S 180 , transmission power may be limited based on an energy margin. For example, the data processor  17  may calculate the energy margin between the output energy limit obtained in operation S 140  and the average output energy calculated in operation S 160 . The data processor  17  may determine whether to limit the target transmission power based on the energy margin, and determine a reduction in the target transmission power, here called a backoff power, upon determining to limit the target transmission power. In some embodiments, when QoS deterioration is predicted due to a reduction in the transmission power, the data processor  17  may attempt to switch in or out an antenna module. An example of the operation S 180  will be further described below with reference to  FIG. 9 . 
       FIG. 3  shows an operation of calculating a target transmission power according to an exemplary embodiment of the inventive concept. Specifically,  FIG. 3  shows an example of the operation S 120  of  FIG. 2  in a wireless communications system employing time-division duplexing (TDD), and may be similarly applied to a wireless communications system employing frequency-division duplexing (FDD).  FIG. 3  will now be described in conjunction with  FIG. 1 . 
     A maximum transmission power P max  required to comply with an output energy limit may correspond to a value obtained by dividing the output energy limit by a measurement period. As such, in may be necessary to control an average transmission power P avg , indicating an average of transmission power values during the measurement period, to be less than the maximum transmission power P max . For example, as illustrated in  FIG. 3 , although the transmission power exceeds the maximum transmission power P max  at some instants in time, the average transmission power P avg  is less than or equal to the maximum transmission power P max  when averaged over the regulated measurement period such that the UE  10  may comply with the SAR regulations. In some embodiments, the data processor  17  may change the transmission power per unit interval, such as, for example, per slot, and where transmission power values of a sound reference signal (SRS), a physical uplink control channel (PUCCH), and a physical uplink shared channel (PUSCH) in a k th  slot are respectively denoted by P SRS (k), P PUCCH (k), and P PUSCH (k), target transmission power P target (k) of the k th  slot may be calculated as shown in [Equation 1].
 
 P   target ( k )= P   SRS ( k )· n   SRS ( k )+ P   PUCCH ( k )· n   PUCCH ( k )+ P   PUSCH ( k )· n   PUSCH ( k )  [Equation 1]
 
     In [Equation 1], n SRS (k), n PUCCH (k), and n PUSCH (k) respectively denote the numbers of symbols of the SRS, the PUCCH, and the PUSCH included in the k th  slot. For example, in a slot  30  of  FIG. 3 , n SRS (k), n PUCCH (k) and n PUSCH (k) may respectively be 2, 2, and 8. As such, when a duration or a length or a period of a symbol is denoted by T symbol , target output energy E target (k) of the k th  slot may be calculated as shown in [Equation 2].
 
 E   target ( k )= T   symbol   ·P   target ( k )  [Equation 2]
 
       FIG. 4  shows a wireless communications device according to an exemplary embodiment of the inventive concept. Specifically, the block diagram of  FIG. 4  illustrates a UE  40  including an antenna module  41  as an example of one of the first to fourth antenna modules  11  to  14  of  FIG. 1 . Descriptions provided above in relation to  FIG. 1  will be omitted herein to avoid redundancy. 
     Referring to  FIG. 4 , the UE  40  may include the antenna module  41 , a back-end module  45 , a data processor  47 , a main processor  48 , and a proximity sensor  46 . The antenna module  41  may include a mixer  41 _ 1  and a power amplifier  41 _ 2  to process an IF signal S_IF provided from the back-end module  45 , and include an antenna  41 _ 3 . The mixer  41 _ 1  may up-convert the IF signal S_IF by using a local oscillator signal LO, and the power amplifier  41 _ 2  may provide, to the antenna  41 _ 3 , a signal amplified based on controlled transmission power. Although not shown in  FIG. 4 , the antenna module  41  may further include elements for processing an RF signal received through the antenna  41 _ 3 , and/or further include switches for switching between a transmission mode and a reception mode. The antenna module  41  may further include a power detector  41 _ 4  and/or a temperature sensor  41 _ 5 . The power detector  41 _ 4  may detect power of the signal output from the power amplifier  41 _ 2 , and the temperature sensor  41 _ 5  may sense temperature of the antenna module  41 , such as, for example, temperature of the power amplifier  41 _ 2  and/or that of the power detector  41 _ 4 . A measurement signal MEA including measurement information indicating the power detected by the power detector  41 _ 4  and/or the temperature sensed by the temperature sensor  41 _ 5  may be provided to the data processor  47 . 
     The data processor  47  may exchange a baseband signal S_BB with the back-end module  45 , and exchange payload data D_PL with the main processor  48 . The main processor  48  may control overall operations of the UE  40 , execute an operating system and/or application programs in some embodiments and then be called an application processor. The main processor  48  may receive proximity information PRX from the proximity sensor  46 , and transmit the received proximity information PRX to the data processor  47 . 
       FIG. 5  shows a method for controlling transmission power, according to an exemplary embodiment of the inventive concept. Specifically, the flowchart of  FIG. 5  shows an alternate example of the operation S 120  of  FIG. 2 , and target output energy may be calculated in the operation S 120 ′ of  FIG. 5  similarly to that as described above in relation to  FIG. 2 . In some embodiments, an alternate operation S 120 ′ may be performed by the data processor  47  of  FIG. 4 , so  FIG. 5  will now be described in conjunction with  FIG. 4 . 
     Referring to  FIG. 5 , the operation S 120 ′ may include operations S 122  and S 124 . In the operation S 122 , measurement information may be obtained. For example, the data processor  47  may obtain the measurement information by using the measurement signal MEA provided from the antenna module  41 . Actual power output from the antenna module  41  may differ from transmission power requested by the data processor  17 . For example, the power amplifier  41 _ 2  may have a high temperature due to high transmission power, where output power of the power amplifier  41 _ 2  may be reduced due to the high temperature. As such, the power detector  41 _ 4  may be used to detect actual rather than requested transmission power of a signal output from the power amplifier  41 _ 2 , and the temperature sensor  41 _ 5  may be used to compensate for temperature characteristics of the power amplifier  41 _ 2  and/or the power detector  41 _ 4 . 
     In the next operation S 124 , target output energy per measurement period and/or time slot may be adjusted. For example, the data processor  47  may adjust the target output energy based on the measurement information. Compensation power P comp  for compensating for target transmission power P target  may be represented by a function of the target transmission power P target , power P DET  detected by the power detector  41 _ 4 , and temperature T SEN  sensed by the temperature sensor  41 _ 5 , as shown in [Equation 3].
 
 P   comp =ƒ( P   target   ,P   DET   ,T   SEN )  [Equation 3]
 
     A function f of [Equation 3] may be previously prepared through tests in a manufacturing process of the UE  40  or the antenna module  41 , and be defined as a mapping table in some embodiments. As such, adjusted target output energy E target (k)′ of a k th  slot may be expressed as shown in [Equation 4].
 
 E   target ( k )′= T   symbol ( P   target ( k )+ P   comp )  [Equation 4]
 
       FIG. 6  shows a method for controlling transmission power, according to an exemplary embodiment of the inventive concept, and  FIG. 7  shows an example of an alternate operation S 140 ′ of  FIG. 6 , according to an exemplary embodiment of the inventive concept. Specifically, the flowchart of  FIG. 6  shows an example of operation S 140  of  FIG. 2 . An output energy limit may be obtained in operation S 140 ′ of  FIG. 6  as described above in relation to  FIG. 2 , and operation S 140 ′ may include operations S 142  and S 144  as illustrated in  FIG. 6 . In some embodiments, operation S 140 ′ may be performed by the data processor  47  of  FIG. 4 , so  FIGS. 6 and 7  will now be described in conjunction with  FIG. 4 . 
     Referring to  FIG. 6 , in the operation S 142 , proximity information PRX may be obtained. For example, the data processor  47  may obtain the proximity information PRX through the main processor  48 , or generate the proximity information PRX based on a reflection coefficient of the antenna module  41 , a correlation between transmitted and received signals, or the like. As such, the data processor  47  may recognize whether an external object is in the proximity of the UE  40  and/or a distance between the external object and the UE  40  based on the proximity information PRX. 
     In the next operation S 144 , an output energy limit may be adjusted. For example, the data processor  47  may adjust the output energy limit to correspond to SAR regulations when an external object is in the proximity of the UE  40 , or increase the output energy limit when an external object is not detected or is spaced away from the UE  40 . Referring to  FIG. 7 , an external object might be detected until a time t 10 , and thus the data processor  47  may set maximum transmission power P max  determined according to SAR regulations. From the time t 10 , the external object might have moved away and not be detected or be detected as being spaced far enough away from the UE  40 , and thus the data processor  47  may set adjusted maximum transmission power P max ′, wherein the adjusted maximum transmission power P max ′ may be greater than the maximum transmission power P max . As such, in an environment where a communications channel is not in a clear condition and thus high transmission power is required, transmission power may be increased after the time t 10  and thus improved QoS may be achieved. 
       FIG. 8  shows a method for controlling transmission power according to an exemplary embodiment of the inventive concept. Specifically, the flowchart of  FIG. 8  shows an alternate example of the operation S 160  of  FIG. 2 . Average output energy may be calculated in an alternate operation S 160 ′ of  FIG. 8  as described above in relation to  FIG. 2 . In some embodiments, operation S 160 ′ may be performed by the data processor  17  of  FIG. 1 , so  FIG. 8  will now be described in conjunction with  FIG. 1 . 
     Referring to  FIG. 8 , the operation S 160 ′ may include operations S 162  and S 164 . In the operation S 162 , the previous average output energy may be obtained. In some embodiments, the data processor  17  may obtain average output energy corresponding to a previous period having a duration equal to a measurement period. The previous average output energy may be an average output energy calculated in an operation S 164  performed before operation S 162 , or an average output energy for which the transmission power limited in operation S 180  of  FIG. 2  is reflected. 
     In the next operation S 164 , the average output energy may be calculated through low-pass filtering. For example, the data processor  17  may calculate the average output energy by low-pass-filtering target output energy and the previous average output energy obtained in operation S 162 . In some embodiments, the data processor  17  may calculate the average output energy by finite impulse response (FIR)-filtering the target output energy and output energy values corresponding to unit intervals included in the previous period. Alternatively, in some embodiments, the data processor  17  may calculate the average output energy by infinite impulse response (IIR)-filtering, such as, for example, by accumulatively filtering the target output energy and the previous average output energy obtained in operation S 162 . For example, when an average output energy corresponding to a previous period including a (k−1) th  slot is denoted by E avg (k−1), an average output energy E avg (k) corresponding to a period including a k th  slot may be calculated as shown in [Equation 5].
 
 E   avg ( k )=(1−α) E   avg ( k− 1)+α· E   target ( k )  [Equation 5]
 
     In [Equation 5], α may have a value between 0 and 1 (0&lt;α&lt;1) and be determined based on a measurement period. For example, α may have a relatively small value when the measurement period is long, such as, for example, when a measurement frequency band is high, or have a relatively large value when the measurement period is short, such as, for example, when the measurement frequency band is low. In some embodiments, the target output energy E target (k) of [Equation 5] may be substituted by the adjusted target output energy E target (k)′ of [Equation 4]. 
       FIG. 9  shows a method for controlling transmission power according to an exemplary embodiment of the inventive concept, and  FIG. 10  shows an example of a lookup table  100  usable to perform an alternate operation S 180 ′ of  FIG. 9  according to an exemplary embodiment of the inventive concept. Specifically, the flowchart of  FIG. 9  shows an example of the operation S 180  of  FIG. 2 . Transmission power may be limited based on an energy margin in an operation S 180 ′ of  FIG. 9  as described above in relation to  FIG. 2 , and the operation S 180 ′ may include operations S 182 , S 184 , and S 186  as illustrated in  FIG. 9 . In some embodiments, the operation S 180 ′ may be performed by the data processor  17  of  FIG. 1 , so  FIGS. 9 and 10  will now be described in conjunction with  FIG. 1 . 
     In the operation S 182 , an energy margin may be calculated. For example, an energy margin ΔE may be represented by a difference between an output energy limit E max  and average output energy E max (k) as shown in [Equation 6].
 
Δ E=E   max   −E   avg ( k )= P   max   ·T   mea   −E   avg ( k )  [Equation 6]
 
     In [Equation 6], T mea  denotes a measurement period. In some embodiments, when the output energy limit E max  is adjusted as described above in relation to  FIGS. 6 and 7 , the energy margin ΔE may be represented based on the adjusted output energy limit E max ′ as shown in [Equation 7].
 
Δ E=E   max   ′−E   avg ( k )= P   max   ′·T   mea   −E   avg ( k )  [Equation 7]
 
     A large value of the energy margin ΔE may mean that high transmission power is usable, and a small value of the energy margin ΔE may mean that limitation of transmission power is required. 
     In the next operation S 184 , a backoff power corresponding to the energy margin may be obtained. In some embodiments, as illustrated in  FIG. 10 , the data processor  17  may refer to the lookup table  100  including a plurality of energy margin-backoff power pairs, and obtain backoff power P backoff  corresponding to the energy margin ΔE from the lookup table  100 . The UE  10  may include a non-volatile memory accessible by the data processor  17 , and the non-volatile memory may store the lookup table  100 . For example, the backoff power P backoff  may be 3.0 dBm when the energy margin ΔE is 4.5, or be 0 dBm when the energy margin ΔE is greater than 9. In some embodiments, the UE  10  may include an artificial neural network trained with a plurality of sample energy margin-backoff power pairs, and the data processor  17  may obtain the backoff power P backoff  corresponding to the energy margin ΔE from the artificial neural network. 
     In the next operation S 186 , the backoff power may be applied to target output energy. For example, the data processor  17  may reduce transmission power by the backoff power, and control the first to fourth antenna modules  11  to  14  based on the reduced transmission power. As described below with reference to  FIG. 11 , the data processor  17  may attempt to switch an antenna module used for communication based on temperatures and/or transmission powers. 
       FIG. 11  shows a method for controlling transmission power according to an exemplary embodiment of the inventive concept. Specifically, the flowchart of  FIG. 11  shows an alternate example of the operation S 186  of  FIG. 9 . Backoff power may be applied to a target output energy in an alternate operation S 186 ′ of  FIG. 11  as described above in relation to  FIG. 9 , and the operation S 186 ′ may include operations S 186 _ 1  to S 186 _ 5  as illustrated in  FIG. 11 . In some embodiments, operation S 186 ′ may be performed by the data processor  17  of  FIG. 1 , so  FIG. 11  will now be described in conjunction with  FIG. 1 . 
     In the operation S 186 _ 1 , backoff power P backoff  may be compared to a threshold value P th . A large value of the backoff power P backoff  may cause a reduction in transmission power, and thus QoS may deteriorate. To minimize QoS deterioration, when the backoff power P backoff  is greater than the threshold value P th , switching of an antenna module may be attempted in operation SW as described below. Otherwise, when the backoff power P backoff  is equal to or less than the threshold value P th  as illustrated in  FIG. 11  operation S 186 _ 2  may be is subsequently performed. 
     In the operation S 186 _ 2 , the backoff power P backoff  may be reflected to transmission power. For example, when the backoff power P backoff  is greater than 0 (zero), the data processor  17  may reduce the transmission power of at least one of the first to fourth antenna modules  11  to  14  by the backoff power. 
     As illustrated in  FIG. 11 , operation SW for attempting to switch the antenna module may include a plurality of operations S 186 _ 3  to S 186 _ 5 . In the operation S 186 _ 3 , QoS Q new  through another antenna module may be obtained. For example, when a communications channel with the BS  1  is formed through the current first antenna module  11 , the data processor  17  may obtain the QoS Q new  provided by a communications channel with the BS  1  through at least one of the second to fourth antenna modules  12  to  14 . The QoS may be defined by, but is not limited to, for example, metrics such as a signal-to-interference-plus-noise ratio (SINR), a reference signal received power (RSRP), a received signal strength indicator (RSSI), a block error rate (BLER), and a bit error rate (BER). In some embodiments, the QoS Q new  may correspond to QoS provided by a corresponding antenna module based on the transmission power reduced due to the backoff power P backoff . 
     In the next operation S 186 _ 4 , the obtained QoS Q new  may be compared to a minimum QoS Q link  required to maintain a link. As illustrated in  FIG. 11 , the operation S 186 _ 5  may be subsequently performed when the obtained QoS Q new  is greater than the minimum QoS Q link , or operation S 186 _ 2  may be subsequently performed when the obtained QoS Q new  is equal to or less than the minimum QoS Q link . 
     In some embodiments, in the operation S 186 _ 4 , different from the illustration of  FIG. 11 , the obtained QoS Q new  may be compared to QoS Q old  provided by a current antenna module. For example, when the QoS Q new  provided by the other antenna module is greater than the QoS Q old  provided by the antenna module currently performing wireless communications (Q new &gt;Q old ), the data processor  17  may switch the antenna module. In some embodiments, the QoS Q old  provided by the current antenna module may correspond to QoS estimated at the transmission power reduced based on the backoff power P backoff . 
     In the operation S 186 _ 5 , the antenna module may be switched. For example, the data processor  17  may select an antenna module providing QoS greater than the minimum QoS Q link  from among the first to fourth antenna modules  11  to  14 , and enable the selected antenna module to perform wireless communication. For example, the data processor  17  may switch the antenna module performing wireless communications from the first antenna module  11  to the second antenna module  12 , and store context of the first antenna module  11  related to wireless communication, e.g., an RSSI or a beam index, in a memory. The data processor  17  may load context of the second antenna module  12  related to wireless communication from the memory and set the second antenna module  12  based on the loaded context. U.S. patent application Ser. No. 16/694,718, which was filed on Nov. 25, 2019 by the present applicant and the disclosure of which is incorporated by reference herein in its entirety, discloses examples of an operation performed to switch an antenna module, and at least one of the examples may be performed in operation S 186 _ 5  of  FIG. 11 . 
       FIG. 12  shows a method for controlling transmission power, according to an exemplary embodiment of the inventive concept. As illustrated in  FIG. 12 , the method for controlling transmission power may include a plurality of operations S 220 , S 240 , S 260 , and S 280 . Compared to the method of  FIG. 2 , remaining output energy may be calculated based on an output energy limit and transmission power may be limited based on the remaining output energy in the method of  FIG. 12 . In some embodiments, the method of  FIG. 12  may be performed by the data processor  17  of  FIG. 1 , so  FIG. 12  will now be described in conjunction with  FIG. 1 . Descriptions provided above in relation to  FIG. 2  will be omitted herein to avoid redundancy. 
     Referring to  FIG. 12 , in the operation S 220 , similar to operation S 120  of  FIG. 2 , target output energy may be calculated. In some embodiments, the target output energy may be calculated as shown in [Equation 2] or [Equation 4], or be adjusted as described above in relation to  FIG. 5 . In the next operation S 240 , similar to operation S 240  of  FIG. 2 , an output energy limit may be obtained. In some embodiments, the output energy limit may be adjusted based on the proximity information PRX as described above in relation to  FIG. 6 . 
     In the next operation S 260 , remaining output energy may be calculated. The remaining output energy may refer to a maximum usable energy complying with the output energy limit. For example, as described below with reference to  FIGS. 13 and 14 , the data processor  17  may divide a measurement period into a plurality of periods having equal durations, and determine output energy of the divided periods based on the remaining output energy. 
     In the next operation S 280 , transmission power may be limited based on the remaining output energy. For example, the output energy of the divided periods may not be limited when the remaining output energy calculated in operation S 260  is sufficient, or the output energy of the divided periods may be limited and thus the transmission power may be limited when the remaining output energy is not sufficient. An example of operation S 280  will be described below with reference to  FIG. 15 . 
       FIG. 13  shows a method for controlling transmission power, according to an exemplary embodiment of the inventive concept, and  FIG. 14  shows an example of an alternate operation S 260 ′ of  FIG. 13 , according to an embodiment of the inventive concept. Specifically, the flowchart of  FIG. 13  shows an alternate example of the operation S 260  of  FIG. 12 . As described above in relation to  FIG. 12 , remaining output energy may be calculated in operation S 260 ′ of  FIG. 13 . In some embodiments, operation S 260 ′ may be performed by the data processor  17  of  FIG. 1 , so  FIGS. 13 and 14  will now be described in conjunction with  FIG. 1 . 
     Referring to  FIG. 13 , the operation S 260 ′ may include operations S 262  and S 264 . In the operation S 262 , previous remaining output energy may be obtained. When maximum transmission power P max  is adjustable as described above in relation to  FIG. 7 , an output energy limit E max  may be expressed as shown in [Equation 8] and refer to the amount of energy usable by the UE  10 . 
     
       
         
           
             
               
                 
                   
                     E 
                     max 
                   
                   = 
                   
                     
                       ∫ 
                       0 
                       
                         T 
                         mea 
                       
                     
                     ⁢ 
                     
                       
                         P 
                         max 
                       
                       ⁢ 
                       dt 
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     8 
                   
                   ] 
                 
               
             
           
         
       
     
     The data processor  17  may divide a measurement period T mea  into a plurality of periods having equal durations. For example, as illustrated in  FIG. 14 , the data processor  17  may divide the measurement period T mea  into M periods (M is an integer greater than 1), and each of the M periods may have a duration T win  corresponding to 1/M of the measurement period T mea . In this specification, the periods divided from the measurement period T mea  may be called windows, and the measurement period T mea  may be divided into first to M th  windows W 1  to W M  as illustrated in  FIG. 14 . Although the sub-periods or windows T win  described herein are of equal duration for ease of description, the sub-periods may be different in alternate embodiments. 
     When the UE  10  is connected to two or more wireless communications systems, all electromagnetic waves due to the connection to the two or more wireless communications systems may be required to comply with SAR regulations. Different wireless communications systems, such as, for example, 5G NR and LTE systems, may define different slot durations and, in some embodiments, a window may have the duration T win  corresponding to a common multiple of slot durations. For example, as illustrated in  FIG. 14 , a slot duration of a first wireless communications system RAT 1  may correspond to ¼ of a slot duration of a second wireless communications system RAT 2 , and thus T win  may be a multiple of the slot duration of the second wireless communications system RAT 2 . In some embodiments, T win  may be several tens of milliseconds (ms) to several hundred ms. Considering that a measurement period may be several seconds to several tens of seconds, different timings between slots of the first and second wireless communications systems RAT 1  and RAT 2  may be ignored. 
     When the UE  10  is connected to a 5G NR system together with an LTE system, transmission power P NR (k) of a k th  slot is defined according to [Equation 1] and, when a window includes K slots of the 5G NR system, output energy E NR (m) in an m th  window due to the 5G NR system may be expressed as shown in [Equation 9]. 
     
       
         
           
             
               
                 
                   
                     
                       E 
                       NR 
                     
                     ⁡ 
                     
                       ( 
                       m 
                       ) 
                     
                   
                   = 
                   
                     
                       ∑ 
                       
                         k 
                         = 
                         1 
                       
                       K 
                     
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     
                       
                         T 
                         
                           NR 
                           , 
                           symbol 
                         
                       
                       · 
                       
                         
                           P 
                           NR 
                         
                         ⁡ 
                         
                           ( 
                           k 
                           ) 
                         
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     9 
                   
                   ] 
                 
               
             
           
         
       
     
     When a window includes L slots of the LTE system and a slot duration of the LTE system is denoted by T LTE,slot , output energy E LTE (m) in the m th  window due to the LTE system may be expressed as shown in [Equation 10]. 
     
       
         
           
             
               
                 
                   
                     
                       E 
                       LTE 
                     
                     ⁡ 
                     
                       ( 
                       m 
                       ) 
                     
                   
                   = 
                   
                     
                       ∑ 
                       
                         l 
                         = 
                         1 
                       
                       L 
                     
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     
                       
                         T 
                         
                           LTE 
                           , 
                           slot 
                         
                       
                       ⁡ 
                       
                         ( 
                         
                           
                             
                               P 
                               
                                 LTE 
                                 , 
                                 PUCCH 
                               
                             
                             ⁡ 
                             
                               ( 
                               l 
                               ) 
                             
                           
                           + 
                           
                             
                               P 
                               
                                 LTE 
                                 , 
                                 PUSCH 
                               
                             
                             ⁡ 
                             
                               ( 
                               l 
                               ) 
                             
                           
                         
                         ) 
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     10 
                   
                   ] 
                 
               
             
           
         
       
     
     As such, energy E(m) output in the m th  window may be expressed as shown in [Equation 11].
 
 E ( m )= E   NR ( m )+ E   LTE ( m )  [Equation 11]
 
     Remaining output energy E remaining (n) in an n th  window (n&gt;M) may be calculated in a sequential manner as shown in [Equation 12]. 
     
       
         
           
             
               
                 
                   
                       
                   
                   ⁢ 
                   
                     
                       
                         
                           E 
                           remaining 
                         
                         ⁡ 
                         
                           ( 
                           1 
                           ) 
                         
                       
                       = 
                       
                         E 
                         max 
                       
                     
                     ⁢ 
                     
                       
 
                     
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     
                       
                         
                           E 
                           remaining 
                         
                         ⁡ 
                         
                           ( 
                           2 
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                       = 
                       
                         
                           
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                             remaining 
                           
                           ⁡ 
                           
                             ( 
                             1 
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                         - 
                         
                           E 
                           ⁡ 
                           
                             ( 
                             2 
                             ) 
                           
                         
                       
                     
                     ⁢ 
                     
                       
 
                     
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     ⋮ 
                     ⁢ 
                     
                       
 
                     
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     
                       
                         
                           E 
                           remaining 
                         
                         ⁡ 
                         
                           ( 
                           M 
                           ) 
                         
                       
                       = 
                       
                         
                           
                             E 
                             remeaining 
                           
                           ⁡ 
                           
                             ( 
                             
                               M 
                               - 
                               1 
                             
                             ) 
                           
                         
                         - 
                         
                           E 
                           ⁡ 
                           
                             ( 
                             M 
                             ) 
                           
                         
                       
                     
                     ⁢ 
                     
                       
 
                     
                     ⁢ 
                     
                       
                         
                           E 
                           remaining 
                         
                         ⁡ 
                         
                           ( 
                           
                             M 
                             + 
                             1 
                           
                           ) 
                         
                       
                       = 
                       
                         
                           
                             E 
                             remaining 
                           
                           ⁡ 
                           
                             ( 
                             M 
                             ) 
                           
                         
                         - 
                         
                           E 
                           ⁡ 
                           
                             ( 
                             
                               M 
                               + 
                               1 
                             
                             ) 
                           
                         
                         + 
                         
                           E 
                           ⁡ 
                           
                             ( 
                             1 
                             ) 
                           
                         
                       
                     
                     ⁢ 
                     
                       
 
                     
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     ⋮ 
                     ⁢ 
                     
                       
 
                     
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     
                       
                         
                           E 
                           remaining 
                         
                         ⁡ 
                         
                           ( 
                           n 
                           ) 
                         
                       
                       = 
                       
                         
                           
                             E 
                             remaining 
                           
                           ⁡ 
                           
                             ( 
                             
                               n 
                               - 
                               1 
                             
                             ) 
                           
                         
                         - 
                         
                           E 
                           ⁡ 
                           
                             ( 
                             n 
                             ) 
                           
                         
                         + 
                         
                           E 
                           ⁡ 
                           
                             ( 
                             
                               n 
                               - 
                               M 
                             
                             ) 
                           
                         
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     12 
                   
                   ] 
                 
               
             
           
         
       
     
     As such, to calculate the remaining output energy E remaining (n) of the current n th  window, the data processor  17  may obtain remaining output energy E remaining (n−1)+E(n−M) of previous M−1 windows. To this end, the data processor  17  may store M output energy values of previous M windows in a memory. 
     In the next operation S 264 , remaining output energy may be calculated based on the previous remaining output energy and target output energy. For example, the data processor  17  may calculate the remaining output energy E remaining (n) of the current n th  window by subtracting target output energy E(n) of the n th  window from the previous remaining output energy E remaining (n−1)+E(n−M) as shown in [Equation 12]. 
       FIG. 15  shows a method for controlling transmission power, according to an exemplary embodiment of the inventive concept. Specifically, the flowchart of  FIG. 15  shows an alternate example of an operation S 280  of  FIG. 12 . As described above in relation to  FIG. 12 , transmission power may be limited based on remaining output energy in an alternate operation S 280 ′ of  FIG. 15 . Compared to operation S 180 ′ of  FIG. 9 , target output energy may be limited in operation S 280 ′ of  FIG. 15 . In some embodiments, the method of  FIG. 15  may be performed by the data processor  17  of  FIG. 1 ,  FIG. 15  will now be described in conjunction with  FIG. 1 , and descriptions provided above in relation to  FIG. 9  will be omitted herein to avoid redundancy. 
     In the operation S 282 , target output energy may be limited. For example, the data processor  17  may limit target output energy E(n) of a current n th  window based on remaining output energy E remaining (n) as shown in [Equation 13]. 
     
       
         
           
             
               
                 
                   
                     E 
                     ⁡ 
                     
                       ( 
                       n 
                       ) 
                     
                   
                   = 
                   
                     { 
                     
                       
                         
                           
                             
                               
                                 E 
                                 ⁡ 
                                 
                                   ( 
                                   n 
                                   ) 
                                 
                               
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               if 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               
                                 
                                   E 
                                   remaining 
                                 
                                 ⁡ 
                                 
                                   ( 
                                   
                                     n 
                                     - 
                                     1 
                                   
                                   ) 
                                 
                               
                             
                             &gt; 
                             
                               β 
                               · 
                               
                                 E 
                                 max 
                               
                             
                           
                         
                       
                       
                         
                           
                             
                               min 
                               ⁡ 
                               
                                 ( 
                                 
                                   
                                     E 
                                     ⁡ 
                                     
                                       ( 
                                       n 
                                       ) 
                                     
                                   
                                   , 
                                   
                                     E 
                                     ⁡ 
                                     
                                       ( 
                                       
                                         n 
                                         - 
                                         M 
                                       
                                       ) 
                                     
                                   
                                 
                                 ) 
                               
                             
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             else 
                           
                         
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     13 
                   
                   ] 
                 
               
             
           
         
       
     
     In [Equation 13], β may be greater than 0 (zero) and less than 1 (0&lt;β&lt;1), and high remaining output energy may be maintained when β has a large value and low remaining output energy may be maintained when β has a small value. In some embodiments, β may be determined based on the size of an error between output energy calculated by the data processor  17  and energy actually radiated by the UE  10 . For example, the UE  10  may include an energy source for wireless communications and another energy source for generating electromagnetic waves, and an error between output energy of the first to fourth antenna modules  11  to  14  and energy radiated from the UE  10  may occur due to various reasons. According to [Equation 13], when the remaining output energy is less than a reference value (i.e., βE max ) due to the target output energy of the current window, the target output energy of the current window may be limited to energy of windows not included in a measurement period (i.e., E(n−M)). 
     In the next operation S 284 , backoff power corresponding to a reduction in output energy may be obtained. In some embodiments, as described above in relation to  FIG. 10 , the data processor  17  may obtain the backoff power with reference to a lookup table including a plurality of output energy reduction-backoff power pairs, or from an artificial neural network trained with a plurality of sample energy margin-backoff power pairs. 
     In the next operation S 286 , the backoff power may be applied to the target output energy. For example, the data processor  17  may reduce transmission power by the backoff power, and control the first to fourth antenna modules  11  to  14  based on the reduced transmission power. As described above in relation to  FIG. 11 , when the backoff power is large, to improve QoS in wireless communication, the data processor  17  may attempt or determine whether to switch an antenna module used for communication. 
       FIG. 16  shows an example of the operation S 280 ′ of  FIG. 15 , according to an exemplary embodiment of the inventive concept.  FIG. 16  will now be described in conjunction with FIG.  15 . 
     Referring to an upper graph of  FIG. 16 , a measurement period T mea  may correspond to a period from a time t 81  to a time t 84 , and an average of transmission power values of windows in the period from the time t 81  to the time t 84  may be less than maximum transmission power P max . Target transmission power of an n th  window W n  corresponding to a period from the time t 84  to a time t 85  may be calculated as indicated by a dashed line and, referring to a middle graph of  FIG. 16 , the target transmission power of the n th  window W n  may be limited based on remaining output energy. That is, when the remaining output energy is not sufficient (i.e., E remaining (n)≤βE max ), transmission power of the n th  window W n  may be limited to transmission power of an (n−M) th  window W n−M  corresponding to a period from the time t 81  to the time t 82 , and thus the average of the transmission power values of the windows in the measurement period T mea  corresponding to a period from the time t 82  to the time t 85  may be less than the maximum transmission power P max . 
     Referring to the middle graph of  FIG. 16 , the measurement period T mea  may correspond to a period from the time t 82  to the time t 85 . Target transmission power of an (n+1) th  window W n+1  corresponding to a period from the time t 85  to a time t 86  may be calculated as indicated by a dashed line and, referring to a lower graph of  FIG. 16 , the target transmission power of the (n+1) th  window W n+1  may be limited based on remaining output energy. That is, when the remaining output energy is not sufficient (i.e., E remaining (n+1)≤βE max ), transmission power of the (n+1) th  window W n+1  may be limited to transmission power of an (n+1−M) th  window W n+1−M  corresponding to a period from the time t 82  to the time t 83 , and thus the average of the transmission power values of the windows in the measurement period T mea  corresponding to a period from the time t 83  to the time t 86  may be less than the maximum transmission power P max . 
       FIG. 17  shows an example of a communications apparatus  170  according to an exemplary embodiment of the inventive concept. In some embodiments, the communications apparatus  170  may be included in the UE  10  of  FIG. 1 . 
     As illustrated in  FIG. 17 , the communications apparatus  170  may include an application-specific integrated circuit (ASIC)  171 , an application-specific instruction set processor (ASIP)  173 , a memory  175 , a main processor  177 , and a main memory  179 . In some embodiments, two or more of the ASIC  171 , the ASIP  173 , and the main processor  177  may communicate with each other. In some embodiments, two or more of the ASIC  171 , the ASIP  173 , the memory  175 , the main processor  177 , and the main memory  179  may be embedded in a chip. 
     As an integrated circuit customized for a specific purpose, the ASIP  173  may support a dedicated instruction set for a specific application, and execute instructions included in the instruction set. The memory  175  may communicate with the ASIP  173  and store, as a non-transitory storage device, a plurality of instructions to be executed by the ASIP  173 . The term “non-transitory” as used herein describes the medium itself, which is tangible rather than a mere signal. For example, the memory  175  may include, but is not limited to, an arbitrary type of memory such as, for example, flash memory, random access memory (RAM), read only memory (ROM), magnetic tape, a magnetic disk, an optical disk, volatile memory, non-volatile memory, or a combination thereof. 
     In some embodiments, the memory  175  may store the above-described output energy limit, the lookup table  100  of  FIG. 10 , and the like. 
     The main processor  177  may control the communications apparatus  170  by executing a plurality of instructions. For example, the main processor  177  may control the ASIC  171  and the ASIP  173 , and process data received through a wireless communications network or user input related to the communications apparatus  170 . The main memory  179  may communicate with the main processor  177  and store, as a non-transitory storage device, a plurality of instructions to be executed by the main processor  177 . For example, the main memory  179  may include, but is not limited to, an arbitrary type of memory as described above. 
     A method for controlling transmission power may be performed by at least one of the elements included in the communications apparatus  170  of  FIG. 17 . In some embodiments, operation of the data processor  17  of  FIG. 1  may be implemented by a plurality of instructions stored in the memory  175 , and the ASIP  173  may perform at least one of operations of the method for controlling transmission power, by executing the plurality of instructions stored in the memory  175 . In some embodiments, at least one of the operations of the method for controlling transmission power may be performed by a hardware block designed through logic synthesis or the like, and the hardware block may be included in the ASIC  171 . In some embodiments, at least one of the operations of the method for controlling transmission power may be implemented by a plurality of instructions stored in the main memory  179 , and the main processor  177  may perform at least one of the operations of the method for controlling transmission power by executing the plurality of instructions stored in the main memory  179 . 
     While the inventive concept has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood that various changes in form and details may be made therein by those of ordinary skill in the pertinent art without departing from the scope and spirit of the inventive concept as defined by the following claims and their equivalents.