Abstract:
The present disclosure relates to a pre-5 th -Generation (5G) or 5G communication system to be provided for supporting higher data rates Beyond 4 th -Generation (4G) communication system such as Long Term Evolution (LTE). According to one embodiment, an apparatus for beamforming includes a detector for measuring at least one change of movement and rotation of an apparatus; and a calculator for determining a beamforming parameter for aligning a beam direction with another apparatus by compensating for the change of the beam direction according to at least one of the movement and the rotation.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) AND CLAIM OF PRIORITY 
       [0001]    The present application is a continuation-in-part of U.S. Non-Provisional patent application Ser. No. 13/549,280 filed Jul. 13, 2012, which is related to and claims the benefit under 35 U.S.C. §119(a) to a Korean patent application filed in the Korean Intellectual Property Office on Jul. 15, 2011 and assigned Serial No. 10-2011-0070330. The entire disclosure of the above-identified patent documents are hereby incorporated by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The present disclosure relates generally to wireless communication systems, and more particularly, to an apparatus and method for beam locking in a wireless communication system. 
       BACKGROUND 
       [0003]    To meet the demand for wireless data traffic having increased since deployment of 4th generation (4G) communication systems, efforts have been made to develop an improved 5th generation (5G) or pre-5G communication system. Therefore, the 5G or pre-5G communication system is also called a “‘Beyond 4G Network’” or a “‘Post Long Term Evolution (LTE) System’.” 
         [0004]    The 5G communication system is considered to be implemented in higher frequency (mmWave) bands, e.g., 28 gigaHertz (GHz) or 60 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 5G communication systems. 
         [0005]    In addition, in 5G 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. 
         [0006]    In the 5G system, Hybrid frequency shift keying (FSK) and quadrature amplitude modulation (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. 
         [0007]    To enhance performance of wireless communication systems, beamforming is often applied. In general, beamforming increases signal reception sensitivity of a particular receiver by giving directionality to the beam using multiple antennas. The beamforming may be categorized according to transmission beamforming and reception beamforming based on which communication element conducts the beamforming operation. 
         [0008]      FIG. 1  depicts beams of a base station applying a beamforming operation in a wireless communication system. Referring to  FIG. 1 , the base station covers a plurality of sectors and forms a plurality of beams having directionality in each sector. When the beamforming is applied, the propagation pattern narrows. Hence, it is necessary to use more beams than antennas in the sector in order to service one base station cell or sector. Because of the narrow beamforming of the base station, a user station can obtain better channel state. 
         [0009]    The user station needs to select the best beam from the multiple beams of the base station and select a new beam according to its rotation or movement. As the beam becomes narrower, the beam is selected more on a more frequent basis. When the user station applies beamforming, the best channel state is attained only when the beam direction of the base station matches the beam direction of the user station. However, unlike the stationary base station, the user station is mobile. Moreover, the direction of the station facing the base station can easily change. As a result, the beam directions of the user station and the base station can be misaligned frequently. 
       SUMMARY 
       [0010]    To address the above-discussed deficiencies of the prior art, it is a primary aspect of the present disclosure to provide an apparatus and a method for maintaining a beam direction of a user station which performs beamforming in a wireless communication system. 
         [0011]    Another aspect of the present disclosure is to provide an apparatus and a method for compensating for a beam direction based on movement and/or rotation of a user station in a wireless communication system. 
         [0012]    According to one aspect of the present disclosure, an apparatus for beamforming in a wireless communication system includes a detector for measuring at least one change of movement and/or rotation of the apparatus, and a calculator for determining a beamforming parameter for aligning a beam direction with another apparatus by compensating for the change of the beam direction according to at least one of the movement and the rotation. 
         [0013]    According to another aspect of the present disclosure, a method for beamforming in a wireless communication system includes measuring at least one change of movement and rotation of an apparatus, and determining a beamforming parameter for aligning a beam direction with another apparatus by compensating for the change of the beam direction according to at least one of the movement and the rotation. 
         [0014]    According to yet another aspect of the present disclosure, a method of a user station in a wireless communication system includes generating a control message informing that a beam locking scheme is supported to maintain a beam direction in a reference direction by compensating for a change of the beam direction caused by movement and/or rotation of the user station, and transmitting the control message to a base station. 
         [0015]    According to another aspect of the present disclosure, a method of a base station in a wireless communication system includes receiving a control message informing that a beam locking scheme is supported to maintain a beam direction in a reference direction by compensating for a change of the beam direction caused by movement and/or rotation of a user station, and determining based on the control message whether the user station supports the beam locking scheme. 
         [0016]    Other aspects, advantages, and salient features of the present disclosure will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses example embodiments of the present disclosure. 
         [0017]    Before undertaking the DETAILED DESCRIPTION below, it may be advantageous to set forth definitions of certain words and phrases used throughout this patent document: the terms “include” and “comprise,” as well as derivatives thereof, mean inclusion without limitation; the term “or,” is inclusive, meaning and/or; the phrases “associated with” and “associated therewith,” as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like; and the term “controller” means any device, system or part thereof that controls at least one operation, such a device may be implemented in hardware, firmware or software, or some combination of at least two of the same. It should be noted that the functionality associated with any particular controller may be centralized or distributed, whether locally or remotely. Definitions for certain words and phrases are provided throughout this patent document, those of ordinary skill in the art should understand that in many, if not most instances, such definitions apply to prior, as well as future uses of such defined words and phrases. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]    For a more complete understanding of the present disclosure and its advantages, reference is now made to the following description taken in conjunction with the accompanying drawings, in which like reference numerals represent like parts: 
           [0019]      FIG. 1  illustrates example beams of a base station adopting beamforming technology in a wireless communication system; 
           [0020]      FIGS. 2A through 2D  illustrate example beam directions of a base station and a user station in a wireless communication system according to an embodiment of the present disclosure; 
           [0021]      FIG. 3  illustrates an example beam direction compensated based on rotation of the user station in the wireless communication system according to an embodiment of the present disclosure; 
           [0022]      FIG. 4  illustrates an example beam locking method in the wireless communication system according to an embodiment of the present disclosure; 
           [0023]      FIG. 5  illustrates an example beam locking method in the wireless communication system according to another embodiment of the present disclosure; 
           [0024]      FIG. 6  illustrates an example beam locking method in the wireless communication system according to yet another embodiment of the present disclosure; 
           [0025]      FIG. 7  illustrates an example beam locking method in the wireless communication system according to another embodiment of the present disclosure; 
           [0026]      FIG. 8  illustrates an example apparatus for locking the beam in the wireless communication system according to an embodiment of the present disclosure; 
           [0027]      FIG. 9  illustrates an example apparatus for locking the beam in the wireless communication system according to another embodiment of the present disclosure; 
           [0028]      FIG. 10  illustrates an example apparatus for locking the beam in the wireless communication system according to another embodiment of the present disclosure; 
           [0029]      FIG. 11  illustrates an example apparatus for locking the beam in the wireless communication system according to another embodiment of the present disclosure; 
           [0030]      FIG. 12  illustrates an example beam locking unit in the wireless communication system according to an embodiment of the present disclosure; 
           [0031]      FIG. 13  illustrates an example beam locking unit in the wireless communication system according to another embodiment of the present disclosure; 
           [0032]      FIG. 14  illustrates example signals between a base station and the user station in the wireless communication system according to an embodiment of the present disclosure; and 
           [0033]      FIG. 15  illustrates an example of beam training when the beam locking is applied in the wireless communication system according to an embodiment of the present disclosure. 
       
    
    
       [0034]    Throughout the drawings, like reference numerals will be understood to refer to like parts, components and structures. 
       DETAILED DESCRIPTION 
       [0035]      FIGS. 2A through 15 , discussed below, and the various embodiments used to describe the principles of the present disclosure in this patent document are by way of illustration only and should not be construed in any way to limit the scope of the disclosure. Those skilled in the art will understand that the principles of the present disclosure may be implemented in any suitably arranged wireless communications system. 
         [0036]    The present disclosure relates to an apparatus and a method for maintaining a beam direction in beamforming of the wireless communication system. Example embodiments of the present disclosure provide a technique for maintaining a beam direction of a user station in a wireless communication system. 
         [0037]      FIGS. 2A through 2D  illustrate example beam directions of a base station and a user station in a wireless communication system according to an embodiment of the present disclosure. 
         [0038]    Referring first to  FIG. 2A , the beam direction for transmission and reception of the base station  210  matches the beam direction for transmission and reception of the user station  220 . When the beam direction of the base station  210  faces the user station  220 , the user station  220  is placed in a beam range of the base station  210 . To increase reliability and efficiency of the data transmission and reception, the user station  220  in the beam range also forms the beam toward the base station  210 . When the beam directions of the base station  210  and the user station  220  are aligned as shown in  FIG. 2A , best communication quality is obtained. 
         [0039]    In general, beam training is used to align the beam direction between the base station  210  and the user station  220 . The beam training is divided into an uplink and a downlink. In the downlink, the base station  210  assigns a particular sequence for the beam training to beam training reference signals of a particular direction, and transmits the reference signals as the beam of the particular direction. Hence, the user station  220  informs the base station  210  of a particular sequence value of the reference signal having the best communication quality among one or more beam training references signals transmitted by the base station  210 . Thus, the aligned beam direction of the base station  210  and the user station  220  can be determined. In the uplink, the user station  220  assigns a particular sequence for the beam training to beam training reference signals of a particular direction, and transmits the reference signals as the beam of the particular direction. The base station  210  informs the user station  220  of a particular sequence value of the reference signal having the best communication quality among the beam training references signals. 
         [0040]    As stated above, the beam training method is adequate for a stationary base station and a stationary user station. However, when the user station  220  frequently moves during a short time, it is difficult to apply the beam alignment method using the beam training. This problem is shown in  FIGS. 2B, 2C and 2D .  FIGS. 2B, 2C and 2D  depict misalignment of the beam direction according to the rotation and the movement of the user station  220 . Referring to  FIG. 2B , as the user station  220  is tilted, the beam directions of the base station  210  and the user station  220  are misaligned according to the tilt. Referring to  FIG. 2C , as the user station  220  rotates, the beam directions of the base station  210  and the user station  220  are misaligned according to the rotation. Referring to  FIG. 2D , as the user station  220  moves, the beam directions of the base station  210  and the user station  220  are misaligned according to the movement. 
         [0041]    As shown in  FIGS. 2B, 2C and 2D , when the user acts or moves, the beam directions between the base station  210  and the user station  220  can become misaligned. In this case, communication quality of the base station  210  and the user station  220  may deteriorate. Further, since the rotation or the movement of the user may be relatively frequent over a relatively short time, it may be hard to overcome the misalignment using general beam training techniques. In more detail, to detect the change of the beam direction of the user station  220  the base station  210  needs to check the change of the beam direction of the user station  220  on a frequent basis. Accordingly, control messages are typically exchanged frequently. As more accurate information of the beam direction change of the user station  220  is required, control messages are exchanged more frequently, which results in system overhead. Hence, the present disclosure provides a method for overcoming the beam direction misalignment according to the rotation or the movement of the user station  220 . 
         [0042]      FIG. 3  depicts an example beam direction compensation based on the rotation of a user station in the wireless communication system according to an embodiment of the present disclosure. 
         [0043]    Referring to  FIG. 3 , when the beam direction between a base station and the user station is aligned, the user station sets the aligned beam direction to a reference direction  301 . For example, the reference direction  301  of the beam direction can be set through beam training. For example, the reference direction  301  of the beam direction can be set to the aligned beam direction based on location information between the base station and the user station. Besides, various schemes can be applied to set the reference direction  301 . 
         [0044]    Next, when the rotation of the user station tilts or rotates the beam direction or when the movement of the user station changes the beam direction, the user station measures the change in accordance with the reference direction. That is, the user station measures a physical change value in three (i.e., three-dimensions) directions. The physical change value of the three directions can be measured as an angle, an angular speed, an angular acceleration, a rotation angle, a rotation angular speed, a rotation acceleration, a travel distance, a travel speed, and a travel acceleration in the horizontal (e.g., azimuthal) directions and the vertical (altitude) direction. The physical change can be measured using various well-known schemes. Herein, the physical change can be measured using any of a variety of sensors. For example, the sensors can include at least one of a compass sensor, an accelerometer, a G-sensor, and a Gyroscope. Alternatively, a Global Positioning System (GPS) can be used. Alternatively, angle of arrival of an electric signal transmitted by then base station can be used. Alternatively, trigonometry using locations of and received signals from the base station or Access Points (APs) can be used. 
         [0045]    The user station maintains the beam direction in the reference direction  301  by compensating for the beam direction according to the physical change value. For example, when a user turns or moves his/her head during the phone call, the beam direction of the user station aligned with the base station changes. When geographical space is represented in orthogonal directions of x, y and z and the beam direction rotates from the reference direction  301  to the z axis by 30 degrees, the beam direction of the user station may be maintained in the reference direction  301  by rotating the beam direction of the user station in the z axis by −30 degrees. Hence, even when the beam direction of the user station rotates by 30 degrees, the base station can communicate with the user station in the existing beam direction regardless of the beam direction rotation of the user station. In other words, when the present algorithm for compensating for the beam direction directly by the user station is applied to the physical direction and location changes caused by rotation or movement of the user station, it is similar to a case in which the base station communicates with the user station that does not physically move or rotate. In this case, the uplink and downlink beamforming may be fulfilled without undue system overhead. 
         [0046]    The technique for maintaining the beam direction sets the beam direction of the user station for sustaining relatively good communication quality between the base station and the user station to the reference direction, measures the physical change value when the beam direction changes, and compensates for the beam direction based on the measured physical change value. Hence, the technique for maintaining the beam direction may be referred to as a beam locking scheme. The beam locking scheme can be widely applied to any station configured to move or rotate while being used in the wireless communication system. 
         [0047]    Now, an operation and structure of an apparatus for the beam locking technique as explained above are described by referring to the drawings. 
         [0048]    Hereafter, it is assumed that the reference direction of the beam is set between the base station and the user station before beam locking. The reference beam direction can be initially set or periodically reset between the base station and the user station. For example, the apparatus can set the beam direction in a plurality of candidate directions, repeatedly transmit a training reference signal, and select the candidate direction of the matching beam direction. In addition, the apparatus can adjust the beam width of the beam formed according to the beamforming technique. 
         [0049]      FIG. 4  illustrates an example beam locking method in the wireless communication system according to an embodiment of the present disclosure. 
         [0050]    Referring to  FIG. 4 , the apparatus measures changes based on the reference direction of the beam; that is, the change of the location according to the movement and the change of the direction and the slope according to the rotation/tilt in step  401 . For example, the apparatus can periodically measure the change at regular time intervals. When there is no movement/rotation/tilt of the apparatus, the change is measured as zero. For example, the change of the location and the change of the direction and the slope can be measured using the sensor, the GPS, the angle of the arrival of the signal, or the trigonometry using the received signal. 
         [0051]    In step  403 , the apparatus compensates for the beam direction. That is, the apparatus calculates a new beamforming parameter which aligns the beam direction altered by the change with the reference direction, and compensates for the beam direction using the new beamforming parameter. In doing so, the new beamforming parameter is determined by a beamforming parameter of the reference direction and the change. For example, the apparatus determines the new beamforming parameter according to a predefined function or rule which uses the beamforming parameter of the reference direction and the change as input variables. Alternatively, the apparatus determines the new beamforming parameter using a mapping table which defines new beamforming parameters based on the change compared with the beamforming parameter of the reference direction. 
         [0052]    The beamforming parameter includes a result value of the function which uses the physical change value as its input variable. In detail, when the beamforming parameter of the reference direction is (α,β,γ), the physical change value is (a, b, c), and the new beamforming parameter changed by the physical change value is (α*,β*,γ*), the beamforming parameter can be determined according to Equation (1). 
         [0000]      α*( α,a,b,c )=α× f   1 ( a,b,c )+ g   1 ( a,b,c )
 
         [0000]      β*( β,a,b,c )=β× f   2 ( a,b,c )+ g   2 ( a,b,c )   (1)
 
         [0000]      γ*( γ,a,b,c )=γ× f   3 ( a,b,c )+ g   3 ( a,b,c )
 
         [0053]    In Equation (1), α, β and γ denote the beamforming parameters in the reference direction, a, b and c denote the physical change values, and α* , β* and γ* denote the new beamforming parameters altered by the physical change values. 
         [0054]    That is, the values for determining the new beamforming parameter are the beamforming parameter of the reference beam direction and the physical change value measured by the user station. Herein, f 1 , f 2 , f 3 , g 1 , g 2  and g 3  can be defined by the predefined function or rule or the mapping table. 
         [0055]    The beamforming parameter can vary according to the selected beamforming scheme. For example, in digital beamforming, the beamforming parameter can include at least one of an index of a precoding codebook used in a digital stage, a beamforming matrix, and a beamforming vector. For another example, in analog beamforming, the beamforming parameter can include phase and amplitude values per antenna. For another example, in a case in which the antenna may be physically moved, the beamforming parameter can be a physical attitude control value such as rotation or slope. For another example, when antennas, antenna groups, or antenna arrays corresponding to the beam direction are equipped in advance and a beam index or an antenna index is assigned to each beam direction, the beamforming parameter can include at least one of the beam index and the antenna index. 
         [0056]    Although not depicted in  FIG. 4 , the apparatus can set the reference direction before measuring the change. For example, the apparatus can set the reference direction through beam training. For example, the apparatus can set the beam directions in multiple candidate directions, repeatedly transmit the training reference signal, and select the candidate direction aligned with the beam direction. In addition, the apparatus can refine the beam to use a relatively narrower beam. 
         [0057]      FIG. 5  illustrates an example beam locking method according to another embodiment of the present disclosure. 
         [0058]    In step  501 , the apparatus determines whether the movement or the rotation occurs. That is, the apparatus determines whether at least one of the location, the slope, and the direction changes. 
         [0059]    When the movement or the rotation occurs, the apparatus measures the change of the location according to the movement and the change of the direction and the slope according to the rotation/slope in step  503 . By contrast, when movement or rotation of the apparatus does not occur, the apparatus may not perform step  503 . That is, with parameters (a,b,c) for the physical change and thresholds (a′,b′,c′) for determining the rotation, the apparatus can measure the change only when at least one of (a,b,c) is greater than or equal to at least a threshold value (a′,b′,c′); that is, only when a≧a′, b≧b′ or c≧c′. For example, the change of the location and the change of the direction and the slope can be measured using the sensor, the GPS, the angle of the arrival of the signal, or the trigonometry using the received signal. 
         [0060]    In step  505 , the apparatus compensates for the beam direction in step  505 . That is, the apparatus calculates a new beamforming parameter which aligns the beam direction altered by the change with the reference direction, and compensates for the beam direction using the new beamforming parameter. In so doing, the new beamforming parameter is determined by the beamforming parameter of the reference direction and the change. For example, the apparatus can determine the new beamforming parameter according to the predefined rule which uses the beamforming parameter of the reference direction and the change as its input variables. Alternatively, the apparatus can determine the new beamforming parameter using the mapping table which defines the new beamforming parameters based on the change against the beamforming parameter of the reference direction. More specifically, the new beamforming parameter can be determined using Equation (1). The beamforming parameter can vary according to the selected beamforming scheme. For example, in digital beamforming, the beamforming parameter can include at least one of the index of the precoding codebook used in the digital stage, the beamforming matrix, and the beamforming vector. For another example, in analog beamforming, the beamforming parameter can include the phase and amplitude values per antenna. For another example, in beamforming which the antenna is physically moved, the beamforming parameter can be the physical attitude control value such as rotation or slope. For another example, when antennas, antenna groups, or antenna arrays corresponding to the beam direction are equipped in advance and the beam index or the antenna index is assigned to each beam direction, the beamforming parameter can include at least one of the beam index and the antenna index. 
         [0061]    Although not depicted in  FIG. 5 , the apparatus can set the reference direction before determining whether the movement or the rotation occurs. For example, the apparatus can set the reference direction through beam training. For example, the apparatus can set the beam directions in multiple candidate directions, repeatedly transmit the training reference signal, and select the candidate direction aligned with the beam direction. In addition, the apparatus can refine the beam in order to use the narrower beam. 
         [0062]      FIG. 6  illustrates an example beam locking method according to another embodiment of the present disclosure. 
         [0063]    In step  601 , the apparatus measures the change of the location and direction according to a movement and change of the direction and the slope according to the rotation/tilt of the apparatus. For example, the apparatus can periodically measure the change at regular time intervals. When there is no movement/rotation/tilt of the apparatus, the change is measured as zero. For example, the change of the location and the change of the direction and the slope can be measured using a sensor, such as a GPS device, the angle of the arrival of the signal, or the trigonometry using the received signal. 
         [0064]    In step  603 , the apparatus determines whether the beam direction is misaligned. For example, when the change is zero, there is no misalignment of the beam direction. When the change is not zero but trivial, the beam direction is not considered to be misaligned. For example, with the parameters (a,b,c) representing the physical change, the parameters (α,β,γ) representing the beam direction determined by the function using the physical change as the input variable, and parameters (α′,β′,γ′) representing the threshold beam direction, the apparatus can determine the misalignment of the beam direction only when at least one of (a,b,c) is greater than or equal to at least one threshold (α′,β′,γ′); that is, only when a≧α′, b≧β′ or c≧γ′, and compensate for the beam direction. The process is completed when no further alignment of the beam direction is to be performed. 
         [0065]    By contrast, when the beam direction is misaligned, the apparatus compensates for the beam direction in step  605 . That is, the apparatus calculates the new beamforming parameter which aligns the beam direction altered by the change with the reference direction, and compensates for the beam direction using the new beamforming parameter. In doing so, the new beamforming parameter is determined by the beamforming parameter of the reference direction and the change. For example, the apparatus determines the new beamforming parameter according to the predefined rule which uses the beamforming parameter of the reference direction and the change as the input variables. Alternatively, the apparatus determines the new beamforming parameter using the mapping table which defines the new beamforming parameters based on the change against the beamforming parameter of the reference direction. More specifically, the new beamforming parameter can be determined according to Equation (1). The beamforming parameter can vary according to the selected beamforming scheme. For example, in digital beamforming, the beamforming parameter includes at least one of the index of the precoding codebook used in the digital stage, the beamforming matrix, and the beamforming vector. For another example, in analog beamforming, the beamforming parameter includes the phase and amplitude values per antenna. For another example, in beamforming in which the antenna is physically moved, the beamforming parameter can be the physical attitude control value such as rotation or slope. For example, when antennas, antenna groups, or antenna arrays corresponding to the beam direction are equipped in advance and the beam index or the antenna index is assigned to each beam direction, the beamforming parameter can include at least one of the beam index and the antenna index. 
         [0066]    Although not depicted in  FIG. 6 , the apparatus can set the reference direction before determining whether the movement or the change in direction occurs. For example, the apparatus can set the reference direction through beam training. For example, the apparatus can set the beam direction in one of the candidate directions, repeatedly transmit the training reference signal, and select the candidate direction aligned with the beam direction. In addition, the apparatus can adjust the beamwidth of the beam. 
         [0067]      FIG. 7  illustrates an example beam locking method in the wireless communication system according to still another embodiment of the present disclosure. 
         [0068]    In step  701 , the apparatus determines whether the movement or the rotation occurs. That is, the apparatus determines whether at least one of the location, the slope, and the direction changes. 
         [0069]    When movement or rotation occurs, the apparatus measures the change of the location according to the movement and the change of the direction and the slope according to the rotation/slope in step  703 . By contrast, when the movement or the rotation does not occur, the apparatus does not perform step  703 . That is, with the parameters (a,b,c) for the physical change and the thresholds (a′,b′,c′) for determining the rotation, the apparatus determine that a change occurs when at least one of (a,b,c) is greater than or equal to at least one threshold (a′,b′,c′); that is, when a≧a′, b≧b′ or c≧c′. For example, the change of the location and the change of the direction and the slope can be measured using a sensor, such as a GPS, the angle of the arrival of the signal, or the trigonometry using the received signal. 
         [0070]    In step  705 , the apparatus determines whether the beam direction is misaligned. For example, when the change is zero, there no misalignment of the beam direction is considered to have occurred. When the change is not zero but trivial, no e misalignment of the beam direction is considered to have occurred. For example, with the parameters (a,b,c) for the physical change, the parameters (α,β,γ) of the beam direction determined by the function using the physical change as the input variable, and the parameters (α′,β′,γ′) of the beam direction of the threshold, the apparatus can determine the misalignment of the beam direction when at least one of (a,b,c) is greater than or equal to at least one threshold (α′,β′,γ′); that is, when a≧α′, b≧β′ or c≧γ′, and compensate for the beam direction. When there is no misalignment of the beam direction, the process is completed. 
         [0071]    When the beam direction is misaligned, the apparatus compensates for the beam direction in step  707 . That is, the apparatus calculates the new beamforming parameter which aligns the beam direction altered by the change with the reference direction, and compensates for the beam direction using the new beamforming parameter. In doing so, the new beamforming parameter is determined by the beamforming parameter of the reference direction and the change. For example, the apparatus can determine the new beamforming parameter according to the specified rule which uses the beamforming parameter of the reference direction and the change as input variables. Alternatively, the apparatus can determine the new beamforming parameter using the mapping table which defines the new beamforming parameters based on the change against the beamforming parameter of the reference direction. More specifically, the new beamforming parameter can be determined according to Equation (1). The beamforming parameter can vary according to the selected beamforming scheme. For example, in digital beamforming, the beamforming parameter can include at least one of the index of the precoding codebook used in the digital stage, the beamforming matrix, and the beamforming vector. For another example, in analog beamforming, the beamforming parameter can include the phase and amplitude values per antenna. For another example, in beamforming in which the antenna is physically moved, the beamforming parameter can include the physical attitude control value such as rotation or slope. For another example, when antennas, antenna groups, or antenna arrays corresponding to the beam direction are equipped in advance and the beam index or the antenna index is assigned to each beam direction, the beamforming parameter can include at least one of the beam index and the antenna index. 
         [0072]    Although not depicted in  FIG. 7 , the apparatus can set the reference direction before determining whether the movement or the rotation occurs. For example, the apparatus can set the reference direction through beam training. For another example, the apparatus can set the beam direction in multiple candidate directions, repeatedly transmit the training reference signal, and select the candidate direction aligned with the beam direction. In addition, the apparatus can refine the beam so as to use the narrower beam. 
         [0073]      FIG. 8  is an example apparatus for beam locking according to an embodiment of the present disclosure. 
         [0074]    As shown in  FIG. 8 , the apparatus includes a beam locking unit  802 , a digital data transceiver  804 , and multiple Radio Frequency (RF) processors  806 - 1  through  806 -N. 
         [0075]    The beam locking unit  802  sets the reference direction of the beam and locks the beam to sustain the reference direction of the beam. That is, the beam locking unit  802  recognizes and measures the movement, the tilt, and rotation of the apparatus, calculates the beamforming parameter for aligning the beam direction with the reference direction, and provides the beamforming parameter to the digital data transceiver  804 . For example, the beamforming parameter includes at least one of the precoding codebook index, the beamforming matrix, and the beamforming vector. 
         [0076]    For example, the beam locking unit  802  can be constructed as shown in  FIG. 12 . Referring to  FIG. 12 , the beam locking unit  802  includes a motion detector  1202  for measuring the change of the location according to the movement and the change of the direction and the slope according to the rotation/tilt, a parameter calculator  1204  for calculating the new beamforming parameter for aligning the beam direction altered by the change with the reference direction, and a beam controller  1206  for controlling the beamforming of the digital data transceiver  804  according to the new beamforming parameter. That is, the beam controller  1206  controls to adjust the beam direction according to the beamforming parameter determined by the parameter calculator  1204 . Herein, the motion detector  1202  can measure the change on the periodic basis at regular time intervals or in the event of a detected motion or rotation of the apparatus. 
         [0077]    For example, the beam locking unit  802  can be constructed as shown in  FIG. 13 . Referring to  FIG. 13 , the beam locking unit  802  includes a motion detector  1302  for measuring the change of the location according to the movement and the change of the direction and the slope according to the rotation/tilt, a misalignment determiner  1304  for determining whether the current beam is misaligned with the reference direction according to the change, a parameter calculator  1306  for, when the misalignment determiner  1304  determines the misalignment, calculating the new beamforming parameter for aligning the changed beam direction with the reference direction, and a beam controller  1306  for controlling the beamforming of the digital data transceiver  804  according to the new beamforming parameter. That is, the beam controller  1308  adjusts the beam direction according to the beamforming parameter determined by the parameter calculator  1306 . Herein, the motion detector  1302  can measure the change on the periodic basis at regular time intervals or in the event of motion or rotation of the apparatus. 
         [0078]    The digital data transceiver  804  converts a transmit bit sequence to a baseband signal and converts baseband signals output from the RF processors  806 - 1  through  806 -N to the receive bit sequence according to a protocol of the communication system. The digital data transceiver  804  can carry out channel coding and decoding, data modulation and demodulation, precoding for multi-antenna mapping, post coding, Analog/Digital (A/D) conversion, Digital/Analog (D/A) conversion, Fast Fourier Transform (FFT), Inverse FFT (IFFT), and digital beamforming. For example, in a data transmission conforming to an Orthogonal Frequency Division Multiplexing (OFDM) protocol, the digital data transceiver  804  generates complex symbols by encoding and modulating the transmit bit sequence, maps the complex symbols to subcarriers, and constitutes OFDM symbols through the IFFT and Cyclic Prefix (CP) insertion. The digital data transceiver  804  performs the digital forming. That is, the digital data transceiver  804  multiplies the signal sequence to transmit in each antenna path by the beamforming vector or the beamforming matrix. In particular, the digital data transceiver  804  conducts the beamforming according to at least one of the precoding codebook index, the beamforming matrix, and the beamforming vector provided from the beam locking unit  802 . 
         [0079]    The RF processors  806 - 1  through  806 -N performs functions, such as signal band conversion and amplification, to transmit and receive wireless signals. That is, the RF processors  806 - 1  through  806 -N up-convert the baseband signals for transmission, which are fed from the digital data transceiver  804 , to RF signals, transmit the RF signals over antennas, and down-convert RF signals received over the antennas to baseband signals. For example, the RF processors  806 - 1  through  806 -N each can include at least one of an amplifier, a mixer, a frequency filter, an oscillator, a Digital to Analog Converter (DAC), an Analog to Digital Converter (ADC), and a phase shifter/controller for controlling the antenna direction. 
         [0080]    Although not depicted in  FIG. 8 , the apparatus can further include a beam trainer for training the beam with another apparatus. For example, to determine the reference direction of the beam of the apparatus, the beam trainer can set the beam direction in each of the candidate directions, repeatedly transmit the training reference signal, and select a feedback direction from the other apparatus as the reference direction. Conversely, to determine the reference direction of the beam of the other apparatus, the beam trainer can receive multiple training reference signals from the other apparatuses and notify the other apparatus of the sequence value of one training reference signal having the best communication quality. In addition, the beam trainer can continually refine the beam in order to allow use of a narrower beam. Prior to the operations of the beam locking unit  802 , the beam trainer can set the reference direction through beam training. 
         [0081]      FIG. 9  illustrates an example apparatus for beam locking according to another embodiment of the present disclosure. 
         [0082]    As shown in  FIG. 9 , the apparatus includes a beam locking unit  902 , a digital data transceiver  904 , a plurality of RF processors  906 - 1  through  906 -N, and a beamformer  908 . 
         [0083]    The beam locking unit  902  sets the reference direction of the beam and locks the beam to maintain the reference direction of the beam. That is, the beam locking unit  902  recognizes and measures the movement, the tilt, and rotation of the apparatus, calculates the beamforming parameter for aligning the beam direction with the reference direction, and provides the beamforming parameter to the beamformer  908 . For example, the beamforming parameter includes the phase and amplitude values of the signals received from each antenna. 
         [0084]    For example, the beam locking unit  902  can be constructed as shown in  FIG. 12 . Referring to  FIG. 12 , the beam locking unit  902  includes the motion detector  1202  for measuring the change of the location according to the movement and the change of the direction and the slope according to the rotation/tilt, the parameter calculator  1204  for calculating the new beamforming parameter for aligning the beam direction altered by the change with the reference direction, and the beam controller  1206  for controlling the beamforming of the beamformer  908  according to the new beamforming parameter. Herein, the motion detector  1202  can measure the change on the periodic basis at regular time intervals or in the event of motion or rotation of the apparatus. 
         [0085]    For example, the beam locking unit  902  can be constructed as shown in  FIG. 13 . Referring to  FIG. 13 , the beam locking unit  902  includes the motion detector  1302  for measuring the change of the location according to the movement and the change of the direction and the slope according to the rotation/tilt, the misalignment determiner  1304  for determining whether the current beam is misaligned with the reference direction according to the change, the parameter calculator  1306  for, when the misalignment determiner  1304  determines the misalignment, calculating the new beamforming parameter for aligning the changed beam direction with the reference direction, and the beam controller  1306  for controlling the beamforming of the beamformer  908  according to the new beamforming parameter. Herein, the motion detector  1302  can measure the change on the periodic basis at regular time intervals or in the event of motion or rotation of the apparatus. 
         [0086]    The digital data transceiver  904  converts a transmit bit sequence to a baseband signal and converts baseband signals output from the RF processors  906 - 1  through  906 -N to the receive bit sequence according to the physical layer standard of the system. The digital data transceiver  904  can perform channel coding and decoding, data modulation and demodulation, precoding for the multi-antenna mapping, post coding, A/D conversion, D/A conversion, FFT processing, and IFFT processing. For example, in the data transmission conforming to the OFDM protocol, the digital data transceiver  904  generates complex symbols by encoding and modulating the transmit bit sequence, maps the complex symbols to subcarriers, and constitutes OFDM symbols through the IFFT and the CP insertion. 
         [0087]    The RF processors  906 - 1  through  906 -N perform functions, such as signal conversion and amplification, to transmit and receive the signals over a radio channel. That is, the RF processors  906 - 1  through  906 -N up-convert the baseband signals for transmission, which are fed from the digital data transceiver  904 , to RF signals, transmit the RF signals over antennas, and down-convert RF signals received over the antennas to baseband signals. For example, the RF processors  906 - 1  through  906 -N each can include at least one of an amplifier, a mixer, a frequency filter, an oscillator, a DAC, an ADC, and a phase shifter/controller for controlling the antenna direction. 
         [0088]    The beamformer  908  includes multiple components, and each component adjusts the phase and the amplitude of the signal in each antenna path. That is, the beamformer  908  performs the beamforming by adjusting the phase and the amplitude of the signal transmitted in each antenna path according to the phase and amplitude values of the signals per antenna fed from the beam locking unit  902 . While the RF processors  906 - 1  through  906 -N each has the single antenna path and the path includes the single component of the beamformer  908  per antenna in  FIG. 9 , each antenna can have the transmit path and the receive path separately. In this case, two components of the beamformer  908  can be provided per antenna. 
         [0089]    Although not depicted in  FIG. 9 , the apparatus can further include a beam trainer for training the beam with the another apparatus. For example, to determine the reference direction of the beam of the apparatus, the beam trainer can set the beam direction in multiple candidate directions, repeatedly transmit the training reference signal, and select a feedback direction from the other apparatus as the reference direction. Conversely, to determine the reference direction of the beam of the other apparatus, the beam trainer can receive multiple training reference signals from the other apparatus and notify the other apparatus of the sequence value of one training reference signal having the best communication quality. In addition, the beam trainer can continually refine the beam in order to use a narrower beam. Prior to operation of the beam locking unit  902 , the beam trainer can set the reference direction through beam training. 
         [0090]      FIG. 10  illustrates an example apparatus for beam locking according to another embodiment of the present disclosure. 
         [0091]    As shown in  FIG. 10 , the apparatus includes a beam locking unit  1002 , a digital data transceiver  1004 , a plurality of RF processors  1006 - 1  through  1006 -N, and an antenna driver  1008 . 
         [0092]    The beam locking unit  1002  sets the reference direction of the beam and locks the beam to maintain the reference direction of the beam. That is, the beam locking unit  1002  recognizes and measures the movement, the tilt, and the rotation of the apparatus, calculates the beamforming parameter for aligning the beam direction with the reference direction, and provides the beamforming parameter to the antenna driver  1008 . For example, the beamforming parameter includes the physical attitude control value such as rotation and tilt of each antenna. 
         [0093]    For example, the beam locking unit  1002  can be constructed as shown in  FIG. 12 . Referring to  FIG. 12 , the beam locking unit  1002  includes the motion detector  1202  for measuring the change of the location according to the movement and the change of the direction and the slope according to the rotation/tilt, the parameter calculator  1204  for calculating the new beamforming parameter for aligning the beam direction altered by the change with the reference direction, and the beam controller  1206  for controlling the beamforming of the antenna driver  1008  according to the new beamforming parameter. Herein, the motion detector  1202  can measure the change on the periodic basis at regular time intervals or in the event of motion or rotation of the apparatus. 
         [0094]    For example, the beam locking unit  1002  can be constructed as shown in  FIG. 13 . Referring to  FIG. 13 , the beam locking unit  1002  includes the motion detector  1302  for measuring the change of the location according to the movement and the change of the direction and the slope according to the rotation/tilt, the misalignment determiner  1304  for determining whether the current beam is misaligned with the reference direction according to the change, the parameter calculator  1306  for, when the misalignment determiner  1304  determines the misalignment, calculating the new beamforming parameter for aligning the changed beam direction with the reference direction, and the beam controller  1306  for controlling the beamforming of the antenna driver  1008  according to the new beamforming parameter. Herein, the motion detector  1302  can measure the change on a periodic basis at regular time intervals or in the event of motion or rotation of the apparatus. 
         [0095]    The digital data transceiver  1004  converts a transmit bit sequence to a baseband signal and converts baseband signals output from the RF processors  1006 - 1  through  1006 -N to the receive bit sequence according to the protocol of the system. The digital data transceiver  1004  can carry out channel coding and decoding, data modulation and demodulation, precoding for the multi-antenna mapping, post coding, A/D conversion, D/A conversion, FFT processing, and IFFT processing. For example, in a data transmission conforming to the OFDM protocol, the digital data transceiver  1004  generates complex symbols by encoding and modulating the transmit bit sequence, maps the complex symbols to subcarriers, and constitutes OFDM symbols through IFFT and CP insertion. 
         [0096]    The RF processors  1006 - 1  through  1006 -N perform functions, such as signal conversion and amplification, to transmit and receive the signals over a radio channel. That is, the RF processors  1006 - 1  through  1006 -N up-convert the baseband signals for transmission, which are fed from the digital data transceiver  1004 , to RF signals, transmit the RF signals over antennas, and down-convert RF signals received over the antennas to baseband signals. For example, the RF processors  1006 - 1  through  1006 -N each can include at least one of an amplifier, a mixer, a frequency filter, an oscillator, a DAC, an ADC, and a phase shifter/controller for controlling the antenna direction. 
         [0097]    The antenna driver  1008  includes multiple components corresponding to the multiple antennas. Each component physically adjusts a signal radiation direction of each antenna. That is, the antenna driver  1008  performs the beamforming by adjusting the signal radiation direction of each antenna according to the physical attitude control value such as rotation and tilt of the antenna fed from the beam locking unit  1002 . 
         [0098]    Although not depicted in  FIG. 10 , the apparatus can further include a beam trainer for training the beam with another apparatus. For example, to determine the reference direction of the beam of the apparatus, the beam trainer can set the beam direction in multiple candidate directions, repeatedly transmit the training reference signal, and select the feedback direction from the other apparatus as the reference direction. Conversely, to determine the reference direction of the beam of the other apparatus, the beam trainer can receive a plurality of training reference signals from the other apparatus and notify the other apparatus of the sequence value of one training reference signal having the best communication quality. In addition, the beam trainer can continually refine the beam in order to use a narrower beam. Prior to operation of the beam locking unit  1002 , the beam trainer can set the reference direction through beam training. 
         [0099]      FIG. 11  illustrates an example apparatus for beam locking according to another embodiment of the present disclosure. 
         [0100]    As shown in  FIG. 11 , the apparatus includes a beam locking unit  1102 , a digital data transceiver  1104 , a plurality of RF processors  1106 - 1  through  1106 -N, and an antenna switch  1108 . 
         [0101]    The beam locking unit  1102  sets the reference direction of the beam and locks the beam to maintain the reference direction of the beam. That is, the beam locking unit  1102  detects and measures the movement, the tilt, and the rotation of the apparatus, calculates the beamforming parameter for aligning the beam direction with the reference direction, and provides the beamforming parameter to the antenna switch  1108 . For example, the beamforming parameter includes the predefined beam index or antenna index. 
         [0102]    For example, the beam locking unit  1102  can be constructed as shown in  FIG. 12 . Referring to  FIG. 12 , the beam locking unit  1102  includes the motion detector  1202  for measuring the change of the location according to the movement and the change of the direction and the slope according to the rotation/tilt, the parameter calculator  1204  for calculating the new beamforming parameter for aligning the beam direction altered by the change with the reference direction, and the beam controller  1206  for controlling the beamforming of the antenna switch  1108  according to the new beamforming parameter. Herein, the motion detector  1202  can measure the change on the periodic basis at regular time intervals or in the event of motion or rotation of the apparatus. 
         [0103]    For example, the beam locking unit  1102  can be constructed as shown in  FIG. 13 . Referring to  FIG. 13 , the beam locking unit  1102  includes the motion detector  1302  for measuring the change of the location according to the movement and the change of the direction and the slope according to the rotation/tilt, the misalignment determiner  1304  for determining whether the current beam is misaligned with the reference direction according to the change, the parameter calculator  1306  for, when the misalignment determiner  1304  determines the misalignment, calculating the new beamforming parameter for aligning the changed beam direction with the reference direction, and the beam controller  1308  for controlling the beamforming of the antenna switch  1108  according to the new beamforming parameter. Herein, the motion detector  1302  can measure the change on the periodic basis at regular time intervals or in the event of motion or rotation of the apparatus. 
         [0104]    The digital data transceiver  1104  converts a transmit bit sequence to a baseband signal and converts baseband signals output from the RF processors  1106 - 1  through  1106 -N to the receive bit sequence according to a protocol of the system. The digital data transceiver  1104  can perform channel coding and decoding, data modulation and demodulation, precoding for the multi-antenna mapping, post coding, A/D conversion, D/A conversion, FFT processing, and IFFT processing. For example, in the data transmission conforming to the OFDM protocol, the digital data transceiver  1104  generates complex symbols by encoding and modulating the transmit bit sequence, maps the complex symbols to subcarriers, and constitutes OFDM symbols through IFFT and the CP insertion. 
         [0105]    The RF processors  1106 - 1  through  1106 -N perform functions, such as signal conversion and amplification, to transmit and receive the signals over a radio channel. That is, the RF processors  1106 - 1  through  1106 -N up-convert the baseband signals for transmission, which are fed from the digital data transceiver  1104 , to RF signals, transmit the RF signals over antennas, and down-convert RF signals received over the antennas to baseband signals. For example, the RF processors  1106 - 1  through  1106 -N each can include at least one of an amplifier, a mixer, a frequency filter, an oscillator, a DAC, an ADC, and a phase shifter/controller for controlling the antenna direction. 
         [0106]    The antenna switch  1108  activates at least one antenna group corresponding to the beam index or the antenna index fed from the beam locking unit  1102 . That is, the antennas of the apparatus are arranged in multiple antenna groups, the antenna groups corresponding to the beam direction, and the beam index or the antenna index is assigned to the antenna groups. Herein, one antenna group includes one antenna, a plurality of antennas, or an antenna array. Accordingly, the antenna switch  1108  connects only the antenna group indicated by the beam index or the antenna index fed from the beam locking unit  1102  and the RF processors  1106 - 1  through  1106 -N, or switches off the other group antennas excluding the indicated antenna group. 
         [0107]    Although not depicted in  FIG. 11 , the apparatus can further include a beam trainer for training the beam with another apparatus. For example, to determine the reference direction of the beam of the apparatus, the beam trainer can set the beam direction in multiple candidate directions, repeatedly transmit the training reference signal, and select the feedback direction from the other apparatus as the reference direction. Conversely, to determine the reference direction of the beam of the other apparatus, the beam trainer can receive a plurality of training reference signals from the other apparatus and notify the other apparatus of the sequence value of one training reference signal having the best communication quality. In addition, the beam trainer can continually refine the beam in order to use a narrower beam. Prior to operation of the beam locking unit  1102 , the beam trainer can set the reference direction through beam training. 
         [0108]    When the user station locks the beam as stated above, the base station can conduct beam training less frequently than with other user stations which does not lock the beam. That is, the base station needs to distinguish the user station which locks the beam and other user stations which does not lock the beam. To determine whether a particular user station performs beamforming, the base station requires control information exchange. For example, whether the user station supports the beam locking can be informed to the base station through a capability negotiation procedure of the user station. 
         [0109]      FIG. 14  depicts example signals transmitted between the base station and the user station in a wireless communication system according to an embodiment of the present disclosure. In step  1401 , the user station  1420  transmits to the base station  1410  capability information including information indicating whether beam locking is supported. In detail, the user station  1420  generates a control message informing that beam locking is supported to maintain the beam direction in the reference direction by compensating for the change of the beam direction according to movement and rotation of the apparatus, and sends the control message to the base station  1410 . For example, the information indicating whether the beam locking is supported can be arranged as shown in Table 1. 
         [0000]    
       
         
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                 Size 
                   
               
               
                 Syntax 
                 (bits) 
                 Description 
               
               
                   
               
             
             
               
                 Beam locking capability 
                 1 
                 0: beam locking is supported 
               
               
                   
                   
                 1: beam locking is not supported 
               
               
                   
               
             
          
         
       
     
         [0110]    For example, the information indicating whether the beam locking is supported can further include detailed items as shown in Table 2. 
         [0000]    
       
         
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                   
                 Size 
                   
               
               
                 Syntax 
                 (bits) 
                 Description 
               
               
                   
               
             
             
               
                 Processing delay  
                 xx 
                 Time taken to compensate for misalignment 
               
               
                 for beam locking 
                   
                 of the beam direction when the misalignment 
               
               
                   
                   
                 of the beam direction occurs 
               
               
                 Direction  
                 xx 
                 A measurable resolution of an angle in tilt or 
               
               
                 resolution 
                   
                 rotation of the user station in a three- 
               
               
                   
                   
                 dimensional space 
               
               
                 Velocity  
                 xx 
                 A resolution for a velocity according to a 
               
               
                 resolution 
                   
                 motion of the user station 
               
               
                   
               
             
          
         
       
     
         [0111]    In step  1403 , the base station  1410  receiving the capability information sends an acknowledge message notifying the capability information reception, to the user station  1420 . For example, the acknowledge message can be arranged as shown in Table 3. 
         [0000]    
       
         
               
               
               
             
           
               
                 TABLE 3 
               
               
                   
               
               
                   
                 Size 
                   
               
               
                 Syntax 
                 (bits) 
                 Description 
               
               
                   
               
             
             
               
                 Beam locking  
                 1 
                 0: beam locking is acknowledged 
               
               
                 capability confirm 
                   
                 1: beam locking is not acknowledged 
               
               
                   
               
             
          
         
       
     
         [0112]    In other various embodiments, step  1403  can be omitted if acknowledgement is not desired or required. 
         [0113]      FIG. 15  depicts an example beam training technique when the beam locking is applied according to an embodiment of the present disclosure. 
         [0114]    In step  1501 , a base station  1510  and a user station  1520  perform beam training. For example, the base station  1510  and the user station  1520  set the beam direction in multiple candidate directions, repeatedly send the training reference signal, and determine the candidate direction aligned with the beam direction. In addition, the base station  1510  and the user station  1520  can continually refine the beam in order to utilize a narrower beam. The beam training is conducted periodically based on the time interval T. 
         [0115]    In step  1503 , during the time T, the user station  1520  activates the beam locking. Namely, the user station  1520  continuously performs the beam locking. Thus, even when the beam training is not performed, a relatively good beam direction may be maintained, the system overhead in the beam training can be reduced, and may be more advantageous in terms of accuracy and time delay. 
         [0116]    In step  1505 , after the time T, the base station  1510  and the user station  1520  conduct beam training again. Advantageously, the time T is longer than the beam training time interval when the beam locking is not applied. 
         [0117]    It will be appreciated that embodiments of the present disclosure according to the claims and description in the specification can be realized in the form of hardware, software or a combination of hardware and software. 
         [0118]    Any such software may be stored in a computer readable storage medium. The computer readable storage medium stores one or more programs (software modules), the one or more programs comprising instructions, which when executed by one or more processors in an electronic device, cause the electronic device to perform a method of the present disclosure. 
         [0119]    Any such software may be stored in the form of volatile or non-volatile storage such as, for example, a storage device like a ROM, whether erasable or rewritable or not, or in the form of memory such as, for example, RAM, memory chips, device or integrated circuits or on an optically or magnetically readable medium such as, for example, a CD, DVD, magnetic disk or magnetic tape or the like. It will be appreciated that the storage devices and storage media are embodiments of machine-readable storage that are suitable for storing a program or programs comprising instructions that, when executed, implement embodiments of the present disclosure. 
         [0120]    Accordingly, embodiments provide a program comprising code for implementing apparatus or a method as claimed in any one of the claims of this specification and a machine-readable storage storing such a program. Still further, such programs may be conveyed electronically via any medium such as a communication signal carried over a wired or wireless connection and embodiments suitably encompass the same. 
         [0121]    As set forth above, since the beam direction is kept in the reference direction by compensating for the change of the beam direction according to the movement and the motion of the apparatus which performs the beam forming in the wireless communication system, the effective beamforming can be fulfilled even when the beam direction abruptly changes. 
         [0122]    While the subject matter of the present disclosure has been shown and described with reference to certain example 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 invention as defined by the appended claims and their equivalents.