Patent Publication Number: US-2022216737-A1

Title: Method for controlling wireless power link, and device therefor

Description:
TECHNICAL FIELD 
     The present disclosure relates to wireless power transfer, and more particularly, to a method of controlling a wireless power transmission link based on out-band communication in a wireless power system. 
     BACKGROUND ART 
     The wireless power transfer technology is a technology for wirelessly transferring power between a power source and an electronic device. For example, the wireless power transfer technology enables charging of the battery of a wireless terminal such as a smartphone or tablet by simply placing the wireless terminal on a wireless charging pad, thereby providing better mobility, convenience, and safety than wired charging using cable charging connectors. The wireless power transfer technology is attracting attention as a replacement for the wired power transfer system in various fields such as electric vehicles, wearable devices such as Bluetooth earphones and 3D glasses, home appliances, furniture, underground facilities, buildings, medical devices, robots, and leisure, in addition to wireless charging of wireless terminals. 
     The wireless power transfer method is also referred to as a contactless power transfer method, a power transfer method with no point of contact, or a wireless charging method. The wireless power transfer system includes a wireless power transmitter configured to supply electrical energy based on the wireless power transfer method and a wireless power receiver configured to receive the electrical energy wirelessly supplied from the wireless power transmitter and provide the power to a power receiving device such as a battery cell. 
     The wireless power transfer technology includes various power transfer methods: a power transfer method based on magnetic coupling, a power transfer method based on radio frequency (RF), a power transfer method based on microwaves, a power transfer method based on ultrasonic waves, and so on. The magnetic coupling-based method is further classified into a magnetic induction method and a magnetic resonance method. 
     The magnetic induction method is a method of wirelessly transferring power based on electromagnetic coupling between a transmitter coil and a receiver coil and charging a load based on an induction current generated when an electromagnetic field output by the transmitter coil is induced in the receiver coil. 
     The magnetic resonance method is similar to the magnetic induction method in that an electromagnetic field is used, but the magnetic resonance method is different from the magnetic induction method in that a transmitter and receiver transmit/receive wireless power based on a specific resonant frequency. 
     In conventional wireless power transfer systems, depending on manufacturers and types and characteristics of applied products, errors may occur in the coupling between the transmitter coil and receiver coil and the measurement accuracy between the wireless power transmitter and wireless power receiver, and as a result, the reliability of determination of misalignment between the transmitter and receiver coils may be degraded. 
     In addition, errors in the determination of the misalignment between the transmitter and receiver coils may cause control errors in release and maintenance of a wireless power transfer link 
     DISCLOSURE 
     Technical Problem 
     One object of the present disclosure is to provide a wireless power transmitter, a wireless power transmission method, a wireless power receiver, a wireless power reception method, and a wireless charging system. 
     Another object of the present disclosure is to provide a wireless power link control method capable of controlling maintenance and release of a wireless power transmission link between a wireless power transmitter and a wireless power receiver based on out-band communication and apparatus therefor. 
     Another object of the present disclosure is to provide a wireless power link control method capable of determining whether a wireless power transfer interface is removed based on distance and location information obtained from a received signal strength indicator (RSSI) and/or direct finding in out-band communication, and apparatus therefor. 
     Another object of the present disclosure is to provide a wireless power link control method by which a wireless power transmitter prevents a wireless power receiver from being damaged by notifying the wireless power receiver of link removal and then stopping power transmission or lowering transmitted power upon detecting that the wireless power receiver deviates from a charging area by periodic acquisition of distance and location information when the wireless power receiver is running on its own power out of the charging area, and apparatus therefor. 
     Another object of the present disclosure is to provide a wireless power link control method by which a wireless power receiver notifies a wireless power transmitter of link removal, requests the wireless power transmitter to stop power transmission, or performs power restrictions to lower a target voltage and/or a power requirement when the wireless power receiver determines that the wireless power receiver is out of a charging area by periodically obtaining information on the distance to the wireless power transmitter and/or information on the location of the wireless power transmitter, and apparatus therefor. 
     A further object of the present disclosure is to provide a wireless power transmission method by which a wireless power transmitter and/or a wireless power receiver releases power restrictions and resumes wireless power transfer when determining that the wireless power transmitter and/or wireless power receiver is sufficiently stable to perform the wireless power transfer while the wireless power transmitter and/or wireless power receiver is in a power limited state due to deviation of the wireless power receiver from a charging area, and apparatus therefor. 
     Technical Solution 
     Specific features of the present disclosure are described below. 
     In an aspect of the present disclosure, a method of controlling a wireless power transmission link by a wireless power transmitter is provided. The method may include: performing a first information acquisition procedure for a wireless power receiver; performing first determination for determining whether a distance between the wireless power transmitter and the wireless power receiver is normal, based on information obtained from the first information acquisition procedure; and performing a connection release procedure for the wireless power transmission link based on a determination result of the first determination. 
     In an embodiment, the first information acquisition procedure may include: measuring a rail voltage and a transmitter coil voltage; and obtaining distance information and location information related to the wireless power receiver based on that the rail voltage is greater than a first threshold voltage and the transmitter coil voltage is greater than a second threshold voltage. 
     In an embodiment, the distance information and the location information may be obtained based on an out-band communication scheme. 
     In an embodiment, the out-band communication scheme may be Bluetooth Low Energy (BLE). The distance between the wireless power transmitter and the wireless power receiver may be determined based on a received signal strength indicator related to a measured BLE signal, and the location of the wireless power receiver may be determined based on a direct finding scheme of the BLE. 
     In an embodiment, the determined distance and/or location may be compared with a predetermined threshold to determine whether to perform the connection release procedure. 
     In an embodiment, the method may include: limiting transmitted power based on abnormality determined by the first determination; performing a second information acquisition procedure for the wireless power receiver; performing second determination for determining again whether the distance between the wireless power transmitter and the wireless power receiver is normal, based on information obtained from the second information obtaining procedure; and performing the connection release procedure based on that the second determination determines that the distance is abnormal. The transmitted power may be limited by lowering the transmitted power to a predetermined level. 
     In an embodiment, the limitation on the transmitted power may be released based on that the second determination determines that the distance is normal. 
     In an embodiment, the connection release procedure may include: notifying connection release; and stopping power transmission. 
     In an embodiment, the notification of the connection release may include sending, by the wireless power transmitter, a request for the connection release to the wireless power receiver through out-band communication. 
     In an embodiment, the first information acquisition procedure may be performed periodically during power transmission control. 
     In another aspect of the present disclosure, a method of controlling a wireless power transmission link by a wireless power receiver is provided. The method may include: performing a first information acquisition procedure for a wireless power transmitter; performing first determination for determining whether a distance between the wireless power receiver and the wireless power transmitter is normal, based on information obtained from the first information acquisition procedure; and performing a connection release procedure for the wireless power transmission link based on a determination result of the first determination. 
     In an embodiment, the first information acquisition procedure may include: measuring a rectified voltage and a receiver coil voltage; and obtaining distance information and location information related to the wireless power transmitter based on that the rectified voltage is greater than a third threshold voltage and the receiver coil voltage is greater than a fourth threshold voltage. 
     In an embodiment, the distance information and the location information may be obtained based on an out-band communication scheme. 
     In an embodiment, the out-band communication scheme may be BLE. The distance between the wireless power receiver and the wireless power transmitter may be determined based on a received signal strength indicator related to a measured BLE signal, and the location of the wireless power transmitter may be determined based on a direct finding scheme of the BLE. 
     In an embodiment, the determined distance and/or location may be compared with a predetermined threshold to determine whether to perform the connection release procedure. 
     In an embodiment, the method may include: limiting power reception based on abnormality determined by the first determination; performing a second information acquisition procedure for the wireless power transmitter; performing second determination for determining again whether the distance between the wireless power receiver and the wireless power transmitter is normal, based on information obtained from the second information obtaining procedure; and performing the connection release procedure based on that the second determination determines that the distance is abnormal. The power reception may be limited by lowering a target rectified voltage and/or a power requirement. 
     In an embodiment, the limitation on the power reception may be released based on that the second determination determines that the distance is normal. 
     In an embodiment, the connection release procedure may include: notifying connection release; and stopping power reception. 
     In an embodiment, the notification of the connection release may include sending, by the wireless power receiver, a request for the connection release to the wireless power transmitter through out-band communication. 
     In an embodiment, the first information acquisition procedure may be performed periodically during power reception control. 
     Advantageous Effects 
     As is apparent from the above description, the present disclosure has effects as follows. 
     The present disclosure may provide a wireless power transmitter, a wireless power transmission method, a wireless power receiver, a wireless power reception method, and a wireless charging system that enable stable and efficient wireless charging. 
     The present disclosure may provide a wireless power link control method capable of controlling maintenance and release of a wireless power transmission link between a wireless power transmitter and a wireless power receiver based on out-band communication and apparatus therefor. 
     The present disclosure may provide a wireless power link control method capable of avoiding unnecessary power wastage in advance by determining whether a wireless power transfer interface is removed based on distance and location information obtained from a received signal strength indicator (RSSI) and/or direct finding in out-band communication, and apparatus therefor. 
     The present disclosure may provide a wireless power link control method by which a wireless power transmitter prevents a wireless power receiver from being damaged by notifying the wireless power receiver of link removal and then stopping power transmission or lowering transmitted power upon detecting that the wireless power receiver deviates from a charging area by periodic acquisition of distance and location information when the wireless power receiver is running on its own power out of the charging area, and apparatus therefor. 
     The present disclosure may provide a wireless power link control method by which a wireless power receiver notifies a wireless power transmitter of link removal, requests the wireless power transmitter to stop power transmission, or performs power restrictions to lower a target voltage and/or a power requirement when the wireless power receiver determines that the wireless power receiver is out of a charging area by periodically obtaining information on the distance to the wireless power transmitter and/or information on the location of the wireless power transmitter, and apparatus therefor. 
     The present disclosure may provide a wireless power transmission method by which a wireless power transmitter and/or a wireless power receiver releases power restrictions and resumes wireless power transfer when determining that the wireless power transmitter and/or wireless power receiver is sufficiently stable to perform the wireless power transfer while the wireless power transmitter and/or wireless power receiver is in a power limited state due to deviation of the wireless power receiver from a charging area, and apparatus therefor. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  is a block diagram of a wireless power system  10  according to an embodiment of the present disclosure. 
         FIG. 2  is a block diagram of the wireless power system  10  according to another embodiment of the present disclosure. 
         FIG. 3A  illustrates examples of various electronic devices to which a wireless power transfer system is introduced. 
         FIG. 3B  illustrates an exemplary Wireless Power Consortium (WPC) near-field communication (NFC) data exchange profile format (NDEF) in a wireless power transfer system. 
         FIG. 4A  is a block diagram of a wireless power transfer system according to another embodiment of the present disclosure. 
         FIG. 4B  is a diagram illustrating an exemplary Bluetooth communication architecture to which the present disclosure is applicable. 
         FIG. 4C  is a block diagram illustrating a wireless power transfer system using Bluetooth Low Energy (BLE) communication according to an embodiment of the present disclosure. 
         FIG. 4D  is a block diagram illustrating a wireless power transfer system using BLE communication according to another embodiment of the present disclosure. 
         FIG. 5  is a state transition diagram for explaining a wireless power transfer procedure. 
         FIG. 6  illustrates a power control method according to an embodiment of the present disclosure. 
         FIG. 7  is a block diagram of a wireless power transmitter according to another embodiment of the present disclosure. 
         FIG. 8  illustrates a wireless power receiver according to another embodiment of the present disclosure. 
         FIG. 9  illustrates a communication frame structure according to an embodiment of the present disclosure. 
         FIG. 10  illustrates a structure of a synchronization pattern according to an embodiment of the present disclosure. 
         FIG. 11  illustrates operating states of a wireless power transmitter and receiver in a shared mode according to an embodiment of the present disclosure. 
         FIG. 12  is a block diagram illustrating a wireless charging certificate format according to an embodiment of the present disclosure. 
         FIG. 13  illustrates a structure of a capability packet of a wireless power transmitter according to an embodiment of the present disclosure. 
         FIG. 14  illustrates a structure of a configuration packet of a wireless power receiver according to an embodiment of the present disclosure. 
         FIG. 15  illustrates an application-level data stream between a wireless power transmitter and receiver according to an embodiment of the present disclosure. 
         FIG. 16  is a flowchart illustrating operations of a wireless power transmitter and receiver according to an embodiment of the present disclosure. 
         FIG. 17  is a flowchart illustrating operations of a wireless power transmitter and receiver according to another embodiment of the present disclosure. 
         FIG. 18  is a flowchart illustrating operations of a wireless power transmitter and receiver according to a further embodiment of the present disclosure. 
         FIG. 19  is a block diagram illustrating state machines for power class 0 (PC0) and power class 1 (PC1) according to an embodiment of the present disclosure. 
         FIG. 20  is a diagram for explaining a procedure for removing a wireless power transfer interface in a wireless power transfer system according to an aspect of the present disclosure. 
         FIG. 21  is a flowchart illustrating an information acquisition procedure of a wireless power transmitter according to an embodiment of the present disclosure. 
         FIG. 22  is a flowchart for explaining a procedure for releasing a connection between a wireless power transmitter and a wireless power receiver based on distance and location information obtained from the information acquisition procedure of the wireless power transmitter of  FIG. 21 . 
         FIG. 23  is a flowchart for explaining an information acquisition procedure of a wireless power receiver according to an embodiment of the present disclosure. 
         FIG. 24  is a flowchart for explaining a procedure for releasing a connection between a wireless power receiver and a wireless power transmitter based on distance and location information obtained from the information acquisition procedure of the wireless power receiver of  FIG. 23 . 
         FIG. 25  is a flowchart for explaining a method for a wireless power transmitter to check the connection state of a wireless power transmission link and release the connection. 
         FIG. 26  is a flowchart for explaining a method for a wireless power receiver to check the connection state of a wireless power transmission link and release the connection. 
     
    
    
     BEST MODE 
     In an aspect of the present disclosure, a method of controlling a wireless power transmission link by a wireless power transmitter is provided. The method may include: performing a first information acquisition procedure for a wireless power receiver; performing first determination for determining whether a distance between the wireless power transmitter and the wireless power receiver is normal, based on information obtained from the first information acquisition procedure; and performing a connection release procedure for the wireless power transmission link based on a determination result of the first determination. 
     Mode for the Disclosure 
     The term “wireless power” used hereinafter refers to any form of energy related to electric, magnetic, and electromagnetic fields transferred from a wireless power transmitter to a wireless power receiver without the use of physical electromagnetic conductors. Wireless power may be called a wireless power signal and may refer to an oscillating magnetic flux enclosed by primary and secondary coils. For example, this document describes power conversion in a system for charging devices including a mobile phone, cordless phone, iPod, MP3 player, and headset wirelessly. In general, the basic principles of wireless power transfer include power transfer based on magnetic coupling, power transfer based on radio frequency (RF), power transfer based on microwaves, and power transfer based on ultrasonic waves. 
       FIG. 1  is a block diagram of a wireless power system  10  according to an embodiment of the present disclosure. 
     Referring to  FIG. 1 , the wireless power system  10  includes a wireless power transmitter  100  and a wireless power receiver  200 . 
     The wireless power transmitter  100  receives power from an external power source S and generates a magnetic field. The wireless power receiver  200  receives power wirelessly by generating currents based on the generated magnetic field. 
     The wireless power transmitter  100  and the wireless power receiver  200  in the wireless power system  10  may transmit and receive various pieces of information required for wireless power transfer. Here, communication between the wireless power transmitter  100  and the wireless power receiver  200  may be performed according to either in-band communication using a magnetic field for wireless power transfer or out-band communication using a separate communication carrier. Out-band communication may also be called out-of-band communication. In the following, the terms are unified as out-band communication. For example, out-band communication includes near-field communication (NFC), Bluetooth, and Bluetooth Low Energy (BLE). 
     Here, the wireless power transmitter  100  may be a fixed or mobile type of wireless power transmitter. For example, the fixed type of transmitter includes a transmitter embedded in an indoor ceiling or wall or furniture such as a table; a transmitter implanted in an outdoor parking lot, bus stop or subway station; or a transmitter installed in a transportation such as a vehicle or train. The mobile type of wireless power transmitter may be implemented as a mobile device with a portable weight or size or as part of another device such as a laptop computer cover. 
     The wireless power receiver  200  should be construed as a comprehensive concept including various types of electronic devices equipped with a battery and various home appliances driven by receiving power wirelessly rather than a power cable. Typical examples of the wireless power receiver  200  include a portable terminal, cellular phone, smartphone, personal digital assistant (PDA), portable media player (PMP), Wibro terminal, tablet, phablet, laptop computer, digital camera, navigation terminal, television, and electric vehicle (EV). 
     The wireless power system  10  may include one or a plurality of wireless power receivers  200 . Although  FIG. 1  illustrates a case where the wireless power transmitter  100  and the wireless power receiver  200  transmit and receive power one-to-one, one wireless power transmitter  100  transmits power to a plurality of wireless power receivers  200 - 1 ,  200 - 2 , . . . ,  200 -M. In particular, when wireless power transfer is conducted based on magnetic resonance, one wireless power transmitter  100  may simultaneously transmit power to multiple wireless power receivers  200 - 1 ,  200 - 2 , . . . ,  200 -M by applying simultaneous transmission or time-division transmission. 
     Although  FIG. 1  illustrates a case where the wireless power transmitter  100  transmits power directly to the wireless power receiver  200 , a wireless power transceiver such as a relay or repeater for increasing the range of wireless power transmission may be provided between the wireless power transmitter  100  and the wireless power receiver  200 . In this case, the wireless power transmitter  100  may transmit power the wireless power transceiver, and the wireless power transceiver may transmit the power to the wireless power receiver  200 . 
     In this document, the wireless power receiver  200  refers to a wireless power receiver, a power receiver, and a receiver. Also, the wireless power transmitter  100  refers to a wireless power transmitter, a power transmitter, and a transmitter. 
       FIG. 3A  illustrates examples of various electronic devices where a wireless power transfer system is introduced. 
     In  FIG. 3A , electronic devices are categorized according to the amount of transferred power in a wireless power transmission system. Referring to  FIG. 3A , low power wireless charging (smaller than about 5 or 20 W) may be applied to wearable devices such as a smart watch, head mounted display (HMD), smart ring, and smart glasses and mobile electronic devices (or portable electronic devices) such as an earphone, remote controller, smartphone, PDA, and tablet PC. 
     Medium power wireless charging (smaller than about 50 or 200 W) may be applied to small and medium-sized home appliances such as a laptop computer, robot cleaner, TV, sound device, vacuum cleaner, and monitor. High power wireless charging (small than about 2 or 22 kW) may be applied to kitchen appliances such as a blender, microwave oven, and electric rice cooker; and personal mobility devices (or electric device/mobility means) such as a wheelchair, electric kickboard, electric bicycle, and electric vehicle. 
     The electronic devices/mobility means described above (or shown in  FIG. 1 ) may each include a wireless power receiver, which will be described later. Therefore, the above-described electronic devices/mobility means may be charged by receiving power wirelessly from a wireless power transmitter. 
     The present disclosure will be described based on a mobile device to which wireless power charging is applied, but this is merely exemplary. That is, the wireless charging method according to the present disclosure may be applied to various electronic devices. 
     Wireless power transfer standards include those studied by Wireless Power Consortium (WPC), Air Fuel Alliance (AFA), and Power Matters Alliance (PMA). 
     WPC standards define baseline power profile (BPP) and extended power profile (EPP). BPP is related to wireless power transmitters and receivers that support power transmission of 5 W, and EPP is related to wireless power transmitters and receivers that support power transmission in the range of 5 and 30 W. 
     Each standard covers various wireless power transmitters and receivers using different power levels and also classifies the wireless power transmitters and receivers into different power classes or categories. 
     For example, the WPC classifies wireless power transmitters and receivers in terms of power classes (PC): PC−1, PC0, PC1, and PC2 and provides standard specifications for each PC. The PC−1 standard is related to wireless power transmitters and receivers that provide guaranteed power less than 5 W. PC−1 applications include wearable devices such as smart watches. 
     The PC0 standard is related to wireless power transmitters and receivers that provide guaranteed power of 5 W. The PC0 standard includes the EPP in which guaranteed power reaches up to 30 W. Although in-band (IB) communication is a mandatory communication protocol for PC0, out-band (OB) communication, which is used as an optional backup channel, may also be used for PC0. Whether a wireless power receiver supports OB may be identified by configuring an OB flag in a configuration packet. If the wireless power transmitter supports OB, the wireless power transmitter may enter an OB handover phase by transmitting a bit pattern for OB handover as a response to the configuration packet. The response to the configuration packet may be an NAK, an ND, or a newly defined 8-bit pattern. PC0 applications include smartphones. 
     The PC1 standard is related to wireless power transmitters and receivers providing guaranteed power ranging from 30 W to 150 W. OB is a mandatory communication channel for PC1, and D3 is used for initialization and link establishment to OB. The wireless power transmitter may enter the OB handover phase by transmitting the bit pattern for OB handover as a response to the configuration packet. PC1 applications include laptop computers or power tools. 
     The PC2 standard is related to wireless power transmitters and receivers providing guaranteed power ranging from 200 W to 2 kW. PC2 applications include kitchen appliances. 
     As described above, PCs may be divided based on power levels, and compatibility within the same PC may be optional or mandatory. Here, the compatibility within the same PC means that power transmission and reception is allowed within the same PC. For example, if a wireless power transmitter of PC x is capable of charging a wireless power receiver with the same PC (i.e., PC x), it may be regarded that compatibility is maintained within the same PC. Similarly to the above, compatibility between different PCs may also be supported. Here, the compatibility between different PCs means that power transmission and reception is allowed between different PCs. For example, if a wireless power transmitter of PC x is capable of charging a wireless power receiver with PC y, it may be regarded that compatibility is maintained between different PCs. 
     The support of compatibility between PCs is an important issue in terms of user experience and infrastructure development. However, maintaining the compatibility between PCs may cause various technical problems as follows. 
     For example, when compatibility within the same PC is supported, a wireless power receiver such a laptop, which is stably charged only when power is transmitted continuously, may have a problem in receiving power reliably from a wireless power transmitter such as a power tool scheme that transmits power discontinuously. When compatibility between different PCs is supported, for example, if a wireless power transmitter with minimum guaranteed power of 200 W transmits power to a wireless power receiver with maximum guaranteed power is 5 W, the wireless power receiver may be damaged due to overvoltage. As a result, it is difficult to take the PC as an indicator/reference for representing/indicating compatibility. 
     Wireless power transmitters and receivers may provide very convenient user experience and interface (UX/UI). In other words, a smart wireless charging service may be provided. The smart wireless charging service may be implemented based on the UX/UI of a smartphone including the wireless power transmitter. For such an application, an interface between the processor of the smartphone and the wireless power receiver allows “drop and play” two-way communication between the wireless power transmitter and receiver. 
     For example, a user may experience the smart wireless charging service at a hotel. If the user enters a hotel room and places the smartphone on a wireless charger in the room, the wireless charger transmits wireless power to the smartphone, and the smartphone receives the wireless power. In this process, the wireless charger transmits, to the smartphone, information about the smart wireless charging service. If the smartphone detects that it is placed on the wireless charger, detects the wireless power reception, or receives the information about the smart wireless charging service from the wireless charger, the smartphone enters a state for asking the user to opt-in into an additional feature. To this end, the smartphone may display a message on the screen with or without an alarm sound. For example, the message may include the following sentences: “Welcome to ### hotel. Select “Yes” to activate smart charging functions: Yes No Thanks.” The smartphone receives a user input selecting Yes or No Thanks and performs the next procedure selected by the user. If Yes is selected, the smartphone transmits the corresponding information to the wireless charger. The smartphone and the wireless charger perform the smart charging function together. 
     The smart wireless charging service may also include receiving auto-filled WiFi credentials. For example, the wireless charger transmits WiFi credentials to the smartphone, and the smartphone automatically inputs the WiFi credentials received from the wireless charger by executing an appropriate app. 
     The smart wireless charging service may also include executing a hotel application that provides hotel promotions or obtaining remote check-in/check-out and contact information. 
     In another example, a user may experience the smart wireless charging service inside a vehicle. If the user gets into the vehicle and places the smartphone on a wireless charger, the wireless charger transmits wireless power to the smartphone, and the smartphone receives the wireless power. In this process, the wireless charger transmits information about the smart wireless charging service to the smartphone. If the smartphone detects that it is placed on the wireless charger, detects the wireless power reception, or receives the information about the smart wireless charging service from the wireless charger, the smartphone enters a state for asking the user about the identity. 
     In this state, the smartphone is automatically connected to the vehicle via WiFi and/or Bluetooth. The smartphone may display a message on the screen with or without an alarm sound. For example, the message may include the following sentences: “Welcome to your car. Select “Yes” to synch device with in-car controls: Yes No Thanks.” The smartphone receives a user input selecting Yes or No Thanks and performs the next procedure selected by the user. If Yes is selected, the smartphone transmits the corresponding information to the wireless charger. The smartphone and wireless charger may perform an in-vehicle smart control function together by executing in-vehicle application/display software. The user may enjoy desired music and check a regular map location. The in-vehicle application/display software may include a function that provides synchronization access for passers-by. 
     In another example, a user may experience smart wireless charging at home. If the user enters a room and places the smartphone on a wireless charger in the room, the wireless charger transmits wireless power to the smartphone, and the smartphone receives the wireless power. In this process, the wireless charger transmits, to the smartphone, information about the smart wireless charging service. If the smartphone detects that it is placed on the wireless charger, detects the wireless power reception, or receives the information about the smart wireless charging service from the wireless charger, the smartphone enters a state for asking the user to opt-in into an additional feature. To this end, the smartphone may display a message on the screen with or without an alarm sound. For example, the message may include the following sentences: “Hi xxx, Would you like to activate night mode and secure the building?: Yes No Thanks”. The smartphone receives a user input selecting Yes or No Thanks and performs the next procedure selected by the user. If Yes is selected, the smartphone transmits the corresponding information to the wireless charger. The smartphone and the wireless charger may at least recognize a user pattern and recommend the user to lock doors and windows, turn off lights, or set an alarm. 
     Herein, ‘profile’ is newly defined as an indicator/reference for representing/indicating compatibility. In other words, when wireless power transmitters and receivers have the same profile, compatibility may be maintained therebetween so that stable power transmission and reception may be allowed. When wireless power transmitters and receivers have different profiles, stable power transmission and reception may not be allowed. The profile may be defined according to compatibility and/or applications regardless of (or independently of) PCs. 
     For example, profiles may be divided into three categories: i) Mobile and Computing, ii) Power Tool, and iii) Kitchen. 
     Alternatively, the profiles may be divided into four categories: i) Mobile, ii) Power Tool, iii) Kitchen, and iv) Wearable. 
     In the ‘Mobile’ profile, the PC may be PC0 and/or PC1. The communication protocol/scheme may be IB and OB, and the operating frequency may be from 87 kHz to 205 kHz. Applications may include smartphones, laptop computers, and so on. 
     In the ‘Power Tool’ profile, the PC may be PC1. The communication protocol/scheme may be IB, and the operating frequency may be from 87 kHz to 145 kHz. Applications may include power tools. 
     In the ‘Kitchen’ profile, the PC may be PC2. The communication protocol/scheme may be based on NFC, and the operating frequency may be less than 100 kHz. Applications may include kitchen or home appliances. 
     In the ‘Power Tool and Kitchen’ profiles, NFC communication may be employed between the wireless power transmitter and receiver. The wireless power transmitter and receiver may confirm that each of them is an NFC device by exchanging a WPC NFC data exchange profile format (NDEF). For example, as shown in  FIG. 3B , the WPC NDEF may include an application profile field (e.g., IB), a version field (e.g., IB), and profile-specific data (e.g., IB). The application profile field indicates whether the corresponding device is one of the following profiles: i) Mobile and Computing, ii) Power Tool, and iii) Kitchen. The upper nibble of the version field indicates the major version, and the lower nibble of the version field indicates the minor version. Also, the profile specific data defines contents for kitchen. 
     In the ‘Wearable’ profile, the PC may be PC−1. The communication protocol/scheme may be IB, and the operating frequency may be from 87 kHz to 205 kHz. Applications may include wearable devices worn on the body of a user. 
     Maintaining compatibility within the same profile may be mandatory, but maintaining compatibility between different profiles may be optional. 
     The above-described profiles (Mobile profile, Power Tool profile, Kitchen profile, and Wearable profile) may be generalized to first to n-th profiles, and new profiles may be added to/substituted for old profiles according to WPC specifications and embodiments. 
     When profiles are defined as described above, a wireless power transmitter may perform power transmission selectively only to a wireless power receiver with the same profile as the wireless power transmitter, thereby enabling more stable power transmission. In addition, the burden on a wireless power transmitter may be reduced, and power transmission to incompatible wireless power receivers may not attempted, thereby preventing the wireless power transmitter from damaging wireless power receivers. 
     PC1 of the ‘Mobile’ profile may be defined by employing an optional extension such as OB based on PC0. PC1 of the ‘Power Tool’ profile may be defined simply as a modified version of PC1 of the ‘Mobile’ profile. The wireless transfer technology has been developed to maintain compatibility within the same profile until now. However, in the future, the wireless transfer technology may be further developed to maintain compatibility between different profiles. The wireless power transmitter or receiver may inform its profile to a peer device in various ways. 
     In the AFA standard, a wireless power transmitter is referred to as a power transmitting unit (PTU), and a wireless power receiver is referred to as a power receiving unit (PRU). PTUs are classified into a plurality of classes as shown in Table 1, and PRUs are classified into a plurality of categories as shown in Table 2. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                   
                   
                 Minimum value 
               
               
                   
                   
                   
                 for maximum 
               
               
                   
                   
                 Minimum category 
                 number of 
               
               
                   
                 P TX     —     IN     —     MAX   
                 support requirement 
                 supported devices 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 Class 1 
                  2 W 
                 1x Category 1 
                 1x Category 1 
               
               
                 Class 2 
                 10 W 
                 1x Category 3 
                 2x Category 2 
               
               
                 Class 3 
                 16 W 
                 1x Category 4 
                 2x Category 3 
               
               
                 Class 4 
                 33 W 
                 1x Category 5 
                 3x Category 3 
               
               
                 Class 5 
                 50 W 
                 1x Category 6 
                 4x Category 3 
               
               
                 Class 6 
                 70 W 
                 1x Category 7 
                 5x Category 3 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                 PRU 
                 P RX     —     OUT     —     MAX′   
                 Exemplary application 
               
               
                   
               
             
            
               
                 Category 1 
                 TBD 
                 Bluetooth headset 
               
            
           
           
               
               
               
               
            
               
                 Category 2 
                 3.5 
                 W 
                 Feature phone 
               
               
                 Category 3 
                 6.5 
                 W 
                 Smartphone 
               
               
                 Category 4 
                 13 
                 W 
                 Tablet PC and Phablet 
               
               
                 Category 5 
                 25 
                 W 
                 Laptop with a small form factor 
               
               
                 Category 6 
                 37.5 
                 W 
                 Regular laptop 
               
               
                 Category 7 
                 50 
                 W 
                 Home appliance 
               
               
                   
               
            
           
         
       
     
     As shown in Table 1, the maximum output power capability of a PTU of class n is larger than or equal to the value of P TX_IN_MAX of the corresponding class. A PRU is not allowed to draw larger power than specified in the corresponding category. 
       FIG. 4A  is a block diagram illustrating a wireless power transmission system according to another embodiment of the present disclosure. 
     Referring to  FIG. 4A , a wireless power transfer system  10  includes a mobile device  450  configured to receive power wirelessly and a base station  400  configured to transmit power wirelessly. 
     The base station  400  may provide inductive or resonant power and include at least one wireless power transmitter  100  and a system unit  405 . The wireless power transmitter  100  may transmit the inductive or resonant power and control transmission. The wireless power transmitter  100  may include: a power conversion unit  110  configured to convert electric energy to a power signal by generating a magnetic field based on primary coil(s); and a communication and control unit  120  configured to control communication with the wireless power receiver  200  and power transmission to transmit an appropriate amount of power. The system unit  405  may control operations of the base station  400  such as input power provisioning, control of a plurality of wireless power transmitters, and control of a user interface. 
     The primary coil may generate an electromagnetic field based on alternating current (AC) power (voltage or current). The primary coil may receive AC power (voltage or current) at a specific frequency output from the power conversion unit  110  and generate a magnetic field at the specific frequency. The magnetic field may be generated in a non-radial or radial form. The wireless power receiver  200  may receive the magnetic field to generate a current. In other words, the primary coil may transmit power wirelessly. 
     For magnetic induction, primary and secondary coils may have arbitrarily suitable shapes. For example, such a coil may be implemented by winding a copper wire around a high permeability member such as ferrite or amorphous metal. The primary coil may also be called a primary core, primary winding, or primary loop antenna. Meanwhile, the secondary coil may be called a secondary core, secondary winding, secondary loop antenna, or pickup antenna. 
     When magnetic resonance is used, the primary and secondary coils may be provided as a primary resonant antenna and a secondary resonant antenna. A resonant antenna may have a resonance structure including a coil and a capacitor. The resonant frequency of the resonant antenna may be determined by the inductance of the coil and the capacitance of the capacitor. Here, the coil may be formed to have a loop shape. In addition, a core may be disposed inside the loop. The core may include a physical core such as a ferrite core or an air core. 
     Energy transfer between the primary resonant antenna and the secondary resonant antenna may be achieved by resonance in a magnetic field. The resonance is a phenomenon in which high efficiency energy transfer occurs between two resonant antennas when the two resonant antennas are coupled to each other. Specifically, when one of the two resonant antennas generates a near field at a resonant frequency and the other resonant antenna is located in the vicinity thereof, the two resonant antennas may be coupled so that high efficiency energy transfer may occur therebetween. If a magnetic field is generated at the resonant frequency between the primary and secondary resonant antennas, the primary and secondary resonant antennas may resonate to each other. Thus, the magnetic field may be radiated to the secondary resonant antenna with high efficiency compared to when the magnetic field generated by the primary resonant antenna is radiated into the free space so that energy may be transferred from the primary resonant antenna to the secondary resonant antenna with high efficiency. The magnetic induction method may be implemented in a similar way to the magnetic resonance. However, in this case, the frequency of the magnetic field does not need to be the resonant frequency. Instead, for the magnetic induction, the loops of the primary and secondary coils need to match with each other, and the distance between the loops needs to be very close. 
     Although not shown in the drawing, the wireless power transmitter  100  may further include a communication antenna. The communication antenna may transmit and receive a communication signal on a communication carrier in addition to magnetic field communication. For example, the communication antenna may transmit and receive a communication signal based on WiFi, Bluetooth, BLE, ZigBee, NFC, and so on. 
     The communication and control unit  120  may transmit and receive information to and from the wireless power receiver  200 . The communication and control unit  120  may include at least one of an IB communication module or an OB communication module. 
     The IB communication module may transmit and receive information based on a magnetic wave having a specific frequency as the center frequency. For example, the communication and control unit  120  may perform IB communication by loading information on a magnetic wave and transmitting the magnetic wave through the primary coil or by receiving a magnetic wave containing information through the primary coil. In this case, a modulation scheme such as binary phase shift keying (BPSK) or amplitude shift keying (ASK) and a coding scheme such as Manchester coding or non-return-to-zero level (NZR-L) coding may be used to load information on magnetic waves or interpret information contained in magnetic waves. When the IB communication is applied, the communication and control unit  120  may transmit and receive information up to a distance of several meters at a data rate of several kbps. 
     The OB communication module may perform OB communication through the communication antenna. For example, the communication and control unit  120  may be provided as a short-range communication module. For example, the short-range communication module may include communication modules based on Wi-Fi, Bluetooth, BLE, ZigBee, NFC, and so on. 
     The communication and control unit  120  may control overall operations of the wireless power transmitter  100 . The communication and control unit  120  may compute and process various information and control each element of the wireless power transmitter  100 . 
     The communication and control unit  120  may be implemented as a computer or a device similar to the computer based on hardware, software, or combination thereof. For hardware implementation, the communication and control unit  120  may be provided as an electronic circuit for processing electric signals and performing control functions. For software implementation, the communication and control unit  120  may be provided as a program for driving the hardware of the communication and control unit  120 . 
     The communication and control unit  120  may control transmission power by controlling an operating point. The operating point to be controlled may correspond to a combination of a frequency (or phase), duty cycle, duty ratio, and voltage amplitude. The communication and control unit  120  may control transmission power by adjusting at least one of the frequency (or phase), duty cycle, duty ratio, or voltage amplitude. In addition, the wireless power receiver  200  may control reception power by controlling the resonant frequency while the transmitter  100  supplies constant power. 
     The mobile device  450  may include the wireless power receiver  200  configured to receive wireless power through the secondary coil and a load  455  configured to receive and store the power received by the wireless power receiver  200  and supply the stored power to devices. 
     The wireless power receiver  200  may include a power pick-up unit  210  and a communication and control unit  220 . The power pick-up unit  210  may receive wireless power through the secondary coil and convert the received wireless power to electric energy. The power pick-up unit  210  may rectify an AC signal obtained from the secondary coil to convert to a direct current (DC) signal. The communication and control unit  220  may control transmission and reception of wireless power (power transmission and reception). 
     The secondary coil may receive wireless power transmitted from the wireless power transmitter  100 . The secondary coil may receive power based on a magnetic field generated by the primary coil. In this case, if the specific frequency is the resonant frequency, the magnetic resonance may be generated between the primary and secondary coils, and thus the secondary coil may receive power more efficiently. 
     Although not shown in  FIG. 4A , the communication and control unit  220  may further include a communication antenna. The communication antenna may transmit and receive a communication signal on a communication carrier in addition to magnetic field communication. For example, the communication antenna may transmit and receive a communication signal based on WiFi, Bluetooth, BLE, ZigBee, NFC, and so on. 
     The communication and control unit  220  may transmit and receive information to and from the wireless power receiver  100 . The communication and control unit  220  may include at least one of an IB communication module or an OB communication module. 
     The IB communication module may transmit and receive information based on a magnetic wave having a specific frequency as the center frequency. For example, the communication and control unit  220  may perform IB communication by loading information on a magnetic wave and transmitting the magnetic wave through the primary coil or by receiving a magnetic wave containing information through the primary coil. In this case, a modulation scheme such as BPSK or ASK and a coding scheme such as Manchester coding or NZR-L coding may be used to load information on magnetic waves or interpret information contained in magnetic waves. When the IB communication is applied, the communication and control unit  220  may transmit and receive information up to a distance of several meters at a data rate of several kbps. 
     The OB communication module may perform OB communication through the communication antenna. For example, the communication and control unit  220  may be provided as a short-range communication module. 
     For example, the short-range communication module may include communication modules based on Wi-Fi, Bluetooth, BLE, ZigBee, NFC, and so on. 
     The communication and control unit  220  may control overall operations of the wireless power transmitter  200 . The communication and control unit  220  may compute and process various information and control each element of the wireless power transmitter  200 . 
     The communication and control unit  220  may be implemented as a computer or a device similar to the computer based on hardware, software, or combination thereof. For hardware implementation, the communication and control unit  220  may be provided as an electronic circuit for processing electric signals and performing control functions. For software implementation, the communication and control unit  220  may be provided as a program for driving the hardware of the communication and control unit  220 . 
     When the OB communication modules or short-range communication modules of the communication and control unit  120  and the communication and control unit  220  employ Bluetooth or BLE, the communication and control unit  120  and the communication and control unit  220  may have a communication architecture as shown in  FIG. 4B . 
       FIG. 4B  is a diagram illustrating an exemplary Bluetooth communication architecture to which the present disclosure is applicable. 
     Referring to  FIG. 4B , (a) shows an exemplary Bluetooth basic rate (BR)/enhanced data rate (EDR) protocol stack supporting a generic attribute profile (GATT), and (b) shows an exemplary BLE protocol stack. 
     Specifically, as shown in (a) of  FIG. 4B , the Bluetooth BR/EDR protocol stack may include an upper control stack  460  and a lower host stack  470  with respect to a host controller interface (HCI)  18 . 
     The host stack (or host module)  470  refers to hardware for transmitting or receiving a Bluetooth packet to or from a wireless transmission/reception module configured to receive a Bluetooth signal of 2.4 GHz. The controller stack  460  may be connected to the Bluetooth module to control operations of the Bluetooth module. 
     The host stack  470  may include a BR/EDR physical (PHY) layer  12 , a BR/EDR baseband layer  14 , and a link manager layer  16 . 
     The BR/EDR PHY layer  12  may transmit and receive a 2.4 GHz radio signal. When Gaussian frequency shift keying (GFSK) modulation is used, the BR/EDR PHY layer  12  may transmit data by hopping 79 RF channels. 
     The BR/EDR baseband layer  14  may transmit a digital signal, select a channel sequence for hopping 1400 times per second, and transmit a time slot with a length of 625 us for each channel. 
     The link manager layer  16  may control overall operations (e.g., link setup, control, security) of Bluetooth connection based on a link manager protocol (LMP). 
     The link manager layer  16  may perform the following functions.
         ACL/SCO logical transport, logical link setup, and control   Detach: if connection is disconnected, the link manager layer  16  may inform a peer device of a reason for the disconnection.   Power control and role switch   Security (authentication, pairing, encryption, etc.)       

     The host controller interface layer  18  may provide an interface between a host module and a controller module so that the host may provide commands and data to the controller and the controller may provide events and data to the host. 
     The host stack (or host module)  470  may include a logical link control and adaptation protocol (L2CAP)  21 , an attribute protocol  22 , a GATT  23 , a generic access profile (GAP)  24 , and a BR/EDR profile  25 . 
     The L2CAP  21  may provide one two-way channel for transmitting data to a specific protocol or profile. 
     The L2CAP  21  may multiplex various protocols, profiles, and so on provided from Bluetooth. 
     The L2CAP of the Bluetooth BR/EDR may use dynamic channels. In addition, the L2CAP of the Bluetooth BR/EDR may support protocol service multiplexers, retransmission, streaming modes and provide segmentation and reassembly, per-channel flow control, and error control. 
     The GATT  23  may act as a protocol for explaining how the attribute protocol  22  is used when services are configured. For example, the GATT  23  may act to specify how the attributes of the attribute protocol (ATT) are grouped together into services and also act to describe features related to the services. 
     Accordingly, the GATT  23  and the ATT  22  may use features to describe the states and services of a device and explain how the features are related to each other and how the features are used. 
     The ATT  22  and the BR/EDR profile  25  may define a service (profile) using the Bluetooth BR/EDR and an application protocol for exchanging data. The GAP  24  may define device discovery, connectivity, and security. 
     As shown in (b) of  FIG. 4B , the BLE protocol stack includes a controller stack  480  configured to process a wireless device interface where timing is important and a host stack  490  configured to process high level data. 
     To implement the controller stack  480 , a communication module including a Bluetooth wireless device and a processor module including a processing device such as a microprocessor may be used. 
     The host stack  490  may be implemented as part of an OS operated on the processor module or implemented as instantiation of a package on the OS. 
     In some examples, the controller stack and the host stack may be operated or executed on the same processing device within the processor module. 
     The controller stack  480  may include a PHY layer  32 , link layer  34 , and a HCI  36 . 
     The PHY layer (wireless transceiver module)  32  is a layer for transmitting and receiving a 2.4 GHz wireless signal. The PHY layer may uses GFSK modulation and frequency hopping including 40 RF channels. 
     The link layer  34  may serve to transmit or receive a Bluetooth packet. Specifically, the link layer  34  may perform advertising and scanning on three advertising channels, generate connection between devices, and exchange a data packet of up to 257 bytes over 37 data channels. 
     The host stack  490  may include a GAP  40 , a L2CAP  41 , a security manager (SM)  42 , an ATT  43 , a GATT  44 , a GAP  25 , and an LE profile  46 . However, the host stack  490  is not limited thereto and may further include various protocols and profiles. 
     The host stack may multiplex various protocols, profiles, and so on provided from Bluetooth based on L2CAP. 
     The L2CAP  41  may provide one two-way channel for transmitting data to a specific protocol or profile. 
     The L2CAP  41  may be configured to multiplex data between higher layer protocols, segment and reassemble packages, and manage multicast data transmission. 
     In BLE, three fixed channels are basically used (one is used for CH signaling, another is used for the SM, and the other is used for the ATT). If necessary, a dynamic channel may also be used. 
     For the BR/EDR, a dynamic channel may be basically used. A protocol service multiplexer, retransmission, streaming mode, and so on may be supported. 
     The SM  42  is a protocol for authenticating devices and providing key distribution. 
     The ATT  43  may define a rule for accessing data of a peer device based on a server-client structure. The ATT has the following 6 message types: Request, Response, Command, Notification, Indication, and Confirmation. 
     {circle around (1)} Request and Response messages: The request message is a message for a client device to request specific information from a server device. The response message is a response to the request message, which is transmitted from the server device to the client device. 
     {circle around (2)} Command message: The command message is a message transmitted from the client device to the server device to instruct a specific operation. The server device sends no response to the command message to the client device. 
     {circle around (3)} Notification message: The Notification message is a message transmitted from the server device to the client device to notify an event. The client device sends no confirmation message to the notification message to the server device. 
     {circle around (4)} Indication and Confirmation messages: The indication message is a message transmitted from the server device to the client device to notify an event. However, unlike the Notification message, the client device transmits the Confirmation message for the Indication message to the server device 
     According to the present disclosure, when long data is requested, the GATT using the ATT  43  may let a client to know the length of data by sending the data length and receive a characteristic value from a server based on a universal unique identifier (UUID). 
     The GAP  45  is a newly implemented layer for BLE technology. The GAP  45  may be used to select a role for communication between BLE devices and control the occurrence of multi-profile operation. 
     In addition, the GAP  45  is mainly used for device discovery, connection creation, and security procedures. The GAP  45  may define a method for providing information to a user, and also define the following attribute types. 
     {circle around (1)} Service: It defines the basic operation of a device based on a combination of data related behaviors. 
     {circle around (2)} Include: It defines a relationship between services. 
     {circle around (3)} Characteristics: It is a data value used for a service. 
     {circle around (4)} Behavior: It is a format readable by a computer defined by a UUID (value type). 
     The LE profile  46  includes profiles dependent on the GATT. The LE profile  46  may be mainly applied to BLE devices. The LE profile  46  may include, for example, Battery, Time, FindMe, Proximity, Time, Object Delivery Service, and so on. Details of the GATT-based profiles are as follows. 
     {circle around (1)} Battery: Battery information exchange 
     {circle around (2)} Time: Time information exchange 
     {circle around (3)} FindMe: Provision of alarm service according to distance 
     {circle around (4)} Proximity: Battery information exchange 
     {circle around (5)} Time: Time information exchange 
     The GATT  44  may act as a protocol for explaining how the ATT  43  is used when services are configured. For example, the GATT  44  may act to define how ATT attributes are grouped together with services and operate to describe features associated with services. For example, the GATT  44  may act to specify how the attributes of the ATT are grouped together into services and also act to describe features related to the services. 
     Accordingly, the GATT  44  and the ATT  43  may use features to describe the states and services of a device and explain how the features are related to each other and how the features are used 
     Hereinafter, procedures for the BLE technology will be briefly described. 
     The BLE procedures may be classified into a device filtering procedure, an advertising procedure, a scanning procedure, a discovering procedure, and a connecting procedure. 
     Device Filtering Procedure 
     The device filtering procedure corresponds to a method of reducing the number of devices that respond to a request, an indication, a notification, etc. in the controller stack. 
     When requests are received from all the devices, it is unnecessary to respond thereto. Thus, the controller stack may reduce the number of transmitted requests to reduce power consumption in the BLT controller stack. 
     An advertisement device or a scanning device may perform the device filtering procedure to limit devices that will receive an advertisement packet, a scan request, or a connection request. 
     Here, the advertising device refers to a device transmitting an advertising event, i.e., a device performing advertising. The advertising device may be referred to as an advertiser. 
     The scanning device refers to a device performing scanning, i.e., a device transmitting a scan request. 
     In BLE, when the scanning device receives some advertisement packets from the advertising device, the scanning device needs to transmit a scan request to the advertisement device. 
     However, if the device filtering procedure is used so that scan request transmission is not required, the scanning device may disregard the advertising packets transmitted from the advertising device. 
     The device filtering procedure may also be used for a connection request procedure. If device filtering is used in the connection request procedure, it is not necessary to transmit a response to the connection request by ignoring the connection request. 
     Advertising Procedure 
     The advertising device performs the advertising procedure to perform undirected broadcast to devices in an area. 
     Here, the undirected broadcast (undirected advertising) is advertising directed to all devices rather than broadcast directed to a specific device. All devices may scan the advertising and make an additional information request or a connection request. 
     However, in directed broadcast (directed advertising), only a device designated as the receiving device may scan advertising and make an additional information request or a connection request. 
     The advertising procedure may be used to establish a Bluetooth connection with a nearby initiating device. 
     Alternatively, the advertising procedure may be used to provide periodic broadcast of user data to scanning devices that are listening on an advertising channel. 
     In the advertising procedure, all advertisements (or advertising events) are broadcast on an advertising physical channel. 
     The advertising device may receive a scan request from a listening device that are listening to obtain additional user data from the advertising device. The advertising device transmits a response to the scan request to the device, which transmits the scan request, over the same advertising physical channel as the advertising physical channel on which the scan request is received. 
     Broadcast user data, which is sent as part of advertisement packets, is dynamic data, whereas scan response data is generally static data. 
     The advertising device may receive a connection request from the initiating device on the advertising (broadcast) physical channel. If the advertising device uses a connectable advertising event and the initiating device is not filtered by the device filtering procedure, the advertising device may stop advertising and enter a connected mode. The advertising device may start advertising again after the connected mode. 
     Scanning Procedure 
     The scanning device, that is, a device that performs scanning performs the scanning procedure to listen to undirected broadcast of user data from advertising devices using advertising physical channels. 
     The scanning device transmits a scan request to the advertising device over the advertising physical channel to request additional data from the advertising device. The advertising device transmits a scan response, which is a response to the scan request, including additional data requested by the scanning device on the advertising physical channel. 
     The scanning device may use the scanning procedure while establishing connection with another BLE device in the BLE piconet. 
     If the scanning device receives a broadcast advertising event and is in an initiator mode capable of initiating a connection request, the scanning device may transmit the connection request to the advertising device over the advertising physical channel in order to initiate a Bluetooth connection with the advertising device. 
     When the scanning device sends the connection request to the advertising device, the scanning device may stop the initiator mode scanning for additional broadcast and enter the connected mode. 
     Discovering Procedure 
     Devices capable of Bluetooth communication (hereinafter referred to as Bluetooth devices) may perform the advertising procedure and scanning procedure to discover nearby devices or to be discovered by other devices within a given area. 
     The discovery procedure is performed asymmetrically. A Bluetooth device attempting to discover other nearby devices is called a discovering device. The discovering device listens to discover devices that advertise a scannable advertising event. An available Bluetooth device discovered by other devices is called a discoverable device. The discoverable device actively broadcasts an advertising event over the advertisement (broadcast) physical channel so that other devices scan the advertising event. 
     Both the discovering device and discoverable device may be already connected to other Bluetooth devices in the piconet. 
     Connecting Procedure 
     The connecting procedure is asymmetric. For the connecting procedure, it is required that other Bluetooth devices perform the scanning procedure while a specific Bluetooth device performs the advertising procedure. 
     That is, the advertising procedure may be the goal, so that only one device will respond to advertising. After receiving an accessible advertising event from the advertising device, the device may initiate connection by sending a connection request to the advertising device over the advertising (broadcast) physical channel. 
     Hereinafter, operation states in the BLE technology such as an advertising state, a scanning state, an initiating state, and a connection state will be briefly reviewed. 
     Advertising State 
     The link layer (LL) enters the advertising state according to an instruction from the host (stack). When the LL is in the advertising state, the LL transmits advertising packet data units (PDUs) for advertising events. 
     Each advertising event may include at least one advertisement PDU, and the advertising PDUs may be transmitted by advertising channel indices in use. The advertising event may be terminated when the advertising event is transmitted by the advertising channel indices where the advertising PDU(s) are used. If the advertising device needs to reserve a space for performing other functions, the advertising event may be terminated earlier. 
     Scanning State 
     The LL enters the scanning state according to an instruction from the host (stack). In the scanning state, the LL listens to advertising channel indices. 
     The scanning state has two types: passive scanning and active scanning. Each scanning type is determined by the host. 
     A separate time or advertising channel index for performing scanning is not defined. 
     In the scanning state, the LL listens to an advertising channel index for a scan window (scanWindow) duration. A scan interval (scanInterval) is defined as the interval between the starting points of two consecutive scan windows. 
     If there is no collision in scheduling, the LL should complete all scan intervals of scan windows as instructed by the host. In each scan window, the LL should scan a different advertising channel index. The LL uses every available advertising channel index. 
     For passive scanning, the LL only receives packets and does not transmit any packets. 
     For active scanning, the LL performs listening to receive an advertising PDU type for requesting advertising PDUs and additional information related to the advertising device from the advertising device. 
     Initiating State 
     The LL enters the initiating state according to an instruction from the host (stack). 
     When the LL is in the initiating state, the LL listens to advertising channel indices. 
     In the initiating state, the LL listens to an advertising channel index for a scan window duration. 
     Connection State 
     The LL enters the connection state when the initiating device, i.e., a device performing a connection request transmits a CONNECT_REQ PDU to the advertising device or when the advertising device receives the CONNECT_REQ PDU from the initiating device. 
     After the LL enters the connection state, connection may be created. However, the connection may not need to be established when the LL enters the connection state. The only difference between a newly created connection and a previously established connection is an LL connection supervision timeout value. 
     When two devices are connected, the two devices perform different roles. 
     An LL performing a master role is called a master, and an LL performing a slave role is called a slave. The master controls the timing of a connection event, and the connection event refers to a synchronization time point between the master and the slave. 
     Hereinafter, packets defined for a Bluetooth interface will be described in brief. BLE devices use the following packets. 
     Packet Format 
     The LL has only one packet format used for both an advertising channel packet and data channel packet. 
     Each packet includes four fields: a preamble field, an access address field, a PDU field, and a CRC field. 
     When one packet is transmitted on an advertising channel, the PDU may be an advertising channel PDU, and when one packet is transmitted on a data channel, the PDU may be a data channel PDU. 
     Advertising Channel PDU 
     The advertising channel PDU has a 16-bit header and a payload of various sizes. 
     The PDU type field of the advertising channel PDU included in the header indicates PDU types defined in Table 3 below. 
     
       
         
           
               
               
             
               
                 TABLE 3 
               
               
                   
               
               
                 PDU Type 
                 Packet Name 
               
               
                   
               
             
            
               
                 0000 
                 ADV_IND 
               
               
                 0001 
                 ADV_DIRECT_IND 
               
               
                 0010 
                 ADV_NONCONN_IND 
               
               
                 0011 
                 SCAN_REQ 
               
               
                 0100 
                 SCAN_RSP 
               
               
                 0101 
                 CONNECT_REQ 
               
               
                 0110 
                 ADV_SCAN_IND 
               
               
                 0111-1111 
                 Reserved 
               
               
                   
               
            
           
         
       
     
     Advertising PDU 
     The following advertising channel PDU types are called the advertising PDU and used in specific events. 
     ADV_IND: Connectable undirected advertising event 
     ADV_DIRECT_IND: Connectable directed advertising event 
     ADV_NONCONN_IND: Non-connectable undirected advertising event 
     ADV_SCAN_IND: Scannable undirected advertising event 
     The PDUs are transmitted by the LL in the advertising state and are received by the LL in the scanning state or initiating state. 
     Scanning PDU 
     The following advertising channel PDU types are called the scanning PDU and used in states described below. 
     SCAN_REQ: SCAN_REQ is transmitted by the LL in the scanning state and received by the LL in the advertising state. 
     SCAN_RSP: SCAN_RSP is transmitted by the LL in the advertising state and received by the LL in the scanning state. 
     Initiating PDU 
     The following advertising channel PDU type is called the initiating PDU. 
     CONNECT_REQ: CONNECT_REQ is transmitted by the LL in the initiating state and received by the LL in the advertising state. 
     Data Channel PDU 
     The data channel PDU has a 16-bit header and a payload of various sizes. The data channel PDU may include a message integrity check (MIC) field. 
     The procedures, states, packet formats, etc. in the BLE technology discussed above may be applied to perform methods proposed in the present disclosure. 
     Referring again to  FIG. 4A , the load  455  may be a battery. The battery may store energy based on power outputted from the power pick-up unit  210 . The mobile device  450  may not mandatorily include the battery. For example, the battery may be provided as a detachable external component. In another example, the wireless power receiver  200  may include a driving means for performing various operations of the electronic device, instead of the battery. 
     Although it is shown that the mobile device  450  includes the wireless power receiver  200  and the base station  400  includes the wireless power transmitter  100 , the wireless power receiver  200  may be identified with the mobile device  450  and the wireless power transmitter  100  may be identified with the base station  400  in a broad sense. 
     When the communication and control unit  120  and the communication and control unit  220  include Bluetooth or BLE as the OB communication module or short-range communication module in addition to the IB communication module, the wireless power transmitter  100  including the communication and control unit  120  and the wireless power receiver  200  including the communication and control unit  220  may be illustrated as a simple block diagram such as  FIG. 4C . 
       FIG. 4C  is a block diagram illustrating a wireless power transfer system using BLE communication according to an embodiment of the present disclosure. 
     Referring to  FIG. 4C , the wireless power transmitter  100  includes the power conversion unit  110  and the communication and control unit  120 . The communication and control unit  120  includes an in-band communication module  121  and a BLE communication module  122 . 
     The wireless power receiver  200  includes the power pickup unit  210  and the communication and control unit  220 . The communication and control unit  220  includes an in-band communication module  221  and a BLE communication module  222 . 
     In one aspect, the BLE communication modules  122  and  222  perform the architectures and operations shown in  FIG. 4B . For example, the BLE communication modules  122  and  222  may be used to establish connection between the wireless power transmitter  100  and the wireless power receiver  200  and exchange control information and packets necessary for wireless power transfer. 
     In another aspect, the communication and control unit  120  may be configured to operate a profile for wireless charging. Here, the profile for wireless charging may be a GATT based on BLE transmission. 
     As shown in  FIG. 4D , the communication and control units  120  and  220  include only the in-band communication modules  121  and  221 , respectively. The BLE communication modules  122  and  222  may be provided separately from the communication and control units  120  and  220 . 
     Hereinafter, a coil or coil unit may be referred to as a coil assembly, a coil cell, or a cell, which includes the coil and at least one element close to the coil. 
       FIG. 5  is a state transition diagram for explaining a wireless power transfer procedure. 
     Referring to  FIG. 5 , power transfer from the wireless power transmitter to the wireless power receiver according to an embodiment of the present disclosure may be broadly divided into a selection phase  510 , a ping phase  520 , an identification and configuration phase  530 , a negotiation phase  540 , a calibration phase  550 , a power transfer phase  560 , and a renegotiation phase  570 . 
     The selection phase  510  is a transition phase including reference numerals S 502 , S 504 , S 508 , S 510 , and S 512  when a specific error or a specific event is detected at the beginning of or during power transfer. The specific error and specific event will be described in detail later. In the selection phase  510 , the wireless power transmitter may monitor whether an object is present on an interface surface. If the wireless power transmitter detects that an object is placed on the interface surface, the wireless power transmitter may transition to the ping phase  520 . In the selection phase  510 , the wireless power transmitter transmits an analog ping signal, which is a power (or pulse) signal with a very short duration. The wireless power transmitter may detect whether an object is present in an active area of the interface surface based on a current change in a transmitter coil or a primary coil. 
     When an object is detected in the selection phase  510 , the wireless power transmitter may measure the quality factor of a wireless power resonance circuit (e.g., a power transmitter coil and/or a resonance capacitor). According to an embodiment of the present disclosure, when an object is detected in the selection phase  510 , the wireless power transmitter may measure the quality factor to determine whether a foreign object exists in the charging area along with the wireless power receiver. The inductance and/or series resistance component of the coil provided in the wireless power transmitter may be reduced due to a change in the environment, and the decrease may reduce the quality factor. To determine the presence or absence of a foreign object based on the measured quality factor, the wireless power transmitter may receive from the wireless power receiver a reference quality factor, which is measured in advance in a state where no foreign object is placed in the charging area. The wireless power transmitter may determine the presence or absence of a foreign object by comparing the measured quality factor with the reference quality factor, which is received during the negotiation phase  540 . However, when the wireless power receiver has a low reference quality factor (for example, the reference quality factor of the wireless power receiver may decrease depending on the type, purpose, characteristics, etc. of the wireless power receiver), the difference between the reference quality factor and the quality factor measured under the presence of a foreign object may be insignificant so that it may be difficult to determine the presence of the foreign object. Accordingly, in this case, other determination factors should be further considered, or the presence of a foreign object should be determined based on another method. 
     In another embodiment of the present disclosure, when an object is detected in the selection phase  510 , the quality factor may be measured within a specific frequency range (e.g., operating frequency range) to determine whether the object is placed with a foreign object in the charging area. The inductance and/or series resistance component of the coil of the wireless power transmitter may be reduced due to a change in the environmental, and thus the resonant frequency of the coil of the wireless power transmitter may be changed (shifted). That is, a quality factor peak frequency, which is a frequency at which the maximum quality factor is measured within the operating frequency band, may be shifted. 
     In the ping phase  520 , if the wireless power transmitter detects an object, the wireless power transmitter wakes up the receiver and transmits a digital ping for identifying whether the detected object is the wireless power receiver. If the wireless power transmitter fails to receive a response signal for the digital ping such as a signal intensity packet from the receiver during the ping phase  520 , the wireless power transmitter may transition back to the selection phase  510 . In addition, if the wireless power transmitter receives a signal indicating the completion of the power transfer such as a charging complete packet from the receiver during the ping phase  520 , the wireless power transmitter may transition back to the selection phase  510 . 
     When the ping phase  520  is completed, the wireless power transmitter may transition to the identification and configuration phase  530  for identifying the receiver and collecting information on the configuration and state of the receiver. 
     During the identification and configuration phase  530 , if the wireless power transmitter receives an unexpected packet or fails to receive a desired packet for a predetermined period of time, if a packet transmission error occurs, or if no power transfer contract is configured, the wireless power transmitter may transition to the selection phase  510 . 
     Based on the value of a negotiation field in a configuration packet, which is received during the identification and configuration phase  530 , the wireless power transmitter may check whether the wireless power transmitter needs to enter the negotiation phase  540 . If negotiation is needed, the wireless power transmitter may enter the negotiation phase  540  and then perform a predetermined a foreign object detection (FOD) detection procedure. On the contrary, if no negotiation is needed, the wireless power transmitter may immediately enter the power transfer phase  560 . 
     In the negotiation phase  540 , the wireless power transmitter may receive a FOD status packet including the reference quality factor. Alternatively, the wireless power transmitter may receive an FOD status packet including a reference peak frequency. Alternatively, the wireless power transmitter may receive an FOD status packet including the reference quality factor and the reference peak frequency. In this case, the wireless power transmitter may determine a quality factor threshold for FOD based on the reference quality factor. The wireless power transmitter may determine a peak frequency threshold for FOD based on the reference peak frequency value. 
     The wireless power transmitter may detect whether a foreign object (FO) exists in the charging area based on the determined quality factor threshold for FOD and the currently measured quality factor (which is measured before the ping phase). The wireless power transmitter may control power transfer according to the FOD result. For example, when the FO is detected, the wireless power transmitter may stop the power transfer, but the present disclosure is not limited thereto. 
     The wireless power transmitter may detect whether an FO exists in the charging area based on the determined peak frequency threshold for FOD and the currently measured peak frequency (which is measured before the ping phase). The wireless power transmitter may control power transfer according to the FOD result. For example, when the FO is detected, the wireless power transmitter may stop the power transfer, but the present disclosure is not limited thereto. 
     When the FO is detected, the wireless power transmitter may return to the selection phase  510 . On the other hand, when the FO is not detected, the wireless power transmitter may enter the power transfer phase  560  through the calibration phase  550 . Specifically, when the FO is not detected, the wireless power transmitter may determine the strength of power received by the receiver and then measure power loss between the receiver and transmitter in the calibration phase  550  in order to determine the strength of power transmitted from the transmitting end. That is, the wireless power transmitter may estimate the power loss based on a difference between the transmitted power of the transmitter and the received power of the receiver in the calibration phase  550 . In one embodiment, the wireless power transmitter may correct the threshold for FOD by reflecting the estimated power loss. 
     During the power transfer phase  560 , if the wireless power transmitter receives an unexpected packet or fails to receive a desired packet for a predetermined period of time, if there is an error in the predetermined power transfer contract (power transfer contract violation), or if charging is completed, the wireless power transmitter may transition to the selection phase  510 . 
     If the wireless power transmitter needs to reconfigure the power transfer contract according to a change in the state of the wireless power transmitter during the power transfer phase  560 , the wireless power transmitter may transition to the renegotiation phase  570 . In this case, if the renegotiation is normally completed, the wireless power transmitter may return to the power transfer phase  560 . 
     In this embodiment, although the calibration phase  550  and the power transfer phase  560  are separated into different phases, the calibration phase  550  may be integrated into the power transfer phase  560 . In this case, the operations in the calibration phase  550  may be performed during the power transfer phase  560 . 
     The power transfer contract may be established based on information about the states and characteristics of the wireless power transmitter and receiver. For example, the wireless power transmitter state information may include information on the maximum amount of transmitted power, information on the maximum number of acceptable receivers, etc. The wireless power receiver state information may include information on required power, etc. 
       FIG. 6  illustrates a power control method according to an embodiment of the present disclosure. 
     Referring to  FIG. 6 , in the power transfer phase  560 , the wireless power transmitter  100  and the wireless power receiver  200  may control the amount of power transmitted for both communication and power transmission/reception. The wireless power transmitter and wireless power receiver operate at a specific control point. The control point represents a combination of the voltage and current provided at the output end of the wireless power receiver when the power transfer is performed. 
     More specifically, the wireless power receiver may select a desired control point such as a desired output current/voltage and the temperature of a specific location of the mobile device and additionally determine an actual control point. The wireless power receiver may calculate a control error value based on the desired control point and the actual control point and transmit the control error value to the wireless power transmitter as a control error packet. 
     In addition, the wireless power transmitter may control the power transfer by configuring/controlling a new operating point such as an amplitude, a frequency, and a duty cycle based on the received control error packet. Thus, the control error packet is transmitted/received at regular time intervals during the power transfer phase. In an embodiment, the wireless power receiver may set the control error value to a negative number to reduce the current of the wireless power transmitter. On the contrary, the wireless power receiver may set the control error value to a positive value to increase the current of the wireless power transmitter. In an induction mode, the wireless power receiver may control the power transfer by transmitting the control error packet to the wireless power transmitter as described above. 
     A resonance mode, which will be described below, may operate in a different way from the induction mode. In the resonance mode, one wireless power transmitter needs to be capable of simultaneously serving a plurality of wireless power receivers. However, when power transfer is controlled as in the induction mode, transmitted power may be controlled by communication with one wireless power receiver, and as a result, it may be difficult to control power transfer to additional wireless power receivers. Therefore, in the resonant mode of present disclosure, the wireless power transmitter may transmit basic power in common, and the wireless power receiver may control the amount of received power by controlling its own resonance frequency. However, the method described with reference to  FIG. 6  is not completely excluded even in the resonance mode operation, and additional transmission power control may be performed according to the method of  FIG. 6 . 
       FIG. 7  is a block diagram of a wireless power transmitter according to another embodiment of the present disclosure. The wireless power transmitter may be included in a wireless power transfer system operating in a magnetic resonance mode or a shared mode. The shared mode may refer to a mode in which a wireless power transmitter performs one-to-many communication and charging with wireless power receivers. The shared mode may be implemented based on magnetic induction or resonance. 
     Referring to  FIG. 7 , a wireless power transmitter  700  may include at least one of a cover  720  configured to cover a coil assembly, a power adapter  730  configured to supply power to a power transmitter  740 , the power transmitter  740 , or a user interface  750  configured to provide power transfer progress and other related information. In particular, the user interface  750  may be optionally included or may be included as another user interface  750  for the wireless power transmitter  700 . 
     The power transmitter  740  may include at least one of a coil assembly  760 , an impedance matching circuit  770 , an inverter  780 , a communication unit  790 , or a control unit  710 . 
     The coil assembly  760  may include at least one primary coil configured to generate a magnetic field. The coil assembly  760  may be referred to as a coil cell. 
     The coil assembly  760  may include at least one primary coil configured to generate a magnetic field. The coil assembly  760  may be referred to as a coil cell. The impedance matching circuit  770  may provide impedance matching between the inverter and the primary coil(s). The impedance matching circuit  770  may generate resonance at a suitable frequency to boost the primary coil current. If the power transmitter  740  is a multi-coil power transmitter, the impedance matching circuit may further include a multiplexer configured to route a signal from the inverter to a subset of the primary coils. The impedance matching circuit may be referred to as a tank circuit. 
     The impedance matching circuit  770  may include a capacitor, an inductor, and a switching device for switching connection thereof. The impedance matching may be performed as follows. First, the reflected wave of wireless power transmitted through the coil assembly  760  is detected. Then, the switching device is switched based on the detected reflected wave so that the connection state of the capacitor or inductor, the capacitance of the capacitor, or the inductance of the inductor is adjusted. In some cases, the impedance matching circuit  770  may be omitted. The present disclosure may include an embodiment in which the wireless power transmitter  700  does not include the impedance matching circuit  770 . 
     The inverter  780  may convert a DC input into an AC signal. The inverter  780  may be a half-bridge inverter or a full-bridge inverter to generate pulse waves and duty cycles at adjustable frequencies. The inverter may also include a plurality of stages to adjust the input voltage level. 
     The communication unit  790  may perform communication with a power receiver. The power receiver performs load modulation to transmit requests and information to the power transmitter. Accordingly, the power transmitter  740  may monitor the amplitude and/or phase of the current and/or voltage of the primary coil in order to demodulate data transmitted by the power receiver based on the communication unit  790 . 
     In addition, the power transmitter  740  may control output power to transmit data through the communication unit  790  based on frequency shift keying (FSK). 
     The control unit  710  may control communication and power transmission of the power transmitter  740 . The control unit  710  may control the power transmission by adjusting the above-described operating point. The operating point may be determined by, for example, at least one of an operating frequency, a duty cycle, and an input voltage. 
     The communication unit  790  and the control unit  710  may be provided as separate units/devices/chipsets or as one unit/device/chipsets. 
       FIG. 8  illustrates a wireless power receiver according to another embodiment of the present disclosure. The wireless power receiver may be included in a wireless power transfer system operating in the magnetic resonance mode or shared mode. 
     In  FIG. 8 , a wireless power receiving device  800  may include at least one of a user interface  820  configured to provide power transfer progress and other related information, a power receiver  830  configured to receives wireless power, a load circuit  840 , or a base  850  configured to support and cover a coil assembly. In particular, the user interface  820  may be optionally included or may be included as another user interface  820  of the power receiver. 
     The power receiver  830  may include at least one of a power converter  860 , an impedance matching circuit  870 , a coil assembly  880 , a communication unit  890 , or a control unit  810 . 
     The power converter  860  may convert AC power received from a secondary coil into a voltage and current suitable for the load circuit. In an embodiment, the power converter  860  may include a rectifier. The rectifier may rectify received wireless power in order to convert the received wireless power from AC power to DC power. The rectifier may use a diode or a transistor to convert the AC power into the DC power and use a capacitor and a resistor to smooth the DC power. A full-wave rectifier, a half-wave rectifier, a voltage multiplier, etc., which are implemented as a bridge circuit, may be used as the rectifier. Additionally, the power converter may adapt the reflected impedance of the power receiver. 
     The impedance matching circuit  870  may provide impedance matching between the secondary coil and a combination of the power converter  860  and the load circuit  840 . In an embodiment, the impedance matching circuit  870  may generate resonance at a frequency near 100 kHz to improve power transfer. The impedance matching circuit  870  may include a capacitor, an inductor, and a switching device for switching a combination thereof. The impedance matching may be performed by controlling the switching device in the impedance matching circuit  870  based on the voltage, current, power, frequency, etc. of the received wireless power. In some cases, the impedance matching circuit  870  may be omitted. The present disclosure may include an embodiment in which the wireless power transmitter  800  does not include the impedance matching circuit  870 . 
     The coil assembly  880  includes at least one secondary coil. In addition, the coil assembly  880  may optionally include an element for shielding a metal part of the receiver from the magnetic field. 
     The communication unit  890  may perform load modulation to provide requests and other information to the power transmitter. 
     To this end, the power receiver  830  may switch the resistor or capacitor to change the reflected impedance. 
     The control unit  810  may control received power. To this end, the control unit  810  may determine/calculate a difference between the actual operating point and desired operating point of the power receiver  830 . In addition, the control unit  810  may adjust/reduce the difference between the actual operating point and desired operating point by adjusting the reflected impedance of the power transmitter and/or performing a request for adjusting the operating point of the power transmitter. When the difference is minimized, optimal power reception may be achieved. 
     The communication unit  890  and the control unit  810  may be provided as separate devices/chipsets or as one device/chipset. 
       FIG. 9  illustrates a communication frame structure according to an embodiment of the present disclosure. The communication frame structure may be a communication frame structure operating in the shared mode. 
     Referring to  FIG. 9 , different types of frames may be used together in the shared mode. For example, a slotted frame having a plurality of slots as shown in (A) and a free-format frame having no specific shape as shown in (B) may be used in the shared mode. Specifically, the slotted frame is a frame for transmission of short data packets from the wireless power receiver  200  to the wireless power transmitter  100 , and the free-format frame is a frame capable of transmission of long data packets due to no slots. 
     Meanwhile, the slotted frame and the free-format frame may be called various names by those skilled in the art. For example, the slotted frame may be referred to as a channel frame, and the free-format frame may be referred to as a message frame. 
     Specifically, the slotted frame may include a synchronization pattern indicating the start of the frame, a measurement slot, 9 slots, and additional synchronization patterns having the same time duration, which are located before the 9 slots, respectively. 
     Here, the additional synchronization pattern is different from the above-described synchronization pattern indicating the start of the frame. Specifically, an additional synchronization pattern may indicate information on adjacent slots (information on two consecutive slots located on the sides of the synchronization pattern), instead of indicating the start of the frame. 
     The synchronization pattern may be located between two consecutive slots among the 9 slots. In this case, the synchronization pattern may provide information on the two consecutive slots. 
     In addition, the 9 slots and the synchronization patterns provided before the 9 slots may have the same time duration. For example, each of the 9 slots may have a time duration of 50 ms. Also, each of the 9 synchronization patterns may have a time duration of 50 ms. 
     On the other hand, the free-format frame shown in (B) may not have a specific form except for the synchronization pattern indicating the start of the frame and the measurement slot. That is, the free-format frame is to perform a different role from the slotted frame. For example, the free-format frame may be used for communication of long data packets (e.g., additional owner information packets) between the wireless power transmitter and the wireless power receiver. Alternatively, when the wireless power transmitter includes a plurality of coils, the free-format frame may be used to select any one of the plurality of coils. 
     Hereinafter, synchronization patterns included in each frame will be described in detail with reference to the drawings. 
       FIG. 10  illustrates a structure of a synchronization pattern according to an embodiment of the present disclosure. 
     Referring to  FIG. 10 , the synchronization pattern includes a preamble, a start bit, a response field, a type field, an information field, and a parity bit. In  FIG. 10 , the start bit is denoted by ZERO. 
     Specifically, the preamble may include consecutive bits, all of which may be set to 0. That is, the preamble may be bits for matching the time length of the synchronization pattern. 
     The number of bits included in the preamble may depend on the operating frequency such that the length of the synchronization pattern is closest to 50 within a range not exceeding 50 ms. For example, when the operating frequency is 100 kHz, the synchronization pattern may include two preamble bits. When the operating frequency is 105 kHz, the synchronization pattern may include three preamble bits. 
     The start bit may be located behind the preamble and denoted by ZERO. ZERO may indicate the type of the synchronization pattern. Here, the synchronization pattern type may include frame synchronization including frame related information and slot synchronization including slot related information. That is, the synchronization pattern may correspond to either the frame synchronization, which is located between consecutive frames and indicates the start of a frame, or the slot synchronization, which is located between consecutive slots among a plurality of slots included in a frame and includes including information on the consecutive slot. 
     For example, if ZERO is 0, it may mean that the synchronization pattern is the slot synchronization between slots. If ZERO is 1, it may mean that the synchronization pattern is the frame synchronization located between frames. 
     The parity bit is the last bit of the synchronization pattern and may indicate information on the number of bits in the data fields (i.e., response field, type field, information field) of the synchronization pattern. For example, when the number of bits included in the data fields of the synchronization pattern is an even number, the parity bit may be 1. Otherwise (when the number of bits is an odd number), the parity bit may be 0. 
     The response field may include information on the response of the wireless power transmitter to communication with the wireless power receiver in a slot before the synchronization pattern. For example, the response field may be set to 00 if the wireless power transmitter does not detect communication with the wireless power receiver. The response field may be set to 01 if the wireless power transmitter has a communication error in communication with the wireless power receiver. The communication error may occur when two or more wireless power receivers attempt to access one slot and thus a collision occurs between the two or more wireless power receivers. 
     The response field may include information on whether a data packet is correctly received from the wireless power receiver. Specifically, the response field may be set to 10 (negative acknowledgement (NAK)) when the wireless power transmitter denies the data packet. The response field may be set to 11 (acknowledgement (ACK)) when the wireless power transmitter confirms the data packet. 
     The type field may indicate the type of the synchronization pattern. Specifically, when the synchronization pattern is the first synchronization pattern of the frame (that is, when the synchronization pattern is the first synchronization pattern of the frame located before the measurement slot), the type field may be set to 1 to indicate the frame synchronization. 
     When the synchronization pattern is not the first synchronization pattern of the frame in the slotted frame, the type field may be set to 0 to indicate the slot synchronization. 
     The value of the information field may be determined according to the synchronization pattern type indicated by the type field. For example, when the type field is 1 (frame synchronization), the information field may indicate the frame type. That is, the information field may indicate whether the current frame is the slotted frame or free-format frame. For example, when the information field is 00, it may indicate the slotted frame. When the information field is 01, it may indicate the free-format frame. 
     On the contrary, when the type field is 0 (slot synchronization), the information field may indicate the state of a next slot located after the synchronization pattern. Specifically, the information field may be set to 00 when the next slot is a slot allocated to a specific wireless power receiver. The information field may be set to 01 when the next slot is locked for temporary use by a specific wireless power receiver. The information field may be set to 10 when the next slot is a slot freely available to any wireless power receiver. 
       FIG. 11  illustrates operating states of a wireless power transmitter and receiver in the shared mode according to an embodiment of the present disclosure. 
     Referring to  FIG. 11 , the wireless power receiver operating in the shared mode may be in any one of a selection phase  1100 , an introduction phase  1110 , a configuration phase  1120 , a negotiation phase  1130 , and a power transfer phase  1140 . 
     According to an embodiment of the present disclosure, the wireless power transmitter may transmit a wireless power signal to detect the wireless power receiver. That is, a process for detecting the wireless power receiver based on the wireless power signal may be referred to as analog ping. 
     Upon receiving the wireless power signal, the wireless power receiver may enter the selection phase  1100 . After entering the selection phase  1100 , the wireless power receiver may detect the presence of an FSK signal on the wireless power signal as described above. 
     That is, the wireless power receiver may perform communication in either an exclusive mode or the shared mode depending on the presence of the FSK signal. 
     Specifically, if the wireless power signal includes the FSK signal, the wireless power receiver may operate in the shared mode. Otherwise, the wireless power receiver may operate in the exclusive mode. 
     When the wireless power receiver operates in the shared mode, the wireless power receiver may enter the introduction phase  1110 . The wireless power receiver may transmit a control information (CI) packet to the wireless power transmitter in the introduction phase  1110  in order to transmit CI packets in the configuration phase, negotiation phase, and power transfer phase. The CI packet may include a header and control related information. For example, the header in the CI packet may be 0X53. 
     In the introduction phase  1110 , the wireless power receiver attempts to request free slots in order to transmit CI packets in the configuration, negotiation, and power transmission phases. The wireless power receiver selects a free slot and transmits the first CI packet. If the wireless power transmitter transmits an ACK for the CI packet, the wireless power transmitter enters the configuration phase. If the wireless power transmitter transmits a NACK, it may be interpreted to mean that another wireless power receiver is in the process of configuring and negotiating. In this case, the wireless power receiver attempts to request free slots again. 
     If the wireless power receiver receives the ACK in response to the CI packet, the wireless power receiver determines the position of a private slot in a frame by counting the remaining synchronization slots until the first frame synchronization. In all subsequent slot-based frames, the wireless power receiver transmits a CI packet through the corresponding slot. 
     If the wireless power transmitter allows the wireless power receiver to proceed to the configuration phase, the wireless power transmitter provides a series of locked slots for exclusive use of the wireless power receiver, which ensures that the wireless power receiver proceeds to the configuration phase without collision. 
     The wireless power receiver transmits sequences of data packets such as two identification data packets (IDHI and IDLO) in the locked slots. After completing this step, the wireless power receiver enters the negotiation phase. In the negotiation phase, the wireless power transmitter continues to provide the wireless power receiver with locked slots for exclusive use. This ensures that the wireless power receiver proceeds to the negotiation phase without collision. 
     The wireless power receiver transmits one or more negotiation data packets in the corresponding locked slots, and in this case, the negotiation data packets may be mixed with private data packets. Eventually, the sequence ends with a specific request (SRQ) packet. After completion of the sequence, the wireless power receiver enters the power transfer phase, and the wireless power transmitter stops providing locked slots. 
     In the power transfer phase, the wireless power receiver transmits a CI packet in an allocated slot and receives power. The wireless power receiver may include a regulator circuit. The regulator circuit may be included in a communication and control unit. The wireless power receiver may self-regulate the reflection impedance of the wireless power receiver based on the regulator circuit. In other words, the wireless power receiver may adjust the reflected impedance to transmit the amount of power required by an external load, which may prevent excessive power reception and overheating. 
     In the shared mode, the wireless power transmitter may not perform power adjustment in response to the received CI packet (depending on the operation mode), and thus, control may be required to prevent an overvoltage state. 
     Hereinafter, authentication between the wireless power transmitter and the wireless power receiver will be described. 
     A wireless power transfer system using IB communication may employ USB-C authentication. The authentication includes authentication of the wireless power transmitter by the wireless power receiver and authentication of the wireless power receiver by the wireless power transmitter. 
       FIG. 12  is a block diagram illustrating a wireless charging certificate format according to an embodiment of the present disclosure. 
     Referring to  FIG. 12 , the wireless charging certificate format may include a wireless charging standard certificate structure version (Qi Authentication Certificate Structure Version), a reserved bit, a PTx and leaf indicator (PTx Leaf), a certificate type, a signature offset, a serial number, an issuer ID, a subject ID, a public key, and a signature. 
     In the wireless charging certificate format, the PTx and leaf indicator is separated from the certificate type so that the PTx and leaf indicator and the certificate type are allocated to different bits in the same byte (B0). 
     The PTx and leaf indicator indicates not only whether the corresponding certificate relates to the wireless power transmitter but also whether the corresponding certificate is a leaf certificate. That is, the PTx and leaf indicator may indicate whether the corresponding certificate is the leaf certificate for the wireless power transmitter or not. 
     The PTx and leaf indicator may be 1 bit. If the PTx and leaf indicator is 0, it may indicate that the corresponding certificate is not the leaf certificate or that the corresponding certificate is the leaf certificate of the wireless power receiver. On the other hand, if the PTx and leaf indicator is 1, it may indicate that the corresponding certificate is the leaf certificate of the wireless power transmitter. 
     The certificate type is, for example, 2 bits. The certificate type may indicate that the corresponding certificate is any one of a root certificate, an intermediate certificate, and a leaf certificate. Alternatively, the certificate type may indicate that the corresponding certificate is for all of them. 
     The wireless power transmitter may inform the wireless power receiver whether the authentication function is supported through a capability packet (in the case of authentication of the wireless power transmitter by the wireless power receiver (authentication of PTx by PRx)). Hereinafter, the structure of indication information (capability packet and configuration packet) regarding whether or not the authentication function is supported will be described in detail. 
       FIG. 13  illustrates a structure of a capability packet of a wireless power transmitter according to an embodiment of the present disclosure. 
     Referring to  FIG. 13 , a capability packet having a corresponding header value of 0X31 is 3 bytes. The first byte (B0) includes a power class and a guaranteed power value. The second byte (B1) includes a reserved bit and a potential power value. The third byte (B2) includes an AI (AI), an AR (AR), a reserved bit, WPID, and Not Res Sens. Specifically, the AI is 1 bit. For example, if the value of the AI is ‘1b’, it indicates that the wireless power transmitter may operate as an AI. In addition, the AR is 1 bit. For example, if the value of the AR is ‘1b’, it indicates that the wireless power transmitter may operate as an AR. 
       FIG. 14  illustrates a structure of a configuration packet of a wireless power receiver according to an embodiment of the present disclosure. 
     Referring to  FIG. 14 , a configuration packet having a header value of 0X51 is 5 bytes. The first byte (B0) includes a power class and a maximum power value. The second byte (B1) includes an AI, an AR, and a reserved bit (Reserve). The third byte (B2) includes Prop, Reserve, ZERO, and Count. The fourth byte (B3) includes a window size and a window offset. The fifth byte (B4) includes Neg, polarity, depth, authentication (Auth), and Reserve. Specifically, the AI is 1 bit. For example, if the AI value is ‘1b’, it indicates that the wireless power receiver may operate as an AI. In addition, the AR is 1 bit. For example, if the AR value is ‘1b’, it indicates that the wireless power receiver may operate as an AR. 
     A message used in an authentication procedure is called an authentication message. The authentication message is used to carry information related to authentication. There are two types of authentication messages. One is an authentication request, and the other is an authentication response. The authentication request is sent by the AI, and the authentication response is sent by the AR. The wireless power transmitter and receiver may be the AI or AR. For example, when the wireless power transmitter is the AI, the wireless power receiver becomes the AR. On the contrary, when the wireless power receiver is the AI, the wireless power transmitter becomes the AR. 
     The authentication request message includes GET_DIGESTS (i.e., 4 bytes), GET_CERTIFICATE (i.e., 8 bytes), and CHALLENGE (i.e., 36 bytes). 
     The authentication response message includes DIGESTS (i.e., 4+32 bytes), CERTIFICATE (i.e., 4+Certificate Chain (3×512 bytes)=1540 bytes), CHALLENGE AUTH (i.e., 168 bytes), and ERROR (i.e., 4 bytes). 
     The authentication message may be called an authentication packet, authentication data, and authentication control information. In addition, the GET_DIGEST message may be referred to as a GET_DIGEST packet, and the DIGESTS message may be referred to as a DIGEST packet. 
       FIG. 15  illustrates an application-level data stream between a wireless power transmitter and receiver according to an embodiment of the present disclosure. 
     Referring to  FIG. 15 , a data stream may include an auxiliary data control (ADC) data packet and/or an auxiliary data transport (ADT) data packet. 
     The ADC data packet is used to open a data stream. The ADC data packet may indicate the type of message included in the stream and the number of data bytes. The ADT data packet is sequences of data including an actual message. An ADC/end data packet is used to notify the end of a stream. For example, the maximum number of data bytes in a data transport stream may be limited to 2047. 
     In order to inform whether the ADC data packet and ADT data packet are normally received, an ACK or NACK is used. Control information required for wireless charging such as a control error (CE) packet or DSR may be transmitted between the transmission timings of the ADC data packet and the ADT data packet. 
     Based on the above data stream structure, authentication-related information or other application-level information may be transmitted/received between the wireless power transmitter and receiver. 
       FIG. 16  is a flowchart illustrating operations of a wireless power transmitter and receiver according to an embodiment of the present disclosure. 
     Referring to  FIG. 16 , a wireless power receiver  1610  may include a first OB communication module (first out-of-band (OOB) communication module)  1611  and a first IB communication module  1612 . A wireless power transmitter  1620  may include a second OB communication module  1621  and a second IB communication  1622 . 
     Each of the first IB communication module  1612  and the second IB communication module  1622  may transmit or receive a packet based on a coil provided therein. 
     Each of the first OB communication module  1611  and the second OB communication module  1621  may transmit or receive a packet on a short-range wireless communication antenna. 
     In an embodiment, each of the first OB communication module  1611  and the second OB communication module  1621  may be a BLE communication module, but the present disclosure is not limited thereto. 
     The first IB communication module  1612  may transmit a random address packet to the second IB communication module  1622  through IB communication (S 1601 ). 
     The second IB communication module  1622  may transmit the received random address (packet) to the second OB communication module  1621  (S 1602 ). 
     The wireless power transmitter  1620  may update a whitelist based on the random address (Whitelist Renewal) (S 1603 ). Here, the whitelist may be updated by the second OB communication module  1621 . However, this is merely an example, and the whitelist may be updated by a controller that is provided in the wireless power transmitter  1620  and configured to control wireless power transmission. 
     The second OB communication module  1621  may transmit a response signal to the wireless power receiver  1610  only when the wireless power receiver  1610  is included in the whitelist (No Response Except Whitelist) (S 1604 ). 
     The wireless power transmitter  1620  in the embodiment of  FIG. 16  may correspond to the wireless power transmitter or the power transmitter disclosed in  FIGS. 1 to 11 . Accordingly, the operations of the wireless power transmitter  1620  in this embodiment may be performed by one of the components of the wireless power transmitter in  FIGS. 1 to 11  or a combination of two or more components. For example, the second IB communication module  1622  of the wireless power transmitter  1620  in this embodiment may be equivalent to the IB communication module  121  of  FIG. 4C or 4D , and the second OB communication module  1621  of the wireless power transmitter  1620  may be equivalent to the OB communication module  122  of  FIG. 4C or 4D . 
     In addition, the wireless power receiver  1610  in the embodiment of  FIG. 16  may correspond to the wireless power receiver or the power receiver disclosed in  FIGS. 1 to 11 . Accordingly, the operations of the wireless power receiver  1610  in this embodiment may be performed by one of the components of the wireless power receiver in  FIGS. 1 to 11  or a combination of two or more components. For example, the first IB communication module  1612  of the wireless power receiver  1610  in this embodiment may be equivalent to the IB communication module  221  of  FIG. 4C or 4D , and the first OB communication module  1611  of the wireless power receiver  1610  may be equivalent to the OB communication module  222  of  FIG. 4C or 4D . 
     In another example, the wireless power transmitter  1620  may establish connection with devices in the whitelist as shown in  FIG. 17 . 
       FIG. 17  is a flowchart illustrating operations of a wireless power transmitter and receiver according to another embodiment of the present disclosure. 
     Referring to  FIG. 17 , a wireless power receiver  1710  may include a first OB communication module  1711  and a first IB communication module  1712 . A wireless power transmitter  1720  may include a second OB communication module  1721  and a second IB communication module  1722 . 
     Each of the first IB communication module  1712  and the second IB communication module  1722  may transmit or receive a packet based on a coil provided therein. 
     Each of the first OB communication module  1711  and the second OB communication module  1721  may transmit or receive a packet on a short-range wireless communication antenna. 
     In an embodiment, each of the first OB communication module  1711  and the second OB communication module  1721  may be a BLE communication module, but the present disclosure is not limited thereto. Specifically, any one of the following technologies: Wi-Fi communication, radio frequency identification (RFID) communication, and Bluetooth communication may be applied. 
     The second IB communication module  1722  may transmit a random address packet to the first IB communication module  1712  through IB communication (S 1701 ). 
     The first IB communication module  1712  may transmit the received random address (packet) to the first OB communication module  1711  (S 1702 ). 
     The wireless power receiver  1710  may update a whitelist based on the random address (Whitelist Renewal) (S 1703 ). Here, the whitelist may be updated by the first OB communication module  1711 . However, this is merely an example, and the whitelist may be updated by a controller or processor that is provided in the wireless power receiver  1710  and configured to control wireless power reception. 
     The first OB communication module  1711  may transmit a response signal to the wireless power transmitter  1720  only when the wireless power transmitter  1720  is included in the whitelist (No Response Except Whitelist) (S 1704 ). 
     According to an embodiment, the wireless power receiver  1710  may actively operate and manage the whitelist for wireless power transmitters to prevent cross-connection. 
     The wireless power transmitter  1720  in the embodiment of  FIG. 17  may correspond to the wireless power transmitter or the power transmitter disclosed in  FIGS. 1 to 11 . Accordingly, the operations of the wireless power transmitter  1720  in this embodiment may be performed by one of the components of the wireless power transmitter in  FIGS. 1 to 11  or a combination of two or more components. For example, the second IB communication module  1722  of the wireless power transmitter  1720  in this embodiment may be equivalent to the IB communication module  121  of  FIG. 4C or 4D . The second OB communication module  1721  of the wireless power transmitter  1720  may be equivalent to the OB communication module  122  of  FIG. 4C or 4D . 
     In addition, the wireless power receiver  1710  in the embodiment of  FIG. 17  may correspond to the wireless power receiver or the power receiver disclosed in  FIGS. 1 to 11 . Accordingly, the operation of the wireless power receiver  1710  in this embodiment may be performed by one of the components of the wireless power receiver in  FIGS. 1 to 11  or a combination of two or more components. For example, the first IB communication module  1712  of the wireless power receiver  1710  in this embodiment may be equivalent to the IB communication module  221  of  FIG. 4C or 4D . The first OB communication module  1711  of the wireless power receiver  1710  may be equivalent to the OB communication module  222  of  FIG. 4C or 4D . 
       FIG. 18  is a flowchart illustrating operations of a wireless power transmitter and receiver according to a further embodiment of the present disclosure. 
     Referring to  FIG. 18 , a wireless power receiver  1810  may include a first OB communication module  1811  and a first IB communication module  1812 . A wireless power transmitter  1820  may include a second OB communication module  1821  and a second IB communication module  1822 . 
     Each of the first IB communication module  1812  and the second IB communication module  1822  may transmit or receive a packet based on a coil provided therein. 
     Each of the first OB communication module  1811  and the second OB communication module  1821  may transmit or receive a packet on a short-range wireless communication antenna. 
     In an embodiment, each of the first OB communication module  1811  and the second OB communication module  1821  may be a BLE communication module, but the present disclosure is not limited thereto. Specifically, any one of the following technologies: Wi-Fi communication, RFID communication, and Bluetooth communication may be applied. 
     The first IB communication module  1812  may transmit a first random address packet to the second IB communication module  1822  through IB communication (S 1801 ). 
     The second IB communication module  1822  may transmit the received first random address (packet) to the second OB communication module  1821  (S 1802 ). 
     The wireless power transmitter  1820  may update a first whitelist based on the first random address (First Whitelist Renewal) (S 1803 ). Here, the first whitelist may be updated by the second OB communication module  1821 . However, this is only an example, and the first whitelist may be updated by a controller or processor provided in the wireless power transmitter  1820  and configured to control wireless power transmission. 
     The wireless power transmitter  1820  may transmit a second random address packet to the first IB communication module  1812  through the second IB communication module  1822  (S 1804 ). 
     The first IB communication module  1812  may transmit the received second random address to the first OB communication module  1811  (S 1805 ). 
     The wireless power receiver  1810  may update a second whitelist based on the second random address (Second Whitelist Renewal) (S 1806 ). Here, the second whitelist may be updated by the first OB communication module  1811 . However, this is only an example, and the second while list may be updated by a controller or processor provided in the wireless power receiver  1810  and configured to control wireless power reception. 
     The first OB communication module  1811  may transmit a response signal to the wireless power transmitter  1820  only when the wireless power transmitter  1820  is included in the second whitelist, and the second OB communication module  1821  may transmit a response signal to the wireless power receiver  1810  only when the wireless power receiver  1810  is included in the first whitelist. The wireless power receiver  1810  and the wireless power transmitter  1820  may perform direct connection based on the first and second whitelists. (No Response Except Whitelist or Direct Connection) (S 1807 ). 
     In the embodiment of  FIG. 18 , the wireless power receiver  1810  and the wireless power transmitter  1820  may establish connection with a device existing in their whitelists. 
     In another example, the wireless power transmitter  1820  may establish connection only with specific peer device(s) designated by the host and/or devices in its own whitelist (i.e., wireless power receivers). 
     In this way, the wireless power transmitter may prevent cross-connection by managing the whitelist for wireless power receivers. The cross-connection prevention may also be performed by the wireless power receiver. That is, the wireless power transmitter and the wireless power receiver may perform a cross check based on whitelist(s) to prevent the cross-connection. 
     The wireless power transmitter  1820  in the embodiment of  FIG. 18  may correspond to the wireless power transmitter or the power transmitter disclosed in  FIGS. 1 to 11 . Accordingly, the operations of the wireless power transmitter  1820  in this embodiment may be performed by one of the components of the wireless power transmitter in  FIGS. 1 to 11  or a combination of two or more components. For example, the second IB communication module  1822  of the wireless power transmitter  1820  in this embodiment may be equivalent to the IB communication module  121  of  FIG. 4C or 4D . The second OB communication module  1821  of the wireless power transmitter  1820  may be equivalent to the OB communication module  122  of  FIG. 4C or 4D . 
     The wireless power receiver  1810  in the embodiment of  FIG. 18  may correspond to the wireless power receiver or the power receiver disclosed in  FIGS. 1 to 11 . Accordingly, the operations of the wireless power receiver  1810  in this embodiment may be performed by one of the components of the wireless power receiver in  FIGS. 1 to 11  or a combination of two or more components. For example, the first IB communication module  1812  of the wireless power receiver  1810  in this embodiment may be equivalent to the IB communication module  221  of  FIG. 4C or 4D . The first OB communication module  1811  of the wireless power receiver  1810  may be equivalent to the OB communication module  222  of  FIG. 4C or 4D . 
       FIG. 19  is a block diagram illustrating state machines for PC0 and PC1 according to an embodiment of the present disclosure. 
     Hereinafter, a device filtering policy will be described. 
     Based on device filtering, a link manager may be configured to respond only to a specific set of devices (i.e., whitelist). That is, the link manager may ignore transmission or requests from devices not included in the whitelist. 
     For example, the device filtering may include an operation of responding to devices with MAC addresses in the whitelist and not responding to devices (advertisers, scanners, initiators, etc.) with MAC addresses out of the whitelist. The device filtering may be performed or managed under specific rules defined for each phase, such as advertising, scanning, and initiating. 
     First, advertisement filtering rules define how the LL of an advertiser processes scan requests and connection requests. For example, the LL of the advertiser may be configured to process scan requests or connect requests from devices in the whitelist. In another example, the LL of the advertiser may be configured to process scan requests received from all devices but process connection requests received from devices in the whitelist. In a further example, the LL of the advertiser may be configured to process connection requests from all devices but process scan requests received from devices in the whitelist. 
     Next, scanner filtering rules define how the LL of a scanner processes advertisement packets. For example, the LL of the scanner may process advertisement packets received from devices in the whitelist. 
     Finally, initiator filtering rules define how the LL of an initiator processes advertisement packets. For example, the LL of the scanner may process reachable advertisement packets from devices in the whitelist. 
     The privacy function of BLE may be implemented so that a device may hide a real address. In this case, the device may perform communication based on a random address rather than the real address. The random address may change over time. The random address may include the following two types of addresses. 
     (1) Static Address 
     The device may perform (or select) an operation of initializing the static address of the device to a new value after each power cycle. However, the device may not change the static address within a power cycle. 
     (2) Private Address 
     The private address may include a non-resolvable private address and a resolvable private address. 
     For the non-resolvable private address, a peer device may not discover a real address corresponding to the non-resolvable used address. 
     For the resolvable private address, the peer device may derive the real address corresponding to the resolvable used address based on the random address and/or the link key of connection. 
     According to the state machines according to  FIG. 19 , OB communication may be limited by a state machine corresponding to IB communication. Accordingly, information exchange through the IB communication is essential in configuration and negotiation phases. Thus, time delay overhead may occur during handover from the IB communication to the OB communication, and the charging start time may slightly increase. 
     According to one embodiment, if a wireless power transmitter and receiver have a previous OB communication connection record and know each other&#39;s configuration information (e.g., MAC address information, etc.), the wireless power transmitter and receiver may store the previous connection record and configuration information in the whitelist. In this case, devices (wireless power transmitter and/or wireless power receiver) stored in the whitelist may skip steps required for the handover to the OB communication (i.e., steps based on the IB communication) and directly perform the handover from IB to OB. (i.e., OB communication connection establishment). The above handover may be referred to as handover for reconnection. 
     The wireless power transmitter and receiver may exchange packets through the OB communication from a phase after the handover is completed. 
     The wireless power transmitter and/or receiver may determine the distance between the wireless power transmitter and receiver by using a received signal strength indicator (RSSI) value or a direct finding method based on the OB communication. In this case, if the RSSI value is above a predetermined level (that is, when a predetermined condition is satisfied), the wireless power transmitter and/or receiver may enter a handover phase for reconnection with devices included in the whitelist and attempt the reconnection. 
     In the state machines according to  FIG. 19 , there is a problem in that only one opportunity is given for the handover to the OB during a charging cycle and subsequent reconnection is impossible. 
     However, the 2.4 GHz band used for BLE communication is largely allocated to other communication, and thus, there may be significant interference between a BLE signal for wireless charging and other signals. If there is a problem in BLE connection in an environment where there is significant interference to OB frequencies for wireless charging, that is, when the handover to the OB fails, opportunities for OB reconnection are required. 
       FIG. 20  is a diagram for explaining a procedure for removing a wireless power transfer interface in a wireless power transfer system according to an aspect of the present disclosure. 
     Herein, a wireless power transfer interface may refer to a wireless power transfer link. 
     Referring to reference number  2001  of  FIG. 20 , while a wireless power transmitter (PTx)  2010  and a wireless power receiver (PRx)  2020  perform wireless charging based on interconnection, the wireless power receiver  2020  may be removed (or separated) from the charging area of the wireless power transmitter  2010  so that magnetic coupling between the two devices may be lost. In this case, the wireless power transmitter  2010  and the wireless power receiver  2020  may be connected through OB communication. 
     The wireless power transmitter  2010  may include: a power block  2011  configured to supply power  2011 ; a DC/DC converter  2012  configured to convert a first DC voltage received from the power block  2011  into a second DC voltage, i.e., a rail voltage (Vrail); an inverter  2013  configured to generate an AC power signal based on the rail voltage (Vrail); and a transmission circuit  2014  having a serial LC (inductor and capacitor) circuit and configured to wirelessly output an AC power signal. 
     The wireless power receiver  2020  may include: a receiving circuit  2021  configured to receive an AC power signal based on a provided LC circuit; a diode rectifier  2022  having a plurality of diodes and configured to convert an AC power signal into a DC power signal; a smoothing element  2023 ; a switch circuit (SW)  2024  configured to block overvoltage and/or overcurrent applied to a load  2025 ; and the load  2025 . 
     Referring to  FIG. 20 , the wireless power receiver  2020  may continuously measure a rectified voltage (Vrect) and/or a second coil voltage (Vcoil2) and determine whether the wireless power transfer interface is removed by comparing the measured voltage with a predetermined threshold value (Vth). 
     For example, when the rectified voltage (Vrect) is less than a first threshold voltage (Vth1), the wireless power receiver  2020  may determine that the wireless power transfer interface is removed. 
     As another example, when the second coil voltage (Vcoil2) is less than a second threshold voltage (Vth2), the wireless power receiver  2020  may determine that the wireless power transfer interface is removed. 
     Here, the rectified voltage and the second coil voltage may be measured from one side of the circuit structure of the wireless power receiver  2020  as shown in  FIG. 20 . 
     For example, the second coil voltage may be measured between a second inductor L 2  and a second capacitor C 2  of the receiving circuit  2021 , and the rectified voltage may be measured between the output end of the diode rectifier  2022  and the switch circuit  2024 . 
     Whether the wireless power transfer interface is removed may also be determined by the wireless power transmitter  2010 . In this case, the wireless power transmitter  2010  may continuously measure a rail voltage (Vrail) and/or a first coil voltage (Vcoil1) and determine whether the wireless power transfer interface is removed by comparing the measured voltage(s) with a predetermined threshold value (Vth). For example, when the rail voltage is less than a third threshold voltage (Vth3), the wireless power transmitter may determine that the wireless power transfer interface is removed. As another example, when the first coil voltage is less than a fourth threshold voltage (Vth4), the wireless power transmitter may determine that the wireless power transfer interface is removed. For example, as shown in  FIG. 20 , the rail voltage may be measured between the DC/DC converter  2012  and the inverter  2013 , and the first coil voltage may be measured between a first capacitor C 1  and a first inductor L 1  of the transmitting circuit  2014 . 
     In wireless power transfer systems, depending on manufacturers and types and characteristics of applied products, errors may occur in the degree of magnetic coupling between a transmitter coil and receiver coil and the measurement accuracy between a wireless power transmitter and wireless power receiver, and as a result, the reliability of determination of misalignment between the transmitter and receiver coils may be degraded. 
     Therefore, if whether the wireless power transfer interface is removed, that is, whether there is misalignment between the transmitter and receiver coils is determined only according to the method described with reference to  FIG. 20 , it may be difficult to guarantee reliability for link maintenance and release. 
     Embodiments 
     According to an embodiment, a wireless power transmitter (or wireless power receiver) may determine whether a wireless power transfer interface is removed based on distance and location information obtained from a received signal strength indicator (RSSI) and/or directive finding. 
     The wireless power transmitter and wireless power receiver may measure a resonance voltage or inverter voltage, measures the degree of magnetic coupling therebetween based on the measured resonance voltage or inverter voltage, and then determine whether charging is possible. Here, the magnetic coupling force or coupling degree between coils may vary due to coil diversity. In addition, the measurement accuracy or performance of the wireless power transmitter and wireless power receiver may vary for each manufacturer. Further, since each device has a different charging area, the magnetic coupling force between coils may vary even under the same coil condition. Therefore, it is necessary to use a new parameter that is not affected by coil characteristics. 
     For example, the wireless power transmitter and/or wireless power receiver may obtain information about the locations of the wireless power transmitter and wireless power receiver and/or information about the distance between the wireless power transmitter and wireless power receiver based on the RSSI or directive finding supported in OB communication (i.e., BLE communication). For example, a BLE controller may obtain distance and location information and transmit the obtained distance and location information to an application layer of the wireless power transmitter (or wireless power receiver) via a host controller interface (HCI). 
     The application layer of the wireless power transmitter (or wireless power receiver) may transmit the distance and location information to the counterpart, i.e., an application layer of the wireless power receiver (or wireless power transmitter). In this case, a packet for carrying the distance and location information may be defined by lengths, types, and data formats predefined for a protocol data unit (PDU) of a packet according to OB communication specifications. 
     The application layer of the wireless power transmitter (or wireless power receiver) may transmit the distance and location information to the counterpart, i.e., the application layer of the wireless power receiver (or wireless power transmitter) based on predefined characteristics. Here, the characteristics may mean a specific message or packet transmitted/received through OB communication. 
     The wireless power transmitter in this embodiment may correspond to the wireless power transmitter or the power transmitter disclosed in  FIGS. 1 to 11 . Accordingly, the operations of the wireless power transmitter in this embodiment may be performed by one of the components of the wireless power transmitter in  FIGS. 1 to 11  or a combination of two or more components. For example, the IB communication operation of the wireless power transmitter in this embodiment may be performed by the IB communication module  121  of  FIG. 4C or 4D , and the OB communication operation and procedure of the wireless power transmitter may be performed by the OB communication module  122  of  FIG. 4C or 4D . In this embodiment, communication (data, packet, or signal) processing, transmission, and reception operations by the wireless power transmitter may be performed by the communication and control unit  120 . 
     In addition, the wireless power receiver in this embodiment may correspond to the wireless power receiver or the power receiver disclosed in  FIGS. 1 to 11 . Accordingly, the operations of the wireless power receiver in this embodiment may be performed by one of the components of the wireless power receiver in  FIGS. 1 to 11  or a combination of two or more components. For example, the IB communication operation of the wireless power receiver in this embodiment may be performed by the IB communication module  221  of  FIG. 4C or 4D , and the OB communication operation and procedure of the wireless power receiver may be performed by the OB communication module  222  of  FIG. 4C or 4D . In this embodiment, the communication (data, packet, or signal) processing, transmission, and reception operations by the wireless power transmitter may be performed by the communication and control unit  220 . 
       FIG. 21  is a flowchart illustrating an information acquisition procedure of a wireless power transmitter according to an embodiment of the present disclosure. 
     Specifically,  FIG. 21  is a diagram for explaining a process in which the wireless power transmitter collects information required to determine whether to release a wireless power transfer interface, i.e., a power link. 
     Referring to  FIG. 21 , the wireless power transmitter may measure a rail voltage (Vrail) and a first coil voltage (Vcoil1) during power transfer (S 2110 ). 
     When the rail voltage (or the amount of change in the rail voltage) is greater than a first threshold voltage (V_Threshold1) and the first coil voltage (or the amount of change in the first coil voltage) is greater than a second threshold voltage (V_Threshold2), the wireless power transmitter may acquire information on the distance to the wireless power receiver and information on the location of the wireless power receiver (S 2120  to S 2140 ). For example, the wireless power transmitter may calculate the separation distance between the wireless power transmitter and wireless power receiver based on an RSSI value measured for an OB signal. For example, the OB signal may be a BLE signal transmitted by the wireless power receiver. The wireless power transmitter may calculate the distance to the wireless power receiver based on the measured RSSI of the BLE signal and obtain two-dimensional or three-dimensional location information according to Bluetooth Direction Finding. 
     The wireless power transmitter may determine whether the separation distance to the wireless power receiver and/or the location of the wireless power receiver is greater than (or deviate from) a predetermined threshold point or threshold (D_Threshold1) (S 2150 ). When the distance to the wireless power receiver and/or the location of the wireless power receiver is greater than the threshold point, the wireless power transmitter may perform a connection release procedure of the wireless power transmitter, which will be described below in  FIG. 22 . 
       FIG. 22  is a flowchart for explaining a procedure for releasing a connection between a wireless power transmitter and a wireless power receiver based on distance and location information obtained from the information acquisition procedure of the wireless power transmitter of  FIG. 21 . 
     Referring to  FIG. 22 , the wireless power transmitter may determine whether the distance between the wireless power transmitter and the wireless power receiver is normal (S 2210 ). For example, when the distance exceeds a predetermined distance threshold, the wireless power transmitter may determine that the distance is abnormal. On the other hand, when the distance is less than or equal to the distance threshold, the wireless power transmitter may determine that the distance is normal. Here, the distance threshold may be a different value from the threshold (D_Threshold1) of  FIG. 21 . In some embodiments, the distance threshold may be set to a value greater than the threshold. 
     When it is determined that the distance is abnormal, the wireless power transmitter may reduce the transmitted power to a predetermined level (S 2220  and S 2230 ). That is, the wireless power transmitter may prevent the wireless power receiver from being damaged by limiting the transmitted power to the predetermined level or less. 
     In some embodiments, even when the magnitude of the rail voltage and/or first coil voltage (or the amount of change in the magnitude) is greater than or equal to a predetermined voltage threshold, if the distance to the wireless power receiver is less than the predetermined distance threshold, the wireless power transmitter may limit the transmitted power to the predetermined level or less without releasing the power link. 
     Subsequently, the wireless power transmitter may perform the information acquisition procedure of the wireless power transmitter (PTx&#39;s information acquisition process) according to steps S 2110  to S 2150  of  FIG. 21  (S 2240 ). 
     The wireless power transmitter may determine again whether the distance between the wireless power transmitter and the wireless power receiver is normal (S 2250 ). 
     When it is determined that the distance is abnormal, the wireless power transmitter may transmit a connection release notification to the wireless power receiver and then stop the power transfer (S 2260  and S 2280 ). 
     When it is determined in step S 2250  that the distance is normal, the wireless power transmitter may resume normal wireless power transmission (S 2260  and S 2290 ). Here, the normal wireless power transmission may refer to a power transmission state before the transmitted power is reduced in step S 2230 . 
     For example, if the wireless power transmitter determines that the distance to the wireless power receiver is abnormal while transmitting power with PC1, the wireless power transmitter may lower the power transmission level from PC1 to PC0. Thereafter, when it is confirmed that the distance to the wireless power receiver is normal, the wireless power transmitter may transmit power by increasing the power transmission level from PC0 to PC1. 
     As another example, the power level reduced by the wireless power transmitter upon the determination that the distance to the wireless power receiver is abnormal may be configured by predetermined parameter in the configuration phase, negotiation phase, or renegotiation phase. 
       FIG. 23  is a flowchart for explaining an information acquisition procedure of a wireless power receiver according to an embodiment of the present disclosure. 
     Specifically,  FIG. 23  is a diagram for explaining a process in which the wireless power receiver collects information required to determine whether to release a wireless power transfer interface, i.e., a wireless power transmission link. 
     Referring to  FIG. 23 , the wireless power receiver may measure a rectified voltage (Vrect) and a second coil voltage (Vcoil2) during power transfer (S 2310 ). 
     When the rectified voltage (or the amount of change in the rectified voltage) is greater than a third threshold voltage (V_Threshold3) and the second coil voltage (or the amount of change in the first second coil voltage) is greater than a fourth threshold voltage (V_Threshold4), the wireless power receiver may acquire information on the distance to the wireless power transmitter and information on the location of the wireless power transmitter (S 2320  to S 2340 ). For example, the wireless power receiver may calculate the separation distance between the wireless power transmitter and wireless power receiver based on an RSSI value measured for an OB signal. For example, the OB signal may be a BLE signal transmitted by the wireless power transmitter. The wireless power receiver may calculate the distance to the wireless power transmitter based on the measured RSSI of the BLE signal and obtain two-dimensional or three-dimensional location information according to Bluetooth Direction Finding. 
     The wireless power receiver may determine whether the separation distance to the wireless power transmitter and/or the location of the wireless power transmitter is greater than (or deviate from) a predetermined threshold point or threshold (D_Threshold2) (S 2350 ). When the distance to the wireless power transmitter and/or the location of the wireless power transmitter is greater than the threshold point, the wireless power receiver may perform a connection release procedure of the wireless power receiver, which will be described below in  FIG. 24   
       FIG. 24  is a flowchart for explaining a procedure for releasing a connection between a wireless power receiver and a wireless power transmitter based on distance and location information obtained from the information acquisition procedure of the wireless power receiver of  FIG. 23 . 
     Referring to  FIG. 22 , the wireless power receiver may determine whether the distance between the wireless power transmitter and the wireless power receiver is normal (S 2410 ). For example, when the distance exceeds a predetermined distance threshold, the wireless power receiver may determine that the distance is abnormal. On the other hand, when the distance is less than or equal to the distance threshold, the wireless power receiver may determine that the distance is normal. Here, the distance threshold may be a different value from the threshold (D_Threshold2) of  FIG. 23 . In some embodiments, the distance threshold may be set to a value greater than the threshold. 
     When it is determined that the distance is abnormal, the wireless power receiver may reduce the received power and target rectified voltage (target Vrect) to a predetermined level (S 2420  and S 2430 ). That is, the wireless power receiver may prevent the wireless power receiver from being damaged by limiting the received power to the predetermined level or less. 
     In some embodiments, even when the magnitude of the rectified voltage and/or second coil voltage (or the amount of change in the magnitude) is greater than or equal to a predetermined voltage threshold, if the distance to the wireless power transmitter is less than the predetermined distance threshold, the wireless power receiver may limit the received power to the predetermined level or less without releasing the power link. 
     Subsequently, the wireless power receiver may perform the information acquisition procedure of the wireless power receiver (PRx&#39;s information acquisition process) according to steps S 2310  to S 2350  of  FIG. 23  (S 2440 ). 
     The wireless power receiver may determine again whether the distance between the wireless power transmitter and the wireless power receiver is normal (S 2450 ). 
     When it is determined that the distance is abnormal, the wireless power receiver may transmit a connection release notification to the wireless power transmitter and then request to stop the power transfer (S 2460  and S 2480 ). 
     When it is determined in step S 2450  that the distance is normal, the wireless power receiver may resume normal wireless power reception (S 2460  and S 2490 ). Here, the normal wireless power reception may refer to a power reception state before the received power or target rectified voltage is reduced in step S 2430 . 
     For example, if the wireless power receiver determines that the distance to the wireless power transmitter is abnormal while receiving power with PC1, the wireless power receiver may lower the power reception level from PC1 to PC0. Thereafter, when it is confirmed that the distance to the wireless power transmitter is normal, the wireless power receiver may receive power by increasing the power reception level from PC0 to PC1. 
     As another example, the level of the received power or target rectified voltage reduced by the wireless power receiver upon the determination that the distance to the wireless power transmitter is abnormal may be configured by predetermined parameter received from the wireless power transmitter in the configuration phase, negotiation phase, or renegotiation phase. 
       FIG. 25  is a flowchart for explaining a method for a wireless power transmitter to check the connection state of a wireless power transmission link and release the connection. 
     Referring to  FIG. 25 , according to an embodiment of the present disclosure, the wireless power transmitter may periodically perform a procedure for distance and location acquisition during wireless power transmission control (S 2510  and S 2520 ). Here, the distance and location acquisition procedure may be performed based on an OB signal, for example, a BLE signal. 
     According to another embodiment of the present disclosure, the wireless power transmitter may determine whether to perform the distance and location acquisition procedure based on a rail voltage and/or a transmitter coil voltage measured during the wireless power transmission control. For example, the wireless power transmitter may perform the distance and location acquisition procedure when the rail voltage and/or the transmitter coil voltage exceed predetermined thresholds, respectively. 
     The wireless power transmitter may determine whether the distance from itself to a wireless power receiver is normal (S 2530 ). For example, when the distance from the wireless power transmitter to the wireless power receiver is greater than a predetermined reference value, the wireless power transmitter may determine that the distance is abnormal. Here, the reference value may be dynamically configured based on at least one of the type, power category, power class, required power, or current transmitted power of the wireless power transmitter and/or wireless power receiver. 
     When it is determined that the distance is abnormal, the wireless power transmitter may request the wireless power receiver to release the wireless power transmission link (S 2550 ). For example, the wireless power transmitter may transmit a connection release request signal to the wireless power receiver through OB communication, but this is merely an example. When the connection release through OB communication fails, the wireless power transmitter may transmit the connection release request signal through IB communication rather than the OB communication. 
       FIG. 26  is a flowchart for explaining a method for a wireless power receiver to check the connection state of a wireless power transmission link and release the connection. 
     Referring to  FIG. 26 , according to an embodiment of the present disclosure, the wireless power receiver may periodically perform a procedure for distance and location acquisition during wireless power reception control (S 2610  and S 2620 ). Here, the distance and location acquisition procedure may be performed based on an OB signal, for example, a BLE signal. 
     According to another embodiment of the present disclosure, the wireless power receiver may determine whether to perform the distance and location acquisition procedure based on a rectified voltage and/or a receiver coil voltage measured during the wireless power reception control. For example, the wireless power receiver may perform the distance and location acquisition procedure when the rectified voltage and/or the receiver coil voltage are less than predetermined thresholds, respectively. 
     The wireless power receiver may determine whether the distance from itself to a wireless power transmitter is normal (S 2560 ). For example, when the distance from the wireless power receiver to the wireless power transmitter is greater than a predetermined reference value, the wireless power receiver may determine that the distance is abnormal. Here, the reference value may be dynamically configured based on at least one of the type, power category, power class, required power, or current transmitted power of the wireless power receiver and/or wireless power transmitter. 
     When it is determined in S 2630  that the distance is abnormal, the wireless power receiver may request the wireless power transmitter to release the wireless power transmission link (S 2650 ). For example, the wireless power receiver may transmit a connection release request signal to the wireless power transmitter through OB communication, but this is merely an example. When the connection release through OB communication fails, the wireless power receiver may transmit the connection release request signal through IB communication rather than the OB communication. 
     The wireless power transmitter in  FIGS. 21 to 26  may correspond to the wireless power transmitter or the power transmitter disclosed in  FIGS. 1 to 11 . Accordingly, the operations of the wireless power transmitter in the embodiments may be performed by one of the components of the wireless power transmitter in  FIGS. 1 to 11  or a combination of two or more components. For example, the IB communication operation of the wireless power transmitter in the embodiments may be performed by the IB communication module  121  of  FIG. 4C or 4D , and the OB communication operation and procedure of the wireless power transmitter may be performed by the OB communication module  122  of  FIG. 4C or 4D . In the embodiments, communication (data, packet, or signal) processing, voltage measurement, location and distance measurement, determination of normality, and transmission and reception operations by the wireless power transmitter may be performed by the communication and control unit  120 . 
     The wireless power receiver in  FIGS. 21 to 26  may correspond to the wireless power receiver or the power receiver disclosed in  FIGS. 1 to 11 . Accordingly, the operations of the wireless power receiver in the embodiments may be performed by one of the components of the wireless power receiver in  FIGS. 1 to 11  or a combination of two or more components. For example, the IB communication operation of the wireless power receiver in the embodiments may be performed by the IB communication module  221  of  FIG. 4C or 4D , and the OB communication operation and procedure of the wireless power receiver may be performed by the OB communication module  222  of  FIG. 4C or 4D . In the embodiments, communication (data, packet, or signal) processing, voltage measurement, location and distance measurement, determination of normality, and transmission and reception operations by the wireless power receiver may be performed by the communication and control unit  220 . 
     The steps of the methods or algorithms described in relation to the embodiments disclosed herein may be directly implemented by hardware and software modules that are executed by a processor or may be directly implemented by a combination thereof. The software module may reside in a storage medium (i.e., memory and/or storage) such as a RAM, flash memory, ROM, EPROM, EEPROM, register, hard disk, removable disk, or CD-ROM. 
     For example, the storage medium may be coupled to the processor, and the processor may read and write information from and to the storage medium. Alternatively, the storage medium may be integral with the processor. The processor and storage medium may reside within an application specific integrated circuit (ASIC). The ASIC may reside within a user terminal. Alternatively, the processor and storage medium may reside as separate components within the user terminal. 
     The above description is merely illustrative of the technical idea of present disclosure, and various modifications and variations may be made without departing from the essential characteristics of present disclosure by those with ordinary knowledge in the technical field to which present disclosure belongs. 
     Therefore, the embodiments disclosed in the present disclosure are intended to illustrate rather than to limit the technical idea of the present disclosure, and the scope of the technical idea of the present disclosure is not limited by these embodiments. The scope of protection of the present disclosure should be construed according to the following claims, and all technical ideas within the scope equivalent thereto should be construed as falling within the scope of the present disclosure. 
     INDUSTRIAL APPLICABILITY 
     The present disclosure may be applied to a wireless power transmitter for wirelessly transmitting power, a wireless power receiver for wirelessly receiving power, and a wireless charging system using the same.