Patent Publication Number: US-2022229628-A1

Title: Method, device and computer program for controlling audio data in wireless communication system, and recording medium therefor

Description:
TECHNICAL FIELD 
     The present disclosure relates to a control of audio data in a wireless communication system, and more specifically, to a control method, an apparatus, a computer program, and a recording medium thereof based on a priority related to audio data in a wireless communication system. 
     BACKGROUND ART 
     Bluetooth is a short-range wireless communication standard and includes BR (Basic Rate)/EDR (Enhanced Data Rate) technology and LE (Low Energy) technology. BR/EDR is also called Bluetooth classic, and includes BR technology applied from Bluetooth 1.0 and EDR technology applied from Bluetooth 2.0. Bluetooth LE (BLE) applied after Bluetooth 4.0 is a technology that supports transmission and reception of relatively large data with low power consumption. 
     The Bluetooth standard includes various profiles. For example, the Hands-Free Profile (HFP) defines what is necessary for one device to function as an audio gateway (AG) such as a smartphone and another device to function as a hands-free device such as a headset. In addition, A2DP (Advance Audio Distribution Profile) defines what is necessary for one device to function as an audio source such as a music player and another device to function as an audio sink such as a speaker. 
     As the spread of wireless devices increases recently, the demand for transmitting and receiving audio data in various topologies of many-to-many or M-to-N connection types is increasing. For example, streaming services that require a 5.1 channel environment are emerging, and it is being discussed to support a 5.1 channel environment using a plurality of Bluetooth portable speakers, breaking away from the limitations of a conventional 5.1 channel dedicated wired speaker. However, since the conventional Bluetooth audio technology was mainly developed in consideration of a use case of a one-to-one connection between two devices, it is not suitable for supporting audio data transmission/reception between multiple devices and delay is a big problem. In addition, as the number of Bluetooth audio devices increases, there is a problem in that power consumption for searching for peripheral devices increases. 
     In addition, in an M-to-N connection, there may be a case where different audio streams with different devices compete at the same time. In this case, there is a problem in that ambiguity occurs as to which audio stream is to be processed. 
     DISCLOSURE 
     Technical Problem 
     A technical problem of the present disclosure is to provide a method and an apparatus for applying an audio policy for audio stream priority. 
     An additional technical problem of the present disclosure is to provide a method and an apparatus for selecting an audio stream based on an audio policy. 
     The technical problems to be achieved in the present disclosure are not limited to the technical problems mentioned above, and other technical problems not mentioned will be clearly understood by those of ordinary skill in the art to which the present disclosure belongs from the following description. 
     Technical Solution 
     A method for a first device to control audio data in a wireless communication system according to an aspect of the present disclosure includes: obtaining an audio policy; receiving information on a plurality of audio streams from one or more second devices; selecting one or more audio streams based on the information on the plurality of audio streams and the audio policy; and performing a setup procedure for the selected one or more audio streams. 
     A device for controlling audio data in a wireless communication system according to a further aspect of the present disclosure includes: a memory; a transceiver; and a processor, wherein the processor comprises: an audio policy management unit configured to obtain an audio policy; an audio stream information management unit configured to receive information on a plurality of audio streams from one or more other devices; and an audio stream select unit configured to select one or more audio streams based on the information on the plurality of audio streams and the audio policy, wherein the processor is configured to: perform a setup procedure for the selected one or more audio streams. 
     The features briefly summarized above with respect to the present disclosure are merely exemplary aspects of the detailed description of the present disclosure that follows, and do not limit the scope of the present disclosure. 
     Technical Effects 
     According to the present disclosure, a method and an apparatus for applying an audio procedure for an audio stream priority may be provided. 
     According to the present disclosure, a method, and an apparatus for selecting an audio stream based on an audio policy may be provided. 
     The technical effects of the present disclosure are not limited to the above-described effects, and other effects not mentioned herein may be understood to those skilled in the art from the following description. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a diagram exemplarily illustrating a conventional audio connection type and an audio connection type to which the present disclosure is applicable. 
         FIG. 2  is a diagram exemplarily illustrating a conventional audio-related protocol and an audio-related protocol stack to which the present is applicable. 
         FIG. 3  is a diagram illustrating examples of 5.1 channel surround system hardware to which the present disclosure is applicable. 
         FIG. 4  is a diagram illustrating an audio data encoding/decoding process to which the present disclosure is applicable. 
         FIG. 5  is a diagram illustrating an example of channel allocation for two devices to which the present disclosure is applicable. 
         FIG. 6  is a diagram for describing a synchronization delay of two streams to which the present disclosure is applicable. 
         FIG. 7  is a diagram for describing a broadcast operation for a plurality of devices to which the present disclosure is applicable. 
         FIG. 8  and  FIG. 9  are diagrams for describing the operation of the ICL type and the INCL type to which the present disclosure is applicable. 
         FIG. 10  is a diagram illustrating a broadcast audio stream state machine to which the present disclosure is applicable. 
         FIG. 11  is a diagram illustrating an audio setup procedure to which the present disclosure is applicable. 
         FIG. 12  is a diagram illustrating a link layer state machine to which the present disclosure is applicable. 
         FIG. 13  is a diagram illustrating an example of an audio topology to which the present disclosure is applicable. 
         FIG. 14  to  FIG. 16  are diagrams illustrating a message exchange process between a server and a client to which the present disclosure is applicable. 
         FIG. 17  is a diagram illustrating a state machine for a call service to which the present disclosure is applicable. 
         FIG. 18  is a diagram illustrating a packet format for each layer to which the present disclosure is applicable. 
         FIG. 19  is a diagram illustrating examples of a data unit format to which the present disclosure is applicable. 
         FIG. 20  is a diagram illustrating examples of an advertisement unit format to which the present disclosure is applicable. 
         FIG. 21  is a flowchart illustrating an audio policy-based audio data control method to which the present disclosure may be applied. 
         FIG. 22  is a diagram for describing a device operation based on an audio policy to which the present disclosure is applicable. 
         FIG. 23  is a diagram illustrating a configuration of a first device and a second device to which the present disclosure may be applied. 
     
    
    
     BEST MODE 
     Hereinafter, with reference to the accompanying drawings, embodiment of the present disclosure will be described in detail so that those of ordinary skill in the art to which the present disclosure belongs can easily implement them. However, the present disclosure may be embodied in several different forms and is not limited to the embodiments described herein. 
     In describing the embodiments of the present disclosure, if it is determined that a detailed description of a well-known configuration or function may obscure the gist of the present disclosure, a detailed description thereof will be omitted. And, in the drawings, parts not related to the description of the present disclosure are omitted, and similar reference numerals are attached to similar parts. 
     In the present disclosure, when a component is “connected”, “coupled” or “accessed” to another component, it may include not only a direct connection relationship, but also an indirect connection relationship in which another component exists in the middle. Also, in the present disclosure, the terms “comprises” or “have” specify the presence of a recited feature, step, operation, element and/or component, but it does not exclude the presence or addition of one or more other features, steps, operations, elements, components and/or groups thereof. 
     In the present disclosure, terms such as “first” and “second” are used only for the purpose of distinguishing one component from other components and are not used to limit the components. And, unless otherwise noted, the terms do not limit the order or importance between the components. Accordingly, within the scope of the present disclosure, a first component in one embodiment may be referred to as a second component in another embodiment, and similarly, a second component in one embodiment may be referred to as a first component in another embodiment. 
     In the present disclosure, the components that are distinguished from each other are for clearly describing each characteristic, and do not necessarily mean that the components are separated. That is, a plurality of components may be integrated to form one hardware unit or a software unit, or one component may be distributed to form a plurality of hardware units or software units. Accordingly, even if not specifically mentioned, such integrated or dispersed embodiments are also included in the scope of the present disclosure. 
     The various embodiments of the present disclosure are not intended to list all possible combinations of components, but rather to illustrate representative aspects of the disclosure, and some or all of the components described in the various embodiments may be applied independently or in combination of two or more. That is, components described in various embodiments of the present disclosure do not necessarily mean essential components, and some may be optional components. Accordingly, an embodiment composed of a subset of components described in one embodiment is also included in the scope of the present disclosure. In addition, embodiments including other components in addition to components described in various embodiments are also included in the scope of the present disclosure. 
     Example methods of the present disclosure are expressed as a series of operations for clarity of description, but this is not intended to limit the order in which the steps are performed, and if necessary, each step may be performed simultaneously or in a different order. In addition, in order to implement the method according to the present disclosure, other steps may be included in addition to the illustrated steps, steps may be included except for some steps, or additional steps may be included except for some steps. 
     Terms used in the present disclosure is for the description of specific embodiments and is not intended to limit the claims. As used in the description of the embodiments and in the appended claims, the singular form is intended to include the plural form as well, unless the context clearly dictates otherwise. Also, the term “and/or” used in the present disclosure may refer to one of the related enumerations, or is meant to refer to and include all possible (or random) combinations of two or more thereof. 
     Definitions of terms used in the present disclosure are as follows. 
     An audio sink is an entity that receives audio data from an audio source. 
     An audio source is an entity that transmits audio data to the audio sink. 
     An audio channel is a single flow of coded or uncoded audio data. 
     An audio stream is a unidirectional logical communication channel that carries audio data flowing from the audio source to the audio sink. Audio data may flow on an audio stream session (ASS). An audio stream may carry audio data for one or more audio channels. 
     An audio group may include one or more synchronized audio streams. 
     A content type indicates a classification of content of an audio group. The classification may include whether the audio was initiated by the user. A content type indicates a classification of content of an audio group. The classification may include whether the audio was initiated by the user. Examples of the content type may include uncategorized audio (UncategorizedAudio), ringtone (Ringtone), system sound (SystemSound), satellite navigation (Satnav), call audio (CallAudio), media (Media), and the like. 
     Metadata is a variable-length data that describes and provides the context of audio data. Metadata may be defined for a higher layer. 
     An audio stream session (ASS) means to a unidirectional or bidirectional transmission/exchange process of an audio stream. An endpoint of an ASS corresponds to an audio input and/or audio output of an audio stream session, and may correspond to one device or a group of devices. The end of the ASS resides on the server and may be configured by the server or by the client. The server may store, change, and manage ASS state. 
     QoS (Quality of Service) means a quality of service for an audio stream and may correspond to a requirement for a specific service. 
     An audio location means a logical spatial rendering location intended for an audio channel within a spatial arrangement of a device for rendering audio. For example, the left and right location of a headset may correspond to an audio location. An audio location may be allocated to an audio channel. 
     CBIS (Connection Based Isochronous Stream) is a term defined in a core layer and is a concept corresponding to an audio stream in an ASS service. A unidirectional CBIS may have one audio stream, and a bidirectional CBIS may have two audio streams. 
     CBISS (Connection Based Isochronous Stream Set) is a term defined in a core layer and is a concept corresponding to an audio group in the ASS service. 
     An audio scene application (ASA) means an audio group performing a specific content type. 
     ASC (Audio Steam Capability) is a set of parameters necessary for configuring an audio session capability. 
     An audio advertisement is to discover the availability of ASA participation. An audio general advertisement is an audio advertisement that does not specify a target, and an audio directed advertisement is an audio advertisement for a specific target. 
     Isochronous data means data that is limited by time. For example, isochronous data may be time-dependent audio, such as television audio that needs to be synchronized with respect to an image of a video, or audio that needs to be synchronized and reproduced in multiple devices constituting a multi-channel. 
     An isochronous channel means a logical transmitting end used to transmit isochronous data from a transmitting device to one or more receiving devices. 
     An isochronous stream means a logical link carrying one or more isochronous channels. 
       FIG. 1  is a diagram exemplarily illustrating a conventional audio connection type and an audio connection type to which the present disclosure is applicable. 
       FIG. 1( a )  illustrates an example of a BR/EDR audio connection type. In the case of BR/EDR, one-to-one connection type is supported. One device (e.g., a smartphone) may function as a central device, and may be connected one-to-one with each of several devices. That is, there may be multiple one-to-one connections. Accordingly, the service such as a phone call through a headset or music reproduction through a speaker may be supported. The center of service in this connection type is an audio source, and an audio sink such as a headset, a speaker, and AVN (Audio Video Navigation) may operate as a peripheral device of the audio source. 
       FIG. 1( b )  illustrates an example of a BLE audio connection type. In the case of BLE, many-to-many connections may be supported. In this case, there may be a plurality of center devices such as a TV, a smart phone, and a gateway etc., and complex M-to-N connection may be configured. Accordingly, services of phone calls and music reproduction through the headset may be supported, and broadcast audio services such as alarms, doorbells, and advertising voices may be supported. The center of the service in this connection type is an audio sink, and the audio service may be used by moving multiple audio sources. 
       FIG. 2  is a diagram exemplarily illustrating a conventional audio-related protocol stack and an audio-related protocol stack to which the present disclosure is applicable. 
       FIG. 2( a )  illustrates an example of an audio-related protocol stack. L2CAP (Logical Link Control &amp; Adaption Protocol) layer functions as arbitration and mediation between the upper layer and the lower layer. In the upper layer, protocols such as RFCOMM (Radio Frequency Communication), AVDTP (Audio/Video Distribution Transport Protocol), AVCTP (Audio/Video Control Transport Protocol) etc. and profiles such as HFP (Hands Free Profile), A2DP (Advanced Audio Distribution Profile), AVRCP (Audio/Video Remote Control Profile) etc. may be included. The lower layer may include a MAC/PHY layer. The MAC (Medium Access Control) layer may include a link manager and a link controller, and the PHY (Physical) layer may include a BR/EDR radio. In addition, Synchronous Connection Oriented (SCO)/extended SCO (eSCO) may provide a synchronous data communication path for voice. As such, in BR/EDR, a protocol stack may be designed for each profile. The L2CAP layer, the BR/EDR protocol, the Generic Access Profile (GAP), and the BR/EDR profile layer may be collectively referred to as the host layer, and the link manager, link controller, and BR/EDR radio layer may be referred to as the controller layer. The interface between the host and the controller may be referred to as a HCI (Host Controller Interface). 
       FIG. 2( b )  illustrates an example of a BLE audio-related protocol stack. Unlike BR/EDR in which protocols are configured for each profile, in BLE, a common protocol stack for various profiles may be designed. This common protocol stack may be referred to as middleware. For example, a common protocol for various profiles such as hearing aids, high quality audio/music, voice recognition, and call/media in the form of middleware may be configured. For example, the middleware may include protocols such as device discovery, stream control (or stream management), codec, and legacy management. In addition, the core layer may include a link layer (Link Layer, LL), an LE Radio (i.e., a PHY layer), and the LL may include functions related to multicast support isochronous channels defined from Bluetooth 5. 
     In addition, the profile and middleware may be referred to as a host layer, the core layer may be referred to as a controller layer, and HCI may be defined between the host and the controller. 
     In addition to the host profile and protocol illustrated in  FIG. 2( b ) , the host may include an LE profile, a generic access profile (GAP), a generic attribute profile (GATT), an Attribute (ATT) protocol, a security manager (SM), and the like. 
     Information transmitted from a host to a controller may be referred to as a HCI command packet. Information transmitted from a controller to a host may be referred to as a HCI event packet. In addition, HCI asynchronous data packets or HCI synchronous data packets may be exchanged between a host and a controller. 
     Also, in addition to the middleware profiles and services illustrated in  FIG. 2( b ) , the middleware may include various profiles and/or services as follows: 
     Audio Session Capability Service (ASCS): Audio Session Capability Service (ASCS) is a service that supports to advertise or discover capabilities related to an audio session; 
     Audio Stream Session Service (Audio Stream Session Service, ASSS): Audio Stream Session Service (ASSS) is a service that supports discovery, setup, establishment, control, and management related to an audio session; 
     Audio Input Management Service (AIMS): a service for managing audio input volume, etc.; 
     Audio Routing Service (ARS): a service for selecting the location of audio inputs and outputs; 
     Audio Middleware Profile (AMP): a basic profile for the behavior of a device to distribute audio; 
     Call Management Profile (CMP): a profile of the roles and procedures of interaction between two devices for a call; 
     Audio General Middleware Profile (AGMP): a basic profile that enables content and/or stream control; 
     Group Identification Service (GIS): a service for the discovery of devices belonging to a group. A Group Identification Service (GIS) or Group Identification Profile (GIP) may allow devices to be discovered as part of a group. A group is defined as a group of devices that operate together to support a specific scenario, and these devices may be referred to as group members. For example, a group of devices that respond to a control command together, such as a pair of hearing aids, a pair of earbuds, or a set of speakers that receive multichannel (e.g., 5.1 CH) audio, may be such examples: 
     Audio Player Management Profile (APMP): a profile that supports the control or interaction of an audio player; 
     Audio Player Management Service (APMS): a service that supports the control or interaction of an audio player; 
     Microphone Management Profile: a profile for microphone status management; 
     Microphone Management Service: a service that supports interfaces and states for microphone state management; 
     Quick Service Discovery Service (QSDS): a service that supports quick discovery of services such as audio player management and call management; 
     Call Bearer Service: a service that supports management of a call interface and a call state for a bearer on a device; 
     Volume Management Profile: a profile that supports audio volume management of a device; 
     Volume Management Service: a service that supports the device&#39;s audio volume interface and status; 
     Volume Offset Management Service: a service for volume management for audio output. 
       FIG. 3  illustrates examples of 5.1 channel surround system hardware to which the present disclosure is applicable. 
     In  FIG. 3 , a LE audio source device may perform a function of an initiator, and a LE audio sink device may perform a function of an acceptor. The initiator means a device that initiates an audio session, and the acceptor means a device that accepts the initiation of an audio session. Here, a source is not always the initiator or a sink is not always the acceptor, and the source may be the acceptor or the sink may be the initiator. 
     For example, an audio source may be a TV device, and an audio sink may be a speaker device. The audio source may transmit audio data to the audio sink. In addition, the audio source may receive feedback data from the audio sink. A plurality of audio sinks may receive audio data corresponding to one of 5.1 channels, respectively, FL (Front Left), FR (Front Right), RL (Rear Left), RR (Rear Right), C (Center), and W (Woofer) and output it through the speaker. 
     An audio encoder or decoder may support various audio formats. For example, the audio format may include Bluetooth Low Energy Audio Codec (BLEAC), Dolby 5.1 CH, Digital Surround Sound (DTS), and the like, and the characteristics of each format are as follows. BLEAC is a mono codec, and the 96 kbps transmission rate of BLEAC may provide the same quality as 256 kbps of SBC (Sub-Band Codec) and 200 kbps of MP3. Dolby 5.1 CH may support a 48 kHz sampling rate, support 1 to 5.1 (or 1 to 6) channels and support a transmission rate of up to 448 kbps. DTS may support 48 kHz or 96 kHz sampling rate, support 2 to 6.1 channels, and support transmission rates of 768 kbps half rate and 1,536 kbps full rate. 
       FIG. 4  is a diagram illustrating an audio data encoding/decoding process to which the present disclosure is applicable. 
     Referring to  FIG. 4( a ) , a DTS format stream or a Dolby 5.1 CH format stream may be input to a DTS decoder or a Dolby 5.1 CH decoder of the transmitting end (Tx) and an audio signal in a PCM (Pulse-Code Modulation) format may be output. The PCM signal may be input to the BLEAC encoder and output as an audio signal in the BLEAC format. Here, optional vendor-specific information may be added. The BLEAC signal may be transmitted to the BLE interface of the receiving end (Rx) through the BLE interface. The receiving end may process the BLEAC signal through the BLEAC decoder and convert it into a signal that can be output through the speaker. 
     Here, a plurality of streams may be transmitted from a transmitting end to a plurality of receiving ends. For example, each of the plurality of streams may include an audio signal corresponding to one channel among 5.1 CHs. The plurality of streams may be received at different times from the plurality of receiving ends, but have isochronous properties that require play or rendering at the same time, and these streams may be called CBIS (Connection Based Isochronous Stream). That is, six CBISs corresponding to 5.1 CH may be transmitted from a transmitting end to a receiving end, and a set of these six CBISs may be referred to as one CBISS (Connection Based Isochronous Steam Set). 
       FIGS. 4( b ) and 4( c )  conceptually illustrates audio streaming through a plurality of streams. One or more audio streams may correspond to CBIS, and an audio group may correspond to CBISS. For example, one audio stream may correspond to one CBIS, and two or more audio streams may correspond to one CBIS. A plurality of CBISs may be included in one audio group or CBISS. 
       FIG. 5  is a diagram illustrating an example of channel allocation for two devices to which the present disclosure is applicable. 
     The receiving end may initiate stream reception according to timing information provided by the transmitting end. For example, the timing information may indicate a time point after a predetermined offset from a time point at which a data unit including the timing information is transmitted. The receiving end may receive audio data corresponding to one or more channels included in the stream. For example, a plurality of channels included in one stream may be allocated to a plurality of receiving ends, respectively. A plurality of channels (or a plurality of audio data) included in one stream may be transmitted in a time division multiplexing (TDM) method. For example, audio data of a first channel may be transmitted at a first timing, and audio data of a second channel may be transmitted at a second timing. 
     The broadcast receiving end may detect a currently obtainable broadcast audio stream, a stream offset value, a stream interval value, and the like, by using information included in a data unit periodically advertised by the transmitting end. 
     In the case of an Isochronous Non-Connection Link (INCL), which is a connectionless-based isochronous link, an isochronous channel may be transmitted/received (e.g., in a broadcast manner) without a connection between a source device and a sink device. From information such as BSG (Broadcast Synch Group) included in the AUX_SYNC_IND Protocol Data Unit (PDU) advertised by the transmitting end, the receiving end may check the INCL stream offset or BSG offset, and determine the anchor point timing. INCL stream transmission may start from the anchor point. A timing difference between two consecutive anchor points may be defined as an interval (e.g., an INCL CH1 interval or an ISO interval of  FIG. 5 ). One or more sub-events may be included in the stream transmission event. 
     In the example of  FIG. 5 , one audio stream may include audio data for two channels. The first channel (CH1) may be allocated to the first device (device #1), and the second channel (CH2) may be allocated to the second device (device #2). At one or more timings after the anchor point, CH1 included in the INCL stream may be transmitted to the device #1, and thereafter, CH2 may be transmitted to the device #2 at one or more timings. In addition, the INCL stream event may include an event for CH1 and an event for CH2. An event for CH1 may include two sub-events. An event for CH2 may include two sub-events. A timing difference between sub-events may be defined as a sub-event interval. 
     Isochronous audio data may have a limited lifetime. That is, the audio data may be invalidated after the predetermined time has expired. For example, a predetermined timeout value may be defined in the ICL channel, and isochronous audio data transmitted to a plurality of devices may be discarded after the predetermined timeout value has expired. For example, a timeout may be expressed as a number of sub-events. 
       FIG. 6  is a diagram for describing a synchronization delay of two streams to which the present disclosure is applicable. 
     It is assumed that a plurality of streams are included in one audio group, and the plurality of streams have isochronism required to be reproduced at the same time. A plurality of streams may be transmitted from one device or may be transmitted from different devices. Also, the plurality of streams may be received by one device or may be received by different devices. 
     Since the Bluetooth communication method does not support simultaneous transmission of a plurality of streams, the plurality of streams may be transmitted in the TDM method on different time resources (or timings) according to a predetermined order. In this case, a difference may occur in the transmission timing of the plurality of streams, and accordingly, a difference may also occur in the reception timing of the plurality of streams. In addition, since a plurality of streams are required to be reproduced simultaneously, the stream received first cannot be reproduced first, but may be reproduced after waiting until the last stream is received. That is, a synchronization delay may occur until a timing at which reception of all streams is completed. 
     In the example of  FIG. 6 , the first stream (CBIS #1) and the second stream (CBIS #2) may be required to be reproduced simultaneously, and may be included in one CBISS. The CBISS anchor point may be same as the anchor point of CBIS #1, and after the CBIS #1 audio data may be transmitted, CBIS #1 audio data subsequent to the time point (e.g., T1) after the CBIS #1 interval may be transmitted. Next, after CBIS #2 audio data is transmitted from the anchor point of CBIS #2, CBIS #2 audio data subsequent to a time point after the CBIS #2 interval (e.g., T2) may be transmitted. After all streams included in one CBISS are received, they may be reproduced simultaneously. That is, the audio data of CBIS #1 and CBIS #2 may be processed and reproduced at the time of completion of reception of CBIS #2, which is transmitted relatively late. 
     Here, the synchronization delay of the CBISS may be defined as a time interval until the reception completion time (T2) of CBIS #2, which is received relatively late from the CBISS. For example, the later time point among the reception completion time T1 of CBIS #1 and the reception completion time T2 of CBIS #2 may be determined as the synchronization delay of the CBISS. That is, a later reception completion time among synchronization delays of a plurality of streams may be determined as a synchronization delay of the CBISS. Specifically, when CBIS #1 and CBIS #2 are bundled into the same single CBISS, the previously received stream CBIS #1 may be reproduced after waiting until the received stream CBIS #2 information is transmitted. 
     The transmitting end (Tx) may inform the receiving end (Rx) of an expected delay value calculated in consideration of the number of CBISs, CBIS events, sub-events, and intervals in advance. For example, the transmitting end may inform the receiving end of the expected delay value when configuring the channel. 
     In the case of a connection-based isochronous connection link (ICL), since the transmitting end and the receiving end are connected, the receiving end may inform the transmitting end of the actual delay value. 
     In the case of INCL, since the transmitting end and the receiving end are not connected, the receiving end cannot inform the transmitting end of the actual delay value. Even if the delay value may be informed from the receiving end to the transmitting end, the transmitting end cannot control the playback time of a specific device in order to synchronize the plurality of devices. 
     For example, even in the case of INCL, when a plurality of CBISs (e.g., six CBISs corresponding to six channels of 5.1 CH) are included in one CBISS, the transmitting end may receive feedback from the receiver to adjust synchronization. Through the feedback, the receiving end may inform the transmitting end of its delay information. 
       FIG. 7  is a diagram for describing a broadcast operation for a plurality of devices to which the present disclosure is applicable. 
     The audio source device may calculate a synchronization delay value for simultaneous reproduction of isochronous streams and transmit it to a plurality of audio sink devices. Each of the sink devices may determine the playback timing based on the delay value provided from the source device. That is, since the source device cannot accurately know the amount of time the sink device takes to receive and process audio data, the sink device may provide the delay value as basic information for determining the playback timing. The sink device may determine a reproduction timing according to its device characteristics and reproduce audio data. 
     For example, in an Isochronous Broadcast operation, a source device (e.g., a TV) may calculate a transmission delay, a rendering delay, etc., and transmit to a sink device (e.g., speaker). The sink device may adjust playback or rendering timing of audio data by reflecting the received delay value. Since device characteristics are different for each sink device manufacturer, the actual playback timing may be determined by the sink device. 
     If the sink device can transmit information to the source device, the sink, the sink device may calculate a delay value and transmit to the source device. Accordingly, the source device may determine the transmission timing based on the delay value provided from the sink device. 
     For example, a feedback channel may be formed through which a sink device (e.g., a speaker) may communicate information to a source device (e.g., a TV). In this case, a unicast operation based on an isochronous connection may be performed. The sink device may calculate a rendering delay value and transmit it to the source device through a feedback channel. Accordingly, the source device may adjust the transmission time of the audio data by reflecting the delay value provided from the sink device. 
     Referring to  FIG. 7 , an isochronous stream operation is exemplarily illustrated in the case where a transmitting end is a TV, and two receiving ends are a first speaker (speaker #1) and a second speaker (speaker #2). The first speaker may be allocated a first stream/channel (e.g., RR channel in 5.1 CH), and the second speaker may be allocated a second stream/channel (e.g., RL channel in 5.1 CH). 
     The first and second speakers may transmit an audio general advertisement or an audio directed advertisement, respectively. At least one of the TV and the first speaker or the second speaker may or may not be connected to each other. 
     When at least one of the TV and the speaker is connected, the speaker may calculate a rendering delay value and report it to the TV. When the TV and the speaker are not connected, the TV may calculate the transmission delay, rendering delay value, and the like, and send it to the speaker. 
     The TV may perform a synchronization operation in consideration of audio content characteristics, audio/video synch, codec characteristics, and the like, and forcibly apply a delay to a specific audio stream. For example, since the audio codec encoding/decoding delay is different from 40 ms for BLEAC, 200 ms for SBC, 100 ms for APT-X, etc., the delay value may be determined according to codec characteristics. In addition, since characteristics of A/V content are different according to games, movies, animations, and the like, a delay value may be determined in consideration of this. Also, a delay value may be determined in consideration of a difference between a media clock and a clock of the BLE interface. The media clock may be confirmed through A/V time scale information. 
     In addition, as shown on the left side of  FIG. 7 , a delay value may be determined in consideration of audio/video signal processing time defined in various broadcasting standards. For example, the time interval between audio-video-audio is 15 ms and 45 ms in Advanced Television Systems Committee (ATSC), 125 ms and 45 ms in ITU-R BT.1359-1, and SMPTE (Society of Motion Picture and Television Engineers) It is defined as 22 ms and 22 ms, and a delay value may be determined in consideration of these time intervals. 
     The TV may configure the rendering delay value of each stream and inform the speaker, or determine the transmission timing of the stream based on the delay value provided from the speaker. 
     The TV may transmit a stream to the speaker based on the determined delay value. That is, the source device or the TV which is the transmitting end may exchange a delay value with the sink device and the speaker(s) which is the receiving end, and may perform an operation of synchronizing by reflecting the delay value. 
       FIG. 8  and  FIG. 9  are diagrams for describing the operation of a ICL type and a INCL type to which the present disclosure is applicable. 
     In BLE, a channel for audio transmission may be classified into an ICL type and an INCL type. Both the ICL channel and the INCL channel may transmit audio data to multiple devices and/or multiple profiles using a stream ID and a channel ID. According to the ICL type and the INCL type, it may be determined what operation is to be performed on the BLE channel for audio data transmission. 
     ICL channels correspond to a connection-based use case that supports unidirectional or bidirectional communication through a point-to-point physical link between one source device and one sink device. In addition, INCL channels correspond to a broadcast use case that supports only unidirectional communication through a point-to-multipoint physical link between one source device and one or more sink devices. 
     The protocol stack of the device may include a profile layer, a channel manager layer, a host layer, and a controller layer in order from an upper layer to a lower layer. Data may be transferred between the profile layer and the channel manager layer in units of channels, and data may be transferred between the channel manager layer and the host layer in units of streams. 
     Referring to  FIG. 8 , in case of the ICL type, a connection between a master (M) and the first slave S1 and a connection between the master M and the second slave S2. In this case, it is possible to divide two channels included in one stream by a channel identifier and transmit to the two slaves. That is, channel ID 1 may be allocated to the S1 and channel ID 2 may be allocated to the S2. Both the channel ID 1 and the Channel ID 2 may be transmitted through the same stream ID 1. In addition, since bidirectional communication is possible based on the connection, the slaves may provide feedback information to the master M. For example, when S1 is a wireless earphone mounted on the right ear and S2 is a wireless earphone mounted on the left ear, it is possible to listen to music transmitted by the master M in stereo through S1 and S2. 
     Referring to  FIG. 9 , in the case of the INCL type, there is no connection between the master M and the slaves (S1, S2), and the slaves may synchronize with a INCL stream offset, an event, a timing of the sub-event based on the synchronization information advertised by the master and may receive broadcast audio data. In addition, the master M may include two profiles (profile #1 and profile #2). The first slave S1 may include the profile #1, and the second slave S2 may include the profile #1 and the profile #2. In Profile #1, the channel ID 1 and the channel ID 2 may be broadcast from the master M through one stream, Stream ID 1, and it is similar to  FIG. 8  that the slaves S1 and S2 respectively receive the channel ID 1 and the channel ID in Profile #1. Additionally, in profile #2, the channel ID 1 may be broadcast from the master M through Stream ID 2, and the second slave S2 may receive Channel ID 1 in profile #2. 
       FIG. 10  is a diagram illustrating a broadcast audio stream state machine to which the present disclosure is applicable. 
     The control of the broadcast audio stream may be described as a broadcast audio stream state machine and state transition at the broadcast transmitting end. 
     The broadcast audio stream state machine may allow a broadcast transmitter to communicate with one or more broadcast receivers (or broadcast discovery clients) in a one-way manner without a connection or not with a broadcast receiver (or broadcast discovery client). The broadcast transmitter may communicate using a broadcast audio advertisement in the form of a Broadcast Audio Source Session (BASS). A broadcast audio stream may be transmitted by a broadcast transmitter. 
     The AUDIO STANDBY state means a state in which a broadcast audio stream is not transmitted. 
     The AUDIO CONFIGURED state means a state in which a broadcast receiver (or a broadcast discovery initiator) starts advertising information for detecting an audio stream through a periodic advertising event. The periodic advertising event may include delivering advertisement metadata, stream configuration, synchronization information, and the like. In this state, no audio data packet is transmitted from the broadcast transmitter. 
     The AUDIO STREAMING state means a state in which a broadcast audio stream is enabled in a broadcast transmitter and an audio data packet may be transmitted. The broadcast transmitter may continuously perform metadata advertising through periodic advertising while transmitting the broadcast audio stream. If a stream is configured in the AUDIO STANDBY state, it may transition to the AUDIO CONFIGURED state, and if the stream is released in the AUDIO CONFIGURED state, it may transition to the AUDIO STANDBY state. If a stream is enabled in the AUDIO CONFIGURED state, it may transition to the AUDIO STREAMING state, and if the stream is disabled in the AUDIO STREAMING state, it may transition to the AUDIO CONFIGURED state. If a stream reconfiguration occurs in the AUDIO CONFIGURED state, it may transition to the AUDIO CONFIGURED state. When content reassignment occurs in the AUDIO STREAMING state, it may transition to the AUDIO STREAMING state. 
       FIG. 11  is a diagram illustrating an audio setup procedure to which the present disclosure is applicable. 
     When there is no discovery result (that is, zero discovery), the AUDIO STANDBY state may be transitioned, and if there is a discovery result, discovery for Audio Stream Capability (ASC) may be performed and transition to the AUDIO STANDBY state. 
     When an ASS (Audio Stream Session) configuration occurs, it may transition to the AUDIO CONFIGURED state. If ASS is released in the AUDIO CONFIGURED state, it may transition to the AUDIO STANDBY state. When reconfiguration occurs in the AUDIO CONFIGURED state, it may transition to the AUDIO CONFIGURED state through the ASS configuration. 
     When ASS is activated, it may transition to AUDIO STREAMING state. If ASS deactivation occurs in the AUDIO STREAMING state, it may transition to the AUDIO CONFIGURED state. If content reassignment occurs in the AUDIO STREAMING state, it may transition to the AUDIO STREAMING state. 
       FIG. 12  is a diagram illustrating a link layer state machine to which the present disclosure is applicable. 
     The operation of the link layer LL may be expressed as (in terms of an isochronous channel) Standby state, Advertising state, Scanning state, Initiating state, Connection state, Synchronized (synchronization) state, and Streaming (Isochronous Broadcasting) state. 
     The Standby state corresponds to a standby state before transitioning to another state. 
     In the Advertising state, the LL may operate as a advertiser transmitting an advertising packet. When a connection is established in the advertising state, the device may operate as a slave. 
     In the Initiating state, the LL may act as an initiator that listens for packets from other advertisers and initiates a connection in response to the packets. When a connection is established in the initiating state, the device may operate as a master. 
     In the Scanning state, the LL may act as a scanner that listens for packets from other advertisers and requests additional information. 
     The synchronized state may refer to a state in which an audio stream may be received or received in synchronization with another device. 
     The streaming state may refer to a state in which an audio stream is transmitted to another synchronized device. 
       FIG. 13  is a diagram illustrating an audio topology to which the present disclosure is applicable. 
     In the case of unicast, unidirectional or bidirectional audio streams may be supported. Unicast audio data transmission/reception based on a connection between a headset and a smartphone may be performed, and the unicast audio data transmission/reception based on a connection between a headset and a smartphone and a connection between the headset and a tablet may be performed. In this case, the server of the unicast audio service may be a headphone, and the client may be a smartphone or tablet. Also, headphones may correspond to an audio sink, and a smartphone or tablet may correspond to an audio source. 
     In the case of broadcast, a notification system, a doorbell, a TV, etc. may transmit audio data in a broadcast manner, and one or more devices may receive the broadcast audio data. In this case, the server of the broadcast audio service may be a notification system, a doorbell, a TV, or the like, and the client may be a headphone. Also, the headphones may correspond to an audio sink, and a notification system, a doorbell, and a TV may correspond to an audio source. 
       FIG. 14  to  FIG. 16  are diagrams illustrating a message exchange procedure between a server and a client to which the present disclosure is applicable. 
     In the example of  FIG. 14  to  FIG. 16 , the client may be an audio source and the server may be an audio sink. Or, the client may be an audio sink and the server may be an audio source. 
       FIG. 14  exemplarily illustrates an audio session capability (ASC) discovery procedure and an ASC update procedure. 
     In the audio session capability discovery procedure of  FIG. 14( a ) , the client may request capability discovery by transmitting an ASC discovery request message to the server, and in response to that, the server may transmit detailed information of the capability by transmitting an ASC discovery response message to the client. 
     In the audio session capability update procedure of  FIG. 14( b ) , the server may transmit an ASC update indication message to the client to inform that the capability update has occurred, and the client may notify the server to perform a capability update by transmitting an ASC update confirmation message. Subsequently, an audio session capability discovery procedure or an ASC discovery procedure may be performed. 
     The format of the message used in the example of  FIG. 14  may be defined as shown in Table 1 below. 
     
       
         
           
               
               
             
               
                 TABLE 1 
               
               
                   
               
             
            
               
                   
                 ASC_DISCOVERY REQUEST 
               
               
                   
                 Direction 
               
               
                   
                 ASC_DISCOVERY RESPONSE 
               
               
                   
                 Sink Locations : Bitmap 
               
               
                   
                 Source Locations : Bitmap 
               
               
                   
                 Number of ASC Records 
               
               
                   
                 Direction 
               
               
                   
                 Codec ID 
               
               
                   
                 Sampling Frequency 
               
               
                   
                 Codec Specific 
               
               
                   
                 Content Protection Type 
               
               
                   
                 Content Protect ion type Specific 
               
               
                   
               
            
           
         
       
     
     The ASC update indication message and the ASC update confirmation message may include information indicating that ASC discovery is required and confirmation information therefor, respectively. 
       FIG. 15  exemplarily illustrate a unicast audio stream configuration procedure and an unicast audio stream establishment procedure. 
     In the unicast audio stream configuration procedure of  FIG. 15( a ) , the client, in the AUDIO STANDBY state, may transmit a Codec configuration request message to the server to inform the server of the codec requesting configuration, and the like. In response, the server may transmit a codec configuration response message to the client to inform the server of QoS and rendering delay values supported by the server. In addition, the client may transmit a QoS negotiation request message to the server to specify a specific audio stream session (ASS), an audio group, and an audio stream to inform the client of QoS and rendering delay values supported by the client. In response, the server may transmit a QoS negotiation response message to the client. Accordingly, bandwidth (BW), bitrate, etc. may be determined by negotiation between the client and the server, and the client and the server may transition to a CONFIGURED state. 
     In the unicast audio stream establishment procedure of  FIG. 15( b ) , the client may transmit an ASS enable request message to the server in the AUDIO CONFIGURED state to inform information on the ASS requesting activation. In response, the server may transmit an ASS enable response message to the client to inform about which ASS to activate. Configuration for connection-based isochronous link parameters may be performed at the client, and CBIS may be established by the client and the server configuring the connection-based isochronous stream connection and related parameters. If the client is the audio sink and the server is the audio source, the server may prepare to play audio data and transmit an ASS Rx ready indication message to the client, and the client may prepare to provide audio data after receiving the ASS reception ready indication notification message. Accordingly, the client and the server may transition to the AUDIO STREAMING state. 
     The format of the message used in the example of  FIG. 15  may be defined as shown in table 2 below. 
     
       
         
           
               
               
             
               
                 TABLE 2 
               
               
                   
               
             
            
               
                   
                 CODEC CONFIGURATION REQUEST 
               
               
                   
                 ASS ID 
               
               
                   
                 ASA ID 
               
               
                   
                 Direction 
               
               
                   
                 Codec ID 
               
               
                   
                 Sampling Frequency 
               
               
                   
                 Codec Specific 
               
               
                   
                 CODEC CONFIGURATION RESPONSE 
               
               
                   
                 ASS ID 
               
               
                   
                 Server Supported QoS (Interleaved, Framed, Transport Latency) 
               
               
                   
                 Presentation delay 
               
               
                   
                 QOS NEGOTIATION REQUEST 
               
               
                   
                 ASS ID 
               
               
                   
                 CBISS ID 
               
               
                   
                 CBIS ID 
               
               
                   
                 Client QoS (Transport Latency) 
               
               
                   
                 Rendering Delay 
               
               
                   
                 QOS NEGOTIATION RESPONSE 
               
               
                   
                 ASS ID 
               
               
                   
                 ASS ENABLE REQUEST / ASS ENABLE RESPONSE 
               
               
                   
                 Number of ASS ID 
               
               
                   
                 ASS ID 
               
               
                   
                 ASA ID 
               
               
                   
                 Content Type 
               
               
                   
                 ASS RX READY COMMAND / ASS RX READY NOTIFICATION 
               
               
                   
                 Number of ASS ID 
               
               
                   
                 ASS ID 
               
               
                   
               
            
           
         
       
     
       FIG. 16  exemplarily illustrates a procedure for disabling an audio stream by a client and a procedure for disabling an audio stream by a server. 
     In the procedure of the client disable audio streams in  FIG. 16( a ) , if the client is an audio source and the server is an audio sink, when the client decides to stop the audio in the AUDIO STREAMING state, an ASS disable request message may be transmitted to the server. Accordingly, the server may stop streaming audio data and transmit an ASS disable response message to the client. Upon receiving this, the client may stop audio data encoding and audio application operation. 
     Alternatively, if the client is an audio sink and the server is an audio source, the client may stop audio data streaming and transmit ASS disable request message to the client. Accordingly, the server may stop audio data encoding and audio application operation and transmit an ASS disable response message to the client. 
     After that, the client and the server may perform connection-based isochronous stream release and related parameter setting release. Here, in preparation for reconnection between the client and the server, device information may be stored in the client and/or the server together with an isochronous stream connection related parameter. Accordingly, the client may release the connection-based isochronous link related parameter setting. Accordingly, the client and the server may transition to the AUDIO CONFIGURED state. 
     In the example of  FIG. 16( b ) , in the procedure of disabling audio streams by the server, if the server is an audio source and the client is an audio sink, when the server decides to stop audio in the AUDIO STREAMING state, an ASS disable indication message may be transmitted to the client. Accordingly, the client may stop streaming audio data and may or may not transmit an ASS disable confirmation message to the server. The server may stop encoding audio data and audio application operation with or without receiving an ASS deactivation response. 
     Alternatively, if the server is an audio sink and the client is an audio source, the server may stop audio data streaming and transmit an ASS disable indication message to the client. Accordingly, the client may stop the audio data encoding and audio application operation, and may or may not transmit an ASS disable confirmation message to the server. 
     After that, the client and the server may perform connection-based isochronous stream release and related parameter configuration release. Here, in preparation for reconnection between the client and the server, device information may be stored in the client and/or the server together with an isochronous stream connection related parameter. Accordingly, the client may release the connection-based isochronous link related parameter configuration. Accordingly, the client and the server may transition to the AUDIO CONFIGURED state. 
     The format of the message used in the example of  FIG. 16  may be defined as shown in table 3 below. 
     
       
         
           
               
               
             
               
                 TABLE 3 
               
               
                   
               
             
            
               
                   
                 ASS DISABLE REQUEST / ASS DISABLE RESPONSE / 
               
               
                   
                 ASS DISABLE INDICATION 
               
               
                   
                 Number of ASS ID 
               
               
                   
                 ASS ID 
               
               
                   
                 (No Contents) 
               
               
                   
               
            
           
         
       
     
     Table 4 below exemplarily shows content reallocation request/response, ASS release request/response, general advertisement, and directed advertisement message formats. 
     
       
         
           
               
               
             
               
                 TABLE 4 
               
               
                   
               
             
            
               
                   
                 REASSIGN CONTENT REQUEST / REASSIGN CONTENT 
               
               
                   
                 RESPONSE 
               
               
                   
                 Number of ASS ID 
               
               
                   
                 ASS ID 
               
               
                   
                 ASA ID 
               
               
                   
                 Content Type 
               
               
                   
                 ASS RELEASE REQUEST / ASS RELEASE RESPONSE 
               
               
                   
                 ASS ID 
               
               
                   
                 GENERAL ADVERTISEMENT 
               
               
                   
                 DIRECTED ADVERTISEMENT 
               
               
                   
                 Content Type 
               
               
                   
                 Meta data 
               
               
                   
               
            
           
         
       
     
       FIG. 17  is a diagram illustrating a state machine for a call service to which the present disclosure is applicable. 
     When a call is received in the AUDIO STANDBY state, it may transition to the CALL ACCEPTING state. When a call is accepted in the CALL ACCEPTING state, it may transition to the CALL ACTIVE state. When a call is rejected in the CALL ACCEPTING state, it may transition to the AUDIO STANDBY state. In the case of hold in which a call cannot be received in the CALL ACCEPTING state, it may transition to the CALL HELD state, and may transition to the CALL ACTIVE state when the hold is released in the CALL HELD state. When the CALL HELD state or the CALL ACTIVE state is terminated, it may transition to the AUDIO STANDBY state. 
     Also, When a call is outgoing in the AUDIO STANDBY sate, it may transition to the CALL INITIATING state. When it answers a call from a remote location or the other party in the CALL INITIATING state, it may transition to the CALL ACTIVE state. When it ends in the CALL INITIATING state, it may transition to the AUDIO STANDBY state. 
     In such a call service state machine, audio data that needs to be delivered to the headset in the AUDIO STANDBY state may occur. For example, audio data may be transmitted to the headset when a response when a phone number is dialed is notified by sound. 
     Alternatively, information definitively indicating various wireless access technology (e.g., 2G, 3G, 4G, 5G, Wi-Fi, GSM, CDMA, WCDMA, etc.) related to the call service. For example, For example, a bearer technology field having a size of 1 octet may be defined. This may be related to the aforementioned call bearer service. 
     In the case of multiway calling, a plurality of lines may exist, and a state machine as shown in  FIG. 17  may be maintained for each line. For example, when the second line transitions from the AUDIO STANDBY state to the CALL ACCEPTING state while the first line is in the CALL ACTIVE state, the first or the second line may transition to the CALL HELD state according to the user&#39;s control. 
     Hereinafter, logical links of Bluetooth system and logical transports will be described. 
     A variety of logical links may be used to support different application data transfer requirements. Each logical link is associated with a logical transport, which may have various characteristics. These characteristics may include flow control, acknowledgment/repeat mechanisms, sequence numbering and scheduling operations, and the like. A logical transport may carry various types of logical links depending on its type. A plurality of logical links may be multiplexed into the same single logical transport. A logical transport may be carried by a physical link on a particular channel. 
     Logical transport identification and real-time (link control) signaling may be included in the packet header, and specific logical link identification may be included in the header of the payload. 
     Table 5 below exemplarily illustrates logical transport types, supported logical link types, supported physical link and physical channel types, and descriptions of logical transports. 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 5 
               
               
                   
               
               
                 Logical 
                 Links 
                 Supported 
                   
                   
               
               
                 transport 
                 supported 
                 by 
                 Bearer 
                 Overview 
               
               
                   
               
             
            
               
                 Connection 
                 Stream 
                 LE 
                 LE 
                 Unidirectional or 
               
               
                 based 
                 (framed or 
                 isochronous 
                   
                 bidirectional 
               
               
                 Isochronous 
                 unframed) 
                 physical 
                   
                 transport in a 
               
               
                 Stream 
                 LE-S or 
                 link 
                   
                 point-to-point 
               
               
                   
                 LE-F 
                   
                   
                 connection for 
               
               
                   
                   
                   
                   
                 transferring 
               
               
                   
                   
                   
                   
                 isochronous data. 
               
               
                 Broadcast 
                 Stream 
                 LE 
                 LE 
                 Unidirectional 
               
               
                 Isochronous 
                 (framed or 
                 isochronous 
                   
                 transport for 
               
               
                 Stream 
                 unframed) 
                 physical 
                   
                 broadcasting data 
               
               
                   
                 LE-S (or 
                 link 
                   
                 in a point to 
               
               
                   
                 LE-F) and 
                   
                   
                 multipoint 
               
               
                   
                 Control 
                   
                   
                 configuration and 
               
               
                   
                 (LEB-C) 
                   
                   
                 unidirectional 
               
               
                   
                   
                   
                   
                 transport for 
               
               
                   
                   
                   
                   
                 controlling the 
               
               
                   
                   
                   
                   
                 broadcast data 
               
               
                   
               
            
           
         
       
     
       FIG. 18  is a diagram illustrating a packet format for each layer to which the present disclosure is applicable. 
       FIG. 18( a )  illustrates an example of link layer (LL) packet format. The LL packet format may include a preamble, an access address (or an access code), a PDU, and a Cyclic Redundancy Code (CRC) field. The preamble may have a size of 1 octet, may be used for frequency synchronization, symbol timing estimation, automatic gain control (AGC) training, and the like at the receiving side, and may be configured with a predetermined bit sequence. The access address may have a size of 4 octets and may be used as a correlation code for a physical channel. A PDU may be defined with a size of 2 to 39 octets in Bluetooth 4.0 version, and may be defined as a size of 2 to 257 octets in version 4.2. The CRC may include a value calculated as a 24-bit long checksum for the PDU. 
       FIG. 18( b )  illustrates an exemplary format of the PDU of  FIG. 18( a ) . PDU may be defined in two types, one is a data channel PDU (Data channel PDU), the other is an advertising channel PDU (Advertising channel PDU). The data channel PDU will be described in detail with reference to  FIG. 19 , and the advertising channel PDU will be described in detail with reference to  FIG. 20 . 
       FIG. 18( c )  illustrates an example of an L2CAP PDU format, which may correspond to an exemplary format of the payload field of  FIG. 18( b ) . The L2CAP PDU may include a Length, a Channel ID, and an Information Payload field. The length field may indicate the size of the information payload, and the information payload field may include higher layer data. The channel identifier field may indicate which upper layer data the information payload field includes. For example, if the value of the channel identifier field is 0x0004, it may indicate ATT (ATTribute protocol), if the value of the channel identifier field is 0x0004, it may indicate SMP (Security Manager Protocol), or another channel identifier indicating a different type of upper layer or middleware Values may be defined and used. 
     When the L2CAP packet of  FIG. 18( c )  is an L2CAP PDU (i.e., a control frame) transmitted on a signaling channel, the information payload field of  FIG. 18( c )  may be configured as shown in  FIG. 18( d ) . The information payload field may include a code (Code), an identifier (Identifier), a length (Length) and data (Data) fields. For example, the code field may indicate the type of the L2CAP signaling message. The identifier field may include a value that matches the request and the response. The length field may indicate the size of the data field. Data fields may contain attributes. An attribute is a unit of arbitrary data, and may include, for example, data at various points in time in various states of the device, such as location, size, weight, temperature, and speed. 
     An attribute may have a format including an attribute type, an attribute handle, an attribute value, and an attribute permission. 
     The attribute type may include a value indicating the type of attribute data identified by a Universally Unique Identifier (UUID). 
     An attribute handle may contain a value assigned by the server to identify attribute data. 
     The attribute value may include the value of attribute data. 
     Attribute permission may be configured by GATT (Generic ATTribute profile), and may include a value indicating the type of allowed access (e.g., whether it can read/write, whether encryption is required, whether authentication is required, whether authorization is required, etc.) to the corresponding attribute data. 
     In point of view of an Attribute protocol (ATT)/Generic Attribute Profile (GATT), a device may serve as a server and/or a client. The server may serve to provide attributes and related values, and the client may play a role of discovering, reading, or writing attributes on the server. 
     In ATT/GATT, it may support the transmission and reception of attribute data between the server and the client. For this, the PDU supported by the ATT protocol may include six method types, that is, request, response, command, notification, indication, and confirmation. 
     A request is sent from the client to the server, and a response from the server is required. A response is sent from the server to the client, and is sent when there is a request from the client. A command is sent from the client to the server, and no response is required. A notification is sent from the server to the client, and confirmation is not required. An indication is sent from the server to the client, and confirmation of the client is required. A confirmation is sent from the client to the server, and is sent when there is an instruction from the server. 
     In addition, GATT may support various profiles. The structure of the GATT-based profile may be described as a service (service) and characteristics (characteristics). A device may support one or more profiles. One profile may include zero or one or more services. A plurality of profiles may use the same service. One service may include one or more characteristics. A characteristic means a data value that is the subject of read, write, indicate, or notify. That is, a service may be understood as a data structure used to describe a specific function or feature, and a service that is a combination of characteristics may indicate an operation performed by a device. All services are implemented by the server and may be accessed by one or more clients. 
       FIG. 19  is a diagram illustrating examples of a data unit format to which the present disclosure is applicable. 
       FIG. 19( a )  illustrates an exemplary format of a data physical channel PDU (Protocol Data Unit). The data channel PDU may be used to transmit a packet on the data physical channel (e.g., channel number 0 to 36). The data physical channel PDU includes a 16 or 24 bit length header and a variable size (e.g., 0 to 251 octet size) payload, and may further include a Message Integrity Check (MIC) field. For example, the MIC field may be included in the case of an encrypted link layer connection in which the payload field size is not 0. 
     As shown in  FIG. 19( b ) , the header fields may include LLID (Logical Link Identifier), NESN (Next Expected Sequence Number), SN (Sequence Number), MD (More Data), CP (CTEInfo Present), RFU (Reserved). for Future Use). The RFU corresponds to a part reserved for future use when necessary, and its value may be usually filled with 0. Also, according to the value of the CP field, the header field may further include a Constant Tone Extension Information (CTEInfo) subfield. In addition, the Length field may indicate the size of the payload, and when the MIC is included, it may indicate the length of the payload and the MIC. 
       FIG. 19( c )  illustrates an exemplary format of an LL Control PDU. The LL Control PDU may correspond to a data physical channel PDU used to control link layer connection. The LL Control PDU may have a fixed value according to an operation code (Opcode). The Opcode field may indicate the type of the LL Control PDU. The control data (CtrData) field may have various formats and lengths specified by the Opcode. 
     For example, the Opcode of the LL Control PDU may have a value (e.g.,0x1F, 0x20, 0x21, 0x22, . . . ) indicating one of LL_CBIS_REQ, LL_CBIS_RSP, LL_CBIS_IND, LL_CBIS_TERMINATE_IND, LL_CBIS_SDU_CONFIG_REQ, and LL_CBIS_SDU_CONFIG_RSP. 
     When the opcode indicates LL_CBIS_REQ, the CtrData field may include information necessary for a CBIS request together with CBISS identification information and CBIS identification information. Similarly, in each case where the Opcode indicates one of LL_CBIS_RSP, LL_CBIS_IND, LL_CBIS_TERMINATE_IND, LL_CBIS_SDU_CONFIG_REQ, LL_CBIS_SDU_CONFIG_RSP, the CtrData may include information required for a CBIS response, a CBIS indication, a CBIS termination indication, a CBIS Service Data Unit (SDU) setup request, and a CBIS SDU setup response. 
       FIG. 19( d )  illustrates an example of audio data PDU format. Audio data PDU may be CBIS PUD or broadcast isochronous PDU. When used in a CBIS stream, the audio data PDU may be defined as CBIS PDU. When used in a broadcast isochronous PDU, the audio data PDU may be defined as broadcast isochronous PDU. 
     The audio data PDU may include a 16-bit length header field and a variable length payload field. Also, the audio data PDU may further include a MIC field. 
     In the case of a CBIS PDU, the format of the header field may include 2-bit LLID, 1-bit NESN, 1-bit SN, 1-bit Close Isochronous Event (CIE), 1-bit RFU, 1-bit Null PDU Indicator (NPI), 1-bit RFU, 9-bit Length subfield. 
     In the case of broadcast isochronous PUD, the format of the header field may include 2-bit LLID, 3-bit Control Subevent Sequence Number (CSSN), 1-bit Control Subevent Transmission Number (CSTF), 2-bit RFU, and 8-bit Length subfield. 
     The payload field of audio data PDU may include audio data. 
       FIG. 20  is a diagram illustrating examples of an advertisement unit format to which the present disclosure is applicable. 
       FIG. 20( a )  shows an exemplary format of an Advertising Physical Channel PDU (Protocol Data Unit). The advertising channel PDU may be used to transmit packets on an advertising physical channel (e.g., channel numbers 37, 38, 39). The advertising channel PDU may consist of a header of 2 octets and a payload of 6 to 37 octets. 
       FIG. 20( b )  shows an exemplary format of a header of an advertising channel PDU. The header may include a PDU type, a Reserved for Future Use (RFU), a transmission address (TxAdd), a reception address (RxAdd), a length (Length), and an RFU field. The length field of the header may indicate the size of the payload. 
       FIG. 20( c )  shows an exemplary format of a payload of an advertising channel PDU. The payload may include an Advertiser Address (AdvA) field with a length of 6 octets and an AdvData field with a length of 0 to 31 octets. The AdvA field may include a public address or a random address of the advertiser. The AdvData field may include zero or more advertising data (AD) structures, and padding if necessary. 
       FIG. 20( d )  shows a format of one AD structure. The AD structure may include three fields. A length field may indicate a length of a AD Data field. That is, a value obtained by subtracting 1 from the value indicated by the length field may correspond to the length of the AD Data field. The AD Type field may indicate a type of data included in the AD Data field. The AD Data field may include advertising data provided from a host of an advertiser. 
     Hereinafter, embodiments of an audio policy according to the present disclosure will be described. 
       FIG. 21  is a flowchart illustrating an audio policy-based audio data control method to which the present disclosure may be applied. 
     In step S 2110 , the first device may obtain an audio policy. The audio policy may include a priority. The priority may be assigned based on various units related to audio transmission/reception. The first device may generate, maintain, and manage the audio policy. Obtaining the audio policy by the first device may include determining a valid audio policy generated or modified and stored in the first device, and referencing the audio policy by the first device. 
     The first device may provide the audio policy to one or more second devices with or without a request. The first device may modify or update the audio policy at the request of one or more the second devices. The modified audio policy may be transmitted to the one or more second devices on a connection basis (e.g., in a unicast or multicast manner) or on a connectionless basis (e.g., in a broadcast manner). 
     Alternatively, one second device may receive or obtain the audio policy generated by the first device, modify the audio policy, and notify the modified audio policy to the first device and/or another second device. Alternatively, one second device may transmit information indicating the modified audio policy to the first device and/or another second device. In addition, the second device may or may not be allowed to modify the audio policy generated by the first device according to the preset authority. 
     In the step S 2120 , the first device may receive information on a plurality of audio streams from one or more second devices. The information about the audio stream may include various information such as a content type and a device type and the like. The information on the plurality of audio streams may be received from one second devices or may be received from different two second devices. 
     Information on the audio stream may be obtained through a discovery procedure or an ASS configuration procedure between the first device and one or more second devices. For example, information on the audio stream may be transmitted/received between the first device and one or more second devices in a STANDBY state or a CONFIGURED state. 
     In step S 2130 , the first device may select one or more audio streams from among the plurality of audio streams based on the information on the plurality of audio streams and the audio policy. 
     When the first device receives information on a plurality of audio streams, the first device may determine a priority of the corresponding audio streams based on an audio policy. When information on a plurality of audio streams having different priorities is received, the first device may select an audio stream having a relatively high priority based on an audio policy. 
     In step S 2140 , the first device may perform a setup procedure for the selected one or more audio stream. When the first device is an audio sink and the one or more second devices are audio sources, the one or more second device associated with the selected audio stream and the first device may perform an audio stream setup procedure, and the first device may receive the audio stream from the one ore more second device and may stream it. When the first device is an audio source and the one or more second device are audio sinks, the one or more second device associated with the selected audio stream and the first device may perform an audio stream setup procedure, and the first device may transmit the audio stream to the one or more second devices. 
     Here, the first device may be a policy server or server that generates, maintains, and manages policies, and the second device may be referred to as a policy client or client. 
     In addition, the plurality of audio streams associated with the one or more second devices may be audio streams transmitted on a connectionless basis (e.g., in a broadcast manner). 
       FIG. 22  is a diagram illustrating a device operation based on an audio policy to which the present disclosure is applicable. 
     In step S 2210 , a policy server may generate an audio policy. For example, the policy server may be a headset, the first policy client #1 may be a smartphone, and the second policy client #2 may be a TV. The policy server may generate an audio policy in which different priorities are given for each content type. Examples of audio policies may be defined as shown in Tables 6 and 7 below. 
     
       
         
           
               
               
               
             
               
                 TABLE 6 
               
               
                   
               
               
                   
                 Name 
                 Description 
               
               
                   
               
             
            
               
                   
                 Content type 
                 Content types supported by the server 
               
               
                   
                 Priority 
                 Priority of each content type 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
             
               
                 TABLE 7 
               
               
                   
               
               
                 Content type 
                 Description 
                 Priority 
               
               
                   
               
             
            
               
                 Ringtone 
                 Phone call 
                 1 
               
               
                 Alert 
                 Emergency alert (fire, etc.) 
                 2 
               
               
                 Voice with machine 
                 Speech recognition service 
                 3 
               
               
                 Media 
                 Media content such as music etc. 
                 4 
               
               
                   
               
            
           
         
       
     
     An example in Table 6 shows that the audio policy gives priority based on the content type. 
     An example in Table 7 shows that different priorities are given to detailed examples of content types. For example, Ringtone may have the highest priority, and Media may have the lowest priority. 
     In step S 2220 , the first and second clients may read the audio policy generated by the server. In step S 2222 , the first and second clients may apply the read audio policy. 
     As a further example, in step S 2224 , the first client may determine to modify the audio policy. Accordingly, in step S 2226 , the first client may transmit an audio policy writing request message to the server. This is an optional process and the client may not modify the audio policy. 
     When the audio policy is modified, the first client that requested the audio policy modification knows the modified audio policy, so in step S 2230  the server may notify the modified audio policy to other clients (i.e., the second client) except for the first client. Alternatively, the server may notify all available clients of the modified audio policy. 
     While the modified audio policy is being applied (that is, while the audio policy is valid), in step S 2240 , information on the first audio stream (Stream #1) may be transmitted from the first client to the server, and information on the second audio stream #2 (Stream #2) may be transmitted from the second client to the server. For example, the information on the first audio stream may include information related to the first priority (Priority #1). The information on the second audio stream may include information on the second priority (Priority #2). 
     Here, information on the priority may include information directly indicating a priority according to the audio policy, or/and may include information that is the basis of the priority according to the audio policy. For example, information on the priority may include a priority value configured by the client based on the content type of the audio stream. Alternatively, the information on the priority may correspond to information on the content type itself of each audio stream. Accordingly, the server may determine the priority value of the corresponding audio stream based on the content type information of the audio stream. 
     In step S 2250 , the server may select the first audio stream based on the information on the audio stream and the audio policy. For example, when it is determined that the first priority related to the first audio stream is higher that the second priority according to the audio policy, the server may select the first audio stream. 
     In step S 2260 , the server may request an audio stream setup for the selected first audio stream from the first client. 
     For example, it is assumed that a user is connecting a headset (i.e., the policy server) to two devices (i.e., a policy client) that are smartphone and TV. The audio policy of the headset may be informed to the smartphone and the TV. 
     If a phone call audio of the smartphone and an audio of the TV are in contention, the headset may compare priorities between the two based on the audio policy. In the audio policy, it is assumed that the TV audio has the fourth highest priority as a media content type, and that the phone call has the first highest priority as a ring tone content type. Accordingly, the headset may stream or play the phone call audio by performing audio stream setup with the smartphone, and the TV audio may not start streaming or playing. 
     Alternatively, while the user is playing the audio of the TV through the headset, a call may be received on the smartphone. In this case, the headset may stream or play the audio of the phone call having higher priority according to the audio policy, and stop streaming or playing the audio of the TV. 
     Alternatively, while the user is making a phone call with the smartphone through the headset, the audio of the TV may be received. In this case, the headset may continue audio streaming or playback of a phone call having a higher priority according to the audio policy, and may not start stream or play the TV audio. 
     In the above examples, it has been described that the audio policy is prioritized based on the content type, but the scope of the present disclosure is not limited thereto. 
     For example, the audio policy may give priority to one or a combination of two or more of a content, a device, a channel, a stream, a profile, a protocol, an audio location, an audio group, ASA, or ASS, which are various units related to audio transmission and reception. 
     As a specific example, the audio policy may give a priority to one or a combination of two or more of a content type, a device type, a channel ID, a stream ID, a profile type, a protocol type, an audio location ID, an audio group ID, a channel type (ICL or INCL), an ASA ID, or an ASS ID, 
     When the priority is given in consideration of a plurality of units, a first priority for the first unit may be defined, and a second priority for a second unit applied when the first priority is the same may be defined. Alternatively, the priority may be defined for a plurality of possible combinations of the first unit and the second unit. A similar method may be applied even when priority is given in consideration of three or more units. 
     For example, the first unit is a content type, and the second unit is the device type. Candidates for the content type may be Ringtone, Alert, Voice with machine, Media, Uncategorized Audio, System Sound, Satnav, and Call Audio. Candidates for the device type may be smartphones, doorbells, TVs, music players, radios, and gaming consoles. However, the scope of the present disclosure is not limited to the examples of the above-described content type candidates or device type candidates, and various content type candidates or various device type candidates may be defined and used. 
     In this case, the priority according to the content type may be primarily applied, and when the same priority of the same content type collides, the priority according to the device type may be secondarily applied. 
     For example, priorities may be defined for each device type as shown in Tables 8 and 9 below. If the content type of the emergency alert collides with an emergency notification-only device (e.g., a fire alarm) and a general-purpose device (e.g., a smartphone), since the same priority is given to content types according to the audio policies in Tables 6 and 7, it is unclear which content/device is to be streamed or played with priority. However, according to the audio policy in Tables 8 and 9, the same content type solves the problem of collision, so that a higher priority may be given to the fire alarm. 
     
       
         
           
               
               
               
             
               
                 TABLE 8 
               
               
                   
               
               
                   
                 Name 
                 Description 
               
               
                   
               
             
            
               
                   
                 Device type 
                 Device types supported by the server 
               
               
                   
                 Priority 
                 Priority of each content type 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
             
               
                 TABLE 9 
               
               
                   
               
               
                 Device type 
                 Description 
                 Priority 
               
               
                   
               
             
            
               
                 Type #1 
                 Dedicated device for emergency notification 
                 1 
               
               
                 Type #2 
                 Media specific device 
                 2 
               
               
                 Type #    3 
                 General-purpose device 
                 3 
               
               
                   
               
            
           
         
       
     
     Alternatively, the priority may be applied to various combinations of content type candidates and device type candidates. For example, the combination of Alert and Doorbell is given highest priority. And, the combination of Alert and Smartphone, the combination of Ringtone and Smartphone, the combination of System sound and Smartphone, the combination of Media and Smartphone, and the combination of Media and TV may be given priority in order. 
     In addition, it may be assumed that there are many clients that may modify the audio policy generated by the server. For example, when different clients modify the audio policy respectively, the last modified policy in time may be applied and the server may notify other clients of this. Alternatively, the right to modify the audio policy may be given to only one specific client. Alternatively, the level of permission for audio policy modification is given differently for each client, the audio policy modified by a client with a relatively high permission level may be applied preferentially, and the audio policy modified by a client with a relatively low permission level may be discarded or prohibited to be modified. 
     In addition, it may be assumed that a plurality of audio data received while the audio policy is applied have the same priority (e.g., the same content type). In this case, audio data whose reception is started earlier in time may be reproduced, and audio data whose reception is started later in time may not be reproduced. Alternatively, audio data whose reception started earlier in time may be stopped, and audio data whose reception started later in time may be reproduced. Alternatively, a plurality of audio data having the same priority may be reproduced simultaneously or in parallel. 
     In addition, a plurality of audio streams with different priorities may be streamed simultaneously. In this case, the volume of the high-priority audio stream may be configured higher and the volume of the low-priority audio stream may be configured lower. For example, when the first audio stream of the Media content type from the TV and the second audio stream of the Alert content type from the doorbell are in contention, the priority of the first audio stream may be given relatively lower than the priority of the second audio stream according to the audio policy. In this case, simultaneous streaming of the first and second audio streams may be supported by lowering the volume of the first audio stream and increasing the volume of the second audio stream. 
       FIG. 23  is a diagram illustrating a configuration of the first device and the second device to which the present disclosure may be applied. 
     The first device  2300  may include a processor  2310 , an antenna unit  2320 , a transceiver  2330 , and a memory  2340 . 
     The processor  2310  may perform baseband-related signal processing and may include a host processor  2311  and a controller processor  2315 . The host processor  2311  and the controller processor  2315  may exchange information through HCI. The host processor  2311  may process operations such as L2CAP, ATT, GATT, GAP, and LE profile layers. The controller processor  2315  may process operations such as LL and PHY layers. The processor  2310  may control the overall operation of the first device  2300  in addition to performing baseband-related signal processing. 
     Antenna unit  2320  may include one or more physical antennas. The transceiver  2330  may include RF (Radio Frequency) transmitter and RF receiver. The memory  2340  may store information processed by the processor  2310  and software, an operating system, and an application related to the operation of the first device  2300 , and may include components such as a buffer and the like. 
     The processor  2310  of the first device  2300  may be configured to implement an operation of the first device (or, the server) in the embodiments described in the present disclosure. 
     For example, the host processor  2311  of the processor  2310  of the first device  2300  may include an audio policy manager  2312 , an audio stream information manager  2313  and audio stream selector  2314 . 
     The audio policy manager  2312  may generate, maintain, and manage an audio policy comprising a priority configured for one or more of a content, a device, a channel, a stream, a profile, a protocol, an audio location, an audio group, an audio scene application, or an audio stream session, associated with the audio stream. For example, the generated or updated audio policy information may be stored in the memory  2340 , and may be obtained by the audio policy manager  2312  if necessary. 
     The audio stream information manager  2312  may generate, maintain, and manage information on an audio stream associated with one or more two devices. The information on the audio stream may include information on one or more of a content, a device, a channel, a stream, a profile, a protocol, an audio location, an audio group, an audio scene application, or an audio stream session, associated with the audio stream. 
     The audio stream selector  2314  may select one or more audio stream from among the plurality of audio streams based on the audio policy information managed by the audio policy manager  2312  and the audio stream information managed by the audio stream information manager  2313 . For example, the selection of the audio stream may be based on priority information of the audio stream. 
     For one or more audio streams selected by the first device  2300 , an audio setup procedure may be performed through the controller processor  2315 . With respect to the setup-completed audio stream, the first device  2300  may perform audio data streaming or reproduction, or the first device  2300  may encode the audio data and transmit the audio stream to one or more second devices  2350 . 
     The second device  2350  may include a processor  2360 , an antenna unit  2370 , transceiver  2380 , and a memory  2390 . 
     The processor  2360  may perform baseband-related signal processing and may include a host processor  2361  and a controller processor  2365 . The host processor  2361  and the controller processor  2365  may exchange information through HCI. The host processor  2361  may process operations such as L2CAP, ATT, GATT, GAP, and LE profile layers. The controller processor  2365  may process operations of the LL layer, the PHY layer, and the like. The processor  2360  may control the overall operation of the second device  2360  in addition to performing baseband-related signal processing. 
     The antenna unit  2370  may include one or more physical antennas. The transceiver  2380  may include an RF transmitter and an RF receiver. The memory  2390  may store information processed by the processor  2360  and software, an operating system, and an application related to the operation of the second device  2350 , and may include components such as a buffer and the like. 
     The processor  2360  of the second terminal device  2350  may be configured to implement the operation of the second device (or client) in the embodiments described in the present disclosure 
     For example, the host processor  2361  of the processor  2360  of the second device  2350  may include an audio policy manager  2362  and an audio stream information manager  2363 . 
     The audio policy manager  2362  may obtain audio policy information provided by a notification from the first device  2300  with or without a request from the second device  2350 . When it is necessary to modify the audio policy, the audio policy manager  2362  may generate an audio policy writing request message and transmit it to the first device  2350  through the controller processor  2365 . 
     The audio stream information manager  2363  may generate, maintain, and manage information on one or more audio streams associated with the second device  2350 . The information on the audio stream may include information on one or more of a content, a device, a channel, a stream, a profile, a protocol, an audio location, an audio group, an audio scene application, or an audio stream session associated with the audio stream. 
     For one or more audio streams selected by the first device  2300 , an audio setup procedure may be performed through the controller processor  2365  of the second device  2350  based on a setup request from the first device  2300 . The second device  2350  may perform audio data streaming or reproduction on the setup-completed audio stream, or the second device  2350  may encode the audio data and transmit the audio stream to the first device  2300 . 
     For an operation of the first device  2300  and the second device  2350 , in the examples of the present disclosure, the descriptions for the server and the client may be applied in the same manner, and overlapping descriptions will be omitted. 
     Various embodiments of the present disclosure may be implemented by hardware, firmware, software, or a combination thereof. For implementation by hardware, various embodiments of the present disclosure may be implemented one or more Application Specific Integrated Circuits (ASICs), Digital Signal Processors (DSPs), Digital Signal Processing Devices (DSPDs), Programmable Logic Devices (PLDs), Field Programmable Gate Arrays (FPGAs), general purpose It may be implemented by a processor (general processor), a controller, a microcontroller, a microprocessor, and the like. 
     The scope of the present disclosure includes software or machine-executable instructions (e.g., operating system, application, firmware, program, etc.) that cause operation according to the method of various embodiments to be executed on a device or computer, and a non-transitory computer-readable medium in which such software or instructions are stored and executed on a device or computer. Instructions that may be used to program a processing system to perform the features described in this present disclosure may be stored on/in a storage medium or computer-readable storage medium, and features described in the present disclosure may be implemented using a computer program product including such the storage medium. The storage medium may include, but is not limited to, a high-speed random access memory such as DRAM, SRAM, DDR RAM or other random access solid state memory device, one or more magnetic disk storage devices, optical disk storage devices, flash memory devices, or may include non-volatile memory such as other non-volatile solid state storage devices. The memory optionally includes one or more storage devices located remotely from the processor(s). The memory or alternatively the non-volatile memory device(s) within the memory includes a non-transitory computer-readable storage medium. Features described in this present disclosure may be stored on any one of the machine readable media to control hardware of the processing system, and it may be incorporated into software and/or firmware that allows the processing system to interact with other mechanisms that utilize results in accordance with embodiments of the present disclosure. Such software or firmware may include, but is not limited to, application codes, device drivers, operating systems, and execution environments/containers. 
     INDUSTRIAL APPLICABILITY 
     Embodiments of the present disclosure may be applied to various wireless communication systems to increase the performance of the wireless communication system.