Patent ID: 12192112

DETAILED DESCRIPTION OF THE INVENTION

Terms used in the specification adopt general terms which are currently widely used by considering functions in the present invention, but the terms may be changed depending on an intention of those skilled in the art, customs, and emergence of new technology. Further, in a specific case, there is a term arbitrarily selected by an applicant and in this case, a meaning thereof will be described in a corresponding description part of the invention. Accordingly, it should be revealed that a term used in the specification should be analyzed based on not just a name of the term but a substantial meaning of the term and contents throughout the specification.

Throughout this specification and the claims that follow, when it is described that an element is “coupled” to another element, the element may be “directly coupled” to the other element or “electrically coupled” to the other element through a third element. Further, unless explicitly described to the contrary, the word “comprise” and variations such as “comprises” or “comprising”, will be understood to imply the inclusion of stated elements but not the exclusion of any other elements. Moreover, limitations such as “or more” or “or less” based on a specific threshold may be appropriately substituted with “more than” or “less than”, respectively.

This application claims priority to and the benefit of Korean Patent Application Nos. 10-2015-0085451, 10-2015-0092534 and 10-2016-0059090 filed in the Korean Intellectual Property Office and the embodiments and mentioned items described in the respective application, which forms the basis of the priority, shall be included in the Detailed Description of the present application.

FIG.1is a diagram illustrating a wireless LAN system according to an embodiment of the present invention. The wireless LAN system includes one or more basic service sets (BSS) and the BSS represents a set of apparatuses which are successfully synchronized with each other to communicate with each other. In general, the BSS may be classified into an infrastructure BSS and an independent BSS (IBSS) andFIG.1illustrates the infrastructure BSS between them.

As illustrated inFIG.1, the infrastructure BSS (BSS1and BSS2) includes one or more stations STA1, STA2, STA3, STA4, and STA5, access points PCP/AP-1and PCP/AP-2which are stations providing a distribution service, and a distribution system (DS) connecting the multiple access points PCP/AP-1and PCP/AP-2.

The station (STA) is a predetermined device including medium access control (MAC) following a regulation of an IEEE 802.11 standard and a physical layer interface for a wireless medium, and includes both a non-access point (non-AP) station and an access point (AP) in a broad sense. Further, in the present specification, a term ‘terminal’ may be used to refer to a non-AP STA, or an AP, or to both terms. A station for wireless communication includes a processor and a transceiver and according to the embodiment, may further include a user interface unit and a display unit. The processor may generate a frame to be transmitted through a wireless network or process a frame received through the wireless network and besides, perform various processing for controlling the station. In addition, the transceiver is functionally connected with the processor and transmits and receives frames through the wireless network for the station.

The access point (AP) is an entity that provides access to the distribution system (DS) via wireless medium for the station associated therewith. In the infrastructure BSS, communication among non-AP stations is, in principle, performed via the AP, but when a direct link is configured, direct communication is enabled even among the non-AP stations. Meanwhile, in the present invention, the AP is used as a concept including a personal BSS coordination point (PCP) and may include concepts including a centralized controller, a base station (BS), a node-B, a base transceiver system (BTS), and a site controller in a broad sense. In the present invention, an AP may also be referred to as a base wireless communication terminal. The base wireless communication terminal may be used as a term which includes an AP, a base station, an eNB (i.e. eNodeB) and a transmission point (TP) in a broad sense. In addition, the base wireless communication terminal may include various types of wireless communication terminals that allocate medium resources and perform scheduling in communication with a plurality of wireless communication terminals.

A plurality of infrastructure BSSs may be connected with each other through the distribution system (DS). In this case, a plurality of BSSs connected through the distribution system is referred to as an extended service set (ESS).

FIG.2illustrates an independent BSS which is a wireless LAN system according to another embodiment of the present invention. In the embodiment ofFIG.2, duplicative description of parts, which are the same as or correspond to the embodiment ofFIG.1, will be omitted.

Since a BSS3illustrated inFIG.2is the independent BSS and does not include the AP, all stations STA6and STA7are not connected with the AP. The independent BSS is not permitted to access the distribution system and forms a self-contained network. In the independent BSS, the respective stations STA6and STA7may be directly connected with each other.

FIG.3is a block diagram illustrating a configuration of a station100according to an embodiment of the present invention.

As illustrated inFIG.3, the station100according to the embodiment of the present invention may include a processor110, a transceiver120, a user interface unit140, a display unit150, and a memory160.

First, the transceiver120transmits and receives a wireless signal such as a wireless LAN packet, or the like and may be embedded in the station100or provided as an exterior. According to the embodiment, the transceiver120may include at least one transmit/receive module using different frequency bands. For example, the transceiver120may include transmit/receive modules having different frequency bands such as 2.4 GHz, 5 GHz, and 60 GHz. According to an embodiment, the station100may include a transmit/receive module using a frequency band of 6 GHz or more and a transmit/receive module using a frequency band of 6 GHz or less. The respective transmit/receive modules may perform wireless communication with the AP or an external station according to a wireless LAN standard of a frequency band supported by the corresponding transmit/receive module. The transceiver120may operate only one transmit/receive module at a time or simultaneously operate multiple transmit/receive modules together according to the performance and requirements of the station100. When the station100includes a plurality of transmit/receive modules, each transmit/receive module may be implemented by independent elements or a plurality of modules may be integrated into one chip. In an embodiment of the present invention, the transceiver120may represent a radio frequency (RF) transceiver module for processing an RF signal.

Next, the user interface unit140includes various types of input/output means provided in the station100. That is, the user interface unit140may receive a user input by using various input means and the processor110may control the station100based on the received user input. Further, the user interface unit140may perform output based on a command of the processor110by using various output means.

Next, the display unit150outputs an image on a display screen. The display unit150may output various display objects such as contents executed by the processor110or a user interface based on a control command of the processor110, and the like. Further, the memory160stores a control program used in the station100and various resulting data. The control program may include an access program required for the station100to access the AP or the external station.

The processor110of the present invention may execute various commands or programs and process data in the station100. Further, the processor110may control the respective units of the station100and control data transmission/reception among the units. According to the embodiment of the present invention, the processor110may execute the program for accessing the AP stored in the memory160and receive a communication configuration message transmitted by the AP. Further, the processor110may read information on a priority condition of the station100included in the communication configuration message and request the access to the AP based on the information on the priority condition of the station100. The processor110of the present invention may represent a main control unit of the station100and according to the embodiment, the processor110may represent a control unit for individually controlling some component of the station100, for example, the transceiver120, and the like. That is, the processor110may be a modem or a modulator/demodulator for modulating and demodulating wireless signals transmitted to and received from the transceiver120. The processor110controls various operations of wireless signal transmission/reception of the station100according to the embodiment of the present invention. A detailed embodiment thereof will be described below.

The station100illustrated inFIG.3is a block diagram according to an embodiment of the present invention, where separate blocks are illustrated as logically distinguished elements of the device. Accordingly, the elements of the device may be mounted in a single chip or multiple chips depending on design of the device. For example, the processor110and the transceiver120may be implemented while being integrated into a single chip or implemented as a separate chip. Further, in the embodiment of the present invention, some components of the station100, for example, the user interface unit140and the display unit150may be optionally provided in the station100.

FIG.4is a block diagram illustrating a configuration of an AP200according to an embodiment of the present invention.

As illustrated inFIG.4, the AP200according to the embodiment of the present invention may include a processor210, a transceiver220, and a memory260. InFIG.4, among the components of the AP200, duplicative description of parts which are the same as or correspond to the components of the station100ofFIG.2will be omitted.

Referring toFIG.4, the AP200according to the present invention includes the transceiver220for operating the BSS in at least one frequency band. As described in the embodiment ofFIG.3, the transceiver220of the AP200may also include a plurality of transmit/receive modules using different frequency bands. That is, the AP200according to the embodiment of the present invention may include two or more transmit/receive modules among different frequency bands, for example, 2.4 GHz, 5 GHz, and 60 GHz together. Preferably, the AP200may include a transmit/receive module using a frequency band of 6 GHz or more and a transmit/receive module using a frequency band of 6 GHz or less. The respective transmit/receive modules may perform wireless communication with the station according to a wireless LAN standard of a frequency band supported by the corresponding transmit/receive module. The transceiver220may operate only one transmit/receive module at a time or simultaneously operate multiple transmit/receive modules together according to the performance and requirements of the AP200. In an embodiment of the present invention, the transceiver220may represent a radio frequency (RF) transceiver module for processing an RF signal.

Next, the memory260stores a control program used in the AP200and various resulting data. The control program may include an access program for managing the access of the station. Further, the processor210may control the respective units of the AP200and control data transmission/reception among the units. According to the embodiment of the present invention, the processor210may execute the program for accessing the station stored in the memory260and transmit communication configuration messages for one or more stations. In this case, the communication configuration messages may include information about access priority conditions of the respective stations. Further, the processor210performs an access configuration according to an access request of the station. According to an embodiment, the processor210may be a modem or a modulator/demodulator for modulating and demodulating wireless signals transmitted to and received from the transceiver220. The processor210controls various operations such as wireless signal transmission/reception of the AP200according to the embodiment of the present invention. A detailed embodiment thereof will be described below.

FIG.5is a diagram schematically illustrating a process in which a STA sets a link with an AP.

Referring toFIG.5, the link between the STA100and the AP200is set through three steps of scanning, authentication, and association in a broad way. First, the scanning step is a step in which the STA100obtains access information of BSS operated by the AP200. A method for performing the scanning includes a passive scanning method in which the AP200obtains information by using a beacon message (S101) which is periodically transmitted and an active scanning method in which the STA100transmits a probe request to the AP (S103) and obtains access information by receiving a probe response from the AP (S105).

The STA100that successfully receives wireless access information in the scanning step performs the authentication step by transmitting an authentication request (S107a) and receiving an authentication response from the AP200(S107b). After the authentication step is performed, the STA100performs the association step by transmitting an association request (S109a) and receiving an association response from the AP200(S109b). In this specification, an association basically means a wireless association, but the present invention is not limited thereto, and the association may include both the wireless association and a wired association in a broad sense.

Meanwhile, an 802.1X based authentication step (S111) and an IP address obtaining step (S113) through DHCP may be additionally performed. InFIG.5, the authentication server300is a server that processes 802.1X based authentication with the STA100and may be present in physical association with the AP200or present as a separate server.

FIG.6is a diagram illustrating a carrier sense multiple access (CSMA)/collision avoidance (CA) method used in wireless LAN communication.

A terminal that performs a wireless LAN communication checks whether a channel is busy by performing carrier sensing before transmitting data. When a wireless signal having a predetermined strength or more is sensed, it is determined that the corresponding channel is busy and the terminal delays the access to the corresponding channel. Such a process is referred to as clear channel assessment (CCA) and a level to decide whether the corresponding signal is sensed is referred to as a CCA threshold. When a wireless signal having the CCA threshold or more, which is received by the terminal, indicates the corresponding terminal as a receiver, the terminal processes the received wireless signal. Meanwhile, when a wireless signal is not sensed in the corresponding channel or a wireless signal having a strength smaller than the CCA threshold is sensed, it is determined that the channel is idle.

When it is determined that the channel is idle, each terminal having data to be transmitted performs a backoff procedure after an interframe space (IFS) time depending on a situation of each terminal, for instance, an arbitration IFS (AIFS), a PCF IFS (PIFS), or the like elapses. According to the embodiment, the AIFS may be used as a component which substitutes for the existing DCF IFS (DIFS). Each terminal stands by while decreasing slot time(s) as long as a random number assigned to the corresponding terminal during an interval of an idle state of the channel and a terminal that completely exhausts the slot time(s) attempts to access the corresponding channel. As such, an interval in which each terminal performs the backoff procedure is referred to as a contention window interval.

When a specific terminal successfully accesses the channel, the corresponding terminal may transmit data through the channel. However, when the terminal which attempts the access collides with another terminal, the terminals which collide with each other are assigned with new random numbers, respectively to perform the backoff procedure again. According to an embodiment, a random number newly assigned to each terminal may be decided within a range (2*CW) which is twice larger than a range (a contention window, CW) of a random number which the corresponding terminal is previously assigned. Meanwhile, each terminal attempts the access by performing the backoff procedure again in a next contention window interval and in this case, each terminal performs the backoff procedure from slot time(s) which remained in the previous contention window interval. By such a method, the respective terminals that perform the wireless LAN communication may avoid a mutual collision for a specific channel.

FIG.7is a diagram illustrating a method for performing a distributed coordination function using a request to send (RTS) frame and a clear to send (CTS) frame.

The AP and STAs in the BSS contend in order to obtain an authority for transmitting data. When data transmission at the previous step is completed, each terminal having data to be transmitted performs a backoff procedure while decreasing a backoff counter (alternatively, a backoff timer) of a random number assigned to each terminal after an AFIS time. A transmitting terminal in which the backoff counter expires transmits the request to send (RTS) frame to notify that corresponding terminal has data to transmit. According to an exemplary embodiment ofFIG.7, STA1which holds a lead in contention with minimum backoff may transmit the RTS frame after the backoff counter expires. The RTS frame includes information on a receiver address, a transmitter address, and duration. A receiving terminal (i.e., the AP inFIG.7) that receives the RTS frame transmits the clear to send (CTS) frame after waiting for a short IFS (SIFS) time to notify that the data transmission is available to the transmitting terminal STA1. The CTS frame includes the information on a receiver address and duration. In this case, the receiver address of the CTS frame may be set identically to a transmitter address of the RTS frame corresponding thereto, that is, an address of the transmitting terminal STA1.

The transmitting terminal STA1that receives the CTS frame transmits the data after a SIFS time. When the data transmission is completed, the receiving terminal AP transmits an acknowledgment (ACK) frame after a SIFS time to notify that the data transmission is completed. When the transmitting terminal receives the ACK frame within a predetermined time, the transmitting terminal regards that the data transmission is successful. However, when the transmitting terminal does not receive the ACK frame within the predetermined time, the transmitting terminal regards that the data transmission is failed. Meanwhile, adjacent terminals that receive at least one of the RTS frame and the CTS frame in the course of the transmission procedure set a network allocation vector (NAV) and do not perform data transmission until the set NAV is terminated. In this case, the NAV of each terminal may be set based on a duration field of the received RTS frame or CTS frame.

In the course of the aforementioned data transmission procedure, when the RTS frame or CTS frame of the terminals is not normally transferred to a target terminal (i.e., a terminal of the receiver address) due to a situation such as interference or a collision, a subsequent process is suspended. The transmitting terminal STA1that transmitted the RTS frame regards that the data transmission is unavailable and participates in a next contention by being assigned with a new random number. In this case, the newly assigned random number may be determined within a range (2*CW) twice larger than a previous predetermined random number range (a contention window, CW).

Uplink Multi-User Transmission

When using orthogonal frequency division multiple access (OFDMA) or multi-input multi-output (MIMO), one wireless communication terminal can simultaneously transmit data to a plurality of wireless communication terminals. Further, one wireless communication terminal can simultaneously receive data from a plurality of wireless communication terminals. For example, a downlink multi-user (DL-MU) transmission in which an AP simultaneously transmits data to a plurality of STAs, and an uplink multi-user (UL-MU) transmission in which a plurality of STAs simultaneously transmit data to the AP may be performed.

In order to perform the UL-MU transmission, the channel to be used and the transmission start time of each STA that performs uplink transmission should be adjusted. In order to efficiently schedule the UL-MU transmission, state information of each STA needs to be transmitted to the AP. According to an embodiment of the present invention, information for scheduling of a UL-MU transmission may be indicated through a predetermined field of a preamble of a packet and/or a predetermined field of a MAC header. For example, a STA may indicate information for UL-MU transmission scheduling through a predetermined field of a preamble or a MAC header of an uplink transmission packet, and may transmit the information to an AP. In this case, the information for UL-MU transmission scheduling includes at least one of buffer status information of each STA, channel state information measured by each STA. The buffer status information of the STA may indicate at least one of whether the STA has uplink data to be transmitted, the access category (AC) of the uplink data and the size (or the transmission time) of the uplink data.

According to an embodiment of the present invention, the UL-MU transmission process may be managed by the AP. The UL-MU transmission may be performed in response to a trigger frame transmitted by the AP. The STAs simultaneously transmit uplink data a predetermined IFS time after receiving the trigger frame. The trigger frame indicates the data transmission time point of the uplink STAs and may inform the channel (or subchannel) information allocated to the uplink STAs. When the AP transmits the trigger frame, a plurality of STAs transmit uplink data through the respective allocated subcarriers at a time point designated by the trigger frame. After the uplink data transmission is completed, the AP transmits an ACK to the STAs that have successfully transmitted the uplink data. In this case, the AP may transmit a predetermined multi-STA block ACK (M-BA) as an ACK for a plurality of STAs.

In the non-legacy wireless LAN system, a specific number, for example, 26, 52, or 106 tones may be used as a resource unit (RU) for a subchannel-based access in a channel of 20 MHz band. Accordingly, the trigger frame may indicate identification information of each STA participating in the UL-MU transmission and information of the allocated resource unit. The identification information of the STA includes at least one of an association ID (AID), a partial AID, and a MAC address of the STA. Further, the information of the resource unit includes the size and placement information of the resource unit.

On the other hand, in the non-legacy wireless LAN system, a UL-MU transmission may be performed based on a contention of a plurality of STAs for a particular resource unit. For example, if an AID field value for a particular resource unit is set to a specific value (e.g., 0) that is not assigned to STAs, a plurality of STAs may attempt random access (RA) for the corresponding resource unit.

FIGS.8and9illustrate an embodiment of an uplink multi-user transmission process of a non-legacy wireless LAN system.

First, referring toFIG.8, an AP transmits a trigger frame310for initiating a UL-MU transmission process. The AP may perform a separate backoff procedure for transmitting the trigger frame310. When the backoff procedure for transmitting the trigger frame310expires in the contention window interval42, the AP transmits the trigger frame310. STAs receive the trigger frame310transmitted by the AP and transmit uplink multi-user data320, that is, the uplink multi-user PLCP protocol data unit (UL MU PPPU) in response thereto. The uplink multi-user data320may be transmitted in a form including at least one of OFDMA and MU-MIMO. When the transmission of the uplink multi-user data320is successful, the AP transmits an M-BA330in response thereto. The M-BA330includes ACK information for STAs that have succeeded in transmitting the uplink multi-user data320. In the embodiment ofFIG.8, STA1, STA2, and STA3succeed in uplink data transmission in response to the trigger frame310, and the AP transmits ACK information for STA1, STA2, and STA3via the M-BA330.

After the UL-MU transmission process is completed, the AP obtains a new backoff counter for contention in the next contention window intervals44and46. In this case, the AP obtains a backoff counter within a contention window determined based on an access category of the next data to be transmitted. The AP contends with STAs based on the new backoff counter and accesses the channel. In the embodiment ofFIG.8, STA5has won the contention in the next contention window interval44of the UL-MU transmission process. Accordingly, the STA5transmits uplink data340to the AP, and the AP transmits an ACK346in response thereto. Also, in the next contention window interval46, the AP has won the contention. Accordingly, the AP transmits downlink data350to the STA2, and the STA2transmits an ACK356in response thereto.

FIG.9illustrates an embodiment in which a transmission of some uplink data has failed in the UL-MU transmission process. In the embodiment ofFIG.9, duplicated descriptions of parts which are the same or corresponding to those of the embodiment ofFIG.8will be omitted.

Referring toFIG.9, the AP transmits a TF-R312. In an embodiment of the present invention, the TF-R312represents a random access based trigger frame. That is, the TF-R312triggers an uplink multi-user data transmission by allocating some or all of the resources for random access. The AP may set an AID field value for a specific resource unit to a predetermined value (for example, 0), to allocate the corresponding resource unit for random access. When a backoff procedure for transmitting the TF-R312expires in the contention window interval42, the AP transmits the TF-R312. The STAs receive the TF-R312transmitted by the AP and transmit uplink multi-user data322in response thereto.

In this case, the uplink multi-user data322transmitted by the STAs may include random access uplink data. The STAs participating in the random access UL-MU transmission transmit uplink data through a resource unit allocated for random access by the TF-R312. Since the resource unit allocated for random access is not assigned to a specific STA, a plurality of STAs may transmit uplink data at the same time and a collision may occur. In the example ofFIG.9, STA2and STA4transmit uplink data through the same resource unit resulting in collision, and STA3and STA5transmit uplink data through the same resource unit resulting in collision. However, STA1has successfully transmitted uplink data to the AP. As described above, in the process of transmitting the uplink multi-user data322, a transmission of only some uplink data may be successful and a transmission of the remaining uplink data may have failed.

For efficient scheduling of the UL-MU transmission, various parameters to be used in a series of transmission processes should be determined. For example, the size of the contention window used in the backoff procedure for transmitting the trigger frame should be determined. Also, as described above, a criterion for determining whether or not the transmission of the uplink multi-user data322is successful should be established. In addition, the succeeding operation and the backoff method according to the success or failure determination should be defined.

According to the embodiment of the present invention, the AP may consider that the transmission process is successful even when a part of data is successfully transmitted in the transmission of the uplink multi-user data322. That is, when uplink data is received from at least one of the STAs indicated by the trigger frame, the AP determines that the UL-MU transmission process is successful. Thus, the AP transmits an M-BA330in response to receiving the uplink multi-user data322. In the embodiment ofFIG.9, STA1succeeds in uplink data transmission in response to the TF-R312, and the AP transmits ACK information for the STA1via the M-BA330. Meanwhile,FIG.9illustrates an embodiment including a random access based UL-MU transmission. However, the present invention is not limited thereto, and the success/failure determination method may be applied to other types of UL-MU transmission processes in the same way.

Since the UL-MU transmission process has been determined to be successful, the AP does not increase the size of the contention window to be used in the backoff procedures in the next contention window intervals44and46. That is, the AP obtains a new backoff counter within a contention window determined based on the access category of the next data to be transmitted, as in the embodiment ofFIG.8. The AP contends with the STAs based on the new backoff counter and accesses the channel.

FIGS.10to12illustrate various embodiments of channel access in a random access based uplink multi-user transmission process. More specifically, the embodiments ofFIGS.10to12illustrate a scheduling method when the AP does not receive any uplink data corresponding to the TF-R. According to the embodiment of the present invention, when the AP does not receive any uplink data corresponding to the trigger frame, it determines that the UL-MU transmission process has failed.

First, according to the embodiment ofFIG.10, the AP may perform retransmission of the TF-R312when the UL-MU transmission process by the TF-R312has failed. For retransmitting the TF-R312, the AP obtains a new backoff counter. In this case, the new backoff counter may be determined within a range of twice the contention window used in obtaining the previous backoff counter. That is, when the UL-MU transmission process has failed, the AP doubles the size of the contention window to be used in the backoff procedure of the next contention window intervals44and46. In the contention window intervals44and46, the AP performs a backoff procedure to retransmit the TF-R312based on the new backoff counter. The retransmission of the TF-R312may be performed until the retransmission is successful within a preset retransmission limit.

In the embodiment ofFIG.10, the UL-MU transmission procedure has failed and the next contention window interval44starts after an extended IFS (EIFS) time. The AP and STAs contend in the contention window interval44, and STA5wins the contention. Accordingly, the STA5transmits uplink data340to the AP, and the AP transmits an ACK346in response thereto. In the next contention window interval46, the AP wins the contention, and the AP retransmits the TF-R312. In response to the retransmission of the TF-R312, the STAs transmit uplink multi-user data323. In the embodiment ofFIG.10, STA1and STA3succeeded in the uplink data transmission in response to the retransmitted TF-R312. When uplink data is received from at least one STA in response to the TF-R312, the AP determines that the UL-MU transmission process is successful. Accordingly, the AP transmits ACK information for STA1and STA3via the M-BA330.

FIG.11illustrates an embodiment of a channel access according to another embodiment of the present invention. In the embodiment ofFIG.11, duplicated descriptions of parts which are the same or corresponding to those of the embodiment ofFIG.10will be omitted.

According to the embodiment ofFIG.11, the AP may increase the size of the contention window without performing retransmission of the TF-R312when the UL-MU transmission process by the TF-R312has failed. When the UL-MU transmission process has failed, the AP may attempt any one of a downlink single-user transmission, a downlink multi-user transmission, and a transmission of a new trigger frame in the next contention window interval. When attempting a downlink single-user transmission or a downlink multi-user transmission, the AP obtains a new backoff counter by doubling the size of the contention window based on the access category of data to be transmitted. When transmitting a new trigger frame, the AP obtains a new backoff counter by doubling the size of the existing contention window based on the access category for the trigger frame. The AP contends with the STAs based on the new backoff counter and accesses the channel.

In the embodiment ofFIG.11, the AP attempts to transmit the downlink multi-user data352after the failure of the UL-MU transmission process. That is, a downlink multi-user transmission interrupt (DL-MU interrupt) occurs, and the AP uses the next transmission opportunity for the downlink multi-user transmission. The UL-MU transmission process has failed and the next contention window interval44starts after an extended IFS (EIFS) time. The AP and STAs contend in the contention window interval44, and STA5wins the contention. Accordingly, the STA5transmits uplink data340to the AP, and the AP transmits an ACK346in response thereto. In the next contention window interval46, the AP wins the contention, and the AP transmits downlink multi-user data352. The STAs receiving the downlink data352from the AP transmit a multiplexed block ACK358in response thereto.

As described above, the AP performs a backoff procedure in the next contention intervals44and46based on a new backoff counter determined in the increased contention window, and transmits downlink multi-user data352when the backoff counter of the backoff procedure expires. In the embodiment ofFIG.11, the AP transmits the downlink multi-user data352after the failure of the UL-MU transmission process. However, the present invention is not limited thereto, and the AP may transmit downlink single-user data or a new trigger frame.

FIG.12illustrates an embodiment of a channel approach according to another embodiment of the present invention. In the embodiment ofFIG.12, duplicated descriptions of parts which are the same or corresponding to those of the embodiment ofFIGS.10and11will be omitted.

According to the embodiment ofFIG.12, when the UL-MU transmission process by the TF-R312has failed, the retransmission of the TF-R312may not be performed and the size of the contention window may not be increased. Due to the characteristic of random access, collisions may occur even in situations where traffic is not congested. Thus, uniformly increasing the size of a contention window may reduce the transmission efficiency. Therefore, when the random access based UL-MU transmission procedure has failed, the AP may attempt the next transmission without increasing the size of the contention window.

The AP may attempt any one of a downlink single-user transmission, a downlink multi-user transmission, and a transmission of a new trigger frame in the next contention window intervals44and46. When attempting a downlink single-user transmission or a downlink multi-user transmission, the AP obtains a new backoff counter within the contention window based on the access category of data to be transmitted. When transmitting a new trigger frame, the AP obtains a new backoff counter within the contention window based on the access category for the trigger frame. The AP contends with the STAs based on the new backoff counter and accesses the channel. The AP may obtain a new backoff counter without increasing the size of the contention window even though the previous UL-MU transmission process has failed.

In the embodiment ofFIG.12, the AP attempts to transmit downlink multi-user data352after the failure of the UL-MU transmission process. The AP and STAs contend in the contention window interval44, and the AP wins the contention. Thus, the AP transmits downlink multi-user data352and the STAs transmit a multiplexed block ACK358in response thereto. In the next contention window interval46, the STA5wins the contention, and the STA5transmits uplink data340. The AP receiving the uplink data340from the STA5transmits an ACK346in response thereto.

FIGS.13to15illustrate an embodiment in which the embodiments ofFIGS.10to12are extended to a general uplink multi-user transmission process. The trigger frame314indicates identification information of each STA participating in the UL-MU transmission and information of allocated resource units. In the embodiments ofFIGS.10to12, the trigger frame314solicits uplink multi-user data transmission of STA1, STA2and STA3. However, the AP does not receive any uplink data in response to the trigger frame314, and performs scheduling for the failure of the UL-MU transmission process. In the embodiments ofFIGS.13to15, duplicated descriptions of parts which are the same or corresponding to those of the embodiments ofFIGS.10to12will be omitted.

First, according to the embodiment ofFIG.13, the AP may perform retransmission of the trigger frame314when the UL-MU transmission process has failed. For the retransmission of the trigger frame314, the AP obtains a new backoff counter. In this case, the new backoff counter can be determined within a range of twice the contention window used in obtaining the previous backoff counter. That is, when the UL-MU transmission process has failed, the AP doubles the size of the contention window to be used in the backoff procedure of the next contention window intervals44and46. In the contention window intervals44and46, the AP performs a backoff procedure to retransmit the trigger frame314based on the new backoff counter. The retransmission of the trigger frame314may be performed until the retransmission is successful within the preset retransmission limit.

According to an embodiment of the present invention, the AP may select an access category for transmitting the trigger frame314. The size of the contention window for transmitting the trigger frame314is determined based on the selected access category. According to an embodiment of the present invention, a minimum contention window value, a maximum contention window value, an AIFS time, a maximum transmission opportunity (TXOP), and the like may be defined for each access category. Accordingly, the size of the contention window for transmitting the trigger frame314is determined between the minimum contention window value and the maximum contention window value set in the corresponding access category. According to an embodiment, an access category separately set for the trigger frame314may be used. According to another embodiment of the present invention, any one of the categories set for the enhanced distributed channel access (EDCA) may be selected as an access category for transmitting the trigger frame314.

In the embodiment ofFIG.13, the AP determines the size of the contention window based on the access category corresponding to the trigger frame314and assigns a backoff counter within the determined contention window. When the UL-MU transmission process has failed and the AP retransmits the trigger frame314, the AP increases the size of the contention window of the access category for the trigger frame314. According to an embodiment, the size of the increased contention window is determined within a range of twice the size of the previous contention window. A new backoff counter for retransmitting the trigger frame314is obtained within the increased contention window.

The AP and the STAs contend in the next contention window intervals44and46, and the terminal whose backoff counter has expired performs transmission. In this case, the AP participates in the contention using the new backoff counter. The AP that has won the contention in the contention window interval46retransmits the trigger frame314. In response to the retransmitted trigger frame314, STA1and ST3transmit uplink multi-user data323. Since uplink data has been received from at least one of the STAs indicated by the trigger frame314, the AP determines that the UL-MU transmission procedure is successful. Accordingly, the AP transmits ACK information for STA1and STA3via the M-BA330.

Next, according to the embodiment ofFIG.14, the AP may increase the size of the contention window without performing the retransmission of the trigger frame314when the UL-MU transmission process has failed. When the UL-MU transmission process has failed, the AP may attempt any one of a downlink single-user transmission, a downlink multi-user transmission, and a transmission of a new trigger frame in the next contention window interval. In this case, the AP may increase the contention window based on the access category of the packet to be transmitted. That is, when attempting a downlink single-user transmission or a downlink multi-user transmission, the AP obtains a new backoff counter by doubling the size of the contention window based on the access category of data to be transmitted. When transmitting a new trigger frame, the AP obtains a new backoff counter by doubling the size of the existing contention window based on the access category for the trigger frame. The AP uses the new backoff counter determined based on the increased contention window to contend with the STAs and access the channel.

In the embodiment ofFIG.14, the AP attempts to transmit the downlink multi-user data352after the failure of the UL-MU transmission process. According to an embodiment of the present invention, a separate access category for downlink multi-user transmission may be defined. In this case, the AP may obtain a new backoff counter by increasing the size of the contention window of the separate access category. According to another embodiment of the present invention, the downlink multi-user transmission may be performed based on a primary access category. In this case, the AP may obtain a new backoff counter by increasing the size of the contention window of the primary access category.

Next, according to the embodiment ofFIG.15, the AP may not retransmit the trigger frame314and may not increase the size of the contention window when the UL-MU transmission process fails. That is, when the UL-MU transmission process has failed, the AP may attempt the next transmission without increasing the size of the contention window.

The AP may attempt any one of a downlink single-user transmission, a downlink multi-user transmission, or a transmission of a new trigger frame in the next contention window intervals44and46. In this case, the AP may determine the contention window based on the access category of the packet to be transmitted. That is, when attempting a downlink single-user transmission or a downlink multi-user transmission, the AP obtains a new backoff counter within a contention window based on the access category of data to be transmitted. When transmitting a new trigger frame, the AP obtains a new backoff counter within the existing contention window based on the access category for the trigger frame. The AP contends with the STAs based on the new backoff counter and accesses the channel.

FIGS.16and17illustrate embodiments of channel access in an uplink multi-user transmission process using a wideband channel According to an embodiment of the present invention, the UL-MU transmission process may be performed through a wideband channel of 20 MHz or more. In the embodiments ofFIGS.16and17, the duplicated descriptions of parts which are the same or corresponding to those of the embodiments ofFIGS.10to15will be omitted.

In the embodiment ofFIGS.16and17, the AP transmits trigger frames314aand314bon the primary channel and the secondary channel to initiate the UL-MU transmission process. The AP may perform a backoff procedure on the primary channel for transmitting the trigger frames314a,314b. When the backoff procedure for transmitting the trigger frame314aexpires in the contention window interval42, the AP transmits the trigger frame314aon the primary channel. The AP performs a CCA for the secondary channel during a PIFS time before the expiration of the backoff procedure. When the secondary channel is in the idle state as a result of the CCA, the AP transmits the trigger frame314aof the primary channel and the trigger frame314bof the secondary channel together. In the embodiment ofFIGS.16and17, the trigger frame314aof the primary channel solicits uplink multi-user data transmission of STA1, STA2and STA3, and the trigger frame314bof the secondary channel solicits uplink multi-user transmission of STA4, STA5and STA6.

Referring toFIG.16, the AP does not receive any uplink data in response to the trigger frames314aand314btransmitted through the primary channel and the secondary channel, and performs scheduling for the failure of the UL-MU transmission process. According to the embodiment ofFIG.16, the AP may perform retransmission of the trigger frames314aand314b. For retransmitting the trigger frames314aand314b, the AP obtains a new backoff counter. A specific embodiment for obtaining the new backoff counter for retransmitting the trigger frames314aand314bis as described above in the embodiment ofFIG.13.

The AP and the STAs contend in the next contention window intervals44and46, and the terminal whose backoff counter has expired performs transmission. In this case, the AP participates in the contention using the aforementioned new backoff counter. The AP that has won the contention in the contention window interval46retransmits the trigger frames314aand314b. In response to the retransmitted trigger frames314aand314b, STA1and ST3transmit uplink multi-user data322aon the primary channel, and STA4, STA5and STA6transmit uplink multi-user data322bon the secondary channel. Since uplink data has been received from at least one of the STAs indicated by the trigger frames314aand314b, the AP determines that the UL-MU transmission process is successful. Accordingly, the AP transmits the M-BA330aand330bincluding ACK information for the five STAs that have successfully transmitted the uplink data.

Next, referring toFIG.17, the AP receives uplink data322cof STA4in response to the trigger frames314aand314btransmitted on the primary channel and the secondary channel. Since uplink data322chas been received from at least one of the STAs indicated by the trigger frames314aand314b, the AP determines that the UL-MU transmission process is successful. The AP transmits the M-BA330aand330bincluding ACK information for the STA4that has successfully transmitted the uplink data.

Since the UL-MU transmission process has been determined to be successful, the AP does not increase the size of the contention window to be used in the backoff procedure in the next contention window interval44. That is, the AP obtains a new backoff counter within the contention window determined based on the access category of the next data352aand352bto be transmitted. The AP contends with the STAs based on the new backoff counter and accesses the channel.

<An EDCA Method of a Multi-User Transmission>

FIG.18illustrates an embodiment of an enhanced distributed channel access (EDCA). Referring toFIG.18, data to be transmitted by a terminal is logically arranged in each access category queue according to a predetermined priority. The access category includes a voice access category (i.e., AC_VO), a video access category (i.e., AC_VI), a best effort access category (i.e., AC_BE) and a background access category (i.e., AC_BK). The terminal contends for channel access based on the parameters set for each access category. In this case, the parameters include a minimum contention window value, a maximum contention window value, an AIFS time, and a maximum TXOP.

Each access category performs internal contention based on the parameters of the access category when the corresponding queue is not empty. That is, a backoff counter is assigned to a corresponding access category based on the parameters of each access category, and internal contention between the access categories is performed based on the assigned backoff counters. The access category whose backoff counter expires first and has won the internal contention is set to the primary access category and data in the queue of the corresponding access category is determined as transmission data. According to an embodiment, in a multi-user transmission, data in a secondary access category may be transmitted with data in the primary access category using TXOP sharing.

In the embodiment ofFIG.18, data to be transmitted to STA2, STA4and SATS are stacked in the queue of AC_VO, and data to be transmitted to STA1and STA3are stacked in the queue of AC_VI. In addition, data to be transmitted to STA2and STA3are stacked in the queue of AC_BE. Therefore, AC_VO, AC_VI and AC_BE perform internal contention using the respective parameters. Hereinafter, in the embodiments ofFIGS.19to24, it is assumed that AC_VI is set as a primary access category and AC_VO and AC_BE are set as a secondary access category as a result of the internal contention.

FIG.19illustrates an embodiment of a downlink multi-user transmission process. In the embodiment ofFIG.19, the AP is a multi-user transmitting terminal, and the STA, STA2, STA3and STA4are multi-user receiving terminals.

The AP may perform a downlink multi-user data transmission when a downlink multi-user (DL-MU) interrupts occur. In the embodiment of the present invention, the DL-MU interrupt indicates an operation in which a predetermined condition for DL-MU data transmission is satisfied, and a multi-user transmitting terminal determines transmission of DL-MU data. The predetermined condition for the DL-MU interrupt to occur includes a case that data to be transmitted to a plurality of STAs is stacked a predetermined size or more in an access category queue, a case that a predetermined time or more has elapsed after data to be transmitted to a plurality of STAs is stacked in an access category queue, and the like. According to an embodiment of the present invention, the AP may generate a separate virtual queue for the DL-MU transmission. In this case, DL-MU interrupts may occur when data of a predetermined size or more is stacked in the virtual queue.

When a DL-MU interrupt occurs, the AP performs a backoff procedure in the contention window interval52for transmitting the downlink multi-user data420. For the backoff procedure to transmit downlink multi-user data420, the AP assigns a backoff counter. According to an embodiment, the AP may determine a contention window based on an access category separately set for DL-MU transmission and assign a backoff counter within the contention window. According to another embodiment, the AP may determine a contention window based on the primary access category of the downlink multi-user data420to be transmitted and may assign a backoff counter within the contention window. The AP performs the backoff procedure in the contention window interval52using the assigned backoff counter after an AIFS time of the set access category.

When the backoff counter of the backoff procedure for transmitting the downlink multi-user data420expires in the contention window interval52, the AP transmits downlink multi-user data420. The downlink multi-user data420may be transmitted in a form including at least one of OFDMA and MU-MIMO. The STAs receive downlink multi-user data420transmitted by the AP and transmit ACK430in response thereto. In the embodiment ofFIG.19, the AP transmits downlink multi-user data420to STA1, STA2, STA3and STA4, and each STA transmits ACK430in response to the reception of the downlink multi-user data420. The ACK430transmitted by a plurality of STAs may be transmitted by being multiplexed in a time domain or a frequency domain.

After the DL-MU transmission process is completed, the AP may perform additional data transmission in the next contention window intervals54and56. If a new DL-MU interrupt does not occur, the AP performs a transmission of downlink single-user data440. In this case, downlink data440of an access category that has obtained the transmission opportunity through internal contention between access category queues of the AP may be transmitted. In the embodiment ofFIG.19, AC_VO has won the internal contention of the AP. The AP transmits the downlink data440of AC_VO to the STA5after a backoff procedure in the contention window interval54. The STA5receives the downlink data440and transmits an ACK445in response thereto.

Thereafter, when the DL-MU interrupt occurs again, the AP performs a backoff procedure for transmitting the downlink multi-user data450in the contention window interval56. When the backoff counter of the backoff procedure expires, the AP transmits downlink multi-user data450. The AP transmits downlink multi-user data450to STA2and STA3, and each STA transmits ACK455in response to the reception of the downlink multi-user data450.

FIGS.20to22illustrate a channel access method when a transmission of some data has failed in the downlink multi-user transmission process. In the embodiment ofFIGS.20to22, the AP transmits downlink multi-user data420to STA1through STA4. However, some downlink data, i.e., downlink data of AC_BE to STA2, has failed to be transmitted. STA1to STA4transmit an ACK432in response to the successfully received downlink data. In each of the embodiments ofFIGS.20to22, duplicated descriptions of parts which are the same or corresponding to those of the previous embodiments will be omitted.

First, referring toFIG.20, the AP considers that the transmission process is successful even when a part of data is successfully transmitted in the transmission of downlink multi-user data420. That is, when the ACK432is received from at least one STA among the STAs to which the downlink multi-user data420is transmitted, the AP determines that the DL-MU transmission process is successful. On the other hand, the AP may attempt to retransmit some downlink data that has failed to be transmitted. According to an embodiment, the AP may retransmit downlink data that has failed to be transmitted through internal contention. The downlink data that has failed to be transmitted contend for transmission in the access category queue of the corresponding data. In the embodiment ofFIG.20, the downlink data441of the AC_BE that has failed to be transmitted in the first DL-MU transmission process is retransmitted through the internal contention of the AP in the next contention window interval54. STA2receives downlink data441and transmits ACK446in response thereto.

Next, according to the embodiment ofFIG.21, when a transmission of some data has failed in the transmission of the downlink multi-user data420, the AP increases the size of the contention window of the access category of the corresponding data. According to an embodiment, the size of the contention window of the access category may be increased to twice the size of the previous contention window. By thus increasing the size of the contention window of the access category, a penalty may be added to the contention when retransmitting the downlink data that has failed to be transmitted. This penalty for the transmission contention may be only applied to the internal contention of the AP. That is, the AP does not increase the sizes of the contention windows of the access categories other than the access category of the downlink data to be retransmitted.

Referring to the embodiment ofFIG.21, in the first DL-MU transmission process, transmission of downlink data of AC_BE has failed. Thus, the AP increases the size of the contention window of AC_BE. AC_BE obtains a new backoff counter within the increased contention window and participates in the internal contention using the new backoff counter. In the next contention window interval54, AC_VO has won the internal contention of the AP. The AP transmits the downlink data440of AC_VO to the STA5after a backoff procedure in the contention window interval54. The STA5receives the downlink data440and transmits an ACK445in response thereto.

After the transmission of downlink data440, a DL-MU interrupt occurs and the AP performs a backoff procedure for transmitting downlink multi-user data452in the contention window interval56. When the backoff counter of the backoff procedure expires, the AP transmits the downlink multi-user data452. The data of AC_BE that has received a new backoff counter and has contended for transmission is transmitted as downlink multi-user data452. The STAs receiving the downlink multi-user data452from the AP transmit an ACK457in response thereto.

Next, according to the embodiment ofFIG.22, when a transmission of some data has failed in the transmission of downlink multi-user data420, the AP decreases the size of the contention window of the access category of the corresponding data. According to an embodiment, the size of the contention window of the access category may be set to the minimum contention window value of the corresponding access category. According to another embodiment, the size of the contention window of the access category may be reduced to a certain percentage value of the size of the previous contention window. By thus decreasing the size of the contention window of the access category, a priority may be added to the contention when retransmitting the downlink data that has failed to be transmitted.

Referring to the embodiment ofFIG.22, the AP decreases the size of the contention window of AC_BE in which the transmission has failed in the first DL-MU transmission process. AC_BE obtains a new backoff counter within the reduced contention window and participates in the internal contention using the new backoff counter. As a result, AC_BE has won the internal contention of the AP in the next contention window interval54. The AP retransmits the downlink data441of AC_BE to the STA2after a backoff procedure in the contention window interval54. The STA2receives the downlink data441and transmits an ACK446in response thereto.

On the other hand, according to an additional embodiment of the present invention, the size of the contention window of the access category that has failed in transmission can be variously adjusted. For example, the increase or decrease ratio of the size of the contention window may be adjusted according to the number of users or the size of channel that has failed in transmission in the previous DL-MU transmission process.

FIGS.23and24illustrate a channel access method when a data transmission of a primary access category has failed in the downlink multi-user transmission process. In the embodiment ofFIGS.23and24, the AP transmits downlink multi-user data420to STA1through STA4. However, some downlink data, i.e., downlink data of AC_VI to STA1, has failed to be transmitted. In this case, the AC_VI is the primary access category of the downlink multi-user data420. STA2to STA4transmit an ACK434in response to the successfully received downlink data. In each of the embodiments ofFIGS.23and24, duplicated descriptions of parts which are the same or corresponding to those of the previous embodiments will be omitted.

According to an embodiment of the present invention, the EDCA of the downlink multi-user data420may be performed based on the primary access category of the corresponding data. That is, the AP determines a contention window based on the primary access category of the downlink multi-user data420and assigns a backoff counter within the contention window. The AP performs a backoff procedure in the contention window interval52using the assigned backoff counter after an AIFS time of the set access category.

In addition, success of the transmission of the downlink multi-user data420may be determined based on whether or not the primary access category data is successfully transmitted. That is, when the transmission of the primary access category data among the downlink multi-user data420is successful, the AP determines that the DL-MU transmission process is successful. However, when the transmission of the primary access category data among the downlink multi-user data420has failed, the AP determines that the DL-MU transmission process has failed. The AP performs retransmission of the primary access category data that has failed to be transmitted. When a DL-MU interrupt occurs during the retransmission, the AP may transmit the primary access category data along with other data remaining in the queue via DL-MU.

Referring toFIG.23, the AP determines a contention window of a primary access category AC_VI whose transmission has failed based on the parameters of the corresponding access category and attempts a retransmission by assigning a new backoff counter. In the next contention window interval54, the primary access category AC_VI wins the contention, and the AP retransmits the downlink data441of the primary access category AC_VI to the STA1. The STA1receives the downlink data441and transmits an ACK446in response thereto.

On the other hand, referring toFIG.24, the AP may increase the size of the contention window due to the failure of the DL-MU transmission process. According to an embodiment, the AP may increase the size of the contention window of the primary access category AC_VI whose transmission has failed. According to another embodiment, the AP may increase the sizes of the contention windows of the entire access categories. The AP obtains a new backoff counter within the increased contention window and performs retransmission of the downlink data441of the primary access category AC_VI using the new backoff counter.

Meanwhile, according to another exemplary embodiment of the present invention, a contention window may be determined based on an access category separately set for a DL-MU transmission, and a transmission of downlink multi-user data420may be performed by assigning a backoff counter within the corresponding contention window. However, success of the transmission of the downlink multi-user data420may be determined based on whether or not the primary access category data has been successfully transmitted. In this case, the AP may perform retransmission of the downlink data441of the primary access category based on the parameters of the access category separately set for the DL-MU transmission.

FIGS.25and26illustrate an embodiment of an EDCA including a multi-user transmission. According to an embodiment of the present invention, the access category queue for EDCA may further comprise an access category queue for multi-user transmission. In this case, the access category queue for the multi-user transmission includes at least one of a queue for a multi-user downlink transmission and a queue for transmitting a trigger frame. According to an embodiment, the queue for the multi-user transmission may be operated as a virtual queue.

Referring toFIG.25, the AP inserts a virtual frame into an access category AC_MU queue for the multi-user transmission. The AP determines the size of the contention window of the access category based on the parameters of AC_MU. According to an embodiment, the AC_MU may have a higher priority than the access categories of data to be transmitted to another STA. For example, the AC_MU may be set to have a higher priority than other access categories where the queue is not empty. The parameters of AC_MU are determined based on the set priority. According to another embodiment of the present invention, the parameters of AC_MU may use parameters of a particular access category selected from other access categories. For example, the parameters of AC_MU may be set equal to parameters of the highest priority access category among the other access categories where the queue is not empty. The AC_MU may use one of the access categories used in the legacy WLAN system equally. According to an embodiment, the parameters of the AC_MU may be set equal to the parameters of AC_VO or AC_VI to assign a priority to the UL-MU transmission. As described above, the parameters of the access category include at least one of a minimum contention window value, a maximum contention window value, an AIFS time, and a maximum TXOP.

According to still another embodiment of the present invention, the AP may adjust the parameters of AC_MU to adjust the priority of a frame of the corresponding queue in the internal contention. When the multi-user transmission is performed with the highest priority such as the DL_MU interrupt, the AP may set the contention window value of the AC_MU to zero. However, when multi-user transmission is not performed, the AP may set the minimum contention window value or the contention window value of the AC_MU to the maximum value of the system. The AP may adjust the parameters of AC_MU based on the system status or the state of the AC_MU queue.

Referring toFIG.26, the AP receives the buffer status report (BSR) of STAs and generates an AC_MU queue using the received buffer status report. According to an embodiment of the present invention, the AC_MU includes an access category for transmitting a trigger frame. The AP may perform a backoff procedure for transmitting the trigger frame when the received buffer status report information is a predetermined amount or more. In this case, the AP determines the size of the contention window based on the parameters of the AC_MU and obtains a backoff counter for transmitting the trigger frame within the determined contention window.

According to the embodiment ofFIG.26, the AP determines whether to transmit a trigger frame based on an internal contention between access category queues for a downlink single-user transmission and an AC_MU queue. More specifically, the access category queues for the downlink single-user transmission includes an AC_VO queue, an AC_VI queue, an AC_BE queue, and an AC_BK queue used in a legacy WLAN system. The AP assigns backoff counters corresponding to the access category queues and the AC_MU queue, respectively. In this case, the backoff counters are assigned based on the parameters of the access category set in the corresponding queue, respectively. The AP may transmit a trigger frame when the backoff counter corresponding to the AC_MU queue expires. As described above, according to the embodiment of the present invention, the AC_MU may have a higher priority than the access categories of data to be transmitted to another STA. Thus, the trigger frame may be transmitted with a higher priority than the frame of the other access categories.

Although the present invention is described by using the wireless LAN communication as an example, the present invention is not limited thereto and the present invention may be similarly applied even to other communication systems such as cellular communication, and the like. Further, the method, the apparatus, and the system of the present invention are described in association with the specific embodiments, but some or all of the components and operations of the present invention may be implemented by using a computer system having universal hardware architecture.

The detailed described embodiments of the present invention may be implemented by various means. For example, the embodiments of the present invention may be implemented by a hardware, a firmware, a software, or a combination thereof.

In case of the hardware implementation, the method according to the embodiments of the present invention may be implemented by one or more of Application Specific Integrated Circuits (ASICSs), Digital Signal Processors (DSPs), Digital Signal Processing Devices (DSPDs), Programmable Logic Devices (PLDs), Field Programmable Gate Arrays (FPGAs), processors, controllers, micro-controllers, micro-processors, and the like.

In case of the firmware implementation or the software implementation, the method according to the embodiments of the present invention may be implemented by a module, a procedure, a function, or the like which performs the operations described above. Software codes may be stored in a memory and operated by a processor. The processor may be equipped with the memory internally or externally and the memory may exchange data with the processor by various publicly known means.

The description of the present invention is used for exemplification and those skilled in the art will be able to understand that the present invention can be easily modified to other detailed forms without changing the technical idea or an essential feature thereof. Thus, it is to be appreciated that the embodiments described above are intended to be illustrative in every sense, and not restrictive. For example, each component described as a single type may be implemented to be distributed and similarly, components described to be distributed may also be implemented in an associated form.

The scope of the present invention is represented by the claims to be described below rather than the detailed description, and it is to be interpreted that the meaning and scope of the claims and all the changes or modified forms derived from the equivalents thereof come within the scope of the present invention.

INDUSTRIAL APPLICABILITY

Various exemplary embodiments of the present invention have been described with reference to an IEEE 802.11 system, but the present invention is not limited thereto and the present invention can be applied to various types of mobile communication apparatus, mobile communication system, and the like.