Method and device for transmitting and receiving data in wireless lan system

TECHNICAL FIELD

0001The present invention generally relates to data transmission/reception technology in a wireless local area network (WLAN) system and, more particularly, to a method and device for transmitting and receiving data to and from an end terminal in a WLAN system including a relay device.

BACKGROUND ART

0002With the development of information and communication technology, various wireless communication technologies have been developed. Among these technologies, a wireless local area network (WLAN) denotes technology for allowing wireless access to the Internet in homes, businesses or specific service areas using a mobile terminal such as a personal digital assistant (PDA), a laptop computer, a portable multimedia player (PMP), a smart phone, or a tablet PC, based on radio frequency (RF) technology.

0003Standards for WLAN technology have been developed as Institute of Electrical and Electronics Engineers (IEEE) 802.11 standards. WLAN technology conforming to the IEEE 802.11a standard is operated based on an orthogonal frequency division multiplexing (OFDM) scheme, and is capable of providing a maximum data rate of 54 Mbps in a 5 GHz band. WLAN technology conforming to the IEEE 802.11b standard is operated based on a direct sequence spread spectrum (DSSS) scheme, and is capable of providing a maximum data rate of 11 Mbps in a 2.4 GHz band. WLAN technology conforming to the IEEE 802.11g standard is operated based on the OFDM or DSSS scheme, and is capable of providing a maximum data rate of 54 Mbps in a 2.4 GHz band.

0004WLAN technology conforming to the IEEE 802.11n standard is operated based on the OFDM scheme in a 2.4 GHz band and a 5 GHz band, and is capable of providing a maximum data rate of 300 Mbps for four spatial streams when a Multiple-Input Multiple-Output OFDM (MIMO-OFDM) scheme is used. WLAN technology conforming to the IEEE 802.11n standard may support a channel bandwidth of up to 40 MHz and is capable of providing a maximum data rate of 600 Mbps in that case.

0005As the popularization of such WLAN technology has been activated and applications using WLANs have been diversified, the requirement for new WLAN technology that supports throughput higher than that of existing WLAN technology is increasing. Very high throughput (VHT) WLAN technology is proposed technology that supports a data rate of 1 Gbps or more. Meanwhile, in a system based on such WLAN technology, a problem arises in that, as the distance between WLAN devices increases, communication efficiency is deteriorated.

DISCLOSURE

Technical Problem

0006An object of the present invention to solve the above problems is to provide a data transmission/reception method for improving the efficiency of a WLAN system.

0007Another object of the present invention to solve the above problems is to provide a data transmission/reception device for improving the efficiency of a WLAN system.

Technical Solution

0008In accordance with an embodiment of the present invention to accomplish the above objects, an association method that is performed by a terminal includes transmitting a probe request frame, receiving a probe response frame that is a response to the probe request frame from a master access point, and transmitting an acknowledgement (ACK) frame that is a response to the probe response frame to a relay device associated with the master access point when it is determined that an operation is performed in an uplink relay mode, based on information included in the probe response frame.

0009Here, the association method may further include transmitting an authentication request frame to the relay device, and receiving an authentication response frame that is a response to the authentication request frame from the master access point.

0010Here, the association method may further include transmitting an association request frame to the relay device, and receiving an association response frame that is a response to the association request frame from the master access point.

0011Here, the probe request frame may include a field indicating whether a relevant frame is a frame transmitted in a relay manner.

0012Here, the probe request frame may be transmitted to the master access point through the relay device.

0013Here, the probe response frame may include at least one of a field indicating whether an operation is performed in an uplink relay mode, and an identifier of the relay device.

0014Here, the authentication request frame may be transmitted to the master access point through the relay device.

0015Here, the association request frame may be transmitted to the master access point through the relay device.

0016Here, the association response frame may include a field indicating whether the terminal has been associated with the master access point in an uplink relay mode.

0017In accordance with another embodiment of the present invention to accomplish the above objects, an association method that is performed by a master access point includes receiving a probe request frame from a relay device associated with the master access point, transmitting a probe response frame, as a response to the probe request frame, to a terminal, the probe response frame including information indicating whether an operation is performed in an uplink relay mode, and receiving an ACK frame that is a response to the probe response frame from the relay device.

0018Here, the association method may further include receiving an authentication request frame from the relay device, and transmitting an authentication response frame that is a response to the authentication request frame to the terminal.

0019Here, the association method may further include receiving an association request frame from the relay device, and transmitting an association response frame that is a response to the association request frame to the terminal.

0020Here, the probe request frame may include a field indicating whether a relevant frame is a frame transmitted in a relay manner.

0021Here, the probe response frame may include at least one of a field indicating whether an operation is performed in an uplink relay mode, and an identifier of the relay device.

0022Here, the association response frame may include a field indicating whether the terminal has been associated with the master access point in an uplink relay mode.

0023In accordance with a further embodiment of the present invention to accomplish the above objects, an association method that is performed by a relay device includes receiving a probe request frame from a terminal, and transmitting the probe request frame to the master access point when the probe request frame is a frame transmitted in a relay manner.

0024Here, the probe request frame may include a field indicating whether a relevant frame is a frame transmitted in a relay manner.

0025Here, the probe request frame may include an SSID filed that may be set to an SSID of the master access point or any value.

0026In accordance with yet another embodiment of the present invention to accomplish the above objects, a data reception method that is performed by a terminal associated with a relay device, including receiving a beacon frame from a master access point associated with the relay device, transmitting a power save (PS)-Poll frame to the relay device when it is determined, based on the beacon frame, that data to be transmitted to the terminal is present in the master access point, receiving a data frame that is a response to the PS-Poll frame from the master access point, and transmitting an ACK frame that is a response to the data frame to the relay device.

0027Here, the terminal may belong to a master-basic service set formed by the master access point and a relay-basic service set formed by the relay device.

0028Here, a certain frame transmitted from the terminal may include information indicating a type of a frame transmitted from a communication entity that has received the certain frame.

0029Here, the PS-Poll frame may be transmitted to the master access point through the relay device.

0030Here, the PS-Poll may include an SIG field that includes information indicating that, after the PS-Poll frame, a null data packet (NDP) response is to be transmitted.

0031Here, the data frame may include a SIG field that includes information indicating that, after the data frame, a normal response is to be transmitted.

0032Here, the data frame may include a duration field in which a period required to protect transmission of at least two ACK frames is set.

0033Here, the ACK frame may be transmitted to the master access point through the relay device.

0034Here, the ACK frame may include a SIG field that includes information indicating that, after the ACK frame, a normal response is to be transmitted.

0035In accordance with still another embodiment of the present invention to accomplish the above objects, a data transmission method that is performed by a master access point associated with a relay device includes transmitting a beacon frame indicating that data to be transmitted to a terminal associated with the relay device is present, receiving a PS-Poll frame from the relay device, and transmitting a data frame to the terminal when it is determined, based on the PS-Poll frame, that the terminal is in a state in which data can be received.

0036Here, the data transmission method may further include receiving an ACK frame that is a response to the data frame from the relay device.

0037Here, the data transmission method may further include retransmitting the data frame to the terminal when an ACK frame that is a response to the data frame is not received from the relay device within a preset relay ACK timeout.

0038Here, the relay ACK timeout may be designated to be longer than ‘SIFS+RX_start_delay+slot time’.

0039Here, the terminal may belong to a master-basic service set formed by the master access point and a relay-basic service set formed by the relay device.

0040Here, the data frame may include a duration field in which a period required to protect transmission of at least two ACK frames is set.

Advantageous Effects

0041In accordance with the present invention, the wireless transmission efficiency of a WLAN system can be improved.

DESCRIPTION OF DRAWINGS

0042<figref idref="DRAWINGS">FIG. 1</figref> is a block diagram showing an embodiment of a station for performing methods according to the present invention;

0043<figref idref="DRAWINGS">FIG. 2</figref> is a conceptual diagram showing an embodiment of the configuration of a WLAN system conforming to IEEE 802.11;

0044<figref idref="DRAWINGS">FIG. 3</figref> is a flowchart showing a terminal association procedure in an infrastructure BSS;

0045<figref idref="DRAWINGS">FIG. 4</figref> is a conceptual diagram showing the infrastructure BSS of a WLAN system;

0046<figref idref="DRAWINGS">FIG. 5</figref> is a block diagram showing an embodiment of a hierarchical AID structure;

0047<figref idref="DRAWINGS">FIG. 6</figref> is a block diagram showing an embodiment of the structure of a TIM information element (IE);

0048<figref idref="DRAWINGS">FIG. 7</figref> is a block diagram showing an embodiment of the structure of a TIM encoded on a block basis;

0049<figref idref="DRAWINGS">FIG. 8</figref> is a flowchart showing an embodiment of a data transmission/reception method;

0050<figref idref="DRAWINGS">FIG. 9</figref> is a conceptual diagram showing an embodiment of a WLAN system including relay devices;

0051<figref idref="DRAWINGS">FIG. 10</figref> is a block diagram showing the logical configuration of a relay device;

0052<figref idref="DRAWINGS">FIG. 11</figref> is a flowchart showing another embodiment of a data transmission/reception method;

0053<figref idref="DRAWINGS">FIG. 12</figref> is a block diagram showing an embodiment of an AID designated on a page ID basis;

0054<figref idref="DRAWINGS">FIG. 13</figref> is a block diagram showing an embodiment of an AID designated on a block index basis;

0055<figref idref="DRAWINGS">FIG. 14</figref> is a block diagram showing an embodiment of an AID designated on a sub-block index basis;

0056<figref idref="DRAWINGS">FIG. 15</figref> is a flowchart showing a further embodiment of a data transmission/reception method;

0057<figref idref="DRAWINGS">FIG. 16</figref> is a conceptual diagram showing yet another embodiment of a data transmission/reception method;

0058<figref idref="DRAWINGS">FIG. 17</figref> is a conceptual diagram showing another embodiment of a WLAN system including relay devices;

0059<figref idref="DRAWINGS">FIG. 18</figref> is a conceptual diagram showing an association method in an uplink relay mode according to an embodiment of the present invention;

0060<figref idref="DRAWINGS">FIG. 19</figref> is a conceptual diagram showing a further embodiment of a WLAN system including relay devices; and

0061<figref idref="DRAWINGS">FIG. 20</figref> is a conceptual diagram showing still another embodiment of a data transmission/reception method.

BEST MODE

0062The present invention may be variously changed and may have various embodiments, and specific embodiments will be described in detail below with reference to the attached drawings.

0063However, it should be understood that those embodiments are not intended to limit the present invention to specific disclosure forms and they include all changes, equivalents or modifications included in the spirit and scope of the present invention.

0064The terms such as “first” and “second” may be used to describe various components, but those components should not be limited by the terms. The terms are merely used to distinguish one component from other components. A first component may be designated as a second component and a second component may be designated as a first component in the similar manner, without departing from the scope based on the concept of the present invention. The term “and/or” includes a combination of a plurality of related items or any of the plurality of related items.

0065It should be understood that a representation indicating that a first component is “connected” or “coupled” to a second component may include the case where the first component is connected or coupled to the second component with some other component interposed therebetween, as well as the case where the first component is “directly connected” or “directly coupled” to the second component. In contrast, it should be understood that a representation indicating that a first component is “directly connected” or “directly coupled” to a second component means that no component is interposed between the first and second components.

0066The terms used in the present specification are merely used to describe specific embodiments and are not intended to limit the present invention. A singular expression includes a plural expression unless a description to the contrary is specifically pointed out in context. In the present specification, it should be understood that the terms such as “include” or “have” are merely intended to indicate that features, numbers, steps, operations, components, parts, or combinations thereof are present, and are not intended to exclude a possibility that one or more other features, numbers, steps, operations, components, parts, or combinations thereof will be present or added.

0067Unless differently defined, all terms used here including technical or scientific terms have the same meanings as the terms generally understood by those skilled in the art to which the present invention pertains. The terms identical to those defined in generally used dictionaries should be interpreted as having meanings identical to contextual meanings of the related art, and are not interpreted as being ideal or excessively formal meanings unless they are definitely defined in the present specification.

0068Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the attached drawings. For easy understanding of the entire part of the invention in the following description of the present invention, the same reference numerals are used to designate the same or similar elements throughout the drawings, and repeated descriptions of the same components will be omitted.

0069Throughout the present specification, a station (STA) denotes any functional medium that includes medium access control (MAC) conforming to the IEEE 802.11 standards and a physical layer interface for a wireless medium. Stations may be classified into a station (STA) that is an access point (AP) and a station (STA) that is a non-AP. The station that is an AP may be simply called an access point (AP), and the station that is a non-AP may be simply called a terminal.

0070A ‘station (STA)’ may include a processor and a transceiver, and may further include a user interface, a display device, etc. The processor denotes a unit devised to generate a frame to be transmitted over a wireless network or process a frame received over the wireless network, and may perform various functions to control the station (STA). The transceiver denotes a unit that is functionally connected to the processor and is devised to transmit and receive a frame over the wireless network for the station (STA).

0071An ‘access Point (AP)’ may denote a centralized controller, a base station (BS), a radio access station, a Node B, an evolved Node B, a relay, a Mobile Multihop Relay (MMR)-BS, a Base Transceiver System (BTS), a site controller, etc., and may include some or all of the functions thereof.

0072A ‘terminal (i.e. non-AP)’ may denote a Wireless Transmit/Receive Unit (WTRU), User Equipment (UE), a User Terminal (UT), an Access Terminal (AT), a Mobile Station (MS), a mobile terminal, a subscriber unit, a Subscriber Station (SS), a wireless device, a mobile subscriber unit, etc., and may include some or all of the functions thereof.

0073Here, the terminal may denote a desktop computer capable of communication, a laptop computer, a tablet PC, a wireless phone, a mobile phone, a smart phone, a smart watch, smart glasses, an e-book reader, a Portable Multimedia Player (PMP), a portable game console, a navigation device, a digital camera, a Digital Multimedia Broadcasting (DMB) player, a digital audio recorder, a digital audio player, a digital picture recorder, a digital picture player, a digital video recorder, a digital video player, etc.

0074<figref idref="DRAWINGS">FIG. 1</figref> is a block diagram showing an embodiment of a station for performing methods according to the present invention.

0075Referring to <figref idref="DRAWINGS">FIG. 1</figref>, a station <b>100</b> may include at least one processor <b>110</b>, memory <b>120</b>, and a network interface device <b>130</b> connected to a network and configured to perform communication. The station <b>100</b> may further include an input interface device <b>140</b>, an output interface device <b>150</b>, and a storage device <b>160</b>. The components included in the station <b>100</b> may be connected to each other through a bus <b>170</b>, and may then perform communication with each other.

0076The processor <b>110</b> may execute program commands stored in the memory <b>120</b> and/or the storage device <b>160</b>. The processor <b>110</b> may denote a central processing unit (CPU), a graphics processing unit (GPU), or an exclusive processor for performing the methods according to the present invention. Each of the memory <b>120</b> and the storage device <b>160</b> may be implemented as a volatile storage medium and/or a nonvolatile storage medium. For example, the memory <b>120</b> may be implemented as read only memory (ROM) and/or random access memory (RAM).

0077The embodiments of the present invention are applied to a WLAN system conforming to the IEEE 802.11 standards, and may also be applied to other communication systems as well as the WLAN system conforming to the IEEE 802.11 standards.

0078For example, the embodiments of the present invention may be applied to the mobile Internet such as a Wireless Personal Area Network (WPAN), a Wireless Body Area Network (WBAN), Wireless Broadband Internet (WiBro), or Worldwide Interoperability for Microwave Access (Wimax), a second generation (2G) mobile communication network such as a Global System for Mobile communication (GSM) or Code Division Multiple Access (CDMA), a 3G mobile communication network such as Wideband Code Division Multiple Access (WCDMA) or CDMA2000, a 3.5G mobile communication network such as High-Speed Downlink Packet Access (HSDPA) or High-Speed Uplink Packet Access (HSUPA), a 4G mobile communication network such as Long-Term Evolution (LTE) or LTE-Advanced, or a 5G mobile communication network.

0079<figref idref="DRAWINGS">FIG. 2</figref> is a conceptual diagram showing an embodiment of the configuration of a WLAN system conforming to IEEE 802.11.

0080Referring to <figref idref="DRAWINGS">FIG. 2</figref>, the WLAN system conforming to IEEE 802.11 may include at least one basic service set (BSS). The BSS denotes a set of stations (STA<b>1</b>, STA<b>2</b> (AP<b>1</b>), STA<b>3</b>, STA<b>4</b>, STA<b>5</b> (AP<b>2</b>), STA<b>6</b>, STA<b>7</b>, STA<b>8</b>) which are successfully synchronized with each other and are capable of communicating with each other, and is not a concept meaning a specific area.

0081BSSs may be classified into an infrastructure BSS and an independent BSS (IBSS). Here, BSS<b>1</b> and BSS<b>2</b> denote infrastructure BSSs and BSS <b>3</b> denotes an IBSS.

0082BSS<b>1</b> may include a first terminal STA<b>1</b>, a first access point STA<b>2</b> (AP<b>1</b>) for providing a distribution service, and a distribution system (DS) for connecting multiple access points STA<b>2</b> (AP<b>1</b>) and STA<b>5</b> (AP<b>2</b>) to each other. In BSS<b>1</b>, the first access point STA<b>2</b> (AP<b>1</b>) may manage the first terminal STA<b>7</b>.

0083BSS<b>2</b> may include a third terminal STA<b>3</b>, a fourth terminal STA<b>4</b>, a second access point STA<b>5</b> (AP<b>2</b>)) for providing a distribution service, and a distribution system (DS) for connecting the multiple access points STA<b>2</b> (AP<b>1</b>) and STA<b>5</b> (AP<b>2</b>) to each other. In the BSS<b>2</b>, the second access point STA<b>5</b> (AP<b>2</b>) may manage the third terminal STA<b>3</b> and the fourth terminal STA<b>4</b>.

0084BSS<b>3</b> denotes an IBSS operating in an ad-hoc mode. In the BSS<b>3</b>, there is no access point that functions as a centralized management entity. That is, in the BSS<b>3</b>, terminals STA<b>6</b>, STA<b>7</b>, and STA<b>8</b> are managed in a distributed manner. In the BSS<b>3</b>, all of the terminals STA<b>6</b>, STA<b>7</b>, and STA<b>8</b> may denote mobile terminals, and access to the distribution system (DS) is not permitted, thus constituting a self-contained network.

0085The access points STA<b>2</b> (AP<b>1</b>) and STA<b>5</b> (AP<b>2</b>) may provide access to the distribution system (DS) via a wireless medium for the terminals STA<b>1</b>, STA<b>3</b>, and STA<b>4</b> connected thereto. Communication between the terminals STA<b>1</b>, STA<b>3</b>, and STA<b>4</b> in the BSS<b>1</b> or BSS<b>2</b> is generally performed via the access point STA<b>2</b> (AP<b>1</b>) or STA<b>5</b> (AP<b>2</b>), but direct communication may be performed between the terminals STA<b>1</b>, STA<b>3</b>, and STA<b>4</b> when a direct link is set up therebetween.

0086Multiple infrastructure BSSs may be connected to each other through the distribution system (DS). The multiple BSSs connected through the distribution system (DS) are called an extended service set (ESS). The entities included in the ESS, that is, STA<b>1</b>, STA<b>2</b> (AP<b>1</b>), STA<b>3</b>, STA<b>4</b>, and STA<b>5</b> (AP<b>2</b>), are capable of communicating with each other, and any terminal STA<b>1</b>, STA<b>3</b>, or STA<b>4</b> may move from a single BSS to another BSS while performing seamless communication in the same ESS.

0087The distribution system (DS) is a mechanism for allowing one access point to communicate with another access point. In accordance with the DS, the access point may transmit frames for terminals coupled to a BSS managed thereby, or may transmit frames for any terminal that has moved to another BSS. Further, the access point may transmit and receive frames to and from an external network, such as a wired network. Such a DS is not necessarily a network and is not limited in its form as long as it is capable of providing a predetermined distribution service defined in the IEEE 802.11 standards. For example, the distribution system may be a wireless network such as a mesh network, or a physical structure for connecting the access points to each other.

0088Each terminal (STA) in the infrastructure BSS may be associated with an access point (AP). When associated with the access point (AP), the terminal (STA) may transmit and receive data.

0089<figref idref="DRAWINGS">FIG. 3</figref> is a flowchart showing a terminal association procedure performed in an infrastructure BSS.

0090Referring to <figref idref="DRAWINGS">FIG. 3</figref>, the STA association procedure performed in the infrastructure IBSS may be chiefly divided into the step of probing an AP (probe step), the step of performing authentication with the probed AP (authentication step), and the step of associating with the AP with which authentication has been performed (association step).

0091The terminal (STA) may first probe neighboring APs using a passive scanning method or an active scanning method. When the passive scanning method is used, the terminal (STA) may probe neighboring APs by overhearing the beacons transmitted from the APs. When the active scanning method is used, the STA may probe neighboring APs by transmitting a probe request frame and receiving a probe response frame which is a response to the probe request frame from the APs.

0092When neighboring APs are probed, the STA may perform the step of performing authentication with each probed AP. In this case, the STA may perform the step of performing authentication with multiple APs. Authentication algorithms conforming to the IEEE 802.11 standards may be classified into an open system algorithm for exchanging two authentication frames with each other and a shared key algorithm for exchanging four authentication frames with each other.

0093Based on the authentication algorithms conforming to the IEEE 802.11 standards, the STA may transmit an authentication request frame and receive an authentication response frame, which is a response to the authentication request frame, from each AP, thus completing authentication with each AP.

0094When authentication has been completed, the STA may perform the step of associating with the AP. In this case, the STA may select a single AP from among the APs with which authentication has been performed, and may perform the step of associating with the selected AP. That is, the STA may transmit an association request frame to the selected AP and receive an association response frame, which is a response to the association request frame, from the selected AP, thus completing association with the selected AP.

0095The WLAN system denotes a local area network in which multiple communication entities conforming to the IEEE 802.11 standards may exchange data with each other in a wirelessly connected state.

0096<figref idref="DRAWINGS">FIG. 4</figref> is a conceptual diagram showing the infrastructure BSS of a WLAN system.

0097Referring to <figref idref="DRAWINGS">FIG. 4</figref>, the infrastructure BSS may include a single access point (AP) and multiple terminals STA<b>1</b> and STA<b>2</b>. The AP may transmit a beacon frame including a service set ID (SSID), which is a unique identifier, in a broadcast manner. The beacon frame may provide information about the presence and association of the AP to terminals that are not associated with the AP, and may notify the terminals associated with the AP of the presence of data that is transmitted to a specific terminal.

0098Each terminal that is not associated with the AP may probe the AP using a passive scanning method or an active scanning method, and may acquire association information from the probed AP. In the case of the passive scanning method, the terminal may probe the AP by receiving a beacon frame from the AP. In the case of the active scanning method, the terminal may probe the AP by transmitting a probe request frame and receiving a probe response frame, which is a response thereto, from the AP.

0099Each terminal that is not associated with the AP may attempt to perform authentication with a specific AP based on association information acquired from the beacon frame or the probe response frame. A terminal that has succeeded in authentication may transmit an association request frame to the corresponding AP, and the AP, having received the association request frame, may transmit an association response frame including the AID of the terminal to the terminal. Via the above procedure, the terminal may be associated with the AP.

0100<figref idref="DRAWINGS">FIG. 5</figref> is a block diagram showing an embodiment of a hierarchical AID structure.

0101Referring to <figref idref="DRAWINGS">FIG. 5</figref>, in the IEEE 802.11 standards, an AID having a hierarchical structure may be used to efficiently manage multiple terminals. An AID assigned to a single terminal may be composed of a page ID, a block index, a sub-block index, and a terminal bit index (STA bit index). The group to which the terminal belongs (i.e. a page group, a block group, or a sub-block group) may be identified using information about individual fields.

0102<figref idref="DRAWINGS">FIG. 6</figref> is a block diagram showing an embodiment of the structure of a traffic indication map (TIM) information element (IE).

0103Referring to <figref idref="DRAWINGS">FIG. 6</figref>, the TIM IE may include an element ID field, a length field, a delivery traffic indication message (DTIM) count field, a DTIM period field, a bitmap control field, and a partial virtual bitmap field. That is, the TIM IE includes information required to indicate a bit corresponding to the AID of a terminal when data to be transmitted to the terminal is buffered in the AP, and this information may be encoded into the bitmap control field and the partial virtual bitmap field.

0104<figref idref="DRAWINGS">FIG. 7</figref> is a block diagram showing an embodiment of the structure of a TIM encoded on a block basis.

0105Referring to <figref idref="DRAWINGS">FIG. 7</figref>, in the IEEE 802.11 standards, the TIM may be encoded on a block basis. A single encoding block may include a block control field, a block offset field, a block bitmap field, and at least one sub-block field.

0106The block control field may denote the encoding mode of the TIM. That is, the block control field may represent a block bitmap mode, a single AID mode, an offset+length+bitmap (OLB) mode, or an inverse bitmap mode. The block offset field may represent the offset of an encoded block. The block bitmap field may represent a bitmap indicating the location of the sub-block in which an AID bit is set. The sub-block bitmap field may represent a bitmap indicating the location of an AID in the sub-block.

0107<figref idref="DRAWINGS">FIG. 8</figref> is a flow diagram showing an embodiment of a data transmission/reception method.

0108Referring to <figref idref="DRAWINGS">FIG. 8</figref>, an access point (AP) may transmit a beacon frame including a TIM IE in a broadcast manner. A terminal (STA) operating in a power saving mode (PSM) may be awakened at intervals of a beacon period, in which a DTIM count becomes 0, and may receive a beacon frame. The terminal (STA) is configured to, when a bit corresponding to its AID is set to ‘1’ in the TIM included in the received beacon frame, transmit a power save (PS)-Poll frame to the AP, thus notifying the AP that the STA is ready to receive data. Upon receiving the PS-Poll frame, the AP may transmit a data frame to the corresponding STA.

0109In the WLAN system, communication entities (i.e. access points, terminals, etc.) share a wireless channel and contend with other entities to access the wireless channel based on a carrier sense multiple access (CSMA)/collision avoidance (CA) scheme. First, each communication entity may check the occupied state of the wireless channel using a physical channel sensing scheme and a virtual channel sensing scheme before accessing the wireless channel.

0110The physical channel sensing scheme may be implemented via channel sensing, which detects whether energy of a predetermined level or more is present in the wireless channel. When energy of a predetermined level or more is detected using the physical channel sensing scheme, the terminal may determine that the wireless channel is occupied by another terminal, and thus may perform again channel sensing after waiting for a random backoff time. Meanwhile, when energy of less than a predetermined level is detected using the physical channel sensing scheme, the terminal may determine that the wireless channel is in an idle state, and may then access the corresponding wireless channel and transmit a signal through the wireless channel.

0111The virtual channel sensing scheme may be implemented by setting a predicted channel occupation time using a network allocation vector (NAV) timer. In the WLAN system, upon transmitting a frame, a communication entity may write the time required to complete the transmission of the corresponding frame in the duration field of the header of the frame. When normally receiving a certain frame through the wireless channel, the communication entity may set its own NAV timer based on a value in the duration field of the header of the received frame. When receiving a new frame before the NAV timer has expired, the communication entity may update the NAV timer based on the value in the duration field of the header of the newly received frame. When the NAV timer has expired, the communication entity may determine that the occupation of the wireless channel has been released, and may then contend for access to a wireless channel.

0112The communication entity may support multiple data rates of a physical layer depending on various modulation schemes and various channel coding rates. Generally, a high data rate for the physical layer enables a large amount of data to be transmitted during a short wireless channel occupation time, but requires high signal quality. In contrast, a low data rate for the physical layer enables data to be transmitted even at low signal quality, but requires a relatively long wireless channel occupation time.

0113Since wireless channel resources are shared among communication entities, the overall capacity of the WLAN system may be increased only when a specific communication entity transmits the largest amount of data during a time period during which the communication entity occupies a wireless channel. That is, the overall capacity of the WLAN system may be increased when the terminal transmits and receives data to and from the AP at the highest possible data rate for the physical layer. The highest data rate for the physical layer may be realized when signal quality is sufficiently secured owing to a short distance between the AP and the terminal. Alternatively, the highest data rate for the physical layer may be realized when signal quality is sufficiently secured in such a way that a communication entity transmits a signal at sufficiently high transmission power. If terminals are located far away from the AP, or if a communication entity uses limited transmission power, the data rate for the physical layer is decreased, thus consequently reducing the overall capacity of the WLAN system.

0114In particular, when the WLAN system is applied to a sensor network, the number of sensor terminals located a long distance from the AP may increase due to the characteristics of the sensor network that supports a wide area. In this case, there is no problem in the downlink quality of the AP for which power may be easily secured, but a problem may arise in the uplink quality of sensor terminals designed at low power. Therefore, a sensor terminal located a long distance from the AP uses a low data rate for an uplink physical layer so as to secure reliable uplink quality, and thus the overall capacity of the WLAN system may be seriously decreased. Further, a low-power terminal consumes more power because it must be awakened for a longer period of time upon transmitting the same data when a low data rate for the physical layer is used.

0115<figref idref="DRAWINGS">FIG. 9</figref> is a conceptual diagram showing an embodiment of a WLAN system including relay devices.

0116Referring to <figref idref="DRAWINGS">FIG. 9</figref>, a master access point (master-AP: M-AP), a first relay device R<b>1</b>, a second relay device R<b>2</b>, and a fifth terminal STA<b>5</b> may constitute a master-basic service set (M-BSS). The first relay device R<b>1</b>, a first terminal STA<b>1</b>, and a second terminal STA<b>2</b> may constitute a first relay BSS (R<b>1</b>-BSS). The second relay device R<b>2</b>, a third terminal STA<b>3</b>, and a fourth terminal STA<b>4</b> may constitute a second relay BSS (R<b>2</b>-BSS). The relay devices R<b>1</b> and R<b>2</b> may be located at the place where signal quality between the master access point (M-AP) and the terminals STA<b>1</b>, STA<b>2</b>, STA<b>3</b>, and STA<b>4</b> is deteriorated. The first relay device R<b>1</b> may relay data transmitted between the master access point (M-AP) and the first and second terminals STA<b>1</b> and STA<b>2</b>. The second relay device R<b>2</b> may relay data transmitted between the master access point (M-AP) and the third and fourth terminals STA<b>3</b> and STA<b>4</b>. That is, the physical area of the master access point (M-AP) may be extended via the relay devices R<b>1</b> and R<b>2</b>.

0117<figref idref="DRAWINGS">FIG. 10</figref> is a block diagram showing the logical configuration of a relay device.

0118Referring to <figref idref="DRAWINGS">FIG. 10</figref>, the relay device may include a relay terminal (R-STA), functioning as a master access point (M-AP), and a relay access point (R-AP), functioning as an access point for terminals belonging to an extended area.

0119The relay terminal (R-STA) may probe the master access point (M-AP) by receiving a beacon frame or a probe response frame transmitted from the master access point (M-AP) according to the same procedure as a normal terminal.

0120Thereafter, the relay terminal (R-STA) may sequentially perform a procedure for authentication with the probed master access point (M-AP) and a procedure for association with the M-AP.

0121When the relay terminal (R-STA) is associated with the master access point (M-AP), the relay access point (R-AP) may serve a relay BSS. That is, the relay access point (R-AP) may transmit its own beacon frame, or alternatively, transmit a probe response frame that is a response to a probe request frame to an end terminal belonging to the relay BSS.

0122If it is determined that association with the relay access point (R-AP) is more beneficial than association with the master access point (M-AP), the end terminal belonging to the relay BSS may perform procedures for authentication and association with the relay access point (R-AP). In contrast, if it is determined that association with the master access point (M-AP) is more beneficial than association with the relay access point (R-AP), the end terminal belonging to the relay BSS may perform procedures for authentication and association with the master access point (M-AP).

0123The relay terminal (R-STA) may relay data transmitted between the master access point (M-AP) and an end terminal. In this case, the relay terminal (R-STA) may relay data that is transmitted using a 4-address field. The 4-address field includes a destination address (DA) field indicating the address of the final destination of data, a source address (SA) field indicating the address of the place where the data was generated, a transmitter address (TA) field indicating the address of the communication entity that physically transmits a frame containing the data, and a receiver address (RA) field indicating the address of the communication entity that is to physically receive the frame containing the data.

0124For example, when desiring to transmit data to an end terminal through a relay device, the master access point (M-AP) may configure and transmit the header address field of a data frame as follows. <ul id="ul0001" list-style="none"><li id="ul0001-0001" num="0000"><ul id="ul0002" list-style="none"><li id="ul0002-0001" num="0125">TA field: address of master access point (M-AP)(i.e. MAC address)</li><li id="ul0002-0002" num="0126">RA field: address of relay device (i.e. MAC address)</li><li id="ul0002-0003" num="0127">DA field: address of end terminal (i.e. MAC address)</li><li id="ul0002-0004" num="0128">SA field: address of master access point (M-AP)(i.e. MAC address)</li></ul></li></ul>

0129The relay terminal (R-STA) may forward a data frame received from the relay access point (R-AP) to the master access point (M-AP), and may forward a data frame received from the master access point (M-AP) to the relay access point (R-AP).

0130When the relay terminal (R-STA) and the master access point (M-AP) are associated with each other and a transfer path is acquired, the relay access point (R-AP) may periodically transmit a beacon frame including an identifier (SSID) identical to that of the master access point (M-AP). Also, the relay access point (R-AP) may transmit a probe response frame in response to a probe request frame from the end terminal, transmit an authentication response frame in response to an authentication request frame from the end terminal, and transmit an association response frame in response to an association request frame from the end terminal. That is, the relay access point (R-AP) may perform the same function as the master access point (M-AP).

0131An end terminal located near the relay device may be associated with a relay-AP (R-AP) located closer to the end terminal than the master access point (M-AP) and may secure high signal quality, thus enabling data to be transmitted at a high data rate of the physical layer.

0132The relay access point (R-AP) may generate a beacon frame including an indicator indicating that the R-AP itself is a communication entity for relaying data transmitted between the master access point (M-AP) and the end terminal, and may transmit the generated beacon frame. Such an indicator may be defined either using one bit in the beacon frame or using the address field of the master access point (M-AP).

0133The relay access point (R-AP) may transmit a data frame to the end terminal using a 4-address field in the same way as the relay terminal (R-STA). Alternatively, the relay access point (R-AP) may transmit a data frame to the end terminal using a 3-address field (SA=TA, RA, and DA) when the SA field is identical to the TA field. Alternatively, the relay access point (R-AP) may transmit a data frame to the end terminal using a 2-address field (RA, TA). When a data frame is received from the end terminal via a 3-address field (SA=TA, RA, DA) or a 2-address field (RA, TA), the relay access point (R-AP) may transmit the corresponding data frame to the relay terminal (R-STA).

0134<figref idref="DRAWINGS">FIG. 11</figref> is a flowchart showing another embodiment of a data transmission/reception method.

0135Referring to <figref idref="DRAWINGS">FIG. 11</figref>, a master access point (M-AP) may serve a M-BSS, and a relay device R may belong to the M-BSS. The relay device R may serve an R-BSS and a first terminal STA<b>1</b> and a second terminal STA<b>2</b> may belong to the R-BSS.

0136When a procedure for authentication with the master access point (M-AP) is completed, the relay device R may perform an association procedure. That is, the relay device R may transmit an association request frame to the master access point (M-AP) (S<b>1100</b>). Here, the association request frame may include an indicator that requests the allocation of AID resources for terminals belonging to the R-BSS.

0137When the association request frame is received from the relay device R, the master access point (M-AP) may acquire the indicator included in the association request frame, and may then determine an AID resource allocation request for terminals belonging to the R-BSS based on the indicator. Therefore, the master access point (M-AP) may transmit an association response frame, including a reference AID to be used to allocate AIDs of the terminals belonging to the R-BSS, to the relay device R (S<b>1110</b>). Here, the reference AID may denote the AID of the relay device R. Meanwhile, when an AID is hierarchically configured, as described above with reference to <figref idref="DRAWINGS">FIG. 5</figref>, the reference AID may be set on a page ID basis, a block index basis, or a sub-block index basis.

0138When the association response frame is received from the master access point (M-AP), the relay device R may allocate AIDs to the first terminal STA<b>1</b> and the second terminal STA<b>2</b> belonging to the R-BSS, based on the reference AID included in the association response frame (S<b>1120</b>). For example, when the reference AID is set on a page ID basis, the relay device R may allocate different AIDs to the first terminal STA<b>1</b> and the second terminal STA<b>2</b> belonging to the R-BSS, within a page ID range indicated by the reference AID.

0139When the reference AID is set on a block index basis, the relay device R may allocate different AIDs to the first terminal STA<b>1</b> and the second terminal STA<b>2</b> belonging to the R-BSS, within a block index range indicated by the reference AID. When the reference AID is set on a sub-block index basis, the relay device R may allocate different AIDs to the first terminal STA<b>1</b> and the second terminal STA<b>2</b> belonging to the R-BSS, within a sub-block index range indicated by the reference AID.

0140<figref idref="DRAWINGS">FIG. 12</figref> is a block diagram showing an embodiment of an AID designated on a page ID basis.

0141Referring to <figref idref="DRAWINGS">FIG. 12</figref>, a master access point (M-AP) may designate the range of AIDs for communication entities, belonging to an R-BSS, on a page ID basis. For example, the master access point (M-AP) may allocate ‘11 00000 000 000b’ as the AID of a relay device R. In this case, the relay device R may allocate AIDs to terminals belonging to the R-BSS within the range of a page ID (i.e. page ID group <b>3</b>(11b)) indicated by its own AID. That is, the relay device R may allocate AIDs to the terminals belonging to the R-BSS within the range of ‘11 00000 000 001b’ to ‘11 11111 111 111b’. Meanwhile, the master access point (M-AP) may allocate the AIDs of other communication entities (e.g. a relay device, a terminal, and the like) belonging to the M-BSS within the range of page ID groups <b>0</b> to <b>2</b> (00b, 01b, 10b). According to this configuration, communication entities constituting a WLAN system may be identified using AIDs that are unique identifiers.

0142<figref idref="DRAWINGS">FIG. 13</figref> is a block diagram showing an embodiment of an AID designated on a block index basis.

0143Referring to <figref idref="DRAWINGS">FIG. 13</figref>, a master access point (M-AP) may designate the range of AIDs for communication entities belonging to an R-BSS on a block index basis. For example, the master access point (M-AP) may allocate ‘00 00001 000 000b’ as the AID of the relay device R. In this case, the relay device R may allocate AIDs to terminals belonging to the R-BSS within the range of a block index indicated by its own AID. That is, the relay device R may allocate AIDs to terminals belonging to the R-BSS within the range of ‘00 00001 000 001b’ to ‘00 00001 111 111b’.

0144<figref idref="DRAWINGS">FIG. 14</figref> is a block diagram showing an embodiment of an AID designated on a sub-block index basis.

0145Referring to <figref idref="DRAWINGS">FIG. 14</figref>, a master access point (M-AP) may designate the range of AIDs for communication entities belonging to an R-BSS on a sub-block index basis. For example, the master access point (M-AP) may allocate ‘00 00000 001 000b’ as the AID of the relay device R. In this case, the relay device R may allocate AIDs to terminals belonging to the R-BSS within the range of a sub-block index indicated by its own AID. That is, the relay device R may allocate AIDs to terminals belonging to the R-BSS within the range of ‘00 00000 001 001b’ to ‘00 00000 001 111b’.

0146Referring back to <figref idref="DRAWINGS">FIG. 11</figref>, the relay device R may transmit information about AID resources allocated to terminals belonging to the R-BSS to the master access point (M-AP) (S<b>1130</b>). At this time, the relay device R may transmit the MAC addresses of terminals belonging to the R-BSS, together with the information about AID resources allocated to the terminals, to the master access point (M-AP). For example, the relay device R may transmit the AID and the MAC address of the first terminal STA<b>1</b> to the master access point (M-AP), and may transmit the AID and the MAC address of the second terminal STA<b>2</b> to the master access point (M-AP).

0147When there is a data frame to be transmitted to the first terminal STA<b>1</b>, the master access point (M-AP) may configure an address field included in the corresponding data frame in the following manner.

First Embodiment of Address Field

0000<ul id="ul0003" list-style="none"><li id="ul0003-0001" num="0000"><ul id="ul0004" list-style="none"><li id="ul0004-0001" num="0148">RA field: MAC address of relay device R</li><li id="ul0004-0002" num="0149">TA field: MAC address of master access point (M-AP)</li><li id="ul0004-0003" num="0150">DA field: MAC address of first terminal STA<b>1</b></li><li id="ul0004-0004" num="0151">SA field: MAC address of master access point (M-AP)</li></ul></li></ul>

Second Embodiment of Address Field

0000<ul id="ul0005" list-style="none"><li id="ul0005-0001" num="0000"><ul id="ul0006" list-style="none"><li id="ul0006-0001" num="0152">RA field: MAC address of relay device R</li><li id="ul0006-0002" num="0153">TA field: MAC address of master access point (M-AP)</li><li id="ul0006-0003" num="0154">DA field: AID of first terminal STA<b>1</b></li><li id="ul0006-0004" num="0155">SA field: MAC address of master access point (M-AP)</li></ul></li></ul>

Third Embodiment of Address Field

0000<ul id="ul0007" list-style="none"><li id="ul0007-0001" num="0000"><ul id="ul0008" list-style="none"><li id="ul0008-0001" num="0156">RA field: AID of relay device R</li><li id="ul0008-0002" num="0157">TA field: MAC address of master access point (M-AP)</li><li id="ul0008-0003" num="0158">DA field: MAC address of first terminal STA<b>1</b></li><li id="ul0008-0004" num="0159">SA field: MAC address of master access point (M-AP)</li></ul></li></ul>

0160Fourth embodiment of address field <ul id="ul0009" list-style="none"><li id="ul0009-0001" num="0000"><ul id="ul0010" list-style="none"><li id="ul0010-0001" num="0161">RA field: AID of relay device R</li><li id="ul0010-0002" num="0162">TA field: MAC address of master access point (M-AP)</li><li id="ul0010-0003" num="0163">DA field: AID of first terminal STA<b>1</b></li><li id="ul0010-0004" num="0164">SA field: MAC address of master access point (M-AP)</li></ul></li></ul>

0165The master access point (M-AP) may transmit a data frame including the address field, configured in the above manner, to the relay device R (S<b>1140</b>). When the data frame is received from the master access point (M-AP), the relay device R may recognize that the final destination of the data frame is the first terminal STA<b>1</b>, via the address field included in the data frame. Therefore, the relay device R may transmit the data frame to the first terminal STA<b>1</b> (S<b>1150</b>).

0166Meanwhile, when the data frame that is transmitted from the relay device R to the first terminal STA<b>1</b> is acquired, the master access point (M-AP) may determine that the relay device R has successfully received the data frame. That is, the master access point (M-AP) may regard the data frame, which is transmitted from the relay device R to the first terminal STA<b>1</b>, as an ACK frame for the data frame, which the M-AP has transmitted to the relay device R. Alternatively, when the data frame has been successfully received from the master access point (M-AP), the relay device R may transmit an ACK frame, as a response thereto, to the master access point (M-AP). When the data frame has been successfully received from the relay device R, the first terminal STA<b>1</b> may transmit an ACK frame, as a response thereto, to the relay device R (S<b>1160</b>).

0167<figref idref="DRAWINGS">FIG. 15</figref> is a flowchart showing a further embodiment of a data transmission/reception method.

0168Referring to <figref idref="DRAWINGS">FIG. 15</figref>, a master access point (M-AP) may serve an M-BSS, and a relay device R may belong to the M-BSS. The relay device R may serve an R-BSS, and a first terminal STA<b>1</b> and a second terminal STA<b>2</b> may belong to the R-BSS.

0169After associating with the master access point (M-AP), the relay device R may transmit an AID resource request frame to the master access point (M-AP) so as to request the M-AP to allocate AID resources for terminals belonging to the R-BSS (S<b>1500</b>). The AID resource request frame may include information about an indicator for requesting the allocation of AID resources for terminals belonging to the R-BSS and information about the size (or number) of AID resources, as shown in the following Table 1.

0000<tables id="TABLE-US-00001" num="00001"><table frame="none" colsep="0" rowsep="0"><tgroup align="left" colsep="0" rowsep="0" cols="3"><colspec colname="1" colwidth="14pt" align="left" /><colspec colname="2" colwidth="35pt" align="left" /><colspec colname="3" colwidth="168pt" align="left" /><thead><row><entry namest="1" nameend="3" rowsep="1">TABLE 1</entry></row><row><entry namest="1" nameend="3" align="center" rowsep="1" /></row><row><entry /><entry>Order</entry><entry>Information</entry></row><row><entry namest="1" nameend="3" align="center" rowsep="1" /></row></thead><tbody valign="top"><row><entry /><entry>1</entry><entry>Indicator for requesting allocation of AID resources</entry></row><row><entry /><entry>2</entry><entry>Size (or number) of AID resources</entry></row><row><entry namest="1" nameend="3" align="center" rowsep="1" /></row></tbody></tgroup></table></tables>

0170When the AID resource request frame is received, the master access point (M-AP) may acquire, from the AID resource request frame, information about the indicator for requesting the allocation of AID resources for terminals belonging to the R-BSS and the size (or number) of the AID resources. That is, by way of the AID resource request frame, the master access point (M-AP) may check the request to allocate AID resources for terminals belonging to the R-BSS and also check the size (or number) of required AID resources. The master access point (M-AP) may generate an AID resource response frame that includes information about AID resources for terminals belonging to the R-BSS, based on the information included in the AID resource request frame, and may transmit the AID resource response frame to the relay device R (S<b>1510</b>).

0171The AID resource information for the R-BSS may be the range of AIDs to be used for terminals belonging to the R-BSS. Further, the AID resource information may be designated so that the range of AIDs does not overlap the range of AIDs to be used for terminals belonging to the M-BSS. For example, referring to <figref idref="DRAWINGS">FIG. 12</figref> described above, information about AID resources may be designated on a page ID basis. In this case, the master access point (M-AP) may designate the range of ‘11 00000 000 001b’ to ‘11 11111 111 111b’ as the range of AIDs for terminals belonging to the R-BSS. Alternatively, referring to <figref idref="DRAWINGS">FIG. 13</figref> described above, information about AID resources may be designated on a block index basis. In this case, the master access point (M-AP) may designate the range of ‘00 00001 000 001b’ to ‘00 00001 111 111b’ as the range of AIDs for terminals belonging to the R-BSS. Alternatively, referring to <figref idref="DRAWINGS">FIG. 14</figref> described above, the AID resource information may be designated on a sub-block index basis. In this case, the master access point (M-AP) may designate the range of ‘00 00000 001 001b’ to ‘00 00000 001 111b’ as the range of AIDs for terminals belonging to the R-BSS.

0172The AID resource response frame may include information about an indicator indicating that AID resources for terminals belonging to the R-BSS are allocated, information indicating the start point of AIDs, and information about the size (or number) of AID resources, as shown in the following Table 2. The AID range may be defined by the start point of AIDs and the size (or number) of AID resources.

0000<tables id="TABLE-US-00002" num="00002"><table frame="none" colsep="0" rowsep="0"><tgroup align="left" colsep="0" rowsep="0" cols="3"><colspec colname="1" colwidth="14pt" align="left" /><colspec colname="2" colwidth="42pt" align="left" /><colspec colname="3" colwidth="161pt" align="left" /><thead><row><entry namest="1" nameend="3" rowsep="1">TABLE 2</entry></row><row><entry namest="1" nameend="3" align="center" rowsep="1" /></row><row><entry /><entry>Order</entry><entry>Information</entry></row><row><entry namest="1" nameend="3" align="center" rowsep="1" /></row></thead><tbody valign="top"><row><entry /><entry>1</entry><entry>Indicator indicating allocation of AID resources</entry></row><row><entry /><entry>2</entry><entry>Start point of AIDs</entry></row><row><entry /><entry>3</entry><entry>Size (or number) of AID resources</entry></row><row><entry namest="1" nameend="3" align="center" rowsep="1" /></row></tbody></tgroup></table></tables>

0173When the AID resource response frame is received from the master access point (M-AP), the relay device R may allocate AIDs to the first terminal STA<b>1</b> and the second terminal STA<b>2</b> belonging to the R-BSS, based on the AID resource information included in the AID resource response frame (S<b>1520</b>). For example, when the range of AIDs received from the master access point (M-AP) is designated on a page ID basis, the relay device R may allocate different AIDs to the first terminal STA<b>1</b> and the second terminal STA<b>2</b> belonging to the R-BSS, within a designated page ID range. When the range of AIDs received from the master access point (M-AP) is designated on a block index basis, the relay device R may allocate different AIDs to the first terminal STA<b>1</b> and the second terminal STA<b>2</b> belonging to the R-BSS within a designated block index range. When the range of AIDs received from the master access point (M-AP) is designated on a sub-block index basis, the relay device R may allocate different AIDs to the first terminal STA<b>1</b> and the second terminal STA<b>2</b> belonging to the R-BSS within a designated sub-block index range.

0174The relay device R may transmit the information about AID resources allocated to the terminals belonging to the R-BSS to the master access point (M-AP)(S<b>1530</b>). In this case, the relay device R may transmit the MAC addresses of the terminals belonging to the R-BSS, together with the information about AID resources allocated to the terminals, to the master access point (M-AP). For example, the relay device

0175R may transmit the AID and the MAC address of the first terminal STA<b>1</b> to the master access point (M-AP), and may transmit the AID and MAC address of the second terminal STA<b>2</b> to the master access point (M-AP).

0176When there is a data frame to be transmitted to the first terminal STA<b>1</b>, the master access point (M-AP) may configure the address field included in the corresponding data frame in the way described above according to the ‘first embodiment of the address field’, ‘second embodiment of the address field’, ‘third embodiment of the address field’ or ‘fourth embodiment of the address field’. That is, the master access point (M-AP) may configure the DA field of the address field included in the data frame as the AID of the first terminal STA<b>1</b>, or the RA field of the address field included in the data frame as the AID of the relay device R.

0177The master access point (M-AP) may transmit a data frame including the address field, configured in this way, to the relay device R (S<b>1540</b>). When the data frame is received from the master access point (M-AP), the relay device R may recognize that the final destination of the data frame is the first terminal STA<b>1</b>, via the address field included in the data frame. Therefore, the relay device R may transmit the data frame to the first terminal STA<b>1</b> (S<b>1550</b>).

0178Meanwhile, when the data frame that is transmitted from the relay device R to the first terminal STA<b>1</b> is acquired, the master access point (M-AP) may determine that the relay device R has successfully received the data frame. That is, the master access point (M-AP) may regard the data frame that is transmitted from the relay device R to the first terminal STA<b>1</b> as an ACK frame for the data frame, which the M-AP has transmitted to the relay device R. Alternatively, when the data frame has been successfully received from the master access point (M-AP), the relay device R may transmit an ACK frame, as a response thereto, to the master access point (M-AP).

0179When the data frame has been successfully received from the relay device R, the first terminal STA<b>1</b> may transmit an ACK frame, as a response thereto, to the relay device R (S<b>1560</b>).

0180<figref idref="DRAWINGS">FIG. 16</figref> is a conceptual diagram showing yet another embodiment of a data transmission/reception method.

0181Referring to <figref idref="DRAWINGS">FIG. 16</figref>, a master access point (M-AP) may serve an M-BSS, and a relay device R may belong to the M-BSS. The relay device R may serve an R-BSS, and a first terminal STA<b>1</b> may belong to the R-BSS. Here, the AID of the relay device R may be allocated based on the AID allocation method, described above with reference to <figref idref="DRAWINGS">FIG. 11</figref>. The AID of the first terminal STA<b>1</b> belonging to the R-BSS may be allocated based on the AID allocation method, as described above with reference to <figref idref="DRAWINGS">FIG. 11</figref> or the AID allocation method, described above with reference to <figref idref="DRAWINGS">FIG. 15</figref>.

0182When data to be transmitted to the first terminal STA<b>1</b> is present, the master access point (M-AP) may set a bit corresponding to the AID of the first terminal STA<b>1</b> in a TIM to ‘1’ so as to indicate the presence of data, and transmit a beacon frame <b>1600</b> including the TIM.

0183When the beacon frame <b>1600</b> is received from the master access point (M-AP), the relay device R may recognize that the bit corresponding to the AID of the first terminal STA<b>1</b> belonging to the R-BSS is set to ‘1’ in the TIM included in the beacon frame <b>1600</b>, and may determine, based on the AID, that data to be transmitted to the first terminal STA<b>1</b> is buffered in the master access point (M-AP). The relay device R may set the bit corresponding to the AID of the first terminal STA<b>1</b> in the TIM to ‘1’ so as to indicate that data to be transmitted to the first terminal STA<b>1</b> is present, and may transmit a beacon frame <b>1601</b> including the TIM.

0184When the beacon frame <b>1601</b> is received from the relay device R, the first terminal STA<b>1</b> may recognize that the bit corresponding to its own AID is set to ‘1’ in the TIM included in the beacon frame <b>1601</b>. That is, the first terminal STA<b>1</b> may be aware that data to be transmitted thereto is present. The first terminal STA<b>1</b> may request the transmission of data by transmitting a PS-Poll frame (or a trigger frame) <b>1602</b> to the relay device R after a contention window (CW) based on a random backoff procedure has elapsed when a channel is in an idle state during distributed coordination function (DCF) interframe space (DIFS) from the time at which the reception of the beacon frame <b>1601</b> is terminated. At this time, the first terminal STA<b>1</b> may indicate that, after the PS-Poll frame (or the trigger frame) <b>1602</b>, an ACK frame <b>1603</b> that is a normal response is to be transmitted by setting the response indication deferral (RID) bit of a signal (SIG) field included in the PS-Poll frame (or the trigger frame) <b>1602</b> to ‘b10’.

0185When the PS-Poll frame (or the trigger frame) <b>1602</b> is received from the first terminal STA<b>1</b>, the relay device R may determine that the first terminal STA<b>1</b> has been awakened (i.e. operated in an awake state), and may then transmit the ACK frame <b>1603</b> that is a response to the PS-Poll frame (or the trigger frame) <b>1602</b> after a short interframe space (SIFS) has elapsed from the time at which the reception of the PS-Poll frame (or the trigger frame) <b>1602</b> is terminated. At this time, the relay device R may indicate that, after the ACK frame <b>1603</b>, a data frame <b>1604</b> that is a long response is to be transmitted by setting the RID bit of a SIG field included in the ACK frame <b>1603</b> to ‘b11’.

0186Meanwhile, the master access point (M-AP) cannot receive the PS-Poll frame (or the trigger frame) <b>1602</b> that is transmitted from the first terminal STA<b>1</b>, but it can receive the ACK frame <b>1603</b> that is transmitted from the relay device R as a response to the PS-Poll frame (or the trigger frame) <b>1602</b>. Therefore, when the ACK frame <b>1603</b> transmitted from the relay device R is received, the master access point (M-AP) may determine that the first terminal STA<b>1</b> has been awakened, and may then transmit a data frame <b>1604</b> to the relay device R after SIFS has elapsed from the reception termination time of the ACK frame <b>1603</b>. At this time, the master access point (M-AP) may indicate that, after the data frame, an ACK frame <b>1605</b> that is a normal response is to be transmitted by setting the RID bit of a SIG field included in the data frame <b>1604</b> to ‘b10’.

0187When the data frame <b>1604</b> has been successfully received, the relay device R may transmit the ACK frame <b>1605</b> that is a response to the data frame <b>1604</b> to the master access point (M-AP) after SIFS has elapsed from the reception termination time of the data frame <b>1604</b>. At this time, the relay device R may indicate that, after the ACK frame <b>1605</b>, a data frame <b>1606</b> that is a long response is to be transmitted by setting the RID bit of a SIG field included in the ACK frame <b>1605</b> to ‘b11’. Here, the data frame <b>1606</b> may include the same information as the data frame <b>1604</b> transmitted from the master access point (M-AP).

0188Thereafter, the relay device R may transmit the data frame <b>1606</b> to the first terminal STA<b>1</b> after SIFS has elapsed from the transmission termination time of the ACK frame <b>1605</b>. Here, the relay device R may indicate that, after the data frame <b>1606</b>, an ACK frame <b>1607</b> that is a normal response is to be transmitted by setting the RID bit of a SIG field included in the data frame <b>1606</b> to ‘b10’. When the data frame <b>1606</b> has been successfully received, the first terminal STA<b>1</b> may transmit the ACK frame <b>1607</b> that is a response to the data frame <b>1606</b> to the relay device R after SIFS has elapsed from the reception termination time of the data frame <b>1606</b>. Here, the first terminal STA<b>1</b> may indicate that, after the ACK frame <b>1607</b>, no data frames are to be transmitted by setting the RID bit of a SIG field included in the ACK frame <b>1607</b> to ‘b00’.

0189Meanwhile, when desiring to transmit a data frame to terminals belonging to the R-BSS in a broadcast (or multicast) manner, the master access point (M-AP) may set a separate broadcast/multicast AID bit allocated to the relay device R, which serves the R-BSS, in a TIM. At this time, the AID allocated to the relay device R may replace the broadcast/multicast AID. The master access point (M-AP) may generate a beacon frame including the TIM in which the AID bit of the relay device R is set, and transmit the generated beacon frame. That is, the AID of the relay device R may be used as an indicator for broadcast (or multicast) transmission to the terminals belonging to the R-BSS.

0190When the beacon frame is received from the master access point (M-AP), the relay device R may recognize that its own AID bit is set in the TIM included in the beacon frame, and may determine, based on the AID bit, that data to be transmitted in a broadcast (or multicast) manner to the terminals belonging to the R-BSS is buffered in the master access point (M-AP). Therefore, the relay device R may set the AID bits of all terminals belonging to the R-BSS in the TIM, generate a beacon frame including the TIM in which the AID bits of all terminals belonging to the R-BSS are set, and transmit the generated beacon frame.

0191When the beacon frame is received from the relay device R, the terminals belonging to the R-BSS may recognize that their own AID bits are set in the TIM included in the beacon frame, and may determine, based on the AID bits, that data to be transmitted thereto is present. The terminals belonging to the R-BSS may request the relay device R to transmit data frames by transmitting PS-Poll frames (or trigger frames) to the relay device R.

0192When the PS-Poll frames (or the trigger frames) are received from the terminals belonging to the R-BSS, the relay device R may determine that the terminals belonging to the R-BSS have been awakened and may then transmit an ACK frame as a response to the PS-Poll frames (or the trigger frames).

0193Meanwhile, the master access point (M-AP) cannot receive the PS-Poll frames (or the trigger frames) transmitted from the terminals belonging to the R-BSS, but may receive the ACK frame transmitted from the relay device R as the response to the PS-Poll frames (or trigger frames). Therefore, when the ACK frame transmitted from the relay device R is received, the master access point (M-AP) may determine that the terminals belonging to the R-BSS have been awakened, and may then transmit a data frame to the relay device R.

0194When the data frame has been successfully received, the relay device R may transmit an ACK frame, as a response to the data frame, to the master access point (M-AP). Thereafter, the relay device R may transmit the data frame to the terminals belonging to the R-BSS in a broadcast (or multicast) manner.

0195<figref idref="DRAWINGS">FIG. 17</figref> is a conceptual diagram showing another embodiment of a WLAN system including relay devices.

0196Referring to <figref idref="DRAWINGS">FIG. 17</figref>, a master access point (M-AP), a first relay device R<b>1</b>, a second relay device R<b>2</b>, a first terminal STA<b>1</b>, a second terminal STA<b>2</b>, a fourth terminal STA<b>4</b>, and a fifth terminal STA<b>5</b> may constitute an M-BSS. The second relay device R<b>2</b>, a third terminal STA<b>3</b>, and the fourth terminal STA<b>4</b> may constitute a second relay BSS (R<b>2</b>-BSS).

0197The first relay device R<b>1</b> may not constitute its own independent relay BSS. In this case, the first relay device R<b>1</b> may function to acquire only uplink frames, which are transmitted from the terminals STA<b>1</b> and STA<b>2</b> to the master access point (M-AP), from the terminals STA<b>1</b> and STA<b>2</b>, and to forward the uplink frames to the master access point (M-AP). That is, the function of a relay access point (R-AP, see <figref idref="DRAWINGS">FIG. 10</figref>) that acts as an access point in the first relay device R<b>1</b> may not be present or may not be used, and only the function of a relay terminal (R-STA, see <figref idref="DRAWINGS">FIG. 10</figref>) may be used to forward the uplink frames acquired from the terminals STA<b>1</b> and STA<b>2</b> to the master access point (M-AP).

0198Since the first relay device R<b>1</b> does not form its own independent relay BSS, it may not independently transmit a beacon frame or a probe response frame. Therefore, when each of the terminals STA<b>1</b> and STA<b>2</b> performs a probe procedure, it can identify the existence of the master access point (M-AP), but cannot identify the existence of the first relay device R<b>1</b>. Further, the first relay device R<b>1</b> may not perform an authentication procedure, an association procedure, etc. with each of the terminals STA<b>1</b> and STA<b>2</b>. That is, each of the terminals STA<b>1</b> and STA<b>2</b> may perform an authentication procedure, an association procedure, etc. with the master access point (M-AP).

0199<figref idref="DRAWINGS">FIG. 18</figref> is a conceptual diagram showing an association method in an uplink relay mode according to an embodiment of the present invention.

0200Referring to <figref idref="DRAWINGS">FIG. 18</figref>, a master access point (M-AP) may denote the master access point (M-AP) shown in <figref idref="DRAWINGS">FIG. 17</figref>, a first relay device R<b>1</b> may denote the first relay device R<b>1</b> shown in <figref idref="DRAWINGS">FIG. 17</figref>, and a first terminal STA<b>1</b> may denote the first terminal STA<b>1</b> shown in <figref idref="DRAWINGS">FIG. 17</figref>. That is, the master access point (M-AP) may constitute an M-BSS. The first relay device R<b>1</b> may be associated with the master access point (M-AP) and may not constitute its own independent relay BSS. The first terminal STA<b>1</b> may belong to the M-BSS served by the master access point (M-AP).

0201The master access point (M-AP) may transmit a beacon frame <b>1800</b> in a broadcast manner. In order to probe a neighboring access point, the first terminal STA<b>1</b> may transmit a probe request frame <b>1801</b>. Here, the first terminal STA<b>1</b> may transmit the probe request frame <b>1801</b> after a contention window (CW) based on a random backoff procedure when a channel is in an idle state during DIFS. The probe request frame <b>1801</b> may include a field indicating whether a relevant frame is a frame transmitted in a relay manner. For example, the first terminal STA<b>1</b> may indicate that the probe request frame <b>1801</b> cannot be transmitted through a certain relay device by setting the field, indicating whether the relevant frame is a frame transmitted in a relay manner, to ‘0’. Further, the first terminal STA<b>1</b> may indicate that the probe request frame <b>1801</b> can be transmitted through a certain relay device by setting the field, indicating whether the relevant frame is a frame transmitted in a relay manner, to ‘1’.

0202The first relay device R<b>1</b> may acquire the probe request frame <b>1801</b> that is transmitted from the first terminal STA<b>1</b>. When the SSID field of the probe request frame <b>1801</b> is set to the SSID of the master access point (M-AP) or any value, the first relay device R<b>1</b> may transmit a probe request frame <b>1802</b> including the same information as the probe request frame <b>1801</b> to the master access point (M-AP) after SIFS has elapsed from the reception termination time of the probe request frame <b>1801</b>.

0203Alternatively, when the field, included in the probe request frame <b>1801</b> and indicating whether the relevant frame is a frame transmitted in a relay manner, indicates that the probe request frame <b>1801</b> can be transmitted through a certain relay device, the first relay device R<b>1</b> may transmit the probe request frame <b>1802</b> having the same information as the probe request frame <b>1801</b> to the master access point (M-AP) after SIFS has elapsed from the reception termination time of the probe request frame <b>1801</b>. In contrast, when the field, included in the probe request frame <b>1801</b> and indicating whether the relevant frame is a frame transmitted in a relay manner, indicates that the probe request frame <b>1801</b> cannot be transmitted through a certain relay device, the first relay device R<b>1</b> may not transmit the probe request frame <b>1801</b> to the master access point (M-AP).

0204Meanwhile, the first relay device R<b>1</b> may set the address field of the probe request frame <b>1802</b> in the following manner. <ul id="ul0011" list-style="none"><li id="ul0011-0001" num="0000"><ul id="ul0012" list-style="none"><li id="ul0012-0001" num="0205">TA field: address (i.e. MAC address) of first relay device</li><li id="ul0012-0002" num="0206">RA field: broadcast address</li><li id="ul0012-0003" num="0207">DA field: broadcast address</li><li id="ul0012-0004" num="0208">SA field: address (i.e. MAC address) of first terminal</li></ul></li></ul>

0209The master access point (M-AP) cannot receive the probe request frame <b>1801</b> that is transmitted from the first terminal STA<b>1</b>, but it can receive the probe request frame <b>1802</b> transmitted from the first relay device R<b>1</b>. The master access point (M-AP) may determine whether the frame from the first relay device R<b>1</b> is being transmitted in a relay manner, based on at least one of the field, included in the probe request frame <b>1802</b> and indicating whether the relevant frame is a frame transmitted in a relay manner, and the address fields of the probe request frame <b>1802</b>.

0210For example, when the field, included in the probe request frame <b>1802</b> and indicating whether the relevant frame is a frame transmitted in a relay manner, indicates that the frame can be transmitted through a certain relay device, the master access point (M-AP) may determine that the probe request frame <b>1802</b> is being transmitted in a relay manner. Alternatively, when the TA field of the address fields included in the probe request frame <b>1802</b> indicates the address of the first relay device R<b>1</b> and the SA field of the address fields indicates the address of the first terminal STA<b>1</b>, the master access point (M-AP) may determine that the probe request frame <b>1802</b> is being transmitted through the first relay device R<b>1</b>.

0211The master access point (M-AP) may generate a probe response frame <b>1803</b> that is a response to the probe request frames <b>1801</b> and <b>1802</b>. The probe response frame <b>1803</b> may include an unlink relay mode field indicating whether the M-AP is operated in an uplink relay mode. For example, the case where the uplink relay mode field is set to ‘0’ may mean that the M-AP is not operated in an uplink relay mode. The case where the uplink relay mode field is set to ‘1’ may mean that the M-AP is operated in an uplink relay mode. Here, the master access point (M-AP) may indicate that it is operated in an uplink rely mode by setting the uplink relay mode field of the probe response frame <b>1803</b> to ‘1’.

0212Also, the probe response frame <b>1803</b> may include the identifier (i.e. MAC address, AID, Partial AID (PAID), or the like) of a relay device for performing uplink relay transmission. Here, the master access point (M-AP) may generate a probe response frame <b>1803</b> including the identifier of the first relay device R<b>1</b>.

0213The master access point (M-AP) may transmit the probe response frame <b>1803</b>, including the uplink relay mode field, the identifier of the first relay device R<b>1</b>, etc., to the first terminal STA<b>1</b>. Here, the master access point (M-AP) may transmit the probe response frame <b>1803</b> to the first terminal STA<b>1</b> after SIFS has elapsed from the reception termination time of the probe request frame <b>1802</b>.

0214Meanwhile, the first terminal STA<b>1</b> may receive the probe response frame <b>1803</b> transmitted from the master access point (M-AP). The first terminal STA<b>1</b> may acquire the uplink relay mode field included in the probe response frame <b>1803</b> and the identifier of the relay device for performing uplink relay transmission, and may recognize, based on the acquired information, that the master access point (M-AP) and the first relay device R<b>1</b> are operated in an uplink relay mode.

0215The first terminal STA<b>1</b> may transmit the ACK frame <b>1804</b> that is a response to the probe response frame <b>1803</b> to the first relay device R<b>1</b> after SIFS has elapsed from the reception termination time of the probe response frame <b>1803</b>. The first relay device R<b>1</b>, having received the ACK frame <b>1804</b>, may transmit an ACK frame <b>1805</b> including the same information as the ACK frame <b>1804</b> to the master access point (M-AP) after SIFS has elapsed from the reception termination time of the ACK frame <b>1804</b>.

0216Meanwhile, since a response to the probe response frame <b>1803</b> is transmitted to the master access point (M-AP) through the first relay device R<b>1</b>, the master access point (M-AP) may define a separate relay ACK timeout for the first terminal STA<b>1</b> that is operated in an uplink relay mode. For example, the relay ACK timeout may be designated to be longer than an existing ACK timeout (i.e. SIFS+reception_start_delay (RX_Start_Delay)+slot time), as given in the following Equation 1. The existing ACK timeout may mean the maximum time during which a first communication entity is waiting for an ACK frame, which is a response to a certain frame, to be received from a second communication entity after having transmitted the certain frame to the second communication entity.

0000<br />relay ACK timeout≧2×ACK timeout  Equation 1

0217Therefore, when a probe ACK frame <b>1805</b> that is a response to the probe response frame <b>1803</b> is not received from the first relay device R<b>1</b> within the relay ACK timeout from the transmission termination time of the probe response frame <b>1803</b>, the master access point (M-AP) may determine that the first terminal STA<b>1</b> has not successfully received the probe response frame <b>1803</b>. In this case, the master access point (M-AP) may retransmit the probe response frame <b>1803</b> to the first terminal STA<b>1</b>.

0218If the above probe procedure has been completed in this way, the first terminal STA<b>1</b> may perform a procedure for authentication with the master access point (M-AP). After a time corresponding to ‘relay ACK timeout+DIFS’ has elapsed, the first terminal STA<b>1</b> may transmit an authentication request frame <b>1806</b> to the first relay device R<b>1</b>. The first relay device R<b>1</b>, having received the authentication request frame <b>1806</b>, may transmit an authentication request frame <b>1807</b>, including the same information as the authentication request frame <b>1806</b>, to the master access point (M-AP) after SIFS has elapsed from the reception termination time of the authentication request frame <b>1806</b>. Here, each of the authentication request frames <b>1806</b> and <b>1807</b> may include an uplink relay mode field indicating whether the relevant device is operated in an uplink relay mode.

0219The master access point (M-AP), having received the authentication request frame <b>1807</b>, may transmit an authentication response frame <b>1808</b> that is a response to the authentication request frame <b>1807</b> to the first terminal STA<b>1</b> after SIFS has elapsed from the reception termination time of the authentication request frame <b>1807</b>. Here, the authentication response frame <b>1808</b> may include an uplink relay mode field indicating whether a relevant device is operated in an uplink relay mode.

0220After the authentication procedure has been completed in this way, the first terminal STA<b>1</b> may perform a procedure for associating with the master access point (M-AP).

0221The first terminal STA<b>1</b> may transmit an association request frame <b>1809</b> to the first relay device R<b>1</b> after DIFS has elapsed from the reception termination time of the authentication response frame <b>1808</b>. The first relay device R<b>1</b>, having received the association request frame <b>1809</b>, may transmit an association request frame <b>1810</b>, including the same information as the association request frame <b>1809</b>, to the master access point (M-AP) after SIFS has elapsed from the reception termination time of the association request frame <b>1809</b>. Here, each of the association request frames <b>1809</b> and <b>1810</b> may include an uplink relay mode field indicating whether a relevant device is operated in an uplink relay mode.

0222The master access point (M-AP), having received the association request frame <b>1810</b>, may transmit an association response frame <b>1811</b> to the first terminal STA<b>1</b> after SIFS has elapsed from the reception termination time of the association request frame <b>1810</b>. Here, the association response frame <b>1811</b> may include a field indicating that the first terminal STA<b>1</b> has been associated with the master access point (M-AP) in an uplink relay mode, the AID of the first terminal STA<b>1</b>, etc.

0223The first terminal STA<b>1</b> may be associated with the master access point (M-AP) via the above-described association procedure. Below, a method for transmitting and receiving data between the master access point (M-AP) and the first terminal STA<b>1</b>, which are associated with each other based on the uplink relay mode, will be described.

0224<figref idref="DRAWINGS">FIG. 19</figref> is a conceptual diagram showing a further embodiment of a WLAN system including relay devices.

0225Referring to <figref idref="DRAWINGS">FIG. 19</figref>, a master access point (M-AP), a first relay device R<b>1</b>, a second relay device R<b>2</b>, a first terminal STA<b>1</b>, a second terminal STA<b>2</b>, a fourth terminal STA<b>4</b>, and a fifth terminal STA<b>5</b> may constitute an M-BSS. The first relay device R<b>1</b>, the first terminal STA<b>1</b>, and the second terminal STA<b>2</b> may constitute a first relay BSS (R<b>1</b>-BSS). The second relay device R<b>2</b>, a third terminal STA<b>3</b>, and the fourth terminal STA<b>4</b> may constitute a second relay BSS (R<b>2</b>-BSS).

0226When the transmission power of the master access point (M-AP) is sufficiently high, each frame may be transmitted in an uplink relay mode. In the uplink relay mode, downlink transmission may be performed such that the master access point (M-AP) directly transmits a frame to the terminals STA<b>1</b>, STA<b>2</b>, and STA<b>4</b>, and uplink transmission may be performed such that each of the terminals STA<b>1</b>, STA<b>2</b>, and STA<b>4</b> transmits a frame to the master access point (M-AP) through the relay device R<b>1</b> or R<b>2</b>.

0227All terminals associated with each of the relay devices R<b>1</b> and R<b>2</b> may be operated in an uplink relay mode. Alternatively, some terminals associated with each of the relay devices R<b>1</b> and R<b>2</b> may be operated in an uplink relay mode, and the remaining terminals may be operated in a normal relay mode (i.e. both uplink transmission and downlink transmission are performed through relays). Since the first terminal STA<b>1</b> and the second terminal STA<b>2</b> associated with the first relay device R<b>1</b> belong to the M-BSS, they may be operated in an uplink relay mode. Since the third terminal STA<b>3</b> associated with the second relay device R<b>2</b> does not belong to the M-BSS, it may be operated in a normal relay mode other than an uplink relay mode. Since the fourth terminal STA<b>4</b> associated with the second relay device R<b>2</b> belongs to the M-BSS, it may be operated in an uplink relay mode.

0228Meanwhile, such an uplink relay mode may be initiated at the request of a specific terminal. For example, the first terminal STA<b>1</b> may request the first relay device R<b>1</b> to be operated in an uplink relay mode when recognizing that the STA<b>1</b> is located in the M-BSS. In this case, the first relay device R<b>1</b> may notify the first terminal STA<b>1</b> of the target beacon transmission time (TBTT) of the master access point (M-AP), and may notify the master access point (M-AP) that the first terminal STA<b>1</b> is operated in an uplink relay mode.

0229When recognizing that the first terminal STA<b>1</b> is operated in an uplink relay mode, the master access point (M-AP) may set a bit corresponding to the AID of the first terminal STA<b>1</b> in a TIM included in a beacon frame to ‘1’ so as to transmit data to the first terminal STA<b>1</b>. The first terminal STA<b>1</b> may receive a beacon frame transmitted from the master access point (M-AP) based on the TBTT of the master access point (M-AP). The first terminal STA<b>1</b> may determine that data to be transmitted thereto is present in the master access point (M-AP) when the bit corresponding to the AID of the STA<b>1</b> is set to ‘1’ in the TIM included in the received beacon frame.

0230<figref idref="DRAWINGS">FIG. 20</figref> is a conceptual diagram showing still another embodiment of a data transmission/reception method according to the present invention.

0231Referring to <figref idref="DRAWINGS">FIG. 20</figref>, a master access point (M-AP) may denote the master access point (M-AP) shown in <figref idref="DRAWINGS">FIG. 19</figref>, a first relay device R<b>1</b> may denote the first relay device R<b>1</b> shown in <figref idref="DRAWINGS">FIG. 19</figref>, and a first terminal STA<b>1</b> may denote the first terminal STA<b>1</b> shown in <figref idref="DRAWINGS">FIG. 19</figref>. That is, the first relay device R<b>1</b> may be associated with the master access point (M-AP), and the first terminal STA<b>1</b> may be associated with the first relay device R<b>1</b>. The first terminal STA<b>1</b> may belong to an M-BSS served by the master access point (M-AP) and an R<b>1</b>-BSS served by the first relay device R.

0232The transmission and reception of frames between the master access point (M-AP), the first relay device R<b>1</b>, and the first terminal STA<b>1</b> may be performed based on an uplink relay mode. In this case, if data to be transmitted to the first terminal STA<b>1</b> is buffered, the master access point (M-AP) may set a bit corresponding to the AID of the first terminal STA<b>1</b> in a TIM to ‘1’, and may transmit a beacon frame <b>2000</b> including the TIM.

0233Since the first terminal STA<b>1</b> is located in the M-BSS, it may receive the beacon frame <b>2000</b> transmitted from the master access point (M-AP). The first terminal STA<b>1</b> may determine that data to be transmitted thereto is buffered in the master access point (M-AP) because the bit corresponding to the AID of the STA<b>1</b> in the TIM included in the received beacon frame <b>2000</b> is set to ‘1’.

0234Therefore, when a channel is in an idle state during DIFS from the reception termination time of the beacon frame <b>2000</b>, the first terminal STA<b>1</b> may transmit a PS-Poll frame (or a trigger frame) <b>2001</b> to the first relay device R<b>1</b> after a contention window (CW) based on a random backoff procedure. At this time, the first terminal STA<b>1</b> may indicate that, after the PS-Poll frame (or the trigger frame) <b>2001</b>, a PS-Poll frame (or a trigger frame) <b>2002</b> that is a normal type response frame is to be transmitted by setting the RID bit of a SIG field included in the PS-Poll frame (or the trigger frame) <b>2001</b> to ‘b10’. Meanwhile, when the PS-Poll frame (or the trigger frame) <b>2001</b> is a null data packet (NDP)-type frame, the first terminal STA<b>1</b> may indicate that, after the PS-Poll frame (or the trigger frame) <b>2001</b>, a PS-Poll frame (or a trigger frame) <b>2002</b> that is an NDP-type response frame is to be transmitted by setting the RID bit of the SIG field to ‘b01’. That is, a certain frame transmitted from the first terminal STA<b>1</b> may include an RID bit that is information indicating the type of the frame transmitted from a communication entity (e.g. the relay device R or the master access point (M-AP)) that has received the certain frame.

0235When the PS-Poll frame (or the trigger frame) <b>2001</b> is received from the first terminal STA<b>1</b>, the first relay device R<b>1</b> may transmit the PS-Poll frame (or the trigger frame) <b>2002</b> to the master access point (M-AP) after SIFS has elapsed from the reception termination time of the PS-Poll frame (or trigger frame) <b>2001</b>. The PS-Poll frame (or the trigger frame) <b>2002</b> may include the same information as the PS-Poll frame (or trigger frame) <b>2001</b> received from the first terminal STA<b>1</b>. At this time, the first relay device R<b>1</b> may indicate that, after the PS-Poll frame (or the trigger frame) <b>2002</b>, a data frame <b>2003</b> that is a long response frame is to be transmitted by setting the RID bit of a SIG field included in the PS-Poll frame (or the trigger frame) <b>2002</b> to ‘b11’.

0236The master access point (M-AP) may determine that, when the PS-Poll frame (or the trigger frame) <b>2002</b> is received from the first relay device R<b>1</b>, the first terminal STA<b>1</b> is in the state in which a frame can be received (i.e. an awake state). Therefore, the master access point (M-AP) may transmit the data frame <b>2003</b> to the first terminal STA<b>1</b> after SIFS has elapsed from the reception termination time of the PS-Poll frame (or the trigger frame) <b>2002</b>. At this time, the master access point (M-AP) may indicate that, after the data frame <b>2003</b>, an ACK frame <b>2004</b> that is a normal type response frame is to be transmitted by setting the RID bit of a SIG field included in the data frame <b>2003</b> to ‘b10’.

0237Meanwhile, since a response to the data frame <b>2003</b> is transmitted through the first relay device R<b>1</b>, the master access point (M-AP) may set a duration field included in the data frame <b>2003</b> to a period corresponding to ‘SIFS+length of ACK frame <b>2004</b>+SIFS+length of ACK frame <b>2005</b>’ to protect the transmission of the ACK frames <b>2004</b> and <b>2005</b>.

0238When the data frame <b>2003</b> is received, the first terminal STA<b>1</b> may transmit the ACK frame <b>2004</b> that is a response to the data frame <b>2003</b> to the first relay device R<b>1</b> after SIFS has elapsed from the reception termination time of the data frame <b>2003</b>. At this time, the first terminal STA<b>1</b> may indicate that, after the ACK frame <b>2004</b>, an ACK frame <b>2005</b> that is a normal type response frame is to be transmitted by setting the RID bit of a SIG field included in the ACK frame <b>2004</b> to ‘b10’.

0239When the ACK frame <b>2004</b> is received, the first relay device R<b>1</b> may transmit the ACK frame <b>2005</b> to the master access point (M-AP) after SIFS has elapsed from the reception termination time of the ACK frame <b>2004</b>. The ACK frame <b>2005</b> may include the same information as the ACK frame <b>2004</b> that is a response to the data frame <b>2003</b>. At this time, the first relay device R<b>1</b> may indicate that, after the ACK frame <b>2005</b>, no frames are to be transmitted by setting the RID bit of a SIG field included in the ACK frame <b>2005</b> to ‘b00’. When the ACK frame <b>2005</b> is received, the master access point (M-AP) may determine that the first terminal STA<b>1</b> has successfully received the data frame <b>2003</b>.

0240Meanwhile, since a response to the data frame <b>2003</b> is transmitted to the master access point (M-AP) through the first relay device R<b>1</b>, the master access point (M-AP) may define a separate relay ACK timeout for the first terminal STA<b>1</b> that is operated in an uplink relay mode. For example, the relay ACK timeout may be designated to be longer than an existing ACK timeout (i.e. SIFS+Reception_start_delay (RX_Start_Delay)+slot time), as given in the above Equation 1. The existing ACK timeout may mean the maximum time during which a first communication entity is waiting for an ACK frame, which is a response to a certain frame, to be received from a second communication entity after having transmitted the certain frame to the second communication entity.

0241Therefore, when an ACK frame <b>2005</b> that is a response to the data frame <b>2003</b> is not received from the first relay device R<b>1</b> within the relay ACK timeout from the transmission termination time of the data frame <b>2003</b>, the master access point (M-AP) may determine that the first terminal STA<b>1</b> has not successfully received the data frame <b>2003</b>. In this case, the master access point (M-AP) may retransmit the data frame <b>2003</b> to the first terminal STA<b>1</b>.

0242In accordance with the present invention, a master access point may extend a service area via a relay device. Since a terminal may secure a good quality link via the relay device, data can be transmitted at high speed. That is, the relay device is used, and thus the efficiency of use of a wireless channel may be improved and the amount of power consumed by the terminal may be reduced.

0243Further, the master access point may allocate available AID resources to a relay device, and the relay device may allocate AIDs among AID resources allocated by the master access point to end terminals. By means of this, the master access point may directly manage the AIDs of end terminals belonging to an R-BSS. Accordingly, the master access point may easily set the AID of the end terminal in a TIM when a data frame is transmitted to an end terminal through the relay device. The relay device may easily map the reception address of a data frame during a procedure for forwarding a data frame received from the master access point to the end terminal.

0244Furthermore, the AID of the relay device may be used as an indicator for broadcast (or multicast) transmission to end terminals belonging to the corresponding R-BSS. Therefore, the master access point may broadcast (or multicast) a data frame to the terminals belonging to the R-BSS using the AID of the relay device.

0245Furthermore, when the master access point transmits a data frame to an end terminal through the relay device, the AID of the relay device, instead of the MAC address of the relay device, may be used as the reception address (i.e. RA field) of the data frame, and thus the length of the data frame may be reduced.

0246Furthermore, when a data frame is transmitted to the end terminal via the relay device, the master access point may use the AID of the end terminal, instead of the MAC address of the end terminal, as the destination address (i.e. DA field) of the data frame, and thus the length of the data frame may be reduced.

0247Furthermore, in accordance with an uplink relay mode, downlink transmission may be performed such that the master access point directly transmits a frame to an end terminal, and uplink transmission may be performed such that an end terminal transmits a frame to the master access point through the relay device. Therefore, when the uplink relay mode is used, wireless channel resources may be efficiently used compared to a normal relay mode in which frames are bidirectionally transmitted through a relay device.

0248The embodiments of the present invention may be implemented in the form of program instructions that are executable via various types of computer means, and may be recorded on a computer-readable medium. The computer-readable medium may include program instructions, data files, and data structures solely or in combination. Program instructions recorded on the computer-readable medium may have been specially designed and configured for the embodiments of the present invention, or may be known to or available to those who have ordinary knowledge in the field of computer software.

0249Examples of the computer-readable storage medium include all types of hardware devices specially configured to store and execute program instructions, such as read only memory (ROM), random access memory (RAM), and flash memory. The hardware devices may be configured to operate as one or more software modules in order to perform the operation according to embodiments of the present invention, and vice versa. Examples of the program instructions include machine language code, such as code created by a compiler, and high-level language code executable by a computer using an interpreter or the like.

0250Although the present invention has been described with reference to the embodiments, those skilled in the art will appreciate that the present invention can be modified and changed in various forms, without departing from the spirit and scope of the invention as disclosed in the accompanying claims.