WO2009064105A2

WO2009064105A2 - Method for selecting the best path in wireless local area network

Info

Publication number: WO2009064105A2
Application number: PCT/KR2008/006649
Authority: WO
Inventors: Jiyoung Huh; Eunkyo Kim; Jae Young Lee; Sihoon Yang; Yongho Seok
Original assignee: Lg Electronics Inc.
Priority date: 2007-11-12
Filing date: 2008-11-12
Publication date: 2009-05-22
Also published as: WO2009064105A3

Abstract

A procedure for selecting the best path from among a direct link setup (DLS) path and an access point (AP) path is disclosed. A method for selecting the best path by a first wireless station from among the DLS path and the AP path includes: receiving a first message, e.g., a path switch request message, comprising measured quality information of a link constituting the DLS path and/or a link constituting the AP path from a second wireless station, a counterpart of the DLS path; and determining whether to switch a data transmission path or a data reception path between the DLS path and the AP path by using the received measured channel quality information. Although there is no explicit request from the counterpart of the DLS link, the path switch request message including the measured channel state information of the DLS link and the link of the AP path is transmitted, so the wireless stations using the DLS service can acquire the channel state information of the links frequently to transmit data by using a path of better channel state.

Description

METHOD FOR SELECTING THE BEST PATH IN WIRELESS

LOCAL AREA NETWORK

Technical Field

[1] The present invention relates to a wireless local area network (WLAN) and, more particularly, to a method for selecting the best path from among a direct link setup (DLS) path and a path (access point (AP) path) that goes by way of an AP. Background Art

[2] Communications in a network according to the IEEE 802.11 standards are presumed to be made within a region called a basic service set (BSS). The BSS region may vary according to the propagation characteristics of a wireless medium, so its boundary is somewhat indefinite. The BSS may be basically classified into two configurations of an independent BSS (IBSS) and an infrastructured BSS. The former, which forms a self-contained network, refers to a BSS not allowed for a connection to a distribution system (DS), while the latter, which includes one or more APs, DSs, or the like, refers to a BSS using APs for every communication process including communication between wireless stations.

[3] The conventional WLAN standards do not allow direct transmission of data between wireless stations generally in the infrastructured BSS, but requesting that data should be necessarily transmitted by way of an AP. Meanwhile, new WLAN standards define a direct link setup (DLS) procedure for direct communication between wireless stations (e.g., QSTAs (Quality of Service Stations)). According to the new WLAN standards, a QSTA sets up a direct link with a peer QSTA by transmitting and receiving a DLS request frame and a corresponding DLS response frame via a QAP (Quality of Access Point) or a legacy AP. With the direct link set up, the QSTA can directly transmit data to the peer QSTA by using the DLS without passing through the AP.

[4] After the direct link is set up according to the DLS procedure, the QSTA may transmit data by using the established direct link, or may transmit data via the QAP likewise as in the related art. Namely, although the direct link is set, data transmission using the AP is also allowed. For example, the QSTA may use a polled transmission opportunity (TXOP), or the like, for a data transmission. Thus, in this manner, although a direct link is established between the two QSTAs, the QSTA may transmit data by using the direct link or may transmit data to the peer QSTA by way of an AP (through AP path).

[5] If a plurality of paths can be used for a data transmission, it would be preferred to transmit data by using a path with a better channel quality as possible in consideration of the characteristics of radio communication in which a data loss may made in the transmission process. However, currently, only the data transmission by using the DLS path after setting the direct link and/or by using the AP path is defined, but not a substantial mechanism for selecting the best one of the two paths. Thus, in the case where the DLS path and the AP path are all available to be used after setting the direct link between two wireless stations, it is required to establish a procedure for selecting a more effective path from among the DLS path and the AP path in transmitting data, and a selection basis. Disclosure of Invention Technical Problem

[6] The present invention is designed to solve such a problem of the related art, and therefore, an object of the present invention is to provide a method for selecting the best path from among a DLS path and an AP path.

[7] Another object of the present invention is to provide a method for effectively selecting the best path by minimizing signaling for acquiring channel quality.

[8] Still another object of the present invention is to provide a method for adaptively selecting the best path from among a DLS path and an AP path even when channel quality is variable with the lapse of time.

[9] Yet another object of the present invention is to provide a method for allowing a reception wireless station, which can easily recognize a channel state of a direct link and a link of an AP path, to spontaneously inform a transmission wireless station (sending station) about a channel quality, although the transmission wireless station, which intends to transmit frames, does not make a corresponding request explicitly.

[10] Another object of the present invention is to provide a method whereby a transmission wireless station, which intends to transmit frames, spontaneously transmits a path switch request message including channel quality information of an AP path, and a reception wireless station (receiving station) determines whether to change (switch) a path by using the channel quality information and informs the transmission wireless station accordingly. Technical Solution

[11] To achieve the above objects, there is provided a method for selecting the best path by a first wireless station from among a direct link setup (DLS) path and an access point (AP) path according to an embodiment of the present invention, including: receiving a first message including measured quality information of a link constituting the DLS path and/or a link constituting the AP path from a second wireless station, a counterpart of the DLS path, and determining whether to change a data transmission path or a data reception path between the DLS path and the AP path by using the received measured quality information.

[12] In one aspect of the embodiment, the method may further include: when the data transmission path is determined to be changed, transmitting a second message for informing the second wireless station about the intention of changing of the data transmission path. In another aspect of the embodiment, the second wireless station may transmit the first message although there is no explicit request from the first wireless station. In this case, the second wireless station may transmit the first message periodically, only when pre-set certain conditions are met, or when there is a change in a channel state of at least one of the link of the DLS path and the link of the AP path.

Advantageous Effects

[13] According to the method for selecting the best path according to embodiment of the present invention, when a direct link is set up between two wireless stations, a path with a better channel quality can be selected from among the DLS path using the direct link and the AP path by way of an AP to transmit data.

[14] According to the embodiment of the present invention using a radio measurement request message including a trigger condition, signaling for acquiring channel quality can be minimized, and in particular, because a measurement trigger message including quality information of a link can be received without requesting information about the link from the peer wireless station, the link state can be effectively recognized. In addition, although the link state is variable, if a specified trigger condition is met, link information can be immediately received, and thus, the best one of the DLS path and the AP path can be adaptively and effectively selected.

[15] According to the embodiment of the present invention in which the reception wireless station, which receives data transmitted via the direct link or the AP path, spontaneously transmits a message requesting a change of a path from the transmission wireless station, the reception wireless station can request the change of a path at an appropriate time when there is an arbitrary change in a link state, and because the reception wireless station does not need to additionally transmit a message requesting channel quality information, unnecessary overhead is not generated.

[16] Moreover, when there is a change in the link state, the transmission wireless station can spontaneously transmit a message requesting a change of a path to the reception wireless station by using channel quality information of the AP path that can be recognized at any time, whereby the transmission wireless station can request the change of the path at an appropriate time when there is an arbitrary change in the link state, and because the reception wireless station does not need to additionally transmit a message requesting channel quality information, unnecessary overhead is not generated.

Brief Description of Drawings

[17] FIG. 1 is a schematic view showing a data transmission path when a direct link is set up between two wireless stations. [18] FIG. 2 is a message flow chart illustrating one example of a procedure for selecting the best path by using a message that does not include a trigger condition according to a first embodiment of the present invention. [19] FIG. 3 is block diagram showing an example of a format of a radio measurement request message including a trigger condition that can be used in the best path selecting method according to a second embodiment of the present invention. [20] FIG. 4 is a block diagram showing an example of a format of a measurement report message that can be used as a response message with respect to FIG. 3. [21] FIG. 5 is a message flow chart illustrating an example of a procedure for selecting the best path by using a message including a trigger condition according to a second embodiment of the present invention. [22] FIG. 6 is a message flow chart illustrating another example of the procedure for selecting the best path by using the message including a trigger condition according to the second embodiment of the present invention. [23] FIG. 7 is a message flow chart illustrating an example of a procedure for selecting the best path when there is no explicit request from a wireless station that has set up a direct link according to a third embodiment of the present invention. [24] FIG. 8 is a message flow chart illustrating an example of a procedure for requesting a change of a path by a reception wireless station which sets up a direct link to receive data, although it does not receive a corresponding explicit request from a transmission wireless station. [25] FIG. 9 is a block diagram showing an example of a format of a path switch request frame. [26] FIG. 10 is a block diagram showing an example of a format of a path switch response frame. [27] FIG. 11 is a message flow chart illustrating an example of a procedure for selecting the best path requesting a change of a transmission path by the transmission wireless station which sets up a direct link to transmit data although the transmission wireless station does not have a corresponding explicit request from a peer wireless station. [28] FIG. 12 is a block diagram showing another example of the format of the path switch request frame. [29] FIG. 13 is a block diagram showing another example of the format of the path switch response frame. [30]

Mode for the Invention

[31] The embodiments of the present invention will now be described with reference to the accompanying drawings.

[32] FIG. 1 is a schematic view showing a data transmission path when a direct link is set up between a first wireless station (STAl) 10 and a second wireless station (STA2) in an infrastructured BSS. With reference to FIG. 1, the data transmission path includes a DLS link including a link © or a link ® and an AP path including a link ®+© or a link ©+©. For example, it is assumed that the first wireless station 10 transmits data to the second wireless station 20. In this case, the first wireless station 10 is a sending station and the second wireless station 20 is a receiving station. When the first wireless station 10 transmits data by using the DLS path, the data is transmitted via the link 3. When the first wireless station 10 transmits data by using the AP path, the data is transmitted from the first wireless station 10 to an AP 30 via the link ® and then transmitted from the AP 30 to the second wireless station 20 via the link ©.

[33] The first wireless station 10 or the second wireless station 20 are arbitrary devices including a medium access control following the definition (stipulation) of IEEE 802.11 standards and a physical layer interface with respect to a wireless medium, which support the DLS. The first and second wireless stations 10 and 20, non-AP stations, may be called a wireless transmit/receive unit (WTRU), a user equipment (UE), a mobile station (MS), a mobile subscriber unit, or the like.

[34] The AP 30 is a function entity having a wireless station function and providing an access with respect to a distributed service by way of a wireless medium for an associated station. The AP 30 may be a QAP (Quality Access Point) or a legacy AP supporting a direct link setup between wireless stations. When the AP 30 is a legacy AP, the DLS procedure is performed according to a TDLS (Tunneled DLS) algorithm. The AP 30 may be also called a base station (BS), a Node B, a site controller, or the like.

[35] In the embodiment of the present invention described hereinafter, it is assumed that channel quality of the DLS path and the AP path or each link quality constituting the paths may be different. Namely, when the first wireless station 10 or the second wireless station 20 transmit data to the peer wireless station by using the DLS path, each uses the link © or the link ®, respectively, and in this case, the quality of the links © and ®, namely, link capability, and a radio environment may not be the same. And, when the first wireless station 10 and the second wireless station 120 transmit data by using the AP path in FIG. 1, they use the link ®+© and the link ©+©, respectively, and in this case, the quality of the links ® and/or that of the links © and © may not be the same.

[36] In the present invention, it is assumed that there is no limitation of methods for acquiring quality information of the links toward the AP 30, namely, links ® and ©. For example, the quality information of the links ® and © may be transmitted from the AP 30 to the wireless stations 10 and 20 according to a corresponding request from the wireless stations 10 and 20 that require the quality information, or may be periodically transmitted from the AP 30 to the wireless stations 10 and 20 even without a corresponding request.

[37] Also, there is no particular limitation of methods for the wireless stations 10 and 20 to request the quality information of the link ® and/or the link © from the AP 30, respectively, and the AP 30 to transmit a response to the request to the wireless stations 10 and 20. For example, the wireless stations 10 and 20 may acquire the quality information of the links by using a radio measurement request message/measurement report message according to a first embodiment of the present invention described hereinafter, but the present invention is not limited thereto.

[38]

[39] <First embodiment

[40] In order to select the best path from among the DLS path and the AP path, one method for the wireless stations 10 and 20 to acquire the quality information of the links © and © and/or the links ® and © is transmitting and receiving a radio measurement request messages without a trigger condition and a measurement report message therefor. Here, 'there is no trigger condition' means that the wireless station, which has received the radio measurement request message, should necessarily measure a channel quality of a requested link according to a certain procedure and then transmit a measurement report message including the measurement result to the wireless station which has requested it.

[41] There is no particular limitation in the formats of the radio measurement request message without a trigger condition and the measurement report message therefor according to the first embodiment of the present invention. For example, as the request message and the report message, a measurement request message and a measurement response message defined in IEEE 802.1 Ik may be used. Alternatively, a message of a format without a triggered reporting field 430 in the radio measureement request message according to a second embodiment of the present invention to be described may be used as the request message.

[42] FIG. 2 is a message flow chart illustrating one example of a procedure for selecting the best path by using a message of the format according to the first embodiment of the present invention. The method for selecting the best path according to this embodiment will now be described with reference to FIGs. 1 and 2. [43] With reference to FIG. 2, a direct link is set up between the first wireless station 10 and the second wireless station 20 (SlOl). There is no particular limitation in the method for setting up the direct link, and for example, the direct link may be established by using a DLS procedure or a TDLS (Tunneled DLS) procedure defined in IEEE 802.11 standards. The direct link may be also set up according to a request of the first wireless station 10 or the second wireless station 20. After the direct link is set up between the first and second wireless stations 10 and 20, the first wireless station 10 initiates a procedure for selecting the best path to transmit frames.

[44] First, the wireless station, e.g., the first wireless station 10, for selecting the best path, transmits a radio measurement request message with respect to the links © and © to the second wireless station 20 (S 102). The radio measurement request message may be transmitted by using a currently used path, e.g., the DLS path. Upon receiving the radio measurement request message, the second wireless station 20 measures channel quality of the links © and © in response to the request, generates a measurement report message including the corresponding result, and transmits it to the first wireless station 10 (S 103). In this embodiment, the second wireless station 20 transmits an unconditional measurement result report message in response to the received radio measurement request message. Here, 'unconditional' means that a process for determining whether or not the second wireless station 20 meets particular conditions based on the measured link quality has not been performed, unlike the second embodiment to be described hereinafter.

[45] The type of the link quality information included in the measurement report message after being measured by the second wireless station 20 is not particularly limited. Namely, in this embodiment, any information may be used so long as it can inform about the quality of the links. According to one aspect of the present embodiment, the link quality information may be displayed, for example, as received channel power indicator (RCPI) information, received signal to noise indicator (RSNI) information, any other types of information, or a plurality of information including at least one of the RCPI and the RSNI.

[46] Subsequently, upon receiving the measurement report message from the second wireless station 20, the first wireless station 10 selects the best path from among the DLS path and the AP path by using the quality information of the link ® the first wireless station 10 already knows and the received quality information of the links © and © (S 104). As described above, there is no particular limitation in the methods for acquiring the quality information of the link ® by the first wireless station 10. In selecting the best path, there is no particular limitation in the conditions for changing the currently used path, e.g., the DLS path, to the AP path, another path, and various methods may be applied in consideration of the link performance and/or radio en- vironments.

[47] For example, it is assumed that the channel quality of the AP path which is not currently used is better than that of the DLS path. In this case, according to one aspect of the present embodiment, the first wireless station 10 may be set to unconditionally change the path from the DLS path to the AP path. In another aspect of the present embodiment, the first wireless station 10 may be set to change the path only when the difference of the channel quality between the both paths is larger than a certain threshold value. In still another aspect of the present invention, the conditions for changing from the AP path to the DLS path and the conditions for changing from the DLS path to the AP path may be set to be different.

[48] Subsequently, when it is determined to change the path to be used for data transmission from the existing path, e.g., the DLS path, to the AP path, another path, according to the determination result in step S 104, the first wireless station 10 transmits a path switch notification message or a path switch request message to the counterpart wireless station 20 (S 105). The path switch notification/request message is to inform the counterpart wireless station 20 that the first wireless station 10 has an intention of changing the path. Meanwhile, if the existing path is determined to be maintained as it is according to the determination result in step S 104, an additional message is not transmitted.

[49] As described above, according to the first embodiment of the present invention, the wireless station that wants to select the best path from among the DLS path and the AP path transmits the radio measurement request message without a trigger condition to the counterpart wireless station, and receives the measurement report message including quality information of the measured link in response. Upon receiving the measurement report message, the wireless station compares the AP path and the DLS path and selects the path of the better channel characteristics from among them.

[50]

[51] <Second embodiment

[52] In the first embodiment as described above, whenever the first wireless station 10 wants to select the best path, it is to transmit the radio measurement request message with respect to a corresponding link to the second wireless station 20, the counterpart wireless station. When the second wireless station 20 transmits the measurement report message including the quality information of the measured link to the first wireless station 10, the first wireless station 10 compares the DLS path and the AP path based on the received quality information to select the best path, each time. The procedure according to the first embodiment of the present invention is disadvantageous in that because the radio measurement request message and its response message need to be exchanged whenever the best path is to be selected, the procedure is much ineffective and cannot be effectively applied for the variable link performance and radio environment.

[53] Thus, in order to overcome such shortcomings of the first embodiment, in the second embodiment of the present invention, the radio measurement request message is not transmitted each time but a new format of messages including set particular conditions is transmitted. And, a response message with respect to the received radio measurement request message is transmitted only when the particular conditions are met. The procedure according to the second embodiment of the present invention can be digested simply as follows.

[54] First, the two wireless stations 10 and 20 which have set up a direct link transmit a radio measurement request message with respect to each transmission link to the mutually counterpart wireless stations. The radio measurement request message may be, for example, the best path selection measurement request message including a trigger condition for triggering a transmission of a measurement report message. Upon receiving the request message, the wireless station measures a link constituting the DLS path (i.e., a direct link used to transmit frames from the wireless station, which has transmitted the radio measurement request message, to the counterpart wireless station) and a link constituting the AP path (i.e., a link used to transmit frames from the AP to the reception wireless station), and determines whether or not the measurement result meets the trigger condition. When the trigger condition is met, the reception wireless station transmits a measurement report message including quality information of at least one of the two links to the wireless station which has transmitted the request message. The quality information may include at least one of the RCPI and the RSNI.

[55] Examples of the new formats of radio measurement request message and the measurement report message that can be used for the method for selecting the best path according to the second embodiment of the present invention are shown in FIGs. 3 and 4, respectively. With reference to FIGs. 3 and 4, each field, sub-fields, and the size of units constituting messages 200 and 300 are shown at upper end portions, and it would be obvious to those skilled in the art that such values are illustrative examples.

[56] FIG. 3 is block diagram showing an example of a format of the radio measurement request message 200 including a trigger condition. The radio measurement request message 200 can be used for the method for selecting the best path according to the second embodiment of the present invention, and it can be, for example, a best path selection measurement request message. The radio measurement request message 200 is to acquire quality information of the links ©, ©, ®, and/or © as shown in FIG. 1, and in the present embodiment, there is no particular limitation in the methods for acquiring the quality information of the links ® and © likewise as in the first embodiment. [57] With reference to FIG. 3, the radio measurement request message 200 is featured to have a triggered reporting field 230, and may further include a randomization interval field 210 and a measurement duration field 220. A maximum random delay time allowed from a measurement time is set in the randomization interval field 210, and when a triggered best path selection measurement is requested as in the present embodiment, the randomization interval field 210 may be set as 0. A duration required for performing the requested measurement is set in the measurement duration field 220, and when the triggered best path selection measurement is requested as in the present invention, the measurement duration field 220 may be also set as '0'.

[58] The triggered reporting field 230 includes trigger condition information including a condition for a wireless station that receives a message including the triggered reporting field to create a measurement report message with respect to a reception link of the wireless station itself, and additional information required for applying the trigger condition. The triggered reporting field 230 includes a trigger condition subfield 232 and a trigger timeout field 238, and may further include a DLS path threshold subfield (RSNIl threshold subfield) 234 and an AP path threshold subfield (RSNIl threshold subfield 236.

[59] The trigger condition subfield 232 includes condition information for the wireless station to determine whether to generate a measurement report message with respect to its data reception link and transmit the same. The trigger condition subfield 232 may include a best unit 232a, a DLS path unit (RSNIl) 232b, and/or an AP path unit (RANI2) 232c (hereinafter, the RSNI is taken as an example, but the RSNI is merely an example for indicating channel quality which may be replaced by a different value or may be included together with a different value).

[60] The best unit 232a is information indicating whether a wireless station that transmits the radio measurement request message 200 wants to receive the measurement report message when a link performance and a radio environment of the link (e.g., the link ©) not in use become better than those of a currently used link (e.g., the link ©). If the transmission wireless station wants to receive the measurement report message, the best unit 232a may be set as T, or otherwise, the best unit 232a may be set as '0', and vice versa.

[61] For example, it is assumed that the second wireless station 20 has received the radio measurement request message 200 including the best unit 232a set as T from the first wireless station 10 via the AP path. In this case, the second wireless station 20 compares and determines the channel quality of the link © not in use rather than the link ©, the currently used link. And only when the channel quality of the link © is determined to have been better, the second wireless station 20 transmits the measurement report message 300 as shown in FIG. 4 to the first wireless station 10. If the second wireless station 20 receives the radio measurement request message 200 including the best unit 232a set as T from the first wireless station 10 via the DLS path, the second wireless station 20 compares and determines the channel quality of the link © not in use rather than the link ©, the currently used link. And only when the channel quality of the link © is determined to have been better, the second wireless station 20 transmits the measurement report message 300 to the first wireless station 10.

[62] In one aspect of the present embodiment, the second wireless station 20 may compare and determine the overall channel quality of the DLS path including the link © and that of the AP path including the links ® and ©, rather than comparing the link © and the link ©, respectively. In this case, the second wireless station 20 should previously know the channel quality of the link ® by receiving it from a different function entity, e.g., the AP 30.

[63] The DLS path unit 232b is information indicating whether or not the wireless station, which has transmitted the radio measurement request message 200, to receive the measurement report message when the quality of the link © constituting the DLS path becomes worse or better than the first threshold value. In this case, if it wants to receive the channel quality information of the link ©, the DLS path unit 432b may be set as T, or otherwise, it may be set as '0'. The first threshold value may be an arbitrary value that can be set by the transmission wireless station or a fixed value. This value is included in the DLS path threshold subunit 234 of the radio measurement request message 200.

[64] For example, it is assumed that the second wireless station 20 has received the best path measurement selection request message 200 including the DLS path unit 232b set as T from the first wireless station via the AP path. In this case, if the RSNI of the link © is larger than the DLS path threshold value (RCPIl), the second wireless station 20 transmits a measurement report message including the RSNI value of the measured link © to the first wireless station 10. When the second wireless station 20 receives the best path selection request message 200 including the DLS path unit 232b set as T from the first wireless station 10 via the DLS path, if the RSNI of the link © is smaller than the DLS path threshold value (e.g., RCPIl), the second wireless station 20 transmits the measurement report message including the RSNI value of the measured link © to the first wireless station 10.

[65] The AP path unit 232c is information indicating whether the wireless station, which has transmitted the radio measurement request message 200, wants to receive the measurement report message, when the quality of the link © constituting the AP link becomes lower or higher than the second threshold value. If the wireless station wants to receive the channel quality information of the link ©, the AP path unit 432cmay be set as T, or otherwise, it may be set as '0'. The second threshold value may be an arbitrary value that may be set by the transmission wireless station or a fixed value which is included in the AP path threshold subunit 236 of the radio measurement request message 200.

[66] For example, it is assumed that the second wireless station 20 has received the best path measurement selection request message 200 having the AP path unit 232c set as T from the first wireless station 10 via the DLS path. In this case, if the RSNI of the link © becomes larger than the AP path threshold value (RCPI2), the second wireless station 20 transmits the measurement report message including the RSNI value of the measured link © to the first wireless station 10. When the second wireless station 20 has received the best path measurement selection request message 200 having the AP path unit 232c set as T from the first wireless station 10 via the AP path, if the RSNI of the link © becomes smaller than the AP path threshold value (RCPI2), the second wireless station 20 transmits the measurement report message including the RSNI value of the measured link © to the first wireless station 10.

[67] With reference to FIG. 3, a value (e.g., 100 TU unit) indicating a minimum interval at which the wireless station, which has received the radio measurement request message 200, generates the measurement report message and transmits it is set in the trigger timeout subfield 438. A trigger timeout timer starts to be operated at the moment when the reception wireless station transmits the measurement report message and stops when a path switch notification message or other radio measurement request message is received before the timer expires.

[68] In the present embodiment, once the reception wireless station transmits the measurement report message as the trigger condition set in the trigger condition subfield 232 primarily met, it cannot generate nor transmit any additional measurement report message although the same trigger condition is met during a period set in the trigger timeout subfield 238. The presence of the trigger timeout subfield 438 is to prevent repeatedly generating and transmitting the measurement report message with respect to the link quality unnecessarily by the reception wireless station.

[69] A threshold value used to apply a DLS path trigger condition is set in the DLS path threshold value subfield 234. When a measured link quality is indicated by using the RSNI, the DLS path threshold value subfield 234 may be, for example, a first RSNI threshold value (RSNIl threshold value). In the present embodiment, the threshold value set in the DLS path subfield 234 is used to determine whether or not the measured quality information of the links constituting the DLS path meets the trigger condition, when the DLS path unit 232b is set as T.

[70] In addition, a threshold value used to apply an AP path trigger condition is set in the

AP path threshold subfield 236. When a measured link quality is indicated by using the RSNI, the AP path threshold value subfield 236 may be, for example, a second RSNI threshold value (RSNI2 threshold value). In the present embodiment, the threshold value set in the AP path subfield 236 is used to determine whether or not the measured quality information of the links constituting the AP path meets the trigger condition when the AP path unit 232c is set as T.

[71] FIG. 4 is a block diagram showing an example of a format of the measurement report message 300, a response message with respect to the radio measurement request message 200 as shown in FIG. 3. The measurement report message 300 may be a triggered best path selection measurement report message, but the present embodiment is not limited thereto.

[72] With reference to FIG. 4, the measurement report message 400 includes an actual measurement start time field 410, a measurement duration field 420, a DLS path field (RSNIl) 430, and an AP path field (RSNI2) 440.

[73] A timing synchronization function (TSF) value at a time when measurement is actually started is set in the actual measurement start time field 410. However, if the actual measurement start time field 410 is included in the triggered best path selection measurement report message like the case as in the present embodiment, a TSF value at a wireless station that generates the measurement report message when a trigger condition is met is set in the actual measurement start time field 410.

[74] Time required for acquiring measurement value included in the measurement report message 400, specifically, quality information included in the DLS path field 430 and/ or the AP path field 440 is set in the measurement duration field 420. For example, time taken for measuring the RSNI of the link © and/or the link © may be included in the measurement duration field 420.

[75] In addition, quality information (e.g., RSNI) measured with respect to a link (e.g., the link ©) constituting the DLS link is included in the DLS path field 430, and quality information (e.g., RSNI) measured with respect to a link (e.g., the link ©) constituting the AP path is included in the AP path field 440. In this case, quality information measured for the both of the DLS path field 430 and the AP path field 440 are not required to be included. For example, only quality information of one link that meets a trigger condition specified for a radio measurement request message received from a counterpart wireless station may be included in the corresponding field.

[76] The procedure for selecting the best path according to the second embodiment of the present invention by using a message having such formats as shown in FIGs. 3 and 4. Here, the selection of the best path refers to a selection of a path of a better channel environment from among the DLS path and the AP path as shown in FIG. 1. Hereinafter, only the procedure in which the first wireless station 10 selects the best path to transmit data to the second wireless station 20 will be described. [77] FIG. 5 is a message flow chart illustrating an example of a procedure for selecting the best path to transmit data by the first wireless station STAl 10 to the second wireless station STA2 20 according to the second embodiment of the present invention.

[78] With reference to FIG. 5, first, a direct link is set up between the first wireless station

10 and the second wireless station 20 (S401). There is no any particular limitation in the method for setting up the direct link, and for example, the direct link may be established by using a DLS procedure defined in IEEE 802.11 standards. The direct link may be also set up according to a request of the first wireless station 10 or the second wireless station 20.

[79] After the direct link is set up between the first and second wireless stations 10 and

20, the first wireless station 10 or the second wireless station 20 may initiate a procedure for selecting the best path to transmit data any time. Hereinafter, only the selection of the best path by the first wireless station 10 will be described.

[80] In order to select the best path, the first wireless station 10 transmits a radio measurement request message including a trigger condition, e.g., the message 20 having such a format as shown in FIG. 3, to the second wireless station 20 (S402). The radio measurement request message may be transmitted by using the DLS path (the link ® in FIG. 1) or the AP path (the links ®+© in FIG. 1), and FIG. 5 shows the case of transmission by using the DLS path. Namely, in the present embodiment, the first wireless station 10 transmits data to the second wireless station 20 by using the DLS path at an interval indicated by 'A'. In the present embodiment, the case where the radio measurement request message 200 includes the trigger condition subfield 232 having the best unit 232a set as T will be described.

[81] Upon receiving the radio measurement request message 200, the second wireless station 20 measures the quality of the links © and © to determine whether or not a situation corresponding to the trigger condition included in the received radio measurement request message 200 has occurred (S403). In the present embodiment, the best unit 432a is set as T as the trigger condition, so the second wireless station 20 determines whether or not the quality of the link © becomes better than that of the link © based on the measured link quality.

[82] If the situation is determined to correspond to the trigger condition according to the determination result in step S403, namely, if the quality of the link © is determined to be better than that of the link ©, the second wireless station 20 transmits a first measurement report message to the first wireless station 10 (S404). The first measurement report message may be, for example, the message 300 having such a format as shown in FIG. 4. However, in the present embodiment, if the situation is determined not to correspond to the trigger condition, although there is a change in the measured value, a measurement report message is not transmitted.

[83] The first measurement report message may be transmitted from the second wireless station 20 to the first wireless station 10 by using the DLS path (i.e., the link ®) or the AP path (i.e., the links ©+©), and in the present embodiment, the former case is illustrated. When the first measurement report message is transmitted, a timer of the trigger timeout included in the radio measurement request message 200 starts to be operated.

[84] The measured link quality information (RCPIl, RCPI2) are included in the DLS path field and the AP path field of the first measurement report message, respectively. In the present embodiment, the best unit is set as T as the trigger condition, so preferably, the measured link quality information is included in both the DLS path field and the AP path field of the measurement report message. However, although the best unit 432a is set as T as the trigger condition, only quality information of a link of a better channel quality among the DLS path field and the AP path field may be included according to an embodiment.

[85] Subsequently, upon receiving the first measurement report message, the first wireless station 10 determines whether to change a data transmission path based on the received link quality information (S405). In this step, the first wireless station 10 selects the best path from among the DLS path and the AP path by using the already known quality information of the link ® and the quality information of the links © and/or © received in step S404. Namely, although the quality of the link © is better than that of the link ©, if the quality of the link ® is not good, the first wireless station may not change the DLS path to the AP path.

[86] In selecting the best path by the first wireless station 10 by using the received quality information of the links, various methods may be applicable in consideration of the link performance and/or radio environments with respect to the conditions for changing the currently used DLS path to the AP path, another path.

[87] For example, it is assumed that the channel quality of the AP path (the links ®+©) not in use is better than that of the DLS path (the link ©) currently being used. In this case, according to one aspect of the present embodiment, the first wireless station 10 may be set to unconditionally change the path from the DLS path to the AP path. In another aspect of the present embodiment, the first wireless station 10 may be set to change the path only when the difference of the channel quality between the respective paths is larger than a certain threshold value. Accordingly, in this embodiment, the best path can be effectively selected by preventing a frequent changing of paths. In still another aspect of the present invention, the conditions for changing from the AP path to the DLS path while using one of the above-described methods as a determination basis and the conditions and/or determination basis for changing from the DLS path to the AP path may be set to be different.

[88] According to such procedure, when it is determined not to change a path although the trigger condition is met in step S405, if there is not much change in the state of the links © and ©, there is a high possibility that the second wireless station 20 repeatedly transmits the same measurement report message to the first wireless station 10. However, in the present invention, such a problem can be prevented in advance by using the trigger timeout subfield of the radio measurement request message. Namely, in the present embodiment, the second wireless station 20 cannot transmit the same measurement report message repeatedly during the time included in the trigger timeout subfield.

[89] After the first wireless station 10 determines to change the data transmission path from the DLS path to the AP path in step S405, it informs the second wireless station 20 or the like about its intention to change the path (S406). To this end, the first wireless station 10 may transmit a path switch notification message. And when the second wireless station receives the first path switch notification message, the operation of the trigger timeout timer is stopped.

[90] In the present embodiment, there is no particular limitation in the type of the first path switch notification message. For example, the first path switch notification message may include a field (e.g., action, BSSUID (Basic Service set Unique Identifier), destination MAC address, and/or source MAC access) generally included in a frame related to a DLS management or a data frame, and a notification type field including information related to the selected best path. The notification type field includes information related to the change of the data transmission path desired to be informed to the counterpart wireless station.

[91] After step S406, the first wireless station 10 transmits data to the second wireless station 20 by using the AP path. Namely, an interval 'B' as illustrated indicates an interval during which the first wireless station 10 transmits data to the second wireless station 20 by using the AP path.

[92] Subsequently, upon receiving the first path switch notification message, the second wireless station 20 determines whether or not the link © is better than the link © (S407). This is because the trigger condition of the radio measurement request message received in step S402 is still valid for the second wireless station 20.

[93] If the link © is determined to be better than the link © according to the determination result in step S407, the second wireless station 20 transmits a second measurement report message to the first wireless station 10 (S408). The process of step S408 is substantially the same as that of step S404, so its detailed description will be omitted.

[94] Upon receiving the second measurement report message, the first wireless station 10 performs a determination procedure for selecting the best path again (S409). The process in this step is substantially the same as step S405, so its detailed description will be omitted. In this step, the first wireless station 10 determines not to change from the AP path to the DLS path in consideration of the state of another link, e.g., the link ®.

[95] After time specified in the trigger timeout subfield lapses, namely, after the timer of the trigger timeout expires, the second wireless station 20 determines whether the trigger condition is met (S410). In this manner, the trigger timeout subfield prevents the same measurement report message from being repeatedly transmitted during the specified time period.

[96] If it is determined that the link © is better than the link © according to the determination result in step S410, the second wireless station 20 transmits a third measurement report message to the first wireless station 10 (S411). Upon receiving the third measurement report message, the first wireless station 10 performs a determination procedure for selecting the best path again, and this time, the first wireless station 10 determines to change the data transmission path from the AP path to the DLS path (S412). And then, the first wireless station 10 informs the second wireless station 20 about its intention to change the path by using the second path switch notification message (S413).

[97] FIG. 6 is a message flow chart illustrating another example of the procedure for selecting the best path to transmit data by the first wireless station STAl 10 to the second wireless station STA2 20 according to the second embodiment of the present invention. The difference from the message flow chart as shown in FIG. 5 will be focused in the following description.

[98] With reference to FIG. 6, first, a direct link is set up between the first wireless station

10 and the second wireless station 20 (S501). To select the best path, the first wireless station 10 transmits a radio measurement request message including a trigger condition, e.g., the message 200 having such a format as shown in FIG. 3, to the second wireless station 20 (S502). The radio measurement request message may be transmitted by using the DLS path (the link © in FIG. 1) or the AP path (the links ®+©). FIG. 5 shows the case of transmission by using the DLS path. Namely, also in the present embodiment, the first wireless station 10 transmits data to the second wireless station 20 by using the DLS path at an interval indicated by 'C.

[99] In the present embodiment, the DLS path unit 232b and the AP path unit 232c of the trigger condition subfield 232 are set as T as trigger conditions included in the radio measurement request message 200. This is to use both the measured qualities of the links © and © to determine whether or not the set trigger conditions are met. In order to determine whether or not the trigger condition is met, each certain value is included in the DLS path threshold value subfield 234 and the AP path threshold value subfield 236, respectively, of the radio measurement request message 200.

[100] In a modification of the present embodiment, only one of the DLS path unit 232b and the AP path unit 232c of the trigger condition subfield 232 may be set as T as the trigger condition. This is to use only one of the measured qualities of the links © and © to determine whether the set trigger condition is met. In order to determine whether or not the trigger condition is met, a certain value is included only in a corresponding one of the DLS path threshold value subfield 234 and the AP path threshold value subfield 236 of the radio measurement request message 200.

[101] Subsequently, upon receiving the radio measurement request message 200, the second wireless station 20 measures quality of the links © and © to determine whether or not a situation corresponding to the trigger condition included in the received radio measurement request message 200 has occurred (S503). In the present embodiment, it is determined whether or not the measured quality of the link © constituting the DLS path which is currently used is smaller than the threshold value included in the DLS path threshold value subfield 234 or whether or not the measured quality of the link © constituting the AP path which is not in use is larger than the threshold value included in the AP path threshold value subfield 236.

[102] If the situation is determined to meet the trigger condition according to the determination result in step S503, the second wireless station 20 transmits a first measurement report message to the first wireless station 10 (S504). When the first measurement report message is transmitted, the timer of the trigger timeout included in the radio measurement request message 200 starts to be operated.

[103] At least one of the measured link quality information (RSNIl, RSNI2) is included in the DLS path field and the AP field of the first measurement report message. In the present embodiment, because the DLS path unit and the AP path unit are all set as T as the trigger conditions, preferably, the measured quality information of the links are included in both the DLS path field and the AP path field of the measurement report message. In this respect, however, if only one of the two trigger conditions is met, only measured quality information of a corresponding link may be included.

[104] Subsequently, upon receiving the first measurement report message, the first wireless station 10 determines whether to change a data transmission path based on the received link quality information (S505). In this step, the first wireless station 10 selects the best path from among the DLS path and the AP path by using the already known quality information of the link ® and the quality information of the links © and/or © received in step S504. In selecting the best path by the first wireless station 10 by using the received quality information of the links, various methods may be applicable in consideration of the link performance and/or radio environments with respect to the conditions for changing the currently used DLS path to the AP path, another path. [105] After the first wireless station 10 determines to change the data transmission path from the DLS path to the AP path in step S505, it informs the second wireless station 20 or the like about its intention to change the path (S506). To this end, the first wireless station 10 may transmit a first path switch notification message. There is no particular limitation in the type of the first path switch notification message.

[106] After step S506, the first wireless station 10 transmits data to the second wireless station 20 by using the AP path. Namely, an interval 'D' as illustrated indicates an interval during which the first wireless station 10 transmits data to the second wireless station 20 by using the AP path.

[107] Subsequently, upon receiving the first path switch notification message, the second wireless station 20 measures again the quality of the links © and © and determines whether or not a situation corresponding to the trigger condition included in the received radio measurement request message 200 has occurred (S507). This is because the trigger condition of the radio measurement request message received in step S502 is still valid for the second wireless station 20. In the present embodiment, it is determined whether or not the measured quality of the link © constituting the AP path which is currently used is smaller than the threshold value included in the AP path threshold value subfield 236 or whether or not the measured quality of the link constituting the DLS path which is not in use is larger than the threshold value included in the DLS path threshold value subfield 234.

[108] If the situation is determined to meet the trigger condition according to the determination result in step S507, the second wireless station 20 transmits a second measurement report message to the first wireless station 10 (S508). When the second measurement report message is transmitted, the timer of the trigger timeout included in the radio measurement request message 200 starts to be operated. At least one of the measured link quality information (RCPIl, RCPI2) is included in the DLS path field and the AP field of the second measurement report message.

[109] Subsequently, upon receiving the second measurement report message, the first wireless station 10 determines whether to change a data transmission path based on the received link quality information (S509). In this step, the first wireless station 10 selects the best path from among the DLS path and the AP path by using the already known quality information of the link ® and the quality information of the links © and/or © received in step S508. In selecting the best path by the first wireless station 10 by using the received quality information of the links, various methods may be applicable in consideration of the link performance and/or radio environments with respect to the conditions for changing the currently used AP path to the DLS path, another path.

[110] After the first wireless station 10 determines to change the data transmission path from the AP path to the DLS path in step S509, it informs the second wireless station 20 or the like about its intention to change the path (S510). To this end, the first wireless station 10 may transmit a second path switch notification message. In the second wireless station 20 which has received the second path switch notification message, the operation of the timer of the trigger timeout is stopped.

[I l l] Subsequently, in the present embodiment, the first wireless station 10 transmits a second radio measurement request message to the second wireless station 20 (S511). There is no particular limitation in the type of the second radio measurement request message. For example, in the second radio measurement request message, the best unit may be set as T, the DLS path unit and/or the AP path unit may be set as T, or the entire trigger conditions may be set as T as the trigger condition(s). And then, the procedure is performed in the same manner as described above according to the set trigger condition(s) until the set DLS path is deactivated or released.

[112]

[113] <Third embodiment

[114] In the first and second embodiments as described above, the first wireless station 10, namely, the transmission wireless station, which wants to select the best path transmits the radio measurement request message including a trigger condition or without any condition to the second wireless station 20, the counterpart, namely, the reception wireless station. The second wireless station 20 transmits the measurement report message including measured link quality information to the first wireless station 10 in response only to the radio measurement request message. Of course, in the second embodiment, if the trigger condition is met, the second wireless station 20 transmits the measurement report message even without a direct request from the first wireless station 10, but this is based on the presumption that the radio measurement request message including the trigger condition has been previously transmitted.

[115] However, the procedures according to the first and second embodiments of the present invention cannot effectively achieve the purpose of the DLS service aimed for selecting the best path from among the DLS path and the AP path and using the same, in the aspect that the measurement report message including the measured quality information is transmitted on the premise of a measurement request from the wireless station that wants to select the best path.

[116] In the example as shown in FIG. 1, when the first wireless station STAl and the second wireless station STA2 use the direct link, they transmit data by using the links © and ®, and when using the AP path, they transmit data by using the links ®+© and ©+©. In this respect, the reception wireless station, rather than the transmission wireless station that transmits data, can more accurately know which link of the direct link and the AP path has a better state, For example, when the first wireless station transmits data to the second wireless station, the AP, the reception station STA of the link ®, and the second wireless station, the reception station STA of the links © and ©, can more accurately know the state of each link. In this case, in the embodiments as described above, the first wireless station requests each link status from the AP and the second wireless station and receives corresponding reports, to thus recognize the status of each link and determine a better data transmission path by using it.

[117] In this case, however, if the first wireless station wants to acquire channel information about the links, it should transmit a message requesting it to the counterparts (AP and the second wireless station), and because the characteristics of the radio channels vary over time, the first wireless station has no choice but to periodically transmit such request message or randomly transmit it at an arbitrary time. When the request message is periodically or randomly transmitted, it may happen that the request message is transmitted although there is no actual change in the state of the links, or the request message is not transmitted even if the state of the links has been changed. In addition, it may happen that immediately after a report message with respect to a previously transmitted request message is received, the request message is transmitted again because of a sudden change in the state of the links. Therefore, in the wireless network in which both the direct link and the AP path are all available to be used, transmission itself of the request message with respect to the channel quality information by the transmission wireless station to the reception wireless station or the AP may work as overhead in the transmission wireless station.

[118] Thus, in the third embodiment of the present invention, in order to overcome such limitations in the first and second embodiments, one wireless station, which sets a DLS link, spontaneously transmits a measurement report message or a path switch request message including a measured channel quality result to its peer wireless station, although there is no explicit radio measurement request message received from the peer wireless station. Here, being 'spontaneous' refers to transmission of the path switch request message or the like although there is no corresponding request from the peer wireless station, and there is no particular limitation in the form of its implementation. For example, the 'spontaneous transmission' may refer to a periodical transmission of a message including a periodically measured quality result, a transmission of a message when a pre-set certain condition is met, a transmission of a message when there is a change in a channel state, or the like.

[119] The example of the procedure according to the third embodiment of the present invention may be substantially the same as the procedures according to the first and second embodiments, except that the process of transmitting the unconditional radio measurement request message or the radio measurement request message including a trigger condition by the first wireless station 10 to the second wireless station 20 as in the procedures according to the first and second embodiments of the present invention as described above is omitted. The reason for transmitting the measurement report message by the second wireless station 20 is an example of the 'spontaneous transmission' as mentioned above, and the third embodiment of the present invention is different from the first embodiment on the condition that the radio measurement request message is received, and the second embodiment on the condition that the trigger condition is met.

[120] FIG. 7 is a message flow chart illustrating an example of a procedure for selecting the best path according to the third embodiment of the present invention. The method for selecting the best path according to the third embodiment of the present invention will now be described briefly with reference to FIGs. 1 and 7.

[121] With reference to FIG. 7, first, a direct link is set up between the first wireless station 10 and the second wireless station 20 (S601). The direct link may be established according to a request of the first wireless station 10 or the second wireless station 20. One of the wireless stations which has established the direct link, e.g., the second wireless station 20, measures channel quality of the links © and ©, generates a measurement report message (e.g., a radio measurement result report message, a link RCPI report frame, or a link RSNI report frame) including the measurement result, and spontaneously transmits it to the first wireless station.

[122] Here, the spontaneous transmission of the measurement report message refers to a transmission of a measurement result obtained periodically or a measurement result obtained when there is a change in a link state, although there is no corresponding request from the first wireless station 10. Also, it refers to a transmission in spite of no request from the first wireless station 10, when a link state of a path (the DLS path or the AP path) not in use becomes better than that of a path (the AP path or the DLS path) currently in use even if there is no change in the link state.

[123] In this case, the spontaneous transmission also includes a transmission of a message (e.g., a path switch request message) including a measurement result after a certain time period in case that although a previously obtained measurement result was spontaneously transmitted, path switching has not been made because of a rejection of the path switching of the first wireless station 10, so the same path is continuously used and a path not in use has a better link state. Here, the reason for setting the period after the certain time period is to prevent the same message from being repeatedly transmitted (to be described). And, although it is arbitrary, the first wireless station 10, which does not wants to continuously receive the same message, may transfer a link measurement value measured by the first wireless station 10 itself to the second wireless station 20, transfer the reason for not switching the path, and/or transfer time until a next message is transmitted, or the like, to the peer wireless station via a measurement request message or a path switch response message.

[124] According to the third embodiment of the present invention, a problem may arise in that when the link state is frequently changed, the measurement report message is also frequently transmitted. Thus, in order to avoid such a problem, a minimum interval for transmitting the measurement report message may be set by using a self-timer or the like. According to the third embodiment of the present invention, once the measurement report message is transmitted, a second measurement report message may be transmitted only after the time set in the timer.

[125] There is no particular limitation in the type of the link quality information included in the measurement report message after being measured by the second wireless station 20. For example, the link quality information may be displayed as RCPI information, RSNI information, or information of any other type, or may be displayed by using a plurality of information including at least one of the RCPI and the RSNI. As the RCPI or RSNI information, an average value of RCPIs or RSNIs during a certain time period, a minimum value, or a value at a particular time point may be used.

[126] Subsequently, upon receiving the measurement report message from the second wireless station 20, the first wireless station 10 selects the best path from among the DLS path and the AP path by using the quality information of the link ® the first wireless station 10 already knows and the received quality information of the links © and © (S603). If it is determined to change a path to be used for a data transmission from the existing path, e.g., the DLS path, to the AP path, another path, according to the determination result in step S603, the first wireless station transmits a path switch notification message or a path switch request message to the counterpart wireless station 20 (S604). The path switch notification/request message is to inform the counterpart wireless station 20 that the first wireless station 10 has an intention of changing the path. Meanwhile, if the existing path is determined to be maintained as it is according to the determination result in step S603, any additional message transmission is not made or an additional message may be transmitted if necessary. In the latter case, for example, although it is arbitrary, the first wireless station 10, which does not wants to continuously receive the same message, may transfer a link measurement value measured by the first wireless station 10 itself to the second wireless station 20, transfer the reason for not switching the path, and/or transfer time until a next message is transmitted, or the like, to the peer wireless station via the measurement request message or the path switch response message.

[127] FIG. 8 is a message flow chart illustrating another example of a procedure for selecting the best path according to the third embodiment of the present invention. The method for selecting the best path according to the third embodiment will be described briefly with reference to FIGs. 1 and 8. [128] With reference to FIG. 8, first, a direct link is set up between the first wireless station 10 and the second wireless station 20 (S701). The direct link may be established according to a request of the first wireless station 10 or the second wireless station 20. The first wireless station 10 transmits data to the second wireless station 20 by using the established direct link (S702). One of the wireless stations which has established the direct link, e.g., the second wireless station 20, measures channel quality of the links © and ©, to check whether there is a change in the channel state between the direct link and the link of the AP path (S703). Upon checking, if there is a change in the channel state, the second wireless station 20 generates a path switch request frame including the measurement result (e.g., a radio measurement result report message, a link RCPI report frame, or a link RNSI report frame), and transmits the same to the first wireless station 10 (S704).

[129] According to the third embodiment of the present invention, a problem may arise in that when the link state is frequently changed, the measurement report message is also frequently transmitted. Thus, in order to avoid such a problem, a minimum interval for transmitting the measurement report message may be set by using a self-timer or the like. According to the third embodiment of the present invention, once the measurement report message is transmitted, a second measurement report message may be transmitted only after the time set in the timer.

[130] There is no particular limitation in the type of the link quality information included in the path switch request frame after being measured by the second wireless station 20. For example, the link quality information may be displayed as RCPI information, RSNI information, or information of any other type, or may be displayed by using a plurality of information including at least one of the RCPI and the RSNI. As the RCPI or RSNI information, an average value of RCPIs or RSNIs during a certain time period, a minimum value, or a value at a particular time point may be used.

[131] FIG. 9 is a block diagram showing an example of a format of the path switch request frame. With reference to FIG. 9, the path switch request frame includes a link identifier field, a dialog token field, a path field, a reason field, a DLS path field (RSNIl or RCPIl), and an AP path field (RSNI2 or RCPI2). The link identifier field is set by a unique value for identifying a set direct link, and the dialog token field is set by a value for identifying exchanging of a path switch request frame and a path switch response frame, a response to the path switch request frame.

[132] The reason field may be a change in a link state, namely, that although the direct link is currently used, the AP path is preferred, or although the AP path is currently used, the direct link is preferred, that the currently used direct link path should be switched to the AP path because of entering a power save mode, or that the AP path should be switched to the direct link because the power save mode is changed to an activate mode, or the like. The DLS path field and the AP path field include the channel quality information, e.g., the RSNI value or the RCPI value, measured with respect to the link © and the link ©, respectively.

[133] Subsequently, with reference to FIG. 8, upon receiving the path switch request frame, the first wireless station 10 determines whether to switch from the currently used DLS path to the AP path or from the AP path or the DLS path (S705). In this determining process, the first wireless station 10 selects a better one of the DLS path and the AP path by comparing the channel quality information included in the received path switch request frame and the channel quality information the first wireless station 10 has directly measured or that of the link ® received from the AP. In this case, if the reception wireless station requests path switching for the reason of entering the power save mode, it should necessarily switch to the AP path irrespective of the link state.

[134] After selecting the path, the first wireless station 10 transmits a path switch response frame including the selection result (S706). If the data transmission path is determined to be changed from the existing DLS path to the AP path according to the determination result in step S705, the path switch response frame includes information indicating acceptance with respect to the received path switch request, a success of the path switching, or the like. In this case, the channel quality information of the link ® may be omitted in transmitting the path switch response frame. Meanwhile, if the existing DLS path is determined to be maintained as it is according to the determination result in step S705, the path switch response frame includes information indicating rejection with respect to the received path switch request, a failure of path switching, or the like. In this case, the channel quality information of the link ® may be also transmitted together with the information indicating the determination result. In this case, the second wireless station 20 may determine whether to transmit the path switch request frame or the like again by using the received channel quality information of the link ® and the channel quality information directly measured and acquired by the second wireless station 20 itself.

[135] FIG. 10 is a block diagram showing an example of a format of the path switch response frame. With reference to FIG. 10, the path switch response frame includes a link identifier field, a dialog token field, a path field, a status field (result (or reason) field), and an AP path field (RSNI3 or RCPI3). The link identifier field is set by a unique value for identifying a set direct link, and the dialog token field is set by a value for identifying exchanging of a path switch request frame and a path switch response frame, a response to the path switch request frame. The status field includes information indicating an acceptance or rejection with respect to a received path switch request, and in this case, the status field may also include information about the reason of rejection. A field for the reason of rejection may be additionally added according to an embodiment. The AP path field may include channel quality information measured in case where the status field includes the information indicating a rejection or in case of acceptance, rather than rejection, according to an embodiment. The AP path field may include the channel quality information, e.g., the RSNI value or the RCPI value, measured for the link ®.

[136] FIG. 11 is a message flow chart illustrating still another example of the process for selecting the best path according to the third embodiment of the present invention. The method for selecting the best path according to the third embodiment of the present invention will now be described briefly.

[137] With reference to FIG. 11, first, a direct link is set up between the first wireless station 10 and the second wireless station 20 (S801). The direct link may be established according to a request of the first wireless station 10 or the second wireless station 20. The first wireless station 10 transmits data to the second wireless station 20 by using one of the DLS path and the AP path, e.g., by using the direct link (S 802). In case of transmitting data by using the AP path, before this step, the first wireless station 10 and the second wireless station 20 further perform a procedure for switching a data transmission path to the AP path by exchanging a request frame and a response frame for switching a reception path (or a transmission path).

[138] One of the wireless stations which transmit and receive data via the direct link, e.g., the first wireless station that transmits data measures channel quality of the link of the AP path, namely, the link ®, to check whether there is a change in the channel state between the direct link and the link of the AP path (S803). Upon checking, if there is a change in the channel state or if there is another reason, or arbitrarily, the first wireless station 10 generates a path switch request frame (e.g., a radio measurement result report message, a link RCPI report frame, a link RSNI report frame, a reception path switch request frame, a transmission path switch request frame, etc., without being limited to the particular names) including the measurement result, and transmits the same to the second wireless station 20 (S804). Here, if the path from the first wireless station 10 to the AP 30, namely, the state of the link ®, has been considerably improved compared to its previous state (the channel quality information of the link ® can be received from the AP periodically or when there is a corresponding request from the first wireless station 10), or if the first wireless station 10 wants to switch to the AP path for some other reasons, the first wireless station 10 may transmit a path switch request frame to the second wireless station 20.

[139] According to the third embodiment of the present invention, a problem may arise in that when the link state is frequently changed, the measurement report message is also frequently transmitted. Thus, in order to avoid such a problem, a minimum interval for transmitting the measurement report message may be set by using a self-timer or the like. According to the third embodiment of the present invention, once the measurement report message is transmitted, a second measurement report message may be transmitted only after the time set in the timer.

[140] There is no particular limitation in the type of the link quality information included in the path switch request frame after being measured by the second wireless station 20. For example, the link quality information may be displayed as RCPI information, RSNI information, or information of any other type, or may be displayed by using a plurality of information including at least one of the RCPI and the RSNI. As the RCPI or RSNI information, an average value of RCPIs or RSNIs during a certain time period, a minimum value, or a value at a particular time point may be used.

[141] FIG. 12 is a block diagram showing an example of a format of the path switch request frame. With reference to FIG. 12, the path switch request frame includes a link identifier field, a dialog token field, a path field, a reason field, and channel quality field (RSNI3 or RCPI3). The link identifier field is set by a unique value for identifying a set direct link, and the dialog token field is set by a value for identifying exchanging of a path switch request frame and a path switch response frame, a response to the path switch request frame. The reason field may be the reason for requesting path switching, for example, a change in a link state, namely, that although the direct link is currently used, the AP path is preferred, or although the AP path is currently used, the direct link is preferred, that the currently used direct link path should be switched to the AP path because of entering a power save mode, or that the AP path should be switched to the direct link because the power save mode is changed to an activate mode, or the like. The channel quality field includes information for supplementing the reason indicated in the reason field, for example, the channel quality information, e.g., the RSNI value or the RCPI value, measured with respect to the link ® when, for example, the status of the AP path has been improved.

[142] Subsequently, with reference to FIG. 11, upon receiving the path switch request frame, the second wireless station 20 determines whether to switch from the currently used DLS path to the AP path or from the AP path or the DLS path (S805). In this determining process, the second wireless station 20 selects a better one of the DLS path and the AP path by comparing the channel quality information included in the received path switch request frame and the channel quality information the first wireless station 10 has directly measured or that of the links ©+© received from the AP, and determines whether to accept or reject a request from the first wireless station 10. In this case, if the reception wireless station requests path switching for the reason of entering the power save mode, it should necessarily switch to the AP path irrespective of the link state.

[143] After selecting the path, the second wireless station 20 transmits a path switch response frame including the selection result (S806). If the data transmission path is determined to be changed from the existing DLS path to the AP path according to the detrmination result in step S805, the path switch response frame includes information indicating acceptance with respect to the received path switch request, a success of the path switching, or the like. In this case, the channel quality information of the links ©+© may be omitted in transmitting the path switch response frame, or may be included to be transmitted together. Meanwhile, if the existing DLS path is determined to be maintained as it is according to the determination result in step S 805, the path switch response frame includes information indicating rejection with respect to the received path switch request, a failure of path switching, or the like. In this case, the channel quality information of the links ©+© may be also transmitted together with the information indicating the determination result. In this case, the second wireless station 20 may determine whether to transmit the path switch request frame or the like again by using the received channel quality information of the links ©+© and the channel quality information directly measured and acquired by the second wireless station 20 itself.

[144] FIG. 13 is a block diagram showing an example of a format of the path switch response frame. With reference to FIG. 13, the path switch response frame includes a link identifier field, a dialog token field, a path field, a status field (result (or reason) field), a DLS path field (RSNIl or RCPIl), and an AP path field (RSNI2 or RCPI2). The link identifier field is set by a unique value for identifying a set direct link, and the dialog token field is set by a value for identifying exchanging of a path switch request frame and a path switch response frame, a response to the path switch request frame. The status field includes information indicating an acceptance or rejection with respect to a received path switch request, and in this case, the status field may also include information about the reason of rejection. A field for the reason of rejection may be additionally added according to an embodiment. The DLS path field and the AP path field may include channel quality information measured in case where the status field includes the information indicating a rejection or in case of acceptance, rather than rejection, according to an embodiment. The DLS path field and the AP path field may include the channel quality information, e.g., the RSNI value or the RCPI value, measured for the links ©+©.

[145] In the embodiments of the present invention, when the second wireless station 20 determines that the path switch request is reasonable (appropriate) by using the information of the RCPIl (RSNIl) and the RCPI2 (RSNI2), it transmits a response frame optionally including the DLS path field and the AP path field together with information of accepting the path switch request in the status field to the first wireless station. Reversely, if it is determined that the path switch request is not acceptable, the second wireless station 20 transmits a response frame including a process result (rejection) and the reason (of rejection) with respect to the path switch request, and both the DLS path field and the AP path field, to the first wireless station. If the request is rejected because the channel state of the direct link is too good or the channel state of the link constituting the AP path is too bad, the measured channel quality information should be necessarily included in the DLS path field and the AP path field.

[146] In the embodiments of the present invention as described above, the first wireless station 10, which sets up the direct link, transmits data to the second wireless station 20 via the AP path, and it can be also applicable in the same manner also for the case where the path switching to the direct link is requested because the channel state of the AP path is too bad or for some other reasons.

[147] In the first to third embodiments of the present invention as described above, the path switch request frame and the path switch response frame transmitted in response to the path switch request frame may be transmitted via the AP path. In this case, the path switch request frame (reception (Rx) path switch request frame or transmission (Tx) path switch request frame) and the path switch response frame (Rx path switch response frame or Tx path switch response frame) with respect to the path switch request frame may be encapsulated in the form of a data frame and transmitted to the counterpart wireless station. The present invention is not limited thereto, and the path switch request frame and the response frame may be transmitted to the counterpart wireless station via the direct link.

[148] As described above, according to the third embodiment of the present invention, the wireless station (reception wireless station), which sets the direct link to select the best path from among the DLS path and the AP path, spontaneously transmits the measurement report message including quality information of a measured link to the counterpart wireless station (transmission wireless station). Upon receiving the measurement report message, the wireless station compares the AP path and the DLS path and then selects a path of better channel characteristics from among the AP path and the DLS path.

[149] The embodiments of the present invention as described in detail above are illustrative for presenting the technical idea of the present invention, and should not be interpreted that the technical idea of the present invention is limited by the embodiments. The scope of the present invention is specified by the claims of the present invention. Industrial Applicability

[150] The present invention is applicable to a protocol or a station for a wireless LAN.

Claims

[1] A method for selecting the best path by a first wireless station from among a direct link setup (DLS) path and an access point (AP) path, the method comprising: receiving a first message comprising measured quality information of a link constituting the DLS path and/or a link constituting the AP path from a second wireless station, a counterpart of the DLS path; and determining whether to switch a data transmission path or a data reception path between the DLS path and the AP path by using the received measured channel quality information.

[2] The method of claim 1, further comprising: when it is determined not to switch the data transmission path, transmitting a second message for providing information indicating that there is no intention of switching the data transmission path and the channel quality information with respect to the link with the first wireless station and an AP to the second wireless station.

[3] The method of claim 1, further comprising: when it is determined to switch the data transmission path, transmitting a second message informing the second wireless station about the intention of switching of the data transmission path.

[4] The method of claim 1, wherein the first message is transmitted by the second wireless station although there is no explicit request from the first wireless station.

[5] The method of claim 4, wherein the second wireless station transmits the first message periodically, only when a pre-set certain condition is met, when there is a change in a channel state of at least one of the link of the DLS path and the link of the AP path, or when channel quality of a link of a path not in use becomes better than that of a currently used path among the DLS path and the AP path.

[6] The method of claim 5, wherein the measured channel quality information comprises a measurement value with respect to at least one of a received signal to noise indicator (RSNI) and a received channel power indicator (RCPI).

[7] A method for selecting the best path by a first wireless station from among a direct link setup (DLS) path and an access point (AP) path, the method comprising: receiving a first message requesting measured quality information of a link constituting the DLS path and/or a link constituting the AP path from a second wireless station, a counterpart of the DLS path, and path switching; and determining whether to switch a data transmission path or a data reception path between the DLS path and the AP path by using the received measured channel quality information. [8] A method for selecting the best path by a first wireless station from among a direct link setup (DLS) path and an access point (AP) path, the method comprising: transmitting a path switch request message including reason information for requesting the path switch to a second wireless station, a counterpart of the DLS path; and receiving a path switch response message from the second wireless station in response to the path switch request message. [9] The method of claim 8, wherein the reason information indicates a change in a power save mode or a change in a link state.