WO2014046491A1

WO2014046491A1 - Active search method in wireless lan system

Info

Publication number: WO2014046491A1
Application number: PCT/KR2013/008460
Authority: WO
Inventors: 정양석; 김주영
Original assignee: 주식회사 케이티
Priority date: 2012-09-20
Filing date: 2013-09-17
Publication date: 2014-03-27

Abstract

An active search method in a wireless LAN system is disclosed. The active search method comprises the steps of: transmitting, through an arbitrary channel, a preceding probe request frame for confirming the existence of an access point; acquiring, from at least one access point, a probe ACK frame that is a response to the preceding probe request frame; setting a maximum waiting time on the basis of the number of probe ACK frames; and performing an active search for an access point in the arbitrary channel for the maximum waiting time. Therefore, the waiting time for receiving a probe response frame can be reduced.

Description

Active Search Method in WLAN System

The present invention relates to an active search method, and more particularly, to an active search method for access point search in a WLAN system.

With the development of information and communication technology, various wireless communication technologies are being developed. Among them, wireless local area network (WLAN) is based on radio frequency technology such as personal digital assistant (PDA), laptop computer, portable multimedia player (PMP), etc. It is a technology that allows a user to access the Internet wirelessly at home, a business, or a specific service area by using a portable terminal.

The standard for WLAN technology is being developed as an Institute of Electrical and Electronics Engineers (IEEE) 802.11 standard. IEEE 802.11a provides a transmission rate of 54 Mbps using an unlicensed band at 5 GHz. IEEE 802.11b applies a direct sequence spread spectrum (DSSS) at 2.4 GHz to provide a transmission rate of 11 Mbps. IEEE 802.11g applies orthogonal frequency division multiplexing (OFDM) at 2.4 GHz to provide a transmission rate of 54 Mbps. IEEE 802.11n applies multiple input multiple output OFDM (MIMO-OFDM) to provide a transmission rate of 300 Mbps for two spatial streams. IEEE 802.11n supports a channel bandwidth of up to 40 MHz, in which case it provides a transmission rate of 600 Mbps.

As the spread of the WLAN is activated and the applications using the same are diversified, there is an increasing need for a new WLAN technology for supporting a higher throughput than the data processing speed supported by IEEE 802.11n. Very high throughput (VHT) WLAN technology is one of IEEE 802.11 WLAN technologies that have been proposed to support data processing speeds of 1 Gbps or more. Among them, IEEE 802.11ac is being developed as a standard for providing very high throughput in the band below 5 GHz, and IEEE 802.11ad is being developed as a standard for providing very high throughput in the 60 GHz band.

In a system based on the WLAN technology, when the terminal searches for an access point through an active search method, the terminal transmits a probe request frame, and the access point transmits a probe request frame. In response to the probe response frame (probe response frame) is transmitted. In an environment in which a plurality of terminals and a plurality of access points exist, each terminal transmits its own probe request frame, and each access point transmits a probe response frame in response to the probe request frame. That is, a large number of probe request frames and probe response frames are generated, and these frames occupy a large number of radio channels. Therefore, the terminal must wait for a long time to wake up to receive the probe response frame from the desired access point.

An object of the present invention for solving the above problems is to provide an active search method for quickly searching for the presence of an access point.

Another object of the present invention for solving the above problems is to provide an active search response method for quickly searching for the presence of an access point.

In accordance with an aspect of the present invention, there is provided an active discovery method, comprising: transmitting a prior probe request frame for confirming the existence of an access point through an arbitrary channel; Obtaining a probe ACK frame that is a response to a request frame, setting a maximum wait time based on the number of probe ACK frames, and performing an active search for an access point in the arbitrary channel during the maximum wait time Steps.

The active searching method may further include transmitting a priority probe request frame on a channel other than the arbitrary channel after the maximum waiting time has passed.

The active searching method may further include transmitting all probe response frames corresponding to the number of probe ACK frames, and then transmitting a prior probe request frame in a channel other than the arbitrary channel.

In the setting of the maximum waiting time, the maximum waiting time may be set to be proportional to the number of probe ACK frames.

Here, the priority probe request frame may be an NDP frame.

Here, the priority probe request frame may include identifier information of the access point.

The acquiring the probe ACK frame may select a probe ACK frame having a predetermined signal strength or more among the acquired probe ACK frames.

According to another exemplary embodiment of the present invention, there is provided a method for acquiring a probe request frame from a terminal, generating a probe ACK frame that is a response to the probe request frame, and the probe. Transmitting an ACK frame.

The active search response method may further include obtaining a probe request frame from the terminal and transmitting a probe response frame in response to the probe request frame.

In the generating of the probe ACK frame, when the first probe request frame includes identifier information of the access point, the probe ACK frame may be generated.

Here, the priority probe request frame may be an NDP frame.

Here, the priority probe request frame may include identifier information of at least one access point.

Here, the probe ACK frame may include transmission time information of a beacon frame transmitted from the access point.

In another aspect of the present invention, there is provided a method for actively searching, comprising: transmitting a prior probe request frame for confirming the existence of an access point through an arbitrary channel; The method may include receiving a probe ACK frame that is a response to a probe request frame, and obtaining transmission time information of a beacon frame included in the probe ACK frame.

The active search method may further include transmitting a prior probe request frame in a channel other than the arbitrary channel before the transmission time of the beacon frame.

The active search method may further include receiving a beacon frame from an access point at a transmission time of the beacon frame.

Here, the priority probe request frame may be an NDP frame.

According to the present invention, since the terminal can confirm the existence of the access point in advance through a process of 'prior probe request frame-receiving probe ACK frame', the terminal must wait to receive a probe response frame from the access point. It can reduce the time to do it.

In addition, the UE may predict the number of transmission of the probe response frame in advance through a 'first probe request frame transmission-receive probe ACK frame' process, and thus the probe response frame does not need to wait until the maximum waiting time. It can reduce the time to wait to receive a message.

In addition, the terminal may determine the radio signal quality of each access point in advance through a 'first probe request frame transmission-probe ACK frame reception' process, and thus active search for the access point having a good radio signal quality Can be done. Through this, the terminal can reduce the search time of the access point, and can prevent the transmission of the probe response frame from the access point having poor radio signal quality, thereby improving the efficiency of the wireless channel.

In addition, the terminal may recognize the transmission time of the beacon frame in advance through the 'first probe request frame transmission-probe ACK frame reception' process, it can receive the beacon frame at the recognized time.

1 is a conceptual diagram illustrating an embodiment of a configuration of an IEEE 802.11 WLAN system.

2 is a conceptual diagram illustrating a connection process of a terminal in an infrastructure BSS.

3 is a conceptual diagram illustrating an embodiment of a data transmission process of an access point.

4 is a conceptual diagram illustrating a configuration of a probe request frame.

5 is a conceptual diagram showing the configuration (1 ~ 14) of the probe response frame.

6 is a conceptual diagram illustrating a configuration (15 to Last-n) of the probe response frame.

7 is a conceptual diagram illustrating an embodiment of an active search method in multiple channels.

8 is a conceptual diagram illustrating another embodiment of an active search method in multiple channels.

9 is a conceptual diagram illustrating an embodiment of a manual search method in multiple channels.

10 is a flowchart illustrating an active search method according to an embodiment of the present invention.

11 is a conceptual diagram illustrating a first embodiment of an active search method.

12 is a conceptual diagram illustrating a second embodiment of an active search method.

13 is a conceptual diagram illustrating a third embodiment of an active search method.

14 is a conceptual diagram illustrating a fourth embodiment of an active search method.

15 is a flowchart illustrating an active search method according to another embodiment of the present invention.

16 is a conceptual diagram illustrating a fifth embodiment of an active search method.

As the present invention allows for various changes and numerous embodiments, particular embodiments will be illustrated in the drawings and described in detail in the written description.

However, this is not intended to limit the present invention to specific embodiments, it should be understood to include all modifications, equivalents, and substitutes included in the spirit and scope of the present invention.

The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting of the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this application, the terms "comprise" or "have" are intended to indicate that there is a feature, number, step, operation, component, part, or combination thereof described in the specification, and one or more other features. It is to be understood that the present invention does not exclude the possibility of the presence or the addition of numbers, steps, operations, components, components, or a combination thereof.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art. Terms such as those defined in the commonly used dictionaries should be construed as having meanings consistent with the meanings in the context of the related art and shall not be construed in ideal or excessively formal meanings unless expressly defined in this application. Do not.

Hereinafter, with reference to the accompanying drawings, it will be described in detail a preferred embodiment of the present invention. In the following description of the present invention, the same reference numerals are used for the same elements in the drawings and redundant descriptions of the same elements will be omitted.

Throughout the specification, a station (STA) is a physical layer for medium access control (MAC) and wireless medium that conforms to the Institute of Electrical and Electronics Engineers (IEEE) 802.11 standard. By any functional medium that includes an interface. The station STA may be divided into a station that is an access point (AP) and a station that is a non-access point (STA). A station (STA), which is an access point (AP), may simply be called an access point (AP), and a station (STA), which is a non-AP, may simply be called a terminal.

The station STA may include a processor and a transceiver, and may further include a user interface and a display device. A processor refers to a unit designed to generate a frame to be transmitted through a wireless network or to process a frame received through a wireless network, and performs various functions for controlling a station (STA). A transceiver is a unit that is functionally connected to a processor and is designed to transmit and receive a frame through a wireless network for a station (STA).

An access point (AP) may refer to a centralized controller, a base station (BS), a node-B, an e-node-B, a base transceiver system (BTS), or a site controller, and the like. Some or all of the features may be included.

The terminal may be a wireless transmit / receive unit (WTRU), a user equipment (UE), a user terminal (UT), an access terminal (AT), a mobile station (MS), May refer to a mobile terminal, a subscriber unit, a subscriber station (SS), a wireless device, or a mobile subscriber unit, and some of them. Or all of the functions may be included.

Here, a desktop computer, a laptop computer, a tablet PC, a wireless phone, a mobile phone, a smart phone, and an e-communication capable of communicating with a terminal may be used. book readers, portable multimedia players (PMPs), portable game consoles, navigation devices, digital cameras, digital multimedia broadcasting (DMB) players, digital audio recorders, digital audio players ), A digital picture recorder, a digital picture player, a digital video recorder, a digital video player, and the like can be used.

Referring to FIG. 1, an IEEE 802.11 WLAN system includes at least one basic service set (BSS). BSS means a set of stations (STA 1, STA 2 (AP 1), STA 3, STA 4, STA 5 (AP 2)) that can be successfully synchronized to communicate with each other, the concept of a specific area is no.

BSS can be classified into Infrastructure BSS (Independent BSS) and Independent BSS (IBSS), and BSS 1 and BSS 2 represent Infrastructure BSS. BSS 1 connects a terminal (STA 1), an access point (STA 2 (AP 1)) providing a distribution service and a plurality of access points (STA 2 (AP 1), STA 5 (AP 2)) It may include a distribution system (DS). In BSS 1, an access point STA 2 (AP 1) manages a terminal STA 1.

BSS 2 connects a terminal (STA 3, STA 4), an access point (STA 5 (AP 2)) providing a distribution service and a plurality of access points (STA 2 (AP 1), STA 5 (AP 2)) It may include a distribution system. In BSS 2, an access point STA 5 (AP 2) manages terminals STA 3 and STA 4.

The independent BSS, on the other hand, is a BSS operating in an ad-hoc mode. Since the IBSS does not include an access point, there is no centralized management entity. That is, in the IBSS, terminals are managed in a distributed manner. In IBSS, all terminals may be mobile terminals, and thus, are not allowed to be connected to the distribution system (DS), thereby forming a self-contained network.

The access points STA 2 (AP 1) and STA 5 (AP 2) provide access to the distribution system DS via the wireless medium for the terminals STA 1, STA 3, and STA 4 coupled thereto. . Communication between terminals STA 1, STA 3, and STA 4 in BSS 1 or BSS 2 is generally performed through an access point STA 2 (AP 1) or STA 5 (AP 2), but a direct link (direct link) If the link is configured, direct communication between the terminals STA 1, STA 3, and STA 4 is possible.

The plurality of infrastructure BSSs may be interconnected through a distribution system (DS). A plurality of BSSs connected through a distribution system (DS) is called an extended service set (ESS). Stations included in the ESS may communicate with each other, and the UE may move from one BSS to another BSS while seamlessly communicating within the same ESS.

The distribution system (DS) is a mechanism for one access point to communicate with another access point, whereby the access point transmits frames to, or moves to, another BSS for the terminals that are associated with the BSS it manages. A frame may be transmitted for one arbitrary terminal. In addition, the access point may transmit and receive frames with an external network such as a wired network. Such a distribution system (DS) does not necessarily need to be a network, and there is no limitation on its form as long as it can provide a predetermined distribution service defined in the IEEE 802.11 standard. For example, the distribution system may be a wireless network such as a mesh network or a physical structure that connects access points to each other.

The active search method according to an embodiment of the present invention to be described below can be applied to the IEEE 802.11 WLAN system described above, and in addition to the IEEE 802.11 WLAN system, a wireless personal area network (WPAN) and a wireless body area network (WBAN). It can be applied to various networks such as.

In order for the STA to transmit and receive data in the intra-structure BSS, the terminal STA must first be connected to the access point AP.

Referring to FIG. 2, the connection process of the STA in the infrastructure BSS is largely 1) a probe step (AP), 2) an authentication step with the detected access point (AP). ) And 3) an association step with an authenticated access point (AP).

The STA may first detect neighboring access points (APs) through a detection process. The detection process is divided into a passive scanning method and an active scanning method. The passive scanning method may be performed by overhearing beacons transmitted by neighboring access points (APs). Meanwhile, the active scanning method may be performed by broadcasting a probe request frame. The AP that receives the probe request frame may transmit a probe response frame corresponding to the probe request frame to the corresponding STA. The STA may know the presence of neighboring access points (APs) by receiving a probe response frame.

Thereafter, the terminal STA may perform authentication with the detected access point AP and may perform authentication with the plurality of detected access points APs. An authentication algorithm according to the IEEE 802.11 standard is divided into an open system algorithm for exchanging two authentication frames and a shared key algorithm for exchanging four authentication frames. Through the process of exchanging an authentication request frame and an authentication response frame based on the authentication algorithm, the terminal STA may perform authentication with the access point AP.

Lastly, the terminal STA selects one of the authenticated access points APs and performs a connection process with the selected access point AP. That is, the terminal STA transmits an association request frame to the selected access point AP, and the access point AP that receives the association request frame receives an association response frame corresponding to the association request frame. frame is transmitted to the corresponding STA. As such, through the process of exchanging the connection request frame and the connection response frame, the STA may perform a connection process with the access point AP.

Referring to FIG. 3, the AP may broadcast a beacon periodically, and may broadcast a beacon including a DTIM at three beacon intervals. Terminals STA 1 and STA 2 of a power save mode (PSM) periodically wake up to receive a beacon, check the TIM or DTIM included in the beacon, and send data to the access point to the access point. Check that it is buffered. In this case, when the buffered data is present, the terminals STA 1 and STA 2 remain awake to receive data from the access point AP, and when the buffered data does not exist, the terminals STA 1 and STA 2. ) Returns to the power saving state (ie the doze state).

That is, if the bit in the TIM corresponding to its AID is set to 1, the STA (STA 1, STA 2) is a PS (Power Save) -Poll frame (notifying that it is awake and ready to receive data) Or, transmit a trigger (trigger frame) to the access point (AP), the access point (AP) confirms that the terminal (STA 1, STA 2) is ready for data reception by receiving a PS-Poll frame, Data or an acknowledgment (ACK) may be transmitted to the terminals STA 1 and STA 2. When the ACK is transmitted to the terminals STA 1 and STA 2, the access point AP transmits data to the terminals STA 1 and STA 2 at an appropriate time. On the other hand, when the bit in the TIM corresponding to its own AID is set to 0, the terminals STA 1 and STA 2 return to the power saving state.

The search method of an access point can be classified into an active search method and a passive search method. In the active search method, the terminal transmits a probe request frame, and the access point receiving the probe request frame transmits a probe response frame in response to the probe request frame.

Referring to FIG. 4, the probe request frame includes a service set identifier (SSID), supported rates, request information, extended supported rates, and manufacturer specific ( vendor specific) information.

5 is a conceptual diagram showing the configuration (1 ~ 14) of the probe response frame, Figure 6 is a conceptual diagram showing the configuration (15 ~ Last-n) of the probe response frame.

5 and 6, the probe response frame contains a lot of information, thus occupying a radio channel for a long time. In an environment where a plurality of terminals and a plurality of access points exist, the terminals generate numerous probe request frames, and in response, the access points generate numerous probe response frames. These probe request frames and probe response frames occupy a radio channel for a long time. In addition, it is not easy for a terminal to receive a probe response frame from a desired access point within a short time, and it is necessary to keep awake state for a long time to search for a desired access point. Will receive.

Referring to FIG. 7, since the terminal does not know in which channel the desired access point exists, the terminal may sequentially perform the same active search process in each channel. The terminal may transmit a probe request frame on channel 1 and wait for a maximum waiting time for receiving a probe response frame that is a response to the probe request frame. After waiting for the maximum waiting time on channel 1, the terminal may move to channel 2 to perform an active discovery process (that is, probe request frame transmission-probe response frame reception).

Referring to FIG. 8, even if the terminal does not receive the probe response frame after the transmission of the probe request frame, the terminal should wait in the corresponding channel for a minimum waiting time. Meanwhile, when receiving at least one probe response frame, the terminal should wait on the corresponding channel for the maximum waiting time. Since the terminal must wait for a minimum waiting time for receiving a probe response frame even in a channel in which the access point does not exist, unnecessary time is consumed.

Referring to FIG. 9, since the UE does not know the transmission time of the beacon, the terminal should receive the beacon for a sufficiently long time and move to another channel. That is, the terminal may wait for a beacon interval in channel 1 to receive a beacon, and move to channel 2 after the beacon interval passes to receive a beacon.

Referring to FIG. 10, the terminal STA may transmit a prior probe request frame for confirming the existence of an access point through an arbitrary channel (S100). First, the probe request frame may mean a newly defined management frame and may mean a frame different from the probe request frame illustrated in FIG. 4.

First, the probe request frame may be used for checking whether an access point exists in a channel, and may be used for requesting a transmission time of a beacon. Therefore, the first probe request frame may be simply configured with only information except for complicated information included in the existing probe request frame (see FIG. 4). For example, the probe request frame may be configured in the form of a null data packet (NDP) frame.

To determine if a particular access point is present in the channel, the probe request frame may first include an identifier of the particular access point (eg, SSID, compressed SSID, basic service set identification (BSSID, etc.)). . Here, the compressed SSID may mean an SSID to which a hash algorithm is applied. The identifier (ID) of the access point may be included in the priority probe request frame alone or in a list form. If the identifier of the access point is not included in the probe request frame, it may be used to confirm the existence of all access points.

When using the priority probe request frame to request transmission time information of a beacon (or auxiliary beacon) transmitted from the access point, the priority probe request frame may be configured as described above. That is, the beacon transmission time information of the specific access point may be requested by first including the identifier of the specific access point in the probe request frame. Here, the auxiliary beacon (that is, short beacon), unlike the existing beacon includes only essential information for the search, has a shorter transmission period than the existing beacon.

When the access point AP receives the priority probe request frame from the terminal STA, the access point AP may generate a probe ACK frame that is a response to the priority probe request frame (S110). In this case, the access point AP may first generate a probe ACK frame when the identifier of the access point included in the probe request frame is the same as its identifier. Alternatively, the access point AP may first generate a probe ACK frame when none of the identifiers of the access point is included in the probe request frame.

The AP may generate a probe ACK frame including its own beacon transmission time information, and may generate a probe ACK frame including its identifier (eg, SSID).

The probe ACK frame is used for notifying the existence of an access point (or for notifying beacon transmission time information). Unlike a conventional probe response frame (see FIGS. 5 and 6), the probe ACK frame may be used as It means a simple response to the reception.

The AP may first transmit a probe ACK frame in response to the probe request frame (S120). In this case, the AP may transmit a probe ACK frame by setting a transmission priority higher than that of other management frames or data frames. For example, the priority of transmission for the probe ACK frame may be increased by adjusting an enhanced distributed channel access (EDCA) parameter. That is, the probe ACK frame may be transmitted by setting a short arbitration interframe space (AIFS), a small CWmin (minimum value of the contention window), and a small CWmax (maximum value of the contention window). When the EDCA parameter is set in this way, the AP may transmit a probe ACK frame within a short time window.

On the other hand, the access points (APs) may first compete for channel access to transmit a probe ACK frame that is a response to the probe request frame. In this case, the access points APs may sequentially transmit probe ACK frames according to a backoff operation. Alternatively, the access points may stop transmitting their probe ACK frame when it recognizes that the probe ACK frame is transmitted from one access point.

The terminal STA may receive a probe ACK frame transmitted from the access point AP (S120). In this case, the STA may receive a probe ACK frame for a prior waiting time shorter than the maximum waiting time. Here, the maximum waiting time means a waiting time for receiving an existing probe response frame (see FIGS. 5 and 6), and the first waiting time means a waiting time for receiving a probe ACK frame. Since the probe ACK frame has a smaller size than the probe response frame, the STA may first set the waiting time shorter than the maximum waiting time. Also, the STA may set a shorter waiting time to receive only some probe ACK frames.

Meanwhile, when receiving a plurality of probe ACK frames, the terminal STA may measure signal strengths of the plurality of probe ACK frames, and select a probe ACK frame having a predetermined signal strength or more among the plurality of probe ACK frames. The access point transmitting the selected probe ACK frame may be selected as a connection target access point. In a later step, the terminal STA may transmit a probe request frame including the identifier of the access point to which the connection is to be made.

The terminal STA may set a maximum waiting time based on the number of received probe ACK frames (S130). That is, the number of probe ACK frames means the number of access points existing in the channel, which means the number of probe response frames to be transmitted. Accordingly, the terminal STA may set a maximum waiting time to receive the predicted number of probe response frames. For example, the terminal may set the maximum wait time relatively long when the number of received probe ACK frames is large, and may set the maximum wait time relatively short when the number of received probe ACK frames is small.

The terminal STA may transmit a probe request frame (S140) and may receive a probe response frame that is a response to the probe request frame (S150). That is, the terminal STA may receive the probe response frame for the maximum waiting time set through step S130.

After the maximum waiting time, the terminal STA may move to another channel to perform an active search process (ie, transmitting a probe request frame first-receiving a probe ACK-transmitting a probe request frame-receiving a probe response frame) (S160). . Meanwhile, even when the maximum waiting time elapses, the terminal STA may move to another channel and perform an active search process when all of the predicted number of probe response frames have been received.

Referring to FIG. 11, the terminal may transmit a priority probe request frame on channel 1 and receive a probe ACK frame that is a response to the priority probe request frame during a priority wait time. Since the UE has received three probe ACK frames, it can be expected that three probe response frames will be transmitted thereafter. Accordingly, the terminal may set a maximum waiting time to receive three probe response frames.

The terminal may transmit a probe request frame on channel 1 and may receive a probe response frame that is a response to the probe request frame for a set maximum waiting time. After the maximum waiting time, the terminal may move to channel 2 and transmit a priority probe request frame.

Since the terminal has not received the probe ACK frame that is a response to the priority probe request frame during the priority wait time in channel 2, the terminal may move to channel 3 after the priority wait time passes. The UE may perform the above active discovery process (ie, probe request frame transmission-probe ACK frame reception-probe request frame transmission-probe response frame reception) as described above in channel 3.

Referring to FIG. 12, the terminal may transmit a priority probe request frame on channel 1 and may receive a probe ACK frame that is a response to the priority probe request frame during a priority waiting time. Since the UE has received two probe ACK frames, it can predict that two probe response frames will be transmitted afterwards. Accordingly, the terminal may set a maximum waiting time to receive two probe response frames.

The terminal may transmit a probe request frame on channel 1 and may receive a probe response frame that is a response to the probe request frame for a set maximum waiting time. If the terminal receives both probe response frames even before the maximum waiting time has elapsed, the terminal may move to channel 2 to perform an active search process.

The terminal may transmit a priority probe request frame on channel 2. Since the terminal has not received the probe ACK frame that is a response to the priority probe request frame during the priority wait time in channel 2, the terminal may move to channel 3 after the priority wait time passes. The UE may perform the above active discovery process (ie, probe request frame transmission-probe ACK frame reception-probe request frame transmission-probe response frame reception) as described above in channel 3.

Referring to FIG. 13, the terminal may transmit a priority probe request frame on channel 1 and receive a probe ACK frame that is a response to the priority probe request frame during a priority waiting time. In this case, the terminal may first set a short wait time to receive only some probe ACK frames. Therefore, the terminal may first receive two probe ACK frames during the waiting time.

Referring to FIG. 14, the terminal may transmit a priority probe request frame on channel 1 and receive a probe ACK frame that is a response to the priority probe request frame during a priority waiting time.

Here, the first probe request frame may include transmission mode information indicating a transmission method of the probe ACK frame. The transmission mode information may indicate two transmission modes. The first transmission mode (ie, AP number checking mode) firstly indicates that all access points that receive the probe request frame should transmit their probe ACK frames. In the second transmission mode (ie, AP presence check mode), if any of the access points receiving the probe request frame first transmits the probe ACK frame, the remaining access points must stop transmitting the probe ACK frame. To indicate.

The transmission mode information may have a size of 1 bit. In this case, '0' means an AP number checking mode and '1' means an AP presence checking mode.

When access points present in channel 1 receive a probe request frame, the APs may check transmission mode information included in the probe request frame. When the transmission mode information indicates the AP number checking mode, all access points present in channel 1 may transmit a probe ACK frame that is a response to the first probe request frame through a channel access competition. Accordingly, the terminal may check the number of access points present in channel 1 through the AP number checking mode.

When the transmission mode information indicates the AP presence check mode, only one access point among the access points existing in the channel 1 may transmit a probe ACK frame that is a response to the first probe request frame. That is, when one access point transmits a probe ACK frame among the access points present in channel 1, the other access points may stop transmitting the probe ACK frame. Accordingly, the terminal may check whether the access point exists in channel 1 through the AP presence check mode.

Thereafter, the terminal may transmit a probe request frame on channel 1 and may receive a probe response frame that is a response to the probe request frame for a maximum waiting time. After the maximum waiting time, the terminal may move to channel 2 and transmit a priority probe request frame.

Referring to FIG. 15, the terminal may transmit a prior probe request frame for confirming the existence of an access point through an arbitrary channel (S200). Here, the priority probe request frame refers to the priority probe request frame described with reference to FIG. 10. That is, the first probe request frame may be used for checking whether an access point exists in a channel, and may be used for requesting a transmission time of a beacon.

First, the probe request frame may be simply configured unlike the existing probe request frame (see FIGS. 5 and 6). For example, the first probe request frame may include an identifier of a specific access point, or may be configured in the form of an NDP frame.

At least one access point may first transmit a probe ACK frame in response to the probe request frame. The access point may generate a probe ACK frame including at least one of its identifier and transmission time information of the beacon (or auxiliary beacon), and may transmit the generated probe ACK frame.

The UE may first receive a probe ACK frame during the waiting time (S210), and may acquire transmission time information of the beacon included in the probe ACK frame. In this case, when receiving a plurality of probe ACK frames, the UE may select one probe ACK frame having the largest signal strength among the plurality of probe ACK frames, and obtain transmission time information of the beacon from the selected probe ACK frame. .

If it is determined that the active search process may be performed in another channel until the transmission time of the beacon, the terminal may move to another channel and perform the active search process (S230). That is, the terminal may transmit a probe request frame first in another channel, receive a probe ACK frame in response thereto, and obtain transmission time information of a beacon (or auxiliary beacon) from the received probe ACK frame. have.

The terminal may receive a beacon from the access point in the transmission time of the beacon (S240).

Referring to FIG. 16, the terminal may transmit a priority probe request frame on channel 1. At least one access point may transmit a probe ACK frame in response to a probe request frame, and the terminal may receive a probe ACK frame transmitted during a first waiting time.

When the plurality of probe ACK frames are received on channel 1, the UE may select one probe ACK frame having the largest signal strength among the plurality of probe ACK frames, and is based on transmission time information of the beacon included in the selected probe ACK frame. As such, the transmission time of the beacon and the auxiliary beacons to be transmitted next can be recognized. For example, when the signal strength of the probe ACK frame 1 is the largest among the plurality of probe ACK frames, the terminal may acquire transmission times of the beacon 1 and the auxiliary beacon 1 to be transmitted next based on the probe ACK frame 1.

If it is determined that the active search process can be performed in another channel until the transmission times of the beacon 1 and the auxiliary beacon 1, the terminal may move to channel 2 to perform the active search process. The terminal may transmit a priority probe request frame on channel 2. At least one access point may transmit a probe ACK frame in response to a probe request frame, and the terminal may receive a probe ACK frame transmitted during a first waiting time.

When a plurality of probe ACK frames are received on channel 2, the UE may select one probe ACK frame having the largest signal strength among the plurality of probe ACK frames, and is based on transmission time information of the beacon included in the selected probe ACK frame. As such, the transmission time of the beacon and the auxiliary beacons to be transmitted next can be recognized. For example, when the signal strength of the probe ACK frame 6 is the largest among the plurality of probe ACK frames, the terminal may acquire transmission times of the beacon 6 and the auxiliary beacon 6 to be transmitted next based on the probe ACK frame 6.

If it is determined that the active search process can be performed in another channel until the transmission times of the beacon 1, the auxiliary beacon 1, the beacon 6, and the auxiliary beacon 6, the terminal may move to channel 3 to perform the active search process. The terminal may transmit a priority probe request frame on channel 3. At least one access point may transmit a probe ACK frame in response to a probe request frame, and the terminal may receive a probe ACK frame transmitted during a first waiting time.

When receiving a plurality of probe ACK frames, the terminal may select one probe ACK frame having the largest signal strength among the plurality of probe ACK frames, and based on the transmission time information of the beacon included in the selected probe ACK frame, The transmission time of the beacon and the auxiliary beacon to be transmitted can be recognized. For example, when the signal strength of the probe ACK frame 9 is the largest among the plurality of probe ACK frames, the terminal may acquire transmission times of the beacon 9 and the auxiliary beacon 9 to be transmitted next based on the probe ACK frame 9.

On the other hand, if it is determined that the active search process cannot be performed in another channel until the transmission time of the next beacon (that is, beacon 1), the terminal may move to channel 1 and receive beacon 1. Thereafter, since the transmission time of the beacon 6 and the transmission time of the beacon 9 overlap, the terminal may first receive the beacon 6 on channel 2, and may move to the channel 3 to receive the auxiliary beacon 9. On the contrary, the terminal may first receive beacon 9 on channel 3, and may move to channel 2 to receive auxiliary beacon 6. That is, when transmission times of beacons overlap, the terminal may determine the reception time of the beacons in each channel in consideration of the transmission times of the beacons and the auxiliary beacons.

Although described with reference to the embodiments above, those skilled in the art will understand that the present invention can be variously modified and changed without departing from the spirit and scope of the invention as set forth in the claims below. Could be.

Claims

In the active search method performed in the terminal,

Transmitting, via any channel, a prior probe request frame to confirm the presence of an access point;

Obtaining a probe acknowledgment (ACK) frame in response to the first probe request frame from at least one access point;

Setting a max waiting time based on the number of probe ACK frames; And

And performing an active search for an access point in the any channel during the maximum waiting time.
The method according to claim 1,

The active search method,

And after the maximum waiting time, transmitting a prior probe request frame in a channel other than the arbitrary channel.
The method according to claim 1,

The active search method,

And receiving all probe response frames corresponding to the number of probe ACK frames, and then transmitting a priority probe request frame in a channel other than the arbitrary channel.
The method according to claim 1,

The setting of the maximum waiting time may include:

And a maximum wait time is set to be proportional to the number of probe ACK frames.
The method according to claim 1,

The first probe request frame is an NDP (null data packet) frame.
The method according to claim 1,

The first probe request frame includes an identifier (ID) information of an access point.
The method according to claim 1,

Acquiring the probe ACK frame,

And selecting a probe ACK frame having a predetermined signal strength or more among the acquired probe ACK frames.
In the active search response method performed in the access point,

Obtaining a priority probe request frame from the terminal;

Generating a probe ACK frame that is a response to the first probe request frame; And

Transmitting the probe ACK frame.
The method according to claim 8,

The active search response method,

Obtaining a probe request frame from the terminal; And

And transmitting a probe response frame in response to the probe request frame.
The method according to claim 8,

Generating the probe ACK frame,

And generating the probe ACK frame when the first probe request frame includes identifier (ID) information of the access point.
The method according to claim 8,

The first probe request frame is a NDP (null data packet) frame, characterized in that the active search response method.
The method according to claim 8,

And wherein the first probe request frame includes identifier information of at least one access point.
The method according to claim 8,

The probe ACK frame,

And a transmission time information of a beacon frame transmitted from the access point.
In the active search method performed in the terminal,

Transmitting, via any channel, a prior probe request frame to confirm the presence of an access point;

Receiving a probe ACK frame in response to the first probe request frame from at least one access point; And

And acquiring transmission time information of a beacon frame included in the probe ACK frame.
The method according to claim 14,

The active search method,

And prior to the transmission time of the beacon frame, transmitting a prior probe request frame in a channel other than the arbitrary channel.
The method according to claim 14,

The active search method,

Receiving a beacon frame from an access point at a transmission time of the beacon frame.
The method according to claim 14,

The first probe request frame is a NDP (null data packet) frame, characterized in that the active search response method.
The method according to claim 14,

And wherein the first probe request frame includes identifier information of an access point.