WO2010044599A2

WO2010044599A2 - Method and apparatus for establishing direct link in wireless local area network system

Info

Publication number: WO2010044599A2
Application number: PCT/KR2009/005894
Authority: WO
Inventors: Yongho Seok
Original assignee: Lg Electronics Inc.
Priority date: 2008-10-15
Filing date: 2009-10-14
Publication date: 2010-04-22
Also published as: WO2010044599A3

Abstract

A method and apparatus for establishing a direct link in a wireless local area network (WLAN) system is provided. The WLAN system operates in an infrastructure mode and comprises an initiating station (STA) and a recipient STA and each of which intends to establish the direct link, and a access point (AP) relaying communication between the initiating STA and the receiver STA. The AP provides location information of the initiating STA and the recipient STA respectively to the recipient STA and the initiating STA in the process of establishing the direct link.

Description

METHOD AND APPARATUS FOR ESTABLISHING DIRECT LINK IN WIRELESS LOCAL AREA NETWORK SYSTEM

The present invention relates to a wireless local area network (WLAN), and more particularly, to a procedure for establishing a direct link in a WLAN system.

Several medium access control (MAC) protocols are defined by the institute of electrical and electronics engineers (IEEE) 802.11e to provide quality of service (QoS) in a wireless local area network (WLAN). One example of the MAC protocols is direct link setup (DLS). The DLS allows direct communication between QoS stations (QSTAs) operating in an infrastructure mode. That is, when the DLS is used, a data frame can be directly transmitted between the QSTAs. On the other hand, when the DLS is not used, all data frames are delivered via an access point (AP).

FIG. 1 is a message flow diagram for a DLS procedure defined by the IEEE 802.11e. Referring to FIG. 1, an initiating QSTA transmits a DLS setup request frame (e.g., DLS.request message) to a QoS AP (QAP). The QAP delivers the received DLS request frame (e.g., DLS.request message) to a recipient QSTA. If the recipient QSTA intends to establish a direct link, the recipient QSTA transmits a DLS response frame (e.g., DLS.response message) to the QAP, and the QAP delivers the received DLS response frame (e.g., DLS.response message) to the initiating QSTA. After the direct link is established between the initiating QSTA and the recipient QSTA through this process, all data frames are transmitted between the initiating QSTA and the recipient QSTA through the established direct link.

In a very high throughput (VHT) WLAN system using a band of 60 GHz, it is considered to use a directional antenna to compensate for narrow service coverage. The directional antenna is an opposite concept of an omni-directional antenna, and implies that a signal is transmitted only in a specific direction by using a beam forming technique. In order to use the beam forming technique, a beam forming process using a beam training sequence needs to be performed in advance. When such a directional antenna is used to transmit a signal in a specific direction where a recipient terminal is located, the signal can be successfully transmitted to a farther distance. An embodiment of the present invention is in association only with the use of the beam forming technique and there is no restriction on a detailed implementation method of the beam forming technique.

In order to use the directional antenna, the beam forming process using the beam training sequence is necessary between devices intending to communicate with each other. In addition to a case where a QSTA communicates with an AP, the beam forming process is also necessary between QSTAs establishing a direct link. That is, when the direct link is established according to a DLS procedure and when QSTAs communicating through the direct link intend to communicate by using the directional antenna, it is necessary to perform the beam forming process.

However, significant overhead is produced when a QSTA establishing a direct link performs the beam forming process by using the beam training sequence in all directions without having any information on a location of a peer QSTA. The overhead produced in the beam forming process is more increased when a beam-width is decreased to expand service coverage.

The present invention provides a procedure of establishing a direct link in a wireless local area network (WLAN) system to reduce overhead produced in a beam forming process between stations intending to communicate by using a directional antenna.

In an aspect, a method for establishing a direct link in a wireless local area network (WLAN) system is provided. The WLAN system operates in an infrastructure mode and comprises an initiating station (STA) and a recipient STA and each of which intends to establish the direct link, and a access point (AP) relaying communication between the initiating STA and the receiver STA. The AP provides location information of the initiating STA and the recipient STA respectively to the recipient STA and the initiating STA in the process of establishing the direct link.

The location information may comprise information on a degree of angle (DoA) of each of the initiating STA and the recipient STA with respect to the AP.

When the location information is provided, the AP may provide signal strength information on the initiating STA and the recipient STA.

The initiating STA and the recipient STA may perform a beam forming process for transmission of a data frame through the direct link established using the location information.

In another aspect, a method of establishing a direct link in a WLAN system by using directional transmission is provided. The method includes transmitting by an initiating STA a direct link setup request message to a AP, transmitting by the AP the direct link setup request message comprising location information of the initiating QSTA to a recipient STA, transmitting by the recipient STA a direct link setup response message to the AP, and transmitting by the AP the direct link setup response message comprising location information of the recipient QSTA to the initiating STA.

A quality of service (QoS) station (QSTA) intending to establish a direct link can know signal strength information together with location information of a peer QSTA in a process of establishing a direct link with the peer QSTA. Therefore, since a QSTA intending to use a directional antenna in transmission using the direct link can know relative location information of the peer QSTA, overhead produced in a process of configuring beam forming can be reduced.

FIG. 1 is a message flow diagram for a direct link setup (DLS) procedure defined by the institute of electrical and electronics engineers (IEEE) 802.11e.

FIG. 2 is a schematic view showing an exemplary structure of a very high throughput (VHT) wireless local area network (WLAN) system according to an embodiment of the present invention.

FIG. 3 is a message flow diagram showing a DLS procedure according to an embodiment of the present invention.

FIG. 4 shows an example of information elements included in a DLS setup request frame transmitted by a quality of service (QoS) access point (QAP) to a QoS station (QSTA)2 in step S22 of FIG. 3.

FIG. 5 shows an example of information elements included in a DLS setup response frame transmitted by a QAP to a QSTA1 in step S24 of FIG. 3.

FIG. 6 is a message flow diagram showing an exemplary process of modifying beam forming when a QSTA1 moves to another location after a direct link is established between the QSTA1 and a QSTA2.

FIG. 7 shows an example of information included in a DLS degree of angle (DoA) request frame.

FIG. 8 shows an example of information included in a DLS DoA response frame.

FIG. 9 is a block diagram of a station supporting a transmission method of the present invention.

Referring to FIG. 2, a WLAN system such as the VHT WLAN system includes one or more basis service sets (BSSs). The BSS is a set of stations (STAs) which are successfully synchronized to communicate with one another, and is not a concept indicating a specific region. As in the WLAN system to which the embodiment of the present invention is applicable, a BSS that supports a super high-rate data processing of 1 GHz or higher in a medium access control (MAC) service access point (SAP) is referred to as a VHT BSS.

The VHT BSS can be classified into an infrastructure BSS and an independent BSS (IBSS). The infrastructure BSS is shown in FIG. 1. Infrastructure BSSs (i.e., BSS1 and BSS2) include one or more non-access point (AP) STAs (i.e., Non-AP STA1, Non-AP STA3, and Non-AP STA4), AP STAs (i.e., AP STA1 and AP STA2) which are STAs providing a distribution service, and a distribution system (DS) connecting the plurality of AP STAs (i.e., AP STA1 and AP STA2). In the infrastructure BSS, an AP STA manages non-AP STAs of the BSS.

On the other hand, the IBSS is a BSS operating in an ad-hoc mode. Since the IBSS does not include the VHT STA, a centralized management entity for performing a management function in a centralized manner does not exist. That is, the IBSS manages the non-AP STAs in a distributed manner. In addition, in the IBSS, all STAs may consist of mobile STAs, and a self-contained network is configured since access to the DS is not allowed.

The STA is an arbitrary functional medium including a medium access control (MAC) and wireless-medium physical layer interface conforming to the institute of electrical and electronics engineers (IEEE) 802.11 standard, and includes both an AP and a non-AP STA in a broad sense. A VHT STA is defined as an STA that supports the super high-rate data processing of 1 GHz or higher in the multi-channel environment to be described below. In the VHT WLAN system to which the embodiment of the present invention is applicable, STAs included in the BSS may be all VHT STAs, or a VHT STA and a legacy STA (i.e., IEEE 802.11n-based HT STA) may coexist.

The STA for wireless communication includes a processor and a transceiver, and also includes a user interface, a display means, etc. The processor is a functional unit devised to generate a frame to be transmitted through a wireless network or to process a frame received through the wireless network, and performs various functions to control STAs. The transceiver is functionally connected to the processor and is a functional unit devised to transmit and receive a frame for the STAs through the wireless network.

Among the STAs, non-AP STAs (i.e., STA1, STA3, STA4, and STA5) are portable terminals operated by users. A non-AP STA may be simply referred to as an STA. The non-AP STA may also be referred to as a terminal, a wireless transmit/receive unit (WTRU), a user equipment (UE), a mobile station (MS), a mobile terminal, a mobile subscriber unit, etc. A non-AP VHT-STA (or simply VHT STA) is defined as a non-AP STA that supports the super high-rate data processing of 1 GHz or higher in the multi-channel environment to be described below.

The AP (i.e., AP1 and AP2) is a functional entity for providing access to the DS through a wireless medium for an associated STA. Although communication between non-AP STAs in an infrastructure BSS including the AP is performed via the AP in principle, the non-AP STAs can perform direct communication when a direct link is set up. In addition to the terminology of an access point, the AP may also be referred to as a centralized controller, a base station (BS), a node-B, a base transceiver system (BTS), a site controller, etc. A VHT AP is defined as an AP that supports the super high-rate data processing of 1 GHz or higher in the multi-channel environment to be described below.

A plurality of infrastructure BSSs can be interconnected by the use of the DS. An extended service set (ESS) is a plurality of BSSs connected by the use of the DS. STAs included in the ESS can communicate with one another. In the same ESS, a non-AP STA can move from one BSS to another BSS while performing seamless communication.

The DS is a mechanism whereby one AP communicates with another AP. By using the DS, an AP may transmit a frame for STAs associated with a BSS managed by the AP, or transmit a frame when any one of the STAs moves to another BSS, or transmit a frame to an external network such as a wired network. The DS is not necessarily a network, and has no limitation in its format as long as a specific distribution service specified in the IEEE 802.11 can be provided. For example, the DS may be a wireless network such as a mesh network, or may be a physical construction for interconnecting APs.

The VHT WLAN system considers the use of a directional antenna for service coverage expansion. In general, in a case where two devices communicating with each other both use a directional antenna, if a beam-width of the directional antenna is β, a beam training sequence for beam forming is required by (360/β)×(360/β) between the two devices. For example, if β is 15, a total of 576 (i.e., 24×24) beam training sequences are required. This implies that, if β is 15, a beam direction selectable by each device is 24, and a total of 576 combinations of all beam directions can be configured by each of the two devices. This also implies that, in order for two quality of service (QoS) stations (QSTAs) establishing a direct link to communicate through the established direct link by using a directional antenna of which the beam-width β is 15, up to 576 beam training sequences are required in the beam forming process.

Therefore, when the VHT WLAN system using the directional antenna directly uses the conventional direct link setup (DLS) procedure, significant overhead may be produced in the beam forming process performed by two QSTAs establishing the direct link. This is because the two QSTAs establishing the direct link exchange a frame only between the QSTAs through the setup procedure, and thus information on a location of a peer QSTA cannot be obtained. For this reason, a large number of beam training sequences are required to perform the beam forming process by the two QSTAs establishing the direct link without having any information on the location of the peer QSTA.

To reduce overhead produced in the beam forming process, information required in the beam forming process is provided by a QoS access point (QAP) to a QSTA in a DLS procedure according to an embodiment of the present invention. That is, since a QAP involving the DLS procedure between two QSTAs has already recognized information on locations of the two QSTAs associated with the QAP or subjected to an authentication process, location information of a peer QSTA is provided to the two QSTAs establishing the direct link so as to reduce overhead produced by the beam forming process performed later by the two QSTAs establishing the direct link.

Referring to FIG. 3, a QAP first communicates with two QSTAs intending to establish a direct link, i.e., QSTA1 and QSTA2, to obtain location information of each QSTA (step S10). Although it is shown in FIG. 3 that the QAP sequentially communicates with the QSTA1 and the QSTA2 to obtain the location information of each QSTA, this is for exemplary purposes only. Thus, the process of obtaining the location information may be performed simultaneously or in a reverse order.

There is no particular restriction on the process of obtaining the location information of the QSTA1 and the QSTA2 by the QAP. For example, each of the QSTA1 and the QSTA2 intending to establish a direct link is subjected to an association process and/or an authentication process with respect to the QAP. In addition, the QSTA1 and the QSTA2 preferentially perform a beam forming process with the QAP at the same time or at a different time of performing the association process and/or the authentication process. Through such a beam forming process, the QAP can know relative location information (e.g., a degree of angle (DoA)) between the QSTAs. The DoA indicates relative location information between QSTAs, and may be a value indicating an angle between the QSTAs with respect to the QAP in a specific direction. For example, if the DoA is a specific value in the range of 150 to 165, the QSTAs are located with an angle in the range of 150 to 165 with respect to the QAP.

The QSTA1 initiating the DLS procedure transmits a request message to establish a direct link with a peer QSTA (i.e., QSTA2), e.g., a DLS setup request frame, to the QAP (step S21). The DLS setup request frame may include the same information as that included in the conventional DLS setup request frame conforming to the IEEE 802.11e. However, the embodiment of the present invention is not limited thereto, and thus among information included in the DLS setup request frame transmitted by the QAP to the QSTA2 in step S22 to be described below, all or some parts of information known or measurable by the QSTA1 may be further included.

Upon receiving the DLS setup request frame from the QSTA1, the QAP transmits a request message to establish a direct link, e.g., a DLS setup request frame, to the QSTA2 (step S22). The DLS setup request frame transmitted by the QAP in this step may include information included in the conventional DLS setup request frame conforming to the IEEE 802.11e and information usefully used by the QSTA2 to recognize a location of the QSTA1 (e.g., a DoA between the QSTA1 and the QSTA2). Further, the DLS setup request frame may optionally include information indicating signal strength between the QSTA1 (or QSTA2) and the QAP as additional information required to recognize the location of the QSTA1.

In general, a terminal can calculate a relative location of a specific terminal if absolute or relative signal strength with respect to the specific terminal is known. In the embodiment of the present invention, if the QSTA2 can know a DoA between the QSTA1 and the QSTA2 with respect to the QAP and signal strength between the QAP and the QSTA1, the QSTA2 can recognize a relative location of the QSTA1 with respect to the QAP. According to the embodiment of the present invention, location information of a peer terminal (i.e., QSTA1) can be utilized in a beam forming process when the QSTA2 uses a direct link with the QSTA1, and an unnecessary beam training sequence can be reduced.

FIG. 4 shows an example of information elements included in the DLS setup request frame transmitted by the QAP to the QSTA2 in step S22 of FIG. 3. Referring to FIG. 4, the DLS setup request frame includes category information, action information, destination medium access control (MAC) address information, source MAC address information, capability information, DLS timeout value information, supported rates information, extended supported rates information, DoA information, DoA accuracy estimate information, destination RCPI information, and source RCPI information. The DoA information and the source RCPI information are used to recognize a relative location of the QSTA1 with respect to the QAP. Optionally, the destination RCPI information can also be used.

Referring back to FIG. 3, upon receiving the direct link setup request message, the QSTA2 transmits a direct link setup response message (e.g., DLS setup response frame) to the QAP (step S23). The DLS setup response frame may include the same information as that included in the conventional DLS setup response frame conforming to the IEEE 802.11e. However, the embodiment of the present invention is not limited thereto, and thus among information included in the DLS setup response frame transmitted by the QAP to the QSTA1 in step S24 to be described below, all or some parts of information known or measurable by the QSTA2 may be further included.

Upon receiving the DLS setup response frame from the QSTA2, the QAP transmits a direct link setup response message (e.g., DLS setup response frame) to the QSTA1 (step S24). The DLS setup response frame transmitted by the QAP in this step may include information included in the conventional DLS setup response frame conforming to the IEEE 802.11e and information usefully used by the QSTA1 to recognize a location of the QSTA2 (e.g., a DoA between the QSTA1 and the QSTA2 with respect to the QAP). Further, the DLS setup response frame may optionally include information indicating signal strength between the QSTA2 (or QSTA1) and the QAP as additional information required to recognize the location of the QSTA2.

In general, a terminal can calculate a relative location of a specific terminal if absolute or relative signal strength with respect to the specific terminal is known. In the embodiment of the present invention, if the QSTA1 can know a DoA between the QSTA1 and the QSTA2 with respect to the QAP and signal strength between the QAP and the QSTA2, the QSTA1 can recognize a relative location of the QSTA2 with respect to the QAP. According to the embodiment of the present invention, location information of a peer terminal (i.e., QSTA2) can be utilized in a beam forming process when the QSTA1 uses a direct link with the QSTA2, and an unnecessary beam training sequence can be reduced.

FIG. 5 shows an example of information elements included in the DLS setup response frame transmitted by the QAP to the QSTA1 in step S24 of FIG. 3. Referring to FIG. 5, the DLS setup response frame includes category information, action information, destination MAC address information, source MAC address information, capability information, DLS timeout value information, supported rates information, extended supported rates information, DoA information, DoA accuracy estimate information, destination RCPI information, and source RCPI information. The DoA information and the source RCPI information are used to recognize a relative location of the QSTA2 with respect to the QAP. Optionally, the destination RCPI information can also be used.

Upon completion of the DLS procedure between the QSTA1 and the QSTA2 as described above, the QSTA1 and the QSTA2 perform a beam training sequence process (step S25). According to the embodiment of the present invention, location information of the QSTA2 is known to the QSTA1 and location information of the QSTA1 is known to the QSTA2, and thus it is not necessary to perform the beam training sequence process for all locations. Instead, according to the embodiment of the present invention, it is enough for each of the QSTA1 and the QSTA2 to perform the beam training sequence process only for a possible areas of its peer QSTA, and thus overhead produced in the beam forming process can be significantly reduced.

Upon completion of the beam forming process required in transmission through a direct link, the QSTA1 and the QSTA2 transmit a data frame or the like to the peer QSTA through the established direct link (step S26). In this case, the QSTA1 and the QSTA2 can transmit the data frame or the like to the peer QSTA by using respective directional antennas, and thus service coverage can be expanded even if a band of 60 GHz is used.

However, in a case where one of two QSTAs moves to another location after a direct link is established between the two QSTAs, the previously configured beam forming needs to be modified. That is, when a terminal moves to another location, beam forming between the two QSTAs establishing the direct link needs to be modified according to the movement, which will be described below.

FIG. 6 is a message flow diagram showing an exemplary process of modifying beam forming when the QSTA1 moves to another location after a direct link is established between the QSTA1 and the QSTA2.

Referring to FIG. 6, the QSTA1 moving to another location communicates with the QAP to re-perform beam forming between the QAP and the QSTA1 (step S31). The beam forming process performed between the QSTA1 and the QAP may follow the conventional method without any change, and there is no particular restriction thereon in the embodiment of the present invention.

The QSTA1 transmits a request message to request information required to reconfigure beam forming with a peer QSTA, i.e., a DLS DoA request frame, to the QAP (step S32). The DLS DoA request frame may include information capable of identifying a direct link requiring reconfiguration of beam forming, for example, may include source MAC address information and destination MAC information. FIG. 7 shows an example of information included in the DLS DoA request frame, and the information may include category information, action information, destination MAC address information, and source MAC address information.

Upon receiving the request message (e.g., DLS DoA request frame) from the QSTA1, the QAP transmits a response message (e.g., DLS DoA response message) in response to the request of the QSTA1 to the QSTA1 (step S33). The DLS DoA response frame may include not only information capable of identifying a direct link requiring reconfiguration of beam forming but also information required for reconfiguration of beam forming. For example, in addition to source MAC address information and destination MAC address information, the DLS DoA response frame may also include DoA information, DoA accuracy estimate information, source RCPI information, and destination RCPI information. FIG. 8 shows an example of information included in the DLS DoA response frame, and the information may include category information, action information, destination MAC address information, source MAC address information, DoA information, DoA accuracy estimate information, destination RCPI information, and source RCPI information.

According to one aspect of the present embodiment, in a case where the QSTA1 moves to another location after a direct link is established and the beam forming with the QAP is modified, the QAP can provide information on the modified location to terminals associated with the direct link, for example, to the QSTA2. The modified location information may be obtained, for example, by transmitting an unsolicited DLS DoA response frame by the QAP to its associated QSTAs (i.e., QSTA1 and QSTA2). The unsolicited DLS DoA response frame is a frame transmitted by the QAP itself to provide modified location information even if there is no explicit request of corresponding QSTAs. Herein, the terminology is for exemplary purpose only.

FIG. 9 is a block diagram showing an AP and an STA according to an embodiment of the present invention. An AP 900 includes a processor 910, a memory 920, and a transceiver 930. An STA 950 includes a processor 960, a memory 970, and a transceiver 980. The

transceiver

930 and 980 transmit/receive a radio signal, and implement an IEEE 802 physical layer. The

transceiver

930 and 980 may support an omni-directional mode and a directional mode. The processor 910 is coupled to the transceiver 930, and the processor 960 is also coupled to the transceiver 980. The processor 910 and 960 implement an IEEE 802 MAC layer. The processor 910 and 960 can implement the aforementioned method for establishing direct link in WLAN system, etc.

The processor 910,960 and/or the transceiver 930,980 may include an application-specific integrated circuit (ASIC), a separate chipset, a logic circuit, and/or a data processing unit. The

memory

920 and 970 may include a read-only memory (ROM), a random access memory (RAM), a flash memory, a memory card, a storage medium, and/or other equivalent storage devices. When the embodiment of the present invention is implemented in software, the aforementioned methods can be implemented with a module (i.e., process, function, etc.) for performing the aforementioned functions. The module may be stored in the memory 920 and may be performed by the processor 910, and the module may be stored in the memory 970 and may be performed by the processor 960. The memory 920 may be located inside or outside the processor 910, and may be coupled to the processor 910 by using various well-known means. The memory 970 may also be located inside or outside the processor 960, and may be coupled to the processor 960 by using various well-known means.

Claims

A method for establishing a direct link in a wireless local area network (WLAN) system,

wherein the VHT WLAN system operates in an infrastructure mode and comprises an initiating station (STA) and a recipient STA, each of which intends to establish the direct link, and a access point (AP) relaying communication between the initiating STA and the receiver STA, and

wherein the AP provides location information of the initiating STA and the recipient STA respectively to the recipient STA and the initiating STA in the process of establishing the direct link.
The method of claim 1, wherein the location information comprises information on a degree of angle (DoA) of each of the initiating STA and the recipient STA with respect to the AP.
The method of claim 2, wherein, when the location information is provided, the AP provides signal strength information on the initiating STA and the recipient STA.
The method of claim 1, wherein the initiating STA and the recipient STA perform a beam forming process for transmission of a data frame through the direct link established using the location information.
A method of establishing a direct link in a WLAN system by using directional transmission, the method comprising:

transmitting by an initiating STA a direct link setup request message to a AP;

transmitting by the AP the direct link setup request message comprising location information of the initiating QSTA to a recipient STA;

transmitting by the recipient STA a direct link setup response message to the AP; and

transmitting by the AP the direct link setup response message comprising location information of the recipient QSTA to the initiating STA.
The method of claim 5, wherein the AP obtains the location information by performing a beam forming process on each of the initiating QSTA and the recipient STA.
The method of claim 5, wherein the direct link setup request message and the direct link setup response message, each of which is transmitted by the AP to the recipient STA or the initiating STA, further comprise signal strength information of the initiating STA and signal strength information of the recipient STA.
The method of claim 7, wherein the initiating STA and the recipient STA perform a beam forming process for transmission of a data frame through the direct link established using the location information and the signal strength information.