WO2019027159A1 - Method for transmitting or receiving frame in wireless lan system and apparatus therefor - Google Patents

Abstract

A method for receiving, by an STA, a WUR PPDU in a WLAN, according to one embodiment of the present invention, comprises the steps of: receiving a WUR PPDU including a WUR preamble and a payload; determining whether the WUR PPDU has been received from a basic service set (BSS) to which the STA belongs or from an overlapping BSS (OBSS), on the basis of the WUR preamble; and decoding the payload of the WUR PPDU if the WUR PPDU has been received from the BSS to which the STA belongs, wherein the STA can determine whether the WUR PPDU has been received from the BSS to which the STA belongs, through a cross correlation between a synchronization sequence included in the WUR preamble and a predetermined sequence known to the STA.

Description

Method and apparatus for transmitting or receiving frames in a wireless LAN system

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wireless LAN system, and more particularly, to a method and apparatus for transmitting or receiving a PPDU through a WAK (wake-up radio).

The standard for wireless LAN technology is being developed as the Institute of Electrical and Electronics Engineers (IEEE) 802.11 standard. IEEE 802.11a and b 2.4. GHz or 5 GHz, the IEEE 802.11b provides a transmission rate of 11 Mbps, and the IEEE 802.11a provides a transmission rate of 54 Mbps. IEEE 802.11g employs Orthogonal Frequency-Division Multiplexing (OFDM) at 2.4 GHz to provide a transmission rate of 54 Mbps. IEEE 802.11n employs multiple input multiple output (OFDM), or OFDM (MIMO-OFDM), and provides transmission speeds of 300 Mbps for four spatial streams. IEEE 802.11n supports channel bandwidth up to 40 MHz, which in this case provides a transmission rate of 600 Mbps.

The IEEE 802.11ax standard, which supports a maximum of 160 MHz bandwidth and supports 8 spatial streams and supports a maximum speed of 1 Gbit / s, has been discussed in the IEEE 802.11ax standard.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method and apparatus for more efficiently and accurately transmitting or receiving a WUR PPDU in an environment where several BSSs coexist.

The present invention is not limited to the above-described technical problems, and other technical problems can be deduced from the embodiments of the present invention.

According to an aspect of the present invention, there is provided a method for receiving a wake-up radio (PPDU) from a station in a wireless local area network (WLAN) Receiving a WUR PPDU comprising a load; Determining whether the WUR PPDU is received from a basic service set (BSS) to which the STA belongs or an overlapping BSS (OBSS) based on the WUR preamble; And decoding the payload of the WUR PPDU if the WUR PPDU is received from a BSS to which the STA belongs, wherein the STA performs a cross correlation between a synchronization sequence included in the WUR preamble and a predetermined sequence known to the STA To determine whether the WUR PPDU is received from the BSS to which the STA belongs.

According to another aspect of the present invention, there is provided a station (STA) for receiving a wake-up radio (PPDU) physical layer protocol data unit, the WUR receiver comprising: And a WUR PPDU including a WUR preamble and a payload via the WUR receiver, and based on the WUR preamble, whether the WUR PPDU is received from a basic service set (BSS) to which the STA belongs or an overlapping BSS (OBSS) And a processor for decoding the payload of the WUR PPDU if the WUR PPDU is received from the BSS to which the STA belongs, wherein the processor is further configured to determine whether the WUR PPDU is received from the synchronization sequence included in the WUR preamble and the STA To determine whether the WUR PPDU is received from the BSS to which the STA belongs, via cross correlation between a predetermined sequence known to the STA.

The STA may determine that the WUR PPDU is received from the BSS to which the STA belongs if the result of the cross-correlation for the synchronization sequence exceeds a threshold.

The STA may obtain bit information of the synchronization sequence through envelope detection of the synchronization sequence. The STA may obtain the cross-correlation based on a bitwise XOR (exclusive OR) operation between the bit information of the synchronization sequence and a predetermined sequence known to the STA.

Wherein the cross correlation is obtained based on an equation 裡 XOR (X _i , Y _i ), where X _i represents the i th bit of the synchronization sequence and Y _i represents the i th bit of the predetermined sequence Lt; / RTI >

Other synchronization sequences are allocated to the BSS and the OBSS, and the synchronization sequence allocated to the BSS and the synchronization sequence allocated to the OBSS may be determined based on the BSS ID or the BSS Color.

The Hamming distance between the synchronization sequence allocated to the BSS and the synchronization sequence allocated to the OBSS may be 3, 5, 7, or 9.

The STA may perform synchronization with respect to the WUR PPDU through autocorrelation of a synchronization sequence included in the WUR preamble.

According to an embodiment of the present invention, since the BSS information is indicated through the WUR preamble, the STA unnecessarily decodes the OBSS WUR PPDU to consume power or wakes up by mistaking the OBSS WUR PPDU as a WUR PPDU transmitted from its BSS Can be solved.

Other technical advantages than the above-described technical effects can be deduced from the embodiments of the present invention.

1 is a diagram showing an example of a configuration of a wireless LAN system.

2 is a diagram showing another example of the configuration of the wireless LAN system.

3 is a diagram for explaining a general link setup process.

4 is a diagram for explaining a backoff process.

5 is a diagram for explaining hidden nodes and exposed nodes.

6 is a diagram for explaining RTS and CTS.

7 to 9 are diagrams for explaining the operation of the STA that has received the TIM.

10 is a diagram for explaining an example of a frame structure used in the IEEE 802.11 system.

11 is a diagram for explaining a WUR receiver usable in a wireless LAN system (e.g., 802.11).

12 is a diagram for explaining the operation of the WUR receiver.

13 shows an example of a WUR packet.

14 illustrates a waveform for a WUR packet.

15 is a diagram for explaining a WUR packet generated using an OFDM transmitter of a wireless LAN.

Figure 16 illustrates the structure of a WUR receiver.

17 shows a WUR PPDU format according to an embodiment of the present invention.

18 shows a flow of a method of receiving a WUR PPDU according to an embodiment of the present invention.

19 is a view for explaining an apparatus according to an embodiment of the present invention.

Hereinafter, preferred embodiments according to the present invention will be described in detail with reference to the accompanying drawings. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following detailed description, together with the accompanying drawings, is intended to illustrate exemplary embodiments of the invention and is not intended to represent the only embodiments in which the invention may be practiced.

The following detailed description includes specific details in order to provide a thorough understanding of the present invention. However, those skilled in the art will appreciate that the present invention may be practiced without these specific details. In some instances, well-known structures and devices are omitted or shown in block diagram form around the core functions of each structure and device in order to avoid obscuring the concepts of the present invention.

As described above, the following description relates to a method and apparatus for efficiently utilizing a channel having a wide bandwidth in a wireless LAN system. To this end, a wireless LAN system to which the present invention is applied will be described in detail.

1 is a diagram showing an example of a configuration of a wireless LAN system.

As shown in FIG. 1, a WLAN system includes one or more Basic Service Sets (BSSs). A BSS is a collection of stations (STAs) that can successfully communicate and synchronize with each other.

The STA is a logical entity including a medium access control (MAC) and a physical layer interface for a wireless medium. The STA includes an access point (AP) and a non-AP STA (Non-AP Station) . A portable terminal operated by a user in the STA is a non-AP STA, and sometimes referred to as a non-AP STA. The non-AP STA may be a terminal, a wireless transmit / receive unit (WTRU), a user equipment (UE), a mobile station (MS), a mobile terminal, May also be referred to as another name such as a Mobile Subscriber Unit.

An AP is an entity that provides a connection to a distribution system (DS) via a wireless medium to an associated station (STA). The AP may be referred to as a centralized controller, a base station (BS), a Node-B, a base transceiver system (BTS), a site controller, or the like.

The BSS can be divided into an infrastructure BSS and an independent BSS (IBSS).

The BBS shown in FIG. 1 is an IBSS. The IBSS means a BSS that does not include an AP, and does not include an AP, so a connection to the DS is not allowed and forms a self-contained network.

2 is a diagram showing another example of the configuration of the wireless LAN system.

The BSS shown in FIG. 2 is an infrastructure BSS. The infrastructure BSS includes one or more STAs and APs. In the infrastructure BSS, communication between non-AP STAs is performed via an AP, but direct communication between non-AP STAs is possible when a direct link is established between non-AP STAs.

As shown in FIG. 2, a plurality of infrastructure BSSs may be interconnected via DS. A plurality of BSSs connected through a DS are referred to as an extended service set (ESS). The STAs included in the ESS can communicate with each other, and within the same ESS, the non-AP STA can move from one BSS to another while seamlessly communicating.

The DS is a mechanism for connecting a plurality of APs. It is not necessarily a network, and there is no limitation on the form of DS if it can provide a predetermined distribution service. For example, the DS may be a wireless network such as a mesh network, or may be a physical structure that links APs together.

Hierarchy

The operation of the STA operating in the wireless LAN system can be described in terms of the layer structure. In terms of device configuration, the hierarchy can be implemented by a processor. The STA may have a plurality of hierarchical structures. For example, the hierarchical structure covered in the 802.11 standard document is mainly a MAC sublayer and a physical (PHY) layer on a DLL (Data Link Layer). The PHY may include a Physical Layer Convergence Procedure (PLCP) entity, a PMD (Physical Medium Dependent) entity, and the like. The MAC sublayer and the PHY conceptually include management entities called a MAC sublayer management entity (MLME) and a physical layer management entity (PLME), respectively. These entities provide a layer management service interface in which a layer management function operates .

In order to provide correct MAC operation, a Station Management Entity (SME) exists in each STA. An SME is a layer-independent entity that may be present in a separate management plane or may appear to be off-the-side. Although the exact functions of the SME are not described in detail in this document, they generally include the ability to collect layer-dependent states from various Layer Management Entities (LMEs) and to set similar values for layer-specific parameters It can be seen as responsible. An SME typically performs these functions on behalf of a generic system management entity and can implement a standard management protocol.

The aforementioned entities interact in various ways. For example, they can interact by exchanging GET / SET primitives between entities. A primitive is a set of elements or parameters related to a specific purpose. The XX-GET.request primitive is used to request the value of a given MIB attribute. The XX-GET.confirm primitive returns the appropriate MIB attribute information value if the Status is "Success", otherwise it is used to return an error indication in the Status field. The XX-SET.request primitive is used to request that the indicated MIB attribute be set to the given value. If the MIB attribute indicates a specific operation, it is requested that the corresponding operation be performed. The XX-SET.confirm primitive confirms that the indicated MIB attribute is set to the requested value if the status is "success", otherwise it is used to return an error condition to the status field. If the MIB attribute indicates a specific operation, this confirms that the corresponding operation has been performed.

In addition, MLME and SME can exchange various MLME_GET / SET primitives through MLME_SAP (Service Access Point). In addition, various PLME_GET / SET primitives can be exchanged between PLME and SME via PLME_SAP and exchanged between MLME and PLME through MLME-PLME_SAP.

Link Setup Process

3 is a diagram for explaining a general link setup process.

In order for a STA to set up a link to a network and transmit and receive data, the STA first discovers a network, performs authentication, establishes an association, establishes an authentication procedure for security, . The link setup process may be referred to as a session initiation process or a session setup process. Also, the process of discovery, authentication, association, and security setting of the link setup process may be collectively referred to as an association process.

An exemplary link setup procedure will be described with reference to FIG.

In step S510, the STA can perform a network discovery operation. The network discovery operation may include a scanning operation of the STA. In other words, in order for the STA to access the network, it must find a network that can participate. The STA must identify a compatible network before joining the wireless network. The process of identifying a network in a specific area is called scanning.

The scanning methods include active scanning and passive scanning.

FIG. 3 illustrates a network discovery operation that includes an exemplary active scanning process. The STA performing the scanning in the active scanning transmits the probe request frame and waits for a response in order to search for the existence of an AP in the surroundings while moving the channels. The responder sends a probe response frame in response to the probe request frame to the STA that transmitted the probe request frame. Here, the responder may be the STA that last transmitted the beacon frame in the BSS of the channel being scanned. In the BSS, the AP transmits the beacon frame, so the AP becomes the responder. In the IBSS, the STAs in the IBSS transmit the beacon frame while the beacon frame is transmitted. For example, the STA that transmits the probe request frame in channel 1 and receives the probe response frame in channel 1 stores the BSS-related information included in the received probe response frame and transmits the next channel (for example, Channel) and perform scanning in the same manner (i.e., transmitting / receiving a probe request / response on the second channel).

Although not shown in Fig. 3, the scanning operation may be performed in a passive scanning manner. In passive scanning, the STA performing the scanning waits for the beacon frame while moving the channels. A beacon frame is one of the management frames in IEEE 802.11, and is transmitted periodically to notify the presence of a wireless network and allow the STA performing the scanning to find the wireless network and participate in the wireless network. In the BSS, the AP periodically transmits the beacon frame. In the IBSS, the beacon frames are transmitted while the STAs in the IBSS are running. Upon receiving the beacon frame, the scanning STA stores information on the BSS included in the beacon frame and records beacon frame information on each channel while moving to another channel. The STA receiving the beacon frame stores the BSS-related information included in the received beacon frame, moves to the next channel, and performs scanning in the next channel in the same manner.

Comparing active scanning with passive scanning, active scanning has the advantage of less delay and less power consumption than passive scanning.

After the STA finds the network, the authentication procedure may be performed in step S520. This authentication process can be referred to as a first authentication process in order to clearly distinguish from the security setup operation in step S540 described later.

The authentication process includes an STA transmitting an authentication request frame to the AP, and an AP transmitting an authentication response frame to the STA in response to the authentication request frame. The authentication frame used for the authentication request / response corresponds to the management frame.

The authentication frame includes an authentication algorithm number, an authentication transaction sequence number, a status code, a challenge text, a robust security network (RSN), a finite cyclic group Group), and the like. This corresponds to some examples of information that may be included in the authentication request / response frame, may be replaced by other information, or may include additional information.

The STA may send an authentication request frame to the AP. Based on the information included in the received authentication request frame, the AP can determine whether or not to allow authentication for the STA. The AP can provide the result of the authentication process to the STA through the authentication response frame.

After the STA has been successfully authenticated, the association process may be performed in step S530. The association process includes an STA transmitting an association request frame to an AP, and an AP transmitting an association response frame to the STA in response to the association request frame.

For example, the association request frame may include information related to various capabilities, a listening interval, a service set identifier (SSID), supported rates, supported channels, an RSN, , Supported operating classes, TIM broadcast request, interworking service capability, and the like.

For example, the association response frame may include information related to various capabilities, a status code, an association ID (AID), a support rate, an enhanced distributed channel access (EDCA) parameter set, a Received Channel Power Indicator (RCPI) A timeout interval (an association comeback time), a overlapping BSS scan parameter, a TIM broadcast response, a QoS map, and the like.

This corresponds to some examples of information that may be included in the association request / response frame, may be replaced by other information, or may include additional information.

After the STA is successfully associated with the network, a security setup procedure may be performed at step S540. The security setup process in step S540 may be referred to as an authentication process through a Robust Security Network Association (RSNA) request / response. The authentication process in step S520 may be referred to as a first authentication process, May also be referred to simply as an authentication process.

The security setup process of step S540 may include a private key setup through 4-way handshaking over an Extensible Authentication Protocol over LAN (EAPOL) frame, for example . In addition, the security setup process may be performed according to a security scheme not defined in the IEEE 802.11 standard.

Medium access mechanism

In a wireless LAN system compliant with IEEE 802.11, the basic access mechanism of Medium Access Control (MAC) is a CSMA / CA (Carrier Sense Multiple Access with Collision Avoidance) mechanism. The CSMA / CA mechanism is also referred to as the Distributed Coordination Function (DCF) of the IEEE 802.11 MAC, which basically adopts a "listen before talk" access mechanism. According to this type of access mechanism, the AP and / or the STA may sense a radio channel or medium for a predetermined time interval (e.g., DCF Inter-Frame Space (DIFS) If the medium is judged to be in an idle status, the frame transmission is started through the corresponding medium, whereas if the medium is occupied status, The AP and / or the STA does not start its own transmission but sets a delay period (for example, a random backoff period) for the medium access and waits for a frame transmission after waiting With the application of an arbitrary backoff period, several STAs are expected to attempt frame transmission after waiting for different time periods, so that collisions can be minimized.

In addition, the IEEE 802.11 MAC protocol provides HCF (Hybrid Coordination Function). The HCF is based on the DCF and the PCF (Point Coordination Function). The PCF is a polling-based, synchronous access scheme that refers to periodically polling all receiving APs and / or STAs to receive data frames. In addition, HCF has EDCA (Enhanced Distributed Channel Access) and HCCA (HCF Controlled Channel Access). EDCA is a contention-based access method for a provider to provide data frames to a large number of users, and HCCA uses a contention-based channel access method using a polling mechanism. In addition, the HCF includes a medium access mechanism for improving QoS (Quality of Service) of the WLAN, and can transmit QoS data in both a contention period (CP) and a contention free period (CFP).

4 is a diagram for explaining a backoff process.

An operation based on an arbitrary backoff period will be described with reference to FIG. When a medium that is in an occupy or busy state is changed to an idle state, several STAs may attempt to transmit data (or frames). At this time, as a method for minimizing the collision, each of the STAs may attempt to transmit after selecting an arbitrary backoff count and waiting for a corresponding slot time. An arbitrary backoff count has a packet number value and can be determined to be one of values in the range of 0 to CW. Here, CW is a contention window parameter value. The CW parameter is given an initial value of CWmin, but it can take a value twice in the case of a transmission failure (for example, in the case of not receiving an ACK for a transmitted frame). If the CW parameter value is CWmax, the data transmission can be attempted while maintaining the CWmax value until the data transmission is successful. If the data transmission is successful, the CWmin value is reset to the CWmin value. The values of CW, CWmin and CWmax are preferably set to 2 ⁿ -1 (n = 0, 1, 2, ...).

When an arbitrary backoff process is started, the STA continuously monitors the medium while counting down the backoff slot according to the determined backoff count value. When the medium is monitored in the occupied state, the countdown is stopped and waited, and when the medium is idle, the remaining countdown is resumed.

In the example of FIG. 4, when a packet to be transmitted to the MAC of the STA3 arrives, the STA3 can confirm that the medium is idle by DIFS and transmit the frame immediately. Meanwhile, the remaining STAs monitor and wait for the medium to be in a busy state. In the meanwhile, data to be transmitted may also occur in each of STA1, STA2 and STA5, and each STA waits for DIFS when the medium is monitored in an idle state and then counts down the backoff slot according to the arbitrary backoff count value selected by each STA. Can be performed. In the example of FIG. 4, STA2 selects the smallest backoff count value, and STA1 selects the largest backoff count value. That is, the case where the remaining backoff time of the STA5 is shorter than the remaining backoff time of the STA1 at the time when the STA2 finishes the backoff count and starts the frame transmission is illustrated. STA1 and STA5 stop countdown and wait for a while while STA2 occupies the medium. When the occupation of STA2 is ended and the medium becomes idle again, STA1 and STA5 wait for DIFS and then resume the stopped backoff count. That is, the frame transmission can be started after counting down the remaining backoff slots by the remaining backoff time. Since the remaining backoff time of STA5 is shorter than STA1, STA5 starts frame transmission. On the other hand, data to be transmitted may also occur in the STA 4 while the STA 2 occupies the medium. At this time, in STA4, if the medium becomes idle, it can wait for DIFS, count down according to an arbitrary backoff count value selected by the STA4, and start frame transmission. In the example of FIG. 6, the remaining backoff time of STA5 coincides with the arbitrary backoff count value of STA4, in which case a collision may occur between STA4 and STA5. If a collision occurs, neither STA4 nor STA5 receive an ACK, and data transmission fails. In this case, STA4 and STA5 can double the CW value, then select an arbitrary backoff count value and perform a countdown. On the other hand, the STA1 waits while the medium is occupied due to the transmission of the STA4 and the STA5, waits for the DIFS when the medium becomes idle, and starts frame transmission after the remaining backoff time.

STA sensing behavior

As described above, the CSMA / CA mechanism includes virtual carrier sensing in addition to physical carrier sensing in which the AP and / or STA directly senses the medium. Virtual carrier sensing is intended to compensate for problems that may occur in media access, such as hidden node problems. For the virtual carrier sensing, the MAC of the wireless LAN system may use a network allocation vector (NAV). NAV is a value indicating to another AP and / or STA the time remaining until the media and / or the STA that is currently using or authorized to use the media are available. Therefore, the value set to NAV corresponds to the period in which the medium is scheduled to be used by the AP and / or the STA that transmits the frame, and the STA receiving the NAV value is prohibited from accessing the medium during the corresponding period. The NAV may be set according to the value of the " duration " field of the MAC header of the frame, for example.

In addition, a robust collision detection mechanism has been introduced to reduce the probability of collision. This will be described with reference to Figs. 5 and 7. Fig. The actual carrier sensing range and the transmission range may not be the same, but are assumed to be the same for convenience of explanation.

5 is a diagram for explaining hidden nodes and exposed nodes.

FIG. 5A is an example of a hidden node, and STA A and STA B are in communication and STA C has information to be transmitted. Specifically, STA A is transmitting information to STA B, but it can be determined that STA C is idle when performing carrier sensing before sending data to STA B. This is because the STA A transmission (ie, media occupancy) may not be sensed at the STA C location. In this case, STA B receives information of STA A and STA C at the same time, so that collision occurs. In this case, STA A is a hidden node of STA C.

FIG. 5B is an example of an exposed node, and STA B is a case of transmitting data to STA A, and STA C has information to be transmitted in STA D. FIG. In this case, if the STA C carries out the carrier sensing, it can be determined that the medium is occupied due to the transmission of the STA B. Accordingly, even if STA C has information to be transmitted to STA D, it is sensed that the media is occupied, and therefore, it is necessary to wait until the medium becomes idle. However, since the STA A is actually out of the transmission range of the STA C, the transmission from the STA C and the transmission from the STA B may not collide with each other in the STA A. Therefore, the STA C is not necessary until the STA B stops transmitting It is to wait. In this case, STA C can be regarded as an exposed node of STA B.

6 is a diagram for explaining RTS and CTS.

5, short signaling packets such as RTS (request to send) and CTS (clear to send) can be used in order to efficiently use the collision avoidance mechanism. The RTS / CTS between the two STAs may allow the surrounding STA (s) to overhear, allowing the surrounding STA (s) to consider whether to transmit information between the two STAs. For example, if the STA to which data is to be transmitted transmits an RTS frame to the STA receiving the data, the STA receiving the data can notify that it will receive the data by transmitting the CTS frame to surrounding STAs.

FIG. 6A is an example of a method for solving a hidden node problem, and it is assumed that both STA A and STA C attempt to transmit data to STA B. FIG. When STA A sends RTS to STA B, STA B transmits CTS to both STA A and STA C around it. As a result, STA C waits until the data transmission of STA A and STA B is completed, thereby avoiding collision.

6 (b) is an illustration of a method for solving the exposed node problem, where STA C overrides the RTS / CTS transmission between STA A and STA B, D, the collision does not occur. That is, STA B transmits RTS to all surrounding STAs, and only STA A having data to be transmitted transmits CTS. Since STA C only receives RTS and does not receive CTS of STA A, it can be seen that STA A is outside the carrier sensing of STC C.

Power Management

As described above, in the wireless LAN system, the STA must perform channel sensing before performing transmission / reception, and always sensing the channel causes continuous power consumption of the STA. The power consumption in the reception state does not differ much from the power consumption in the transmission state, and maintaining the reception state is also a large burden on the STA which is limited in power (that is, operated by the battery). Thus, if the STA keeps listening for sustained channel sensing, it will inefficiently consume power without special benefits in terms of WLAN throughput. To solve this problem, the wireless LAN system supports the power management (PM) mode of the STA.

The STA's power management mode is divided into an active mode and a power save (PS) mode. STA basically operates in active mode. An STA operating in active mode maintains an awake state. The awake state is a state in which normal operation such as frame transmission / reception and channel scanning is possible. Meanwhile, the STA operating in the PS mode operates by switching between a sleep state (or a doze state) and an awake state. The STA operating in the sleep state operates with minimal power and does not perform frame scanning nor transmission and reception of frames.

As the STA sleeps for as long as possible, power consumption is reduced, which increases the operating time of the STA. However, since it is impossible to transmit / receive frames in the sleep state, it can not be operated unconditionally for a long time. If the STA operating in the sleep state exists in the frame to be transmitted to the AP, it can switch to the awake state and transmit the frame. On the other hand, when there is a frame to be transmitted to the STA by the AP, the STA in the sleep state can not receive it, and it is unknown that there is a frame to receive. Therefore, the STA may need to switch to the awake state according to a certain period to know whether there is a frame to be transmitted to it (and to receive it if it exists).

The AP may transmit a beacon frame to the STAs in the BSS at regular intervals. The beacon frame may include a Traffic Indication Map (TIM) information element. The TIM information element may include information that indicates that the AP has buffered traffic for the STAs associated with it and will transmit the frame. The TIM element includes a TIM used for indicating a unicast frame and a delivery traffic indication map (DTIM) used for indicating a multicast or broadcast frame.

7 to 9 are views for explaining the operation of the STA receiving the TIM in detail.

Referring to FIG. 7, in order to receive a beacon frame including a TIM from an AP, the STA changes from a sleep state to an awake state, and analyzes the received TIM element to find that there is buffered traffic to be transmitted to the STA . After the STA performs contending with other STAs for medium access for PS-Poll frame transmission, it may transmit a PS-Poll frame to request AP to transmit data frame. The AP receiving the PS-Poll frame transmitted by the STA can transmit the frame to the STA. The STA may receive a data frame and send an acknowledgment (ACK) frame to the AP. The STA can then be switched to the sleep state again.

As shown in FIG. 7, the AP operates according to an immediate response scheme for transmitting a data frame after a predetermined time (for example, SIFS (Short Inter-Frame Space)) after receiving the PS-Poll frame from the STA . On the other hand, if the AP does not prepare the data frame to be transmitted to the STA after receiving the PS-Poll frame for the SIFS time, the AP can operate according to a deferred response method, which will be described with reference to FIG.

In the example of FIG. 8, the operation of switching the STA from the sleep state to the awake state, receiving the TIM from the AP, competing, and transmitting the PS-Poll frame to the AP is the same as the example of FIG. If the AP receives the PS-Poll frame and fails to prepare the data frame for SIFS, it can send an ACK frame to the STA instead of transmitting the data frame. After the AP transmits the ACK frame and the data frame is ready, it can transmit the data frame to the STA after performing the contention. The STA transmits an ACK frame indicating that the data frame has been successfully received to the AP, and can be switched to the sleep state.

Figure 9 is an example of an AP transmitting a DTIM. STAs may transition from the sleep state to the awake state to receive a beacon frame containing the DTIM element from the AP. STAs can know that a multicast / broadcast frame will be transmitted through the received DTIM. The AP can transmit data (i.e., multicast / broadcast frame) directly without transmitting / receiving a PS-Poll frame after transmitting a beacon frame including DTIM. The STAs may receive data while continuing to hold the awake state after receiving the beacon frame including the DTIM, and may switch to the sleep state again after the data reception is completed.

Frame structure general

10 is a diagram for explaining an example of a frame structure used in the IEEE 802.11 system.

The Physical Layer Protocol Data Unit (PPDU) frame format may include a Short Training Field (STF) field, a Long Training Field (LTF) field, a SIGN (SIGNAL) field, and a Data field. The most basic (e.g., non-HT (High Throughput)) PPDU frame format may consist of L-STF (Legacy-STF), L-LTF (Legacy-LTF), SIG field and data field only.

STF is a signal for signal detection, AGC (Automatic Gain Control), diversity selection, precise time synchronization, etc., and LTF is a signal for channel estimation and frequency error estimation. STF and LTF may be collectively referred to as a PLCP preamble, and the PLCP preamble may be a signal for synchronization and channel estimation of the OFDM physical layer.

The SIG field may include a RATE field and a LENGTH field. The RATE field may contain information on the modulation and coding rate of the data. The LENGTH field may contain information on the length of the data. Additionally, the SIG field may include a parity bit, a SIG TAIL bit, and the like.

The data field may include a SERVICE field, a physical layer service data unit (PSDU), a PPDU TAIL bit, and may also include a padding bit if necessary. Some bits in the SERVICE field may be used for synchronization of the descrambler at the receiving end. The PSDU corresponds to an MPDU (MAC Protocol Data Unit) defined in the MAC layer and may include data generated / used in an upper layer. The PPDU TAIL bit can be used to return the encoder to the 0 state. The padding bits may be used to match the length of the data field to a predetermined unit.

The MPDU is defined according to various MAC frame formats, and the basic MAC frame is composed of a MAC header, a frame body, and a frame check sequence (FCS). The MAC frame is composed of MPDUs and can be transmitted / received via the PSDU of the data part of the PPDU frame format.

The MAC header includes a Frame Control field, a Duration / ID field, an Address field, and the like. The frame control field may contain control information necessary for frame transmission / reception. The period / ID field may be set to a time for transmitting the frame or the like.

The period / ID field included in the MAC header can be set to a 16-bit length (e.b., B0 to B15). The content included in the period / ID field may vary depending on the frame type and subtype, whether it is transmitted during the contention free period (CFP), the QoS capability of the transmitting STA, and the like. (i) In a control frame whose subtype is PS-Poll, the period / ID field may contain the AID of the transmitting STA (e.g., via 14 LSB bits) and 2 MSB bits may be set to one. (ii) In frames transmitted during the CFP by a point coordinator (PC) or a non-QoS STA, the duration / ID field may be set to a fixed value (e.g., 32768). (iii) In other frames transmitted by other non-QoS STAs or control frames transmitted by the QoS STA, the duration / ID field may include a duration value defined for each frame type. In a data frame or a management frame transmitted by the QoS STA, the duration / ID field may include a duration value defined for each frame type. For example, if B15 = 0 in the duration / ID field indicates that the duration / ID field is used to indicate TXOP Duration, B0-B14 can be used to indicate the actual TXOP duration. The actual TXOP Duration indicated by B0 to B14 may be any of 0 to 32767, and the unit may be microseconds (us). However, when the period / ID field indicates a fixed TXOP Duration value (e.g., 32768), B15 = 1 and B0 to B14 = 0. In addition, if B14 = 1 and B15 = 1 are set, the period / ID field is used to indicate AID, and B0 to B13 indicate one of AIDs from 1 to 2007. The specific contents of the Sequence Control, QoS Control, and HT Control subfields of the MAC header can refer to the IEEE 802.11 standard document.

 The frame control field of the MAC header may include Protocol Version, Type, Subtype, To DS, From DS, More Fragment, Retry, Power Management, More Data, Protected Frame, Order subfields. The contents of each subfield of the frame control field may reference an IEEE 802.11 standard document.

Wake-Up Radio (WUR)

Referring to FIG. 11, a general description of a wake-up radio receiver (WURx) compatible with a wireless LAN system (e.g., 802.11) will be described.

11, the STA includes a primary connectivity radio (PCR) (eg, IEEE 802.11a / b / g / n / ac / ax wireless LAN) and a wake- WUR) (eg, IEEE 802.11ba).

The PCR is used for data transmission and reception, and can be turned off when there is no data to be transmitted or received. When the PCR is turned off as described above, the WURx of the STA can wake up the PCR when there is a packet to be received. Therefore, user data is transmitted and received through PCR.

WURx is not used for user data, but can only wake up the PCR transceiver. WURx can be in the form of a simple receiver without a transmitter and is active while PCR is off. The target power consumption of WURx in the active state preferably does not exceed 100 microW (uW). In order to operate at such a low power, a simple modulation scheme such as an on-off keying (OOK) scheme can be used, and a narrow bandwidth (e.g., 4 MHz, 5 MHz) can be used. The coverage range (e.g., distance) to which WURx is targeted may currently be equivalent to 802.11.

12 is a diagram for explaining the design and operation of the WUR packet.

Referring to FIG. 12, a WUR packet may include a PCR part 1200 and a WUR part 1205.

The PCR part 1200 is for coexistence with a legacy WLAN system, and the PCR part may be referred to as a wireless LAN preamble. At least one or more of the L-STF, L-LTF, and L-SIG of the legacy wireless LAN may be included in the PCR part 1200 to protect WUR packets from other PCR STAs. Accordingly, the 3rd party legacy STA can know that the WUR packet is not intended for itself through the PCR part 1200 of the WUR packet, but the medium of the PCR is occupied by another STA. However, WURx does not decode the PCR part of the WUR packet. This is because WURx that supports narrowband and OOK demodulation does not support the reception of PCR signals.

At least a portion of the WUR part 1205 may be modulated in an on-off keying (OOK) manner. In one example, the WUR part may include at least one of a WUR preamble, a MAC header (e.g., a recipient address, etc.), a frame body, and a frame check sequence (FCS). On the other hand, OOK modulation may be performed by modifying the OFDM transmitter.

WURx 1210 consumes very little power, less than 100 uW, as described above, and can be implemented with a small and simple OOK demodulator.

Since the WUR packet needs to be designed to be compatible with the WLAN system, the WUR packet includes a preamble (eg, OFDM scheme) of a legacy wireless LAN and a new LP-WUR signal waveform (eg, OOK scheme) can do.

13 shows an example of a WUR packet. The WUR packet of FIG. 13 includes a PCR part (e.g., a legacy wireless LAN preamble) for coexistence with a legacy STA.

Referring to FIG. 13, the legacy wireless LAN preamble may include L-STF, L-LTF, and L-SIG. Also, the wireless LAN STA (eg, 3rd party) can identify the end of the WUR packet through the L-SIG. For example, the L-SIG field may indicate the length of the payload of the WUR packet (e.g., OOK modulated).

The WUR part may include at least one of a WUR preamble, a MAC header, a frame body, and an FCS. The WUR preamble may include, for example, a PN sequence. The MAC header may include a receiver address. The frame body may contain other information needed for wake-up. The FCS may include a cyclic redundancy check (CRC).

FIG. 14 illustrates a waveform for the WUR packet of FIG. Referring to Fig. 14, in the OOK modulated WUR part, one bit can be transmitted per 1 OFDM symbol length (e.g., 4 usec). Thus, the data rate of the WUR part may be 250 kbps.

15 is a diagram for explaining generation of a WUR packet using an OFDM transmitter of a wireless LAN. In the wireless LAN, a phase shift keying (PSK) -OFDM transmission scheme is used. However, generating a WUR packet by adding a separate OOK modulator for OOK modulation increases the implementation cost of the transmitter. Therefore, a method of generating an OOK modulated WUR packet by reusing an OFDM transmitter will be described.

According to the OOK modulation scheme, a bit value 1 is a symbol (ie, on) having any power in a symbol or having a power equal to or higher than a threshold value, a bit value 0 is a symbol having no power in a symbol, (i.e., off). Of course, conversely, it is also possible to define the bit value 1 as the power off.

In the OOK modulation scheme, the bit value 1/0 is indicated on / off of the power at the corresponding symbol position. This simple OOK modulation / demodulation scheme has the advantage of reducing the power consumed in signal detection / demodulation of the receiver and the cost for implementing it. In addition, OOK modulation to turn signals on and off may be performed by reusing existing OFDM transmitters.

The left graph of FIG. 15 shows the real part and the imaginary part of the normalized amplitude for one symbol period (eg, 4 usec) for the OOK modulated bit value 1 by reusing the OFDM transmitter of the existing wireless LAN. lt; / RTI > shows an imaginary part. The OOK modulation result for the bit value 0 corresponds to the power off, so that the illustration is omitted.

The right graph of FIG. 15 shows normalized power spectral density (PSD) on the frequency domain for the OOK modulated bit value 1 by reusing the OFDM transmitter of the existing wireless LAN. For example, center 4 MHz in the band may be used for WUR. In FIG. 15, it is assumed that WUR operates at a 4 MHz bandwidth, but this is for convenience of explanation, and frequency bandwidths of different sizes may be used. However, it is desirable for WUR to operate at a bandwidth smaller than the operation bandwidth of the PCR (e.g., a conventional WLAN) for power reduction.

In FIG. 15, it is assumed that the subcarrier spacing (e.g., subcarrier spacing) is 312.5 kHz and the bandwidth of the OOK pulse corresponds to 13 subcarriers. The 13 subcarriers correspond to about 4 MHz (i.e., 4.06 MHz = 13 * 312.5 kHz) as mentioned above.

In the conventional OFDM transmitter, the input sequence of IFFT (inverse fast Fourier transform) is defined as s = {13 subcarrier tone sequence} and IFFT for the corresponding sequence s is performed as X _t = IFFT (s) When a CP (cyclic prefix) is attached, it becomes about 4 us symbol length.

The WUR packet may be referred to as a WUR signal, a WUR frame, or a WUR PPDU. The WUR packet may be a packet for broadcast / multicast (e.g., a WUR beacon) or a packet for unicast (e.g., a packet for waking up and awakening the WUR mode of a particular WUR STA).

Figure 16 illustrates the structure of a WURx (WUR receiver). Referring to FIG. 16, WURx may include a RF / analog front-end, a digital baseband processor, and a simple packet parser. 16 is an exemplary configuration, and the WUR receiver of the present invention is not limited to Fig.

In the following, a WLAN STA with a WUR receiver is briefly referred to as a WUR STA. The WUR STA may be referred to briefly as the STA.

- OOK modulation with Manchester coding

According to one embodiment of the present invention, Manchester coding may be used for OOK symbol generation. According to Manchester coding, 1-bit information is indicated via two sub-information (or two coded bits). For example, when 1-bit information '0' passes through Manchester coding, two lower information bits '10' (i.e., On-Off) are output. Conversely, when 1-bit information '1' passes Manchester coding, two lower information bits '01' (i.e., Off-On) are output. However, the On-Off order of the lower information bits may be reversed according to the embodiment.

A method of generating 1 OOK symbol based on the Manchester coding scheme will be described. For convenience of explanation, the 1 OOK symbol corresponds to 3.2 us in the time domain and corresponds to K subcarriers in the frequency domain, but the present invention is not limited thereto.

First, based on Manchester coding, a method of generating an OOK symbol for 1-bit information '0' will be described. (1) The OOK symbol length is (i) 1.6 us for the first lower information bit '1' And 1.6 us for the second lower information bit '0'.

(i) The signal corresponding to the first lower information bit '1' maps β to odd-numbered subcarriers among K subcarriers, maps 0 to even-numbered subcarriers, performs IFFT . For example, in the case of performing IFFT by mapping? In two frequency bands at two subcarrier intervals, a periodic signal of 1.6 us is repeated twice in the time domain. The first or second signal of the 1.6 us periodic signal repeated twice may be used as a signal corresponding to the first lower information bit '1'. β is a power normalization factor, for example, 1 / sqrt (ceil (K / 2)). For example, consecutive K subcarriers used for signal generation corresponding to the first lower information bit '1' of the total 64 subcarriers (ie, the 20 MHz band) are, for example, [33-floor (K / 2): 33 + ceil (K / 2) -1].

(ii) The signal corresponding to the second lower information bit '0' may be obtained by mapping 0 to K subcarriers and performing IFFT. For example, consecutive K subcarriers used for signal generation corresponding to the second lower information bit '0' of the total 64 subcarriers (ie, the 20 MHz band) are [33-floor (K / 2): 33 + ceil (K / 2) -1].

The OOK symbol for the 1-bit information '1' may be obtained by placing a signal corresponding to the lower information bit '1' after the signal corresponding to the lower information bit '0'.

- Symbol Reduction

For example, one symbol length for WUR may be set to be smaller than 3.2 us. For example, one symbol may be set to information + CP of 1.6us, 0.8us or 0.4us.

(ie, 1, 5, 9, ....) satisfies the mod (subcarrier index, 4) = 1 among K consecutive subcarriers, eg, power normalization factor * 1 may be mapped and the remaining subcarriers may be nulled (eg, 0 mapped). β can be 1 / sqrt (ceil (K / 4)). In this way,? * 1 can be mapped at four subcarrier intervals. When IFFT is performed by mapping? * 1 at intervals of four subcarriers in the frequency domain, signals of 0.8us length are repeated in the time domain. One of these signals can be used as a signal corresponding to information bit 1.

(ii) 0.8 us, information bit 0: A time domain signal can be obtained by mapping 0 to K subcarriers and performing an IFFT, and one 0.8us length signal can be used.

(ie, 1, 9, 17...) satisfying mod (subcarrier index, 8) = 1 among K consecutive subcarriers, , power normalization factor * 1 may be mapped and the remaining subcarriers may be nulled (eg, 0 mapped). β can be 1 / sqrt (ceil (K / 8)). In this way,? * 1 can be mapped at 8 subcarrier intervals. When IFFT is performed by mapping? * 1 at intervals of 8 subcarriers in the frequency domain, signals having a length of 0.4us are repeated in the time domain. One of these signals can be used as a signal corresponding to information bit 1.

(iv) 0.4 us, information bit 0: a time domain signal can be obtained by mapping 0 to K subcarriers and performing IFFT, and one of these signals can be used for 0.4us length.

OBSS detection in WUR

To wake up the PCR, the WUR packet that the AP sends to the STA can be sent to the same range as the PCR. Therefore, the WUR packet transmitted by the AP may be affected by the WUR packet transmitted by the neighbor AP. In addition, when a WUR packet transmitted from an OBSS (overlapping basic service set) is received by the STA, the STA may unnecessarily consume power in decoding the WUR packet to confirm that the WUR packet is its own, Can erroneously wake up the PCR.

In order to solve such a problem, a STA needs a method for determining whether a received WUR packet corresponds to its own BSS or OBSS.

In an embodiment of the present invention, a method for determining a BSS using a WUR preamble in a PHY layer before a WUR receiver of a STA receives a WUR packet and before decoding a MAC header of a WUR packet is proposed.

17 shows a WUR PPDU format according to an embodiment of the present invention.

Referring to FIG. 17, one BPSK symbol is added after the legacy preamble of the WUR PPDU to prevent the existing PCR STAs from false detection of the WUR PPDU as its own PPDU, and the WUR part is dummy, It starts after the symbol. The WUR preamble may include parts for AGC (auto-gain control) / synchronization and parts for WUR PPDU information / detection.

Information for WUR PPDU and information for WUR signal detection can be indicated through a preamble. In order to minimize the overhead of the preamble at this time, instead of using the SIG field as in the frame format of the existing WLAN, A sequence indicating specific information can be used. On the other hand, the structure of the WUR preamble in FIG. 17 is only an example, and the synchronization part and the WUR PPDU information part may be configured as one in the WUR preamble or the PPDU information may be indicated using the synchronization part.

As shown in FIG. 17, since the WUR PPDU starts with the WUR preamble, it can be considered to use the WUR preamble part to quickly determine whether the WUR PPDU received by the STA is the OBSS WUR PPDU.

Example 1. OBSS detection using synchronous part of WUR preamble

WUR In order to measure the time offset of the PPDU, the WUR sync part may be composed of a sequence with good auto / cross correlation characteristics. For example, the synchronization sequence may be a pseudo-random sequence (or PN sequence), a maximum length sequence (ML), a gold sequence, a Golay sequence, or a Hadamard sequence Lt; / RTI >

Hereinafter, it is assumed for the sake of convenience that the synchronization sequence is composed of a PN sequence, but the present invention is not limited thereto.

When a synchronization sequence is configured through a PN (pseudo-noise) -sequence, a different synchronization sequence may be used for each BSS. Upon receiving the WUR PPDU from the AP, the STA compares the synchronization sequence of the received WUR PPDU with the synchronization sequence used by the BSS, which is known to the STA, and determines whether the synchronization sequence of the WUR PPDU is a synchronization sequence of its own BSS . The STA can determine the BSS through the synchronization sequence of the WUR PPDU.

The STA can use the following methods to detect the synchronization sequence of the WUR PPDU.

As an example in which the STA detects the synchronization sequence, the synchronization sequence is composed of a sequence having an excellent correlation characteristic, and the STA can detect the synchronization sequence using the correlation characteristic. For example, the STA receiving the WUR signal from the AP may take auto-correlation through the received WUR signal to synchronize and take a cross-correlation with an already known synchronization sequence It is possible to detect the time when the maximum value appears. In this way, the STA takes a cross correlation with a synchronization sequence already known to the received WUR signal, recognizes the received WUR signal as its own BSS signal when the value obtained from the cross correlation result exceeds a threshold value, . Alternatively, the STA may not perform the synchronization process and the OBSS detection at the same time but may determine the BSS using the obtained value by performing the cross correlation on the corresponding WUR signal after the synchronization process is finished. However, when the sequence is detected by taking the cross-correlation, the power consumption may be increased.

In another example where the STA detects the synchronization sequence, the STA may perform an envelope detection on the synchronization sequence after the synchronization process is finished to decode information about the synchronization sequence. The STA can then determine whether the corresponding WUR signal is its own BSS signal through a simple logical operation (XOR) of the decoded sequence and its BSS sequence.

On the other hand, since the synchronization sequence is configured using a different sequence for each BSS, other synchronization sequences in the West can have a constant Hamming distance or a sequence having an error correction capability.

The Hamming distance (HD) between synchronization sequences can be set to an odd number in order to reduce a judgment error due to a bit flip at the time of error correction. For example, HD may be one of 3, 5, 7, or 9, but is not limited thereto.

The sequence assigned to the BSS can be determined using the following method.

For example, a sequence used by an AP may be set for each BSS using a least significant bit (LSB) of a BSSID or a BSS Color. For example, if the number of OBSSs to consider is 4 or 8, the number of synchronization sequences needed to distinguish the BSSs is 4 or 8. The LSB used to set the synchronization sequence assigned to each BSS may be 2-bit / 3-bit.

On the other hand, if the number of synchronization sequences is less than the number of BSS Colors or less than the number of OBSSs, at least some BSSs may use the same synchronization sequence.

In order to reduce the power consumption of the WUR receiver, the correlation of the synchronization sequence may be performed using the sequence information bits obtained through envelope detection and the bits of the sequence known to the STA. For example, correlation may be performed through simple logic operations such as exclusive OR (XOR).

As an example, sequence detection may be performed using the following correlation.

(i) 裡 XOR (y_d, x_known): y_d is information (eg, each bit value of 0/1) of the synchronization sequence detected through envelope detection, wherein the synchronization sequence value is May be a synchronization sequence value. x_known may be information (e.g., each bit value of 0/1) of the synchronization sequence assigned to the BSS of the STA. The x_known may inform the AP to the STA via PCR or WUR. If the sum of the bitwise XOR operation results is 0, the STA determines that it is its own BSS signal, and if it is not 0, it can determine that it is a signal to the OBSS. The STA can reduce the power consumption by omitting decoding of a signal determined to be an OBSS signal. For example, when y_d contains N bits y ₁ y ₂ y _{3 ..} y _N and x_known contains N bits x ₁ x ₂ x ₃ ... x _N , _{y 1, x 1) + XOR} (y 2, x 2) + XOR (y 3, x 3) + ... + XOR (y N, if the calculated value of x _N) is 0, the WUR PPDU their BSS (Eg, Intra-BSS WUR PPDU). If the calculated value exceeds 0, the WUR PPDU can be judged as another BSS signal (eg, Inter-BSS WUR PPDU). In this example, it is assumed that the threshold value of the OBSS determination is 0 for convenience of explanation. However, the present invention is not limited to this case. For example, the calculation value may be K (where K = 1, 2 or 4) The STA may determine that the corresponding WUR PPDU is sent from its BSS. In another example, the threshold K may vary depending on the length of the synchronization sequence or sequence known to the STA.

(ii) [Sigma] [XOR (y_d, x_seq)]: y_d may be information on the synchronization sequence detected through envelope detection. The STA may perform error correction on the synchronization sequence through an equation (i.e., select a sequence with the smallest sum value) to determine a synchronization sequence. The STA can determine whether the received WUR signal is its own BSS signal by determining the identity of the synchronization sequence determined by the STA and the synchronization sequence allocated to its BSS.

As another example, instead of using the PN-sequence for the synchronization sequence, the BSSID or BSS Color allocated to the BSS may be used as the synchronization sequence. When the BSSID or BSS Color information is used as a synchronization sequence, the STA can immediately determine whether the WUR signal is its own BSS signal when performing synchronization with the received WUR signal. After performing synchronization for OBSS detection, the STA can detect the OBSS signal by determining whether the received BSSID or BSS color information matches the received synchronization sequence. Since the BSSID is 32-bit, if the entire BSSID is used as the synchronization sequence, the overhead for the synchronization sequence can be increased. Therefore, instead of using the entire BSSID, the 24-bit of the BSSID except the redundancy can be used as a synchronous sequence.

Example 2. OBSS detection using signature sequence

A signature sequence may be used to indicate information about the WUR payload, such as the data rate. At this time, the information about the BSS can also be indicated using the signature sequence, whereby the STA can detect the OBSS signal.

For example, the signature sequence may be configured as follows (i) to (iv) in consideration of the number of data rates and the number of BSSs, and the present invention is not limited thereto.

In the examples described below, when the information for the data rate indication is N-bit, the total data rates supported in the WUR may be ^2N .

(i) 1-bit information for data rate indication & 4 BSSs

The number of signature sequences required is eight because the BSS needs to inform the STA about the two data rates. That is, two signature sequences are assigned to each BSS, and a total of four BSSs are present, so that a total of eight signature sequences are required. The AP may use two signature sequences assigned to its BSS among the eight signature sequences in total. For example, the AP may select one of the two signature sequences and transmit it to the STA.

The eight signature sequences may have the same Hamming distance, or may have the same error correction capability. The hamming distance can be set to the number of holes. For example, the hamming distance may be 3, 5, 7, or 9.

The indexes of the two signature sequences available to the AP may be set using the BSSID / BSS color information. For example, of the eight signature sequences, two signature sequences available to the AP may be determined through the BSSID / BSS color information.

The STA can receive information on the WUR signature sequence used in its BSS through PCR. For example, the STA may receive information about a signature sequence through a PCR beacon frame or a PCR trigger frame, or may acquire information from an AP during an association process.

The STA compares the signature sequence included in the received WUR signal with the signature sequence that it knows, so that the STA can know whether the received WUR signal is its own BSS signal or OBSS signal.

(ii) 1-bit information for data rate indication & 6 BSSs

A total of twelve signature sequences are required. a signature sequence can be constructed in the same way as in (i). The STA may receive information on two signature sequences including information on its BSS and data rate from the AP and use it to determine whether it is the data rate of the WUR signal and whether it is an OBSS signal.

(iii) 2-bit information for data rate indication & 4 BSSs

Four signature sequences are assigned to each BSS, and there are a total of four BSSs, so a total of 16 signature sequences are required. a signature sequence can be constructed / used in the same way as (i). The STA obtains information about the four signature sequences from the AP. The STA may compare the signature sequence of the received WUR signal with the four signature sequences obtained from the AP to determine whether the data rate and the OBSS signal are present.

(iv) 2-bit information for data rate indication & 6 BSSs

Four signature sequences are assigned to each BSS, and there are a total of six BSSs, so a total of 24 signature sequences are required. a signature sequence can be constructed / used in the same way as (i). The STA obtains information about the four signature sequences from the AP. The STA may compare the signature sequence of the received WUR signal with the four signature sequences obtained from the AP to determine whether the data rate and the OBSS signal are present.

On the other hand, if the number of data rates and the number of BSSs in (i) to (iv) increases, the number of signature sequences required increases greatly, and the overhead for the signature sequence can become large. Therefore, according to another embodiment of the present invention, a separate sequence may be allocated to each of the information on the data rate and the information on the BSS in order to minimize the overhead of the signature sequence.

In one example, a signature sequence for the BSS may be sent prior to the sequence for the data rate to indicate first whether to OBSS over the data rate.

In this case, the sequence indicating the data rate need not be configured differently for each BSS. In other words, the sequence for the data rate can be used in common with the BSS.

The information on the data rate and the number of BSSs can be considered in the case of (i) to (iv).

For example, the 1-bit information for the data rate indication and the signature sequence for the BSS number of 4 can be configured as follows. Four signature sequences may be used for BSS indication. The indexes of the four signature sequences used by the BSS may be determined using BSSID or BSS Color information.

The signature sequence for the BSS indication can be set considering the Hamming distance. For example, the signature sequence for BSS indication may be composed of a sequence having the same odd Hamming distance or a sequence having the same error correction performance. Hamming distance can be 3, 5, 7 or 9. The signature sequence for the BSS indication may be configured using a PN sequence, a ML sequence, a Golay sequence, or the like.

The signature sequence transmitted via the WUR preamble may consist of a signature sequence for BSS indication and a signature sequence for data rate indication. The STA can perform detection for each sequence upon receipt of the WUR preamble.

Since a separate sequence is set for each BSS but the same sequence is set for the data rate, a large number of sequences are not necessary and the overhead can also be reduced.

18 shows a flow of a WUR PPDU transmission / reception method according to an embodiment of the present invention. Fig. 18 is an embodiment of the above-described embodiments, and the present invention is not limited to Fig.

Referring to FIG. 18, the STA receives a WUR PPDU including a WUR preamble and a payload (1805).

The STA may acquire time synchronization based on the synchronization sequence included in the WUR PPDU (1810). For example, the STA may perform synchronization on the WUR PPDU through autocorrelation to the synchronization sequence included in the WUR preamble.

Based on the synchronization sequence of the WUR preamble, the STA determines whether the received WUR PPDU is received from a basic service set (BSS) to which the STA belongs or from an overlapping BSS (1815). For example, the STA may receive a WUR PPDU from a BSS to which the STA belongs by cross-correlation between a synchronization sequence included in the WUR preamble and a predetermined sequence known to the STA (e.g., a sequence signaled by the AP to the STA via PCR or WUR) Or not.

In one example, the STA may determine that the WUR PPDU is received from the BSS to which the STA belongs if the result of the cross-correlation for the synchronization sequence exceeds the threshold.

As another example, the STA may obtain bit information of the synchronization sequence through envelope detection for the synchronization sequence. The STA may obtain cross-correlation based on bitwise XOR (exclusive OR) operations between the bit information of the synchronization sequence and a predetermined sequence known to the STA. For example, the cross-correlation is obtained based on the equation Σ [XOR (X _i , Y _i )], where 'X _i ' represents the i-th bit of the synchronization sequence and 'Y _i 'Lt; th > bit.

Different synchronization sequences are allocated to the BSS and OBSS, and the synchronization sequence allocated to the BSS and the synchronization sequence allocated to the OBSS can be determined based on the BSS ID or the BSS Color. The Hamming distance between the synchronization sequence allocated to the BSS and the synchronization sequence allocated to the OBSS may be 3, 5, 7, or 9.

If the received WUR PPDU is received from the BSS to which the STA belongs, the STA decodes the payload of the WUR PPDU (1820).

If the received WUR PPDU is received from the OBSS, the STA may ignore the WUR PPDU (1825).

19 is a diagram for explaining an apparatus for implementing the above-described method.

The wireless device 100 of FIG. 19 may correspond to the specific STA of the above description, and the wireless device 850 of the above description.

STA 100 may include processor 110, memory 120 and transceiver 130 and AP 150 may include processor 160, memory 170 and transceiver 180. [ The transceivers 130 and 180 transmit / receive wireless signals and may be implemented at a physical layer such as IEEE 802.11 / 3GPP. Processors 110 and 160 are implemented in the physical layer and / or MAC layer and are coupled to transceivers 130 and 180.

Processors 110 and 160 and / or transceivers 130 and 180 may include application specific integrated circuits (ASICs), other chipsets, logic circuits, and / or data processors. The memories 120 and 170 may comprise read-only memory (ROM), random access memory (RAM), flash memory, memory card, storage medium and / or other storage unit. When an embodiment is executed by software, the method described above may be executed as a module (e.g., process, function) that performs the functions described above. The module may be stored in memory 120,170 and executed by processor 110,160. The memory 120, 170 may be located inside or outside the process 110, 160 and may be coupled to the process 110, 160 by well known means.

The transceiver 130 of the STA may include a transmitter (not shown) and a receiver (not shown). The receiver of the STA may include a main connected radio receiver for receiving the main attached radio (e.g., IEEE 802.11a / b / g / n / ac / ax) signal and a WUR receiver for receiving the WUR signal have. The STA's transmitter may include a main connected radio transmitter for transmitting the main connected radio signal.

The transceiver 180 of the AP may include a transmitter (not shown) and a receiver (not shown). The transmitter of the AP may correspond to the OFDM transmitter. The AP may reuse the OFDM transmitter to transmit the WUR payload in an OOK manner. For example, the AP may OOK modulate the WUR payload via an OFDM transmitter, as described above.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The foregoing description of the preferred embodiments of the present invention has been presented for those skilled in the art to make and use the invention. While the foregoing is directed to preferred embodiments of the present invention, those skilled in the art will appreciate that various modifications and changes may be made by those skilled in the art from the foregoing description. Accordingly, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

The present invention can be applied to various wireless communication systems including IEEE 802.11.

Claims (14)

1. A method of receiving a wake-up radio (WUR) physical layer protocol data unit (PPDU) in a wireless local area network (WLAN)

   Receiving a WUR PPDU including a WUR preamble and a payload;

   Determining whether the WUR PPDU is received from a basic service set (BSS) to which the STA belongs or an overlapping BSS (OBSS) based on the WUR preamble; And

   Decoding the payload of the WUR PPDU if the WUR PPDU is received from a BSS to which the STA belongs,

   Wherein the STA determines whether the WUR PPDU is received from a BSS to which the STA belongs by cross-correlation between a synchronization sequence included in the WUR preamble and a predetermined sequence known to the STA.
2. The method according to claim 1,

   The STA determines that the WUR PPDU is received from the BSS to which the STA belongs if the result of the cross-correlation for the synchronization sequence exceeds a threshold.
3. The method according to claim 1,

   The STA obtains bit information of the synchronization sequence through envelope detection of the synchronization sequence, and based on a bitwise XOR (exclusive OR) operation between the bit information of the synchronization sequence and a predetermined sequence known to the STA To obtain the cross-correlation.
4. The method of claim 3,

   The cross-correlation is obtained based on the equation _{Σ [XOR (X i, Y} i)],

   'X _i ' denotes the i-th bit of the synchronization sequence, and 'Y _i ' denotes the i-th bit of the predetermined sequence.
5. The method according to claim 1,

   Different synchronization sequences are allocated to the BSS and the OBSS,

   Wherein a synchronization sequence assigned to the BSS and a synchronization sequence assigned to the OBSS are determined based on a BSS ID or a BSS Color.
6. 6. The method of claim 5,

   Wherein a Hamming distance between a synchronization sequence allocated to the BSS and a synchronization sequence allocated to the OBSS is 3, 5, 7 or 9.
7. The method according to claim 1,

   Further comprising performing synchronization for the WUR PPDU through autocorrelation to a synchronization sequence included in the WUR preamble.
8. A station (STA) for receiving a wake-up radio (PPDU) physical layer protocol data unit (WDU)

   WUR receiver; And

   Receiving a WUR PPDU including a WUR preamble and a payload through the WUR receiver, and based on the WUR preamble, whether the WUR PPDU is received from a basic service set (BSS) to which the STA belongs or from an overlapping BSS And if the WUR PPDU is received from the BSS to which the STA belongs, decoding the payload of the WUR PPDU,

   Wherein the processor determines whether the WUR PPDU is received from a BSS to which the STA belongs by cross-correlation between a synchronization sequence included in the WUR preamble and a predetermined sequence known to the STA.
9. 9. The method of claim 8,

   Wherein the processor determines that the WUR PPDU is received from the BSS to which the STA belongs if the result of the cross-correlation for the synchronization sequence exceeds a threshold.
10. 9. The method of claim 8,

    Wherein the processor is configured to obtain bit information of the synchronization sequence through envelope detection for the synchronization sequence, and to perform a bitwise XOR (exclusive OR) operation between the bit information of the synchronization sequence and a predetermined sequence known to the STA To obtain the cross-correlation.
11. 11. The method of claim 10,

    The cross-correlation is obtained based on the equation _{Σ [XOR (X i, Y} i)],

    'X _i ' denotes the i-th bit of the synchronization sequence, and 'Y _i ' denotes the i-th bit of the predetermined sequence.
12. 9. The method of claim 8,

    Different synchronization sequences are allocated to the BSS and the OBSS,

    Wherein a synchronization sequence assigned to the BSS and a synchronization sequence assigned to the OBSS are determined based on a BSS ID or a BSS Color.
13. 13. The method of claim 12,

    Wherein the Hamming distance between the synchronization sequence allocated to the BSS and the synchronization sequence allocated to the OBSS is 3, 5, 7, or 9.
14. 9. The method of claim 8,

    Wherein the processor performs synchronization for the WUR PPDU through autocorrelation to a synchronization sequence included in the WUR preamble.

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