WO2018084495A1 - Method for transmitting or receiving wake up radio packet in wireless lan system, and device therefor - Google Patents

Abstract

According to one embodiment of the present invention, a method by which an access point (AP) transmits a wake up radio (WUR) packet in a wireless LAN (WLAN) system comprises the steps of: generating a WUR preamble sequence having a plurality of on-off keying (OOK) on symbols; and transmitting, to a station (STA), the WUR packet including the WUR preamble sequence and a WUR payload, wherein the WUR preamble sequence includes a synchronization sequence and a control field, and an OOK off symbol for dividing the synchronization sequence and the control field can be set between the end of the synchronization sequence and the start of the control field.

Description

Method for transmitting or receiving wake-up radio packet in wireless LAN system and apparatus therefor

The present invention relates to a wireless LAN system, and more particularly, to a method and apparatus for transmitting or receiving a WUR packet for waking a primary connectivity radio (PCR) through a wake up radio (WUR).

The standard for WLAN technology is being developed as an Institute of Electrical and Electronics Engineers (IEEE) 802.11 standard. IEEE 802.11a and b are described in 2.4. Using unlicensed band at GHz or 5 GHz, IEEE 802.11b provides a transmission rate of 11 Mbps and IEEE 802.11a provides a transmission rate of 54 Mbps. IEEE 802.11g applies orthogonal frequency-division multiplexing (OFDM) at 2.4 GHz to provide a transmission rate of 54 Mbps. IEEE 802.11n applies multiple input multiple output OFDM (MIMO-OFDM) to provide a transmission rate of 300 Mbps for four spatial streams. IEEE 802.11n supports channel bandwidths up to 40 MHz, in this case providing a transmission rate of 600 Mbps.

The WLAN standard uses a maximum of 160MHz bandwidth, supports eight spatial streams, and supports IEEE 802.11ax standard through an IEEE 802.11ac standard supporting a speed of up to 1Gbit / s.

It is an object of the present invention to provide a method and apparatus for more accurately transmitting or receiving a WUR packet including a WUR preamble and a WUR payload.

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

In the WLAN system according to an aspect of the present invention for achieving the above technical problem, a method for transmitting an access point (WUR) packet (WUR) packet in a wireless LAN (WLAN) system, a plurality of on-off keying (OOK) on generating a WUR preamble sequence with (on) symbols; And transmitting a WUR packet including the WUR preamble sequence and the WUR payload to a station, wherein the WUR preamble sequence includes a sync sequence and a control field, the end of the sync sequence and the control field. Between the start of OOK off symbol for the separation of the synchronization sequence and the control field may be set.

An access point (AP) for transmitting a wake up radio (WUR) packet according to another aspect of the present invention for achieving the above technical problem, a WUR preamble having a plurality of on-off keying (OOK) on symbols A processor for generating a sequence; And a transmitter for transmitting a WUR packet including the WUR preamble sequence and the WUR payload to a station under control of the processor, wherein the WUR preamble sequence includes a synchronization sequence and a control field, wherein the synchronization sequence Between the end of and the start of the control field, a OOK off symbol for distinguishing the synchronization sequence and the control field may be set.

In another aspect of the present invention, a method for receiving a WUR packet from a station in a WLAN system includes a WUR preamble sequence and a WUR payload. Receiving a WUR packet; And performing synchronization on the WUR packet based on a plurality of on-off keying (OOK) on symbols included in the WUR preamble sequence, wherein the WUR preamble sequence includes a synchronization sequence and a control field. It may include, but between the end of the synchronization sequence and the start of the control field, a OOK off symbol for distinguishing the synchronization sequence and the control field may be set.

According to another aspect of the present invention, a station apparatus for performing the above-described WUR packet reception method may be provided.

The number of the OOK off symbols set between the end of the synchronization sequence and the start of the control field may be one.

Phase rotation is applied to the last N symbols located immediately before the WUR payload among the plurality of OOK on symbols included in the WUR preamble sequence, or when the last N symbols are correlated. It may be set to bipolar symbols representing a loudness. For example, the phase rotation applied to the last N symbols may be π / 4, π / 2 or π.

The first frequency sequence used to generate the plurality of OOK on symbols of the WUR preamble sequence and the second frequency sequence used to generate the OOK on symbol symbols of the WUR payload may be different. For example, the first frequency sequence corresponds to a CAZAC sequence, a Zadoff-Chu sequence, or a Golay sequence, and the second frequency sequence corresponds to a bipolar sequence. This may be the case.

A cyclic shift may be applied to the last N symbols located immediately before the WUR payload among the plurality of OOK on symbols included in the WUR preamble sequence. For example, different cyclic shift values may be applied to each of the last N symbols.

According to an embodiment of the present invention, when the WUR preamble sequence includes a plurality of OOK on symbols for the synchronization sequence and the control field, a OOK off symbol for distinguishing the synchronization sequence from the control field is set between the control field and the synchronization sequence. As a result, time synchronization for transmitting and receiving WUR packets may be accurately performed.

In addition to the above-described technical effects, other technical effects can be inferred from the embodiments of the present invention.

1 is a diagram illustrating an example of a configuration of a WLAN system.

2 is a diagram illustrating another example of a configuration of a WLAN system.

3 is a diagram illustrating a general link setup process.

4 is a diagram for describing a backoff process.

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

6 is a diagram for explaining an RTS and a CTS.

7 to 9 are diagrams for explaining the operation of the STA receiving the TIM.

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

FIG. 11 is a diagram illustrating a WUR receiver usable in a WLAN system (e.g., 802.11).

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

13 shows an example of a WUR packet.

14 illustrates a waveform for a WUR packet.

FIG. 15 illustrates a WUR packet generated using an OFDM transmitter of a wireless LAN.

16 illustrates the structure of a WUR receiver.

17 illustrates a WUR preamble and a WUR payload according to an embodiment of the present invention.

18 illustrates a WUR preamble and a WUR payload according to another embodiment of the present invention.

19 shows a WUR preamble and a WUR payload according to another embodiment of the present invention.

20 illustrates a WUR preamble and a WUR payload according to another embodiment of the present invention.

21 illustrates a flow of a WUR packet transmission / reception method according to an embodiment of the present invention.

22 is a diagram for explaining an apparatus according to an embodiment of the present invention.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. The detailed description, which will be given below with reference to the accompanying drawings, is intended to explain exemplary embodiments of the present invention and is not intended to represent the only embodiments in which the present invention may be practiced.

The following detailed description includes specific details in order to provide a thorough understanding of the present invention. However, one of ordinary skill in the art appreciates 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, centering on 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 an apparatus therefor for efficiently utilizing a channel having a wide band in a WLAN system. To this end, first, a WLAN system to which the present invention is applied will be described in detail.

1 is a diagram illustrating an example of a configuration of a WLAN system.

As shown in FIG. 1, the WLAN system includes one or more basic service sets (BSSs). A BSS is a set of stations (STAs) that can successfully synchronize and communicate with each other.

An STA is a logical entity that includes a medium access control (MAC) and a physical layer interface to a wireless medium. The STA is an access point (AP) and a non-AP STA (Non-AP Station). Include. The portable terminal operated by the user among the STAs is a non-AP STA, and when referred to simply as an STA, it may also refer to a non-AP STA. A non-AP STA is a terminal, a wireless transmit / receive unit (WTRU), a user equipment (UE), a mobile station (MS), a mobile terminal, or a mobile subscriber. It may also be called another name such as a mobile subscriber unit.

The AP is an entity that provides an associated station (STA) coupled to the AP to access a distribution system (DS) through a wireless medium. The AP may be called a centralized controller, a base station (BS), a Node-B, a base transceiver system (BTS), or a site controller.

BSS can be divided into infrastructure BSS and Independent BSS (IBSS).

The BBS shown in FIG. 1 is an IBSS. The IBSS means a BSS that does not include an AP. Since the IBSS does not include an AP, access to the DS is not allowed, thereby forming a self-contained network.

2 is a diagram illustrating another example of a configuration of a WLAN system.

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

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

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

Hierarchy

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

In order to provide correct MAC operation, a Station Management Entity (SME) is present in each STA. An SME is a layer-independent entity that can appear to be in a separate management plane or appear to be off to the side. While the exact features of the SME are not described in detail in this document, they generally do not include the ability to collect layer-dependent states from various Layer Management Entities (LMEs), and to set similar values for layer-specific parameters. You may seem to be in charge. SMEs can generally perform these functions on behalf of general system management entities and implement standard management protocols.

The aforementioned entities interact in a variety of ways. For example, entities can interact by exchanging GET / SET primitives. A primitive means a set of elements or parameters related to a particular purpose. The XX-GET.request primitive is used to request the value of a given MIB attribute (management information based attribute information). The XX-GET.confirm primitive is used to return 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 a given value. If the MIB attribute means a specific operation, this is to request that the operation be performed. And, the XX-SET.confirm primitive confirms that the indicated MIB attribute is set to the requested value when status is "success", otherwise it is used to return an error condition in the status field. If the MIB attribute means a specific operation, this confirms that the operation has been performed.

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

link set up  process

3 is a diagram illustrating a general link setup process.

In order for an STA to set up a link and transmit / receive data with respect to a network, an STA first discovers the network, performs authentication, establishes an association, and authenticates for security. It must go through the back. The link setup process may also be referred to as session initiation process and session setup process. In addition, a process of discovery, authentication, association, and security establishment of a link setup process may be collectively referred to as association process.

An exemplary link setup process will be described with reference to FIG. 3.

In step S510, the STA may perform a network discovery operation. The network discovery operation may include a scanning operation of the STA. That is, 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. A network identification process existing in a specific area is called scanning.

There are two types of scanning methods, active scanning and passive scanning.

3 exemplarily illustrates a network discovery operation including an active scanning process. In active scanning, the STA performing scanning transmits a probe request frame and waits for a response to discover which AP exists in the vicinity while moving channels. The responder transmits a probe response frame to the STA that transmits the probe request frame in response to the probe request frame. Here, the responder may be an STA that last transmitted a beacon frame in the BSS of the channel being scanned. In the BSS, the AP transmits a beacon frame, so the AP becomes a responder. In the IBSS, since the STAs in the IBSS rotate and transmit a beacon frame, the responder is not constant. For example, an STA that transmits a probe request frame on channel 1 and receives a probe response frame on channel 1 stores the BSS-related information included in the received probe response frame and stores the next channel (eg, number 2). Channel) to perform scanning (i.e., probe request / response transmission and reception on channel 2) in the same manner.

Although not shown in FIG. 3, the scanning operation may be performed by a passive scanning method. In passive scanning, the STA performing scanning waits for a beacon frame while moving channels. The beacon frame is one of management frames in IEEE 802.11. The beacon frame is notified of the existence of a wireless network and is periodically transmitted to allow the STA performing scanning to find the wireless network and participate in the wireless network. In the BSS, the AP periodically transmits a beacon frame, and in the IBSS, STAs in the IBSS rotate and transmit a beacon frame. When the STA that performs the scanning receives the beacon frame, the STA stores the information on the BSS included in the beacon frame and records beacon frame information in each channel while moving to another channel. Upon receiving the beacon frame, the STA may store BSS related information included in the received beacon frame, move to the next channel, and perform scanning on the next channel in the same manner.

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

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

The authentication process includes a process in which the STA transmits an authentication request frame to the AP, and in response thereto, the AP transmits an authentication response frame to the STA. An authentication frame used for authentication request / response corresponds to a 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, and 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, and may be replaced with other information or further include additional information.

The STA may send an authentication request frame to the AP. The AP may determine whether to allow authentication for the corresponding STA based on the information included in the received authentication request frame. The AP may provide a result of the authentication process to the STA through an authentication response frame.

After the STA is successfully authenticated, the association process may be performed in step S530. The association process includes a process in which the STA transmits an association request frame to the AP, and in response thereto, the AP transmits an association response frame to the STA.

For example, the association request frame may include information related to various capabilities, beacon listening interval, service set identifier (SSID), supported rates, supported channels, RSN, mobility domain. Information about supported operating classes, TIM Broadcast Indication Map Broadcast request, interworking service capability, and the like.

For example, an association response frame may include information related to various capabilities, status codes, association IDs (AIDs), support rates, Enhanced Distributed Channel Access (EDCA) parameter sets, Received Channel Power Indicators (RCPI), Received Signal to Noise Information, such as an indicator, a mobility domain, a timeout interval (association comeback time), an overlapping BSS scan parameter, a TIM broadcast response, and a QoS map.

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

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

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

Media access mechanism

In a WLAN system according to IEEE 802.11, a basic access mechanism of MAC (Medium Access Control) is a carrier sense multiple access with collision avoidance (CSMA / CA) mechanism. The CSMA / CA mechanism is also called the Distributed Coordination Function (DCF) of the IEEE 802.11 MAC. It basically employs a "listen before talk" access mechanism. According to this type of access mechanism, the AP and / or STA may sense a radio channel or medium during a predetermined time period (e.g., during a DCF Inter-Frame Space (DIFS), before starting transmission. When the medium determines that the medium is in an idle state, the frame transmission is started through the medium, while the medium is occupied. If it is detected that the AP and / or STA does not start its own transmission, it waits by setting a delay period (for example, a random backoff period) for medium access and attempting frame transmission. By applying a random backoff period, since several STAs are expected to attempt frame transmission after waiting for different times, collisions can be minimized.

In addition, the IEEE 802.11 MAC protocol provides a hybrid coordination function (HCF). HCF is based on the DCF and the Point Coordination Function (PCF). The PCF refers to a polling-based synchronous access scheme in which polling is performed periodically so that all receiving APs and / or STAs can receive data frames. In addition, the HCF has an Enhanced Distributed Channel Access (EDCA) and an HCF Controlled Channel Access (HCCA). EDCA is a competition based approach for providers to provide data frames to multiple users, and HCCA uses a non-competition based channel access scheme using a polling mechanism. In addition, the HCF includes a media access mechanism for improving the quality of service (QoS) 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 describing a backoff process.

An operation based on an arbitrary backoff period will be described with reference to FIG. 4. When a medium that is occupy or busy 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, STAs may select a random backoff count and wait for the corresponding slot time, respectively, before attempting transmission. The random backoff count has a packet number value and may be determined as one of values ranging from 0 to CW. Here, CW is a contention window parameter value. The CW parameter is given CWmin as an initial value, but may take a double value in case of transmission failure (eg, when an ACK for a transmitted frame is not received). When the CW parameter value is CWmax, data transmission can be attempted while maintaining the CWmax value until the data transmission is successful. If the data transmission is successful, the CW parameter value is reset to the CWmin value. The CW, CWmin and CWmax values are preferably set to 2 ⁿ -1 (n = 0, 1, 2, ...).

Once the random backoff process begins, the STA continues to monitor the medium while counting down the backoff slots according to the determined backoff count value. If the medium is monitored as occupied, the countdown stops and waits; if the medium is idle, it resumes the remaining countdown.

In the example of FIG. 4, when a packet to be transmitted to the MAC of the STA3 arrives, the STA3 may confirm that the medium is idle as much as DIFS and transmit the frame immediately. Meanwhile, the remaining STAs monitor and wait for the medium to be busy. In the meantime, data may also be transmitted in each of STA1, STA2, and STA5, and each STA waits for DIFS when the medium is monitored idle, and then counts down the backoff slot according to a random backoff count value selected by the 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. In other words, 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. STA1 and STA5 stop counting for a while and wait for STA2 to occupy the medium. When the occupation of the STA2 ends and the medium becomes idle again, the STA1 and the STA5 resume the stopped backoff count after waiting for DIFS. 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 the STA5 is shorter than that of the STA1, the STA5 starts frame transmission. Meanwhile, while STA2 occupies the medium, data to be transmitted may also occur in STA4. At this time, when the medium is in an idle state, the STA4 waits for DIFS, performs a countdown according to a random backoff count value selected by the STA4, and starts frame transmission. In the example of FIG. 6, the remaining backoff time of STA5 coincides with an arbitrary backoff count value of STA4. In this case, a collision may occur between STA4 and STA5. If a collision occurs, neither STA4 nor STA5 receive an ACK, and thus data transmission fails. In this case, STA4 and STA5 may double the CW value, select a random backoff count value, and perform a countdown. Meanwhile, the STA1 waits while the medium is occupied due to transmission of the STA4 and STA5, waits for DIFS when the medium is idle, and starts frame transmission after the remaining backoff time passes.

Of STA Sensing  action

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 sense the medium. Virtual carrier sensing is intended to compensate for problems that may occur in media access, such as a hidden node problem. For virtual carrier sensing, the MAC of the WLAN system may use a network allocation vector (NAV). The NAV is a value in which an AP and / or STA currently using or authorized to use a medium instructs another AP and / or STA how long to remain until the medium becomes available. Therefore, the value set to NAV corresponds to a period in which the medium is scheduled to be used by the AP and / or STA transmitting the corresponding frame, and the STA receiving the NAV value is prohibited from accessing the medium during the period. The NAV may be set, for example, according to the value of the "duration" field of the MAC header of the frame.

In addition, a robust collision detect mechanism has been introduced to reduce the possibility of collision. This will be described with reference to FIGS. 5 and 7. Although the actual carrier sensing range and transmission range may not be the same, it is assumed to be the same for convenience of description.

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

5A illustrates an example of a hidden node, in which STA A and STA B are in communication and STA C has information to transmit. In more detail, although STA A is transmitting information to STA B, it may be determined that the medium is idle when STA C performs carrier sensing before sending data to STA B. This is because transmission of STA A (ie, media occupation) may not be sensed at the location of STA C. In this case, since STA B receives the information of STA A and STA C at the same time, a collision occurs. At this time, STA A may be referred to as a hidden node of STA C.

FIG. 5B is an example of an exposed node, and STA B is a case in which STA C has information to be transmitted from STA D while transmitting data to STA A. FIG. In this case, when STA C performs carrier sensing, it may be determined that the medium is occupied by the transmission of STA B. Accordingly, since STA C is sensed as a medium occupancy state even if there is information to be transmitted to STA D, it must wait until the medium becomes idle. However, since STA A is actually outside the transmission range of STA C, transmission from STA C and transmission from STA B may not collide with STA A's point of view, so STA C is unnecessary until STA B stops transmitting. To wait. At this time, STA C may be referred to as an exposed node of STA B.

6 is a diagram for explaining an RTS and a CTS.

In order to efficiently use a collision avoidance mechanism in an exemplary situation as shown in FIG. 5, a short signaling packet such as a request to send (RTS) and a clear to send (CTS) may be used. 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, when an STA to transmit data transmits an RTS frame to an STA receiving the data, the STA receiving the data may inform the neighboring STAs that they will receive the data by transmitting the CTS frame.

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

FIG. 6 (b) illustrates an example of a method for solving an exposed node problem, and STA C overhears RTS / CTS transmission between STA A and STA B so that STA C may use another STA (eg, STA). It may be determined that no collision will occur even if data is transmitted to D). That is, STA B transmits the RTS to all neighboring STAs, and only STA A having the data to actually transmit the CTS. Since STA C receives only RTS and not STA A's CTS, it can be seen that STA A is out of STC C's carrier sensing.

Power management

As described above, in the WLAN system, channel sensing must be performed before the STA performs transmission and reception, and always sensing the channel causes continuous power consumption of the STA. The power consumption in the receive state is not significantly different from the power consumption in the transmit state, and maintaining the receive state is also a great burden for the power limited STA (ie, operated by a battery). Therefore, if the STA maintains the reception standby state in order to continuously sense the channel, it inefficiently consumes power without any particular advantage in terms of WLAN throughput. In order to solve this problem, the WLAN system supports a power management (PM) mode of the STA.

The power management mode of the STA is divided into an active mode and a power save (PS) mode. The STA basically operates in the active mode. The STA operating in the active mode maintains an awake state. The awake state is a state in which normal operation such as frame transmission and reception or channel scanning is possible. On the other hand, 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 at the minimum power, and does not perform frame scanning as well as channel scanning.

As the STA operates in the sleep state for as long as possible, power consumption is reduced, so the STA has an increased operation period. However, it is impossible to operate unconditionally long because frame transmission and reception are impossible in the sleep state. If there is a frame to be transmitted to the AP, the STA operating in the sleep state may transmit the frame by switching to the awake state. On the other hand, when the AP has a frame to transmit to the STA, the STA in the sleep state may not receive it and may not know that there is a frame to receive. Accordingly, the STA may need to switch to the awake state according to a specific period in order to know whether or not the frame to be transmitted to (or, if there is, receive it) exists.

The AP may transmit a beacon frame to 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 indicating that the AP has buffered traffic for STAs associated with the AP and transmits a frame. The TIM element includes a TIM used to inform unicast frames and a delivery traffic indication map (DTIM) used to inform multicast or broadcast frames.

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

Referring to FIG. 7, the STA may switch from the sleep state to the awake state to receive a beacon frame including the TIM from the AP, interpret the received TIM element, and know that there is buffered traffic to be transmitted to the AP. . After contending with other STAs for medium access for PS-Poll frame transmission, the STA may transmit a PS-Poll frame to request an AP to transmit a data frame. After receiving the PS-Poll frame transmitted by the STA, the AP may transmit the frame to the STA. The STA may receive a data frame and transmit an acknowledgment (ACK) frame thereto to the AP. The STA may then go back to sleep.

As shown in FIG. 7, the AP may operate according to an immediate response method of transmitting a data frame after a predetermined time (for example, a short inter-frame space (SIFS)) after receiving a PS-Poll frame from an STA. Can be. Meanwhile, when the AP fails to prepare a data frame to be transmitted to the STA during the SIFS time after receiving the PS-Poll frame, the AP may operate according to a deferred response method, which will be described with reference to FIG. 8.

In the example of FIG. 8, the STA switches from the sleep state to the awake state to receive the TIM from the AP and transmits the PS-Poll frame to the AP through contention as in the example of FIG. 7. If the AP does not prepare a data frame during SIFS even after receiving the PS-Poll frame, the AP may transmit an ACK frame to the STA instead of transmitting the data frame. When the data frame is prepared after transmitting the ACK frame, the AP may transmit the data frame to the STA after performing contention. The STA may transmit an ACK frame indicating that the data frame was successfully received to the AP and go to sleep.

9 illustrates an example in which the AP transmits a DTIM. STAs may transition from a sleep state to an awake state to receive a beacon frame containing a DTIM element from the AP. STAs may know that a multicast / broadcast frame will be transmitted through the received DTIM. The AP may transmit data (ie, multicast / broadcast frame) immediately after the beacon frame including the DTIM without transmitting and receiving the PS-Poll frame. The STAs may receive data while continuously awake after receiving the beacon frame including the DTIM, and may switch back to the sleep state after the data reception is completed.

Frame structure general

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

The Physical Layer Protocol Data Unit (PPDU) frame format may include a Short Training Field (STF), a Long Training Field (LTF), a SIG (SIGNAL) field, and a Data field. The most basic (eg, non-HT) PPDU frame format may include only a legacy-STF (L-STF), a legacy-LTF (L-LTF), a SIG field, and a data field.

The STF is a signal for signal detection, automatic gain control (AGC), diversity selection, precise time synchronization, etc. The LTF is a signal for channel estimation, frequency error estimation, and the like. The STF and LTF may be referred to as a PLCP preamble, and the PLCP preamble may be referred to as a signal for synchronization and channel estimation of an OFDM physical layer.

The SIG field may include a RATE field and a LENGTH field. The RATE field may include information about modulation and coding rate of data. The LENGTH field may include information about the length of data. In addition, 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 of 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 zero. The padding bit may be used to adjust the length of the data field in 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 may consist of MPDUs and may be transmitted / received through the PSDU of the data portion 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 include control information required for frame transmission / reception. The duration / ID field may be set to a time for transmitting the corresponding frame.

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

WUR (Wake-Up Radio)

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

Referring to FIG. 11, an STA includes a primary connectivity radio (PCR) (eg, IEEE 802.11a / b / g / n / ac / ax WLAN) and a wake up radio for main wireless communication. WUR) (eg, IEEE 802.11ba) can be supported.

PCR is used for data transmission and reception, and may be turned off when there is no data to transmit and receive. As such, when the PCR is turned off, the WURx of the STA may wake up the PCR when there is a packet to receive. Therefore, user data is transmitted and received through PCR.

WURx is not used for user data, it can only serve to 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. It is desirable that the target power consumption of the WURx in the activated state does not exceed 100 microwatts (uW). In order to operate at such low power, a simple modulation scheme, for example, an on-off keying (OOK) scheme, may be used, and a narrow bandwidth (e.g., 4 MHz, 5 MHz) may be used. The reception range (e.g., distance) that WURx targets may be equivalent to the current 802.11.

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

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

The PCR part 1200 is for coexistence with the legacy WLAN system, and the PCR part may be referred to as a WLAN preamble. In order to protect the WUR packet from another PCR STA, at least one or more of L-STF, L-LTF, and L-SIG of the legacy WLAN may be included in the PCR part 1200. Accordingly, the 3rd party legacy STA may know that the WUR packet is not intended for the user through the PCR part 1200 of the WUR packet, and that 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, which supports narrowband and OOK demodulation, does not support PCR signal reception.

At least a part of the WUR part 1205 may be modulated by an on-off keying (OOK) method. For 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 of 100 uW or less as described above and can be implemented with a small and simple OOK demodulator.

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

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

Referring to FIG. 13, the legacy WLAN preamble may include L-STF, L-LTF, and L-SIG. The WLAN STA (e.g., 3rd Party) may detect the start of a WUR packet through the L-STF. In addition, the WLAN STA (e.g., 3rd Party) can determine the end of the WUR packet through the L-SIG. For example, the L-SIG field may indicate the length of the payload (e.g., OOK modulated) of the WUR packet.

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 the 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 the waveform for the WUR packet of FIG. 13. Referring to FIG. 14, in the OOK modulated WUR part, 1 bit may be transmitted per 1 OFDM symbol length (e.g., 4 usec). Thus, the data rate of the WUR part may be 250 kbps.

FIG. 15 illustrates generation of a WUR packet using an OFDM transmitter of a wireless LAN. In a WLAN, a phase shift keying (PSK) -OFDM transmission scheme is used. Generating a WUR packet by adding a separate OOK modulator for OOK modulation has a disadvantage of increasing an implementation cost of a transmitter. Therefore, a method of generating a OOK modulated WUR packet by reusing an OFDM transmitter will be described.

According to the OOK modulation scheme, bit value 1 is modulated into a symbol (i.e., on) having a power above a threshold, and bit value 0 is modulated into a symbol (i.e., off) having a power below a threshold. Of course, it is also possible to define bit value 1 as power off.

As described above, in the OOK modulation scheme, a bit value 1/0 is indicated through on / off of power at a corresponding symbol position. Such a simple OOK modulation / demodulation scheme has an advantage of reducing power consumption and cost for realizing the signal detection / demodulation of the receiver. In addition, OOK modulation for turning on / off a signal may be performed by reusing an existing OFDM transmitter.

The left graph of FIG. 15 shows real parts and imaginary parts of normalized amplitude during one symbol period (eg, 4 usec) for OOK modulated bit value 1 by reusing the OFDM transmitter of the existing WLAN. (imaginary) shows the part. Since the OOK modulation result for the bit value 0 corresponds to power off, illustration is omitted.

The right graph of FIG. 15 shows normalized power spectral density (PSD) in the frequency domain for OOK modulated bit value 1 by reusing an OFDM transmitter of an existing WLAN. For example, a center 4 MHz in that band may be used for the WUR. In FIG. 15, it is assumed that the WUR operates with a 4 MHz bandwidth. For convenience of description, a frequency bandwidth of another size may be used. However, it is preferable to operate the WUR with a bandwidth smaller than that of the PCR (e.g., existing wireless LAN) 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 an existing OFDM transmitter, an input sequence of an inverse fast Fourier transform (IFFT) is defined as s = {13 subcarrier tone sequence}, and IFFT of the corresponding sequence s is performed as X _t = IFFT (s), and a length of 0.8 usec is used. CP (cyclic prefix) adds 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., WUR beacon) or a packet for unicast (e.g., a packet for terminating and waking up the WUR mode of a specific WUR STA).

16 illustrates the structure of a WURx (WURx). Referring to FIG. 16, the WURx may include an 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.

Hereinafter, a WLAN STA having a WUR receiver will be referred to simply as a WUR STA.

WUR  preamble

As described above, on off keying modulation (OOK) may be used for the WUR PPDU transmitted to wake up the PCR. For example, the WUR PPDU may include a WUR preamble and WUR data, but is not limited thereto. The WUR PPDU may include a control field. For example, the WUR PPDU may include a WUR preamble, a WUR control field, and a WUR payload. The WUR preamble may include a sync part and a physical layer (PHY) header.

Hereinafter, embodiments of a WUR preamble sequence for synchronization will be described.

For example, the WUR preamble may be configured by repeatedly repeating the same symbol or by repeating the same sequence within one symbol in order to time-synchronize the WUR packet. More specifically, assuming that the length of one symbol is 4 us, the WUR preamble may be configured by repeating the same 4us symbol, or a small sub-symbol size in one 4 us symbol may be repeated. Alternatively, the WUR preamble may be configured by repeating the sub-symbols several times.

For robust transmission, the WUR preamble may be transmitted using a symbol length longer than 4 us symbol length. For example, one symbol of the WUR preamble may have a length of 8 us, 16 us, and the like, but is not limited thereto.

In consideration of the fact that the WUR signal is transmitted using the OOK modulation scheme, the WUR preamble may correspond to a structure in which the ON sequence is repeatedly transmitted. For example, the synchronization sequence in the WUR preamble for synchronization may be configured by repeating the On symbol.

Example 1

For example, both the WUR preamble part and the WUR data part (e.g., WUR payload) constituting the WUR PPDU may be transmitted based on OOK modulation. In this case, the same frequency sequence may be used to generate the WUR preamble and the OOK symbol for data transmission. For example, the frequency sequence for generating the OOK symbol of the WUR preamble may be the same as the frequency sequence for generating the OOK symbol of the WUR data.

When the OOK symbol generated using the same frequency sequence is used for the WUR preamble and the WUR payload, and both the end of the WUR preamble and the start of the WUR payload are on symbols, the STA cannot know the end of the WUR preamble because the STA cannot know the end of the WUR preamble. It is difficult to accurately measure the synchronization of packets. Therefore, a solution for such a problem is required.

The STA can measure the time synchronization offset through auto-correlation / cross-correlation. In this case, to distinguish between the WUR preamble and the WUR payload, the frequency sequence of the ON symbol corresponding to the last repetition symbol or the last sub symbol of the WUR preamble may be changed in phase or set as a complementary sequence.

In addition, in order to clearly show the difference in self-correlation / cross-correlation, two symbols or sub-symbols set in a phase shift or complementary sequence may be placed at the end of the WUR preamble.

In addition, when the sequence of the WUR preamble is all set to the on symbol, the sequence of the WUR preamble may be set as shown in FIG. 17 so that the difference in self-correlation / cross-correlation can be clearly shown.

Referring to FIG. 17, the sequence of the WUR preamble is set to P P P P P P. Where P is a OOK On symbol and -P represents a OOK on symbol or a symbol with negative magnitude. For example, the last symbol of the WUR preamble sequence may be set to a bipolar symbol of on symbol. That is, if the on symbol is 1, the last symbol of the WUR preamble sequence is set to -1. Therefore, the last symbol of the WUR preamble sequence is set to a symbol representing a loudness when performing correlation.

As another example, phase rotation may be performed on the last symbol of the sequence of the WUR preamble as shown in FIG. 18. The phase rotation value may be, for example, π / 4, π / 1 or π.

Example 2

As another example, to distinguish between the WUR preamble part and the WUR payload part, a frequency sequence used for the OOK on symbol may be set differently in the WUR preamble part and the WUR payload part.

19 illustrates a WUR preamble part and a WUR payload part according to an embodiment of the present invention. In FIG. 19, A represents a frequency sequence corresponding to a OOK on symbol in the WUR preamble part, and B represents a frequency sequence corresponding to a OOK on symbol in the WUR data part. 0 represents a frequency sequence corresponding to the OOK off symbol.

At this time, A and B are more preferable as the orthogonal characteristics appear larger. For example, if the correlation operation becomes 0 for A and B, it is easy for the STA to distinguish between the WUR preamble and the WUR data.

For example, in the case of the WUR preamble part, a sequence having good self-correlation / cross-correlation property is preferably used for synchronization. For example, a OOK on symbol of the WUR preamble part may be generated using the CAZAC, Zadoff-Chu, and Golay sequences. However, since the WUR payload part does not require a separate STA operation for additional time synchronization, a sequence in which signals are easily detected unlike the WUR preamble sequence, for example, a bipolar sequence is a OOK on symbol of the WUR payload. Can be used for production.

As such, when different sequences are used for the on symbols of the WUR preamble part and the WUR data part, the STA performs autocorrelation for time synchronization even if both the last symbol of the WUR preamble part and the start symbol of the WUR data part are on symbols. You can see the difference between the two parts. Therefore, the timing error due to the data part can be reduced.

Example 3

According to an embodiment of the present invention, a cyclic shift (CS) may be applied in terms of time with respect to the last on symbol of the WUR preamble.

In addition, the CS may be applied to a plurality of symbols (e.g., two symbols) so that the STA can clearly distinguish the WUR preamble and the WUR payload when performing the self / cross correlation.

In addition, when CS is applied to a plurality of symbols, the CS value applied to each symbol may be different.

20 illustrates a WUR preamble part and a WUR payload part according to an embodiment of the present invention. In FIG. 20, when the CS value is 2 in the last symbol of the WUR preamble part in time, the last OOK on symbol may be shifted by 2 in time.

The present invention is not limited to CS in terms of time, and according to another embodiment, CS may be applied for on symbol of a WUR preamble in frequency.

On the other hand, the sequence configuration of Examples 1 to 3 described above can be equally applied to the case where the WUR preamble of the WUR PPDU is composed of a sequence for synchronization and a control field (e.g., PHY header or signature sequence). By setting the WUR sync sequence according to the above-described embodiment, the STA can distinguish the end of the sync sequence from the start of the control field in the WUR preamble, and thus can accurately measure the timing offset.

As another example, the information field that comes first of the control field may be started with an off symbol so that the synchronization sequence and the control field can be more clearly distinguished.

For example, when the synchronization sequence of the WUR preamble is set to P P P P... P-P as shown in FIG. 17, the off symbol may be added immediately before the start of the control field or the control field may start with the Off symbol. However, when the control field starts with an off symbol, the size of information that can be transmitted in the control field may be restricted. For example, the number of off symbols may be one, and the present invention is not limited thereto.

Meanwhile, examples of Examples 1 to 3 described above are separately described for convenience of description, but each example does not necessarily constitute an independent invention, and two or more examples may be combined within a range not conflicting with each other.

21 illustrates a flow of a WUR packet transmission / reception method according to an embodiment of the present invention. Descriptions overlapping with those described above may be omitted, and the rights of the present invention are not limited to the embodiment of FIG. 21.

Referring to FIG. 21, the STA enters a WUR mode (2110). For example, the STA can turn off PCR and enter WUR mode. The STA may acquire parameters required for WUR mode operation from the AP through PCR before entering the WUR mode.

The AP generates a WUR packet (2115). The WUR packet may be for PCR wake-up of the STA or may be a WUR beacon transmitted periodically, but is not limited thereto. The WUR packet may include a WUR preamble sequence and a WUR payload. The WUR preamble sequence may have a number of on-off keying (OOK) on symbols.

The AP transmits a WUR packet to the station STA that includes the WUR preamble sequence and the WUR payload (2120). The WUR packet may be transmitted in a unicast method, a broadcast method, or a multicast method according to the type of the corresponding WUR packet.

The STA performs synchronization on the WUR packet based on the WUR preamble sequence included in the WUR packet (2125).

The STA decodes the WUR packet based on the synchronization result (2130).

Meanwhile, according to an embodiment of the present invention, the WUR preamble sequence may include a synchronization sequence and a control field. At this time, between the end of the synchronization sequence and the start of the control field, a OOK off symbol for distinguishing the synchronization sequence and the control field may be set. For example, the number of OOK off symbols set between the end of the synchronization sequence and the start of the control field may be one. The control field may correspond to a PHY header or a signature sequence for indicating a WUR data rate and the like, but is not limited thereto.

In addition, among the OOK on symbols included in the WUR preamble sequence, a phase rotation is applied to the last N symbols located immediately before the WUR payload, or the last N symbols are negative when correlation is performed. It may be set to bipolar symbols representing magnitude. For example, the phase rotation applied to the last N symbols may be π / 4, π / 2 or π.

In addition, the first frequency sequence used to generate the plurality of OOK on symbols of the WUR preamble sequence and the second frequency sequence used to generate the OOK on symbol symbols of the WUR payload may be different from each other. For example, the first frequency sequence may correspond to a CAZAC sequence, a Zadoff-Chu sequence, or a Golay sequence, and the second frequency sequence may correspond to a bipolar sequence. Can be.

In addition, a cyclic shift may be applied to the last N symbols located immediately before the WUR payload among the plurality of OOK on symbols included in the WUR preamble sequence. For example, different cyclic shift values may be applied to each of the last N symbols.

FIG. 22 is a diagram for describing an apparatus for implementing the method as described above.

The wireless device 100 of FIG. 22 may correspond to a specific STA of the above-described description, and the wireless device 850 may correspond to the AP of the above-described description.

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

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 include read-only memory (ROM), random access memory (RAM), flash memory, memory cards, storage media and / or other storage units. When an embodiment is executed by software, the method described above can be executed as a module (eg, process, function) that performs the functions described above. The module may be stored in the memories 120 and 170 and may be executed by the processors 110 and 160. The memories 120 and 170 may be disposed inside or outside the processes 110 and 160, and may be connected to the processes 110 and 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 is configured to receive a main connection radio (eg, WLAN) receiver and a WUR signal for receiving a main connection radio (eg, IEEE 802.11 a / b / g / n / ac / ax, etc.) signal. It may include a WUR receiver. The transmitter of the STA may include a primary connected radio transmitter for transmitting the primary 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 an OFDM transmitter. The AP may transmit the WUR payload by the OOK scheme by reusing the OFDM transmitter. For example, as described above, the AP may OOK modulate the WUR payload through an OFDM transmitter.

The detailed description of the preferred embodiments of the invention disclosed as described above is provided to enable any person skilled in the art to make and practice the invention. Although the above has been described with reference to a preferred embodiment of the present invention, those skilled in the art will understand that the present invention can be variously modified and changed from the above description. Thus, 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 (15)

1. In a WLAN system, an access point (AP) transmits a wake up radio (WUR) packet,

   Generating a WUR preamble sequence having a plurality of on-off keying (OOK) on symbols; And

   Transmitting a WUR packet including the WUR preamble sequence and a WUR payload to a station (STA),

   The WUR preamble sequence includes a synchronization sequence and a control field,

   A OOK off symbol for distinguishing the sync sequence from the control field is set between the end of the sync sequence and the start of the control field.
2. The method of claim 1,

   And the number of the OOK off symbols set between the end of the synchronization sequence and the start of the control field is one.
3. The method of claim 1,

   Phase rotation is applied to the last N symbols located immediately before the WUR payload among the plurality of OOK on symbols included in the WUR preamble sequence, or when the last N symbols are correlated. WUR packet transmission method, which is set with bipolar symbols representing loudness.
4. The method of claim 3, wherein

   Wherein the phase rotation applied to the last N symbols is [pi] / 4, [pi] / 2 or [pi].
5. The method of claim 1,

   Wherein the first frequency sequence used to generate the plurality of OOK on symbols of the WUR preamble sequence and the second frequency sequence used to generate the OOK on symbol symbols of the WUR payload sequence are different from each other.
6. The method of claim 5, wherein

   The first frequency sequence corresponds to a CAZAC sequence, a Zadoff-Chu sequence, or a Golay sequence,

   The second frequency sequence corresponds to a bipolar sequence.
7. The method of claim 1,

   A cyclic shift is applied to the last N symbols located immediately before the WUR payload among the plurality of OOK on symbols included in the WUR preamble sequence.
8. The method of claim 7, wherein

   WRC packet transmission method, wherein different cyclic shift values are applied to each of the last N symbols.
9. In an access point (AP) for transmitting a wake up radio (WUR) packet,

   A processor for generating a WUR preamble sequence having a plurality of on-off keying (OOK) on symbols; And

   A transmitter for transmitting a WUR packet including the WUR preamble sequence and a WUR payload to a station under control of the processor,

   The WUR preamble sequence includes a synchronization sequence and a control field,

   An OOK off symbol is set between the end of the sync sequence and the start of the control field to distinguish the sync sequence from the control field.
10. In a method for receiving a WUR (wake up radio) packet from a station (STA) in a WLAN system,

    Receiving a WUR packet comprising a WUR preamble sequence and a WUR payload; And

    Performing synchronization on the WUR packet based on a plurality of on-off keying (OOK) on symbols included in the WUR preamble sequence,

    The WUR preamble sequence includes a synchronization sequence and a control field,

    Between the end of the synchronization sequence and the start of the control field, a OOK off symbol for distinguishing the synchronization sequence and the control field is set.
11. The method of claim 10,

    A phase rotation of π / 4, π / 2 or π is applied to the last N symbols located immediately before the WUR payload among the plurality of OOK on symbols included in the WUR preamble sequence, or N symbols are set to bipolar symbols representing a loudness when performing correlation.
12. The method of claim 10,

    And a first frequency sequence used for the plurality of OOK on symbols of the WUR preamble sequence and a second frequency sequence used for the OOK on symbol symbols of the WUR payload are different from each other.
13. The method of claim 12,

    The first frequency sequence corresponds to a CAZAC sequence, a Zadoff-Chu sequence, or a Golay sequence,

    The second frequency sequence corresponds to a bipolar sequence.
14. The method of claim 10,

    A cyclic shift is applied to the last N symbols located just before the WUR payload among the plurality of OOK on symbols included in the WUR preamble sequence.
15. The method of claim 14,

    WRC packet reception method, wherein different cyclic shift values are applied to each of the last N symbols.

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