WO2018151432A1 - Method for transmitting or receiving wake-up radio frame in wireless lan system, and device therefor - Google Patents

Abstract

A method by which an access point (AP) transmits a wake-up radio (WUR) frame in a wireless LAN (WLAN) system, according to one embodiment of the present invention, comprises the steps of: determining, on the basis of a pseudo noise (PN) sequence in a time domain, on/off of multiple on-off keying (OOK) symbols to be included in a WUR preamble; mapping the PN sequence to tones of respective on symbols among the multiple OOK symbols in a frequency domain; and transmitting the WUR frame including the WUR preamble, wherein all of the length of the PN sequence, the number of multiple OOK symbols, and the number of tones in which the WUR preamble is transmitted are set to be the same, and the PN sequence is a binary sequence including multiple bits, and the OOK symbol corresponding to a bit having a value of one in the binary sequence can be determined as an on symbol.

Description

Method for transmitting or receiving wake-up radio frame 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 frame through a wake up radio (WUR) to wake up a primary connectivity radio (PCR).

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.

An object of the present invention is to provide a method and apparatus therefor for more accurately and efficiently transmitting or receiving a WUR frame including a WUR preamble.

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-described technical problem, the access point (AP) transmits a WUR (wake up radio) frame, in the time domain to the PN (pseudo noise) sequence Determining on / off of the plurality of on-off keying (OOK) symbols to be included in the WUR preamble based on the; Mapping the PN sequence to tones of each on symbol of the plurality of OOK symbols in a frequency domain; And transmitting a WUR frame including the WUR preamble, wherein the length of the PN sequence, the number of the plurality of OOK symbols, and the number of tones to which the WUR preamble is transmitted are equally set. Is a binary sequence including a plurality of bits, and a OOK symbol corresponding to a bit having a value of 1 in the binary sequence may be determined as an on symbol.

According to another aspect of the present invention, an access point (AP) for transmitting a wake up radio (WUR) frame includes a plurality of on-off keyings (OOKs) to be included in a WUR preamble based on a pseudo noise (PN) sequence in a time domain. A processor that determines on / off of symbols and maps the PN sequence to tones of each on symbol of the plurality of OOK symbols in a frequency domain; And a transmitter for transmitting a WUR frame including the WUR preamble under control of the processor, wherein the length of the PN sequence, the number of the plurality of OOK symbols, and the number of tones to which the WUR preamble is transmitted are the same. The PN sequence is set to be a binary sequence including a plurality of bits, and a OOK symbol corresponding to a bit having a value of 1 in the binary sequence may be determined as an on symbol.

The OOK symbol corresponding to the bit having a zero value in the binary sequence is determined as an off symbol, and all zeros may be mapped to the tones of the off symbol.

The WUR preamble having the plurality of OOK symbols with the PN sequence or zero mapped in the frequency domain according to on / off may be transmitted through an orthogonal frequency divisional multiplex (OFDM) transmitter.

The PN sequence may be set differently for each BSS based on the identifier of the AP or the basic service set (BSS) color, or the PN sequence may be set differently for each STA based on an association identifier (API) or a partial AID (PAID). Can be.

The PN sequence may be assigned through an association procedure or a capability negotiation procedure on a primary connectivity radio (PCR).

The WUR frame may further include at least one measurement symbol that provides a criterion for the WUR STA receiving the WUR frame to determine on / off of each of the plurality of OOK symbols.

The at least one measurement symbol is all set to an on symbol and may be located before the WUR preamble.

According to an embodiment of the present invention, not only can the WUR preamble be generated by using the same PN sequence in the time domain and the frequency domain, but also time synchronization for the WUR frame can be performed accurately and efficiently.

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.

Figure 17 shows the frame format of the WUR signal to wake up the PCR.

18 illustrates a WUR frame according to another embodiment of the present invention.

19 shows a WUR preamble according to an embodiment of the present invention.

20 shows a flow of a WUR frame transmission and reception method according to an embodiment of the present invention.

21 is a view 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 setup 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, the STA 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.

Sensing behavior of the STA

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 in 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 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.

Wake-Up Radio (WUR)

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. 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 a symbol (ie, on) in which any power in a symbol is loaded or has a power above a threshold, and bit value 0 is a symbol in which no power in the symbol is loaded or has a power below a threshold. modulated to (ie, off). 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

Hereinafter, a method of configuring a preamble of a WUR PPDU and a method of performing time synchronization will be described.

As described above, the proposed WUR signal is generated through OOK modulation to reduce the reception power consumption of the receiver and is transmitted using an OFDM transmitter using only some tones in the available band.

Since the WUR frame for waking the PCR is transmitted with a symbol power of 0 or 1 based on OOK modulation, it is difficult to perform time synchronization using L-STF / L-LTF as in the past.

Accordingly, an embodiment of the present invention proposes a method for reducing a timing offset in a receiver when transmitting a WUR signal using OOK modulation.

Figure 17 shows the frame format of the WUR signal to wake up the PCR.

Referring to FIG. 17, the WUR frame includes an L-Part before the WUR part for coexistence with PCR (e.g., legacy WLAN). The WUR part may include a WUR-preamble, a WUR-SIG, and a WUR-body. The WUR-Body may include control information rather than user data for the WUR STA.

The L-PART is for a third party STA (e.g., PCR STA), not a WUR receiver, and the WUR receiver may not decode the L-part.

The WUR part may be transmitted in narrow bandwidth on some of the available tones included in the band in which the L-part is transmitted. For example, the narrow band may be any one of 1,2,4,8,10 MHz. When OFDM numerology of 11a is used, narrowband 1,2,4,8,10 MHz correspond to 4,8,13,26,32 tones, respectively, and the length of the frequency sequence constituting the WUR ON symbol is each tone. May be equal to As another example, when the 11x numerology is used, the narrow bands 1,2,4,8,10 MHz correspond to 13, 26, 52, 103, and 128 tones, respectively.

Threshold for Envelop Detection

The WUR receiver may detect the OOK modulated WUR signal through envelope detection (ED) of the received signal. According to an embodiment of the present invention, symbols of the WUR preamble may be used to set a threshold for envelop detection of a received signal.

(i) As an example, the measurement symbol s for measuring the received signal may be additionally inserted into the WUR preamble. In order to accurately measure the power of the received signal, the measurement symbols s may all be set as OOK on symbols. In addition, the added measurement symbol may be used not only to measure the received signal but also to additionally indicate other information. For example, when the added measurement symbol is 6-symbol, BSS color information (i.e. 6-bit) may be transmitted through the corresponding symbols.

(ii) As another example, the measurement may be performed using symbols of the preamble designed for timing synchronization and packet detection without inserting additional symbols into the preamble. If the OFF symbol is present in the preamble, the measurement performance may be degraded due to the OFF symbol. To compensate for this, the measurement may be performed only through successive ON symbols in the preamble sequence.

(iii) As another example, similarly to (ii), the symbol of the preamble is used for the measurement, but in order to prevent the WUR STA from measuring the Off symbol, the WUR STA may measure the threshold using only symbols corresponding to a predetermined order. . For example, when the 9-bit preamble sequence is transmitted and the position of the measurement symbol is the 1st, 4th, and 7th symbols, the preamble sequence may be set so that the corresponding symbol does not become an OFF symbol. For example, the preamble sequence may be set such that the preamble sequence does not have 0 in 1, 4, and 7th as [1 1 0 1 0 1 1 1 0].

Meanwhile, the threshold measurement method of the present invention is not limited to the frame structure of FIG. 17, and the threshold value may be measured using another frame structure.

18 illustrates a WUR frame according to another embodiment of the present invention.

Referring to FIG. 18, a symbol for setting a threshold value for distinguishing whether information of a received signal is 1 or 0 may be transmitted before the WUR preamble.

That is, the OOK symbol s for setting the WUR ED threshold may be transmitted before the WUR preamble in order to set the threshold for WUR ED (envelop detection). The number of OOK symbols for setting the WUR ED threshold may be two or more. In addition, all of the OOK symbols for setting the WUR ED threshold may be OOK ON symbols.

As another example, a OOK symbol for setting the WUR ED threshold shown in FIG. 18 may be included in the WUR preamble. For example, the OOK symbol for setting the WUR ED threshold is located at the head of the WUR preamble, and the preamble sequence may be divided into a sequence for measurement and a preamble sequence for synchronization and packet detection.

The present invention is not limited to a method of transmitting a symbol by adding a part for measuring a threshold value as shown in FIG. 18 or by adding corresponding sequence information to a preamble. As described above, for example, the measurement may be performed only with the preamble without additional symbols. Some or all of the preamble symbols may be used to measure the received signal. Alternatively, the measurement may be performed using only specific symbols of the preamble. In this case, a sequence may be set such that the corresponding symbol becomes a OOK on symbol.

● Sequence for WUR  preamble

17 and / or 18, the WUR preamble may be set to a known sequence for time synchronization of the WUR signal. According to the OOK modulation characteristic, the preamble may be configured with the number of symbols corresponding to the sequence length.

In the following examples of the preamble, a description of a symbol for threshold measurement is omitted, but a symbol for threshold measurement may be set before or after the WUR preamble proposed for time synchronization.

 As a known sequence for the WUR preamble configuration, a fixed sequence may be used regardless of a broadcast / multicast / unicast transmission scheme or another sequence may be used depending on the transmission scheme. If a fixed sequence is used, the implementation is simple, but overhead for an indication of a transmission scheme may occur. When different sequences are used according to the transmission scheme, the WUR receiver may determine whether the WUR frame received through the WUR preamble is a broadcast / multicast / unicast scheme. In this case, overhead may be reduced since it is not necessary to transmit additional information to indicate whether the broadcast / multicast / unicast method is used.

When the preamble is configured using the known sequence, the WUR preamble may be transmitted as follows.

(i) in the frequency domain PN  code / Sequence  To Configure Known Sequences in the Time Domain

According to the bandwidth used in the frequency domain, a signal corresponding to 4,8,13,16,26,32 tones may be transmitted in one WUR symbol. In this case, the information carried on the tones may correspond to a pseudo noise (PN) sequence. For example, the length of the PN sequence may be equal to the number of available tones. If the number of available tones is 13, the length of the PN sequence may also be 13.

As a specific example, a known sequence (WPS, Preamble Sequence) for the WUR preamble is [1 1 1 0 1 0 1] in the time domain and a PN sequence of length 13 in the frequency domain is [1 0 1 1 0 1 0 0 1 1 1 0 1]. In this case, the signal carried in the preamble symbol k in the frequency domain may be represented by PS (k) * PN code. For example, the length of the entire sequence may correspond to 7 * 13 = 91. For convenience of explanation, it is assumed that PS is a binary code, but this is only an example. 1/0 of the binary code may be replaced with -1/1.

A WUR receiver receiving a WUR preamble transmitted by applying a predetermined PN sequence to a random PS performs cross correlation using a PN sequence and a received signal that are already known about a symbol corresponding to a length of the preamble. Timing synchronization can be performed.

In this case, the WUR receiver takes a cross correlation instead of auto correlation for the received signal for timing synchronization because of the following characteristics of the PN_sequence.

Tx: Tx_seq = Data * PN_seq

Rx: Tx_seq * PN_seq = Data * PN_seq * PN_seq = Data

When each PN_seq is multiplied with each other for a certain period of time, 1 appears only when the same PN_seq is multiplied by each other.

Accordingly, the WUR receiver may perform time synchronization by windowing the length of the preamble with respect to the received signal and performing cross correlation with the PN_sequence corresponding to the window size for each window.

(ii) same in time domain and frequency domain PN In sequence  How to use

In the above (i) example, the frequency sequences for the PS and the OOK on symbols are set differently, but in the present embodiment, the PS may be set to be the same as the PN sequence. For example, the lengths of the PS and PN sequences are the same, and the number of available tones for transmitting the WUR signal is the same as the length of the PN sequence. As such, one PN sequence may be applied to both the time domain and the frequency domain of the WUR preamble.

19 shows a WUR preamble according to an embodiment of the present invention.

Referring to FIG. 19, the WUR preamble consists of the same number of symbols as the length of a predetermined PN seq. The information carried in each symbol in the frequency domain is obtained by multiplying the bit value of PN_seq of the symbol by PN_seq, and the obtained information is mapped to each tone.

The WUR receiver receiving the WUR preamble configured through the above method performs cross correlation between the received signal and the PN sequence using a known PN sequence, and performs timing synchronization based on the cross correlation result.

Meanwhile, different PN sequences may be used according to transmission modes, or different PN sequences may be used for each BSS. As an example, different PN sequences may be determined for each BSS using BSS color and / or AP ID.

In addition, different PN sequences may be used for each STA in order to reduce the influence of interference due to transmission of several WUR frames within one BSS. The PN sequence may be assigned when the STA associates with the AP or when performing capability negotiation. For example, the PN sequence allocated to each STA may be determined by AID or P-AID.

20 illustrates a flow of a WUR frame transmission method according to an embodiment of the present invention. Descriptions overlapping with the above description may be omitted.

Referring to FIG. 20, the AP determines on / off of a plurality of on-off keying (OOK) symbols to be included in a WUR preamble based on a pseudo noise (PN) sequence in the time domain (2005).

The AP maps the PN sequence to tones of each on symbol of the plurality of OOK symbols in the frequency domain (2010).

The AP transmits a WUR frame including the WUR preamble (2015).

The length of the PN sequence, the number of OOK symbols, and the number of tones to which the WUR preamble is transmitted may all be set the same. The PN sequence is a binary sequence including a plurality of bits, and a OOK symbol corresponding to a bit having a value of 1 in the binary sequence may be determined as an on symbol.

A OOK symbol corresponding to a bit having a zero value in a binary sequence is determined as an off symbol, and all zeros may be mapped to tones of the off symbol.

A WUR preamble having a PN sequence or a number of OOK symbols mapped to 0 in the frequency domain according to on / off may be transmitted through an orthogonal frequency divisional multiplex (OFDM) transmitter.

The PN sequence may be set differently for each BSS based on an identifier of an AP or a basic service set (BSS) color, or the PN sequence may be set differently for each STA based on an association identifier (AID) or a partial AID (PAID).

The PN sequence may be assigned through an association procedure or a capability negotiation procedure on a primary connectivity radio (PCR).

The WUR frame may further include at least one measurement symbol that provides a criterion for the WUR STA receiving the WUR frame to determine on / off of each of the plurality of OOK symbols.

At least one measurement symbol is all set to an on symbol and may be located before the WUR preamble.

In the above description, the WUR part includes a WUR preamble part and a control information part, and it has been described that the L-Part for PCR is included before the WUR part, but terms according to embodiments of the present invention are referred to by different names. May be For example, the WUR preamble part may be referred to as a WUR sync field, and the control information part may also be referred to as a WUR data field. In addition, the entirety including the WUR sync field and the L-Part (i.e., non-WUR part) for PCR may be referred to as a preamble.

In addition, multiple data rates may be supported for WUR frames. For example, data rates of 62.5 kbps and 250 kbps can be supported in the WUR frame. The data rate actually used may be indicated via a synchronization sequence. For example, a data rate of 62.5 kbps may be used when the first sync sequence is used, and a data rate of 250 kbps may be used when the second sync sequence is used. As such, a plurality of WUR sync sequences may be supported.

21 is a view for explaining an apparatus for implementing the method as described above.

The wireless device 100 of FIG. 21 may correspond to a specific STA of the above description, and the wireless device 850 may correspond to the AP of the above 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 may include a main connected radio receiver for receiving a main connected radio signal (eg, a wireless LAN such as IEEE 802.11 a / b / g / n / ac / ax) and a WUR receiver for receiving a WUR signal. have. 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 (14)

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

   Determining on / off of a plurality of on-off keying (OOK) symbols to be included in the WUR preamble based on a pseudo noise (PN) sequence in the time domain;

   Mapping the PN sequence to tones of each on symbol of the plurality of OOK symbols in a frequency domain; And

   Transmitting a WUR frame including the WUR preamble,

   The length of the PN sequence, the number of the plurality of OOK symbols, and the number of tones to which the WUR preamble is transmitted are all set equal.

   The PN sequence is a binary sequence including a plurality of bits, wherein a OOK symbol corresponding to a bit having a value of 1 in the binary sequence is determined as an on symbol.
2. The method of claim 1,

   The OOK symbol corresponding to the bit having a zero value in the binary sequence is determined to be an off symbol, and all zeros are mapped to the tones of the off symbol.
3. The method of claim 2,

   And the WUR preamble having the PN sequence or the plurality of OOK symbols mapped to 0 in the frequency domain on / off is transmitted via an orthogonal frequency divisional multiplex (OFDM) transmitter.
4. The method of claim 1,

   The PN sequence is set differently for each BSS based on the identifier or basic service set (BSS) color of the AP, or

   The PN sequence is configured differently for each STA based on an association identifier (AID) or a partial AID (PAID).
5. The method of claim 4, wherein

   Wherein the PN sequence is assigned via an association procedure or a capability negotiation procedure on a primary connectivity radio (PCR).
6. The method of claim 1,

   The WUR frame further comprises at least one measurement symbol that provides a criterion for the WUR STA receiving the WUR frame to determine on / off of each of the plurality of OOK symbols.
7. The method of claim 6,

   And the at least one measurement symbol is all set to an on symbol and is located before the WUR preamble.
8. In an access point (AP) for transmitting a wake up radio (WUR) frame,

   Determine on / off of a plurality of on-off keying (OOK) symbols to be included in the WUR preamble based on a pseudo noise (PN) sequence in the time domain, and each of the plurality of OOK symbols in the frequency domain A processor for mapping the PN sequence to tones of on symbols; And

   A transmitter for transmitting a WUR frame including the WUR preamble according to control of the processor,

   The length of the PN sequence, the number of the plurality of OOK symbols, and the number of tones to which the WUR preamble is transmitted are all set equal.

   The PN sequence is a binary sequence including a plurality of bits, wherein an OOK symbol corresponding to a bit having a value of 1 in the binary sequence is determined as an on symbol.
9. The method of claim 8,

   The OOK symbol corresponding to the bit having a zero value in the binary sequence is determined to be an off symbol, and all zeros are mapped to tones of the off symbol.
10. The method of claim 9,

    And the transmitter corresponds to an orthogonal frequency divisional multiplex (OFDM) transmitter.
11. The method of claim 8,

    The PN sequence is set differently for each BSS based on the identifier or basic service set (BSS) color of the AP, or

    The PN sequence is set differently for each STA based on an association identifier (AID) or a partial AID (PAID).
12. The method of claim 11,

    Wherein the PN sequence is assigned via an association procedure or a capability negotiation procedure on a primary connectivity radio (PCR).
13. The method of claim 8,

    The WUR frame further includes at least one measurement symbol that provides a criterion for the WUR STA receiving the WUR frame to determine on / off of each of the plurality of OOK symbols.
14. The method of claim 13,

    Wherein the at least one measurement symbol is set to all on symbols and is located before the WUR preamble.

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