WO2018124498A1 - Method for transmitting or receiving wake up radio frame in wireless lan system and apparatus 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: a step for generating a WUR frame including a WUR preamble part and a control information part on the basis of an on-off keying (OOK) method; and a step for transmitting the WUR frame generated on the basis of the OOK method, wherein a last symbol among a plurality of symbols, which are included in the WUR preamble part, is set as an off symbol so as to distinguish the WUR preamble part and the control information part, and a synchronization sequence for the WUR frame can be repetitively transmitted, in a time domain, at least twice on predetermined symbols located prior to the off symbol of the WUR preamble part.

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, a method of transmitting an WUR frame by an access point (AP) is based on an on-off keying (OOK) scheme. Generating a WUR frame including a WUR preamble part and a control information part; And transmitting the WUR frame generated based on the OOK scheme, wherein a last symbol of the plurality of symbols included in the WUR preamble part is turned off to distinguish the WUR preamble part and the control information part. off), and the predetermined sequence located before the off symbol of the WUR preamble part, the synchronization sequence for the WUR frame may be repeatedly transmitted at least two times in the time domain.

According to another aspect of the present invention, an access point (AP) for transmitting a WUR frame includes a WUR preamble part and a control information part based on an on-off keying (OOK) scheme. A processor for generating a WUR frame comprising a; And a transmitter for transmitting the WUR frame generated based on the OOK scheme according to the control of the processor, wherein the plurality of symbols included in the WUR preamble part to distinguish the WUR preamble part and the control information part. The last symbol is set to an off symbol, and the synchronization sequence for the WUR frame may be repeatedly transmitted at least twice in the time domain on predetermined symbols located before the off symbol of the WUR preamble part.

In another aspect of the present invention, a method for receiving a WUR frame by a station in a WLAN system is based on a WUR preamble part of a WUR frame. Performing time synchronization and packet detection on the WUR frame; And decoding a control information part of the WUR frame based on an on-off keying (OOK) method, wherein a plurality of symbols included in the WUR preamble part to distinguish the WUR preamble part and the control information part The last symbol is set to an off symbol, and the synchronization sequence for the WUR frame may be repeatedly received at least twice in the time domain on predetermined symbols located before the off symbol of the WUR preamble part. .

According to another aspect of the present invention, a station (STA) apparatus for receiving the above-described WUR frame may be provided.

The number of repetitive transmissions of the synchronization sequence may be greater than the total number of the predetermined symbols. For example, the predetermined symbols are two 4 us symbols, and if the length of the sync sequence is 0.8 us, the number of repetitive transmissions of the sync sequence is 10, and if the length of the sync sequence is 1.8 us, the repeat of the sync sequence The number of transmissions may be five.

One symbol length in the WUR preamble part may be set to 0.8 us, 1.6 us or 2 us, and one symbol length in the control information part may be set to 4 us.

The last N symbols including the off symbol in the WUR preamble part may have a preset on-off pattern for packet detection for the WUR frame.

The WUR preamble part further includes a signal strength measurement part that provides a reference for on-off determination of each symbol when performing envelope detection on the control information part, and all of the at least one symbol included in the signal strength measurement part It can be set to an on symbol.

The control information part includes a first field having first control information and a first cyclic redundancy check (CRC) and a second field having second control information and a second CRC, wherein the first control information includes a BSS color. The second control information includes a single-user (SU) / multi-user (MU) indicator, a downlink (DL) / uplink (UL) indicator, a station ID, a bandwidth, a transmission opportunity duration, a WUR frame. It may include at least one of the number of symbols and the length of the WUR frame.

According to an embodiment of the present invention, the last symbol of the WUR preamble part is set to the OOK off symbol so that the WUR preamble part can be clearly distinguished from the control information part in the WUR frame, and the synchronization sequence is repeatedly transmitted in the WUR preamble part. This allows time synchronization for the WUR frame to be performed accurately.

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 frame structure according to an embodiment of the present invention.

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

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

20 illustrates a control information part included in a WUR frame according to an embodiment of the present invention.

21 is a flowchart illustrating a WUR frame transmission and 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 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 a 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. 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

Hereinafter, a structure of a WUR frame (i.e., WUR PPDU) for transmitting a WUR signal will be described. As mentioned above, the WUR frame may include an L-part (e.g., L-STF, L-LTF, L-SIG) for coexistence with legacy STAs operating in the same band. The legacy STA may perform packet detection and WUR frame protection through L-part reception. Since the L-part is a part for the legacy STA, the WUR STA may bypass the L-part.

Example 1

The WUR frame may include a WUR preamble and a control information part. For example, the same OOK symbols as the data part (eg, a OOK symbol generated in the same manner as the OOK symbol of the data part) may be set in the WUR preamble part, and the WUR preamble part may include a training symbol for time synchronization and packet detection. (s) (eg, two OOK ON symbols) and one OOK OFF symbol.

If the same symbol is repeatedly transmitted in the WUR preamble (eg, two repeated transmissions of the same OOK ON symbol), the WUR STA performs correlation (eg, auto / cross correlation) on the symbol repeatedly transmitted while receiving the WUR frame. By performing this, a time offset may be measured and time synchronization may be performed.

Termination of the WUR preamble may be indicated by setting the last symbol of the WUR preamble as the OOK OFF symbol. For example, the end of the WUR preamble is indicated, so that an error in time offset measurement that may be caused by confusing the data part and the WUR preamble when the WUR STA performs synchronization may be reduced.

As such, the WUR STA may perform packet detection for the WUR frame using bit information of the repeatedly transmitted OOK ON symbol and 1 OOK Off symbol. For example, the WUR STA may check whether the WUR frame is received through the reception of the bit information 110.

When the WUR STA performs envelope detection on the OOK symbol, a threshold is required for on / off determination of the data symbol, and the STA may use the WUR preamble to measure the threshold. For example, the WUR STA determines a threshold value through the signal strength of the WUR preamble, and performs envelope detection on the data part to determine that a symbol section in which a signal above the threshold is detected is a OOK on symbol, and a section in which a signal below the threshold is detected. May be determined to be a OOK off symbol.

As another example, a separate measurement symbol is added to the WUR preamble as a purpose for measuring the strength of the signal, and the WUR STA may determine a threshold for on / off determination of the data symbol through the corresponding measurement symbol.

Meanwhile, the number of OOK on symbols included in the WUR preamble is not limited to two, and more OOK on symbol symbols such as 5, 7, and 9 may be included in the WUR preamble. For example, the number of OOK On symbols included in the WUR preamble may be set equal to the length of a pseudo noise (PN) sequence.

17 illustrates a WUR frame structure according to an embodiment of the present invention.

Referring to FIG. 17A, the WUR frame includes a WUR preamble part and a control information part. The WUR preamble includes two OOK on symbols and one OOK off symbol, and the OOK off symbol is located at the end of the WUR preamble. The WUR STA may perform time synchronization and packet detection through the WUR preamble.

Referring to FIG. 17B, the WUR frame further includes a signal power measurement part for measuring the signal strength (e.g., signal power). The signal power measurement part may include one or more symbols, and the symbol included in the signal power measurement part may be a OOK on symbol. Although the signal power measurement part of FIG. 17B is positioned between the WUR preamble part and the control information part, the present invention is not limited thereto and the signal power measurement part may be included in the WUR preamble part.

Example 2

As a variation on Example 1, as an example of the present invention, the synchronization sequence may be set to a pseudo noise (PN) sequence (a pseudo random sequence such as an e.g., M-sequence).

The PN sequence may have a length of 2 ⁿ -1. For example, the PN sequence may correspond to 7, 15, 31 .. up to 128 symbol lengths in the time domain, but is not limited thereto. In this case, an off symbol may be attached to the end of the PN sequence to indicate the end of the synchronization sequence (eg, WUR preamble). For example, 1-bit 0 may be appended to the end of the PN sequence.

For example, a synchronization sequence (e.g., WUR preamble) may be transmitted through a normal OOK symbol. Alternatively, the synchronization sequence may be transmitted through a OOK symbol based on Manchester coding.

As another example, the length of the OOK symbol for the WUR preamble may be configured by setting one of 0.8us, 1.6us, and 2us.

The use of the PN sequence as the synchronization sequence is just one example, and according to another embodiment of the present invention, a sequence (e.g., Hardarmad, Golay, etc.) having excellent auto / cross correlation property may be used as the synchronization sequence. In this case, the sync part of the WUR preamble may be configured by adding an off symbol to the end of the sequence.

For example, an OFF symbol (eg, 1-bit 0) is indicated at the end of a synchronization sequence regardless of the length and type of the synchronization sequence to indicate the end of the synchronization sequence and to distinguish the synchronization sequence from other parts. It may be attached.

Meanwhile, in order to reduce power consumption, the WUR STA may perform synchronous measurement through cross correlation between bit information obtained by performing envelope detection and a previously known sequence.

Example 3

For example, the WUR preamble is configured by repeating the same time sequence (e.g., a time domain sequence) for time synchronization, and the length of the time sequence for the WUR preamble may have a length smaller than the OOK symbol. For example, assuming that one OOK symbol has a length of 4 us, the length of a time sequence repeated in the WUR preamble may be 0.8 us or 1.6 us. As such, the WUR preamble may be configured by repeating a time sequence shorter than 1 OOK symbol.

Meanwhile, the number of repetitions of the time sequence may vary according to the number of symbols constituting the WUR preamble. For example, if the WUR preamble is a 2-symbol and the time sequence is 0.8 us long, the time sequence is repeated 10 times. If the WUR preamble is a 2-symbol and the time sequence is 1.6 us long, the time sequence is repeated five times. The last symbol can be set to the OOK OFF symbol to signal the end of the WUR preamble.

As another example, two or more symbols may be set for the WUR preamble, and the length of each symbol for the WUR preamble may be set smaller than 4 us. For example, one symbol of the WUR preamble is set to be shorter than one symbol of the WUR data part, so that more symbols may be included in the WUR preamble. The WUR STA performs self / cross correlation on a repeating sequence to measure and compensate for a time offset. can do.

In addition, for packet detection for the WUR frame, a symbol for packet detection may be added after the last symbol of the WUR preamble.

On the other hand, due to the influence of the channel, the strength of the signal may change significantly. Therefore, a separate symbol for measuring signal strength may be set in the WUR frame. For example, the symbol for measuring the signal strength may be one or more OOK ON symbols.

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

Referring to FIG. 18A, a time sequence of 1.6 us length is repeated five times in the WUR preamble part, and the last symbol of the WUR preamble is set as a OOK off symbol. If one symbol in the WUR preamble is 4 us, the WUR preamble includes a total of three symbols. The time sequence is transmitted five times on two of the three symbols. The WUR STA may perform time synchronization and packet detection through the WUR preamble.

Referring to FIG. 18B, parts for time synchronization and parts for packet detection / signal power measurement are distinguished in the WUR preamble. Specifically, a time sequence of 1.6 us length is repeated five times in the part for time synchronization. The part for packet detection / signal power measurement may include one or more OOK symbols, and in FIG. 18B, it is assumed that four OOK symbols are included in the part for packet detection / signal power measurement. The OOK symbols for packet detection / signal power measurement may be set to predefined on / off values. For example, when the OOK symbols for packet detection / signal power measurement are OFF-ON-ON-OFF, the WUR STA performs packet detection through bit information 0110 and performs signal power measurement through two OOK on symbols. Can be.

Referring to FIG. 18C, parts for time synchronization / packet detection and parts for signal power measurement are distinguished in the WUR preamble. At least one OOK off symbol may be set between a part for time synchronization / packet detection and a part for signal power measurement to distinguish the two. The part for measuring signal power may include at least one OOK on symbol.

Example 4

According to an example of the present invention, as a modification to Example 3, a specific training sequence may be repeatedly transmitted in the time domain instead of repeating a time sequence in one or two or more symbols of the WUR preamble. Through the WUR STA can measure the time offset of the WUR PPDU and perform synchronization. The length of the training sequence may be 2 ⁿ −1 (eg 7, 15, 31,...), And the training sequence may be repeatedly transmitted two or more times in the time domain to improve synchronization performance.

The training sequence may be transmitted through the normal OOK symbol. Alternatively, the training sequence may be transmitted through a OOK symbol based on Manchester coding.

As another example, the length of the OOK symbol for transmitting the training sequence may be set to one of 0.8us, 1.6us, and 2us.

Also in this example, the OOK OFF symbol may be set at the end of the synchronization sequence part to indicate the end of the synchronization sequence (e.g., repetitive training sequence).

Example 5

In Examples 1 to 4, it is assumed that an AP or the like transmits a WUR frame through an existing OFDM transmitter. However, as another example of the present invention, a predefined sequence for a WUR preamble through a single carrier transmission scheme (eg, SC-FDMA) is used. May be transmitted.

 For example, a Golay sequence having excellent autocorrelation characteristics may be used as a sequence for the WUR preamble, and the Golay sequence may be transmitted on a single carrier. The receiver (e.g., WUR STA) may perform autocorrelation using a previously set / defined Golay sequence, thereby measuring / adjusting a time offset.

In this example, the OFF symbol may be set at the end to indicate the end of the WUR preamble.

Packet detection may be performed through the corresponding sequence or through predefined bit information (e.g., on / off pattern) as described in Example 1.

Since the WUR preamble is transmitted on a single carrier, at least one symbol for signal strength measurement may be added in the preamble to measure the signal strength of the OOK symbol. The symbol for measuring the signal strength may be a OOK symbol.

19 illustrates a WUR frame structure according to an embodiment of the present invention.

Referring to FIG. 19A, a Golay sequence is set for time synchronization and packet detection in a WUR preamble, and a OOK off symbol is set at the end of the Golay sequence. Thereafter, at least one on symbol for measuring signal strength may be set.

Referring to FIG. 19B, unlike FIG. 19A, an On symbol for measuring signal strength is omitted.

In the examples of Examples 1 to 5 described above, the number of symbols for synchronization and packet detection is three including the Off symbol, and more symbols are used to improve performance or more to reduce overhead. Fewer symbols may be used.

Meanwhile, due to the influence of the channel, the strength of the signal in the symbol may vary. For example, as the strength of the signal varies, an error may occur in the on / off determination of the signal when the envelope is detected. According to an embodiment of the present invention, the OOK pilot symbol s may be transmitted in the WUR payload to reduce the performance decrease due to such an error. The pilot symbol may be set to an ON symbol. The frequency sequence of the pilot symbol may be different from the sequence for the OOK symbol of the payload. When there are a plurality of pilot symbols, the interval between pilot symbols may correspond to, for example, 5/10/20 symbols.

Control Information Part

The WUR frame may include control information. For the aforementioned examples, control information may be transmitted in the following manner.

(i) The control information part may be set as one field, for example, an SIG field.

(ii) The control information part may be set to multiple fields, for example two fields, to reduce the early indication of control information and the power consumption of the WUR receiver. The WUR STA may determine whether to receive the corresponding WUR frame (e.g., whether to decode the remaining WUR frame located after the first field) through a first field located at the head of the plurality of fields corresponding to the control information part.

20 illustrates a case in which a control information part includes a plurality of fields according to an embodiment of the present invention. For convenience, it is assumed that many fields are two fields.

For example, in order to detect an error of each field, a separate field CRC may be included.

If it is determined that the WUR STA is not information corresponding to itself by checking control information in the first field, the WUR STA may not perform decoding on the remaining WUR frames. The first field may include a BSS color and a CRC. The second field may include at least one of SU / MU indicator, DL / UL indicator, STA ID (eg, P-AID, GID), BW, TXOP duration, symbol number (N_sym), and frame length information. It doesn't work.

21 illustrates a WUR PPDU transmission / reception method according to an embodiment of the present invention. Descriptions overlapping with the above description may be omitted. For convenience of description, it is assumed that the WUR transmitter transmitting the WUR frame is an AP and the WUR receiver receiving the WUR frame is an STA. However, the present invention is not limited thereto, and for example, the WUR transmitter may be another STA. In addition, in order to prevent the issue from blurring, only the signal transmission and reception through the WUR is shown except for signal transmission and reception through PCR, but the AP and STA of FIG. 21 may transmit / receive signals through PCR before and after the WUR mode operation. .

Referring to FIG. 21, the AP generates a WUR frame including a WUR preamble part and a control information part based on an on-off keying (OOK) method (2105).

The AP transmits a WUR frame generated based on the OOK scheme (2110).

The STA performs time synchronization and packet detection on the WUR frame based on the WUR preamble part of the WUR frame (2115).

The STA decodes the control information part of the WUR frame in the OOK method based on the time synchronization result (2120).

In order to distinguish between the WUR preamble part and the control information part, the last symbol among a plurality of symbols included in the WUR preamble part may be set to an off symbol.

In addition, on predetermined symbols located before the last off symbol of the WUR preamble part of the WUR preamble part, a synchronization sequence for the WUR frame may be repeatedly transmitted at least twice in the time domain.

For example, the number of repetitive transmissions of a synchronization sequence may be greater than the total number of predetermined symbols. As a specific example, the predetermined symbols are two 4 us symbols, the number of repetitive transmissions of the synchronization sequence is 10 when the length of the synchronization sequence is 0.8 us, and the number of repetitive transmissions of the synchronization sequence is 5 when the length of the synchronization sequence is 1.8 us. Can be.

As another example, one symbol length in the WUR preamble part may be set shorter than one symbol length in the control information part. As a specific example, one symbol length in the WUR preamble part may be set to 0.8 us, 1.6 us or 2 us, and one symbol length in the control information part may be set to 4 us.

The last N symbols, including the last off symbol in the WUR preamble part, may have a preset on-off pattern for packet detection for the WUR frame.

The WUR preamble part may further include a signal strength measurement part that provides a criterion for on-off determination of each symbol when performing envelope detection on the control information part. At least one symbol included in the signal strength measuring part may be set to all on symbols.

The control information part may include a first field having first control information and a first cyclic redundancy check (CRC) and a second field having second control information and a second CRC. The first control information may include a BSS color. The second control information includes a single-user (SU) / multi-user (MU) indicator, a downlink (DL) / uplink (UL) indicator, a station ID, a bandwidth, a transmission opportunity duration, a number of WUR frame symbols, and a WUR. It may include at least one of the frame length.

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.

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 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 (15)

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

   Generating a WUR frame including a WUR preamble part and a control information part based on an on-off keying (OOK) scheme; And

   Transmitting the WUR frame generated based on the OOK scheme,

   In order to distinguish between the WUR preamble part and the control information part, a last symbol among a plurality of symbols included in the WUR preamble part is set to an off symbol,

   And on the predetermined symbols located before the off symbol of the WUR preamble part, the synchronization sequence for the WUR frame is repeatedly transmitted at least twice in the time domain.
2. The method of claim 1,

   And the number of repetitive transmissions of the synchronization sequence is greater than the total number of predetermined symbols.
3. The method of claim 2,

   The predetermined symbols are two 4 us symbols,

   When the length of the synchronization sequence is 0.8 us, the number of repetitive transmissions of the synchronization sequence is 10,

   And the number of repetitive transmissions of the synchronization sequence is 5 when the length of the synchronization sequence is 1.8 us.
4. The method of claim 1,

   1 symbol length in the WUR preamble part is set to 0.8 us, 1.6 us or 2 us, and 1 symbol length in the control information part is set to 4 us.
5. The method of claim 1,

   And the last N symbols including the off symbol in the WUR preamble part have a preset on-off pattern for packet detection for the WUR frame.
6. The method of claim 1,

   The WUR preamble part may further include a signal strength measurement part that provides a reference for on-off determination of each symbol when performing envelope detection on the control information part,

   At least one symbol included in the signal strength measurement part is all set to the on symbol, WUR frame transmission method.
7. The method of claim 1,

   The control information part includes a first field having first control information and a first cyclic redundancy check (CRC) and a second field having second control information and a second CRC,

   The first control information includes a BSS color,

   The second control information includes a single-user (SU) / multi-user (MU) indicator, a downlink (DL) / uplink (UL) indicator, a station ID, a bandwidth, a TXOP duration (transmitting opportunity duration), a number of WUR frame symbols, and WUR frame transmission method comprising at least one of the WUR frame length.
8. In a method for receiving a WUR (wake up radio) frame (STA) in a WLAN system,

   Performing time synchronization and packet detection on the WUR frame based on the WUR preamble part of the WUR frame; And

   Decoding a control information part of the WUR frame based on an on-off keying (OOK) method;

   In order to distinguish between the WUR preamble part and the control information part, a last symbol among a plurality of symbols included in the WUR preamble part is set to an off symbol,

   And on a predetermined symbol located before the off symbol of the WUR preamble part, a synchronization sequence for the WUR frame is repeatedly received at least twice in the time domain.
9. The method of claim 8,

   And a number of repetitive receptions of the synchronization sequence is greater than the total number of predetermined symbols.
10. The method of claim 9,

    The predetermined symbols are two 4 us symbols,

    When the length of the sync sequence is 0.8 us, the number of times of repeated reception of the sync sequence is 10,

    And the number of repetitive receptions of the synchronization sequence is 5 when the length of the synchronization sequence is 1.8 us.
11. The method of claim 8,

    1 symbol length in the WUR preamble part is set to 0.8 us, 1.6 us or 2 us, and 1 symbol length in the control information part is set to 4 us.
12. The method of claim 8,

    The last N symbols including the off symbol in the WUR preamble part have a preset on-off pattern for packet detection for the WUR frame.
13. The method of claim 8,

    The WUR preamble part may further include a signal strength measurement part that provides a reference for on-off determination of each symbol when performing envelope detection on the control information part,

    At least one symbol included in the signal strength measurement part is all set to the on symbol, WUR frame receiving method.
14. The method of claim 8,

    The control information part includes a first field having first control information and a first cyclic redundancy check (CRC) and a second field having second control information and a second CRC,

    The first control information includes a BSS color,

    The second control information includes a single-user (SU) / multi-user (MU) indicator, a downlink (DL) / uplink (UL) indicator, a station ID, a bandwidth, a TXOP duration (transmitting opportunity duration), a number of WUR frame symbols, and WUR frame receiving method comprising at least one of the WUR frame length.
15. In an access point (AP) for transmitting a wake up radio (WUR) frame,

    A processor for generating a WUR frame including a WUR preamble part and a control information part based on an on-off keying (OOK) scheme; And

    And a transmitter for transmitting the WUR frame generated based on the OOK scheme under the control of the processor.

    In order to distinguish between the WUR preamble part and the control information part, a last symbol among a plurality of symbols included in the WUR preamble part is set to an off symbol,

    On a predetermined symbol located before the off symbol of the WUR preamble part, the synchronization sequence for the WUR frame is repeatedly transmitted at least twice in the time domain.

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