WO2014107031A1 - 무선랜 시스템에서 채널 액세스 방법 및 장치 - Google Patents
무선랜 시스템에서 채널 액세스 방법 및 장치 Download PDFInfo
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- WO2014107031A1 WO2014107031A1 PCT/KR2014/000016 KR2014000016W WO2014107031A1 WO 2014107031 A1 WO2014107031 A1 WO 2014107031A1 KR 2014000016 W KR2014000016 W KR 2014000016W WO 2014107031 A1 WO2014107031 A1 WO 2014107031A1
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W74/00—Wireless channel access, e.g. scheduled or random access
- H04W74/08—Non-scheduled or contention based access, e.g. random access, ALOHA, CSMA [Carrier Sense Multiple Access]
- H04W74/0808—Non-scheduled or contention based access, e.g. random access, ALOHA, CSMA [Carrier Sense Multiple Access] using carrier sensing, e.g. as in CSMA
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W72/00—Local resource management
- H04W72/04—Wireless resource allocation
- H04W72/044—Wireless resource allocation based on the type of the allocated resource
- H04W72/0446—Resources in time domain, e.g. slots or frames
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W48/00—Access restriction; Network selection; Access point selection
- H04W48/16—Discovering, processing access restriction or access information
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W84/00—Network topologies
- H04W84/02—Hierarchically pre-organised networks, e.g. paging networks, cellular networks, WLAN [Wireless Local Area Network] or WLL [Wireless Local Loop]
- H04W84/10—Small scale networks; Flat hierarchical networks
- H04W84/12—WLAN [Wireless Local Area Networks]
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W88/00—Devices specially adapted for wireless communication networks, e.g. terminals, base stations or access point devices
- H04W88/02—Terminal devices
Definitions
- the following description relates to a wireless communication system, and more particularly, to a channel access method and apparatus in a WLAN system.
- WLAN is based on radio frequency technology, and can be used in homes, businesses, or businesses by using portable terminals such as personal digital assistants (PDAs), laptop computers, and portable multimedia players (PMPs). It is a technology that allows wireless access to the Internet in a specific service area.
- PDAs personal digital assistants
- PMPs portable multimedia players
- IEEE 802.11n supports High Throughput (HT) with data throughput up to 540 Mbps or more, and also uses multiple antennas at both the transmitter and receiver to minimize transmission errors and optimize data rates.
- HT High Throughput
- MIMO Multiple Inputs and Multiple Outputs
- IEEE 802.11 WLAN system a technical standard for supporting M2M communication is being developed as IEEE 802.11ah.
- M2M communications you may want to consider a scenario where you occasionally communicate a small amount of data at low speeds in an environment with many devices.
- Communication in a WLAN system is performed in a medium shared between all devices.
- M2M communication spending a large amount of time for channel access of one device may not only reduce the overall system performance, but also prevent power saving of each device.
- a station (STA) of a specific type is allowed to attempt channel access without checking a traffic indication map (TIM) provided by an access point (AP). If a particular type of STA (for example, a non-TIM STA) accesses a channel without knowing the channel usage of another STA, the channel usage efficiency, which is a limited resource of the entire network as well as its own unnecessary power consumption, may be reduced. It causes dropping problems.
- STA station
- TIM traffic indication map
- AP access point
- An object of the present invention is to provide an improved channel access method that can be applied to a WLAN system.
- a method of performing a channel access by a station (STA) in a WLAN system may include: a second from another STA when the channel is in an idle state; Deferring transmission of the first frame until a frame is detected; And transmitting the first frame when the second frame is detected.
- a station (STA) apparatus for performing channel access in a WLAN system includes: a transceiver; And a processor.
- the processor when the channel is idle, defers transmission of the first frame until a second frame from another STA is detected; When the second frame is detected, the first frame may be set using the transceiver.
- Deferred transmission of the first frame may be performed when the channel is determined to be idle when the STA wakes up.
- Deferred transmission of the first frame may be performed when the first frame is transmitted when the STA wakes up and a response frame for the first frame transmitted when the STA wakes up is not received. .
- Transmitting the first frame when the STA wakes up may include transmitting the first frame if it is determined that the channel is in an idle state without delaying transmission of the first frame.
- a timer may be set for the STA, and transmission of the first frame may be prohibited while the timer is running.
- the first frame may be transmitted.
- the timer can be stopped.
- the timer may be started when the first frame is transmitted when the STA wakes up, or may be started when no response frame is received for the first frame transmitted when the STA wakes up. Can be.
- Transmitting the first frame when the STA wakes up may include transmitting the first frame if it is determined that the channel is in an idle state without delaying transmission of the first frame.
- the length of the timer may be set to a maximum Transmission Opportunity (TXOP) duration.
- TXOP Transmission Opportunity
- the transmission of the first frame may include transmitting the first frame after performing a backoff process.
- the first frame may be any one of a power save (PS) -Poll frame, a trigger frame, a data frame, or an RTS frame.
- PS power save
- the second frame may be either a frame from another STA or a beacon frame from an access point (AP).
- AP access point
- the STA may be a Non-TIM (Traffic Indication Map) STA.
- a method and apparatus for improving a channel access method in a WLAN system may be provided.
- FIG. 1 is a diagram illustrating an exemplary structure of an IEEE 802.11 system to which the present invention can be applied.
- FIG. 2 is a diagram illustrating another exemplary structure of an IEEE 802.11 system to which the present invention can be applied.
- FIG. 3 is a diagram illustrating another exemplary structure of an IEEE 802.11 system to which the present invention can be applied.
- FIG. 4 is a diagram illustrating an exemplary structure of a WLAN system.
- FIG. 5 is a diagram illustrating a link setup process in a WLAN system.
- FIG. 6 is a diagram for describing a backoff process.
- 7 is a diagram for explaining hidden nodes and exposed nodes.
- FIG. 8 is a diagram for explaining an RTS and a CTS.
- FIG. 9 is a diagram for describing a power management operation.
- 10 to 12 are diagrams for explaining in detail the operation of the STA receiving the TIM.
- FIG. 13 illustrates a collision between transmission of a Non-TIM STA and transmission of another STA.
- FIG. 14 is a view for explaining an example of the present invention for PS-Poll frame transmission of a Non-TIM STA.
- 15 is a view for explaining another example of the present invention for PS-Poll frame transmission of a Non-TIM STA.
- 16 is a view for explaining another example of the present invention for PS-Poll frame transmission of a Non-TIM STA.
- 17 is a view for explaining an example of the present invention for data frame transmission of a Non-TIM STA.
- FIG. 18 is a diagram for explaining an example of the present invention for RTS frame transmission of a Non-TIM STA.
- 19 and 20 are diagrams for explaining examples of the present invention using a timer for channel access deferral of a Non-TIM STA.
- 21 illustrates a channel access method of a non-TIM STA according to an embodiment of the present invention.
- 22 is a block diagram illustrating a configuration of a wireless device according to an embodiment of the present invention.
- each component or feature may be considered to be optional unless otherwise stated.
- Each component or feature may be embodied in a form that is not combined with other components or features.
- some components and / or features may be combined to form an embodiment of the present invention.
- the order of the operations described in the embodiments of the present invention may be changed. Some components or features of one embodiment may be included in another embodiment or may be replaced with corresponding components or features of another embodiment.
- Embodiments of the present invention may be supported by standard documents disclosed in at least one of the wireless access systems IEEE 802 system, 3GPP system, 3GPP LTE and LTE-A (LTE-Advanced) system and 3GPP2 system. That is, steps or parts which are not described to clearly reveal the technical spirit of the present invention among the embodiments of the present invention may be supported by the above documents. In addition, all terms disclosed in the present document can be described by the above standard document.
- CDMA code division multiple access
- FDMA frequency division multiple access
- TDMA time division multiple access
- OFDMA orthogonal frequency division multiple access
- SC-FDMA single carrier frequency division multiple access
- CDMA may be implemented with a radio technology such as Universal Terrestrial Radio Access (UTRA) or CDMA2000.
- TDMA may be implemented with wireless technologies such as Global System for Mobile communications (GSM) / General Packet Radio Service (GPRS) / Enhanced Data Rates for GSM Evolution (EDGE).
- GSM Global System for Mobile communications
- GPRS General Packet Radio Service
- EDGE Enhanced Data Rates for GSM Evolution
- OFDMA may be implemented in a wireless technology such as IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802-20, Evolved UTRA (E-UTRA).
- Wi-Fi IEEE 802.11
- WiMAX IEEE 802.16
- E-UTRA Evolved UTRA
- FIG. 1 is a diagram showing an exemplary structure of an IEEE 802.11 system to which the present invention can be applied.
- the IEEE 802.11 architecture may be composed of a plurality of components, and by their interaction, a WLAN may be provided that supports transparent STA mobility for higher layers.
- the Basic Service Set (BSS) may correspond to a basic building block in an IEEE 802.11 LAN. 1 exemplarily shows that there are two BSSs (BSS1 and BSS2) and two STAs are included as members of each BSS (STA1 and STA2 are included in BSS1 and STA3 and STA4 are included in BSS2). do.
- an ellipse representing a BSS may be understood to represent a coverage area where STAs included in the BSS maintain communication. This area may be referred to as a basic service area (BSA).
- BSA basic service area
- the most basic type of BSS in an IEEE 802.11 LAN is an independent BSS (IBSS).
- the IBSS may have a minimal form consisting of only two STAs.
- the BSS (BSS1 or BSS2) of FIG. 1, which is the simplest form and other components are omitted, may correspond to a representative example of the IBSS.
- This configuration is possible when STAs can communicate directly.
- this type of LAN may not be configured in advance, but may be configured when a LAN is required, which may be referred to as an ad-hoc network.
- the membership of the STA in the BSS may be dynamically changed by turning the STA on or off, the STA entering or exiting the BSS region, and the like.
- the STA may join the BSS using a synchronization process.
- the STA In order to access all services of the BSS infrastructure, the STA must be associated with the BSS. This association may be set up dynamically and may include the use of a Distribution System Service (DSS).
- DSS Distribution System Service
- FIG. 2 is a diagram illustrating another exemplary structure of an IEEE 802.11 system to which the present invention can be applied.
- components such as a distribution system (DS), a distribution system medium (DSM), and an access point (AP) are added in the structure of FIG. 1.
- DS distribution system
- DSM distribution system medium
- AP access point
- the station-to-station distance directly in the LAN can be limited by PHY performance. In some cases, this distance limit may be sufficient, but in some cases, communication between more distant stations may be necessary.
- the distribution system DS may be configured to support extended coverage.
- the DS refers to a structure in which BSSs are interconnected. Specifically, instead of the BSS independently as shown in FIG. 1, the BSS may exist as an extended type component of a network composed of a plurality of BSSs.
- DS is a logical concept and can be specified by the nature of the distribution system medium (DSM).
- DSM distribution system medium
- the IEEE 802.11 standard logically distinguishes between wireless medium (WM) and distribution system media (DSM).
- Each logical medium is used for a different purpose and is used by different components.
- the definition of the IEEE 802.11 standard does not limit these media to the same or to different ones.
- the plurality of media logically different, the flexibility of the IEEE 802.11 LAN structure (DS structure or other network structure) can be described. That is, the IEEE 802.11 LAN structure can be implemented in various ways, the corresponding LAN structure can be specified independently by the physical characteristics of each implementation.
- the DS may support the mobile device by providing seamless integration of multiple BSSs and providing logical services for handling addresses to destinations.
- An AP means an entity that enables access to a DS through WM for associated STAs and has STA functionality. Data movement between the BSS and the DS may be performed through the AP.
- STA2 and STA3 shown in FIG. 2 have the functionality of a STA, and provide a function to allow associated STAs STA1 and STA4 to access the DS.
- all APs basically correspond to STAs, all APs are addressable entities. The address used by the AP for communication on the WM and the address used by the AP for communication on the DSM need not necessarily be the same.
- Data transmitted from one of the STAs associated with an AP to the STA address of that AP may always be received at an uncontrolled port and processed by an IEEE 802.1X port access entity.
- transmission data (or frame) may be transmitted to the DS.
- FIG. 3 is a diagram illustrating another exemplary structure of an IEEE 802.11 system to which the present invention can be applied. 3 conceptually illustrates an extended service set (ESS) for providing wide coverage in addition to the structure of FIG. 2.
- ESS extended service set
- a wireless network of arbitrary size and complexity may be composed of DS and BSSs.
- this type of network is called an ESS network.
- the ESS may correspond to a set of BSSs connected to one DS. However, the ESS does not include a DS.
- the ESS network is characterized by what appears to be an IBSS network at the LLC (Logical Link Control) layer. STAs included in the ESS can communicate with each other, and mobile STAs can move from within one BSS to another BSS (within the same ESS) transparently to the LLC.
- LLC Logical Link Control
- BSSs can be partially overlapped, which is a form commonly used to provide continuous coverage.
- the BSSs may not be physically connected, and logically there is no limit to the distance between the BSSs.
- the BSSs can be located at the same physical location, which can be used to provide redundancy.
- one (or more) IBSS or ESS networks may be physically present in the same space as one (or more than one) ESS network.
- the ad-hoc network is operating at the location of the ESS network, if IEEE 802.11 networks are physically overlapped by different organizations, or if two or more different access and security policies are required at the same location. It may correspond to an ESS network type in a case.
- FIG. 4 is a diagram illustrating an exemplary structure of a WLAN system.
- an example of an infrastructure BSS including a DS is shown.
- BSS1 and BSS2 constitute an ESS.
- an STA is a device that operates according to MAC / PHY regulations of IEEE 802.11.
- the STA includes an AP STA and a non-AP STA.
- Non-AP STAs are devices that users typically handle, such as laptop computers and mobile phones.
- STA1, STA3, and STA4 correspond to non-AP STAs
- STA2 and STA5 correspond to AP STAs.
- a non-AP STA includes a terminal, a wireless transmit / receive unit (WTRU), a user equipment (UE), a mobile station (MS), and a mobile terminal. May be referred to as a Mobile Subscriber Station (MSS).
- the AP may include a base station (BS), a node-B, an evolved Node-B (eNB), and a base transceiver system (BTS) in other wireless communication fields.
- BS base station
- eNB evolved Node-B
- BTS base transceiver system
- FIG. 5 is a diagram illustrating a general link setup process.
- an STA 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.
- a process of discovery, authentication, association, and security establishment of a link setup process may be collectively referred to as association process.
- 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.
- 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.
- the responder may be an STA that last transmitted a beacon frame in the BSS of the channel being scanned.
- the AP transmits a beacon frame, so the AP becomes a responder.
- the responder is not constant.
- 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.
- the scanning operation may be performed by a passive scanning method.
- 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.
- the AP periodically transmits a beacon frame
- the IBSS STAs in the IBSS rotate and transmit a beacon frame.
- 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.
- 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.
- active scanning has the advantage of less delay and power consumption than passive scanning.
- step S520 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.
- 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.
- 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.
- 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.
- AIDs association IDs
- EDCA Enhanced Distributed Channel Access
- RCPI Received Channel Power Indicators
- 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.
- 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.
- RSNA Robust Security Network Association
- 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. .
- the security setup process may be performed according to a security scheme not defined in the IEEE 802.11 standard.
- IEEE 802.11n In order to overcome the limitation of communication speed in WLAN, IEEE 802.11n exists as a relatively recently established technical standard. IEEE 802.11n aims to increase the speed and reliability of networks and to extend the operating range of wireless networks. More specifically, IEEE 802.11n supports High Throughput (HT) with data throughput of up to 540 Mbps and also uses multiple antennas at both the transmitter and receiver to minimize transmission errors and optimize data rates. It is based on Multiple Inputs and Multiple Outputs (MIMO) technology.
- HT High Throughput
- MIMO Multiple Inputs and Multiple Outputs
- the next generation WLAN system supporting Very High Throughput is the next version of the IEEE 802.11n WLAN system (e.g., IEEE 802.11ac), which is 1 Gbps at the MAC Service Access Point (SAP).
- IEEE 802.11ac the next version of the IEEE 802.11n WLAN system
- SAP MAC Service Access Point
- the next generation WLAN system supports MU-MIMO (Multi User Multiple Input Multiple Output) transmission in which a plurality of STAs simultaneously access a channel in order to use the wireless channel efficiently.
- MU-MIMO Multi User Multiple Input Multiple Output
- the AP may simultaneously transmit packets to one or more STAs that are paired with MIMO.
- whitespace may be referred to as a licensed band that can be preferentially used by a licensed user.
- An authorized user refers to a user who is authorized to use an authorized band and may also be referred to as a licensed device, a primary user, an incumbent user, or the like.
- an AP and / or STA operating in a WS should provide protection for an authorized user. For example, if an authorized user such as a microphone is already using a specific WS channel, which is a frequency band divided in a regulation to have a specific bandwidth in the WS band, the AP may be protected. And / or the STA cannot use a frequency band corresponding to the corresponding WS channel. In addition, the AP and / or STA should stop using the frequency band when the authorized user uses the frequency band currently used for frame transmission and / or reception.
- the AP and / or STA should be preceded by a procedure for determining whether a specific frequency band in the WS band is available, that is, whether there is an authorized user in the frequency band. Knowing whether there is an authorized user in a specific frequency band is called spectrum sensing. As the spectrum sensing mechanism, energy detection, signal detection, and the like are used. If the strength of the received signal is greater than or equal to a predetermined value, it may be determined that the authorized user is in use, or if the DTV preamble is detected, the authorized user may be determined to be in use.
- M2M communication refers to a communication method that includes one or more machines (Machine), may also be referred to as MTC (Machine Type Communication) or thing communication.
- a machine refers to an entity that does not require human direct manipulation or intervention.
- a device such as a meter or a vending machine equipped with a wireless communication module, as well as a user device such as a smartphone that can automatically connect and communicate with a network without a user's operation / intervention, may be used. This may correspond to an example.
- the M2M communication may include communication between devices (eg, device-to-device (D2D) communication), communication between a device, and an application server.
- D2D device-to-device
- Examples of device and server communication include communication between vending machines and servers, point of sale devices and servers, and electricity, gas or water meter readers and servers.
- applications based on M2M communication may include security, transportation, health care, and the like. Considering the nature of these applications, M2M communication should generally be able to support the transmission and reception of small amounts of data at low speeds in the presence of very many devices.
- M2M communication should be able to support a large number of STAs.
- WLAN system it is assumed that a maximum of 2007 STAs are associated with one AP, but in M2M communication, there are methods for supporting a case where a larger number (approximately 6000 STAs) are associated with one AP. Is being discussed.
- many applications are expected to support / require low data rates in M2M communication.
- an STA may recognize whether data to be transmitted to it is based on a TIM (Traffic Indication Map) element, and methods for reducing the bitmap size of the TIM are discussed. It is becoming.
- TIM Traffic Indication Map
- M2M communication is expected to be a lot of traffic with a very long transmission / reception interval. For example, very small amounts of data are required to be sent and received every long period (eg, one month), such as electricity / gas / water use. Accordingly, in the WLAN system, even if the number of STAs that can be associated with one AP becomes very large, it is possible to efficiently support the case where the number of STAs having data frames to be received from the AP is very small during one beacon period. The ways to do this are discussed.
- WLAN technology is rapidly evolving and, in addition to the above examples, technologies for direct link setup, media streaming performance improvement, support for high speed and / or large initial session setup, support for extended bandwidth and operating frequency, etc. Is being developed.
- a basic access mechanism of MAC 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.
- 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.
- DIFS DCF Inter-Frame Space
- a delay period for example, a random backoff period
- HCF hybrid coordination function
- 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.
- 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.
- 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).
- QoS quality of service
- FIG. 6 is a diagram for describing a backoff process.
- the random backoff count has a pseudo-random integer value and may be determined to be one of values in the range of 0 to CW.
- 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).
- 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.
- 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. 6, STA2 selects the smallest backoff count value and STA1 selects the largest backoff count value.
- 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.
- 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.
- the STA4 waits for DIFS, performs a countdown according to a random backoff count value selected by the STA4, and starts frame transmission.
- the remaining backoff time of STA5 coincides with an arbitrary backoff count value of STA4.
- 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.
- 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.
- 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.
- 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.
- the value set to NAV corresponds to a period during 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 (or channel access) during the period. prohibit or defer.
- the NAV may be set, for example, according to the value of the "duration" field of the MAC header of the frame.
- 7 is a diagram for explaining hidden nodes and exposed nodes.
- STA A illustrates an example of a hidden node, in which STA A and STA B are in communication and STA C has information to transmit.
- STA A may be 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.
- STA B since STA B receives the information of STA A and STA C at the same time, a collision occurs.
- STA A may be referred to as a hidden node of STA C.
- FIG. 7B is an example of an exposed node
- STA B is a case in which STA C has information to be transmitted from STA D while transmitting data to STA A.
- FIG. 7B 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.
- FIG. 8 is a diagram for explaining an RTS and a CTS.
- a short signaling packet such as a request to send (RTS) and a clear to send (CTS) may be used.
- RTS request to send
- CTS clear to send
- 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.
- 8A 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. 8A 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. 8 (b) is an example of a method of solving an exposed node problem, and STA C overhears RTS / CTS transmission between STA A and STA B so that STA C is a different 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.
- STA C overhears RTS / CTS transmission between STA A and STA B so that STA C is a different 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
- 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.
- the WLAN system supports a power management (PM) mode of the STA.
- PM power management
- 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.
- 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.
- 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.
- FIG. 9 is a diagram for describing a power management operation.
- the AP 210 transmits a beacon frame to STAs in a BSS at regular intervals (S211, S212, S213, S214, S215, and S216).
- the beacon frame includes a traffic indication map (TIM) information element.
- the TIM information element includes information indicating that the AP 210 is present with buffered traffic for STAs associated with it and will transmit 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.
- DTIM delivery traffic indication map
- the AP 210 may transmit the DTIM once every three beacon frames.
- STA1 220 and STA2 222 are STAs operating in a PS mode.
- the STA1 220 and the STA2 222 may be configured to receive a TIM element transmitted by the AP 210 by switching from a sleep state to an awake state at every wakeup interval of a predetermined period. .
- Each STA may calculate a time to switch to the awake state based on its local clock. In the example of FIG. 9, it is assumed that the clock of the STA coincides with the clock of the AP.
- the predetermined wakeup interval may be set such that the STA1 220 may switch to the awake state for each beacon interval to receive the TIM element. Accordingly, the STA1 220 may be switched to an awake state when the AP 210 first transmits a beacon frame (S211) (S221). STA1 220 may receive a beacon frame and obtain a TIM element. When the obtained TIM element indicates that there is a frame to be transmitted to the STA1 220, the STA1 220 sends a PS-Poll (Power Save-Poll) frame requesting the AP 210 to transmit the frame, and the AP 210. It may be transmitted to (S221a). The AP 210 may transmit the frame to the STA1 220 in response to the PS-Poll frame (S231). After completing the frame reception, the STA1 220 switches to the sleep state again.
- S211 beacon frame
- S221a Power Save-Poll
- the AP 210 When the AP 210 transmits the beacon frame for the second time, the AP 210 does not transmit the beacon frame at the correct beacon interval because the medium is busy, such as another device accessing the medium. It can be transmitted at a delayed time (S212). In this case, the STA1 220 switches the operation mode to the awake state according to the beacon interval, but fails to receive the delayed beacon frame, and switches back to the sleep state (S222).
- the beacon frame may include a TIM element set to DTIM.
- the AP 210 delays transmission of the beacon frame (S213).
- the STA1 220 may operate by switching to an awake state according to the beacon interval, and may obtain a DTIM through a beacon frame transmitted by the AP 210. It is assumed that the DTIM acquired by the STA1 220 indicates that there is no frame to be transmitted to the STA1 220 and that a frame for another STA exists. In this case, the STA1 220 may determine that there is no frame to receive, and then switch to the sleep state again.
- the AP 210 transmits the frame to the STA after transmitting the beacon frame (S232).
- the AP 210 transmits a beacon frame fourthly (S214).
- the STA1 220 cannot adjust the wakeup interval for receiving the TIM element because the STA1 220 cannot obtain information indicating that there is buffered traffic for itself through the previous two times of receiving the TIM element.
- the wakeup interval value of the STA1 220 may be adjusted.
- the STA1 220 may be configured to switch the operating state by waking up once every three beacon intervals from switching the operating state for TIM element reception every beacon interval. Accordingly, the STA1 220 cannot acquire the corresponding TIM element because the AP 210 maintains a sleep state at the time when the AP 210 transmits the fourth beacon frame (S214) and transmits the fifth beacon frame (S215).
- the STA1 220 may operate by switching to an awake state and may acquire a TIM element included in the beacon frame (S224). Since the TIM element is a DTIM indicating that a broadcast frame exists, the STA1 220 may receive a broadcast frame transmitted by the AP 210 without transmitting the PS-Poll frame to the AP 210. (S234). Meanwhile, the wakeup interval set in the STA2 230 may be set in a longer period than the STA1 220. Accordingly, the STA2 230 may switch to the awake state at the time S215 at which the AP 210 transmits the beacon frame for the fifth time (S215) and receive the TIM element (S241).
- the STA2 230 may know that there is a frame to be transmitted to itself through the TIM element, and transmit a PS-Poll frame to the AP 210 to request frame transmission (S241a).
- the AP 210 may transmit the frame to the STA2 230 in response to the PS-Poll frame (S233).
- the TIM element includes a TIM indicating whether a frame to be transmitted to the STA exists or a DTIM indicating whether a broadcast / multicast frame exists.
- DTIM may be implemented through field setting of a TIM element.
- 10 to 12 are diagrams for explaining the operation of the STA receiving the TIM in detail.
- the STA may switch from a sleep state to an awake state to receive a beacon frame including a TIM from an AP, interpret the received TIM element, and know that there is buffered traffic to be transmitted to the AP. .
- the STA may transmit a PS-Poll frame to request an AP to transmit a data frame.
- 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.
- ACK acknowledgment
- the AP may operate according to an immediate response method after transmitting a data frame after a predetermined time (for example, short inter-frame space (SIFS)) after receiving a PS-Poll frame from the 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. 11.
- a predetermined time for example, short inter-frame space (SIFS)
- SIFS short inter-frame space
- the STA transitions 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. 10. 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.
- 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.
- APs that can support Automatic Power Save Delivery can support APSD using APSD subfields in capability information fields such as beacon frames, probe response frames, or associative response frames (or reassociation response frames). May signal that there is.
- the STA capable of supporting the APSD may indicate whether to operate in the active mode or the PS mode using the Power Management field in the FC field of the frame.
- APSD is a mechanism for delivering downlink data and a bufferable management frame to a STA in PS operation.
- the Power Management bit of the FC field of the frame transmitted by the STA in the PS mode using the APSD is set to 1, through which buffering at the AP may be triggered.
- APSD defines two delivery mechanisms (Unscheduled-APSD) and U-APSD (Scheduled-APSD).
- the STA may use the U-APSD to allow some or all of the bufferable units (BUs) to be delivered during an unscheduled service period (SP).
- the STA may use the S-APSD to allow some or all of the BU to be delivered during the scheduled SP.
- the STA may inform the AP of the requested transmission duration, and the AP may transmit a frame to the STA during the SP.
- the STA may receive several PSDUs at once from the AP using its SP.
- the STA may recognize that there is data that the AP wants to send to itself through the TIM element of the beacon. Thereafter, the STA may transmit a trigger frame to the AP at a desired time point, and may request that the AP transmit data while notifying the AP that its SP is started. The AP may transmit an ACK in response to the trigger frame. Thereafter, the AP may transmit a RTS to the STA through competition, receive a CTS frame from the STA, and then transmit data to the STA.
- the data transmitted by the AP may consist of one or more data frames.
- the STA may recognize this and terminate the SP.
- EOSP end of service period
- the STA may transmit an ACK indicating the successful data reception to the AP.
- the STA can start its own SP to receive data when desired, and can receive multiple data frames within one SP, thereby enabling more efficient data reception. .
- An STA using U-APSD may not receive a frame transmitted by the AP during the service period due to interference. Although the AP may not detect the interference, the AP may determine that the STA did not receive the frame correctly. Using U-APSD coexistence capability, the STA can inform the AP of the requested transmission duration and use it as an SP for U-APSD. The AP may transmit a frame during the SP, thereby improving the possibility of receiving the frame in a situation where the STA is interrupted. U-APSD can also reduce the likelihood that a frame transmitted by the AP during the SP will not be successfully received.
- the STA may transmit an Add Traffic Stream (ADDTS) request frame including a U-APSD coexistence element to the AP.
- ADDTS Add Traffic Stream
- the U-APSD coexistence element may include information about the requested SP.
- the AP may process the requested SP and transmit an ADDTS response frame in response to the ADDTS request frame.
- the ADDTS request frame may include a status code.
- the status code may indicate response information for the requested SP.
- the status code may indicate whether or not to allow the requested SP, and may further indicate the reason for the rejection when rejecting the requested SP.
- the AP may send a frame to the STA during the SP.
- the duration of the SP may be specified by the U-APSD coexistence element included in the ADDTS request frame.
- the start of the SP may be a time point at which the AP normally receives by transmitting a trigger frame to the AP.
- the STA may enter a sleep state (or a doze state) when the U-APSD SP expires.
- the Physical Layer Convergence Protocol (PLCP) Packet 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.
- STF Short Training Field
- LTF Long Training Field
- SIGNAL SIG
- Data field e.g., Data field
- L-STF legacy-STF
- L-LTF legacy-LTF
- SIG field et Data Unit
- PPDU frame format e.g., HT-mixed format PPDU, HT-greenfield format PPDU, VHT (Very High Throughput) PPDU, etc.
- an additional (or other type) may be used between the SIG field and the data field.
- the STF, LTF, and SIG fields may be included.
- 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 PCLP 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.
- the SIG field may include a parity bit, a SIG TAIL bit, and the like.
- the data field may include a SERVICE field, a PLC 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 a MAC PDU 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.
- MAC PDUs are defined according to various MAC frame formats, and basic MAC frames are composed of a MAC header, a frame body, and a frame check sequence (FCS).
- FCS frame check sequence
- the MAC frame consists of a MAC PDU and can be transmitted / received through the PSDU of the data portion of the PPDU frame format.
- the null-data packet (NDP) frame format means a frame format of a type that does not include a data packet. That is, the NDP frame refers to a frame format including only PLCP header parts (ie, STF, LTF, and SIG fields) in the general PPDU format and not including the remaining parts (ie, data fields).
- the NDP frame may be referred to as a short frame format.
- An STA that is allowed to active polling may perform polling to the AP immediately after wakeup. That is, an STA that is allowed to active polling may perform a polling operation (eg, transmission of a PS-Poll frame) without having to listen to a beacon after waking up.
- a polling operation eg, transmission of a PS-Poll frame
- Such a STA may be referred to as a non-TIM STA in that polling may be performed without checking a TIM element included in the beacon frame.
- an STA performing polling when there is data to be transmitted to itself according to a TIM element included in a beacon frame may be referred to as a TIM STA.
- Active polling can be classified into a scheduled active polling type and an unscheduled active polling type.
- the AP schedules a wakeup time of the STA, and the STA wakes up at the scheduled time to perform an operation for uplink / downlink (UL / DL) transmission, and the STA is a beacon There is no need to track it.
- the AP may allow the STA or STA group to transmit an uplink frame at any point in time when the STA or STA group wakes up, and the STA does not need to track the beacons.
- the active polling STA that does not track the beacon may miss the information, time stamp information, etc. updated through the beacon. Therefore, the active polling STA may request that the AP provide such information immediately upon waking up. The AP may immediately provide the information to the STA, or may inform the STA to receive the information through the next beacon. To this end, the AP may provide the STA with a timer for receiving the next beacon.
- a Non-TIM STA While a TIM STA is defined to wake up every listen interval to receive beacons and to check for and operate according to the TIM included in the beacon, a Non-TIM STA needs to wake up at every listening interval to receive beacons. none. Accordingly, the Non-TIM STA may wake up at an arbitrary time point (eg, during a listening interval) and transmit a PS-Poll frame, a trigger frame, an uplink data frame, or an RTS frame to the AP for data transmission and reception.
- a non-TIM STA transmits a PS-Poll frame, a trigger frame, an uplink data frame, or an RTS frame to an AP at any point in time
- another STA in a hidden node relationship with the non-TIM STA is sent to the AP. If a frame is being transmitted, a collision may occur between a PS-Poll frame, a trigger frame, an uplink data frame, or an RTS frame transmitted by the non-TIM STA and a frame transmitted by the other STA.
- FIG. 13 illustrates a collision between transmission of a Non-TIM STA and transmission of another STA.
- STA1 and STA2 are in a hidden node relationship, and STA2 is a non-TIM STA.
- the STA1 may acquire a Transmission Opportunity (TXOP) and access a channel (or medium) through an RTS and a CTS frame exchange process with the AP. Meanwhile, when the STA2 wakes up at a certain time while operating in the sleep mode, the STA2 may transmit a PS-Poll frame without receiving a beacon from the AP.
- TXOP Transmission Opportunity
- the STA2 when STA2 wakes up, it shows that the PS-Poll frame is transmitted after a probe delay (PD) and a random backoff (RBO) time.
- PD probe delay
- RBO random backoff
- the STA2 since the RTS / CTS frame between the STA1 and the AP cannot be received by the STA2 in the sleep state, the STA2 cannot know whether the STA1 is in the channel (or the medium).
- the STA2 since the STA2 cannot sense the channel usage (that is, transmission of the data frame of the STA1) of the hidden node STA1, the STA2 determines that the channel is idle and transmits the PS-Poll frame through the backoff process.
- STA2 transmits the PS-Poll frame to the same AP while STA1 transmits the data frame to the AP, a collision may occur between the data frame from STA1 and the PS-Poll from STA2.
- the AP may not correctly receive the PS-Poll frame from STA2, and thus may not transmit an ACK frame or a data frame to STA2. Since STA2 did not receive an ACK frame for a specific time (for example, SIFS) after transmitting the PS-Poll frame, it is determined that a frame transmission error has occurred and retransmission of the PS-Poll frame after ERBO (Exponential Random Backoff) time. Try.
- SIFS Specific Time
- the non-TIM STA attempts to transmit a PS-Poll frame, a trigger frame, an uplink data frame, or an RTS frame without knowing the channel usage / occupation state, unnecessary power consumption of the non-TIM STA is increased. And worsen overall network performance. Therefore, it is required to prevent such a problem.
- the present invention proposes methods for improving the channel access scheme of the Non-TIM STA.
- FIG. 14 is a view for explaining an example of the present invention for PS-Poll frame transmission of a Non-TIM STA.
- the non-TIM STA wakes up from the sleep mode and does not simply perform channel sensing in the process of sensing the channel before transmitting the PS-Poll / Trigger / Data / RTS frame.
- the present invention relates to a method of transmitting a PS-Poll / trigger / data / RTS frame through a backoff process only after detecting / receiving an arbitrary frame from another STA.
- determining that the channel is idle means that channel access of the other STA is not detected as a result of channel sensing of the non-TIM STA, and the channel access is based on information included in the frame transmitted by the other STA. It means that NAV or the like which is prohibited / deferred is not set. That is, despite the situation that the channel access is allowed according to the operation of the existing STA, according to the operation of the non-TIM STA proposed in the present invention until the PS-Poll / trigger / It is distinguished from the previously defined STA operation in that it delays the transmission of the data / RTS frame.
- the STA1 may acquire a TXOP through an RTS / CTS exchange and transmit a data frame to the AP. Meanwhile, during the TXOP of STA1, STA2, which is a non-TIM STA, wakes up from the sleep mode and performs channel sensing before attempting to transmit a PS-Poll frame. Since STA1 and STA2 are hidden node relationships, STA2 may determine that the channel is idle because STA1 cannot know that the channel is in use (that is, data frame transmission).
- the STA2 may operate to wait for receiving one frame from another STA without being directly allowed to transmit the PS-Poll frame even if the channel sensing result is idle.
- the non-TIM STA that wakes up from the sleep mode checks again that the channel is idle when both channel conditions are satisfied and the condition that a frame from another STA is received is satisfied. It can then be said that attempting channel access in accordance with the EDCA scheme is allowed.
- the period of waiting for receiving one frame from another STA may be limited to a maximum TXOP period (that is, a maximum value of the TXOP limit (for example, 8160 ms)). That is, when an STA is idle, one STA waits to receive one frame from another STA during the maximum TXOP period, and attempts to access the channel according to the EDCA scheme when no frame is received during the maximum TXOP period. This can reduce the inefficiency that no STA uses the channel if the channel is actually idle but it is determined by error that a frame from another STA is not receiving.
- a maximum TXOP period that is, a maximum value of the TXOP limit (for example, 8160 ms)
- the STA2 may transmit a PS-Poll frame through a backoff process.
- the non-TIM STA wakes up and determines that the channel is idle as a result of channel sensing, it receives a frame from another STA while waiting, and the frame indicates information indicating a channel occupancy of the other STA (eg, a duration field). If a non-TIM STA determines that the channel is not idle even after the completion of the frame, the operation accordingly (that is, do not proceed with the back-off count during the channel occupancy period of the other STA, etc.) ) Can be performed.
- a channel occupancy of the other STA eg, a duration field
- channel access may be attempted through an off process.
- 15 is a view for explaining another example of the present invention for PS-Poll frame transmission of a Non-TIM STA.
- FIG. 15 An example of the present invention described with reference to FIG. 15 illustrates that a non-TIM STA wakes up from a sleep mode and senses a channel before transmitting a PS-Poll / trigger / data / RTS frame and the PS-Poll / trigger when the channel is idle. If you transmit / data / RTS frames, but do not receive a response frame for the transmitted PS-Poll / trigger / data / RTS frame, defer the retransmission of PS-Poll / trigger / data / RTS frame.
- the present invention relates to a method of transmitting a PS-Poll / trigger / data / RTS frame through a backoff process only after detecting / receiving an arbitrary frame from another STA.
- the period of waiting for receiving any frame from another STA may be limited to the maximum TXOP period (that is, the maximum value of the TXOP limit (for example, 8160 ms)). That is, if a PS-Poll / Trigger / Data / RTS frame is transmitted and a response frame (eg, ACK, CTS, or data frame) is not received, the Non-TIM STA receives one frame from another STA during the maximum TXOP period. If the frame is not received during the maximum TXOP period, the channel access is attempted according to the EDCA scheme. This can reduce the inefficiency that no STA uses the channel if the channel is actually idle but it is determined by error that a frame from another STA is not receiving.
- the maximum TXOP period that is, the maximum value of the TXOP limit (for example, 8160 ms)
- the STA1 may acquire a TXOP through an RTS / CTS exchange and transmit a data frame to the AP. Meanwhile, during the TXOP of STA1, STA2, which is a non-TIM STA, wakes up from the sleep mode, checks whether the channel is idle during the probe delay PD, and then performs a backoff process for a random backoff (RBO) time. After that, the PS-Poll frame can be transmitted.
- RBO random backoff
- the PS-Poll frame is transmitted instead of performing a backoff for retransmission of the PS-Poll frame.
- a predetermined time for example, SIFS
- the PS-Poll frame is transmitted instead of performing a backoff for retransmission of the PS-Poll frame.
- the deferral of a PS-Poll frame is until STA2 receives some frame from another STA.
- the non-TIM STA that wakes up from the sleep mode may first attempt channel access if the channel is idle. If the primary channel access is not successful, a frame from another STA may be detected. When the condition of being received / received is satisfied, it can be said that attempting to access the secondary channel according to the EDCA scheme after confirming that the channel is idle is allowed.
- 16 is a view for explaining another example of the present invention for PS-Poll frame transmission of a Non-TIM STA.
- FIG. 16 An example of the present invention described with reference to FIG. 16 illustrates that a non-TIM STA wakes up from a sleep mode and senses a channel before transmitting a PS-Poll / trigger / data / RTS frame and the PS-Poll / trigger when the channel is idle. If you transmit / data / RTS frames, but do not receive a response frame for the transmitted PS-Poll / trigger / data / RTS frame, defer the retransmission of PS-Poll / trigger / data / RTS frame.
- the present invention relates to a method of transmitting a PS-Poll / trigger / data / RTS frame through a backoff process only after detecting / receiving a beacon frame.
- the STA1 may acquire a TXOP through an RTS / CTS exchange and transmit a data frame to the AP.
- STA2 which is a non-TIM STA, wakes up from the sleep mode, checks whether the channel is idle during the probe delay PD, and then performs a backoff process for a random backoff (RBO) time.
- RBO random backoff
- the PS-Poll frame is transmitted instead of performing a backoff for retransmission of the PS-Poll frame.
- the postponement of the PS-Poll frame is until STA2 receives the beacon frame.
- the non-TIM STA that wakes up from the sleep mode may first attempt channel access if the channel is idle. If the primary channel access is not successful, the beacon frame is detected / received. When the condition is satisfied, it can be said that attempting to access the secondary channel according to the EDCA scheme after confirming that the channel is idle is allowed.
- the PS2 delays retransmission of the PS-Poll frame and continues even if an ACK or BA frame from the AP is detected. Therefore, the PS-Poll frame transmission may be delayed and the PS-Poll frame may be retransmitted through the backoff process only after detecting / receiving a beacon frame from the AP.
- the non-TIM STA may enter the sleep mode again from the time point when the primary channel access fails to the next beacon frame reception time. Thereby, additional power consumption can be saved.
- Non-TIM STA or an STA capable of active polling wakes up and transmits a PS-Poll frame.
- Non-TIM STA or active polling
- the same principle may be applied when the allowed STA) wakes up and transmits a trigger frame or a data frame. If a non-TIM STA (or STA that allows active polling) wakes up and wants to transmit a data frame, an RTS / CTS frame exchange process may be added before the data frame is transmitted.
- the Non-TIM STA (or STA that is allowed for active polling) wakes up at a scheduled time point (eg, target awake time (TWT)) or any time that is not scheduled to transmit a PS-Poll frame.
- the trigger frame may be transmitted, the data frame may be transmitted directly, or the RTS frame may be transmitted before the data frame is transmitted. In such cases, the same principle proposed in the present invention can be applied.
- 17 is a view for explaining an example of the present invention for data frame transmission of a Non-TIM STA.
- the STA2 wakes up from the sleep mode and reports the data frame first if the channel is idle, delays the data frame retransmission if it does not receive a response to the data frame,
- a frame for example, an ACK / BA frame from the AP
- a method of attempting to retransmit the data frame through a backoff process using the EDCA scheme is shown. This may be understood to be similar to the PS-Poll transmission scheme of FIG. 15.
- the STA2 when the STA2 wakes up from the sleep mode, the STA2 first transmits and reports a data frame. If the STA2 does not receive a response to the data frame, the STA2 postpones retransmission of the data frame and detects a beacon frame from the AP. In this case, a scheme of retransmitting a data frame through a backoff process using an EDCA scheme (ie, a scheme similar to the PS-Poll transmission scheme of FIG. 16) may be applied.
- an EDCA scheme ie, a scheme similar to the PS-Poll transmission scheme of FIG. 16
- the STA2 waking up from the sleep mode does not immediately transmit a data frame. However, if any frame from another STA is detected / received, the STA2 attempts to transmit the data frame through the EDCA method.
- a scheme ie, a scheme similar to the PS-Poll transmission scheme of FIG. 14 may be applied.
- FIG. 18 is a diagram for explaining an example of the present invention for RTS frame transmission of a Non-TIM STA.
- the non-TIM STA may transmit the RTS frame through the backoff in the EDCA method before transmitting the uplink data frame.
- the data frame may be transmitted.
- the STA1 when the STA2 wakes up from the sleep mode, the STA1 first transmits and reports an RTS frame. If the STA2 does not receive a response (for example, a CTS frame) for the RTS frame, the STA2 wakes up in the sleep mode. Delaying, and when any frame from another STA (for example, ACK / BA frame from the AP) is detected, a method of attempting to retransmit the RTS frame through the back-off process in the EDCA method. This may be understood to be similar to the PS-Poll transmission scheme of FIG. 15.
- the STA2 wakes up the first RTS frame, and if it does not receive a response to the data frame, delays the RTS frame retransmission and detects the beacon frame from the AP.
- a scheme of retransmitting an RTS frame through a backoff process using an EDCA scheme ie, a scheme similar to the PS-Poll transmission scheme of FIG. 16 may be applied.
- the STA2 even if the STA2 wakes up from the sleep mode, the STA2 does not immediately transmit the RTS frame even when the channel is idle. If any frame from another STA is detected / received, the STA2 attempts to transmit the RTS frame through the EDCA method.
- a scheme ie, a scheme similar to the PS-Poll transmission scheme of FIG. 14 may be applied.
- 19 and 20 are diagrams for explaining examples of the present invention using a timer for channel access deferral of a Non-TIM STA.
- PS-Poll / trigger / data / RTS frame when a non-TIM STA wakes up from a sleep mode and senses a channel before transmitting a PS-Poll / trigger / data / RTS frame and the channel is idle.
- PS-Poll / trigger / data / RTS frame is transmitted, but if PS-Poll / trigger / data / RTS frame is not received, PS-Poll / trigger / data / RTS frame is not received. It may be set to defer retransmission of the frame.
- the predetermined time may be determined based on a predetermined timer.
- the timer may be started at the time when the Non-TIM STA transmits the PS-Poll / Trigger / Data / RTS frame.
- a predetermined timer may be started. That is, it can be expressed that channel access is prohibited or delayed while the timer is running.
- the PS-Poll / trigger / data / RTS frame may be transmitted through a backoff process.
- the timer may be stopped if any frame or beacon frame from another STA is detected / received while the timer is in operation.
- a PS-Poll / trigger / data / RTS frame is processed through a backoff process when the timer expires.
- the point in time at which the PS-Poll / trigger / data / RTS frame is attempted to be transmitted after the timer is started may be referred to as the time point at which the frame is received from another STA (or beacon received from the AP) or the timer expires. .
- the PS2 may first transmit the PS-Poll frame and may start the PS-Poll timer when the ACK frame is not received. During the timer operation, retransmission of the PS-Poll frame is delayed. If any frame (for example, an ACK / BA frame from the AP) or a beacon frame is detected during the timer operation, a retransmission of the PS-Poll frame may be attempted through the EDCA scheme through a backoff process. .
- the STA2 when the STA2 wakes up from the sleep mode and reports the channel as idle, it may first transmit a PS-Poll frame and may start the PS-Poll timer when the ACK frame is not received. During the timer operation, retransmission of the PS-Poll frame is delayed. If the timer expires even if no frame (for example, an ACK / BA frame from the AP) or a beacon frame is detected from another STA, the STA2 retransmits the PS-Poll frame through a backoff process in an EDCA manner. You can try
- the timer used in the example of the present invention described with reference to FIGS. 19 and 20 may be set longer than the conventional probe delay PD.
- the timer may be set equal to the maximum TXOP duration.
- the present invention is not limited thereto, and a timer value may be appropriately set according to network policy, performance of STA, user setting, and the like.
- the STA After the Non-TIM STA fails to transmit the PS-Poll / Trigger / Data / RTS frame, after waiting / delaying for a predetermined time according to various examples proposed in the present invention, the STA performs a backoff according to the RBO or ERBO. After performing the retransmission of the PS-Poll / trigger / data / RTS frame can be attempted.
- performing the backoff process according to the ERBO is similar to the operation of the previously defined STA. Therefore, the new operation of the STA is defined to increase the complexity of the implementation. It may be preferable compared to.
- 21 illustrates a channel access method of a non-TIM STA according to an embodiment of the present invention.
- the Non-TIM STA may determine that the channel is idle through channel sensing. That is, assume a state in which the channel is determined to be idle even by virtual carrier sensing such as NAV.
- the Non-TIM STA may postpone transmission of the first frame (eg, a PS-Poll frame, a trigger frame, a data frame, or an RTS frame).
- the first frame eg, a PS-Poll frame, a trigger frame, a data frame, or an RTS frame.
- the channel is determined to be idle, the channel access can be attempted.
- the Non-TIM STA operation proposed in the present invention the channel is idle and additional conditions must be satisfied. It works to try.
- the Non-TIM STA attempts to transmit the first frame when a second frame (eg, any frame from another STA or a beacon frame from the AP) is received or when a predetermined timer expires. can do. For example, if any one of the reception of the second frame and the predetermined timer expiration is satisfied first, the transmission of the first frame may be attempted.
- a second frame eg, any frame from another STA or a beacon frame from the AP
- the Non-TIM STA may transmit the first frame when the conditions of steps S2110 and S2130 are satisfied.
- the first frame may be transmitted first.
- the first frame can be transmitted as long as the channel is in an idle state without considering the delay for the first frame (that is, without considering whether the condition described in step S2130 is satisfied).
- step S2110 may be performed when primary transmission of the first frame fails (that is, reception of a response frame for the first frame) fails. That is, the steps S2110 to S2140 may be understood to be applied to retransmission of the first frame after the transmission of the first frame fails.
- the predetermined timer may operate to start when the first frame is primarily transmitted or when it is determined that transmission of the first frame has failed.
- FIG. 21 Although the example method described in FIG. 21 is represented by a series of operations for simplicity of description, it is not intended to limit the order in which the steps are performed, and each step may be performed simultaneously or in a different order as necessary. have. In addition, not all the steps illustrated in FIG. 21 are necessary to implement the method proposed by the present invention.
- 22 is a block diagram illustrating a configuration of a wireless device according to an embodiment of the present invention.
- the STA 10 may include a processor 11, a memory 12, and a transceiver 13.
- the transceiver 13 may transmit / receive a radio signal, for example, may implement a physical layer according to the IEEE 802 system.
- the processor 11 may be connected to the transceiver 13 to implement a physical layer and / or a MAC layer according to the IEEE 802 system.
- the processor 11 may be configured to perform an operation of the STA according to the various embodiments of the present invention described above.
- a module for implementing the operation of the STA according to various embodiments of the present invention described above may be stored in the memory 12 and executed by the processor 11.
- the memory 12 may be included in the processor 11 or installed outside the processor 11 and connected to the processor 11 by a known means.
- the processor 11 of the STA 10 may be configured to implement various examples of the present invention in which a STA operating in a non-TIM mode in a WLAN system performs channel access.
- the processor 11 may be configured to perform channel sensing. If it is determined that the channel is in an idle state, the processor 11 may determine whether or not a second frame from another STA (eg, any frame from another STA or a beacon frame from an AP) is detected or predetermined. It may be set to postpone the transmission of the first frame (eg, PS-Poll frame, trigger frame, data frame or RTS frame) until the timer expires. When the second frame is detected or the predetermined timer expires, the processor 11 may be configured to transmit the first frame using the transceiver 13.
- a second frame from another STA eg, any frame from another STA or a beacon frame from an AP
- the processor 11 may be configured to transmit the first frame using the transceiver 13.
- the specific configuration of the STA apparatus as described above may be implemented so that the above-described matters described in various embodiments of the present invention may be independently applied or two or more embodiments may be simultaneously applied, and overlapping descriptions will be omitted for clarity.
- Embodiments of the present invention described above may be implemented through various means.
- embodiments of the present invention may be implemented by hardware, firmware, software, or a combination thereof.
- a method according to embodiments of the present invention may include one or more Application Specific Integrated Circuits (ASICs), Digital Signal Processors (DSPs), Digital Signal Processing Devices (DSPDs), and Programmable Logic Devices (PLDs). It may be implemented by field programmable gate arrays (FPGAs), processors, controllers, microcontrollers, microprocessors, and the like.
- ASICs Application Specific Integrated Circuits
- DSPs Digital Signal Processors
- DSPDs Digital Signal Processing Devices
- PLDs Programmable Logic Devices
- FPGAs field programmable gate arrays
- processors controllers, microcontrollers, microprocessors, and the like.
- the method according to the embodiments of the present invention may be implemented in the form of a module, a procedure, or a function that performs the functions or operations described above.
- the software code may be stored in a memory unit and driven by a processor.
- the memory unit may be located inside or outside the processor, and may exchange data with the processor by various known means.
Abstract
Description
Claims (15)
- 무선랜 시스템에서 스테이션(STA)이 채널 액세스를 수행하는 방법에 있어서,채널이 유휴(idle) 상태인 경우에, 다른 STA으로부터의 제 2 프레임이 검출(detect)될 때까지 제 1 프레임의 전송을 연기(defer)하는 단계; 및상기 제 2 프레임이 검출되면 상기 제 1 프레임을 전송하는 단계를 포함하는, 채널 액세스 수행 방법.
- 제 1 항에 있어서,상기 제 1 프레임의 전송을 연기하는 단계는,상기 STA이 웨이크업하였을 때 상기 채널이 유휴 상태라고 결정되는 경우에 수행되는, 채널 액세스 수행 방법.
- 제 1 항에 있어서,상기 제 1 프레임의 전송을 연기하는 단계는,상기 STA이 웨이크업하였을 때 상기 제 1 프레임을 전송하고, 상기 STA이 웨이크업하였을 때 전송된 제 1 프레임에 대한 응답 프레임이 수신되지 않는 경우에 수행되는, 채널 액세스 수행 방법.
- 제 3 항에 있어서,상기 STA이 웨이크업하였을 때 상기 제 1 프레임을 전송하는 것은,상기 제 1 프레임의 전송을 연기하지 않고, 채널이 유휴 상태인 것으로 결정되면 상기 제 1 프레임을 전송하는 것을 포함하는, 채널 액세스 수행 방법.
- 제 1 항에 있어서,상기 STA에 대해서 타이머가 설정되고,상기 타이머가 동작중(running)에 상기 제 1 프레임의 전송이 금지되는, 채널 액세스 수행 방법.
- 제 5 항에 있어서,상기 제 2 프레임이 검출되기 전에 상기 타이머가 만료(expire)되는 경우, 상기 제 1 프레임이 전송되는, 채널 액세스 수행 방법.
- 제 5 항에 있어서,상기 타이머가 만료되기 전에 상기 제 2 프레임이 검출되는 경우, 상기 타이머는 중지(stop)되는, 채널 액세스 수행 방법.
- 제 5 항에 있어서,상기 타이머는,상기 STA이 웨이크업하였을 때 상기 제 1 프레임을 전송하는 경우에 시작(start)되거나, 또는상기 STA이 웨이크업하였을 때 전송된 제 1 프레임에 대한 응답 프레임이 수신되지 않는 경우에 시작되는, 채널 액세스 수행 방법.
- 제 8 항에 있어서,상기 STA이 웨이크업하였을 때 상기 제 1 프레임을 전송하는 것은,상기 제 1 프레임의 전송을 연기하지 않고, 채널이 유휴 상태인 것으로 결정되면 상기 제 1 프레임을 전송하는 것을 포함하는, 채널 액세스 수행 방법.
- 제 5 항에 있어서,상기 타이머의 길이는 최대 TXOP(Transmission Opportunity) 듀레이션으로 설정되는, 채널 액세스 수행 방법.
- 제 1 항에 있어서,상기 제 1 프레임의 전송은, 백오프 과정을 수행한 후에 상기 제 1 프레임을 전송하는 것을 포함하는, 채널 액세스 수행 방법.
- 제 1 항에 있어서,상기 제 1 프레임은, PS(Power Save)-Poll 프레임, 트리거 프레임, 데이터 프레임, 또는 RTS 프레임 중의 어느 하나인, 채널 액세스 수행 방법.
- 제 1 항에 있어서,상기 제 2 프레임은, 다른 STA으로부터의 프레임, 또는 액세스 포인트(AP)로부터의 비콘 프레임 중의 어느 하나인, 채널 액세스 수행 방법.
- 제 1 항에 있어서,상기 STA는 Non-TIM(Traffic Indication Map) STA인, 채널 액세스 수행 방법.
- 무선랜 시스템에서 채널 액세스를 수행하는 스테이션(STA) 장치에 있어서,송수신기; 및프로세서를 포함하고,상기 프로세서는, 채널이 유휴(idle) 상태인 경우에, 다른 STA으로부터의 제 2 프레임이 검출(detect)될 때까지 제 1 프레임의 전송을 연기(defer)하고; 상기 제 2 프레임이 검출되면 상기 송수신기를 이용하여 상기 제 1 프레임을 전송하도록 설정되는, 채널 액세스 수행 STA 장치.
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US20150341961A1 (en) | 2015-11-26 |
KR20150105337A (ko) | 2015-09-16 |
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