WO2013151311A1 - 무선랜 시스템에서 채널 액세스 방법 및 장치 - Google Patents
무선랜 시스템에서 채널 액세스 방법 및 장치 Download PDFInfo
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- WO2013151311A1 WO2013151311A1 PCT/KR2013/002736 KR2013002736W WO2013151311A1 WO 2013151311 A1 WO2013151311 A1 WO 2013151311A1 KR 2013002736 W KR2013002736 W KR 2013002736W WO 2013151311 A1 WO2013151311 A1 WO 2013151311A1
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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
- H04W74/0816—Non-scheduled or contention based access, e.g. random access, ALOHA, CSMA [Carrier Sense Multiple Access] using carrier sensing, e.g. as in CSMA carrier sensing with collision avoidance
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W52/00—Power management, e.g. TPC [Transmission Power Control], power saving or power classes
- H04W52/02—Power saving arrangements
- H04W52/0209—Power saving arrangements in terminal devices
- H04W52/0212—Power saving arrangements in terminal devices managed by the network, e.g. network or access point is master and terminal is slave
- H04W52/0216—Power saving arrangements in terminal devices managed by the network, e.g. network or access point is master and terminal is slave using a pre-established activity schedule, e.g. traffic indication frame
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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
- H04W74/04—Scheduled or contention-free access
- H04W74/06—Scheduled or contention-free access using polling
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W28/00—Network traffic management; Network resource management
- H04W28/02—Traffic management, e.g. flow control or congestion control
- H04W28/0215—Traffic management, e.g. flow control or congestion control based on user or device properties, e.g. MTC-capable devices
- H04W28/0221—Traffic management, e.g. flow control or congestion control based on user or device properties, e.g. MTC-capable devices power availability or consumption
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W4/00—Services specially adapted for wireless communication networks; Facilities therefor
- H04W4/70—Services for machine-to-machine communication [M2M] or machine type communication [MTC]
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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
- H04W74/002—Transmission of channel access control information
- H04W74/006—Transmission of channel access control information in the downlink, i.e. towards the terminal
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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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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02D—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN INFORMATION AND COMMUNICATION TECHNOLOGIES [ICT], I.E. INFORMATION AND COMMUNICATION TECHNOLOGIES AIMING AT THE REDUCTION OF THEIR OWN ENERGY USE
- Y02D30/00—Reducing energy consumption in communication networks
- Y02D30/70—Reducing energy consumption in communication networks in wireless communication networks
Definitions
- the following description relates to a wireless communication system, and more particularly, to a method and apparatus for accessing a channel in a WLAN system at a listening interval.
- 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 When the number of devices increases, such as M2M communication, spending a large amount of time for channel access of one device may not only degrade the overall system performance, but may also hinder power saving of each device.
- the present invention provides a new channel access scheme for efficiently supporting an operation of a device that receives data without receiving a traffic indication map (TIM).
- TIM traffic indication map
- a method of performing channel access in a station (STA) of a wireless communication system the station access the channel to an access point (Access Point, AP) at a listening interval Attempting to, wherein the station is characterized in that the Non-TIM (Traffic Indication Map) mode.
- STA station
- AP access point
- Non-TIM Traffic Indication Map
- a station (STA) apparatus for performing channel access in a wireless communication system according to another embodiment of the present invention, a transceiver; And a processor, wherein the processor is configured to attempt channel access to an access point at a listening interval, and wherein the station is in a Non-TIM (Traffic Indication Map) mode.
- STA station
- a transceiver for performing channel access in a wireless communication system
- the processor is configured to attempt channel access to an access point at a listening interval, and wherein the station is in a Non-TIM (Traffic Indication Map) mode.
- Non-TIM Traffic Indication Map
- the start point of the listening interval may be determined by either the time point at which the station transmits the configuration information in the power management mode to the access point or the time point at which the response frame is received in response to the setting information.
- the station may attempt to access the channel without receiving a beacon frame from the access point in the listening interval.
- the channel access may comprise transmission of a power save-pol (PS-Poll) of the station.
- PS-Poll power save-pol
- the station may include a sensor type STA.
- the station may perform the channel access at a time earlier than the time at which the listening interval starts.
- the previous time point may be a value set as a system parameter or a preset value through a management process between the station and the access point.
- the next channel access may be performed at the time when the listening interval has elapsed from the first time point rather than the second time point.
- the station may attempt to access the channel at least once every listening interval.
- a new channel access method and apparatus for efficiently supporting an operation of a device that receives data without receiving a traffic indication map (TIM) 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.
- 13 is a diagram for explaining a group-based AID.
- FIG. 14 is a diagram for describing a channel access mechanism of a non-TIM STA.
- 15 is a diagram for describing an improved channel access mechanism according to an example of the present invention.
- 16 is a diagram for explaining an improved channel access mechanism according to another example of the present invention.
- FIG 17 illustrates a channel access method according to an example of the present invention.
- FIG. 18 illustrates an improved channel access mechanism using a listening interval according to an example of the present invention.
- 19 is a view for explaining a transmission time of a next PS-Poll according to an example of the present invention.
- FIG. 20 illustrates a channel access method according to an example of the present invention.
- 21 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. It may include information about supported operating classes, TIM Broadcast Indication Map Broadcast request, interworking service capability, and the like.
- SSID service set identifier
- supported rates supported channels
- RSN mobility domain. It may include 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.
- the beacon listening interval indicates how often the STA under the power saving mode wakes up to listen to the beacon management frame.
- the beacon listening interval may be transmitted to the AP through a Listen Interval Field indicating the listening interval to the AP.
- This parameter is a listening interval parameter of MLMEASSOCIATE.request Ehsms MLME-REASSOCIATE.request primitives and may be expressed in units of beacon intervals.
- the length of the listening interval field may be set to two octets, but it is not necessarily so.
- 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, it may be determined that the authorized user is 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 intervention 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 to a network and perform communication 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
- PCF Point Coordination Function
- EDCA Enhanced Distributed Channel Access
- HCCA HCF Controlled Channel Access
- EDCA is a competition based approach for providers to provide data frames to multiple users
- 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 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.
- 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 in a situation in which data is transmitted 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. 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 receiving the frame, 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 fails to 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.
- the STAs In the method of operating a power saving mode based on the TIM (or DTIM) protocol described with reference to FIGS. 9 to 12, the STAs have a data frame to be transmitted for themselves through STA identification information included in the TIM element. You can check.
- the STA identification information may be information related to an association identifier (AID) which is an identifier assigned to the STA at the time of association with the AP.
- AID association identifier
- the AID is used as a unique identifier for each STA within one BSS.
- the AID may be assigned to one of values from 1 to 2007.
- 14 bits may be allocated for an AID in a frame transmitted by an AP and / or STA, and an AID value may be allocated up to 16383, but in 2008, 16383 is set as a reserved value. It is.
- the TIM element according to the existing definition is not suitable for the application of M2M application, where a large number of (eg, more than 2007) STAs may be associated with one AP.
- the TIM bitmap size is so large that it cannot be supported by the existing frame format, and is not suitable for M2M communication considering low transmission rate applications.
- M2M communication it is expected that the number of STAs in which a received data frame exists during one beacon period is very small. Therefore, considering the application example of the M2M communication as described above, since the size of the TIM bitmap is expected to be large, but most bits have a value of 0, a technique for efficiently compressing the bitmap is required.
- bitmap compression technique there is a method of defining an offset (or starting point) value by omitting consecutive zeros in front of a bitmap.
- the compression efficiency is not high. For example, when only frames to be transmitted to only two STAs having AIDs of 10 and 2000 are buffered, the compressed bitmap has a length of 1990 but all have a value of 0 except at both ends. If the number of STAs that can be associated with one AP is small, the inefficiency of bitmap compression is not a big problem, but if the number of STAs increases, such inefficiency may be a factor that hinders overall system performance. .
- the AID may be divided into groups to perform more efficient data transmission.
- Each group is assigned a designated group ID (GID).
- GID group ID
- AIDs allocated on a group basis will be described with reference to FIG. 13.
- FIG. 13A illustrates an example of an AID allocated on a group basis.
- the first few bits of the AID bitmap may be used to indicate a GID.
- the first two bits of the AID bitmap may be used to represent four GIDs.
- the first two bits (B1 and B2) indicate the GID of the corresponding AID.
- FIG. 13A illustrates another example of an AID allocated on a group basis.
- the GID may be allocated according to the location of the AID.
- AIDs using the same GID may be represented by an offset and a length value.
- GID 1 is represented by an offset A and a length B, it means that AIDs A through A + B-1 on the bitmap have GID 1.
- FIG. 13 (b) it is assumed that AIDs of all 1 to N4 are divided into four groups. In this case, AIDs belonging to GID 1 are 1 to N1, and AIDs belonging to this group may be represented by offset 1 and length N1.
- AIDs belonging to GID 2 may be represented by offset N1 + 1 and length N2-N1 + 1
- AIDs belonging to GID 3 may be represented by offset N2 + 1 and length N3-N2 +
- GID AIDs belonging to 4 may be represented by an offset N3 + 1 and a length N4-N3 + 1.
- channel access may be allowed only to STA (s) corresponding to a specific group during a specific time interval, and channel access may be restricted to other STA (s).
- a predetermined time interval in which only specific STA (s) are allowed to access may be referred to as a restricted access window (RAW).
- RAW restricted access window
- FIG. 13C illustrates a channel access mechanism according to the beacon interval when the AID is divided into three groups.
- the first beacon interval (or the first RAW) is a period in which channel access of an STA corresponding to an AID belonging to GID 1 is allowed, and channel access of STAs belonging to another GID is not allowed.
- the first beacon includes a TIM element only for AIDs corresponding to GID 1.
- the second beacon frame includes a TIM element only for AIDs having GID 2, so that only the channel access of the STA corresponding to the AID belonging to GID 2 is allowed during the second beacon interval (or second RAW).
- the third beacon frame includes a TIM element only for AIDs having GID 3, and thus only channel access of the STA corresponding to the AID belonging to GID 3 is allowed during the third beacon interval (or third RAW).
- the fourth beacon frame again includes a TIM element for only AIDs having GID 1, and thus only channel access of the STA corresponding to the AID belonging to GID 1 is allowed during the fourth beacon interval (or fourth RAW). Then, even in each of the fifth and subsequent beacon intervals (or fifth and subsequent RAWs), only channel access of the STA belonging to the specific group indicated in the TIM included in the beacon frame may be allowed.
- the order of GIDs allowed according to beacon intervals is cyclic or periodic, but is not limited thereto. That is, by including only the AID (s) belonging to a particular GID (s) in the TIM element, allowing channel access only to the STA (s) corresponding to the particular AID (s) during a particular time period (eg, a particular RAW). And operate in a manner that does not allow channel access of the remaining STA (s).
- the group-based AID allocation scheme as described above may also be referred to as a hierarchical structure of the TIM. That is, the entire AID space may be divided into a plurality of blocks, and only channel access of STA (s) (that is, STAs of a specific group) corresponding to a specific block having a non-zero value may be allowed. Accordingly, the TIM can be divided into small blocks / groups so that the STAs can easily maintain the TIM information and manage the blocks / groups according to the class, quality of service (QoS), or purpose of the STA. 13 illustrates a two-level hierarchy, but a hierarchical TIM may be configured in the form of two or more levels.
- QoS quality of service
- the entire AID space may be divided into a plurality of page groups, each page group may be divided into a plurality of blocks, and each block may be divided into a plurality of sub-blocks.
- the first N1 bits represent a page ID (i.e., PID)
- the next N2 bits represent a block ID
- the next N3 bits Indicates a sub-block ID and may be configured in such a way that the remaining bits indicate the STA bit position within the sub-block.
- the present invention proposes a method for efficiently supporting a STA receiving data from an AP without TIM signaling in order to improve a channel access operation of the STA in a WLAN system.
- FIG. 14 is a diagram for describing a channel access mechanism of a non-TIM STA.
- the STA may inform the AP of its existence through a management operation such as an association process or a negotiation process, and establish a preference for downlink transmission. I can tell you. For example, the indication and confirmation of such information may be performed through an association request / response process or a probe request / response process between the STA and the AP.
- a management operation such as an association process or a negotiation process
- the preference of the STA for downlink transmission may include one of a method of recognizing whether downlink data exists through a TIM and receiving downlink data accordingly, or a method of receiving downlink data without being based on the TIM.
- a meter or sensor type STA (referred to herein as S-STA) is a fixed period (e.g., based on the characteristics of the application (e.g. gas meter reading) to minimize power consumption). It may be assumed that the device operates in a sleep mode for a long time and then wakes up for a short time to perform channel access.
- One purpose of the AP to provide the TIM information to the STA is to increase the efficiency of resource usage by allowing the STA to access the channel only in the time resource indicated by the TIM.
- the signaling overhead of transmitting the TIM information to the S-STA in each beacon is rather inefficient in network resource usage. May cause. Therefore, it can be said that the S-STA needs to inform the status of data buffering at the AP while taking the overhead of TIM signaling.
- a mode operating without being instructed by the TIM may be referred to as a non-TIM mode, while a mode operating according to the instruction by the TIM may be referred to as a TIM mode.
- the AP stores downlink data to be transmitted to the STA until it receives the PS-Poll from the STA. Since the Non-TIM STA can transmit the PS-Poll without being limited to the TIM, the Non-TIM STA can transmit the PS-Poll to the AP at any time. When the AP receives the PS-Poll from the Non-TIM STA, the AP may transmit downlink data on the corresponding STA stored to the STA and receive an ACK frame from the STA.
- the AP does not know in advance when the S-STA (or non-TIM STA) transmits the PS-Poll, preference information on the TIM signaling during negotiation / association with the S-STA (for example, Downlink data is prepared from the time point at which the PS-Poll operation is performed without TIM signaling) or from the time when downlink data for the corresponding S-STA is generated until the downlink data is transmitted to the corresponding S-STA. And must be stored.
- the amount of data for an individual S-STA is not large, in the case where there are a large number of S-STAs accessing channels according to various types and periods, buffering and / or managing data for all S-STAs is a system or It can put a heavy burden on the AP.
- the present invention proposes a new channel access scheme (specifically, a new PS-Poll mechanism) for S-STA (or Non-TIM STA) to solve such inefficiency.
- the PS-Poll transmission time point and / or transmission period of the S-STA (or non-TIM STA) is set in advance, so that the AP manages downlink data based on the transmission time point and / or transmission period information. Suggest a solution. Accordingly, by reducing the burden on the AP to maintain the data of the S-STAs for a long time, the buffer / memory resources of the AP can be used more efficiently.
- 15 is a diagram for describing an improved channel access mechanism according to an example of the present invention.
- the S-STA may transmit a PS-Poll transmission based on TIM signaling through a management process (for example, an association request / response process and a probe request / response process) with the AP.
- a management process for example, an association request / response process and a probe request / response process
- the S-STA may perform negotiation for one or more of the PS-Poll transmission time point or transmission period while notifying the AP that it will operate in a mode that is not based on the TIM (ie, Non-TIM mode). That is, the S-STA may exchange information with respect to the transmission time and / or transmission period of the PS-Poll and the AP through a specific management frame.
- the STA will be determined based on its application characteristics (e.g., reporting rate, channel access rate) to inform the AP. It may be. Alternatively, the AP may proactively determine and inform the S-STA based on the load and status of the network (eg, based on network access load, software update period, etc.).
- application characteristics e.g., reporting rate, channel access rate
- the AP may proactively determine and inform the S-STA based on the load and status of the network (eg, based on network access load, software update period, etc.).
- the information on the PS-Poll transmission time and / or transmission period informed to the other party from either the S-STA or the AP may be modified (or updated) in the other party and returned back.
- the AP may modify the information as it is or considering the network load. May be generated and notified to the STA through a predetermined response frame.
- the S-STA generates a modified information based on its application characteristics, etc.
- the AP may inform the AP through the response frame.
- the STA may transmit the PS-Poll to the AP accordingly.
- the STA since the STA must undergo a contention for the media in order to transmit the PS-Poll, it should be understood that the STA attempts the transmission at that time. That is, the transmission and reception of the PS-Poll may not be performed correctly at a preset transmission time / cycle.
- the PS-Poll transmission possible (or transmission permission) time / period is set in advance, the operation of the AP and the STA will be described.
- the AP prepares data before a preset PS-Poll transmission time point of the STA (for example, an S-STA or a Non-TIM STA), and then prepares the data if the PS-Poll from the STA is successfully received. It may transmit to the STA.
- a preset PS-Poll transmission time point of the STA for example, an S-STA or a Non-TIM STA
- the AP may prepare data in advance with margin in consideration of this.
- the time that the AP prepares data may include a time for receiving and buffering data to be transmitted to the STA from the server.
- the AP If the AP does not have enough time to prepare data and receives the PS-Poll from the STA but cannot transmit the data immediately, the AP transmits an ACK frame for the PS-Poll first and then the data is raced to the STA. It may also be transmitted (see FIG. 11 above). According to the proposal of the present invention, the AP can prepare and buffer the data before the required time by targeting a specific point in time, instead of continuously buffering the data after the association / negotiation process with the STA. Will be reduced.
- An STA may transmit the PS-Poll to the AP through competition according to a preset time / cycle for transmitting the PS-Poll. Since the S-STA is often in the sleep (or doze) mode for a long period of time, the S-STA may operate to wake up at a preset time / period of the PS-Poll transmission and transmit the PS-Poll to the AP through contention. .
- the PS-Poll transmission time point of the STA may correspond to a target wake time of the STA.
- the PS-Poll transmission may continue to fail.
- the STA transmits the PS-Poll based on the TIM
- the possibility that the other STA occupies the medium at that time cannot be excluded. Therefore, even if the STA attempts to transmit PS-Poll several times and eventually fails, attempting to transmit the PS-Poll without restriction may cause problems such as excessive power consumption of the STA.
- a specific timer for example, a PS-Poll transmittable timer or channel
- PS-Poll transmittable timer or channel related to PS-Poll transmission or channel access of an STA (for example, an S-STA or a Non-TIM STA)
- an STA for example, an S-STA or a Non-TIM STA
- the specific timer may be defined as operating at an interval starting from the aforementioned PS-Poll transmission possible time point to a predetermined boundary time point.
- the STA may attempt to transmit the PS-Poll
- the AP may expect to transmit the PS-Poll from the STA.
- the PS-Poll transmission time rather than setting the PS-Poll transmission time as a fixed time, it is to define (or limit) the time window (or time interval) that the STA is allowed to transmit the PS-Poll (that is, access to the channel). Can be understood. Accordingly, within the interval defined by the PS-Poll transmission possible time and the timer, the PS-Poll transmission (or channel access) of the STA may be performed based on contention.
- This timer may be set at both the AP and the STA.
- the STA enters the doze state when the timer started at the preset PS-Poll transmission time expires and at the next PS-Poll transmission possible time (or next transmission time determined based on the PS-Poll transmission period).
- the PC may wake up and attempt to transmit the PS-Poll during the time interval.
- the AP prepares and buffers data for the STA at (or before) the preset PS-Poll transmission time, and discards the buffered data when the timer started at the PS-Poll transmission time expires. can be discarded.
- timing synchronization between the AP and the STA may not match due to a problem such as clock drift.
- the STA knows that the PS-Poll transmission is allowed, and the STA transmits the PS-Poll to the AP, but the AP has already discarded data because the corresponding time window has expired. You may not receive the data correctly. That is, strictly applying the PS-Poll transmission allowance time window of the STA may not properly perform channel access or data transmission / reception of the STA.
- the STA may allow the PS-Poll transmission at any time.
- the AP may operate to maintain data without discarding the STA.
- the operation scheme not to prohibit the transmission of the PS-Poll by the STA even after the timer expires is the PS-Poll of the STA defined (or limited) according to the PS-Poll transmission time (or wake-up time) and the specific timer. It may be understood as an alternative to the setting for the transmission (or channel access) time window or as an exception.
- the AP and the STA may be set in advance through a management operation such as a negotiation / association process.
- channel access such as PS-Poll transmission and reception of the S-STA (or non-TIM STA) may be reliably guaranteed.
- 16 is a diagram for explaining an improved channel access mechanism according to another example of the present invention.
- the PS-Poll transmission (or channel access) allowance time of the S-STA (or non-TIM STA) is included within a specific beacon interval (time window between two consecutive beacons).
- the AP allows PS-Poll transmission (or channel access) allowance window of S-STA (or non-TIM STA) to beacon signal and PS-Poll transmission (or channel access) of other type STA (or TIM STA) Information on the separation configuration of the time window may be included and transmitted to the STAs.
- the specific time window in each beacon interval is S-STA (or Non).
- the time is limited to the interval allowing PS-Poll transmission (or channel access) of the TIM STA, and the other time window is limited to the interval allowing PS-Poll transmission (or channel access) of another type of STA (or TIM STA).
- Information on the split configuration of the window may be informed to each STA.
- the separate setting of the time window means setting the time window such that the S-STA (or non-TIM STA) and another type of STA (or TIM STA) do not allow channel access within the same time window.
- only S-STAs (or non-TIM STAs) can channel access in certain time windows, and other types of STAs (or TIM STAs) are not allowed to access channels.
- Channel access of the STA (or non-TIM STA) is not allowed and may be referred to as setting a time window so that only another type of STA (or TIM STA) can access the channel.
- the information on the separation setting of the time window may include, for example, a method of informing the TIM STA of a time window in which channel access is not allowed, a method of informing a TIM STA of a time window in which channel access is allowed, and a non-TIM STA.
- the method may include one or more of a method of notifying a time window in which channel access is not allowed, and a method of notifying a non-TIM STA in which time window is allowed in channel access.
- channel access is allowed only to the first type of STA (eg, S-STA or Non-TIM STA) as described above, and the second type of STA (eg, STA or TIM STA of a type other than S-STA).
- the AP informs the specific STA of the time and period (or interval) information of the time window and the specific STA only within the time window set according to the time and period.
- PS-Poll (or channel access) of the may be allowed or not allowed.
- channel access is not allowed in the time window for the first type STA through a management operation such as negotiation / association process to the second type STA (or for the first type STA within a specific beacon interval).
- Channel access is allowed in the remaining time window other than the time window).
- a time point (or length of a time interval), and / or a position in time of a specific time window is indicated.
- the notification may be preset in advance through a management operation such as a negotiation / association process between the AP and the STA.
- FIG 17 illustrates a channel access method according to an example of the present invention.
- the AP may provide the STA with configuration information regarding a time window in which access of the TIM mode STA is not allowed (or a time window in which only access of the Non-TIM mode STA is allowed).
- the time window may be set periodically.
- the time window may be specified by a start time point and a time interval (or a timer).
- channel access eg, PS-Poll transmission
- the STA is a non-TIM mode STA in step S1720
- channel access eg, PS-Poll transmission
- the time window may be referred to as a window in which only access of the Non-TIM mode STA is restricted.
- the AP may buffer data for the STA in advance before the time window for channel access of the non-TIM mode STA, and discard the data after the time window expires.
- channel access may be performed in a time interval indicated by the TIM for the STA during a time interval other than the time window.
- the STA may define a listening interval to inform how often to wake up under the power saving mode to listen to the beacon management frame from the AP, and inform the AP of the defined listening interval information.
- the terminal in the power saving mode may check the TIM signaling by periodically waking up using the defined listening interval and receiving a beacon management frame from the AP in the awake state.
- the listening interval of the terminal in the power saving mode should be set depending on the transmission period of the beacon frame (eg, set to a multiple of the beacon interval).
- the operation in the power saving mode of the STA according to the listening interval set according to the TIM signaling mode (TIM mode) and the non-TIM mode (Non-TIM mode) mode may be defined differently.
- STAs eg, TIM STAs
- STAs operating in the non-TIM mode eg, non-TIM STAs or S-STAs
- the beacon frame is received at the listening interval, while the STA operating in the non-TIM mode performs channel access at the listening interval (for example, the PS-Poll frame is performed. Transmission). That is, the operation in the power saving mode according to the listening interval of the STA may be set differently according to the operation mode of the STA.
- the non-TIM STA instead of receiving a beacon frame, proposes an improved channel access mechanism for performing channel access by transmitting at least one PS-Poll (or trigger frame) at every listening interval.
- FIG. 18 illustrates an improved channel access mechanism using a listening interval according to an example of the present invention.
- An STA (eg, an S-STA or Non-TIM STA) that does not confirm TIM signaling indicates when to inform the AP to switch to power management mode or when to receive a response to the notification to switch to power management mode. It can be set as the starting point of the listening interval. For example, the STA may start when the STA transmits a frame in which an index of a power management (PM) field is set to 1 or receives a response frame (ACK frame) in response to the frame. Can be set. (In FIG. 18, the time point at which the response frame is received is illustrated as being set as the start point of the listening interval.)
- PM power management
- ACK frame response frame
- the AP and the STA may set a start point of a listening interval in consideration of a transmission and processing delay occurring when transmitting and receiving a frame.
- the STA may wake up according to the listening interval and perform channel access (eg, transmission of PS-Poll) to the AP. If the STA is a Non-TIM STA or S-STA, the STA does not need to receive the beacon frame at the listening interval.
- the STA may perform channel access by transmitting at least one PS-Poll (or trigger frame) at every listening interval instead of receiving the beacon frame.
- the AP may buffer data from a specific time point to a time point at which the UE transmits the PS-Poll in accordance with the listening interval, and may transmit the buffered data to the STA when the PS-Poll is successfully received. If the PS-Poll is not received from the STA when the PS-Poll is to be received, the AP may discard the buffered data after a predetermined time elapses.
- the predetermined time may be a value negotiated through a management procedure between the STA and the AP in advance, or may be determined based on a predetermined parameter and a specific timer in the system.
- the data buffering start time of the AP may be from a time point at which data to be transmitted to the STA is received from an outsource such as a server.
- the time point at which the AP buffers and discards data may be set to a value associated with a listening interval of the STA, for example, a value having a period equal to the listening interval, and may be periodically operated.
- the STA may be configured to transmit the PS-Poll at a specific time point according to the listening interval. For example, as in the example illustrated in FIG. 18, the STA may perform channel access at a specific time point at which the listening interval is repeated at intervals.
- the STA may not always transmit PS-Poll at a time point to be correctly transmitted. Accordingly, although the STA transmits the PS-Poll at a time delayed from the correct transmission time, it may occur that the AP has already discarded the buffering data and thus cannot transmit data to the STA. In this case, the next transmission time of the PS-Poll may be determined as the time when the listening interval elapses from the time when the PS-Poll should be transmitted, not the time when the listening interval has elapsed since the actual PS-Poll is transmitted. That is, even if a transmission delay of the PS-Poll occurs, the STA may transmit the PS-Poll again according to a preset listening interval without considering the occurrence of the delay. A detailed example of this is shown in FIG. 19.
- FIG. 19 is a view for explaining a transmission time of a next PS-Poll according to an example of the present invention.
- the STA fails to transmit the PS-Poll at the correct transmission time point (1910, the first time point), and transmits the PS-Poll at the delayed time point (1920, the second time point). Even if the transmission time of the next PS-Poll is the time when the listening interval has elapsed from the first time point, and the time when the listening interval has not elapsed from the second time point.
- the STA may transmit the PS-Poll to the AP in advance at a prior time (prior time) than the time for the next transmission of the PS-Poll.
- the prior time may be set as a system parameter in advance or may be set through a pre-management procedure between the STA and the AP.
- the AP continues the data buffering and discarding operation according to the preset listening interval.
- the STA attempts to access the channel only at a specific time point set to a listening interval.
- the STA according to the present embodiment can basically attempt channel access (eg, transmit a PS-Poll) within a period not exceeding an interval boundary of a predetermined listening interval. That is, the STA may attempt channel access (for example, transmitting PS-Poll) to the AP at least once every listening interval.
- FIG. 20 illustrates a channel access method according to an example of the present invention.
- the STA may provide listening interval information indicating the channel access interval to the AP.
- the start point of the listening interval may be set to any one of a time point at which the STA notifies the AP of switching to the power management mode and a time point of receiving a response to the notification of switching to the power management mode.
- the STA may perform channel access (eg, PS-Poll transmission) to the AP according to the listening interval.
- the AP may buffer data for the STA in advance before the channel access estimated time for the channel access of the STA, and discard the data after a predetermined time elapses from the expected channel access.
- improved interval information may be used instead of the listening interval for the STA for power saving.
- the described listening interval may be replaced with improved interval information such as a polling interval and a maximum idle period for STAs for power saving.
- Interval information such as a polling interval or a maximum idle period, may be used as interval / period information on how often the STA should transmit the PS-Poll to check the indication of the buffered frame of the AP.
- the third embodiment may be implemented using the listening interval information, it may be understood that the third embodiment may be implemented using the improved section information instead of the listening interval information.
- the STA may inform the AP that the STA does not listen to the beacon through Bit Indication of the conventional section information field. For example, the STA may set the two octet long listening interval field to 0 or all to 1 to inform the AP that it does not listen to the beacon.
- 21 is a block diagram illustrating a configuration of a wireless device according to an embodiment of the present invention.
- the AP 10 may include a processor 11, a memory 12, and a transceiver 13.
- the STA 20 may include a processor 21, a memory 22, and a transceiver 23.
- the transceivers 13 and 23 may transmit / receive wireless signals and, for example, may implement a physical layer in accordance with the IEEE 802 system.
- the processors 11 and 21 may be connected to the transceivers 13 and 21 to implement a physical layer and / or a MAC layer according to the IEEE 802 system. Processors 11 and 21 may be configured to perform operations according to the various embodiments of the present invention described above.
- modules for implementing the operations of the AP and the STA according to various embodiments of the present invention described above may be stored in the memories 12 and 22 and executed by the processors 11 and 21.
- the memories 12 and 22 may be included in the processors 11 and 21 or may be installed outside the processors 11 and 21 and connected to the processors 11 and 21 by known means.
- 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 (14)
- 무선 통신 시스템의 스테이션(STA)에서 채널 액세스를 수행하는 방법에 있어서,청취 인터벌에서 액세스 포인트로 채널 액세스를 위한 PS-Poll (Power Save-Poll)을 전송하는 단계를 포함하고,상기 스테이션은 상기 액세스 포인트로부터 전송되는 TIM (Traffic Indication MAP) 요소에 의해 제한되지 않는 Non-TIM 모드로 동작하고,상기 PS-Poll의 전송 시점은 상기 TIM 요소에 의해 제한되지 않는 것을 특징으로 하는, 채널 액세스 수행 방법.
- 제 1 항에 있어서,상기 청취 인터벌의 시작점은 상기 스테이션이 상기 액세스 포인트로 전력 관리 모드로의 설정 정보를 전송하는 시점 또는 상기 설정 정보에 대한 응답으로 응답 프레임을 수신하는 시점 중 어느 하나인 것을 특징으로 하는 채널 액세스 수행 방법.
- 제 1 항에 있어서,상기 스테이션은 센서 타입 STA을 포함하는, 채널 액세스 수행 방법.
- 제 1 항에 있어서,소정 횟수의 이전 청취 인터벌 동안 연속적으로 상기 PS-Poll의 전송이 실패한 경우,상기 스테이션은 상기 청취 인터벌의 시작점보다 이전 시점에 상기 PS-Poll을 전송하는 것을 특징으로 하는, 채널 액세스 수행 방법.
- 제 4 항에 있어서,상기 이전 시점은 시스템 파라미터로 설정된 값이거나, 상기 스테이션 및 상기 액세스 포인트 사이의 관리 과정을 통해 기 설정된 값인 것을 특징으로 하는, 채널 액세스 수행 방법.
- 제 1 항에 있어서,상기 PS-Poll의 전송이 상기 청취 인터벌의 제 1 시점보다 지연된 제 2 시점에 수행되더라도,다음 번 PS-Poll의 전송 시점은 상기 제 2 시점이 아닌 상기 제 1 시점으로부터 기산되는 것을 특징으로 하는, 채널 액세스 수행 방법.
- 제 1 항에 있어서,상기 스테이션은 매 청취 인터벌 마다 적어도 한번 상기 채널 액세스를 시도하는 것을 특징으로 하는, 채널 액세스 수행 방법.
- 무선 통신 시스템에서 채널 액세스를 수행하는 스테이션(STA) 장치에 있어서,송수신기; 및프로세서를 포함하고,상기 프로세서는, 청취 인터벌에서 액세스 포인트(Access Point, AP)로부터 전송되는 TIM (Traffic Indication MAP) 요소에 의해 제한되지 않는 Non-TIM 모드로 설정되고,상기 PS-Poll의 전송 시점은 상기 TIM 요소에 의해 제한되지 않는 것을 특징으로 하는, 채널 액세스 수행 장치.
- 제 8 항에 있어서, 상기 프레서서는,상기 액세스 포인트로 전력 관리 모드로의 설정 정보를 전송하는 시점 또는 상기 설정 정보에 대한 응답으로 응답 프레임을 수신하는 시점 중 어느 하나를 상기 청취 인터벌의 시작점으로 설정하는 것을 특징으로 하는, 채널 액세스 수행 스테이션 장치.
- 제 8 항에 있어서,상기 스테이션은 센서 타입 STA을 포함하는, 채널 액세스 수행 스테이션 장치.
- 제 8 항에 있어서,소정 횟수의 이전 청취 인터벌 동안 연속적으로 상기 PS-Poll의 전송이 실패한 경우,상기 프로세서는 상기 청취 인터벌의 시작점보다 이전 시점에 상기 PS-Poll 전송하도록 설정되는 것을 특징으로 하는, 채널 액세스 수행 스테이션 장치.
- 제 11 항에 있어서,상기 이전 시점은 시스템 파라미터로 설정된 값이거나, 상기 스테이션 및 상기 액세스 포인트 사이의 관리 과정을 통해 기 설정된 값인 것을 특징으로 하는, 채널 액세스 수행 스테이션 장치.
- 제 8 항에 있어서, 상기 프로세서는상기 PS-Poll의 전송이 상기 청취 인터벌의 제 1 시점보다 지연된 제 2 시점에 수행되더라도,상기 제 2 시점이 아닌 상기 제 1 시점으로부터 다음 번 PS-Poll의 전송 시점을 기산하는 것을 특징으로 하는, 채널 액세스 수행 스테이션 장치.
- 제 8 항에 있어서,상기 프로세서는 매 청취 인터벌 마다 적어도 한번 상기 PS-Poll을 전송하도록 설정되는 것을 특징으로 하는, 채널 액세스 수행 스테이션 장치.
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EP13772881.2A EP2836046B1 (en) | 2012-04-02 | 2013-04-02 | Method and apparatus for accessing channel in wlan system |
KR1020147030576A KR101988320B1 (ko) | 2012-04-02 | 2013-04-02 | 무선랜 시스템에서 채널 액세스 방법 및 장치 |
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CA2869300A CA2869300C (en) | 2012-04-02 | 2013-04-02 | Method and apparatus for accessing channel in wlan system |
US15/435,750 US9894607B2 (en) | 2012-04-02 | 2017-02-17 | Method and apparatus for accessing channel in WLAN system |
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- 2013-04-02 WO PCT/KR2013/002736 patent/WO2013151311A1/ko active Application Filing
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Also Published As
Publication number | Publication date |
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CN104335664B (zh) | 2018-04-20 |
KR101988320B1 (ko) | 2019-06-12 |
KR20150011345A (ko) | 2015-01-30 |
CA2869300C (en) | 2019-10-01 |
EP2836046B1 (en) | 2018-05-30 |
US20170164283A1 (en) | 2017-06-08 |
CA2869300A1 (en) | 2013-10-10 |
US9615286B2 (en) | 2017-04-04 |
EP2836046A1 (en) | 2015-02-11 |
EP2836046A4 (en) | 2015-11-25 |
US9894607B2 (en) | 2018-02-13 |
JP2015512597A (ja) | 2015-04-27 |
CN104335664A (zh) | 2015-02-04 |
JP6155323B2 (ja) | 2017-06-28 |
US20150334592A1 (en) | 2015-11-19 |
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