Method and apparatus for transmitting data frame in wlan system

TECHNICAL FIELD The present invention relates to a wireless local area network (WLAN) system, and more particularly to a method of transmitting a data frame by a station (STA) in a WLAN system and a wireless apparatus.

BACKGROUND OF THE INVENTION [0002] Among the wireless communication technologies, a wireless local area network (WLAN) is a technology where wireless access is possible wirelessly in homes or companies or in a region that provides a particular service by using a portable terminal, such as a personal digital assistant (PDA), laptop, portable game player (PMP), etc.

[0003] To overcome the speed limit of communication, which is considered a weakness in WLAN technology, the IEEE 802.1 In standard has recently been standardized as a technology standard. The goal in the IEEE 802.1 In standard is to increase the speed and reliability of the network and extend the range of the wireless network.

More specifically, for High Throughput (HT) - (High bandwidth) processing with a data rate of 540 Mbps or higher, minimizing transmission errors to optimize the data rate, the IEEE 802.1 In standard is based on Multiple Inputs and Multiple Outputs (MIMO) - ( many inputs have multiple outputs), in which many antennas are used on both sides of each transmitter and receiver.

[0004] When WLAN propagation is activated and WLAN applications are varied, in the STA station, necessary for the new WLAN system to support higher bandwidth than supported by the IEEE 802.1 In standard, the speed of data processing increases. A next-generation WLAN system that supports very high bandwidth - Very High Throughput (VHT) is the next version of the IEEE 802.1 In WLAN system and is one of the IEEE 802.11 WLAN systems that have been recently proposed for supporting data processing speed 1

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Gbps or higher at the service access point - MAC Service Access Point (SAP).

[0005] The next generation WLAN system supports a Multi-User transmission scheme

Multiple Input Multiple Output (MU-MIMO) - (Multiple users - many inputs have multiple outputs), where many non-AP STA stations access the radio channel at the same time for effective use of the radio channel. According to the MU-MIMO transmission scheme, the AP may transmit a frame to one or more MIMO-paired non-AP STAs at the same time.

[0006] The AP and many of the non-AP STA paralleling MIMOs may have different possibilities. Bandwidth, Modulation Coding Scheme (MCS) and Forward Error Correction (FEC), which may be supported, may vary according to the type of non-AP STA station, destinations, channel environment, etc. If the channel bandwidth to be used for transmitting STA stations having different capabilities can be freely adjusted in the TXOP (transmission opportunity) period, an interference can be generated with an AP or an STA or both that transmit and receive frames in the frequency band. Accordingly, reliability can become problematic when frames are transmitted and received.

[0007] US 2008/0080553 A1 relates to techniques and technologies that are provided for dynamically selecting one of the default channel throughputs and alternative channel capacity for transmitting information over a wireless communication link that connects the transmitter node to the receiver node. The transmitter node and receiver node are designed to transmit and receive in the default channel throughput and in the alternative channel throughput.

[0008] US 2009/0196180 A1 relates to dynamic allocation of a wake-up time block for recognized radio networks. In one application, without the need for a central controller, peer-to-peer nodes collectively detect local use of communication spectrum and use blanks together

Spacing for communication links between nodes. Sharing local views of spectrum usage among each other allows nodes to dynamically allocate non-overlapping time-frequency blocks of communication links between nodes for efficiently using empty gaps. The blocks are dimensionally matched for optimal packaging of available empty spaces. The nodes regularly adjust the bandwidth and other parameters of all reserved blocks in response to demand, so that the packed blocks in available empty spaces maintain a fair distribution of the entire band of empty spaces between active communication links, minimizes the termination of all communications, reduces the competition load between nodes competing for free intervals and maintains non-overlapping blocks.

[0009] US 2010/0061342 A1 relates to methods that provide high-throughput control fields that, in addition to other functions, provide efficient TXOP switching periods in wireless networks. In various example applications of this invention, the receiving station can only transmit to the granting station. Also in various example applications of this invention, frames may be sent at different data rates. For example, data rates of 802.11.a, 11.b, 11.g, and 11.n can be used.

Technical problem The present idea provides a method in which a wireless local area network (WLAN) system can frame to multiple STA stations by using a multi-user transmission scheme multiple multi-output (MU-MIMO) inputs.

Summary of the Invention [0011] In an aspect, the method of transmitting a data frame in a wireless LAN is defined by independent claim 1. A particular exemplary application of the method is defined in claim 2. In another aspect, a wireless apparatus is defined by independent patent claim 3 A particular example of the camera application is

EP 2 589 164 B1 defined by claim 4.

Advantageous Effects of the Invention [0013] In the TXOP period, an access point (AP) transmits a data frame using a multi-band transmission scheme. Accordingly, the entire WLAN system bandwidth can be improved, since the data can be transmitted to the STA station with different channel bandwidth capacities through efficient use of the channel bands in the WLAN system.

[0014] When a channel band is selected in the TXOP period for transmitting a data frame, a narrower bandwidth is selected than used to transmit the previous data frame. Accordingly, interferences between other STA stations can be avoided when the frames are transmitted and received.

[0015] The TXOP period is allocated until the data frame is matched with the particular channel band and the data is transmitted during the TXOP period. Other (non-target) STA station transmission may access other subchannels waiting in idle state and may transmit and receive an additional data frame. Accordingly, the bandwidth can be improved.

Brief description of the drawings [0016]

FIG. 1 is a diagram showing the configuration of a WLAN system to which an exemplary embodiment of the invention may be applied;

FIG. 2 is a block diagram showing an example of a PPDU format according to an example of the use of the invention;

FIG. 3 is a diagram showing an example of a method for transmitting a PPDU according to an example not forming part of the invention;

FIG. 4 is a diagram showing another example of a method for transmitting a PPDU according to an example not forming part of the invention;

FIG. 5 is a diagram showing still another example of a method for transmitting a PPDU according to an example of the invention;

FIG. 6 is a diagram showing an example of CCA measurement that may be used for exemplary application of the invention;

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FIG. 7 is a diagram illustrating a method for transmitting a PPDU in accordance with an example of the invention;

FIG. 8 is a diagram illustrating a method for transmitting a PPDU according to another example not forming part of the invention;

FIG. 9 shows an example of allocating pilot sequences according to channel bands;

FIG. 10 and 11 are diagrams illustrating examples in which channels suitable for exemplary applications of the invention are used; and FIG. 12 is a block diagram showing a wireless apparatus in which methods for transmitting a PPDU according to exemplary applications of the invention may be used.

[0017] FIG. 1 is a diagram showing the configuration of a WLAN system to which exemplary embodiments of this invention may be used.

[0018] Referring to FIG. 1, the WLAN system includes one or more Basic Service Set (BSS) (Basic Service Sets). BSS is a set of stations (STA) that can communicate with each other through successful synchronization. BSS is not an idea pointing to a specific area.

[0019] The BSS infrastructure includes one or more non-AP STAs STA1, STA2, STA3, STA4, and STA5, an AP (Access Point) providing service distribution and a Distribution System (DS) connecting multiple APs. In the BSS infrastructure, the AP access point manages non-AP STA stations in BSS.

[0020] On the other hand, Independent BSS (IBSS) (Independent BSS) is supported in Ad-Hoc mode. IBSS does not have a centralized management unit to perform management functions because it does not contain an AP access point. That is, in IBSS, non-AP STA stations are managed in a distributed manner. In IBSS, all STA stations can consist of mobile STA stations. All STAs form an independent network because they do not have access to DS.

[0021] The STA station is a certain functional medium, including Medium Access Control (MAC) and the interface of the physical medium layer to meet the standards of the Institute of Electrical and Electronics Engineers (IEEE) 802.11. Here and

Further, the STA denotes both the AP access point and the non-AP STA station.

[0022] The non-AP STA is an STA that is not an AP. The non-AP STA station may also be according to another terminology, for example a mobile terminal, a wireless device, a Wireless Transmit / Receive Unit (WTRU), a User Equipment (UE), a Mobile Station (MS). (Mobile station), mobile subscriber unit or simply a user. For the convenience of the description, it has been assumed here that the nonAP STA station is an STA station.

[0023] The AP is a functional medium that provides access to DS through the radio medium for the associated STA. In a BSS infrastructure including an AP, communication between the STAs is essentially done via an AP access point. If a direct link is established between the STAs, the STAs can directly communicate with each other. The AP may also be a central controller, Base Station (BS), node-B (Node-B), Base Transceiver System (BTS) or local controller according to other terminology.

[0024] Many BSS BSS infrastructures shown in FIG. 1 can be connected via the Distribution System (DS). Many BSS connected through DS are called Extended Service Set (ESS). The AP access point and / or the STA station included in the ESS can communicate with each other. In the same ESS, the STA can move from one BSS to another BSS simultaneously providing uninterrupted communication.

[0025] In a WLAN system according to the IEEE 802.11 standard, the basic access mechanism for Medium Access Control (MAC) is the Carrier Sense Multiple Access with Collision Avoidance mechanism (CSMA / CA) (Multiple Access with media avoidance detection collision) ). The CSMA / CA mechanism is also called Distributed Coordination Function (DCF) of IEEE 802.11 MAC (Distributed Coordination Function). This mechanism essentially adopts the "listen before talk" access mechanism (listen before speaking). According to this type of access mechanism, the AP and / or STA detects a radio channel or medium prior to transmission. If, as a result of detection, the medium is determined to be idle,

The AP and / or STA access point starts sending a data frame through the medium. If, as a result of the detection, the medium is determined to be in a busy state, the AP and / or the STA does not start transmission and sets the delay time for access to the medium and waits.

[0026] The CSMA / CA mechanism includes the detection of a virtual medium, in addition to the detection of the physical medium in which the AP and / or the STA directly detects the medium. Detecting virtual media is for overcoming a problem that can arise when accessing a medium, such as a hidden node problem. For the detection of virtual media, the MAC layer of the WLAN system uses Network Allocation Vector (NAV). NAV is the value at which the AP and / or STA station using the medium now or having the rights to use the medium instructs another AP and / or another STA to use the remaining time until the medium becomes available. Accordingly, the value set as NAV corresponds to the period,

[0027] The IEEE 802.11 MAC protocol, along with the DCF provides a Hybrid Coordination Function (HCF) based on Point Coordination Function (PCF), in which the receiving of an AP or reception of an STA or both periodically check the data frame using DCF and the synchronous access scheme based on checking. HCF includes Enhanced Distributed Channel Access (EDCA), in which the provider uses an access scheme for delivering a data frame to several users as a competition-based scheme and HCF Controlled Channel Access (HCCA) (Access to HCF controlled channel) using a channel access scheme not based on competition using the checking mechanism.

[0028] In the EDCA of a contention-based channel access scheme, a frame

Having 8 types of user priorities are allowed to access different parts of the medium. Each frame reaching the MAC layer from the top layer has a particular user priority value, and the MAC header of each QoS data frame contains a user priority value.

[0029] For transmitting a QoS data frame containing priorities, the QoS AP and / or the QoS STA station performs 4 access categories (ACs). The frame reaching the MAC layer is assigned the priority of the user corresponding to the AC. Accordingly, if success in EDCA competition is achieved, an EDCA TXOP (Transmission Possibility) is obtained. The TXOP period is the time period during which the given STA station has the right to initiate transmission via the radio media. The TXOP period is used to allocate a certain time during which the AP or a given STA or both may transmit a frame and guarantee the transmission of the frame. The transmission start time and the maximum TXOP transmission time are determined by the AP. In the case of EDCA TXOP,

[0030] The set of EDCA parameters (i.e., core element of the EDCA schema) is a field indicating parameters for the user priority traffic. For example, a set of EDCA parameters can be given as listed in Table 1. For the EDCA parameter set a reference can be made to Paragraph 7.3.2.29 "IEEE 802.1 In, Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) ) Specifications, Amendment 5: Enhancements for Higher Throughput "(IEE 802.1 In, Part 11, MAC Access Control Specifications for Wireless LAN Medium and Physical Layer (PHY), Amendment 5: Improvements for Higher Throughputs") disclosed in October 2009.

[Table 1]

<td colspan="5">[Table]</td>

<td>AC</td><td>CWmin</td><td>CWmax</td><td>AIFSN</td><td>TXOP limit</td>

<td>AC_BK</td><td>aCWmin</td><td>aCWmax</td><td>7</td><td>0</td>

<td>AC_BE</td><td>aCWmin</td><td>aCWmax</td><td>3</td><td>0</td>

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<td>AC_VI</td><td>(ACWmin + 1) / 2-1</td><td>aCWmin</td><td>2</td><td>3,008 ms</td>

<td>AC_VO</td><td>(ACWmin + 1) / 4-1</td><td>(ACWmin + 1) / 2-1</td><td>2</td><td>1.504 ms</td>

[0031] Values ​​such as AIFSN [AC], CWmin [AC], and CWmax [AC] (i.e., EDCA parameter set) can be transmitted on the signal frame (beacon frame) by the AP and can be transmitted to each other. STA stations. In general, priorities become higher when AIFSN [AC] and CWmin [AC] values ​​decrease. Accordingly, a larger bandwidth is used in a given traffic environment because the delay in access to the channel is shortened. As described above, the given STA determines the transmission time based on the TXOP period when the transmission starts. AP access point transfers AIFSN [AC], CWmin [AC], and CWmax [AC] (ie EDCA parameters) and TXOP Limit [AC] (ie EDCA TXOP time) in the signal frame (beacon frame) and transmits the signal frame to each STA station. [0032] The TXOP period may be received by transmitting a trial frame of the reaction, exchanging RTS frames (send request) and CTS frames (free to send), and transmitting CTS to the custom frame. The TXOP period information may be transmitted by the AP and may be included in the EDCA parameter set information elements contained in the above frames.

[0033] In contrast to the existing WLAN system, a higher bandwidth is required in the next generation WLAN system. This is called VHT (Very High Throughput). For this purpose, the new generation WLAN system is designed to support transmission in a channel with an 80 MHz bandwidth, an adjacent channel with a capacity of 160 MHz and an adjacent channel with a capacity of 160 MHz or higher. In addition, for higher bandwidth, the next-generation WLAN provides the MU-MIMO transmission scheme (Multi User-Multiple

Input Multiple Output - Many users have many inputs to go through). In a new generation of WLAN system, an AP can transmit a data frame to one or more MIMO-pair STAs at the same time. In a WLAN system such as shown in FIG. 1, the AP 10 may transmit data to the STA group of STAs 21, STA 22, STA 23, STA 24 and STA 30 associated with the AP 10 at the same time. Here, the data transmitted to the STA station can be

EP 2 589 164 B1 transmitted via various spatial streams. The data frame transmitted by the AP 10 can be called PPDU (Physical Layer Convergence Procedure (PLCP) Protocol Data Unit - Physical Layer Convergence Protocol (PLCP) data unit) which is produced at the physical layer - Physical Layer (PHY) of the WLAN system. and transmitted. In the examples of this invention, it is assumed that the group of STA target stations MUMIMATED with the AP 10 includes STA1 21, STA2 22, STA3 23 and STA4 24. In this case, the data may not be transmitted to a given STA station of the STA group Target transmission because the spatial stream is not allocated to the given STA. In the meantime, the STAa 30 station may be associated with the AP 10 access point, but it is assumed that

[0034] FIG. 2 is a block diagram showing an example of a PPDU 200 format in accordance with an exemplary application of the invention.

[0035] Referring to FIG. 2, PPDU 200 may include L-STF 210 field, LLTF 220 field, L-SIG 230 field, VHT-SIG A 240 field, VHT-STF 250 field, VHT-LTF 260 field, VHT-SIG field B 270 and data field 280.

[0036] The PLCP sublayer constituting the PHY layer adds the necessary information to the PHY Service Data Unit (PSDU) received from the MAC (Medium Access Control) layer, transforms

PSDU on data field 280, generates PPDU 200 by adding field L-STF 210, field L-LTF 220, field L-SIG 230, field VHT-SIG A 240, fields VHT-STF 250, fields VHT-LTF

260 and VHT-SIG B 270 fields to data field 280 and transmit them to one or more STA stations through a physical medium dependent sublayer (PMD) forming the PHY layer.

[0037] The L-STF 210 is used to obtain frame timing, convergence of automatic gain control - Automatic Gain Control (AGC), coarse frequency reception, and so on.

[0038] The L-LTF field 220 is used to estimate the channel for demodulating the L-SIG field 230 and the field VHT-SIG A 240.

[0039] The L-STA station uses an L-SIG 230 field for receiving a PPDU 200 and for obtaining data.

[0040] The VHT-SIG field A 240 is a field associated with the joint control information necessary for the STA MIMO stations to pair with the AP. The VHT-SIG field A 240 contains control information for interpreting the received PPDU 200. The field VHT-SIG A 240 includes spatial stream information, band information, and ID identifying information about whether each of the plurality of STA MIMO pairs uses a block encoding. time - space (Space Time Block Coding) (STBC) for each of the multiple STIM MIMO stations, group identifier (i.e., ID information about the STA transmission station group), information about the spatial stream allocated to the STA station included in the STA transmission station destination group indicated by the group identifier and the information regarding the short guard protection interval (GI) of the target transmission station STA. Here the group identifier can contain information about whether the MIMO transmission scheme used now is the MU-MIMO transmission scheme or the single user transmission scheme (SU) MIMO.

[0041] The VHT-STF 250 field is used to improve the operation of AGC estimation in the MIMO transmission scheme.

[0042] VHT-LTF 260 fields are used for STAs for estimating the MIMO channel. Because the next-generation WLAN system supports the MUMIMO transmission scheme, so many VHT-LTF 260 fields can be set as there are spatial streams in which the PPDU 200 is transmitted. In addition, if a full channel is served and implemented, the number of VHT LTF fields can be increased.

[0043] The VHT-SIG field B 270 comprises dedicated control information that is necessary for a plurality of STA MIMO stations to receive a PPDU 200 and for receiving data. Accordingly, only if the common control information included in the field VHT-SIG A 240 indicates that now the received PPDU 200 is transmitted in accordance with the MU-MIMO transmission scheme, the STA can be designated to receive the VHT-SIG B 270 fields. the page, if the common control information indicates that the now received PPDU 200 is for a single STA station (including the SU-MIMO transmission scheme), the STA can be designated to not decode the VHT-SIG B 270 fields.

[0044] The VHT-SIG field B 270 includes information about modulation, coding and speed matching of each STA station. The size of the VHT-SIG B 270 field can be

The MIMO transmission and the channel bandwidth used to transmit the PPDU are different according to the type (MU-MIMO or SU-MIMO) of the type.

[0045] Data fields 280 comprise data to be transmitted to the STA. The data field 280 includes a servicing field for resetting the data service unit (PLDU) to which the MAC data protocol protocol unit data unit (MPDU) in the MAC layer is transmitted and a scrambler (mixer), a tail field containing the bit sequence necessary to return the convolutional encoder to zero state and padding bits to standardize the length of the data field.

[0046] In the meantime, in a WLAN system such as the one shown in FIG. 1, the STAs associated with the AP may have different channel capacity. Here the simplest way in which the AP can transmit data to multiple STAs according to the MU-MIMO transmission scheme is to include the channel bandwidth information to be used for transmission in the PPH field VHT-SIG B field such as shown in FIG. 2. In this case, each STA may know the band of the transmitted PPDU channel by decoding the VHT-SIG B field.

[0047] If the PPDU format is used such as shown in FIG. 2, the channel band is included in the VHT-SIG A 240 field and transmitted. In this case, many STAs having different channel bandwidth capacities may know the common bandwidth of the channel. In a WLAN environment in which a plurality of STAs having different channel capacity capabilities as described above coexists, a method for efficiently transmitting a PPDU during a TXOP period in accordance with the MU-MIMO transmission scheme must be discussed.

[0048] FIG. 3 is a diagram showing an example of a method for transmitting a PPDU according to an exemplary application not forming part of the invention.

[0049] Referring to FIG. 3, the AP access point and many MU-MIM stations evaporated STA 21, 22, 23 and 24 have the same capacity of 40 MHz. Since all STAs have the same channel capacity, the data can be efficiently transmitted in accordance with the MU-MIMO transmission scheme, using the channel band information contained in the VHT-SIG A PPDU field.

[0050] The TXOP period is allocated to the STA stations 21, 22, 23 and 24 associated with the AP 10 at step S310. The allocation of the TXOP period may be effected when the information regarding the TXOP period received by the AP 10 is transmitted to the STA. Information regarding the TXOP period can be included in the signal frame (beacon frame) or in the trial response frame and sent out.

In addition, the TXOP period can be allocated by exchanging RTS (Request to Send

- Send request) and CTS frame (Clear to Send). Here, the channel band available in the TXOP period can be determined according to the value of the channel bandwidth parameter included in the CTS frame.

[0051] When transmitting a PPDU over a TXOP period, the AP 10 sets up the VHT-SIG A field channel information so that it indicates 40 MHz and transmits the PPDU to multiple STA stations according to the MU-MIMO transmission scheme at step S320. STAs 21, 22, 23 and 24 can check the channel bandwidth used to transmit data contained in the PPDU, based on the channel bandwidth information contained in the received PPDU, and thus can receive data. This method can also be applied to the case where the capacity of the channel of the STA station is 80 MHz channel bandwidth, and the adjacent 160 MHz channel band, or non-adjacent 160 MHz channel band. The channel band adapted to the PPDU transmitted by the AP 10A access point can have any value lower than the channel throughput capability.

[0052] Unlike in FIG. 3, AP access point and MU-MIMO-steamed STA stations may have different channel capacity. In the case where a PPDU is transmitted having a format such as that shown in FIG. 2, the STAs may not be informed about the different bandwidths of the channel, because the channel bandwidth information is included in the VHTSIG A field and transmitted. Accordingly, the AP has channel bandwidth information in the VHT-SIG A field, transmits a PPDU including a VHT-SIG A field, and transmits a PPDU to each STA station that can receive a PPDU. This is described in detail in a reference to FIG. 4.

[0053] FIG. 4 is a diagram showing another example of a method for transmitting a PPDU according to an example not forming part of the invention.

[0054] Referring to FIG. 4, the AP 10 access point and many MU-MIM stationsPATED STA 21, 22, 23 and 24 have different channel capacity, and different channel capacity options may not have the same value.

[0055] TXOPs are allocated to STAs 21, 22, 23 and 24 associated with AP 10. Allocation of the TXOP period may be performed when information parts relating to the TXOP period are received by the AP 10 and transmitted to the STA station. . Information regarding the TXOP period is included in the signal frame or the trial response frame and sent out. In addition, the TXOP period can be allocated by exchanging RTS frames (Request to Send) and CTS frames (Clear to Send). Here, the channel bandwidth available over the TXOP period can be determined according to the value of the channel bandwidth parameter included in the CTS frame.

[0056] In case 1, the AP 10 may transmit a PPDU having a 20 MHz channel band in the TXOP period at step S410. All STA1 21, STA2 22, STA3 23 and STA4 24 stations have the capacity of 20 MHz or wider. Accordingly, the AP 10 can transmit PPDU to all paired STAs. If this is not the case where there is no data to be transmitted to a given STA, a given number of spatial streams can be allocated to each STA and each of the STAs can receive the PPDU through the respective spatial streams. [0057] In case 2, the AP 10 may transmit a PPDU having a 40 MHz channel bandwidth in the TXOP period at step S420. Here, STA1 21 can not receive the relevant data because it has a 20 MHz bandwidth capability.

[0058] In case 3, the AP 10 can transmit PPDUs having bandwidth of 80 MHz in the TXOP period at step S430. Here, STA1 21 and STA2 22 and STA3 23 stations can not receive relevant data,

Because the STA 21 has the capacity of 20 MHz channel capacity and the station

STA2 22 and STA3 23 have a capacity of 40 MHz.

Accordingly, the AP 10 transmits data only to the STA4 station

24. This method may be implemented such that the group ID identifier indicates a target transmission station STA group comprising stations STA1 to STA4, but the number of spatial streams used to transmit data to STA1 21, STA2 22 and STA3 23 is set to 0.

[0059] As described above, the number of target transmission STAs to which the AP may transmit data according to the MU-MIMO transmission scheme is varied according to the channel capacity of the STA stations included in the target transmission station STA group. For this purpose, another method of transmitting data to a plurality of STAs having different channel capacity may be used.

[0060] FIG. 5 is a diagram showing still another example of a method for transmitting a PPDU in accordance with an example of the invention.

[0061] Referring to FIG. 5, the AP 10 access point and many MU-MIM stations evaporated STA 21, 22, 23 and 24 have adequate channel capacity, and channel capacity may not have the same value.

[0062] TXOP periods are allocated to STA stations 21, 22, 23 and 24 associated with the AP 10 at step S510. The allocation of TXOP periods may be effected when portions of information related to TXOP periods received by the AP 10 are transmitted to the STA. Information on TXOP periods can be included in the signal frame (beacon frame) or probe response frame and then broadcast. In addition, TXOP periods can be allocated by exchanging a Request to Send (RTS) frame and a Free send frame - Clear to Send (CTS). Here, the channel bandwidth available over the TXOP period can be determined according to the value of the channel bandwidth parameter included in the CTS frame. More specific,

The value set in the channel bandwidth parameter for the CTS frame can be the same or smaller than the one set in the channel bandwidth for the RTS frame and

The signal may be transmitted via a channel indicated by a parameter corresponding to the CTS frame. If the available channel throughput in the TXOP period is greater than the 20 MHz bandwidth, the AP and / or the STA may transmit the PPDU several times, using bandwidth that is less than or equal to the bandwidth available over the TXOP period. In the following example applications, it was assumed that the channel throughput for the TXOP period is 80 MHz.

The AP 10 transmits PPDU to a plurality of STA MU-MIMs evaporated in a TXOP period at step S520. The VHT-SIG A field transmitted by the AP 10 includes information about the bandwidth of the channel. The same channel bandwidth is allocated to all STAs based on the VHT-SIG field A. When transmitting the PPDU to multiple MU-MIMO-pairing STAs in a TXOP period, the AP 10 transmits a PPDU appropriate for the channel capacity of each STA. Here, the AP 10 can divide the transmission period into periods and transmit a PPDU adapted to the different bandwidths of the channel.

[0064] When the TXOP period is set between the AP 10 and the STAs 21, 22, 23 and 24, the data, control and management frames, etc. may be freely transmitted and received without new content during a given period. First, the AP 10 transmits a PPDU containing channel capacity information indicating the 80 MHz bandwidth in the VHT-SIG A field to the STA4 24 station at S521. Next, the AP 10 transmits a PPDU containing channel capacity information indicating the 40 MHz bandwidth in the VHT-SIG A field, to the STA2 22, STA3 23 and STA4 24 stations at step S522. Next, the AP 10 transmits a PPDU containing channel capacity information indicating the 20 MHz channel throughput in the VHT-SIG A field, to STA1 21, STA2 22, STA3 23 and STA4 24 stations at step S523.

[0065] After transmission to the STA4 24 station all data intended to be transmitted to the STA4 24 station via 80 MHz PPDU transmission, when

Because the channel throughput is adopted by repeated channel transmission performed over a TXOP period, the PPDU does not need to be transmitted to STA4 24. Accordingly, 40 MHz of the PPDU can be transmitted only to STA2 22 and STA3 23. Similarly, transmission of all data to be transmitted to STA2 22 and STA3 23 to STA2 22 and STA3 23 via 40 MHz PPDU transmission stage, PPDU does not have to be transmitted to STA2 22 and STA3 23. Accordingly, 20 MHz PPDU can only be transmitted to STA1 21 station.

[0066] Which PPDU the AP 10 transmits to some of the multiple MU-MIMO-pairing STAs can be given by the group ID and information indicating the number of allocated spatial streams. In a WLAN system such as shown in FIG. 5, in the case where the group ID identifier indicates a group of STAs comprising STA11, STA2, STA3 and STA4, when the number of spatial streams allocated to a given STA is set to 0, the data is not transmitted to the given STA.

This means that the PPDU is not normally transmitted to a given STA station, but it means that the PPDU can be transmitted to other STA data from the STA group group indicated by the group ID.

[0067] In the case where the access point AP performs multi-channel transmission using different channel bands over a TXOP period, as shown in FIG. 5, the channel band used to transmit the PPDU must be the same or narrower than the channel band used for the previously transmitted PPDU. That is, a method is proposed for receiving from a wider bandwidth channel to a narrower channel bandwidth. When setting the TXOP period, Network Allocation Vector (NAV) is set in the remaining STAs, other than the STA MU-MIMO station, which is paired with the AP, and thus the PPDU is not transmitted to the remaining STAs. The STAa station (i.e. the STA station operating in the dormant state) does not recognize NAV. Consequently, the remaining subchannels can be used by STA stations, because the remaining subchannels remain in the idle state during which the AP access point transmits 20 MHz PPDU. In this case, because the AP does not measure the Clear Channel rating

EP 2 589 164 B1

Assessment (CCA) during the TXOP period, a collision may occur if the AP ends the 20 MHz PPDU transmission and transmits 40 MHz PPDU or 80 MHz PPDU or both.

[0068] When the above channel bandwidth adaptation is used, the PPDU having the highest channel bandwidth is first transmitted as in the exemplary embodiment shown in FIG. 5. Referring again to FIG. 5, the AP 10 first transmits PPDU having a bandwidth of 80 MHz, and then transmits PPDUs having a bandwidth of 40 MHz and 20 MHz.

Here, before transmitting the first PPDU during the TXOP period, the AP needs to check if the channel band is in the idle state. For example, if in a TXOP period an 80 MHz channel is specified as idle, the AP does not need to perform CCA measurement for subsequent 80 MHz, 40 MHz and 20 MHz channels, and can transmit PPDU in the order of 80 MHz, 40 MHz and 20 channels MHz. If the maximum channel bandwidth supported by the WLAN system is further increased, the CCA measurement can be carried out according to the given channel capacity.

For this purpose, the AP will perform CCA measurement based on the PPDU value having the largest channel bandwidth of the PPDUs to be transmitted. In an exemplary application for PPDU transmission, such as shown in FIG. 5, a CCA measurement is performed, if 80 MHz bandwidth is available. If the CCA measurement for the maximum channel bandwidth is not first performed, a CCA measurement must be performed according to the appropriate channel bandwidth before transmitting the PPDU to the channel in question. However, as a general rule, CCA measurement is not carried out during the TXOP period. This is an advantage of the PPDU transmission / reception scheme, which is accompanied by the allocation of the TXOP period. This is described with reference to FIG. 6.

[0071] FIG. 6 is a diagram showing an example of a CCA measurement that can be adopted for an exemplary application of the invention.

[0072] Referring to FIG. 6, the AP checks if the frequency bands are idle when performing a CCA measurement for the main channel during the disconnect interval. At the same time, before

By transmitting the PPDU, the AP approaches CCA for 80 MHz channel through Point InterFrame Space (PIFS). If all 80 MHz bandwidths are inactive during PIFS as a result of CCA measurement, the AP may transmit PPDUs having 80 MHz bandwidth.

[0073] In a multi-band transmission scheme in which the AP approaches transmits the PPDU several times by using different channel bands during the TXOP period, the existing Short InterFrame Space (SIFS) and the existing Reduced InterFrame Space (RIFS)) (Decreased space between frames) can be applied to InterFrame Space (IFS)) (Space between frames) when PPDUs are transmitted.

[0074] FIG. 7 is a diagram illustrating a method for transmitting a PPDU in accordance with an example of the invention.

[0075] Referring to FIG. 7, TXOP periods are allocated to STAs 21, 22, and 24 associated with the AP 10 at step S710. The allocation of TXOP periods may be effected when portions of information related to TXOP periods received by the AP 10 are transmitted to the STA. Information regarding the TXOP period can be included in the signal frame (beacon frame) or the probe response frame and then broadcast. TXOP periods may be allocated as in step S510 according to the example application described with reference to FIG. 5.

[0076] The AP 10 checks whether during the contention period at step S720 the 80 MHz channel is idle and then transmits the PPDU at step S730 during the TXOP period. The AP 10 transmits PPDU to STA stations 21, 22, 23 and 24. Here, STAs 21, 22, 23 and 24 transmit corresponding ACK acknowledgment frames in response to a PPDU received from the AP 10 at the step S740). The confirmation frame can be a concept including a block confirmation frame. The procedure of the AP 10 transmitting the PPDU to the STA group of stations (21, 22, 23 and 24) of the transmitting confirmation frame is described below.

[0077] The AP 10 first transmits 80 MHz of PPDU to the STA4 station 24 at step S731. Once the PPDU has been successfully received, STA4 24

It transmits the confirmation frame to the AP 10 at step S741.

Then, the AP 10 transmits 40 MHz of PPDU to STA2 22, STA3 23 and STA4 24 at step S732. In the meantime, STA2 22, STA3 23 and STA4 24 may transmit corresponding confirmation frames in response to a 40 MHz PPDU, but the AP 10 may transmit the remaining 20 MHz PPDU to STA1 21, STA2 22, STA3 23 and STA4 24 before the frames confirmations will be received at stage S733. After receiving the 20 MHz PPDU, the STA1 station 21 transmits a confirmation frame to the AP 10 in the response to the 20 MHz PPDU at step S742. Stations STA2 22, STA3 23 and STA4 24 transmit respective block acknowledgments to the AP 10 in response to 40 MHz PPDU and 20 MHz PPDU at steps S743, S744 and S745. The order in which the STAs station transmits the corresponding confirmation frames is not limited to that shown in FIG.

[0078] FIG. 8 is a diagram illustrating a method for transmitting a PPDU according to another example not forming part of the invention. The STA station can not receive data that is transmitted over a wider bandwidth than its channel bandwidth capability, but it can bypass the bandwidth indicated by the channel bandwidth information included in the PPDU and receive data based on its channel bandwidth capability.

[0079] Referring to FIG. 8, the AP 10 transmits PPDU to multiple STA stations: STA1 21, STA2 22, STA3 23 and STA4 24 during the allocated TXOP period. Here, the VHT-SIG A PPDU field contains information about the bandwidth indicating the bandwidth of 80 MHz. In addition, data matching the bandwidth according to the given capacity of the channel are transmitted to each of the STA stations. Accordingly, the AP will transmit 20 MHz PPDU to STA1 station 21, 40 MHz PPDU to STA2 22 and STA3 23 and 80 MHz PPDU to STA4 24 stations.

[0080] Each STA station may receive data using the channel bandwidth indicated by the channel bandwidth information included in the VHT-SIG A PPDU field, and the channel band for data transmission having a lower bandwidth

The maximum bandwidth of the channel is in accordance with the channel capacity.

[0081] A rule is needed to determine channel throughput so that the STA receives a PPDU and receives data based on its channel capacity, as described above. For example, the STA may be set to determine a lower value of the signaled channel bandwidth and maximum usable channel throughput as the channel throughput to be used. Here, the signaled bandwidth can be the value indicated by the channel bandwidth information that is included in the VHT-SIG A PPDU field transmitted by the AP.

[0082] The maximum usable throughput of the channel may correspond to the channel capacity bandwidth of the given STA and may be a value that is transmitted from the STA to the AP when the STA is associated with the AP. In addition, the maximum usable bandwidth of a channel can be determined based on the channel bandwidth information contained in the management action frame informing about the mode of operation of the STA station. Table 2 below shows the format of the notification frame about the operation mode containing the channel bandwidth information.

[Table 2]

<td colspan="2">[Table]</td>

<td>Order</td><td>information</td>

<td>one</td><td>Category</td>

<td>2</td><td>Action</td>

<td>3</td><td>The width of the channel</td>

[0083] The category field is set to a value indicating that the frame can be used in a new generation of WLAN supporting VHT. The operating field is set to a value indicating that the frame is a notification frame of the operation mode. The channel width field contains information about the bandwidth of the channel. Table 3 below shows the format of the channel bandwidth field.

EP 2 589 164 B1 [Table 3]

<td colspan="2">[Table]</td>

<td>Value</td><td>Importance</td>

<td>0</td><td>20 MHz</td>

<td>one</td><td>40 MHz</td>

<td>2</td><td>80 MHz</td>

<td>3</td><td>160 MHz or 80 + 80 MHz</td>

<td>Other</td><td>reserve</td>

[0084] The STA may transmit a mode notification notification frame to another STA or other AP access point, or both. The mode notification frame is used to limit the bandwidth of a PPDU channel that is transmitted from another STA station or from another AP access point or from both to a given STA. For example, if the AP wants to receive a 20 MHz PPDU, the AP may send a notification frame of the mode of operation to the STA in the BSS. If the AP spends the channel width set to 0, the STAs in the BSS carry out the transmission using 20 MHz PPDU. This is also true when the STA sends the right frame.

[0085] When the AP is transmitting 20 MHz, 40 MHz and 80 MHz PPDU based on the channel capacity of the STA channel, the AP needs to consider the perpendicularity and position of the pilot sequences for consideration.

[0086] First, the pilot sequences forming respectively the 20 MHz, 40 MHz and 80 MHz channel bandwidths may not be perpendicular to each other. Second, the positions of the pilot sequence lift may not be exactly matched to each other. That is, at different throughputs, perpendicularity in the elevator, in which the data tone and pilot tone overlap, can not be guaranteed. To guarantee the perpendicular data tone and pilot tone, the data tone can be changed to null data tone. FIG. 9 shows an example of allocating pilot sequences according to channel capacity. When a ton of data overlapping a pilot tone is allocated as a ton of data (null data tone), perpendicularity can be guaranteed.

[0087] In the meantime, if it is an environment in which PPDU transmission in accordance with

With the MU-MIMO transmission scheme, a proper gain may be obtained, the AP would transmit the PPDU to the appropriate STA station by properly performing the beamforming. That is, although the channel bandwidths used to transmit data from the AP to the respective STAs are different, the interference between them is small. In this case, as described above, although the pilot tones are not perpendicular to each other, the entire implementation of the MU-MIMO transmission may not be significantly impeded.

[0088] FIG. 10 and 11 are diagrams illustrating examples in which channels suitable for exemplary applications of the invention are used.

[0089] Assuming that the TXOP period is once set to 80 MHz bandwidth, the AP will transmit the PPDU to the STA station: STA1, 2, 3, and 4 via multiple bandwidth transmission. Although the AP is transmitting 40 MHz PPDU or 20 MHz PPDU after transmitting the entire 80 MHz PPDU, other terminals can not use redundant subchannels. For other terminals to be able to access subchannels that are in an idle state, the TXOP period can be set to the PPDU transmission period up to the given channel throughput.

[0090] Referring to FIG. 10, the TXOP period is set for a period during which the 80 MHz PPDU is transmitted to the STA4 24 station and the 40 MHz PPDU is transmitted to STA2 22, STA3 23 and STA4 24. The STAa station is not included in the target STA station group to which they will be transmitted PPDU via the AP 10 access point, it can implement a competition mechanism after transmitting 80 MHz PPDU and 40 MHz PPDU in the TXOP period, gain access to the channel and then transmit and receive the corresponding PPDU. The competition mechanism may be implemented differently according to the channel capacity to be used by the STAa station. The STAa station can transmit and receive the corresponding PPDU by using bandwidth from the channel capacity having an idle state checked by the competition mechanism.

[0091] Referring to FIG. 11, the TXOP period is set for a period during which the 80 MHz PPDU is transmitted to STA4 24. A STAa station can implement a rival mechanism after transmitting 80 MHz PPDU in the TXOP period, gain access to the channel and then transmit and receive appropriate

EP 2 589 164 B1

PPDU. The competition mechanism may be implemented differently according to the bandwidth to be used by the non-AP STA station. Station

STAa can transmit and receive the appropriate PPDU using bandwidth from the idle channel bandwidth checked by the competition mechanism.

[0092] FIG. 12 is a block diagram showing a wireless apparatus in which methods for transmitting a PPDU according to exemplary applications of the invention may be used.

[0093] Referring to FIG. 12, the wireless 1200 comprises a processor 1210, memory 1220 and a transceiver (transceiver) 1230. The transceiver 1230 transmits and / or receives a radio signal and performs the physical layer of the IEEE 802.11 standard. The processor 1210 is functionally connected to the transceiver 1230 and is set to implement the MAC layer or PHY layer or both to perform the exemplary applications of the invention shown in FIG. 2 to 11, in which a data frame such as the PPDU format is produced, a transmission channel is selected and the data frame is transmitted over the transmission channel. Processor 1210 and / or transceiver 1230 may include an application-specific integrated circuit (ASIC), a separate chipset, a logic circuit, and / or a data processing unit. When the exemplary application of the invention is implemented in the software, the above-mentioned methods can be used in the module (i.e., process, function, etc.) for performing the aforementioned functions. This module may be stored in the memory 1220 and may be implemented by the processor 1210. The memory 1220 may be located inside or outside the processor 1210 and may be connected to the processor 1210 using well-known means.