WO2010082784A2

WO2010082784A2 - Method and apparatus for transmitting/receiving data in wireless communication network

Info

Publication number: WO2010082784A2
Application number: PCT/KR2010/000267
Authority: WO
Inventors: Yoo-Seung Song; Sok-Kyu Lee
Original assignee: Electronics And Telecommunications Research Institute
Priority date: 2009-01-15
Filing date: 2010-01-15
Publication date: 2010-07-22
Also published as: WO2010082784A3

Abstract

A method for transmitting data to at least one station by an access point in a wireless communication network includes: broadcasting a multiuser ready-to-send (muRTS) message for a very high throughput (VHT) station; broadcasting a legacy RTS message for a legacy station; receiving a clear-to-send (CTS) message transmitted by the VHT station or the legacy station; and transmitting the data to the VHT station or the legacy station which has transmitted the CTS message.

Description

METHOD AND APPARATUS FOR TRANSMITTING/RECEIVING DATA IN WIRELESS COMMUNICATION NETWORK

The present invention relate to a method and apparatus for transmitting/receiving data; and, more particularly, to a method and apparatus for transmitting/receiving data in a wireless communication network.

Recent development of communication technology is followed by intensive study in the wireless communication field. Wireless LAN technology has evolved into the Institute of Electrical and Electronics Engineers (IEEE) 802.11n, which increases the data rate from the conventional level of tens of Mbps up to 600 Mbps. In order to guarantee a higher data rate, a Task Group (TGac) has been created within the IEEE 802.11 Working Group (WG) to study next generation wireless LAN technology, and is in the process of establishing a new standard to enable Gbps-level data transmission. For reference, IEEE 802.11a/b/g and IEEE 802.11n standards are referred to as legacy and High Throughput (HT) modes, respectively. In addition, the standard newly discussed by IEEE 802.11ac is referred to as a Very High Throughput (VHT) mode.

A number of methods have been proposed to transmit data at a Gbps-level rate in wireless communication networks, such as increasing the bandwidth, employing more transmitting/receiving antennas, etc. The method of increasing the bandwidth to improve the data rate has a problem in that, besides degraded MAC efficiency, the limited frequency resources make it difficult to increase the bandwidth. The method of employing more transmitting/receiving antennas has a problem in that transmitters or receivers have spatial limitation or unnecessarily large size. Therefore, wireless LAN technology for supporting a Gbps-level rate requires that such problems of both methods be dealt with.

One of the outstanding issues of the TGac concerns multichannel MAC support. Except for broadcasting/ multicasting, communication has conventionally been based on single channels, which solely enable one-to-one communication between an access point (AP) and a station (STA). However, it is expected that, in the next generation wireless LAN technology, a multichannel MAC function will be added to enable simultaneous communication between a single access points and a plurality of stations. This necessitates development of MAC protocol technology to support such a function.

An embodiment of the present invention is directed to a method and apparatus for transmitting/receiving data so that a single access point can conduct simultaneous, parallel communication with a plurality of stations, thereby improving the data rate and the throughput of MAC.

Another embodiment of the present invention is directed to a method and apparatus for transmitting/ receiving data so that communication is possible with very high throughput stations, which support next generation wireless LAN specifications, as well as with legacy stations supporting legacy specifications.

Other objects and advantages of the present invention can be understood by the following description, and become apparent with reference to the embodiments of the present invention. Also, it is obvious to those skilled in the art to which the present invention pertains that the objects and advantages of the present invention can be realized by the means as claimed and combinations thereof.

In accordance with an embodiment of the present invention, a method for transmitting data to at least one station by an access point in a wireless communication network includes: broadcasting a multiuser ready-to-send (muRTS) message for a very high throughput (VHT) station; broadcasting a legacy RTS message for a legacy station; receiving a clear-to-send (CTS) message transmitted by the VHT station or the legacy station; and transmitting the data to the VHT station or the legacy station which has transmitted the CTS message.

In accordance with another embodiment of the present invention, a method for receiving data from an access point by a station in a wireless communication network includes: receiving an muRTS message broadcasted by the access point; transmitting a CTS message to the access point; and receiving the data which is transmitted from the access point and to which beamforming is applied.

In accordance with another embodiment of the present invention, an apparatus for transmitting data to at least one station in a wireless communication network includes: a transmission unit configured to broadcast an muRTS message for a VHT station or a legacy RTS message for a legacy station; and a reception unit configured to receive a CTS message transmitted by the VHT station or the legacy station, wherein the transmission unit transmits the data to the VHT station or the legacy station which has transmitted the CTS message.

In accordance with another embodiment of the present invention, an apparatus for receiving data from an access point in a wireless communication network includes: a reception unit configured to receive an muRTS message broadcasted by the access point; and a transmission unit configured to transmit a CTS message to the access point, wherein the reception unit receives the data which is transmitted from the access point and to which beamforming is applied.

In accordance with another embodiment of the present invention, a method for receiving data from at least one station by an access point in a wireless communication network includes: receiving an muRTS message transmitted by a VHT station or a legacy RTS message transmitted by a legacy station during a predetermined maximum observation interval; transmitting a multiuser CTS (muCTS) message to the VHT station or a legacy CTS message to the legacy station; and finishing receiving the muRTS message or the legacy RTS message and receiving the data transmitted from the VHT station or the legacy station when the legacy CTS message is transmitted during the maximum observation interval or when the muRTS message or the legacy RTS message is not receivable any more.

In accordance with another embodiment of the present invention, a method for transmitting data to an access point by a station in a wireless communication network includes: transmitting an muRTS message to the access point during a predetermined maximum observation interval; receiving an muCTS message transmitted from the access point; and transmitting the data to the access point when the access point transmits a legacy CTS message to a legacy station during the maximum observation interval or when the access point is not capable of receiving the muRTS message or the legacy RTS message any ore.

In accordance with another embodiment of the present invention, an apparatus for receiving data from at least one station in a wireless communication network includes: a reception unit configured to receive an muRTS message transmitted by a VHT station or a legacy RTS message transmitted by a legacy station during a predetermined maximum observation interval; and a transmission unit configured to transmit an muCTS message to the VHT station or a legacy CTS message to the legacy station, wherein the reception unit finishes receiving the muRTS message or the legacy RTS message and receives the data transmitted from the VHT station or the legacy station when the transmission unit transmits the legacy CTS message during the maximum observation interval or when the reception unit is not capable of receiving the muRTS message or the legacy RTS message any more.

In accordance with another embodiment of the present invention, an apparatus for transmitting data to an access point in a wireless communication network includes: a transmission unit configured to transmit an muRTS message to the access point during a predetermined maximum observation interval; and a reception unit configured to receive an muCTS message transmitted from the access point, wherein the transmission unit transmits the data to the access point when the access point transmits a legacy CTS message to a legacy station during the maximum observation interval or when the access point is not capable of receiving the muRTS message or the legacy RTS message any more.

In accordance with the exemplary embodiments of the present invention, a single access point can conduct simultaneous, parallel communication with a plurality of stations, thereby improving the data rate and the throughput of MAC.

The exemplary embodiments of the present invention are also advantageous in that communication is possible not only with very high throughput stations supporting next generation wireless LAN specifications, but also with legacy stations supporting legacy specifications.

Fig. 1 illustrates the configuration of a wireless communication network in accordance with an embodiment of the present invention.

Fig. 2 illustrates a process of transmitting/ receiving data in accordance with an embodiment of the present invention.

Fig. 3 illustrates the configuration of a wireless communication network in accordance with an embodiment of the present invention.

Fig. 4 illustrates a process of transmitting/ receiving data in accordance with an embodiment of the present invention.

Fig. 5 illustrates a process of transmitting/ receiving data in accordance with another embodiment of the present invention.

Fig. 6 illustrates a process of transmitting/ receiving data in accordance with still another embodiment of the present invention.

Exemplary embodiments of the present invention will be described below in more detail with reference to the accompanying drawings. The present invention may, however, be embodied in different forms and should not be constructed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the present invention to those skilled in the art. Throughout the disclosure, like reference numerals refer to like parts throughout the various figures and embodiments of the present invention.

The present invention relates to a method and apparatus for transmitting/receiving data between an access point and a station in a wireless communication network, particularly in a next generation wireless communication network supporting a Gbps-level rate. It is expected that, in the next generation wireless communication network, the access point or the station will have a plurality of antennas in order to improve the data rate. Therefore, the present invention is directed to a MAC protocol for transmitting/receiving data between a single access point and at least two stations in a parallel manner, and a control of the MAC protocol.

Another consideration in the present invention is compatibility. A very high throughput access point, which supports a Gbps-level rate, should be able to communicate not only with very high throughput stations which also support a Gbps-level rate, but also with legacy stations which support no more than the conventional Mbps-level rate. Therefore, the present invention is directed to a MAC protocol for enabling the access point to conduct parallel communication with very high throughput stations and legacy stations, and a control of the MAC protocol.

Hereinafter, a method for transmitting/receiving data in accordance with an embodiment of the present invention will be described in more detail with reference to a downlink and an uplink, respectively.

<Downlink Channel>

Specifically, Fig. 1 illustrates a network configuration in which wireless communication is conducted to transmit data at a Gbps-level rate by using a plurality of antennas. Referring to Fig. 1, an access point (hereinafter, referred to as AP) 102 is configured to communicate with four stations (hereinafter, referred to as STAs) 114, 116, 118 and 120. In order to improve the data rate, both the AP 102 and the

STAs

114, 116, 118 and 120 have at least two antennas.

The AP 102 receives data DATA 1, DATA 2, DATA 3 and DATA 4, which are to be transmitted to the

STAs

114, 116, 118 and 120, respectively. The received data DATA 1, DATA 2, DATA 3 and DATA 4 are encoded by four

encoders

104, 106, 108 and 110 included in the AP 102, and are outputted as data streams, respectively. It is noted that the number of data streams outputted by each encoder is the same as the number of antennas for transmitting the data. The AP 102 illustrated in Fig. 1 has a total of eight antennas, which means that each data is supposed to be transmitted via two antennas. Consequently, each of the

encoders

104, 106, 108 and 110 encodes the received data and outputs two data streams.

The data streams outputted by the

encoders

104, 106, 108 and 110 are inputted to a precoder 112. The precoder 112 precodes the inputted data streams. After the precoder 112 finishes the precoding, the data streams become independent of one another, and beams are formed between the AP 102 and the

respective STAs

114, 116, 118 and 120 so that the respective data streams can be transmitted via the beams to the

corresponding STAs

114, 116, 118 and 120 without interference.

Each of the

STA

114, 116, 118 and 120 illustrated in Fig. 1 has two antennas, which receive the data transmitted by the AP 102. The

STAs

114, 116, 118 and 120 then decode the received signals into data by using respective decoders.

Specifically, Fig. 2 illustrates a control process of a MAC protocol, which is required when an AP transmits data to each STA. Each data the transmission of which has been determined by a MAC protocol of Fig. 2 is encoded by a physical (PHY) layer of Fig. 1, and is transmitted wirelessly via physical antennas.

Hereinafter, an AP supporting a very high throughput function (as used in next generation wireless communication technology) will be referred to as a VHT-AP. An STA supporting the VHT function will similarly be referred to as a VHT-STA, and a legacy STA supporting no VHT function will be referred to as an L-STA.

It will be assumed in the embodiment of Fig. 2 that a single VHT-AP transmits data to two VHT-STAs and two L-STAs. If the wireless channel is idle after a DIFS interval at step S202, the VHT-AP starts backoff at step S204. If data transmission is enabled after the backoff, the VHT-AP broadcasts a multiuser ready-to-send message (hereinafter, referred to as an muRTS message) at step S206. The muRTS message can only be decoded by the VHT-AP, unlike conventional RTS messages transmitted to L-STAs. After broadcasting the muRTS message to the VHT-

STAs

1 and 2, the VHT-AP broadcasts a legacy RTS message (hereinafter, simply referred to as RTS) for the L-

STAs

1 and 2 at step S208. It is also possible to reverse the order of broadcasting the muRTS message and the RTS message depending on the manner of implement.

After receiving the muRTS or RTS message, the VHT-STAs and L-STAs recognize that the VHT-AP is ready to transmit data. Among them, the VHT-STA1, VHT-STA2 and L-STA1, which want to receive data, transmit a clear-to-send message (hereinafter, referred to as a CTS message) to the VHT-AP in response to the muRTS or RTS message, respectively, at step S210. The VHT-STA1, VHT-STA2 and L-STA1 may start CTS message transmission at the same time. After receiving the CTS message, the VHT-AP transmits data to each STA which has transmitted the CTS message at step S212. The VHT-AP may start to transmit data to each STA at the same time.

As mentioned above, beamforming may be applied to avoid interference when the VHT-AP transmits data to each STA. Beamforming may not be applied when control messages (e.g. muRTS, RTS, CTS) are transmitted/received.

Meanwhile, data transmitted by the VHT-AP may include null data for transmission time adjustment. Referring to Fig. 2, each data transmitted to the VHT-STA1, VHT-STA2 and L-STA1 has a different length, which means that, even if data transmission has started at the same time, the transmission inevitably ends at the different time. Considering this, data transmitted to the L-STA1 and VHT-STA2 includes null data, as illustrated in Fig. 2, and has the same length as data transmitted to the VHT-STA1, which is the longest. This prevents any collision between data transmission intervals or transmission resources.

After data transmission is completed at the same time, each STA that has received the data (i.e. VHT-SAT1, VHT-STA2 and L-STA1) transmits a reception acknowledge (ACK) message to the VHT-AP after a SIFS interval at step S214. Transmission of the ACK message by each STA may start at the same time. This completes data transmission by the VHT-AP. If a transmission failure occurs in the above process, retransmission is tried through the same process.

After the VHT-AP has received the ACK message at the step S214, the next data transmission may proceed. Specifically, the VHT-AP conducts backoff after a DIFS interval, as illustrated in Fig. 2, and sequentially broadcasts an muRTS message and an RTS message at

steps

216 and 218, respectively. In response to this, the VHT-STA2 and L-STA2 transmit a CTS message to the VHT-AP at step S220. The VHT-AP transmits data for the VHT-STA2 and data for the L-STA2, which includes null data, at step S222, and receives ACK messages after a SIFS interval at step S224.

<Uplink Channel>

Specifically, Fig. 3 illustrates a configuration of a network in which wireless communication is conducted to transmit data at a Gbps-level rate by using a plurality of antennas. Referring to Fig. 3, four

STAs

302, 304, 306 and 308 communicate with an AP 310. In order to improve the data rate, both the AP 310 and the

STAs

302, 304, 306 and 308 have at least two antennas.

[0045] The

STAs

302, 304, 306 and 308 receive data DATA1, DATA2, DATA3 and DATA4, respectively, which are to be transmitted to the AP 310. The received data are encoded by encoders included in the

respective STAs

302, 304, 306 and 308, and are outputted as data streams. It is noted that the number of the data streams outputted by each encoder is the same as the number of antennas through which the data are transmitted. Each STA illustrated in Fig. 3 transmits data through two antennas. Therefore, each encoder included in the

respective STAs

302, 304, 306 and 308 receives and encodes a single data and outputs two data streams. The data outputted by each encoder is mapped onto two antennas of each

STA

302, 304, 306 and 308, and is transmitted to the AP 310. The

STAs

302, 304, 306 and 308 require no information regarding the wireless channel, which means that no beamforming needs to be applied during data transmission, that is, precoding is unnecessary.

The AP 310, which is supposed to receive data from the

STAs

302, 304, 306 and 308, should have at least the same number of antennas as the total number of antennas of the STAs, which are supposed to communicate with the AP 310. This is because, if the number of antennas of the AP 310 is less than the total number of antennas of the STAs, signals transmitted by the plurality of STAs may fail to be separated. The AP 310 illustrated in Fig. 3 has the same number (i.e. eight) of antennas as the total number of antennas of the

STAs

302, 304, 306 and 308.

After receiving data from the

STAs

302, 304, 306 and 308, the AP 310 can separate the signals by a postdetector 312 based on postdetection technology. Since the postdetection technology has little relevance to the scope of the present invention, detailed description thereof will be omitted herein. Signals separated by the postdetector 312 are inputted to

decoders

314, 316, 318 and 320, which decode the inputted signals into corresponding data.

In a network configuration as illustrated in Fig. 3, the time at which the

respective STAs

302, 304, 306 and 308 start to transmit data to the AP 310 may differ. However, the

STAs

302, 304, 306 and 308 cannot perform the data transmission and reception at the same time, nor does the AP 310.

Methods for transmitting/receiving data in accordance with embodiments of the present invention will now be described with reference to Figs. 4, 5 and 6. It will be assumed in the following embodiments that a maximum observation interval is previously set so that as many STAs as possible are collected, which want to transmit data, during the maximum observation interval. If a specific condition is met, the STAs simultaneously transmit data to the VHT-AP.

Referring to Fig. 4, two VHT-STAs and two L-STAs transmit data to a VHT-AP. The initial DIFS interval is followed by a maximum observation interval. Each of the VHT-SA1 and VHT-SA2 transmits an muRTS to the VHT-AP at step S402. It is noted that, even if two or more STAs simultaneously transmit signals to the VHT-AP, it can separate and decode the signals by photodetection technology. In response to the muRTS, the VHT-AP transmits a multiuser CTS message (hereinafter, referred to as an muCTS message) to the VHT-

SAs

1 and 2 at step S404. The VHT-

STAs

1 and 2 send no data and stand by. Subsequently, the L-STA1 sends an RTS message to the VHT-AP within the maximum observation interval at step S406. In response to this, the VHT-AP transmits a CTS message to the L-STA1 at step S408.

In accordance with the present invention, if any L-STA transmits an RTS message during the maximum observation interval or if the AP transmits a CTS message during the same interval, the AP finishes receiving any muRTS or RTS message even though the maximum observation interval has not expired. The AP then receives data from a VHT-STA or L-STA, which has duly transmitted an muRTS or RTS message.

Since the L-STA1 has transmitted an RTS message at step S406 (or the VHT-AP has transmitted a CTS message at step S408) in Fig. 4, the VHT-AP finishes receiving any muRTS or RTS message even though the maximum observation interval has not expired. The VHT-STA1, VHT-STA2 and L-STA1 then start to transmit data at step S410. The data transmission may start at the same time. In order to control the transmission time, null data is inserted into data from the VHT-STA1 and L-STA1 with reference to data from the VHT-STA2, which is the longest. Each data is transmitted without being precoded.

After the VHT-STA1, VHT-STA2 and L-STA1 complete data transmission, the VHT-AP transmits an ACK message to each of the VHT-STA1, VHT-STA2, and L-STA1 at step S412. The ACK message is precoded so that it is transmitted to each STA without interference by applying beamforming. The transmission of the ACK message to each STA may start at the same time.

The DIFS interval is followed by a maximum observation interval. At step S502, the VHT-SAT1 and L-STA1 then transmit an muRTS message and an RTS message to the VHT-AP, respectively. In response to the muRTS message and the RTS message, the VHT-AP transmits a CTS message at step S504. The VHT-AP then finishes receiving any muRTS or RTS message because the L-STA1 has transmitted an RTS message, even though the maximum observation interval has not expired. At step S506, the VHT-STA1 and L-STA1 start to transmit data. The data transmitted by the VHT-STA1 includes null data for transmission time adjustment. After data transmission is completed, the VHT-AP transmits an ACK message to each of the VHT-STA1 and L-STA1 at step S508. The ACK message is precoded so that it is transmitted to each STA without interference by applying beamforming. The transmission of the ACK message to each STA may start at the same time.

As has been described with reference to Figs. 4 and 5, which illustrate methods for transmitting/receiving data in accordance with the present invention, STAs that want to transmit data are collected for the maximum observation interval so that a batch of data can be transmitted. It is noted, however, that if an L-STA transmits an RTS message (or if the AP transmits a CTS message in response to it) within the maximum observation interval, the collected STAs start to transmit data, even though the maximum observation interval has not expired.

Fig. 6 illustrates a process of transmitting/ receiving data in accordance with another embodiment of the present invention.

The DIFS interval is followed by a maximum observation interval. The VHT-STA1 then transmits an muRTS message to the VHT-AP at step S602. In response to the muRTS message, the VHT-AP transmits an muCTS message at step S604. The VHT-STA3 transmits an muRTS message at step S606, and the VHT-AP transmits an muCTS message at step S608. The VHT-STA2 transmits an muRTS message at step S610, and the VHT-AP transmits an muCTS message at step S612. The VHT-STA4 transmits an muRTS message at step S614, and the VHT-AP transmits an muCTS message at step S616.

It has been assumed in the embodiment of Fig. 6 that the VHT-AP can communicate with up to four STAs. Thus, since the VHT-STA4 has transmitted an muRTS message at step S614 and the VHT-AP has transmitted an muCTS message at step S616, the VHT-AP can no longer receive any muRTS or RTS message. As a result, data transmission starts even before the maximum observation interval expires at step S618.

If a specific condition (transmission of the RTS message by the L-STA or transmission of the CTS message by the AP in response to it) does not occur until the maximum observation interval expires, VHT-STAs, which have transmitted the muRTS messages during the maximum observation interval, can start to transmit data.

With reference to longest data from the VHT-STA2, null data is inserted into data from the remaining VHT-STAs, and data transmission starts at the same time. After the data transmission is completed, the VHT-AP transmits an ACK message at step S620. The ACK message is precoded so that it is transmitted to each STA without interference by applying beamforming. The transmission of the ACK message to each STA may start at the same time.

As mentioned above, the basic idea of the methods for transmitting/receiving data in accordance with the exemplary embodiments of the present invention is as follows: the AP collects STAs, which want to transmit data, during the maximum observation interval, and receives a batch of data from the corresponding STAs after the maximum observation interval expires. However, if a specific condition is met (e.g. if an L-STA transmits an RTS message, if the AP transmits a CTS message in response to it, or if a maximum allowable number of STAS transmit RTS messages) during the maximum observation interval, STAs can start to transmit data even before the maximum observation interval expires.

The present application contains a subject matter related to Korean Patent Application Nos. 10-2009-0003201, 10-2009-0003203 and 10-2009-0129632, filed on January 15, 2009, January 15, 2009 and December 23, 2009, respectively, which are incorporated herein by reference in their entirety.

While the present invention has been described with respect to the specific embodiments, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the following claims.

Claims

A method for transmitting data to at least one station by an access point in a wireless communication network, comprising:

broadcasting a multiuser ready-to-send (muRTS) message for a very high throughput (VHT) station;

broadcasting a legacy RTS message for a legacy station;

receiving a clear-to-send (CTS) message transmitted by the VHT station or the legacy station; and

transmitting the data to the VHT station or the legacy station which has transmitted the CTS message.
The method of claim 1, wherein transmission of the data to the VHT station or the legacy station starts simultaneously.
The method of claim 1, wherein the data comprises null data for transmission time adjustment.
The method of claim 1, further comprising forming a beam with regard to the VHT station or the legacy station in order to transmit the data.
The method of claim 1, wherein the CTS message is transmitted simultaneously.
The method of claim 1, further comprising simultaneously receiving a reception acknowledge message transmitted from the VHT station or the legacy station after the data transmission has been completed.
A method for receiving data from an access point by a station in a wireless communication network, comprising:

receiving an muRTS message broadcasted by the access point;

transmitting a CTS message to the access point; and

receiving the data which is transmitted from the access point and to which beamforming is applied.
An apparatus for transmitting data to at least one station in a wireless communication network, comprising:

a transmission unit configured to broadcast an muRTS message for a VHT station or a legacy RTS message for a legacy station; and

a reception unit configured to receive a CTS message transmitted by the VHT station or the legacy station,

wherein the transmission unit transmits the data to the VHT station or the legacy station which has transmitted the CTS message.
An apparatus for receiving data from an access point in a wireless communication network, comprising:

a reception unit configured to receive an muRTS message broadcasted by the acess point; and

a transmission unit configured to transmit a CTS message to the access point,

wherein the reception unit receives the data which is transmitted from the access point and to which beamforming is applied.
A method for receiving data from at least one station by an access point in a wireless communication network, comprising:

receiving an muRTS message transmitted by a VHT station or a legacy RTS message transmitted by a legacy station during a predetermined maximum observation interval;

transmitting a multiuser CTS (muCTS) message to the VHT station or a legacy CTS message to the legacy station; and

finishing receiving the muRTS message or the legacy RTS message and receiving the data transmitted from the VHT station or the legacy station when the legacy CTS message is transmitted during the maximum observation interval or when the muRTS message or the legacy RTS message is not receivable any more.
The method of claim 10, wherein the data starts to be transmitted simultaneously from the VHT station or the legacy station.
The method of claim 10, wherein the data comprises null data for transmission time adjustment.
The method of claim 10, further comprising simultaneously transmitting a reception acknowledge message to the VHT station or the legacy station after the data reception is completed.
The method of claim 10, further comprising receiving the data transmitted from the VHT station after the maximum observation interval expires when the legacy CTS message is not transmitted until the maximum observation interval expires.
A method for transmitting data to an access point by a station in a wireless communication network, comprising:

transmitting an muRTS message to the access point during a predetermined maximum observation interval;

receiving an muCTS message transmitted from the access point; and

transmitting the data to the access point when the access point transmits a legacy CTS message to a legacy station during the maximum observation interval or when the access point is not capable of receiving the muRTS message or the legacy RTS message any more.
The method of claim 15, further comprising transmitting the data to the access point after the maximum observation interval expires when the access point does not transmit the legacy CTS message until the maximum observation interval expires.
An apparatus for receiving data from at least one station in a wireless communication network, comprising:

a reception unit configured to receive an muRTS message transmitted by a VHT station or a legacy RTS message transmitted by a legacy station during a predetermined maximum observation interval; and

a transmission unit configured to transmit an muCTS message to the VHT station or a legacy CTS message to the legacy station,

wherein the reception unit finishes receiving the muRTS message or the legacy RTS message and receives the data transmitted from the VHT station or the legacy station when the transmission unit transmits the legacy CTS message during the maximum observation interval or when the reception unit is not capable of receiving the muRTS message or the legacy RTS message any more.
The apparatus of claim 17, wherein the reception unit is configured to receive the data transmitted from the VHT station after the maximum observation interval expires when the transmission unit is not capable of transmitting the legacy CTS message any more until the maximum observation interval expires.
An apparatus for transmitting data to an access point in a wireless communication network, comprising:

a transmission unit configured to transmit an muRTS message to the access point during a predetermined maximum observation interval; and

a reception unit configured to receive an muCTS message transmitted from the access point,

wherein the transmission unit transmits the data to the access point when the access point transmits a legacy CTS message to a legacy station during the maximum observation interval or when the access point is not capable of receiving the muRTS message or the legacy RTS message any more.
The apparatus of claim 19, wherein the transmission unit is configured to transmit the data to the access point after the maximum observation interval expires when the access point does not transmit the legacy CTS message until the maximum observation interval expires.