KR20070049045A - Method and apparatus for avoiding collision in wireless lan - Google Patents

Abstract

The present invention relates to a medium access method for preventing collision in a WLAN in which a HT (High Throughput) station and an 802.11 legacy station coexist in a WLAN. The present invention relates to legacy stations that receive a frame when the HT station transmits a frame in an HT format. In a WLAN environment where HT stations and legacy stations coexist by sending a reset frame in a format that can be interpreted by all stations, allowing the HT stations to equally reset the latency for accessing the medium, legacy stations can be used without additional modification. They will be able to participate in competition for media access under the same conditions.

Description

Method and apparatus for avoiding collision in wireless LAN

1a to 1b is a view showing the structure of a frame for preventing a collision (collision) in a wireless LAN,

2 is a view illustrating a structure of a frame for preventing collision in a WLAN in which an HT station and a legacy station coexist;

FIG. 3 is a diagram for describing a method for controlling media access of stations when using the frame shown in FIG. 2;

4 is a view for explaining a medium access method of stations according to an embodiment of the present invention;

5 is a flow chart sequentially showing the operation of the HT station according to the present invention;

6 is a structural diagram of an HT station according to the present invention;

7 is a view for explaining a medium access method of stations in a sequence using Block ACK,

8 is a diagram illustrating a medium access method between stations in a sequence of transmitting fragment frames.

The present invention relates to a wireless LAN, and more particularly, to a method for preventing collision in a WLAN in which a high throughput (HT) station and an 802.11 legacy station coexist.

In a wireless LAN environment, MAC (Medium Access Control) of CSMA / CA (Carrier Sensing Multiple Access with Collision Avoidance) is used. CSMA / CA transmits a signal for confirmation in case there is no data transmission on the cable of the network, and confirms that the confirmation signal is transmitted without collision, and then sends data.

Briefly looking at the principle of CSMA / CA, the station detects a carrier of whether another station is transmitting data and waits when it knows that another station is transmitting. A random time is allocated as the time until the transmission start, and retransmission detection is performed to confirm that there are no other carriers, and then data transmission is started.

CSMA / CA uses physical carrier sensing and virtual carrier sensing at the same time for carrier sensing. Physical carrier sensing uses a received power above a certain value in the PHY. ) Is a technique of sensing a carrier by determining whether the medium is detected by a medium to <Busy> or <Idle>, and the virtual carrier sensing is performed when the MPDU can be accurately extracted from the received PPDU. This is a technique that virtually considers a medium as <Busy> during a predetermined time of using a medium by interpreting a <Duration / ID> field, one of the header fields. Stations use these two carrier sensing techniques to determine if the medium is <Busy> and not access the medium for a <Busy> period.

As shown in FIG. 1A, the MAC header of a frame transmitted in a general 802.11 WLAN includes <duration> information, which is a time from when the frame is transmitted until an ACK frame is received. Stations that have received the MAC headers do not attempt to access the medium during the <duration> time, so that no collision occurs. This is because all the stations in the WLAN receive the frame even if the transmitted frame is sent to a specific station. In FIG. 1B, a structure of a transmission frame used in 802.11a is illustrated. As shown in FIG. 1B, since a SIGNAL field includes RATE and LENGTH information, the duration information can be predicted when interpreted to clear channel assessment. Mechanism becomes possible.

As such, virtual carrier sensing is effective CSMA / CA application only when MPDU / PSDU (MAC Protocol Data Unit / PHY Service Data Unit) is correctly interpreted without error. That is, virtual carrier sensing is possible only when MAC header value can be read normally.

However, when transmitting using a high data rate, such as an unstable channel condition, or if the receiving station cannot process the data rate, the received MPDU / PSDU cannot be interpreted. Since carrier sensing is impossible, the CSMA / CA scheme operates inefficiently, thereby increasing the possibility of collision. Here, the HT station refers to a terminal having an improved data transmission capability than a legacy legacy station, that is, a station conforming to the 802.11 a / b / g standard, such as a MIMO (Multi Input Multi Output) station.

In 802.11n, which is currently being standardized, in order to solve such a problem, when the HT station and the legacy station coexist in the WLAN as shown in FIG. 3, the physical layer (PHY) header of the frame may be formatted so that legacy stations can understand them. (L-Preamble, L-SIG), and the <duration> information included in the existing MAC header is included in the PHY header. This <duration> information indicates the time from the L_SIG to the completion of receiving the ACK frame. A method of presenting has been proposed. Hereinafter, this <duration> time will be referred to as extended phy protection (EPP).

FIG. 3 is a diagram for explaining media access control of stations when using such an EPP. As shown, using EPP can prevent collisions between stations, but inequality in media control occurs.

In detail below, even though the legacy station can interpret the PHY header, an error occurs since it cannot interpret the part corresponding to the HT format, and the PHY (baseband) layer has an error in the MAC layer. Inform. The time when the error is notified is the end of EPP. From this point, the MAC waits for the time corresponding to the EIFS time (SIFS + ACKtime + DIFS), while other HT stations wait only for DIFS and contention. ) To participate.

That is, when an error occurs because the legacy station cannot interpret the frame of the HT format, unlike the HT stations in the MAC of the legacy station, the EIFS (Extended InterFrame Space, EIFS) is different from the DIFS (DCF InterFrame Space, 34us for IEEE 802.11a). Legacy stations that receive frames in HT format are not able to participate fairly in the race for media control because they take a time off of 94us) for IEEE 802.11a and participate in the backoff. For reference, after completing the first HT data reception, the CCA state of the legacy station becomes <idle>, but since the reception period, i.e., the EPP is not over, the legacy station does not generate an error in the MAC until the timer expires. Do not inform. This is true even if the ACK frame is a legacy format that the legacy station can interpret.

In conclusion, legacy stations start EIFS at the end of EPP, i.e., when the reception of the ACK frame is completed, but HT stations start DIFS at the same time, so legacy stations are comparable to other HT stations in competition for media access. There is a problem of being relatively disadvantageous.

It is an object of the present invention to provide a method and apparatus for ensuring fairness of media access between stations in a WLAN in which an HT station and a legacy station coexist.

In order to achieve the above object, the present invention provides a method of transmitting a frame of an HT format in a WLAN in which a high throughput (Legacy) station and a legacy station coexist with different data transmission capabilities, including (a) an HT station and HT format frame by inserting information indicating that the medium is in use until the transmission of the acknowledgment frame (ACK) for the frame is completed in the physical layer (PHY) header of the format that all legacy stations can interpret Generating a; (b) transmitting the frame in the HT format; And (c) transmitting a reset frame in a format that both the HT station and the legacy station can interpret, so that the stations receiving the transmitted HT format frame reset the waiting time for accessing the medium equally. It is characterized by.

In this case, in the step (c), after receiving the acknowledgment frame for the frame of the HT format, the reset frame is transmitted before the DIFS (DCF Interframe Space) elapses.

In addition, when the acknowledgment frame is a Block ACK frame for a plurality of HT frames, the HT frame becomes a first frame among the frames of the HT format. Meanwhile, a CF-end frame or a QOS null frame may be used as the reset frame.

The present invention also provides a computer-readable recording medium having recorded thereon a program for executing a method of transmitting a frame of an HT format in a WLAN in which an HT station and a legacy station coexist with different data transmission capacities.

The present invention also provides a physical layer (PHY) of a format that can be interpreted by both the HT station and the legacy station in an apparatus for transmitting an HT format frame in a WLAN in which an HT station and a legacy station coexist with different data transmission capacities. A transmission frame generation unit inserting information indicating that a medium is in use until a transmission of an acknowledgment frame (ACK) for the frame is completed, into a header to generate a HT format frame; A reset frame generation unit for generating a reset frame in a format that both the HT station and the legacy station can interpret, so that the stations receiving the frame in the HT format reset the waiting time for accessing the media equally; And a transmitter for transmitting the frame of the HT format and the reset frame.

In this case, when the frame of the HT format is the first frame among a plurality of fragment frames, the acknowledgment frame is an acknowledgment frame for the last frame of the fragment frames.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 4 is a diagram for describing a method of guaranteeing fairness for media access between stations in a WLAN according to an embodiment of the present invention. Herein, the WLAN is a concept including an infrastructure BSS (Basic Service Set) and an IBSS (Independent Basic Service Set), which are also the same below.

As shown in FIG. 4, the HT station according to the present invention transmits a frame of the HT format, and after receiving the ACK frame and SIFS elapses, transmits a small reset frame to the WLAN. Here, the reset frame is a frame having a function of resetting the timers of all stations equally. Here, the reset frame is not limited to a specific format, and a header without a CF-end or payload is a frame having a function of resetting the MAC timer. QOS-null or the like, which is a frame having only one, can be used as a reset frame here. Meanwhile, in FIG. 4, it is assumed that stations receiving the reset frame immediately start the backoff. However, according to an embodiment, the station may wait the predetermined time and then start the backoff. In addition, in FIG. 4, the HT station transmits the reset frame after SIFS has elapsed after receiving the ACK frame. However, the present invention may be implemented by changing the time.

In more detail, the HT stations receiving the ACK frame start counting DIFS after the reception of the ACK frame is completed, and the legacy stations receiving the ACK frame count the EIFS as shown in FIG. 3 since the EPP has expired. To start. However, the originating station that anticipates this situation has a reset frame that resets the timers of the stations equally so that all stations can start backoff for medium use evenly after SIFS after reception of the ACK frame is completed. send. Receiving a reset frame, HT stations counting DIFS and legacy stations counting EIFS reset the latency timer for accessing the medium and simultaneously participate in competition for the use of the medium. However, since the HT stations start the backoff after DIFS passes after receiving the ACK, it is preferable to transmit the reset frame after DIACK passes after the ACK is transmitted.

5 is a flowchart sequentially showing the operation of the HT station according to the present invention. Since the originating station transmitting the HT format transmission frame can know in advance the time until the ACK frame is completed for the transmission frame, the originating station inserts information indicating the time, that is, the EPP, into the legacy format PHY header. A transmission frame of the HT format is generated (510). Next, the originating station generates a reset frame for transmitting the transmission frame and causing the HT stations and legacy stations in the WLAN to reset the wait time timer in the same manner (520). After the transmission frame is transmitted through the WLAN (530), if an ACK frame for the transmission frame is received (540), after the predetermined time has elapsed, the reset frame generated in step 520 is transmitted (550). Here, as described above, a frame such as CF-end or QoS-null may be used as the reset frame. Meanwhile, step 620, which is a process of generating a reset frame, may be implemented in a different order from other steps.

6 is a structural diagram of an HT station according to the present invention.

As shown in FIG. 6, the HT station according to the present invention includes a transmission frame generator 620, a transmitter 630, and a reset frame generator 640.

The transmission frame generation unit 620 inserts EPP information indicating that the medium is in use until the completion of the transmission of the ACK frame to the physical layer (PHY) header of the format that both the HT station and the legacy station can interpret. To generate a transmission frame of the HT format, and the reset frame generation unit 640 is for causing stations that receive the transmission frame of the HT format to reset the waiting time for accessing the media equally, and both the HT station and the legacy station Create a reset frame with a format that can be interpreted.

The transmitter 630 transmits the transmission frame generated by the transmission frame generator 620 and the reset frame generated by the reset frame generator 640 to the stations through the WLAN 610. After transmitting the frame, it is preferable to receive an ACK frame for it and to transmit a reset frame when SIFS elapses.

On the other hand, in the above, it is assumed that the sequence for receiving the ACK frame for one transmission frame, the present invention can be applied even when a plurality of frames are transmitted in one sequence. Hereinafter, these cases will be described with reference to FIGS. 9 and 10.

FIG. 7 is a diagram for explaining a method of guaranteeing fairness for media access between stations in a sequence using Block ACK. It is common to send one frame and then receive an ACK frame for it. However, as shown in FIG. 7, when an originating station transmits several frames, it requests information about whether the transmitted frames have been successfully received. The receiving station may transmit a Block ACK frame indicating the successful reception of the plurality of frames at once. In this case, EPP is included in the PHY header of the legacy format in the first frame, and the EPP is set to expire at the completion of transmission of the Block ACK request frame. In addition, as shown in FIG. 7, the originating station receives a Block ACK frame and transmits a reset frame after SIFS has elapsed.

FIG. 8 is a diagram for describing a method of guaranteeing fairness for media access between stations in a sequence of transmitting fragment frames.

In this embodiment, the originating station transmits one frame divided into three fragment frames, and unlike FIG. 7, the receiving station transmits an ACK frame for each fragment frame. In this embodiment, EPP information is included in the PHY header of the legacy format in the fragment frame 0, and the EPP expires at the time when the transmission of the ACK frame 2, which is the last frame in the sequence, is completed. In addition, as shown in FIG. 8, in the present embodiment, when the source station receives the ACK frame 2 and SIFS elapses, the reset station transmits the reset frame.

Meanwhile, the above-described embodiments of the present invention can be written as a program that can be executed in a computer, and can be implemented in a general-purpose digital computer that operates the program using a computer-readable recording medium.

The computer-readable recording medium may be a magnetic storage medium (for example, a ROM, a floppy disk, a hard disk, etc.), an optical reading medium (for example, a CD-ROM, a DVD, etc.) and a carrier wave (for example, the Internet). Storage medium).

So far I looked at the center of the preferred embodiment for the present invention. Those skilled in the art will appreciate that the present invention can be implemented in a modified form without departing from the essential features of the present invention. Therefore, the disclosed embodiments should be considered in descriptive sense only and not for purposes of limitation. The scope of the present invention is shown in the claims rather than the foregoing description, and all differences within the scope will be construed as being included in the present invention.

According to the present invention, when a HT station transmits a frame of an HT format in a WLAN environment in which a HT station and a legacy station coexist, a legacy station receiving the HT format competes for use of a medium under the same conditions as other HT stations without further modification. You will be able to participate in

Claims (19)

In a method of transmitting a frame of the HT format in a WLAN where a high throughput (HT) station and a legacy station coexist with different data transmission capabilities, (a) Information indicating that the medium is in use until the transmission of the acknowledgment frame (ACK) for the frame is completed in a physical layer (PHY) header of a format that both the HT station and the legacy station can interpret. Inserting to generate a frame in an HT format; (b) transmitting the frame in the HT format; And (c) transmitting a reset frame in a format that both the HT station and the legacy station can interpret, causing the stations receiving the transmitted HT format frame to reset the waiting time for media access equally. How to feature. The method of claim 1, Step (c) is, And transmitting the reset frame after receiving an acknowledgment frame for the frame of the HT format and before the DIFS (DCF Interframe Space) elapses. The method of claim 1, The acknowledgment frame is a Block ACK frame for a plurality of HT frames, the HT frame is characterized in that the first frame of the frame of the HT format. The method of claim 1, Wherein the frame of the HT format is a first frame of a plurality of fragment frames, and the acknowledgment frame is an acknowledgment frame for the last frame of the fragment frames. The method of claim 1, Step (b) is characterized in that for transmitting the reset frame when the Short Interframe Space (SIFS) elapses after the acknowledgment frame is received. The method of claim 1, The reset frame is characterized in that the CF-end frame or QOS null frame. The method of claim 1, The wireless LAN is characterized in that the infrastructure BSS (Basic Service Set) or IBSS (Independent Basic Service Set). The method of claim 1, And the legacy station is a station compliant with IEEE 802.11 a / b / g standard. The method of claim 1, The HT station is characterized in that the Multi Input Multi Output (MIMO) station. A computer-readable recording medium having recorded thereon a program for executing the method of claim 1 on a computer. An apparatus for transmitting a frame of an HT format in a WLAN in which an HT station and a legacy station coexist with different data transmission capacities, HT by inserting information indicating that the medium is in use until the transmission of the acknowledgment frame (ACK) for the frame is completed in the physical layer (PHY) header of the format that both the HT station and the legacy station can interpret A transmission frame generation unit generating a frame of a format; A reset frame generation unit for generating a reset frame in a format that both the HT station and the legacy station can interpret, so that the stations receiving the HT format frame reset the waiting time for accessing the medium equally; And And a transmitter for transmitting the frame of the HT format and the reset frame. The method of claim 11, And the transmitting unit transmits the reset frame before the DIFS (DCF Interframe Space) elapses after the acknowledgment frame for the frame of the HT format is received. The method of claim 11, The acknowledgment frame is a Block ACK frame for a plurality of frames, the frame of the HT format is characterized in that the first frame of the frame. The method of claim 11, Wherein the frame of the HT format is a first frame of a plurality of fragment frames, and the acknowledgment frame is an acknowledgment frame for the last frame of the fragment frames. The method of claim 11, And the transmitting unit transmits the reset frame when a short interframe space (SIFS) elapses after the acknowledgment frame is received. The method of claim 11, And the reset frame is a CF-end frame or a QOS null frame. The method of claim 11, The wireless LAN device characterized in that the infrastructure BSS (Basic Service Set) or IBSS (Independent Basic Service Set). The method of claim 11, And the legacy station is a station compliant with IEEE 802.11 a / b / g standard. The method of claim 11, The HT station is a device characterized in that the Multi Input Multi Output (MIMO) station.

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