KR20050000940A - Method for transmitting data by using an access point in point coordinator function mode - Google Patents

Abstract

PURPOSE: A method for transmitting data using an AP(Access Point) in a PCF(Point Coordination Function) mode is provided to reduce unnecessary overheads caused due to a CF(Contention Free) poll for stations having null frames by sorting out only stations having data to be transmitted and carrying out a CF poll for them. CONSTITUTION: Stations having large-capacity multimedia data sends poll request frames to an AP respectively. At this moment, the poll request frames of the first and third stations which have data to transmit are transmitted to the AP through a channel contention. The poll request frame of the second station which doesn't have data to transmit is not delivered to the AP. In this case, the AP makes out a new poll list in the received order of the poll request frames. The AP respectively transmits CP poll frames to the first station and the second station in the order of the new poll list at a CFP(Contention Free Period) using a round-robin scheduling method.

Description

Data transfer method using an access point in point adjustment function mode {METHOD FOR TRANSMITTING DATA BY USING AN ACCESS POINT IN POINT COORDINATOR FUNCTION MODE}

The present invention relates to a method of transmitting multimedia data using an access point in a point coordination function mode. More specifically, the present invention deletes a station having no data to be transmitted in the contention free period of the point coordination function mode, and then executes a poll by creating a new survey list consisting only of stations with data to be transmitted. In addition, the present invention relates to an effective data transmission method that can reduce unnecessary overhead, that is, unnecessary investigation of a station having no data to transmit.

Recently, a new WLAN technology has been developed to connect a wireless network with various digital devices. In this regard, in the IEEE 802.11 WLAN standard, two adjustments in a LAN module are performed so that communication between stations and STAs and access control to a wireless medium can be performed while sharing a wireless medium. Functions are distributed coordination function (DCF) and point coordination function (PCF). The DCF and PCF are technically implemented through an access point (AP). Here, the access point (AP) is to convert the frame of the 802.11 network to another type of frame for delivery to another network, performs the bridging function of wireless and wired, and also the synchronization and data transmission of DCF and PCF It plays a role of relay and plays an important role in the efficiency of WLAN and resource management.

The DCF is a rule applied when accessing a wireless medium based on competition, and is based on access delay and frame notification. DCF is a carrier sense multiple access / collision avoidance (CSMA / CA) scheme that detects carriers on a transmission line in a wireless LAN and avoids collisions so that collisions do not occur. Exponential back-off based on exponential function to effectively share a given channel while avoiding collisions as much as possible. Delay before attempting transmission again when a data transmission signal on a transmission medium collides on a WLAN. It is executed by acquiring a license through channel competition.

The PCF is a set of rules used to provide central management of access to the medium at the access point (AP). PCF provides Contention Free (CF) service, which is the point coordinator (PC) within the access point (AP) that is responsible for the central coordination of access to wireless media during contention-free services. This is because the media can transmit data without contention through a special station called a point function. The PCF transmits a sequence of access points (APs) to a plurality of terminal devices in a poll (computer or terminal control device) in a non-competition period (CF period, CFP) during which the contention-free service proceeds Inquire the presence or absence of a request, and instruct the terminal device to start transmission when there is a request, and transmit a channel right through each station (STA) through a transmission control method that inquires about the next terminal device if there is no request. It is a service that is given to each other in turn. When the contention period (CP) is reached after the end of the non-competition period (CFP), channel competition is performed through backoff to obtain a right to use. The start of the contention-free period (CFP) begins by broadcasting the beacon frame (B) at the access point (AP) and ends the CF-End frame (CF-End). Terminate with. This beacon frame (B) is a network allocation vector (Network Allocation Vector, NAV: used to implement a virtual carrier detection function) using the value of the station (STA) that wants to use the channel while participating in the current network. During the competition period (CFP) only serves to suspend the independent operation to comply with the control of the access point (AP).

1 is a diagram schematically showing a data transmission state in a contention free period (CFP) of the conventional PCF mode.

First, the access point AP broadcasts a beacon frame B to inform all stations STA 1, 2, 3 under access point AP management that it is a contention free period (CFP). At this time, each station STA receiving the beacon frame B stops all individual operations, and after the beacon frame B, the access point AP acquires control of the wireless medium, Investigate the STA in the polling list. Here, the survey list is a list of authorized stations authorized to transmit frames during the contention-free period (CFP), and each station (STA) may be included in the survey list through a predetermined process of requesting a join request to an access point. have.

Based on this survey, the access point (AP) can be configured in a round-robin scheduling (COP) process during each contention-free period (CFP). Polling the station STA, each station that receives the survey can transmit the necessary data to the desired station through the access point AP.

For example, as shown in FIG. 1, in a contention free period (CFP), an access point (AP) sends a contention free survey frame (Contention Free-Poll, CF-investigation) to station 1 in the order listed in the survey list. Each station receiving this CF-irradiated frame has received an authorization from the access point (AP) to transmit one frame capable of carrying data.

The station 1 receiving the CF-irradiation frame transmits the data to the access point (AP) in the CF-irradiation frame when there is data to be transmitted to the station 2. The AP then sends an acknowledgment (ACK) to station 1 and then sends a CF-investigation frame to station 2 with the data to be sent from station 1 to station 2.

The station 2 which receives the CF-irradiation frame then transmits data to the access point (AP) to transmit to station 1 with an acknowledgment (ACK). The AP then sends an acknowledgment (ACK) to station 2 and then sends a CF-investigation frame to station 3.

Thereafter, the station 3 receives the CF-investigation frame and sends the data to the access point (AP) to transmit to the station 2 with an acknowledgment (ACK), thereby ending the PCF period.

However, as shown in FIG. 2, since stations 1 and 2 are included in the survey list (see FIG. 3) even when there is no data to send, the access points AP are null in the order of the survey list. Will send a frame. Accordingly, the CF-investigation and acknowledgment (ACK) process is uniformly performed to stations 1 and 2 that have no data to transmit, thereby causing unnecessary overhead.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to select a station having data to be transmitted in a contention free period of a point coordination function (PCF) mode, create a survey list, and execute a contention free investigation. In addition, the present invention provides a data transmission method for reducing unnecessary overhead of transmitting a contention free investigation frame even to a station having no data to transmit.

1 is a diagram illustrating a state in which a survey frame and data are transmitted in a conventional contention free period.

2 is a view illustrating a state in which a null frame of a station is transmitted in a conventional contention free period.

FIG. 3 shows a survey list with stations with null frames in relation to FIG.

4 is a block diagram of a survey request frame according to an embodiment of the present invention.

5 is a diagram illustrating a state in which a survey request frame of FIG. 4 is transmitted in a contention period according to an embodiment of the present invention.

FIG. 6 illustrates a new survey list in which stations with null frames have been deleted in connection with FIG.

7 is a flowchart illustrating a data transmission process in a contention free period according to an embodiment of the present invention.

8 is a flowchart illustrating a data transmission process in a contention free period according to another embodiment of the present invention.

In order to achieve the above object, the present invention provides a method for transmitting a survey request frame to an access point through channel contention for stations having data to be transmitted in a contention period in order to request a survey, The received access point includes the step of creating a survey list in the order of request, and the access point transmits the survey frames to the station in the order of the created survey list using a sequential execution method in a contention free period. A data transmission method using an access point in a point adjustment function mode is provided.

In another embodiment, the present invention provides a method for transmitting a survey frame to a corresponding station according to a survey list in a contention-free period, and a null frame when a station receiving a survey frame from the access point has no data to transmit. Requesting deletion from the survey list while transmitting to the access point, and the access point deletes the station that has requested the deletion from the survey list to create a new survey list. The present invention provides a data transmission method using an access point.

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

4 shows a management frame structure for stations with a large amount of multimedia transmission data to request polls from an access point (AP) in a contention period (CP).

The survey request frame includes an FC field, a persistence / ID field, an RA field, a BSSID field, and an FCS field.

The FC (Frame Control) field consists of two bytes, the first two bits of the protocol version, the next two bits of the frame type, and the four bits of the subtype. In addition, each of ToDS and FromDS has one bit, additional bits, retries, power management, additional data, wired equivalent privacy (WEP), and each bit for sequence.

The Duration / ID field may be used for a Network Allocation Vector (NAV) setting, a frame transmitted during a contention free period, and a power saving survey frame.

The RA (Receiver Address) field is a MAC address of a station to receive a frame. Like the Ethernet, the RA (Receiver Address) field is a 48-bit MAC identifier corresponding to a station to transmit to a higher protocol layer for a frame operation.

The Basic Service Set ID (BSSID) field is referred to as a 'basic service set identifier' field and is assigned an MAC address of an access point (AP) 's air interface. The BSSID is used to distinguish WLANs in the same area. The ad hoc network generates a random BSSID by setting the universal / local bit to 1 to avoid collision with an officially designated MAC address.

The Association ID (Association ID) field is assigned an AID to assist control and management functions when the station associates with an AP. When the join request is approved, the access point (AP) responds with status code 0 (success) and association ID (AID). The AID is a numeric identifier used to logically identify a mobile station requiring buffered frame delivery. When the frame is buffered, the AID of the destination station provides a logical link between the frame and the destination.

The Frame Check Sequence (FCS) field is a field used to check the integrity of a received frame, and is often called a cyclic redundancy check (CRC). When a frame is transmitted wirelessly, the FCS is calculated before transmitting over radio frequency or infrared. Meanwhile, the receiving station calculates the FCS from the received frame and compares it with the received FCS. If the two match, the receiving station determines that the frame is intact. If there is no error, the receiving station sends an acknowledgment (ACK) to the transmitting station. In case of an error in 802.11, the receiving station does not transmit a message, and the transmitting station waits for a predetermined time and then transmits a frame again if it does not receive an acknowledgment (ACK).

FIG. 5 shows a state in which each station STA transmits an inquiry request frame of FIG. 4 through contention to an access point AP in a contention period CP.

First, among each higher frame, stations with a large amount of multimedia data in the contention period CP send a survey request frame to the access point AP. At this time, in relation to the survey request frame structure of FIG. 4, the survey request frames of the station 1 and the station 3 having data to be transmitted are transmitted to the access point (AP) through channel competition, and the survey request of the station 2 having no data to transmit The frame is not transmitted to the access point (AP). In this case, the access point AP creates a new survey list ('STA 1 → STA 3') as shown in FIG. 6 in the order in which the survey request frame is received.

The access point (AP) is a sequence of a new survey list using a round-robin scheduling (COP) to take up the central processing unit for a certain unit of time in a contention-free period (CFP) As a result, a contention free investigation frame is transmitted to the station 1 and the station 3 having the data to be transmitted.

In this way, the access point AP transmits the irradiation frame only to stations 1 and 3 that have data to send, thereby avoiding unnecessary overhead.

In addition, when the station 2 receives the survey frame during the contention-free period, the station 2 transmits the data to be transmitted, and sends a null frame to the access point AP, and requests the AP to delete it from the survey list. . In this case, the access point AP deletes the station 2 that sent the null frame from the survey list, and then creates a new survey list ('STA 1 → STA 3') as shown in FIG.

In this way, the access point (AP) deletes from the survey list for the station 2 that has no data to transmit and selects only the stations 1 and 3 that have the data to send and creates a new survey list, thereby creating a contention free period (CFP) for the next PCF mode. The AP may transmit / receive CF-investigation, acknowledgment (ACK) and data only for stations 1 and 3 that have data to transmit. This prevents the access point AP from transmitting the CF-irradiation frame to the station 2 that will send a null frame during CF-irradiation for each station, thereby preventing unnecessary overhead in advance.

FIG. 7 is a flowchart illustrating a data transmission process using an access point (AP) through the survey request frame in a contention period (CP) with respect to FIG. 5.

First, the access point AP transmits a beacon frame B (S100). Each station STA that receives the beacon frame B sends a join request to the access point AP, and the access point AP that accepts the join request sends a join response after authentication to the station. The process is completed (S110). As a result, each station can gain access to the network.

When the next combining process is completed, the survey request frame of the stations that actually have data to be transmitted is transmitted to the access point AP through the mutual channel contention in the contention period CP (S120). If the station STA2 has no data to transmit, the survey request frame is not transmitted to the access point AP. Here, stations with data to transmit may transmit a small amount of data together when transmitting a survey request frame.

After a plurality of stations (STA) having data to be transmitted compete for a channel in the contention period (CP), and when the channel competition (S130) of the station (STA1 and 3) in the case of the access request (AP) The survey list is newly created in the order in which it is sent to (S140). At this time, if the stations missing from the channel contention among the stations having data to be transmitted may retransmit the survey request frame in the next contention period CP (S150).

Finally, according to the new survey list, the access point AP transmits a contention-free survey frame (CF-irradiation) in order to a station having data to transmit (S160). As a result, since the new survey list includes only stations STA1 and 3 having data to be transmitted, the conventional unnecessary overhead of transmitting a CF-irradiation frame to a station STA2 having no data to transmit is prevented. It becomes possible.

8 is a flowchart illustrating a data transmission process using an access point (AP) in a contention free period (CFP) according to another embodiment of the present invention.

First, the access point AP transmits a beacon frame B (S200). Each station receiving the beacon frame B sends a join request to the access point AP, and the access point AP that accepts the join request sends a join response after authentication to the station, thereby completing the joining process. (S210). As a result, each station can gain access to the network.

Next, when the combining process is completed, the access point (AP) transmits a contention free survey (CF-investigation) frame to the station in the order of the survey list for data transmission (S220).

Each station receiving a CF-investigation frame from the access point (AP) transmits an acknowledgment (ACK) to the access point (AP) with data to be transmitted, and the access point (AP) checks whether there is data to be transmitted ( S230). The access point AP transmits each data in the order of the survey list to the station STA3 to which the data received from the station STA1 is to be delivered (S240). At this time, the station STA2 having no data to send sends a request frame to the access point AP to be deleted from the survey list while sending a null frame to the access point AP (S250). The access point AP deletes from the survey list for the station STA2 that sent the null frame (S260) and creates a new survey list (S270). As a result, the new poll list contains only the stations STA2 and 3 with the data to be transmitted, and the station STA2 to send null frames is deleted. This can avoid unnecessary overhead.

Although the present invention has been described in detail above, those skilled in the art to which the present invention pertains may variously modify the present invention without departing from the spirit and scope of the present invention as defined in the appended claims. It is apparent that the present invention may be modified or modified. Therefore, a simple change according to an embodiment of the present invention will not be possible without departing from the technology of the present invention.

According to the present invention having the above-described configuration, stations having a large amount of multimedia data transmit a survey request frame to an access point through competition, and perform a contention-free survey by selecting only a station to transmit data based on the survey request information. By doing so, it is possible to reduce unnecessary overhead due to contention-free investigation even for a station having a conventional null frame, thereby reducing the waiting time of each station, thereby improving the performance of the wireless network.

Claims (10)

Sending, by the access point, the survey request frame to the access point via channel contention for the stations with data to transmit in the contention period; An access point receiving the survey request frame, creating a survey list according to the requested order; And And the access point transmitting the survey frames to the station in the order of the created survey list in a sequential execution manner in a contention free period. The method of claim 1, wherein the transmission of the survey request frame in the contention period also includes data transmission. The method of claim 1, wherein the survey list includes only stations having data to be transmitted. The method of claim 1, wherein when the survey request frame is transmitted, a station having no data to transmit does not transmit the survey request frame to an access point. Receiving a survey request frame from a station having data to transmit in a contention period; Creating a survey list according to the order of stations that have transmitted the survey request frame; And And transmitting a survey frame to a station to transmit data in a contention-free period according to the survey list. In the contention free period, the access point transmits a survey frame to the corresponding station according to the survey list; Requesting deletion from the survey list while transmitting a null frame to the access point if the station receiving the survey frame from the access point has no data to transmit; And And accessing the access point by deleting a station that has requested a deletion from the survey list, thereby creating a new survey list. 7. The method of claim 6, wherein the survey list includes only stations having data to be transmitted. 8. The method of claim 7, wherein the access point transmits a survey frame only to stations having data to transmit according to the new survey list. Transmitting a survey frame to a corresponding station according to a survey list in a contention free period; Requesting deletion from the survey list while transmitting a null frame when the station receiving the survey frame has no data to send; And And deleting a station making a deletion request from the survey list to create a new survey list. 10. The method of claim 9, wherein the access point transmits a survey frame only to a station having data to transmit according to the new survey list.