KR20040104776A - Method for wireless local area network communication in contention free period - Google Patents

Abstract

PURPOSE: A wireless LAN communication method during a CFP(Contention Free Period) is provided to effectively transmit data by stations during a CFP, and to enable each station to perceive a time for transmitting self data and to convert into a power-saving mode if the self data is not transmitted, thereby minimizing power loss. CONSTITUTION: A station receives a beacon transmitted by an AP(S2), and stores an ACK number through data transmission period information loaded on the beacon(S4). If the AP performs a polling process, the station receives a polling signal(S6), and decides whether to transmit self data(S8). If so, the station transmits the data to the AP(S10). If a CFP is not terminated(S12,S14), a next station transmits data. If the CFP is terminated, the station waits for a next CFP.

Description

Wireless LAN communication method without contention section {METHOD FOR WIRELESS LOCAL AREA NETWORK COMMUNICATION IN CONTENTION FREE PERIOD}

The present invention relates to a wireless LAN communication method, and more particularly, to a wireless LAN communication method for improving a polling mechanism in a contention free period (hereinafter referred to as "CFP").

Currently, there are several standards that can transmit data wirelessly. Examples include Bluetooth, which is used to form a small network wirelessly, third generation mobile communication using WCDMA, and wireless LAN based on IEEE 802.11. Among them, the wireless LAN using the 802.11 standard is successful, and its use is gradually expanded.

The 802.11 standard technology uses frequency hopping (FH), direct sequence (DS) frequency spreading, and infrared (InfraRed (IR)). Early 802.11 products were limited to 2 Mbps, but 802.11b, standardized in 1999, supports speeds up to 11 Mbps. Meanwhile, 802.11a is based on a technique called orthogonal frequency division multiplexing (OFDM) and operates in a frequency band different from that of 802.11b.

As described above, the physical layer of 802.11 is divided into frequency hopping and direct sequence spreading techniques, and orthogonal frequency division multiplexing techniques. Data link consisting of a sublayer of 802.11 Medium Access Control (hereinafter referred to as "MAC") and a sublayer of 802.2 Logic Link Control (hereinafter referred to as "LLC") over the physical layer. There is a hierarchy.

Among them, 802.11 converts a frame of an 802.11 network into another frame for transmission to another network, that is, an access point (hereinafter referred to as an "AP") that performs wireless and wired bridging functions, and one station. Wireless medium, a concept that includes a radio frequency or infrared physical layer for transmitting frames from one station to another station, a station such as a laptop or PDA, and a wireless network interface and computing device, and It consists of four physical components, a distributed system that connects multiple access points to form a wider coverage area.

The network has a basic service set (hereinafter, referred to as a "BSS"), which is a group of stations communicating with each other. A BSS is a standalone BSS in which a station communicates directly with another station, and an infrastructure BSS in which a station must communicate with another station via an access point. Comparing the two, the latter requires more transmission capacity when communicating than the former. However, the fact that the access point can record the station entering power saving mode and then frame buffer for the station and that the stations must all be within reach of the access point are complex to keep the mobile stations in a relationship. This is advantageous in that the use of the physical layer is unnecessary.

There are two media access methods for data transmission in 802.11. One is Contention Based Access and the other is Contention Free Based Access. Often, the former is called a Distributed Coordinator Function (hereinafter referred to as "DCF") and the latter is called a Point Coordinator Function (hereinafter referred to as "PCF").

The PCF controls the data transfer in the Contention Free Period (hereinafter referred to as "CFP"), where the access point has a list of nodes called a polling list for data transfer that does not require contention. Polling each node in the order in the list in the CFP interval to enable contention-free data transmission. In other words, only the polled station has a right to transmit data, and the PCF can be referred to as a polling and response protocol.

1 is a diagram illustrating an example of operations of an access point and a station in a conventional CFP.

1 shows data transmission in the CFP section. This contention-free transmission protocol is based on a polling scheme controlled by a point coordinator (hereinafter referred to as a "PC"). The PC will have a shared media control capability from the start of the CFP, which includes the functionality of the PC.

First, after the PCF Inter-Frame Space (hereinafter referred to as "PIFS"), the AP transmits a beacon frame and starts the CFP section by the PCF. The CFP duration is defined in the beacon frame. In addition, the maximum usable CFP duration is defined by a Management Information Base (“MIB”) value called CFPMaxDuration, which is typically 2.5 times the length of the beacon interval.

In order to access the medium for the first time using PCF, a frame interval as much as PIFS is required. Otherwise, all frame intervals are short inter-frame spaces (hereinafter referred to as "SIFS") as shown in FIG. Becomes

The CFP duration may end when the MIB value set for the beacon ends, but also ends when the PC sends a CF-END frame. In PCF, a station polled by a PC has the right to send data.

Referring to FIG. 1, when describing an operation, an AP first transmits a DTIM beacon frame sent to all stations of a network when a Delivery Traffic Indication Map (hereinafter, referred to as "DTIM") count becomes zero. Send and announce the start of CFP by PCF. At this time, the beacon frame includes information about the duration of the CFP.

The AP constructs a list of stations that can be polled by the PC. During the CFP, the stations in the list are polled in turn, allowing the stations on the list to send data without channel contention. Stations polled by the AP send one data frame, and the AP receiving the data frame transmits an acknowledgment (Ack). The acknowledgment sends a polling frame to the next station in the polling list so that the station can send data. The station sends an acknowledgment for polling to the AP, with any data to send.

On the other hand, when an error occurs in a frame sent by the polled station to the AP, the PC polls again to the station sending the error frame after SIFS. If the PC has a problem with a polling frame sent to a station on the polling list, or if that station has not received a polling frame from the AP, the PC will poll again for the station that was the subject of the polling frame after PIFS. If a node polled from a PC does not actually have data to send, it sends a null frame to notify it, and the PC that received the null frame polls the next station in the polling list.

This conventional approach requires that stations be polled each time in order to be able to transmit data, and stations are wasting power because the station must always be in active mode when it does not need to send or receive data. do.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a WLAN communication method that enables stations to know the order of data transmission in a contention free manner and to transmit data when the order becomes. .

In another aspect, the present invention is to make it possible to reduce the power used by the station by using the above method.

1 is a diagram illustrating an example of operations of an access point and a station in a conventional CFP.

2 is a view showing a beacon frame to which a new element is added according to an embodiment of the present invention.

3 is a view showing the operation of the station according to an embodiment of the present invention.

4 shows an example of mapping an association ID (hereinafter referred to as "AID") and an ACK number.

5 illustrates an example of operations of an access point and a station in a CFP according to the present invention.

In order to achieve the above object, the WLAN communication method according to the present invention transmits a beacon carrying data transmission time information of all stations constituting the basic service set, and the stations constituting the basic service set receive it. Storing data transmission time information contained in the beacon; and transmitting, by the corresponding station, data to the access point according to the data transmission time information. The station determines a data transmission time by receiving a polling frame or an acknowledgment frame transmitted by the access point. The data transmission time information is a number indicating a data transmission order of the stations constituting the basic service set, and the station counts the number of acknowledgment frames transmitted by the access point so that the counted number indicates its own data transmission order. When it is equal to the number indicated, data is transmitted to the access point. When counting the number of acknowledgment frames, the counted count is reset when the counted number reaches the maximum station number. On the other hand, the station receives the data transmitted by the other station through the access point through the access point through the acknowledgment frame of the access point for the station that sent the data just before the data transmission.

In the present invention, since the station knows the time of data transmission and reception, it is possible to reduce the power loss by switching to the power saving mode when it is not the time of data transmission and reception.

In order to achieve the above object, the WLAN communication method according to the present invention may generate a beacon containing data transmission time information of all stations in which an access point forms a basic service set, so that all the stations may store the data transmission time information. Transmitting the beacons to all the stations so that the beacon receives data transmitted by a first station that determines a data transmission time based on the stored data transmission time information, and the access point receives the first beacon. Receiving the data transmitted by the first station and transmitting an acknowledgment frame for this, and the stations to confirm the data transmission time using the acknowledgment frame transmitted by the access point. If there is data to be transmitted to the second station by the access point, the data may be transmitted in the acknowledgment frame.

Meanwhile, after the access point transmits the beacon, the polling frame is transmitted to a station to transmit data first. The access point newly updates the data transmission time information of the stations and generates a new beacon including the updated data transmission time information when there is a change due to the participation and withdrawal of the stations constituting the basic service set. At this time, the access point stores the information of the station that finally transmitted the data in the previous beacon period, and the data transmission time information so that the next station of the station that finally transmitted the data in the previous beacon period transmits data first. Configure Meanwhile, when a frame transmission error occurs, the access point may further include polling a corresponding station to retransmit data.

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

2 is a view showing a beacon frame to which a new element is added according to an embodiment of the present invention.

Beacon frame is frame control (1), persistent ID (2), receiving station address (3), sending station address (4), basic service set ID (5), sequence control (6), data transmission time information (7). , And frame check sequence 8.

The frame control 1 consists of two bytes. In more detail, the first two bits indicate the protocol version. The next two bits represent the type of the frame, and the four bits represent the subtype. The beacon frame has a value of 00 because it is a managed type and has a value of 1000 because it belongs to the beacon type. In addition, ToDS and FromDS each have 1 bit, additional pieces, retries, power management, additional data, WEP (Wired Equivalent Privacy), and 1 bit for each order.

The persistent ID 2 may be used for setting a network allocation vector (NAV), a frame transmitted during a contention free period, and a power saving investigation frame.

The receiving station address 3 is a 48-bit IEEE MAC identifier corresponding to a station that transmits to a higher protocol layer for the operation of a frame, similar to Ethernet, and the transmitting station address 4 is a 48-bit IEEE MAC identifier of a transmitting station. The basic service set ID (5) 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 sequence control 6 is a filter used for fragment reassembly and discarding duplicate frames, and is composed of a 4-bit fragment number field and a 12-bit sequence number field.

The data transmission time information 7 corresponds to a part of an 802.11 frame body, which can store up to 2,304 bytes of data. The data transmission timing information 7 is a newly defined element and is defined as follows in the preferred embodiment. First, one byte indicating that the seventh element is an element ID, and a length field for sequentially listing the stations contained in the data transmission time information is one byte, and two bytes for the association ID of each station. It consists of a combined ID field of length. In FIG. 2, a total of 10 stations participate in the basic service set. Therefore, the AID has a total of 10 (= 20 bytes) and has a total of 22 bytes including 1 byte for each element ID and length field. have.

Finally, the Frame Check Sequence (FCS) 8 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 over the air, the FCS is calculated before transmitting over radio 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 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.

3 is a view showing the operation of a station according to an embodiment of the present invention.

First, the station receives a beacon transmitted by the AP (S2). The received beacon has a CFP duration, and the beacon starts the CFP section by the PCF. The station receiving the beacon stores an acknowledgment number (ACK Number) through the data transmission time information contained in the beacon (S4). Each station may store acknowledgment numbers of all stations, but preferably stores only its own acknowledgment number. How to know its confirmation response number through the beacon will be described in detail with reference to FIG.

4 shows an example of mapping an association ID (hereinafter referred to as "AID") and an acknowledgment number. There are a total of five stations, that is, nodes A to E, and nodes A, B, C, D, and E are sequentially described in the AID field of the data transmission time information. For example, station A has a right to transmit data first because the acknowledgment number is "0", and station C has a right to transmit data third because the acknowledgment number is "2".

The AP polls immediately after receiving the beacon so that the station can transmit data. If the AP contains the data to be sent to the station A in the current CFP interval, the AP sends the data contained in the buffer to the station A with polling. When the AP polls, the station receives the polling (S6). Upon receiving the poll, the station should determine whether it is time to send data (S8). Whether it is the turn to send data is determined by whether the number of acknowledgments received from the AP matches with the number of acknowledgments that the user has stored. That is, when the AP polls for the first time, since the number of acknowledgments sent by the AP is "0", it is time for the station A to transmit data. Station A transmits data to the AP (S10). If there is no data to send, send null frame. When station A sends data, the AP sends an acknowledgment, where station A to station E counts the number of acknowledgments as "1". Meanwhile, in the preferred embodiment, the AP transmits the acknowledgment to the station B in the acknowledgment frame for the data transmitted by the station A to the AP when there is data to be transmitted to the station B to transmit the data next to the station A. Load the data to send. If the CFP section does not end (S12), the next station transmits data and if the end is completed, the next CFP section waits.

If station A sends data and the CFP interval has not ended, station B has the right to send data because the number of acknowledgments received by stations is "1". The station B transmits data (S10), and upon receiving an acknowledgment from the AP, increases the number of acknowledgments so that the acknowledgment number becomes "2". When the acknowledgment is "2", station C has the right to transmit data, and stations A, B, D, and E increase the number of acknowledgments by "1" and wait for their turn (S16). If the CFP section ends (S18), the next CFP section waits.

The next CFP section starts when the AP transmits a beacon to the stations, and the AP prepares a new polling list and reflects the beacon when a new station joins or leaves an existing station in the basic service set. On the other hand, when creating a new polling list, it is preferable to create a polling list so that the next station of the station that has finally transmitted data in the previous CFP section can transmit data first. For example, if you sent data to station C, you can set the acknowledgment numbers of stations D, E, A, B, and C to be 0, 1, 2, 3, and 4, respectively, when you create a new beacon. have.

If an error occurs in the data transmission process, for example, if the station C fails to transmit data to the AP at the time of data transmission, the AP polls the station C and gives a data transmission opportunity. The AP polls the station D when the station C fails to transmit data even after receiving a predetermined number of times determined by the user, for example, three polls. In other words, if an error occurs in one CFP section, it returns to the previous polling and response mechanism, and executes the process of the present invention again in the next CFP section.

On the other hand, in the present invention, since the stations can know when to send or receive data, the stations can turn the power into an active mode only when they send and receive data, and when not, the power save mode. For example, stations A, B, D, and E are in sleep mode when station C transmits data, and stations C, and D are active mode when station C transmits data and the AP transmits an acknowledgment frame. Shall be.

5 illustrates an example of operations of an access point and a station in a CFP according to the present invention.

First, the beacon is transmitted by the AP, and the CFP by the PCF starts. The AP polls for data transmission of the station. 5 shows a situation in which only the polling frame is transmitted because there is no data to be transmitted by the AP in the first station. The first station sends data to the AP with an acknowledgment for the polling frame. The AP sends data to station 2 with an acknowledgment of the data transmission of the first station. At this time, all stations count the number of acknowledgments by the acknowledgment frame transmitted by the AP. When counting, the station transmits data when the counting number matches its acknowledgment number. If the total number of stations is counted, it is desirable to reset the counting to give the first station the right to send data.

Those skilled in the art will appreciate that the present invention can be embodied in other specific forms without changing the technical spirit or essential features. For example, in the above description, the counting is implemented by increasing the number. However, the counter has the same effect even if it is implemented by decreasing the number. Therefore, it should be understood that the embodiments described above are exemplary in all respects and not restrictive. The scope of the present invention is shown by the following claims rather than the detailed description, and all changes or modifications derived from the meaning and scope of the claims and their equivalents should be construed as being included in the scope of the present invention. do.

According to the present invention made as described above, stations can efficiently transmit data in a contention free period. On the other hand, since each station knows when it transmits data, it can minimize power loss by switching to a power saving mode when it does not transmit data.

Also, in the present invention, when an error occurs during data transmission, it can be switched in the same manner as in the prior art.

Claims (12)

(a) When the access point transmits a beacon containing data transmission time information of all stations constituting the basic service set, the stations constituting the basic service set receive the data and store the data transmission time information contained in the beacon. Making; And (b) the station transmitting data to the access point according to the data transmission time information; Wireless communication method of the contention-free section comprising a The method of claim 1, wherein in step (b), the station determines a data transmission time by receiving a polling frame or an acknowledgment frame transmitted by the access point. Wireless communication method of competition section The data transmission time information of claim 2, wherein the data transmission time information is a number indicating a data transmission order of stations constituting the basic service set, and the station counts the number of acknowledgment frames transmitted by the access point. The wireless communication method of the contention-free period characterized in that the data is transmitted to the access point when the number indicating the data transmission order of the own. 4. The method of claim 3, wherein when counting the number of acknowledgment frames, the counted count is reset when the counted number reaches the maximum number of stations. 3. The station of claim 2, wherein the station receives data that another station transmits on its own through the access point through an acknowledgment frame of the access point to the station that sent the data just before the data is transmitted. Wireless communication method of the contention-free section characterized in that receiving The wireless communication method according to any one of claims 1 to 5, wherein the station enters a power saving mode when it is not at the time of receiving data or at the time of transmission. Generating, by an access point, a beacon containing data transmission time information of all stations constituting a basic service set, and transmitting the beacon to all stations so that all stations can store the data transmission time information; Receiving, by the access point, data transmitted by a first station that determines a data transmission time based on the stored data transmission time information; And The access point receiving data transmitted by the first station and transmitting an acknowledgment frame thereto; The wireless communication method of a contention-free period, characterized in that for checking the transmission time of the stations using the acknowledgment frame transmitted by the access point. The wireless communication method according to claim 7, wherein the data is transmitted in the acknowledgment frame when the access point has data to be transmitted to the second station. 8. The method of claim 7, further comprising: transmitting, by the access point, a polling frame to a station to transmit data first after transmitting the beacon. 8. The method of claim 7, wherein the access point newly updates the data transmission time information of the stations and includes the updated data transmission time information when there is a change due to the participation and withdrawal of the stations constituting the basic service set. Comprising a step of generating a beacon wireless communication method of the contention-free period characterized in that it further comprises 12. The apparatus of claim 10, wherein the access point stores information of a station that has finally transmitted data in a previous beacon section and allows the next station of the station that has finally transmitted data in a previous beacon section to transmit data first. Comprising the transmission time information and generating a beacon including the same, the wireless communication method of the contention-free period characterized in that it further comprises 12. The radio of any of claims 7 to 11, wherein the access point further comprises polling a corresponding station to retransmit data when a frame transmission error occurs. LAN communication method