KR101443210B1 - Method for transmitting a contention data - Google Patents

Abstract

The present invention relates to a wireless network communications system and, especially, to a method to transmit contention data which is transmitted and received between access points and stations. The present invention is a data transmitting method available to be executed in a device transmitting and receiving contention data to an access point, and includes: a first step of accessing contention data from an upper layer or generating the contention data by itself; a second step of generating a random number for backoff to transmit the contention data; a third step of checking whether a beacon for changing the random number is received from the access point; a fourth step of standing by for a predetermined period based on the confirmation on the beacon received when a changed random number reaches a target value; and transmitting the contention data after the predetermined period.

Description

[0001] METHOD FOR TRANSMITTING A CONTENTION DATA [0002]

The present invention relates to a wireless network communication system, and more particularly, to a method of transmitting contention data transmitted between an access point and a station.

The characteristics of the environment such as wireless and power lines are that there is a lot of noise and the signal transmission medium is shared. In this environment, a carrier sense multiple access with collision avoidance function (ARQ) using ARQ (Automatic Repeat reQuest) with the purpose of giving a fair transmission opportunity to a plurality of stations and ensuring reliable data transmission collision avoidance (hereinafter referred to as CSMA / CA) type media access control protocol (MAC protocol) is mainly used. Currently, the most widely used wireless Internet standard is IEEE 802.11, which implements one-to-many communication in a wireless environment based on CSMA / CA.

The MAC protocol of the IEEE 802.11 standard includes a Distributed Coordination Function (DCF) and a Point Coordination Function (PCF). DCF is a MAC protocol designed to grant fair transmission opportunities to all stations participating in communication. It is a MAC protocol in which all stations to which a frame is transmitted participate fairly in channel competition, And transmits the frame. DCF is based on CSMA / CA method.

FIG. 1 illustrates a process in which stations transmit and receive frames using a DCF. In the DCF, each station checks whether another frame is being transmitted to the transmission medium before transmitting the frame. If another frame is being transmitted, it waits until the transmission is terminated, and it can attempt to transmit a new frame after the frame transmission is completed and the DIFS (DCF interframe space) time has elapsed. After the DIFS has elapsed, a section called a contention window is started. In this contention window, a plurality of stations compete to transmit frames to each other. The contention window is divided into backoff slots having a predetermined length as shown in FIG. A plurality of stations select a time slot for randomly transmitting a frame, and a station selecting the fastest time slot transmits a new frame. In this process, the probability that each time slot is selected is the same, so that the stations can equally distribute the transmission opportunity through the DCF for a sufficiently long time.

Meanwhile, in DCF, in order to secure the reliability of data transmission, a station receiving a data frame transmits an ACK (positive acknowledgment) control frame as a response signal. After all the data frames are transmitted, an ACK control frame is transmitted after a time of SIFS (Short InterFrame Space), and the frame is successfully transmitted when this process is normally completed.

On the other hand, PCF is a MAC protocol designed to arbitrarily grant transmission authority to stations, unlike DCF. The PCF specifies a special station called a point coordinator (PC) and allows the PC to control the communication of the entire network. The PC grants transmission rights (transmission rights) to individual stations as needed or in a predetermined manner. The station to which the transmission right is assigned transmits one frame, and after the frame transmission is completed, the PC repeats the process of newly granting transmission right. In this way, the PCF gives the transmission authority by the PC without competition process, so that the transmission opportunity can be arbitrarily adjusted so as to be given more to the specific station.

The worst-case performance of the frame transmission is not ensured because the stations participating in the communication using the DCF may continuously fail to acquire the transmission right through the contention. Thus, the DCF is not suitable for time-critical applications such as multimedia content streaming services or online games. On the other hand, the PCF controls the entire traffic, so it can allocate as much bandwidth as required by a PC according to the PC's judgment. For this reason, the IEEE 802.11 standard provides a contention-free communication service by using a DCF as a base and using a PCF periodically by dividing a communication time. At this time, a time interval using the DCF is called a contention period (CP), and a time interval using the PCF is called a contention free period (CFP). Therefore, the communication channel of the network using the PCF is composed of a repeated contention period and a contention free period. An example in which DCF and PCF are repeated and communication is shown in Fig.

The contention free period (CFP) is initiated by the PC sending a beacon frame to the stations. When the PC sends a beacon control frame in the contention period (CP), all other stations stop the DCF and stop the channel access so that the PC can control the network. The ending point of the contention free period (CFP) is also defined in the same way. The contention-free period (CFP) is terminated when the PC transmits a control frame called CF-End, and from that point on, other stations start the DCF and start a competition process for obtaining a transmission right. Within the contention free period (CFP), the PC uses a control frame called a poll to grant transmission rights to the stations. The PC transmits a poll frame by designating a station, and if the station designated by the poll frame has a data frame to transmit at that moment, the PC transmits the data frame after SIFS. If there is no data frame transmission even after the PIFS (PCF interframe space) has elapsed after the poll frame is transmitted, the PC determines that there is no data frame to be transmitted by the corresponding station and transmits the poll frame to another station. In this way, the PC can manage the communication of the entire network by allowing transmission only to the designated station.

Referring to FIG. 2, it can be seen that a data frame is transmitted by a poll at the beginning and end of a contention free period (CFP). When a PC transmits a beacon, a contention free period (CFP) Transmits a poll frame to each station, and the station designated by the poll does not transmit or transmit a data frame depending on the situation. In the case of FIG. 2, the PC transmits three poll signals within one contention-free period (CFP). Three poll signals may be transmitted once for three different stations or three times for one station. In the case of FIG. 2, the data frame is transmitted only by the second poll signal among the three poll signals. In addition, the third poll signal includes an ACK signal for transmission of the data frame by the second poll. The PC determines that three poll signals have been completed, and then transmits a CF-End frame to terminate the contention-free period. After that, all the stations start DCF and transmit data frames by channel competition.

As described above, the IEEE 802.11 standard simultaneously provides both a contention-based communication service and a contention-free communication service using DCF and PCF. However, in the communication service defined in the IEEE 802.11 standard, each station transmits a registration request frame to an access point through a random time delay (Random Backoff) algorithm in a contention period constituting a superframe. Even if there is no contention data, such as deletion, the access point (AP) must allocate time for the contention period, which leads to a decrease in channel utilization efficiency. That is, since the length of the contention period of the superframe is fixed, a new scheme for extending the contention-free period by varying the length of the contention period is required.

On the other hand, the beam radiation pattern required for performing communication between the access point and the stations compliant with the IEEE 802.11 standard has a pattern radiated with the same radius in all directions. Since such a beam radiation pattern is a pattern radiated in all directions at the same transmission power, there is a restriction that the stations should be configured to be located within the propagation radius of the access point with respect to the access point. Even if the stations are located within the propagation radius, the same transmission power is radiated to all directions, which may lead to transmission / reception performance deterioration due to radiated energy dispersion.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a wireless network communication system that simultaneously provides a contention-based communication service and a contention-free communication service, To provide a competitive data transmission method capable of maximizing channel utilization efficiency,

It is still another object of the present invention to improve the transmission / reception performance by dividing the beam radiation pattern necessary for performing communication between the access point and the stations into sectors, concentrating the beam patterns in the divided sections, The present invention also provides a competitive data transmission method capable of transmitting competition data by expanding the radio wave arrival radius.

According to an aspect of the present invention, there is provided a method for transmitting contention data to an access point (AP), for example, a method executable in a station,

A first step of accessing or creating the competition data from an upper layer;

A second step of generating a counting random number for backoff for transmitting the contention data;

A third step of checking whether a beacon is received to change the random number from an access point;

A fourth step of waiting for a predetermined interval when the change value of the random number reaches a target value according to whether the beacon is received or not;

And a fifth step of transmitting the contention data after the predetermined period.

According to still another aspect of the present invention,

Scanning the beacon reception sensitivity for each of the divisional sections determined for all directions before the first step;

And setting an antenna beam pattern for a section having the best reception sensitivity,

In the above embodiments, the predetermined interval is SIFS (Short InterFrame Space)

Further, the presence or absence of the contention period existence information is checked in the payload in the received beacon, and if the contention absence information is present, the third step is repeatedly checked without proceeding to the fourth step.

Also, in the above embodiments, the scan time of the scan step is set to a value calculated by the following equation.

Scan time = beacon period * M * N (where M and N are the number of the transmission interval and the reception interval, respectively)

According to another aspect of the present invention, there is provided a method for transmitting contention data in an access point for transmitting and receiving data to and from a plurality of stations,

Inserting presence / absence information of a contention area into a beacon payload in a superframe for data communication with a station;

Transmitting a beacon in which the presence / absence information of the contention period is inserted for each predetermined segment section;

Checking whether to receive the contention data after waiting for a predetermined interval after the transmission of the beacon;

Terminating the contention period or receiving contention data according to whether the contention data is received;

And transmitting a poll packet after completing the contention period.

The determined interval is SIFS, and the poll packet is a PIFS (PCF InterFrame Space) after the beacon transmission.

According to the embodiment of the present invention, if the contention data is transmitted in the contention period, the contention data can be transmitted ahead of the DIFS-SIFS period ahead of the transmission time of the contention data after the previous DIFS, It is possible to increase the channel utilization efficiency as a result of reducing the interval and expanding the noncontact interval. As a result,

A beam radiation pattern necessary for communication between an access point (AP) and a station (STA) is segmented by sector, and a beam pattern is concentrated and emitted in a divided section, And the data transmission / reception performance can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram for explaining an example of frame transmission in an IEEE 802.11 DCF; FIG.
2 is a diagram for explaining an example of frame transmission in an IEEE 802.11 PCF;
3 is a view for explaining a beam radiation pattern according to an embodiment of the present invention.
4 is a diagram illustrating a competitive data transmission process that can be executed in a station according to an embodiment of the present invention;
FIG. 5 is a diagram illustrating an example of a frame when contention data is transmitted according to FIG. 4. FIG.
6 is a diagram for explaining a process up to the transmission of competitive data that can be executed in an access point according to an embodiment of the present invention;
FIG. 7 is an illustration of a superframe when there is no contention data received by FIG. 6; FIG.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the description of the present invention, if it is determined that the related functions or configurations, for example, the detailed configuration of the station device and the access point, and the description of the MAC protocol may unnecessarily obscure the gist of the present invention, a detailed description thereof will be omitted. .

3 is a view for explaining a beam radiation pattern according to an embodiment of the present invention. Referring to FIG. 3, a wireless LAN system in which a plurality of stations (STAs) are distributed around an access point (AP) Respectively. Each station (STA) may be a CCTV as an example, and an access point (AP) may be a relay device connected to a plurality of CCTVs corresponding to a station (STA) to relay surveillance images.

In the illustrated WLAN system, each station (STA) and an access point constitute a wireless communication network that simultaneously provides a contention-based communication service and a non-contention-based communication service. For example, ) Exchanges competitive data such as registration and termination, and mutually transmits and receives necessary data in noncontact sections.

Meanwhile, for the implementation of the present invention, an access point (AP) and each station (STA) emits a directional beam for communication for each predetermined sector in all directions. That is, as shown in FIG. 3, the access point (AP) sequentially emits a directional beam to sector 1, sector 2, sector 3, and sector 4, and the station (STA) The beacon in all directions transmitted by the access point (AP) can be received. In this case, the scan time can be set according to the following equation, and if the scan time is set to a value larger than the following scan time, beacons in all directions can be received. For reference, performing the Rx Beam training at the time of receiving a beacon enables reception beam training for all receiving paths and setting the best receiving path for all directions.

Scan time = beacon period * M * N (where M and N are the number of sectors and the number of receive subdivisions, respectively)

When the scanning of the beacon reception sensitivity is completed for all sectors partitioned by the sector as described above, the station STA sets the antenna beam pattern for the division period having the best reception sensitivity, and then transmits the antenna beam pattern to the corresponding access point (AP) The registration request frame, which is one of the contention data, is transmitted. This process will be described below with reference to FIG. 3, reference numeral 100 denotes a radius of an antenna beam emitted in all directions.

FIG. 4 is a view for explaining a contention data transmission process that can be executed in a station (STA) according to an embodiment of the present invention, and FIG. 5 illustrates a frame when contention data is transmitted according to FIG. .

Referring to FIG. 4, the STA determines the transmission time of the contention data under the control of the access point (AP). To this end, the access point (AP) inserts "contention presence / absence information" into a beacon payload in a superframe for data communication with the station (STA) and transmits the information. The "information on the presence or absence of a competitive section" can be defined as information for indicating whether there is a competitive section or not. If there is a contention period, the STA transmits the contention data according to the method shown in FIG. 4, and if there is no contention period, the station STA does not change the random number C, Waiting to be.

Referring again to FIG. 4, if there is contention data to be transmitted preferentially in the STA, the STA accesses or generates the contention data from an upper layer such as a link layer, Random number C is randomly generated (step S10). Then, it is checked whether a beacon for changing the random number is received from the access point AP (step S12). If the beacon is normally received, the station (STA) checks the presence / absence of contention information in the beacon payload and if there is information indicating the presence of a contention period (step S14), the counting random number C is decreased (step S16) And then proceeds to step S18. Then, in step S18, it is determined whether the counted random number C has reached the target value "0 ". If the counted random number C has not reached the target value, the process returns to step S12 and waits. However, if the counted random number C that has been reduced as a result of the check reaches the target value, the process proceeds to step S20 and transmits the contention data (Asso_req) after waiting for a predetermined interval, i.e., SIFS . After receiving the contention data, the access point transmits, for example, a registration response packet (Asso_rsp) after SIFS after reception. After the SIFS, the noncontact communication service (Contention_Free_Period) is performed after two packets (the competition data such as the registration request packet and the registration response packet) are transmitted and received.

If the contention data is transmitted in the contention period as described above, since the contention data can be transmitted ahead of the DIFS-SIFS + contention window period rather than the time at which the contention data is transmitted after the previous DIFS, As a result, the channel utilization efficiency can be increased.

For reference, in the embodiment shown in FIG. 4, the presence / absence information of presence / absence of contention is checked in step S14, but this is only one option. For example, if the access point has completed registration for all stations (STA), the access point can notify the deletion of the contention slot through the "presence / absence of contention information ", so step S14 described above can be processed as an option.

Meanwhile, FIG. 6 is a view for explaining a process from the access point (AP) according to an embodiment of the present invention to the execution of competitive data transmission. FIG. Super frame.

Referring to FIG. 6, an access point (AP), in order to indicate the presence or absence of a contention period in a beacon payload in a superframe for data communication with a station (STA) Information "(step S30). Thereafter, a beacon in which "presence / absence of presence / absence of contention section" is inserted is selected (step S32) by selecting one of predetermined sectors in all directions. In this case, a method in which the beacon transmission beam is radiated so that the radiant energy is concentrated in the divided section can be used. An example of such a beam forming method is described in " Beamforming: A Versatile Approach to Spatial Filtering ", IEEE ASSP MAGAZINE, pp.4-24, APRIL 1988, published by Barry D. Van Veen and Kevin M. Buckley.

When the beacon transmission is performed for the selected one division period, as described above with reference to FIG. 4, the competition data is transmitted according to FIG. 4 when there is competing data to be transmitted to find the division period with the highest reception sensitivity.

After transmitting the beacon, the access point AP waits for a predetermined interval as shown in FIG. 7, i.e., SIFS (step S34), and checks whether content data is received (step S36). If the contention data is received as a result of the check, the process proceeds to step S38 where the contention data is received (for example, registration process). On the other hand, if the PIFS time period has elapsed without receiving the contention data The competition section is terminated. That is, as shown in FIG. 7, after a beacon transmission, a poll packet is transmitted after the PIFS and a PCF function is performed (a contention-free interval processing (step S42)). In FIG. 7, a process of selecting one segment and transmitting the beacon after the beacon has been described. However, each step shown in FIG. 7 should be performed sequentially for all of the segmented segments.

According to the above-described method, in an environment in which there is no further registration request, the contention period is reduced and the contention-free period is extended, resulting in an increase in channel utilization efficiency.

Further, in the embodiment of the present invention, the beam radiation pattern necessary for communication between the access point (AP) and the stations (STA) is segmented by sectors, and the beam pattern is concentrated and emitted in the segmented section, There is an advantage that the transmission / reception performance can be improved by expanding the radio wave arrival distance within the range.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of illustration, It will be readily apparent that various substitutions, modifications, and alterations can be made herein.

Claims (7)

A method for transmitting contention data in an apparatus that transmits contention data to an access point,
A first step of accessing or creating the competition data from an upper layer;
A second step of generating a counting random number for backoff for transmitting the contention data;
A third step of checking whether a beacon is received to change the random number from an access point;
A fourth step of waiting for a predetermined interval when the change value of the random number reaches a target value according to whether the beacon is received or not;
And a fifth step of transmitting the contention data after the predetermined period. The method of claim 1, further comprising: scanning the beacon reception sensitivity for each of the predetermined division intervals before the first step;
And setting an antenna beam pattern for a segment having the best reception sensitivity. The method of claim 1 or 2, wherein the determined interval is SIFS. The method as claimed in claim 1 or 2, further comprising the step of checking presence or absence of contention information in the payload in the received beacon and checking the third step without proceeding to the fourth step if the contention absence information is present. A method of transmitting data in a competitive manner. The method of claim 2, wherein the scan time of the scan step is set to a value calculated by the following equation.
Scan time = beacon period * M * N (where M and N are the number of the transmission interval and the reception interval, respectively) A data transmission method that is executable in an access point apparatus that transmits and receives data to and from each of a plurality of stations,
Inserting presence / absence information of a contention area into a beacon payload in a superframe for data communication with a station;
Transmitting a beacon in which presence / absence information of the contention period is inserted to a sequentially selected section of a predetermined section;
Checking whether to receive the contention data after waiting for a predetermined interval after the transmission of the beacon;
Terminating the contention period or receiving contention data according to whether the contention data is received;
And transmitting a poll packet after completing the contention period. 7. The method of claim 6, wherein the determined interval is a Short InterFrame Space (SIFS), the poll packet is transmitted after the beacon transmission and after the PIFS (PCF interframe space) interval, and the PIFS is longer than the SIFS. / RTI >

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