KR101404993B1 - Method for transmitting a data - Google Patents

Abstract

The present invention relates to a wireless network communication system and, particularly, to a method for transmitting data by selecting stations having periodic uplink data comprising the following steps of: receiving data from more than one station in a contention-free period with a poll method; checking whether the received data is periodic uplink data from a relevant station based on the data received from each station; selecting stations periodically transmitting uplink data according to the check result, and pre-registering the stations as a sync group, and generating and transmitting a sync poll frame defining a data transmission start time (sync_time) for each pre-registered station; registering relevant stations as a sync group when data is normally received from pre-registered stations within a predetermined time after the defined data transmission start time; and transmitting a sync poll frame requesting data transmission to the stations registered at the sync group in a contention-free period.

Description

{METHOD FOR TRANSMITTING A DATA}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wireless network communication system, and more particularly, to a method of selecting and transmitting data with stations having only periodic upstream data.

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 provides both a competitive communication service and a non-contention-based communication service using the DCF and the PCF. In a communication environment in which there is a large amount of periodic upward data, such as a remote meter reading and a CCTV system, There is a need for a new data transmission method for more efficient data transmission because the preamble overhead is long. Referring to FIG. 3 illustrating a general poll-based interval-free transmission frame in the case where only uplink data exists,

3, in an environment in which uplink data, that is, data STA1, STA2, and STA3 to be transmitted from each station STA1, STA2, and STA3 are periodically generated, a preamble Since the overhead (IFS + (P1 + A1) transmission time) is uniformly defined as shown in the figure, the overhead for transmission of the poll frame Pn, n = 1, 2, 3 and the response frame Ack, It is necessary to have a method for reducing the amount of water.

SUMMARY OF THE INVENTION Accordingly, the present invention has been made to solve the above-mentioned problems occurring in the prior art, and it is an object of the present invention to provide a data transmission method capable of reducing a preamble overhead period in a wireless communication environment in which only periodic upstream data exists,

It is still another object of the present invention to provide an access point data transmission method capable of normally transmitting uplink data even when an error occurs in data indicating transmission of periodic uplink data.

According to an aspect of the present invention, there is provided a method for transmitting contention data in an access point capable of wireless communication with a plurality of stations,

Receiving data from one or more stations in a poll-based contention-free period;

Checking whether the data is periodic uplink data from a corresponding station based on data received from each station;

According to the result of the check, only the stations that periodically transmit uplink data are selected and preliminarily registered in a SYNC group, and a sink poll frame defining a preliminarily registered data transmission start time (SYNC_TIME) for each station is generated and transmitted ;

Registering a corresponding station as a sink group when data is normally received within a designated time after lapse of the defined data transmission start time from each preliminarily registered station;

And transmitting a sync frame requesting data transmission to stations registered in the sync group in a contention-free period.

Further comprising the step of deleting the station from the sink group in response to the registration deletion request from the station registered in the sink group,

And deleting the corresponding station from the sink group if data is not received after the data transmission start time (SYNC_TIME) predefined for each station registered in the sink group.

In addition, the sync frame of the data transmission method according to the above-described embodiment of the present invention is composed of a poll frame and a response frame for each station,

A data transmission start time (SYNC_TIME) information defining a data transmission start time of the station;

A data transmission response period (SYNC_CNT) information defining a data transmission response period for receiving the sync pole frame;

And data transmission time (POLL_D) information allocated for data transmission to the corresponding station,

The preamble of the sync pause frame may further include at least additional information (SYNC_SET) for indicating whether to utilize the information received before the occurrence of an error, as information for preparing an error situation of the sync pause frame.

According to the embodiment of the present invention as described above, when a sync frame is generated and transmitted to the stations registered in the sync group, a preamble overhead is required for every Pn frame, Only the preamble overhead section of the sync pause frame is required. As a result, the channel utilization efficiency can be increased by shortening the overhead section.

Further, even if an error occurs in the data for instructing the transmission of the periodic uplink data, the present invention can obtain the effect of periodically transmitting the uplink data normally using the previously stored information.

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;
FIG. 3 is a diagram illustrating an example of a conventional poll-based interval transmission frame in the case of only uplink data. FIG.
4 is a diagram for explaining a process of selecting a station transmitting periodic uplink data according to an embodiment of the present invention and registering the stations as a sync group.
FIG. 5 is a diagram illustrating a sync frame according to an embodiment of the present invention. FIG. 5 is a diagram illustrating a frame in which poll frames and acknowledgment (ack) frames of a destination are composed of one sync pole frame.
6 is a diagram showing a detailed configuration example of a sync pole frame shown in FIG. 5;
Fig. 7 is a diagram showing an example of the frame body configuration of the pole frame (P1 frame) shown in Fig. 6;
8 is a diagram illustrating an example of a preamble structure of a sync pole frame shown in FIG.
FIG. 9 is a diagram illustrating a frame for explaining a data transmission response period (SYNC_C) for receiving a sync pole frame according to an embodiment of the present invention; FIG.
FIG. 10 is a diagram illustrating an example of a frame for explaining utilization of SYNC_SET information according to an embodiment of the present invention; FIG.
FIG. 11 is a view for explaining a transmission interval in which a sync-type contention-free period and a poll-type contention-free period coexist according to an embodiment of the present invention; 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. .

FIG. 4 is a view for explaining a process of selecting a station transmitting periodic uplink data according to an embodiment of the present invention and registering the station as a sync group. FIG. (SYNC POLL) Frame Example A frame diagram is shown in which a poll frame and a response frame, each having a different destination, are formed of one sync pole frame. FIG. 6 is a detailed block diagram of the sync pole frame shown in FIG. 5, FIG. 7 is a diagram showing a frame body diagram of the pole frame (P1 frame) shown in FIG. 6, The preamble structure of the sync pole frame shown in FIG.

Referring first to FIG. 4, an access point (AP) receives data from at least one station (STA) in a contention-free contention-free period (step S10). Then, the access point AP checks whether it is periodic uplink data from the corresponding station based on data received from each station (step S12). Periodic uplink data refers to data that each station repeatedly transmits the measured data or surveillance data by a predetermined cycle, such as in the remote meter reading or CCTV system.

On the other hand, if it is determined that the periodic uplink data is the result of the check, the access point (AP) preliminarily registers the station as a SYNC group and transmits a data transmission response And sets the response period (SYNC_C) information. For reference, when the data transmission response period "SYNC_C" is set to "1 ", the station transmits data every time it receives a sync pole frame, Is a multiple of two. In FIG. 9, since the data transmission response period SYNC_C has a value of "2 ", the station transmits only when the sequence number SN is a multiple of 2.

Referring again to FIG. 4, an access point (AP) preliminarily registered as a SYNC group by selecting only the stations transmitting periodic uplink data, then transmits data transmission start time SYNC_TIME for each preliminarily registered station, And transmits the generated sync frame to the station side (step S14). When analyzing the uplink data periodically transmitted from the station, the data transmission start time (SYNC_TIME) and the data transmission time (POLL_D) of each station can be known. Therefore, the access point generates a sync frame containing the data transmission start time (SYNC_TIME) and data transmission time (POLL_D) information, and transmits it to the station side.

As will be described later, if the stations STA1 and STA2 are the stations already registered in the sink group and the STA3 is the newly pre-registered station, the access point AP generates and transmits a sync frame as shown in FIG. STA2, and STA3 in accordance with the data transmission start time (SYNC_TIME) defined by each station (STAn), because the sync frame includes the data transmission start time (SYNC_TIME) .

For reference, the sync pause frame configured according to the embodiment of the present invention includes poll frames (P1, P2, P3) and response ack frames (A1, A2, A3) And each of the pole frames P1, P2, and P3 and the response frames A1, A2, and A3 includes FH, a frame body, and an FCS as shown in FIG. As shown in FIG. 7, a frame body (FRAME) of a poll frame (for example, P1) includes data transmission start time (SYNC_TIME) information defining a data transmission start time of the station, A data transmission response period (SYNC_C) information defining a data transmission response period, and a data transmission time (POLL_D) information allocated for data transmission to the corresponding station. As shown in FIG. 8, at least the additional information (SYNC_SET) indicating whether to utilize the information received before the occurrence of the error is further included as information for preparing for the error situation of the sync pole frame at the preamble of the sync pole frame .

Referring again to FIG. 4, when the access point AP generates and transmits a sync frame containing information as shown in FIGS. 6 to 8 as described above, (STA1, STA2, STA3) to the access point (AP) as shown in Fig. 5 in accordance with the data transmission start time (SYNC_TIME). When the data STA3 is normally received (step S16) within the designated time after the elapse of the data transmission start time (SYNC_TIME3) defined by the preliminarily registered station STA3, the access point AP performs normal registration do.

If the pre-registered station is normally registered as a sink group, the access point (AP) then transmits a data transmission request to the station (STA1, STA2, STA3) registered in the sink group in a contention- A polling frame is generated and transmitted, so that periodic uplink data is received from each station.

As described above, when a single sync frame is generated and transmitted to stations registered in the sync group, as shown in FIG. 2, compared with the conventional scheme requiring preamble overhead of every Pn frame, Only one preamble overhead (IFS + SYNC (transmission time)) period is required as shown in FIG. 5A, and as a result, the channel utilization efficiency can be increased.

Meanwhile, de-registration of the station registered in the sink group can be performed according to the request of the station and can be performed by the access point. That is, if there is a registration deletion request from a station registered in the sink group, the access point may delete the station from the sink group in response to the registration deletion request,

The access point may further include a step of deleting the corresponding station from the sink group if data is not received after the data transmission start time (SYNC_TIME) predefined for each station registered as a sink group.

9 is a diagram illustrating a frame for explaining a data transmission response period (SYNC_C) for receiving a sync pole frame according to an exemplary embodiment of the present invention. FIG. 10 is a diagram for explaining the use of SYNC_SET information according to an exemplary embodiment of the present invention. FIG. 11 is a view for explaining a transmission interval in which a sync-type contention-free period and a poll-type contention-free period are present together according to an embodiment of the present invention.

Referring to FIG. 9, each station transmits a transmission time point of uplink data by using a sequence number (SN), a data transmission response period (SYNC_C) information, and a data transmission start time (SYNC_TIME) . That is, the station selects a sync contention period (SYNC_CFn) to transmit the uplink data by comparing the sequence number SN with the data transmission response period (SYNC_C), and the data transmission start time after receiving the sync pole frame in the selected sync contention- (SYNC_TIME), the uplink data is transmitted.

Meanwhile, there is a need for a method for transmitting normal uplink data even when an error occurs as shown in FIG. 10 in data indicating transmission of periodic uplink data due to signal interference of the wireless environment and various other factors. To this end, in the embodiment of the present invention, SYNC_SET is used as additional information indicating whether or not to use the received information before an error occurs. This additional information SYNC_SET is also included in the preamble of the sync pole frame shown in FIG. The access point sets SYNC_SET to " 0 "if there is no change in the transmission period of the uplink data, and sets it to" 1 "in the initial setting step and fluctuation, Even if an error occurs in the second received sync frame, if the SYNC_SET information included in the second sync frame is "0 ", the uplink data is transmitted in the normal time using the previously stored (set) SYNC_TIME and SYNC_C .

Therefore, the present invention is a useful invention having the effect of regularly transmitting uplink data periodically using previously stored information even if an error occurs in data indicating transmission of periodical uplink data.

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 (5)

Receiving data from one or more stations in a poll-based contention-free period;
Checking whether the data is periodic uplink data from a corresponding station based on data received from each station;
According to the result of the check, only the stations that periodically transmit the uplink data are selected and preliminarily registered in the SYNC group, and a sink poll frame defining the preliminarily registered data transmission start time (SYNC_TIME) for each station is generated and transmitted ;
Registering a corresponding station as a sink group when data is normally received within a designated time after lapse of the defined data transmission start time from each preliminarily registered station;
And transmitting a sync frame for requesting data transmission to stations registered in the sync group in a contention-free period. The method of claim 1, further comprising, if there is a registration deletion request from a station registered in the sink group, deleting the station in the sink group in response to the request. The method of claim 1, further comprising: deleting a corresponding station from the sink group if data is not received repeatedly after a predefined data transmission start time (SYNC_TIME) for each station registered as the sink group An access point data transmission method. The method of any one of claims 1 to 3, wherein the sync pole frame comprises a poll frame and a response frame for each station,
A data transmission start time (SYNC_TIME) information defining a data transmission start time of the station;
A data transmission response period (SYNC_C) information defining a data transmission response period for receiving the sync pole frame;
And data transmission time (POLL_D) information allocated for data transmission to the corresponding station. 6. The apparatus of claim 4, wherein the preamble of the sync pause frame further includes at least information (SYNC_SET) indicating whether to utilize the information received before the occurrence of the error, A data transmission method of an access point.

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