KR100352896B1 - A method for transmitting data at MAC layer in wireless LAN system - Google Patents

Abstract

A method for processing data transmission of a media access control (MAC) layer in a wireless local area network (LAN) system, the method comprising: a first step of receiving a data frame and sequence number information thereof from an upper layer data link layer; A second step of determining whether the sequence number of the received data frame overlaps with the corresponding number of the packet data unit (MAC PDU) of the media access control layer stored in the transmission buffer; As a result of the determination, if duplicated, the received frame is discarded, and if not overlapped, the received frame is constructed by mutually number mapping the MAC PDUs and stored in the transmission buffer, and storing the mapping information for a predetermined time. step; The contents of the transmission buffer are adjusted based on the error confirmation response information for each MAC PDU transmitted from the receiver and received through the lower physical layer, and the mapped stored sequence number, but the MAC PDU normally received is the transmission buffer. A fourth step of deleting and preparing to retransmit the received failed MAC PDU; And a fifth step of sequentially transmitting the MAC PDUs stored in the transmission buffer, thereby improving data transmission efficiency.

Description

A method for transmitting data at MAC layer in wireless LAN system in wireless local area network system

The present invention relates to a processing method in a media access control (MAC) layer for preventing duplicate retransmission in a wireless local area network (LAN) system. More particularly, the present invention relates to efficient data transmission in a wireless LAN system. In the case of applying a hybrid ARQ (hereinafter referred to as HARQ), a media in a wireless local area network system performing retransmission for HARQ in a MAC layer so that channel coding rate and retransmission can be organically combined. The present invention relates to a data transmission processing method of an access control layer.

Wireless LAN systems use narrowband-based transmission technology with spread spectrum in broadband, and mainly use the Industrial-Scientific-Medical (ISM) band. The ISM band designated for industrial, scientific and medical use includes the frequency bands 902-928 MHz, 2.4-2.4835 GHz, and 5.725-5.850 GHz. In the case of the ISM band, many wireless LAN products are used because no authorization procedure is required, but compatibility between the products has emerged as a problem. In order to solve this problem, standardization of wireless LAN was conducted mainly by Institute of Electrical and Electronic Engineers (IEEE) and European Telecommunications Standards Institute (ETSI).

In wireless data communications, especially in the wireless LAN environment, the MAC function being standardized with the physical layer allows multiple stations to access a shared channel while supporting maximum performance. Commonly used approaches in wireless LAN include contention-based carrier sense multiple access (CSMA) and time division multiple access (TDMA) based on time multiplexing. Application of one scheme and schemes using CDMA techniques are also under consideration.

In the IEEE 802.11 wireless LAN protocol, the radio channel is made by the physical layer and the MAC layer. Therefore, error detection is made through a CRC added to the Packet Data Unit (hereinafter referred to as PDU) of the MAC, the radio connection is controlled by CSMA / CA, and retransmission due to an error on the radio link is a data link. It is done in the hierarchy. The retransmission method due to data transmission error not only adds a lot of overhead on the wireless channel, but also cannot compensate for signal distortion due to the channel environment. Thus, to compensate for such signal distortion, forward error correction (FEC) coding is used. The FEC coding is performed by adding a CRC to the transmission data and then coding the same by using a predetermined algorithm, and adding additional information to the transmission frame and transmitting the additional data when an error occurs at the receiving end. It is to be able to recover using information.

In order to improve the efficiency of data transmission, error recovery by FEC coding, CRC error detection, and retransmission of an errored data frame should be organically performed. However, in the current wireless LAN architecture, FEC coding is performed at the physical layer, CRC checking is performed at the MAC layer, and retransmission is performed at the data link layer to perform independent operations. In addition, since the PDU of the datalink layer is segmented and transmitted again to fit the physical layer in the MAC layer, the actual retransmission unit is not a PDU size in the MAC layer but a PDU unit in the datalink layer. In this case, from the MAC layer point of view, there is a problem of retransmitting a normally transmitted PDU.

The present invention was created to solve the above problems, and its object is to perform a retransmission mechanism required by the MAC layer to support reliable data transmission in a wireless LAN system supporting low-speed mobility, thereby providing a data link layer. It is an object of the present invention to provide a data access processing method of a media access control layer in a LAN system, which enables efficient data transmission by implementing a method for solving a duplicate transmission problem of MAC PDUs that may occur during retransmission.

1 is a diagram illustrating a protocol layer structure and an interface of a wireless section supported by IEEE 802.11,

2 is a diagram illustrating a frame form of a MAC layer of an IEEE 802.11 wireless LAN,

3 is a view for explaining an example of the structure of a MAC PDU to be used for retransmission in the MAC layer according to the present invention,

4 is a flowchart illustrating a data transmission processing procedure in a MAC layer according to the present invention.

※ Explanation of code for main part of drawing

11: physical layer 11a, 11b: sublayer of physical layer

11c: management layer of the physical layer 12: media access control layer

12a: sublayer of the media access control layer

12b: management layer of the media access control layer

In order to achieve the above object, a method of processing data transmission of a MAC layer in a LAN system according to the present invention includes: a first step of receiving a data frame and sequence number information thereof from a data link layer, which is an upper layer; A second step of determining whether the sequence number of the received data frame overlaps with the corresponding number of the packet data unit (MAC PDU) of the media access control layer stored in the transmission buffer; As a result of the determination, if duplicated, the received frame is discarded, and if not overlapped, the received frame is constructed by mutually number mapping the MAC PDUs and stored in the transmission buffer, and storing the mapping information for a predetermined time. step; The contents of the transmission buffer are adjusted based on the error confirmation response information for each MAC PDU transmitted from the receiver and received through the lower physical layer, and the mapped stored sequence number, but the MAC PDU normally received is the transmission buffer. A fourth step of deleting and preparing to retransmit the received failed MAC PDU; And a fifth step of sequentially transmitting the MAC PDU stored in the transmission buffer.

The sequence number of the data frame is received in the form of a parameter, and the error confirmation response information is transmitted in addition to the header of the MAC PDU in the receiving MAC layer when transmitting data of the receiving side.

In addition, the added header is controlled to have a variable length depending on whether or not the MAC PDU to be transmitted includes error acknowledgment information, and the error acknowledgment information indicates whether or not the acknowledgment information is included in the transmitting MAC PDU. And an indicator, a length of acknowledgment information, a corresponding MAC PDU number for the acknowledgment, and information on whether the corresponding MAC PDU is in error.

In addition, in the MAC of the receiving side, MAC PDUs in which no error occurs are stored in the receiving buffer, and the MAC PDUs are combined and transmitted to the upper layer according to the order control in the MAC layer.

Hereinafter, a method of processing data transmission of a MAC layer in a LAN system according to a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a diagram illustrating a protocol layer structure and an interface of a wireless section supported by IEEE 802.11, and the physical layer 11 includes a physical medium dependent (PMD) sublayer 11a that is responsible for a physical transmission function. It is composed of a physical layer control part (PLCP) sublayer 11b in charge and a management layer 11c in charge of management thereof, and the MAC layer 12 is a MAC part in charge of actual transmission of data. A layer 12 includes a MAC sublayer 12a and a management layer 12b that performs management thereof. In addition, an interface between the layers is defined through a service access point (SAP) shown in the figure.

Substantial wireless channel access uses a carrier sense multiple access with collision avoidance plus acknowledgment (CSMA / CA + Ack) scheme. In other words, 802.11 uses CSMA / CA + Ack to access radio channel resources, which checks the signal level of the channel before data transmission, and suspends transmission when the signal level is determined to be above a certain level. Wait until it is not used. If the channel becomes empty after waiting, the terminal performs channel access again after a predetermined time, and transmits data when the channel acquisition is successful. After that, it waits for a response to the transmitted data to secure the reliability of the wireless channel.

In this case, when the wireless LAN network relies only on the distributed coordination function (DCF), each terminal has an equal qualification and performs competitive channel acquisition over all channels, and one terminal (PCF) In case of supporting Point Coordination Function, since channel management is performed by PCF, collisions can be reduced through non-competitive methods.

FIG. 2 is a diagram illustrating a frame form of a MAC layer of an IEEE 802.11 wireless LAN. As shown in the figure, basically, the frame structure of the IEEE 802.11 is indicated by the frame control header of the frame. The control header includes protocol version, type of frame and detailed functions, and there is a 'From / To DS' flag set according to whether a distribution server (DS) service is used or not. do. In addition, there is a bit indicating whether a PDU of one higher layer is divided into multiple MAC layer PDUs and a flag indicating retransmission for CSMA / CA scheme transmission, and there are also flags related to power control and security. do. The subsequent field is selected based on the information of the control header. When a long data transmission is required, time information may be transmitted and received as a duration ID. The reason why there are four Address (1-4) fields is that when each terminal wants to connect indirectly, not only the addresses of the terminals but also the address of the AP to which each terminal is connected.

As can be seen from the hierarchical structure of FIG. 1 and the frame structure of the MAC layer of FIG. 2, error detection is performed by the CRC located at the end of the MAC PDU. FEC coding is performed in the physical layer, which plays a role of reducing the probability of an error in error checking in the CRC. However, even in this case, if the error is not recovered and the CRC check detects an error, the MAC notifies the upper layer of the error occurrence. The upper layer, that is, the data link layer, that is notified of an error occurrence, performs retransmission of the corresponding data frame by a predetermined mechanism. The data frame of the data link layer becomes a PDU of an upper layer in the MAC, and the MAC layer divides the data to fit its own PDU, that is, configures and transmits the MAC PDU. Assuming that data frames in the data link layer are divided into three PDUs in the MAC layer, even if one of the three MAC PDUs detects an error at the receiving end due to an error in transmission, the data link layer at the data link layer Retransmission is performed with the data frame. That is, three MAC PDUs must be retransmitted for retransmission of the data link layer. This may increase the amount of retransmission data in a random error channel environment.

Accordingly, in the present invention, by transmitting the error from the receiving side to the transmitting side in the MAC PDU unit on the basis of the above, the transmitting side supports the retransmission of the MAC PDU unit of the MAC layer. To this end, first, when the transmitting side performs data transmission, the sequence number for the data frame is transmitted from the data link layer to the physical layer, and second, the receiving physical layer transmits the sequence number of the received MAC PDU to the transmitting side. Be notified.

The first requirement is implemented by passing a sequence number for the corresponding data frame as a parameter in the interface between the data link layer and the MAC layer. For the second requirement, since the receiving side must transmit the sequence number of the MAC PDU to the transmitting side, the shape of the MAC PDU frame for this is changed and implemented. In addition, the MAC layer at the receiving side stores MAC PDUs in which a CRC error does not occur in the receiving buffer.

3 is a view for explaining an example of the structure of a MAC PDU to be used for retransmission in the MAC layer according to the present invention.

In the figure, whether the MAC Ack Indicator field 31 includes error status acknowledgment information for the previous MAC PDU received so far in the header portion of the MAC PDU data 35 to be transmitted when the receiver transmits data. Information indicating the value is indicated by one bit of '0' or '1'. The Length field 32 indicates the length of error acknowledgment response information (ACK / NAK) and related information, such as ACK indicating no error and NAK indicating there is an error, and is represented by 7 bits. Start SEQ number 33 is indicated by 16 bits as a corresponding MAC PDU number to which acknowledgment information is transmitted, that is, a corresponding MAC PDU number to know acknowledgment information about which MAC PDU. The MAC PDU Recv_info 34 indicates whether the received MAC PDU is an error, that is, whether the corresponding MAC PDU is ACK or NAK, in the form of a bitmap, and displays 8-112 bits.

As such, the MAC layer at the receiving side adds the information 31 + 32 + 33 + 34 to the header portion of the MAC PDU 35 having the same form as the existing MAC PDU (see FIG. 2). In addition, the added information is controlled to have a variable length to add.

That is, when the MAC Ack Indicator 31 is '0', padding data is padded for 7 bits thereafter. In addition, when the MAC Ack Indicator 31 is '1', the size of the reference number 33 and 34 information added by the length field 32 is determined, and a maximum of 7 bits for processing in octets. The extra part of the part is treated as padding.

The MAC layer of the transmitting side that has received the ACK-related information in the form of FIG. 3 described above from the receiving side deletes the corresponding PDU having received the ACK information in the transmission buffer, and retransmits only the PDU having received the NAK. In addition, in the MAC layer of the present invention, when new data transmission is requested from the data link layer, which is an upper layer, whether a new data transmission layer is duplicated between the newly received higher data link layer PDU and the MAC PDU stored in the transmission buffer based on the sequence number of the data link layer. Checks and discards duplicate data link layer PDUs. If the PDUs are not duplicated, they are divided into MAC PDUs, and the information is added to the frame mapping information table between the MAC layer and the data link layer.

When receiving MAC PDU from the transmitting side through the physical layer, the receiving MAC layer is stored in the receiving buffer for order control and transferred to the higher data link layer only when it is recovered to the data link layer PDU without error. In addition, when a PDU is transmitted to the transmitting side, as shown in FIG. 3, status information on the reception up to now is added to the header of the PDU.

4 is a flowchart illustrating a data transmission processing procedure in a MAC layer according to the present invention.

First, a data PDU is received from a data link layer which is an upper layer, and sequence number information of the upper layer PDU is received in a parameter form (S401).

The sequence number of the received data link PDU is compared with the data link sequence number of the MAC PDU stored in the transmission buffer (S402) to compare and determine whether the two (the upper layer PDU number and the corresponding number of the MAC PDU) overlap each other. In operation S403, if the comparison result is duplicated, the upper layer PDU received in step S401 is discarded (S404). If not, the sequence number information of the upper layer PDU is stored in a mapping table and the upper layer PDU is stored. The partition is configured as a MAC PDU (S405).

Subsequently, it is determined whether there is a MAC PDU received through the physical layer (S406). If so, the contents of the transmission buffer are readjusted based on the ACK / NAK information (see FIG. 3) included in the received MAC PDU, The corresponding MAC PDU is planted in the transmission buffer, and the MAC PDU corresponding to the NAK is prepared to be retransmitted at the next transmission (S407).

As a result of the determination in step S406, if there is no MAC PDU to be transmitted (S408), if not, to start again from the step S401, and if it is determined whether it is necessary to report the error response confirmation information on the MAC PDU to the other party; If it is necessary to report (S409), as shown in FIG. 3, the transmission frame is configured by adding information required for reporting to the header of the MAC PDU to be transmitted in step S408 (S410). After setting the ACK Indicator information 31 to '0', this is added to the header of the MAC PDU to be transmitted in S408 to configure a transmission frame (S411), and finally, the transmission frame configured in the above step S410 or S411 is transmitted. After that, the process starts from step S401 again (S412).

As described in detail above, according to the method of processing data transmission of a MAC layer in a LAN system according to the present invention, retransmission is performed in a random error channel environment by minimizing redundant transmission data of a MAC PDU that may occur during retransmission in an existing data link layer. By reducing the amount of data, it creates the effect of improving the data transmission efficiency in a wireless LAN system.

Claims (6)

A first step of receiving a data frame and sequence number information thereof from an upper link data link layer; A second step of determining whether the sequence number of the received data frame overlaps with the corresponding number of the packet data unit (MAC PDU) of the media access control layer stored in the transmission buffer; As a result of the determination, if duplicated, the received frame is discarded, and if not overlapped, the received frame is constructed by mutually number mapping the MAC PDUs and stored in the transmission buffer, and storing the mapping information for a predetermined time. step; The contents of the transmission buffer are adjusted based on the error confirmation response information for each MAC PDU transmitted from the receiver and received through the lower physical layer, and the mapped stored sequence number, but the MAC PDU normally received is the transmission buffer. A fourth step of deleting and preparing to retransmit the received failed MAC PDU; And And a fifth step of sequentially transmitting MAC PDUs stored in the transmission buffer. The method of claim 1, The sequence number of the data frame is received in the form of a parameter, the data transmission processing method of the media access control layer in a wireless local area network system. The method of claim 1, And transmitting the error confirmation response information in addition to the header of the MAC PDU in the MAC layer of the receiving side when transmitting the data of the receiving side, in the wireless local area network system. The method of claim 3, wherein The added header is controlled to have a variable length depending on whether or not the error information acknowledgment information is included in the MAC PDU to be transmitted, the data access processing method of the media access control layer in a wireless local area network system. The method according to claim 3 or 4, The error acknowledgment information includes an indicator indicating whether the acknowledgment information is included in the transmitting MAC PDU, a length of acknowledgment information, a corresponding MAC PDU number for the acknowledgment, and information on whether the corresponding MAC PDU is in error. And a data access processing layer of a media access control layer in a wireless local area network system. The method of claim 1, In the MAC of the receiving side, MAC PDUs in which no error occurs are stored in the reception buffer, and the MAC PDUs are combined and transferred to the upper layer according to the order control in the MAC layer. How to handle data transfer in the access control layer.