KR20020038180A - An adaptation coding method based on channel status for wireless LAN system - Google Patents

Abstract

PURPOSE: An adaptive coding method based on a channel environment in a radio LAN(Local Area Network) system is provided, which assures a reduction of a re-transport traffic and a reliability of data transport in a radio interval. CONSTITUTION: According to a coding method of packet data for HARQ(Hybrid ARQ) while receiving/transmitting packet data by applying HARQ to a radio LAN(Local Area Network) system, a packet data unit and indicator information showing coding rate as to the packet data unit are coded and transported respectively. And a corresponding coding rate information of the above transported packet data unit is stored for a prefixed time. Then, a coding rate of a packet data unit transported next time is adjusted, on the basis of error check response information as to the transported packet data unit and the stored coding rate information.

Description

An adaptation coding method based on channel status for wireless LAN system

The present invention relates to an adaptive coding method based on a channel environment in a wireless local area network (LAN) system, and more particularly, to improve transmission efficiency in transmitting data in a wireless LAN system, hybrid ARQ (hereinafter, referred to as HARQ). In this regard, the present invention relates to a method for changing a forward error correction (FEC) coding rate in a channel coding process so as to efficiently adapt to a physical channel environment.

In general, wireless LANs use narrowband and infrared-based transmission techniques with spread spectrum in broadband.

Spread-spread and unlicensed narrowband wireless LANs use the Industrial Scientific Medical (ISM) band, while infrared LANs use the frequency band just below visible light. The ISM bands designated for industrial, scientific and medical purposes include the frequency bands 902-928 MHz, 2.4-2.4835 GHz, and 5.725-5.850 GHz. In North America, the use of the ISM band eliminates the need for approval from the FCC, so almost all products use it except Motorola's Altair Plus II. However, wireless LAN products have been implemented in a form that depends on the product to use the unlicensed band, causing problems with compatibility with other company's products.

To solve this problem, the Institute of Electrical and Electronic Engineers (IEEE) established the 802.11 committee in July 1990 and drafted a wireless LAN standard. Through this, it is possible to recognize each other through definition of frequency signal that can be used by the company, to adapt to various environments, and to standardize various services and related technologies so that equipment between different types of devices can communicate with each other. The focus is on ensuring there are no problems with performance.

At the same time, the European Telecommunications Standards Institute (ETSI) has established a High Performance Radio Local Area Network (HIPERLAN) to promote the standardization of wireless LAN equipment in Europe.

Medium access control (MAC), which is being standardized with the physical layer in wireless data communication, especially wireless LAN environments, allows multiple stations to access shared channels with maximum performance. MAC in wireless LAN is closely related to techniques in wired LAN. Commonly used approaches in wireless LAN include contention based carrier sense multiple access (CSMA) and time division multiple access (TDMA) based on time multiplexing. One scheme and a scheme using code division multiple access (CDMA) techniques are possible. The wireless LAN, which has emerged as a solution to the problems caused by the maintenance of the line and the movement of the terminal, is providing an effort to provide an improved form of technology and services based on standard methods such as IEEE 802.11 and HIPERLAN.

In the 802.11 wireless LAN protocol, the radio channel is made by the physical layer and the MAC layer. Accordingly, error detection and control is performed by the MAC layer, transmission control is controlled by CSMA / CA, and error detection is performed by CRC. In this case, the distortion of the signal due to other interference signals generated on the radio channel can only be corrected by retransmission. Therefore, for efficient transmission, it may be an alternative to use an error correction code, that is, forward error coding (FEC), as a method of adapting to an error of a physical channel. That is, a bit error rate due to signal distortion is solved through FEC coding, and a method of performing retransmission for a non-recoverable data frame is required. However, because FEC coding increases the amount of data transmitted on the radio channel, it must be able to adapt dynamically to the channel environment.

SUMMARY OF THE INVENTION The present invention has been made in view of the above technical background, and an object thereof is to implement an adaptive coding method that enables efficient data transmission by dynamically adapting to a channel environment in a wireless LAN system supporting low-speed mobility. The purpose of the present invention is to provide an adaptive coding method based on a channel environment in a LAN system to reduce retransmission traffic of a network and to ensure reliability of data transmission.

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 an IEEE 802.11 wireless LAN,

3 is a diagram illustrating a structure of a data block transmitted through a physical channel from a MAC layer according to the present invention;

4 is a state diagram for coding rate adaptation determination for a PDU of a MAC layer according to the present invention;

5 is a flowchart of an adaptive coding method based on a channel environment in a wireless local area network (LAN) system 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, an adaptive coding method based on a channel environment in a wireless local area network system according to the present invention is applied to a method of coding packet data for HARQ when transmitting and receiving packet data by applying HARQ to a wireless LAN system. A method comprising: first coding and transmitting a packet data unit and an indicator indicating a coding rate thereof; A second step of storing specified coding rate information of the transmitted packet data unit for a preset time; And a third step of adjusting a coding rate of the next packet data unit to be transmitted based on the error whether acknowledgment response information and the stored reference coding rate information for the transmitted packet data unit provided from the receiving side.

In addition, when the error checking response information indicates that there is an error in the third step, if the reference code rate is adjusted to a coding rate one step higher than the previous coding rate, and when the error checking response information indicates no error, If the coding rate is set to the corresponding coding rate of the packet data unit transmitted without the error, and error information acknowledgment information indicating that there is no error without changing the current coding rate state is continuously received up to a preset number of times, reference coding Adjust the rate to the next lower coding rate.

In addition, the preset reference coding rate information storage time is set to a time sufficient to obtain an error acknowledgment response information for any packet data unit to identify a transmission result.

In addition, the reference code rate information storage time is set to a time sufficient to identify the transmission result by acquiring error confirmation response information for any packet data unit.

In addition, the acknowledgment information is provided through a physical layer, and the coding rate is adjusted in a MAC layer, which is an upper layer of the physical layer.

Hereinafter, an adaptive coding method based on a channel environment in a wireless local area network 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.

FIG. 2 is a diagram illustrating a frame form of an IEEE 802.11 wireless LAN. As shown in the figure, basically, the frame structure of an IEEE 802.11 frame is preceded by a frame control header. 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.

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. Therefore, when using the PCF function, it is possible to differentially support time-sensitive traffic such as voice.

Together with these features, 802.11 supports reliable data transmission using the order of RTS / CTS / DATA / ACK. That is, since the node to transmit data transmits the RTS, it informs other nodes sharing the same channel to occupy the channel for the time of 'Duration ID', and the receiving node responds with the CTS. Thereafter, the node receiving the data for the time occupied by the 'duration ID' of the RTS / CTS transmits an ACK, thereby informing successful reception.

However, even if channel acquisition is achieved by such an access method, distortion of the signal due to interference or the like on the assigned channel cannot be prevented. In this case, a CRC error is detected, and the transmitting side performs retransmission by the RLC frame in the data link layer. Although the portion of adding CRC in data transmission is shown as a frame of MAC layer, it is generally handled hardware by physical layer.

The retransmission method and the FEC coding can be used to recover the bit error due to the distortion of the signal, and when the encoder capable of performing the FEC coding is added to the physical layer, the error recovery capability can be improved according to the coding rate. Coding methods mainly used in current mobile communication systems include turbo coding and convolutional coding. The application of this coded value is obtained through an acknowledgment signal reported from the receiving side. Since the wireless LAN system operates by sharing a common channel, the transmitting side and the receiving side use the same wireless channel. Therefore, the coding rate to be applied to the next transmission is determined according to the coding rate of the data received from the transmitting side and whether there is an error. This coding rate is operated based on the CRC check result in the MAC layer and the coding rate information transmitted from the physical layer. In order to notify the receiver of the coding rate in the physical layer, a process of inserting an indicator including coding rate information applied to the data of the transmitter in the first part of the data frame of the physical layer by applying the highest rate coding among the configurable coding rates need.

3 is a diagram illustrating a structure of a data block transmitted through a physical channel from a MAC layer according to the present invention. It consists of a code rate indicator part and a MAC PDU part. The MAC PDU uses the frame structure of the existing IEEE 802.11 shown in FIG. 2 without modification and separately inserts a coding rate indicator indicating the FEC coding rate used to code these MAC PDUs in the physical layer. This indicator uses the coding method and the coding rate with the strongest error rate adaptation characteristics regardless of the coding rate of the MAC PDU. Therefore, the receiving side decodes a coding rate indicator by a predetermined coding method and coding rate, and performs decoding on the MAC PDU based on this information.

4 is a state diagram for coding rate adaptation determination for a PDU of the MAC layer according to the present invention.

As shown in the figure, the MAC layer changes the coding rate according to the report of the error confirmation response information on the received frame in the physical layer. As in the case of (b), when the coding rate is increased, acknowledgment information (NAK) is reported from the physical layer indicating that an error has occurred in the received data frame, and it is determined that the channel environment is deteriorated. In the case of (a), when the data frame is decoded without error in the physical layer (when there is no CRC error), the coding rate is lowered to increase channel utilization efficiency. In this state diagram, the current coding rate, which is the basis, represents the coding rate for the actually received MAC PDU, and the state transition is performed according to the CRC check result based on the state in which the coding rate of the MAC PDU is applied. For example, assuming that the coding rate for the MAC PDU received at the current physical layer is 1/2 coding, the current state is state 1. After decoding the MAC PDU, if an error exists when CRC error checking is performed, the coding rate to be applied at the next transmission is State 0 in 1/2 coding of State 1 as in the case of (b). The coding rate shifted to 1/3 of the state is used. When the coding rate is lowered as in case of (a), in case of real-time response as in the case of (b) which raises the coding rate, a ping-pong phenomenon may occur in which the coding rate is changed at every transmission according to the channel condition. Can be. Therefore, when the coding rate is lowered, it is necessary to secure a grace time enough to judge that the channel condition is improved.

To this end, it is necessary to reduce the coding rate only when consecutively receiving n data PDUs having no reception error in the current coding rate. To this end, the coding rate information and the counter are recorded at the time of transmission, and the count is increased when a PDU of the same coding rate is received at the time of reception, and when the coding rate is changed, the coding rate information is changed and the count is initialized. . When the counter value exceeds n, the rate change is performed. This will be described in detail with reference to FIG. 5.

5 is a flowchart for determining and changing a coding rate in a MAC layer according to the present invention.

First, the transmitting side records the current coding rate and initializes the coding count (S501). The receiving side determines whether or not the MAC PDU has been received (S502), and if not, the transmitting side determines whether the MAC PDU is transmitted (S503), and when transmitting, codes the transmitting PDU at the current coding rate (S504). The coding count of step S501 is increased by one and the process is performed again from step S502 (S505).

When the MAC PUD is received in step S502, the transmitting MAC layer determines whether there is a CRC error in the received PDU based on error check response information (ACK / NAK) reported from the receiving side (S506). If it is determined that an error exists, the current coding rate recorded in the step S501 is changed based on the received coding rate, the coding count is initialized, and the process starts again from the step S502 (S507).

If it is determined in step S506 that no error exists, the reception coding rate is compared with the current coding rate (S508). If not, the current coding rate is changed to the reception coding rate and the coding count is initialized to 0. After that, the process starts again from step S501 (S509, S510).

If the reception coding rate and the current coding rate are the same as the comparison result of step S508, the coding count is increased by '1' (S511), and after determining whether the increased coding count exceeds the preset number n (S512), If it is, the current coding rate is changed to a lower coding rate of the next step, the code count is initialized, and the process starts again from the step S502 (S513).

In conclusion, the technical features of the present invention are summarized as follows.

In addition to data coded in a frame of a physical layer in a wireless LAN, a coding rate indicator indicating a coding rate applied to a MAC PDU is added to allow a receiver to apply decoding based on this information.

In addition, the coding rate used for data transmission is changed based on information on whether an error of the PDU received in the MAC layer and coding rate information.

In addition, when an error of the received MAC PDU occurs, by changing the reference coding rate to a coding rate higher than the coding rate of the error reception PDU, it is possible to immediately adapt to the channel environment during the transmission of the MAC PDU.

In addition, if the coding rate of the MAC PDU normally received without error is different from the current reference coding rate, the reference coding rate is set to the coding rate of the received MAC PDU, so that it can be applied when the MAC PDU is transmitted.

When n data frames are continuously received without a CRC error without changing the current coding rate state, the reference coding rate is changed to have a lower coding rate of the next step.

As described in detail above, an adaptive coding method based on a channel environment in a wireless local area network (LAN) system according to the present invention implements an adaptive coding method for dynamically adapting to a channel environment to enable efficient data transmission, By reducing the retransmission traffic and improving the reliability of data transmission, the wireless LAN system to which the present invention is applied can ensure better user mobility and can efficiently use radio resources.

Claims (7)

In the method of coding packet data for HARQ when transmitting and receiving packet data by applying HARQ to a wireless LAN system, A first step of coding and transmitting a packet data unit and indicator information indicating a coding rate thereof; A second step of storing corresponding coding rate information of the transmitted packet data unit for a preset time; And And a third step of adjusting a coding rate of a next packet data unit to be transmitted based on the error checking response information and the stored coding rate information for the transmitted packet data unit provided from a receiving side. Adaptive Coding Method Based on Channel Environment in Wireless Local Area Network System. The method of claim 1, In the third step, if the error confirmation response information indicates that there is an error, the coding rate is adjusted to have a higher coding rate than the previous coding rate. Adaptive Coding Method. The method of claim 1, In the third step, if the error confirmation response information indicates that there is no error, the coding rate is set to the corresponding coding rate of the packet data unit transmitted without the error. Based adaptive coding method. The method of claim 3, wherein In a wireless local area network system, if the error checking response information indicating no error is continuously reported up to a preset number of times without changing the current coding rate state, the reference coding rate is changed to the next lower coding rate. Adaptive coding method based on the channel environment of The method of claim 1, The preset coding rate information storage time is set to a time sufficient to acquire transmission error identification response information for an arbitrary packet data unit and identify a transmission result. Based adaptive coding method. The method according to any one of claims 1 to 5, The acknowledgment information is provided through a physical layer, and the coding rate is adjusted in the MAC layer, which is an upper layer of the physical layer. The method of claim 1, And the indicator information is coded by applying the highest rate coding among the configurable coding rates.