KR20050098372A - Method and apparatus for improving the efficiency of wireless channel - Google Patents

Abstract

The present invention relates to a method and apparatus for transmitting a data frame, and more particularly, when a data frame is retransmitted through a transmitting node in a wireless network environment, using a data frame response signal generated at a receiving side, a cause of data frame retransmission. The present invention relates to a data frame transmission method for improving the utilization rate of an 802.11 based wireless channel by retransmitting a data frame.

Description

Method and apparatus for transmitting data frame for improving utilization of wireless channel

The present invention relates to the transmission of data frames, and more particularly, to a method and an apparatus for improving the utilization rate of a wireless channel when retransmitting the data frame by distinguishing a cause of data frame transmission failure in data frame transmission.

In general, when transmitting and receiving data through a wired or wireless network, in order to use the functions of the network efficiently, it is made according to a standardized communication protocol of what, how, and when to communicate between entities that want to communicate. It's called a protocol.

This communication protocol is based on the OSI 7 layer (Open Systems Interconnection 7-layer) as a basic structure, and is appropriately configured according to each network characteristic such as whether it is a wired or wireless network or what medium is used to transmit data. .

The data link layer is the second layer among the seven tradeoffs of Open System Interconnection (OSI). The data link layer is a layer that controls the movement of data so that data can enter and exit through physical links in the network. The data is cut into frames and delivered to the physical layer, the error is recovered by exchanging acknowledgments (ACKs) between the sender and the receiver, and the control bits within the frame are verified to verify that the data in the frame is correct.

On the other hand, when several components of the IEEE 802 series are associated with the OSI model, the data link layer is composed of an LLC layer (Logical Link Control) and a MAC (Media Access Control) layer, with 802.2 being a common link layer. If you are defining an LLC, 802.11 is an additional feature defined in the MAC to support mobile network access.

The MAC is a set of rules that determine how to access the medium and transmit data, and provides the operation of the core frame to allow the user to control the transmission of data to the air. Provide interaction.

In particular, in wired and wireless networks, carrier sensing is used to control access to the transmission medium in order to check whether a transmitting node can use a receiving node, and collision detection (CSMA / CD in wired Ethernet) is controlled. In the 802.11-based wireless network, collision avoidance (CSMA / CA, Carrier Sense Multiple Access / Collision Avoidance) method is used to control access to the transmission medium using Carrier Sense Multiple Access / Collision Ditection. By controlling access to the system, the transmission capacity is not wasted due to data frame collisions.

In particular, in a wireless network environment, when a data frame transmitted from the transmitting node 10 reaches the receiving node 20 in connection with transmitting and receiving data frames, the receiving node 20 acknowledges that the data frame has been normally received. An acknowledgment (ACK) is transmitted to the transmitting node 10, and the above acknowledgment acknowledgment is generally referred to as ACK (abbreviation of Acknowledgment), and this method transmits data through unreliable medium such as WLAN. In case of transmission, the method is used in 802.11 to provide reliability for data reception.

 In the existing wireless network environment, a data frame transmission process may be largely comprised of a data frame transmission process performed by the transmitting node 10 and a data frame receiving and processing process performed by the receiving node 20.

First, a process occurring in the transmitting node 10 during the data frame transmission process will be described with reference to FIG. 2. After the transmitting node 10 transmits the data frame to the receiving node 20, when the transmitting node 10 receives an acknowledgment (ACK) from the receiving node 20, the transmitting node 10 receives the data frame. The transmission is determined to be successful and the transmission is completed.

Meanwhile, referring to FIG. 3, after the transmitting node 10 transmits the data frame, the data node receiving and processing process is performed in the receiving node 20. When the transmitting node 10 transmits the data frame, the data frame is first received at the physical layer of the receiving node 20 (S21), and the received signal strength indicator (Received Signal Strength Indication) of the received data frame is large. It means that the better signal, the RSSI is measured (S22), and then the data frame is transmitted to the MAC layer of the receiving node (20) (S23). Then, the MAC layer of the receiving node 20 checks whether an error exists in the data frame received through a cyclic redundancy check (CRC) (S24), and if there is no error, from the transmitting node 10 It is determined that the reception of the data frame is successfully performed, and after generating a positive acknowledgment for the received data frame (S25), the frame response signal is transmitted to the transmitting node (S26).

If an error is found, it is determined that the frame reception has failed and discards the frame (S27), and waits for the data frame to be retransmitted from the transmitting node 10.

When the data frame is discarded at the receiving node 20 as described above, or when the receiving node 20 transmits a positive acknowledgment to the transmitting node 10 but the transmitting node 10 does not receive this positive acknowledgment (shown in FIG. Or a data frame transmitted by the transmitting node 10 is collided with a data frame of the neighboring node 30 that was being transmitted at the same time, and thus the data node is lost during the transmission of the data frame. In the case of not receiving a positive acknowledgment (ACK) from the node 20, the transmitting node 10 determines that a data frame transmission has failed because a collision with neighboring nodes 30 occurs during data frame transmission. As shown in Fig. 4, when a random point of time is selected within the size of the contention window, a time delay from the beginning of the size of the contention window to a randomly selected time point is delayed. Then (d1), and retransmits the first data frame.

On the other hand, as shown in FIG. 5, when the transmitting node 10 retransmits the data frame firstly, and a collision a2 occurs with the neighboring node again, and the retransmission of the primary data frame fails, the secondary retransmission is necessary. Each time the data frame is retransmitted, the size of the contention window used in the random backoff d2 is larger than the contention window size used in the previous random backoff d1, and then random backoff is performed (d2). FIG. 5 shows that the size of the contention window 2W to be used in the second random backoff d2 is twice as large as the contention window size W used in the first random backoff d1. Whenever the transmitting node 10 does not receive an acknowledgment frame from the receiving node 20, it is determined that a collision error with the neighboring node 30 has occurred, the size of the contention window is increased, and the data frame is retransmitted. When more than one neighbor node selects the same view and transmits the data frame, it is possible to prevent the data frame from being lost by reducing the probability of collision again.

However, in the existing wireless network environment, data frames are retransmitted depending on only an acknowledgment (ACK) transmitted from the receiving node 20, which considers only collision errors with neighboring nodes as a cause of data frame retransmission. This means that if the receiving node needs to receive the distorted data frame and retransmit the data frame due to errors in the transmitting node channel itself or other physical phenomena such as fading, Whenever the transmitting node 10 retransmits the data frame to the receiving node 20, random backoff is performed by increasing the size of the contention window, which results in a waste of radio channels.

For example, in FIG. 5, after performing the first random backoff d1 to retransmit the data frame first, the channel node of the transmitting node 10 during the first retransmission is distorted to the receiving node 20. Even when data is received and secondary retransmission is possible without having to execute a random backoff, the size of the contention window (2W) for executing the second random backoff (d2) as in the case of collision with the neighbor node is determined. If the data frame is second retransmitted after doubling the contention window size (W) used at the first random backoff (d1), the second random backoff (d2) becomes unnecessary and is allocated to the wireless channel. Delaying too much time compared to the existing time decreases the utilization of the wireless channel.

Therefore, not only when a data frame needs to be retransmitted due to a collision with a neighbor node 30, but also when a data frame needs to be retransmitted due to an error occurring in the wireless channel itself, the channel error is coped with when the cause of the transmission failure is a channel error. If a proper retransmission scheme is used, and if the cause of the transmission failure is a collision with neighboring nodes, an appropriate retransmission scheme that avoids the collision may use the radio channel more efficiently.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a data frame transmission method and apparatus for adaptively changing a data frame transmission method according to a cause of a data frame transmission error.

However, the objects of the present invention are not limited to the above-mentioned objects, and other objects not mentioned will be clearly understood by those skilled in the art from the following description.

In order to achieve the above object, a data frame transmission apparatus according to an embodiment of the present invention comprises a transmitting node 100 and a receiving node 200 existing in a wireless network environment, and the transmitting node 100 includes a frame transmitting and receiving unit 110. And a frame transmission method selector 120, wherein the receiving node 200 includes a frame transceiver 210, a frame error checker 220, a frame RSSI checker 230, and a frame response generator 240. It includes.

In a wireless network environment, a data frame transmission method according to an embodiment of the present invention includes the steps of a transmitting node 100 transmitting a data frame to a receiving node 200, and a receiving node 200 with respect to the received data frame. Checking whether there is an error, checking error of the data frame, checking the RSSI of the frame to classify the cause of transmission failure according to the size of the RSSI, and forming an appropriate frame response according to the result of the error checking and the RSSI size comparison. Transmitting to the transmitting node 100, determining a retransmission method of the data frame in the transmitting node 100 according to the frame response received from the receiving node 200, and data frame according to the data transmission method determined according to the frame response Retransmitting the.

Hereinafter, a data retransmission method and an apparatus using the method will be described in detail with reference to the accompanying drawings.

In general, when data frame transmission is performed between a transmitting node and a receiving node in a wireless network environment, when the wireless channel becomes unstable due to a fading phenomenon or the like, the receiving power drops and RSSI falls. If the RSSI value falls, the signal to noise ratio (SNR) becomes small and thus frame transmission fails.

On the other hand, if a collision occurs with a data frame of a neighbor node during data frame transmission, a strong strength signal due to signals generated by neighboring nodes is detected in a frequency band that can be received by a receiving node, thereby increasing RSSI. do. However, signals other than the signals generated by the transmitting node among the received signals become noises and have a small SNR value, thereby failing to transmit the frame.

Therefore, if the RSSI value measured when the frame is normally received as the threshold value is used, and the result of comparing the RSSI value measured at the physical layer of the receiving node 200 with the threshold value of the RSSI is used, the cause of the data frame transmission failure may be caused. Whether it is due to a channel error of the transmitting node 100 or a collision error with a neighboring node can be distinguished. If the RSSI value of the received frame is larger than the RSSI threshold, the data frame transmission has failed due to a collision error with neighboring nodes, and conversely, if the RSSI value of the received frame is smaller than the RSSI threshold, the transmitting node It may be determined that data frame transmission has failed due to a channel error of.

First, the improved frame receiving and processing performed in the receiving node 200 according to the embodiment of the present invention will be described with reference to FIG. 6.

When the transmitting node transmits the data frame, the receiving node receives the data frame through the physical layer (S211), measures the RSSI of the received frame (S212), and then transfers the data frame to the MAC layer (S220). Thereafter, the MAC layer checks whether there is an error in the data frame received through a cyclic redundancy check (CRC) (S221). If no error is found, the data frame is successfully received from the transmitting node. A positive acknowledgment is generated (S242), and this frame response signal is transmitted to the transmitting node (S213). If an error is found, the RSSI value of the received frame is set to the threshold of the RSSI because the receiving of the data frame has failed. Compared to the value (S230), the cause of the transmission failure is classified according to the result of comparing the RSSI value.

If the RSSI value of the received data frame is larger than the threshold value of the RSSI, it is determined that the cause of the data frame error is due to a collision error with a neighbor node and discards the frame (not shown). If the RSSI value of the received data frame is smaller than the threshold value of the RSSI, it is determined that the cause of the data frame error is due to a channel error of the transmitting node, and transmits a data frame transmission failure due to the channel error of the transmitting node 100. A negative acknowledgment (NACK) is generated to inform the node 100 (S241), and the negative acknowledgment (NACK) is transmitted to the transmitting node 100 (S213). 7 is a flowchart illustrating a data frame retransmission process performed by the transmitting node 100 according to a preferred embodiment of the present invention, and shows a process of determining and retransmitting a data frame transmission method according to a frame response received from the receiving node 200. Giving.

First, after the transmitting node 100 transmits a data frame to the receiving node 200 (S100), it is determined whether the receiving node 200 receives an affirmative acknowledgment (ACK) from the receiving node 200 (S110). If the acknowledgment (ACK) is received, the data frame transmission is successful, and thus the data frame transmission is completed.

If the positive acknowledgment (ACK) is not received, it is determined whether a negative acknowledgment (NACK) is received from the receiving node 200 (S120).

If the transmitting node 100 receives a negative acknowledgment (NACK), an error occurs in the channel of the transmitting node 100 during data frame transmission, and if the transmitting node 100 does not receive a negative acknowledgment (NACK), the transmitting node 100 ) Corresponds to a case in which no frame response is received within a predetermined time, and thus a collision error occurs with neighboring nodes when transmitting a data frame.

When the transmitting node 100 receives a negative acknowledgment (NACK), it is determined whether the data frame is retransmitted primary (S122). If the data frame is retransmitted primary, random backoff is not performed. If the data frame is not retransmitted and the data frame is not retransmitted first, without increasing the size of the contention window (S132), random backoff is performed using the contention window size used during the previous data frame retransmission. After the implementation (S140), the data frame is retransmitted to the receiving node 200 (S150).

If the transmitting node does not receive a negative acknowledgment (NACK) due to a collision error with the neighbor node, it is determined whether the data frame is retransmitted primary (S121), and if the data frame is retransmitted primary, After performing random backoff using the value of the contention window that is already set (S132) (S140), the data frame is retransmitted to the receiving node (S150), and if the data frame is not the first retransmission, random The size of the contention window to be used for the backoff is increased to the size of the contention window previously used (S131), random backoff is performed (S140), and the data frame is retransmitted to the receiving node (S150).

At this time, the size of the contention window can be increased in various ways. For example, you can increase the size of the competing window by an exponential function of 2, such as 2, 4, or 8 times the initial competing window size, or 3, like 3, 6, or 9 times the initial competing window size. It can be increased by exponential function of.

After determining the data transmission method according to the above-described procedure, after the transmitting node 100 retransmits the data frame toward the receiving node 200, it is confirmed whether an acknowledgment (ACK) has been received from the receiving node 200. (S160). At this time, when the transmitting node 100 receives an acknowledgment (ACK) from the receiving node 200, the data frame transmission or data frame retransmission procedure is completed because data transmission or data frame retransmission is successful. do. If the acknowledgment (ACK) is not received, it is determined whether a negative acknowledgment (NACK) is received again (S110), and the data frame is transmitted according to the data frame transmission method obtained by repeating the data frame transmission method determination procedure. Resend.

8 illustrates a method of transmitting a data frame in the transmitting node 100 according to a preferred embodiment of the present invention. In the data frame transmission, the transmitting node 100 receives a receiving node due to a channel error of the transmitting node 100. In case of sending a wrong data frame, the first retransmission process of the data frame is shown. When the transmitting node 100 transmits a data frame, the receiving node 200 performs an error check on the received data frame, and if there is an error in the received data frame, sends a negative acknowledgment (NACK) to the transmitting node 100. To send). The negative acknowledgment (NACK) at this time means that data is retransmitted because an error has occurred in the channel of the transmitting node 100, not because of a collision with neighboring nodes, so that the transmitting node 100 receives a negative acknowledgment ( If the data frame is to be first retransmitted after receiving the NACK, the transmitting node 100 first retransmits the data frame without performing a random backoff.

FIG. 9 illustrates another data frame retransmission method according to an exemplary embodiment of the present invention, in which the transmitting node 100 transmits the primary data frame from the receiving node 200 within a predetermined time due to a collision with a neighboring node. The third retransmission process is performed when no frame response is received (B), the second retransmission is performed, and a negative acknowledgment (NACK) is received from the receiving node 200. As shown in FIG. 8, after the transmitting node 100 retransmits the primary data frame due to a radio channel error, the transmitting node 100 does not receive an acknowledgment (ACK) from the receiving node 200 and thus the secondary data frame is secondary. If retransmission is required, random backoff is performed using the contention window of size W for the first time (D1), and then second retransmission of the data frame. If the negative acknowledgment (NACK) is received even after the second retransmission, the random backoff is again performed without changing the size (W) of the contention window used in the previous random backoff (D1) (D2). Retransmit the data frame three times.

However, when the data frame transmission fails due to the channel error as described above, the data frame retransmission method for responding to the channel error is not limited to maintaining the size of the contention window using the negative acknowledgment signal.

For example, when the transmitting node 100 receives a negative acknowledgment (NACK) from the receiving node 200 due to a channel error, it informs the physical layer of the transmitting node 100 that the channel situation is poor, and thus the poor channel. It may be possible to perform a modulation method that overcomes the situation. For example, if a channel error occurs in 802.11b that supports two modes of transmission, such as 11 Mbps and 5.5 Mbps, the transmission rate is reduced from the MAC of the transmitting node 100 to the physical layer. It may be able to adapt to channel errors by requesting transmission.

10 schematically illustrates a configuration of a data frame retransmission system according to a preferred embodiment of the present invention, and is composed of a transmitting node 100 and a receiving node 200.

The receiving node 200 is associated with the transmission and reception of the data frame, the frame transceiver 210 for measuring the RSSI value of the received data frame, and the frame error check unit 220 for checking whether there is an error in the received data frame ), A frame RSSI check unit 230 which distinguishes a cause of a data frame transmission failure by comparing the RSSI value and the RSSI threshold of the received data frame, an acknowledgment acknowledgment (ACK) according to the error check result and the RSSI value comparison result; The frame response generator 240 generates a negative acknowledgment (NACK). The data frame response generated by the frame response generator 230 is transmitted to the transmitting node 100 through the frame transceiver 210.

The transmitting node 100 is composed of a frame transmission and reception unit 110 and a frame retransmission method selection unit 120. The frame retransmission method selection unit 120 determines whether the frame response received through the frame transmission / reception unit 110 is a positive acknowledgment (ACK) or a negative acknowledgment (NACK), and then the data frame is 1 for each case. The method determines whether to retransmit the data frame and then retransmits the data frame to the receiving node 200 or reduces the transmission rate according to the selected data retransmission method, and then retransmits the data frame.

The present invention described above is capable of various substitutions, modifications, and changes without departing from the spirit of the present invention for those skilled in the art to which the present invention pertains. It is not limited to drawing.

According to the practice of the present invention, the following effects are obtained.

First, it is possible to adaptively respond to the occurrence of a transmission error in data frame transmission.

Secondly, since the random backoff is selectively modified according to the cause of transmission error during data frame transmission, the utilization rate of the radio channel is improved.

1 is an exemplary diagram illustrating a transmitting node 10, a receiving node 20, and a neighboring node 30 in a wireless network.

2 illustrates a transmitting node 10 and a receiving node 20 in a conventional wireless communication environment. When the data frame transmission from the transmitting node 10 to the receiving node 20 succeeds, the receiving node 20 Exemplary diagram showing an acknowledgment (ACK) for the successful transmission of the frame to the transmitting node (10).

3 is a flowchart illustrating a process of receiving and processing data frames in a receiving node 20 in a conventional wireless communication environment.

4 illustrates a case in which a collision error a1 occurs for the first time during data transmission and thus does not receive an acknowledgment (ACK) from the receiving node 20 in a conventional wireless communication environment. After a delay of any time (d1) in (10) is an exemplary diagram showing that the data is retransmitted.

FIG. 5 illustrates a data retransmission process performed when a data collision occurs continuously during data transmission (a2) in a conventional wireless communication environment.

6 is a flowchart illustrating a process of receiving and processing data frames in a receiving node 200 according to an embodiment of the present invention.

7 is a flowchart illustrating a data frame transmission process performed by the transmitting node 100 according to an embodiment of the present invention.

8 illustrates an embodiment according to the present invention and illustrates an example of a data frame retransmission process performed when a transmitting node 100 receives a negative acknowledgment (NACK) for the first time due to an error in a wireless channel.

FIG. 9 illustrates another embodiment according to the present invention, in which a data frame retransmission process is performed when a transmitting node 100 receives a negative acknowledgment due to an error in a wireless channel after retransmitting a data frame primarily. It is an exemplary view shown.

10 is a block diagram schematically illustrating an apparatus for transmitting a data frame according to an embodiment of the present invention.

<Description of the symbols for the main parts of the drawings>

100: transmitting node 110: frame transceiver

120: frame transmission method selection unit 200: receiving node

210: frame transceiver 220: frame error check unit

230: frame RSSI check unit 240: frame response generation unit

Claims (6)

In a wireless network environment, Transmitting a data frame; Error checking on the transmitted data frame; Comparing RSSI values of the transmitted data frames; Generating a response to the transmitted data frame according to a RSSI value comparison result; Determining a retransmission scheme for the data frame according to the response to the transmitted data frame; And And retransmitting the data frame according to the determined retransmission scheme. The method of claim 1, wherein if the RSSI value of the transmitted data frame is smaller than the threshold value of the RSSI, it is determined as a channel error, and if the RSSI value of the transmitted data frame is larger than the threshold value of the RSSI, the collision error is determined. Data frame transmission method. The method of claim 1, And the response is a negative acknowledgment or timeout event. The method of claim 2, The retransmission method is at least one of a method for retransmission immediately and a method for retransmission after a delay. The method of claim 3, wherein If the response is a timeout event and the retransmission is a primary retransmission, the size of the contention window in the retransmission is equal to the size of the contention window in the transmission. A frame transceiver for transmitting a data frame; And And a frame transmission method selection unit configured to determine a retransmission method for the data frame according to the response to the transmitted data frame and to retransmit the data frame according to the determined retransmission method.