KR20060003195A - Method and apparatus for transmitting data in ad hoc network - Google Patents

Abstract

The present invention relates to a data transmission method and apparatus in an ad hoc network.

In a data transmission method in an ad hoc network according to an embodiment of the present invention, the method further includes increasing a hop count value set in a received data frame by one hop, and a predetermined threshold value required to occupy a radio link according to the increased hop count value. Reconfiguring the data link, and forwarding the received data frame by occupying the wireless link according to the reset threshold.

According to the present invention, it is possible to reduce the waste of network resources consumed by the retransmission by increasing the probability of successful transmission of data frames having many hops.

Ad hoc network, RTS threshold, retry limit, backoff algorithm

Description

Method and apparatus for transmitting data in ad hoc network

1 is a view showing an ad hoc network for explaining a conventional technology.

2 is a view showing an ad hoc network for explaining the problems of the prior art.

3 is a flowchart illustrating a data packet transmission process of a source node according to an embodiment of the present invention.

4 is a flowchart illustrating a data transmission process in an ad hoc network according to an embodiment of the present invention.

5 is a flowchart illustrating a data transmission process according to another embodiment of the present invention.

6 is a flowchart illustrating a data transmission process according to another embodiment of the present invention.

7 is a block diagram illustrating a network device according to an embodiment of the present invention.

<Explanation of symbols on main parts of the drawings>

210: control unit 220: count unit

230: transceiver

The present invention relates to a data transmission method and apparatus, and more particularly, to a method and apparatus for data transmission in an ad hoc network to increase the probability of successful transmission of data frames having a large number of hops.

A mobile ad hoc network (MANET) secures communication using a wireless link without being based on an infrastructure between mobile network devices (hereinafter referred to as nodes). It is a network. Wireless networks, such as ad hoc networks, use limited network resources compared to wired networks. Therefore, as a main concern for ad hoc network communication, research is being conducted on a method for more efficiently using limited network resources.

One conventional method for efficiently using network resources in an ad hoc network is to have data packets sent from the source node transmitted to the destination node along the shortest path. This will be described with reference to FIG. 1.

1 is a diagram illustrating an ad hoc network consisting of five nodes, meaning that each node connected by an arrow is one hop away.

When node 1 intends to transmit a data packet destined for node 4, the path through which the data packet can travel is the first path 110 via node 5 and the second path 120 through node 2 and node 3. There is. As shown, the data packet transmitted through the first path 110 passes through two hops, and the data packet transmitted through the second path 120 passes through three hops.

Since a data packet consumes network resources every one hop, it is desirable to allow the data packet to be transmitted over a shorter path (less hops). Accordingly, according to the related art, the data packet transmitted from the node 1 is transmitted to the node 4 through the first path 110.

The shortest path for transmitting data packets between each node can be confirmed through a hello packet. The hello packet is a message exchanged periodically by each node in the ad hoc network to understand the state of neighbor nodes and the topology of the entire network.

Although transmitting data packets through the shortest path is effective in saving network resources, if the traffic is concentrated in the shortest path region at a specific time, the transmission efficiency of the data packet is reduced by the competition of neighboring nodes to preempt the radio link. It may fall. Therefore, in order to efficiently use the entire network, an algorithm for finding a routing path in consideration of load balance may be used.

That is, when traffic is concentrated on the shortest path, even if the transmission path of the data packet becomes long, the path remaining bandwidth is selected and the data packet is transmitted to increase the efficiency of the overall network resource usage.

As described above, the prior art focuses on finding a routing path of transmitted data packets as a method for efficient use of network resources. However, apart from finding routing paths, data packets that pass through multiple nodes (which have a high number of hops) need to be prioritized over data packets that have passed fewer hops, thus increasing transmission success.

For example, in FIG. 2, a first data packet in which node 5 is a source node and node 4 is a destination node may be transmitted to a destination in only one hop. If transmission of the first data packet fails, Node 5 only needs to occupy the radio link once more in order to retransmit it.

On the other hand, the second data packet in which node 1 is the source node and node 4 is the destination node can be transmitted to the destination only after passing three hops in total. After the second data packet is transmitted to node 3 through two hops, the second data packet is discarded at node 3 because node 3 fails to preempt the radio link or because of the network congestion several times. In this case, the second data packet should be transmitted again from node1.

In this case, nodes 1 to 3 must preempt the radio link again for the transmission of the second data packet, and additional use of more network resources is required than in the case of retransmission of the first data packet described above.

Therefore, in the transmission of data packets, a need arises to increase the success rate of the data packets having more hops.

 The purpose of the present invention is to reduce the waste of network resources due to retransmission by increasing the transmission success rate as the number of hop frames is increased.

The objects of the present invention are not limited to the above-mentioned objects, and other objects that are 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 transmission method in an ad hoc network according to an embodiment of the present invention is to increase the hop count value set in the received data frame by one hop, the wireless link according to the increased hop count value Resetting a predetermined threshold required to occupy the data, and forwarding the data frame by occupying a wireless link in accordance with the reset threshold.

Specific details of other embodiments are included in the detailed description and the drawings.

Advantages and features of the present invention and methods for achieving them will be apparent with reference to the embodiments described below in detail with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but can be implemented in various different forms, and only the embodiments make the disclosure of the present invention complete, and those of ordinary skill in the art to which the present invention belongs. It is provided to fully inform the person having the scope of the invention, which is defined only by the scope of the claims. Like reference numerals refer to like elements throughout.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

3 is a flowchart illustrating a data packet transmission process of a source node according to an embodiment of the present invention.

The first source node generates a data frame to be transmitted (S110).

The source node packetizes a data frame to be transmitted, and at this time, sets information indicating a number of hops through which each packet is forwarded (hereinafter, referred to as a hop count value) (S120). The hop count value of the data packet transmitted by the source node is set to 0. Then, each time the data packet passes through each node, the forwarding nodes increase the hop count value by one.

The hop count value may be set in a TTL field (Time to Live) in the header area of a general data packet, but the present invention is not limited thereto, and the hop count value may be set by delimiting some of the other fields constituting the data packet. Can be.

The source node having the hop count value set to 0 transmits data packets having the hop count value set (S130).

In general, when the size of a data frame is large, a node transmits and receives a data packet generated by packetizing it. However, for convenience of description, the node will be omitted as follows and each node transmits and receives a data frame.

4 is a flowchart illustrating a data transmission process according to an embodiment of the present invention.

When receiving a data frame having an initial hop count value set (S210), the node (hereinafter referred to as a receiving node) that receives the determination determines whether the received data frame should be forwarded for another node (S220). Whether to forward the data frame may be determined based on a destination address set in the received data frame. That is, when the destination address set in the received data frame is the address of another node or is set to multicast or broadcast, the receiving node forwards it. In addition, the data frame received by the receiving node may be received directly from the source node, or may be relayed by another node.

When the data frame needs to be forwarded, the receiving node increases the hop count value set in the data frame by one hop (S230).

Thereafter, according to the increased hop count value, the transmission request threshold (RTS threshold), which determines whether to apply the Request to Send / Clear to Send (RTS / CTS) procedure, is reset (S240).

In general, in an ad hoc network, a transmitting node initiates transmission of a data frame through an RTS frame. The RTS frame also serves a variety of purposes, in addition to reserving the radio link for transmission of data frames, and stopping the transmission of data frames of the nodes that have received them.

If the destination node receives the RTS frame, it responds with a CTS frame. Like the RTS frame, the CTS frame stops transmitting data frames of other nodes. Once the RTS / CTS exchange is complete, the transmitting node can safely transmit data frames without being interrupted by other nodes.

While it is advantageous to reserve the radio link using this RTS / CTS procedure for the transmission of large data frames, using the RTS / CTS procedure for the transmission of small data frames results in wastage of network resources. do. The criterion for determining whether the RTS / CTS procedure is applied is an RTS threshold value, and its size is set to 2347 bytes in the IEEE802.11 standard.

Conventionally, the RTS / CTS procedure is used to transmit a data frame having a size larger than the RTS threshold, and only a data frame is simply sent for a data frame having a size smaller than the RTS threshold.

However, data frames that have passed a large number of hops, even small data frames, may be RTS / CTS procedure to securely secure the radio link before transmission, thereby reducing the possibility that the data frame is discarded due to transmission failure.

To this end, in the step of resetting the RTS threshold (S240), the RTS threshold may be set in inverse proportion to the hop count value of the data frame to be forwarded. An example thereof is shown in Table 1.

 Table 1

Hop count value RTS threshold One 2347 2 2147 3 1947 ... ...

Resetting of the RTS threshold value according to the hop count value may be set differently according to the situation of the network.

Meanwhile, as another embodiment of the present invention, when forwarding a data frame having a hop count greater than or equal to a certain size, the RTS threshold may be set to 0 so that the transmission is always performed after the RTS / CTS procedure.

As described above, a data frame having a larger hop count value may have an RTS / CTS procedure in its transmission even though the data frame has a smaller size. The RTS / CTS procedure ensures secure transmission of data frames by reserving the use of a radio link and increases the probability of successful transmission of data frames.

When the RTS threshold is newly set, the receiving node compares the size of the received data frame with the size of the reset RTS threshold (S250).

As a result of the comparison, if the size of the data frame is greater than or equal to the RTS threshold, the radio link is preempted through the RTS / CTS procedure, and then transmission of the data frame is attempted (S260). If the size of the data frame is smaller than the RTS threshold, the RTS / CTS procedure is performed. It is possible to immediately try to transmit the data frame without going through (S270).

5 is a flowchart illustrating a data transmission process according to another embodiment of the present invention.

Steps S310 to S330 of the illustrated process may be performed in the same manner as steps S210 to S230 shown in FIG. 4.

After increasing the hop count value by one hop (S330), the receiving node according to the increased hop count value, a long retry count and a short retry count (hereinafter referred to as a retry limit value). Reset) (S340).

The retry limit value represents a limit number of times that a specific node can try to retransmit a data frame that failed to transmit. If an infinite retransmission of a specific data frame fails to be transmitted, another data frame cannot be relayed. Therefore, a node relaying the data frame attempts to retransmit up to a preset retry limit. Although the node attempts to retransmit by the retry limit, it discards the data frame that failed to transmit and prepares to transmit another data frame.

Among the retry limits, the long retry limit is applied to a data frame of a size larger than the RTS threshold, and the default value is 4 in the IEEE802.11 standard. That is, data frames requiring RTS / CTS procedures prior to transmission are retransmitted up to four times before being discarded as transmission failures. On the other hand, the short retry limit is applied to data frames smaller than the RTS threshold, and the default setting is 7 in the IEEE802.11 standard.

According to an embodiment of the present invention, the retry limit value may be set to be proportional to the hop count value, and an example thereof is shown in Table 2.

[Table 2]

Hop count value Long retry limit Short retry limit One 4 7 2 5 8 3 6 9 … … …

According to an embodiment of the present invention, when the number of hop frames passed increases the retry limit, the node relaying the data frame attempts to retransmit more data before the data frame is discarded due to a transmission failure. do. Accordingly, the possibility of successful data frame transmission at the relay node is increased, thereby reducing the waste of network resources used for retransmission from the source node because the data frames that have passed many hops are discarded at the relay node.

When the retry limit value is newly set (S340), an attempt is made to transmit the received data frame (S350).

If data frame transmission fails, the number of retries is increased once (S370). The number of retries is initially set to zero, and is incremented by one each time a retransmission of the same data frame is attempted.

If the number of retry attempts is smaller than the retry limit value set in step S340 (S380), the process subsequent to step S350 for attempting data frame transmission is repeated, otherwise the corresponding data frame is discarded (S390).

6 is a flowchart illustrating a data transmission process according to another embodiment of the present invention.

The illustrated process represents a case where a receiving node occupies a radio link through a backoff algorithm.

Steps S410 to S430 of the illustrated process may be performed in the same manner as steps S210 to S230 illustrated in FIG. 4.

After increasing the hop count value by one hop (S430), the receiving node resets the initial value of the backoff timer (competition window) for the backoff algorithm according to the increased hop count value (S440).

The backoff timer is divided into a plurality of slots and the number of slots (the size of the competitive window) is one less than the square of two (eg, 31, 63, 127, 255, etc.). The node randomly selects one of the numbers mapped to each slot and waits for its selected slot before attempting to occupy the radio link. The probability of selecting each slot is the same, and when multiple nodes attempt to transmit data frames, the node that selects the first slot (the smallest random number) will preempt the radio link.

Nodes that fail to occupy the radio link retry to transmit data frames, and each time the number of retries increases, the size of the backoff timer increases by one less than the next power of two (e.g. If the initial value is 31, the size of the backoff timer is increased to the first retry 63 and the second retry 127). The backoff timer is reset to the initial value when the data frame is successfully transmitted or when the frame is discarded because the number of retransmission attempts of the data frame reaches the retry limit.

Table 3 shows the initial value of the backoff timer according to an embodiment of the present invention.

Table 3

Hop count value Back off timer initial value 0 or 1 63 slots 2 or 3 31 slots 4 or 5 15 slots ... ...

According to an exemplary embodiment of the present invention, the data frame that has passed a large number of hops may have a smaller initial value when the backoff timer is set in the transmission. If the initial value of the backoff timer is small, the probability of selecting a slot as fast as that is high, and accordingly, a node that transmits the data frame having a large number of hops may preempt the radio link to increase the probability of success of the data frame.

According to another embodiment of the present invention, when a hop count value of a data frame to be forwarded is greater than or equal to a certain threshold, the receiving node does not increase the size of the backoff timer even if it fails to transmit the data frame and retransmits it. You can also keep the value.

The receiving node which resets the initial value of the backoff timer preempts the radio link by the backoff algorithm and transmits a data frame (S450).

The methods described with reference to FIGS. 4 to 6 may be used by combining one or more methods according to another embodiment of the present invention.

In addition, in the description of the present invention, the meaning that the various threshold values (RTS threshold value, retry limit value, initial value of backoff timer, etc.) are set to be proportional or inversely proportional to the hop count value means that the mathematically obvious proportionality or inverse proportion is meant. In other words, the larger the hop count value, the larger the threshold value is expressed as being proportional, and the larger the hop count value, the smaller the threshold value is expressed as being inversely proportional. Therefore, in the case of Table 3, it can be expressed that the threshold value is set in inverse proportion to the hop count value.

7 is a block diagram illustrating a network device according to an embodiment of the present invention.

When the illustrated network device relays the received data frame, the controller 210 controls the relaying of the data frame by resetting thresholds required to occupy the radio link according to the hop count value, and the hop count set in the received data frame. And a counting unit 220 for increasing a value and a transceiver 230 for performing wireless communication with other network devices.

The counting unit 220 determines whether the received data frame should be forwarded for another node, and if it should be forwarded, increases the hop count value set in the data frame by one hop. Whether to forward the data frame may be determined based on a destination address set in the received data frame. That is, when the destination address set in the received data frame is the address of another node or is set to multicast or broadcast, the receiving node forwards it.

When the controller 210 forwards the received data frame, the controller 210 resets the threshold values necessary to occupy the radio link according to the hop count value increased by one hop by the counter 220.

These thresholds may be the aforementioned RTS threshold, retry limit, or backoff timer initial value, and the like.

The resetting of the RTS threshold value, the retry limit value, and the backoff timer initial value according to the hop count value are as described with reference to FIGS. 4 to 6. Also, the controller 210 may reset one or more of an RTS threshold value, a retry limit value, and an initial value of the backoff timer at the same time.

The transceiver 230 transmits and receives a data frame with another node using a wireless link.

Although embodiments of the present invention have been described above with reference to the accompanying drawings, those skilled in the art to which the present invention pertains may implement the present invention in other specific forms without changing the technical spirit or essential features thereof. You will understand that. Therefore, it should be understood that the embodiments described above are exemplary in all respects and not restrictive.

According to the data transmission method and apparatus in the ad hoc network of the present invention as described above, it is possible to reduce the waste of network resources consumed in the retransmission by increasing the probability of successful transmission of data having a large number of hops.

Claims (5)

Increasing the hop count value set in the received data frame by one hop; Resetting a predetermined threshold required to occupy a radio link according to the increased hop count value; And Forwarding the received data frame by occupying a wireless link in accordance with the reset threshold. 2. The method of claim 1 wherein the threshold comprises at least one of an RTS threshold or a retry limit. 3. The method of claim 2, wherein the RTS threshold is reset in inverse proportion to the increased hop count value and the retry limit is reset to be proportional to the increased hop count value. 3. The method of claim 2, wherein the threshold further comprises an initial value of a backoff timer. 5. The method of claim 4, wherein the backoff timer initial value is reset to be inversely proportional to the increased hop count value.

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