KR101779702B1 - Method for selecting relay node in wireless network, method and system for cooperative communications using that - Google Patents

Method for selecting relay node in wireless network, method and system for cooperative communications using that Download PDF

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KR101779702B1
KR101779702B1 KR1020160025856A KR20160025856A KR101779702B1 KR 101779702 B1 KR101779702 B1 KR 101779702B1 KR 1020160025856 A KR1020160025856 A KR 1020160025856A KR 20160025856 A KR20160025856 A KR 20160025856A KR 101779702 B1 KR101779702 B1 KR 101779702B1
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node
packet
relay
relay node
transmission
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KR20170103285A (en
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김선명
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금오공과대학교 산학협력단
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W40/00—Communication routing or communication path finding
    • H04W40/02—Communication route or path selection, e.g. power-based or shortest path routing
    • H04W40/12—Communication route or path selection, e.g. power-based or shortest path routing based on transmission quality or channel quality
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W40/00—Communication routing or communication path finding
    • H04W40/02—Communication route or path selection, e.g. power-based or shortest path routing
    • H04W40/22—Communication route or path selection, e.g. power-based or shortest path routing using selective relaying for reaching a BTS [Base Transceiver Station] or an access point
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W74/00—Wireless channel access
    • H04W74/08—Non-scheduled access, e.g. ALOHA
    • H04W74/0808—Non-scheduled access, e.g. ALOHA using carrier sensing, e.g. carrier sense multiple access [CSMA]
    • H04W74/0816—Non-scheduled access, e.g. ALOHA using carrier sensing, e.g. carrier sense multiple access [CSMA] with collision avoidance
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W74/00—Wireless channel access
    • H04W74/08—Non-scheduled access, e.g. ALOHA
    • H04W74/0833—Random access procedures, e.g. with 4-step access
    • H04W74/0841—Random access procedures, e.g. with 4-step access with collision treatment
    • H04W74/085—Random access procedures, e.g. with 4-step access with collision treatment collision avoidance

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  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Mobile Radio Communication Systems (AREA)

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for selecting a relay node in a wireless network and a cooperative communication method and system using the same, and more particularly, to a method and apparatus for selecting a relay node in a wireless network, Calculating a channel contention level according to the channel contention level; Calculating a transmission efficiency using the calculated packet transmission time and channel contention level, and selecting a relay node to relay data packets based on the calculated transmission efficiency; And transmitting the data packet to the destination node through the selected relay node candidate.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a method for selecting a relay node in a wireless network,

The present invention relates to a method of selecting a relay node in a wireless network and a cooperative communication method and system using the same in a wireless network. More particularly, the present invention relates to a method of selecting a relay node in a wireless network, And performs cooperation communication based on the transmission rate and the channel competition level in the wireless network through the selected relay node, so that the data transmission efficiency and delay can be improved through the relay node optimized for the multi- The present invention relates to a relay node selection method in a wireless network and a cooperative communication method and system using the same in a wireless network.

IEEE 802.11 WLANs are widely deployed because of their ease of deployment and low cost. The IEEE 802.11 standard defines a medium access control (MAC) protocol for inter-node channel sharing. A distributed coordination function (DCF) has been proposed for competition based channel competition. DCF has two kinds of data transmission methods. The transmission method of the two ends is the basic method and the RTS / CTS (request-to-send / clear-to-send) method. The basic method is a mandatory implementation and utilizes a two-way handshaking mechanism, namely data and ACK method (DATA-ACK). The RTS / CTS method uses a four-way handshaking mechanism to reserve a channel before transmitting a long data packet. Four-way handshaking uses the RTS-CTS-DATA-ACK packet. This method has been proposed to solve the hidden terminal problem.

IEEE 802.11 DCF is basically CSMA / CA (carrier sense multiple access with collision avoidance). Packet collision on the media is solved using a binary exponential backoff algorithm. A node with a data packet to transmit must ensure that the media is idle before transmission. The node arbitrarily selects a backoff counter that is less than the current contention window value and reduces the backoff counter value by 1 for each slot when the medium is idle. If the medium is Busy, it does not decrease. When the backoff counter becomes zero, the node transmits a data packet.

The most basic technique for improving the capacity of a wireless LAN is to provide a higher transmission speed in the physical layer. IEEE 802.11a / b / g has been standardized to extend the physical layer to provide higher speeds. These standards provide multiple transmission rates. The transmission rate changes dynamically depending on channel conditions. In order to use multiple speeds, a speed adjustment method in the MAC layer is required.

The use of multiple transmission rates improves the performance of the wireless LAN, but this feature causes a performance anomaly problem. In a wireless LAN using CSMA / CA, the channel access probability is the same regardless of the node's transmission rate. When a node gains access to a channel, a node with a lower rate occupies more channel time than a node with a higher rate. Therefore, the more nodes with lower speed, the lower the overall network performance. That is, in multi-rate wireless LANs, network performance is affected by low speed nodes.

Cooperative communication has been proposed to mitigate performance anomaly problems with the help of higher speed relay nodes. Cooperative communication is based on the fact that it is much faster to transmit through a relay node with a higher rate than to transmit data packets directly to a destination node with a lower transmission rate. Several MAC protocols have been proposed for using cooperative communication in WLAN.

When there is more than one relay node between the source node and the destination node, the existing MAC protocol chooses one relay node only considering the transmission speed. That is, the source node selects a relay node having the minimum packet transmission time required to transmit the packet to the destination node. The packet transmission time is calculated by the packet size and the transmission rate. However, these methods do not work well in a multi-flow environment. The nodes cooperate to deliver each other's packets over the network. With the competition of the shared channel, efficiency at one node is affected not only by the transmission rate but also by the transmission in its neighbor. Therefore, each multi-hop flow compete with other flows through the neighbor channel. That is, this channel competition means inter-flow interference. If the source node chooses a relay node only considering the transmission speed without considering the surrounding transmission, a node that may affect the transmission of another flow in the multi-flow environment may be selected. This can lead to serious collisions and congestion and can easily degrade the performance of the multi-hop network. Therefore, the source node must select the relay node considering the transmission around it.

A brief description of CoopMAC, which is one of the conventional cooperative communication MAC protocol methods, will be described. Describes the problems of the conventional cooperative communication MAC protocol for the CoopMAC protocol.

1 is an explanatory diagram of a packet exchange procedure in a conventional cooperative communication MAC protocol.

A control packet exchange in the CoopMAC protocol, which is a conventional cooperative communication MAC protocol, is shown in Fig. 1 (a). In addition, a data packet exchange in the Coop MAC protocol is shown in FIG. 1 (b).

In the CoopMAC protocol, the source node first sends a data packet to an intermediate node with a higher transmission rate and the intermediate node transmits to an access point (AP) to reduce the total transmission delay and increase the efficiency.

In the CoopMAC protocol, each node maintains and manages a CoopTable. The cooperation table includes the transmission rate between the source node and the relay node, the transmission rate between the relay node and the destination node, and the update time information of the entry. The cooperative table (CoopTable) is updated by the node listening to the other nodes' transmissions (RTS, CTS, DATA, and ACK) and measuring their transmission rate.

After eavesdropping and measuring the transmission, the node stores the relay node in the cooperative table (CoopTable) when the following condition (1) is satisfied.

Figure 112016020905692-pat00001

here,

Figure 112016020905692-pat00002
,
Figure 112016020905692-pat00003
,
Figure 112016020905692-pat00004
Refers to the transmission rate between the source node S and the destination node D, the transmission rate between the source node and the relay node H, and the transmission rate between the relay node and the destination node, respectively.

If there is more than one data to send to the queue, the source node looks up the relay node candidates in the CoopTable. If there is more than one relay node candidate, the node with the minimum transmission time is selected as the relay node. Transfer time is

Figure 112016020905692-pat00005
to be. Here, the overhead is omitted
Figure 112016020905692-pat00006
Is the size of the data packet in bits.

If the relay node is successfully found, the source node sends the CoopRTS packet to the relay node. After receiving the CoopRTS packet, the relay node checks whether the source node can perform the desired service. If so, the relay node sends a helper ready to send (HTS) packet. Finally, the destination node sends the CTS packet to the source node.

After receiving the CTS packet, the source node sends the data packet to the relay node. The relay node sends this packet back to the destination node. However, if the cooperative transmission between the source node and the destination node is not required and the relay node can not be successfully found, it operates like the existing 802.11 DCF.

A problem of the conventional cooperative communication MAC protocol will be described. Conventional cooperative MAC protocols are based on 802.11 DCF using CSMA / CA. In DCF, when data is transferred between a source node and a destination node, neighboring nodes must stop their transmission. Otherwise, it will cause collision and erroneous communication. This can be a problem if nodes outside the transmission range of the source node and the destination node want to transmit data. Another node may select a node within the transmission range of the source node and the destination node as a relay node for cooperative communication. The other node then sends the packet to the selected relay node. However, the selected relay node hears the transmission of the source node and the destination node and sets the NAV, so that it can not respond to the transmission of the other node. Therefore, the other node waits until a timeout occurs, and the time for accessing the channel becomes longer.

In addition, DCF can not consume radio resources in terms of spatial reuse. Each flow compares the other flow and the shared channel with each other in the neighborhood. DCF does not transmit simultaneously to avoid collisions and interference. If the source node does not select the appropriate relay node, radio resources are wasted and network performance is degraded.

2 is an explanatory diagram of a conventional multi-flow environment.

2, there are two source nodes S0 and S1, two destination nodes D0 and D1, and two relay nodes H0 and H1 in a multi-flow environment. The transmission speed between S0 and D0 is 1 Mbps, the transmission speed between S0 and H0 is 5.5 Mbps, the transmission speed between S0 and H1 is 5.5 Mbps, the transmission speed between H0 and D0 is 5.5 Mbps, and the transmission between H1 and D0 The speed is 11 Mbps each. S1 transfers data directly to D1 at a rate of 11 Mbps. The nodes S0, D0, H0, and H1 are within the same transmission range. The nodes S1, D1, and H1 are in the same transmission range.

3 is an explanatory diagram of a delay process of a non-responding relay node in a conventional multi-flow environment.

When a data packet is transmitted between the source node S1 and the destination node D1, the relay node H1 receives the data packet and sets its own network allocation vector (NAV). At this time, the source node S0 wants to transmit its own data packet to the destination node D0 and calculates the packet transmission time. The packet transmission time from the source node S0 to the destination node D0 (S0-> H1-> D0) via the relay node H1 and the packet transmission time from the source node S1 to the destination node D0 (S1-> H1-> D0) The packet transmission time is 363.64 ((= 1000 / 5.5 + 1000 / 5.5) and 272.73 ((= 1000 / 5.5 + 1000/11) respectively. In the calculation, the packet size is assumed to be 1000 bits. Therefore, the source node S0 selects the relay node H1 having the smallest packet transmission time as its relay node. Then, the source node S0 transmits an RTS packet to the relay node H1.

However, the relay node H1 can not respond to the RTS packet because its NAV is already set. Therefore, a timeout occurs at the source node S0 and the source node SO must directly communicate with the destination node D0 or select another relay node H0 to perform cooperative communication. As a result, the efficiency of the network decreases and the delay increases.

4 is an explanatory diagram of a process for preventing simultaneous transmission in a conventional multi-flow environment.

As shown in Fig. 4, the source node S0 and the destination node D0, and the source node S1 and the destination node D1 are in different transmission ranges. This means that data packets can be transmitted at the same time.

If the source node SO has a data packet to be transmitted to the destination node D0, the relay node H1 having the smallest packet transmission time is selected as the relay node. Then, the source node S0 transmits the RTS packet to the relay node H1, and the relay node H1 replies with the HTS packet. The HTS packet of the relay node H1 is received by the source node S1 and the destination node D1. Since the source node S1 is within the transmission range of the relay node H1, the data packet can not be transmitted to the destination node D1. That is, the transmission (S0-> H1-> D0 transmission) from the source node S0 to the destination node D0 via the relay node H1 and the transmission (S1-> D1 transmission) directly from the source node S1 to the destination node D1 can be performed simultaneously none.

Thus, if a source node selects a relay node based on the transmission rate without considering the possibility of interflow interference as described above, a node that may affect the transmission of another flow may be selected incorrectly. In this case, serious collisions or congestion may occur, and the performance of the multi-hop network may be significantly reduced.

Korean Registered Patent No. 10-1502602 (Registered on Mar. 5, 2015)

In a multi-flow environment, the source node must consider not only the transmission speed but also the transmission of the neighboring node when selecting the relay node. In this way, the source node can transmit data packets at the same time, or the relay node can immediately respond to the data packet, thereby improving performance.

To this end, the embodiments of the present invention allow a source node to select a relay node considering both a data transmission rate and a channel contention level (a data collision probability between nodes), and transmit the transmission rate and channel A method for selecting a relay node in a wireless network and capable of having superior performance in data transmission efficiency and delay through a relay node optimized for a multi-flow environment by performing cooperative communication based on a competition level, And to provide a cooperative communication method and system.

According to a first aspect of the present invention, there is provided a method for transmitting a packet, the method including: calculating a channel contention level according to a packet transmission time and a collision probability with the surrounding node using a packet received from an adjacent node; The source node calculates transmission efficiency using the calculated packet transmission time and channel contention level, and selecting a relay node to relay data packets based on the calculated transmission efficiency; And the source node transmitting the data packet to the destination node through the selected relay node candidate, may be provided.

Wherein the step of calculating the channel contention level comprises the steps of: determining an address of the source and destination nodes, a packet time received from the source node, a transmission rate between the source and destination nodes, and a channel competition level measured at the source node To calculate the packet transmission time and the channel contention level for surrounding nodes.

The step of calculating the channel contention level may calculate a first packet transmission time when the packet is relayed to the destination node via the relay node and a second packet transmission time when the packet is directly transmitted to the destination node .

The selecting of the relay node may include: determining a relay node candidate according to a preset transmission time condition; Calculating a direct-to-relay transmission time ratio of the determined relay node candidate; Calculating a transmission efficiency using the calculated direct transmission time ratio and channel competition level; And selecting an adjacent node having the highest transmission efficiency as the relay node among the relay node candidates.

The determining of the relay node candidate may determine an adjacent node as the relay node candidate in which the calculated first packet transmission time is less than the calculated second packet transmission time.

The step of calculating the direct-to-relay transmission time ratio may calculate the ratio of the calculated second packet transmission time and the calculated first packet transmission time as a direct transmission time ratio.

The method includes determining whether a transmission efficiency of the selected relay node exceeds a predetermined transmission probability value; Determining a relay node whose transmission efficiency of the selected relay node exceeds a preset transmission probability value as a final relay node; And directly communicating from the source node to the destination node if the transmission efficiency of the selected relay node is less than a preset transmission probability value.

The method comprising the steps of: using the packet received from the surrounding node to determine the address of the source and destination nodes stored in the relay table, the packet time received from the source node, the transmission rate between the source and destination nodes, And the step of calculating the transmission efficiency may calculate the transmission efficiency according to the updated relay table.

According to a second aspect of the present invention, there is provided a method for transmitting a packet, the method including: calculating a channel contention level according to a packet transmission time and a collision probability with the surrounding node using a packet received from an adjacent node; The source node calculates transmission efficiency using the calculated packet transmission time and channel contention level, and selecting a relay node to relay data packets based on the calculated transmission efficiency; The source node generates a Relay Request-To-Send (rRTS) packet including a transmission rate and a channel contention level using the selected relay node address, transmission rate, and channel contention level, Transmitting a packet to the relay node and the destination node; After the relay node receives the rRTS packet from the source node, it generates a helper-to-send (HTS) packet including a transmission rate and a channel contention level, and transmits the generated HTS packet to the source node and the destination node ; After the destination node receives the HTS packet from the relay node, it generates a relay clear-to-send (rCTS) packet including a transmission rate and a channel contention level and transmits the generated rCTS packet to the relay node and the source Transmitting to the node; And a cooperative communication method in a wireless network, wherein the source node transmits a data packet to the relay node and the relay node transmits a data packet to the destination node.

The method comprising the steps of: the destination node receiving a data packet and transmitting an acknowledgment (ACK) packet; Confirming whether transmission of the relayed data packet is successful according to the received ACK packet after the relay node relays the data packet; And when the relay node fails to relay the data packet, the relay node may retransmit the data packet to the destination node.

The method comprising the steps of: the relay node transmitting the data packet to a source node; The source node receiving a data packet from a relay node, comparing the received data packet with a data packet transmitted to the relay node, and confirming whether the data packet is successfully transmitted; And if the data packet is a transmission failure, the source node may retransmit the data packet to the relay node to request relay of the data packet again.

Wherein the step of transmitting the generated rRTS packet to the relay node and the destination node comprises the steps of: transmitting the relay node address, the data transmission rate between the source node and the destination node, the data transmission rate between the source node and the relay node, It is possible to generate the rRTS packet by inserting the channel contention level of the source node.

Wherein the step of transmitting the generated HTS packet to the source node and the destination node comprises the steps of: determining a data transmission rate between the relay node and the source node, a data transmission rate between the relay node and the destination node, Level can be inserted to generate an HTS packet.

The step of transmitting the generated rCTS packet to the relay node and the source node inserts a data transmission rate between the destination node and the source node, a data transmission rate between the destination node and the relay node, and a channel contention level of the destination node in the CTS packet lt; RTI ID = 0.0 > rCTS < / RTI >

According to a third aspect of the present invention, there is provided a method for calculating a channel contention level according to a packet transmission time and a collision probability with the surrounding node using a packet received from an adjacent node, , Selects a relay node to relay the data packet based on the calculated transmission efficiency, and transmits a relay transmission request (rRTS: Relay) to the relay node using the selected relay node address, transmission rate and channel contention level Request-To-Send) packet to the relay node and the destination node; A relay node for receiving a rRTS packet from the source node, generating a helper-to-send (HTS) packet, and transmitting the generated HTS packet to a source node and a destination node; And a destination node for generating a Relay Clear-to-Send (rCTS) packet after receiving the HTS packet from the relay node and transmitting the generated rCTS packet to the relay node and the source node, A cooperative communication system in a wireless network may be provided in which a source node transmits a data packet to a relay node and the relay node transmits the data packet to a destination node.

When the destination node receives the data packet and transmits an acknowledgment (ACK) packet, the relay node checks whether the relayed data packet is successfully transmitted according to the received ACK packet after relaying the data packet, If the relay transmission of the data packet fails, the relay node can retransmit the packet to the destination node.

The source node receives the data packet from the relay node, compares the received data packet with the data packet transmitted to the relay node to check whether or not the data packet has been successfully transmitted, and if the data packet fails transmission, The data packet may be retransmitted and the relay of the data packet may be requested again.

The source node generates an rRTS packet by inserting a relay node address, a data transmission rate between the source node and the destination node, a data transmission rate between the source node and the relay node, and a channel contention level of the source node in the predefined RTS packet can do.

The relay node may generate a HTS packet by inserting a data transmission rate between the relay node and the source node, a data transmission rate between the relay node and the destination node, and a channel contention level of the relay node into the predetermined HTS packet.

The destination node may generate a rCTS packet by inserting a data transmission rate between the destination node and the source node, a data transmission rate between the destination node and the relay node, and a channel contention level of the destination node into the predefined CTS packet.

The embodiments of the present invention are arranged such that the source node selects a relay node by taking into consideration not only the data transmission rate but also the channel contention level (the data collision probability between the nodes), and the transmission rate and the channel contention level Based communication system, it is possible to have excellent performance in data transmission efficiency and delay through a relay node optimized for a multi-flow environment.

1 is an explanatory diagram of a packet exchange procedure in a conventional cooperative communication MAC protocol.
2 is an explanatory diagram of a conventional multi-flow environment.
3 is an explanatory diagram of a delay process of a non-responding relay node in a conventional multi-flow environment.
4 is an explanatory diagram of a process for preventing simultaneous transmission in a conventional multi-flow environment.
5 is an exemplary view of a format of a relay table according to an embodiment of the present invention.
6 is a graph illustrating throughput and collision probability according to the number of nodes in a general DCF method and an RTS / CTS method.
7 is a flowchart of a method for selecting a relay node in a wireless network according to an embodiment of the present invention.
8 is a flowchart illustrating a cooperative communication method using a method of selecting a relay node in a wireless network according to an embodiment of the present invention.
9 is an exemplary diagram of a packet format of a cooperative communication method according to an embodiment of the present invention.
10 is a timing diagram for a cooperative communication method using a relay node selection method in a wireless network according to an embodiment of the present invention.
11 is a schematic diagram of a topology for simulating a cooperative communication system in a wireless network according to an embodiment of the present invention.
FIGS. 12 and 13 are results of performance according to the number of source nodes in a cooperative communication method and a conventional cooperative communication method according to an embodiment of the present invention.
FIG. 14 and FIG. 15 are the results of the performance according to the size change of the data packet in the cooperative communication method and the conventional cooperative communication method according to the embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. Will be described in detail with reference to the portions necessary for understanding the operation and operation according to the present specification. In describing the embodiments of the present invention, description of technical contents which are well known in the technical field to which the present invention belongs and which are not directly related to the present specification will be omitted. This is for the sake of clarity without omitting the unnecessary explanation and without giving the gist of the present invention.

In describing the components of the present specification, the same reference numerals may be given to components having the same name, and the same reference numerals may be given to different drawings. However, even in such a case, it does not mean that the corresponding component has different functions according to the embodiment, or does not mean that it has the same function in different embodiments, and the function of each component is different from that of the corresponding embodiment Based on the description of each component in FIG.

The method of selecting a relay node in a wireless network according to an embodiment of the present invention selects a relay node considering not only the transmission rate of a data packet but also how much transmission is performed around a relay node to be selected. The method of selecting a relay node in a wireless network according to an exemplary embodiment of the present invention may be referred to as a transmission rate and channel contention level (TRCCL) protocol. A cooperative communication method and system and a simulation result in a wireless network using a relay node selection method in a wireless network will be described.

In a multi-flow environment, network performance degrades due to interference of flows due to shared channel competition. Therefore, the conventional cooperative MAC protocol is not suitable in a multi-flow environment. Therefore, the source node must select the relay node considering the transmission speed as well as the transmission of the neighbor node.

5 is an exemplary view of a format of a relay table according to an embodiment of the present invention.

Each node maintains and manages a relay table (RelayTable) shown in FIG. Each node tries to update the relay table when other nodes transmit packets such as RTS (request to send), CTS (clear to send), DATA, and ACK.

There are five field information in the relay table. The first two field information is the MAC address of the source and destination nodes contained in the packet being transmitted. The Time field records the time of the last packet received from the source node. In the transmission rate field, the transmission rate between the source node S and the destination node D

Figure 112016020905692-pat00007
) Is stored. In the last field, the channel competition level measured at the source node (
Figure 112016020905692-pat00008
) Is stored.

Herein, in the embodiment of the present invention, the collision probability is used as a criterion indicating the channel competition level. Each node records the collision probability. And transmits the packet to the surrounding node including the collision probability. As the number of neighboring nodes competing for a channel to transmit data increases, the probability of collision increases. A high probability of collision means that there are many nodes around and that they are competing for channels to transmit data. Therefore, if a node with a high probability of collision is selected as a relay node, there is a high possibility of inter-flow interference problem. In addition, it is likely that NAV is being set because of the transmission of another node. Therefore, you should avoid choosing these nodes as relay nodes.

6 is a graph illustrating throughput and collision probability according to the number of nodes in a general DCF method and an RTS / CTS method.

The result of simulation in an IEEE 802.11a network with a data packet transmission rate of 11 Mbps and a control packet transmission rate of 1 Mbps is shown in FIG. Here, it is assumed that all the nodes are within the transmission range and the data packet size is 1000 bytes. The basic method of DCF and the RTS / CTS method have almost the same collision probability.

As shown in FIG. 6, the best system efficiency is shown at a collision probability of about 0.18. As the probability of collision increases, the efficiency decreases. In addition, the efficiency is lowered even if it is lower than 0.18. The reason for having the best efficiency at the collision probability near 0.18 is that there are a proper number of nodes and they can reduce the number of slots wasted by back-off in order to transmit data. If the number of nodes is too small, channel waste due to backoff occurs. Figure 6 is a system-wide outcome, and will yield the best performance when no collision occurs at each node. Also, as the probability of collision increases, the efficiency will decrease. Therefore, it is preferable that the collision probability is low.

The relay node selection method according to an embodiment of the present invention selects an optimal relay node considering both the packet transmission time and the channel contention time. These two values can be easily calculated using the information in the relay table. The packet transmission time is the transmission time between the source node and the destination node and includes all the relay time consumed in the intermediate nodes.

7 is a flowchart of a method for selecting a relay node in a wireless network according to an embodiment of the present invention.

As shown in FIG. 7, the source node calculates the packet transmission time for neighboring nodes using the relay table (S702). Here, the source node can calculate the channel contention level according to the packet transmission time and the collision probability with the surrounding node using the packet received from the surrounding node. Specifically, the source node uses the relay table storing the addresses of the source and destination nodes, the packet time received from the source node, the transmission rate between the source and destination nodes, and the channel competition level measured at the source node, The packet transmission time and the channel competition level can be calculated.

When there is data to be transmitted by the source node, the source node uses the information contained in the relay table to determine the packet transmission time

Figure 112016020905692-pat00009
) Is calculated as shown in the following equation (2).

Figure 112016020905692-pat00010

here,

Figure 112016020905692-pat00011
S denotes a source node ID, D denotes a destination node ID, and i denotes an ID of a node around the source node. Also, L is the packet size in bits
Figure 112016020905692-pat00012
Is the overhead of the relayed data packet.
Figure 112016020905692-pat00013
Means that the source node S sends the packet to the relay node i and the relay node i again sends this packet to the destination node D. [

If the packet is directly transmitted from the source node S to the destination node D without passing through the relay node i, the packet transmission time is calculated as follows.

Figure 112016020905692-pat00014

here,

Figure 112016020905692-pat00015
The packet transmission time,
Figure 112016020905692-pat00016
Denotes the transmission rate between the source node S and the destination node D. [

Thereafter, the source node determines a relay node candidate according to a preset transmission time condition (S704). After calculating the packet transmission time in step S702, the source node determines a node satisfying the following equation (4) as a relay node candidate.

Figure 112016020905692-pat00017

here,

Figure 112016020905692-pat00018
Is the first packet transmission time when the source node S transmits the packet to the relay node i and the relay node i again transmits this packet to the destination node D,
Figure 112016020905692-pat00019
Represents the second packet transmission time when the source node S transmits the packet to the destination node D. The source node can calculate the first packet transmission time when the packet is relayed to the destination node D via the relay node i and the second packet transmission time when the packet is directly transmitted to the destination node D. [ And the source node can determine the neighboring node having the calculated first packet transmission time less than the second packet transmission time as the relay node candidate.

The source node calculates the direct-to-relay transmission time ratio of the relay node candidate (S706). The source node can calculate the ratio of the calculated second packet transmission time and the calculated first packet transmission time as a direct transmission time ratio. Here, the direct-to-relay transmission time ratio is referred to as a direct-to-relay transmission time ratio (DRT). DRT is the ratio of the second packet transmission time when the source node directly communicates with the destination node and the first packet transmission time through the relay node. For relay node candidate i

Figure 112016020905692-pat00020
Is calculated as shown in the following equation (5).

Figure 112016020905692-pat00021

here,

Figure 112016020905692-pat00022
(DRT) for the relay node i.

Then, the source node calculates the transmission efficiency using the direct transmission time ratio (S708). Here, the source node can calculate the transmission efficiency using the calculated first and second packet transmission times and the channel contention level. The higher the DRT value of the relay node or the lower the channel competition level, the better the performance of the system. The transmission efficiency when the source node transmits the packet to the destination node through the relay node candidate i

Figure 112016020905692-pat00023
) Is calculated according to the following equation (6).

Figure 112016020905692-pat00024

here,

Figure 112016020905692-pat00025
The transmission efficiency,
Figure 112016020905692-pat00026
(DRT) for the relay node i,
Figure 112016020905692-pat00027
Represents the channel competition level (i.e., collision probability) of the relay node candidate i.

The source node selects a neighboring node having the highest transmission efficiency among the relaying node candidates as a relaying node (S710). If an optimal relay node is selected, the system performance can be improved. To this end, the source node selects the largest transmission efficiency among the relay node candidates (

Figure 112016020905692-pat00028
) Can be selected as the following formula (7). &Quot; (7) " That is, the source node can select the relay node to relay the data packet based on the calculated transmission efficiency.

Figure 112016020905692-pat00029

here,

Figure 112016020905692-pat00030
Represents a relay node candidate set.

Then, the source node checks whether the transmission efficiency of the relay node exceeds 1 (S712). That is, the source node calculates the transmission efficiency of the selected relay node i (

Figure 112016020905692-pat00031
Is satisfied with the condition of the following formula (8).

Figure 112016020905692-pat00032

Here, the transmission efficiency (Ef) value is 1 when direct communication is performed without passing through the relay node.

If the transmission efficiency of the relay node exceeds 1 (S712), the source node transmits a data packet through the selected relay node (S714). Therefore, the transmission efficiency of the selected relay node (

Figure 112016020905692-pat00033
) Value is greater than 1, it means that relay communication is efficient, and thus relay communication is performed.

On the other hand, if the transmission efficiency of the relay node is less than 1 (S712), the source node directly transmits the data packet (S716). Here, the transmission efficiency (

Figure 112016020905692-pat00034
) Value is less than 1, relay communication is inefficient and direct communication is performed.

As described above, after the step of selecting the surrounding node as the relay node, the source node determines whether or not the transmission efficiency of the selected relay node exceeds a predetermined transmission probability value (e.g., 1). When the transmission efficiency of the selected relay node is less than a preset transmission probability value, the source node determines whether the destination node is the destination node And can communicate directly with the node.

The source node may select an adjacent node that exceeds the predetermined transmission probability value as a relay node and communicate directly from the source node to the destination node if the transmission probability value is less than a preset transmission probability value.

7, the source node uses the packet received from the surrounding node to calculate the address of the source and destination nodes stored in the relay table, the packet time received from the source node, the transmission rate between the source and destination nodes, And updating at least one of the channel contention levels measured at the source node.

After the updating process, the source node can calculate the transmission efficiency according to the updated relay table.

8 is a flowchart illustrating a cooperative communication method using a method of selecting a relay node in a wireless network according to an embodiment of the present invention.

8, in the collaborative communication method according to the embodiment of the present invention, the source node S0, the relay node H0, and the destination node D0 respectively transmit Relay Request-To-Send (rRTS) (RRTS-HTS-rCTS-RTS-RTS-RTS-RTS) sequentially transmitting a helper-to-send (HTS) packet, a relay clear-to-send (rCTS) packet, a DATA packet and an acknowledgment DATA-ACK) to the destination node.

Hereinafter, a specific operation of each step of the cooperative communication method according to the embodiment of the present invention shown in FIG. 8 will be described.

First, the source node calculates the channel contention level according to the packet transmission time and the collision probability with the surrounding node using the packet received from the surrounding node.

The source node calculates the transmission efficiency using the calculated packet transmission time and channel contention level, and selects a relay node to relay the data packet based on the calculated transmission efficiency (S802).

Then, the source node inserts a relay node address, a transmission rate, and a channel contention level to generate an rRTS packet including a transmission rate and a channel contention level of the source node (S804).

The source node transmits the rRTS packet to the relay node (S806). In addition, the source node transmits the rRTS packet to the destination node (S808).

After selecting the relay node, the source node inserts the relay node address, transmission rate, and channel contention level information into the rRTS packet, and then transmits the rRTS packet to the relay node and the destination node.

Then, the relay node generates an HTS packet including the transmission rate and the channel contention level of the relay node (S810).

The relay node transmits the generated HTS packet to the source node and the destination node (S812). That is, after receiving the rRTS packet, the relay node transmits the HTS packet to the source node and the destination node.

Then, the destination node generates an rCTS packet including the transmission rate of the destination node and the channel contention level (S814).

Then, the destination node transmits the generated rCTS packet to the relay node (S816). In addition, the destination node transmits the generated rCTS packet to the source node (S818).

Thus, the destination node receives the HTS packet and transmits the rCTS packet to the relay node and the source node.

Thereafter, the source node transmits the data packet to the relay node (S820).

Then, in order to relay the data packet, the relay node transmits the data packet to the destination node (S822). Further, the relay node transmits the data packet to the source node in the transmission response to the source node (S824).

As such, the source node sends the data packet to the relay node and the relay node sends the packet back to the destination node.

Thereafter, the source node confirms whether the received data packet and the transmitted data packet are identical (S826).

If the received data packet and the transmitted data packet are not identical to each other (S826), the source node repeats the procedure of transmitting the data packet from step S820. On the other hand, if the received data packet and the transmitted data packet are the same (S826), the source node can confirm that the data packet transmission is completed to the relay node. That is, the source node receives the data packet transmitted by the relay node, and confirms that the data packet transmitted by the source node is transmitted to the relay node.

Meanwhile, the destination node receives the data packet and transmits the ACK packet to the relay node (S828).

The relay node receives the ACK packet from the destination node (S830). Here, after relaying the data packet from the source node to the destination node, the relay node receives the ACK packet to confirm that the relayed data packet has been successfully transmitted.

The relay node checks whether the transmission of the relayed data packet is successful according to the received ACK packet (S832).

If the transmission of the relayed data packet is not successful (S832), the relay node retransmits the data packet to the destination node (S834). That is, if the relay of the data packet fails, the retransmission of the packet is performed by the relay node, not the source node.

On the other hand, if the relayed data packet is successfully transmitted (S832), the cooperative communication method can repeatedly perform the process of transmitting the next data packet until the last data packet is transmitted.

9 is an exemplary diagram of a packet format of a cooperative communication method according to an embodiment of the present invention.

The cooperative communication method according to the embodiment of the present invention uses three new control packets in addition to the control packets such as the RTS packet, the CTS packet, and the ACK packet used in the IEEE 802.11 MAC. A cooperative communication method according to an embodiment of the present invention includes a new control packet including a relay request-to-send (rRTS) packet, a relay clear-to-send (rCTS) packet, and a helper-to-send To perform cooperative communication.

9 (a), the cooperative communication method according to the embodiment of the present invention includes a relay node address (6 bytes), a source node (S) and a destination node (6 bytes) in a predetermined general RTS packet D, a data transmission rate between the source node S and the relay node H, and channel contention level information of the source node to generate an rRTS packet. A total of 9 bytes corresponding to this additional information is added to a general RTS packet so that an rRTS packet can be generated.

As shown in FIG. 9 (b), the cooperative communication method according to the embodiment of the present disclosure includes a data transmission rate between a destination node D and a source node S in a predetermined general CTS packet, a destination node D and a relay node H A helper node, and a channel contention level information of a destination node to generate an rCTS packet. A total of 3 bytes corresponding to this additional information is added to a general CTS packet so that an rCTS packet can be generated.

As shown in FIG. 9 (c), the cooperative communication method according to the embodiment of the present disclosure includes a data transmission rate between a relay node H and a source node S in a predetermined general HTS packet, a relay node H and a destination node D And the channel contention level information of the relay node to generate a new HTS packet. A total of 3 bytes corresponding to this additional information is added to a general HTS packet so that a new HTS packet can be generated.

Meanwhile, in the cooperative communication method according to the embodiment of the present invention, the collision probability is used to indicate the channel competition level. The range of collision probability values is 0 to 1. The range of numbers that can be expressed using 1 byte is 0 to 255. Therefore, the cooperative communication method converts the collision probability value as shown in Equation (9) before transmitting the rRTS packet, the rCTS packet, and the HTS packet.

Figure 112016020905692-pat00035

here,

Figure 112016020905692-pat00036
Is the collision probability
Figure 112016020905692-pat00037
Is a value that is converted from 0 to 255. And
Figure 112016020905692-pat00038
Rounds the value of x. The node that received the rRTS packet, the rCTS packet, and the HTS packet sends its own relay table (RelayTable)
Figure 112016020905692-pat00039
Divide the value by 255
Figure 112016020905692-pat00040
And stores it.

Thereafter, if there is data to be transmitted to the destination node D by the source node S, the relay node candidate is searched for using the relay table to satisfy the above formula (4).

If there is no node satisfying the above Equation (4), the source node directly transmits the data packet to the destination node according to the rRTS-HTS-rCTS-DATA-ACK procedure shown in FIG.

On the other hand, if there is more than one relay node candidate, the source node selects the node having the highest transmission efficiency (Ef) among these relay node candidates as the relay node. Then, the source node confirms whether the transmission efficiency (Ef) value of the selected relay node candidate satisfies the above formula (8).

If the condition of Equation (8) is not satisfied, the source node directly transmits the data to the destination node. On the other hand, if the condition of Equation (8) is satisfied, the source node transmits the data packet to the destination node via the selected relay node as shown in FIG.

10 is a timing diagram for a cooperative communication method using a relay node selection method in a wireless network according to an embodiment of the present invention.

As shown in Fig. 10, the relay node H1 is within the transmission range of the source node S0 and the destination node D0, and the source node S1 and the destination node D1. However, the relay node H0 is only within the transmission range of the source node SO and the destination node D0. Therefore, the collision probability of the relay node H1 is higher than that of the relay node H0.

Here, there is an ongoing packet transmission between the source node S1 and the destination node D1. The relay node H1 receives the packet from the source node S1 and the destination node D1 and sets its NAV.

At this time, the source node S0 tries to transmit the data packet and selects the relay node H0 having the highest transmission efficiency (Ef) as the relay node. The source node S0 transmits the rRTS packet to the relay node H0 and the destination node D. [ The relay node H0 replies the HTS packet to the source node SO and the destination node D0.

The destination node D0 transmits the rCTS packet to the source node SO and the relay node HO. Then, the source node S0 transmits the data packet to the relay node H0, and the relay node H0 delivers the data packet to the destination node D0. The destination node D0 transmits an ACK packet to the relay node H0.

11 is a schematic diagram of a topology for simulating a cooperative communication system in a wireless network according to an embodiment of the present invention.

The cooperative communication system in the wireless network according to the embodiment of the present invention will explain simulation results based on the topology structure shown in FIG. In order to verify the simulation results according to the embodiment of the present invention, the results of the conventional CoopMAC protocol are compared and analyzed.

The wireless network has a transmission rate (e.g., 1, 2, 5.5 and 11 Mbps) determined by the distance between the source node and the destination node. The control packet is transmitted at 1 Mbps. In the simulation process, it is largely divided into two transmission groups (for example, upper and lower). Here, the transmission group is classified into a transmission range. There are one source node S0, one destination node D0, and two relay nodes H0 and H1 in the lower group. In the upper group, there is one destination node D1 and one relay node H1. The number of source nodes is variable from 0 to 20. The source nodes are located next to each other. It is assumed that no error occurs in the channel.

The main performance factors in cooperative communication systems in wireless networks are efficiency and delay. The delay is the time taken from when the packet arrives at the MAC layer queue to when it is successfully transmitted to the destination node.

FIGS. 12 and 13 are results of performance according to the number of source nodes in a cooperative communication method and a conventional cooperative communication method according to an embodiment of the present invention.

The collaborative communication method according to the embodiment of the present invention is shown in FIGS. 12 to 15 in the TRCCL protocol, and the conventional cooperative communication method is indicated by the CoopMAC protocol.

That is, the performance (e.g., throughput and delay) according to the change in the number of source nodes in the upper transmission group in the TRCCL protocol and the CoopMAC protocol is shown in FIGS. 12 and 13. FIG. Here, the packet size is 1500 bytes. Each source node generates a data packet of 2 Mbps. The Throughput and Delay of D0 and D1 shown in FIGS. 12 and 13 are the results measured at the destination nodes D0 and D1.

12 shows the throughput, that is, the efficiency result. If there is no source node in the upper group, there is no difference in performance between the conventional CoopMAC and the TRCCL protocol according to the present specification.

As the number of source nodes increases, the TRCCL protocol according to the present invention has better performance than the conventional CoopMAC protocol. In the conventional CoopMAC protocol, only the packet transmission time is considered when the source node S0 selects the relay node. For this reason, the conventional CoopMAC protocol always determines the relay node H1 having the fast transmission rate as the relay node regardless of the number of the source nodes in the upper group. Therefore, as the number of source nodes in the upper transmission range group increases, the efficiency at D0 sharply decreases. In addition, the performance at the destination node D1 also decreases due to the influence of the relay node H1.

However, in the TRCCL protocol according to the present specification, the source node SO considers the packet transmission time and the channel contention level together when selecting the relay node. Therefore, the TRCCL protocol according to the present invention can select a different relay node according to the number of source nodes in the upper transmission range group. That is, when the number of source nodes is small in the simulation topology shown in FIG. 11, the source node S0 selects the relay node H1, and when it is larger, the relay node H0 is selected and communicated. As the number of source nodes in the upper transmission range group increases, the efficiency at the destination node D0 decreases very slowly. Also, the performance at the destination node D1 is superior to that of CoopMAC because there is no influence of the relay node H1.

The delay performance results are shown in Fig.

Regardless of the number of source nodes in the parent group, the TRCCL protocol according to the present disclosure has better performance than the CoopMAC protocol. From the results at the destination node D1, both the TRCCL protocol and the CoopMAC protocol according to the present invention increase in delay as the number of source nodes increases. However, the delay of the TRCCL protocol according to the present invention is always lower than that of the CoopMAC protocol. This is because the probability of collision increases when the number of source nodes increases.

In the TRCCL protocol according to the present specification, the relay node H0 can be selected as the relay node by considering the collision probability when the source node SO selects the relay node. Therefore, the delay is kept low because the transmission in the upper group and the transmission in the lower group can be performed simultaneously without affecting each other. The delay result of the destination node D0 of the TRCCL protocol according to the present invention increases slowly as the number of source nodes increases.

However, it can be seen that the result of D0 of the conventional CoopMAC protocol increases sharply. Even the result at the destination node D0 of the conventional CoopMAC protocol is worse than the result at the destination node D1. This is because the conventional CoopMAC protocol considers only the packet transmission time without considering the collision probability when selecting the relay node. Therefore, in the conventional CoopMAC protocol, a relay node H1 having a short value is selected as a relay node and data transmission is attempted. Then, problems related to the above-mentioned conventional CoopMAC protocol occur and performance is degraded.

FIG. 14 and FIG. 15 are the results of the performance according to the size change of the data packet in the cooperative communication method and the conventional cooperative communication method according to the embodiment of the present invention.

The number of source nodes in the upper group is fixed to 10 in the simulation according to the size conversion of the data packet. The data packet size is variable from 200 bytes to 2000 bytes. Thus, the source node generates data packets between 0.267 Mbps and 2.67 Mbps.

14, the TRCCL protocol according to the present invention always performs better than the conventional CoopMAC. Here, performance is increased as the packet size increases because the simulations are carried out while changing the other conditions to the same and varying only the packet size. The TRCCL protocol according to the present invention improves the efficiency relatively quickly. However, it can be seen that the conventional CoopMAC protocol slowly increases the efficiency.

Referring to the delay result according to the size change of the data packet shown in FIG. 15, when the packet size increases, the packet transmission time also increases. The overall delay also increases. It can be seen that the TRCCL protocol according to the present invention increases more slowly than the conventional CoopMAC.

Thus, in the conventional MAC protocol for cooperative communication, the source node selects the relay node based on the transmission rate. These methods are not suitable for multi-flow environments because they do not consider the influence of other flows. The non-responding relay node may cause radio resources to be wasted in the transmission process. Also, performance is degraded due to multi-flow interference sharing the channel. In order to solve this problem, a method of selecting a relay node in a wireless network according to an embodiment of the present invention, a cooperative communication method and system using the method, a relay node is selected according to a transmission rate and a channel competition level, And performs cooperative communication based on the transmission rate and the channel competition level in the wireless network.

12 to 15, it can be seen that the cooperative communication method according to the embodiment of the present invention has better performance in efficiency and delay than the conventional cooperative communication method.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or essential characteristics thereof. Therefore, the embodiments disclosed in the present invention are intended to illustrate rather than limit the scope of the present invention, and the scope of the technical idea of the present invention is not limited by these embodiments. The scope of protection of the present invention should be construed according to the following claims, and all technical ideas within the scope of equivalents should be construed as falling within the scope of the present invention.

S0, S1: source node
H0, H1: relay node
D0, D1: Destination node

Claims (20)

Calculating a channel contention level according to a packet transmission time and a collision probability with the surrounding node using a packet received from the surrounding node;
The source node calculates transmission efficiency using the calculated packet transmission time and channel contention level, and selecting a relay node to relay data packets based on the calculated transmission efficiency; And
The source node sending a data packet to the destination node via the selected relay node,
The selecting of the relay node may include: determining a relay node candidate according to a preset transmission time condition; Calculating a direct-to-relay transmission time ratio of the determined relay node candidate; Calculating a transmission efficiency using the calculated direct transmission time ratio and channel competition level; And selecting an adjacent node having the highest transmission efficiency among the relay node candidates as a relay node. The method according to claim 1,
The step of calculating the channel contention level
A packet is transmitted to neighboring nodes using a relay table in which addresses of the source and destination nodes, packet time received from the source node, transmission speed between the source and destination nodes, and channel competition level measured at the source node are stored A method for selecting a relay node in a wireless network that calculates time and channel contention levels. The method according to claim 1,
The step of calculating the channel contention level
And calculating a first packet transmission time when the packet is relayed to the destination node via the relay node and a second packet transmission time when the packet is directly transmitted to the destination node. delete The method of claim 3,
The step of determining the relay node candidate
And determining the neighboring node whose calculated first packet transmission time is less than the calculated second packet transmission time as the relay node candidate. The method of claim 3,
The step of calculating the direct to transit transmission time ratio
And calculating a ratio of the calculated second packet transmission time and the calculated first packet transmission time as a direct transmission time ratio. The method according to claim 1,
Determining whether a transmission efficiency of the selected relay node exceeds a predetermined transmission probability value;
Determining a relay node whose transmission efficiency of the selected relay node exceeds a preset transmission probability value as a final relay node; And
If the transmission efficiency of the selected relay node is less than a preset transmission probability value, directly communicating from the source node to the destination node
Further comprising the steps of: The method according to claim 1,
Using at least one of the address of the source and destination nodes stored in the relay table, the packet time received from the source node, the transmission rate between the source and destination nodes, and the channel contention level measured at the source node using the packet received from the surrounding node Further comprising:
Wherein the step of calculating the transmission efficiency calculates a transmission efficiency according to the updated relay table. Calculating a channel contention level according to a packet transmission time and a collision probability with the surrounding node using a packet received from the surrounding node;
The source node calculates transmission efficiency using the calculated packet transmission time and channel contention level, and selecting a relay node to relay data packets based on the calculated transmission efficiency;
The source node generates a Relay Request-To-Send (rRTS) packet including a transmission rate and a channel contention level using the selected relay node address, transmission rate, and channel contention level, Transmitting a packet to the relay node and the destination node;
After the relay node receives the rRTS packet from the source node, it generates a helper-to-send (HTS) packet including a transmission rate and a channel contention level, and transmits the generated HTS packet to the source node and the destination node ;
After the destination node receives the HTS packet from the relay node, it generates a relay clear-to-send (rCTS) packet including a transmission rate and a channel contention level and transmits the generated rCTS packet to the relay node and the source Transmitting to the node; And
Wherein the source node transmits a data packet to the relay node and the relay node transmits a data packet to the destination node
Wherein the cooperative communication method comprises: 10. The method of claim 9,
Receiving a data packet from the destination node and transmitting an acknowledgment (ACK) packet;
Confirming whether transmission of the relayed data packet is successful according to the received ACK packet after the relay node relays the data packet; And
When the relay node fails to relay the data packet, the relay node retransmits the data packet to the destination node
Further comprising the steps of: 10. The method of claim 9,
The relay node transmitting the data packet to a source node;
The source node receiving a data packet from a relay node, comparing the received data packet with a data packet transmitted to the relay node, and confirming whether the data packet is successfully transmitted; And
If the data packet is a transmission failure, the source node retransmits the data packet to the relay node and requests relay of the data packet again
Further comprising the steps of: 10. The method of claim 9,
The step of transmitting the generated rRTS packet to the relay node and the destination node
In a wireless network generating an rRTS packet by inserting a relay node address, a data transmission rate between a source node and a destination node, a data transmission rate between a source node and a relay node, and a channel contention level of a source node in the predefined RTS packet Cooperative communication method. 10. The method of claim 9,
The step of transmitting the generated HTS packet to the source node and the destination node
A cooperative communication method in a wireless network for generating HTS packets by inserting a data transmission rate between a relay node and a source node, a data transmission rate between a relay node and a destination node, and a channel contention level of a relay node into a predetermined CTS packet . 10. The method of claim 9,
The step of transmitting the generated rCTS packet to the relay node and the source node
A cooperative communication method in a wireless network that generates an rCTS packet by inserting a data transmission rate between a destination node and a source node, a data transmission rate between a destination node and a relay node, and a channel contention level of a destination node in a CTS packet. Calculating a channel contention level according to a packet transmission time and a collision probability with the surrounding node using a packet received from an adjacent node, calculating transmission efficiency using the calculated packet transmission time and channel contention level, Selects a relay node to relay the data packet based on the transmission efficiency, generates a Relay Request-To-Send (rRTS) packet using the selected relay node address, transmission rate, and channel contention level, A source node transmitting to a node and a destination node;
A relay node for receiving a rRTS packet from the source node, generating a helper-to-send (HTS) packet, and transmitting the generated HTS packet to a source node and a destination node; And
And a destination node for generating a Relay Clear-to-Send (rCTS) packet after receiving the HTS packet from the relay node and transmitting the generated rCTS packet to the relay node and the source node,
Wherein the source node sends a data packet to a relay node and the relay node sends the data packet to a destination node. 16. The method of claim 15,
The relay node
When the destination node receives the data packet and transmits an acknowledgment (ACK) packet, it checks whether the relayed data packet is successfully transmitted according to the received ACK packet after relaying the data packet, And if the transmission fails, the relay node retransmits the packet to the destination node. 16. The method of claim 15,
The source node
And a control unit for receiving a data packet from the relay node, comparing the received data packet with a data packet transmitted to the relay node to check whether or not the data packet is successfully transmitted, And re-requests the relay of the data packet. 16. The method of claim 15,
The source node
In a wireless network generating an rRTS packet by inserting a relay node address, a data transmission rate between a source node and a destination node, a data transmission rate between a source node and a relay node, and a channel contention level of a source node in the predefined RTS packet Cooperative communication system. 16. The method of claim 15,
The relay node
A cooperative communication system in a wireless network that generates HTS packets by inserting data transmission speeds between relay nodes and source nodes, data transmission speeds between relay nodes and destination nodes, and channel contention levels of relay nodes into a predetermined HTS packet . 16. The method of claim 15,
The destination node
A cooperative communication system in a wireless network that generates an rCTS packet by inserting a data transmission rate between a destination node and a source node, a data transmission rate between a destination node and a relay node, and a channel contention level of a destination node in a predetermined CTS packet.
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