CN101494879B - Medium Control Method Supporting Cooperative Communication in Wireless Local Area Network - Google Patents

Abstract

The invention relates to a medium control method for supporting cooperative communication in a wireless local area network in the technical field of wireless local area network transmission. The present invention determines whether the relay node is available through the triangle interaction of the control frame, if available, and adopts the triangle data transmission mode according to the previous estimation of the packet error rate. The present invention retains the advantages of the traditional MAC protocol, and when the packet error rate is high, the saturated throughput of the entire network is improved by cooperative support for cooperative communication, the average delay time is reduced, and the packet loss rate is reduced. The present invention retains the backoff process of IEEE 802.11b, so the fair performance of nodes is the same as that of IEEE 802.11b. The invention is used in the wireless local area network and has the characteristics of less protocol modification and excellent performance improvement. When the channel fading is relatively obvious, the present invention can effectively improve the performance of the wireless network. When the packet error rate is relatively large, the throughput can be increased by about 17%, and the packet loss rate is less than 1/10 of the original.

Description

Medium Control Method Supporting Cooperative Communication in Wireless Local Area Network

technical field

The invention relates to a method in the technical field of wireless local area network (WLAN) transmission, in particular to a medium control method for supporting cooperative communication in the wireless local area network.

Background technique:

For the application of cooperative communication in wireless networks, predecessors have done a lot of work. Part of the research work is the theoretical analysis of the physical layer, and gives the performance comparison of different cooperative communication protocols and coding methods in the fading channel; another part of the work is based on the traditional wireless LAN MAC layer protocol (IEEE802.11b). The concept of communication is introduced into the MAC layer protocol design to improve the performance of the wireless LAN.

After searching the literature of the prior art, it was found that Pei Liu et al. published "CoopMAC: A Cooperative MAC For Wireless LANs" (CoopMAC: a cooperative MAC protocol applied to wireless LANs), this paper designs a MAC protocol that different nodes in wireless LANs can cooperate with each other. The specific way of mutual cooperation between nodes is as follows: each node saves a table CoopTable, which saves the information of possible relay nodes for each pair of links from this node to other nodes. Now suppose there is a node A that wants to send a data packet to B. Before A starts to transmit, it first searches CoopTable to see if there is an available relay node. If not, the IEEE 802.11b protocol is used. If there is a relay node C in the table, it is determined whether C is available through a triangular control frame exchange. If C is unavailable, A enters the backoff process. If C is available, A sends the data packet to C first, and then C delays the SIFS time to send the data packet to B. Through theoretical analysis and simulation, this document proves that CoopMAC can improve the performance of the entire network if there are a few nodes with relatively slow rates in the wireless local area network. Its disadvantage is that the cooperation mode of CoopMAC is only limited to the MAC layer, and cannot support the cooperation mode of the physical layer.

Contents of the invention

Aiming at the deficiencies of the prior art, the present invention provides a medium control method that supports cooperative communication in a wireless local area network, called C-MAC, so that by modifying the transmission mode of data packets, when the packet error rate of the direct link is compared with When it is high, the throughput of the entire network is improved and the average delay is reduced.

The present invention is realized through the following technical solutions, the transmission of the control frame of the present invention uses the mode of triangular exchange, what the source sends is the CoopRTS frame, what the relay node sends is the RTR frame, what the destination node sends is the CTS frame, if the source node can After receiving the RTR frame of the relay node and the CTS frame of the destination node, the relay node is available; at the same time, the packet error rate is calculated based on the statistical value of the previously sent data packet and the received ACK frame, according to the packet error rate and the threshold relationship, which determines whether the relay node participates in data transmission, where:

The transmission of the control frame uses a triangular exchange method. During the interaction process, the CTS is the CTS of IEEE802.11, and the frame format of the RTR is basically the same as that of the CTS. The only difference is that the subtype in the frame control is marked as RTR. CoopRTS is modified on the basis of IEEE 802.11 RTS frame format. The RTS frame includes five parts: frame control, duration, destination address, source address and checksum. CoopRTS adds two parts after the source address part of the RTS: the address of the relay node and the rate from the relay node to the destination node. In this way, CoopRTS contains part of the information of the third node.

The manner of the triangular interaction of the frame is as follows: Assume that there are three nodes, a source node S, a destination node D and a potential relay node R. First, the source node S sends the control frame CoopRTS to the destination node D. The frame format of CoopRTS contains the address of the relay node that can participate in the transmission, assuming that this node is R. All nodes within the transmission range of node S can listen to this CoopRTS frame, but only the relay node R can accept the frame CoopRTS, and then send a frame RTR to the source node S, indicating that R meets the rate requirements in the CoopRTS frame format and can participate in data For transmission, when sending RTR, R needs to start the sending timer and wait for the arrival of a CTS in the network. When the destination node D monitors the RTR packet sent by the relay node R, the destination node D can determine that the relay node R can participate in data transmission, and then the destination node D sends a frame CTS to the source node S. CTS can be received by every node in the network. When the relay node R receives the CTS, it stops sending the timer and prepares to participate in data transmission. If no CTS is received, R waits for the timer to expire and enters the backoff process. When the source node S receives the CTS, the source node S can start the data transmission process.

The data transmission mode of the triangle is the cooperative communication mode of the physical layer. Data transmission is divided into two time slots: in the first time slot, the source node S sends a data packet to the destination node D, and R listens to and saves the packet at the same time, and the destination node D continues to wait for the data packet from the relay node R after receiving the packet. The same packet came. In the second time slot, R sends the packet saved in the first time slot to the destination node D, so that the destination node D receives two copies of the same data packet from different channels.

Compared with the prior art, the present invention has the following advantages: firstly, the present invention is based on IEEE 802.11bMAC, and only modifies the control frame exchange mode and data transmission mode, so the modification range of the protocol is not large. Secondly, by modifying the data transmission mode, the MAC layer can support the cooperative communication mode of the physical layer, and then cooperate with the joint decoding of the physical layer. When the packet error rate of the fading channel is slightly large, the C-MAC of the present invention can reduce the packet error rate. , to increase the throughput of the entire network.

The IEEE 802.11b is used when the packet error rate is relatively low, and the present invention is used to reduce the total packet error rate when the packet error rate is high. The present invention retains the advantages of the traditional MAC protocol, and when the packet error rate is high, the saturated throughput of the entire network is improved by cooperative support for cooperative communication, the average delay time is reduced, and the packet loss rate is reduced. The present invention is based on the IEEE 802.11b protocol and retains the IEEE 802.11b backoff process, so the fair performance of the nodes is the same as that of the IEEE 802.11b. The invention is applied to the wireless local area network and has the characteristics of less protocol modification and excellent performance improvement. When the channel fading is obvious, the invention can effectively improve the performance of the wireless network. Compared with the traditional MAC protocol, when the packet error rate is relatively large, the throughput can be increased by about 17%, and the packet loss rate is less than 1/10 of the original.

Description of drawings

Fig. 1 is a working diagram of the present invention without a relay node.

Fig. 2 is a diagram of the working mode of the present invention in the case of a relay node.

FIG. 3 is a structural diagram of a table used by each node to store relay node information in the present invention.

Fig. 4 is a comparative schematic diagram of saturation throughput of the present invention and 802.11b under different packet error rates;

In the figure: In the case of data packet length L=1024 bytes, number of data streams 10, relay node rate 11Mbps, and 802.11b saturation throughput under different packet error rates, including comparison of theoretical results and simulation results.

Fig. 5 is a schematic diagram of the comparison between the saturation throughput of the present invention and 802.11b under different packet error rates;

Figure: In the case of data packet length L = 1024 bytes, number of data streams 10, relay node rates are 11Mbps and 5.5Mbps respectively, and 802.11b saturate throughput under different packet error rates including theoretical results and simulations Comparison of results.

Fig. 6 is a comparative schematic diagram of saturation throughput of the present invention and 802.11b under different packet lengths;

In the figure: when the number of data streams is 10, the rate of the relay node is 11Mbps.

Fig. 7 is a schematic diagram of the cumulative distribution function of the MAC layer service time of the present invention and 802.11b;

In the figure: when the length of the data packet is L=1024 bytes, the number of data streams is 10, the rate of the relay node is 11 Mbps, and the packet error rate of the direct link is 0.3.

Fig. 8 is a schematic diagram of the packet loss rate of the present invention and 802.11b under different packet error rates;

In the figure: the data packet length L=1024 bytes, the number of data streams is 10, and the relay node rate is 11 Mbps.

Fig. 9 is a schematic diagram of comparison of packet loss rates between C-MAC and IEEE 802.11b in the present invention under different packet error rates.

Detailed ways

The embodiments of the present invention are described in detail below in conjunction with the accompanying drawings: this embodiment is implemented on the premise of the technical solution of the present invention, and detailed implementation methods and specific operating procedures are provided, but the protection scope of the present invention is not limited to the following the described embodiment.

The overall working process of this embodiment is shown in Figures 1 and 2. The technical terms (IEEE 802.11 standard) have the following meanings:

NAV (Network Allocation Vector): Network Allocation Vector

SIFS (Short InterFrame Space): short interframe space

DIFS (DCF InterFrame Space): DCF (distribution coordination function) interframe space

Backoff: Backoff process

ACK: IEEE 802.11MAC layer confirmation frame

1) Figure 1 is how CMAC works when there is no relay node. Specifically, after the source node sends CoopRTS and there is no response from the relay node, the destination node will reply with a CTS frame after waiting for two SIFS times, and then start the 802.11 data transmission mode. It can be seen from Fig. 1 that the relay node Sr did not reply the frame RTR, so the destination node Sd replied CTS after waiting for two SIFS. In this way, the source node Ss sends data packets in the data transmission mode of IEEE802.11b. During the entire process, the channel is occupied by the transmission of Ss and Sd, and other nodes (STA1 and STA2) are in a waiting state, and allocate vectors to the new network according to the monitored control frames (such as CoopRTS, CTS).

2) Figure 2 is the working mode of CMAC when there are relay nodes. Relay node Sr replies frame RTR after receiving CoopRTS, and then destination node sends CTS to source node Ss. Both the source node Ss and the relay node Sr participate in the subsequent data transmission process. Ss sends it once first, and then Sr sends it again, so that Sd receives two copies of a data packet. During this entire process, the channel is occupied by the transmission of Ss, Sr and Sd, and other nodes (STA1 and STA2) are in a waiting state, and allocate vectors to the new network according to the monitored control frames (such as CoopRTS, CTS).

The specific implementation of this embodiment includes two parts: the exchange of control frames and the transmission of data packets:

1. The interaction process of the control frame

There are three frames participating in the triangular exchange of control information in this embodiment: CoopRTS, RTR, and CTS. Please refer to the frame format above. CTS is the CTS frame used in IEEE 802.11. The frame format of RTR is basically the same as CTS, only one bit indicating the frame type is different.

The following is the frame format of RTS in the IEEE 802.11 standard. Bytes:

2 2 6 6 4

frame control duration Destination address source address checksum

The details of frame control are as follows:

Number of bits:

2 2 4 1 1 1 1 1 1 1 1 1 1

protocol type Subtype TODS FromDS More Frag Retry PwrMgmt MoreData ProtectedFrame order

Protocol: protocol version

Type: frame type (control frame is Control, data frame is Data)

Subtype: The subtype of the frame (RTS, CTS, RTR, ACK, etc.)

To DS: (whether) send to the distributed system

From DS: (whether) from a distributed system

More Frag: The upper layer data (whether) is divided into fragments

Retry: (whether) to retry

Pwr Mgmt: (whether) enable power management

More Data: When the power saving mode is enabled, this bit indicates (whether) more data is sent to the destination node

Protected Frame: Set to 1 if this frame is protected by a link layer security protocol

Order: This bit is set to 1 when the frame or the data fragments of the upper layer are transmitted in order

The frame format of IEEE 802.11 CTS is as follows:

frame control duration source address checksum

CoopRTS is modified based on the IEEE 802.11b RTS frame, and the frame format is shown in Figure 3. Compared with the RTS in IEEE 802.11b, the CoopRTS frame has two more RRA (the MAC address of the relay node) and Rrd (the rate from the relay node to the destination node). At the same time, each node needs to maintain a table RelayTable. The format is shown in Figure 3. There are 6 areas in total, which are: (1) RE: whether to enable relay; (2) IR: whether this node is a relay node; ( 3) RA: the destination node of this transmission; (4) TA: the source node of this transmission; (5) RRA: the MAC address of the relay node; (6) Rrd: the rate from the relay node to the destination node. This table needs to be updated in real time during the interaction process of the control frame, and the information of this table will be used during the data transmission process.

First explain the meaning of the parameters that appear below. Let the sending time of all frames be in the form of Tx (taking CoopRTS as an example, the transmission time of CoopRTS frame in the network is T _CoopRTS ), SIFS and DIFS are frame interval time (IEEE 802.11 standard). CTStimout indicates the timing time for the timer to wait for the frame CTS, and if it exceeds CTStimout, it means timeout. Then the interaction process of the control frame is as follows:

source node S

1) When the source node S has a data packet to send, S first searches whether there is a potential relay node (how to search is not within the scope of the description of this embodiment, but locally saves a list of potential relay nodes), if not, Then use the IEEE 802.11b protocol; if there is a potential relay node, S sends a CoopRTS frame to D, and sets the sending timer. The time is:

CTS _timeout ＝2T _SIFS +2T _CTS +T _CoopRTS

Then set the RelayTable, the first value of the RelayTable is temporarily not set, and the next five values can be set, and the last two values are found according to the previous search process.

2) If the source node S does not receive the RTR frame from the relay node after T _SIFS + T _CTS time, but receives the CTS frame from the destination node after 2T _SIFS + 2T _CTS time from the start of sending, it means that the relay node is unavailable , so the source node S uses the IEEE 802.11b method for sending data packets.

3) If S does not receive the CTS frame from D, it may be that a frame collision has occurred, and S enters the backoff process and waits for the next sending opportunity.

4) If S receives R's RTR frame and D's CTS frame, it means that the relay node is available and the channel is also available, S sets the first value of RelayTable, and then starts sending data packets to D.

中继节点R

Relay node R

1) Because all nodes in the same hop can monitor the CoopRTS packet sent by S, each node compares the RRA of the CoopRTS frame with its own MAC address, and if they are different, discard the CoopRTS packet and set the NAV (Network Allocation Vector) . If it is the same, check whether it can support the rate indicated by Rrd. If yes, this node is the relay node R for this data transmission. R sets the last four values of RelayTable according to the content of CoopRTS, and the first two values are RE and IR. Both are set to true. Then R sends an RTR frame to S after a delay of SIFS. Because R needs to listen to a CTS frame sent by D to determine the smooth progress of this data transmission, so R sets the sending timer when sending RTR, and the time is:

CTS _timeout = T _SIFS + T _CTS

2) If R does not receive the CTS, R considers that the transmission is terminated. So R clears the RelayTable, and then enters the backoff process. Otherwise, R enters the waiting process and monitors the data packets sent from S.

目的节点D

Destination node D

1) If D receives the CoopRTS frame sent by S, D will set the last five values of RelayTable, and the last four values are all in CoopRTS. Then D starts to delay 2SIFS, and sends a CTS frame to S when the delay is over.

2) If no RTR frame is heard from R during the delay, D clears the RelayTable at the end of the delay, and then sends a CTS frame to S.

3) If D monitors the RTR frame sent by R during the delay process, D terminates the delay process and sets RE as true. Then D sends a CTS frame to S after a delay of SIFS.

2. Data transmission process

If no relay is available, the data transmission process is the same as IEEE 802.11b. But if there is a relay available, the relay participates. Specific steps are as follows:

source node S

When the source node starts the data transmission process, S first checks the RE bit of the RelayTable, if it is true, it means that the relay node is available, and S sets the duration of the data packet sending process as:

Duration _DATAS = 3T _SIFS -T _DATAR +T _ACK

Here, Duration _DATAS represents the duration of data packets sent by S in the network, and Duration _DATAR represents the duration of data packets sent by relay node R in the network. Otherwise, S sends data packets according to the data transmission mode of IEEE 802.11b.

Regardless of whether S receives the ACK returned by D (successful transmission) or S's sending timer expires (sending failure), S immediately clears the RelayTable and prepares for the next transmission.

中继节点R

Relay node R

When the data packet sent by S is monitored by other nodes within one hop, the node that is not the relay node R processes it according to IEEE 802.11b, discards the packet, and updates the NAV. The relay node R receives and saves the packet, and makes some small modifications to the frame casting of the packet, changing the duration:

T _DATAR = T _SIFS + T _ACK

After the SIFS delay, R sends the data packet to the destination node D. Since R does not need D to send back an ACK frame, the sending timer of R is set to:

T _Timeout = T _DATAR

When the sending timer expires, R knows that its work has been completed, so R can clear the RelayTable, and then enter the backoff process.

目的节点D

Destination node D

If a relay node is available, D's physical layer waits until it receives a packet from R, and through a joint decoding process, gives the MAC layer a decoded frame. The MAC layer then sends an ACK frame back to S.

According to such modification, in this embodiment, at the MAC layer, it is possible to control whether the relay node participates in the data transmission process. Cooperating with the encoding method of the physical layer and the joint decoding process, the packet error rate can be reduced in fading channels, thereby improving the overall performance of the network. And when the channel quality is relatively good, that is, when the packet error rate is relatively low, since the data transmission process of this embodiment will be longer than IEEE 802.11b, so even if the packet error rate will decrease, the overall performance will decrease instead. .

The advantages of this embodiment can only be reflected when the packet error rate of the direct link is relatively large, so it can be considered to combine the C-MAC of this embodiment with IEEE 802.11b: when the packet error rate is relatively small, IEEE 802.11 is still used b. When the packet error rate is greater than a certain value, the C-MAC of this embodiment is used.

A relatively simple method is used here to determine the packet error rate. When the number of tests is large, the frequency of an event approaches its probability of occurrence. This embodiment uses this principle to estimate the packet error rate, but this method can only be used when the channel is relatively stable, that is, the packet error rate does not change very frequently. Each node has two counters. When sending a data packet (whether it is retransmitted or not), the sending counter is incremented by one, and if an ACK is received, the receiving counter is incremented by one. Considering that the packet error rate will change, the counter needs to be reset after a period of time. This range depends on the channel stability. In the middle of the simulation, the sending counter is reset every 3000 packets. Thus, the packet error rate can be estimated as:

As shown in FIG. 4 , the source node S judges the process of using the C-MAC and IEEE802.11b of this embodiment before sending. Wherein TH _B and TH _C are thresholds of packet error rates when using IEEE 802.11b and C-MAC in this embodiment, respectively.

The threshold of the packet error rate is completed by comparing the simulation and analysis, and the results are given in the following performance comparison.

The performance comparison of C-MAC and IEEE 802.11b in this embodiment under different packet error rates

Use NS2 (network simulation) to build a simulation platform, and the parameters used in the simulation are shown in Table 1.

form one

MAC Header 272bits PHY Header 192bits CoopRTS 432bits CTS 304bits RTR 304bits ACK 304bits Data rate for PHY header 1Mbps Slot Time 20us SIFS 10us DIFS 50us wxya 31 slots wxya   1023 slots retryLimit 4

In the simulation model, the transmission radius of the node is 250m, and the sensing radius is 550m. All nodes are fixed and randomly distributed within a hop. The simulation focuses on the performance comparison and threshold selection between C-MAC and IEEE 802.11b in this embodiment under different packet error rates. Generally speaking, the packet error rate (p) after adopting the relay node and the packet error rate (p) of the direct link is a function relationship f(p). To simplify the simulation, f(p)=p ² is assumed in the simulation. This is a very rough estimate of f(p), and it has been proved theoretically that the upper bound of f(p) approximates the square law relationship.

Fig. 5 is a comparison between the theoretical value and the simulated value of the saturated throughput of C-MAC and IEEE 802.11b in this embodiment under different packet error rates. The focus of this figure is the threshold point, that is, the packet error rate of the direct link when the network throughput of the C-MAC in this embodiment is equal to the throughput of IEEE 802.11b. This picture compares the simulated and theoretical thresholds, and it can be seen that the two values are very close. This embodiment also compares the simulated and theoretical thresholds when other network parameters are used, and the results are shown in Table 2. In the table, L represents the length of the data packet, R represents the rate of the relay node, and N represents the number of data streams in the network.

Table II

TH_B Theoretical value Simulation value L=1024 bytes, R=11M, N=10 0.2467 0.2452 L=512 bytes, R=11M, N=10 0.2833 0.2769 L=1024 bytes, R=11M, N=5 0.2453 0.2434 L=2048 bytes, R=11M, N=10 0.2194 0.2240 L=1024 bytes, R=5.5M, N=10 0.3841 0.3882

From this table, it can be seen that the theoretical value and the simulated value are very close under different network parameters, so it can be considered to use the theoretical value instead of the simulated value. At the same time, from this table, you can see what kind of impact different parameters have on the threshold. First of all, the impact of the number of data streams N on the threshold is negligible, which can be seen by comparing the cases of N=10 and N=5; secondly, the length L of the data packet has a certain influence on the threshold, compared with L=512,1024 , This can be found in the case of 2048 bytes. A larger data packet length can reduce the threshold, so when considering the packet error rate, it is more beneficial for the C-MAC in this embodiment to use a large data packet; finally, the rate R of the relay node has a great influence on the threshold. Comparing the situation of R=11M and R=5.5M, it can be found that under the same conditions of other parameters, R=11M is about 0.14 larger than the threshold of R=5.5M, which is a relatively large number for the packet error rate up.

At the same time, since the rate of the relay node is the most influential factor on the threshold, and the rate of the relay node is known to the source node S, S can use this to determine whether to use the C-MAC or IEEE 802.11b of this embodiment. Set the threshold. In the simulation, when R=11M, TH _B was set to 0.26, and when R=5.5M, TH _B was set to 0.4.

Figure 6 is a comparison diagram of the network throughput when the speed of the relay node is 11M and 5.5M respectively. It can be seen from Figure 7 that the rate of the relay node has a great influence on the threshold, and at the same time has a great influence on the overall throughput of the network. When R=11M, the network throughput is much larger than when R=5.5M. When the packet error rate of the direct link is 0.4, the increase is about 13%.

Figure 7 is a comparison of network throughput when using different packet lengths. It can be seen that sending large data packets can improve the network throughput no matter for C-AMC or IEEE 802.11b, but the C-MAC of this embodiment improves more. At the same time, it can be seen in FIG. 7 that there are some jumping points when using the C-MAC of this embodiment, especially L=2048 bytes is the most obvious, which also reflects the impact of different packet lengths on the threshold size.

Fig. 8 is the cumulative distribution function of the service time of the MAC layer when the packet error rate of C-MAC and IEEE 802.11b in this embodiment is 0.3. Since the complete transmission time of C-MAC in this embodiment is longer than that of IEEE 802.11b, when the service time is relatively small, the cumulative distribution function value of C-MAC in this embodiment is smaller than that of IEEE802.11b. When the service time is getting longer and longer, because the C-MAC in this embodiment has the advantage of a relatively small packet error rate, the cumulative distribution function value of the C-MAC in this embodiment will exceed IEEE 802.11b.

Figure 9 is a comparison of packet loss rates between C-MAC and IEEE 802.11b in this embodiment under different packet error rates. It can be seen that the packet error rate has a greater impact on the packet loss rate when using IEEE 802.11b, because the number of retransmissions of data packets has an upper limit, and the packet error rate will increase the number of retransmissions. When the number of retransmissions reaches the upper limit, the packet is discarded. However, C-MAC has an advantage in the packet error rate, so when the error rate of the direct link is high, the increase in the packet loss rate is not obvious.

Claims (3)

1. intermedium control method of in WLAN (wireless local area network), supporting collaboration communication, it is characterized in that: the mode of triangle exchange is used in the transmission of control frame, what sent in the source is the CoopRTS frame, what via node sent is the RTR frame, what destination node was sent is the CTS frame, if source node can receive the RTR frame of via node and the CTS frame of destination node, via node can be used so; Statistical value to the ACK frame of the packet that sends before and reception calculates Packet Error Ratio simultaneously, and according to the relation of this Packet Error Ratio and threshold value, whether the decision via node participates in transfer of data, wherein:

The mode of triangle exchange is used in the transmission of described control frame, in its reciprocal process, CTS is exactly the CTS of IEEE802.11, the frame format of RTR is the same substantially with CTS, unique difference is that the subtype in the frame control is designated as RTR, CoopRTS revises on the basis of IEEE 802.11 RTS frame formats and comes, the frame of RTS comprises five parts: frame control, duration, destination address, source address and verification and, CoopRTS increases two parts in the source address part back of RTS: relay node address and via node are to the speed of destination node.

2. the intermedium control method of in WLAN (wireless local area network), supporting collaboration communication according to claim 1, it is characterized in that, the mode of the triangle exchange of described frame is as follows: suppose to exist three nodes, source node S, destination node D and potential via node R, at first, source node S is sent control frame CoopRTS to destination node D, the address that in the frame format of CoopRTS, has comprised the via node that can participate in transmitting, suppose that this node is R, all nodes in node S transmission model can both listen to this CoopRTS frame, but have only via node R can accept frame CoopRTS, send frame RTR to source node S then and represent that R meets the rate requirement in the CoopRTS frame format, can participate in transfer of data, R need start transmission timer when sending RTR, waits for the arrival of a CTS in the network;

When destination node D listens to the RTR bag that via node R sends, destination node D just can determine that via node R can participate in transfer of data, destination node D sends frame CTS to source node S then, CTS can be received by each node in the network, after the relaying node R is received CTS, just stop transmission timer, prepare to participate in transfer of data; If do not receive CTS, R arrived with regard to the waiting timer time, entered backoff procedure; When source node S received CTS, source node S just can begin data transmission procedure.

3. the intermedium control method of in WLAN (wireless local area network), supporting collaboration communication according to claim 1, it is characterized in that, the mode of described triangle exchange, transfer of data is divided into two time slots in the collaboration communication of its physical layer: at first time slot, source node S sends packet to destination node D, R monitors simultaneously and this bag is preserved, and destination node D receives the same packet that the continuation wait of bag back comes from the relaying node R; At second time slot, R issues destination node D to the bag that first time slot is preserved, and destination node D has just received with a packet from two next copies of different channels like this.

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