CN113347736B - MIMO-based mobile ad hoc network multipoint communication method - Google Patents
MIMO-based mobile ad hoc network multipoint communication method Download PDFInfo
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- H04W74/00—Wireless channel access, e.g. scheduled or random access
- H04W74/08—Non-scheduled or contention based access, e.g. random access, ALOHA, CSMA [Carrier Sense Multiple Access]
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Abstract
The invention discloses a mobile ad hoc network multipoint communication method based on MIMO, which judges whether to reserve a channel or refresh a NAV value according to different sensed channel states based on the traditional point-to-point information transmission process, and in a sensing range, according to RTS (request to send) of the reserved channel i Whether it is the same target node and the maximum R MAX Determining whether to finish the binary exponential backoff, enter a NAV mechanism or finish the binary exponential backoff and enter a same-node backoff mechanism according to the number; at the moment, the same parallel sub-channel can be reserved for 2 or more, and then waiting time slots T are passed according to different time, different nodes and 0 and sending CTS-x groups with different x assignments according to the number of the RTS groups, so that the reservation times can be increased under the support of the multi-packet receiving capability of the MIMO system, and the multipoint-to-point communication is realized.
Description
Technical Field
The invention relates to the technical field of wireless mobile ad hoc network communication, in particular to a mobile ad hoc network multipoint communication method based on MIMO.
Background
The mobile Ad Hoc network can also be called an Ad Hoc network, and is a special wireless mobile network without a center, self-organization and multi-hop routing, wherein nodes in the network are connected through wireless, and the positions of the nodes are flat, and fixed communication equipment is not required for connection. Nodes in the network can move anywhere and can join or leave the network at any time, so that the network topology structure of the network can be changed at any time, and the network topology structure has the characteristics of low deployment cost, easiness in setting and the like. However, it is a hot issue of research at present to realize faster utilization of channel resources, effective data transmission, communication establishment, and network throughput improvement in a mobile ad hoc network, and a medium access control layer protocol for controlling and solving a node access channel plays a critical role, so how to design a new protocol, and the problems of network throughput improvement, wireless channel utilization efficiency, and delay reduction are currently the most concerned.
With the continuous development of Multiple Input Multiple Output (MIMO) technology, combining the mobile ad hoc network technology with the MIMO technology can more flexibly realize network networking. MIMO has space diversity and space multiplexing gain, and can realize multi-packet reception capability in combination with corresponding coding techniques, such as space-time space-frequency coding. The carrier sense multiple access/collision avoidance protocol design of the prior medium access control layer only allows a single point-to-point communication mode, informs other nodes of the use right that the nodes reserve the channel in a competition mode by sending an RTS packet, and when the other nodes receive the RTS packet and detect the duration of a MAC frame header, the nodes finish backoff and adjust a NAV value, then send CTS to confirm the sending node and send a data packet, and simultaneously informs the nodes in a hidden node: the channel is already occupied; some technologies provide a MAC mechanism (DAP mechanism) based on spatial multiplexing gain for cdma systems, where the mechanism includes several node groups and a single-group network with multiple users, a time axis is divided into consecutive transmission cycles consisting of several time slots, and each time a packet generated in a previous transmission cycle after a single-group network in the system is polled is successfully received, one transmission cycle ends. The existing basic method is to design a MAC protocol based on spatial multiplexing and diversity gain of the MIMO technology, so as to maximally reduce time delay and improve network throughput, however, this method cannot perfectly solve collisions and collisions during communication, and the problem of low transmission efficiency caused by the fact that the previous MAC layer protocol only supports single point-to-point communication at the same time.
Disclosure of Invention
The purpose of the invention is as follows: aiming at the problems in the prior art, the invention provides a mobile ad hoc network multipoint communication method based on MIMO, the existing medium access control layer protocol only supports one-to-one node communication in a wireless mobile ad hoc network within the same time, namely point-to-point communication, but the invention utilizes the method of combining the MIMO spatial multiplexing and diversity gain technology with the mobile ad hoc network MAC protocol, is mainly applied to the conditions of researching complex and changeable environments such as emergency rescue and disaster relief, and the like, and focuses on two aspects of point-to-point spatial multiplexing (CSMA/CA) and parallel communication capability (SD-MAC, MIMA-MAC).
The technical scheme is as follows: in order to achieve the purpose, the technical scheme adopted by the invention is as follows:
a mobile ad hoc network multipoint communication method based on MIMO comprises the following steps:
step S1, after the information transmission of the previous frame is completed, initializing a node to be transmitted, and reserving a time slot induction channel; the node monitors the channel state information through the carrier wave and judges whether the channel is idle or not;
step S2, when the channel is monitored to be in an idle state, firstly entering a binary exponential backoff mechanism, selecting a time slot value at the moment in a contention window CW by a node, and setting a backoff timer as follows:
backoff timer = CW unit time
Where CW ∈ {0,1,2, \ 8230;, 2 i+2 -1, i is the ith backoff and has a maximum value of 6; the node continuously monitors the channel, and when the channel is in an idle state, the timer value is reduced by 1 until the backoff timer first reaches 0; at which point the node sends an RTS i Grouping to reserve a channel;
when the channel is in a busy state, the backoff timer is suspended and is used for refreshing a network allocation vector NAV value according to the duration of the frame header information;
s3, the node which successfully avoids the node 0 firstly sends RTS to the rest nodes in the monitoring range i (ii) a And judging whether the rest nodes are the RTS i A target node of the packet; when the rest nodes are not the target nodes of the group, ending binary exponential backoff, suspending a backoff timer, and updating a NAV value;
step (ii) ofS4, when the binary exponential backoff count value of the node is less than 0 and the node is backed off, RTS is received i When grouping, judging whether the grouping is consistent with the target node and is less than the maximum receiving antenna number A r When the target nodes are consistent and less than A r When the binary exponential back-off is finished, the binary exponential back-off enters a co-address back-off mechanism SNB, and a corresponding time slot value is randomly generated, wherein the time slot value is less than T 0 2; when the target node is consistent but larger than A r Or when the target nodes are not consistent, ending binary exponential backoff, entering an NAV mechanism, and updating an NAV value;
step S5, the node which firstly ends the co-address back-off sends RTS i+1 Grouping; target node judgment RTS in interception range i Whether the number of the packets reaches R MAX (ii) a Wherein R is MAX ＝A r (ii) a When RTS is used i The number of the packets is less than R MAX The target node waits for a time slot T 0 To receive the remainder (R) MAX -i) RTS packets, when RTS i The number of packets is equal to R MAX According to different time, different nodes and waiting time slot T 0 Sending different CTS-x groups in;
the sending of different CTS-x packets in step S6 and step S5 specifically includes:
when waiting for time slot T 0 In the correct reception of R MAX Upon receipt of a packet, the target node replies to a CTS-T packet, where x assigns a value of T, representing the correct receipt of R MAX A group of the data; when waiting for time slot T 0 Internally correct reception of R MAX Grouping and simultaneously receiving RTS grouping sent by nodes which are out of the listening range of the sending node but in the listening range of the target node, replying a CTS-H grouping by the target, wherein x is assigned to H to indicate that R is correctly received MAX Grouping and receiving RTS grouping sent by a hidden node;
s7, the node judges whether the node is out of the interception range of the sending node and within the interception range of the target node according to different x values of the received CTS-x PACKET, when the node is normally sent and the target node normally receives, the node is not hidden, or the sending node and the target node are both within respective interception ranges, and the node sends a PACKET after waiting for a short interframe space SIFS to realize communication with the target node; when the node is a hidden node, other nodes in the NAV mechanism directly update the NAV value, and the node sending the RTS packet finishes binary exponential backoff and enters the NAV mechanism;
s8, when the target node successfully sends an acknowledgement frame ACK, the transmission of the frame is ended; and when the target node does not send the acknowledgement frame ACK, repeating the step S2-7 and retransmitting the frame.
Has the advantages that:
the MIMO-based mobile ad hoc network multipoint communication method modifies the traditional medium access control layer carrier sense multiple access/collision avoidance protocol, combines the MIMO technology multi-packet receiving capability, designs and provides a new flow chart, maximizes the number of data packets capable of simultaneously sending a reservation channel under the condition that the maximum number of receiving antennas is not exceeded, and waits for a time slot T according to different moments, different nodes and the number of waiting time slots 0 And the number of the RTS groups is used for sending CTS-x groups with different x assignments to judge subsequent data packets or adjust the NAV value of the RTS groups, so that the channel utilization rate and the network throughput are greatly improved. Judging whether to reserve channel or refresh NAV value according to different channel state, and in the interception range, according to RTS received from reserved channel i Whether it is the same target node and maximum R MAX The number determines whether to finish binary exponential backoff, enter NAV mechanism or finish binary exponential backoff and enter same-node backoff mechanism, at this moment, the same parallel sub-channel can reserve 2 or more, and then according to different moments, different nodes and waiting time slot T 0 And sending CTS-x groups with different x assignments according to the number of the RTS groups, so that the reservation times can be increased under the support of the multi-packet receiving capability of the MIMO system, and the multipoint-to-point communication is realized.
Drawings
FIG. 1 is a schematic diagram of node communication transmission operation provided by the present invention;
FIG. 2 is a flow chart of a MIMO-based mobile ad hoc network multicast communication method provided by the present invention;
fig. 3 is a schematic diagram of signal transmission operation in an implementation case in which the maximum number Ar of receiving antennas is 2 and a plurality of nodes to be transmitted all enter a same-node backoff mechanism according to an embodiment of the present invention;
fig. 4 shows that the maximum number Ar of receiving antennas is 2, and other nodes to be transmitted and RTS transmission are performed according to the embodiment of the present invention i Frame object inconsistent and correct reception of R MAX A signal transmission working schematic diagram in an implementation case under the condition of the number of frames;
fig. 5 is a schematic diagram of transmission operation of an embodiment of the present invention, in which the maximum number Ar of receiving antennas is 2, the number of RMAX frames is correctly received, and an RTS packet sent by a node outside the sensing range of the sending node and within the sensing range of the target node is received at the same time.
Detailed Description
The present invention will be further described with reference to the accompanying drawings.
The invention provides a mobile ad hoc network multipoint communication method based on MIMO, and a transmission communication flow comprises four stages: the first stage is as follows: a competition reservation channel for sending request to send RTS frame grouping; and a second stage: reply to a different channel clear frame packet, i.e., clear to send frame (CTS-x); and a third stage: after receiving the transmission permission frame, transmitting a data packet; a fourth stage: and successfully sending an acknowledgement frame ACK, finishing the transmission communication, and if not, reserving the competition channel again and resending the data packet. The transmission communication flow is shown in fig. 2.
Step S1, after the information transmission of the previous frame is completed, initializing a node to be transmitted, and reserving a time slot induction channel; and the node monitors the channel state information through the carrier wave and judges whether the channel is idle or not.
Step S2, when the channel is monitored to be in an idle state, firstly entering a binary exponential backoff mechanism, selecting a certain time slot value in a contention window CW, and setting a backoff timer as follows:
backoff timer = CW × (unit time)
Where CW ∈ {0,1,2, \ 8230;, 2 i+2 -1}, i is the ith backoff, and the maximum value of backoff timer is 6; the node keeps listening to the channel, when the channel is in idle state, the timer value is decreased by 1 until the first of backoff timerFirstly reaching 0; at this point the node sends an RTS i The channel is reserved by grouping.
When the channel is in a busy state, the backoff timer is suspended, and the network allocation vector NAV value is refreshed according to the duration of the frame header information.
S3, the node which successfully avoids the node 0 firstly sends RTS to the rest nodes in the monitoring range i (ii) a Judging whether the rest nodes are the target nodes of the group or not; and when the rest nodes are not the target nodes of the group, ending binary exponential backoff, suspending a backoff timer, and updating the NAV value. If the packet is the destination node of the packet, the process proceeds to step S5.
Step S4, when the binary exponential backoff count value of the node is less than 0 and the node is backed off, RTS is received i When grouping, judging whether the grouping is consistent with the target node and is less than the maximum receiving antenna number A r When the target nodes are consistent and less than A r When the binary exponential backoff is finished, entering a co-address backoff mechanism SNB, and randomly generating a corresponding time slot value, wherein the time slot value is less than T 0 2; when the target node is consistent but larger than A r Or when the target nodes are not consistent, ending binary exponential backoff, entering a NAV mechanism, and updating the NAV value.
Step S5, the node which firstly ends the co-address back-off sends RTS i+1 Grouping; target node judgment RTS in interception range i Whether the number of the packets reaches R MAX (ii) a Wherein R is MAX ＝A r (ii) a When RTS is used i The number of the groups is less than R MAX The target node waits for a time slot T 0 To receive the remainder (R) MAX -i) RTS packets, when RTS i The number of packets is equal to R MAX According to different time, different nodes and waiting time slot T 0 Different CTS-x packets are sent in.
Steps S1-S5 are the first stage, each node continuously monitors the channel, determines whether to send RTS packet to reserve a competition channel or enter a NAV mechanism according to the idle state of the channel, and refreshes the NAV value; in waiting time slot T 0 If the target node does not receive the packet larger than or equal to the RMAX, the same purpose is achieved in the interception rangeOther nodes of the target node enter the same-node back-off mechanism after receiving RTSi, so that the T can be ensured 0 Receiving enough RTS reservation channels to improve the network throughput greatly;
the sending of different CTS-x packets in step S6 and step S5 specifically includes:
when waiting for time slot T 0 In the correct reception of R MAX Upon receipt of a packet, the target node replies to a CTS-T packet, where x assigns a value of T, representing the correct receipt of R MAX A group of the data; while waiting for time slot T 0 Internally correct reception of R MAX Grouping and simultaneously receiving RTS grouping sent by nodes which are out of the monitoring range of the sending node but in the monitoring range of the target node, replying a CTS-H grouping by the target, wherein x is assigned with H to indicate that R is correctly received MAX And receives RTS packet sent by hidden node.
Step S6 is the second stage, according to different time, different nodes and waiting time slot T 0 Different CTS-x packets are sent in.
S7, the node judges whether the node is out of the interception range of the sending node and in the interception range of the target node according to different x values of the received CTS-x grouping, when the node is normally sent and the target node normally receives, the node is not hidden, or the sending node and the target node are both in respective interception ranges, and the node waits for SIFS and then sends a PACKET; when the node is a hidden node, other nodes in the NAV mechanism directly update the NAV value or the node sending the RTS packet finishes binary exponential backoff and enters the NAV mechanism.
Step S7 is a third stage, namely a stage for preparing to send data packets or refreshing NAV values
S8, when the target node successfully sends an acknowledgement frame ACK, the transmission of the frame is ended; and when the target node does not send the acknowledgement frame ACK, repeating the step S2-7 and retransmitting the frame.
Step S8 is a fourth stage, the target node sends a successful ACK to inform each node that the channel is in an idle state, and reservation competition can be carried out; and if unsuccessful, retransmitting.
Suppose a network is inIn an ideal state, due to the characteristics of the mobile ad hoc network nodes of moving along with Time and moving along with Time, the Time points of the nodes reaching the Slot Time Slot of the induction channel are inconsistent. First, a new frame is transmitted, a node which reaches the time slot first senses that the channel is in an idle state and enters binary exponential backoff first, and at this time, a plurality of nodes may be in the backoff mechanism, for example, the backoff timer of node a reaches 6 randomly (CW e {0,1,2, \ 8230;, 2;, 2 ∈ CW × (CW e {0,1, 2) } unit time due to the inconsistency of the random selection of the counter value of the backoff algorithm i+2 -1, i is the ith backoff, if transmission fails, i is increased by 1, and if transmission succeeds, 1 is recovered, with a maximum of 6 being defined. After the backoff time is selected, the node listens to the detection channel once every time it passes a slot: if the channel is sensed to be idle, the counter is decremented by one; if the channel is detected to be busy, suspending the counter value, adjusting the NAV value, waiting for the channel to be idle again, and continuing to count down from the last remaining time after the DISF. The node that finishes the backoff first sends RTS i Frame grouping, nodes in the listening range are subjected to RTS i Frame grouping and information reading are carried out, and the target node receives the first RTS i Waiting time slot T after frame grouping 0 And the other sending nodes in the band will make the following judgments: if the target nodes are consistent and less than Ar (maximum number of receiving antennas), the binary backoff is ended, SNB backoff is entered, and the node which ends first sends the rest (R) MAX-i ) The RTS frame group still receives the residual RTS frame group at other nodes of SNB back-off, judges whether the RTS frame group is less than Ar again, and continues SNB back-off if the RTS frame group is less than Ar; if the channel is larger than or equal to the preset channel, entering a NAV mechanism and waiting for the channel to be idle; if the binary system is started to retreat and receives RTS frame grouping, the nodes are judged to be inconsistent or the nodes are always larger than Ar, then a NAV mechanism is entered, and the channel is waited for to be idle. If in the waiting time slot T 0 In the correct reception of R MAX Upon receipt of the CTS-T packet, the destination node replies with a CTS-T packet, where the x value assigned T indicates correct reception of R MAX A group of the data; if in the waiting time slot T 0 Internally correct reception of R MAX Packets and also received outside the listening range of the sending node but at the targetIf nodes in the node listening range also send RTS packets, the CTS-H packets are replied, wherein x is assigned H to represent that R is correctly received MAX Grouping and receiving RTS grouping sent by a hidden node; and then sending a data packet reply acknowledgement frame ACK to finish the whole transmission communication at this time. The method has the advantages that the MIMO technology can be fully utilized to realize the improvement of a plurality of pairs of nodes of the mobile ad hoc network on the utilization rate of the channel and the great increase of the network throughput.
In the following, 3 embodiments are sequentially provided with reference to fig. 3 to 5, and the multicast method provided by the present invention is specifically explained.
Example 1:
referring to fig. 3, after a previous frame is transmitted or a NAV value is ended, a DIFS is passed through by nodes a, C, and D (node ABCD represents any node in the nodes that may perform transmission communication, which is only one possible case in this embodiment), and a channel is still in an idle state, then node a and node D first enter a binary exponential backoff stage and randomly select a certain time slot in a Contention Window (Contention Window) according to a rule, a backoff timer (backoff timer) value is set at the time slot position, at this time, the backoff timer value of node a is 7, the backoff timer value of node D is 5, both nodes that are in backoff will continuously monitor the channel, and if the channel is idle, the counter value is decremented by 1; when the node A and the node D are in the backoff process, the node C detects that the channel is in an idle state after the DIFS, the node C also adds the backoff process and sets a backoff timer value of 4; at this time, three nodes continuously compete for backoff in the process of competing for the channel until the node D which finishes backoff first sends RTS 1 Frame grouping and broadcasting to all nodes in the listening range, at which point the target node B receives the RTS 1 After frame grouping, setting the maximum RTS grouping number R of the frame according to the maximum receiving antenna number of 2 MAX Is 2 and starts waiting for a waiting time slot T 0 Time to receive the remainder (R) MAX -i) RTSs. Node A and node C receive RTS 1 After grouping, reading the target node information in the frame header and judging whether the target node information is consistent with the target node of the target node: when the node A and the node C both judge that the node D is consistent with the target node thereof, the node A and the node C immediately finish the processBundling binary exponential backoff, entering a same-node backoff mechanism, randomly selecting a corresponding time slot value according to a rule, then performing a same-node backoff reciprocal process, and firstly selecting a node A which finishes the same-node backoff and sending RTS 2 Grouping frames and broadcasting the frames to all nodes in the interception range, wherein the node C which does not finish backoff of the same node at the moment receives RTS 2 After frame grouping, according to R set by receiving node MAX Value to determine that it has been unable to send an RTS frame packet any more, it is due to receiving an RTS 2 And the frame grouping is finished, the same node retreats and refreshes the NAV value, and the channel is waited to be idle again. In the process of passing through the waiting time slot T 0 The target node B then receives the correct number of RTS' s i And sending a CTS-T frame group after the number of the frames, and successfully finishing the transmission process of the frame after the node A and the node D receive the channel clearing confirmation frame CTS-T, send a data packet and receive an ACK confirmation frame sent by the target node D again.
Example 2
Referring to fig. 4, after a DIFS is passed through after a previous frame is transmitted by nodes a, B, and D (node ABCD represents any node in the nodes that may perform transmission communication, which is only one possible case in this embodiment), and a channel is still in an idle state, the nodes a, B, and D enter a binary exponential backoff stage and randomly select a certain time slot in a Contention Window (Contention Window) according to a rule, and then set a backoff timer (backoff timer) value at the time slot position, where the node a backoff timer value is 7, the node B backoff timer value is 5, the node D backoff timer value is 7, and all three nodes that are in backoff continuously monitor the channel, and if the channel is idle, subtract 1 from the counter value; node B, which first completes backoff, sends RTS 1 Frame grouping and broadcasting to all nodes in the listening area, at which point the target node C receives the RTS 1 After frame grouping, setting the maximum RTS grouping number R of the frame according to the maximum receiving antenna number of 2 MAX Is 2 and starts waiting for a waiting time slot T 0 Time to receive the remainder (R) MAX -i) RTSs. Node A and node D receive RTS 1 After grouping, reading the target node information in the frame header and judging whether the target node information is consistent with the target node: node A determines and selfIf the target nodes are consistent, the target nodes immediately finish binary exponential backoff, enter a same-node backoff mechanism, randomly select corresponding time slot values according to rules, then perform a same-node backoff reciprocal process, and receive RTS at the same time 1 If the node D of the frame grouping judges that the node D is inconsistent with the target node of the node D, the node D of the frame grouping receives RTS 1 And the frame grouping immediately finishes binary exponential backoff, suspends the backoff timer value and refreshes the NAV value. Node A sends RTS after finishing same node back-off 2 The frame is grouped and broadcast to the rest of nodes in the listening range, and node D receives RTS 2 The frame packet continues to refresh the NAV value and waits for the channel to be idle again. Passing through waiting time slot T 0 After time, node C correctly receives R MAX And if the RTS frame group is received, sending a CTS-T channel clearing confirmation frame group to the nodes in the monitoring range to allow the node A and the node B to send data packets until the target node sends a confirmation frame ACK and the nodes A and B receive the ACK, and ending the transmission process of the frame.
Example 3
Referring to fig. 5, after a previous frame is transmitted or a NAV value is ended, a channel is still in an idle state after DIFS is passed through by nodes a, B, and C (node ABCD represents any node in the nodes that may perform transmission communication, which is only one possible case in this embodiment), and then the node a and the node B first enter a binary exponential backoff stage and randomly select a certain time slot in a Contention Window (Contention Window) according to a rule, a backoff timer value is set at the time slot position, the node a backoff timer value is 5, the node B is 7, and then the two nodes start to continuously monitor a channel state to contend for a reservation channel, and if the channel is monitored to be in the idle state, the backoff timer value is decreased by 1. And in the back-off process of the node A and the node B, after the node C passes the DIFS, the node C also starts to back off the random binary exponential and selects a timer value of 6. Firstly, the node A finishing binary exponential backoff sends RTS to the interception range 1 Frame grouping, at which point the target node D receives RTS 1 After frame grouping, setting the maximum RTS grouping number R of the frame according to the maximum receiving antenna number of 2 MAX Is 2 and starts waiting for a waiting time slot T 0 Time to receive the remainder(R MAX -i) RTS, and node B receives RTS 1 After the frame is grouped, the header frame information is read, then the target node is judged to be consistent with the target node, then the target node immediately finishes binary exponential backoff, enters a same-node backoff mechanism, selects a corresponding time slot according to a rule, starts backoff, and sends RTS after the backoff is finished 2 And (5) grouping frames. Node C is out of the monitoring range of the sending nodes A and B and does not receive RTS 1 、RTS 2 Frame grouping, the binary exponential backoff is continued and RTS is sent after finishing 3 And (5) grouping frames. Passing through waiting time slot T 0 Thereafter, the target node correctly receives R MAX One packet but simultaneously accepts RTS in the sensing range of the target node outside the sensing range of the transmitting node 3 The target node sends a CTS-H frame packet to inform the transmitting node that it is allowed to receive the previous R MAX The nodes send data packets, and send RTS after the nodes are out of the sensing range of the sending node and in the sensing range of the target node 3 The node of (b) refreshes the NAV value and waits for the channel to be idle again due to the reception of the CTS-H packet. And the node A and the node B send data packets after receiving the CTS-H group, and finish the transmission process of the frame after correctly sending the data packets and receiving an acknowledgement frame ACK.
The above description is only of the preferred embodiments of the present invention, and it should be noted that: it will be apparent to those skilled in the art that various modifications and adaptations can be made without departing from the principles of the invention, and such modifications and adaptations are intended to be within the scope of the invention.
Claims (1)
1. A mobile ad hoc network multipoint communication method based on MIMO is characterized by comprising the following steps:
step S1, after the information transmission of the previous frame is completed, initializing a node to be transmitted, and reserving a time slot induction channel; the node monitors the channel state information through the carrier wave and judges whether the channel is idle or not;
step S2, when the channel is monitored to be in an idle state, firstly entering a binary exponential backoff mechanism, selecting a time slot value of the channel in the contention window CW by the node, and setting a backoff timer as follows:
backoff timer = CW × (unit time)
Where CW ∈ {0,1,2, \ 8230;, 2 i+2 -1, i is the ith backoff and has a maximum value of 6; the node continuously monitors the channel, and when the channel is in an idle state, the timer value is reduced by 1 until the backoff timer reaches 0 firstly; at which point the node sends an RTS i Grouping to reserve a channel;
when the channel is in a busy state, the backoff timer is suspended and is used for refreshing a network allocation vector NAV value according to the duration of the frame header information;
s3, the node which successfully avoids the node 0 firstly sends RTS to the rest nodes in the monitoring range i (ii) a And judging whether the rest nodes are the RTS i A target node of the packet; when the rest nodes are not the target nodes of the group, ending binary exponential backoff, suspending a backoff timer, and updating a NAV value;
step S4, when the binary exponential backoff count value of the node is less than 0 and the node is backed off, RTS is received i When grouping, judging whether the grouping is consistent with the target node and is less than the maximum receiving antenna number A r When the target nodes are consistent and less than A r When the binary exponential backoff is finished, entering a co-address backoff mechanism SNB, and randomly generating a corresponding time slot value, wherein the time slot value is less than T 0 2; when the target node is consistent but larger than A r Or when the target nodes are inconsistent, ending binary exponential backoff, entering an NAV mechanism, and updating an NAV value;
step S5, the node which firstly finishes the co-address back-off sends RTS i+1 Grouping; target node judgment RTS in interception range i Whether the number of packets reaches R MAX (ii) a Wherein R is MAX ＝A r (ii) a When RTS is used i The number of the groups is less than R MAX The target node waits for a time slot T 0 To receive the remainder (R) MAX -i) RTS packets, when RTS i The number of packets is equal to R MAX According to different time, different nodes and waiting time slot T 0 Sending different CTS-x groups in;
the sending of different CTS-x packets in step S6 and step S5 specifically includes:
when waiting for time slot T 0 In the correct reception of R MAX Upon receipt of a packet, the target node replies to a CTS-T packet, where x assigns a value of T, representing correct reception of R MAX A group of the data; while waiting for time slot T 0 Internally correct reception of R MAX Grouping and simultaneously receiving RTS grouping sent by nodes which are out of the monitoring range of the sending node but in the monitoring range of the target node, replying a CTS-H grouping by the target, wherein x is assigned with H to indicate that R is correctly received MAX Grouping and receiving RTS grouping sent by a hidden node;
s7, the node judges whether the node is out of the interception range of the sending node and within the interception range of the target node according to different x values of the received CTS-x PACKET, when the node is normally sent and the target node normally receives, the node is not hidden, or the sending node and the target node are both within respective interception ranges, and the node sends a PACKET after waiting for a short interframe space SIFS to realize communication with the target node; when the node is a hidden node, other nodes which are in the NAV mechanism directly update the NAV value, and the node which sends the RTS packet finishes binary exponential backoff and enters the NAV mechanism;
s8, when the target node successfully sends an acknowledgement frame ACK, the transmission of the frame is ended; and when the target node does not send the acknowledgement frame ACK, repeating the steps S2-S7 and retransmitting the frame.
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