CN108966361B - Dynamic back-off method based on WiFi mesh network beacon frame broadcast - Google Patents
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Abstract
The invention discloses a dynamic backoff method based on WiFi mesh network beacon frame broadcasting, which comprises the following steps: establishing a WiFi mesh network; broadcasting Beacon frames periodically by the nodes; writing the size of a competition window and the backoff order of a node into a Beacon frame before each broadcast; broadcasting the modified Beacon frame periodically by the node; extracting parameters from the Beacon frame; setting a competition window threshold; determining CWDWhether the value of (c) exceeds a set contention window threshold value CWTHR；CWD>CWTHRSetting a window of a current node; CWD<CWTHRThe window of the current node is set. The invention can write the size of the competition window and the backoff order of the node into the Beacon frame in the WiFi mesh network for broadcasting, so that the current node can dynamically adjust the competition window by combining the blocking condition of the target node and the dynamic backoff method. The invention increases the throughput of the WiFi mesh network, reduces the packet loss rate and improves the transmission performance of the system. The invention is applied to the communication between the nodes of the WiFi mesh network.
Description
Technical Field
The invention belongs to the technical field of communication, and further relates to a backoff method in the technical field of wireless communication, in particular to a dynamic backoff method based on WiFi mesh network beacon frame broadcasting. The invention is suitable for the WiFi mesh network.
Background
WiFi Mesh Networks (WMNs) are widely recognized as a promising and practical solution for broadband Internet access wireless solutions, combining WLAN (Wireless Local Area Networks) with mobile NetworksThe ad-hoc network has the advantages of flexible networking, multi-hop, high throughput and the like. In WMNs, Media Access Control (MAC) adopts CSMA/CA protocol in IEEE802.11 Distributed Coordination Function (DCF) mechanism to solve the random access collision problem. The monitoring is performed by a physical carrier and a virtual carrier, and if a channel is always idle in a Distributed Inter-frame Spacing (DIFS), a node may send a data packet. Before transmitting data, a node needs to randomly select a backoff value within a Contention Window (CW) to perform a backoff procedure. In each time slot of the backoff procedure, the node monitors whether the channel is idle, and if the channel is idle, the value of the backoff counter is decremented by 1. Otherwise, the backoff counter will be frozen. When the value of the backoff counter is decreased to 0, the node may transmit data. The Binary Exponential Backoff (BEB) algorithm is an important component of the CSMA/CA protocol, and simply, when a node successfully transmits a packet, the CW is reset to CWmin. When a node encounters a collision or a data transmission failure, the current CW is doubled, CW 2iCWminWhere i is the backoff stage. With a back-off mechanism, the actual transmission times of some nodes waiting for transmission may be staggered on the timeline to prevent collisions. The CSMA/CA protocol ensures the fairness of node access to a certain extent, and reduces the probability of conflict.
However, this conventional fixed-parameter CSMA/CA protocol is not suitable for WMNs, mainly for two reasons. First, due to the multi-hop communication characteristics of WMNs, the collision probability will increase significantly. The second reason is that the degree of collision of the gateway node and its neighbors becomes a bottleneck for the overall network performance, since all traffic load must eventually merge into the gateway node. In addition, the conventional CSMA/CA protocol resets the value of the contention window to CW after a successful transmission by a nodemin. Therefore, the node which has just successfully transmitted will obtain the backoff value in the minimum contention window, and there will be a greater chance of obtaining the right to access the channel in the next data transmission, which results in unfair contention among the nodes. More importantly, it is largeThe quantum nodes will have the same contention window value (i.e., CW) after successful transmissionmin) Then, it is very likely that these nodes select similar or identical backoff values during the backoff process, so that the probability of collision is significantly increased.
There are many studies on the improvement of the back-off algorithm, and the back-off algorithm can be classified into the following categories. The first category is an improved algorithm based on the contention window update rule. The paper "MACAW: A media access protocol for wireless LAN's" published by Alen Demers et al proposes a back-off algorithm that multiplies by a Linear reduction (MILD). In the algorithm, when the node transmission is successful, the CW is reduced by 1, and when the node transmission is failed, the CW is expanded to 1.5 times of the current value. H Wu et al, in its published article "Enhancement of IEEE802.11 distributed coordination function with Exponential in computational Exponential Decrease backward decision algorithm", propose a back-off algorithm with Exponential Increase Exponential Decrease (EIED). When the node transmits successfully, the CW is reduced to 1/R of the current windowDDoubling; when node transmission fails, CW is expanded to current RIThereby improving the performance of the DCF mechanism. The second category is based on improved back-off algorithms for implementing collision-free networks. The basic idea proposed by J Barcelo et al in its published paper "Fairness and conversion of CSMA with Enhanced Collision Avoidance (ECA)" is that each node, after successful transmission, uses a deterministic backoff count to build a collision-free mechanism between competing nodes in a fully decentralized manner.
The adjustment factors of the contention window in the first type of improved back-off algorithm are generally fixed, the adaptive capability is poor, and when the network environment changes, no significant performance improvement may be brought. The second category of improved back-off algorithms focuses on successful transmission by the nodes rather than creating a recovery process after collisions, thus improving the performance of the network. However, collisions in an actual network are inevitable, and the improved method is not effective in handling the situation after a burst, and the system cannot be adjusted according to the network condition later because the mechanism uses a determined backoff value once the transmission is successful.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provides a dynamic backoff method based on WiFi mesh network beacon frame broadcasting, which can dynamically adjust the size of a contention window, ensure timely forwarding and reduce conflicts.
The invention relates to a dynamic backoff method based on WiFi mesh network beacon frame broadcasting, which is characterized by comprising the following steps:
(1) establishing an IEEE 802.11-based WiFi mesh network in an ad-hoc mode;
(2) each node periodically broadcasts Beacon frames to other nodes in the network;
(3) modifying the Beacon frame before broadcasting: the contention window size CW of the current node is set before each broadcastDAnd back-off order kDWriting the elements into the reserved elements of the Beacon frame body;
(4) broadcasting the modified Beacon frame in the node period: will contain the contention window size CWDAnd back-off order kDThe Beacon frame is broadcasted for the nodes needing to send information;
(5) when the node has data to be sent to the target node, executing the steps (6) to (8) to set dynamic backoff; when the node has no data to send, returning to execute the steps (2) to (4) and continuously broadcasting the modified Beacon frame to other nodes in the network;
(6) the node extracts parameters from the Beacon frame: a node with data to be transmitted receives a Beacon frame broadcasted by a target node, and extracts the CW with the size of a contention window from the retainable elements of a Beacon frame bodyDAnd back-off order kDTwo values;
(7) setting a contention window threshold value with reference to the maximum value of the contention window: setting a threshold value CW of a contention windowTHRDividing the current network load into a high-flow load and a low-flow load according to the size of a target node competition window;
(8) judging the size of a target node competition window: determining a contention window size CW of a target nodeDWhether or not the value of (A) exceeds the settingOf the contention window threshold value CWTHR：
If CWD>CWTHRIf so, indicating that the network congestion condition is serious, and executing the step (9);
if CWD<CWTHRIf so, the network is smooth, and the step (10) is executed;
(9)CWD>CWTHRwhen the data transmission is successful, the competition window of the current node is slowly reduced, the competition fairness of the node is improved, one-time dynamic backoff is completed, and the step (5) is returned to be executed to wait for the next data transmission;
(10)CWD<CWTHRand (3) introducing an adjusting coefficient, setting the competition window of the current node to be a smaller value, enabling the nodes to be rapidly forwarded, reducing the competition window according to an IEEE802.11 protocol after successful transmission, completing one dynamic backoff, returning to the step (5) and waiting for the next data transmission.
The invention uses the competition window size CW of the node itselfDAnd back-off order kDWriting the information into a Beacon frame for broadcasting, and extracting CW (continuous wave) after the current node receives the Beacon frame broadcasted by the target nodeD、kDAnd adjusting the size of a competition window of the current node according to a designed dynamic back-off method to adapt to the current network condition, wherein the forwarding processes among the nodes are coordinated with each other, so that the throughput of the communication system is improved, and the packet loss rate of the communication system is reduced.
Compared with the prior art, the invention has the following advantages:
firstly, because the invention adds the contention window size CW of the node into the Beacon frame periodically broadcast by each nodeDAnd back-off order kDThe value of (3) enables a node needing to send data to obtain the blocking condition of a target node in real time, and dynamically adjusts the size of a competition window according to a designed backoff method, so that the data sending of the current node is delayed or advanced according to the network state of the target node, a data packet can be timely forwarded, the collision probability is reduced, and the data transmission efficiency is improvedThe efficiency of data transmission between nodes is improved.
Secondly, under the condition of serious network congestion, different competition window reduction strategies are implemented according to the backoff order of the transmission after each successful transmission, the higher the backoff order is, the smaller the competition window reduction is, the higher the probability of obtaining the channel use right in the next competition is, and the higher the fairness of the competition among the nodes is.
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FIG. 1 is an application scenario of the present invention;
FIG. 2 is a flow chart of the steps of the present invention;
FIG. 3 is a flow chart diagram illustrating the steps of the present invention;
FIG. 4 is a schematic diagram of modification of Beacon frame in the present invention;
FIG. 5 is a diagram illustrating the structure of an information element according to the present invention;
FIG. 6 is a diagram of a simulated network topology;
fig. 7 is a graph of simulation results.
Detailed Description
The present invention will be described in detail below with reference to the accompanying drawings.
Example 1
The existing wireless network mostly adopts an IEEE802.11 protocol, a CSMA/CA mechanism is used in the protocol to solve the problem of multi-user competition, the load of the wireless network is larger and larger along with the rapid development of communication equipment, a Binary Exponential Back-off (BEB) algorithm in the CSMA/CA protocol can generate a large amount of conflicts in a network with serious congestion, and the communication efficiency is seriously reduced. The existing backoff algorithm improvement has the following problems that the adjustment factor of a contention window in the backoff algorithm is fixed, the self-adaptive capacity is poor, and in addition, some backoff algorithms only focus on the successful transmission of nodes, but not on the recovery process after collision. Aiming at the problems, the invention provides a dynamic backoff method based on WiFi mesh network beacon frame broadcasting, which dynamically adjusts the size of a contention window of a current node according to a periodically acquired parameter of a target node and a designed backoff method so as to adapt to the current network condition, reduce the conflict among the nodes and accelerate the forwarding among the nodes.
Referring to fig. 2 and fig. 3, the dynamic backoff method based on the beacon frame broadcast of the WiFi mesh network of the present invention includes the following steps:
(1) an IEEE802.11 based WiFi mesh network is established in ad-hoc mode.
(2) Each node periodically broadcasts Beacon frames to other nodes in the network.
(3) Modifying the Beacon frame before broadcasting: the contention window size CW of the current node is set before each broadcastDAnd back-off order kDAnd writing into the reserved element of the Beacon frame body.
(4) Broadcasting the modified Beacon frame in the node period: will contain the contention window size CWDAnd back-off order kDThe Beacon frame is broadcasted for nodes needing to send information, and the dynamic broadcasting of the current network parameters is realized by utilizing the characteristic of periodic broadcasting.
(5) And (4) when the node has data to be sent to the target node, executing the steps (6) to (8) to set dynamic back-off. And (4) when the node has no data to send, returning to execute the steps (2) to (4) and continuously broadcasting the modified Beacon frame to other nodes in the network.
(6) The node extracts parameters from the Beacon frame: a node with data to be transmitted receives a Beacon frame broadcasted by a target node, and extracts the CW with the size of a contention window from the retainable elements of a Beacon frame bodyDAnd back-off order kDAnd taking the values of the two parameters as the standard for judging the network state of the target node.
(7) Setting a contention window threshold value with reference to the maximum value of the contention window: setting a threshold value CW of a contention windowTHRAnd dividing the current network load into a high-flow load and a low-flow load according to the size of a target node competition window.
(8) Judging the size of a target node competition window: by the contention window size CW contained in the received periodically broadcast Beacon frameDDynamically judging the current contention window size CW of the target nodeDWhether or not the value of (A) exceeds the settingOf the contention window threshold value CWTHR：
If CWD>CWTHRAnd (9) executing the back-off strategy step (9) of the high-blocking network state when the network blocking degree is higher.
If CWD<CWTHRAnd (5) when the network blocking degree is low, executing the back-off strategy step (10) of the low-blocking network state.
(9)CWD>CWTHRAnd (3) introducing a compensation coefficient to avoid collision during data forwarding caused by an excessively small contention window, properly increasing the contention window of the current node, slowly reducing the contention window of the current node after successful transmission, improving the node contention fairness, completing one dynamic backoff, returning to the step (5) of executing, and waiting for next data transmission.
(10)CWD<CWTHRAnd (3) introducing an adjusting coefficient under the condition of low network blocking degree and in order to avoid unnecessary time delay caused by an overlarge contention window, setting the contention window of the current node to be a small value so that the nodes can be quickly forwarded, reducing the contention window according to an IEEE802.11 protocol after successful transmission, completing one dynamic backoff, returning to the step (5) of executing, and waiting for next data transmission.
The conventional backoff algorithm and the existing improved backoff algorithm change the size of a contention window of a node regularly, defaults to current network congestion when information transmission fails, does not consider the congestion degree of the network, changes the size of the contention window of the node mechanically according to the rule, causes unnecessary time delay when the network congestion degree is low, and generates a lot of unnecessary conflicts when the network congestion degree is high. In order to solve the existing problems, the invention considers that the network state is firstly obtained, the blocking condition of the network state is judged, then different back-off strategies are implemented according to different network blocking degrees, and the size of a competition window of a node needing to send data is adjusted to adapt to the current network state under different network blocking degrees. By dimensioning CW the contention window of the node itselfDAnd back-off order kDWriting into periodically broadcast Beacon frames, dynamicThe method and the device for obtaining the network state give out the optimal back-off strategy under different network states, so that the forwarding processes among the nodes are coordinated, the throughput of the communication system is improved, and the packet loss rate of the communication system is reduced.
In addition, after the nodes successfully transmit data, the conventional backoff algorithm directly resets the size of the contention window to the minimum value of the contention window no matter how large the current contention window is, which may cause that the nodes successfully completing data transmission have a high probability of obtaining the use right of the next channel, so that unfair contention occurs between the nodes. The invention properly reduces the competition window of the current node on the basis of the size of the competition window after the current node is successfully transmitted, thereby avoiding the unfair competition among the nodes caused by the rapid reduction of the competition window.
Example 2
The dynamic backoff method based on the WiFi mesh network Beacon frame broadcast is the same as that in embodiment 1, the Beacon frame is modified before broadcast in step (3), and the method for modifying the Beacon frame is as follows:
the Beacon frame is a frame which is periodically broadcasted by the node to other nodes in the network, and aims to enable the other nodes to know the existence of the current node, and when the other nodes have data to be sent to the current node, the MAC address of the current node is obtained in advance through the Beacon frame, and the data are accurately sent to the current node. The periodic broadcast of the Beacon Frame provides a basis for the dynamic back-off method of the present invention, see the Frame structure of the Beacon Frame in fig. 4, where the Frame Body (Frame Body) can be divided into a part in which information elements can be written and a part in which information elements cannot be written, and the parts in which the IDs of the elements in the part in which information elements can be written are 17-31, 175-. The invention aims to ensure that each node broadcasts the size CW of the competition window of the current node before periodically broadcasting the Beacon frame in the WiFi mesh networkDAnd back-off order kDThe value of (2) is written into the reserved element in the Beacon frame body according to the format of the information element, see FIG. 5. the format of the information element is divided into three parts including an element of one fieldA plain ID; the information length of one field; a piece of variable length information.
Example 3
The dynamic back-off method based on the beacon frame broadcast of the WiFi mesh network is the same as that in the embodiment 1-2, the threshold value of the contention window is set in the step (7), and the threshold value CW of the contention windowTHRThe setting method comprises the following steps:
the initial value of the contention window in the IEEE802.11 protocol is the minimum value CW of the contention windowmin(ii) a When collision occurs between nodes or data transmission fails, the current contention window is doubled, i.e., CW is 2kCWminWhere k is the backoff order. When the maximum backoff order specified in the IEEE802.11 protocol is 6 and the backoff order is 6, the contention window reaches the maximum CW specified in the protocolmax＝26CWminWhen network congestion is serious, a large number of conflicts are caused by the fixed growth mode, and the conflict is reduced by implementing different back-off strategies on the same network state. The invention is directed to the maximum value CW of the reference contention windowmaxSetting a threshold value of a competition window, reasonably dividing the busy condition of the network by setting a reasonable threshold value, and setting the threshold of the competition window by using the golden section rate to ensure that the threshold value CW of the competition windowTHRIs composed of
CWTHR＝0.618×CWmax
If the contention window of the node is larger than the threshold value of the contention window, the blocking condition of the network is serious, and if the contention window of the node is smaller than the threshold value of the contention window, the network is smooth. Tests prove that the setting of the contention window threshold can effectively divide the network state and improve the system performance after different backoff strategies are implemented aiming at different network states.
Example 4
Dynamic back-off method based on beacon frame broadcast of WiFi mesh network is the same as CW described in embodiments 1-3, step (9)D>CWTHRA method for properly increasing the competition window of the current node by introducing a compensation coefficient comprises the following steps:
(9.a) introducing a compensation coefficient, when the competition window of the target node is larger than the threshold value of the competition window, the current network blocking is serious, and at the moment, even if the current node quickly sends data to the target node, the target node cannot forward the data in time, so that the competition window of the current node is set to be a larger value, the current node delays the data sending, and the occurrence of conflict is reduced. But in order to avoid the situation that an excessively large contention window increases unnecessary back-off time and delay during setting, a compensation coefficient B which is larger than 0 and smaller than 1 is introduced,
compensating the competition window CW of the target node when the competition window CW of the current node is compensatedDWhen the compensation coefficient B is increased, the compensation coefficient B is reduced, so that an overlarge competition window is avoided during setting.
(9.B) appropriately increasing the contention window of the current node using the compensation coefficient B according to the following formula,
in the formula CWSIs the contention window size, k, of the current nodeDBackoff order, CW, for the target nodeDIs the contention window size, CW, of the target nodemaxAnd CWminIs the maximum value and the minimum value of a contention window specified in an IEEE802.11 protocol, and the backoff order k when the contention window is largeDIt is also relatively large to avoid the backoff order kDCausing the set contention window to be too large, and using the compensation factor B to appropriately reduce the size of the contention window, CW, of the target nodeDThe larger the compensation coefficient B is, the smaller it is.
(9.c) introducing a regulation factor when the competition window is larger than the threshold value after one successful transmission
Slowly reducing the current window after successful transmission using the following equation
After each node in the conventional IEEE802.11 protocol successfully transmits data, the contention window is directly initialized to the minimum CW of the contention windowminThe node that successfully transmits data obtains a small contention window, and when network congestion is severe, contention windows of other nodes are generally large, and the node that successfully transmits in the following channel contention has a high probability of occupying the channel again, resulting in unfair contention among nodes. Therefore, when the network blockage is serious, the invention combines the size of the current competition window of the node which successfully transmits the data with the current competition window to slowly reduce the size of the competition window per se, and the CW of the competition window of the current node is followedSThe adjustment factor S is decreased, i.e. the current contention window CW after successful transmissionSThe larger nodes can have higher priority to carry out the next data transmission, thereby ensuring the fair competition among the nodes.
In the case of severe network congestion, some existing improved backoff mechanisms use a certain backoff value once transmission is successful, so that the system cannot adjust according to the network condition afterwards. After successful transmission, the invention implements different competition window reduction strategies according to the backoff order of the transmission, the higher the backoff order is, the smaller the competition window reduction is, thereby realizing the dynamic adjustment of the competition window, obtaining the channel use right with higher probability in the next competition, and leading the competition among the nodes to have higher fairness.
Example 5
Similar to the dynamic backoff method in embodiments 1 to 4, the step (10) of introducing an adjustment coefficient to set the contention window of the current node to a smaller value includes the following steps:
(10.a) introducing an adjustment coefficient K, introducing an adjustment coefficient K when the competition window is larger than the threshold value, wherein the adjustment coefficient K is defined as
In the conventional IEEE802.11 protocol, regardless of whether transmission failure is caused by network congestion, the size of the contention window of the current node is doubled in each transmission failure, which causes unnecessary delay when the network is unobstructed. The invention introduces an adjustment coefficient K which is more than 1 and less than 2, and effectively controls the size of the competition window of the current node to grow rapidly when the network is smooth.
(10.b) setting a smaller contention window for the current node by adjusting the coefficient K according to the following formula
Contention window CW from a target nodeDCW of target node of smaller settingSThe smaller the size, so that the node can access the channel quickly and the packet can be forwarded more quickly.
(10.c) after successful completion of one transmission, the contention window CW of the current nodeSDirectly reducing the size of the contention window to the minimum value CW of the contention window, and because the network is smooth enough at the moment, the size of the contention window of the current node is reset to the minimum value CW of the contention window after the data is successfully transmitted according to the conventional contention window updating mechanism of CSMA/CAS＝CWmin。
Under the condition that the network is smooth, the invention introduces an adjusting coefficient K to set the competition window of the current node to be a smaller value, and reduces the competition window according to the traditional competition window updating mechanism of CSMA/CA after the data is successfully transmitted, thereby realizing the rapid forwarding of the data between the nodes.
The invention will be further described with reference to the following figures.
Example 6
The dynamic back-off method based on the beacon frame broadcast of the WiFi mesh network is similar to embodiments 1-5, referring to fig. 1,
the research scene is a WiFi mesh network, the network consists of a plurality of network devices and Access points (AP, Access points), wherein the network comprises a gateway (GW, Gate Way) for accessing Internet, and each host in the network can Access Internet through multi-hop communication between the GW and the AP.
The specific steps of the implementation of the present invention will be described in detail with reference to fig. 2 and 3.
An IEEE802.11 based WiFi mesh network is established in ad-hoc mode.
As can be seen from fig. 4, the free available part of the Beacon Frame is a Frame Body (Frame Body) part, and the length of the Frame Body can be arbitrarily chosen between fields 0 and 2320. The frame body part can be divided into a part which can be used as an information element and a part which can not be used as the information element, the format of the information element is composed of three parts as shown in figure 4, and the format of the information element is an element ID of one field; the information length of one field; a portion of variable length information. The information elements with the element IDs of 17-31, 175-220 and 222-255 are reserved information elements in the IEEE802.11 protocol, so the invention writes the values of the contention window size and the backoff order of the node into the reserved element part according to the format of the information elements, and completes the modification of the Beacon frame.
And 5, extracting parameters from the Beacon frame: the current node receives the Beacon frame broadcast by the target node, and extracts the CW with the size of the competition window from the reserved elements of the frame bodyDAnd back-off order kDTwo values.
CWTHR＝0.618×CWMAX
The traditional binary exponential back-off algorithm is an important component in the CSMA/CA protocol. Briefly, when a node successfully transmits data, its contention window is reset to CWmin(ii) a When collision occurs between nodes or data transmission fails (no ACK is received), the current contention window is doubled, i.e., CW is 2iCWminWhere i is the backoff order. The maximum backoff order specified in the IEEE802.11 protocol is 6, and if the node still detects a collision at this time, the current packet is discarded. The fixed rule causes a large number of collisions when the network congestion condition is severe, and unfair competition among nodes occurs. The dynamic back-off method is used for determining the size CW of the competition window of the target nodeDThe threshold value exceeding the competition window is high flow load, and the threshold value not exceeding the competition window is low flow load.
If CWD>CWTHRStep 8 is performed.
If CWD<CWTHRStep 9 is performed.
Step 8, CWD>CWTHRPerforming window setting of current node
CWDExceeding the threshold value indicates the current network resistanceThe Backoff Time Backoff Time is related to the size of the contention window as shown in the following equation
Backoff Time＝random[0,CW]×slotTime
Wherein CW is a backoff contention window of the current node and satisfies CW ∈ [ ]min,CWmax]。CWminAnd CWmaxThe size of (c) is specified by a mac (media Access control) layer in an IEEE802.11 protocol, and the slotted time is composed of three parts of a Channel monitoring cca (clear Channel association) time, a propagation delay, and a transmit/receive switching (Rx/TxHardware turn) time of an antenna in a physical layer. When the network congestion is serious, the contention window of the current node is increased appropriately according to the following formula,
in the formula CWSIs the size of the contention window of the current node, since kDA large CW is caused which also increases unnecessary back-off time and delay, the invention uses a factor larger than 0 and smaller than 1
Compensate for it when CWDWhen the size of the pipe is increased, the pipe is enlarged,
it will be reduced.
To avoid as much as possible unfair contention caused by a rapid decrease in the contention window after each successful transmission, the current window is slowly decreased after a successful transmission using the following equation
With CWSIn the case of the increase in the number of,
will be reduced, i.e. in the successful transmissionThe nodes with larger back-off orders have higher priority to carry out the next data transmission, thereby ensuring the fair competition among the nodes to a great extent.
Step 9, CWD<CWTHRPerforming window setting of current node
CWDIf the network load is not lighter than the threshold value, a smaller contention window is set for the current node according to the following formula so that the node can quickly access the channel,
small CWs from target nodeDIndicating that we can set a smaller CWSSo that the node has fast access to the channel and the data packets can be forwarded faster. Wherein the coefficient part is defined as
The coefficient is greater than 1 and less than 2, which effectively controls the rapid growth of the contention window.
Since the blocking degree of the network is small enough at this time, the contention window is reset to the initial value CW after the successful data transmission, still following the conventional contention window update mechanism of CSMA/CAS＝CWmin。
The invention realizes dynamic adjustment of the competition window of the node based on the broadcast Beacon frame, increases the throughput of the communication system and reduces the packet loss rate.
The technical effects of the present invention will be explained in the following by simulation and the results thereof
Example 7
The dynamic back-off method based on the WiFi mesh network beacon frame broadcast is the same as embodiments 1-6,
to verify the improvement of network communication performance by the Dynamic backoff method (DBS) in the present invention, DBS was compared with the existing ELBA (exponential linear backoff method) and BEB (binary exponential backoff method) in IEEE802.11 protocol using ns-3, a discrete event network simulator developed by berkeley division, university of california.
The simulated network topology structure diagram is shown in fig. 6, all nodes are spaced by 100m and distributed in a two-dimensional square space, each host sends udp data packets to the gateway node, the size of the data packets is 64 bytes to 1024 bytes, and the intervals of the data packets are from 0.006s to 0.0025 s. Assuming that all nodes always have data packets to transmit, the transmission rate is 6Mbps, and the basic access mode of DCF in IEEE802.11 protocol is adopted.
The simulated comparison of the throughput of the different methods was made by varying the size of the data packet from 64 bytes to 1024 bytes with a data packet generation interval of 0.005 seconds as shown in fig. 7. In the figure, the abscissa is the size of the data packet, the ordinate is the throughput, the solid line with boxes is the throughput of the DBS method of the present invention, the dotted line with a difference sign is the throughput of the ELBA method, and the dotted line with an asterisk is the throughput of the BEB method, simulation results show that the performance of the DBS method is superior to that of the BEB and ELBA, the throughput increases significantly initially with increasing size of the data packet, and then the throughput decreases gradually as the attenuation due to collisions becomes greater than the throughput gain due to increasing size of the data packet. When the data packet is smaller or larger, the advantages of the invention are more obvious when the throughput difference of the three methods is larger, the throughput of the three methods is very close when the size of the data packet is about 100 bytes, but the throughput of the DBS method of the invention is always larger than that of the BEB method and the ELBA method.
In short, the dynamic backoff method based on the beacon frame broadcast of the WiFi mesh network disclosed by the present invention comprises the following steps: establishing a WiFi mesh network; broadcasting Beacon frames periodically by the nodes; modifying the Beacon frame before each broadcast; broadcasting the modified Beacon frame periodically by the node; extracting parameters from the Beacon frame; setting a competition window threshold; determining CWDWhether the value of (c) exceeds a set contention window threshold value CWTHR；CWD>CWTHRSetting a window of a current node; CWD<CWTHRThe window of the current node is set. The inventionThe size of a contention window and a backoff order of a node can be added into a Beacon frame in a Wi-Fi mesh network for broadcasting, so that the current node can dynamically adjust the contention window of the current node by combining the blocking condition of a target node and a dynamic backoff method. The invention increases the throughput of the Wi-Fi mesh network, reduces the packet loss rate and improves the transmission performance of the system. The method is applied to the communication between the nodes of the WiFi mesh network.
Claims (3)
1. A dynamic back-off method based on WiFi mesh network beacon frame broadcasting is characterized by comprising the following steps:
(1) establishing an IEEE 802.11-based WiFi mesh network in an ad-hoc mode;
(2) each node periodically broadcasts Beacon frames to other nodes in the network;
(3) modifying the Beacon frame before broadcasting: writing the size of a competition window and the backoff order of the current node into a retainable element of a Beacon frame body before each broadcast;
(4) broadcasting the modified Beacon frame in the node period: broadcasting a Beacon frame containing the size of a contention window and a backoff order for nodes needing to send information;
(5) when the node has data to be sent to the target node, executing the steps (6) to (8) to set dynamic backoff; when the node has no data to send, returning to execute the steps (2) to (4) and continuously broadcasting the modified Beacon frame to other nodes in the network;
(6) the node extracts parameters from the Beacon frame: the node with data to be sent receives the Beacon frame broadcast by the target node, and extracts the CW with the size of the target competition window from the retainable elements of the Beacon frame bodyDAnd back-off order kDTwo values;
(7) setting a contention window threshold value with reference to the maximum value of the target contention window: setting a threshold value CW of a contention windowTHRDividing the current network load into a high-flow load and a low-flow load according to the size of a target node competition window;
(8) judging the size of a target node competition window: determining a target nodeOf the contention window size CWDWhether the value of (c) exceeds a set contention window threshold value CWTHR：
If CWD>CWTHRIf so, indicating that the network congestion condition is serious, and executing the step (9);
if CWD<CWTHRIf so, the network is smooth, and the step (10) is executed;
(9)CWD>CWTHRwhen the data is transmitted, introducing a compensation coefficient, properly increasing the competition window of the current transmitting node to reduce the conflict in the network, slowly reducing the competition window of the current node after successful transmission, improving the competition fairness of the node, completing one dynamic backoff, and returning to the step (5) for waiting for the next data transmission;
introducing a compensation coefficient, properly increasing the contention window of the current sending node, and slowly reducing the contention window of the current sending node after successful transmission, comprising the following steps:
(9.a) introducing a compensation coefficient, when the competition window of the target node is larger than the threshold value of the competition window, introducing a compensation coefficient B which is larger than 0 and smaller than 1,
compensating the contention window of the current transmitting node when CWDWhen the compensation coefficient B is increased, the compensation coefficient B is reduced;
(9.B) appropriately increasing the contention window of the current transmitting node using the backoff factor B according to the following formula,
in the formula CWSIs the contention window size, k, of the current transmitting nodeDBackoff order, CW, for the target nodeDIs the contention window size, CW, of the target nodemaxAnd CWminIs the maximum and minimum values of the contention window specified in the IEEE802.11 protocol;
(9.c) in successIntroducing an adjustment coefficient when a contention window is larger than a threshold value after completing one transmission
Slowly reducing the current sending node window after successful transmission using the following equation
Contention window CW with current transmitting nodeSThe adjustment factor S is decreased, i.e. the contention window CW after successful transmissionSLarger nodes can have higher priority to carry out next data transmission, thereby ensuring fair competition among the nodes;
(10)CWD<CWTHRwhen the data is transmitted, introducing an adjusting coefficient, setting the competition window of the current transmitting node to be a smaller value, enabling the nodes to be rapidly transmitted, reducing the competition window according to an IEEE802.11 protocol after the data is successfully transmitted, completing one dynamic back-off, and returning to execute the step (5) to wait for the next data transmission;
introducing an adjusting coefficient, setting the competition window of the current sending node to be a smaller value, and reducing the competition window according to an IEEE802.11 protocol after successful transmission, wherein the method comprises the following steps:
(10.a) introducing an adjustment coefficient K, introducing an adjustment coefficient K when the competition window is larger than the threshold value, wherein the adjustment coefficient K is defined as
The adjusting coefficient K is more than 1 and less than 2;
(10.b) setting a smaller contention window, setting a smaller contention window for the current transmitting node by adjusting the coefficient K according to the following formula
Contention window CW from a target nodeDCWs of smaller set transmitting nodesSThe smaller the size;
(10.c) transmitting the contention window CW of the current transmitting node after completing one transmissionSDirectly reducing the data transmission rate to the minimum value of the contention window, and after the data is successfully transmitted, still following the traditional contention window updating mechanism of CSMA/CA, resetting the size of the contention window of the current transmitting node to the minimum value CW of the contention windowS＝CWmin。
2. The dynamic backoff method based on WiFi mesh network Beacon broadcast of claim 1, wherein the Beacon frame is modified before broadcast in step (3), and the method for modifying Beacon frame is as follows:
writing the size of a competition window and the backoff order of a node into a reserved element of an information element part defined in a protocol standard; all nodes in the WiFi mesh network write the values of the size of a competition window and the backoff order of the current node into a reserved element in a Beacon frame body according to the format of an information element before broadcasting a frame; the ID of the reserved element is 17-31, 175-220, 222-255, and the format of the information element is divided into three parts including an element ID of one field; the information length of one field; a piece of variable length information.
3. The dynamic backoff method of claim 1, wherein the step (7) of setting the contention window threshold value is that of setting a contention window threshold value CWTHRThe setting method comprises the following steps:
at maximum value CW of contention windowmaxFor reference, the threshold value CW of the contention windowTHRIs arranged as
CWTHR＝0.618×CWmax。
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Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102595648A (en) * | 2011-12-31 | 2012-07-18 | 重庆邮电大学 | Adaptive carrier sense multiple access (CSMA)/conditional access (CA) method based on institute of electrical and electronics engineers (IEEE)802.15.4 |
| CN103298027A (en) * | 2012-02-24 | 2013-09-11 | 华为技术有限公司 | Method and device for controlling network congestion and network system |
| CN104052745A (en) * | 2014-06-18 | 2014-09-17 | 中南大学 | Contention window adjusting method taking 802.11e VoIP application as orientation |
| CN105611570A (en) * | 2015-12-20 | 2016-05-25 | 华南理工大学 | Vehicle ad hoc network MAC layer back-off method based on channel state judgment |
-
2018
- 2018-07-23 CN CN201810811368.4A patent/CN108966361B/en active Active
Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102595648A (en) * | 2011-12-31 | 2012-07-18 | 重庆邮电大学 | Adaptive carrier sense multiple access (CSMA)/conditional access (CA) method based on institute of electrical and electronics engineers (IEEE)802.15.4 |
| CN103298027A (en) * | 2012-02-24 | 2013-09-11 | 华为技术有限公司 | Method and device for controlling network congestion and network system |
| CN104052745A (en) * | 2014-06-18 | 2014-09-17 | 中南大学 | Contention window adjusting method taking 802.11e VoIP application as orientation |
| CN105611570A (en) * | 2015-12-20 | 2016-05-25 | 华南理工大学 | Vehicle ad hoc network MAC layer back-off method based on channel state judgment |
Non-Patent Citations (5)
| Title |
|---|
| Adaptive Contention Window Control Scheme in Wireless Ad Hoc Networks;Myung Woo Lee et al.;《IEEE》;20180531;全文 * |
| Enhancement of IEEE 802.1 1 Distributed Coordination Function with Exponential Increase Exponential Decrease Backoff Algorithm;Nai-Oak Song et al.;《IEEE》;20031231;全文 * |
| Improving Performance by a Dynamic Adaptive Success-Collision Backoff Algorithm for Contention-Based Vehicular Network;GUILU WU et al.;《IEEE》;20180214;全文 * |
| 一种优先级区分的机载无线网络ＭＡＣ层自适应退避算法;卓琨等;《航空学报》;20160425;全文 * |
| 一种动态退避的无线传感器网络ＭＡＣ协议;张怀相等;《杭州电子科技大学学报（自然科学版）》;20180331;全文 * |
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