CN108934081B - Wireless vehicle-mounted network channel access method - Google Patents
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Abstract
The invention discloses a wireless vehicle-mounted network channel access method, which comprises the following steps: firstly, receiving a beacon message request sent by a vehicle node, and generating a beacon by the beacon message request; then, carrying out interception on the DIFS time slot of the channel; then judging whether the channel is idle according to the DIFS time slot intercepted in the last step, and if the channel is idle, accessing the vehicle node into the channel; if not, the vehicle node executes a backoff process and accesses a channel; and finally, broadcasting the beacon of the vehicle node based on the 802.11p MAC protocol, thereby ending the wireless vehicle-mounted network channel access process. The invention improves the adaptivity of the back-off mechanism, effectively relieves the problem of node access channel conflict caused by the fact that multiple nodes select the same back-off counter due to a constant contention window, and has good application prospect.
Description
Technical Field
The invention belongs to the field of vehicle-mounted electronic wireless communication, and particularly relates to a wireless vehicle-mounted network channel access method.
Background
IEEE 802.11p VANET is a multi-hop mobile wireless communication network, vehicles communicate with roadside infrastructure by installing communication and computer equipment, and the communication modes mainly include vehicle-to-vehicle (V2V) communication and vehicle-to-roadside infrastructure (V2I) communication.
As shown in fig. 1, in V2V communication, a vehicle node periodically generates a beacon message sending request at an application layer and generates a beacon, the beacon includes speed, position, acceleration, driving direction and other road state information of the node, periodically broadcasts a beacon message after accessing a CCH and transmits the beacon message to neighbor nodes in a communication range, a node a establishes a neighbor list according to the received beacon message and updates the neighbor information list according to the received beacon message, and if the beacon message of a neighbor node is not received after a certain time, the node a determines that a neighbor node B has left, and deletes the information of the neighbor node B in the list.
The IEEE 802.11p MAC applies a Distributed Coordination Function (DCF) for channel access control. The node perceives a distributed interframe space (DIFS) before accessing the channel, and if the node detects that the channel is idle, the node immediately accesses the channel. Otherwise, the node starts the backoff process by randomly selecting a Backoff Counter (BC) from (0, w). Here, w represents the contention window size of the current node, and the value of w starts from the minimum value (CWmin) and doubles each time a collision occurs until the maximum value (CWmax) is reached.
The IEEE 802.11p VANET exchanges status information of vehicles, such as current position, driving speed, driving direction, etc., of the vehicles in real time through a broadcast beacon. A Media Access Control (MAC) layer controls a node to access a channel by using a Distributed Coordination Function (DCF) technology, and in the method, a backoff process is executed by using a constant contention window, namely, the value of the contention window is continuous CWmin in the whole backoff process. However, since no feedback is provided for the transmission of the broadcast information, the method may cause the performance degradation of the 802.11p broadcast channel, and especially in the dense access environment, the probability that a plurality of nodes select the same backoff counter is higher, and then the access channel collides at the same time, the packet loss rate and the data frame retransmission times are increased, and finally the success rate of the channel access is reduced, and the channel resources are wasted; in a sparse environment, selecting a constant contention window may cause a long idle channel.
Disclosure of Invention
The invention aims to provide a wireless vehicle-mounted network channel access method to relieve competition conflict caused by using a constant competition window when a node broadcasts a safety information frame in an IEEE 802.11p vehicle-mounted network technology.
The technical solution for realizing the purpose of the invention is as follows: a wireless vehicle-mounted network channel access method comprises the following steps:
step 2, monitoring the DIFS time slot of the channel;
step 3, judging whether the channel is idle according to the DIFS time slot intercepted in the step 2, and if the channel is idle, accessing the vehicle node to the channel; if not, the vehicle node executes a backoff process and accesses a channel;
and 4, broadcasting the beacon of the vehicle node, thereby finishing the wireless vehicle-mounted network channel access.
Further, the vehicle node executes a back-off process and accesses a channel, specifically:
step 3-1, the vehicle nodes are independently grouped;
3-2, randomly selecting a backoff counter value by each vehicle node;
and 3-3, according to the grouping of the vehicle nodes in the step 3-1 and the backoff counter value of each vehicle node in the step 3-2, each vehicle node sequentially executes a backoff process and accesses a channel.
Further, the vehicle nodes in step 3-1 perform autonomous grouping, specifically:
step 3-1-1, determining the number k of groups; the method specifically comprises the following steps:
assuming that the size of each group is n after the vehicle nodes are independently grouped, the method comprises the following steps of
Wherein N is the number of vehicle nodes;
and 3-1-2, randomly selecting an integer in the interval [1, k ] for each vehicle node, and grouping the vehicle nodes with the same integer.
Further, the randomly selecting a backoff counter value by each vehicle node in step 3-2 specifically comprises:
step 3-2-1, determining a minimum competition window array CWMin [ k ] and a maximum competition window array CWMax [ k ];
step 3-2-2, forming a contention window pair (CWmin [ i ], CWmax [ i ]) by using the ith minimum contention window CWmin [ i ] and the ith maximum contention window CWmax [ i ] corresponding to the minimum contention window array CWmin [ k ] and the maximum contention window array CWmax [ k ]; wherein i is an integer, i belongs to [1, k ];
3-2-3, according to the randomly selected integer of each vehicle node in the step 3-1-2, each vehicle node selects a corresponding competition window pair (CWMin, CWMax);
and 3-2-4, randomly selecting one value of each vehicle node in the range of the corresponding competition window pair (CWMin, CWMax) as the backoff counter value of the vehicle node.
Compared with the prior art, the invention has the remarkable advantages that: 1) the vehicle nodes are independently grouped to compete for channels, so that competition among the nodes is reduced; 2) the selected value of the back-off counter is determined according to the contention window pair (CWMin, CWMax), thereby greatly relieving the node access channel conflict problem caused by the fact that the nodes select the same back-off counter due to constant contention windows; 3) the size of the competition window array can be adjusted according to networks of different scales, so that the self-adaptability of a back-off mechanism is improved; 4) in the invention, the difference epsilon between CWmax and CWmin in any pair of contention window pairs (CWmin, CWmax) determines the number of selectable backoff counters.
The present invention is described in further detail below with reference to the attached drawings.
Drawings
Fig. 1 is a schematic diagram of vehicle-to-vehicle communication in a vehicle-mounted network VANET.
Fig. 2 is a flow chart of a wireless vehicular network channel access method of the present invention.
FIG. 3 is a schematic diagram of a vehicle node location in an embodiment of the present invention.
Fig. 4 is a schematic diagram illustrating a back-off process performed in order after nodes select the same contention window array and perform autonomous grouping in the embodiment of the present invention.
Detailed Description
The invention is described in further detail below with reference to the figures and the embodiments.
With reference to fig. 2, a method for accessing a wireless vehicular network channel includes the following steps:
And 2, monitoring the DIFS time slot of the channel.
Step 3, judging whether the channel is idle according to the DIFS time slot intercepted in the step 2, and if the channel is idle, accessing the vehicle node to the channel; and if not, the vehicle node executes a backoff process and accesses the channel.
The vehicle node executes a backoff process and accesses a channel, specifically:
and 3-1, carrying out autonomous grouping on the vehicle nodes. The method specifically comprises the following steps:
step 3-1-1, determining the number k of groups; the method specifically comprises the following steps:
assuming that the size of each group is n after the vehicle nodes are independently grouped, the method comprises the following steps of
And 3-1-2, randomly selecting an integer in the interval [1, k ] for each vehicle node, and grouping the vehicle nodes with the same integer.
And 3-2, randomly selecting a backoff counter value by each vehicle node. The method specifically comprises the following steps:
step 3-2-1, determining a minimum competition window array CWMin [ k ] and a maximum competition window array CWMax [ k ]; wherein the minimum contention window array Cwmin [ k ] is:
CWmin[k]＝{0,ε+1,2ε+2,…,(k-1)(ε+1)}
the maximum contention window array CWmax [ k ] is:
CWmax[k]＝{ε,2ε+1,3ε+2,…,k(ε+1)-1}
wherein ε is the difference between CWmax and CWmin in the contention window pair (CWmin, CWmax),
wherein, Tc *＝Tcσ is the duration of the idle slot, TcIs the transit time at which the collision occurred; t isc＝Th+ L/R + EIFS, where L is the packet length, R is the data rate, ThIs the preamble and header duration of PLCP, and EIFS is the extended frame interval.
Step 3-2-2, forming a contention window pair (CWmin [ i ], CWmax [ i ]) by using the ith minimum contention window CWmin [ i ] and the ith maximum contention window CWmax [ i ] corresponding to the minimum contention window array CWmin [ k ] and the maximum contention window array CWmax [ k ]; wherein i is an integer, i belongs to [1, k ];
3-2-3, according to the randomly selected integer of each vehicle node in the step 3-1-2, each vehicle node selects a corresponding competition window pair (CWMin, CWMax);
and 3-2-4, randomly selecting one value of each vehicle node in the range of the corresponding competition window pair (CWMin, CWMax) as the backoff counter value of the vehicle node.
And 3-3, according to the grouping of the vehicle nodes in the step 3-1 and the backoff counter value of each vehicle node in the step 3-2, each vehicle node sequentially executes a backoff process and accesses a channel. The method specifically comprises the following steps:
firstly, aiming at vehicle node groups, according to the sequence of integers randomly selected by each group of vehicle nodes in the interval [1, k ] from small to large, each group of vehicle nodes sequentially execute a back-off process and access a channel;
and secondly, aiming at the positions among the vehicle nodes in each group of vehicle nodes, each vehicle node sequentially executes a backoff process and accesses a channel according to the sequence from small to large of the backoff counter value selected by each vehicle node.
And step 4, broadcasting the beacon of the vehicle node based on the 802.11p MAC protocol, thereby ending the wireless vehicle-mounted network channel access.
The invention improves the adaptivity of the back-off mechanism, effectively relieves the problem of node access channel conflict caused by the fact that multiple nodes select the same back-off counter due to a constant contention window, and has good application prospect.
The present invention will be described in further detail with reference to examples.
Examples
Referring to fig. 3, on a two-way road, vehicle node A, B, C, D, E, F, G, H, I, J, etc. travels in the direction shown in the figure. A wireless vehicle-mounted network channel access method comprises the following steps:
And 2, monitoring the DIFS time slot of the channel.
And 3, judging whether the channel is idle or not according to the DIFS time slot intercepted in the step 2. In this embodiment, if it is determined that the channel is not idle, the vehicle node executes a backoff process and accesses the channel, and the vehicle node A, B, C, E, J, F is taken as an example in conjunction with fig. 4.
Step 3-1, the vehicle nodes A, B, C, E, J, F perform autonomous grouping; the method specifically comprises the following steps:
step 3-1-1, assuming that the scale of each group of the vehicle nodes after the vehicle nodes are independently grouped is 3, and the number of the vehicle nodes in the embodiment is 12, the number K of the groups is 12/3 or 4;
in steps 3-1-2, the vehicle nodes A, B, C, E, J, F all randomly select an integer in the interval [1, 4], and if the vehicle node A, B, C selects the integer 2 in the interval [1, 4] and the vehicle node E, J, F selects the integer 3 in the interval [1, 4], the vehicle nodes A, B, C are grouped together and the vehicle nodes E, J, F are grouped together.
Step 3-2, selecting a backoff counter by each vehicle node, specifically:
step 3-2-1, the minimum competition window array is CWMin [4], the maximum competition window array is CWMax [4 ];
step 3-2-2, constructing competition window pairs (Cwmin [1], Cwmax [1]), (Cwmin [2], Cwmax [2]), (Cwmin [3], Cwmax [3]), (Cwmin [4], Cwmax [4 ]);
3-2-3, according to the integer 2 selected by the vehicle node A, B, C and the integer 3 selected by the vehicle node E, J, F in the step 3-1-2, selecting a competition window pair (Cwmin 2, Cwmax 2) by the vehicle node A, B, C and selecting a competition window pair (Cwmin 3, Cwmax 3) by the vehicle node E, J, F; in this embodiment, the values of (Cwmin 2, Cwmax 2) are (15,31) and the values of (Cwmin 3, Cwmax 3) are (32, 48);
and 3-2-4, randomly selecting 16, 20 and 24 as backoff counters of the vehicle node A, B, C by the vehicle node A, B, C in the range of (15 and 31), and randomly selecting 34, 42 and 44 as backoff counters of the vehicle node E, J, F by the vehicle node E, J, F in the range of (32 and 48).
Step 3-3, according to the grouping of the vehicle nodes in the step 3-1 and the backoff counter value of each vehicle node in the step 3-2, each vehicle node sequentially executes a backoff process and accesses a channel, specifically:
firstly, the vehicle node a executes a backoff process by using the backoff counter 16, in the process, the backoff counters of the other vehicle nodes B, C, E, J, F are all frozen until the backoff counter value 16 of the vehicle node a is reduced to 0, the vehicle node a is accessed to the channel, the transmission is completed, and the channel is idle. And then the vehicle node B executes a backoff process by using the residual backoff counter 4, wherein the backoff counters of the other vehicle nodes C, E, J, F are all frozen in the backoff process until the backoff counter value 4 of the vehicle node B is reduced to 0, the vehicle node B is accessed to the channel, the transmission is completed, and the channel is idle. And finally, the vehicle node C executes a backoff process by using the remaining backoff counter 4, wherein the backoff counters of the other vehicle nodes E, J, F are all frozen in the backoff process until the backoff counter value 4 of the vehicle node C is reduced to 0, the vehicle node C is accessed to the channel, the transmission is completed, and the channel is idle.
The backoff counter selected by the vehicle node E, J, F is larger, and after the vehicle nodes A, B, C complete transmission, the vehicle nodes E, J, F sequentially perform the backoff process and access the channel to complete transmission as described above.
And step 4, broadcasting the beacon of the vehicle node based on the 802.11p MAC protocol, thereby ending the wireless vehicle-mounted network channel access.
The invention effectively reduces the probability of data packet collision caused by that a plurality of nodes select the same backoff counter, and improves the performance of a vehicle-mounted network channel access mechanism.
Claims (5)
1. A wireless vehicle-mounted network channel access method is characterized by comprising the following steps:
step 1, receiving a beacon message request sent by a vehicle node, and generating a beacon by the vehicle node, wherein the beacon message request is periodically generated by the vehicle node in a VANET application layer;
step 2, monitoring the DIFS time slot of the channel;
step 3, judging whether the channel is idle according to the DIFS time slot intercepted in the step 2, and if the channel is idle, accessing the vehicle node to the channel; if not, the vehicle node executes a backoff process and accesses a channel; the vehicle node executes a backoff process and accesses a channel, specifically:
step 3-1, the vehicle nodes are independently grouped; the method specifically comprises the following steps:
step 3-1-1, determining the number k of groups; the method specifically comprises the following steps:
assuming that the size of each group is n after the vehicle nodes are independently grouped, the method comprises the following steps of
Wherein N is the number of vehicle nodes;
3-1-2, randomly selecting an integer in the interval [1, k ] for each vehicle node, and selecting the vehicle nodes with the same integer to be grouped;
3-2, randomly selecting a backoff counter value by each vehicle node;
3-3, according to the grouping of the vehicle nodes in the step 3-1 and the backoff counter value of each vehicle node in the step 3-2, each vehicle node sequentially executes a backoff process and accesses a channel;
and 4, broadcasting the beacon of the vehicle node, thereby finishing the wireless vehicle-mounted network channel access.
2. The wireless vehicle-mounted network channel access method according to claim 1, wherein the step 3-2 of randomly selecting the backoff counter value by each vehicle node specifically comprises:
step 3-2-1, determining a minimum competition window array CWMin [ k ] and a maximum competition window array CWMax [ k ];
step 3-2-2, forming a contention window pair (CWmin [ i ], CWmax [ i ]) by using the ith minimum contention window CWmin [ i ] and the ith maximum contention window CWmax [ i ] corresponding to the minimum contention window array CWmin [ k ] and the maximum contention window array CWmax [ k ]; wherein i is an integer, i belongs to [1, k ];
3-2-3, according to the randomly selected integer of each vehicle node in the step 3-1-2, each vehicle node selects a corresponding competition window pair (CWMin, CWMax);
and 3-2-4, randomly selecting one value of each vehicle node in the range of the corresponding competition window pair (CWMin, CWMax) as the backoff counter value of the vehicle node.
3. The wireless vehicular network channel access method of claim 2, wherein the minimum contention window array CWmin [ k ] is:
CWmin[k]＝{0,ε+1,2ε+2,…,(k-1)(ε+1)}
the maximum contention window array CWmax [ k ] is:
CWmax[k]＝{ε,2ε+1,3ε+2,…,k(ε+1)-1}
wherein ε is the difference between CWmax and CWmin in the contention window pair (CWmin, CWmax),
wherein,
σ is the duration of the idle slot, TcIs the transit time at which the collision occurred; t isc＝Th+ L/R + EIFS, where L is the packet length, R is the data rate, ThEIFS is an extended frame interval for the preamble and header duration of PLCP.
4. The wireless vehicular network channel access method according to claim 3, wherein in step 3-3, according to the grouping of the vehicle nodes in step 3-1 and the backoff counter value of each vehicle node in step 3-2, each vehicle node sequentially executes a backoff process and accesses the channel, specifically:
firstly, aiming at vehicle node groups, according to the sequence of integers randomly selected by each group of vehicle nodes in the interval [1, k ] from small to large, each group of vehicle nodes sequentially execute a back-off process and access a channel;
and secondly, aiming at the positions among the vehicle nodes in each group of vehicle nodes, each vehicle node sequentially executes a backoff process and accesses a channel according to the sequence from small to large of the backoff counter value selected by each vehicle node.
5. The wireless vehicular networking channel access method of claim 1, wherein the broadcasting of the beacon of the vehicle node in step 4 is based on an 802.11p MAC protocol.
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