CN111263318B - Broadcast transmission fairness control algorithm for cooperative vehicle security system - Google Patents
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Abstract
The invention provides a broadcast transmission fairness control algorithm for a cooperative vehicle security system, which comprises the following steps: the discovery of the vulnerable node, the announcement of the vulnerable node and the transmission improvement of the vulnerable node. The invention has the beneficial effects that: the invention discovers the broadcast fairness problem of the vehicle networking cooperative vehicle safety system through experiments, weak nodes with abnormal transmission may exist in the network, and the packet delivery rate of the weak nodes is obviously lower than that of general nodes; secondly, a new broadcast grouping structure comprising a sending rate domain and a weak address domain is designed, a feedback control-based weak node discovery, announcement and transmission improvement algorithm is provided, and finally, experiments verify that the new algorithm can effectively eliminate the weak nodes and improve the transmission fairness of each node of the internet of vehicles.
Description
Technical Field
The invention relates to the technical field of broadcast transmission fairness control algorithms in vehicle safety systems, in particular to a broadcast transmission fairness control algorithm for a cooperative vehicle safety system.
Background
A Cooperative Vehicle Safety System (CVSS) periodically broadcasts a single-hop data packet containing basic state information such as vehicle speed, acceleration, position and the like, so that the positions of neighbor vehicles are tracked, potential traffic hazards are detected, and a warning is given in time to avoid collision among the vehicles. Thus, CVSS plays an important role in internet of vehicles security applications.
The transmission period setting of the broadcast packet directly affects the performance of the CVSS. On one hand, if the sending period is set too large (the sending rate is too small), the updating of the safety prompt cannot keep up with the dynamic change of the vehicle running condition, and the safety alarm mechanism cannot play a preset role. On the other hand, if the transmission cycle is set too small (the transmission rate is too large), collisions between data packets will increase, resulting in a decrease in the acceptance rate of data packets. Since vehicle tracking relies on periodically broadcast data packets, channel congestion can severely impact the tracking performance of the CVSS, eventually causing the safety warning mechanism to fail.
In order to solve the above problems, it is necessary to study how to reasonably adjust the transmission rate of the broadcast packet of the vehicle, so as to prevent the waste caused by the idle channel and avoid the transmission failure caused by the congestion of the channel. In order to optimize the channel resources of the internet of vehicles, a research scheme considers that different broadcast sending rates are set for vehicles with different safety requirements, the channel resource allocation is optimized, and the channel utilization rate is reasonably improved.
However, current research mainly focuses on the overall performance of the car networking broadcast system, such as the overall network delivery arrival rate of broadcast packets and the overall network message generation rate, and does not consider the specific performance difference of each node in the car networking after configuring different broadcast transmission rates. In other words, when nodes in the car networking broadcast messages at different rates, the problem is not sufficiently studied whether the nodes affect each other and how much the nodes affect each other, and whether the receiver can receive the data of the source node at the rate set by the sender.
Disclosure of Invention
The invention aims to provide a broadcast transmission fairness control algorithm in a cooperative vehicle safety system, which can improve the packet delivery rate of vulnerable nodes. Aiming at the broadcast fairness problem of the vehicle networking cooperative vehicle safety system, weak nodes with abnormal transmission may exist in the network; a new broadcast grouping structure comprising a sending rate domain and a disadvantaged address domain is designed, a feedback control-based disadvantaged node discovery, announcement and transmission improvement algorithm is provided, and finally, experiments verify that the new algorithm can effectively eliminate disadvantaged nodes and improve the transmission fairness of each node of the internet of vehicles. Broadcast transmission fairness control algorithm for cooperative vehicle safety system
The invention is realized by the following measures: a collaborative vehicle security system broadcast transmission fairness control algorithm, wherein the control algorithm comprises the steps of:
s1: and (3) discovering the vulnerable nodes: since the packet is lost due to the transmission collision, and a part of packets sent by the packet are not correctly received, which finally causes the appearance of the vulnerable node, since the transmission vulnerable node may exist in the car networking, firstly, the problem of how to find the vulnerable node is solved, and in the broadcast packet structure of the invention, a "sending rate field" (1 byte) and a "vulnerable address field" (4 bytes) are respectively added, as shown in fig. 3;
combining two value fields added in the broadcast packet, the discovery steps of the disadvantaged node are as follows:
(1) before transmitting the broadcast packet, the transmitting node i fills the current transmission rate R in the "transmission rate field" of the packeti_ref；
(2) After receiving the broadcast of the node i, the receiving node j reads the sending rate set by the source end i in the sending rate domain, and at the same time, regularly counts the actual receiving rate R of the packets from the node ii_sta；
(3) If R isi_sta/Ri_refIf the result is greater than the set threshold th, the node i can be judged as a weak node;
s2: and (3) notification of the disadvantaged node:
once the receiver j determines that the node i is a disadvantaged node, the specific process steps are as follows:
(1) the receiving node j fills the IP address of the node i in the weak address field in the self broadcast message and sends the broadcast;
(2) after the sending node i receives the broadcast of j, if the IP address of the sending node i exists in the weak address field, the sending node i can be confirmed to be a weak node, and the problem occurs in the broadcast transmission of the sending node i;
s3: transmission improvement of vulnerable nodes:
the transmission abnormality of the vulnerable node is caused by the fact that the packet sent by the vulnerable node collides with the packet sent by other nodes for many times, and the receiver cannot correctly receive the data because the wireless signals are mutually overlapped and interfered, according to the five steps of the step S1 and the step S2, if the sending node i confirms that the sending node i is the vulnerable node, measures need to be taken, and the number of times of collision in transmission is reduced as much as possible;
the factors influencing the grouping collision times of the vulnerable nodes are analyzed, so that a transmission improvement strategy is proposed in a targeted manner.
The specific implementation process is as follows:
considering first the case where node i successfully sends a broadcast packet, since the broadcast application has no ACK acknowledgement frame mechanism, the time T for sending a broadcast frame may be written as:
T＝tDIFS+tBO+tData+tSIFS (1)
wherein, tDataTime of transmission of a frame, tBOFor BackOff time, tDIFSFor distributed interframe space time, tSIFSIs a short inter-frame gap time. The units of the above time are seconds.
According to tDataIs defined as
Wherein, R is the sending rate and the unit is Mb/s; l is the broadcast packet length, in bytes (B).
Substituting equation (2) into equation (1), there are
tBOAssociated only with contention window values, taken generally
And CWmin、slot、tDIFSAnd tSIFSAll are fixed parameters of the MAC layer, so the sum of the first 3 terms of the formula can be recorded as a constant coefficient t0Then there is
Considering the number of collisions m (t) within time [0, t ], assuming that m (t) obeys a poisson distribution with a rate λ, a mathematical expectation is taken for m (t),
E[M(t)]＝λt
according to the property of poisson distribution, there are
Wherein, N is the number of nodes in the network, eta is the collision probability, T is the time (unit: second) for sending a broadcast frame, and L is the length (unit: byte B) of the broadcast packet;
according to equation (5), the mathematical expectation of the number of collisions occurring M (t) within the time [0, t ] can be written as
For the numerator denominator of the expression on the right side of formula (6) to be simultaneously divided by L, have
Wherein the collision probability eta only matches the node number N and the initial competition window CWminAnd the maximum retransmission time m, and when the three physical quantities are determined, the collision probability eta can be regarded as a constant.
As can be seen from equation (7), when the other physical quantity is constant, the smaller the length L of the broadcast packet, the smaller the number of collisions per unit time. Accordingly, the length of the broadcast packet for a particular transmission disadvantaged node is reduced to minimize the chance of the node colliding with other nodes when transmitting packets.
However, the length L of the broadcast packet is not smaller, the better, firstly, the secure broadcast packet contains basic state information such as vehicle speed, acceleration, position, etc., it is impossible to compress the packet length at will, secondly, the broadcast packet on the application layer will be encapsulated layer by layer on the network layer and the MAC layer, the header information of each layer is inevitably added, considering that the IP header length of the network layer is 20 bytes, the header length of the MAC layer of the 802.11 wireless local area network is 30B, the transmission of the header and the header will occupy channel resources, if the broadcast content as the application load is too short, after each broadcast message is encapsulated on the MAC layer, the effective information will be very small, only the transmission resources will be wasted, and the transmission efficiency of the node will become low.
Therefore, assuming that the general length of the broadcast packet is L, the broadcast packet of the transmitting disadvantaged node may be set to k × L. k is a proportionality coefficient, and is generally 0.8-0.6.
The core flow of the broadcast transmission fairness control algorithm is as follows:
fairness problem proposition
The experimental environment is as follows: 100 vehicle nodes are arranged in the internet of vehicles. In order to avoid interference, 1 monitoring node which does not send broadcast is arranged, and other nodes are all broadcast nodes. A node with a sending rate of 12/s is defined as a high-speed node, and a node with a sending rate of 4/s is defined as a low-speed node. The corresponding transmit power is set to ensure that each vehicle is within transmission range of each other. The duration of the experiment was 10 seconds. The broadcast packet length L is 500B.
Experiment 1 was divided into three cases:
case a: 99 high-speed nodes +1 monitoring node
Case B: 20 low speed +79 high speed nodes +1 monitoring node
Case C: 99 low speed +1 listening nodes
Packet delivery of three cases of whole-network broadcast packets is shown in figure 1.
As shown in fig. 1, when all high-speed broadcast nodes are in the car networking, the channel competition is intense, and the packet delivery rate is only about 85%. When partial nodes reduce the sending rate according to the self safety requirement, the delivery rate is increased to 91%. If all nodes adopt low-rate transmission, the delivery rate can reach 98%. Therefore, according to the traffic safety requirements of different vehicles, different broadcasting rates are set for different vehicle nodes, channel capacity resources can be reasonably configured, and the utilization rate of channels is effectively improved.
However, for case B, fig. 1 only counts the broadcast performance of the whole network, and does not study the situation of each node. The following specific statistical case B represents packet delivery of the node, as shown in fig. 2.
As can be seen from fig. 2, when there are multiple rate nodes in the same network, unfairness problems may occur in transmission. On the whole, the differentiated node sending rate ensures reasonable distribution of channel resources, the system delivery success rate is higher, but individual nodes (such as the node 9) have transmission bottleneck phenomenon, and the packet delivery success rate is only about 70%.
Comparing fig. 1 and fig. 2, it is explained that the packet delivery rate of the entire network cannot represent the broadcast transmission/reception situation of all nodes. When each terminal of the Internet of vehicles broadcasts packets according to different sending rates, some weak nodes exist, the delivery rate is far lower than the average value, and therefore certain potential safety hazards are brought to driving safety depending on CVSS. Therefore, there is a need to investigate the fairness of vehicle networking in conjunction with vehicle security system broadcasting.
Experimental verification of the improved algorithm:
the experimental environment is as above:
according to the result of case B of experiment 1, the No. 9 low speed node transmits an anomaly. Therefore, according to the feedback control mechanism, the algorithm automatically sets the broadcast packet length of the transmission disadvantaged node No. 9 to 80% of the initial value, i.e., l (t) × 500.8 ═ 400B, and other experimental conditions are not changed. The experimental node performance before and after the improvement is shown in fig. 4, and the specific increase of the number of transmission packets is shown in fig. 5.
according to the result of experiment 3, the numbers 6, 9 and 16 low-speed nodes transmit abnormality. It can be seen that as the network load increases, channel contention and collisions are exacerbated, and the number of vulnerable nodes also begins to increase. Therefore, according to the feedback control mechanism, the algorithm automatically sets the broadcast packet length of the 3 vulnerable nodes to 80% of the initial value, i.e., l (t) 500 × 0.8 — 400B, and other experimental conditions are not changed. The experimental node performance before and after improvement is shown in fig. 6. The invention has the beneficial effects that: the invention discovers the broadcast fairness problem of the vehicle networking cooperative vehicle safety system through experiments, and weak nodes with abnormal transmission may exist in the network; secondly, a new broadcast grouping structure comprising a sending rate domain and a weak address domain is designed, a feedback control-based weak node discovery, announcement and transmission improvement algorithm is provided, and finally, experiments verify that the new algorithm can effectively eliminate the weak nodes and improve the transmission fairness of each node of the internet of vehicles.
Drawings
Fig. 1 is a graph showing the comparison of the delivery rate of the whole network broadcast packet in the three cases of experiment 1 of the present invention.
Fig. 2 is a diagram showing a comparison of packet delivery rates of respective nodes in case B of experiment 1 of the present invention.
Fig. 3 is a diagram illustrating a broadcast packet structure according to the present invention.
FIG. 4 is a graph showing the comparison of delivery rates before and after the transmission improvement algorithm used in experiment 2 of the present invention.
Fig. 5 is a diagram showing the comparison of the number of packets received by node 9 before and after the improvement of experiment 2 of the present invention.
FIG. 6 is a comparative illustration of delivery rates before and after the transmission improvement algorithm used in experiment 3 of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. Of course, the specific embodiments described herein are merely illustrative of the invention and are not intended to be limiting.
Referring to fig. 1 to 6, the present invention provides a technical solution of a control algorithm for controlling fairness of broadcast transmission in cooperation with a vehicle security system, wherein the control algorithm includes the following steps:
s1: and (3) discovering the vulnerable nodes: since the packet is lost due to the transmission collision, and a part of packets sent by the packet are not correctly received, which finally causes the appearance of the vulnerable node, since the transmission vulnerable node may exist in the car networking, firstly, the problem of how to find the vulnerable node is solved, and in the broadcast packet structure of the invention, a "sending rate field" (1 byte) and a "vulnerable address field" (4 bytes) are respectively added, as shown in fig. 3;
combining two value fields added in the broadcast, the weak node discovery steps are as follows:
(1) before transmitting the broadcast packet, the transmitting node i fills the current transmission rate R in the "transmission rate field" of the packeti_ref；
(2) After receiving the broadcast of the node i, the receiving node j reads the sending rate set by the source end i in the sending rate domain, and at the same time, regularly counts the actual receiving rate R of the packets from the node ii_sta；
(3) If R isi_sta/Ri_refIf the result is greater than the set threshold th, the node i can be judged as a weak node;
s2: and (3) notification of the disadvantaged node:
once the receiver j determines that the node i is a disadvantaged node, the specific process steps are as follows:
(1) the receiving node j fills the IP address of the node i in the weak address field in the self broadcast message and sends the broadcast;
(2) after the sending node i receives the broadcast of j, if the IP address of the sending node i exists in the weak address field, the sending node i can be confirmed to be a weak node, and the problem occurs in the broadcast transmission of the sending node i;
s3: transmission improvement of vulnerable nodes:
the transmission abnormality of the vulnerable node is caused by the fact that the packet sent by the vulnerable node collides with the packet sent by other nodes for many times, and the receiver cannot correctly receive the data because the wireless signals are mutually overlapped and interfered, according to the five steps of the step S1 and the step S2, if the sending node i confirms that the sending node i is the vulnerable node, measures need to be taken, and the number of times of collision in transmission is reduced as much as possible;
the factors influencing the grouping collision times of the vulnerable nodes are analyzed, so that a transmission improvement strategy is proposed in a targeted manner.
The specific implementation process is as follows:
considering first the case where node i successfully sends a broadcast packet, since the broadcast application has no ACK acknowledgement frame mechanism, the time T for sending a broadcast frame may be written as:
T＝tDIFS+tBO+tData+tSIFS (1)
wherein, tDataTime of transmission of a frame, tBOFor BackOff time, tDIFSFor distributed interframe space time, tSIFSIs a short inter-frame gap time. The units of the above time are seconds.
According to tDataIs defined as
Wherein, R is the sending rate and the unit is Mb/s; l is the broadcast packet length, in bytes (B).
Substituting equation (2) into equation (1), there are
tBOAssociated only with contention window values, taken generally
And CWmin、slot、tDIFSAnd tSIFSAll are fixed parameters of the MAC layer, so the sum of the first 3 terms of the formula can be recorded as a constant coefficient t0Then there is
Considering the number of collisions m (t) within time [0, t ], assuming that m (t) obeys a poisson distribution with a rate λ, a mathematical expectation is taken for m (t),
E[M(t)]＝λt
according to the property of poisson distribution, there are
Wherein, N is the number of nodes in the network, eta is the collision probability, T is the time (unit: second) for sending a broadcast frame, and L is the length (unit: byte B) of the broadcast packet;
according to equation (5), the mathematical expectation of the number of collisions occurring M (t) within the time [0, t ] can be written as
For the numerator denominator of the expression on the right side of formula (6) to be simultaneously divided by L, have
Wherein the collision probability eta only matches the node number N and the initial competition window CWminAnd the maximum retransmission time m, and when the three physical quantities are determined, the collision probability eta can be regarded as a constant.
As can be seen from equation (7), when the other physical quantity is constant, the smaller the length L of the broadcast packet, the smaller the number of collisions per unit time. Accordingly, the length of the broadcast packet for a particular transmission disadvantaged node is reduced to minimize the chance of the node colliding with other nodes when transmitting packets.
However, the length L of the broadcast packet is not smaller, the better, firstly, the secure broadcast packet contains basic state information such as vehicle speed, acceleration, position, etc., it is impossible to compress the packet length at will, secondly, the broadcast packet on the application layer will be encapsulated layer by layer on the network layer and the MAC layer, the header information of each layer is inevitably added, considering that the IP header length of the network layer is 20 bytes, the header length of the MAC layer of the 802.11 wireless local area network is 30B, the transmission of the header and the header will occupy channel resources, if the broadcast content as the application load is too short, after each broadcast message is encapsulated on the MAC layer, the effective information will be very small, only the transmission resources will be wasted, and the transmission efficiency of the node will become low.
Therefore, assuming that the general length of the broadcast packet is L, the broadcast packet of the transmitting disadvantaged node may be set to k × L. k is a proportionality coefficient, and is generally 0.8-0.6.
The core flow of the broadcast transmission fairness control algorithm is as follows:
discover phase// discovery
th＝80％
node j receive packets from node i
read Ri_ref
calculate Ri_sta
If(Ri_sta/Ri_ref>th){do nothing}
If(Ri_sta/Ri_ref≦th){enter Announcement phase；
enter Transmission improvement；
}
Annuncement phase/Announcement
node j broadcast packet attach to node i IP address
node i confirm vsulnerable Transmission improvement phase// Transmission improvement
node i set L(t)＝k*L。
Fairness problem proposition
The experimental environment is as follows: 100 vehicle nodes are arranged in the internet of vehicles. In order to avoid interference, 1 monitoring node which does not send broadcast is set, other nodes are all broadcast nodes, a node with a sending rate of 12/s is defined as a high-speed node, a node with a sending rate of 4/s is defined as a low-speed node, corresponding transmitting power is set, each vehicle is guaranteed to be within a transmission range of each other, the experimental time length is 10 seconds, and the broadcast packet length L is 500B.
Experiment 1 was divided into three cases.
Case a: 99 high-speed nodes +1 monitoring node
Case B: 20 low speed +79 high speed nodes +1 monitoring node
Case C: 99 low speed +1 listening nodes
Packet delivery of three cases of whole-network broadcast packets is shown in figure 1.
As shown in fig. 1, when all high-speed broadcast nodes are in the car networking, the channel competition is intense, and the packet delivery rate is only about 85%. When the sending rate of part of nodes is reduced according to the self safety requirement, the delivery rate is increased to 91%, if all the nodes are sent at low rate, the delivery rate can reach 98%, and therefore different broadcasting rates are set for different vehicle nodes according to the traffic safety requirements of different vehicles, channel capacity resources can be reasonably configured, and the utilization rate of channels is effectively improved.
However, for case B, fig. 1 only counts the broadcast performance of the whole network, and does not study the situation of each node. The following specific statistical case B represents packet delivery of the node, as shown in fig. 2.
As can be seen from fig. 2, when there are multiple rate nodes in the same network, there may be an unfairness problem during transmission, and as a whole, differentiated node sending rates ensure reasonable allocation of channel resources, the system delivery success rate is relatively high, but individual nodes (e.g., node 9) have transmission bottleneck, and the packet delivery success rate is only about 70%.
Comparing fig. 1 and fig. 2, it is explained that the packet delivery rate of the entire network cannot represent the broadcast transmission/reception situation of all nodes. When each terminal of the Internet of vehicles broadcasts packets according to different sending rates, some weak nodes exist, the delivery rate is far lower than the average value, and therefore certain potential safety hazards are brought to driving safety depending on CVSS.
Experimental verification of the improved algorithm:
the experimental environment is as indicated above.
according to the result of case B of experiment 1, the No. 9 low speed node transmits an anomaly. Therefore, according to the feedback control mechanism, the algorithm automatically sets the broadcast packet length of the transmission disadvantaged node No. 9 to 80% of the initial value, i.e., l (t) × 500.8 ═ 400B, and other experimental conditions are not changed. The experimental node performance before and after the improvement is shown in fig. 4, and the specific increase of the number of transmission packets is shown in fig. 5.
according to the result of experiment 3, the numbers 6, 9 and 16 low-speed nodes transmit abnormality. It can be seen that as the network load increases, channel contention and collisions are exacerbated, and the number of vulnerable nodes also begins to increase. Therefore, according to the feedback control mechanism, the algorithm automatically sets the broadcast packet length of the 3 vulnerable nodes to 80% of the initial value, i.e., l (t) 500 × 0.8 — 400B, and other experimental conditions are not changed. The experimental node performance before and after improvement is shown in fig. 6.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.
Claims (1)
1. A coordinated vehicle security system broadcast transmission fairness control algorithm, the control algorithm comprising the steps of:
s1: and (3) discovering the vulnerable nodes:
(1) before transmitting the broadcast packet, the transmitting node i fills the current transmission rate R in the "transmission rate field" of the packeti_ref；
(2) After receiving the broadcast of the node i, the receiving node j reads the sending rate set by the source end i in the sending rate domain, and at the same time, regularly counts the actual receiving rate R of the packets from the node ii_sta；
(3) If R isi_sta/Ri_refIf the result is greater than the set threshold th, the node i can be judged as a weak node;
s2: and (3) notification of the disadvantaged node:
(1) the receiving node j fills the IP address of the node i in the weak address field in the self broadcast message and sends the broadcast;
(2) after the sending node i receives the broadcast of j, if the IP address of the sending node i exists in the weak address field, the sending node i can be confirmed to be a weak node, and the problem occurs in the broadcast transmission of the sending node i;
s3: transmission improvement of vulnerable nodes:
the transmission abnormality of the vulnerable node is caused by the fact that the packet sent by the vulnerable node collides with the packet sent by other nodes for many times, and the receiver cannot correctly receive the data because the wireless signals are mutually overlapped and interfered, according to the five steps of the step S1 and the step S2, if the sending node i confirms that the sending node i is the vulnerable node, measures need to be taken, and the number of times of collision in transmission is reduced as much as possible;
the specific implementation process is as follows:
considering first the case where node i successfully sends a broadcast packet, since the broadcast application has no ACK acknowledgement frame mechanism, the time T for sending a broadcast frame may be written as:
T＝tDIFS+tBO+tData+tSIFS (1)
wherein, tDataTime of transmission of a frame, tBOFor BackOff time, tDIFSFor distributed interframe space time, tSIFSThe unit of the time is seconds;
according to tDataIs defined as
Wherein, R is the sending rate and the unit Mb/s; l is the broadcast packet length, unit byte (B);
substituting equation (2) into equation (1), there are
tBOAssociated only with contention window values, taken generally
And CWmin、slot、tDIFSAnd tSIFSAre all fixed parameters of the MAC layer,so the sum of the first 3 terms of the formula can be recorded as constant coefficient t0Then there is
Considering the number of collisions m (t) within time [0, t ], assuming that m (t) obeys a poisson distribution with a rate λ, a mathematical expectation is taken for m (t),
E[M(t)]＝λt
according to the property of poisson distribution, there are
Wherein, N is the number of nodes in the network, eta is the collision probability, T is the time for sending a broadcast frame, and L is the length of a broadcast packet;
according to equation (5), the mathematical expectation of the number of collisions occurring M (t) within the time [0, t ] can be written as
For the numerator denominator of the expression on the right side of formula (6) to be simultaneously divided by L, have
Wherein the collision probability eta only matches the node number N and the initial competition window CWminAnd the maximum retransmission time m, and when the three physical quantities are determined, the collision probability eta can be regarded as a constant.
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| CN101946471A (en) * | 2008-02-14 | 2011-01-12 | 高通股份有限公司 | Traffic management for multi-hop wireless communication |
| CN102362541A (en) * | 2009-03-25 | 2012-02-22 | 株式会社山武 | Wireless communication system and parent node search method |
| CN109150346A (en) * | 2018-11-01 | 2019-01-04 | 南通大学 | A kind of method that car networking broadcast background flows down transmission of video |
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