CN112995953A - Method and system for reducing workshop communication time delay based on random linear network coding - Google Patents
Method and system for reducing workshop communication time delay based on random linear network coding Download PDFInfo
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Abstract
The invention discloses a method and a system for reducing workshop communication time delay based on random linear network coding, wherein the method comprises the following steps: establishing a workshop communication scene; carrying out random linear network coding on an original data packet, and broadcasting the coded data packet; carrying out random linear network coding on the coded data packet again and sending the coded data packet to a target vehicle; the target vehicle feeds back the state information; the target vehicle decodes the received data packet subjected to secondary coding to obtain an original data packet; and the resource vehicle updates the sending queue and returns to the encoding step, and the process is circulated until all data packets corresponding to the required information are obtained through decoding. The system comprises: the device comprises a request module, a primary coding module, a secondary coding module, a feedback module, a decoding module and a circulation module. By using the method and the device, the transmission time delay of the workshop communication can be shortened. The method and the system for reducing the time delay of the workshop communication based on the random linear network coding can be widely applied to the time delay field of the workshop communication.
Description
Technical Field
The invention relates to the field of time delay of workshop communication, in particular to a method and a system for reducing workshop communication time delay based on random linear network coding.
Background
With the development of intelligent transportation systems and internet of things technologies, car networking is widely regarded as a typical application, an important component of which is Vehicle-to-Vehicle (V2V), and V2V uses vehicles as information nodes in a network, and when information required by one Vehicle is owned by one or more nearby vehicles, a connection can be established for information transmission. However, when the vehicle is used as an information node, the communication range of the vehicle is limited, and the vehicle is in a high-speed driving state during communication, and the reason that the time for stably and continuously transmitting information in the V2V network is short is all that needs to ensure that the information transmission between the vehicles can be completed in a short stable communication time period. Therefore, reducing the time delay of the vehicle-to-vehicle communication becomes an urgent problem to be solved in the V2V network.
Disclosure of Invention
In order to solve the above technical problems, an object of the present invention is to provide a method and a system for reducing inter-vehicle communication delay based on random linear network coding, so as to reduce inter-vehicle communication delay.
The first technical scheme adopted by the invention is as follows: a method for reducing workshop communication time delay based on random linear network coding comprises the following steps:
s1, responding to the request of the target vehicle, and establishing a vehicle-to-vehicle communication scene;
s2, M resource vehicles in a workshop communication scene perform random linear network coding on M original data packets in a sending queue, and broadcast the coded data packets to intermediate vehicles;
s3, the n intermediate vehicles carry out random linear network coding on the coded data packet again, and send the data packet after secondary coding to the target vehicle;
s4, the target vehicle takes the number of the received secondary coded data packets as state information i, and feeds the state information i back to the intermediate vehicle and the resource vehicle;
s5, judging that the number of the state information i is equal to M, and decoding the received secondary coded data packets by the target vehicle to obtain M original data packets;
and S6, updating the sending queue by the resource vehicle and returning to the step S2, and circulating until the target vehicle decodes to obtain all data packets corresponding to the required information, and finishing the information transmission of the current workshop communication.
Further, still include:
and acquiring the time delay probability distribution of the workshop communication scene and calculating the time delay mean value.
Further, the step of establishing a vehicle-to-vehicle communication scenario in response to the request of the target vehicle specifically includes:
the target vehicle is used as an information sink node, the resource vehicle is used as an information source node, and the intermediate vehicle is used as an intermediate node;
and constructing a multi-source single-sink wireless broadcast network as a workshop communication scene.
Further, the target vehicle feeds back the state information i to the intermediate vehicle and the resource vehicle by using the number of the received secondary-coded data packets as the state information i, and the step specifically includes:
if the feedback information i received by the intermediate nodes is less than or equal to M-n, the n intermediate nodes continuously encode local data packets and send the data packets to the sink node;
if the feedback information i received by the intermediate nodes is larger than M-n, the n- (M-i) intermediate nodes farthest from the sink node do not participate in the transmission work any more, and the rest M-i intermediate nodes continue to participate in the encoding and transmission work of the data packet.
Further, the step of obtaining the time delay probability distribution of the workshop communication scene specifically includes:
calculating the receiving probability according to the state information and obtaining a transition matrix P according to the receiving probabilityT；
According to the transferMatrix PTObtaining a state matrix S of the information sink nodes after t time slotst；
According to the state matrix StCalculating the time delay probability distribution of the workshop communication scene;
and obtaining a time delay mean value according to the time delay probability distribution of the workshop communication scene.
Further, the receiving probability is calculated according to the state information, and a transition matrix P is obtained according to the receiving probabilityTThis step, in particular, comprises:
judging that i is more than or equal to 0 and is less than or equal to M-n of the state information;
reception probability P ═ P0 P1 ... Pn-1 Pn]1×(n+1)Wherein, in the step (A),
judging that i is more than or equal to M-1 and the state information M-n is more than or equal to M-1;
reception probability P ═ P0′ P1′ ... PM′-i-1 P′M-i 0 0...]1×(n+1)，
Combining all P and P' to generate a transition matrix PT：
Further, the expression of the time delay mean value is as follows:
E(t)＝∑t×Pt
in the above formula, e (t) represents a mean time delay value, t represents a time delay passing through a certain time slot, and Pt represents a probability that the time delay is t.
Further, still include:
the minimum size of the code field is dynamically selected according to the number n of intermediate vehicles.
Further, the step of dynamically selecting the minimum size of the code field according to the number of intermediate vehicles is characterized in that:
calculating the intermediate vehicle n ∈ [1,9 ]]Minimum generation probability P corresponding to coding field size q of 2 to 256min；
Each group of [ n, q, P ]min]Uploading to a system;
uploading the number of intermediate vehicles and the required minimum probability in a workshop communication scene to a system;
the system selects the minimum coding domain size meeting the requirement, and sends the minimum coding domain size to a target vehicle, an intermediate vehicle and a resource vehicle in a workshop communication scene;
the encoding and decoding operations are performed on a coded field of this size.
The second technical scheme adopted by the invention is as follows: the system for reducing the communication time delay of the workshop based on the random linear network coding comprises the following modules:
the request module responds to a request of a target vehicle and establishes a workshop communication scene;
the primary coding module is used for performing random linear network coding on the M original data packets in the sending queue by the M resource vehicles in a workshop communication scene and broadcasting the coded data packets to the intermediate vehicle;
the secondary coding module is used for carrying out random linear network coding on the coded data packet again by the n intermediate vehicles and sending the data packet subjected to secondary coding to the target vehicle;
the feedback module is used for feeding the state information i back to the intermediate vehicle and the resource vehicle by taking the number of the received secondary coded data packets as the state information i by the target vehicle;
the decoding module is used for judging that the number of the state information i is equal to M, and the target vehicle decodes the received data packets subjected to secondary coding to obtain M original data packets;
and the circulation module is used for updating the sending queue by the resource vehicle and returning to the step S2, and circulating until the target vehicle decodes to obtain all data packets corresponding to the required information, and the information transmission of the current workshop communication is finished.
The method and the system have the beneficial effects that: the random linear network coding is applied to a workshop communication scene, the transmission time delay of workshop communication is shortened, and the minimum coding domain size of vehicles for random linear network coding is dynamically selected according to the number of intermediate vehicles, so that the transmission time delay of workshop communication is shortened.
Drawings
FIG. 1 is a flow chart of the steps of the method for reducing the time delay of communication between vehicles based on random linear network coding according to the present invention;
FIG. 2 is a flow chart of the method for reducing the time delay of the communication between the vehicles based on the random linear network coding according to the present invention;
FIG. 3 is a block diagram of a system for reducing communication delay between vehicles based on random linear network coding according to the present invention;
FIG. 4 is a schematic diagram of a vehicle-to-vehicle communication scenario in accordance with an embodiment of the present invention;
FIG. 5 is a diagram of a multi-source single-sink wireless broadcast network corresponding to a shop communication scenario in accordance with an embodiment of the present invention;
fig. 6 is a schematic diagram of a state change process of a target vehicle when there are two intermediate vehicles in the system according to the embodiment of the present invention.
Detailed Description
The invention is described in further detail below with reference to the figures and the specific embodiments. The step numbers in the following embodiments are provided only for convenience of illustration, the order between the steps is not limited at all, and the execution order of each step in the embodiments can be adapted according to the understanding of those skilled in the art.
Referring to fig. 1 and 3, the present invention provides a method for reducing inter-vehicle communication delay based on random linear network coding, which comprises the following steps:
s1, responding to the request of the target vehicle, and establishing a vehicle-to-vehicle communication scene;
s2, M resource vehicles in a workshop communication scene perform random linear network coding on M original data packets in a sending queue, and broadcast the coded data packets to intermediate vehicles;
s3, the n intermediate vehicles carry out random linear network coding on the coded data packet again, and send the data packet after secondary coding to the target vehicle;
specifically, when there are two intermediate vehicles, the state change process of the target vehicle refers to fig. 6.
S4, the target vehicle takes the number of the received secondary coded data packets as state information i, and feeds the state information i back to the intermediate vehicle and the resource vehicle;
s5, judging that the number of the state information i is equal to M, and decoding the received secondary coded data packets by the target vehicle to obtain M original data packets;
and S6, updating the sending queue by the resource vehicle and returning to the step S2, and circulating until the target vehicle decodes to obtain all data packets corresponding to the required information, and finishing the information transmission of the current workshop communication.
Further as a preferred embodiment of the method, the method further comprises:
and acquiring the time delay probability distribution of the workshop communication scene and calculating the time delay mean value.
Further as a preferred embodiment of the method, the step of establishing a vehicle-to-vehicle communication scenario in response to a request from a target vehicle specifically includes:
the target vehicle is used as an information sink node, the resource vehicle is used as an information source node, and the intermediate vehicle is used as an intermediate node;
and constructing a multi-source single-sink wireless broadcast network as a workshop communication scene.
In particular, a plant communication scenario refers to fig. 4, and a multi-source single-sink wireless broadcast network refers to fig. 5.
As a further preferred embodiment of the method, the target vehicle uses the number of the received secondary-coded data packets as the state information i, and feeds back the state information i to the intermediate vehicle and the resource vehicle, which specifically includes:
if the feedback information i received by the intermediate nodes is less than or equal to M-n, the n intermediate nodes continuously encode local data packets and send the data packets to the sink node;
if the feedback information i received by the intermediate nodes is larger than M-n, the n- (M-i) intermediate nodes farthest from the sink node do not participate in the transmission work any more, and the rest M-i intermediate nodes continue to participate in the encoding and transmission work of the data packet.
Carrying out basic analysis on the effectiveness of generating a data packet by an intermediate node and the probability of receiving the data packet by an information sink node in a workshop communication scene:
1) in each round of transmission, i.e., in the transmission of M original packets at S2-S5, the state of the sink node refers to the number of linearly independent encoded packets that have been received by the sink node. If i linearly independent encoded packets have been received, the state of the sink node is i. After a time slot is passed from the intermediate node to the sink node, the sink node receives k (k is more than 0 and less than or equal to n) linearly independent data packets, and the state of the sink node is changed to i + k. When the state of the sink node is M, the state saturation will not change any more. The saturation state of the sink node is M, so that the maximum number of steps of the state transition is n only when the state i of the sink node is not more than M-n, and the maximum number of steps of the state transition is M-i when the state i of the sink node is more than M-n, at this time, if n intermediate nodes all participate in recoding, at least n- (M-i) recoding data packets which are linearly related are necessarily generated, and the n- (M-i) data packets can also be called as redundant data packets, so that when i is more than M-n, only M-i intermediate nodes are adopted in the scheme to participate in recoding work.
And measuring time delay by using the number of time slots, and defining that each source node or intermediate node completes one time of encoding and data packet transmission in one time slot.
2) Each source node applies random linear network coding to code M original data packets in a sending queue, and the coded data packets are as follows:
P(A1)＝a1(1)r1+a1(2)r2+a1(3)r3+…+a1(M)rM
P(A2)＝a2(1)r1+a2(2)r2+a2(3)r3+…+a2(M)rM
……
P(Am)＝am(1)r1+am(2)r2+am(3)r3+…+am(M)rM
wherein P (A)α) Is composed of a source node AαTransmitted encoded data packet, rβIs the beta-th original data packet in the transmission queue, aα(β) is the coding coefficient of the β -th original packet in the transmit queue at the α -th source node, where α ∈ [1, m]，β∈[1,M]。
3) After a first time slot, each intermediate node has an opportunity to receive the coded data packet broadcast by each information source node, so that even if packet loss exists in a wireless channel, the intermediate node receives at least one coded data packet with a maximum probability, and the u (u is more than or equal to 1 and less than or equal to m) coded data packets are received by each intermediate node after the first time slot, and u of different intermediate nodes may be different. The intermediate node recodes the u coded data packets received by the intermediate node and sends the encoded data packets to the sink node.
4) When the feedback information i received by the intermediate node is less than or equal to M-n, the recoded data packet sent to the sink node can be written in a matrix form as follows:
wherein P (C)γ) Is an intermediate node CγTransmitted re-encoded data packet, cγ(beta) is the coding coefficient of the gamma intermediate node after recoding the beta original data packet, which is called Cn×MIs a re-encoding coefficient matrix, RM×1Is a matrix of primitive packets in which γ ∈ [1, n ]]，β∈[1,M]。
When the feedback information i received by the intermediate node is larger than M-n, the recoding data packet sent to the sink node is written into a matrix form as follows:
wherein P (C)γ) Is an intermediate node CγTransmitted re-encoded data packet, C(M-i)×MFor re-encoding the coefficient matrix, RM×1Is a matrix of original packets, where gamma ∈ [1, M-i ]]。
The i linearly independent data packets that have been received by the sink node can be written in matrix form as follows:
wherein P (B)δ) Is the received delta-th data packet, dδ(beta) is the coding coefficient for the beta-th original packet in the received delta-th packet, Di×MIs a coefficient matrix, R, of data packets received by the sink nodeM×1Is a matrix of primitive packets, where δ ∈ [1, i ]]，β∈[1,M]。
Let us assume that the sink node receives each re-encoded data packet P (C)γ) When i is less than or equal to M-n, the data packet received by the sink node can be represented in the form of a matrix as follows:
when i > M-n, the data packets that have been received by the sink node can be represented in the form of a matrix as follows:
where E is the coefficient matrix updated by the sink node after having received the data packet.
When the state i of the sink node is less than or equal to M-n, the probability that the n recoded data packets sent by the intermediate node of each time slot are all effective, namely the probability that the n recoded data packets are not only linearly independent of each other, but also linearly independent of the existing i data packets of the sink node
When the state of the information sink node is more than M-n, the probability that the M-i recoded data packets sent by the middle node of each time slot are all effective
Where i is the current state of the sink node; q is the coding domain size of the random linear network coding; m is the number of original packets, i.e. the length of the transmit queue; n is the number of intermediate nodes.
According to the obtained probability formula and simulation result that the data packet is valid, when the coding field size q reaches 256, namely the coding field is GF (256), the probability that all the data packets sent by the intermediate node are valid is close to 1 (approximately equal to 0.996) no matter what value the state i of the sink node takes.
From the above analysis, we choose the encoding field to be GF (256), where the packets received by the sink node are all valid packets, so that the state of the sink node changes only depending on the number of packets received per time slot, and the packet loss of the wireless channel between the intermediate node and the sink node conforms to bernoulli profile. Each time slot intermediate node sends n (or M-i) recoded data packets to the sink node, and according to Bernoulli distribution, the probability (receiving probability) that the sink node successfully receives k data packets in each time slot is as follows:
where k is the number of successfully received re-encoded data packets per time slot sink node, peThe packet loss rate of each wireless channel between the intermediate node and the sink node is the same, and the packet loss rates of the wireless channels are specified to be the same because the vehicles are in the same environment.
Further, as a preferred embodiment of the method, the step of obtaining the time delay probability distribution of the vehicle-to-vehicle communication scenario specifically includes:
calculating the receiving probability according to the state information and obtaining a transition matrix P according to the receiving probabilityT；
According to a transition matrix PTIs obtained byState matrix S of sink nodes after t time slotst；
According to the state matrix StCalculating the time delay probability distribution of the workshop communication scene;
and obtaining a time delay mean value according to the time delay probability distribution of the workshop communication scene.
In particular, the amount of the solvent to be used,
further, as a preferred embodiment of the method, the receiving probability is calculated according to the state information and the transition matrix P is obtained according to the receiving probabilityTThis step, in particular, comprises:
judging that i is more than or equal to 0 and is less than or equal to M-n of the state information;
reception probability P ═ P0 P1 … Pn-1 Pn]1×(n+1)Wherein, in the step (A),
judging that i is more than or equal to M-1 and the state information M-n is more than or equal to M-1;
reception probability P ═ P0′ P1′ … P′M-i-1 P′M-i 0 0…]1×(n+1)，
Combining all P and P' to generate a transition matrix PT。
Note that: p 'in different rows in transfer matrix'k′Are not equal, e.g. when the sink node state i is M-n +1, i.e. PTLine M-n + 2:
when the sink node state i ═ M-n + 2, i.e., PTLine M-n + 3:
each row of the transition matrix from top to bottom corresponds to the probability of transitioning a different number of steps when the state i of the sink node goes from 0 to M-1.
According to the transition matrix, a state matrix can be further obtained, namely a matrix formed by probabilities corresponding to all possible situations that the sink node is transitioned from the state at the previous moment to the state at the next moment through one time slot.
StIs the state matrix of the information sink node after t time slots, and S is solvedtIs a recursive process, in order to solve StWe first need to solve for St-1Therefore our solution process is from S1In which P isT(row1) refers to the first row of the transfer matrix.
Is the probability that the state of the sink node transitions from η to μ after the tth time slot, where η, μ ∈ [0, M-1 ∈ [ ]]，t∈[1,+∞)。
When the state of the sink node is shifted to μ ═ M after t time slots, it means that the sink node receives M linearly independent encoded data packets after t time slots, and the transmission of the first generation data packet is completed, and all μ ═ M in the state matrix corresponding to the time slot
The sum of (a) is the probability that the system completes the transmission task of a generation of data packets through t time slots, that is, the probability that the system time delay is t:
wherein eta is ∈ [0, M-1 ]]，t∈[1,+∞)。
Further as a preferred embodiment of the method, the expression of the time delay mean value is as follows:
E(t)＝∑t×Pt
in the above formula, E (t) represents the mean time delay, t represents the time delay passing through a certain time slot, PtRepresenting the probability of a time delay of t.
Further as a preferred embodiment of the method, the method further comprises the following steps:
the minimum size of the code field is dynamically selected according to the number n of intermediate vehicles.
As a further preferred embodiment of the method, the step of dynamically selecting the minimum size of the code field according to the number of intermediate vehicles is characterized in that:
calculating the intermediate vehicle n ∈ [1,9 ]]Minimum generation probability P corresponding to coding field size q of 2 to 256min；
Each group of [ n, q, P ]min]Uploading to a system;
uploading the number of intermediate vehicles and the required minimum probability in a workshop communication scene to a system;
the system selects the minimum coding domain size meeting the requirement, and sends the minimum coding domain size to a target vehicle, an intermediate vehicle and a resource vehicle in a workshop communication scene;
the encoding and decoding operations are performed on a coded field of this size.
Specifically, the larger the coding domain of the network coding is, the larger the overhead of coding and decoding and storage of the node is, and thus the communication delay is increased. The probability that all valid packets are generated when the sink node state i is M-n is lowest, which we refer to as the minimum generation probability. Therefore, as long as the minimum generation probability is high enough, no matter what state the sink node is, the intermediate node can generate valid data packets with a very high probability. And because the minimum probability is related to the number of intermediate nodes n, the method dynamically selects the minimum size of the coding field according to the number of intermediate nodes n.
As shown in fig. 2, the system for reducing the communication delay between vehicles based on random linear network coding includes:
the request module responds to a request of a target vehicle and establishes a workshop communication scene;
the primary coding module is used for performing random linear network coding on the M original data packets in the sending queue by the M resource vehicles in a workshop communication scene and broadcasting the coded data packets to the intermediate vehicle;
the secondary coding module is used for carrying out random linear network coding on the coded data packet again by the n intermediate vehicles and sending the data packet subjected to secondary coding to the target vehicle;
the feedback module is used for feeding the state information i back to the intermediate vehicle and the resource vehicle by taking the number of the received secondary coded data packets as the state information i by the target vehicle;
the decoding module is used for judging that the number of the state information i is equal to M, and the target vehicle decodes the received data packets subjected to secondary coding to obtain M original data packets;
and the circulation module is used for updating the sending queue by the resource vehicle and returning to the step S2, and circulating until the target vehicle decodes to obtain all data packets corresponding to the required information, and the information transmission of the current workshop communication is finished.
The contents in the above method embodiments are all applicable to the present system embodiment, the functions specifically implemented by the present system embodiment are the same as those in the above method embodiment, and the beneficial effects achieved by the present system embodiment are also the same as those achieved by the above method embodiment.
While the preferred embodiments of the present invention have been illustrated and described, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.
Claims (10)
1. The method for reducing the communication time delay of the workshop based on the random linear network coding is characterized by comprising the following steps of:
s1, responding to the request of the target vehicle, and establishing a vehicle-to-vehicle communication scene;
s2, M resource vehicles in a workshop communication scene perform random linear network coding on M original data packets in a sending queue, and broadcast the coded data packets to intermediate vehicles;
s3, the n intermediate vehicles carry out random linear network coding on the coded data packet again, and send the data packet after secondary coding to the target vehicle;
s4, the target vehicle takes the number of the received secondary coded data packets as state information i, and feeds the state information i back to the intermediate vehicle and the resource vehicle;
s5, judging that the number of the state information i is equal to M, and decoding the received secondary coded data packets by the target vehicle to obtain M original data packets;
and S6, updating the sending queue by the resource vehicle and returning to the step S2, and circulating until the target vehicle decodes to obtain all data packets corresponding to the required information, and finishing the information transmission of the current workshop communication.
2. The method for reducing the time delay of the communication between the vehicles based on the random linear network coding as claimed in claim 1, further comprising:
and acquiring the time delay probability distribution of the workshop communication scene and calculating the time delay mean value.
3. The method for reducing the time delay of vehicle-to-vehicle communication based on the random linear network coding as claimed in claim 2, wherein the step of establishing the vehicle-to-vehicle communication scenario in response to the request of the target vehicle specifically comprises:
the target vehicle is used as an information sink node, the resource vehicle is used as an information source node, and the intermediate vehicle is used as an intermediate node;
and constructing a multi-source single-sink wireless broadcast network as a workshop communication scene.
4. The method for reducing the time delay of vehicle-to-vehicle communication based on the random linear network coding as claimed in claim 3, wherein the target vehicle uses the number of the received secondary coded data packets as the status information i, and feeds the status information i back to the intermediate vehicle and the resource vehicle, which specifically includes:
if the feedback information i received by the intermediate nodes is less than or equal to M-n, the n intermediate nodes continuously encode local data packets and send the data packets to the sink node;
if the feedback information i received by the intermediate nodes is larger than M-n, the n- (M-i) intermediate nodes farthest from the sink node do not participate in the transmission work any more, and the rest M-i intermediate nodes continue to participate in the encoding and transmission work of the data packet.
5. The method for reducing the vehicle-to-vehicle communication delay based on the random linear network coding as claimed in claim 4, wherein the step of obtaining the delay probability distribution of the vehicle-to-vehicle communication scene specifically comprises:
calculating the receiving probability according to the state information and obtaining a transition matrix P according to the receiving probabilityT；
According to a transition matrix PTObtaining a state matrix S of the information sink nodes after t time slotst；
According to the state matrix StCalculating the time delay probability distribution of the workshop communication scene;
and obtaining a time delay mean value according to the time delay probability distribution of the workshop communication scene.
6. The method for reducing the time delay of the workshop communication based on the stochastic linear network coding as claimed in claim 5, wherein the receiving probability is calculated according to the state information and the transition matrix P is obtained according to the receiving probabilityTThis step, in particular, comprises:
judging that i is more than or equal to 0 and is less than or equal to M-n of the state information;
reception probability P ═ P0 P1 ...Pn-1 Pn]1×(n+1)Wherein, in the step (A),
k is the number of successfully received re-encoded data packets per time slot sink node, peThe packet loss rate of each wireless channel between the intermediate node and the sink node;
judging that i is more than or equal to M-1 and the state information M-n is more than or equal to M-1;
reception probability P ═ P'0 P′1 ... P′M-i-1 P′M-i0 0 ...]1×(n+1)，
K is the number of successfully received re-encoded data packets per time slot sink node, peThe packet loss rate of each wireless channel between the intermediate node and the sink node;
combining all P and P' to generate a transition matrix PT。
7. The method for reducing the time delay of the workshop communication based on the random linear network coding as claimed in claim 6, wherein the expression of the mean value of the time delay is as follows:
E(t)＝∑t×Pt
in the above formula, E (t) represents the mean time delay, t represents the time delay passing through a certain time slot, PtRepresenting the probability of a time delay of t.
8. The method for reducing the time delay of the vehicle-to-vehicle communication based on the random linear network coding as claimed in claim 7, further comprising:
the minimum size of the code field is dynamically selected according to the number n of intermediate vehicles.
9. The method for reducing the inter-vehicle communication delay based on the random linear network coding as claimed in claim 8, wherein the step of dynamically selecting the minimum size of the code domain according to the number of the intermediate vehicles is characterized in that:
calculating the intermediate vehicle n ∈ [1,9 ]]Minimum generation probability P corresponding to coding field size q of 2 to 256min；
Each group of [ n, q, P ]min]Uploading to a system;
uploading the number of intermediate vehicles and the required minimum probability in a workshop communication scene to a system;
the system selects the minimum coding domain size meeting the requirement, and sends the minimum coding domain size to a target vehicle, an intermediate vehicle and a resource vehicle in a workshop communication scene;
the encoding and decoding operations are performed on a coded field of this size.
10. The system for reducing the communication time delay of the workshop based on the random linear network coding is characterized by comprising the following modules:
the request module responds to a request of a target vehicle and establishes a workshop communication scene;
the primary coding module is used for performing random linear network coding on the M original data packets in the sending queue by the M resource vehicles in a workshop communication scene and broadcasting the coded data packets to the intermediate vehicle;
the secondary coding module is used for carrying out random linear network coding on the coded data packet again by the n intermediate vehicles and sending the data packet subjected to secondary coding to the target vehicle;
the feedback module is used for feeding the state information i back to the intermediate vehicle and the resource vehicle by taking the number of the received secondary coded data packets as the state information i by the target vehicle;
the decoding module is used for judging that the number of the state information i is equal to M, and the target vehicle decodes the received data packets subjected to secondary coding to obtain M original data packets;
and the circulation module is used for updating the sending queue and returning to the encoding step by the resource vehicle, and circulating until the target vehicle decodes to obtain all data packets corresponding to the required information, and finishing the information transmission of the workshop communication.
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