CN111464437B - Multipath transmission path optimization method based on forward time delay in vehicle-mounted heterogeneous network - Google Patents

Multipath transmission path optimization method based on forward time delay in vehicle-mounted heterogeneous network Download PDF

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CN111464437B
CN111464437B CN202010389891.XA CN202010389891A CN111464437B CN 111464437 B CN111464437 B CN 111464437B CN 202010389891 A CN202010389891 A CN 202010389891A CN 111464437 B CN111464437 B CN 111464437B
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CN111464437A (en
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陈跃
赵海涛
蔡舒祺
赵厚麟
朱洪波
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Nanjing University of Posts and Telecommunications
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L45/00—Routing or path finding of packets in data switching networks
    • H04L45/24—Multipath
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W4/00—Services specially adapted for wireless communication networks; Facilities therefor
    • H04W4/30—Services specially adapted for particular environments, situations or purposes
    • H04W4/40—Services specially adapted for particular environments, situations or purposes for vehicles, e.g. vehicle-to-pedestrians [V2P]
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W40/00—Communication routing or communication path finding
    • H04W40/02—Communication route or path selection, e.g. power-based or shortest path routing
    • H04W40/12—Communication route or path selection, e.g. power-based or shortest path routing based on transmission quality or channel quality

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Abstract

The invention provides a multipath transmission path optimization method based on forward time delay in a vehicle-mounted heterogeneous network, which comprises the following steps of firstly, comparing two transmission paths, and calculating to obtain forward time delay difference between different paths; screening paths according to the throughput prediction and the available bandwidth; then, inputting all transmission paths, and comparing the forward delay differences to obtain the path with the shortest forward delay; partitioning data of a sending buffer area into data packets, wherein the size of each data packet is equal to the size of a message segment of a path; and finally, transmitting the data packet with a low sequence number after the partition on the obtained path with small forward delay. The invention can obviously reduce the disorder problem of the data packet at the receiver, can improve the total throughput of the system and improve the network utilization rate.

Description

Multipath transmission path optimization method based on forward time delay in vehicle-mounted heterogeneous network
Technical Field
The invention belongs to the technical field of vehicle networking, and particularly relates to a multipath transmission path optimization method based on forward time delay in a vehicle-mounted heterogeneous network.
Background
In recent years, with the continuous development of industrial technology and internet technology, the cost of hardware equipment is greatly reduced and network equipment is more and more widely popularized, more and more terminal equipment is provided with a plurality of network interfaces, and meanwhile, the network interfaces arranged on vehicles are more and more complex and diversified. The new generation of vehicle-mounted network can realize the communication between vehicles in the moving process and the communication between the vehicles and roadside infrastructure when the vehicles move at low speed or are static, and can provide various vehicle safety message transmission, intelligent traffic information services, multimedia digital services and the like for the vehicles. The multi-path transmission can improve the data transmission efficiency by improving the utilization rate of channel resources, so that the throughput can be improved by applying the multi-path transmission to the vehicle-mounted heterogeneous network.
One of the major challenges with multipath transmission is the problem of receiver packet misordering. When multiple paths are used for transmission, a packet scheduler is needed, and the packet scheduler determines the selected path and the data packet to be transmitted. Multipath transmission is a reliable method to ensure that the receiver receives the same sequence of packets as the sender. The Round-Robin algorithm used in the traditional multipath transmission does not consider the difference of parameters such as bandwidth and time delay between sub-streams, and sequentially sends data packets to each sub-stream. Because parameters such as delay, bandwidth and the like of different paths in the vehicle-mounted heterogeneous network are different, data packets received by a receiving party are out of order, and the data packets need to be reordered. These out-of-order packets are accumulated in the limited receive buffer and may cause buffer congestion and affect communication performance between vehicles. Therefore, it is necessary to design an effective path scheduling optimization method to avoid less reordering work and to prevent the performance degradation of multipath transmission.
Disclosure of Invention
The purpose of the invention is as follows: the invention provides a multipath transmission path scheduling optimization method based on forward time delay in a vehicle-mounted heterogeneous network, which can obviously reduce the disorder problem of data packets at a receiver, improve the total throughput of a system and improve the network utilization rate.
The invention content is as follows: the invention provides a multipath transmission path scheduling optimization method based on forward time delay in a vehicle-mounted heterogeneous network, which comprises the following steps:
(1) comparing the two transmission paths, and calculating to obtain the forward time delay difference between different paths;
(2) screening paths according to the throughput prediction and the available bandwidth;
(3) inputting all transmission paths, and comparing forward delay differences to obtain a path with the shortest forward delay;
(4) partitioning data of a sending buffer area into data packets, wherein the size of each data packet is equal to the size of a message segment of a path;
(5) and (4) transmitting the data packet with low sequence number after the partition in the step (4) on the path with small forward delay obtained in the step (3).
Further, the step (1) is realized as follows:
Figure BDA0002485380640000021
indicating that the sender is at time
Figure BDA0002485380640000022
Packet 1 is sent to the receiver via path 1,
Figure BDA0002485380640000023
indicating that the sender is at time
Figure BDA0002485380640000024
Packet 2 is transmitted to the receiving side via path 2, Δ s represents the transmission time difference between two data packets, and the transmission time difference between two data packets can be calculated by equation (1):
Figure BDA0002485380640000025
Figure BDA0002485380640000026
indicating that the receiving party is at time
Figure BDA0002485380640000027
Receiving the data packet 1 sent by the path 1,
Figure BDA0002485380640000028
indicating that the receiving party is at time
Figure BDA0002485380640000029
Receiving the data packet 2 sent by the path 2, Δ r represents the receiving time difference of two data packets, and the receiving time difference of two data packets is calculated by formula (2):
Figure BDA00024853806400000210
let Δ T be clkS-clkT for both sending and receivingClock difference between, T1The forward delay of the data packet 1 is represented, the forward delay of the data packet 1 is calculated by formula (3), the forward delay of the data packet 2 is calculated by formula (4) in the same way, and finally, the forward delay difference Δ p between the two paths can be obtained by formula (5):
Figure BDA00024853806400000211
Figure BDA00024853806400000212
Δp＝T1-T2 (5)
further, the step (2) comprises the steps of:
(21) the predicted throughput based on RTT and packet loss rate is formulated as:
Figure BDA00024853806400000213
wherein, RTT is a round trip time of a path, d is a packet loss rate, b is a number of packets receiving ACK acknowledgement, where d is equal to 1;
(22) let P0N represents all available paths, the parameters of which are: RTT (round trip time)iRound trip time, d, of available path iiFor the packet loss rate, BW, of path iiFor the available bandwidth of i of a path, the maximum throughput is:
Figure BDA0002485380640000031
in the case of limited available bandwidth for the best path, then:
Ck＝Cmaxand Ck＞BWk (8)
Wherein, CkFor the throughput, BW, of path kkFor the available bandwidth of path k, the throughput of path kThe amount is equal to the maximum throughput, and its throughput is greater than its available bandwidth, then the set of filtered paths is:
P＝{k|Ck＝Cmaxand Ck＞BWk}。 (9)
Further, the step (3) includes the steps of:
(31) inputting the screened path set P, and each path corresponds to a mark variable Sum to yield the path PiWith other paths pjE, comparing by p;
(32) if Δ pipj<0, then path piCorresponding marker variable Sum [ i ]]Plus 1, if Δ pipj>0, then path pjCorresponding tag variable Sum [ j ]]Plus 1, if Δ pipjIf the path is equal to 0, a random variable Bernoulli factor is created to decide which path corresponds to the marking variable plus 1;
(33) and outputting the maximum Sum value of the marking variable, wherein the path corresponding to the output marking variable is the optimal path.
Further, the step (5) is realized as follows:
selecting the data packet with lower sequence number to be sent on the path with smaller forward delay, when the sub-stream on path i needs to transmit data, the scheduler will index idx in the sending buffer according to equation (10)iSelecting a data packet:
Figure BDA0002485380640000032
wherein, Δ pi,pjIs the forward delay difference, x, between path i and path jiIs the average throughput of path i, after sending one packet, the other packets with higher indices will be shifted to fill the buffer.
Has the advantages that: compared with the prior art, the invention has the beneficial effects that: at present, vehicle-mounted communication devices are more and more, network resources are more and more scarce, and services are split into a plurality of sub-streams for transmission by utilizing the multi-interface characteristics of terminals and cooperating with a plurality of terminals. Under different bandwidth and delay conditions, the invention is compared with FIFO, MTCS and Kim-2012 through NS-3 simulation, and the simulation result shows that the invention not only can obviously reduce the occupation of the reordering buffer zone, but also improves the overall throughput of the system, thereby improving the network utilization rate and saving network resources.
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FIG. 1 is a diagram of a forward delay variation topology;
FIG. 2 is a flowchart of a path algorithm for comparing forward delay differences to obtain the shortest forward delay;
fig. 3 is a diagram of packet allocation.
Detailed Description
The invention is described in further detail below with reference to the drawings.
The invention provides a multipath transmission path optimization method based on forward time delay in a vehicle-mounted heterogeneous network, which specifically comprises the following steps:
step 1: and comparing the two transmission paths, and calculating to obtain the forward time delay difference between different paths.
As shown in figure 1 of the drawings, in which,
Figure BDA0002485380640000041
indicating that the sender (S) is at time
Figure BDA0002485380640000042
Packet 1 is sent to the receiver via path 1,
Figure BDA0002485380640000043
indicating that the sender is at time
Figure BDA0002485380640000044
Packet 2 is transmitted to the receiving side via path 2, Δ s represents the transmission time difference between two data packets, and the transmission time difference between two data packets can be calculated by using equation (1).
Figure BDA0002485380640000045
Figure BDA0002485380640000046
Indicating that the receiving party is at time
Figure BDA0002485380640000047
Receiving the data packet 1 sent by the path 1,
Figure BDA0002485380640000048
indicating that the receiving party is at time
Figure BDA0002485380640000049
When the data packet 2 sent by the path 2 is received, Δ r represents the receiving time difference of the two data packets, and the receiving time difference of the two data packets is calculated by the formula (2).
Figure BDA00024853806400000410
Let Δ T be clkS-clkT be the clock difference between the transmitting and receiving parties, T1The forward delay of the data packet 1 is represented, the forward delay of the data packet 1 is calculated by a formula (3), the forward delay of the data packet 2 is calculated by a formula (4) in the same way, and finally, the forward delay difference Δ p between the two paths can be obtained by a formula (5).
Figure BDA0002485380640000051
Figure BDA0002485380640000052
Δp＝T1-T2 (5)
Step 2: the paths are screened according to the throughput prediction and available bandwidth.
Firstly, a prediction throughput formula based on RTT and packet loss rate is as follows:
Figure BDA0002485380640000053
RTT is the round trip time of the path, d is the packet loss rate, b is the number of packets receiving ACK acknowledgement, where d is equal to 1. The throughput of each path can be predicted according to the formula.
Let P0N represents all available paths, the parameters of which are: RTT (round trip time)iRound trip time, d, of available path iiFor the packet loss rate, BW, of path iiIs the available bandwidth of i of the path.
The maximum throughput is:
Figure BDA0002485380640000054
in the case of limited available bandwidth for the best path, then:
Ck＝Cmaxand Ck＞BWk (8)
Wherein, CkFor the throughput, BW, of path kkFor the available bandwidth of path k, the throughput of path k is equal to the maximum throughput, and its throughput is greater than its available bandwidth, then the set of filtered paths is:
P＝{k|Ck＝Cmaxand Ck＞BWk} (9)
And step 3: and inputting all transmission paths, and comparing the forward delay differences to obtain the path with the shortest forward delay.
As shown in fig. 2, first, a filtered path set P is input, and each path corresponds to a flag variable Sum, so that the path P is yieldediWith other paths pjE.g., p, for comparison.
If Δ pipj<0, then path piCorresponding marker variable Sum [ i ]]Plus 1, if Δ pipj>0, then path pjCorresponding tag variable Sum [ j ]]Plus 1, if Δ pipjIf 0, a random variable Bernoulli factor is created to decideWhich path corresponds to the flag variable incremented by 1.
And outputting the maximum Sum value of the marking variable, wherein the path corresponding to the output marking variable is the optimal path.
And 4, step 4: the data of the transmission buffer is partitioned into data packets, and the size of each data packet is equal to the message segment size of the path.
Assuming that a multipath transmission sender uses a shared transmission buffer between sub-streams, data from the application layer is sufficient to fill the buffer. The data in the send buffer is partitioned into packets, each of which has a size equal to the MSS (message segment size) of the path. The data in the send buffer is partitioned into packets, each of which has a size equal to the MSS (message segment size) of the path.
And 5: and (4) transmitting the data packet with low sequence number after the partition in the step (4) on the path with small forward delay obtained in the step (3).
The data packet with the lower sequence number is selected to be sent on the path with the smaller forward delay, in particular, when the sub-stream on path i requires data to be transmitted, the scheduler will index idx in the send buffer according to equation (10)iSelecting a data packet:
Figure BDA0002485380640000061
wherein x isiIs the average throughput (bytes/sec) of path i, which always selects the packet at index 0. After sending one packet, the other packets with higher indices will be shifted to fill the buffer, as shown in fig. 3. The packet scheduling algorithm employs the Pull mechanism, that is, the generated data packets are stored in a transmit buffer and assigned to a sub-stream only when the sub-stream has an open window for transmitting data, e.g., after receiving an ACK.

Claims (2)

1. A multipath transmission path optimization method based on forward time delay in a vehicle-mounted heterogeneous network is characterized by comprising the following steps:
(1) comparing every two transmission paths, and calculating to obtain forward time delay differences among different paths;
(2) screening paths according to the throughput prediction and the available bandwidth;
(3) inputting all transmission paths, and comparing forward delay differences to obtain a path with the shortest forward delay;
(4) partitioning data of a sending buffer area into data packets, wherein the size of each data packet is equal to the message segment size MSS of a path;
(5) sending the data packet with low sequence number after the partition in the step (4) on the path with small forward delay obtained in the step (3);
the step (1) is realized by the following steps:
Figure FDA0003255818380000011
indicating that the sender is at time
Figure FDA0003255818380000012
Packet 1 is sent to the receiver via path 1,
Figure FDA0003255818380000013
indicating that the sender is at time
Figure FDA0003255818380000014
Packet 2 is transmitted to the receiving side via path 2, Δ s represents the transmission time difference between two data packets, and the transmission time difference between two data packets can be calculated by equation (1):
Figure FDA0003255818380000015
Figure FDA0003255818380000016
indicating that the receiving party is at time
Figure FDA0003255818380000017
Receiving the data packet 1 sent by the path 1,
Figure FDA0003255818380000018
indicating that the receiving party is at time
Figure FDA0003255818380000019
Receiving a data packet 2 sent by a path 2, where Δ r represents a receiving time difference between two data packets, and calculating the receiving time difference between two data packets by using formula (2):
Figure FDA00032558183800000110
let Δ T be clkS-clkT be the clock difference between the sending and receiving parties, T1The forward delay of the data packet 1 is represented, the forward delay of the data packet 1 is calculated by a formula (3), the forward delay of the data packet 2 is calculated by a formula (4) in the same way, and finally, the forward delay difference Δ p between the two paths can be obtained by a formula (5):
Figure FDA00032558183800000111
Figure FDA00032558183800000112
△p＝T1-T2； (5)
the step (2) comprises the following steps:
(21) the predicted throughput based on RTT and packet loss rate is formulated as:
Figure FDA0003255818380000021
wherein, RTT is a round trip time of a path, d is a packet loss rate, b is a number of packets receiving ACK acknowledgement, where d is equal to 1;
(22) let P0N represents all available paths, the parameters of which are: RTT (round trip time)iRound trip time, d, of available path iiFor the packet loss rate, BW, of path iiFor the available bandwidth of i of a path, the maximum throughput is:
Figure FDA0003255818380000022
in the case of limited available bandwidth for the best path, then:
Ck＝Cmaxand Ck>BWk (8)
Wherein, CkFor the throughput, BW, of path kkFor the available bandwidth of path k, the throughput of path k is equal to the maximum throughput, and its throughput is greater than its available bandwidth, then the set of filtered paths is:
P＝{k|Ck＝Cmaxand Ck>BWk}； (9)
The step (5) is realized as follows:
selecting the data packet with lower sequence number to be sent on the path with smaller forward delay, when the sub-stream on path i needs to transmit data, the scheduler will index idx in the sending buffer according to equation (10)iSelecting a data packet:
Figure FDA0003255818380000023
wherein, Δ pi,pjIs the forward delay difference, x, between path i and path jiIs the average throughput of path i, after sending one packet, the other packets with higher indices will be shifted to fill the buffer.
2. The method for optimizing the multipath transmission path based on the forward delay in the vehicular heterogeneous network according to claim 1, wherein the step (3) comprises the steps of:
(31) inputting the screened path set P, and each path corresponds to a mark variable Sum to yield the path PiWith other paths pjE, comparing by p;
(32) if Δ pipj<0, then path piCorresponding marker variable Sum [ i ]]Plus 1, if Δ pipj>0, then path pjCorresponding tag variable Sum [ j ]]Plus 1, if Δ pipjIf the path is equal to 0, a random variable Bernoulli factor is created to decide which path corresponds to the marking variable plus 1;
(33) and outputting the maximum Sum value of the marking variable, wherein the path corresponding to the output marking variable is the optimal path.
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