A vehicle running status field model-based information transmission frequency optimization method in the Internet of Vehicles, wherein a running status field model is established according to the real-time running status of a road vehicle to describe the degree of risk of the vehicle, the degree of risk is used to dynamically adjust the transmission frequency of safety-critical information, and the transmission frequency of non-safety-critical information is adjusted through the real-time transmission frequency of safety-critical information;
- and the method comprises the following steps:
- (1) acquiring real-time road information through the Internet of Vehicles, including vehicle velocity V, vehicle distance r, road width d and vehicle type m;
- (2) with the vehicle as objective i as the reference system, establishing a vehicle running status field model:
- describing the degree of risk of the vehicle according to the Doppler effect and the running status field model, as shown in formula (1);
- {
- E
- i
- =
- K
- K
- -
- V
-
- cos
-
- θ
- ·
- G
-
- M
- i
- |
- r
-
- |
- 2
- V
- =
- V
- i
- -
- V
- 0
- M
- i
- =
- m
- i
- ′
- |
- V
- i
-
- |
- 2
- M
- 0
- =
- m
- 0
- ′
- ·
- |
- V
- 0
-
- |
- 2
- F
- 0
- =
- E
- i
- ·
- M
- 0
- (
- 1
- )
- wherein K and G are constants;
- the value of K is the maximum velocity allowed by the road, K=150 km/h, G=1, and Mi is the relative mass of the vehicle as objective i and is related to the vehicle type and the vehicle velocity;
- and V0 is the velocity of the vehicle as observer 0, Vi is the velocity of the vehicle as objective i, and θ is an included angle between the connection direction of the vehicle as objective i and the vehicle as observer 0 and the movement direction of the vehicle as objective i and is calculated by formula (2);
- θ
- =
-
- {
-
- 2
- -
- arcsin
-
-
- d
- r
-
-
- vehicle
-
-
- as
-
-
- observer
-
-
- 0
-
-
- is
-
-
- in
-
-
- front
-
-
- of
-
-
- vehicle
-
-
- as
-
-
- objective
-
-
- i
-
- 2
- +
- arcsin
-
-
- d
- r
-
- vehicle
-
-
- as
-
-
- observer
-
-
- 0
-
-
- is
-
-
- behind
-
- vehicl
-
-
- e
-
-
- as
-
-
- objective
-
-
- i
- m is the vehicle type;
- and formula (3) is obtained after normalization;
- m
- i
- ′
- =
- m
- i
- m
- i
- +
- 1
- (
- 3
- )
- F0 is the degree of risk of the vehicle as observer 0 in the running status field E;
- FMAX is defined as the maximum degree of risk of the vehicle as observer:
- F
- MAX
- =
- K
- K
- -
- V
- ·
- GM
- i
-
- M
- 0
-
- s
-
- 2
- (
- 4
- )
- wherein s is the minimum safe distance for vehicle running and is related to the current velocity of the vehicle;
- (3) calculating the transmission frequency of safety-critical information:
- calculating the real-time transmission frequency of WSM according to the obtained degree of risk of the vehicle:
- f
- WSM
- =
- {
- ⌊
- F
- 0
- F
- MAX
- ×
- 10
- ⌋
- F
- 0
- ≤
- F
- MAX
- 10
- F
- 0
- >
- F
- MAX
- (
- 5
- )
- wherein F0 is the risk intensity of the vehicle as observer 0, and FMAX is the maximum risk intensity;
- and when F0≤FMAX, the vehicle is in a steady status, the transmission frequency of WSM is automatically adjusted with the ratio of F0 to FMAX;
- when F0>FMAX, the vehicle is in a risk status, and at this time, the transmission frequency of WSM is the largest;
- (4) calculating the maximum transmission frequency of non-safety-critical information
- the calculation formula for the number c of non-WSM that can be transmitted by the IEEE 802.11p link in a WSM cycle is
- c
- =
- T
- f
- ;
- wherein T is the current maximum throughput of the link, and f is the transmission frequency of WSM;
- and by judging whether the remaining space of the send buffer at the MAC layer is larger than c, the maximum distribution frequency fu max of non-safety-critical messages of the IEEE 802.11p link is obtained as follows:
- f
- u
-
-
- max
- =
- {
- f
- ·
- c
- L
- MAX
- -
- L
-
- (
- t
- )
- ≥
- c
- f
-
- (
- L
- MAX
- -
- L
-
- (
- t
- )
- )
- L
- MAX
- -
- L
-
- (
- t
- )
- <
- c
- (
- 6
- )
- wherein LMAX is the maximum load value of the link, and L(t) is the current load value of the link;
- when the distribution frequency of non-WSM of the IEEE 802.11p link reaches fu max, WSM and non-WSM reach Pareto Optimality, and both obtain the maximum transmission benefit;
- (5) selecting a link:
- the set of links is N{0,1,2 . . . i}, wherein 0 represents the 802.11p link, and 1-i represent other links;
- acquiring the data message type, if the type is safety-critical information WSM, directly transmitting the data message by the 802.11p link, and if the type is non-safety-critical information, selecting a transmission link;
- and selecting a link according to the delayed response time RTT and the link load L(T), and determining whether to transmit on the 802.11p link or a link rather than 802.11p, as shown in formula (7);
- W
- LS
- -
- i
- =
- {
- (
- RTT
- RTT
- max
- +
- L
-
- (
- t
- )
- L
- max
- -
- L
- safe
-
- (
- t
- )
- )
- 802.11
-
- p
- if
-
-
- i
- =
- 0
- (
- RTT
- RTT
- max
- +
- L
-
- (
- t
- )
- L
- max
- )
- i
- if
-
-
- i
- ≠
- 0
- (
- 7
- )
- wherein WLS-0 is the selection weight of the 802.11p link, WLS-i is the selection weight of the ith link, RTTmax is the maximum allowable delayed response time of the link, and Lmax is the maximum load of the link;
- and Lsafe is the estimated safety-critical information traffic, i∈N, and the expression thereof is (8);
- Lsafe(t)=fWSM·P·R (8)
- wherein fWSM is the transmission frequency of safety-critical information obtained in step (3);
- and P is the number of security applications in the current network, R is the average communication distance between vehicles collected in the current network, and such parameters are obtained by communications between vehicles and the network;
- when the i link exists to let WLS-i≤WLS-0, the i link is selected to transmit the non-safety-critical information message, and if WLS-i>WLS-0 for any link i, the 802.11p link is selected to transmit the non-safety-critical information message;
- when it is determined that the non-safety-critical information message is transmitted on the 802.11p link, entering step (6);
- and if the non-safety-critical information message is transmitted on a link rather than 802.11p, transmitting according to the transmission mechanism of the underlying layer of the link;
- (6) calculating the distribution frequency of non-safety-critical data message;
- If the data message p is distributed to the IEEE 802.11p link, it is required to calculate the maximum distribution frequency fu max of non-WSM of the IEEE 802.11p link by formula (6), and then the two latest non-safety-critical messages arriving on the IEEE 802.11p link are used to calculate the instantaneous distribution frequency fu of non-safety-critical information on the IEEE 802.11p link at this time;
- f
- u
- =
- 1
- t
- 2
- -
- t
- 1
- (
- 9
- )
- wherein t1, t2 are the arrival time of two adjacent non-safety-critical information messages on the link;
- when fu≤fu max, the non-safety-critical message is transmitted in the 802.11p link, and when fu>fu max, the non-safety-critical message is discarded to ensure the normal transmission of safety-critical messages.