METHOD FOR SELECTING CONTENT FORWARDING NODE IN VEHICLE AD-HOC NETWORK ON THE BASIS OF SERVICE TYPE

Abstract

A method for selecting a content forwarding node in a vehicle ad-hoc network on the basis of service type, comprising the following steps: calculating a bandwidth occupation proportion factor according to the type of requested content information and a bandwidth occupation situation of a neighboring vehicle which can perform forwarding in a one-hop transmission range; defining a virtual arrival time of a candidate forwarding vehicle to an initial request vehicle according to the distance between the neighboring vehicle and the initial request vehicle and a driving speed of the neighboring vehicle; calculating a forwarding node impact factor according to the bandwidth occupation proportion factor and the virtual arrival time; and selecting a forwarding node according to the forwarding node impact factor.

Claims

1. A method for selecting a content forwarding node in a vehicle ad-hoc network on the basis of service type, comprising the following steps: S1, calculating a bandwidth occupation proportion factor according to the type of requested content information and a bandwidth occupation situation of a neighboring vehicle which can perform forwarding in a one-hop transmission range; S2, defining a virtual arrival time of a candidate forwarding vehicle to an initial request vehicle according to the distance between the neighboring vehicle and the initial request vehicle and a driving speed of the neighboring vehicle; S3, calculating a forwarding node impact factor according to the bandwidth occupation proportion factor in step S1 and the virtual arrival time in step S2; and S4, selecting a forwarding node according to the forwarding node impact factor.

2. The method for selecting a content forwarding node in a vehicle ad-hoc network on the basis of service type according to claim 1, wherein in step S1, the bandwidth occupation proportion factor is calculated as follows: S1-1, a content vehicle y receives request information at time t, acquires the type of requested content according to a name of the requested content contained in the received request information, and determines an occupied bandwidth BW and occupied time t.sub.need required for transmitting the content; S1-2, the vehicle y calculates an idle available bandwidth BW.sub.free(V.sub.i) of a vehicle Vi; and S1-3, the vehicle y calculates the band occupation proportion factor $K_i=\frac{B{W}_{free}\left(i\right)-BW}{B{W}_{total}}$ of a vehicle i according to the determined BW, a total bandwidth BW.sub.total and the idle bandwidth of the neighboring vehicle, wherein i=(1, 2, ..., N), and N is the total number of the neighboring vehicles of the vehicle y.

3. The method for selecting a content forwarding node in a vehicle ad-hoc network on the basis of service type according to claim 1, wherein in step S2, the virtual arrival time is defined as follows: S2-1, candidate forwarding nodes are one-hop neighboring vehicles of the content vehicle y; the distance between the candidate forwarding vehicle and a target vehicle x is calculated by the formula D(.sub.i,x)= |X.sub.i-X.sub.x|, wherein X.sub.i and X.sub.x are respectively the abscissas of the vehicles i and x, and the vehicle i is a neighboring vehicle of the vehicle y; S2-2, according to different vehicle driving directions, when the driving directions of the vehicle i and the vehicle x are the same, if the speed v.sub.i of the vehicle i is less than the speed v.sub.x of the vehicle x, then the vehicle i is removed from the candidate forwarding nodes; and if the speed v.sub.i of the vehicle i is greater than the speed v.sub.x of the vehicle x, then the virtual arrival time is $T_{\left(i,x\right)}=\frac{D_{\left(i,x\right)}}{v_i-v_x};$ and when the driving directions of the vehicle i and the vehicle x are opposite, if the two vehicles get away from each other, then the vehicle i is removed from the candidate forwarding nodes; and if the two vehicles get close to each other, then the virtual arrival time is $T_{\left(i,x\right)}=\frac{D_{\left(i,x\right)}}{v_i-v_x}$ .

4. The method for selecting a content forwarding node in a vehicle ad-hoc network on the basis of service type according to claim 1, wherein in step S3, the forwarding node impact factor is calculated with the following method: let the number of the one-hop neighboring vehicles of the vehicle y be N, the vehicle i is one of the neighboring vehicles; a forwarding node vehicle i selection impact factor F.sub.1 = K.sub.1 -T.sub.(1,x) is calculated according to the bandwidth occupation proportion factor of the forwarding node and the virtual arrival time, wherein K.sub.i and T.sub.(i,x) are respectively normalized values of the bandwidth occupation proportion factor K.sub.i and the virtual arrival time T.sub.(i,x), and denote the impact degrees of the bandwidth and moving speed of the candidate forwarding vehicle on forwarding vehicle selection; and F.sub.i denotes a successful selection probability of the forwarding node.

5. The method for selecting a content forwarding node in a vehicle ad-hoc network on the basis of service type according to claim 1, wherein in step S4, the forwarding node is selected with the following method: selecting from the neighboring vehicles of the vehicle y a vehicle with the greatest impact factor as a forwarding node thereof; adding an ID of the vehicle, the required bandwidth, and the occupied time information to RFR information, transmitting out the RFR information; and updating the channel bandwidth idleness situation of the forwarding vehicle at the current time after the forwarding vehicle receives the RFR information.

6. The method for selecting a content forwarding node in a vehicle ad-hoc network on the basis of service type according to claim 5, wherein in step S4, after the vehicle receives the RFR information, the vehicle updates the channel bandwidth idleness situation thereof as follows: S4-1, the vehicle receiving the RFR information first determines whether the vehicle is selected as the forwarding vehicle; if yes, then determining whether the idle bandwidth is greater than a bandwidth threshold value; and if no, then doing nothing; S4-2, if the idle bandwidth is not greater than the bandwidth threshold value, then transmitting ACK information to inform that the vehicle cannot become the forwarding vehicle thereof; if the idle bandwidth is greater than the bandwidth threshold value, then continuing to determine whether the vehicle is selected by a plurality of content vehicles; if yes, then selecting the farthest content vehicle as the forwarding vehicle; and if not, then confirming that the vehicle becomes the forwarding vehicle; and S4-3, the forwarding vehicle transmits the ACK information to the content vehicle; the content vehicle receives the ACK information, and then transmits content information; and the forwarding vehicle receives and forwards the content information.

7. The method for selecting a content forwarding node in a vehicle ad-hoc network on the basis of service type according to claim 6, wherein in step S4-3, when the forwarding vehicle performs forwarding, the vehicle determines whether selection times exceeds a threshold value; if no, then jumping to step S1 after the forwarding; and if yes, then aborting the transmission of the content.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] FIG. 1 is a flow chart of the method for selecting a content forwarding node in a vehicle ad-hoc network on the basis of service type;

[0031] FIG. 2 is a schematic view for comparing two content information arrival success rates with the increase of the number of vehicles; and

[0032] FIG. 3 is a schematic view for comparing two average path lengths required for successfully transmitting the information with the increase of the number of vehicles.

DETAILED DESCRIPTION

[0033] The present invention will be further described hereafter in combination with the drawings and specific embodiments. The present invention provides a method for selecting a content forwarding node in a vehicle ad-hoc network on the basis of service type. As shown in FIG. 1, the overall flow thereof comprises the following steps:

[0034] 1) A content vehicle receiving request information determines whether an initial request vehicle is in a communication range thereof; if yes, then directly transmitting a content data packet; and if not, then going to the next step.

[0035] 2) Calculating a bandwidth occupation proportion factor according to the type of requested content information and a bandwidth occupation situation of a neighboring vehicle which can perform forwarding in a one-hop transmission range; [0036] 2.1) A content vehicle y receives request information at time t, acquires the type of requested content according to a name of the requested content contained in the received request information, and determines an occupied bandwidth BW and occupied time t.sub.need required for transmitting the content; [0037] 2.2) The vehicle y calculates an idle available bandwidth BW.sub.free(Vi) of a vehicle Vi; and [0038] 2.3) The vehicle y calculates the band occupation proportion factor of a vehicle i according to the determined BW, a total bandwidth BW.sub.total and the idle bandwidth of the neighboring vehicle, wherein i=(1, 2, ..., N), and N is the total number of the neighboring vehicles of the vehicle y.

[0039] 3) Defining a virtual arrival time of a candidate forwarding vehicle to the initial request vehicle according to the distance between the neighboring vehicle and the initial request vehicle and a driving speed of the neighboring vehicle; the definition method is specifically as follows:

[0040] 3.1) Candidate forwarding nodes are one-hop neighboring vehicles of the content vehicle y; the distance between the candidate forwarding vehicle and a target vehicle x is calculated by the formula D.sub.(i,x)= |X.sub.i-X.sub.x|, wherein X.sub.i and X.sub.x are respectively the abscissas of the vehicles i and x, and the vehicle i is a neighboring vehicle of the vehicle y;

[0041] 3.2) According to different vehicle driving directions, when the driving directions of the vehicle i and the vehicle x are the same, if the speed v.sub.i of the vehicle i is less than the speed v.sub.x of the vehicle x, then the vehicle i is getting farther and farther from the vehicle x, and the vehicle i is removed from the candidate forwarding nodes; and if the speed v.sub.i of the vehicle i is greater than the speed v.sub.x of the vehicle x, then the virtual arrival time is

[00005]$T_{\left(i,x\right)}=\frac{D_{\left(i,x\right)}}{v_i-v_x};$

and when the driving directions of the vehicle i and the vehicle x are opposite, if the two vehicles get away from each other, then the two vehicles cannot meet in the next period of time, and the vehicle i is removed from the candidate forwarding nodes; and if the two vehicles get close to each other, then the virtual arrival time is

[00006]$T_{\left(i,x\right)}=\frac{D_{\left(i,x\right)}}{v_i+v_x}.$

[0042] 4) Calculating a forwarding node impact factor according to the bandwidth occupation proportion factor in step S1 and the virtual arrival time in step S2: let the number of the one-hop neighboring vehicles of the vehicle y be N, the vehicle i is one of the neighboring vehicles; a forwarding node vehicle i selection impact factor F.sub.i = K.sub.i - T.sub.(i,x) is calculated according to the bandwidth occupation proportion factor of the forwarding node and the virtual arrival time, wherein K.sub.i and T.sub.(i,x) are respectively normalized values of the bandwidth occupation proportion factor K.sub.i and the virtual arrival time T.sub.(i,x);

[00007]$\overline{K_i}=\frac{K_i}{{\displaystyle \underset{k=1}{\overset{N}{.Math.}}{K}_k}},\overline{T_{\left(i,x\right)}}=\frac{T_{\left(i,x\right)}}{{\displaystyle \underset{k=1}{\overset{N}{.Math.}}{T}_{\left(k,x\right)}}}$

and denote the impact degrees of the bandwidth and moving speed of the candidate forwarding vehicle on forwarding vehicle selection; and F.sub.i denotes a successful selection probability of the forwarding node, for example, the factor -1 denotes that the impact factor is negatively correlated with the successful selection probability of the forwarding node.

[0043] 5) Selecting from the neighboring vehicles of the vehicle y a vehicle with the greatest impact factor as a forwarding node thereof; adding an ID of the vehicle, the required bandwidth, and the occupied time information to RFR information, and transmitting out the RFR information.

[0044] 6) The vehicle receiving the RFR information first determines whether the vehicle is selected as the forwarding vehicle; if yes, then determining whether the idle bandwidth is greater than a bandwidth threshold value; and if no, then doing nothing.

[0045] 7) If the idle bandwidth is not greater than the bandwidth threshold value, then transmitting ACK information to inform that the vehicle cannot become the forwarding vehicle thereof; if the idle bandwidth is greater than the bandwidth threshold value, then continuing to determine whether the vehicle is selected by a plurality of content vehicles; if yes, then selecting the farthest content vehicle as the forwarding vehicle; and if not, then confirming that the vehicle becomes the forwarding vehicle.

[0046] 8) The forwarding vehicle transmits the ACK information to the content vehicle; the content vehicle receives the ACK information, and then transmits content information; the forwarding vehicle receives and forwards the content information; when the forwarding vehicle performs forwarding, the vehicle determines whether selection times exceeds a threshold value; if no, then jumping to step S1 after the forwarding; and if yes, then aborting the transmission of the content.

[0047] According to the above method steps, the method steps of the present invention can be summarized as follows: [0048] 1. After a content vehicle receives request information, the content vehicle comprehensively selects a content forwarding node according to a neighboring vehicle available transmission bandwidth table maintained thereby and in combination with the factors such as vehicle position, driving direction, driving speed and the like; [0049] 2. When the request information arrives at the content vehicle, the content vehicle first determines whether an initial request vehicle is in the communication range thereof; if yes, then content data information is directly transmitted; and if not, then the content vehicle determines a bandwidth required for the transmission according to the type of the requested content information, and calculates a bandwidth occupation proportion factor according to the bandwidth occupation situation of a neighboring vehicle which can perform forwarding in a one-hop transmission range; then, a virtual arrival time of a candidate forwarding vehicle to an initial request vehicle is defined according to the distance between the neighboring vehicle and the initial request vehicle and a driving speed of the neighboring vehicle; [0050] 3. A candidate forwarding vehicle impact factor is calculated by comprehensively considering the bandwidth occupation proportion factor and the virtual arrival time; the content forwarding node is determined according to the impact factor; an ID of the determined forwarding vehicle, the required channel bandwidth, and the occupied time are added to RFR information; and after the forwarding vehicle receives the RFR information, the forwarding vehicle updates the channel bandwidth idleness situation thereof at the current time.

[0051] In the embodiment, the method of the present invention is compared with an existing method for returning content along an original path directly, and the specific result is as follows:

[0052] FIG. 2 shows a schematic view for comparing the content information arrival success rates of the two methods with the increase of the number of vehicles. It can be seen from FIG. 2 that the content arrival success rate of the method of the present invention is obviously higher than that of the method for returning content along an original path directly. The reason is: due to the movement of the vehicles in the network, during service returning, the vehicle forwarding the request information earlier may have moved out of the communication range, such that the communication link cannot be established to transmit the content information, thus having a low content arrival rate. The method for selecting a content forwarding node in the present invention avoids the content loss due to the movement of vehicles, considers the difference of service types, and further avoids the content transmission failure due to different bandwidth requirements, thus having a high success rate. With the increase of vehicles, the performance of the algorithm of the present invention is gradually improved; under the premise that the number of content requests remains unchanged, the more vehicles in the network, the more available forwarding vehicles, the higher the forwarding success rate is, and the higher the content arrival success rate is. With the increase of the number of vehicles in the range, the performance of the comparison algorithm of the existing method has a rising trend slower than the algorithm of the present invention because the increase of the number of vehicles cannot solve the problem of content transmission failure due to the movement of vehicles. Therefore, the content arrival success rate of the existing method is obviously lower than that of the present invention.

[0053] FIG. 3 shows a schematic view for comparing two average path lengths required for successfully transmitting the information with the increase of the number of vehicles. It can be seen that the average path length required for successfully transmitting the information according to the method of the present invention is less than that of the original path return method. Owing to the movement of vehicle nodes, a path better than the original path of the request information to the content vehicle may exist. The method of the present invention can find and utilize the better path, and the existing method can only return along the original path.