1 Introduction
2 Related works
3 Background of vehicular communications
3.1 The architecture of vehicular networks
-
Inter-vehicle communication - This is also known as vehicle-to-vehicle (V2V) communication or pure ad hoc networking. In this category, the vehicles communicate among each other with no infrastructure support. Any valuable information collected from sensors on a vehicle, or communicated to a vehicle, can be sent to neighbouring vehicles.
-
Vehicle-to-roadside communication - This is also known as vehicle-to-infrastructure (V2I) communication. In this category, the vehicles can use cellular gateways and wireless local area network access points to connect to the Internet and facilitate vehicular applications [14].
-
Inter-roadside communication - This is also known as hybrid vehicles-to-roadside communication. Vehicles can use infrastructure to communicate with each other and share the information received from infrastructure with other vehicles in a peer-to-peer mode through ad hoc communication. Besides that, vehicles can communicate with infrastructure either in single-hop or multi-hop fashion depending on their position. This architecture includes V2V communication and provides greater flexibility in content sharing.
3.2 The special characteristics of VANETs
-
Higher transmission power and storage - The network nodes (vehicles) in VANETs are usually equipped with higher power and storage than those in MANETs.
-
Higher computational capability - Operating vehicles can afford higher computing, communication and sensing capabilities than MANETs.
-
Predictable mobility - Unlike MANETs, the movement of the network nodes in a VANET can be predicted because they move on a road network. If the current velocity and road trajectory information are known, then the future position of the vehicle can be predicted.
3.3 Challenging routing requirements of VANETs
4 Vehicular reliability model
4.1 Highway mobility model
4.2 Link reliability model
-
Vehicles are moving in the same direction(13)
-
Vehicles are moving in opposite directions(14)
4.3 Route reliability definition
5 The reliability based routing protocol AODV-R
-
XPos, YPos contain the coordinates of the vehicle that generates/processes this RREQ.
-
Speed contains the current velocity of the vehicle that generates/processes this RREQ.
-
Direction contains the movement angle of the vehicle that generates/processes this RREQ.
-
Link_reliability contains the value of the link reliability between the sender and receiver of this RREQ.
-
Route_reliability contains the final value of the whole route reliability between the source node and the destination node. This value is used by the source node to decide which route will be chosen in case of multiple routes between the source and the destination are found.
-
Route_reliability contains the value of the route reliability of this route entry. This value is updated every time a route with a higher reliability value is found for the same destination.
5.1 Route discovery process in AODV-R
6 Simulation setup and results
6.1 Performance metrics
-
Average packet delivery ratio (PDR) represents the average ratio of the number of successfully received data packets at the destination node to the number of data packets supposed to be delivered.
-
Links failures represent the average number of link failures during the routing process. This metric shows the efficiency of the routing protocol in avoiding link failures.
-
Routing control overhead expresses the ratio of the total generated routing control messages to the total number of data messages supposed to be received.
-
Average end-to-end delay represents the average time between the sending and receiving times for packets received.
6.2 Effect of different velocities on the routing performance
Velocity in the third lane (km/h) | AODV | AODV-R | ||||
---|---|---|---|---|---|---|
Avg% | LL% | UL% | Avg% | LL% | UL% | |
60 | 51.36 | 46.86 | 55.86 | 64.41 | 60.23 | 68.59 |
80 | 49.82 | 46.21 | 51.75 | 63.83 | 60.57 | 66.08 |
100 | 47.01 | 43.95 | 50.09 | 62.10 | 58.89 | 64.65 |
120 | 42.83 | 39.40 | 45.93 | 59.85 | 56.17 | 63.53 |
140 | 37.86 | 34.62 | 41.08 | 56.07 | 53.55 | 58.66 |
Velocity in the third lane (km/h) | AODV | AODV-R | ||||
---|---|---|---|---|---|---|
Avg | LL | UL | Avg | LL | UL | |
60 | 0.038 | 0.029 | 0.043 | 0.062 | 0.053 | 0.068 |
80 | 0.058 | 0.048 | 0.065 | 0.082 | 0.073 | 0.087 |
100 | 0.06 | 0.056 | 0.068 | 0.094 | 0.089 | 0.104 |
120 | 0.066 | 0.057 | 0.076 | 0.118 | 0.107 | 0.122 |
140 | 0.097 | 0.088 | 0.102 | 0.128 | 0.117 | 0.136 |
Velocity in the third lane (km/h) | AODV | AODV-R | ||||
---|---|---|---|---|---|---|
Avg | LL | UL | Avg | LL | UL | |
60 | 214.3 | 195.6 | 232.9 | 134.1 | 122.7 | 145.4 |
80 | 242.8 | 226.2 | 259.3 | 141.7 | 127.2 | 163.1 |
100 | 304.4 | 289.1 | 336.6 | 175.4 | 153.3 | 201.4 |
120 | 365.1 | 339.8 | 390.3 | 221.7 | 205.1 | 238.2 |
140 | 501.6 | 479.8 | 523.1 | 261.7 | 241.5 | 281.8 |
Velocity in the third lane (km/h) | AODV | AODV-R | ||||
---|---|---|---|---|---|---|
Avg% | LL% | UL% | Avg% | LL% | UL% | |
60 | 41.297 | 38.64 | 43.96 | 49.59 | 44.94 | 54.23 |
80 | 44.29 | 40.47 | 48.03 | 52.64 | 50.05 | 55.23 |
100 | 47.29 | 43.92 | 50.65 | 54.83 | 50.00 | 58.21 |
120 | 49.28 | 44.84 | 53.72 | 55.60 | 52.03 | 59.16 |
140 | 51.27 | 48.77 | 53.78 | 57.29 | 54.16 | 60.42 |
6.3 Effect of different data packet sizes on the routing performance
Data packet size (bytes) | AODV | AODV-R | ||||
---|---|---|---|---|---|---|
Avg% | LL% | UL% | Avg% | LL% | UL% | |
500 | 50.27 | 48.66 | 51.86 | 66.71 | 60.76 | 63.73 |
1,000 | 49.82 | 46.21 | 51.75 | 66.08 | 60.57 | 63.33 |
1,500 | 48.28 | 44.86 | 51.04 | 64.58 | 59.79 | 62.18 |
2,000 | 46.09 | 42.80 | 48.03 | 63.80 | 57.84 | 61.15 |
2,500 | 43.19 | 40.02 | 46.04 | 62.46 | 58.07 | 60.77 |
3,000 | 39.32 | 36.97 | 41.66 | 62.85 | 57.15 | 60.00 |
Data packet size (bytes) | AODV | AODV-R | ||||
---|---|---|---|---|---|---|
Avg | LL | UL | Avg | LL | UL | |
500 | 0.049 | 0.044 | 0.052 | 0.057 | 0.053 | 0.061 |
1,000 | 0.06 | 0.056 | 0.063 | 0.066 | 0.06 | 0.069 |
1,500 | 0.075 | 0.069 | 0.077 | 0.082 | 0.077 | 0.088 |
2,000 | 0.078 | 0.072 | 0.08 | 0.091 | 0.086 | 0.096 |
2,500 | 0.079 | 0.075 | 0.083 | 0.098 | 0.095 | 0.104 |
3,000 | 0.085 | 0.078 | 0.088 | 0.101 | 0.094 | 0.105 |
Data packet size (bytes) | AODV | AODV-R | ||||
---|---|---|---|---|---|---|
Avg | LL | UL | Avg | LL | UL | |
500 | 269.5 | 249.9 | 297 | 142.8 | 128.4 | 157.1 |
1,000 | 282.8 | 256.2 | 305.3 | 146.7 | 123.2 | 165.1 |
1,500 | 316.6 | 294.4 | 338.7 | 163.7 | 142.9 | 184.4 |
2,000 | 361.1 | 333.4 | 386.7 | 188.9 | 156.2 | 211.5 |
2,500 | 414.4 | 385 | 433.7 | 212.8 | 186 | 239.5 |
3,000 | 494.8 | 480.8 | 532.7 | 256.4 | 235.4 | 287.3 |
Data packet size (bytes) | AODV | AODV-R | ||||
---|---|---|---|---|---|---|
Avg% | LL% | UL% | Avg% | LL% | UL% | |
500 | 43.02 | 40.96 | 45.07 | 52.48 | 51.46 | 53.49 |
1,000 | 44.29 | 40.47 | 48.03 | 52.64 | 50.05 | 55.23 |
1,500 | 47.59 | 44.12 | 51.07 | 56.80 | 54.48 | 59.12 |
2,000 | 49.32 | 47.29 | 52.68 | 55.76 | 53.24 | 58.29 |
2,500 | 51.28 | 49.98 | 55.16 | 56.41 | 53.57 | 59.24 |
3,000 | 55.52 | 52.39 | 58.66 | 58.17 | 54.22 | 62.11 |