Message broadcasting in vanet

1. A method for broadcasting a message in a vehicular ad hoc network, comprising:

receiving the message at a first communication device mounted on a first vehicle that is transmitted from a second vehicle;

identifying a first number of vehicles that are within a communication range of the first communication device;

calculating a first count-down time based on the first number of vehicles, where the first count-down time decreases as the first number of vehicles increases; and

if the first communication device does not receive the message again before the first count-down time ends, broadcasting the message when the first count-down time ends.

2. The method according to claim 1 , wherein the first number of vehicles are out of a communication range of the second vehicle.

3. The method according to claim 1 , further comprising determining that the first communication device is not out of a valid range of the message.

4. The method according to claim 1 , further comprising determining that a lifetime of the message has not expired when the message is received at the first communication device.

5. The method according to claim 1 , wherein calculating the first count-down time comprises:

identifying a first group of vehicles that are within both the communication range of the first communication device and a communication range of the second vehicle;

obtaining a first set of numbers, wherein each number indicates how many vehicles are within a communication range of a corresponding vehicle included in the first group;

sorting the first set of numbers together with the first number of vehicles to obtain a number sequence; and

calculating the first count-down time based on a position of the first number in the number sequence.

6. The method according to claim 5 , wherein the first number of vehicles is equal to a number included in the first set of numbers, and further comprising determining a position of the first number of vehicles in the number sequence and a position of the number included in the first set of numbers in the number sequence based on a distance between the first vehicle and the second vehicle and a distance between the second vehicle and a vehicle corresponding to the number included in the first set of numbers that is equal to the first number of vehicles.

7. The method according to claim 1 , further comprising:

identifying, after the first communication device receives the message from a vehicle other than the second vehicle, a second number of vehicles which are within the communication range of the first communication device and have not received the message;

calculating a second count-down time based on the second number if the second number doesn't equal to zero, where the greater the second number the shorter the second count-down time; and

if not all the second number of vehicles receive the message before the second count-down time ends, broadcasting the message when the second count-down time ends.

8. A vehicle mounted communication system, the communication system comprising:

a receiver and a transmitter; and

a processing device configured to:

after the receiver receives a message from a first vehicle, identify a first number of vehicles that are within a communication range of the communication system;

calculate a first count-down time based on the first number of vehicles, where the first count-down time decreases as the first number of vehicles increases; and

if the message is not received by the receiver again before the first count-down time ends, control the transmitter to broadcast the message when the first count-down time ends.

9. The vehicle mounted communication system according to claim 8 , wherein the first number of vehicles are out of a communication range of the first vehicle.

10. The vehicle mounted communication system according to claim 8 , wherein the processing device is further configured to determine that the system is not out of a valid range of the message based on position information of the system.

11. The vehicle mounted communication system according to claim 8 , wherein the processing device is further configured to determine that a lifetime of the message has not expired when the message is received by the receiver.

12. The vehicle mounted communication system according to claim 8 , wherein the processing device is further configured to:

identify a first group of vehicles that are within both the communication range of the communication system and the communication range of the first vehicle;

obtain a first set of numbers, wherein each number indicates how many vehicles are within a communication range of a corresponding vehicle included in the first group;

sort the first set of numbers together with the first number of vehicles to obtain a number sequence; and

calculate the first count-down time based on the position of the first number in the number sequence.

13. The vehicle mounted communication system according to claim 12 , wherein the first number of vehicles is equal to a number included in the first set of numbers and the processing device is further configured to:

determine a position of the first number of vehicles in the number sequence and a position of the number included in the first set of numbers in the number sequence based on a distance between the first vehicle and the second vehicle and a distance between the second vehicle and a vehicle corresponding to the number included in the first set of numbers that is equal to the first number of vehicles.

14. The vehicle mounted communication system according to claim 8 , wherein the processing device is further configured to:

identify, after the receiver receives the message from a vehicle other than the first vehicle, a second number of vehicles which are within the communication range of the communication system and have not received the message;

calculate a second count-down time based on the second number if the second number doesn't equal to zero, where the greater the second number the shorter the second count-down time; and

if not all the second number of vehicles receive the message before the second count-down time ends, control the transmitter to broadcast the message when the second count-down time ends.