Friday, August 11, 2017
Summary of “A Tutorial Survey on Vehicular Ad Hoc Networks”
Summary of “A Tutorial Survey on Vehicular Ad Hoc Networks”
The concept of using wireless communication to provide safety and comfort in vehicles has appeared since 1980s. In the last few years, the research in this field shows a large increase because of these reasons:
- Adaptation and decreasing cost of IEEE 802.11 technologies
- The embrace of vehicle manufactures of information technology to provide safety and comfort
- The commitment of large government to allocate wireless spectrum for VANET communication
The main goals of VANET summarized as follow:
- Road safety
- Transportation efficiency
- Reduce the impact of transportation on the environment
One-hop broadcast communication plays an important role to provide information for safety-related applications. For this reason, two different messages are used as follow:
- Event-driven (DEN)
are sent when an hazardous event happens.
- Periodic (CAM)
are sent periodically to inform the surrounding cars about the cars knowledge such as: geographical position, speed, acceleration and so on. It is suggested that these messages send 10 times per second with maximum latency of 100ms and minimum range of 150 m.
Unfortunately, using broadcast communication causes that we can not use the predefined schemes in IEEE 802.11 to alleviate the collision among the contending nodes. In this case, schemes like RTS/CTS and ACK packets cause more collisions. As a result, IEEE 802.11 converts to a simple CSMA scheme for broadcast communication. Therefore, well-known problem of hidden and exposed terminals is problematic and must be revised. Because the periodic messages overloaded the control channel, adaptive transmit power and rate control are required.
- The main challenges of VANET is as follow:
- No central communication coordinator or handshaking protocol
- The necessity of on shared control channel to broadcast each cars knowledge to the surroundings
- Dynamic network topology
- Diversity of network traffic density
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