Technical Specifications
Two categories of draft standards provide outlines for vehicular networks. These standards constitute a category of IEEE standards for a special mode of operation of IEEE 802.11 for vehicular networks called Wireless Access in Vehicular Environments (WAVE). 802.11p is an extension to 802.11 Wireless LAN medium access layer (MAC) and physical layer (PHY) specification. As of November 2006 Draft 1.3 of this standard is approved . 802.11p aims to provide specifications needed for MAC and PHY layers for specific needs of vehicular networks. IEEE 1609 is a family of standards which deals with issues such as management and security of the network:
- 1609.1 -Resource Manager: This standard provides a resource manager for WAVE, allowing communication between remote applications and vehicles.
- 1609.2 -Security Services for Applications and Management Messages
- 1609.3 -Networking Services: This standard addresses network layer issues in WAVE.
- 1609.4 -Multi-channel Operation: This standard deals with communications through multiple channels.
The current state of these standards is trial-use. A vehicular communication networks which complies with the above standards supports both vehicular on-board units (OBU) and roadside units (RSU). RSU acts similar to a wireless LAN access point and can provide communications with infrastructure. Also, if required, RSU must be able to allocate channels to OBUs. There is a third type of communicating nodes called Public Safety OBU (PSOBU) which is a vehicle with capabilities of providing services normally offered by RSU. These units are mainly utilized in police cars, fire trucks, and ambulances in emergency situations.
As mentioned before DSRC provides several channels (seven 10 MHz channels in North America) for communications. Standards divide the channels into two categories: a control channel and service channels. Control channel is reserved for broadcasting and coordinating communications which generally takes place in other channels. Although DSRC devices are allowed to switch to a service channel, they must continuously monitor the control channel. There is no scanning and association as there is in normal 802.11. All such operations are done via a beacon sent by RSUs in the control channel. While OBUs and RSUs are allowed to broadcast messages in the control channels, only RSUs can send beacon messages.
In North America DSRC devices operate over seven 10 MHz channels. Two of the channels are used solely for public safety applications which means that they can only be used for communications of message with a certain priority or higher.
Although 802.11p and 1609 drafts specify baselines for developing vehicular networks, many issues are not addressed yet and more research is required.
Read more about this topic: Vehicular Communication Systems
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