802.11p is the basis for
dedicated short-range communications (DSRC), a
U.S. Department of Transportation project based on the
Communications Access for Land Mobiles (CALM) architecture of the
International Organization for Standardization for vehicle-based communication networks, particularly for applications such as toll collection, vehicle safety services, and commerce transactions via cars. The ultimate vision was a nationwide network that enables communications between vehicles and roadside access points or other vehicles. This work built on its predecessor ASTM E2213-03 from
ASTM International. In Europe, 802.11p is used as a basis for the ITS-G5 standard, supporting the GeoNetworking protocol for vehicle to vehicle and vehicle to infrastructure communication. ITS G5 and GeoNetworking is being standardised by the
European Telecommunications Standards Institute group for
Intelligent Transport Systems.
Context Because the communication link between the vehicles and the roadside infrastructure might exist for only a short time interval, the IEEE 802.11p amendment defines a method to exchange data through that link without the need to establish a
basic service set (BSS), thus without the need to wait on the association and authentication procedures to complete prior to exchanging data. For that purpose, IEEE 802.11p-enabled stations use the wildcard
BSSID (a value of all 1s) in the header of the frames they exchange, and may start sending and receiving data frames as soon as they arrive on the communication channel. Because such stations are neither associated nor authenticated, the authentication and data confidentiality mechanisms provided by the
IEEE 802.11 standard (and its amendments) cannot be used. These kinds of functionality must then be provided by higher network layers.
Timing advertisement This amendment adds a new management frame for timing advertisement, which allows IEEE 802.11p enabled stations to synchronize themselves with a common time reference. The only time reference defined in the IEEE 802.11p amendment is
UTC.
Receiver performance Some optional enhanced
channel rejection requirements (for both adjacent and nonadjacent channels) are specified in this amendment in order to improve the immunity of the communication system to out-of-channel interference. They only apply to
OFDM transmissions in the 5 GHz band used by the
IEEE 802.11a physical layer.
Frequency band IEEE 802.11p standard typically uses channels of 10 MHz bandwidth in the 5.9 GHz band (5.850–5.925 GHz). This is half the bandwidth as used in 802.11a, or double the transmission time per data symbol. This allows the receiver to better cope with the characteristics of the radio channel in vehicular communications environments, especially echoes of signals reflected by moving objects. == History==