WLAN IEEE 802.11p testing

Wi-Fi in a very challenging environment

The main requirements for this dedicated short range communications (DSRC) technology were low latency, ad-hoc networking, support for distances of up to one kilometer and the ability to handle the high speed of the vehicles (relative velocities of up to around 500 km/h) in an extreme multipath environment. IEEE 802.11p is based on the first OFDM-based Wi-Fi standard IEEE 802.11a, but uses for example a half-clock mode for the 10 MHz bandwidth channel for more robustness. It operates in dedicated frequency bands reserved for ITS services, typically at 5.9 GHz. In contrast to standard WLAN configurations, there are no access points (AP) in 802.11p. Instead, stations (STA) communicate directly in a peer-to-peer network with each other.

Your 802.11p test challenges

The standard defines several transmitter and receiver tests such as EVM, TX power, spectrum emissions and sensitivity. There are two important adaptations in 802.11p for ITS: a much stricter spectrum mask as well as stricter adjacent and nonadjacent channel rejection requirements. The adjacent channel rejection measures the ability of a receiver to demodulate and decode a desired signal in the presence of an interfering signal in an adjacent or nonadjacent channel. Moreover, for vehicular environments, fading has an enormous impact on the received signal quality. Not only does the channel itself change very quickly versus time, but Doppler shift, which is determined by the relative velocity between the transmitter and receiver, also occurs. This makes repeatable real-time fading simulation essential.