As the communication range of a WLAN connection is limited to a few hundred metres, every vehicle also acts as a router for message forwarding. The routing algorithm will be based on the position of the vehicles, and can handle rapid changes to the ad hoc network topology (see Figure 1).
The implementation of C2C wireless communications thus calls not only for robust RF performance, a physical layer function which can readily be verified with the use of an instrument such as a spectrum analyser – the MS2830A from Anritsu is a good example. The system designer must also implement a sophisticated test plan for verifying the protocol layer performance, to show that it can handle rapid changes in network topology without dropping packets or losing connections. As above, standard test specifications might not capture the full depth of testing required under the provisions of ISO 26262, and this looks set to demand a new approach to the design and implementation of test routines from automotive RF engineers.
eCall: another safety-critical technology
The European Union’s eCall system, and the similar ERA-GLONASS (in Russia) combines mobile communications and satellite positioning to provide fast, reliable assistance to motorists in the event of an accident.
Both systems rely on satellite location data, the first on GPS, the latter on GLONASS. When in-vehicle sensors trigger events such as airbag deployment, eCall