  The question of robust direct communication in vehicular networks is
discussed. In most state-of-the-art approaches, there is no central entity
controlling channel access, so there may be arbitrary interference from other
parties. Thus, a suitable channel model for Vehicle-to-X (V2X) communication is
the Arbitrarily Varying Channel (AVC). Employing multiple antennas on a vehicle
or sending over multiple frequencies to make use of diversity are promising
approaches to combat interference. In this setup, an important question about
diversity is how many antennas or orthogonal carrier frequencies are necessary
in order to avoid system breakdown due to unknown interference in AVCs. For
Binary Symmetric AVCs (AVBSC) and a physically meaningful identical
state-constrained jammer, the deployment of a third, uncorrelated receiving
antenna or the parallel transmission over three different orthogonal
frequencies avoids symmetrizability and thus ensures positivity of the capacity
of the overall communication channel. Furthermore, the capacity of the
identical state-constrained composite AVBSC is continuous and shows
super-activation, a phenomenon which was hitherto deemed impossible for
classical communication without secrecy constraints. Subsuming, spatial and
frequency diversity are enablers for reliable communication over communication
channels with arbitrarily varying interference.
