  A hybrid analog-digital combiner for broadcast vehicular communication is
proposed. It has an analog part that does not require any channel state
information or feedback from the receiver, and a digital part that uses maximal
ratio combining (MRC). We focus on designing the analog part of the combiner to
optimize the received signal strength along all azimuth angles for robust
periodic vehicle-to-vehicle (V2V) communication, in a scenario of one dominant
component between the communicating vehicles (e.g., highway scenario). We show
that the parameters of a previously suggested fully analog combiner solves the
optimization problem of the analog part of the proposed hybrid combiner.
Assuming $L$ directional antennas with uniform angular separation together with
the special case of a two-port receiver, we show that it is optimal to combine
groups of $\lceil L/2\rceil$ and $\lfloor L/2\rfloor$ antennas in analog domain
and feed the output of each group to one digital port. This is shown to be
optimal under a sufficient condition on the sidelobes level of the directional
antenna. Moreover, we derive a performance bound for the hybrid combiner to
guide the choice of antennas needed to meet the reliability requirements of the
V2V communication links.
