Safety in Vehicular Networks--on the Inevitability of Short-Range Directional Communications

Safety implies high dependability and strict timeliness under worst-case conditions. These requirements are not met with existing standards aimed at inter-vehicular communications V2V in vehicular networks. On-going research targets medium-range omnidirectional V2V communications and short-range directional communications, which we refer to as neighbor-to-neighbor N2N communications. Focusing on the latter, we investigate the time-bounded message dissemination TBMD problem as it arises in platoons and ad hoc vehicle strings, referred to as cohorts. Informal specifications of TBMD, of a solution, are given. We show how to guarantee cohort-wide dissemination of any N2N message generated by a cohort member, either spontaneously or upon receipt of a V2V message. Dissemination time bounds are given for worst-case conditions regarding N2N channel contention and N2N message losses. These results add to previously demonstrated merits of short-range directional communications as regards safety in vehicular networks.