  Conversely to mainstream cellular networks where uplink / downlink data
traffic is centrally managed by eNodeBs, in vehicle-to-vehicle (V2V) broadcast
communications \textit{mode-3} eNodeBs engage solely in subchannel assignment
but ultimately do not intervene in data traffic control. Accordingly, vehicles
communicate directly with their counterparts utilizing the allotted
subchannels. Due to its loosely controlled one-to-all nature, V2V
\textit{mode-3} is advantageous for time-critical applications. Nevertheless,
it is imperative that the assignment of subchannels is accomplished without
conflicts while at the same time satisfying quality of service (QoS)
requirements. To the best of our knowledge, there exists no unified framework
for V2V \textit{mode-3} that contemplates both prevention of allocation
conflicts and fulfillment of QoS. Thus, four types of conditions that are of
forceful character for attaining QoS-aware conflict-free allocations have been
identified: $(i)$ assure differentiated QoS per vehicle, $(ii)$ preclude
intra-cluster subframe conflicts, $(iii)$ secure minimal time dispersion of
allotted subchannels and $(iv)$ forestall one-hop inter-cluster subchannel
conflicts. Such conditions have been systematized and merged in an holistic
manner allowing non-complex manipulation to perform subchannel allocation
optimization. In addition, we propose a surrogate relaxation of the problem
that does not affect optimality provided that certain requisites are satisfied.
