  The vehicular ad-hoc network (VANET) based on dedicated short-range
communication (DSRC) is a distributed communication system, in which all the
nodes share the wireless channel with carrier sense multiple access/collision
avoid (CSMA/CA) protocol. However, the backoff mechanism of CSMA/CA in the
channel contention might cause uncertain transmission delay and impede a
certain quality of service (QoS) of applications. Moreover, there still exists
a possibility of parlous data-packets collision, especially for broadcast or
non-acknowledgement (NACK) transmissions. The original contributions of this
paper are summarized as follows: (1) Model the packets collision probability of
broadcast or NACK transmission in VANET with the combination theory and
investigate the potential influence of miss my packets (MMP) problem. (2) Based
on the software define vehicular network (SDVN) framework and QoS requirement,
a novel link-level scheduling strategy, which determines the start-sending time
for each connection, is proposed to maximize packets delivery ratio (PDR).
Alternatively, maximizing PDR has been converted to the overlap minimization
among transmission durations. (3) Meanwhile, an innovative transmission
scheduling greedy search (TSGS) algorithm is originally proposed to mitigate
computational complexity. Extensive simulations have been done in a unified
platform Veins combining SUMO and OMNET++. And numerous results show that the
proposed algorithm can effectively improve the PDR by at least 15%, enhance the
collision-avoidance performance by almost 40%, and reduce the MMP ratio by
about 3% compared with the random transmitting, meanwhile meet the QoS
requirement.
