  In this paper, we focus on the performance analysis of a semi-persistent
scheduling scheme for vehicular safety communications, motivated by the Mode 4
medium access control protocol in 3GPP Release 14 for Cellular-V2X. An
analytical model is built and a fixed point method is used to calculate the
collision probability and average delay in both fully connected and partially
connected cases under the assumption of perfect PHY performance. We use Monte
Carlo simulation to verify the results obtained in the analytical model. The
simulation results show that our analytical model can give a good estimation of
the collision probability and average delay. We verify that a trade-off between
delay and collision probability can be achieved with a flexible resource block
selection. Monte Carlo simulation results show that with the flexible resource
selection scheme average delay can be shortened significantly with only a small
compromise in collision probability.
