Abstract
5G NR V2X has been designed to support advanced connected and automated
driving V2X services. These services are characterized by variable
traffic patterns that can generate packet collisions in decentralized
systems where vehicles autonomously select their radio resources like
5G NR V2X mode 2. 5G NR V2X introduces a re-evaluation mechanism at the
MAC layer to detect and avoid possible packet collisions before a
vehicle transmits in selected resources. Most of the studies conducted
to date on 5G NR V2X do not consider the re-evaluation mechanism
despite being a mandatory MAC feature. This paper advances the state of
the art with an in-depth analysis and evaluation of the operation and
performance of re-evaluation in 5G NR V2X mode 2 under different traffic
patterns and mode 2 configurations. The study shows that re-evaluation
is effective in avoiding collisions with periodic traffic but its
effectiveness decreases with aperiodic traffic and of variable size.
The study also shows that re-evaluation is effective in avoiding
collisions generated by the retransmission of packets. However, its
overall impact on the performance of 5G NR V2X mode 2 is small, while
it can have a relevant implementation cost due to the frequent
re-evaluation checks and resource reselections. This raises questions on
the current design of the re-evaluation mechanism that is a mandatory
feature in 5G NR V2X mode 2.