  As development Internet-of-Vehicles (IoV) technology and demand for
Intelligent Transportation Systems (ITS) increase, there is a growing need for
real-time data and communication by vehicle users. Traditional request-based
methods face challenges such as latency and bandwidth limitations. Mode 4 in
Connected Vehicle-to-Everything (C-V2X) addresses latency and overhead issues
through autonomous resource selection. However, Semi-Persistent Scheduling
(SPS) based on distributed sensing may lead to increased collision.
Non-Orthogonal Multiple Access (NOMA) can alleviate the problem of reduced
packet reception probability due to collisions. Moreover, the concept of Age of
Information (AoI) is introduced as a comprehensive metric reflecting
reliability and latency performance, analyzing the impact of NOMA on C-V2X
communication system. AoI indicates the time a message spends in both local
waiting and transmission processes. In C-V2X, waiting process can be extended
to queuing process, influenced by packet generation rate and Resource
Reservation Interval (RRI). The transmission process is mainly affected by
transmission delay and success rate. In C-V2X, a smaller selection window (SW)
limits the number of available resources for vehicles, resulting in higher
collision rates with increased number of vehicles. SW is generally equal to
RRI, which not only affects AoI in queuing process but also AoI in the
transmission process. Therefore, this paper proposes an AoI estimation method
based on multi-priority data type queues and considers the influence of NOMA on
the AoI generated in both processes in C-V2X system under different RRI
conditions. This work aims to gain a better performance of C-V2X system
comparing with some known algorithms.
