  The rapid development of the fifth generation mobile communication systems
accelerates the implementation of vehicle-to-everything communications.
Compared with the other types of vehicular communications, vehicle-to-vehicle
(V2V) communications mainly focus on the exchange of driving safety information
with neighboring vehicles, which requires ultra-reliable and low-latency
communications (URLLCs). However, the frame size is significantly shortened in
V2V URLLCs because of the rigorous latency requirements, and thus the overhead
is no longer negligible compared with the payload information from the
perspective of size. In this paper, we investigate the frame design and
resource allocation for an urban V2V URLLC system in which the uplink cellular
resources are reused at the underlay mode. Specifically, we first analyze the
lower bounds of performance for V2V pairs and cellular users based on the
regular pilot scheme and superimposed pilot scheme. Then, we propose a frame
design algorithm and a semi-persistent scheduling algorithm to achieve the
optimal frame design and resource allocation with the reasonable complexity.
Finally, our simulation results show that the proposed frame design and
resource allocation scheme can greatly satisfy the URLLC requirements of V2V
pairs and guarantee the communication quality of cellular users.
