Latency of Cellular-Based V2X: Perspectives on TTI-Proportional Latency and TTI-Independent Latency

Vehicle-to-everything (V2X) is a form of wireless communication that is extremely sensitive to latency, because the latency is directly related to driving safety. The V2X systems developed so far have been based on the LTE system. However, the conventional LIE system is not able to support the latency requirements of latency-aware V2X. Fortunately, the state-of-the-art cellular technology standard includes the development of latency reduction schemes, such as shortened transmission time intervals (TTI) and self-contained subframes. This paper verifies and analyzes the latency of cellular-based V2X with shortened TTI, which is one of the most efficient latency reduction schemes. To verify the feasibility of V2X service, we divide the V2X latency into two types of latency, TTI-independent latency and TTI-proportional latency. Moreover, using system-level simulations considering additional overhead from shortened TTI, we evaluate the latency of cellular-based V2X systems. Based on this feasibility verification, we then propose cellular based V2X system design principles in terms of shortened TTI with only one ORDM symbol and while sustaining radio resource control connection.