This paper provides an overview of the LTE-V standard supporting sidelink or V2V communications using the PC5 interface in LTE. The paper reviews the physical layer changes introduced under Release 14 for LTE-V, its communication modes 3 and 4, and the LTE-V evolutions under discussion in Release 15 to support 5G V2X communications and autonomous vehicles' applications. Modes 3 and 4 support direct V2V communications, but differ on how they allocate the radio resources. Resources are allocated by the cellular network under Mode 3. Mode 4 does not require cellular coverage, and vehicles autonomously select their radio resources using a distributed scheduling scheme supported by congestion control mechanisms. Mode 4 is considered the baseline mode, and represents an alternative to 802.11p or DSRC. In this context, the paper also presents a detailed analysis of the performance of LTE-V sidelink Mode 4, and proposes a modification to its distributed scheduling.

The C-V2X or LTE-V standard has been designed to support V2X (Vehicle to Everything) communications. The standard is an evolution of LTE, and it has been published by the 3GPP in Release 14. This new standard introduces the C-V2X or LTE-V Mode 4 that is specifically designed for V2V communications using the PC5 sidelink interface without any cellular infrastructure support. In Mode 4, vehicles autonomously select and manage their radio resources. Mode 4 is highly relevant since V2V safety applications cannot depend on the availability of infrastructure-based cellular coverage. This paper presents the first analytical models of the communication performance of C-V2X or LTE-V Mode 4. In particular, the paper presents analytical models for the average PDR (Packet Delivery Ratio) as a function of the distance between transmitter and receiver, and for the four different types of transmission errors that can be encountered in C-V2X Mode 4. The models are validated for a wide range of transmission parameters and traffic densities. To this aim, this study compares the results obtained with the analytical models to those obtained with a C-V2X Mode 4 simulator implemented over Veins.

V2X (Vehicle to everything) communications can be currently supported by standards based on IEEE 802.11p (e.g. DSRC or ITS-G5) or LTE-V2X (also known as Cellular V2X or C-V2X) technologies. There has been an intense debate in the community on which technology achieves best performance. However, existing studies do not take into account the variability present in the generation and size of V2X messages. This variability can significantly impact the operation and performance of the Medium Access Control (MAC). This study progresses the state of the art by conducting an in-depth evaluation of both technologies under different message traffic patterns. In particular, we consider aperiodic and periodic messages of constant or variable size based on the standardized ETSI Cooperative Awareness Messages (CAMs). This study considers different scenarios and possible configurations of IEEE 802.11p and LTE-V2X. We demonstrate that IEEE 802.11p can better cope with variations in the size and time interval between messages. We also demonstrate (and characterize) that the LTE-V2X sensing-based semipersistent scheduling faces certain inefficiencies when transmitting aperiodic messages of variable size. These inefficiencies result in that IEEE 802.11p generally outperforms LTE-V2X when transmitting aperiodic messages of variable size except when the channel load is very low.

No abstract

No abstract