# On the Impact of Multiple Access Interference in LTE-V2X and NR-V2X Sidelink Communications +
## 1 Introduction  
Vehicular communications are envisioned as a major enabler to allow intelligent transportation systems (ITS) and smart cities to become completely integrated, especially in very densely populated places. The transition to a cellular radio access infrastructure is planned as a strategic necessity to develop automated driving and its integration into the larger transport ecosystem [1], supported by all the involved actors (i.e., network operators and vehicle manufacturers). From this perspective, vehicular communications have advantages beyond just safety applications. Vehicles with vehicle-to-everything (V2X) connectivity can aid in improving traffic management, which results in greener automobiles and cheaper fuel costs [2]. The vehicle safety and non-safety applications lay the foundation for Cooperative-Intelligent Transportation Systems (C-ITSs), which the European Commission has been promoting [3], as well as Cooperative, Connected, Automated, and Autonomous Mobility (CCAM) [4]. C-ITS services were given 75 MHz of the spectrum in the 5.9 GHz band by the US Federal Communications Commission (FCC) in 1999. Throughout the past 20 years, the allocation has spurred a great deal of research to design and implement V2X communications (e.g., the CAMP collaboration in the US [5], the Car 2 Car Communication Consortium in Europe, [6] and many more research initiatives). Subsequently, starting with Release 14 (Rel-14), the 3 rd Generation Partnership Project (3 GPP) concentrated on developing the cellular V2X technology, establishing several specification standards to advance the V2X technology. In this domain, different communication modes can be identified, e.g., Vehicle-to-Vehicle (V2V), Vehicle-to-Network (V2N) or Infrastructure (V2I), Vehicle-to-Road Side Unit (V2R), and Vehicle-to-Pedestrian (V2P). The definition of higher layer standards, message formats, protocols, and applications (such as [7] in Europe and [8] in the US) came after the development of the first IEEE 802.11-based radio standards [9]. Cross-domain alliances have been established as a tangible result, such as the 5G Automotive Association (5 GAA), which is very active in defining development plans and use cases for various service classes as well as in stating precise requirements (such as E2E latency, bit rates, availability, and loss rates) for standardization bodies such as the 3 GPP [10]. Most challenging use cases, e.g., vehicle platooning or cooperative collision avoidance (CCA), present difficulties and opportunities for Cellular-V2X (C-V2X) communications [11]. Additionally, due to the stringent latency requirement (even below 20 ms [10]), direct radio communication between vehicles, i.e., sidelink communication, is preferable to allocating resources through the cellular infrastructure. However, the achievable performance is limited by multiple access interference in C-V2X sidelink communication, particularly in congested metropolitan environments. Additionally, 3 GPP Rel-14 Mode 3 and Mode 4 are sometimes called the baseline modes for sidelink LTE-V2X [12]. The Semi-persistent Scheduling (SPS) scheme, exploited for resource allocation, may not be able to deliver the necessary level of service depending on the distances and relative positions between vehicles [13]. It is crucial to characterize the performance of such systems analytically, to plan and manage the settings for vehicle platooning. With Release 15 (Rel-15), the 3 GPP started a new cellular V2X standard based on the 5G New Radio (NR) air interface. Then, based on the 5G NR air interface, Release 16 (Rel-16) is the first to enable NR-V2X sidelink communication, and serves as the foundation for upcoming improvements and extensions for both NR-V2X and non-V2X sidelink applications [14]. From the start of the work on NR-V2X, 3 GPP decided that NR-V2X needed to complement LTE-V2X and not replace it [15]. LTE-V2X is envisioned to support basic active safety applications, whereas NR-V2X will support more advanced applications, including connected and automated driving.