Performance analysis of multiple access protocols for sidelink vehicular communications

The term ”Intelligent Transportation System (ITS)” refers to all systems that make use of communication, information processing, and technology to enhance the current mobility ex- perience and to improve infrastructure productivity, mobility, and safety. The new technolo- gies that make up the so-called ITS need to be properly tested and verified, obtaining, when- ever possible, simple yet accurate analytical models to study and optimize their operation. Strict standards are in place to meet the ever-changing vehicle application, communication and service requirements of connected vehicles, such as Cellular Vehicle-to-everything (C- V2X) communications. 3rd Generation Partnership Project (3GPP) has created standards for Vehicle-to-everything (V2X) based on the Long-Term Evolution (LTE) and 5th Genera- tion New Radio (5G-NR) Air Interface, which go under the names Long-Term Evolution-V2X (LTE-V2X), and New Radio-V2X (NR-V2X), respectively, to facilitate connected and au- tonomous driving use cases. The performance of both technologies is significantly influenced by the resource allocation mechanism and multiple-access interference in scenarios with high mobility. The C-V2X approaches must be able to handle the demands of the V2X appli- cations. Vehicle platooning benefits from Sidelink (SL) communications to meet stringent latency requirements at the cost of uncertainty in reliability due to multiple-access inter- ference. In this context, Intelligent Reflective Surface (IRS) is a disruptive communication approach that allows the possibility of controlling the propagation environment and improv- ing the quality of wireless communications, making it a promising option to improve V2X applications. In this thesis, we propose an analytical framework to model the performance of the LTE- V2X mode 4 and NR-V2X mode 2 SL protocols. Furthermore, we examine how to integrate IRS and use Virtual Line-of-sight (VLOS) SL communications in vehicle platoons driving in urban scenarios. We evaluated the effectiveness, particularly concerning Sensing-based Semi-persistent Scheduling (SB-SPS) defined in a vehicle platooning scenario, depending on the available resources, the number of interfering vehicles, and their relative positions. A Nakagami-Lognormal composite channel model is assumed and Moment Matching Approx- imation (MMA) is used to approximate the statistics of Signal-to-Interference plus Noise Ratio (SINR). Compared to existing studies in the literature, the proposed model offers a compact, yet accurate approximation of achievable performance in terms of packet success rate and allows planning and adapting the configuration and parameter setup of the vehicle platoon. The results confirm a improvement in performance with NR-V2X versus LTE-V2X, particularly for many vehicles with a high distance between vehicles, providing a concise, yet accurate, modeling rationale without having to resort to extensive computer simulation or experimental measurements. The analysis further shows conditions in which VLOS SL communication induced by IRS can also outperform the corresponding Line-of-sight (LOS) propagation scenario. Keywords: C-V2X, LTE-V2X, Mode 4, NR-V2X, Mode 2, Vehicular Communications, SL Communications, IRS, LOS, VLOS, Multiple-access interference, Platooning.