Toward 6G sidelink communication

In many countries, next-generation connected and autonomous vehicles (CAVs) will rely on short-range C-V2X sidelink communication. NR-V2X, based on the 5G NR air interface, introduces several enhancements over LTE-V2X to support advanced vehicular use cases. In the 5G NR-V2X autonomous mode (Mode 2), vehicles independently select radio resources for transmissions using a distributed sensing mechanism. Despite improvements in Releases 16 and 17, such as feedback mechanisms, resource coordination, and resource re-evaluation, collisions persist due to decentralized sensing, a dynamic channel environment, and half-duplex constraints. Incorrect resource selections can lead to persistent collisions, especially in periodic traffic scheduled via semi-persistent scheduling (SPS). The introduction of aperiodic traffic, essential for advanced use cases, further increases instability and collision risk. This thesis explores resource allocation improvements at the MAC and PHY layers to meet stringent vehicular network demands. Specifically, it investigates full-duplex (FD) and non-orthogonal multiple access (NOMA) in NR-V2X Mode 2. FD transceivers enable vehicles to detect resource collisions in real-time, facilitating adaptive resource allocation, while NOMA, through successive interference cancellation (SIC), allows decoding of overlapping transmissions, reducing packet loss and improving spectral efficiency. The study evaluates these technologies across periodic and aperiodic broadcast traffic using semi-persistent (SB-SPS) and dynamic scheduling (SB-DS), along with blind retransmissions. Extensive simulations show that FD improves short-range reliability, while SIC-based NOMA enhances mid-range performance. Notable gains are observed even with practical, non-ideal SIC implementations, demonstrating that receiver-based interference management can outperform complex allocation protocols. These findings highlight the potential of FD and NOMA integration to enhance V2X scalability and robustness, paving the way for future 6G vehicular communication systems capable of supporting increasingly complex autonomous driving requirements.