MCS Adaptation and its role in improving MAC Scheduling for Variable Packet Sizes in NR-V2X.

This paper investigates the significance of assuming an adaptive Modulation and Coding Scheme (MCS) when scheduling packets of varying sizes in New Radio V2X (NR-V2X). It is envisaged that many existing and future event driven vehicular services will exhibit significant variance in packet sizes, both between applications and within the same application. To ensure a sufficient quality of service, NR-V2X and its predecessor Cellular V2X (C-V2X) must be able to effectively schedule these diverse packet sizes. As such, this paper analyses the impact of fixed vs adaptive MCS selection and shows that assuming an adaptive approach is preferable in all cases, especially when dealing with varying packet sizes. A fixed MCS is commonly assumed in literature and this paper shows that such an assumption can have a large negative performance impact on the MAC layer scheduler. We further evaluate that considering an MCS range exceeding that specified in the current standard is extremely beneficial and evaluate the performance of alternative MCS selection schemes that minimise disruption in the MAC layer grant mechanism. We find that the default standardised MCS selection mechanism still remains preferable.