Resource Scheduling under Knock-Out Congestion Control in New Radio (NR) Sidelink Mode 2

For resource scheduling in New Radio (NR) Sidelink Mode 2, the 3GPP Release 16 eliminated a step from the Release 14 resource selection algorithm, i.e., Received Signal Strength Indicator (RSSI)-based sorting of candidate resources. However, we show that this change can have detrimental effects when combined with congestion control. Packet knock-outs on the access layer is explicitly suggested in standards and a facilities layer packet knock-out (Cooperative Awareness Message (CAM) generation rule) has been established as a standard for congestion control. The absence of the RSSI-based candidate sorting for resource selection makes it difficult to utilize the residual quasi-periodicity after packet knock-outs, and increases packet collisions. We demonstrate that in case of the CAM generation rule, the reintroduction of the RSSI-based sorting step increases the packet reception ratio (PRR) within 300 m of the transmitter by more than 5% compared to the default Release 16 algorithm. It contrasts with a surprising finding that the new grant breaking feature for aperiodic traffic underperforms the default Release 16 scheduling algorithm in the same conditions. The findings suggest that the value of the RSSI-based sorting of candidate resources should be reevaluated in NR vehicle-to-everything (V2X) congestion control.