Improving NR-V2X Autonomous Mode Through Resource Re-Evaluation

Abstract

In the context of 5G Vehicle-to-Everything (V2X) autonomous mode, 3GPP introduced a resource re-evaluation mechanism to reduce collision occurrences. This mechanism requires stations to perform an additional check for available resources before transmission, to detect possible late-arriving reservations from other stations. The findings of this paper confirm that, while mandatory, the resource re-evaluation brings minimal performance enhancements to the overall system. Building upon this observation, the paper proposes a standard-compliant resource allocation mechanism named Double Initial Transmission (DIT), which leverages the resource re-evaluation more effectively. Focusing on scenarios with prevalent periodic traffic, the paper introduces an innovative approach: the first packet within a sequence of periodic packets is transmitted twice, utilizing two different resources. The first transmission reserves a resource for the subsequent one. After transmitting the first packet, the resource used for its initial transmission is released, while the second resource is reserved periodically for the following packets. This strategy significantly reduces the probability of periodic collisions and has a minimal impact on the overall channel occupation. Furthermore, in instances of potential collisions on the second resource, the re-evaluation mechanism conducted before transmission serves as a proactive measure, detecting and addressing conflicts before they occur. The paper aims to provide an analysis of this modified resource allocation strategy and its implications for improving the performance of 5G NR-V2X, particularly in the context of periodic traffic scenarios.