5G NR V2X Resource Re-Selection and Pre-emption Mechanism

The resource selection process is segmented into distinct phases: sensing phase where UEs monitor and collect resource status information, selection phase where candidate resources are identified based on sensing results, and reservation phase where specific resources are allocated for transmission. This segmentation reduces system complexity by breaking down the autonomous resource selection into manageable, standardized steps while maintaining high allocation efficiency.

UEs perform preliminary sensing and resource assessment actions before actual transmission occurs. The sensing phase collects information about channel conditions, other V2X users, and resource availability in advance, allowing the selection algorithm to make informed decisions without real-time complexity. This preliminary action enables efficient resource allocation while reducing the computational burden during critical transmission moments.

The resource pre-emption mechanism is designed to be dynamic rather than static. Pre-emption is only triggered when specific conditions are met, such as when a high-priority packet arrives and existing resource allocations cannot accommodate it. The mechanism dynamically adjusts resource allocations based on real-time traffic priorities and channel conditions, ensuring high reliability for critical packets while minimizing unnecessary pre-emption events that would increase latency.

The system changes key parameters such as pre-emption thresholds, priority levels, and resource reservation durations based on traffic conditions and service requirements. For time-sensitive applications, the system adjusts parameters to minimize pre-emption latency, while for reliability-critical applications, it tightens pre-emption triggers. This parameter adaptation allows the system to optimize the trade-off between reliability and latency for different V2X scenarios.

The system implements feedback mechanisms where receiving UEs send acknowledgment signals to transmitting UEs about successful packet reception. Based on this feedback, transmitting UEs determine whether retransmission is necessary. This feedback-driven approach ensures high reliability by performing retransmissions only when needed, avoiding unnecessary resource consumption from redundant transmissions while maintaining robust error correction for challenging channel conditions.

The system supports multiple retransmission opportunities but does not always utilize them. Instead of forcing a fixed number of retransmissions, the system performs partial retransmission actions based on actual channel conditions and packet importance. For critical safety packets, the system may employ excessive retransmission actions to ensure delivery, while for less critical data, it uses fewer retransmissions, optimizing the balance between reliability and resource consumption.