Random Access in Unlicensed Carrier Aggregation

The patent implements dynamic cell selection for random access preamble transmission. Instead of fixed association between downlink and uplink cells, the UE dynamically selects an uplink cell from a TAG based on real-time channel occupancy detection. This dynamic adaptation allows the system to respond to changing interference conditions in unlicensed spectrum, resolving the contradiction between protocol compliance and transmission reliability.

The patent introduces an intermediary mechanism (CCA/LBT procedure and TAG-based cell selection) between the PDCCH order reception and random access preamble transmission. The UE performs channel assessment and selects an appropriate uplink cell as an intermediary step, rather than directly transmitting on the associated uplink cell. This intermediary process enables the system to navigate around interference while maintaining protocol integrity.

The patent performs LBT procedure as a preliminary action before random access preamble transmission. By checking channel occupancy in advance and selecting an unoccupied uplink cell beforehand, the system ensures reliable transmission while minimizing delays during the actual access procedure. The preliminary channel assessment prevents failed transmissions and retransmission delays.

The patent implements dynamic timing adaptation where the LBT procedure and cell selection process are performed adaptively based on traffic conditions and interference levels. When the channel is clear, the procedure completes quickly; when interference is detected, the system dynamically adjusts by selecting alternative cells, thereby optimizing the balance between reliability and delay.

The patent leverages the existing TAG (Timing Advance Group) structure, which was originally designed for timing alignment purposes, and repurposes it for flexible cell selection in random access. The TAG already contains multiple uplink cells with established timing relationships, so the UE can select from these pre-configured cells without requiring entirely new control logic. This universal reuse of existing structures provides flexibility while limiting complexity growth.

The patent enables the UE to autonomously perform cell selection based on simple LBT outcomes and pre-configured TAG information. The UE self-determines which uplink cell to use based on channel conditions without requiring complex network control or additional signaling. This self-service approach provides adaptability while keeping device complexity manageable by using local decision-making based on straightforward criteria.