NR/NR-U Initial Access with SSB-Linked RACH Collision Avoidance
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Solution Overview
Problem
In 5G wireless systems, collisions frequently occur between beam-formed signals during initial access, such as synchronization signal blocks, random access channel resources, and control channels, due to severe path losses and non-line-of-sight issues, which hinder effective communication between base stations and wireless transmit receive units.
Innovation Solution
The proposed solution involves a wireless transmit receive unit assessing RACH occasions based on semi-static UL/DL configuration and SS block indications to determine valid transmission opportunities, allowing for the transmission of RACH only in collision-free slots, and employing techniques like preamble subset partitioning and redundancy versions to manage collisions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If beam-formed signals are used to compensate severe path loss, then coverage and signal strength are improved, but signal collisions occur during initial access
Solution Approach 1:
The patent segments the random access channel resources by associating different RACH occasions with different synchronization signal block (SSB) beams. This segmentation allows WTRUs to select specific RACH occasions corresponding to their detected SSB beam, thereby reducing collisions between beam-formed signals during initial access while maintaining the coverage benefits of beamforming.
2Reliability
If multiple RACH occasions are configured for different SSB beams, then collision reduction is achieved, but system complexity increases
Solution Approach 1:
The patent applies preliminary action by configuring RACH occasion associations with SSB beams in advance through system information broadcasting. The base station pre-establishes the mapping relationships between SSB beams and RACH occasions, allowing WTRUs to autonomously determine appropriate RACH occasions based on detected SSB beams without requiring complex real-time coordination, thus reducing system complexity while maintaining collision avoidance.
3Productivity
If WTRU autonomously determines valid RACH occasions, then access efficiency is improved, but error in occasion selection may occur
Solution Approach 1:
The patent implements feedback mechanisms where the base station monitors RACH transmissions and provides feedback through random access responses (RAR). When a WTRU selects an incorrect RACH occasion or experiences transmission failure, the base station can indicate through RAR whether the transmission was successful or provide correction information, allowing the WTRU to adjust future selections and improving overall reliability while maintaining autonomous operation.
Data Source
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AI summary
Methods, systems, and devices for addressing collisions of possible random access channel (RACH) occasions. A wireless transmit receive unit (WTRU) may receive configuration information, the configuration indicating a plurality of physical random access channel (PRACH) preamble subsets, wherein each PRACH preamble subset is associated with a respective synchronization signal (SS) block. The WTRU may also receive a plurality of SS block transmissions, select a first SS block transmission of the plurality of SS block transmissions, select a first PRACH preamble based on selecting the first SS block, wherein the first PRACH preamble is one of the PRACH preambles comprised in the PRACH preamble subsets indicated as being associated with the first SS block by the configuration information, and transmit the first PRACH preamble in a random access channel (RACH) occasion.