UE PRACH Occasion Selection Under FBE Channel Occupancy
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Solution Overview
Problem
The determination of valid random access channel (RACH) occasions (RO) and PRACH transmission over frame based equipment (FBE) mode in unlicensed spectrum is not adequately addressed, particularly in 5G NR systems, leading to issues with bandwidth usage compliance and inefficient channel access.
Innovation Solution
A method for determining valid ROs for PRACH transmission by obtaining indications of RACH occasion positions, synchronization signal block positions, frame periods, and channel occupancy time, ensuring non-overlap with downlink signals and idle frame parts, and performing Listen Before Talk (LBT) procedures as indicated by cell-specific configurations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If RACH occasions are determined without considering FBE frame period and channel occupancy time, then random access procedure can be performed, but bandwidth usage regulations are violated and channel access efficiency deteriorates
Solution Approach 1:
The patent applies preliminary action by determining valid RACH occasions in advance based on FBE frame period and channel occupancy time indications before actual random access transmission. The UE identifies which RO positions fall within valid channel occupancy periods and excludes those in idle frame parts, ensuring regulatory compliance is established beforehand rather than discovered during transmission attempts.
Solution Approach 2:
The patent applies parameter changes by dynamically adjusting the selection of RACH occasions based on received indications of FBE frame period, channel occupancy time, and UL/DL patterns. The UE modifies its RO selection parameters to align with the actual channel occupancy schedule, changing from static RO selection to dynamic parameter-based selection that adapts to unlicensed spectrum conditions.
2Productivity
If RACH occasions are selected without validating against downlink signal positions, then PRACH transmission can proceed, but interference with downlink signals increases and communication reliability decreases
Solution Approach 1:
The patent applies preliminary anti-action by proactively identifying and excluding RACH occasions that would overlap with downlink signal positions. The UE receives indications of actual transmitted SSB positions and uses this information to determine valid RO positions that do not conflict with downlink transmissions, preventing interference before it occurs rather than dealing with it after transmission.
3Quantity of substance
If all possible RACH occasion positions are used for PRACH transmission, then random access capacity increases, but invalid transmissions increase and channel access efficiency decreases
Solution Approach 1:
The patent applies the taking out principle by extracting and removing invalid RACH occasion positions from the set of all possible RO positions. The UE receives indications of FFP information, COT information, and UL/DL patterns, then identifies and excludes RO positions that fall within idle frame parts or conflict with downlink signals, keeping only the valid subset for PRACH transmission.
Data Source
AI summary
A communication method being applied to a user equipment (UE) and includes: obtaining a first indication indicating at least one of possible random access channel (RACH) occasion (RO) positions, actual transmitted synchronization signal block (SSB) positions, frame based equipment (FBE) frame period (FFP) information, or uplink/downlink (UL/DL) pattern within the FFP; obtaining a second indication indicating channel occupancy time (COT) information; and determining, based on the first indication and the second indication, valid RO for physical RACH (PRACH) transmission.