RACH Configurations for NR Shared Spectrum LBT Delays
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Solution Overview
Problem
In wireless communication networks, especially in 5G NR systems, the listen before talk (LBT) procedure can lead to skipped transmission of synchronization signals and misconfiguration of random access resources, causing interference and performance degradation due to the indefinite nature of LBT procedures.
Innovation Solution
Implementing a method where base stations perform LBT at the beginning of a DMTC window, transmit synchronization signals over directional beams in a predetermined sequence, and signal additional random access resources outside the dedicated window, allowing UEs to monitor and transmit random access signals on these beams after a successful LBT procedure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If LBT procedure is performed on shared spectrum channel, then channel access is achieved, but transmission timing becomes indefinite causing misconfiguration of RACH resources
Solution Approach 1:
The base station performs LBT procedure at a predetermined timing (beginning of DMTC window) before RACH resource allocation. By preliminarily determining channel availability and establishing a fixed timing relationship between LBT completion and RACH resource configuration, the system avoids timing misconfiguration while ensuring reliable channel access.
2Reliability
If LBT procedure delays beyond dedicated RACH resources, then channel availability is ensured, but dedicated RACH resources become unusable
Solution Approach 1:
The system dynamically adjusts RACH resource configuration based on LBT procedure completion timing. When LBT completes before the DMTC window, the base station signals additional RACH resources within the window. When LBT delays beyond the window, the base station signals RACH resources in subsequent occasions. This dynamic adaptation ensures both channel availability and efficient RACH resource utilization.
3Object-affected harmful factors
If synchronization signal transmission is skipped due to LBT failure, then interference is avoided, but UE synchronization and RACH configuration are impacted
Solution Approach 1:
The base station monitors LBT procedure outcomes and provides feedback to UEs regarding synchronization signal transmission status and RACH resource configuration. When LBT succeeds, the base station transmits synchronization signals and configures corresponding RACH resources. When LBT fails, the base station signals alternative RACH resources in subsequent occasions. This feedback mechanism ensures UEs can reliably synchronize and access the network despite LBT-induced variability.
Data Source
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AI summary
Random access channel (RACH) configurations for new radio (NR) shared spectrum (NR-SS) networks are disclosed. A base station may perform a listen before talk (LBT) procedure on a shared communication channel at a beginning of a discovery measurement timing configuration (DMTC) window. In response to a successful LBT, the base station may transmit synchronization signals over a plurality of directional beams according to a predetermined sequence. The user equipment (UE) may determine the predetermined sequence through the detected synchronization signals. The base station may signal configuration of additional random access resources when the LBT procedure delays beyond dedicated random access resources. The base station may then monitor for UEs to transmit random access signals from each direction corresponding to directional beams within the additional random access resources according to the predetermined sequence.