NR-U PRACH Resource Selection for Low-Latency Access
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In 5G New Radio (NR) systems, especially in unlicensed spectrum, wireless transmit/receive units (WTRUs) face challenges in initial access due to severe path losses and interference from hidden nodes, which affect the reliability and efficiency of random access procedures, particularly in millimeter wave (mmW) systems.
Innovation Solution
The WTRU determines whether to use a first type of PRACH transmission without listen-before-talk (LBT) or a second type with LBT, randomly selects PRACH resources associated with a synchronization signal block (SSB), transmits a PRACH preamble, and performs a second LBT for hidden node detection, adjusting power ramping based on detection results for retransmissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the WTRU performs listen-before-talk (LBT) before PRACH transmission, then collision with other transmissions is reduced, but random access delay increases
Solution Approach 1:
The patent applies dynamics by making the LBT procedure conditional rather than static. The WTRU dynamically decides whether to perform LBT based on whether it detects a synchronization signal block (SSB) in the downlink. When SSB is detected, LBT is skipped (fast PRACH); when not detected, LBT is performed (standard PRACH). This dynamic adaptation resolves the contradiction by allowing low-delay operation when conditions permit while maintaining collision avoidance when necessary.
Solution Approach 2:
The patent changes the parameter of LBT execution from a fixed binary choice to a conditional variable state. The decision to perform LBT or not is changed based on the detection state of SSB. This parameter change enables the system to switch between two operational modes (fast PRACH without LBT and standard PRACH with LBT), thereby optimizing the trade-off between delay and collision reduction根据不同 channel conditions.
2Reliability
If the WTRU transmits PRACH preamble with higher power, then path loss compensation is improved, but energy consumption increases
Solution Approach 1:
The patent applies preliminary action by performing SSB detection before PRACH transmission. The WTRU first monitors for and detects the SSB in the downlink, which provides channel state information and timing reference. Based on this preliminary detection, the WTRU can determine the appropriate transmit power level for the PRACH preamble, avoiding unnecessary high-power transmissions when the channel conditions don't require them, thus resolving the contradiction between path loss compensation and energy consumption.
3Reliability
If the WTRU performs beamforming with multiple antenna elements, then beamforming gain increases, but device complexity increases
Solution Approach 1:
The patent applies partial action by using beamforming selectively rather than continuously. The WTRU performs beamforming operations only when necessary for PRACH transmission, particularly when using the fast PRACH procedure without LBT where beam directionality is more critical. The base station performs beamforming on the SSB transmission to cover multiple directions, and the WTRU responds with targeted beamforming only for the access preamble. This partial application of beamforming reduces overall device complexity while maintaining sufficient beamforming gain when needed.
Data Source
AI summary
Systems and methods are disclosed for performing random access (RA) in 5G New Radio (NR) systems, including New Radio in unlicensed spectrum (NR-U) systems. A wireless transmit/receive unit (WTRU) may receive a configuration for physical random access channel (PRACH) resources. The WTRU may determine whether to use a first type of PRACH transmission or a second type of PRACH transmission. For the first type of PRACH transmission, the WTRU may select a PRACH resource, without performing listen-before-talk (LBT), immediately following reception of an synchronization signal block (SSB). For the second type of PRACH transmission, the WTRU may randomly select the PRACH resource associated with the SSB, and perform a first LBT on the selected PRACH resource. The WTRU may transmit a PRACH preamble in the selected PRACH resource. The WTRU may perform a second LBT for random access response (RAR) reception for hidden node detection.