PRACH Resource Mapping for 5G Beam Failure Recovery
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Solution Overview
Problem
5G NR technology faces challenges in beam failure recovery and efficient PRACH resource utilization due to signal degradation from UE movement and line-of-sight blocking, requiring improved mechanisms for beam identification and handover.
Innovation Solution
An association between downlink reference signals (CSI-RS, SS blocks, PBCH blocks) and PRACH resources (preambles, RACH occasions) is established for beam identification and recovery, allowing flexible PRACH designs with reduced bandwidth and cyclic shift for synchronous transmissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If beamforming is employed to improve link budget and signal quality, then received signal power increases and transmission power requirements decrease, but the system becomes vulnerable to beam failure due to UE movement, angular rotation, or line-of-sight blocking
Solution Approach 1:
The system pre-establishes multiple beam associations between downlink reference signals (CSI-RS, SS blocks, PBCH blocks) and PRACH resources before beam failure occurs. When beam failure is detected, the UE can immediately switch to a pre-configured alternative beam without requiring complex real-time beam searching, thus resolving the contradiction between maintaining reliable beamforming links and adapting to beam failure conditions.
2Ease of operation
If PRACH resources are allocated for all uplink requests including those requiring TA command and C-RNTI, then comprehensive coverage is achieved, but resource utilization efficiency decreases when TA and C-RNTI are not required
Solution Approach 1:
The patent segments PRACH resources into different types based on whether TA command and C-RNTI are required. Separate PRACH configurations are defined for requests requiring full response (TA + C-RNTI) versus those requiring only uplink grant. This segmentation allows the system to allocate appropriate resources for each case, improving overall PRACH resource utilization efficiency while maintaining comprehensive coverage for all uplink request types.
Data Source
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AI summary
A User Equipment (UE) including a wireless transceiver and a controller is provided. The wireless transceiver performs wireless transmission and reception to and from a cellular station. The controller selects a downlink reference signal associated with a candidate beam among a plurality of downlink reference signals including Channel State Information-Reference Signal (CSI-RS) resources, Synchronization Signal (SS) blocks, or Physical Broadcast Channel (PBCH) blocks, and determines one from a plurality sets of Physical Random Access Channel (PRACH) preambles and RACH occasions for the selected downlink reference signal according to an association configured between the downlink reference signals and PRACH resources. Also, the controller uses the determined set of PRACH preamble and RACH occasion to perform a PRACH transmission to the cellular station via the wireless transceiver.