NR Random Access Procedure for SSB Beam Selection and MsgB Multiplexing
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Solution Overview
Problem
The 2-step random access procedure in NR wireless communication systems faces challenges in determining the SSB selection and reporting, RNTI usage, and MCS selection for combined msgB transmissions, especially when multiple SSBs are mapped to one RO, leading to uncertainties in beam selection and message multiplexing for multiple UEs.
Innovation Solution
The proposed solution involves improved SSB reporting by UEs, where multiple SSBs with satisfactory signal metrics are indicated in msgA, allowing the base station to determine a suitable beam and RNTI for combined msgB transmissions, and selecting a common MCS based on UE priorities and signal qualities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If multiple SSBs are mapped to one RO to support more UEs, then the quantity of UEs served increases, but the difficulty of detecting and measuring SSB selection and beam quality increases
Solution Approach 1:
The base station pre-configures and signals to UEs the mapping relationships between SSBs and ROs, along with the associated preambles. This preliminary action enables UEs to make informed selections without real-time complexity, resolving the measurement difficulty while supporting multiple UEs.
Solution Approach 2:
The system segments the random access procedure into distinct phases: SSB measurement and selection by UE, mapping to appropriate RO based on pre-configured relationships, and base station detection. This segmentation simplifies the overall complexity of handling multiple SSBs and UEs.
2Loss of substance
If combined msgB transmissions are used for multiple UEs to reduce overhead, then signaling overhead decreases, but the reliability of message transmission decreases due to uncertainty in beam and RNTI selection
Solution Approach 1:
The base station determines and prepares appropriate beams and RNTIs in advance based on the received msgA and SSB indications. This preliminary determination ensures that combined msgB transmissions use reliable, pre-selected parameters, maintaining transmission reliability while achieving overhead reduction through combining.
Solution Approach 2:
The UE provides feedback in msgA about its selected SSB and beam quality metrics. The base station uses this feedback to make informed decisions about beam and RNTI selection for the combined msgB transmission, ensuring reliability while maintaining efficiency.
3Measurement precision
If SSB reporting is improved by indicating multiple SSBs in msgA to enhance beam selection accuracy, then beam selection precision improves, but the complexity of the random access procedure increases
Solution Approach 1:
The base station pre-configures the mapping between SSBs, ROs, and preambles, and signals this information to UEs before random access. This preliminary configuration enables UEs to report multiple SSBs with their quality metrics without increasing procedural complexity, as the evaluation rules are predetermined.
Solution Approach 2:
The system dynamically adapts to different scenarios by allowing flexible reporting of multiple SSBs with varying quality metrics. The base station dynamically selects the most appropriate SSB and beam based on the reported information, achieving high precision while managing complexity through adaptive decision-making.
Data Source
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AI summary
Embodiments of the present disclosure provide methods and apparatuses for random access procedure. A method at a user equipment (UE) comprises selecting a synchronization signal and physical broadcast channel block (SSB) with a signal measured metric satisfying a criterion. The method further comprises transmitting a first message including a random access channel (RACH) preamble on a RACH occasion and data on an uplink shared channel (USCH) to a base station. The RACH preamble and the RACH occasion are selected based on a mapping of the SSB to the RACH preamble and the RACH occasion. The method further comprises receiving a second message from the base station as a response to the first message.