Multi-Beam PRACH Preamble Transmission for Spatial Diversity
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Solution Overview
Problem
Current mobile wireless communication systems face challenges in optimizing UE Tx beam selection for PRACH preambles, leading to suboptimal spatial diversity and increased retry rates, particularly in beamformed deployments where UL/DL reciprocity may not hold, and distinguishing between legacy and beam-changing UEs is resource-intensive.
Innovation Solution
The method involves transmitting a physical random access channel preamble using multiple transmission beams within the same random access channel occasion and detecting beam switching operations to select the best beam, allowing for improved spatial diversity and reduced retry rates by indicating a preferred transmission beam, thereby enhancing cell coverage and reducing RACH resource subdivision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single transmission beam is used for PRACH preamble transmission, then the device complexity is reduced, but the spatial diversity gain is insufficient leading to increased retry rates
Solution Approach 1:
The patent segments the PRACH preamble transmission across multiple transmission beams within the same random access channel occasion. The UE transmits the same preamble using different beams (e.g., first beam, second beam) in different time slots or symbols, enabling spatial diversity without requiring complex multi-beam management procedures. This segmentation approach improves reliability by ensuring at least one transmission succeeds while keeping the implementation relatively simple.
Solution Approach 2:
The patent employs preliminary action by having the network entity prepare and indicate multiple random access channel occasions within a single RACH occasion structure before the UE performs beam switching. The network configures the timing and resources in advance, allowing the UE to switch beams between transmissions without complex real-time coordination, thus improving spatial diversity while managing complexity.
2Reliability
If multiple transmission beams are used for PRACH preamble transmission, then the spatial diversity gain is improved, but the RACH resource requirements increase
Solution Approach 1:
The patent merges multiple random access channel occasions into a single RACH occasion structure. Multiple occasions are combined in the time domain within one RACH occasion, allowing the UE to transmit preambles using different beams without requiring separate RACH occasions for each beam. This merging approach provides spatial diversity gain while avoiding a proportional increase in overall RACH resource requirements.
Solution Approach 2:
The patent makes the RACH occasion structure universal by designing it to accommodate multiple beams and multiple occasions within a single framework. The same RACH occasion can serve multiple functions: carrying preambles from different beams, supporting both beam-switching and non-beam-switching UEs, and providing flexible resource allocation. This multi-functionality reduces the need for dedicated resources for each beam.
3Reliability
If beam switching is detected and preferred beam indication is provided, then the Msg3 coverage is improved, but the signaling complexity increases
Solution Approach 1:
The patent implements self-service by enabling the network entity to autonomously detect beam switching operations through analysis of received preamble transmissions. The network entity monitors the RACH occasion, identifies which beams were used by comparing received signal characteristics against configured beam patterns, and determines beam switching without requiring explicit UE signaling. This self-detection capability improves Msg3 coverage through accurate beam identification while avoiding additional signaling complexity.
Solution Approach 2:
The patent employs feedback mechanisms where the network entity provides preferred beam indication to the UE based on detected beam switching operations. The network analyzes which beam(s) provided the best reception quality and feeds back this information to guide the UE's subsequent transmissions. This feedback loop improves Msg3 coverage by ensuring transmissions use the optimal beam while maintaining manageable signaling complexity through efficient feedback formats.
Data Source
AI summary
Systems, methods, apparatuses, and computer program products for enabling multi-beam PRACH. One method may include transmitting a physical random access channel preamble based upon at least two different transmission beams in the same random access channel occasion; and receive a message configured to indicate a preferred transmission beam of the transmission beams used with the physical random access channel preamble.