PDCCH-Ordered RACH with Multiple Msg1 for Beam Misalignment
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Solution Overview
Problem
Existing wireless communication systems experience significant latency and signaling distortion during random access procedures due to beam misalignment and pathloss, leading to delayed connectivity establishment and increased latency in receiving connection responses.
Innovation Solution
Implementing multiple Msg1 transmissions during a configured RAR window, facilitated by PDCCH orders, to enhance beam diversity and reduce latency in both contention-free and contention-based random access procedures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If single Msg1 transmission is used during random access procedure, then signaling overhead is reduced, but latency increases and connectivity establishment fails due to beam misalignment
Solution Approach 1:
The random access procedure is segmented into multiple Msg1 transmission attempts, each with its own RAR window opportunity. Instead of a single transmission, the UE transmits Msg1 multiple times across different RAR windows, dividing the connectivity establishment process into discrete transmission segments that increase the probability of successful reception despite beam misalignment or pathloss conditions.
Solution Approach 2:
The system performs preliminary actions by configuring multiple RAR window opportunities and corresponding Msg1 transmission occasions before the random access procedure begins. The network pre-configures the UE with multiple RAR window parameters and Msg1 transmission configurations, enabling the UE to proactively attempt multiple transmissions without waiting for failure conditions, thereby reducing overall latency.
2Reliability
If multiple Msg1 transmissions are implemented, then connectivity establishment reliability improves, but signaling overhead increases
Solution Approach 1:
Multiple Msg1 transmissions are performed periodically across different RAR window opportunities rather than continuously. Each transmission occurs at predetermined intervals defined by the RAR window configuration, allowing the system to maintain reliability through repeated attempts while controlling signaling overhead by spacing transmissions appropriately and stopping upon successful connectivity establishment.
3Productivity
If beam diversity is enhanced through multiple transmissions, then signaling throughput improves, but system complexity increases
Solution Approach 1:
Beam diversity is enhanced by introducing a time dimension to the transmission process. Instead of only varying spatial beams, the system transmits Msg1 multiple times across different time opportunities (RAR windows), adding temporal diversity to the beam transmission strategy. This dimensional expansion improves signaling throughput by capturing varying channel conditions over time without requiring complex spatial beam management at each transmission instant.
Data Source
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AI summary
Methods, systems, and devices for multiple random access channel (RACH) message 1 (Msg1) transmission for physical downlink control channel (PDCCH) ordered RACH are described. A user equipment (UE) may perform the multiple Msg1 transmission as part of a CFRA or CBRA procedure for access. The UE may perform the multiple Msg1 transmissions in a cyclic consecutive manner during configured RACH occasions or according to explicit time and frequency indications of a random access response (RAR) window. Based on the multiple Msg1 transmission procedure, the UE may reduce latency for random access procedure on the RACH and improve signaling throughput. In some cases, the UE may support beam correspondence and may perform multiple Msg1 transmissions to enhance multi-beam diversity during RACH transmission by performing transmission corresponding to RACH occasions mapped to different synchronization signal blocks (SSBs).