R1-2600052
discussion
Discussion on 6G PRACH Design and RACH Procedure
From FUTUREWEI
Summary
Futurewei presents three proposals for the 6G RAN1 study item, focusing on PRACH and RACH design. They first propose designing scalable PRACH formats for both TN and NTN, then propose two options for expanding PRACH preamble sets, and finally propose studying solutions to improve MSG3 reliability in the upper mid-band.
Position
Futurewei identifies shortcomings in NR PRACH and RACH designs for 6G scenarios, arguing that existing NR PRACH formats are customized for specific TN deployments and cannot be reused for NTN scenarios without GNSS without introducing non-scalable new formats. They propose designing new 6G PRACH formats that are inherently scalable and flexible for both TN and NTN, considering time-varying RTT and Doppler shifts in NTN. For the PRACH preamble set, they argue simply expanding beyond 64 preambles increases false detection and inter-cell interference by reducing root sequence reuse pattern size, and thus propose either extending Zadoff-Chu sequences or designing a new sequence. For RACH in the upper mid-band (7-24 GHz), they propose studying solutions to increase MSG3 transmission reliability to address coverage gaps caused by higher path loss while reusing existing 5G mid-band site grids.
Key proposals
- Proposal 1 (Sec 2.1): RAN1 should strive to design PRACH formats that are scalable and flexible for both TN and NTN.
- Proposal 2 Option 1 (Sec 2.1): RAN1 considers expanding PRACH preamble sets using Zadoff-Chu sequences as a starting point.
- Proposal 2 Option 2 (Sec 2.1): RAN1 considers expanding PRACH preamble sets using a new sequence design.
- Proposal 3 (Sec 2.2): RAN1 studies potential solutions that increases the reliability of 6GR RACH MSG3 transmissions in the upper mid-band (at about 7 – 24 GHz).