5G • 5G-Advanced (Rel-18)
Massive Delay PRACH Enhancements
Random Access Preamble Formats for Long Delay Satellite Profiles
Extended preamble formats and guard times allowing UEs to execute random access over satellite distances exceeding 1,000 km without preamble collision.
Technical Explanation
Terrestrial 5G PRACH assumes propagation distances under 100 km. Satellites in LEO orbit 600 to 1,200 km away, creating massive round-trip propagation delays. Rel-18 introduces extended preamble formats with wide cyclic prefixes and guard periods that absorb hundreds of kilometers of differential delay across large satellite beam footprints.
Key Functions
- Extends random access preamble formats to accommodate multi-millisecond propagation delays
- Provides wide cyclic prefixes preventing interference with adjacent OFDM data symbols
- Enables initial cell attachment across satellite spot beams spanning 500 km in diameter
- Supports accurate initial Timing Advance calculation for orbiting space platforms
Specifications
3GPP TS 38.211, TS 38.321 (Rel-18)
Interfaces
Uu (PRACH)
Related 5G Concepts
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