5G • RAN
Msg1 PRACH
Random Access Preamble (Msg1)
First step in 4-step RACH where UE transmits a random access preamble sequence on PRACH.
Technical Explanation
In Step 1 of random access, the UE randomly selects a preamble from available contention-based preambles (or uses a dedicated preamble assigned for contention-free access) and transmits it on an allocated PRACH occasion. This provides the gNodeB with initial arrival timing for distance estimation.
Key Functions
- Transmits Zadoff-Chu or short preamble sequence on PRACH
- Enables gNodeB to measure initial round-trip propagation delay
- Initiates contention-based (CBRA) or contention-free (CFRA) access
Specifications
3GPP TS 38.211, TS 38.213
Interfaces
Uu
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