Uplink Channels — PUSCH, PUCCH, PRACH
PUSCH (Physical Uplink Shared Channel) carries user data — uses LDPC. PUCCH (Physical Uplink Control Channel) carries ACK/NACK, SR, CSI. PRACH (Physical Random Access Channel) carries access preambles.
PUSCH Deep Dive
PUSCH supports two waveforms: CP-OFDM (default) and DFT-s-OFDM (transform precoded, lower PAPR for cell-edge). Codebook-based vs non-codebook-based transmission. UL DMRS Type 1/2. Frequency hopping for diversity.
PUCCH Formats
Format 0/1: 1-2 bits, short. Format 2: >2 bits, short. Format 3: large payload, long. Format 4: multi-user multiplexed. HARQ-ACK codebooks (semi-static, dynamic Type 2, Type 3).
PRACH Procedures
4-step RACH (Msg1-Msg4) and 2-step RACH (MsgA, MsgB Rel-16). Long preamble formats (0, 1, 2, 3) for large cells. Short formats (A1-A3, B1-B4, C0, C2) for dense urban.
SRS Configuration
Sounding Reference Signal — UE transmits, gNB measures UL channel for codebook selection, beam refinement, timing-advance maintenance.
Timing Advance
T_TA = (N_TA + N_TA,offset) · T_c. UE applies TA to all uplinks. Range covers cells up to 100 km in long-PRACH-format mode.
UL Power Control
Open-loop: pathloss-based. Closed-loop: TPC commands in DCI. Per-channel (PUSCH, PUCCH, SRS) independent loops. Sub-PRB power adjustment for FR2.