1 Dissect a format
DCI format explorer
Choose a format to see its job, who it addresses, where it is monitored, and the fields it carries. Notice how non-fallback formats grow far larger as they expose BWP switching, multi-layer MIMO, CBG retransmission and more.
Direction
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Search space
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RNTI
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Approx size
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Key fields
2 The map
Three families
0_x — Uplink grants
0_0 fallback PUSCH · 0_1 full-feature PUSCH · 0_2 compact/URLLC. Addressed by C-RNTI (and friends).
1_x — Downlink assignments
1_0 fallback PDSCH · 1_1 full-feature PDSCH · 1_2 compact/URLLC.
2_x — Group-common
2_0 SFI · 2_1 pre-emption · 2_2 TPC PUSCH/PUCCH · 2_3 TPC SRS. One DCI, many UEs.
3 Why fallback exists
Robust by design
Fallback formats (0_0 / 1_0) have a fixed, minimal field set and a size that doesn't depend on fancy RRC configuration. That makes them decodable during initial access, beam failure, or any time the UE and gNB might disagree on configuration — the always-works safety net.
Because their size is predictable, fallback formats are also the anchor the DCI size-budget alignment rules pad everything else toward.
4 Knowledge check