5G • RAN
DAI
Downlink Assignment Index
Counters in DCI Format 1_0/1_1 preventing HARQ-ACK codebook misalignment when PDCCH drops occur.
Technical Explanation
If a UE fails to detect a PDCCH scheduling a PDSCH, it would not generate a HARQ-ACK bit, misaligning the gNodeB's feedback codebook. The Downlink Assignment Index solves this by embedding two counters in DCI: Counter DAI (accumulated PDSCH count up to current carrier/slot) and Total DAI (total scheduled PDSCHs across all component carriers).
Key Functions
- Prevents HARQ-ACK codebook bit-shift errors caused by missed PDCCHs
- Counter DAI tracks running total of scheduled PDSCH transmissions
- Total DAI signals carrier-wide total across component carriers
Specifications
3GPP TS 38.213
Interfaces
Uu
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