Why Non adaptive transmission applicable only in UL?

Question

Why LTE supports only in UL non adaptive transmission ?

Answer 1

Hi,

Your question is bit confusing for me. In UL there are 2 types of re-transmission
-> Adaptive
-> Non Adaptive

1. Adaptive
   UE does "Adaptive retransmission" if it detects PDCCH(DCI 0 and NDI not-toggled). UE does not care about HARQ feedback (PHICH), it just retransmits based on DCI 0 information

2. Non adaptive
   UE figures out that it is using "Non-Adaptive retransmission" if it got "HARQ feedback (PHICH=NACK)" but does not get DCI 0 over PDCCH and instead uses predefined sequence.

Comments

Thanks for the answer. This i understood, But why we don't have same mechanism in DL HARQ.

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Hi Himani,
UL Uses the specific process in a specific subframe. Every 8 subframes UE repeats the process id. As a result, eNB knows exactly when each HARQ process comes.
UL HARQ Process ID = (SFN x 10 + subframe) modulo 8
but
In DL, Network sends these (Process ID, RV) in PDCCH DCI0 message. UE doesn't know which Process ID to look for until it gets the DL data.HARQ re-transmission for given HARQ process id can be scheduled any time. So if we use Adaptive or Non-Adaptive in DL it will cause signalling overhead.

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As per your above comment For DL , However ENB sends DCI0 for re transmission then how non adaptive creates signalling overhead here.