LTE: Difference between Adaptive and non-adaptive HARQ ?

Answer 1

Please check this link:
http://www.sharetechnote.com/html/BasicProcedure_LTE_HARQ.html

Answer 2

HARQ is synchronous in the UL. Whenever, a re-transmission occurs in UL, it can be either Adaptive and Non-adaptive

Adaptive
a. triggered when NDI bit is not toggled relative to the previous transmission. This information should be present in the PDCCH DCI0.
b. MCS and RB's may change as per resources allocated by the eNB on PDCCH DCI0 transmission

Non-adaptive
a. trigerred when NACK is received on PHICH
b. use same resources as per the previous transmission i.e. MCS and RB's remains unchanged

Answer 3

Adaptive Transmission:
a. triggered when NDI bit is not toggled relative to the previous transmission. This information should be present in the PDCCH DCI0.
b. MCS and RB's may change as per resources allocated by the eNB on PDCCH DCI0 transmission

Non-adaptive Transmission:
a. trigerred when NACK is received on PHICH
b. use same resources as per the previous transmission i.e. MCS and RB's remains unchanged

Notes:
1. If ACK is there on PHICH and PDCCH carriers the NDI bit as not toggled then NON-ADAPTIVE re-transmission will occur
2. If NACK is there on PHICH and no PDCCH is received then UE will store the data in the HARQ buffer and no re-transmission will occur