Why do we need NDI bit in HARQ process?However we have ACK/NACK mechanism then why do we need to NDI?

Question

Without MAC HARQ configuration how MSG3 is receiving ACK/NACK form ENB , As per my knowledge MAC configuration comes after connection request then how this is possible?

Answer 1

as PHICH is not so reliable so, UE trusting only on NDI bit. once NDI bit toggled then only UE release the buffered data.

Comments

In that case why do you need PHICH, however UE is not considering so you can use only NDI right?

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Hello,

it's depend upon which type of HARQ we are using in case of Non adaptive retransmission UE relay only on PHICH. but in adaptive retransmission it also checking NDI bit to clear the buffer.

Answer 2

Harq retransmissions are limited , so if data is not decoded by ue then it will send the nack. Sending nack does not mean next will be retx . So on the basis of ndi, ue will know that it is new or retx.