Does HARQ use Chase or Incremental Combining in MAC layer during RLC ACK/NACK?

Hi Experts,

I have one question in LTE.
How we will know whether HARQ use is Chase Combining or Incremental Combining in MAC layer during RLC ACK/NACK?
In logs or in parameter dump?
As for example oss command or something like that…

Because chase combining will increase too much retx and bler and incremental too has some types where only retransmitted packets should be used to reduce bler.
But how can we indentify either in logs, kpi or oss command?

I feel Layer 2 is more interesting than Layer 3, as everything is deal by MAC as transporter to lower and upper layer where in RF we rarely see.
Obviously RRC is main connection, but MAC is main transporter to both layer lower and uper.

And MAC is toughest part to study. And understand.
Every protocol is important, but MAC is toughest part.

Protocol industry doesn’t give importance to RF Optimisation, because we are associated with lower and uper layer knowledge.
Layer 2 is kind of bouncher to us and we stuck there.
As RF is left with no scope.
If Huawei, then getting into Ericsson is tough.
If Ericsson, geting into other vendors is tough.
UE testing sees a good future as 3gpp won’t change.

You can check it with DCI format used in Downlink i.e. 1, 1a, 1b, 1d, 2a, 2b, 2c.
There is field redundancy version to be used by UE.

RRC Connection setup uses SRB0 or 1?

Srb1 is at complete.

The redundancy version is signalled separately for downlink.
The RV bits inform the UE of the puncturing pattern applied to the channel coded transport block.

It uses Srb0.

Complete uses srb1.
But redundancy version will indicate harq process.

Do you mean adaptive or non adaptive?
That’s decided by UE, but for redundancy version even I read lot, but finally concluded it’s not decided by UE but indicated by eNodeB.
Through DCi format.

Other can comment…

eNodeB has info about RVI and MCs which it can used by downlink flexibilble in adaptive retransmission whereas in non adaptive it doesn’t change.

For harq in uplink this one used which depend as below.


Yes, thanks @ankgitm.
Uplink has both, downlink uses adaptive.

I think redundancy version id indicates whether it is chase combining or type 2 or type 3 in harq may be.

Type 1 is chase combining.
Type 2 or 3 is incremental redundancy.
Yes as per bit of field RV it’s decided.

I got it. RVI id, if 3 then it will be type 3.
Redundancy version id.

Which one is better in ReTx: incremental redundancy or chase combining?

Any specific advantage of IR?

Dis. of IR → It’s increasing complexity and required more memory at UE side.

See this: