In Rel10, what are those 4 bits in format1b used for?

Specs & Protocol Testing
1

Hi All.
I have a question.

In release 10, format1b is said to have 4 bit harq.
What are those bits used for?

2

UE needs to report HARQ feedback for each TB.
In case of carrier aggregation (2 CC in this case), UE may get upto 4TBs (2 TB on primary cell and 2 more on secondary cell) in a TTI.
So, UE need 4 bits to acknowledge these 4 TBs.

3

Thanks! But what about id it is TDD set up single cell?
These 4 bits have any use there?

4

In case of TDD, for some DL/UL configs, we have less UL slots than DL slots.
Those cases we need to send HARQ feedback of multiple DL slots in a single UL slot.
There UE will use concepts like HARQ bundling/multiplexing to send feedback of for multiple DL slots.
These cases it needs more bits.

5

Oh I get it… Thank you​:pray::pray::pray::pray: so much sir!