Carrier Aggregation activation/deactivation/signalling

Dear Experts,
I have some query with respect to Carrier Aggregation.

  1. How does eNB decides to activate/deactivate carrier aggregation apart from BSR report recieved from UE?
  2. RRC signalling and DCI information is always carried on pdcch of pcell or it can be carried on scell as well?
  3. CQI and HARQ ack/nack is transmitted on pcell pucch/pusch or it can transmitted on both?

MAC ce used for activation/deactivation from rel 10 onwards.

Pdcch signalling through pcell and scell also possible depends on implementation.

We can use seperate harq feedback for pcell and scell using pucch format 1b

Activation- Based on RLC buffer threshold. Deactivation- Based on SCell deactivation timer expiry (explicit)or based on poor RF of UE (CQI, HARQ NACK implicitly )

RRC signalling always on PCell. DCI (SCell Scheduling ) can be through SCell or any other cell (cross carrier scheduling)

CQI and HARQ ack/nack is always on PCell Uplink.

For CA UE activation: Based on UE traffic volume which enodeB monitor like:
CaMgtCfg.ActiveBufferLengthThd=9KB (default setting in Huawei)
and CaMgtCfg.ActiveBufferDelayThd=50msec.

Secondly, CA will deactive if UE Signal quality degraded. Thanks.

CA activation is 2 types:

  1. Blind based
  2. Volume based

For CA deactivation it’s seen during Handover from pcell to scell we need to release scell.

CA activation is never done blindly. CA addition can be done blind not activation.

Ok in my knowledge once added it’s activated as well.
Please tell difference between addition and activation?

It means blind scell addition?

Activation means BO spliting amongst pcell and scell.
There is no point in spliting BO if there is no sufficint data in buffer.

Addition is RRC procedure which can be blind, coverage based or volume and coverage based. Activation is dobe through MAC CE at L2.


Blind based: how it will activate/Add by PCell to SCell?
W/o Signal Quality measurement which is very important and how enodeB activate w/o check UE buffer data size?
I think only Scell change possible in Blind based or event based A6.

No I seen addition as well blind based.
A6 always on based of threshold configured.

Blind addition is used where pcc and scc coverage footprints and identical and exactly overlapped.
We used it in early stage of CA implementation but now disabled it.

Yes there is one Flag in Huawei of SccBlindCfgSiwtch but at same time there are multiple serving cell, I think eNodeB take decision own wisely.
A6 event use for intrafreq handover between Scell.

Yes, only for colocated cell like cells having same azimuth of L900/L1800 and for inter-eNode cell ScellBlindCA this switch is Off.

Yes only for intra Freq ho between scell.

So it mean that there will be no need for A4 event (sent by UE → eNodeB) after RRC connection Reconfiguration (From enodeB to UE) to add “Scell” If SCellCA Flag is True.
I think eNodeB Add Scell randomly.

eNB add scell without measurement. But which scell to add is based on prioritizes configured in eNb for scell addition.

Yes, a top-priority candidate SCell if fail then choose the next one.

A4 event not linked with CA.
It’s used when neighbour become better then configured threshold.
It’s used for load balancing.

A4 event is use for SCell addition in CA.

I see heard first time A4 used for scell addition.
Maybe in New 3GPP release specified.