What about the case where uplink data has to be transmitted?
True. Just refreshed my memory. Thanks. Must be thinking of some other contention-free scenario.
There are both types of RACH used: 5G | ShareTechnote
It depends upon whether scell for UL is o same TAG or not.
Atleast i have not seen RACH for UL CA.
But I think I need to check again.
Seems it is there for Scell, the the procedure is tricky.
Sorry, I missed that part.
I agree with you that sometime RACH required for UL CA.
Read this:
To enable multiple timing advances in 3GPP Release 11, the term Timing Advance Group (TAG) was introduced [4]. A TAG includes one or more serving cells with the same UL timing advance and the same DL timing reference cell. If a TAG contains the PCell, it is named as Primary Timing Advance Group (pTAG). If a TAG contains only SCell(s), it is named as Secondary Timing Advance Group (sTAG). From RF (3GPP RAN4) perspective in 3GPP Release 11 carrier aggregation is limited to a maximum of two downlink carriers. In consequence only two TAGs are allowed. The initial UL time alignment of sTAG is obtained by an eNB initiated random access procedure the same way as establishing the initial timing advance for a single carrier in 3GPP Release 8.
The SCell in a sTAG can be configured with RACH resources and the eNB requests RACH access on the SCell to determine timing advance. I.e. the eNodeB initiates the RACH transmission on the secondary cells by a PDCCH order send on the primary cell. The message in response to a SCell preamble is transmitted on the PCell using RA-RNTI that conforms to 3GPP Release 8. The UE will then track the downlink frame timing change of the SCell and adjust UL transmission timing following the timing advance commands from the eNB. In order to allow multiple timing advance commands, the relevant MAC timing advance command control element has been modified. The control element consists of a new 2 bit Timing Advance Group Identity (TAG Id) and a 6 bit timing advance command field (unchanged compared to 3GPP Release 8) as shown in Fig. 2-2. The Timing Advance Group containing the PCell has
the Timing Advance Group Identity 0.
Yes… was going through the same.
Actually UE supporting UL CA are very less, and UL traffic very low in networks.
And UL consumes more device power. Ultimately it reduced UL coverage of UE due to power division in 2 uplinks.
So no operator is much interested in UL ca performance.
It’s interesting.
This is true for normal traffic dimensioning, but just the exact opposite on huge venues, where people mostly upload.
Got it.
I usually work.with simulators so this is pretty common scenarios for me.
I am more versed with what is allowed in 3gpp.and what is not than what is actually in use👍🏻
There mostly dedicated base stations are used to serve large crowd.
There coverage levels, UL RF is very good.
So UE remains with ample of power even if it is divided in 2 uplinks.
Problem is to get good dominance and good SINR with multiple gNBs.
@ran_core_consultant
The reason that the vendor has not implemented contention free random access in 5G NR yet