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In downlink, does RLC forms different PDUs for each UE scheduled to receive data this TTI or just a single PDU?

+1 vote
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MAC notifies RLC of a transmission opportunity asking for data each TTI. So does RLC respond with multiple PDUs one for each UE (with different RLC SNs for each of the PDU). Or just sends down one PDU (with one RLC SN) having data of all the scheduled UEs?
This same question could be put this way too: Are the RLC SNs assigned independently for each UE or are they assigned by incrementing by 1 every TTI?

posted Feb 20, 2017 by Mayank Gupta

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1 Answer

+2 votes

My understanding is each bearer is its own RLC entity. A particular bearer will be one of the types such as TM, UM and AM.
In normal case (without MIMO), eNodeB schedules one MAC PDU for an UE but one MAC PDU header consists of multiple MAC PDU sub headers and each MAC PDU sub header carries the information of embedded MAC SDUs.
When eNodeB MAC asks for RLC PDU, RLC entity of each bearer prepares RLC SDU and sends to MAC layer.
This way my perception of RLC is that per TTI MAC can send multiple RLC PDUs for each UE.

Please make me correct if my understanding of RLC entity is wrong.

answer Feb 20, 2017 by Harshita
Thanks for answering!
So basically each bearer for each UE has its own RLC SN count going on.
Also MAC requests data for a particular UE not a bearer, right? Then how does RLC decides which bearer to send? I don't think that's written in the RLC spec, or is it.
(I am new into LTE field that's why every line has a question :) )
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