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WF on PRACH handling in dual connectivity

3GPP TSG RAN WG1 # 78bis Ljubljana , Slovenia, 06 th – 10 nd October2014 Agenda item 7.2.2.1. R1-14xxxx. WF on PRACH handling in dual connectivity. InterDigital , …. Background. In RAN1#76bis, the following working assumption was taken:

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WF on PRACH handling in dual connectivity

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  1. 3GPP TSG RAN WG1 #78bis Ljubljana, Slovenia, 06th– 10nd October2014 Agenda item 7.2.2.1 R1-14xxxx WF on PRACH handlingin dual connectivity InterDigital, …

  2. Background • In RAN1#76bis, the following working assumption was taken: “Power control changes are not allowed in the middle of subframe in asynchronous case in dual connectivity” • Motivations for the above include at least: • Creates RF issues (e.g. transient period) • Loss of orthogonality for DM-RS (OCC) and PRACH • In RAN1#77, the following agreement was made: “PRACH to PCell has the highest priority” • 36.213 section 6.1.1 specifies: “In case a random access procedure is initiated by a "PDCCH order" in subframe n, the UE shall, if requested by higher layers, transmit random access preamble in the first subframen+k2 , k2 >= 6 , where a PRACH resource is available.”

  3. Observations • In PCM2, prioritization of PRACH to Pcell over other signals is achievable at least in the following cases: • Retransmission of a PRACH preamble to Pcell (which can be anticipated by the UE) • Initial transmission of PRACH to Pcell in UE-initiated PRACH procedure (whose timing can be selected by the UE) • Initial transmission of PRACH to Pcell in RACH procedure initiated by PDCCH order, occurring more than 6 subframes after reception of order • In above cases, the UE can determine the proper transmission level of an overlapping transmission in the other CG without any reduction of processing time compared to R8 • Overlapping transmission can be PUSCH/PUCCH or PRACH • In PCM2, the only case involving reduction of processing time is: • Initial transmission of PRACH, occurring exactly 6 subframes after reception of PDCCH order

  4. Proposal • Confirm the working assumption from RAN1#76bis: “Power control changes are not allowed in the middle of subframe in asynchronous case in dual connectivity” • For PCM2, in case Pcell PRACH is to be transmitted in a CG and a PUCCH/PUSCH/PRACH is being transmitted in the other CG in the overlapping subframe starting earlier • If Pcell PRACH is transmitted in the subframe starting exactly 6 ms after reception of a PDCCH order and Pcmax would be exceeded • The UE may deprioritize the Pcell PRACH transmission (FFS it is scaled or dropped) • In all other cases, Pcell PRACH shall be prioritized over PUCCH/PUSCH/PRACH of other CG

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