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`R1-080612
`
`Reply to RAN2 LS on RACH Power Control Optimisation Use case
`Rel-8
`LTE
`
`3GPP TSG-RAN WG1 #51bis
`Sevilla, Spain, January 14 – 18, 2008
`
`Title:
`Release:
`Work Item:
`
`Response to:
`Source:
`To:
`Cc:
`
`Contact Person: Jung A. Lee
`E-mail Address:
`jalee@alcatel-lucent.com
`
`R1-080004 (R2-075463)
`RAN1
`RAN WG2
`RAN WG3, RAN WG4
`
`
`
`
`
`1. Overall Description
`
`RAN 1 would like to thank RAN2 on their LS on RACH power control optimisation to support SON [1]. In particular,
`RAN2 inquires about necessary eNB or UE measurements required to optimize the RACH transmission power control
`configurations such as PRACH transmission power setting or power ramping step setting. In addition, RAN2 asks
`RAN1 to inform relevant WGs to define required signalling for measurements to be delivered over interfaces.
`2. Questions/Answers
`
`Question:
`
`“RAN WG2 kindly requests RAN WG1 to study on the necessary eNB or UE measurements from RAN WG1 perspective
`to support this use case, particularly on the issue of RACH transmission power control, and standardise the necessary
`measurement definitions. RAN WG2 also requests RAN WG1 to inform the relevant WGs (e.g., RAN WG4 to define
`performance requirements and RAN WG2, WG3 and SA WG5 to define signallings for the measurements to be
`delivered over interfaces) about any decisions made.”
`
`Answer:
`
`Power control for PRACH was discussed in RAN1#51bis. It was agreed that open-loop power control is employed. UE
`computes the PRACH transmit power based on eNB signalled power control parameters. Path loss compensation is
`applied at the UE based on a measurement of the DL reference signal. The PRACH transmit power for N_pre’th
`transmission is computed as
`
`P_ preamble(N_pre) = min(Pmax, PL + Po_pre + (N_pre-1)*dP_rampup)
`
`where PL is downlink pathloss, Po_pre is the cell specific parameter that defines the desired target (received) power
`level at the eNB, N_pre is the number of preambles transmitted, and dP_rampup is the cell specific power step size for
`retransmission. Note that, in order for the UE higher layers not to have to deal with the pathloss estimate PL, PL should
`be applied at UE Layer 1. As a consequence, rather than providing Layer 1 with the desired preamble transmission
`power, higher layers should provide Layer 1 with the path-loss-normalized desired power Po_pre + (N_pre-
`1)*dP_rampup.
`
`eNB measurement: To determine the initial power control parameter, total received power on PRACH resource is
`needed. This can be an average quantity over the configured PRACH resources. Whether this measurement needs to be
`specified in the standard is FFS.
`
`UE measurement: Downlink path loss estimate is needed at the UE. For initial access and uplink synchronization, path
`loss to the serving cell is estimated. For handover, the path loss to the target cell needs to be estimated.
`
`HTC/ZTE EXHIBIT 1010
`
`

`

`Signalling: Table 1 below summarizes the RACH power control parameters and the required signalling methods. The
`power control parameters, ie preamble target power level Po_pre, and power step size for retransmission dP_rampup,
`need to be signalled to the UE. This may be done through DBCH in case of contention based RACH and through
`DBCH or dedicated signalling in case of non-contention based RACH. Additionally, to support handover with non-
`contention based RACH, signalling via X2 between the serving cell and the target cell is required. Dynamic range of
`these power control parameters are still under study.
`
`
`
`
`
`Table 1: Summary of power control parameters and signaliing method for RACH.
`RACH use case
`Signalling method
`Parameter
`• Preamble target power level Po_pre
`• Power step size for retransmission
`dP_rampup
`
`All contention based RACH
`
`DBCH
`
`Non-contention based
`RACH:
`
`UL synchronization upon DL
`data arrival in
`RRC_CONNECTED state
`
`Non-contention based RACH
`during handover
`
`DBCH or Dedicated signalling
`
`• Preamble target power level Po_pre
`• Power step size for retransmission
`dP_rampup
`
`Dedicated signalling to UE
`Exchanged via X2 to serving
`cell
`
`• Preamble target power level Po_pre
`• Power step size for retransmission
`dP_rampup
`
`3. Actions
`Actions to RAN2
`
`RAN1 kindly asks RAN2 to take into account the response in their further discussion.
`Actions to RAN3
`
`RAN1 kindly asks RAN3 to take into account the response in their further discussion.
`Actions to RAN4
`
`RAN1 kindly asks RAN4 to take into account the response in their further discussion.
`
`4. Date of Next TSG-RAN WG1 Meetings
`
`3GPP RAN1#52
`
`11 – 15 Feb 2008
`
`Sorrento, Italy
`
`3GPP RAN1#52bis
`
`31 Mar – 4 Apr 2008 Shenzhen, China
`
`5. References
`
`[1] 3GPP R1-08004 (R2-075463), “LS on RACH power control optimisation use case”, RAN2.
`[2] 3GPP R1-080445, “Power control for RACH,” Alcatel-Lucent, RAN1#51bis, Sevilla, Spain, January 2008.
`[3] 3GPP R1-080357, “Power control for PRACH,” Ericsson, RAN1#51bis, Sevilla, Spain, January 2008.
`
`
`
`HTC/ZTE EXHIBIT 1010-2
`
`