R1-073676
`
`3GPP TSG RAN WG1 #50 Meeting
`Athens, Greece, August 20-24, 2007
`
`
`
`Nokia Siemens Networks, Nokia
`Source:
`Power control headroom reports for EUTRAN uplink
`Title:
`Agenda item: 7.4.2
`Document for: Discussion/Decision
`
`1. Introduction
`In this contribution we address the topic of power control headroom reporting in E-UTRAN LTE Uplink. We propose
`that the UE measures the used power, and then reports the difference between this and the maximum UE transmission
`power. We also propose a flexible power control headroom reporting scheme which is based on a set of e-Node B
`configurable parameters, and can support both periodic and event-triggered signalling (but also a combination of these
`two reporting methods).
`
`2. Power control headroom report
`The latest agreement on the power control for PUSCH is summarized in [1]. Basically the power spectral density (PSD)
`is determined by; (i) an open loop power control (OLPC) component calculated at the UE, and (ii) a closed loop power
`control (CLPC) correction transmitted by the eNode-B. A similar approach (but using different OLPC parameters and
`independent closed loop commands) has been agreed for the PUCCH [2]. Given such a power control scheme, it is
`unknown by the eNode-B at which PSD level the different terminals are operating. Information on the PSD is important
`for performing correct radio resource management decisions at the eNode-B, especially when allocating the
`transmission format (bandwidth and modulation & coding) to the different terminals. Not knowing the PSD used by a
`certain terminal could e.g. cause the allocation of a too high transmission bandwidth (given the maximum eUE power
`capabilities), thus resulting in a lower SINR. Information on the PSD used at the eUE can be obtained from the power
`control headroom reports, provided that the eNode-B knows the transmission bandwidth used when the power
`measurement was performed. Information on the PSD is primarily critical for the PUSCH as the transmission format for
`this channel is adaptively adjusted. On the other hand, the transmission format on the PUCCH is more constant per user,
`i.e. constant bandwidth, MCS, etc. It is therefore suggested that the UE only measures the power control headroom for
`the PUSCH as this is the only case where such a measurement is needed before adjusting the allocated bandwidth
`and/or modulation and coding scheme.
`
`Note: Alternatively to the power control headroom, the eUE could signal to the eNode-B the measured path-loss which
`is input to the OL standardized PC formula in [1]. Knowing the measured path loss at the eUE the eNode-B can easily
`calculate the PSD used at the terminal.
`
`2.1 Definition of ‘Power Control Headroom’
`In HSUPA the power control headroom is defined as the difference between the “nominal” maximum transmission
`power and the power measured at the UE. We propose to use the same measure in E-UTRAN uplink:
`
`Power Control Headroom = 10⋅log10 (PMAX) - 10⋅log10 (PMEASURED),
`
`where PMAX is the maximum eUE Tx power, and PMEASURED is the measured eUE Tx power. The power control
`headroom is calculated per TTI. It is FFS whether the power control headroom should be averaged before being
`reported to the eNode-B, and whether the averaging should be done in linear or in logarithmic domain.
`
`Apple Inc. v. Cellular Communications Equipment LLC
`APPL-1017 / Page 1 of 3
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`2.2 Proposed Power Control Headroom reporting scheme
`We suggest the following criteria for sending a power control headroom report in the uplink:
`
`1.
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`2.
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`3.
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`4.
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`5.
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`6.
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`A power control headroom report is transmitted after N closed loop PC corrections have been (correctly)
`received by the terminal.
`
`After the OLPC component of the PSD is modified at the terminal (based on an updated path loss measurement),
`the eUE measures the power control headroom for M (consecutive) TTIs and afterwards transmits a power
`control headroom report.
`
`The UE sends a power control headroom report if the difference between the current and the latest path loss
`measurement is higher than a given threshold (X dB).
`
`A report is also triggered in case the power control headroom reaches a certain value, e.g. the eUE Tx power
`comes close (<Y dB) to its maximum possible value PMAX.
`
`A power control headroom report is in any case transmitted every P TTIs (periodic signaling).
`
`However, the UE is not allowed to transmit a power control headroom report if the time elapsed from the last
`report is < K TTIs (this criteria is introduced to limit the signaling overhead).
`
`Notice that standardizing the proposed criteria would allow the implementation of a variety of different reporting
`schemes by appositely tuning the parameters N, M, X, K, Y and P.
`
`2.3 Signaling of Power Control Headroom Reports
`Transmission of power control headroom measurement reports could be performed by means of either RRC or MAC
`signaling. Though this is mainly a RAN2 issue, we propose using MAC signaling to convey power control headroom
`reports from the eUEs to the eNode-B mainly due to the following two reasons: (i) MAC signaling is also used to report
`power headroom information in HSUPA, and (ii) MAC has been proposed as signaling protocol for the transmission of
`uplink buffer status reports in EUTRAN [3].
`
`Whether power control headroom and buffer status reports should be signaled using a fixed size MAC header as in
`HSUPA or separate MAC messages should be used is FFS (shall be discussed in RAN2).
`
`3. Conclusions
`In this contribution we have addressed power control headroom reports in EUTRAN uplink. We have underlined the
`importance of power control headroom reports, especially in relation to the allocation of the uplink transmission
`bandwidth and MCS to the different users. We recommend RAN1 to reach an agreement on the following points:
`
`- The power control headroom is measured and reported for the PUSCH only. No need to have power control
`headroom measured for the PUCCH as this channel is allocated constant bandwidth and MCS per user.
`
`- The “power control headroom” per TTI is defined as 10⋅log10 (PMAX) - 10⋅log10 (PMEASURED), where PMAX is the
`maximum eUE Tx power and PMEASURED is the measured eUE Tx power. It is FFS whether the power control
`headroom should be averaged before being reported to the eNode-B, and whether the averaging should be done
`in linear or in logarithmic domain
`
`- The standard should include the reporting rules and parameters described in Section 2.3. Notice that any of the
`reporting mechanisms can be deactivated by setting the corresponding parameter accordingly. The reporting
`parameters could be transmitted using the RRC protocol.
`
`-
`
`Power headroom reports are transmitted in the uplink using MAC signaling (same used in HSUPA), but with
`the possibility to define separate reports for the power control headroom and the buffer status (to be discussed
`in RAN2).
`
`APPL-1017 / Page 2 of 3
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`

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`4. References
`[1] R1-073224 - “Way Forward on Power Control of PUSCH” - CATT, Ericsson, et al. - 3GPP TSG RAN
`WG1, meeting #49-bis, Orlando, USA, 25th - 29th June, 2007.
`[2] R1-073209 - “Way Forward on Uplink Power Control of PUCCH” - CATT, Ericsson et al. - 3GPP TSG
`RAN WG1, meeting #49-bis, Orlando, USA, 25th - 29th June, 2007.
`[3] R2-060829, “Buffer Reporting for E-UTRAN” - Nokia - 3GPP TSG RAN WG1, meeting #52, Athens,
`Greece, 27th - 31st March, 2006.
`
`
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`APPL-1017 / Page 3 of 3