WO2015171038A1

WO2015171038A1 - A method and a user equipment for power headroom reporting

Info

Publication number: WO2015171038A1
Application number: PCT/SE2015/050067
Authority: WO
Inventors: Yufei Blankenship; Daniel Larsson; Xinghua SONG
Original assignee: Telefonaktiebolaget L M Ericsson (Publ)
Priority date: 2014-05-08
Filing date: 2015-01-23
Publication date: 2015-11-12

Abstract

The present disclosure relates generally to telecommunication systems, and in particular, to methods, systems, devices and computer programs for Power Headroom Reporting (PHR) in telecommunication systems. In accordance with one example embodiment, a power headroom reporting method (100) for dual connectivity is disclosed. In one example embodiment, the method (100) is performed by a user equipment and may comprise: acquiring (110), from a MeNB, information relevant for a power headroom calculation; acquiring (120), from a SeNB, information relevant for the power headroom calculation; performing (130) a power headroom calculation on the basis of the received information from the MeNB as well as the received information from the SeNB; and optionally transmitting(140), to the MeNB and/or the SeNB,a power headroom report including a report of the performed power headroom calculation.

Description

A METHOD AND A USER EQUIPMENT FOR POWER HEADROOM REPORTING TECHNICAL FIELD

The present disclosure relates generally to telecommunication systems, and in particular, to a method, a user equipment, a computer program product and a carrier for Power Headroom Reporting (PHR) in telecommunication systems.

BACKGROUND

This section is intended to provide a background to the various embodiments of the technology that are described in this disclosure. Therefore, unless otherwise indicated herein, what is described in this section should not be interpreted to be prior art by its mere inclusion in this section.

Detailed descriptions of radio communication networks and systems can be found in literature, such as in Technical Specifications published by, e.g., the 3^rd Generation Partnership Project (3GPP). 3GPP Long Term Evolution (LTE) is the fourth-generation radio communication technologies standard developed within the 3^rd Generation Partnership Project (3GPP) to improve the Universal Mobile Telecommunication System (UMTS) standard to cope with future requirements in terms of improved services such as higher data rates, improved efficiency, and lowered costs. The

Universal Terrestrial Radio Access Network (UTRAN) is the radio access network of a UMTS and Evolved UTRAN (E-UTRAN) is the radio access network of an LTE system. In an UTRAN and an E-UTRAN, a terminal sometimes referred to as user equipment (UE) is wirelessly connected to a Radio Base Station (RBS). The RBS is commonly referred to as a NodeB (NB) in UMTS, and as an evolved NodeB (eNodeB or eNB) in LTE. An RBS is a general term for a radio network node capable of transmitting radio signals to a UE and receiving signals transmitted by a UE.

LTE uses orthogonal frequency division multiplexing (OFDM) in the downlink and discrete Fourier transform (DFT)-spread OFDM in the uplink. The basic LTE downlink physical resource can thus be seen as a time-frequency grid as illustrated in Figure 1 , where each resource element corresponds to one OFDM subcarrier during one OFDM symbol interval. In the time domain, LTE downlink transmissions are organized into radio frames of 10 ms, each radio frame consisting of ten equally-sized subframes of length Tsubframe = 1 ms, see Figure 2. Furthermore, the resource allocation in LTE is typically described in terms of resource blocks, where a resource block corresponds to one slot (0.5 ms) in the time domain and 12 contiguous subcarriers in the frequency domain. A pair of two adjacent resource blocks in time direction (1.0 ms) is known as a resource block pair. Resource blocks are numbered in the frequency domain, starting with 0 from one end of the system bandwidth.

Dual connectivity

With reference to Figure 3, dual connectivity to anchor and booster cells (i.e., MeNB and SeNB) will now be briefly introduced. A dual connectivity framework is currently being considered for LTE Release 12 (hereinafter abbreviated Rel-12). Dual

Connectivity refers to the operation where a given UE consumes, or utilizes, radio resources provided by at least two different network points (e.g. a Master eNB (MeNB) and a Secondary eNB (SeNB)) that are e.g. connected with a backhaul while in the so- called RRC_CONNECTED mode (RRC is an abbreviation for Radio Resource Control). A UE in dual connectivity generally maintains simultaneous connections to anchor and booster nodes, where the anchor node is also called the master eNB (MeNB) and the booster node is called the secondary eNB (SeNB). As the name implies, the anchor node may terminate the control plane connection towards the UE and is thus the controlling node of the UE. The UE may also read system information from the anchor. In addition to the anchor, the UE may be connected to one or several booster nodes for added user plane support. The MeNB and SeNB may be communicatively connected to each other via an Xn interface, which is currently selected to be the same as the X2 interface between two eNBs. The roles of the anchor node and the booster node, respectively, may be defined from a UE's point of view. A node that acts as an anchor to one UE may act as booster to another UE. Similarly, though the UE reads the system information from the anchor node, a node acting as a booster to one UE may or may not distribute system information to another UE. The following roles may be defined for the MeNB and the SeNB, respectively:

MeNB:

■ Provides system information

^■ Terminates control plane

^■ Can terminate user plane

SeNB:

^■ Terminates only user plane

In one application, dual connectivity allows a UE to connect two network nodes to receive data from both network nodes to increase its data rate. This user plane aggregation achieves similar benefits as carrier aggregation using network nodes that are not connected by low-latency backhaul and/or network connection. Due to this lack of low-latency backhaul, the scheduling and HARQ-ACK (Hybrid Automatic Repeat Request Acknowledgement) feedback from the UE to each of the network nodes may need to be performed separately. That is, it would be expected the UE should have two uplink (UL) transmitters to transmit UL control and data to the connected nodes. Power Headroom Reporting (PHR)

In LTE, an eNB may configure the UE to send Power Headroom Reports (PHR), e.g. periodically or at regular intervals. Thus, the UE may be configured to provide regular PHRs on its power usage to the eNB. There are two different types of PHR defined for LTE, i.e. Type 1 and Type 2. Type 1 reporting typically reflects the power headroom assuming PUSCH-only transmission (PUSCH stands for Physical Uplink Shared

Channel) on a carrier, while Type 2 reporting assumes combined PUSCH and PUCCH transmission (PUCCH stands for Physical Uplink Control Channel).

The Power Headroom reporting (PHR) procedure may be used to provide a serving eNB with information about the difference between a nominal UE maximum transmit power and an estimated power for UL-SCH (Uplink Shared Channel) transmission per activated Serving Cell and also with information about the difference between a nominal UE maximum power and an estimated power for UL-SCH and PUCCH transmission on a Primary Cell (PCell). Power headroom reporting may be used for link adaptation and scheduling in the UL. For Carrier Aggregation (CA), both Type 1 and Type 2 PHR may be reported. While Type 1 PH may always be included whenever PHR is triggered, Type 2 PH is generally only reported for simultaneous PUCCH and PUSCH transmission.

> Type 1 PHR: PH assuming PUSCH-only transmission on the carrier. Type 1

PHR can be transmitted under a variety of UL scenarios as listed below.

UE transmits PUSCH with PUCCH in subframe / for serving cell c

> V=0 (real transmission on PUSCH), include PCMAX._C field that reports ^PcMAX-^c

UE transmits PUSCH without PUCCH in subframe for serving cell c

> V=0 (real transmission on PUSCH), include PCMAX._C field that reports PCMAX.C

UE does not transmit PUSCH in subframe / for serving cell c

> V=1 (PUSCH reference format), no PCMAX._C field

Though not reported, PH calculation uses pcMAx._c( _ _WHERE ^CMAX,C(') _js computed assuming MPR=0dB, A-MPR=0dB, P-MPR=0dB and ΔΤο =0dB.

> Type 2 PHR: Only for primary cell. PH assuming simultaneous PUSCH and

PUCCH transmission. Type 2 PHR can be transmitted under a variety of UL scenarios as listed below.

- UE transmits PUSCH simultaneous with PUCCH in subframe / for the primary cell

> V=0 (real transmission on PUCCH), include PCMAX._C field that reports PCMAX._C

UE transmits PUSCH without PUCCH in subframe / for the primary cell

> V=1 (PUCCH reference format), no PCMAX._C field

Though not reported, PH calculation uses PCMAX.C- U E transmits PUCCH without PUSCH in subframe / for the primary cell

V=0 (real transmission on PUCCH) , include PCMAX._C field that reports P_CMAX,_C

U E does not transmit PUCCH or PUSCH in subframe / for the primary cell

V=1 (PUCCH reference format), no PCMAX._C field

Though not reported, PH calculation uses

¾IAX,C ^') _ _WHERE ¾IAX,C ^') j_S computed assuming M PR=0dB, A-M PR=0dB, P-M PR=0dB and ΔΤο =0dB.

An Extended PHR MAC Control Element (see e.g. Fig. 4) may be defined as follows: - Ci: this field indicates the presence of a PH field for the Secondary Cell (SCell) with SCelllndex i as specified in the standard. A Ci field set to "1 " indicates that a PH field for the SCell with SCelllndex i is reported. A Ci field set to "0" indicates that a PH field for the SCell with SCelllndex i is not reported;

- R: reserved bit, set to "0";

- V: this field indicates if the PH value is based on a real transmission or a reference format. For Type 1 PH, V=0 indicates real transmission on PUSCH and V=1 indicates that a PUSCH reference format is used. For Type 2 PH, V=0 indicates real transmission on PUCCH and V=1 indicates that a PUCCH reference format is used. Furthermore, for both Type 1 and Type 2 PH, V=0 indicates the presence of the octet comprising the associated PCMAX.c field, and V=1 indicates that the octet containing the associated PCMAX.c field is omitted;

- Power Headroom (PH): this field indicates the power headroom level. The length of the field is typically, but not necessarily, 6 bits. The reported PH and the corresponding power headroom levels are listed in the standard.

- P: this field indicates whether the UE applies power backoff due to power

management (as allowed by P-MPRc). The UE shall set P=1 if the corresponding PCMAX.c field would have had a different value if no power backoff due to power management had been applied; - PCMAX.c: if present, this field indicates the PCMAX.c or ^{CM c} used for calculation of the preceding PH field. The reported PCMAX.c and the corresponding nominal UE transmit power levels are also listed in the standard. The power headroom report may comprise PH information for both the scheduling eNB and the non-scheduling eNB. However, generally the eNB does not know the configuration of the other eNB. The configuration knowledge which is not available may e.g. include:

if simultaneousPUCCH-PUSCH is configured or not;

- if there is no actual fransmission, or if there is actual transmission of PUSCH or PUCCH or both.

Due to that the MeNB (master eNB) and the SeNB (secondary eNB) each operate its own scheduler independently; there is no or little coordination between the MeNB and the SeNB. It is thus difficult for the MeNB or the SeNB to have a reasonably good estimation of UE's power headroom when supporting the two uplink connections simultaneously. The existing PHR mechanism also does not support an

unsynchronized network where the UE may be required to transmit two partially overlapping subframes.

SUMMARY

It is in view of the above considerations and others that the various embodiments have been made. A general object is to provide methods and apparatuses for reporting power headroom in support of dual connectivity.

This general object has been addressed by the independent claims. Advantageous embodiments are defined by the dependent claims.

In one of its aspects, this disclosure presents a method of Power Headroom Reporting (PHR) for dual connectivity. The method is performed by a User Equipment (UE). The method comprises acquiring information relevant for a Power Headroom (PH) calculation from a Master evolved NodeB (MeNB); acquiring information relevant for a PH calculation from a Secondary evolved NodeB (SeNB); and performing a PH calculation on the basis of the acquired information from the MeNB as well as the acquired information from the SeNB.

In one embodiment, acquiring information relevant for a PH calculation from the MeNB comprises receiving a data message from the MeNB. This data message includes data field(s), wherein the data field(s) comprise(s) or otherwise indicate(s) one or several parameters relevant for the PH calculation.

In one embodiment, acquiring information relevant for a PH calculation from the SeNB comprises receiving a data message from the SeNB. This data message includes data field(s), wherein the data field(s) comprise(s) or otherwise indicate(s) one or several parameters relevant for the PH calculation.

In one embodiment, the method further comprises transmitting a power headroom report including a report of the performed PH calculation. For example, the power headroom report may be transmitted in a Medium Access Control (MAC) Control Element (CE), wherein the MAC CE includes a PH field containing the report of the performed PH calculation. Furthermore, the power headroom report may be transmitted to either of or both of the MeNB and the SeNB.

In one embodiment, the PH calculation takes a total configured transmit power into consideration. For example, the PH calculation may recognize a total maximum transmit power of all serving radio cells for the MeNB and the SeNB.

In another of its aspects, this disclosure presents a UE for PHR for dual connectivity. The UE comprises means adapted to acquire information relevant for a PH calculation from a MeNB; means adapted to acquire information relevant for a PH calculation from a SeNB; and means adapted to perform a PH calculation on the basis of the acquired information from the MeNB as well as the acquired information from the SeNB. In one embodiment, the UE comprises means adapted to receive a data message from the MeNB, the data message having data field(s), wherein the data field(s) comprise(s) or otherwise indicate(s) one or several parameters relevant for the PH calculation. In one embodiment, the UE comprises means adapted to receive a data message from the SeNB, the data message having data field(s), wherein the data field(s) comprise(s) or otherwise indicate(s) one or several parameters relevant for the PH calculation.

In one embodiment, the UE further comprises means adapted to transmit a power headroom report including a report of the performed PH calculation. In one

embodiment, the UE comprises means adapted to transmit the power headroom report in a MAC CE, wherein the MAC CE includes a PH field containing the report of the performed PH calculation. In one embodiment, the UE comprises means adapted to transmit the power headroom report to either of or both of the MeNB and the SeNB.

In one embodiment, the means adapted to perform the PH calculation is configured to take a total configured transmit power into consideration. In one embodiment, the means adapted to perform the PH calculation is configured to recognize a total maximum transmit power of all serving radio cells for the MeNB as SeNB.

In still another of its aspects, this disclosure presents a computer program for power headroom reporting in dual connectivity. The computer program comprises instructions which when executed on at least one processor of an apparatus causes the apparatus to acquire information relevant for a PH calculation from a MeNB; acquire information relevant for a PH calculation from a SeNB; and perform a PH calculation on the basis of the acquired information from the MeNB as well as the acquired information from the SeNB. A carrier may comprise the computer program, and the carrier may be one of an electronic signal, an optical signal, a radio signal, or a computer readable storage medium.

Performing a PH calculation on the basis of information relevant for the PH calculation received, or otherwise collected, from several network nodes (such as a MeNB and a SeNB) may allow the UE to perform improved PH calculations when the UE operates in dual connectivity. Accordingly, when the UE subsequently transmits its power headroom report (PHR) to a network node, this network node may benefit from the improved PH calculation. Herein described methods may thus allow the UE to calculate (or, compute) and, hence, also report useful power headroom information that may assist network nodes such as eNBs with the scheduling and link adaption. For example, MeNBs and SeNBs may benefit from such useful power headroom reports.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects, features and advantages will be apparent and elucidated from the following description of various embodiments, reference being made to the accompanying drawings, in which:

Figure 1 illustrates the LTE downlink physical resource;

Figure 2 illustrates the LTE time-domain structure; Figure 3 illustrates a dual connectivity scenario; Figure 4 illustrates an Extended PHR MAC Control Element;

Figure 5 is a flowchart of a method in accordance with an embodiment; Figure 6 illustrates an example implementation of a UE;

Figure 7 illustrates an example carrier in the form of a computer-readable medium, wherein the computer-readable medium comprises computer program; and

Figure 8 illustrates that an UE may be required to transmit partially overlapping subframes to the MeNB and the SeNB in an unsynchronized network. DETAILED DESCRIPTION

The invention will now be described more fully hereinafter with reference to the accompanying drawings, in which certain embodiments are shown. The invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully

convey the scope of the technology to those persons skilled in the art. Like reference numbers refer to like elements or method steps throughout the description. With reference to figure 5, an example embodiment of a method 100 of power headroom reporting for dual connectivity will be described. Thus, according to one embodiment, a method 100 of power headroom reporting for dual connectivity is provided. More particularly, a power headroom reporting (PHR) method for dual connectivity is performed by a UE.

The method 100 may comprise the following method steps, or actions:

the UE collecting 1 10 (e.g., obtaining, or acquiring) information relevant for a power headroom (PH) calculation from a first network node (e.g. a MeNB); the UE collecting (e.g., obtaining, or acquiring) 120 information relevant for the PH calculation from a second, different, network node (e.g. a SeNB); and the UE performing 130 a PH calculation (or, computation) on the basis of the collected information from the first network node as well as the collected information from the second network node. Collecting the information from the first network node and/or second network node may comprise receiving a data message (from the network node in question) having data field(s), wherein the data field(s) comprise(s) or otherwise indicate(s) one or several parameters relevant for the PH calculation. The PH calculation performed by the UE may be made, or performed, in accordance with one or several of the examples which are detailed in this disclosure.

Furthermore, the method may comprise the additional method step, or action, of transmitting 140 a power headroom report including a report of the performed PH calculation. The power headroom report may be transmitted 140 to the first network node and/or the second network node. If the power headroom report is transmitted to only one of the first network node and the second network node, the network node receiving the power headroom report may forward (thus, transmit) the power headroom report to the other network node, e.g. via an X2 interface or the like.

According to another aspect, a UE for power headroom reporting in dual connectivity is provided, see Figure 6. The UE 10 may comprise means 11 , 12, 13 adapted to collect/acquire information relevant for a power headroom (PH) calculation from a first network node (e.g. a MeNB). The UE may also comprise means 11 , 12, 13 adapted to collect/acquire information relevant for the PH calculation from a second, different, network node (e.g. a SeNB). Moreover, the UE 10 may comprise means 12 adapted to perform a PH calculation on the basis of the collected information from the first network node as well as the collected information from the second network node. The PH calculation performed by the UE may be made, or performed, in accordance with one or several of the examples which are detailed herein. Furthermore, the UE 10 may comprise means 1 1 adapted to transmit a power headroom report including a report of the performed PH calculation. The power headroom report may be transmitted to the first network node and/or the second network node. In one example implementation which is illustrated in figure 6, the UE 10 comprises a communications interface 1 1 , a processor 12 and a memory 13. The communications interface 11 may comprise a transmitter (Tx) and a receiver (Rx), or alternatively a transceiver (Tx/Rx). The memory 13 may store computer program code which, when run in the processor 12, causes the UE 10 to:

- receive or acquire (by the receiver 1 1) information relevant for a power

headroom (PH) calculation from a first network node (e.g. a MeNB);

receive or acquire (by the receiver 1 1) information relevant for the PH calculation from a second, different, network node (e.g. a SeNB); and perform a PH calculation on the basis of the collected (or received, or acquired information from the first network node as well as the collected (or received, or acquired) information from the second network node. Receiving said information from the first network node and/or second network node may comprise receiving (or acquiring) a data message having data field(s), wherein the data field(s) comprise(s) or otherwise indicate(s) one or several parameters relevant for the PH calculation. The PH calculation performed by the UE may be made, or performed, in accordance with one or several of the examples which are detailed in this disclosure.

Yet further, the transmitter 1 1 may be configured to transmit a power headroom report including a report of the performed PH calculation. The power headroom report may be transmitted to the first network node and/or the second network node.

According to still another embodiment, a computer program for power headroom reporting in dual connectivity is provided, see Figure 7. The computer program comprises instructions which when executed on at least one processor 12 of an apparatus 10 (e.g. a UE) causes the apparatus 10 to:

collect (or receive, or acquire) information relevant for a power headroom (PH) calculation from a first network node (e.g. a MeNB);

collect (or receive, or acquire) information relevant for the PH calculation from a second, different, network node (e.g. a SeNB); and

perform a PH calculation on the basis of the collected (or received, or acquired) information from the first network node as well as the collected (or received, or acquired) information from the second network node. The PH calculation performed by the UE may be made, or performed, in accordance with one or several of the examples which are detailed in this disclosure. A carrier may comprise the computer program. This carrier may, for example, be one of an electronic signal, an optical signal, a radio signal, or a computer readable storage medium 60 as schematically illustrated in figure 7. Performing a PH calculation on the basis of information relevant for the PH calculation received, or otherwise collected, from several network nodes (such as a MeNB and a SeNB) may allow the UE to perform improved PH calculations when the UE operates in dual connectivity. Accordingly, when the UE subsequently transmits its power headroom report (PHR) to a network node, this network node may benefit from the improved PH calculation. Herein described methods may allow the UE to calculate (or, compute) and, hence, also report useful power headroom information that may assist network nodes such as eNBs with the scheduling and link adaption. For example, MeNBs and SeNBs may benefit from such useful power headroom reports. Some embodiments described in this disclosure may enable each eNB to individually configure dualConnectivityPHR for the UE so that each eNB may choose (or choose not) to have the UE reporting the other eNB's PH in addition to its own PH.

Some embodiments described in this disclosure may enable each eNB to individually configure simultaneousPUCCH-PUSCH for the UE, and to provide the relevant power headroom report when two eNBs have two independent simultaneousPUCCH-PUSCH configuration.

This disclosure presents methods for the UE to calculate and report the power headroom information in the context of dual-connectivity, based on which the scheduler of MeNB and SeNB can use e.g. for scheduling purpose. The disclosure also presents methods for the UE to handle PHR in the unsynchronized network when two UL subframes may be misaligned.

Various detailed embodiments

1. PHR Construction for the other eNB

Let eNB* be the eNB that PHR is sent to and let eNB' be the other eNB that provides dual-connectivity to the UE together with eNB*. For example, when the UE constructs (or, configures) the PHR to be sent to MeNB, eNB* is the MeNB while eNB' is the SeNB. Alternatively, when the UE constructs the PHR to be sent to SeNB, eNB* is the SeNB while eNB' is the MeNB.

One new PHR MAC CE format may be introduced for dual-connectivity. The PHR may be of variable length. When configured by eNB*, PHR sent to eNB* always include PH of eNB'. Typically, but not necessarily, Type 1 PH is always included for both eNB* and eNB'. Whether or not Type 2 PH is included for a given eNB may depend on if simultaneousPUCCH-PUSCH is configured by the given eNB for the UE. extendedPHR should preferably, but not necessarily, always be configured as "setup" in dual-connectivity. As in the existing systems, E-UTRAN typically configures extendedPHR only if phr-Config is configured. The UE shall release extendedPHR if phr-Config is released. 1. 1 Include PH of eNB' to eNB* or not

This should preferably, but not necessarily, be configurable at a higher layer. A new field "dualConnectivityPHR" that is configurable in MeNB and SeNB individually is proposed. The following procedure can thus be used:

• If phr-Config is configured in eNB*,

o if eNB* has dualConnectivityPHR =setup, UE includes PH of eNB' in its PHR to eNB*;

o else, UE does not include PH of eNB' in its PHR to eNB*.

1.2. Type 1 or Type 2 PH

MeNB and SeNB should advantageously exchange their configuration

simultaneousPUCCH-PUSCH for the given UE. A reason for exchanging the information is to enable proper reception of the MAC Control Element (CE) for PHR report, as presence and/or absence of the fields, and the length of each field generally needs to be known before receiving the MAC CE. In addition, the MeNB and SeNB will exchange the number of configured cells in UL.

• If simultaneousPUCCH-PUSCH is not configured on the other eNB (eNB'), then the PHR sent to the current eNB (eNB*) includes only the Type 1 PH for all serving cells under eNB'. • If simultaneousPUCCH-PUSCH is configured on the other eNB (eNB'), then the PHR sent to the current eNB (eNB*) includes: Type 1 PH for all serving cells under eNB', and Type 2 PH for the primary cell of eNB'.

An alternative approach could be that the UE reports one PHR report only comprising the PHR reports for type 1 and an addition report for type 2. The type 2 report may comprise a type 2 report for both the PCell on the MeNB and the Scell on the SeNB, independently from if a certain nodes has configured simultaneousPUCCH-PUSCH or not. 1.3. PH calculation

One option is to reuse existing PH calculations (i.e. not introduce any new PH calculation). While it would be possible to reuse existing PH computations, examples 1- 4 described hereinbelow propose novel PH calculations for dual-connectivity. For Examples 1-3: V=0' for a cell indicates that the PH of eNB' is calculated based on actual transmission of PUSCH (and PUCCH if applicable), as in existing systems; V=1 ' for a cell indicates that the new PH computation is used in a field for eNB'. The new PH computation can be inserted in either Type 1 or Type 2 report.

Example 1 : The PH calculation for eNB* reuses the existing schemes while the PH calculation for eNB' use a different mechanism. No virtual PH is reported for eNB'. In case that there is no PUSCH (or PUCCH, if applicable) in one serving cell, the desired power for this transmission is set to zero. Take type 1 PH as an example, if there is no PUSCH (or PUCCH, if applicable) transmission for eNB' in one serving cell, the PH for this serving cell eNB* reports the total available power that can be used considering parallel transmissions for all the remaining cells including both eNB* and eNB'. The 'V field associated with the serving cell in the header of the PHR MAC Control Element could indicate whether it is an actual PHR or whether it is the new PH value as described above. In this case, V=0' indicates that the PH of eNB' is calculated based on actual transmission of PUSCH; V=1 ' indicates that the PH of eNB' is the difference between the overall UE maximum transmit power and the estimated power for UL-SCH transmission across all serving cells of MeNB and SeNB.

An example for describing how to report the PH for a given serving cell c on the eNB' is given below. The example assumes that the request power is calculated per serving cell c across eNB* and eNB', as indicated by ^{c e} i^eNB*,eNB'} _{Note thgt the notation} c e {eNB*, eNB } ς|_8ηο^_{83 ce}|| _{c w} ere cell c is a component carrier configured for UL transmission, and cell c is a component carrier of eNB* or eNB'.

^0_PUSCH,c

"^H typel.ceeNB' (0 (0 ^~ J 1 Λ _Λ , f _\

c≡{eNB*,eNBⁿ, + ^TR c V ) ⁺ J c V )

While the PH calculation for eNB' above has been described as Type 1 , a similar calculation can be done for Type 2 PH, where the new PH construction is used when V=1.

Example 2: The PH calculation for eNB* reuses the existing schemes while the PH for eNB' is calculated as the difference between the maximum configured power for eNB' (if it is defined) and desired power for this serving cell. No virtual PH is reported for eNB'. In case that there is no PUSCH (or PUCCH, if applicable) in one serving cell, the desired power for this transmission is set to zero. One advantage of doing this is if there is a strict (or, hard) power limitation for each eNB, it is possible to determine whether the power limitation happens in eNB'. This could be done as by summing the desired power over all the serving cells for the eNB' 2_J (^ CMAX_eA¾' (0 ^_ ^^typel.eNB'c ( ) (2) and, furthermore, compare it to the Pcmax_eNB'. Similar to the example 1 , formula (3) below gives an example how the PH for the eNB' may be calculated:.

Example 3: The PH calculation for eNB* reuses the existing schemes while the PH for eNB' is calculated as the difference between the total maximum configured power and desired power for this serving cell. No virtual PH is reported for eNB'. In case that there is no PUSCH (or PUCCH, if applicable) in one serving cell, the desired power for this transmission is set to zero. One advantage of doing this is that it is possible to determine whether a power limitation happens in the case when there is no strict (or, hard) power limitation for each eNB. Below is an example given for how to calculate the PH for the eNB'.

{ 101og₁₀(M_PUSC¾ ( )) + P₀ __PUSCHp (j) +a_c (j)^■ PL_c + _c ( +f_c ( }

Example 4: In addition to the above example another way is to define an additional, new power headroom, that is reported for a given eNB. Example 4 proposes a new MAC CE format for PHR, where the CE comprises a new PH field (as compared to Examples 1 -3). This is particularly true for the eN B' as the eNB* is not in control of the scheduling for eNB', hence eNB* may only be interested in total power that is requested for eN B'. This new PH field can be reported in combination with reporting PH for each serving cell on both eNB* and eNB'. Alternatively the UE may report only PH per serving cell for eNB* and then for eNB' the UE reports only the new PH calculation as given by this alternative.

In one embodiment, this PH value is calculated as the difference between the total configured power Pcmax and the total required transmission power for all the serving cells. ( ( - ∑ { 101Og₁₀ ( _{pusCH c} (/^')) + 0) + <¾ 0) " (0 + (0 } In another embodiment, this PH value is calculated as the difference between the total configured power Pcmax_eNB' and the total required transmission power for all the serving cells.

^CMAX eNB ' (^/) - X { ¹⁰¹°g₁₀ (^PUSCH, c( ) + ^ 0_PUSCH, c

(6)

1.4. The PCMAX,_C field that reports P_CMAX,C or ^ΜΑΧ,^{Ο '})

Currently the PCMAX._C field may be present or absent, and it may report PCMAX, C or

¾VIAX,^C ) p_or dual-connectivity, this field can advantageously be modified to better assist the operation of dual-connectivity. Example 1 : Instead of tying this to the 'V field to the presence and/or absence of the PCMAX._C field, this field should advanategosuly always be included for cells of eNB' (though UE may not have to always include it for cells of eNB*, which is generally case in existing systems). The value of the field is a per-cell maximum output power. This is because the eNB* does not know the parameters that allow it to calculate ^CMAX,^C ) ₀ eNB'. Even with ^ΜΑΧ,^Ο ) computed assuming MPR=0dB, A-MPR=0dB, P-MPR=0dB and ΔΤ₀ =0dB, the eNB* may not know PEMAX._C ΔΤΙΒ_,Ο- Also, for unsynchronized networks, this field may capture the power level that is available for eNB' considering that parallel transmission for eNB* may need to be supported. The PCMAX._C field is repurposed to report 'left-over power' to eNB' rather than ^CMAX,^C ) |_n another alternative, actual power headroom may be reported instead of ^CMAX,^C ) considering that there is UL transmission to eNB* assuming no UL transmission to eNB'. When there is no UL transmission to eNB*, the PCMAX._C field maintains the existing meaning. Example 2: Similar to alternative 1 , the field PCMAX._C may always be included for cells of eNB'. However, the value of the field is the maximum output power allowed across multiple cells, not per-cell. This value may be maximum output power allowed across all configured cells (i.e., Pcmax), or it can be the maximum output power allowed for a eNB (i.e., P_cmax,MeNB, Pcmax,seNB )■ One example is, for type 2 PHR for the special cell for the SeNB (pSCell), the total configured power Pcmax is reported intead of the

Pcmax.c.

Example 3: This PCMAX._C field can be omitted by eNBs exchange info on PEMAX._C they each configure on their serving cell(s), and additionally assume that ^CMAX,^C ) j_S calculated with ΔΤ|_Β=0.

2. Subframe for which PH of the other eNB is reported

For synchronized networks, the subframes of MeNB and SeNB are typically, but not necessarily, aligned. PHR of subframe i include {PH of subframe of MeNB, PH of subframe i of SeNB}, if dualConnectivityPHR =setup.

For unsynchronized networks: • If there is no transmission on eNB',

o PH of eNB' is virtual assuming a reference PUSCH format, and a reference PUCCH format if simultaneousPUCCH-PUSCH is configured.

• If there is a subframe transmitted earlier on eNB' that overlaps with the subframe i of eNB*, and there is no subframe trasmitted later on eNB',

o PHR sent to eNB* on subframe i includes the PH calculated for the earlier subframe on eNB'.

• If there is a subframe transmitted later on eNB' that overlaps with the subframe i of eNB*, and there is no subframe trasmitted earlier on eNB',

o Option 1 : PHR sent to eNB* on subframe i includes the virtual PH calculated for eNB'. Advantage: PH calculation does not have to wait for the later subframe on eNB'.

o Option 2: PHR sent to eNB* on subframe i includes the PH calculated for the later subframe on eNB'. Advantage: PH is actual. However, the PH calculation may have to wait for the later subframe on eNB'.

• If there are two consecutive subframes transmitted on eNB' that overlaps with the subframe i of eNB*, one earlier, one later,

o Option 1 : PHR sent to eNB* on subframe i includes the virtual PH calculated for eNB'.

o Option 2: PHR sent to eNB* on subframe i includes the PH calculated for the earlier subframe on eNB'.

o Option 3: PHR sent to eNB* on subframe i includes the PH which is set to be min (PH of earlier subframe on eNB', PH of later subframe on eNB'}. Overall, one possible solution is that PHR sent to eNB* on subframe i includes the PH which is set to be m/>7{PH of earlier subframe on eNB', PH of later subframe on eNB'}, Here, PH of eNB' may be calculated using one of the alternatives described in Section 1.3 As indicated in Figure 8, a UE may be required to transmit partially overlapping subframes to MeNB and SeNB in an unsynchronized network.

As discussed earlier, the power headroom report (PHR) provides the eNB with information about the difference between the nominal UE maximum transmit power and the estimated power for UL-SCH transmission in each Serving Cell. Power headroom report is required for link adaptation and scheduling in the UL.

Take for example the PHR to the MeNB as an example, the PHR may include PH information of all activated cells from both MeNB and SeNB. The PH for MeNB may be calculated in a similar way as carrier aggregation while some further optimizations could be considered in PH calculation for the SeNB. Since an exemplary purpose of reporting PH information of SeNB to MeNB (vice versa) is to provide the power usage of SeNB so that the MeNB could derive the total power usage on all active cells, a PH may be reported by taking the total configured transmit power into consideration.

If the UE transmits PUSCH without PUCCH for serving cell c, power headroom may be computed using:

^O _FUS(¾(/) +«_c 0) " ^P + (0 + fc (0 }

If the UE transmits PUCCH without PUSCH for serving cell c, power headroom may be computed using

KJUCCH ^{+ PL}c + h(ⁿ CQI J ⁿHARQ J ⁿSR } + ^AF_PUCCH (F) + A_TxD (F^>) + g(i)}

If the UE transmits PUSCH with PUCCH for serving cell c, power headroom may be computed using ^mSeNBp (0 =

If for example the UE does not transmit PUCCH or PUSCH in subframe i for serving cell c, power headroom may be computed using

^^ SeNB.c (0 ⁼ ^ CMAX.c (0

Where

configured UE total transmit power in subframe i.

^ac U) _t ^PLc _t ^aTF,A0 _and fc (0 are defined in section 5.1.1.1 of the reference "3GPP TS 36.213 V11.1.0 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer procedures (Release 1 1)". With this information, it is possible for the MeNB to derive whether there is a power limitation and how much total power is available by computing using:

It should be noted that the total nominal UE maximum power may be assumed to be reported in the above solution. It should also be noted that the nominal UE maximum transmit power may be different in dual connectivity. Modifications and other variants of the described embodiment(s) will come to mind to one skilled in the art having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the embodiment(s) is/are not to be limited to the specific examples disclosed and that modifications and other variants are intended to be included within the scope of this disclosure. Although specific terms may be employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

Claims

A method (100) of Power Headroom Reporting, PHR, for dual connectivity, the method (100) being performed by a User Equipment, UE, and comprising: acquiring (110) information relevant for a Power Headroom, PH, calculation from a Master evolved NodeB, MeNB;

acquiring (120) information relevant for a PH calculation from a

Secondary evolved NodeB, SeNB; and

performing (130) a PH calculation on the basis of the acquired information from the MeNB as well as the acquired information from the SeNB.

The method according to claim 1 , wherein acquiring (110) information relevant for a PH calculation from the MeNB comprises receiving a data message from the MeNB, the data message having data field(s), wherein the data field(s) comprise(s) or otherwise indicate(s) one or several parameters relevant for the PH calculation.

The method according to claim 1 or 2, wherein acquiring (120) information relevant for a PH calculation from the SeNB comprises receiving a data message from the SeNB, the data message having data field(s), wherein the data field(s) comprise(s) or otherwise indicate(s) one or several parameters relevant for the PH calculation.

The method according to any one of the claims 1-3, further comprising:

transmitting (140) a power headroom report including a report of the performed PH calculation.

The method according to claim 4, comprising:

transmitting (140) the power headroom report in a Medium Access Control, MAC, Control Element, CE, wherein the MAC CE includes a PH field containing the report of the performed PH calculation.

6. The method according to claim 4 or 5, comprising: transmitting (140) the power headroom report to either of or both of the MeNB and the SeNB.

7. The method according to any one of the claims 1-6, wherein the PH calculation takes a total configured transmit power into consideration.

8. The method according to claim 7, wherein the PH calculation recognizes a total maximum transmit power of all serving radio cells for the MeNB and the SeNB. 9. A User Equipment, UE (10), for Power Headroom Reporting, PHR, for dual connectivity, the UE (10) comprising:

means (1 1) adapted to acquire information relevant for a Power

Headroom, PH, calculation from a Master evolved NodeB, MeNB;

means (1 1) adapted to acquire information relevant for a PH calculation from a Secondary evolved NodeB, SeNB; and

means (12, 13) adapted to perform a PH calculation on the basis of the acquired information from the MeNB as well as the acquired information from the SeNB. 10. The UE (10) according to claim 9, comprising:

means (1 1) adapted to receive a data message from the MeNB, the data message having data field(s), wherein the data field(s) comprise(s) or otherwise indicate(s) one or several parameters relevant for the PH calculation. 1 1. The UE (10) according to claim 9 or 10, comprising:

means (1 1) adapted to receive a data message from the SeNB, the data message having data field(s), wherein the data field(s) comprise(s) or otherwise indicate(s) one or several parameters relevant for the PH calculation. 12. The UE (10) according to any one of the claims 9-1 1 , further comprising:

means (1 1) adapted to transmit a power headroom report including a report of the performed PH calculation.

13. The UE (10) according to claim 12, comprising: means (1 1) adapted to transmit the power headroom report in a Medium Access Control, MAC, Control Element, CE, wherein the MAC CE includes a PH field containing the report of the performed PH calculation. 14. The UE (10) according to claim 12 or 13, comprising:

means (1 1) adapted to transmit the power headroom report to either of or both of the MeNB and the SeNB.

15. The UE (10) according to any one of the claims 9-14, wherein the means (12, 13) adapted to perform a PH calculation is configured to take a total configured transmit power into consideration.

16. The UE (10) according to claim 15, wherein the means (12, 13) adapted to perform the PH calculation is configured to recognize a total maximum transmit power of all serving radio cells for the MeNB and the SeNB.

17. Computer program for power headroom reporting in dual connectivity, the

computer program comprising instructions which when executed on at least one processor of an apparatus causes the apparatus to:

acquire information relevant for a Power Headroom, PH, calculation from a Master evolved NodeB, MeNB;

acquire information relevant for a PH calculation from a Secondary evolved NodeB, SeNB; and

perform a PH calculation on the basis of the acquired information from the MeNB as well as the acquired information from the SeNB.

18. A carrier (60) comprising the computer program according to claim 17, wherein the carrier (60) is one of an electronic signal, an optical signal, a radio signal, or a computer readable storage medium.