Method and apparatus for power headroom reporting in a wireless communication system

A method and apparatus are disclosed for power headroom reporting in a wireless communication system. The method includes a UE (User Equipment) being configured with at least a first cell and a second cell. The method also includes the UE reports a PHR (Power Headroom Report) on the first cell in a subframe, wherein the PHR contains the power headroom value of the second cell, and the power headroom value of the second cell is derived using a specific PUSCH resource assignment regardless of whether there is PUSCH (Physical Uplink Shared Channel) transmission in the second cell in the subframe or not.

FIELD

This disclosure generally relates to wireless communication networks, and more particularly, to a method and apparatus for power headroom reporting in a wireless communication system.

BACKGROUND

An exemplary network structure for which standardization is currently taking place is an Evolved Universal Terrestrial Radio Access Network (E-UTRAN). The E-UTRAN system can provide high data throughput in order to realize the above-noted voice over IP and multimedia services. The E-UTRAN system's standardization work is currently being performed by the 3GPP standards organization. Accordingly, changes to the current body of 3GPP standard are currently being submitted and considered to evolve and finalize the 3GPP standard.

SUMMARY

A method and apparatus are disclosed for power headroom reporting in a wireless communication system. The method includes a UE (User Equipment) being configured with at least a first cell and a second cell. The method also includes the UE reports a PHR (Power Headroom Report) on the first cell in a subframe, wherein the PHR contains the power headroom value of the second cell, and the power headroom value of the second cell is derived using a specific PUSCH resource assignment regardless of whether there is PUSCH (Physical Uplink Shared Channel) transmission in the second cell in the subframe or not.

DETAILED DESCRIPTION

In particular, the exemplary wireless communication systems devices described below may be designed to support one or more standards such as the standard offered by a consortium named “3rd Generation Partnership Project” referred to herein as 3GPP, including the Chairman's Notes for RAN1#74 and Document Nos. R1-133396, “Physical Layer Aspects of Dual Connectivity”, InterDigital Communications, R1-133182, “Physical layers aspects of dual connectivity”, ETRI, R1-133436, “Physical layer aspects of dual connectivity”, Ericsson, ST-Ericsson, and TS 36.213 V11.4.0 “E-UTRA Physical layer procedures (Release 11)”. The standards and documents listed above are hereby expressly incorporated by reference in their entirety.

In RAN1#74 meeting, there is the possible conclusion about the L1 impact of higher-layer aspects of small cell enhancement, as described in the Chairman's Notes for Chairman's Notes for RAN1#74 as follows:

Depending on the detailed architecture, dual connectivity may have impacts on the following aspects of L1 operation. Details of these impacts would need further study and would depend on factors such as:whether the UE has the capability for simultaneous transmissionthe level of synchronisation and coordination between eNBs
Possible areas of L1 impact include:DL HARQ operation and feedbackUL power control operation, scaling and PHRUL transmit timing controlInteractions between different UL channelsRACH procedureCSS transmissionSR transmissionRLM

Also, in RAN1#74, a contribution proposes to have additional consideration for power control including the aspect of Power Headroom Report (PHR), as described in 3GPP R1-133396 as follows:

Inter-eNB CA with simultaneous uplink transmissions can however reuse most of the UE behavior specified for LTE CA R11, with additional considerations for power control (e.g. including aspects of PHR) and how to handle specific cases of simultaneous uplink transmissions with respect to different combinations of PUCCH, PUSCH and PRACH. Some specific band combination(s) with too small separation may also require TDM operation, this would only be necessary if support for such combinations is required.

What RAN will assume as the minimal UE capabilities for inter-eNB CA will thus greatly impact what type of realization may be in scope for further study.

In addition, two contributions in 3GPP R1-133182 and R1-133436 propose that the UE could report PHR to an eNB (evolved Node B) wherein the report would include PHR of both macro and small eNBs, or of both master and secondary eNBs. In particular, 3GPP R1-133182 states:

Uplink Power Control Issues:

Although the non-ideal backhaul condition requires separate power control between the macro and small cell nodes, some degree of coordination between the nodes is necessary so that each node can estimate the power headroom for the its cell group and its dependence on the transmission for the other cell group.

For power limited UEs, uplink subframes can be grouped into following three types.Subframes dedicated for the master eNBSubframes dedicated for the secondary eNBSubframes for both the master and secondary eNBs

For subframes dedicated to either the master eNB or the secondary eNB, the uplink scheduling and power control can be done completely independently between the nodes. For subframes for both the master and secondary eNBs, information about the scheduling and power control of the other node can be helpful for each node, for example, the UE can provide power headroom reports about cells belonging to the other cell group to each node.

2.1.5 UL Power Control and PHR

A specific area that would be impacted on the physical layer of the dual connectivity is design of UL power control in case the UE transmits on multiple carriers simultaneously. The issue is here very similar to UL power control handling for UL carrier aggregation, i.e. that the UE needs to share its power on all UL carriers where it is transmitting simultaneously. The main difference between CA and dual connectivity is the backhaul delay between the network nodes. Transmitting PUCCH simultaneously on multiple UL carriers is not necessarily an issue as the total consumed power for PUCCH is relatively low and hence the UE would seldom reach it maximum transmission power. For PUSCH it is however more an issue as here the total available power may be closer to be exceeded. To ease the situation it would be useful for each corresponding eNB to know the available power headroom for the UE on all the UEs UL carriers. Hence, the eNB need a PHR report for each corresponding carrier.

Proposal

The UE reports a PHR separately to each cell and the corresponding PHR contains the PHR for all UL carriers the UE has configured

As specified in Section 5.1 in 3GPP TS 36.213, Type 1 power headroom reflects the UE's power headroom for PUSCH (Physical Uplink Shared Channel). In general, the power headroom calculation considers the UE maximum available transmit power for PUSCH and the estimated PUSCH transmit power for a serving cell c in a subframe i. If there is no PUSCH in the subframe, a virtual power headroom would be calculated and reported, while assuming no PUSCH resources, zero code rate, and some specific parameters in general. More specifically, the following assumptions would be made:Assume that PCMAX,c(i) is the configured UE transmit power in subframe i for serving cell c and {circumflex over (P)}CMAX,c(i) is the linear value of PCMAX,c(i).Assume that MPUSCH,c(i) is the bandwidth of the PUSCH resource assignment expressed in number of resource blocks valid for subframe i and serving cell c.Assume that PO_PUSCH,c(j) is provided by higher layers for serving cell c where the value j depends on PUSCH (re)transmissions corresponding to a semi-persistent grant or a dynamic scheduled grant or random access response grant.Assume that PLcis the downlink pathloss estimate calculated in the UE for serving cell c in dB, and the αc(j) is the parameter provided by higher layers for each serving cell c.Assume that ΔTF,c(i) is the value derived by the data bits size for the uplink PUSCH transmission in subframe i for serving cell c. In addition, if the data bits size is zero, the data code-rate is zero and ΔTF,c(i) should be zero.Assume that fc(i) is the close-loop PUSCH power control adjustment state in subframe i for serving cell c.

For Type 1 virtual power headroom,
PHtype1,c(i)={tilde over (P)}CMAX,c(i)−{PO_PUSCH,c(1)αc(1)·PLc+fc(i)}

Based on the contributions discussed in 3GPP R1-133396, R1-133182, R1-133436, for the UE configured with inter-eNB CA (Carrier Aggregation) with simultaneous uplink transmissions, the UE could alleviate or reduce power issues by reporting PHR of all UL carriers to each Node. Assuming there are PUSCH transmissions both on master and secondary cells in a subframe, the PHR to one eNB would contain the actual power headroom values of both master and secondary cells, according to current 3GPP TS 36.213. However, in view of the non-ideal backhaul between master and secondary eNBs, the macro cell and small cell would be scheduled separately. Thus, it would be impossible for one eNB to get the timely information of allocated PUSCH resources in the other eNB. As a result, it would be difficult to estimate the actual power headroom of the other eNB.

Furthermore, if simultaneous PUCCH (Physical Uplink Control Channel) and PUSCH transmissions are configured for a UE, there may be similar difficulties in determining reflecting the UE power headroom of PUSCH and PUCCH for Type 2 power headroom.

The general concept of the invention is that when a UE reports to a first eNB power headroom of the cells belonging to second eNB, the reported power headroom would be virtual values. In one embodiment, the virtual power headroom value of a cell could be derived assuming a specific PUSCH resource assignment regardless of whether there is PUSCH transmission on the cell in the subframe or not. A zero PUSCH resource assignment means the term 10 log10(MPUSCH,c(i)) is either zero or not included in the derivation of virtual power headroom value. Furthermore, the specific PUSCH resource assignment could be zero or a value configured by higher layer.

In addition, the calculation of virtual power headroom values of the cells belonging to the second eNB would not contain dynamically scheduled PUSCH resources if there is PUSCH transmission on the cell. Thus, it would be beneficial for the first eNB, which receive the PHRs, to get the power information of the second eNB, such as pathloss information and/or power requirements.

Furthermore, the virtual power headroom value of a cell could be derived using a zero code-rate, the term PO_PUSCH,c(1), or the term αc(1), as specified in 3GPP TS 36.213 V11.4.0. Also, the term {tilde over (P)}CMAX,c(i) for virtual power headroom calculation could be computed using MPR=0 dB, A-MPR=0 dB, P-MPR=0 dB and ΔTC=0 dB, as specified in 3GPP TS 36.213 V11.4.0.

FIG. 5is a flow chart500in accordance with one exemplary embodiment. In step505, a UE is configured with at least a first cell and a second cell. In step510, the UE reports a PHR (Power Headroom Report) on the first cell in a subframe, wherein the PHR contains the power headroom value of the second cell, and the power headroom value of the second cell is derived using a specific PUSCH resource assignment regardless of whether there is PUSCH transmission in the second cell in the subframe or not.

In one embodiment, the specific PUSCH resources assignment could be zero. Alternatively, the specific PUSCH resources assignment could be configured by higher layer.

In one embodiment, the zero code-rate is used for the derivation of the power headroom value of the second cell. More specifically, the term ΔTF,c(i) is zero for the derivation of the power headroom value of the second cell. Furthermore, the parameter αc(1) of pathloss (PL) of the second cell is used for the derivation of the power headroom value of the second cell. In addition, the term {tilde over (P)}CMAX,c(i), representing the UE maximum transmit power of second cell, is computed using MPR=0 dB, A-MPR=0 dB, P-MPR=0 dB, and ΔTc=0 dB.

In one embodiment, the power headroom value of the second cell could be Type 1 power headroom or Type 2 power headroom. Furthermore, the power headroom value of the second cell is derived using the following formula or equation:
{tilde over (P)}CMAX,c(i)−{PO_PUSCH,c(1)+αc(1)·PLc+fc(i)}.

Alternatively, the power headroom value of the second cell could be derived using the following formula or equation:

In one embodiment, the PHR also contains the state information of cell activation and cell deactivation. Furthermore, the second cell could be activated and/or configured with PUCCH. In addition, the first cell and the second cell could be controlled by different eNBs. More specifically, the first cell could be controlled by a macro eNB, a small eNB, a master eNB, or a secondary eNB. Similarly, the second cell could be controlled by a macro eNB, a small eNB, a master eNB, or a secondary eNB. Also, the first cell could be a macro cell, a small cell, a master cell, or a secondary cell. Similarly, the second cell could be a macro cell, a small cell, a master cell, or a secondary cell. In one embodiment, the first cell is a master cell and the second cell is a secondary cell. In one embodiment, the first cell is a secondary cell and the second cell is a master cell respectively.

In one embodiment, the PUSCH transmission could be dynamically scheduled by PDCCH (Physical Downlink Control Channel) with CRC (Cyclic Redundancy Check) scrambled by C-RNTI (Cell Radio Network Temporary Identifier). Alternatively, the PUSCH transmission could be scheduled on a semi-persistence basis by PDCCH with CRC scrambled by SPS (Semi-Persistent Scheduling) C-RNTI. Furthermore, the PUSCH transmission does not contain the semi-persistent scheduled transmission which is scheduled by PDCCH with CRC scrambled by SPS C-RNTI.

In one embodiment, the subframe in the second cell could be a UL (Uplink) subframe, a DL (Downlink) subframe, or a special subframe.

Referring back toFIGS. 3 and 4, the device300includes a program code312stored in memory310. Furthermore, in one embodiment, the CPU could execute program code312(i) to configure a UE with at least a first cell and a second cell, and (ii) to report a PHR (Power Headroom Report) on the first cell in a subframe, wherein the PHR contains the power headroom value of the second cell, and the power headroom value of the second cell is derived using a specific PUSCH resource assignment regardless of whether there is PUSCH transmission in the second cell in the subframe or not. In addition, the CPU308can execute the program code312to perform all of the above-described actions and steps or others described herein.

FIG. 6is a flow chart600in accordance with one exemplary embodiment. In step605, a UE is configured with at least a first cell and a second cell. In step610, the UE reports a PHR (Power Headroom Report) on the first cell in a subframe, wherein the PHR contains the power headroom value of the second cell, and the power headroom value of the second cell is derived using a specific PUCCH (Physical Uplink Control Channel) format and a specific value of h(nCQI,nHARQ,nSR) regardless of whether there is PUCCH transmission in the second cell in the subframe or not. The term h(nCQI,nHARQ,nSR) could be a PUCCH format dependent value with consideration of the bit number of CQI (Channel Quality Indication), HARQ (Hybrid Automatic Repeat Request), or SR (Scheduling Request).

In one embodiment, the specific PUCCH format could be PUCCH format 1a. Furthermore, the specific PUCCH format could be configured by higher layer, or a PUCCH format configured for HARQ-ACK (Hybrid Automatic Repeat Request Acknowledgment) feedback.

In one embodiment, the power headroom value of the second cell could be Type 2 power headroom. Furthermore, the power headroom value of the second cell is derived using the following formula:

In one embodiment, the term ΔF_PUCCH(F) could be zero for the derivation of the power headroom value of the second cell, wherein ΔF_PUCCH(F) is provided by higher layers, and its value corresponds to a PUCCH format (F) relative to PUCCH format 1a. Furthermore, the specific value of h(nCQI,nHARQ,nSR) could be zero or could be configured by a higher layer. In addition, the power parameter ΔT×D(F′) of the second cell is assumed to be zero for the derivation of the power headroom value of the second cell. More specifically, the value of ΔT×D(F′) is provided by higher layers for each PUCCH format F′ if the UE is configured by higher layers to transmit PUCCH on two antenna ports. Also, the term {tilde over (P)}CMAX,c(i), representing the UE maximum transmit power of the second cell, is computed using MPR=0 dB, A-MPR=0 dB, P-MPR=0 dB, and ΔTC=0 dB.

In one embodiment, the PHR also contains the state information of cell activation and cell deactivation. Furthermore, the second cell could be activated and/or configured with PUCCH. In addition, the first cell and the second cell could be controlled by different eNBs. More specifically, the first cell could be controlled by a macro eNB, a small eNB, a master eNB, or a secondary eNB. Similarly, the second cell could be controlled by a macro eNB, a small eNB, a master eNB, or a secondary eNB. Also, the first cell could be a macro cell, a small cell, a master cell, or a secondary cell. Similarly, the second cell could be a macro cell, a small cell, a master cell, or a secondary cell. In one embodiment, the first cell is a master cell and the second cell is a secondary cell. In one embodiment, the first cell is a secondary cell and the second cell is a master cell respectively.

In one embodiment, the PUSCH transmission could be dynamically scheduled by PDCCH (Physical Downlink Control Channel) with CRC (Cyclic Redundancy Check) scrambled by C-RNTI (Cell Radio Network Temporary Identifier). Alternatively, the PUSCH transmission could be scheduled on a semi-persistence basis by PDCCH with CRC scrambled by SPS (Semi-Persistent Scheduling) C-RNTI. Furthermore, the PUSCH transmission does not contain the semi-persistent scheduled transmission which is scheduled by PDCCH with CRC scrambled by SPS C-RNTI.

In one embodiment, the subframe in the second cell could be a UL (Uplink) subframe, a DL (Downlink) subframe, or a special subframe.

Referring back toFIGS. 3 and 4, the device300includes a program code312stored in memory310. In one embodiment, the CPU308could execute program code312(i) to configure a UE with at least a first cell and a second cell, and (ii) to report a PHR on the first cell in a subframe, wherein the PHR contains the power headroom value of the second cell, and the power headroom value of the second cell is derived using a specific PUCCH format and a specific value of h(nCQI,nHARQ,nSR) regardless of whether there is PUCCH transmission in the second cell in the subframe or not. In addition, the CPU308can execute the program code312to perform all of the above-described actions and steps or others described herein.