U.S. patent application number 15/309231 was filed with the patent office on 2017-03-23 for user terminal, radio base station and radio communication method.
This patent application is currently assigned to NTT DOCOMO, INC.. The applicant listed for this patent is NTT DOCOMO, INC.. Invention is credited to Huiling Jiang, Liu Liu, Kazuki Takeda, Lihui Wang.
Application Number | 20170086149 15/309231 |
Document ID | / |
Family ID | 54392574 |
Filed Date | 2017-03-23 |
United States Patent
Application |
20170086149 |
Kind Code |
A1 |
Takeda; Kazuki ; et
al. |
March 23, 2017 |
USER TERMINAL, RADIO BASE STATION AND RADIO COMMUNICATION
METHOD
Abstract
The present invention is designed to reduce the decrease of
uplink throughput in the event a user terminal connects with a
plurality of radio base stations. A user terminal (20) according to
an example of the present invention provides a user terminal that
connects with a plurality of radio base stations (10) including a
first radio base station and a second radio base station, and this
user terminal has a transmission section (203) that transmits
uplink signals of a plurality of types to each radio base station,
and a control section (401) that controls the transmission power of
the uplink signals based on the priorities of the uplink signals
for each radio base station, and, every time there are uplink
signals of the same type, the control section configures the
priority for the first radio base station higher than the priority
for the second radio base station.
Inventors: |
Takeda; Kazuki; (Tokyo,
JP) ; Liu; Liu; (Beijing, CN) ; Wang;
Lihui; (Beijing, CN) ; Jiang; Huiling;
(Beijing, CN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NTT DOCOMO, INC. |
Tokyo |
|
JP |
|
|
Assignee: |
NTT DOCOMO, INC.
Tokyo
JP
|
Family ID: |
54392574 |
Appl. No.: |
15/309231 |
Filed: |
May 8, 2015 |
PCT Filed: |
May 8, 2015 |
PCT NO: |
PCT/JP2015/063243 |
371 Date: |
November 7, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04W 52/365 20130101;
H04W 52/34 20130101; H04W 52/146 20130101; H04W 88/06 20130101;
H04W 8/24 20130101; H04W 72/04 20130101 |
International
Class: |
H04W 52/36 20060101
H04W052/36; H04W 8/24 20060101 H04W008/24; H04W 52/14 20060101
H04W052/14 |
Foreign Application Data
Date |
Code |
Application Number |
May 8, 2014 |
JP |
2014-096660 |
Claims
1. A user terminal that communicates by using a first cell group
(CG) and a second CG, the user terminal comprising: a transmission
section that transmits uplink signals of a plurality of types in
each CG; and a control section that allocates power to an uplink
signal of a given type to transmit in the first CG more
preferentially than the uplink signal of the given type to transmit
in the second CG.
2. The user terminal according to claim 1, wherein the control
section preferentially allocates power to the uplink signals to
transmit in each CG, in an order of a PRACH, a channel including
UCI, a PUSCH not including UCI and an SRS.
3. The user terminal according to claim 2, wherein the control
section preferentially allocates power in an order of a PRACH of
the first CG, a PRACH of the second CG, a channel of the first CG
including UCI, a channel of the second CG including UCI, a PUSCH of
the first CG not including UCI, a PUSCH of the second CG not
including UCI, an SRS of the first CG and an SRS of the second
CG.
4. The user terminal according to claim 1, wherein, when the user
terminal supports asynchronous dual connectivity, the control
section does not change, in a middle of a subframe, power of a
signal that is being transmitted.
5. The user terminal according to claim 4, wherein the transmission
section transmits user terminal capability information to represent
whether or not asynchronous dual connectivity can be supported.
6. The user terminal according to claim 1, further comprising a PH
reporting generating section that calculates a PH (Power Headroom)
for each CG based on maximum uplink signal transmission power and
uplink signal transmission power that is demanded by the CG, and
generates a PH report.
7. A radio base station that communicates with a user terminal by
using a predetermined cell group, the user terminal communicating
by using a first cell group (CG) and a second CG, the radio base
station comprising: a transmission section that transmits control
signals for controlling transmission power of uplink signals; and a
receiving section that receives the uplink signals, the
transmission power of which is controlled based on the control
signals, wherein the uplink signals are controlled so that power is
more preferentially allocated to an uplink signal of a given type
to transmit in the first CG than the uplink signal of the given
type to transmit in the second CG.
8. A radio communication method for a user terminal that
communicates by using a first cell group (CG) and a second CG, the
radio communication method comprising: transmitting uplink signals
of a plurality of types in each CG; and allocating power to an
uplink signal of a given type to transmit in the first CG more
preferentially than the uplink signal of the given type to transmit
in the second CG.
9. (canceled)
10. The user terminal according to claim 2, wherein, when the user
terminal supports asynchronous dual connectivity, the control
section does not change, in a middle of a subframe, power of a
signal that is being transmitted.
11. The user terminal according to claim 3, wherein, when the user
terminal supports asynchronous dual connectivity, the control
section does not change, in a middle of a subframe, power of a
signal that is being transmitted.
Description
TECHNICAL FIELD
[0001] The present invention relates to a user terminal, a radio
base station, a radio communication method and a radio
communication system in a next-generation mobile communication
system.
BACKGROUND ART
[0002] In the UMTS (Universal Mobile Telecommunications System)
network, the specifications of long term evolution (LTE) have been
drafted for the purpose of further increasing high speed data
rates, providing lower delay and so on (see non-patent literature
1).
[0003] In LTE, as multiple access schemes, a scheme that is based
on OFDMA (Orthogonal Frequency Division Multiple Access) is used in
downlink channels (downlink), and a scheme that is based on SC-FDMA
(Single Carrier Frequency Division Multiple Access) is used in
uplink channels (uplink).
[0004] Successor systems of LTE--referred to as, for example,
"LTE-advanced" or "LTE enhancement" --have been under study for the
purpose of achieving further broadbandization and increased speed
beyond LTE, and the specifications thereof have been drafted as LTE
Rel. 10/11 (LTE-A). The system band of LTE Rel. 10/11 includes at
least one component carrier (CC), where the LTE system band
constitutes one unit. Such bundling of a plurality of CCs into a
wide band is referred to as "carrier aggregation" (CA).
[0005] In LTE Rel. 12, which is a more advanced successor system of
LTE, various scenarios to use a plurality of cells in different
frequency bands (carriers) are under study. When a plurality of
cells are formed by the same radio base station in effect, the
above-described CA is applicable. On the other hand, when a
plurality of cells are formed by completely different radio base
stations, dual connectivity (DC) may be applied.
CITATION LIST
Non-Patent Literature
[0006] Non-Patent Literature 1: 3GPP TS 36.300 "Evolved Universal
Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial
Radio Access Network (E-UTRAN); Overall Description; Stage 2"
SUMMARY OF INVENTION
Technical Problem
[0007] As noted earlier, when a plurality of cell groups are formed
by the same radio base station in effect (for example, when CA is
employed), the radio base station can control uplink transmission
power by taking into account the uplink transmission power of user
terminals in each cell in a comprehensive manner. However, as in
dual connectivity, when a plurality of radio base stations
independently control the uplink transmission power of user
terminals, this may result in a decrease of uplink throughput, a
deterioration of communication quality, and so on.
[0008] The present invention has been made in view of the above,
and it is therefore an object of the present invention to provide a
user terminal, a radio base station, a radio communication method
and a radio communication system that can reduce the decrease of
uplink throughput when a user terminal connects with a plurality of
radio base stations.
Solution to Problem
[0009] The user terminal according to an example of the present
invention provides a user terminal that communicates by using a
first cell group (CG) and a second CG, and this user terminal has a
transmission section that transmits uplink signals of a plurality
of types in each CG, and a control section that allocates power to
an uplink signal of a given type to transmit in the first CG more
preferentially than the uplink signal of the given type to transmit
in the second CG.
Advantageous Effects of Invention
[0010] According to the present invention, the decrease of uplink
throughput when a user terminal connects with a plurality of radio
base stations can be reduced.
BRIEF DESCRIPTION OF DRAWINGS
[0011] FIG. 1 provide schematic diagrams of carrier aggregation and
dual connectivity;
[0012] FIG. 2 provide diagrams to show example cell structures in
carrier aggregation and in dual connectivity;
[0013] FIG. 3 is a diagram to show an example case of connecting
with each radio base station by way of UL-CA in dual
connectivity;
[0014] FIG. 4 is a diagram to show the priorities of uplink signals
in UL-CA of LTE Rel. 11;
[0015] FIG. 5 provide diagrams to show examples of priorities of
uplink signals in each eNB/CG;
[0016] FIG. 6 is a diagram to show examples of priorities of uplink
signals in dual connectivity according to a first embodiment;
[0017] FIG. 7 is a diagram to show examples of priorities of uplink
signals in dual connectivity according to a first embodiment;
[0018] FIG. 8 is a diagram to show an example case in which a
power-limited state begins in the middle of a subframe;
[0019] FIG. 9 is a conceptual diagram to explain transmission power
control according to a second embodiment;
[0020] FIG. 10 is a diagram to show an example flowchart for
determining power distribution based on differences between the
priorities of signals transmitted at the same time,
[0021] FIG. 11 is a diagram to show an example of determining power
distribution based on differences between the priorities of signals
transmitted at the same time;
[0022] FIG. 12 is a diagram to show an example of a schematic
structure of a radio communication system according to an
embodiment of the present invention;
[0023] FIG. 13 a diagram to show an example of an overall structure
of a radio base station according to an embodiment of the present
invention;
[0024] FIG. 14 a diagram to shown an example of a functional
structure of a radio base station according to an embodiment of the
present invention;
[0025] FIG. 15 is a diagram to show an example of an overall
structure of a user terminal according to an embodiment of the
present invention; and
[0026] FIG. 16 is a diagram to show an example of a functional
structure of a user terminal according to an embodiment of the
present invention.
DESCRIPTION OF EMBODIMENTS
[0027] Now, embodiments of the present invention will be described
below in detail with reference to the accompanying drawings.
[0028] Carrier aggregation and dual connectivity are both
techniques to allow a user terminal to connect and communicate with
a plurality of cells at the same time, and are applied to, for
example, a HetNet (Heterogeneous Network). Here, the "HetNet,"
which is under study in LTE-A systems, refers to a structure in
which small cells, each having a local coverage area of a radius of
approximately several tens of meters, are formed within a macro
cell having a wide coverage area of a radius of approximately
several kilometers. Note that carrier aggregation may be referred
to as "intra-eNB CA," and dual connectivity may be referred to as
"inter-eNB CA."
[0029] FIG. 1 provide schematic diagrams of carrier aggregation and
dual connectivity. In the examples shown in FIG. 1, a user terminal
UE communicates with radio base stations eNB1 and eNB2.
[0030] FIG. 1 show control signals that are transmitted and
received via a physical downlink control channel (PDCCH) and a
physical uplink control channel (PUCCH). For example, downlink
control information (DCI) is transmitted using the PDCCH, and
uplink control information (UCI) is transmitted via the PUCCH. Note
that an enhanced physical downlink control channel (EPDCCH:
Enhanced PDCCH) may be used instead of the PDCCH.
[0031] FIG. 1 A shows communication among radio base stations eNB1
and eNB2 and the user terminal UE by way of carrier aggregation. In
the exampled shown in FIG. 1A, eNB1 is a radio base station to form
a macro cell (hereinafter referred to as the "macro base station"),
and eNB2 is a radio base station to form a small cell (hereinafter
referred to as the "small base station").
[0032] For example, the small base station may be structured like
an RRH (Remote Radio Head) that connects with the macro base
station. When carrier aggregation is employed, one scheduler (for
example, the scheduler provided in macro base station eNB1)
controls the scheduling of multiple cells.
[0033] In a structure in which a scheduler provided in a macro base
station controls the scheduling of multiple cells, each base
station may be connected using, for example, an ideal backhaul that
provides a high speed channel such as optical fiber.
[0034] FIG. 1B shows communication among radio base stations eNB1
and eNB2 and a user terminal UE by way of dual connectivity. In the
example shown in FIG. 1B, eNB1 and eNB2 are both macro base
stations.
[0035] When dual connectivity is employed, a plurality of
schedulers are provided independently, and these multiple
schedulers (for example, the scheduler provided in macro base
station eNB1 and the scheduler provided in macro base station eNB2)
each control the scheduling of one or more cells they have control
over.
[0036] In the structure in which the scheduler provided in macro
base station eNB1 and the scheduler provided in macro base station
eNB2 each control the scheduling of one or more cells they have
control over, each base station may be connected using, for
example, a non-ideal backhaul to produce delays that cannot be
ignored, such as the X2 interface.
[0037] Consequently, it is generally assumed that, in dual
connectivity, close coordinated control between eNBs equivalent to
carrier aggregation cannot be executed. Consequently, downlink
L1/L2 control (PDCCH/EPDCCH) and uplink L1/L2 control (UCI feedback
by the PUCCH/PUSCH) needs to be carried out independently in each
eNB.
[0038] FIG. 2 provide diagrams to show example cell structures in
carrier aggregation and dual connectivity. In FIG. 2, the UE is
connected with five cells (C1 to C5). C1 is a PCe11 (Primary Cell),
and C2 to C5 are SCells (Secondary Cells).
[0039] As shown in FIG. 2A, in carrier aggregation, uplink control
signals are transmitted via the PCe11, so that the SCells do not
have to have the functions of the PCell.
[0040] On the other hand, as shown in FIG. 2B, in dual
connectivity, each radio base station is configured in a cell group
(CG), which is formed with one cell or a plurality of cells. Each
cell group is comprised of one or more cells formed by the same
radio base station, or one or more cells formed by the same
transmission point such as a transmitting antenna apparatus, a
transmission station, and so on.
[0041] Here, the cell group to include the PCell is referred to as
the "master cell group (MCG)," and the cell groups other than the
MCG will be referred to as "secondary cell groups (SCGs)." In each
cell group, two or more cells can execute carrier aggregation.
[0042] Also, the radio base station where the MCG is configured is
referred to as the "master base station (MeNB: Master eNB)," and
the radio base stations where the SCGs are configured are referred
to as "secondary base stations (SeNBs: Secondary eNBs)."
[0043] The total number of cells to constitute the MCG and the SCGs
is configured to be equal to or less than a predetermined value
(for example, five (cells)). This predetermined value may be set in
advance, or may be configured semi-statically or dynamically
between the radio base stations eNB and the user terminal UE. Also,
depending on the implementation of the user terminal UE, the value
of the sum of the cells to constitute the MCG and the SCGs and the
combination of cells that can be configured may be reported to the
radio base stations eNB in the form of user terminal capability
information (UE capability information).
[0044] In dual connectivity, as noted earlier, significant backhaul
delays may be produced between eNBs. Consequently, each eNB
transmits and receives control information to and from UEs
independently, so that, even in SeNBs, a cell (also referred to as
a "special cell," a "PUCCH configured cell" and so on) that is
special and has functions (common search space, the PUCCH, etc.)
equivalent to those of the PCell is required. In the example FIG.
2B, cell C3 is configured as a cell of that kind.
[0045] As described above, in dual connectivity, a user terminal
has to connect with each of a plurality of radio base stations in
at least one uplink serving cell. Furthermore, a study is in
progress to carry out UL-CA (uplink carrier aggregation) to involve
two or more uplink serving cells for each radio base station. FIG.
3 is a diagram to show an example case of connecting with each
radio base station by way of UL-CA in dual connectivity. In FIG. 3,
the user terminal connects with the MeNB and the SeNB via
UL-CA.
[0046] Here, uplink signal transmission timings are controlled
separately between the MeNB and the SeNB. Furthermore, uplink
signal transmission power control is also carried out separately
between the MeNB and the SeNB. Consequently, cases might occur in
which, in timings where uplink signal transmissions for the MeNB
and the SeNB overlap, there is a demand to transmit uplink signals
beyond the maximum allowable power (Pcmax) of the user terminal. In
the following description, "power-limited" will refer to the state
in which transmission power is limited because uplink signal
transmissions to exceed the maximum allowable power of a user
terminal are in demand.
[0047] When this takes place, the user terminal has to lower the
transmission power down to or below the maximum allowable power by
reducing the transmission power, by dropping transmitting signals,
and so on, based on some rules. Here, UL-CA of LTE Rel. 11 provides
for configuring priorities for uplink signals of a plurality of
types to transmit to one radio base station, and allowing a user
terminal to adjust transmission power based on these priorities so
that the total of each CC's transmission power does not exceed the
maximum allowable power.
[0048] FIG. 4 is a diagram to show the priorities of uplink signals
in UL-CA of LTE Rel. 11. As shown in FIG. 4, in Rel. 11, the PRACH
has the highest priority, followed by the lower priorities of the
PUCCH, PUSCH w/UCI (PUSCH including UCI), the PUSCH w/o UCI (PUSCH
not including UCI), and the SRS, in order. Note that each channel
in FIG. 4 represents the signal to be transmitted via that channel,
and will be represented likewise in the following description.
[0049] In UL-CA of LTE Rel. 11, when the transmission periods of
signals of varying priorities overlap and the power-limited state
is produced, the signals of the lower priorities may be subjected
to power scaling, or may be controlled not to be transmitted (that
is, dropped). Furthermore, when signals of the same priority
overlap and the power limited state is produced, control may be
executed so that power scaling is applied to both signals in the
same ratio.
[0050] However, LTE Rel. 12 provides no stipulation regarding the
priorities between CGs/eNBs in dual connectivity. Consequently,
when a user terminal manipulates the transmission power of uplink
signals for each CG/eNB, there is a threat of causing an uplink
signal quality deterioration that is not intended by the radio base
stations, which then might result in increased retransmissions, a
decrease of throughput, and so on.
[0051] In order to solve this problem, the present inventors have
studied adequately configuring the priorities of uplink signals in
transmission to the MeNB and the SeNB when dual connectivity is
employed. As a result of this, the present inventors have come up
with the idea of prioritizing transmitting given uplink signal for
the MeNB over transmitting the same given uplink signals for the
SeNB. According to this structure, a user terminal can reduce the
impact of the limitation of the maximum allowable power by
increasing the priority of important control signals.
[0052] Furthermore, the present inventors have also come up with
the idea of executing adequate power control by taking into account
the above-mentioned priorities when the transmission timings of
uplink signals are not synchronized between a plurality of radio
base stations.
[0053] Now, embodiment of the present invention will be described
below in detail. Note that, although, for ease of explanation,
examples will be described below in which a user terminal connects
with two radio base stations (MeNB and SeNB) in dual connectivity,
this is by no means limiting. For example, the present invention is
applicable to cases where a user terminal connects and communicates
with three or more radio base stations that each execute control
with an independent scheduler. Furthermore, it is equally possible
to employ a structure in which a user terminal connects with cell
groups, instead of radio base stations, so that radio base stations
or cell groups will be hereinafter also referred to as "eNBs" or
"CGs."
[0054] Also, hereinafter, priorities in each eNB/CG will maintain
the order of priorities (priority rule) shown in FIG. 5. FIG. 5
provide diagrams to show examples of the priorities of uplink
signals in each eNB/CG. FIG. 5A shows examples of priorities in the
MeNB/MCG, and FIG. 5B shows examples of priorities in the SeNB/SCG.
These priorities show the same order of priorities as in UL-CA of
Rel. 11 shown in FIG. 4 (the order of the PRACH, the PUCCH, the
PUSCH w/UCI, the PUSCH w/o UCI and the SRS). By employing such
structures, it is possible to carry out processes in user terminals
in a uniform way with Rel. 11, and reduce the cost of
implementation. Note that the priorities in each eNB/CG are not
limited to the order of priorities of FIG. 5, and other orders of
priorities may be used as well.
First Embodiment
[0055] With a first embodiment of the present invention, every
uplink signal for the MCG/MeNB is assigned a higher priority than
an uplink signal of the same type for the SCG/SeNB.
[0056] According to an example of the first embodiment, the
priority rule is configured so that all uplink signals for the
MeNB/MCG are prioritized over all uplink signals for the SeNB/SCG.
FIG. 6 is a diagram to show an example of the priorities of uplink
signals in dual connectivity according to the first embodiment. As
shown in FIG. 6, in this priority rule, the UL-CA priorities in the
MeNB/MCG (FIG. 5A) are configured higher than the UL-CA priorities
in the SeNB/SCG (FIG. 5B).
[0057] By following this priority rule, it is possible to prevent
deterioration in the MCG/MeNB due to the power-limited state, and
apply dual connectivity without sacrificing the macro cell
coverage.
[0058] Note that, in the above example, the SRS and/or the PUSCH
w/o UCI may be made an exception, and their priorities may be
lowered significantly in both the MeNB/SeNB, regardless of the
priority rule. For example, in FIG. 6, the priorities of the PUSCH
w/o UCI and the SRS for the MeNB may be made lower than that of the
PUSCH w/UCI for the SeNB. By this means, it is possible to further
reduce the negative influence that is produced when MeNB channels
of lower priorities consume power and signals that relate to the
connectivity and delays of the SeNB in a significant way such as
the PRACH and the PUCCH for the SeNB cannot secure power.
[0059] Furthermore, in the above example, the PRACH and the PUCCH
may be made an exception, and their priorities may be increased
significantly in both the MeNB/SeNB, regardless of the above
priority rule. For example, in FIG. 6, the priorities of the PRACH
and the PUCCH for the SeNB may be made higher than that of the
PUSCH w/UCI for the MeNB. By this means, it is possible to further
reduce the negative influence that is produced when MeNB channels
of lower priorities consume power and signals that relate to the
connectivity and delays of the SeNB in a significant way such as
the PRACH and the PUCCH for the SeNB cannot secure power.
[0060] According to another example of the first embodiment, every
time there are uplink signals of the same type, the MeNB/MCG has a
higher priority than the SeNB/SCG, and their priorities are
configured to neighbor each other. To "neighbor each other" here
means, in other words, not configuring the priorities of signals of
other types between the priorities of signals of the same type.
[0061] FIG. 7 is a diagram to show examples of the priorities of
uplink signals in dual connectivity according to the first
embodiment. In FIG. 7, the priority rule is configured so that the
priorities in each eNB/CG are the same as in UL-CA of Rel. 11.
According to this priority rule, the priority of each signal is
configured higher in the MeNB/MCG than in the SeNB/SCG. That is,
according to the present embodiment, the priorities of uplink
signals of the same type are taken together, and the priority rule
is configured to be the same as in each eNB/CG.
[0062] By following this priority rule, it is possible to
preferentially allocate power to signals of higher priorities
regardless of the eNB/CG. In particular, the priority of the PUSCH,
the bandwidth of which easily widens and which is therefore likely
to be a cause of the power-limited state, can be made relatively
low, so that it is possible to reduce the impact on important
control signals such as the PRACH, the PUCCH and so on.
[0063] Note that a structure may be possible in which a given
signal has the same priority between the MeNB/MCG and the SeNB/SCG.
That is, a structure may be employed, in which, every time there
are signals of the same type, the priority for the MeNB/MCG is
configured to be equal to the priority for the SeNB/SCG. In this
case, when the power-limited state is assumed, signals of the same
priority may be subjected to scaling in equal power or in an equal
ratio, or may be dropped at the same time.
[0064] As described above, according to the first embodiment, even
in dual connectivity, transmission power for signals of high
priorities can be secured, so that it is possible to reduce the
decrease of uplink throughput.
[0065] Note that, when a user terminal holds a plurality of
priority rules, the priority rule to apply may be determined based
on information related to priority rules, which is reported in
downlink control information (DCI) from radio base stations, higher
layer signaling (for example, RRC signaling), broadcast signals
(for example, SIBs) and so on. For example, a structure may be
employed in which the priority rules of FIG. 6 and FIG. 7 are
applied on a switched basis, based on the information reported.
Second Embodiment
[0066] When uplink signal transmission timings are not synchronized
between a plurality of eNBs/CGs connected in dual connectivity
(hereinafter also referred to as "asynchronous dual connectivity"),
it may be difficult to follow the uplink signal priority rules
described with the first embodiment.
[0067] This problem will be described in detail with reference to
FIG. 8. FIG. 8 is a diagram to show an example case where the power
limited state begins in the middle of a subframe. In FIG. 8, the
horizontal axis is time, and the vertical direction is the power
that is allocated to transmission signals. Furthermore, the maximum
allowable power of a user terminal is Pcmax, and fixed in the
period illustrated.
[0068] Referring to the example of FIG. 8, first, a user terminal
starts the transmission process for the PUSCH w/o UCI in the
SeNB/SCG. At this time, no uplink signal is transmitted in the
MeNB/MCG, so that the user terminal can transmit the signal with
the transmission power demanded by the SeNB.
[0069] Next, while the PUSCH w/o UCI is transmitted in the
SeNB/SCG, the PUSCH w/UCI starts being transmitted in the MeNB/MCG.
In this case, there is a risk of entering the power limited state.
According to the priority rule of FIG. 6 or FIG. 7, the PUSCH w/UCI
in the MeNB/MCG has a higher priority than the PUSCH w/o UCI in the
SeNB/SCG, so that it is necessary to lower the transmission power
of the latter in the middle of the subframe and control the total
transmission power not to exceed Pcmax.
[0070] After the transmission of the PUSCH w/o UCI is complete in
the SeNB/SCG, the PUCCH starts being transmitted. In this case,
there is a risk of entering the power limited state. For example,
according to the priority rule of FIG. 7, the PUCCH in the SeNB/SCG
has a higher priority than the PUSCH w/UCI in the MeNB/MCG, so that
it is necessary to lower the transmission power of the latter in
the middle of the subframe and control the total transmission power
not to exceed Pcmax.
[0071] However, it is generally settled that the operation to
change the power of a signal that is being transmitted in the
middle of a subframe is not preferable. If such operation is
allowed, for example, problems might occur where gaps that are
produced between channel estimation reference signals and data
signals make demodulation based on channel estimation difficult,
where the amplitude of an orthogonal code changes in the middle of
the code sequence, and, when other UEs are multiplexed, the
orthogonality weakens, and demultiplexing becomes difficult.
[0072] Consequently, when the priority rule shown in FIG. 6 is
employed, when an MeNB/MCG transmission takes place in the middle
of a subframe, it is not preferable to change the power of the
signal that is being transmitted in the SeNB/SCG. Furthermore, when
the priority rule shown in FIG. 7 is employed, when a transmission
of a signal of a higher priority occur in the middle of a subframe,
it is not preferable to change the power of the signal that is
being transmitted. In this way, in asynchronous dual connectivity,
it is not always possible to follow the priorities in power
distribution, and cases might occur in which how to determine
transmission power is not clear.
[0073] So, with a second embodiment of the present invention, in
asynchronous dual connectivity, control is executed so that the
transmission power of a signal is not changed in the middle of an
uplink subframe (UL subframe), and the priorities described with
the first embodiment are followed. To be more specific, in dual
connectivity according to the present embodiment, power limited
detection is carried out, and power scaling/dropping is applied
when the power limited state is detected, by taking future uplink
transmission signals into account, regardless of whether eNBs/CGs
are synchronized or not synchronized.
[0074] First, before the transmission power of a given UL subframe
is determined with respect to a given eNB/CG, the transmission
power of all UL subframes of other eNBs/CGs having entirely or
partly simultaneous transmission intervals with that UL subframe is
investigated. In this case, the UL grants/DL assignments to command
the transmission of this UL subframe and preceding or following
overlapping UL subframes are detected and demodulated, and the UL
transmission conditions (the bandwidth, the modulation scheme, the
UL transmission power that is required based on these) are
investigated.
[0075] Next, based on the result of the above investigation of UL
transmission conditions, whether or not there is a part to be
power-limited in the transmission timing of the UL subframes is
calculated. Here, if there is a part to be power-limited, the
priorities of signals in this part are compared. For example, the
priorities of FIG. 6 and FIG. 7 can be used.
[0076] As a result of comparing priorities, the power allocated to
the UL subframe of the lower priority (non-priority) is reduced
(scaled or dropped) down to a value where the required power can be
adequately distributed to the UL subframe of the higher priority
(priority).
[0077] FIG. 9 is a conceptual diagram to explain the transmission
power control of the second embodiment. In FIG. 9, one UL subframe
that transmits signals in the MeNB has a partially simultaneous
transmission interval with two UL subframes that transmit signals
in the SeNB.
[0078] Before determining the transmission power of the MeNB UL
subframe, a user terminal investigates the UL transmission power in
the two SeNB UL subframes that overlap with the UL subframe, and
recognizes that there is a part to be power limited, based on the
information of UL grants/DL assignments that have been received.
Then, the priorities of the signals in that part are compared and
the transmission power of the UL subframes to transmit the signals
of the lower priorities is adjusted so that sufficient power is
allocated to the signal to be prioritized.
[0079] Now, an example case of applying the transmission power
control of the second embodiment will be described with reference
to the example of FIG. 8. Here, the priority rule shown in FIG. 7
is applied. First, before transmitting the PUSCH w/o UCI of the
SeNB/SCG, a user terminal investigates the UL transmission
conditions of the PUSCH w/UCI of the MeNB/MCG in subframes that
overlap with that subframe. According to FIG. 7, the PUSCH w/o UCI
of the SeNB/SCG has a lower priority than the other signals, and
therefore is transmitted with reduced transmission power.
[0080] Next, before transmitting the PUSCH w/UCI of the MeNB/MCG,
the user terminal investigates the UL transmission conditions of
the PUSCH w/o UCI and the PUCCH of the SeNB/SCG in the overlapping
subframes. According to FIG. 7, the PUSCH w/UCI of the MeNB/MCG has
a higher priority than the PUSCH w/o UCI of the SeNB/SCG, but has a
lower priority than the PUCCH of the SeNB/SCG, and therefore is
transmitted with reduced transmission power.
[0081] Next, before transmitting the PUCCH of the SeNB/SCG, the
user terminal investigates the UL transmission conditions of the
PUSCH w/UCI of the MeNB/MCG in the overlapping subframes. According
to FIG. 7, the PUCCH of the SeNB/SCG has a higher priority than the
PUSCH w/UCI of the MeNB/MCG, and therefore is transmitted with the
transmission power required by the SeNB.
[0082] As described above, according to the second embodiment,
transmission power control is executed by taking into account not
only currently-transmitting uplink signals, but also uplink signals
that are planned to be transmitted in the future, so that, even in
dual connectivity, it is possible to secure transmission power for
signals of high priorities, without changing transmission power in
the middle of subframes, and reduce the decrease of uplink/downlink
throughput.
[0083] (Variation 1)
[0084] Note that, although, with the above example of the second
embodiment, the transmission power of a given UL subframe for a
given eNB/CG is determined by taking into account the transmission
power of all UL subframes of other eNB/CGs having entirely or
partially-simultaneous transmission intervals with that UL
subframe, additional UL subframes may be taken into consideration
as well. To be more specific, the transmission power of UL
subframes not having simultaneous transmission intervals with that
UL subframe may be taken into consideration. For example, UL
subframes that follow that UL subframe may be taken into account.
Furthermore, it is also possible to take into account UL subframes
that follow UL subframes of other eNBs/CGs having entirely or
partially simultaneous transmission periods with that UL subframe.
For example, referring to the example of FIG. 8, when determining
the transmission power of the PUSCH w/o UCI in the SeNB/SCG, it may
be possible to take the UL transmission conditions of the PUCCH of
the SeNB/SCG into account, in addition to the PUSCH w/UCI of the
MeNB/MCG. By this means, it is possible to execute power control
adequately by taking into account the priorities and power limited
state of future signals.
[0085] (Variation 2)
[0086] Furthermore, in asynchronous dual connectivity, in order to
fix the transmission power in a subframe and secure the
transmission priorities of uplink signals, as shown with the second
embodiment, a user terminal needs to read the UL grants/DL
assignments for future transmission signals and calculate the
transmission power, and, furthermore, know whether or not the power
limited state will occur, and, if the power limited state will
occur, how much extra power will be required. Process like this
requires additional operations in the user terminal, which means
that the load of terminal implementation is likely to grow
heavier.
[0087] So, in systems in which dual connectivity is used, user
terminal capability information (UE capability information) may be
stipulated as follows. For example, user terminal capability
information to represent whether or not asynchronous dual
connectivity can be supported may be stipulated. Furthermore, user
terminal capability information to represent whether or not the
transmission power of future transmission signals can be calculated
in advance may be stipulated. Also, user terminal capability
information to represent whether or not transmission power can be
shared between eNBs/CGs on a dynamic basis may be stipulated as
well. These pieces of information are reported from user terminals
to radio base stations before dual connectivity is configured.
Based on these pieces of user terminal capability information, the
radio base stations carry out communication so that the user
terminals can execute adequate transmission power control.
[0088] Here, if a user terminal has any of these capabilities, the
radio base stations may judge that the transmission power control
of the second embodiment can be applied. Furthermore, if it is
determined that the transmission power control according to the
second embodiment cannot be applied to the user terminal, it is
preferable to distribute power semi-statically in advance, on a per
eNB/CG basis, so that arrangements may be made accordingly.
[0089] (Variation 3)
[0090] The above-described embodiments of the present invention may
be structured to determine the distribution of power based on
differences between the priorities of signals that are transmitted
at the same time. For example, referring to FIG. 7, assuming that
priorities are configured with increments of 1 so that the priority
of the PRACH of the MeNB/MCG is 1 and the priority of the SRS of
the SeNB/SCG is 10, the differences between the priorities of
transmitting signals (subframes) can be calculated within a range
of -9 to +9.
[0091] FIG. 10 is a diagram to show an example of a flowchart for
determining the distribution of power based on differences between
the priorities of signals that are transmitted at the same time.
Note that, in the process of applying power scaling, power dropping
may be applied instead.
[0092] First, before transmitting uplink signals of a given eNB/CG
in a given subframe, the user terminal calculates the priority
differences .DELTA..sub.1 and .DELTA..sub.2 between subframes (step
S10). Here, .DELTA..sub.1 is determined by subtracting the priority
of subframe i-1 from the priority of subframe i, and .DELTA..sub.2
is determined by subtracting the priority of subframe i from the
priority of subframe i+1. Note that subframe i is the above given
subframe, subframe i-1 is a subframe of another eNB/CG that
overlaps subframe i and that is transmitted before subframe i, and
subframe i+1 is a subframe of another eNB/CG that overlaps subframe
i and that is transmitted after subframe i.
[0093] Next, whether or not the absolute value of .DELTA..sub.l
(|.DELTA..sub.1|) is greater than the absolute value of
.DELTA..sub.2 (|.DELTA..sub.2|) is determined (step S20). If
|.DELTA..sub.1| is greater than |.DELTA..sub.2| (step S20: YES),
power scaling is applied to subframe i (step S21).
[0094] On the other hand, when |.DELTA..sub.1| is not greater than
|.DELTA..sub.2| (step S20: NO), then, whether or not
|.DELTA..sub.1| and |.DELTA..sub.2| are equal is additionally
determined (step S22). When |.DELTA..sub.1| and |.DELTA..sub.2| are
equal (step S22: YES), power scaling is applied to the SeNB
subframe (step S23). Also, when |.DELTA..sub.1| and |.DELTA..sub.2|
are not equal (step S22: NO), power scaling is applied to subframe
i+1 and subframe i-1 (step S24).
[0095] FIG. 11 is a diagram to show an example of determining power
distribution based on differences between the priorities of signals
to be transmitted at the same time. In FIG. 11, the upper part
shows the state before power is distributed, and the lower part
shows the state after power is distributed, according to the
present embodiment. In FIG. 11, the priorities of subframes i-1, i
and i+1 are 1, 2 and 7, respectively. Consequently, .DELTA..sub.1=1
and .DELTA..sub.2=5 hold.
[0096] Before the power distribution in FIG. 11, the transmission
interval of subframe i is power-limited. Following the flowchart of
FIG. 10, the process of step S24 is executed, and power scaling is
applied to subframes i-1 and i+1. As a result of this, as shown in
the lower part of FIG. 11, the power of the MeNB/MCG is
maintained.
[0097] When |.DELTA..sub.1| is greater than |.DELTA..sub.2|, this
is equivalent to the case where the priority of subframe i-1 is
relatively high compared to subframe i and subframe i+1. In such
cases, by applying power scaling to subframe i, it is possible to
secure transmission power for subframe i-1, which has a relatively
high priority, and maintain quality. Also, when |.DELTA..sub.1| and
|.DELTA..sub.2| are equal, it is possible to control not to change
the transmission power of MeNB subframes, which are important in
securing connectivity between user terminals and the network, by
applying power scaling to the SeNB subframes. Furthermore, the case
where |.DELTA..sub.1| is smaller than |.DELTA..sub.2| means the
priorities of subframe i-1 and subframe i are substantially equal,
relatively, and the priority of subframe i+1 is low. Under these
circumstances, it is possible to provide opportunities to secure
power for subframe i by applying power scaling to subframe i-1 and
subframe i+1.
[0098] Note that, although FIG. 10 shows an example of the method
of determining power distribution, this is by no means limiting.
For example, when .DELTA..sub.1<0 and .DELTA..sub.2<0 (for
example, when the priorities of subframes i-1, i, i+1 are 7, 2 and
1, respectively), the flowchart, in which the steps S21 and S24 in
FIG. 10 are switched, may be used. Also, when
.DELTA..sub.1.DELTA..sub.2<0 holds (for example, when the
priorities of subframes i-1, i and i+1 are 5, 7 and 4,
respectively), it is possible to use the flowchart, which replaces
step S20 of FIG. 10 with determining whether or not .DELTA..sub.l
is greater than .DELTA..sub.2.
[0099] (Variation 4)
[0100] Also, with the embodiments described above, power
scaling/dropping is executed as appropriate. To be more specific,
it is possible to select between the following two patterns of
implementation methods. The first method of implementation is the
method of applying power scaling/dropping in one step. In this
case, a user terminal determines, when transmitting a given UL
subframe, whether or not the sum of the transmission power of all
CCs of both CGs exceeds Pcmax. When excess is identified as a
result of this, power scaling/dropping is applied according to the
priority rule of the second embodiment. According to this
structure, differences between CGs are not taken into
consideration, and, power scaling/dropping that is optimal on an
overall scale can be applied following the priorities of all.
[0101] Also, executing power scaling/dropping in two steps is the
other method of implementation. A user terminal, when transmitting
a given UL subframe, first determines whether or not the sum of the
transmission power per eNB/CG exceeds a predetermined value (for
example, the maximum transmission power per CG). As a result of
this, when the sum of the transmission power exceeds a
predetermined value in any of the eNBs/CGs, power scaling/dropping
is applied in that CG, and the transmission power is kept within
the predetermined value per eNB/CG. Note that, this UE operation
and the priority rule are the same as those in UL-CA of Rel. 11.
After that, whether or not the sum of the transmission power of
each eNB/CG exceeds Pcmax is determined, and, if excess is
identified, power scaling/dropping is applied following the
priority rule between eNBs/CGs, as described earlier with the
second embodiment. According to this structure, in the first step
(decision per eNB/CG), a certain level of power scaling can be
executed by existing processes. Since the process of comparing
priorities between CGs can be spared, it is possible to simplify
the terminal processes, reduce the cost of the circuit structure,
and so on.
[0102] (Variation 5)
[0103] Also, according to the embodiments described above, power
scaling/dropping is applied to the transmission power of each
channel (signal) in each CC, depending on the decisions as to
whether or not the power limited state is present. Power
scaling/dropping is produced as a result of the power limited
state, and therefore there is a possibility that "the difference
between the maximum transmission power of e UE and the transmission
power demanded by an eNB," which originally is supposed to be
reported in a PHR (Power Headroom Report), cannot be reported.
[0104] So, in dual connectivity, PHRs are calculated, on a per
eNB/CG basis, using the values before power scaling/dropping is
applied as a result of the power limited state. That is, the
difference between the transmission power value initially required
by each eNB and the maximum transmission power of each eNB/CG is
calculated as a PH, and a PHR is reported. Note that, when the
maximum transmission power of each eNB/CG is not configured, PHs
may be calculated using each CC's maximum transmission power or the
maximum transmission power per user terminal. According to this
structure, it is possible to adequately report how much extra power
is present with respect to the transmission power demanded by the
eNBs.
[0105] (Structure of Radio Communication System)
[0106] Now, a structure of a radio communication system according
to an embodiment of the present invention will be described below.
In this radio communication system, the radio communication methods
according to the above embodiments or variations are employed.
[0107] FIG. 12 is a schematic structure diagram to show an example
of the radio communication system according to an embodiment of the
present invention. As shown in FIG. 12, a radio communication
system 1 is comprised of a plurality of radio base stations 10 (11
and 12), and a plurality of user terminals 20 that are present
within cells formed by each radio base station 10, and that are
configured to be capable of communicating with each radio base
station 10. The radio base stations 10 are each connected with a
higher station apparatus 30, and are connected to a core network 40
via the higher station apparatus 30.
[0108] In FIG. 12, the radio base station 11 is, for example, a
macro base station having a relatively wide coverage, and forms a
macro cell C1. The radio base stations 12 are, for example, small
base stations having local coverages, and form small cells C2. Note
that the number of radio base stations 11 and 12 is not limited to
that illustrated in FIG. 10.
[0109] The macro cell C1 and the small cells C2 may use the same
frequency band or may use different frequency bands. Also, the
radio base stations 11 and 12 are connected with each other via an
inter-base station interface (for example, optical fiber, the X2
interface, etc.).
[0110] Note that the macro base station 11 may be referred to as an
"eNodeB" (eNB), a "radio base station," a "transmission point," and
so on. The small base stations 12 are radio base stations having
local coverages, and may be referred to as "RRHs" (Remote Radio
Heads), "pico base stations," "femto base stations," "HeNBs" (Home
eNodeBs), "transmission points," "eNodeBs" (eNBs) and so on.
[0111] The user terminals 20 are terminals to support various
communication schemes such as LTE, LTE-A and so on, and may include
both mobile communication terminals and stationary communication
terminals. The user terminals 20 can communicate with other user
terminals 20 via the radio base stations 10.
[0112] The higher station apparatus 30 may be, for example, an
access gateway apparatus, a radio network controller (RNC), a
mobility management entity (MME) and so on, but is by no means
limited to these.
[0113] In the radio communication system 1, as radio access
schemes, OFDMA (Orthogonal Frequency Division Multiple Access) is
applied to the downlink, and SC-FDMA (Single-Carrier Frequency
Division Multiple Access) is applied to the uplink. Note that the
uplink and downlink radio access schemes are not limited to
combinations of these.
[0114] Also, in the radio communication system 1, a downlink shared
channel (PDSCH: Physical Downlink Shared Channel), which is used by
each user terminal 20 on a shared basis, downlink control channels
(PDCCH (Physical Downlink Control Channel), EPDCCH (Enhanced
Physical Downlink Control Channel), etc.), a broadcast channel
(PBCH) and so on are used as downlink channels. User data, higher
layer control information and predetermined SIBs (System
Information Blocks) are communicated in the PDSCH. Downlink control
information (DCI) is communicated by the PDCCH and the EPDCCH.
Also, synchronization signals, MIBs (Master Information Blocks) and
so on are communicated by the PBCH.
[0115] Also, in the radio communication system 1, an uplink shared
channel (PUSCH: Physical Uplink Shared Channel), which is used by
each user terminal 20 on a shared basis, and an uplink control
channel (PUCCH: Physical Uplink Control Channel) are used as uplink
channels. User data and higher layer control information are
communicated by the PUSCH.
[0116] FIG. 13 is a diagram to show an overall structure of a radio
base station 10 according to the present embodiment. The radio base
station 10 has a plurality of transmitting/receiving antennas 101
for MIMO communication, amplifying sections 102,
transmitting/receiving sections (receiving sections) 103, a
baseband signal processing section 104, a call processing section
105 and a communication path interface 106. Note that, the
transmitting/receiving sections 103 are comprised of transmitting
sections and receiving sections.
[0117] User data to be transmitted from the radio base station 10
to a user terminal 20 on the downlink is input from the higher
station apparatus 30 to the baseband signal processing section 104,
via the communication path interface 106.
[0118] In the baseband signal processing section 104, the user data
is subjected to a PDCP (Packet Data Convergence Protocol) layer
process, user data division and coupling, RLC (Radio Link Control)
layer transmission processes such as an RLC retransmission control
transmission process, MAC (Medium Access Control) retransmission
control (for example, an HARQ (Hybrid Automatic Repeat reQuest)
transmission process), scheduling, transport format selection,
channel coding, an inverse fast Fourier transform (IFFT) process
and a precoding process, and the result is forwarded to each
transmitting/receiving section 103. Furthermore, downlink control
signals are also subjected to transmission processes such as
channel coding and an inverse fast Fourier transform, and forwarded
to each transmitting/receiving section 103.
[0119] Each transmitting/receiving section 103 converts the
downlink signals, pre-coded and output from the baseband signal
processing section 104 on a per antenna basis, into a radio
frequency band. The amplifying sections 102 amplify the radio
frequency signals having been subjected to frequency conversion in
the transmitting/receiving sections 103, and transmitted from the
transmitting/receiving antennas 101.
[0120] On the other hand, as for uplink signals, radio frequency
signals that are received in the transmitting/receiving antennas
101 are each amplified in the amplifying sections 102. Each
transmitting/receiving section 103 receives the uplink signals
amplified in the amplifying sections 102. The
transmitting/receiving sections 103 convert the received signals
into baseband signals through frequency conversion, and output the
resulting signals to the baseband signal processing section
104.
[0121] In the baseband signal processing section 104, user data
that is included in the uplink signals that are input is subjected
to a fast Fourier transform (FFT) process, an inverse discrete
Fourier transform (IDFT) process, error correction decoding, a MAC
retransmission control receiving process, and RLC layer and PDCP
layer receiving processes, and forwarded to the higher station
apparatus 30 via the communication path interface 106. The call
processing section 105 performs call processing such as setting up
and releasing communication channels, manages the state of the
radio base station 10 and manages the radio resources.
[0122] The interface section 106 transmits and receives signals to
and from the higher station apparatus 30 via a predetermined
interface. Furthermore, the interface section 106 transmits and
receives signals to and from neighboring radio base stations
(backhaul signaling) via an inter-base station interface (for
example, optical fiber, the X2 interface, etc.).
[0123] FIG. 14 is a diagram to show a principle functional
structure of the baseband signal processing section 104 provided in
the radio base station 10 according to the present embodiment. A
shown in FIG. 14, the baseband signal processing section 104
provided in the radio base station 10 is comprised at least of a
control section 301, a transmission signal generating section 302,
a mapping section 303, a demapping section 304 and a received
signal decoding section 305.
[0124] The control section 301 controls radio resource scheduling
for downlink signals and uplink signals based on command
information from the higher station apparatus 30, feedback
information from each user terminal 20 and so on. That is, the
control section 301 functions as a scheduler. Note that, when
another radio base station 10 and/or the higher station apparatus
30 functions as the scheduler of the radio base station 10, the
control section 301 does not have to function as a scheduler.
[0125] To be more specific, the control section 301 controls the
scheduling of downlink reference signals, downlink data signals
that are transmitted in the PDSCH, downlink control signals that
are transmitted in the PDCCH and/or the EPDCCH, and so on. Also,
the control section 301 also controls the scheduling of uplink data
signals that are transmitted in the PUSCH, uplink control signals
that are transmitted in the PUCCH or the PUSCH, RA preambles that
are transmitted in the PRACH, and so on. These pieces of allocation
control-related information are reported to the user terminals 20
by using downlink control signals (DCI).
[0126] The control section 301 controls the transmission signal
generating section 302 and the mapping section 303 so as to adjust
the uplink signal transmission power of user terminals 20 connected
with the radio base station 10.
[0127] To be more specific, the control section 301 commands the
transmission signal generating section 302 to generate transmission
power control (TPC) commands for controlling the transmission power
of uplink signals based on PHRs and channel state information (CSI)
reported from the user terminals 20, the uplink data error rate,
the number of times of HARQ retransmissions and so on, and controls
the mapping section 303 to include the TPC commands in downlink
control information (DCI) and report this to the user terminals 20.
By this means, the radio base station 10 can specify the uplink
signal transmission power to request to the user terminals 20. Note
that the PHRs may be included and reported in MAC CE as well.
[0128] The control section 301 acquires information about the
uplink transmission power for each radio base station 10 the user
terminals 20 are connected with, based on the PHRs reported from
the user terminals 20. To be more specific, the control section 301
acquires information about the transmission power of the cell where
the subject radio base station belongs, based on real PHRs reported
from the user terminals 20. Note that, as information about the
transmission power of cells where the subject radio base station
does not belong, the control section 301 may estimate the PUSCH
bandwidth, channel states (path loss and so on), transmission power
density (PSD), MCS level, channel quality and so on of cells formed
by other radio base stations 10. Also, the control section 301 may
estimate (calculate) the total extra transmission power of the user
terminals 20 from these pieces of information.
[0129] The DL signal generating section 302 generates the downlink
control signals, downlink data signals and downlink reference
signals that are determined to be allocated in the control section
301, and outputs these signals to the mapping section 303. To be
more specific, the downlink control signal generating section 302
generates DL assignments, which report downlink signal allocation
information, and UL grants, which report uplink signal allocation
information, based on commands from the control section 301. The
data signals that are generated in the data signal generating
section 303 are subjected to a coding process and a modulation
process, based on coding rates and modulation schemes that are
determined based on CSI from each user terminal 20 and so on.
[0130] The mapping section 303 maps the downlink signals generated
in the transmission signal generating section 302 to radio
resources based on commands from the control section 301, and
outputs these to the transmitting/receiving sections 103.
[0131] The demapping section 304 demaps the signals received in the
transmitting/receiving sections 103 and outputs the separated
signals to the received signal decoding section 305. To be more
specific, the demapping section 304 demaps the uplink signals
transmitted from the user terminals 20.
[0132] The received signal decoding section 305 decodes the signals
(for example, delivery acknowledgement signals (HARQ-ACK))
transmitted from the user terminals 20 in uplink control channels
(the PRACH, the PUCCH, etc.), the data signals transmitted in the
PUSCH, and so on, and outputs the results to the control section
301. Also, information included in the MAC CE reported from the
user terminals 20 is also output to the control section 301.
[0133] FIG. 15 is a diagram to show an overall structure of a user
terminal 20 according to the present embodiment. As shown in FIG.
15, the user terminal 20 has a plurality of transmitting/receiving
antennas 201 for MIMO communication, amplifying sections 202,
transmitting/receiving sections 203, a baseband signal processing
section 204 and an application section 205. Note that,
transmitting/receiving sections 203 may be comprised of
transmitting sections and receiving sections.
[0134] As for downlink data, radio frequency signals that are
received in a plurality of transmitting/receiving antennas 201 are
each amplified in the amplifying sections 202. Each
transmitting/receiving section 203 receives the downlink signals
amplified in the amplifying sections 202. The
transmitting/receiving sections 203 convert the received signals
into baseband signals through frequency conversion, and output the
resulting signals to the baseband signal processing section
204.
[0135] In the baseband signal processing section 204, the baseband
signals that are input are subjected to an FFT process, error
correction decoding, a retransmission control receiving process,
and so on. Downlink user data is forwarded to the application
section 205. The application section 205 performs processes related
to higher layers above the physical layer and the MAC layer.
Furthermore, in the downlink data, broadcast information is also
forwarded to the application section 205.
[0136] Meanwhile, uplink user data is input from the application
section 205 to the baseband signal processing section 204. The
baseband signal processing section 204 performs a retransmission
control transmission process (for example, an HARQ transmission
process), channel coding, pre-coding, a discrete Fourier transform
(DFT) process, an IFFT process and so on, and the result is
forwarded to each transmitting/receiving section 203. The baseband
signal that is output from the baseband signal processing section
204 is converted into a radio frequency band in the
transmitting/receiving sections 203. The amplifying sections 202
amplify the radio frequency signals having been subjected to
frequency conversion, and transmit the resulting signals from the
transmitting/receiving antennas 201.
[0137] FIG. 16 is a diagram to show a principle functional
structure of the baseband signal processing section 204 provided in
the user terminal 20. As shown in FIG. 16, the baseband signal
processing section 204 provided in the user terminal 20 is
comprised at least of a control section 401, a transmission signal
generating section 402, a mapping section 403, a demapping section
404, a received signal decoding section 405, a power limit
detection section 406 and a PH report generating section 411.
[0138] The control section 401 acquires the downlink control
signals (signals transmitted in the PDCCH) and downlink data
signals (signals transmitted in the PDSCH) transmitted from the
radio base stations 10, from the received signal decoding section
405. Based on the downlink control signals, results of deciding
whether or not retransmission control is possible in response to
the downlink data signals, and so on, the control section 401
controls the generation of uplink control signals (for example,
delivery acknowledgement signals (HARQ-ACK), etc.), uplink data
signals and so on. To be more specific, the control section 401
controls the transmission signal generating section 402 and the
mapping section 403.
[0139] The transmission signal generating section 402 generates
uplink control signals such as, for example, delivery
acknowledgement signals (HARQ-ACK) and channel state information
(CSI), based on commands from the control section 401. Also, the
transmission signal generating section 402 generates uplink data
signals based on commands from the control section 401. Note that,
when a UL grant is included in a downlink control signal reported
from the radio base stations, the control section 401 commands the
transmission signal generating section 402 to generate an uplink
data signal.
[0140] The mapping section 403 maps the uplink signals generated in
the transmission signal generating section 402 to radio resources
based on commands from the control section 401, and output the
result to the transmitting/receiving section 203.
[0141] Also, the control section 401 controls the uplink
transmission power of the user terminals 20. To be more specific,
the control section 401 controls the transmission power of each
cell (CC) based on signaling (for example, TPC commands) from each
radio base station 20. Here, the control section 401 has the
priority rule for uplink signals for each radio base station 10,
and, when a plurality of uplink signals are transmitted in the same
timing, the transmission power of each uplink signal is controlled
with reference to these priorities.
[0142] As a priority rule, every time there are uplink signals of
the same type, the control section 401 configures the priority of a
first radio base station (for example, an MeNB) higher than the
priority of a second radio base station (for example, an SeNB). For
example, the priorities of all UL signals for the MeNB may be
configured higher than the priorities of all UL signals for the
SeNB (an example of the first embodiment). Also, every time there
are uplink signals of the same type, the priority for the first
radio base station and the priority for the second radio base
station may be configured to neighbor each other. Furthermore, the
relationship between signals in priority may be configured so that
the same order as in UL-CA of Rel. 11 is maintained regardless of
the eNBs (another example of the first embodiment). Note that the
priorities of signals between the eNBs/CGs preferably represent the
same order as that in UL-CA of Rel. 11. That is, from the highest
one, the PRACH, the PUCCH, the PUSCH including UCI, the PUSCH not
including UCI and the SRS are preferably included in the order of
priorities.
[0143] Note that, when a plurality of priority rules are
stipulated, the control section 401 may determine the priority rule
to apply based on information related to priority rules, which is
reported in downlink control information (DCI) in downlink control
channels (PDCCH and EPDCCH) from the radio base stations 10, higher
layer signaling (for example, RRC signaling), broadcast signals
(for example, SIBs) and so on.
[0144] Also, the control section 401 executes transmission power
control in cooperation with the power limit detection section 406
so that the control section 401 ensures that the transmission power
of signals is not changed in the middle of uplink subframes (UL
subframes), and the above rules are followed. To do so, from the UL
grants/DL assignments that are received, the control section 401
outputs the UL transmission conditions (the bandwidth, the
modulation scheme, the UL transmission power that is demanded based
on these, and so on) to the power limit detection section 406.
[0145] When there is a period in which a given UL subframe is
planned to be transmitted to a given eNB/CG (transmission-planned
period), the power limit detection section 406 investigates the
transmission power of all UL subframes of other eNBs/CGs having
partially or entirely simultaneous transmission intervals with that
UL subframe, based on the information of UL transmission conditions
received as input from the control section 401, determines whether
or not the total transmission power of uplink signals for each
eNB/CG exceeds the maximum allowable power (Pcmax), and outputs the
decision to the control section 401 (second embodiment).
[0146] When there is a part that is determined by the power limit
detection section 406 to exceed the maximum allowable power (that
is, to be power-limited), the control section 401 compares the
priorities of signals in this part. The control section 401 reduces
(by way of scaling or dropping) the allocation of power for the UL
subframes of the lower priorities (nonpreferential UL subframes)
down to a value where the power demanded by the UL subframes of the
higher priorities (preferential UL subframes) can be adequately
distributed.
[0147] Also, before making the above decision, the power limit
detection section 406 may, for each eNB/CG in the
transmission-planned period, decide whether or not the transmission
power of each UL subframe exceeds a predetermined value (for
example, the maximum transmission power per eNB/CG), and output the
decisions to the control section 401 (variation 4).
[0148] When, according to the decisions from the power limit
detection section 406, the sum of transmission power exceeds the
predetermined value in any of the eNBs/CGs, the control section 401
applies power scaling/dropping to each eNB/CG to keep the
transmission power of every eNB/CG within the predetermined
value.
[0149] Note that the transmission signal generating section 402
preferably generates user terminal capability information (UE
capability information) for reporting the above configurations
and/or the like to the radio base stations 10. For example, user
terminal capability information to represent whether or not
asynchronous dual connectivity can be supported, whether or not the
transmission power of future transmitting signals can be
calculated, whether or not transmission power can be shared on a
dynamic basis between eNBs/CGs and so on may be generated
(variation 2).
[0150] Based on commands from the control section 401, the PH
reporting generating section 411 calculates the PH (Power Headroom)
of each eNB/CG from the maximum transmission power of uplink
signals from that eNB/CG and the uplink signal transmission power
initially demanded by the eNB/CG, generates a PHR and outputs this
to the transmission signal generating section 402 (variation
5).
[0151] The demapping section 404 demaps the signals received in the
transmitting/receiving section 203, and outputs the separated
signals to the received signal decoding section 405. To be more
specific, the demapping section 404 demaps the downlink signals
transmitted from the radio base stations 10.
[0152] The received signal decoding section 405 decodes the
downlink control signals (PDCCH signals) transmitted in the
downlink control channel (PDCCH), and outputs the scheduling
information (uplink resource allocation information), information
about the cells to which delivery acknowledgement signals in
response to the downlink control signals are fed back, TPC commands
and so on, to the control section 401.
[0153] Now, although the present invention has been described in
detail with reference to the above embodiments, it should be
obvious to a person skilled in the art that the present invention
is by no means limited to the embodiments described herein. For
example, the above-described embodiments may be used separately, or
may be used in combinations. The present invention can be
implemented with various corrections and in various modifications,
without departing from the spirit and scope of the present
invention defined by the recitations of claims. Consequently, the
description herein is only provided for the purpose of illustrating
examples, and should by no means be construed to limit the present
invention in any way.
[0154] The disclosure of Japanese Patent Application No.
2014-096660, filed on May 8, 2014, including the specification,
drawings and abstract, is incorporated herein by reference in its
entirety.
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