U.S. patent application number 12/888587 was filed with the patent office on 2011-01-20 for radio communication method, terminal apparatus, base station apparatus, and radio communication system.
This patent application is currently assigned to FUJITSU LIMITED. Invention is credited to Akira Ito.
Application Number | 20110013617 12/888587 |
Document ID | / |
Family ID | 41113022 |
Filed Date | 2011-01-20 |
United States Patent
Application |
20110013617 |
Kind Code |
A1 |
Ito; Akira |
January 20, 2011 |
RADIO COMMUNICATION METHOD, TERMINAL APPARATUS, BASE STATION
APPARATUS, AND RADIO COMMUNICATION SYSTEM
Abstract
A radio communication method in a radio communication system
which performs radio communication between a terminal apparatus and
a base station apparatus, the radio communication method including:
selecting one of a first transmission method or a second
transmission method on the basis of transmission power of
transmission signal transmitted from the terminal apparatus, in the
base station apparatus; and transmitting the transmission signal to
the base station apparatus by the selected first or second
transmission method, in the terminal apparatus.
Inventors: |
Ito; Akira; (Kawasaki,
JP) |
Correspondence
Address: |
KATTEN MUCHIN ROSENMAN LLP
575 MADISON AVENUE
NEW YORK
NY
10022-2585
US
|
Assignee: |
FUJITSU LIMITED
Kawasaki-shi
JP
|
Family ID: |
41113022 |
Appl. No.: |
12/888587 |
Filed: |
September 23, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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PCT/JP2008/000717 |
Mar 25, 2008 |
|
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12888587 |
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Current U.S.
Class: |
370/344 ;
375/260; 455/522 |
Current CPC
Class: |
H04W 52/367 20130101;
H04L 1/0025 20130101; H04L 5/0023 20130101; H04L 27/0008 20130101;
H04W 52/42 20130101; H04L 5/0007 20130101; H04L 27/2614 20130101;
H04W 52/288 20130101 |
Class at
Publication: |
370/344 ;
375/260; 455/522 |
International
Class: |
H04B 7/208 20060101
H04B007/208; H04K 1/10 20060101 H04K001/10 |
Claims
1. A radio communication method in a radio communication system
which performs radio communication between a terminal apparatus and
a base station apparatus, the radio communication method
comprising: selecting one of a first transmission method using
multi-carrier or a second transmission method using single-carrier
based on transmission power of transmission signal transmitted from
the terminal apparatus, in the base station apparatus; and
transmitting the transmission signal to the base station apparatus
by the selected first or second transmission method, in the
terminal apparatus.
2. The radio communication method according to claim 1, wherein the
second transmission method is selected if the transmission power
must be reduced in a case where the transmission signal is
transmitted by the first transmission method, and the first
transmission method is selected if not.
3. The radio communication method according to claim 1, wherein the
second transmission method is selected if the transmission power
must be reduced based on transmission data amount in a case where
the transmission signal is transmitted by the first transmission
method, and the first transmission method is selected if not.
4. The radio communication method according to claim 1, wherein the
second transmission method is selected if the transmission power
must be reduced based on an instruction in a case where the
instruction to reduce the transmission power is received and the
transmission signal is transmitted by the first transmission
method, and the first transmission method is selected if not.
5. The radio communication method according to claim 1, wherein the
second transmission method is selected if a second decrease width
is larger than a first decrease width by comparing the first
decrease width from maximum transmission power of the transmission
power corresponding to position of the terminal apparatus with the
second decrease width from the maximum transmission power of the
transmission power based on upper limit value of out-of-band
emission power, and the first transmission method is selected if
not.
6. The radio communication method according to claim 5, wherein the
second decrease width is a decrease width from the maximum
transmission power by the first transmission method.
7. The radio communication method according to claim 5, wherein the
second decrease width takes difference decrease width according to
the first or second transmission method, a modulation scheme, or
number of resource blocks.
8. The radio communication method according to claim 5, wherein the
second decrease width is read from a table indicating the second
decrease width and is compared with the first decrease width.
9. The radio communication method according to claim 8, wherein the
modulation scheme and the number of resource blocks are determined,
and the second decrease width corresponding to the determined
modulation scheme and number of resource blocks is read from the
table, and is compared with the first decrease width.
10. The radio communication method according to claim 5, wherein
the first decrease width includes a decrease width of transmission
power corresponding to transmission data amount.
11. The radio communication method according to claim 5, wherein
the first decrease width includes a decrease width of transmission
power corresponding to an instruction if the instruction to reduce
the transmission of the terminal apparatus is received.
12. The radio communication method according to claim 1, wherein
PAPR of the first transmission method is larger than PAPR of the
second transmission method.
13. The radio communication method according to claim 1, wherein
the first transmission method is OFDM and the second transmission
method is SC-FDMA.
14. A terminal apparatus for performing radio communication with a
base station apparatus, the terminal apparatus comprising: a
reception unit which receives from the base station apparatus
transmission method selection information indicating selected
transmission method, which is selected one of a first transmission
method using multi-carrier or a second transmission method using
single-carrier based on transmission power of transmission signal
transmitted from the terminal apparatus; and a transmission unit
which transmits the transmission signal to the base station
apparatus by the first or second transmission method based on the
transmission method selection information.
15. A base station apparatus for performing radio communication
with a terminal apparatus, the base station apparatus comprising: a
selection unit which selects one of a first transmission method
using multi-carrier or a second transmission method using
single-carrier based on transmission power of transmission signal
transmitted from the terminal apparatus; and a transmission unit
which transmits transmission method selection information
indicating the selected first or second transmission method to the
terminal apparatus, wherein the terminal apparatus transmits the
transmission signal by the selected first or second transmission
method.
16. A radio communication system, comprising: a terminal apparatus;
and a base station apparatus, wherein radio communication is
performed between the terminal apparatus and the base station
apparatus, the base station apparatus includes: a selection unit
which selects one of a first transmission method using
multi-carrier or a second transmission method using single-carrier
based on transmission power of transmission signal transmitted from
the terminal apparatus; and a transmission unit which transmits
transmission method selection information indicating the selected
first or second transmission method, and the terminal apparatus
includes: a reception unit which receives the transmission method
selection information; and a transmission unit which transmits the
transmission signal to the base station apparatus by the first or
said second transmission method based on the transmission method
selection information.
17. A radio communication system, comprising: a terminal apparatus;
and a base station apparatus, wherein radio communication is
performed between the terminal apparatus and the base station
apparatus, the base station apparatus or the terminal apparatus
includes: a modulation unit which is adaptable to a plurality of
transmission method selected in accordance with magnitude of
transmission power; and a transmission unit which transmits signal
modulated by the modulation unit, and the plurality of transmission
method include SC-FDMA method and OFDM method, and a selection is
performed to switch from the OFDM method to the SC-FDMA method in
response to increase in the transmission power.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of International
Application No. PCT/JP2008/000717, filed on Mar. 25, 2008, now
pending, herein incorporated by reference.
TECHNICAL FIELD
[0002] The present invention relates to a radio communication
method, a terminal apparatus, a base station apparatus, and a radio
communication system.
BACKGROUND ART
[0003] In 3GPP (3rd Generation Partnership Project), LTE (Long Term
Evolution, or Evaluated UTRA and UTRAN) is under investigation as a
next-generation radio communication standard (Non-Patent Document 1
illustrated below, for example).
[0004] In LTE, OFDM (Orthogonal Frequency Division Multiplexing) is
utilized for a downlink from a base station to a terminal, and
SC-FDMA (Single-Carrier Frequency Division Multiple Access) is
utilized for an uplink from the terminal to the base station.
[0005] The OFDM is a transmission method in which a frequency band
is divided into a plurality of sub-carriers and data are
transmitted while carried directly on each sub-carrier. On the
other hand, the SC-FDMA is a transmission method in which data
transformed by DFT (Discrete Fourier Transform) is carried on the
sub-carrier and is transmitted. FIG. 18 and FIG. 19 illustrate
configuration examples of signal processing circuits employed in
SC-FDMA and OFDM, respectively. Referring to FIG. 18, a DFT
(Discrete Fourier Transform) unit 101 is included in front of a
sub-carrier mapping unit, and DFT-processed signal is input
successively into the sub-carrier mapping unit 102, an IDFT
(Inverse Discrete Fourier Transform) unit 103, and a CP (Cyclic
Prefix) insertion unit 104. Referring to FIG. 19, transmission data
is input into a sub-carrier mapping unit 111 and then input
successively into an IDFT unit 112 and a CP insertion unit 113.
[0006] On the other hand, the base station or the terminal uses an
amplifier to transmit data. The amplifier has a problem that
linearity cannot be maintained and the data are distorted, when an
input power is large. When the data are distorted, out-of-band
emission power increases. An upper limit value of the out-of-band
emission power (hereinafter, "ACLR") is determined by an ACLR
(Adjacent Carrier Leakage Ratio) standard, and when the data
distortion is large, the ACLR can no longer be satisfied.
[0007] In consideration of the ACLR, the SC-FDMA is a favorable
method due to its low PAPR (Peak to Average Power Ratio), and
therefore SC-FDMA is applied to the uplink from the terminal in
LTE.
Non-Patent Document 1: 3GPP TS 36. 211V8. 0. 0 (2007-09)
Non-Patent Document 2: Hikmet Sari, Geroges Karam and Isabell
Jeanclaude, "Transmission Techniques for Digital Terrestrial TV
Broadcasting", IEEE Communication Magazine, pp. 100-109, February
1995
DISCLOSURE OF THE INVENTION
Problems to be Solved by the Invention
[0008] Although the SC-FDMA is advantageous in terms of the PAPR,
because the sub-carrier which is continuous on a frequency axis is
used, the sub-carrier cannot be selected non-continuously on the
frequency axis, and the SC-FDMA has a constraint in terms of
scheduling during resource allocation and the like. Also, as
illustrated in FIG. 20 (Non-Patent Document 2, for example), errors
are likely to occur in relation to another method even under an
identical reception E/N condition.
[0009] Accordingly, it is an object of the present invention to
improve inconvenient which occurs when the SC-FDMA is applied.
[0010] More preferably, it is an object to improve in consideration
of scheduling flexibility or quality when the SC-FDMA is
applied.
Means for Solving the Problem
[0011] According to an aspect of the present invention, a radio
communication method in a radio communication system which performs
radio communication between a terminal apparatus and a base station
apparatus, the radio communication method including: selecting one
of a first transmission method or a second transmission method on
the basis of transmission power of transmission signal transmitted
from the terminal apparatus, in the base station apparatus; and
transmitting the transmission signal to the base station apparatus
by the selected first or second transmission method, in the
terminal apparatus.
[0012] Also, according to an another aspect of the present
invention, a radio communication method in a radio communication
system which performs radio communication between a terminal
apparatus and a base station apparatus, the radio communication
method including: selecting a first transmission method if the
terminal apparatus transmits transmission signal by MIMO or
selecting a second transmission method if not, in the base station
apparatus; and transmitting the transmission signal to the base
station apparatus by the selected first or second transmission
method, in the terminal apparatus.
[0013] Furthermore, according to an another aspect of the present
invention, a terminal apparatus for performing radio communication
with a base station apparatus, the terminal apparatus including: a
reception unit which receives from the base station apparatus
transmission method selection information indicating selected
transmission method, which is selected one of a first transmission
method or a second transmission method on the basis of transmission
power of transmission signal transmitted from the terminal
apparatus; and a transmission unit which transmits the transmission
signal to the base station apparatus by the first or second
transmission method on the basis of the transmission method
selection information.
[0014] Furthermore, according to an another aspect of the present
invention, a terminal apparatus for performing radio communication
with a base station apparatus, the terminal apparatus including: a
reception unit which receives from the base station apparatus
transmission method selection information indicating that a first
transmission method is selected if the terminal apparatus transmits
by MIMO or a second transmission method is selected if not; and a
transmission unit which transmits the transmission signal to the
base station apparatus by the first or second transmission method
on the basis of the transmission method selection information.
[0015] Furthermore, according to an another aspect of the present
invention, a base station apparatus for performing radio
communication with a terminal apparatus, the base station apparatus
including: a selection unit which selects one of a first
transmission method or a second transmission method on the basis of
transmission power of transmission signal transmitted from the
terminal apparatus; and a transmission unit which transmits
transmission method selection information indicating the selected
first or second transmission method to the terminal apparatus,
wherein the terminal apparatus transmits the transmission signal by
the selected first or second transmission method.
[0016] Furthermore, according to an another aspect of the present
invention, a base station apparatus for performing radio
communication with a terminal apparatus, the base station apparatus
including: a selection unit which selects a first transmission
method if the terminal apparatus transmits transmission signal by
MIMO or selects a second transmission method if not; and a
transmission unit which transmits transmission method selection
information indicating the selected first or second transmission
method to the terminal apparatus, wherein the terminal apparatus
transmits the transmission signal by the selected first or second
transmission method.
[0017] Furthermore, according to an another aspect of the present
invention, a radio communication system, including: a terminal
apparatus; and a base station apparatus, wherein radio
communication is performed between the terminal apparatus and the
base station apparatus, the base station apparatus includes: a
selection unit which selects one of a first transmission method or
a second transmission method on the basis of transmission power of
transmission signal transmitted from the terminal apparatus; and a
transmission unit which transmits transmission method selection
information indicating the selected first or second transmission
method, and the terminal apparatus includes: a reception unit which
receives the transmission method selection information; and a
transmission unit which transmits the transmission signal to the
base station apparatus by the first or said second transmission
method on the basis of the transmission method selection
information.
[0018] Furthermore, according to an another aspect of the present
invention, a radio communication system, including: a terminal
apparatus; and a base station apparatus, wherein radio
communication is performed between the terminal apparatus and the
base station apparatus, the base station apparatus includes: a
selection unit which selects a first transmission method if the
terminal apparatus transmits transmission signal by MIMO, or
selects a second transmission method if not; and a transmission
unit which transmits transmission method selection information
indicating the selected first or second transmission method, and
the terminal apparatus includes: a reception unit which receives
the transmission method selection information; and a transmission
unit which transmits the transmission signal to the base station
apparatus by the first or second transmission method on the basis
of the transmission method selection information.
[0019] Furthermore, according to an another aspect of the present
invention, a radio communication system, including: a terminal
apparatus; and a base station apparatus, wherein radio
communication is performed between the terminal apparatus and the
base station apparatus, the base station apparatus or the terminal
apparatus includes: a modulation unit which is adaptable to a
plurality of transmission method selected in accordance with
magnitude of transmission power; and a transmission unit which
transmits signal modulated by the modulation unit, and the
plurality of transmission method include SC-FDMA method and OFDM
method, and a selection is performed to switch from the OFDM method
to the SC-FDMA method in response to increase in the transmission
power.
ADVANTAGEOUS EFFECT OF THE INVENTION
[0020] According to the present invention, the inconvenient which
occurs when the SC-FDMA is applied, can be improved.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 illustrates a configuration example of a radio
communication system;
[0022] FIG. 2 illustrates a configuration example of a terminal
apparatus;
[0023] FIG. 3 illustrates a configuration example of a base station
apparatus;
[0024] FIG. 4 illustrates an example of an MPR table;
[0025] FIG. 5 illustrates an example of a sequence diagram
indicating an overall operation;
[0026] FIG. 6 illustrates a flowchart of an operational example
indicating transmission method determination processing;
[0027] FIG. 7A and FIG. 7B illustrate examples of transmission
power decrease widths;
[0028] FIG. 8 illustrates a flowchart of another operational
example of transmission method determination processing;
[0029] FIG. 9 illustrates an example of an MPR table;
[0030] FIG. 10 illustrates a flowchart of another operational
example of transmission method determination processing;
[0031] FIG. 11 illustrates another configuration example of a base
station apparatus;
[0032] FIG. 12 illustrates another configuration example of a base
station apparatus;
[0033] FIG. 13 illustrates a flowchart of another operational
example of transmission method determination processing;
[0034] FIG. 14 illustrates a flowchart of another operational
example of transmission method determination processing;
[0035] FIG. 15 illustrates another configuration example of a
terminal apparatus;
[0036] FIG. 16 illustrates another configuration example of a base
station apparatus;
[0037] FIG. 17 illustrating a flowchart of another example of
overall processing;
[0038] FIG. 18 illustrates a configuration example of a signal
processing circuit in a case where SC-FDMA is employed;
[0039] FIG. 19 illustrates a configuration example of a signal
processing circuit in a case where OFDM is employed; and
[0040] FIG. 20 illustrates a graph of characteristic example of
SC-FDMA and OFDM.
EXPLANATION OF REFERENCE NUMERALS
[0041] 1 radio communication system [0042] 10 (10-1 to 10-3)
terminal apparatus [0043] 11 known signal reception unit [0044] 12
path loss calculation unit [0045] 13 transmission power calculation
unit [0046] 14 known signal transmission unit [0047] 15
.DELTA.(maximum power-current power) transmission unit [0048] 17
scheduling transmission unit [0049] 18 transmission method
reception unit [0050] 19 data signal modulation unit [0051] 20 data
signal transmission unit [0052] 50 (50-1 to 50-4) base station
apparatus [0053] 51 known signal transmission unit [0054] 52
.DELTA.(maximum power-current power) reception unit [0055] 53
scheduling request reception unit [0056] 54 MPR table [0057] 55
transmission method determination unit [0058] 56 transmission
method transmission unit [0059] 57 data reception unit [0060] 60
transmission bit count table [0061] 70 network reception unit
BEST MODE FOR CARRYING OUT THE INVENTION
[0062] Best mode for carrying out the present invention will be
described below.
First Embodiment
[0063] First, a first embodiment will be described. FIG. 1
illustrates a configuration example of a radio communication system
1. The radio communication system 1 includes terminal apparatuses
("terminals" hereinafter) 10-1 to 10-3 and base station apparatuses
("base stations" hereinafter) 50-1 to 50-4. Dotted lines indicate
cell ranges of the respective base stations 50-1 to 50-4. When the
terminals 10-1 to 10-3 are positioned in a cell, the terminals 10-1
to 10-3 can perform radio communication with the corresponding base
stations 50-1 to 50-4.
[0064] FIG. 2 and FIG. 3 illustrates configuration examples of the
terminal 10 and the base station 50, respectively. The terminal 10
includes a known signal reception unit 11, a path loss calculation
unit 12, a transmission power calculation unit 13, a known signal
transmission unit 14, a .DELTA.(maximum power-current power)
transmission unit (.DELTA. transmission unit hereinafter) 15, a
transmission data buffer 16, a scheduling request transmission unit
17, a transmission method reception unit 18, a data signal
modulation unit 19, and a data signal transmission unit 20.
[0065] The known signal reception unit 11 receives a known signal
from the base station 50 and outputs the received known signal to
the path loss calculation unit 12. For example, the known signal is
transmitted periodically from the base station 50.
[0066] The path loss calculation unit 12 calculates a downlink
direction propagation path loss (a path loss PL) relative to the
base station 50 on the basis of the known signal, and outputs the
calculated path loss PL to the transmission power calculation unit
13.
[0067] The transmission power calculation unit 13 calculates a
transmission power on the basis of the path loss PL and so on. A
following equation is used in the calculation.
P t = P max .times. min { 1 , max [ R min , ( PL PL x - ile ) x ] }
[ Numeral 1 ] ##EQU00001##
[0068] Here, P.sub.t indicates a data transmission power of the
terminal 10 envisaged in accordance with the position of the
terminal 10, P.sub.max is a maximum transmission power determined
from capacity of the terminal 10, PL is the path loss, and
PL.sub.x-ile and R.sub.min are constants of power control. The
maximum transmission power P.sub.max and the two constants
PL.sub.x-ile, R.sub.min are stored in a memory, for example, the
transmission power calculation unit 13 reads from the memory, and
calculates together with the path loss PL from the path loss
calculation unit 12.
[0069] The known signal transmission unit 14 transmits the known
signal periodically to the base station 50, for example.
[0070] The .DELTA. transmission unit 15 calculates a difference
.DELTA. between the maximum transmission power P.sub.max and the
transmission power P.sub.t, and transmits the calculated difference
.DELTA. to the base station 50. The difference .DELTA. indicates a
decrease width from the maximum transmission power P.sub.max
corresponding to a current position of the terminal 10. Note that
the difference .DELTA. may be calculated by the transmission power
calculation unit 13.
[0071] The transmission data buffer 16 stores transmission data
from an application unit or the like.
[0072] The scheduling request transmission unit 17 transmits a
scheduling request to the base station 50 when transmission data is
transmitted. The scheduling request transmission unit 17 calculates
data amount of the transmission data stored in the transmission
data buffer 16 or the like, and transmits the scheduling request
including the data amount and a data rate.
[0073] The transmission method reception unit 18 receives a
transmission method transmitted from the base station 50 and
outputs to the data signal modulation unit 19.
[0074] The data signal modulation unit 19 reads the transmission
data from the transmission data buffer 16 and modulates the
transmission data on the basis of the transmission method from the
transmission method reception unit 18.
[0075] The data signal transmission unit 20 transmits the modulated
transmission data to the base station 50.
[0076] On the other hand, as illustrated in FIG. 3, the base
station 50 includes a known signal transmission unit 51, a
.DELTA.(maximum power-current power) reception unit (A reception
unit hereinafter) 52, a scheduling request reception unit 53, an
MPR (Maximum Power Reduction) table 54, a transmission method
determination unit 55, a transmission method transmission unit 56,
and a data reception unit 57.
[0077] The known signal transmission unit 51 transmits the known
signal to the terminal 10 periodically, for example.
[0078] The A reception unit 52 receives the difference .DELTA. from
the terminal 10 and outputs to the transmission method
determination unit 55.
[0079] The scheduling request reception unit 53 receives the
scheduling request from the terminal 10 and outputs to the
transmission method determination unit 55.
[0080] The MPR table 54 stores respective values of a transmission
method (OFDM or SC-FDMA), a modulation scheme (QPSK, 16QAM, and so
on), a number of resource blocks (a number of sub-carriers that can
be allocated on a frequency axis), and a reduction amount (a
transmission power reduction amount hereinafter) P.sub.r from the
maximum transmission power of the terminal 10.
[0081] The terminal 10 includes an amplifier to transmit the
transmission data, and the transmission power reduction amount
P.sub.r is a value indicating a decrease width by which the
transmission power must be reduced from the maximum transmission
power in order to satisfy so-called ACLR (the upper limit value of
out-of-band emission power) due to constraint of the amplifier in
the terminal 10.
[0082] FIG. 4 illustrates an example of the MPR table 54. As
illustrated in FIG. 4, the value of the transmission power
reduction amount P.sub.r differ in accordance with the transmission
method, the modulation scheme, and the number of resource
blocks.
[0083] The reason is that transmission waveform transmitted from
the terminal 10 differs according to the transmission method and so
on, and the transmission power reduction amount P.sub.r takes
different value according to the transmission waveform. If the
transmission method is different even if the modulation scheme and
the number of resource brocks are same, the transmission power
reduction amount P.sub.r is different. The reason is that in OFDM,
the PAPR of the transmission power is larger than in SC-FDMA, and
therefore the transmission power must be reduced to satisfy the
ACLR.
[0084] Returning to FIG. 3, the transmission method determination
unit 55 determines the transmission method by selecting one of OFDM
and SC-FDMA in accordance with the difference .DELTA. and a maximum
value of the transmission power reduction amount P.sub.r read from
the MPR table 54. Determination processing will be described below.
The transmission method determination unit 55 performs the
determination processing when the scheduling request reception unit
53 receives the scheduling request, for example.
[0085] The transmission method transmission unit 56 transmits the
determined transmission method. The terminal 10 transmits the
transmission data on the basis of the transmission method (see FIG.
2).
[0086] The data reception unit 57 receives the transmission data
from the terminal 10 and performs reception processing on the basis
of the transmission method.
[0087] Next, the transmission method determination processing will
be described in detail. FIG. 5 illustrates an example of a sequence
diagram indicating an overall operation, and FIG. 6 illustrates a
flowchart indicating an example of the transmission method
determination processing.
[0088] First, the known signal transmission unit 51 of the base
station 50 transmits the known signal to the terminal 10 (S10).
[0089] Next, the transmission power calculation unit 13 of the
terminal 10 calculates the difference .DELTA. between the maximum
transmission power P.sub.max and the transmission power P.sub.t of
the terminal 10 corresponding to its position (S11).
[0090] Next, the scheduling request transmission unit 17 of the
terminal 10 transmits the scheduling request (S12). The .DELTA.
transmission unit 15 transmits the difference .DELTA. at the
transmission timing of the scheduling request. The .DELTA.
transmission unit 15 outputs the calculated difference .DELTA. to
the scheduling request transmission unit 17, and the scheduling
request transmission unit 17 may transmit the scheduling request
including the difference .DELTA..
[0091] Next, the transmission method determination unit 55 of the
base station 50 determines the transmission method (S13).
[0092] Next, the processing shifts to the transmission method
determination processing (FIG. 6), in which the transmission method
determination unit 55 compares the maximum value of the
transmission power reduction amount P.sub.r with the difference
.DELTA. (S20). If the maximum value of the transmission power
reduction amount P.sub.r is larger than the difference .DELTA., the
transmission method determination unit 55 selects SC-FDMA (S21). On
the other hand, if the maximum value of the transmission power
reduction amount P.sub.r and the difference .DELTA. are identical
or the difference .DELTA. is larger than the maximum value of the
transmission power reduction amount P.sub.r, the transmission
method determination unit 55 selects OFDM (S22).
[0093] Alternatively, the transmission method determination unit 55
may select SC-FDMA if the base station 50 detects that the
transmission power of the mobile station exceeds a predetermined
threshold, and may select OFDM if the base station 50 detects that
the transmission power of the mobile station is smaller than the
predetermined threshold.
[0094] The reason for comparing the two values in this manner will
now be described with reference to FIG. 7A and FIG. 7B. FIG. 7A
illustrates an example in which the transmission power is set on
the ordinate and the maximum value of the transmission power
reduction amount P.sub.r is larger than the difference .DELTA..
FIG. 7B illustrates an opposite example.
[0095] As described above, the difference .DELTA. indicates the
transmission power decrease width from the maximum transmission
power corresponding to the position of the terminal 10. On the
other hand, (the maximum value of) the transmission power reduction
amount P.sub.r indicates (a maximum value of) the decrease width by
which the transmission power must be reduced from the maximum
transmission power due to the constraints of the amplifier in order
to satisfy the linearity of the amplifier in the terminal 10 and
thereby satisfy the ACLR (the upper limit value of the out-of-band
emission power). If (the maximum value of) the transmission power
reduction amount P.sub.r is larger than the difference .DELTA. (see
FIG. 7A), this indicates that the terminal 10 should be capable of
transmission at the decrease width .DELTA. in accordance with its
position, but the terminal 10 may transmit by excess reduced power
due to the constraints of the amplifier.
[0096] A case in which the transmission power is reduced further
due to the constraints of the amplifier corresponds to a case in
which the terminal 10 is far from the base station 50. In other
words, as described in the prior art, the PAPR is larger in OFDM
than in SC-FDMA, and therefore, in OFDM, an average transmission
power must be reduced below that of SC-FDMA in order to satisfy the
linearity of the amplifier and thereby satisfy the ACLR standard.
If the terminal 10 is positioned far from the base station 50, data
is transmitted at the maximum transmission power as much as
possible in order to increase a reception characteristic of the
base station 50.
[0097] However, since the PAPR is large in OFDM, the average
transmission power must be reduced to satisfy the linearity of the
amplifier. If there is a case where the transmission power must be
reduced in accordance with OFDM, SC-FDMA has better the reception
characteristic of the base station 50, in which the average
transmission power is large, than OFDM.
[0098] Hence, if the transmission power is reduced further due to
the constraints of the amplifier, or in other words if the maximum
value of the transmission power reduction amount P.sub.r is larger
than the difference .DELTA. (FIG. 7A), the transmission method
determination unit 55 selects SC-FDMA as the transmission
method.
[0099] On the other hand, if the difference .DELTA. is equal to or
greater than (the maximum value of) the transmission power
reduction amount P.sub.r (FIG. 7B), the power decrease width
.DELTA. corresponding to the position is equal to or greater than
(the maximum value of) the transmission power reduction width
P.sub.r from the constraints of the amplifier, and therefore the
transmission power is reduced sufficiently to satisfy the
constraints of the amplifier. If the transmission power can be
reduced in this manner, data can be transmitted sufficiently even
if the terminal 10 is close to the base station 50, and even if
data are transmitted using OFDM having a high PAPR, both the
linearity of the amplifier and the ACLR are satisfied.
[0100] Hence, if the transmission power is low, or in other words
if the transmission power reduction amount P.sub.r is equal to or
smaller than the difference .DELTA., the transmission method
determination unit 55 selects OFDM. By the selection of OFDM, a
radio characteristic is improved in comparison with SC-FDMA and
scheduling is flexible.
[0101] In the first embodiment, the transmission method
determination unit 55 reads from the MPR table 54 the maximum value
(4.5 dB in the example illustrated in FIG. 4) of the transmission
power reduction amount P.sub.r. Alternatively, the maximum value of
the transmission power reduction amount P.sub.r is stored in the
MPR table 54 alone as a threshold. The transmission method
determination unit 55 may then compare the threshold with the
difference .DELTA..
[0102] Returning to FIG. 5, the transmission method transmission
unit 56 of the base station 50 notifies the determined transmission
method to the terminal 10 (S14).
[0103] The data signal modulation unit 19 of the terminal 10
modulates the transmission data in accordance with the notified
transmission method (S15).
[0104] Next, the data signal transmission unit 20 of the terminal
10 transmits the data signal to the base station 50 (S16).
[0105] Next, the data reception unit 57 of the base station 50
demodulates the data signal in accordance with the selected
transmission method (S17). The series of processes is then
terminated.
[0106] Hence, in this embodiment, data are not transmitted
uniformly by SC-FDMA on the uplink, and the data may be transmitted
after switching to OFDM, for example. OFDM has better radio
characteristic than SC-FDMA, and therefore an improvement in the
radio characteristic can be achieved in comparison with a case in
which the data are transmitted uniformly by SC-FDMA.
[0107] Further, with OFDMA, resource allocation scheduling not
using sub-carriers that are continuous on the frequency axis can be
performed, and therefore scheduling flexibility can be secured in
comparison with a case in which the data are transmitted uniformly
by SC-FDMA.
[0108] As a result, an improvement in throughput can be
achieved.
[0109] Note that in the example described above, the determinations
as to whether or not the transmission power of the terminal 10 has
exceeded the predetermined threshold and whether or not the maximum
value of the transmission power reduction amount P.sub.r is larger
than the difference .DELTA. are made in the base station 50, but
the mobile station may include the transmission method
determination unit 55.
[0110] By inputting the difference .DELTA. and the transmission
power as is into the transmission method determination unit 55 of
the mobile station from the transmission power calculation unit 13,
the transmission method can be determined by the mobile
station.
[0111] More specifically, when the transmission method
determination unit 55 of the mobile station detects that its own
transmission power has exceeded the predetermined threshold or that
the maximum value of the transmission power reduction amount
P.sub.r is larger than the difference .DELTA., the transmission
method determination unit 55 controls the data modulation unit 19
such that transmission is performed using the SC-FDMA method.
[0112] Also, when the transmission method determination unit 55 of
the mobile station detects that its own transmission power is lower
than the predetermined threshold or that the maximum value of the
transmission power reduction amount P.sub.r is smaller than the
difference .DELTA., the transmission method determination unit 55
controls the data modulation unit 19 such that transmission is
performed using the OFDM method.
[0113] Preferably, before switching the method, the base station 50
can notify the switch destination method (the SC-FDMA method or the
OFDM method) before the method is switched by making the switch
destination method transmit to the base station 50 from the data
signal transmission unit 20. Even if the notification is not
performed, the switch destination method can be detected by having
the base station 50 perform reception processing in relation to
both methods respectively.
[0114] Further, an embodiment in which the positions of the base
station and the mobile station are interchanged may be applied.
Second Embodiment
[0115] Next, a second embodiment will be described. In the first
embodiment, the transmission method determination unit 55 compares
the maximum value of the transmission power reduction amount
P.sub.r with the difference .DELTA.. In the second embodiment, the
transmission method is determined by comparing the transmission
power reduction amount P.sub.r with the difference .DELTA., after
selecting the modulation method and the number of resource blocks,
and reading corresponding items from the MPR table 54.
[0116] The overall configuration of the radio communication system
1 and the respective configurations of the terminal 10 and the base
station 50 are identical to those of the first embodiment (see FIG.
1 to FIG. 3). Further, the processing up to the point at which the
base station 50 receives the scheduling request from the terminal
10 (S12 of FIG. 5) is similar to that of the first embodiment.
[0117] The transmission method determination unit 55 inputs the
scheduling request from the scheduling request reception unit 53,
and performs the transmission method determination processing
(S13).
[0118] FIG. 8 illustrates flowchart indicating operational example
of the transmission method determination processing, and FIG. 9
illustrates an example of the MPR table 54.
[0119] When the transmission method determination unit 55 selects
the transmission method (S30), the transmission method
determination unit 55 selects on the basis of a determined format
(the modulation scheme and the number of resource blocks)
(S31).
[0120] For example, the transmission method determination unit 55
determines a format in which the modulation scheme is "16QAM" and
the number of resource blocks is "1". The transmission method
determination unit 55 then reads corresponding items from the MPR
table 54. FIG. 9 illustrates an example of the MPR table 54
indicating the corresponding items. The transmission method
determination unit 55 then reads the transmission power reduction
amount P.sub.r of the OFDM method from the corresponding items. In
the example illustrated in FIG. 9, the transmission power reduction
amount P.sub.r is "3". The transmission method determination unit
55 compares the read transmission power reduction amount P.sub.r
(="3") of the OFDM method with the difference .DELTA., and then
selects SC-FDMA if the transmission power reduction amount P.sub.r
is greater than the difference .DELTA., and selects OFDM if the
transmission power reduction amount P.sub.r is equal to or smaller
than the difference .DELTA., similarly to the first embodiment
(S32). Subsequent processing is similar to that of the first
embodiment.
[0121] The reason why the transmission method determination unit 55
reads the transmission power reduction amount P.sub.r of OFDM, from
among the two transmission power reduction amounts P.sub.r of OFDM
and SC-FDMA, is that the power reduction amount P.sub.r of OFDM is
larger than that of SC-FDMA and strict condition becomes
standard.
[0122] Note that in the second embodiment, the format may be
determined by the scheduling request reception unit 53 rather than
the transmission method determination unit 55. In this case, the
scheduling request reception unit 53 outputs the determined format
to the transmission method determination unit 55, and the
transmission method determination unit 55 performs the processing
described above on the basis of the format.
Third Embodiment
[0123] Next, a third embodiment will be described. The transmission
method is selected further taking the transmission bit count into
consideration in the third embodiment in comparison with the second
embodiment.
[0124] The terminal 10 transmits to the base station 50 the
scheduling request including a data amount (the transmission bit
count) (FIG. 2, S12 of FIG. 5). If the transmission bit count is
small, the terminal 10 can reduce the transmission power further.
The transmission method determination unit 55 sets a decrease width
corresponding to the transmission bit count as .DELTA.1 and
determines the transmission method by comparing (.DELTA.+.DELTA.1)
(decrease width (.DELTA.+.DELTA.1) hereinafter) with the
transmission power reduction amount P.sub.r.
[0125] The configurations of the radio communication system 1, the
terminal 10, and the base station 50 according to the third
embodiment are similar to those of the first embodiment. However
not that the transmission method determination unit 55 determines
the power decrease width .DELTA.1 corresponding to the transmission
bit count. For example, the determination is such that the
transmission method determination unit 55 includes a table of
decrease widths .DELTA.1 corresponding to transmission bit counts
and reads the decrease width .DELTA.1 corresponding to the
transmission bit count from the table of decrease width .DELTA.1.
Alternatively, the transmission method determination unit 55 stores
inside a formula for calculating the decrease width from the
transmission bit count, may calculates and determine the decrease
width .DELTA.1 from the formula. Alternatively, the bas station
apparatus 50 further includes a transmission bit count table 60 as
illustrated in FIG. 11, and the transmission method determination
unit 55 may read the decrease width .DELTA.1 corresponding to the
transmission bit count.
[0126] FIG. 10 illustrates a flowchart indicating an example of
transmission method determination processing according to the third
embodiment. This processing is similar to the processing of the
first embodiment up to the point at which the base station 50
receives the scheduling request.
[0127] If the transmission method determination unit 55 inputs the
scheduling request from the scheduling request reception unit 53,
the transmission method determination unit 55 determines the power
decrease width .DELTA.1 on the basis of the transmission bit count
included in the scheduling request (S41) and selects the
transmission method corresponding to the format in the similar
manner to the second embodiment (S40, S42).
[0128] And, if the power reduction amount P.sub.r of OFDM is larger
than the decrease width (.DELTA.+.DELTA.1), the transmission method
determination unit 55 selects SC-FDMA, and if the power reduction
amount P.sub.r of OFDM is not larger than the decrease width
(.DELTA.+.DELTA.1), the transmission method determination unit 55
selects OFDM (S43). In other words, if the amount of transmission
data is small enough to be transmitted at a low transmission power,
OFDM is selected, and if not, SC-FDMA is selected. Subsequent
processing is similar to that of the first embodiment.
[0129] Further, note that in the third embodiment, an encoding
ratio may be used in addition to the transmission bit count. The
transmission bit count table 60 stores decrease widths .DELTA.1
corresponding to encoding ratios. When the scheduling request
reception unit 53 receives the scheduling request, the scheduling
request reception unit 53 determines the encoding ratio and outputs
to the transmission method determination unit 55. The transmission
method determination unit 55 then determines the transmission
method by reading the decrease width .DELTA.1 corresponding to the
encoding ratio from the table 60.
Fourth Embodiment
[0130] Next, a fourth embodiment will be described. In the fourth
embodiment, if the base station 50 receives an instruction to
reduce the power of the terminal 10 from a network (another base
station, for example, although the network may be the base station
50 itself), the transmission method is determined taking into
consideration a power decrease width 42 corresponding to the
instruction.
[0131] The instruction is also known as an Overload Indicator, and
if the transmission power of the terminal 10 is large such that
interference is applied to the terminal of another cell, the
transmission power of the terminal 10 is reduced in accordance with
the instruction.
[0132] The configuration of the radio communication system 1 and
the terminal 10 is similarly to their counterparts in the first
embodiment. FIG. 12 illustrates a configuration example of the base
station 50. As illustrated in the FIG. 12, the base station 50
includes a network reception unit 70 so as to be capable of
receiving the instruction (Overload Indicator) from another base
station via the network.
[0133] FIG. 13 illustrates a flowchart indicating an example of the
transmission method selection processing. The processing up to the
point at which the base station 50 receives the scheduling request
(S12 in FIG. 5) is similar to that of the first embodiment.
[0134] If the network reception unit 70 receives the instruction
from another base station, the network reception unit 70 outputs
the power decrease width 42 corresponding to the instruction (S50).
For example, the network reception unit 70A includes inside a
table, and reads the corresponding decrease width 42 from the table
and outputs.
[0135] The transmission method determination unit 55 determines the
format in a similar manner to the second embodiment (S52), reads
the corresponding items from the MPR table 54, compares the
decrease width (.DELTA.+.DELTA.2) with the transmission power
reduction amount P.sub.r of OFDM, and determines the transmission
method (S51, S53).
[0136] More specifically, if the power reduction amount P.sub.r of
OFDM is larger than the decrease width (.DELTA.+.DELTA.2), the
transmission method determination unit 55 selects SC-FDMA, and if
the power reduction amount P.sub.r of OFDM is not larger than the
decrease width (.DELTA.+.DELTA.2), the transmission method
determination unit 55 selects OFDM (S53). In other words, if
transmission can be performed at a sufficiently low transmission
power in accordance with the instruction, OFDM is selected, and if
not, SC-FDMA is selected. Subsequent processing is similar to that
of the first embodiment and so on.
Fifth Embodiment
[0137] Next, a fifth embodiment will be described. The fifth
embodiment is an example of a case in which the transmission method
is determined according to whether or not the terminal 10 performs
MIMO (Multiple-Input Multiple-Output) transmission.
[0138] MIMO is a method for obtaining a transmission signal by
receiving transmission signal transmitted from a plurality of
transmission antennae in a single reception antenna and
synthesizing the reception signal such that the reception signal is
canceled. MIMO is used to obtain further throughput in an
environment having a favorable reception SIR (Signal to
Interference Ratio).
[0139] However, if transmission is performed using SC-FDMA, the
reception signal is processed on a reception side by using a
frequency equalizer, and due to the frequency equalizer,
inter-stream interference cannot be eliminated. As a result,
weighting coefficients relating respectively to the MIMO
inter-stream interference and multipath interference become
contradictory, and problem to deteriorate the reception signal
characteristic occurs.
[0140] On the other hand, in OFDM, the reception side may not use
the frequency equalizer and the sub-carrier is orthogonal, and
therefore multipath interference does not occur during reception
signal processing even if any weighting coefficient is used.
Accordingly, reception can be performed using the weighting
coefficient for eliminating the inter-stream interference of
MIMO.
[0141] Hence, the transmission method determination unit 55
according to the fifth embodiment selects OFDM if MIMO transmission
is to be performed, and selects SC-FDMA if MIMO transmission is not
to be performed (S60 to S62 in FIG. 14).
[0142] The scheduling request transmission unit 17 of the terminal
10 transmits the scheduling request including an information
indicating whether or not MIMO transmission is to be performed. The
transmission method determination unit 55 may read the information
from the scheduling request, and determine the transmission
method.
[0143] If MIMO transmission is performed, the data is transmitted
from the terminal 10 by using OFDMA, and therefore the radio
characteristic of the reception signal deteriorates to a smaller
extent than if transmission is performed by using SC-FDMA.
Sixth Embodiment
[0144] Next, a sixth embodiment will be described. In the first to
fifth embodiments, the calculation of the difference .DELTA. is
performed in the terminal 10. The sixth embodiment is an example of
a case in which the base station 50 calculates the difference
.DELTA..
[0145] FIG. 15 and FIG. 16 illustrates a configuration example of
the terminal 10 and the base station 50 respectively, and FIG. 17
illustrates a sequence diagram of overall processing. In the sixth
embodiment, the base station 50 calculates the difference .DELTA.,
and therefore the base station 50 includes the known signal
reception unit 11, the path loss calculation unit 12, and the
transmission power calculation unit 13.
[0146] The known signal transmission unit 14 of the terminal 10
transmits the known signal to the base station 50 (S70).
[0147] Next, the known signal reception unit 11 of the base station
50 receives the known signal, and the transmission power
calculation unit 13 calculates the difference .DELTA. between the
maximum transmission power P.sub.max and the transmission power
P.sub.t corresponding to the current position, by using (Numeral 1)
and so on (S71). Subsequent processing is similar to that of the
first embodiment. The sixth embodiment may also be applied to any
of the second to fourth embodiments.
* * * * *