U.S. patent application number 13/856869 was filed with the patent office on 2013-08-29 for mobile station, base station, uplink transmission method, and downlink transmission 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 Kenichi Higuchi, Teruo Kawamura, Yoshihisa Kishiyama, Mamoru Sawahashi.
Application Number | 20130223413 13/856869 |
Document ID | / |
Family ID | 40526115 |
Filed Date | 2013-08-29 |
United States Patent
Application |
20130223413 |
Kind Code |
A1 |
Kawamura; Teruo ; et
al. |
August 29, 2013 |
MOBILE STATION, BASE STATION, UPLINK TRANSMISSION METHOD, AND
DOWNLINK TRANSMISSION METHOD
Abstract
A mobile station includes a channel quality estimation unit
configured to estimate downlink channel quality based on a
reference signal from a base station and to output the estimated
downlink channel quality as channel estimation information; an
acknowledgement information determining unit configured to
determine whether a downlink data channel from the base station is
correctly received and to output the determination result as
acknowledgement information; and an acknowledgement information
prioritizing unit configured to cause the acknowledgement
information to be preferentially transmitted to the base station if
transmission timings of the channel estimation information and the
acknowledgement information coincide.
Inventors: |
Kawamura; Teruo; (Kanagawa,
JP) ; Kishiyama; Yoshihisa; (Kanagawa, JP) ;
Higuchi; Kenichi; (Kanagawa, JP) ; Sawahashi;
Mamoru; (Kanagawa, JP) |
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Applicant: |
Name |
City |
State |
Country |
Type |
NTT DOCOMO, INC.; |
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US |
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Assignee: |
NTT DOCOMO, INC.
Tokyo
JP
|
Family ID: |
40526115 |
Appl. No.: |
13/856869 |
Filed: |
April 4, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12680208 |
May 19, 2010 |
8437294 |
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PCT/JP2008/067522 |
Sep 26, 2008 |
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13856869 |
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Current U.S.
Class: |
370/336 |
Current CPC
Class: |
H04L 5/006 20130101;
H04L 25/0228 20130101; H04W 72/0446 20130101; H04L 1/0026 20130101;
H04L 1/0079 20130101; H04L 27/2647 20130101; H04L 1/1671
20130101 |
Class at
Publication: |
370/336 |
International
Class: |
H04W 72/04 20060101
H04W072/04 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 1, 2007 |
JP |
2007-258107 |
Claims
1.-3. (canceled)
4. A base station, comprising: a frame management unit configured
to manage frame information indicating a frame where a mobile
station transmits, via uplink, acknowledgement information for at
least a data channel transmitted via downlink; and an allocation
information signal generating unit configured to generate uplink
radio resource allocation information based on the frame
information.
5. The base station as claimed in claim 4, further comprising: a
determining unit configured to determine, based on the frame
information, a timing when transmission timings of channel
estimation information and the acknowledgement information from the
mobile station coincide in the same frame.
6. The base station as claimed in claim 5, wherein the determining
unit is configured to count a number of times when the transmission
timings of the channel estimation information and the
acknowledgement information from the mobile station coincide in the
same frame and when the number of times reaches a predetermined
value, to output a signal requesting to stop or postpone
transmission of data.
7. The base station as claimed in claim 5, wherein when the
determining unit determines the timing at which the transmission
timings of the channel estimation information and the
acknowledgement information from the mobile station coincide in the
same frame, the allocation information signal generating unit is
configured to generate the uplink radio resource allocation
information that causes the mobile station to transmit the channel
estimation information and the acknowledgement information via an
uplink data channel.
8.-9. (canceled)
Description
TECHNICAL FIELD
[0001] The present invention generally relates to a mobile station,
a base station, an uplink transmission method, and a downlink
transmission method for a communication system employing
single-carrier frequency division multiple access as an uplink
radio access method.
BACKGROUND ART
[0002] In "Evolved Universal Mobile Telecommunications System
(UMTS) Terrestrial Radio Access" (E-UTRA), single-carrier frequency
division multiple access (SC-FDMA) is employed as an uplink radio
access method. See, 3GPP TS 36.211, "E-UTRA; Physical Channels and
Modulation (Release 8)" for the uplink radio access method.
[0003] In SC-FDMA, as exemplified in FIG. 1, mobile stations (or
terminals, user devices, users, etc.; in this example, users A, B,
C, D, and E) in a cell transmit signals using different time and
frequency resources (the minimum unit of resources is called a
resource block) to achieve orthogonality between the signals from
the mobile stations. Also in SC-FDMA, a consecutive frequency band
is allocated to each mobile station to achieve single-carrier
transmission with a low peak-to-average power ratio (PAPR). This in
turn makes it possible to reduce power consumption of the mobile
stations and to provide wider coverage than multicarrier
transmission. Allocation of time and frequency resources is
determined by a scheduler of the base station based on propagation
conditions of users and QoS (e.g., data rate, error rate, and/or
delay) of data to be transmitted. This approach makes it possible
to allocate time and frequency resources that provide good
propagation conditions to respective users and thereby to increase
the throughput.
[0004] In SC-FDMA, an uplink control channel is used to transmit a
channel quality indicator (CQI) used for frequency scheduling and
adaptive modulation and coding of a downlink data channel and to
transmit acknowledgement information used for retransmission
control of downlink data. The acknowledgement information is
generated, for example, based on the result of error detection such
as cyclic redundancy check (CRC). When no error is detected,
acknowledge (ACK) is transmitted as the acknowledgement
information; and when an error is detected, negative acknowledge
(NACK) is transmitted as the acknowledgement information.
DISCLOSURE OF INVENTION
Problems to be Solved by the Invention
[0005] In uplink single-carrier transmission, there are two methods
for multiplexing a control channel and a data channel. Referring to
FIG. 2, the first method is used when data are transmitted via
uplink. In the first method, a control channel is
time-division-multiplexed with a data channel. The second method is
used when data are not transmitted via uplink. In the second
method, a control channel is transmitted using time and frequency
resources dedicated for control information. The time and frequency
resources dedicated for control information refer to a narrowband
channel that is separated from a data channel in the frequency
domain but is provided in the same subframe. The narrowband channel
is called a physical uplink control channel (PUCCH). See 3GPP TS
36.211, "E-UTRA; Physical Channels and Modulation (Release 8)" for
methods of multiplexing an uplink control channel and a data
channel.
[0006] When there are no uplink data to be transmitted, an uplink
control channel is transmitted using radio resources of PUCCH. When
transmitting an uplink control channel via PUCCH, transport formats
are necessary for a case where a CQI and acknowledgement
information (ACK/NACK information) are multiplexed and transmitted
simultaneously, a case where only a CQI is transmitted, and a case
where only ACK/NACK information is transmitted. Also, there is a
case where scheduling request information and/or a precoding matrix
indicator (PMI) for downlink MIMO are transmitted in addition to
the CQI and/or the ACK/NACK information. For this reason, it is
necessary to provide various transport formats. This in turn
complicates configurations and operations of mobile stations and
base stations.
[0007] One object of the present invention is to provide a mobile
station, a base station, an uplink transmission method, and a
downlink transmission method that make it possible to prevent the
increase in the number of transport formats for PUCCH resulting
from multiplexing the CQI and the ACK/NACK information.
Means for Solving the Problems
[0008] An aspect of the present invention provides a mobile station
that includes a channel quality estimation unit configured to
estimate downlink channel quality based on a signal from a base
station and to output the estimated downlink channel quality as
channel estimation information; an acknowledgement information
determining unit configured to determine whether a downlink data
channel from the base station is correctly received and to output
the determination result as acknowledgement information; and an
acknowledgement information prioritizing unit configured to cause
the acknowledgement information to be preferentially transmitted to
the base station if transmission timings of the channel estimation
information and the acknowledgement information coincide.
[0009] A second aspect of the present invention provides a base
station that includes a frame management unit configured to manage
frame information indicating a frame where a mobile station
transmits, via uplink, acknowledgement information for at least a
data channel transmitted via downlink; and an allocation
information signal generating unit configured to generate uplink
radio resource allocation information based on the frame
information.
[0010] A third aspect of the present invention provides an uplink
transmission method performed by a mobile station. The method
includes the steps of estimating downlink channel quality based on
a signal from a base station and outputting the estimated downlink
channel quality as channel estimation information; determining
whether a downlink data channel from the base station is correctly
received and outputting the determination result as acknowledgement
information; and if transmission timings of the channel estimation
information and the acknowledgement information coincide,
preferentially transmitting the acknowledgement information to the
base station.
[0011] A fourth aspect of the present invention provides a downlink
transmission method performed by a base station. The method
includes the steps of generating frame information indicating
frames where a mobile station transmits, via uplink, downlink
channel estimation information and acknowledgement information for
a data channel transmitted via downlink; and generating uplink
radio resource allocation information based on the frame
information.
Advantageous Effect of the Invention
[0012] An aspect of the present invention provides a mobile
station, a base station, an uplink transmission method, and a
downlink transmission method that make it possible to prevent the
increase in the number of transport formats for PUCCH resulting
from multiplexing the CQI and the ACK/NACK information.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a drawing used to describe allocation of radio
resources in a single-carrier transmission scheme;
[0014] FIG. 2 is a drawing used to describe allocation of uplink
radio resources;
[0015] FIG. 3 is a block diagram of a mobile station according to
an embodiment of the present invention;
[0016] FIGS. 4A and 4B are drawings illustrating transmission
timings of CQI and ACK/NACK information;
[0017] FIG. 5 is a block diagram of a base station according to an
embodiment of the present invention;
[0018] FIG. 6 is a drawing illustrating transmission timings of CQI
and ACK/NACK information;
[0019] FIG. 7 is a block diagram of a mobile station according to
another embodiment of the present invention; and
[0020] FIG. 8 is a block diagram of a base station according to
another embodiment of the present invention.
EXPLANATION OF REFERENCES
[0021] 30 Mobile station [0022] 302 OFDM signal demodulation unit,
304 demodulation and decoding unit, 306 downlink channel quality
estimation unit, 308 ACK/NACK determining unit, 310 buffer, 312
channel coding unit, 314 data modulation unit, 316 SC-FDMA signal
generating unit [0023] 50 base station [0024] 502
synchronization-detection and channel-estimation unit, 504 coherent
detection unit, 506 channel decoding unit, 508 uplink channel
condition estimation unit, 510 scheduling and
CQI-non-transmission-period-determining unit, 512
radio-frame-number-and-subframe-number management unit, 514
uplink-resource-allocation-information-signal generating unit, 518
OFDM signal generating unit [0025] 70 Mobile station [0026] 702
OFDM signal demodulation unit, 704 demodulation and decoding unit,
706 downlink channel quality estimation unit, 708 ACK/NACK
determining unit, 714 channel coding unit, 716 data modulation
unit, 716 SC-FDMA signal generating unit [0027] 80 Base station
[0028] 802 synchronization-detection and channel-estimation unit,
804 coherent detection unit, 806 channel decoding unit, 808 uplink
channel condition estimation unit, 810 scheduler, 812
radio-frame-number-and-subframe-number management unit, 814
uplink-resource-allocation-information-signal generating unit, 818
OFDM signal generating unit
BEST MODE FOR CARRYING OUT THE INVENTION
[0029] Embodiments of the present invention are described below
with reference to the accompanying drawings.
First Embodiment
Mobile Station
[0030] A mobile station 30 according to a first embodiment of the
present invention is described below with reference to FIG. 3. As
shown in FIG. 3, the mobile station 30 of the first embodiment
includes a receiving unit and a transmitting unit. The receiving
unit includes an OFDM (orthogonal frequency division multiplexing)
signal demodulation unit 302, a demodulation and decoding unit 304
for demodulating and decoding uplink resource allocation
information, a downlink channel quality estimation unit 306, and an
ACK/NACK determining unit 308 for determining ACK/NACK information
for downlink data channels. The transmitting unit includes a buffer
310, a channel coding unit 312, a data modulation unit 314, and an
SC-FDMA signal generating unit 316.
[0031] The OFDM signal demodulation unit 302 receives an
OFDM-modulated signal from a base station (not shown) via an
antenna, a duplexer, and a power amplifier (not shown) and
OFDM-demodulates the received signal. The OFDM demodulation process
performed by the OFDM signal demodulation unit 302 includes signal
processing such as orthogonal detection, analog-to-digital (A/D)
conversion, and, fast Fourier transformation. The OFDM signal
demodulation unit 302 outputs the demodulated signal to the
demodulation and decoding unit 304, the downlink channel quality
estimation unit 306, and the ACK/NACK determining unit 308.
[0032] The demodulation and decoding unit 304 receives the
demodulated signal from the OFDM signal demodulation unit 302 and
extracts, from the received signal, a signal including uplink
resource allocation information to be used by the mobile station 30
when transmitting an uplink signal to the base station. The
demodulation and decoding unit 304 demodulates and decodes the
extracted signal and thereby obtains the uplink resource allocation
information. Then, the demodulation and decoding unit 304 outputs
the obtained uplink resource allocation information to the SC-FDMA
signal generating unit 316.
[0033] The downlink channel quality estimation unit 306 receives
the demodulated signal from the OFDM signal demodulation unit 302
and measures downlink channel conditions based on a pilot channel
(may also be called a reference signal) in the received signal. The
downlink channel quality estimation unit 306 outputs the measured
downlink channel conditions as a channel quality indicator (CQI) to
the buffer 310. A CQI is represented by a value obtained by
converting a measurement of reception quality, such as a
signal-to-interference ratio (SIR) or a
signal-to-interference-noise ratio (SINR), of the pilot channel by
using a predetermined method.
[0034] The ACK/NACK determining unit 308 receives the demodulated
signal from the OFDM signal demodulation unit 302 and determines
whether there is an error in a packet (downlink data channel) in
the received signal by using an error detection technique such as
CRC. The ACK/NACK determining unit 308 outputs acknowledge (ACK) if
no error is detected or negative acknowledge (NACK) if an error is
detected to the buffer 310.
[0035] The buffer 310 receives the CQI from the downlink channel
quality estimation unit 306 and receives the ACK/NACK information
for the downlink data channel from the ACK/NACK determining unit
308. The mobile station 30 transmits the CQI to the base station at
regular intervals determined in advance between the mobile station
30 and the base station. Therefore, the buffer 310 receives the CQI
at predetermined intervals from the channel quality estimation unit
306. Meanwhile, the buffer 310 receives the ACK/NACK information
irregularly. This is because the ACK/NACK determining unit 308
determines the presence of an error and outputs ACK/NACK
information only when a data channel is included in a signal
transmitted from the base station (i.e., only when data are
transmitted). Therefore, the buffer 310, at a given timing,
receives only the CQI, only the ACK/NACK information, or both of
the CQI and the ACK/NACK information.
[0036] The buffer 310 determines whether only the CQI, only the
ACK/NACK information, or both of the CQI and the ACK/NACK
information are received. When only the CQI is received, the buffer
310 outputs the CQI to the channel coding unit 312 When only the
ACK/NACK information is received, the buffer 310 outputs the
ACK/NACK information to the channel coding unit 312 When both of
the CQI and the ACK/NACK information are received, the buffer 310
discards the CQI and outputs the ACK/NACK information to the
channel coding unit 312 according to a rule determined between the
mobile station 30 and the base station. For example, the buffer 310
may include an acknowledgement information prioritizing unit that
preferentially outputs the ACK/NACK information when both of the
CQI and the ACK/NACK information are received.
[0037] The channel coding unit 312 receives either the CQI or the
ACK/NACK information from the buffer 310 and performs channel
coding on the received information to generate a signal. The
channel coding unit 312 outputs the generated signal to the data
modulation unit 314.
[0038] The data modulation unit 314 performs predetermined
modulation processing on the signal received from the channel
coding unit 312 and thereby generates, for each block, a sequence
including information (CQI or ACK/NACK information) to be returned
to the base station. The data modulation unit 314 outputs the
generated sequence to the SC-FDMA signal generating unit 316.
[0039] The SC-FDMA signal generating unit 316 performs processing
such as discrete Fourier transformation (DFT), subcarrier mapping
in the frequency domain based on the uplink resource allocation
information received from the demodulation and decoding unit 304,
inverse fast Fourier transformation (IFFT), and addition of cyclic
prefixes on the sequence received from the data modulation unit
314, and thereby generates an SC-FDMA signal to be transmitted via
uplink. The generated SC-FDMA signal is transmitted via the power
amplifier, the duplexer, and the antenna to the base station.
[0040] Operations of the mobile station 30 of this embodiment are
described below with reference to FIG. 4A. FIG. 4A is a drawing
illustrating transmission timings of the CQI and the ACK/NACK
information. In FIG. 4A, the horizontal axis indicates time. Also
in FIG. 4A, dotted lines indicate subframes used for transmissions
from the mobile station 30, arrows in the upper row indicate
timings at which the ACK/NACK information is transmitted, and
arrows in the lower row indicate timings at which the CQI is
transmitted. In this example, the CQI is transmitted in subframe #1
and the ACK/NACK information is transmitted in subframe #2.
[0041] As described above, the CQI is transmitted from the mobile
station 30 to the base station at predetermined intervals. In the
example shown in FIG. 4A, the CQI is transmitted once in four
subframes, i.e., in subframe #1, subframe #5., and so on.
Meanwhile, the ACK/NACK information is transmitted irregularly,
i.e., when the mobile station 30 receives a data channel from the
base station. In the example shown in FIG. 4A, the ACK/NACK
information is transmitted in subframe #1, subframe #5, subframe
#7, and so on. According to the predetermined intervals, the CQI is
to be transmitted in subframe #5, and therefore both of the CQI and
the ACK/NACK information are to be transmitted in subframe #5.
However, when both of the CQI and the ACK/NACK information are
received, the buffer 310 of the mobile station 30 of this
embodiment discards the CQI and outputs only the ACK/NACK
information. Therefore, in subframe #5, the CQI is not transmitted
and only the ACK/NACK information is transmitted. This cancellation
of transmission of the CQI is indicated by an oval-shaped dotted
line and a diagonal line. The oval-shaped line and the diagonal
line are also shown at another subframe (subframe #9) and indicate
simultaneous transmission of the CQI and the ACK/NACK information
is also prevented in subframe #9.
[0042] One subframe includes two slots on the time axis and
typically has a length of 1 ms.
[0043] As described above, in the mobile station 30 of the first
embodiment, the buffer 310 receives a CQI from the channel quality
estimation unit 306 and ACK/NACK information from the ACK/NACK
determining unit 308, determines whether both of the CQI and the
ACK/NACK information are received at the same time, and if both of
them are received at the same time, outputs only the ACK/NACK
information to the channel coding unit 312. With this
configuration, the CQI and the ACK/NACK information are not
multiplexed. This in turn eliminates the need to provide transport
formats for multiplexing the CQI and the ACK/NACK information and
thereby makes it possible to reduce the number of transport
formats. Also with this configuration, since the ACK/NACK
information is returned every time when a data channel is
transmitted from the base station, communications between the
mobile station 30 and the base station are maintained properly.
[0044] As an alternative, when the CQI and the ACK/NACK information
are received at the same time, the buffer 310 may be configured to
temporarily store the CQI instead of discarding it. In this case,
for example, the buffer 310 preferentially outputs the ACK/NACK
information, determines whether it is possible to transmit the CQI
in the next subframe following the subframe where the ACK/NACK
information is transmitted, and if it is possible, outputs the
temporarily stored CQI to the channel coding unit 312 so that the
CQI is transmitted in the next frame. With this configuration, as
exemplified in FIG. 4B, the ACK/NACK information is transmitted in
subframe #5 (where, according to the predetermined intervals, the
CQI and the ACK/NACK information would have been (multiplexed and)
transmitted at the same time) and the CQI is transmitted in the
next subframe #6. Thus, this configuration enables the base station
to perform scheduling based on the CQI transmitted from the mobile
station 30.
[0045] Also, instead of in the next subframe following the subframe
where the ACK/NACK information is transmitted, the temporarily
stored CQI may be transmitted in any one of subsequent subframes
following the subframe where the ACK/NACK information is
transmitted.
[0046] Meanwhile, if the CQI and the ACK/NACK information are
multiplexed and transmitted simultaneously as an information signal
from the mobile station, the coverage of the information signal
tends to become smaller compared with a case where only the CQI or
the ACK/NACK information is transmitted. This in turn may reduce
the communication quality of a user (mobile station) near the cell
edge and may cause the user to become unable to communicate. To
prevent such problems, it is necessary to increase the transmission
power. However, increasing the transmission power increases the
power consumption of the mobile station. With the mobile station 30
of this embodiment, since the CQI and the ACK/NACK information are
not multiplexed, the above problems can be prevented.
Base Station
[0047] A base station 50 according to the first embodiment of the
present invention is described below with reference to FIG. 5. The
base station 50 provides communication services to the mobile
station 30 (shown in FIG. 3). As shown in FIG. 5, the base station
50 includes a receiving unit and a transmitting unit. The receiving
unit includes a synchronization-detection and channel-estimation
unit 502, a coherent detection unit 504, a channel decoding unit
506, an uplink channel condition estimation unit 508 for estimating
uplink channel conditions of users, a scheduling and
CQI-non-transmission-period-determining unit 510, and a
radio-frame-number-and-subframe-number management unit 512.
[0048] The transmitting unit includes an
uplink-resource-allocation-information-signal generating unit 514
and an OFDM signal generating unit 518.
[0049] The synchronization-detection and channel-estimation unit
502 receives a signal (SC-FDMA signal) from a mobile station via an
antenna, a duplexer, and a power amplifier (not shown). The
synchronization-detection and channel-estimation unit 502
determines a reception timing based on an uplink pilot channel (or
a synchronization channel) in the received signal, estimates uplink
channel conditions based on the reception conditions of the uplink
pilot channel, and generates information for channel compensation.
Then, the synchronization-detection and channel-estimation unit 502
outputs the generated information to the coherent detection unit
504.
[0050] The coherent detection unit 504 receives the signal from the
mobile station via the antenna, the duplexer, and the power
amplifier (not shown). The coherent detection unit 504 demodulates
the received signal based on the information received from the
synchronization-detection and channel-estimation unit 502, and
outputs the demodulated signal to the channel decoding unit
506.
[0051] The channel decoding unit 506 properly channel-decodes the
demodulated signal received from the coherent detection unit 504
and thereby reproduces and outputs a CQI or ACK/NACK
information.
[0052] The uplink channel condition estimation unit 508 receives
the SC-FDMA signal from the mobile station via the antenna, the
duplexer, and the power amplifier (not shown), and estimates uplink
channel conditions (or uplink channel quality) based on a pilot
channel (or a reference signal) in the received signal. The uplink
channel condition estimation unit 508 outputs the estimated uplink
channel conditions (as channel estimation information) to the
scheduling and CQI-non-transmission-period-determining unit
510.
[0053] The scheduling and CQI-non-transmission-period-determining
unit 510 performs downlink scheduling based on quality of service
(QoS) of each user, such as a requested data rate, a buffer status,
a desired error rate, and a delay, and on the estimated uplink
channel conditions received from the uplink channel condition
estimation unit 508. Also, the scheduling and
CQI-non-transmission-period-determining unit 510 selects
destination mobile stations (more particularly, user numbers) based
on the estimated uplink channel conditions, and determines
allocation of uplink resources to be used for communications by the
selected mobile stations (hereafter, for descriptive purposes, the
selected mobile stations may be represented by the mobile station
30). Also, the scheduling and
CQI-non-transmission-period-determining unit 510 receives, from the
radio-frame-number-and-subframe-number management unit 512, a frame
number of a frame to be used by the mobile station 30 to transmit
ACK/NACK information to the base station 50. The
radio-frame-number-and-subframe-number management unit 512 manages
frame numbers (e.g., subframe numbers as shown in FIGS. 4A and 4B)
to be used by mobile stations to transmit ACK/NACK information.
[0054] Also, the scheduling and
CQI-non-transmission-period-determining unit 510 determines
transmission timings (subframes) of the CQI and the ACK/NACK
information from the mobile station 30. The scheduling and
CQI-non-transmission-period-determining unit 510 can determine
transmission timings of the CQI because it is transmitted at
predetermined intervals from the mobile station 30 as described
above with reference to FIGS. 4A and 4B. Also, the scheduling and
CQI-non-transmission-period-determining unit 510 can determine the
transmission timing of the ACK/NACK information based on the frame
number received from the radio-frame-number-and-subframe-number
management unit 512.
[0055] Further, the scheduling and
CQI-non-transmission-period-determining unit 510 counts the number
of timings (frames) or the number of times when transmission
timings of the CQI and the ACK/NACK information coincide and the
mobile station 30 transmits only the ACK/NACK information. If the
number of timings exceeds a predetermined value, the scheduling and
CQI-non-transmission-period-determining unit 510 determines the
next timing when transmission timings of the CQI and the ACK/NACK
information coincide and outputs a downlink data transmission stop
signal to a downlink data signal generating unit (not shown) to
prevent transmission of ACK/NACK information at the determined
timing. Effects of this configuration are described later.
[0056] The scheduling and CQI-non-transmission-period-determining
unit 510 outputs allocated resource numbers (resource numbers of
the allocated resources) to the
uplink-resource-allocation-information-signal generating unit 514
and the coherent detection unit 504. The scheduling and
CQI-non-transmission-period-determining unit 510 also outputs the
selected user numbers to the
uplink-resource-allocation-information-signal generating unit 514
and the channel decoding unit 506.
[0057] The uplink-resource-allocation-information-signal generating
unit 514 associates the allocated resource numbers with the
allocated user numbers to generate uplink resource allocation
information and outputs the generated uplink resource allocation
information to the OFDM signal generating unit 518.
[0058] When receiving the downlink data transmission stop signal
from the scheduling and CQI-non-transmission-period-determining
unit 510, the downlink data signal generating unit (not shown)
stops and postpones the transmission of data specified by the
downlink data transmission stop signal.
[0059] The OFDM signal generating unit 518 receives the uplink
resource allocation information from the
uplink-resource-allocation-information-signal generating unit 514
and also receives other downlink channels (such as a downlink data
signal, a reference signal (common pilot signal), and control
information (control channel)) to which resources are allocated
taking into account downlink channel conditions and QoS of users.
Based on scheduling information, the OFDM signal generating unit
518 generates an OFDM signal including a downlink data signal, the
uplink resource allocation information, and the other downlink
channels. The OFDM signal generating process performed by the OFDM
signal generating unit 518 includes signal processing such as
mapping, inverse fast Fourier transformation (IFFT),
digital-to-analog (D/A) conversion, and orthogonal modulation. The
OFDM signal generated by the OFDM signal generating unit 518 is
transmitted via the power amplifier, the duplexer, and the antenna
(not shown) to the mobile stations.
[0060] Next, advantageous effects of the base station 50 of the
first embodiment are described.
[0061] As described above, the mobile station 30 (FIG. 3)
preferentially transmits the ACK/NACK information to prevent
simultaneous transmission of the CQI and the ACK/NACK information.
For this reason, in some cases, the base station 50 does not
receive the CQI at predetermined intervals. However, based on the
predetermined intervals and the frame numbers being managed by the
radio-frame-number-and-subframe-number management unit 512, the
base station 50 can determine timings (frames) where the
transmission timings of the CQI and the ACK/NACK information
coincide. Therefore, even if the CQI is not received at the
determined timings, the base station 50 does not misidentify such
events as communication problems. Also, even if the CQI is not
received at the timings (frames) where the transmission timings of
the CQI and the ACK/NACK information coincide, the base station 50
can perform scheduling based on previously received CQIs and
properly maintain communications with the mobile station 30.
[0062] Thus, the base station 50 of this embodiment allows the
mobile station 30 to function as described above, and thereby makes
it possible to reduce the number of transport formats and to
increase the coverage.
[0063] As described above with reference to FIG. 45, the buffer 310
of the mobile station 30 may be configured to temporarily store the
CQI and to transmit the CQI in the next (or any subsequent)
subframe (timing) following a subframe (timing) when the ACK/NACK
information is transmitted. This configuration allows the base
station 50 to more frequently receive updated CQIs and is therefore
preferable in to/ms of smooth communications with the mobile
station 30.
[0064] Also, the scheduling and
CQI-non-transmission-period-determining unit 510 of the base
station 50 may be configured to count the number of times when the
mobile station 30 transmits only the ACK/NACK information because
transmission timings of the CQI and the ACK/NACK information
coincide. The scheduling and
CQI-non-transmission-period-determining unit 510 determines the
next timing when transmission timings of the CQI and the ACK/NACK
information coincide after the number of times exceeds a
predetermined value, and outputs a downlink data transmission stop
signal to the downlink data signal generating unit (not shown) to
prevent transmission of downlink data. When receiving the downlink
data transmission stop signal, the downlink data signal generating
unit stops (or postpones) the transmission of the downlink data.
Since the data are not transmitted, the mobile station 30 does not
transmit ACK/NACK information. In other words, in a given frame
where the transmission timings of the CQI and the ACK/NACK
information coincide, the mobile station 30 transmits only the CQI
and does not transmit the ACK/NACK information. As a result, the
base station 50 can receive the CQI in the frame. This
configuration provides advantageous effects as described below.
[0065] The mobile station 30 of this embodiment preferentially
transmits the ACK/NACK information over the CQI to prevent
simultaneous transmission of the CQI and the ACK/NACK information.
Therefore, in some cases, a base station may not be able to receive
the CQI for a long period of time. To prevent this problem, the
base station 50 of this embodiment is configured to stop
transmission of data if the number of times when the mobile station
30 refrains from transmitting the CQI exceeds a predetermined value
and thereby to allow the mobile station 30 to transmit the CQI.
[0066] Thus, the base station 50 of this embodiment also makes it
possible to receive an updated CQI within a predetermined period of
time and thereby to properly perform scheduling.
[0067] The base station 50 is preferably configured to signal (or
report) to the mobile station 30 that the transmission of data is
stopped (or postponed).
[0068] Instead of counting the number of times when the CQI is not
transmitted from the mobile station 30, the base station 50 may be
configured to define a CQI transmission determining period as shown
in FIG. 6 and to determine whether the CQI is transmitted again
within the CQI transmission determining period after the last
transmission of CQI from the mobile station 30. If the CQI is not
transmitted within the CQI transmission determining period, the
base station 50 stops (or postpones) transmission of data so that
the CQI is transmitted from the mobile station 30.
Second Embodiment
Mobile Station
[0069] A mobile station 70 according to a second embodiment of the
present invention is described below with reference to FIG. 7. As
shown in FIG. 7, the mobile station 70 of the second embodiment
includes a receiving unit and a transmitting unit. The receiving
unit includes an OFDM signal demodulation unit 702, a demodulation
and decoding unit 704 for demodulating and decoding uplink resource
allocation information, a downlink channel quality estimation unit
706, and an ACK/NACK determining unit 708 for downlink data
channels. The transmitting unit includes a channel coding unit 712,
a data modulation unit 714, and an SC-FDMA signal generating unit
716.
[0070] The OFDM signal demodulation unit 702 receives an
OFDM-modulated signal from a base station (not shown) via an
antenna, a duplexer, and a power amplifier (not shown), and
OFDM-demodulates the received signal. The OFDM demodulation process
performed by the OFDM signal demodulation unit 702 includes signal
processing such as orthogonal detection, analog-to-digital (A/D)
conversion, and fast Fourier transformation. The OFDM signal
demodulation unit 702 outputs the demodulated signal to the
demodulation and decoding unit 704, the downlink channel quality
estimation unit 706, and the ACK/NACK determining unit 708.
[0071] The demodulation and decoding unit 704 receives the
demodulated signal from the OFDM signal demodulation unit 702 and
extracts, from the received signal, a signal including uplink
resource allocation information to be used by the mobile station 70
when transmitting an uplink signal to the base station. The
demodulation and decoding unit 704 demodulates and decodes the
extracted signal and thereby obtains the uplink resource allocation
information. In this embodiment, as described later, the base
station allocates resources to the mobile station 70 such that the
mobile station 70 can transmit the CQI and the ACK/NACK information
by using resources (physical uplink shared channel (PUSCH)) used
for data transmission. More particularly, the base station reports
an allocated frequency band (or bandwidth) and a subframe number
via the uplink resource information. Alternatively, this uplink
scheduling information may be reported from the base station to the
mobile station 70 via a separate signal.
[0072] The demodulation and decoding unit 704 also extracts, from
the received signal, a signal including information regarding a
modulation scheme specified by the base station and thereby obtains
modulation scheme information. Further, the demodulation and
decoding unit 704 extracts, from the received signal, a signal
including information regarding a modulation rate (channel coding
rate) specified by the base station and thereby obtains modulation
rate (channel coding rate) information.
[0073] The demodulation and decoding unit 704 outputs the obtained
uplink resource allocation information to the SC-FDMA signal
generating unit 716, outputs the modulation scheme information to
the data modulation unit 714, and outputs the channel coding rate
to the channel coding unit 712.
[0074] The downlink channel quality estimation unit 706 receives
the demodulated signal from the OFDM signal demodulation unit 702
and measures downlink channel conditions (or downlink channel
quality) based on a pilot channel (or a reference signal) in the
received signal. The downlink channel quality estimation unit 706
outputs the measured downlink channel conditions as a CQI to the
channel coding unit 712.
[0075] The ACK/NACK determining unit 708 receives the demodulated
signal from the OFDM signal demodulation unit 702 and determines
whether there is an error in a packet (downlink data channel) in
the received signal. The ACK/NACK determining unit 708 outputs
acknowledge (ACK) if no error is detected or negative acknowledge
(NACK) if an error is detected to the channel coding unit 712.
[0076] The channel coding unit 712 receives the CQI from the
downlink channel quality estimation unit 706 and receives the
ACK/NACK information for the downlink data channel from the
ACK/NACK determining unit 708. The channel coding unit 712 performs
channel coding on the received CQI and the ACK/NACK information
based on the channel coding rate information received from the
demodulation and decoding unit 704 and thereby generates a signal.
The channel coding unit 712 outputs the generated signal to the
data modulation unit 714.
[0077] The data modulation unit 714 modulates the signal received
from the channel coding unit 712 based on the modulation scheme
information received from the demodulation and decoding unit 704,
and thereby generates, for each block, an information sequence to
be transmitted to the base station. The data modulation unit 714
outputs the generated sequence to the SC-FDMA signal generating
unit 716.
[0078] The SC-FDMA signal generating unit 716 performs processing
such as discrete Fourier transformation (DFT), subcarrier mapping
in the frequency domain based on the uplink resource allocation
information received from the demodulation and decoding unit 704,
inverse fast Fourier transformation (IFFT), and addition of cyclic
prefixes on the sequence received from the data modulation unit
714, and thereby generates an SC-FDMA signal to be transmitted via
uplink. The generated SC-FDMA signal is transmitted via the power
amplifier, the duplexer, and the antenna to the base station.
[0079] Thus, based on the uplink resource allocation information
reported from the base station, the mobile station 70 of the second
embodiment allocates the PUSCH specified by the base station to the
CQI and the ACK/NACK information such that they are multiplexed. In
other words, the CQI and the ACK/NACK information are transmitted
at the same time to the base station via the PUSCH.
Base Station
[0080] A base station 80 according to the second embodiment of the
present invention is described below with reference to FIG. 8. The
base station 80 provides communication services to the mobile
station 70 (shown in FIG. 7). As shown in FIG. 8, the base station
80 includes a receiving unit and a transmitting unit. The receiving
unit includes a synchronization-detection and channel-estimation
unit 802, a coherent detection unit 804, a channel decoding unit
806, an uplink channel condition estimation unit 808 for estimating
uplink channel conditions of users, a scheduler 810, and a
radio-frame-number-and-subframe-number management unit 812. The
transmitting unit includes an
uplink-resource-allocation-information-signal generating unit 814
and an OFDM signal generating unit 818.
[0081] The synchronization-detection and channel-estimation unit
802 has substantially the same functions and configurations as
those of the synchronization-detection and channel-estimation unit
502 of the base station 50 (FIG. 5) of the first embodiment. The
coherent detection unit 804 has substantially the same functions
and configurations as those of the coherent detection unit 504 of
the base station 50 (FIG. 5) of the first embodiment. Also, the
channel decoding unit 806 has substantially the same functions and
configurations as those of the channel decoding unit 506 of the
base station 50 (FIG. 5) of the first embodiment. Therefore,
descriptions of those units are omitted here.
[0082] The uplink channel condition estimation unit 808 receives an
SC-FDMA signal from the mobile station via an antenna, a duplexer,
and a power amplifier (not shown), and estimates uplink channel
conditions (or uplink channel quality) based on a pilot channel (or
a reference signal) in the received signal. The uplink channel
condition estimation unit 808 outputs the estimated uplink channel
conditions to the scheduler 810.
[0083] The scheduler 810 performs downlink scheduling based on
quality of service (QoS) of each user, such as a requested data
rate, a buffer status, a desired error rate, and a delay, and on
the estimated uplink channel conditions received from the uplink
channel condition estimation unit 808. Also, the scheduler 810
selects destination mobile stations (more particularly, user
numbers) and determines allocation of uplink resources to be used
for communications by the selected mobile stations (hereafter, for
descriptive purposes, the selected mobile stations may be
represented by the mobile station 70). Further, the scheduler 810
receives, from the radio-frame-number-and-subframe-number
management unit 812, a frame number of a frame to be used by the
mobile station 70 to transmit ACK/NACK information to the base
station 80. The radio-frame-number-and-subframe-number management
unit 812 manages frame numbers (e.g., subframe numbers as shown in
FIGS. 4A and 4B) used by mobile stations to transmit ACK/NACK
information.
[0084] Also, the scheduler 810 determines transmission timings
(subframes) of the CQI and the ACK/NACK information from the mobile
station 70. The scheduler 810 can determine the transmission timing
of the CQI because it is transmitted at predetermined intervals
from the mobile station 70 as described in the first embodiment
with reference to FIGS. 4A and 4B. Also, the scheduler 810 can
determine the transmission timing of the ACK/NACK information based
on the frame number received from the
radio-frame-number-and-subframe-number management unit 812.
[0085] Based on the determined transmission timings, the scheduler
810 determines allocation of uplink resources. For example, when
the mobile station 70 is to transmit only the CQI, the scheduler
810 determines allocation of uplink resources such that the PUCCH
is allocated to the CQI. Meanwhile, when the mobile station is to
transmit only the ACK/NACK information, the scheduler 810
determines allocation of uplink resources such that the PUCCH is
allocated to the ACK/NACK information. Meanwhile, when the mobile
station 70 is to transmit both the CQI and the ACK/NACK
information, the scheduler 810 determines allocation of uplink
resources such that the CQI and the ACK/NACK information are
multiplexed in the PUSCH that is normally used for data
transmission. This uplink scheduling information may be reported
via a separate signal.
[0086] The scheduler 810 outputs allocated resource numbers (e.g.,
allocated frequency bands (or bandwidth) and subframe numbers) to
the uplink-resource-allocation-information-signal generating unit
814 and the coherent detection unit 804. Also, the scheduler 810
outputs the selected user numbers to the
uplink-resource-allocation-information-signal generating unit 814
and the channel decoding unit 806.
[0087] The uplink-resource-allocation-information-signal generating
unit 814 associates the allocated resource numbers with the
allocated user numbers to generate uplink resource allocation
information and outputs the generated uplink resource allocation
information to the OFDM signal generating unit 818.
[0088] The OFDM signal generating unit 818 receives the uplink
resource allocation information from the
uplink-resource-allocation-information-signal generating unit 814
and also receives other downlink channels (such as a downlink
reference signal (common pilot signal) and control information
(control channel)) to which resources are allocated taking into
account downlink channel conditions and QoS of users. Based on
scheduling information, the OFDM signal generating unit 818
generates an OFDM signal including the uplink resource allocation
information and the other downlink channels. The OFDM signal
generating process performed by the OFDM signal generating unit 818
includes signal processing such as mapping, inverse fast Fourier
transformation (IFFT), digital-to-analog (D/A) conversion, and
orthogonal modulation. The OFDM signal generated by the OFDM signal
generating unit 818 is transmitted via the power amplifier, the
duplexer, and the antenna (not shown) to the mobile stations.
[0089] Thus, when the mobile station 70 (FIG. 7) is to transmit
both the CQI and the ACK/NACK information at the same time to the
base station 80, the scheduler 810 of the base station 80 of this
embodiment determines allocation of uplink resources such that the
PUSCH is allocated to the CQI and the ACK/NACK information, and the
allocated uplink resources are reported to the mobile station 70
via uplink resource allocation information. The mobile station 70
returns the CQI and the ACK/NACK information to the base station 80
based on the uplink resource allocation information. Accordingly,
the CQI and the ACK/NACK information to be transmitted to the base
station 80 are not multiplexed in the PUCCH. This in turn
eliminates the need to provide transport formats for multiplexing
the CQI and the ACK/NACK information in the PUCCH and thereby makes
it possible to reduce the number of transport formats.
[0090] Although the present invention is described above based on
various embodiments, the present invention is not limited to the
above embodiments and variations and modifications may be made
without departing from the scope of the present invention.
[0091] For example, in the mobile station 30 of the first
embodiment, the buffer 310 determines whether the CQI and the
ACK/NACK information are to be transmitted at the same timing
(subframe). Alternatively, this may be done by a different
component of the mobile station 30, or an additional component may
be added to the mobile station 30 for this purpose. Also in the
first embodiment, the buffer 310 is configured to receive the CQI
from the downlink channel quality estimation unit 306 and the
ACK/NACK information from the ACK/NACK determining unit 308, and to
preferentially output the ACK/NACK information if the CQI and the
ACK/NACK information are to be transmitted at the same timing
(subframe). As an alternative configuration, the mobile station 30
may further include a CQI blocking unit between the downlink
channel quality estimation unit 306 and the buffer 310. When the
CQI and the ACK/NACK information are to be transmitted at the same
timing (subframe), the CQI blocking unit prevents the CQI from
being input to the buffer 310 so that the ACK/NACK information is
preferentially output from the buffer 310.
[0092] As described with reference to FIG. 4B, the buffer 310 may
be configured to temporarily store the CQI when the CQI and the
ACK/NACK information are to be transmitted in the same subframe and
to transmit the CQI in the next subframe following the subframe
where the ACK/NACK information is transmitted. Alternatively, the
buffer 310 may be configured to transmit the CQI in any one of the
second and subsequent subframes after the subframe where the
ACK/NACK information is transmitted.
[0093] Although the present invention is described above in
different embodiments, the distinctions between the embodiments are
not essential for the present invention, and the embodiments may be
used individually or in combination.
[0094] The base station 50 of the first embodiment includes the
scheduling and CQI-non-transmission-period-determining unit 510
that stops (or postpones) transmission of data to the mobile
station 30 if the number of times when only the ACK/NACK
information is transmitted (the CQI is not transmitted) exceeds a
predetermined value. Instead of stopping (or postponing)
transmission of data, as in the base station 80 of the second
embodiment, the scheduling and
CQI-non-transmission-period-determining unit 510 may be configured
to request the mobile station 30 to transmit the CQI and the
ACK/NACK information by multiplexing them in the PUSCH.
[0095] The above embodiments may also be expressed as follows:
[0096] According to a first aspect of the present invention, a
mobile station includes a channel quality estimation unit
configured to estimate downlink channel quality based on a signal
from a base station and to output the estimated downlink channel
quality as channel estimation information; an acknowledgement
information determining unit configured to determine whether a
downlink data channel from the base station is correctly received
and to output the determination result as acknowledgement
information; and an acknowledgement information prioritizing unit
configured to cause the acknowledgement information to be
preferentially transmitted to the base station if transmission
timings of the channel estimation information and the
acknowledgement information coincide. The acknowledgement
information prioritizing unit is connected to the channel quality
estimation unit and the acknowledgement information determining
unit. When receiving the channel estimation information and the
acknowledgement information at the same time, the acknowledgement
information prioritizing unit discards the channel estimation
information.
[0097] According to a second aspect of the present invention, a
mobile station includes a channel quality estimation unit
configured to estimate downlink channel quality based on a signal
from a base station and to output the estimated downlink channel
quality as channel estimation information; an acknowledgement
information determining unit configured to determine whether a
downlink data channel from the base station is correctly received
and to output the determination result as acknowledgement
information; and an acknowledgement information prioritizing unit
configured to cause the acknowledgement information to be
preferentially transmitted to the base station if transmission
timings of the channel estimation information and the
acknowledgement information coincide. The acknowledgement
information prioritizing unit is connected to the channel quality
estimation unit and the acknowledgement information determining
unit. When receiving the acknowledgement information and the
channel estimation information at the same time, the
acknowledgement information prioritizing unit sequentially outputs
the acknowledgement information and the channel estimation
information such that the channel estimation information is
transmitted after a predetermined number of subframes from when the
acknowledgement information is transmitted.
[0098] According to a third aspect of the present invention, a base
station includes a frame management unit configured to manage frame
information indicating a frame where a mobile station transmits,
via uplink, acknowledgement information for at least a data channel
transmitted via downlink; an allocation information signal
generating unit configured to generate uplink radio resource
allocation information based on the frame information; and a
determining unit configured to determine, based on the frame
information, a timing when transmission timings of channel
estimation information and the acknowledgement information from the
mobile station coincide.
[0099] According to a fourth aspect of the present invention, a
base station includes a frame management unit configured to manage
frame information indicating a frame where a mobile station
transmits, via uplink, acknowledgement information for at least a
data channel transmitted via downlink; an allocation information
signal generating unit configured to generate uplink radio resource
allocation information based on the frame information; and a
determining unit configured to determine, based on the frame
information, a timing when transmission timings of channel
estimation information and the acknowledgement information from the
mobile station coincide. The determining unit counts the number of
times when the transmission timings of the channel estimation
information and the acknowledgement information from the mobile
station coincide, and if the number of times reaches a
predetermined value, outputs a signal requesting to stop or
postpone transmission of data.
[0100] According to a fifth aspect of the present invention, a base
station includes a frame management unit configured to manage frame
information indicating a frame where a mobile station transmits,
via uplink, acknowledgement information for at least a data channel
transmitted via downlink; an allocation information signal
generating unit configured to generate uplink radio resource
allocation information based on the frame information; and a
determining unit configured to determine, based on the frame
information, a timing when transmission timings of channel
estimation information and the acknowledgement information from the
mobile station coincide. When the determining unit determines the
timing at which the transmission timings of the channel estimation
information and the acknowledgement information from the mobile
station coincide, the allocation information signal generating unit
generates the uplink radio resource allocation information that
causes the mobile station to transmit the channel estimation
information and the acknowledgement information via an uplink data
channel.
[0101] The present international application claims priority from
Japanese Patent Application No. 2007-258107 filed on Oct. 1, 2007,
the entire contents of which are hereby incorporated herein by
reference.
* * * * *