U.S. patent application number 11/487352 was filed with the patent office on 2007-09-20 for wireless communication device and wireless communication method.
This patent application is currently assigned to FUJITSU LIMITED. Invention is credited to Daisuke Jitsukawa, Hiroyuki Seki, Kotaro Shiizaki, Kenji Suda.
Application Number | 20070217388 11/487352 |
Document ID | / |
Family ID | 37397513 |
Filed Date | 2007-09-20 |
United States Patent
Application |
20070217388 |
Kind Code |
A1 |
Shiizaki; Kotaro ; et
al. |
September 20, 2007 |
Wireless communication device and wireless communication method
Abstract
The present invention relates to a wireless communication device
and a wireless communication method that improve a throughput
without increasing an overhead of a wireless frame. The wireless
communication device performing communications by using a wireless
frame containing a control channel and a data channel, for
improving the throughput without increasing the overhead of the
wireless frame, comprises a structuring unit allocating, as second
control information, part of control information used for
communication control to the data channel with respect to a
transmitted wireless frame to be transmitted to one other wireless
communication device.
Inventors: |
Shiizaki; Kotaro; (Kawasaki,
JP) ; Seki; Hiroyuki; (Kawasaki, JP) ; Suda;
Kenji; (Kawasaki, JP) ; Jitsukawa; Daisuke;
(Kawasaki, JP) |
Correspondence
Address: |
BINGHAM MCCUTCHEN LLP
2020 K Street, N.W.
Intellectual Property Department
WASHINGTON
DC
20006
US
|
Assignee: |
FUJITSU LIMITED
|
Family ID: |
37397513 |
Appl. No.: |
11/487352 |
Filed: |
July 17, 2006 |
Current U.S.
Class: |
370/349 |
Current CPC
Class: |
H04L 1/0031 20130101;
H04L 1/0038 20130101; H04L 1/0079 20130101; H04L 1/0088 20130101;
H04L 1/0003 20130101; H04W 24/02 20130101; H04L 1/0028 20130101;
H04L 1/0009 20130101 |
Class at
Publication: |
370/349 |
International
Class: |
H04J 3/24 20060101
H04J003/24 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 14, 2006 |
JP |
JP2006-069037 |
Claims
1. A wireless communication device performing communications by
using a wireless frame containing a control channel and a data
channel, comprising: a structuring unit allocating, as second
control information, part of control information used for
communication control to the data channel with respect to a
transmitted wireless frame.
2. A wireless communication device according to claim 1, further
comprising a rate determination unit determining, based on
information of a channel status with a wireless communication
device as a transmission destination, redundancy of the data
channel with respect to the transmitted wireless frame, wherein the
structuring unit, when the determined redundancy of the data
channel becomes higher than redundancy of the control channel,
allocates the second control information to the data channel.
3. A wireless communication device according to claim 1, wherein
the structuring unit dually allocates the second control
information to the control channel and to the data channel.
4. A wireless communication device according to claim 1, wherein
the structuring unit allocates, as first control information, the
information used for the demodulation process and for the decoding
process in the wireless communication device receiving the
transmitted wireless frame to the control channel, and sets other
control information as the second control information.
5. A wireless communication device according to claim 1, wherein
the structuring unit sets, as the second control information,
control information related to a received wireless frame in the
control information with respect to the transmitted wireless
frame.
6. A wireless communication device according to claim 1, further
comprising: an error detection unit detecting an error in data
allocated to the received control channel; an estimating unit
estimating the control information that should be allocated to the
received control channel; and a demodulating/decoding unit
demodulating and decoding, if an error is detected by the error
detection unit, the data allocated to the received data channel by
using the control information estimated by the estimating unit.
7. A wireless communication device according to claim 6, further
comprising generation unit extracting the control information
contained in the data demodulated and decoded by the
demodulating/decoding unit, and generating the control channel and
the data channel that should be transmitted by using the extracted
control information.
8. A wireless communication device performing communications by
using a wireless frame containing a control channel and a data
channel, comprising: an error detection unit detecting an error in
data allocated to the received control channel; an estimating unit
estimating control information that should be allocated to the
received control channel; and a demodulating/decoding unit
demodulating and decoding, if an error is detected by the error
detection unit, the data allocated to the received data channel by
using the control information estimated by the estimating unit.
9. A wireless communication device according to claim 8, further
comprising a generation unit extracting control information
contained in the data demodulated and decoded by the
demodulating/decoding unit, and generating respective data
allocated to the control channel and to the data channel by using
the extracted control information with respect to the transmitted
wireless frame.
10. A wireless communication method using a wireless frame
containing a control channel and a data channel, comprising: a
structuring step of allocating, as second control information, part
of control information used for communication control to the data
channel with respect to a transmitted wireless frame.
11. A wireless communication method according to claim 10, further
comprising a rate determination step of determining, based on
information of a channel status with a wireless communication
device as a transmission destination, redundancy of the data
channel with respect to the transmitted wireless frame, wherein the
structuring step allocates, when the determined redundancy of the
data channel becomes higher than redundancy of the control channel,
the second control information to the data channel.
12. A wireless communication method according to claim 10, wherein
the structuring step dually allocates the second control
information to the control channel and to the data channel.
13. A wireless communication method according to claim 10, wherein
the structuring step allocates, as first control information, in
the pieces of control information, the information used for the
demodulating process and for the decoding process in the wireless
communication device receiving the transmitted wireless frame to
the control channel, and sets other control information as the
second control information.
14. A wireless communication method according to claim 10, wherein
the structuring step sets, with respect to the transmitted wireless
frame, as the second control information, the control information
related to a received wireless frame in the control
information.
15. A wireless communication method according to claim 10, further
comprising: an error detection step of detecting an error in data
allocated to the received control channel; an estimating step of
estimating the control information that should be allocated to the
received control channel; and a demodulating/decoding step of
demodulating and decoding, if an error is detected in the error
detection step, the data allocated to the received data channel by
use of the control information estimated in the estimating
step.
16. A wireless communication method according to claim 15, further
comprising a generation step of extracting the control information
contained in the data demodulated and decoded in the
demodulating/decoding step, and of generating respective data
allocated to the control channel and to the data channel with
respect to the transmitted wireless frame.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a wireless communication
device and a wireless communication method that perform
communications by use of a wireless frame containing a control
channel and a data channel.
[0003] 2. Description of the Related Art
[0004] In a cellular mobile communication system, cells as
communication areas covered by respective base stations are located
so as to be neighboring to each other or partially overlapped with
each other. Each base station connects each mobile station to the
mobile communication system by performing wireless communications
with a plurality of mobile stations located within each
corresponding cell. In this type of cellular mobile communication
system, an important subject is to improve a throughput in the
mobile station located at the cell edge. Generally, an error rate
characteristic deteriorates in the cell edge, because the received
power from the base station covering the cell is attenuated, and
the mobile station is susceptible to interference by the signals
from the base stations located in other cells in the periphery.
[0005] A method of solving such a problem is a method of giving, as
for transmission signals to the mobile station at the cell edge,
more of redundancy of the data than the transmission signals to
other mobile stations. This is the method of transmitting the data
repeatedly inserting the information having the same content with
respect to the transmission signals to the mobile station at the
cell edge. This method, however, causes the transmission frame to
be upsized and leads to an increase of an overhead of the
transmission frame. Further, even when fixing a transmission frame
length, it follows that a substantial data transmission quantity
decreases.
[0006] Another method is that the transmission data to the mobile
station at the cell edge is subjected to error correction coding
that exhibits the higher redundancy than the transmission data to
other mobile stations. Proposed in regard to this method is a
scheme (refer to Non-Patent document 1) that turbo encoding having
a one-third (1/3) coding rate is used for the transmission data to
the mobile station in the vicinity of the base station, and the
low-rate turbo encoding having the coding rates such as 1/5 and 1/9
that are equal to or lower than 1/3 is used for the transmission
data to the mobile station at the cell edge (refer to "3rd
Generation Partnership Project, "Lower rate extension of channel
coding to the rate <1/3", 3 GPP TSG RAN WG1 meeting #42 bis
(R1-051082), 2005-10, Agenda Item 8.7."). With this scheme, even in
the communications to the mobile station located at the cell edge
in a transmission environment of very poor quality, it is expected
to prevent the deterioration in the error rate characteristic and
the decrease in the throughput by using the low-rate turbo encoding
with the increased redundancy.
[0007] In the conventional arts described above, however, though
capable of improving the decrease in the throughput with respect to
a data channel for transmitting to the mobile station located at
the cell edge, a problem about the transmission of a control
channel still remains. This problem will hereinafter be explained
with reference to FIGS. 14, 15 and 16. FIG. 14 is a diagram showing
a frame format used for the conventional cellular mobile
communication system. FIG. 15 is a diagram showing a coding
switchover method corresponding to a cell location in the prior
art. FIG. 16 is a diagram showing a transmitting/receiving state in
the prior art.
[0008] The frame format as shown in FIG. 14 is used for the
communications between the base station and the mobile station. The
wireless frame is assembled by a pilot channel (PICH), a control
channel (CCH) and a data channel (DCH). The coding switchover
method proposed in the conventional art described above is a
technique targeting on the data channel in the wireless frame.
Generally, as for the control channel, convolutional coding having
the coding rate "1/3" is used in common with the respective mobile
stations.
[0009] FIG. 15 shows an example of such a case that a base station
500 covering a cell 510 performs the communications with a mobile
station 501 located in the vicinity of the base station 500 and
with a mobile station 502 located at the cell edge. In the
conventional art, 16 QAM (Quadrature Amplitude Modulation)
modulation method and the turbo encoding having the coding rate
"1/3" are used for the data channel in the signals to the mobile
station 501 located in the vicinity of the base station 500, and
QPSK (Quadrature Phase Shift Keying) modulation method and the
convolutional coding having the coding rate "1/3" are used for the
control channel. Such a design is made that the transmission of the
control channel totally exhibits a more preferable error rate
characteristic than by the transmission of the data channel in the
vicinity of the base station 500.
[0010] On the other hand, the communications with the mobile
terminal 502 located at the cell edge involve such a change that
the QPSK modulation method and the low-rate turbo encoding with its
coding rate equal to or lower than the coding rate "1/3" are used
for the data channel, and involve using, for the control channel,
the QPSK modulation method and the convolutional coding having the
coding rate "1/3" as they are. Namely, in the mobile station
located at the cell edge, the data channel uses the coding having
the larger redundancy than the control channel has, and therefore
such a phenomenon might occur that the error rate characteristic of
the control channel becomes lower than the error rate
characteristic of the data channel at the cell edge.
[0011] In the conventional arts, the control channel contains
control information for correctly demodulating and decoding user
data allocated to the data channel, and hence, as shown in FIG. 16,
if the mobile station 502 detects that an error occurs in the
control channel, the mobile station 502 prompts the base station
500 to execute retransmission. Accordingly, in the conventional
arts, it follows that the retransmission is repeated if the error
frequently occurs in the control channel and that a decrease in
transmission efficiency of the whole system is brought about.
[0012] For solving these problems, it is considered that the
redundancy of the coding used for the control channel is set larger
than the coding redundancy for the data channel. In this method,
however, the control channel generally uses a format common to all
the mobile stations, and therefore, when increasing the redundancy
for the control channel and upsizing the control channel, it
follows that the whole transmission frame gets excessively upsized.
Further, even when fixing the transmission frame length, it follows
that the substantial transmission quantity decreases due to the
increase in the overhead of the control channel. Hence, this type
of method results in increasing the overhead of the transmission
frame.
SUMMARY OF THE INVENTION
[0013] It is an object of the present invention to provide a
wireless communication device and a wireless communication method
that improve a throughput without increasing the overhead of the
wireless frame.
[0014] The present invention adopts the following configurations in
order to solve the problems described above. Namely, according to
the present invention, a wireless communication device performing
communications by using a wireless frame containing a control
channel and a data channel, comprises a structuring unit
allocating, as second control information, part of control
information used for communication control to the data channel with
respect to a transmitted wireless frame to be transmitted to one
other wireless communication device.
[0015] Given herein as the control information used for the
communication control are, for example, information on a modulation
method, a coding rate etc about the wireless frame to be
transmitted, and information such as CQI (Channel Quality
Information), a modulation method and a coding rate that should be
utilized for the wireless frame to be transmitted to the present
wireless communication device from the other wireless communication
device as a transmission destination. In the present invention,
there is transmitted the wireless frame in which part of these
control information is allocated as the second control information
to the data channel.
[0016] Hence, according to the present invention, in the wireless
communication device receiving the transmitted wireless frame, even
if an error occurs in the received control channel, without making
a retransmission request, the control information, which might have
been utilized if the error would not occur, is estimated, and the
user data can be demodulated and decoded by using this estimated
control information.
[0017] With this scheme, according to the present invention,
without increasing an overhead of the wireless frame, even in the
case of performing the communications with the mobile station in a
channel status of which quality is as poor as in the vicinity of a
cell edge, it is possible to reduce the retransmission due to
occurrence of the error in only the control channel and to improve
the throughput.
[0018] Further, the wireless communication device according to the
present invention may further comprise a rate determination unit
determining, based on information of a channel status with a
wireless communication device as a transmission destination,
redundancy of the data channel with respect to the transmitted
wireless frame, wherein the structuring unit, when the determined
redundancy of the data channel becomes higher than redundancy of
the control channel, may allocate the second control information to
the data channel.
[0019] In the present invention, the redundancy of the data channel
of the transmitted wireless frame is changed based on the
information of the channel status with the wireless communication
device as the transmission destination. Then, as a result of being
changed, if the redundancy of the data channel gets higher than the
redundancy of the control channel, the second control information
is allocated to the data channel.
[0020] Accordingly, in the present invention, for instance, if poor
of the channel status with the other wireless communication device
as the communication partner device and if increasing the
redundancy of the data channel, the second control information is
allocated to the data channel and is, whereas if not, allocated to
the control channel as conventional.
[0021] With this scheme, the proper wireless frame can be used
corresponding to the channel status while improving the throughput
by reducing the retransmission, and the extra overhead of the
wireless frame can be reduced.
[0022] Moreover, in the wireless communication device according to
the present invention, the structuring unit may dually allocate the
second control information to the control channel and to the data
channel.
[0023] Further, in the wireless communication device according to
the present invention, the structuring unit may allocate, as first
control information, in the control information, the information
used for the demodulation process and for the decoding process in
the wireless communication device receiving the transmitted
wireless frame to the control channel, and may set other
information as the second control information.
[0024] In the present invention, in the wireless communication
device receiving the transmitted wireless frame, the
easy-to-estimate information is allocated to the control channel,
and other hard-to-estimate information are allocated to the data
channel.
[0025] Hence, according to the present invention, in the wireless
communication device on the receiving side, if the error occurs in
only the control channel, the data allocated to the data channel
can be demodulated and decoded by using the control information to
be estimated, and therefore the occurrence of the retransmission
can be further reduced.
[0026] Still further, in the wireless communication device
according to the present invention, the structuring unit, with
respect to the transmitted wireless frame, may set, as the second
control information, the control information related to the
received wireless frame in the control information.
[0027] Herein, in the control information, the control information
for the wireless frame received from the other wireless
communication device is, for example, the CQI and is exemplified
such as a modulation method indicated to the other wireless
communication device by the present wireless communication device.
These information are the hard-to-estimate information in the
wireless communication device receiving the wireless frame, and are
allocated to the data channel.
[0028] With this scheme, according to the present invention, even
if the error occurs in the control channel, the other wireless
communication device can generate the transmitted wireless frame by
using the second control information allocated to the data channel,
and it is therefore possible to reduce the occurrence of the
retransmission.
[0029] Yet further, according to the present invention, a wireless
communication device performing communications by using a wireless
frame containing a control channel and a data channel, comprises an
error detection unit detecting an error in data allocated to the
received control channel, an estimating unit estimating the control
information that should be allocated to the received control
channel, and a demodulating/decoding unit demodulating and
decoding, if an error is detected by the error detection unit, the
data allocated to the received data channel by using the control
information estimated by the estimating unit.
[0030] The wireless communication device according to the present
invention specifies a configuration of the wireless communication
device on the side of receiving the wireless frame transmitted by
the wireless communication device described above. Namely, if the
error occurs in the data allocated to the control channel, since
this data allocated to the control channel can not be used, the
data allocated to the received data channel is demodulated and
decoded based on the control information estimated by the
estimating unit.
[0031] Moreover, the wireless communication device according to the
present invention may further comprise a generation unit extracting
the control information contained in the data demodulated and
decoded by the demodulating/decoding unit, and generating
respective pieces of data allocated to the control channel and the
data allocated to the data channel by use of the extracted control
information with respect to the transmitted wireless frame that
should be transmitted.
[0032] According to the present invention, even if the error occurs
in the control channel, the transmitted wireless frame can be
generated by using the control information in the data channel, and
hence the occurrence of the retransmission can be reduced.
[0033] It should be noted the present invention may also be a
program for actualizing any one of the functions described above.
Further, the present invention may also be a readable-by-computer
storage medium stored with this program.
[0034] According to the present invention, it is possible to
actualize the wireless communication device and the wireless
communication method that improve the throughput without increasing
the overhead of the wireless frame.
BRIEF DESCRIPTION OF THE DRAWINGS
[0035] FIG. 1 is a diagram showing an example 1 of a frame format
in the embodiment;
[0036] FIG. 2 is a diagram showing an example 2 of the frame format
in the embodiment;
[0037] FIG. 3 is a diagram showing a transmitting/receiving state
in the embodiment;
[0038] FIG. 4 is a diagram showing a frame format in a first
embodiment;
[0039] FIG. 5 is a diagram showing a device configuration of a base
station in the first embodiment;
[0040] FIG. 6 is a diagram showing an example of an MCS table;
[0041] FIG. 7 is a diagram showing a device configuration of a
mobile station in the first embodiment;
[0042] FIG. 8 is a diagram showing a receiving operation of the
mobile station in the first embodiment;
[0043] FIG. 9 is a diagram showing a frame format (a case of not
conducting in-band) in a second embodiment;
[0044] FIG. 10 is a diagram showing a frame format (a case of
conducting the in-band) in the second embodiment;
[0045] FIG. 11 is a diagram showing the device configuration of the
base station in the second embodiment;
[0046] FIG. 12 is a diagram showing the device configuration of the
mobile station in the second embodiment;
[0047] FIG. 13 is a diagram showing an example of the receiving
operation of the mobile station in the second embodiment;
[0048] FIG. 14 is a diagram showing a conventional frame
format;
[0049] FIG. 15 is a diagram showing a coding switchover method in
accordance with a conventional cell location; and
[0050] FIG. 16 is a diagram showing a transmitting/receiving state
in the prior art.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Outline of Embodiments of the Invention
[0051] For discussing embodiments of the present invention, at
first, an outline of the embodiments of the present invention will
be explained with reference to FIGS. 1 and 2. FIGS. 1 and 2 are
diagrams showing an example of a transmission frame format used in
the embodiments of the present invention. In the embodiments,
control information allocated to a control channel in the frame
format shown in FIG. 14 is segmented into two parts (a control
information part 1 and a control information part 2), wherein the
control information part 2 thereof is allocated to a data
channel.
[0052] As a method of segmenting the control information, there is
considered a method by which the control information part 2
contains such a piece of information as to be changed each time
performing the transmission and unable to be easily estimated in a
receiving-side device, while the control information part 1
contains other pieces of information that can be easily estimated
in the receiving-side device. Specifically, for instance, the
information about a modulation method, a coding rate, etc is
contained in the control information part 1, and the information
such as CQI (Channel Quality Information) representing a channel
status is contained in the control information part 2. This is
because the information about the modulation method supported by a
system to some extent, which is fixed as in the case of QPSK
(Quadrature Phase Shift Keying) and 16 QAM (Quadrature Amplitude
Modulation), is data that falls within a fixed range even when
changed and is therefore considered to be the data easy to be
estimated in the receiving-side device, while the information such
as the CQI is data that momentarily changes and is unfixed in width
of this change and is therefore considered not to be the data that
can be easily estimated in the receiving-side device.
[0053] Considered is an example where the thus-segmented control
information part 1 and control information part 2 are allocated as
shown in FIGS. 1 and 2. FIG. 1 shows an example in which the
control information part 2 is allocated dually to the control
channel and to the data channel. FIG. 2 shows an example in which
the control channel contains only the control information part 1,
and the control information part 2 is allocated to the data
channel. In the example shown in FIG. 2, a length of the control
channel is shorter than a length of the conventional control
channel illustrated in FIG. 14.
[0054] FIG. 3 is a diagram showing a transmitting/receiving state
in the embodiment using the frame format as described above. In the
transmitting/receiving state in the case of the conventional art
shown in FIG. 16, if an error occurs in the control information,
the receiving-side device requests a transmitting-side device to
retransmit without decoding user data; and, in the
transmitting/receiving state in the embodiment shown in FIG. 3,
even if the error occurs in the control information, a possibility
that the user data is correctly demodulated and decoded is improved
by estimating the control information part 1.
[0055] In a case where a mobile station is located in the vicinity
of a base station and so on, however, in such an environment that
the control channel has a more preferable error rate characteristic
than the data channel has, there is no merit in allocating a part
of the control channel to the data channel, and hence the
conventional message format shown in FIG. 14 should be employed. In
the embodiment, the frame format is changed over corresponding to
respective coding rates used in the data channel and in the control
channel. To be specific, if the coding rate of the data channel
exhibits higher redundancy than the coding rate of the control
channel, the control information part 2 is allocated to the data
channel, and, whereas if the coding rate of the data channel
exhibits the lower redundancy than the coding rate of the control
channel, the conventional frame format is used. In the following
discussion, a scheme of allocating the control information part 2
to the data channel is referred to also as [conducting the
in-band].
First Embodiment
[0056] A wireless communication system in a first embodiment of the
present invention will hereinafter be described with reference to
the drawings. Configurations in the following embodiments are
exemplifications, and the present invention is not limited to the
configurations in the embodiments.
[0057] [System Architecture]
[0058] The wireless communication system in the first embodiment
shall be, as shown in FIG. 15, configured by a base station device
(which will hereinafter simply be termed a base station) 500, and a
mobile station devices (which will hereinafter be simply termed
mobile stations) 501 and 502. The configuration illustrated in FIG.
15 is nothing more than one example adopted for the sake of
explanatory convenience, wherein a plurality of base stations and a
plurality of mobile stations may exist, and an unillustrated
control device etc may further be provided. Hereinafter, as shown
in FIG. 15, the explanation will be made along with such a case
example that the base station 500 covering a cell 510 performs
communications respectively with the mobile station 501 located in
the vicinity of the base station 500 and with the mobile station
502 located at the cell edge.
[0059] [Frame Format]
[0060] The frame format used in the wireless communication system
in the first embodiment will be explained with reference to FIG. 4.
FIG. 4 is a diagram showing the frame format in the first
embodiment, and shows the format of a frame (a frame of a downlink)
to be transmitted from the base station 500 to the mobile station
501 or 502. The frame format in the first embodiment corresponds to
the example shown in FIG. 1, which has been described in the item
of the Outline of Embodiment of the Invention, and has a structure
wherein the control information part 2 is dually allocated to the
control channel (CCH) and to the data channel (DCH).
[0061] In the first embodiment, the control information is
segmented in a way that sets downlink control information as the
control information part 1 (PART 1) and uplink control information
as the control information part 2 (PART 2). The downlink control
information contains a modulation method, a coding rate, a data
length, etc that are related to the data transmitted in the form of
the frame. On the other hand, the uplink control information
contains the CQI estimated by the base station, the modulation
method and the coding rate that are indicated to the mobile station
by the base station and a result of a cyclic redundancy check
(which will hereinafter be abbreviated to CRC) of a transmission
message to the base station from the mobile station.
[0062] The uplink control information segmented as the control
information part 2 is, it follows, allocated to the data channel.
In-band information (IN-BAND) is further allocated to the data
channel. A reason why this in-band information is allocated to the
data channel lies in keeping a control channel size unchanged. The
data channel size can be judged from the data length contained in
the downlink control information, and therefore no problem arises
even when the in-band information is thus allocated thereto.
[0063] The in-band information contains presence/absence
information showing whether the control information part 2 is
allocated to the data channel or not (presence or absence of the
in-band) and allocation information showing a location where the
control information part 2 in the data channel is allocated. A
piece of identifying information expressed by, e.g., a numerical
value may be set in the presence/absence information field, wherein
such a scheme may be taken that when [0] is set, this represents no
existence of the control information part 2, and, when [1] is set,
this represents existence of the control information part 2. An
offset address from, e.g., the head of the data channel may also be
set in the allocation information field.
[0064] It should be noted the data contained in the control
information part 1 and the control information part 2 are not
limited to the data described above, and the data structure thereof
changes corresponding to the system. For instance, a spreading
ratio, a code multiplexing count, etc can be contained as the
downlink control information in a CDMA (Code Division Multiple
Access) system, an antenna count etc can be contained as the
downlink control information in a MIMO (Multi Input Multi Output)
system, and a guard interval length etc can be contained as the
downlink control information in an OFDM (Orthogonal Frequency
Division Multiplexing) system. Further, in the case of a system
where the transmitting-side device computes reception timing of a
signal from each of the receiver devices and indicates transmission
timing of the receiving-side device corresponding thereto,
information such as a timing adjustment notifying bit for
actualizing this scheme can be contained as the uplink control
information.
[0065] [Base Station]
[0066] A device configuration of the base station 500 in the first
embodiment will hereinafter be described with reference to FIG. 5.
FIG. 5 is a block diagram showing the device configuration related
to transmitting functions of the base station 500 in the first
embodiment. The base station 500 in the first embodiment includes,
as the transmitting functions, a pilot generation unit 101, a
control information part 1 generation unit 102, a control
information part 2 generation unit 103, a data generation unit 104,
a data structuring unit 105, a modulation unit 106, a control
information making unit 107, a modulation unit 108, a multiplexing
unit 109, a transmission unit 110, a transmitting antenna 115, a
receiving antenna 115, a reception unit 121, an uplink transmission
frame decoding unit 122, a rate determining unit 123, a channel
estimating unit 124 and a CQI information generation unit 125.
Among these components, the receiving antenna 120, the reception
unit 121 and the uplink transmission frame decoding unit 122 are,
though taking a charge of the receiving functions, taken up herein
as the functional units that acquire the information to be utilized
in the functional units taking the transmitting functions.
[0067] The reception unit 121, upon receiving the signals
transmitted from the mobile station and received by the receiving
antenna 120, executes processes such as a frequency conversion, an
analog/digital conversion and demodulation upon the received
signals. The reception unit 121 sends the signals, which have
undergone these predetermined processes, to the uplink transmission
frame decoding unit 122. Further, the reception unit 121 sends a
pilot signal in the receiving signals to the channel estimating
unit 124.
[0068] The channel estimating unit 124 compares the pilot signal
transferred from the reception unit 121 with an already-known pilot
signal, thereby obtaining a channel estimation value related to the
uplink to the base station from the mobile station as a sender.
This channel estimation value may also be obtained from, e.g.,
calculation by the least-squares method. The present invention does
not limit this channel estimating method. This channel estimation
value is transferred to the uplink transmission frame decoding unit
122 and the CQI information generation unit 125.
[0069] The uplink transmission frame decoding unit 122 demodulates
and decodes the signals received from the reception unit 121 by use
of the channel estimation value received from the channel
estimating unit 124, and acquires the CQI transmitted from the
mobile station as a signal sender of these signals from the decoded
signals. The thus-acquired CQI is transferred to the rate
determining unit 123.
[0070] The CQI information generation unit 125 generates the CQI
related to the uplink based on the channel estimation value etc
transferred from the channel estimating unit 124. This CQI may also
be generated and acquired by dividing, for example, with respect to
SINR (Signal to Interference and Noise Ratio), desired power of
each symbol ("S") by interference noise power ("I"). The desired
power of each symbol is obtained by squaring, e.g., an absolute
value of the channel estimation value, and the interference noise
power is obtained by taking, e.g., a correlation between the
receiving signal and the pilot signal. It is to be noted that the
present invention does not limit these CQI calculation methods. The
uplink-related CQI generated by the CQI information generation unit
125 is transferred to the rate determining unit 123.
[0071] The rate determining unit 123 receives the CQI transferred
from the uplink transmission frame decoding unit 122, i.e., the
downlink-related CQI generated in the mobile station and the CQI
transferred from the CQI information generation unit 125, i.e., the
uplink-related CQI generated in the base station, and determines
the predetermined coding rate and modulation method on the basis of
these CQIs. The rate determining unit 123 determines the coding
rate and the modulation method of the data channel to be
transmitted on the basis of the SINR contained in, e.g., the
downlink-related CQI, and determines the coding rate and the
modulation method to be contained in the uplink control information
on the basis of the SINR contained in the uplink-related CQI.
[0072] The rate determining unit 123 previously retains an MCS
(Modulation Coding Scheme) table as shown in FIG. 6, and determines
the coding rate and the modulation method of the data channel by
referring to this MCS table. FIG. 6 shows an example of the MCS
table, wherein the SINR is associated with the MCS. This is the
table example in a case where the CQI transmitted from each of the
mobile stations is the SINR. An identification number related to
combination of the modulation method and the coding rate is set in
an MCS field.
[0073] The rate determining unit 123, when the SINR is transmitted
as the CQI from the uplink transmission frame decoding unit 122,
refers to the MCS table and thus determines the MCS associated with
this SINR. For example, if the SINR is 3.5 decibels (dB), the rate
determining unit 123 selects MCS=2. This selection leads to such
determination that the modulation method of the data channel is
QPSK and the coding rate is 3/4. The thus determined modulation
method and coding rate of the data channel are sent to the data
structuring unit 105 and to the control information part 1
generation unit 102.
[0074] The rate determining unit 123 similarly determines, based on
the uplink-related CQI transferred from the CQI information
generation unit 125, the modulation method and the coding rate that
should be indicated to the mobile station by referring to the MCS
table. The determined modulation method and coding rate are
transferred, together with the CQI transferred from the CQI
information generation unit 125, to the control information part 2
generation unit 103. It should be noted that the first embodiment
has exemplified the example of determining the modulation method
etc on the basis of the SINR contained in the CQI, however, the
determination thereof may also be made using CQIs other than this
CQI.
[0075] The pilot generation unit 101, the control information part
1 generation unit 102, the control information part 2 generation
unit 103 and the data generation unit 104 are provided
corresponding to the frame format used in the first embodiment, and
generate pieces of data in charge of these respective units. To be
specific, the control information part 1 generation unit 102
generates the downlink control information on the basis of the
downlink-related modulation method and decoding method transferred
from the rate determining unit 123. The control information part 2
generation unit 103 generates the uplink control information on the
basis of the uplink-related modulation method and decoding method
transferred from the rate determining unit 123 and also the
uplink-related CQI transferred from the CQI information generation
unit 125. Herein, the CQI contained in the uplink control
information generated by the control information part 2 generation
unit 103 contains the uplink-related CQI generated by the CQI
information generation unit 125. Note that the CQI contained in the
uplink control information may also contain the CQI generated by
the mobile station and extracted by the uplink transmission frame
decoding unit 122.
[0076] The pilot data generated by the pilot generation unit 101 is
transferred to the multiplexing unit 109, the control information
part 1 (the downlink control information) generated by the control
information part 1 generation unit 102 is transferred to the
control information making unit 107, the control information part 2
(the uplink control information) generated by the control
information part 2 generation unit 103 is transferred respectively
to the control information making unit 107 and to the data
structuring unit 105, and the user data generated by the data
generation unit 104 is transferred to the data structuring unit
105.
[0077] The control information making unit 107 assembles the
control information part 1 and the control information part 2
together and thus generates control information data to be
allocated to the control channel in the frame format shown in FIG.
4. The control information making unit 107 encodes this control
information data at a predetermined coding rate. The coding rate
and the coding method implemented by the control information making
unit 107 involve using a coding rate and a coding method that are
fixed in the system, wherein, for instance, a convolutional coding
method using a coding rate "1/3" is employed. The encoded control
information data undergoes the predetermined modulation process by
the modulation unit 108 and is transferred to the multiplexing unit
109. The modulation method implemented by the modulation unit 108
involves using a method fixed in the system, wherein, for example,
the QPSK is employed. Note that the coding rate, the coding method
and the modulation method related to the control channel involve
the use of the methods fixed in the system and may also be
adjustably retained in a table etc. Moreover, the present invention
does not limit the coding rate, the coding method and the
modulation method related to the control channel.
[0078] The data structuring unit 105 generates the data to be
allocated to the data channel in the frame format shown in FIG. 4.
Hereat, the data structuring unit 105 compares the coding rate of
the data channel that is received from the rate determining unit
123 with the coding rate of the control channel that is fixed in
the system, thereby determining whether or not the control
information part 2 received from the control information part 2
generation unit 103 is allocated to the data channel. Specifically,
the data structuring unit 105, if the coding rate of the data
channel is lower than the coding rate of the control channel,
allocates the control information part 2 to a predetermined
location in the data channel, and, in cases other than this, does
not allocate the control information part 2 to the data
channel.
[0079] The data structuring unit 105, in the case of allocating the
control information part 2 to the data channel, attaches the
in-band information, which [presence] set in the presence/absence
information field and the allocation of the control information
part 2 set in the allocation information field, to the head of the
data to be allocated to the data channel. The data structuring unit
105, if the control information part 2 is not allocated to the data
channel, attaches the in-band information which [absence] set in
the presence/absence information field and the initial value set in
the allocation information field. The thus-generated data is coded
at the coding rate transferred from the rate determining unit 123
and is transferred to the modulation unit 106. The coding method
implemented by the data structuring unit 105 involves using the
method fixed in the system, wherein normally a turbo encoding
method is employed. The coded data is modulated by the modulation
unit 106 in a way that uses the modulation method determined by the
rate determining unit 123, and is transferred to the multiplexing
unit 109.
[0080] The multiplexing unit 109 multiplexes the pilot signal, the
control information signal and the data signal, which have been
each modulated, and transfers these multiplexed signals to the
transmission unit 110. The multiplexed signals transferred to the
transmission unit 110 are subjected to the processes such as the
digital/analog conversion and the frequency conversion, and are
transmitted from the transmitting antenna 115.
[0081] [Mobile Station]
[0082] A device configuration of each of the mobile stations 501
and 502 in the first embodiment will hereinafter be described with
reference to FIG. 7. FIG. 7 is a block diagram showing the device
configuration related to receiving functions of the mobile stations
501 and 502 in the first embodiment. Note that the mobile stations
501 and 502 are each the same device, and hence the following
discussion shall deal with the mobile station 501. The mobile
station 501 in the first embodiment includes, as the receiving
functions, a receiving antenna 130, a demultiplexing unit 132, a
demodulation unit 133, a data decoding unit 134, an error detection
unit 135, a demodulation unit 136, a control information selecting
unit 138, an error detection unit 139, a channel estimating unit
141, a control information estimating unit 142, a CQI information
generation unit 143, an uplink transmission frame generation unit
148, a transmission unit 149 and a transmitting antenna 150. Among
these components, the transmitting antenna 150, the transmission
unit 149 and the uplink transmission frame generation unit 148 are,
though taking a charge of the transmitting functions, taken up
herein as the functional units for notifying the base station 500
of the CQI.
[0083] The receiving unit 131, upon receiving the signals
transmitted from the base station 500 and received by the receiving
antenna 130, executes the processes such as the frequency
conversion and the analog/digital conversion upon these received
signals. The signals undergoing these predetermined processes are
demultiplexed by the demultiplexing unit 132 into the pilot signal,
the control information signal and the data signal. The pilot
signal is transferred to the channel estimating unit 141, the
control information signal is transferred to the demodulation unit
136, and the data signal is transferred to the demodulation unit
133.
[0084] The channel estimating unit 141 compares the pilot signal
transferred from the demultiplexing unit 132 with the already-known
pilot signal, thereby obtaining a channel estimation value related
to the downlink to the mobile station 501 from the base station
500. The present invention does not restrict this channel
estimating method, and therefore the channel estimation value may
also be obtained from, e.g., the calculation by the least-squares
method. This channel estimation value is transferred to the
demodulation units 133 and 136 and the CQI information generation
unit 143.
[0085] The CQI information generation unit 143 generates the CQI on
the basis of the channel estimation value etc transferred from the
channel estimating unit 141. The generation method by the CQI
information generation unit 143 is the same as by the CQI
information generation unit 125 in the base station device, and
hence its explanation is herein omitted.
[0086] The demodulation unit 136 demodulates the control
information signal transferred from the demultiplexing unit 132 on
the basis of the channel estimation value transferred from the
channel estimating unit 141. Further, the demodulation unit 136
demodulates the control information signal by the demodulation
method corresponding to the modulation method (QPSK) implemented by
the base station 500 with respect to the control information
signal. This demodulation method involves utilizing the method
fixed in the system as the base station 500 retains the
corresponding modulation method by way of the fixed-in-system
method. The demodulated control information signal is transferred
to the control information decoding unit 137.
[0087] The control information decoding unit 137 decodes the
control information signal transferred from the demodulation unit
136 by the decoding method corresponding to the coding rate (1/3)
and the coding method (the convolutional coding method) implemented
by the base station 500 with respect to the control information
signal. This decoding method involves utilizing the method fixed in
the system as the base station 500 retains the corresponding coding
rate and coding method by way of the fixed-in-system method. The
decoded control information data is sent to the error detection
unit 139 and to the control information selecting unit 138.
[0088] The error detection unit 139 detects an error by checking
the CRC allocated to the control channel. The error detection unit
139 sends a detection result to the control information selecting
unit 138.
[0089] The control information selecting unit 138 selects the
control information used for the demodulation of the data channel
in accordance with the detection result sent from the error
detection unit 139. The control information selecting unit 138, if
the detection result shows no error (normal), acquires the control
information part 1 and the control information part 2 in the
control information data sent from the control information decoding
unit 137. The modulation method in the control information part 1
is transferred to the demodulation unit 133, and the coding rate in
the control information part 1 is transferred to the data decoding
unit 134. The control information part 2 is transferred as it is to
the data decoding unit 134. Whereas if the detection results shows
occurrence of the error, the control information selecting unit 138
sends the control information part 1 estimated by the control
information estimating unit 142 respectively to the demodulation
unit 133 and to the data decoding unit 134, and notifies the data
decoding unit 134 of the occurrence of the error.
[0090] The control information estimating unit 142 estimates the
control information part 1 on the basis of the SINR contained in
the CQI given from the CQI information generation unit 143. The
control information part 1 is, as described above, the information
generated in the base station 500 on the basis of the SINR that is
fed back from the mobile station 501, and can therefore be
generated in the mobile station 501 as well. Namely, the control
information estimating unit 142 previously retains the MCS table as
shown in FIG. 6 and determines the coding rate and the modulation
method by referring to this MCS table. The control information part
1 is obtained by employing the thus-determined coding rate and
modulation method. The thus-estimated control information part 1 is
sent to the control information selecting unit 138.
[0091] The demodulation unit 133 demodulates the data signal
transferred from the demultiplexing unit 132 on the basis of the
channel estimation value transferred from the channel estimating
unit 141. The demodulation unit 133 further demodulates this
demodulated data signal by the demodulation method corresponding to
the modulation method received from the control information
selecting unit 138. The demodulated data is sent to the data
decoding unit 134.
[0092] The data decoding unit 134 decodes the demodulated data on
the basis of the coding rate and the coding method received from
the control information selecting unit 138. The decoded data is
transferred to the error detection unit 135. Moreover, the data
decoding unit 134 extracts the in-band information allocated to the
head of the decoded data. The data decoding unit 134, if the
[presence] is set in the presence/absence information field of this
in-band information, extracts the control information part 2 from
the decoded data on the basis of the location (address) information
set in the same location information field. The data decoding unit
134, based on the error detection result of which the error
detection unit 135 has notified, if this detection result shows no
error (normal), outputs the decoded user data to other functional
units (unillustrated), and sends the control information part 2 to
the uplink transmission frame generation unit 148.
[0093] Note that as for this control information part 2, if the
information showing [absence] is set in the presence/absence
information field of the in-band information, the control
information part 2 received from the control information selecting
unit 138 may be sent to the uplink transmission frame generation
unit 148, and, if the information showing [presence] is set in the
presence/absence information field of the in-band information, the
control information part 2 extracted by the data decoding unit 134
may also be sent.
[0094] The error detection unit 135 detects the error by checking
the CRC with respect to the decoded data. This error detection
result is fed back to the data decoding unit 134.
[0095] The uplink transmission frame generation unit 148 sets, as
the control information, the control information part 2 received
from the data decoding unit 134 and the CQI information received
from the CQI information generation unit 143, and generates a
transmission frame from this control information and from the user
data received from other functional units (unillustrated). At this
time, the uplink transmission frame generation unit 148 encodes the
control information at the predetermined coding rate (1/3) and by
the predetermined coding method (convolutional coding), and
modulates the coded control information by the fixed-in-system
modulation method (QPSK). Further, the user data undergoes the
predetermined coding at the coding rate contained in the control
information part 2 received from the data decoding unit 134, and is
modulated by the modulation method contained in the same control
information part 2. The thus-generated uplink transmission frame is
subjected to the processes such as the digital/analog conversion
and the frequency conversion and is transmitted from the
transmitting antenna 150.
OPERATIONAL EXAMPLE
[0096] Operations of the base station 500 and the mobile stations
501 and 502 in the first embodiment will hereinafter be explained.
To start with, the transmitting operation of the base station 500
in the first embodiment will be explained with reference to FIG.
5.
[0097] The base station 500, when transmitting the data to the
mobile station 501, transmits the data without conducting the
in-band of the control information part 2. This is because the data
structuring unit 105 determines not to allocate the control
information part 2 to the data channel, since the coding rate of
the data channel regarding the transmitted wireless frame that is
determined by the rate determining unit 123 does not get lower than
the coding rate of the control channel that is fixed in the
system.
[0098] On the other hand, the base station 500, on the occasion of
transmitting the data to the mobile station 502, transmits the data
conducted the in-band of the control information part 2. In this
case, a CQI value of which the mobile station 502 notifies is very
poor quality, and the coding rate of the data channel, which is
determined by the rate determining unit 123, becomes lower than the
fixed-in-system coding rate of the control channel. This being the
case, the data structuring unit 105 allocates the control
information part 2 to the data channel.
[0099] Next, a receiving operation of each of the mobile stations
501 and 502 in the first embodiment will be explained with
reference to FIG. 8. FIG. 8 is a flowchart showing an example of
the receiving operation of each of the mobile stations 501 and 502
in the first embodiment.
[0100] The demultiplexing unit 132, upon receiving the received
signals from the reception unit 131, demultiplexes these received
signals into the pilot signal, the control information signal and
the data signal. The channel estimating unit 141 estimates the
channel between the base station and the mobile station from the
thus-demultiplexed pilot signal (S801). The thus-estimated channel
estimation value is sent to the demodulation unit 136 related to
the control information signal, and the control information signal
is demodulated based on the channel estimation value by the
demodulation unit 136. Further, the demodulation unit 136
demodulates the control information signal by the demodulation
method corresponding to the modulation method (QPSK) implemented by
the base station 500 (S802). Still further, the control information
decoding unit 137 decodes the thus-demodulated control information
data by the decoding method corresponding to the coding rate (1/3)
and the coding method (convolutional coding) implemented by the
base station 500 (S802).
[0101] The decoded control information data is sent to the error
detection unit 139, wherein the CRC is checked by the error
detection unit 139. As a result, if judged to have no error (S803;
YES), the control information selecting unit 138 transfers the
control information part 1 contained in the control information
data to the demodulation unit 133 and to the data decoding unit
134. The demodulation unit 133 demodulates the data signal sent
from the demultiplexing unit 132 on the basis of the channel
estimation value given from the channel estimating unit 141, and
further demodulates the data signal by the demodulation method
corresponding to the modulation method contained in the control
information part 1 received from the control information selecting
unit 138 (S804). Note that at this time, the control information
selecting unit 138, when the control information part 2 is
allocated to the control channel, extracts and transfers this
control information part 2 to the data decoding unit 134.
[0102] While on the other hand, if the error detection unit 139
judges that there is an error (S803; NO), the control information
estimating unit 142 estimates the modulation method and the coding
rate from the CQI (SINR) given from the CQI information generation
unit 143 (S805). An estimation method by this control information
estimating unit 142 is the same as the determination method of
determining the modulation method and the coding rate by the rate
determining unit 123 of the base station 500. This estimated
modulation method is sent to the demodulation unit 133, while the
estimated coding rate is sent to the data decoding unit 134. With
this operation, if the error occurs in the control channel, the
demodulation unit 133 demodulates the data by the modulation method
estimated by the control information estimating unit 142
(S806).
[0103] The data decoding unit 134, if the error occurs in the
control channel, executes predetermined decoding corresponding to
the coding rate estimated by the control information estimating
unit 142, and, if the error does not occur in the control channel,
executes predetermined decoding corresponding to the coding rate
set in the control information part 1 of the control channel
(S807). The decoded CRC is checked by the error detection unit 135,
thereby checking whether or not the error occurs in the data
allocated to the data channel. Then, if judged to have the error in
the data (S808; NO), a retransmission request is made.
[0104] The data decoding unit 134, if judged to have no error from
the information, showing whether or not the error occurs in the
control channel, of which the control information selecting unit
138 has notified (S809; YES), sends the control information part 2
in the control channel to the uplink transmission frame generation
unit 148. Whereas if judged to have the error (S809; NO) and if the
in-band is conducted (S810; YES), the data decoding unit 134 sends
the control information part 2 allocated (in-band) into the data
channel to the uplink transmission frame generation unit 148
(S811). Note that if the error occurs in the control channel (S809;
NO) and if the in-band is not conducted (S810; NO), the
retransmission request is made.
Operation and Effect in Embodiment
[0105] The wireless communication system in the first embodiment
involves employing the frame format, wherein the control
information, which should be originally transmitted by the control
channel, is segmented into the control information part 1
consisting of the downlink control information and into the control
information part 2 consisting of the uplink control information,
and the control information part 2 is dually allocated to the
control channel and to the data channel.
[0106] In the base station 500, the data structuring unit 105
compares the data channel coding rate determined by the rate
determining unit 123 with the fixed-in-system coding rate of the
control channel, and thus determines whether or not the control
information part 2 is allocated (in-band) into the data channel.
The rate determining unit 123 determines the coding rate etc of the
data channel, corresponding to the channel status (CQI) with the
mobile station as the transmission destination. Then, in the case
of transmitting to the mobile station that is located in the
vicinity of the base station 500 and in a good channel status as
the mobile station 501 is, the wireless frame format without
conducting the in-band of the control information part 2 is used.
On the other hand, in the case of transmitting to the mobile
station that is located at the cell edge and in a channel status of
very poor quality as the mobile station 502 is, the wireless frame
format with conducting the in-band of the control information part
2 is used.
[0107] Thus, in the first embodiment, the determination is made
corresponding to the channel status with the mobile station as the
transmission destination so as not to conduct the in-band in the
case of the preferable channel status (the case where the coding
rate of the data channel does not become lower than the coding rate
of the control channel) and so as to conduct the in-band in the
case of the poor channel status (the case where the coding rate of
the data channel gets lower than the coding rate of the control
channel).
[0108] The use of this type of frame format, according to the first
embodiment, eliminates the necessity of increasing the size of the
control channel and does not cause an extreme rise in the overhead
of the transmission frame.
[0109] In the mobile station, the control information signal in the
control channel is demodulated and decoded by the fixed-in-system
demodulation method, coding rate and decoding method. The
demodulated and decoded control information data is checked the CRC
by the error detection unit 139, thereby checking whether or not
the error exists in the control information data. Herein, if judged
to have the error, the control information data can not be used,
and hence the control information estimating unit 142 estimates the
modulation method and the coding rate on the basis of the CQI
generated by the CQI information generation unit 143. Hereafter,
the data in the data channel is, if no error exists in the control
channel, demodulated and decoded based on the control information
in the control channel, and is, if the error exists in the control
channel, demodulated and decoded by the modulation method, the
coding rate and the decoding method that are estimated by the
control information estimating unit 142.
[0110] Thus, in the first embodiment, even when the error occurs in
the data in the control channel, the control information, which
should be allocated to the control channel concerned, is estimated
by the same method as the generation method of the base station 500
as a generator of the control information, and the data channel is
demodulated and decoded by use of the thus-estimated control
information.
[0111] Accordingly, if the error occurs in the control channel,
there was no alternative but to prompt the retransmission to be
done, however, according to the first embodiment, the data channel
can be demodulated and decoded based on the equal control
information, thereby eliminating the necessity of prompting the
retransmission to be done. With this effect, even when the error
frequently occurs in the control channel in the communications with
the mobile station located at the cell edge, it is possible to
avoid a phenomenon of causing a decrease in transmission efficiency
of the system as a whole by repeating the retransmission.
[0112] Further, in the mobile station, if the error occurs in the
control channel and when the control information part 2 is
allocated (in-band) into the data channel, the uplink transmission
frame is generated based on the control information part 2 in the
data channel.
[0113] Thus, in the first embodiment, even if originally unable to
acquire the uplink control information contained in the control
information due to the occurrence of the error in the control
channel, the uplink transmission control information is allocated
(in-band) into the data channel, and therefore the frame for the
uplink transmission is generated by use of the uplink transmission
control information conducted the in-band.
[0114] Accordingly, this configuration also enables a
retransmission request frequency to be decreased and, more
essentially, a throughput of the whole system to be improved.
Second Embodiment
[0115] The wireless communication system according to a second
embodiment of the present invention will hereinafter be described.
The wireless communication system according to the first embodiment
discussed above uses the frame format corresponding to the example
shown in FIG. 1 as discussed in the item of Outline of Embodiments
of the Invention, i.e., the frame format having the structure in
which the control information part 2 is dually allocated to the
control channel (CCH) and to the data channel (DCH). The wireless
communication system in the second embodiment uses the frame format
corresponding to the example illustrated in FIG. 2 discussed in the
item of Outline of Embodiments of the Invention. The description
shall be focused on different functional units from those in the
first embodiment with respect to the base station 500 and the
mobile stations 501, 502 that configure the wireless communication
system in the second embodiment. A configuration in the second
embodiment in the following discussion is an exemplification, and
the present invention is not limited to the following
configuration. Note that the system architecture is the same as in
the case of the first embodiment, and hence its explanation is
omitted.
[0116] [Frame Format]
[0117] The frame format used in the wireless communication system
in the second embodiment will be described with reference to FIGS.
9 and 10. FIGS. 9 and 10 are diagrams each showing the frame format
in the second embodiment, and illustrating the format of the frame
(the downlink frame) transmitted from the base station 500 to the
mobile station 501 or 502. The frame format in the second
embodiment corresponds to the example shown in FIG. 2 discussed in
the item of Outline of Embodiments of the Invention, and has a
structure in which the control information part 2 is allocated to
only the data channel (DCH). FIG. 9 shows the frame format in a
case where the in-band is not conducted, and FIG. 10 shows the
frame format in a case where the in-band is conducted.
[0118] The segmentation method of the control information in the
second embodiment shall be the same as that in the first
embodiment. Namely, the downlink control information is defined as
the control information part 1 (PART 1), and the uplink control
information is defined as the control information part 2 (PART 2).
Further, the detailed information contained in the uplink control
information and the detailed information contained in the downlink
control information are the same as those in the first
embodiment.
[0119] In the frame format in the second embodiment, a header
channel (HCH) is attached. The header channel contains the in-band
information and the CRC. The in-band information contains the
presence/absence information showing whether the control
information part 2 is allocated (in-band) in the data channel or
not and the allocation information showing a location where the
control information part 2 in the data channel is allocated. A
piece of identifying information showing [presence] in the case of
conducting the in-band is set in the presence/absence information
field, and the identifying formation showing [absence] in the case
of conducting none of the in-band is set in the presence/absence
information field. A piece of information showing, in the case of
conducting the in-band, an in-band location of the control
information part 2 in the data channel, is set in the allocation
information field. A CRC bit related to the data contained in the
header channel is set in the CRC field.
[0120] In the frame format in the case of conducting none of the
in-band shown in FIG. 9, both of the control information part 1 and
the control information part 2 are allocated to the control
channel, and only the user data is allocated to the data channel.
On the other hand, in the frame format in the case of conducting
the in-band shown in FIG. 10, the control information part 1 is
allocated to the control channel, while the control information
part 2 is allocated to the data channel. In this case, the user
data and the control information part 2 are each allocated to the
data channel.
[0121] [Base Station]
[0122] A device configuration of the base station 500 in the second
embodiment will hereinafter be described with reference to FIG. 11.
FIG. 11 is a block diagram showing the device configuration related
to the transmitting functions of the base station 500 in the second
embodiment. The base station 500 in the second embodiment includes,
as the transmitting functions, in addition to the configuration in
the first embodiment, a header generation unit 171 and a modulation
unit 172. As the functional units other than these units, the
functions related to the data structuring unit 105 and the
multiplexing unit 109 are changed, and hence these units are
exclusively explained, while the remaining functional units are the
same as those in the first embodiment and are therefore omitted in
their explanations.
[0123] The data structuring unit 105 generates the data that is
allocated to the data channel in the frame format shown in FIG. 9
or 10. Hereat, the data structuring unit 105 compares the coding
rate of the data channel that is received from the rate determining
unit 123 with the fixed-in-system coding rate of the control
channel, and thus determines whether the control information part 2
received from the control information part 2 generation unit 103 is
conducted the in-band or not. Specifically, the data structuring
unit 105, if the coding rate of the data channel is lower than the
coding rate of the control channel, allocates the control
information part 2 to a predetermined location in the data channel
but does not allocate the control information part 2 into the data
channel in cases other than this. The data structuring unit 105, in
the case of conducting the in-band of the control information part
2, notifies the header generation unit 171 of a purport that the
in-band is conducted and of a location (an offset address etc) of
the control information part 2.
[0124] The header generation unit 171 generates, based on the
notification given from the data structuring unit 105, the in-band
information data and the CRC data that are allocated to the header
channel. The header generation unit 171, with respect to the
in-band information data, sets the presence or absence of the
in-band, of which the data structuring unit 105 has notified, in
the presence/absence information field, and sets the
similarly-notified location of the control information part 2 in
the allocation information field, thereby generating the in-band
information data. Then, the header generation unit 171 generates
the CRC bit on the basis of the thus-generated in-band information
data.
[0125] The header generation unit 171 encodes the thus-generated
data by the predetermined coding rate. The coding rate and the
coding method implemented by this header generation unit 171
involve using the fixed-in-system coding rate and coding method,
wherein, for example, the convolutional coding method having the
coding rate 1/3 is used. The coded data is subjected to the
predetermined modulation process by the modulation unit 172 and is
transferred to the multiplexing unit 109. The modulation method
implemented by the modulation unit 172 also involves using the
fixed-in-system method, wherein, for instance, the QPSK is used.
Note that the coding rate, the coding method and the modulation
method concerning the header channel involve employing the
fixed-in-system methods and may also be retained adjustably in a
table and so on. Moreover, the present invention does not limit the
coding rate, the coding method and the modulation method related to
the header channel.
[0126] The multiplexing unit 109 multiplexes each of the modulated
pilot signal, control information signal, data signal and header
signal, and transfers these multiplexed signals to the transmission
unit 110. The multiplexed signals transferred to the transmission
unit 110 undergo the processes such as the digital/analog
conversion and the frequency conversion, and are transmitted from
the transmitting antenna 115.
[0127] [Mobile Station]
[0128] A device configuration of each of the mobile stations 501
and 502 in the second embodiment will hereinafter be described with
reference to FIG. 12. FIG. 12 is a block diagram showing the device
configuration related to the receiving functions of the mobile
stations 501 and 502 in the second embodiment. Note that the mobile
stations 501 and 502 are each the same device, and hence the
following discussion shall deal with the mobile station 501. The
mobile station 501 in the second embodiment includes, as the
receiving functions, in addition to the configuration in the first
embodiment, a demodulation unit 181 and a header decoding unit 182.
As the functional units other than these units, the functions
related to the demultiplexing unit 132, the control information
selecting unit 138 and the data decoding unit 134 are changed, and
hence these units are exclusively explained, while the remaining
functional units are the same as those in the first embodiment and
are therefore omitted in their explanations.
[0129] The demultiplexing unit 132, upon receiving the received
signals from the reception unit 131, at first demultiplexes the
header signal and the pilot signal therefrom. The demultiplexed
pilot signal is transferred to the channel estimating unit 141. The
header signal is transferred to the demodulation unit 181. The
demultiplexing unit 132, when receiving the decoded data from the
header decoding unit 182, refers to the in-band information in the
received data, thereby judging the presence or absence of the
in-band. To be specific, the demultiplexing unit 132, when the
identifying information showing [presence] is set in the
presence/absence information field in the in-band information,
judges that the in-band is set, and further acquires the location
information of the control information part 2 set in the allocation
information field. Conversely, the demultiplexing unit 132, when
the identifying information showing [absence] is set in the
presence/absence information field in the in-band information,
judges that the in-band is not conducting.
[0130] In the second embodiment, the sizes of the control channel
and of the data channel change depending on the presence of the
in-band (see FIGS. 9 and 10), and therefore the demultiplexing unit
132 demultiplexes the control channel and the data channel in
accordance with a result of the judgment as to the presence of the
in-band. The demultiplexed control information signal is
transmitted together with the in-band information to the
demodulation unit 133.
[0131] The demodulation unit 181 demodulates the header signal
transferred from the demultiplexing unit 132 on the basis of the
channel estimation value transferred from the channel estimating
unit 141. Moreover, the demodulation unit 181 demodulates the
header signal by the demodulation method corresponding to the
modulation method (QPSK) implemented by the base station 500. This
demodulation method involves utilizing the fixed-in-system method
as the corresponding modulation method is retained as the
fixed-in-system method in the base station 500. The demodulated
header signal is transferred to the header decoding unit 182.
[0132] The header decoding unit 182 decodes the header signal
transferred from the demodulation unit 181 by the decoding method
corresponding to the coding rate (1/3) and the coding method
(convolutional coding method) implemented by the base station 500
with respect to the header signal. This decoding method involves
utilizing the fixed-in-system method as the corresponding coding
rate and the corresponding coding method are retained as the
fixed-in-system method in the base station 500. The decoded pieces
of data, i.e., the in-band information and the CRC are sent to the
demultiplexing unit 132.
[0133] The control information selecting unit 138 receiving the
in-band information via the demodulation unit 136 and via the
control information decoding unit 137 from the demultiplexing unit
132, selects the control information used for the demodulation of
the data channel, corresponding to this in-band information and to
a detection result sent from the error detection unit 139. The
control information selecting unit 138, when the [presence] is set
in the presence/absence information field in the in-band
information and when the detection result shows no error, sends the
modulation method in the control information part 1 transmitted
from the control information decoding unit 137 to the demodulation
unit 133, and sends the coding rate therein to the data decoding
unit 134. The control information selecting unit 138, when the
[absence] is set in the presence/absence information field in the
in-band information and when the detection result shows no error
(normal), acquires respectively the control information part 1 and
the control information part 2 in the control information data sent
from the control information decoding unit 137. The modulation
method in the control information part 1 is sent to the
demodulation unit 133, the coding rate therein is sent to the data
decoding unit 134, and the control information part 2 is sent as it
is to the data decoding unit 134. Further, when the [presence] is
set in the presence/absence information field in the in-band
information and when the detection result shows the error
occurrence, the control information selecting unit 138 sends the
control information part 1 estimated by the control information
estimating unit 142 to the demodulation unit 133 and to the data
decoding unit 134, respectively. When the [absence] is set in the
presence/absence information field in the in-band information and
when the detection result shows the error occurrence, the control
information selecting unit 138 specifies a process of a request for
the retransmission (unillustrated).
[0134] The data decoding unit 134 decodes the demodulated data on
the basis of the coding rate and the coding method received from
the control information selecting unit 138. The decoded data is
transferred to the error detection unit 135. Further, the data
decoding unit 134 extracts the control information part 2 from the
decoded data on the basis of the in-band information transferred
via the demodulation unit 133 from the demultiplexing unit 132. To
be specific, the data decoding unit 134, if the identifying
information showing the [presence] is set in the presence/absence
information field in the in-band information, extracts the control
information part 2 from the decoded data on the basis of the
location (address) set in the same allocation information field.
The data decoding unit 134, based on the error detection result of
which the error detection unit 135 has notified, if this detection
result shows no error (normal), outputs the decoded user data to
other functional units (unillustrated), and sends the control
information part 2 to the uplink transmission frame generation unit
148. Further, the data decoding unit 134, if the identifying
information showing the [absence] is set in the presence/absence
information field in the in-band information and if the error
detection result of which the error detection unit 135 has notified
shows no error (normal), outputs the decoded user data to other
functional units (unillustrated), and sends the control information
part 2 transmitted from the control information selecting unit 138
to the uplink transmission frame generation unit 148.
OPERATIONAL EXAMPLE
[0135] Operations of the base station 500 and the mobile stations
501, 502 in the second embodiment will hereinafter be described. To
begin with, the transmitting operation of the base station 500 in
the second embodiment will be explained with reference to FIG.
11.
[0136] The base station 500, when transmitting the data to the
mobile station 501, transmits the data without conducting the
in-band of the control information part 2. This is because the data
structuring unit 105 determines not to allocate the control
information part 2 to the data channel, since the coding rate of
the data channel regarding the transmitted wireless frame that is
determined by the rate determining unit 123 does not get lower than
the fixed-in-system coding rate of the control channel. In this
case, the information showing the [absence] is set in the
presence/absence information field in the in-band information
generated by the header generation unit 171.
[0137] On the other hand, the base station 500, on the occasion of
transmitting the data to the mobile station 502, transmits the data
conducted the in-band of the control information part 2. In this
case, a CQI value of which the mobile station 502 notifies is very
poor quality, and the coding rate of the data channel, which is
determined by the rate determining unit 123, becomes lower than the
fixed-in-system coding rate of the control channel. This being the
case, the data structuring unit 105 allocates the control
information part 2 to the data channel. In this case, the
information showing the [presence] is set in the presence/absence
information field in the in-band information generated by the
header generation unit 171, and the location information of the
control information part 2 in the data channel is set in the
allocation information field.
[0138] Next, a receiving operation of each of the mobile stations
501 and 502 in the second embodiment will be explained with
reference to FIGS. 12 and 13. FIG. 13 is a flowchart showing an
example of the receiving operation of each of the mobile stations
501 and 502 in the second embodiment.
[0139] The demultiplexing unit 132, upon receiving the received
signals from the reception unit 131, demultiplexes the pilot signal
and the header signal from these received signals. The channel
estimating unit 141 estimates the channel between the base station
and the mobile station from the thus-demultiplexed pilot signal
(S1301). The thus-estimated channel estimation value is sent to the
demodulation unit 181 related to the header signal, and the header
signal is demodulated based on the channel estimation value by the
demodulation unit 181. Further, the demodulation unit 181
demodulates the header signal by the demodulation method
corresponding to the modulation method (QPSK) implemented by the
base station 500 (S1302). Still further, the header decoding unit
182 decodes the thus-demodulated header data by the decoding method
corresponding to the coding rate (1/3) and the coding method
(convolutional coding) implemented by the base station 500
(S1302).
[0140] The demultiplexing unit 132 checks the decoded CRC allocated
to the header channel and thus judges whether the error occurs in
the header channel or not. Herein, if the error exists in the
header channel (S1303; NO), the processing is terminated. Whereas
if no error exists in the header channel (S1303; YES), the
demultiplexing unit 132 grasps, based on the in-band information
transferred from the header decoding unit 182, whether the in-band
of the control information part 2 is conducted or not, and
demultiplexes the control signal and the data signal from the
receiving signals.
[0141] The demodulation unit 136 demodulates the demultiplexed
control signal on the basis of the channel estimation value.
Further, the demodulation unit 136 demodulates the control
information signal by the demodulation method corresponding to the
modulation method (QPSK) implemented by the base station 500
(S1304). Still further, the control information decoding unit 137
decodes the demodulated control information data by the decoding
method corresponding to the coding rate (1/3) and the coding method
(convolutional coding) implemented by the base station 500
(S1304).
[0142] The decoded control information data is sent to the error
detection unit 139 and is CRC-checked by the error detection unit
139. As a result, if judged to have no error (S1305; YES), the
control information selecting unit 138 transfers the control
information part 1 contained in the control information data to the
demodulation unit 133 and to the data decoding unit 134. The
demodulation unit 133 demodulates the data signal given from the
demultiplexing unit 132 on the basis of the channel estimation
value given from the channel estimating unit 141, and further
demodulates the data signal by the demodulation method
corresponding to the modulation method contained in the control
information part 1 received from the control information selecting
unit 138 (S1306). Note that at this time, the control information
selecting unit 138, if the control information part 2 is allocated
in the control channel, extracts and transfers this control
information part 2 to the data decoding unit 134.
[0143] Whereas if the error detection unit 139 judges that the
error exists (S1305; NO), the control information estimating unit
142 estimates the modulation method and the coding rate from the
CQI (SINR) given from the CQI information generation unit 143
(S1307). The estimating method by this control information
estimating unit 142 is the same as the determination method of
determining the modulation method and the coding rate by the rate
determination unit 123 in the base station 500. This estimated
modulation method is sent to the demodulation unit 133, and the
estimated coding rate is sent to the data decoding unit 134. With
this operation, if the error occurs in the control channel, the
demodulation unit 133 demodulates the data by the modulation method
estimated by the control information estimating unit 142
(S1308).
[0144] The data decoding unit 134, if the error occurs in the
control channel, executes the predetermined decoding corresponding
to the coding rate estimated by the control information estimating
unit 142, and, whereas if the error does not occur in the control
channel, executes the predetermined decoding corresponding to the
coding rate set in the control information part 1 of the control
channel (S1309). The error detection unit 135 checks the decoded
CRC, thereby checking whether or not the error occurs in the data
allocated to the data channel. Then, if judged to have the error
(S1310; NO), the retransmission request is made.
[0145] The data decoding unit 134, if judged to have no error from
the information showing whether or not the error occurs in the
control channel of which the control information selecting unit 138
has notified (S1311; YES), sends the control information part 2 in
the control channel to the uplink transmission frame generation
unit 148. Whereas if judged to have the error (S1311; NO) and if
the in-band is conducted (S1312; YES), the data decoding unit 134
sends the control information part 2 allocated (in-band) to the
data channel of the uplink transmission frame generation unit 148
(S1313). Note that if judged to have the error in the control
channel (S1311; NO) and if the in-band is not conducted (S1312;
NO), the retransmission request is made.
Operation and Effect in Embodiment
[0146] In the wireless communication system in the second
embodiment, the case of conducting the in-band involves employing
the frame format in which the control information part 2 is
allocated to only the data channel. Corresponding to this frame
format, in the frame in the second embodiment, the header channel
containing the in-band information is attached. This is because the
size of the control channel in this frame format is variable
depending on the case of conducting the in-band and the case of
conducting none of the in-band.
[0147] With this operation, the mobile station receiving the frame
can judge the presence or absence of the in-band simply by
referring to the in-band information in this header channel.
Further, the attached in-band information after all contains
nothing but the presence/absence information and the allocation
information, and therefore the overhead of the transmission frame
does not extremely increase.
[0148] Further, when transmitting to the mobile station in the
channel status that is as bad as requiring the in-band, the uplink
control information is allocated to the data channel, and hence the
size of the control channel can be reduced. This, according to the
second embodiment, enables the overhead of the transmission frame
to be reduced.
[0149] <Others>
[0150] The disclosures of Japanese patent application
No.JP2006-069037, filed on Mar. 14, 2006 including the
specification, drawings and abstract are incorporated herein by
reference.
* * * * *