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Description
Title of Invention
WIRELESS COMMUNICATION DEVICE, WIRELESS COMMUNICATION
5 SYSTEM, WIRELESS COMMUNICATION METHOD, AND PROGRAM
Technical Field
[0001]
The present disclosure relates to a wireless communication device, a
10 wireless communication system, a wireless communication method, and a program.
Background Art
[0002]
Currently, in third generation partnership project (3GPP), standardization of
15 a wireless communication system for 4G has been promoted. In 40, a technology
such as relay, carrier aggregation, coordinated multiple point transmission and
reception (CoMP), and multi user multi input multi output (MU-MIMO) has been
attracting attention.
[0003]
20 Relay is considered as an important technology to improve a throughput of a
cell edge. In addition, carrier aggregation is a technology that can handle a band
width of 20MHzx5=100MHz by handling, for example, five frequency bands each
having a band width of 20MHz, together. By such carrier aggregation,
improvement of a maximum throughput can be expected.
25 [0004]
In addition, CoMP is a technology in which a plurality of base stations
transmit and receive data in cooperation in order to improve coverage of a high data
rate. In addition, MU-MIMO is a technology that improves a system throughput so
that a plurality of users use a resource block of the same frequency and the same time,
30 on which spatial multiplexing is performed. As described above, further
improvement ofthe performance in 4G (LTE-Advanced) by various technologies has
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been discussed.
[0005]
Here, MV-MIMO is described in detail. In 3.9G (LTE), there are
technologies of MU-MIMO and single user MINO (SV-MIMO). For example, as
5 discussed in Patent literature 1, SV-MIMO is a technology in which a plurality of
channels are used so that single user equipment (DE) performs spatial multiplexing
of the plurality of channels although spatial multiplexing is not performed between
pieces ofVE.
[0006]
10 On the other hand, as described above, MU-MIMO is a technology in which
each VE uses a resource block of the same frequency and the same time, on which
spatial multiplexing is performed (spatial multiplexing is performed between pieces
of UE). However, in MU-MIMO that is realized in 3.90, each VE handles a mere
single channel. On the contrary, in 40, MV-MIMO in which each UE can handle a
15 plurality of channels is being realized.
[0007]
In order to achieve such MU-MIMO in 40, it has been studied that two
types (VI and V2) of transmission weight are used in a base station. The VI is
transmission weight that realizes directivity, and the V2 is transmission non-
20 directional weight, the main purpose of which is to adjust a phase. The VI and V2
can be determined, for example, in UE. To be more specific, the UE receives a
reference signal that is transmitted from a base station, obtains a channel matrix H
from the reception result of the reference signal, and determines optimal V1 and V2
for the channel matrix H.
25
Citation List
Patent Literature
[0008]
30
Patent Literature 1: JP 2005-184730A
Summary of Invention
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Technical Problem
[0009]
However, high calculation load in UE for determining transmission weight
VI and transmission weight V2 is concerned because the transmission weight VI and
5 transmission weight V2 are complex numbers.
[0010]
Therefore, in the present disclosure, there are proposed a new and improved
wireless communication device, wireless communication system, wireless
communication method, and program that can suppress calculation load in a
10 communication partner for determining transmission weight.
Solution to Problem
[0011]
According to an embodiment of the present disclosure, there is provided a
15 wireless communication device including a communication unit that transmits a
reference signal, a fIrst multiplication unit that performs multiplication of fIrst
transmission weight that is determined based on reception of the reference signal by
a communication partner, and a second multiplication unit that performs
multiplication of second transmission weight that is determined based on reception of
20 the reference signal by the communication partner. The communication unit
transmits a reference signal with weight that is obtained by multiplying the reference
signal by the fIrst transmission weight after determination of the fIrst transmission
weight.
[0012]
25 The wireless communication device may further includes a reference signal
management unit that manages a resource for transmitting the reference signal with
weight.
[0013]
The reference signal management unit may allocate a resource for
30 transmitting the reference signal with weight and a resource for transmitting the
reference signal after determination ofthe fIrst transmission weight.
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[0014]
The reference signal management unit may allocate more resources for
transmitting the reference signal than the resource for transmitting the reference
signal with weight.
5 [0015]
The reference signal management unit may allocate a resource so that
transmission frequency of the reference signal on a time axis becomes higher than
transmission frequency of the reference signal with weight on the time axis.
[0016]
10 The reference signal management unit may allocate a resource so that a
density of a resource for transmitting the reference signal on a frequency axis
becomes higher than a density of a resource for transmitting the reference signal with
weight on the frequency axis.
[0017]
15 The wireless communication device may further include a scheduler that
allocates a resource for communication of a first scheme or a second scheme to each
communication partner. The scheduler may allocate a resource within a first
frequency range for the communication of the first scheme, and allocate a resource
within a second frequency range for the communication ofthe second scheme.
20 [0018]
The first frequency range may be a frequency range to which a resource for
transmitting the reference signal with weight is allocated. The second frequency
range may be a frequency range to which a resource for transmitting the reference
signal is allocated.
25 [0019]
The first scheme may be multi user multi input multi output (MU-MIMO),
the second scheme may be single user multi input multi output (SU-MIMO).
[0020]
The wireless communication device may further include a scheduler that
30 allocates a resource for communication of a first scheme or a second scheme to each
communication partner. The scheduler may allocate, for the communication of the
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first scheme, a resource within a frequency range to which a resource for transmitting
the reference signal with weight is allocated, and allocate, for the communication of
the first scheme or the second scheme, a resource within a frequency range to which
a resource for transmitting the reference signal is allocated.
5 [0021]
Update frequency of the second transmission weight may be higher than
update frequency ofthe first transmission weight.
[0022]
The first transmission weight may be weight for forming directivity, and the
10 second transmission weight may be non-directional weight for adjusting a phase.
[0023]
Further, according to another embodiment of the present disclosure, there is
provided a program for causing a computer to function as a wireless communication
device that includes a communication unit that transmits a reference signal, a first
15 multiplication unit that performs multiplication of first transmission weight that is
determined based on reception of the reference signal by a communication partner,
and a second multiplication unit that performs multiplication of second transmission
weight that is determined based on reception of the reference signal by the
communication partner. The communication unit may transmit a reference signal
20 with weight that is obtained by multiplying the reference signal by the first
transmission weight after determination ofthe first transmission weight.
[0024]
Further, according to another embodiment of the present disclosure, there is
provided a wireless communication method including transmitting a reference signal,
25 multiplying the reference signal by first transmission weight that is determined based
on reception of the reference signal by a communication partner, and transmitting a
reference signal with weight that is obtained by multiplying the reference signal by
the first transmission weight.
[0025]
30 Further, according to another embodiment of the present disclosure, there is
provided a wireless communication system including a first wireless communication
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device, and a second wireless communication device that includes, a communication
unit that transmits a reference signal, a first multiplication unit that performs
multiplication of first transmission weight that is determined based on reception of
the reference signal by the first wireless communication device, and a second
5 multiplication unit that performs multiplication of second transmission weight that is
determined based on reception of the reference signal by the first wireless
communication device. The communication unit transmits a reference signal with
weight that is obtained by multiplying the reference signal by the first transmission
weight after determination of the first transmission weight.
10 [0026]
Further, according to another embodiment of the present disclosure, there is
provided a wireless communication device including a communication unit that
receives a reference signal from a communication partner, and a weight
determination unit that determines first transmission weight and second transmission
15 weight based on a reception result of the reference signal by the communication unit.
When a reference signal with weight that is obtained by multiplying the reference
signal by the first transmission weight is received by the communication unit, the
weight determination unit determines the second transmission weight based on a
reception result of the reference signal with weight.
20 [0027]
Further, according to another embodiment of the present disclosure, there is
provided a wireless communication device including a scheduler that allocates a
resource for communication of a first scheme or a second scheme to each
communication partner. The scheduler allocates a resource within a first frequency
25 range for the communication of the first scheme, and allocates a resource within a
second frequency range for the communication of the second scheme.
[0028]
The first scheme may be multi user multi input multi output (MU-MIMO),
and the second scheme may be single user multi input multi output (SU-MIMO).
30
Advantageous Effects of Invention
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[0029]
As described above, according to the present disclosure, calculation load in
a communication partner for detennining transmission weight can be suppressed.
5 Brief Description of Drawings
[0030]
[Fig. 1] Fig. 1 is an illustrative diagram illustrating a configuration of a wireless
communication system according to an embodiment of the present disclosure.
[Fig. 2] Fig. 2 is an illustrative diagram illustrating an example of multiplication
10 order of transmission weight.
[Fig. 3] Fig. 3 is an illustrative diagram illustrating relationship ofVI and V2.
[Fig. 4] Fig. 4 is an illustrative diagram illustrating a determination method using a
comparative example of the transmission weight VI and transmission weight
V2 MD.
15 [Fig. 5] Fig. 5 is an illustrative diagram illustrating a determination method using a
comparative example of transmission weight in a case in which MU-MIMO and SDMIMO
are present.
[Fig. 6] Fig. 6 is an illustrative diagram illustrating a configuration of a base station
according to an embodiment ofthe present disclosure.
20 [Fig. 7] Fig. 7 is an illustrative diagram illustrating of a configuration of a weight
multiplication unit.
[Fig. 8] Fig. 8 is an illustrative diagram illustrating a configuration of a weight
multiplication unit according to a variant.
[Fig. 9] Fig. 9 is an illustrative diagram illustrating a configuration of a mobile
25 station according to an embodiment.
[Fig. 10] Fig. lOis an illustrative diagram illustrating a fIrst embodiment of the
present disclosure.
[Fig. 11] Fig. 11 is an illustrative diagram illustrating a second embodiment of the
present disclosure.
30 [Fig. 12] Fig. 12 is an illustrative diagram illustrating a third embodiment of the
present disclosure.
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[Fig. 13] Fig. 13 is an illustrative diagram illustrating a resource allocation example
of a VI*CSCRS and a CSI_RS according to a fourth embodiment.
[Fig. 14] Fig. 14 is an illustrative diagram illustrating a specific example of resource
allocation according to a fifth embodiment.
5 [Fig. 15] Fig. 15 is an illustrative diagram illustrating a specific example of resource
allocation according to a sixth embodiment.
[Fig. 16] Fig. 16 is an illustrative diagram illustrating a specific example of resource
allocation according to a seventh embodiment.
[Fig. 17] Fig. 17 is a flowchart illustrating an operation of a base station according to
10 the embodiments of the present disclosure.
[Fig. 18] Fig. 18 is a flowchart illustrating an operation of a mobile station according
to the embodiments of the present disclosure.
Description ofEmbodiments
15 [0031]
Hereinafter, preferred embodiments of the present invention will be
described in detail with reference to the appended drawings. Note that, in this
specification and the drawings, elements that have substantially the same function
and structure are denoted with the same reference signs, and repeated explanation is
20 omitted.
[0032]
In addition, in this specification and drawings, a plurality of elements
having substantially the same function and structure may be distinguished so as to be
denoted with different alphabets after the same reference numeral. For example, a
25 plurality of configurations having substantially the same function and structure such
as mobile stations 20A, 20B, and 20C may be distinguished as appropriate.
However, when there is no particular need to distinguish a plurality of elements
having substantially the same function- and structure individually, the plurality of
elements are denoted with the mere same reference numeral. For example, when
30 there is no particular need to distinguish mobile stations 20A, 20B, and 20C, the
mobile stations are merely referred to as mobile station 20.
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[0033]
In addition, "Description of Embodiments" is made in accordance with the
order of the following items.
1. Outline of a wireless communication system
5 1-1. Configuration ofthe wireless communication system
1-2. Transmission weight (VI and V2)
1-3. Feedback scheme of transmission weight
1-4. Dynamic switching
1-5. Comparative example
10 2. Basic configuration of a base station
3. Basic configuration of a mobile station
4. Description of each embodiment
4-1. First embodiment
4-2. Second embodiment
15 4-3. Third embodiment
4-4. Fourth embodiment
4-5. Fifth embodiment
4-6. Sixth embodiment
4-7. Seventh embodiment
20 5. Operation of the base station and the mobile station
6. Conclusion
[0034]
<1. Outline of a wireless communication system>
Currently, in 3GPP, standardization of a wireless communication system for
25 4G has been promoted. An embodiment of the present disclosure can be applied to
the wireless communication system for 4G as an example, and, first, the outline of
the wireless communication system for 4G is described.
[0035]
[1-1. Configuration of a wireless communication system]
30 Fig. 1 is an illustrative diagram illustrating a configuration of a wireless
communication system 1 according to an embodiment of the present disclosure. As
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illustrated in Fig. 1, the wireless communication system 1 according to the
embodiment of the present disclosure includes a base station 10 and a plurality of
mobile stations 20. Note that the base station 10 maya wireless communication
device such as eNodeB, a relay node, or home eNodeB that is a household small base
5 station in 40. In addition, the mobile station 20 may be a wireless communication
device such as a relay node or UE in 40.
[0036]
The base station 10 controls communication with the mobile station 20 in a
cell. In addition, the base station 10 is operated using three sectors so that each of
10 the sectors has, for example, an angle of 120 degrees as illustrated in Fig. 1. In
addition, the base station 10 includes a plurality of antennas, and can form directivity
in a plurality of directions in each of the sectors (four directions in the example
illustrated in Fig. 1) by multiplying a transmission signal from each of the antennas
by transmission weight V1 that is described later.
15 [0037]
Therefore, the base station 10 can perform multiplexing so that mobile
stations 20A and 20B that exist in different directions when viewed from the base
station 10 are spatially separated. That is, the base station 10 can communicate
with the plurality of the mobile stations 20 by MU-MIMO. Note that the base
20 station 10 can also communicate with the mobile stations 20 by SU-MIMO.
[0038]
The mobile station 20 is a wireless communication device that
communicates with the base station 10 by MU-MIMO or SU-MIMO. The mobile
station 20 moves in accordance with the movement of a moving body such as a user
25 and a vehicle. Note that, in the embodiment, the mobile station 20 is described as
an example of a wireless communication device that wirelessly communicates with
the base station 10, and the embodiment can be also applied to a wireless
communication device that is installed in a fixed manner.
[0039]
30 [1-2. Transmission weight (VI and V2)]
In 4G, in the realization of the MU-MIMO, it is has been studied that
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transmission weight that is referred to as V2 is used in addition to the VI that is
described above (double codebook scheme). The VI is transmission weight that
realizes directivity as described above. Such VI has a characteristic such as
coverage of a wide frequency area and lower update frequency than that of the V2.
5 [0040]
On the other hand, the V2 is transmission non-directional weight, the main
purpose of which is to adjust a phase. More specifically, the V2 is used for
maximizing reception power by adjusting a phase of each path between antennas of
the mobile station 20 and the base station 10. In addition, the V2 has a
10 characteristic such as coverage of a narrow frequency area and higher update
frequency than that of the VI.
[0041]
The base station 10 according to the embodiment realizes MU-MIMO by
multiplying transmission data by such transmission weight VI and transmission
15 weight V2. Note that, as illustrated in Fig. 2, the base station 10 may multiply
transmission data by transmission weight in order of V2 and VI, and may multiply
transmission data by transmission weight in order ofVI and V2.
[0042]
Fig. 3 is an illustrative diagram illustrating a relationship of VI and V2.
20 As illustrated in Fig. 3, when the base station 10 includes 8 antennas, these antennas
operate as two set of linear array antennas 4A and 4B each of which is constituted of
four elements. Note that the linear array antennas 4A and 4B operate as array
antennas having the same directivity as illustrated in Fig. 3.
[0043]
25 In addition, the V2 operates so that two code words of transmission data are
distributed into the two set of linear array antennas 4A and 4B by changing the phase.
That is, the V2 operates so as to change the phase of a transmission signal to be
supplied to the linear array antennas 4A and 4B that perform transmission in the
same direction. On the other hand, the VI is applied to each antenna as illustrated
30 in Fig. 3 and operates so that the linear array antennas 4A and 4B form directivity.
[0044]
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Specific examples of the above-described VI and V2 are described below.
Note that "d" in "Formula 1" that represents the VI indicates a distance from a
reference antenna, "A" indicates a wavelength, "8" indicates a direction of beam, and
"i" indicates an antenna number. In addition, "H" in "Formula 2" that represents V2
5 indicates a channel matrix.
[0045]
[Math. 1]
1
VI(i :::: exp(-j21ft A. *dlsinO(i)
) exp(-j21f1A*d2sin8(i»
exp(- j21C / A. *d3 sin O(i»
[0046]
10 [Math. 2]
V2 :::: [1 1]. [1 1] 1 -l'j-j
[0047]
As illustrated in "Formula 2", the V2 is transmission weight that is
represented as plus or minus 1, or plus or minus j. Note that the j indicates an
15 imaginary number. Thus, a load for multiplying a certain matrix by the V2 is small.
On the other hand, the VI is transmission weight that is described by a directional
vector, and is not a matrix that is represented by plus or minus 1 and plus or minus j.
Therefore, in calculation using the VI, calculation load is increased.
[0048]
20 Note that when transmission data of the base station 10 is "S" and reception
data of the mobile station 20 is "R", the reception data R of the mobile station 20 can
be represented as the following "Formula 3" or "Formula 4".
[0049]
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[Math. 3]
R=H·Vl·V2·S
[0050]
[Math. 4]
R=H·V2·Vl·S
5
[0051 ]
[1-3. Feedback scheme oftransmission weight]
As a feedback scheme of MIMO for determining the above-described
transmission weight VI and transmission weight V2, three schemes of implicit
10 feedback, explicit feedback, and SRS-based feedback are conceivable. In 40; as a
feedback scheme of MIMO for determining the transmission weight VI and
transmission weight V2, the use of the implicit feedback is determined because a
load on a feedback circuit is small. For reference, each of the feedback schemes in
3.9G (LTE) is described below.
15 [0052]
(1) Implicit feedback
In a base station, 16 types of transmission weight (VI) to transmission
weight (V16) are prepared (pre-coded) for a coodbook that has been designed in
beforehand. A mobile station that receives a reference signal from the base station
20 obtains a channel matrix H between the base station and mobile station. In addition,
the mobile station pre-determines HV having the highest reception· power from
among HV (1),HV (2),...,HV (16). After that, the mobile station provides feedback
of an index number that indicates V that makes reception power maximum, to the
base station. The base station transmits data using the V corresponding to the index
25 that is fed back.
[0053]
(2) Explicit feedback
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The base station transmits a reference signal, and the mobile station that
receives the reference signal from the base station obtains a channel matrix H
between the base station and the mobile station similarly to the case of the implicit
feedback. In addition, the mobile station provides feedback of the channel matrix H
5 as-is, to the base station. The base station calculates and creates a desired
transmission weight from the channel matrix H in downlink that is fed back from the
mobile station. In addition, the base station transmits data using the created
transmission weight. In this explicit feedback, there is a problem that a resource
that is used for feedback becomes larger than that of the implicit feedback because a
10 channel matrix H is transmitted as-is at the time of feedback.
[0054]
(3) SRS-based feedback
The mobile station transmits a reference signal, and the base station that
receives the reference signal from the mobile station obtains a channel matrix in
15 uplink between the mobile station and the base station. When the reversibility of a
channel can be established (in a case of a TDD mode), the base station can makes a
virtual channel matrix in downlink from the channel matrix. A scheme in which a
virtual channel matrix in downlink is made as described above is the SRS-based
feedback. In the SRS-based feedback, there is a problem such that, when
20 calibration is not performed in which variations of analog circuits in the base station
are compensated, the reversibility of channels in uplink and downlink (channel
matrix that includes a characteristic ofthe analog circuit) is not established.
[0055]
[1-4. Dynamic switching]
25 In 4G (LTE-Advanced), it is has been studied that setting of MIMO is
dynamically switched between MU-MIMO and SU-MIMO. In addition, in MUMIMO
in 4G, the use of eight streams has been studied. In the case ofeight streams,
one matrix for phase adjustment ofV2 as described in "1-2. Transmission weight (VI
and V2)" is used.
30 [0056]
The example IS described above 10 which MU-MIMO IS realized by
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combining VI having a 4x4 matrix and V2 having a 2x2 matrix. On the other hand,
mere V2 having an 8x8 matrix is used for SU-MIMO. In addition, each element of
the V2 having the 8x8 matrix is represented by the plus or minus 1 and plus or minus
j, similarly to the V2 having the 2x2 matrix. Note that j indicates an imaginary
5 humber.
[0057]
As described above, different V2 are used for MU-MIMO and SU-MIMO,
and, in this specification, V2 for MU-MIMO is referred to as V2_MU, and weight
for SU-MIMO is referred to as V2_SU, thereby distinguishing the two ofV2.
10 [0058]
[1-5. Comparative example]
In 4G and the embodiments, as described in "1-3. Feedback scheme of
transmission weight," the transmission weight V1 and transmission weight V2_MU
are detenruned by implicit feedback. Here, in order to clarify the technical
15 significance of the embodiments, a detennination method using a comparative
example ofthe transmission weight VI and transmission weight V2_MU is described
with reference to Fig. 4.
[0059]
Fig. 4 is an illustrative diagram illustrating the detennination method using
20 a comparative example of the transmission weight VI and transmission weight
V2_MU. In Fig. 4, the horizontal axis indicates a time. In addition, CSI indicates
a channel state infonnation reference signal (CSCRS).
[0060]
As illustrated in Fig. 4, the base station transmits a CSCRS (step 1), and the
25 mobile station obtains a channel matrix H from the CSI RS received from the base
station. In addition, the mobile station evaluates optimal VI for the obtained
channel matrix H, among four types of VI candidate. For example, the mobile
station selects VI that makes reception power maximum, among four types of VI
candidate. In addition, the mobile station evaluates and selects optimal V2_MU.
30 After that, the mobile station provides feedback of Index_VI that indicates the
selected VI and Index_V2 that indicates V2_MU to the base station (step 2). The
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base station determines VI and V2 MU on the basis of the feedback from the mobile
station.
[0061]
When the base station and the mobile station determines VI and V2_MU,
5 the base station and the mobile station updates the only V2_MU multiple times (step
3) followed by updating the VI and V2_MU (step 4). As described above, update
frequency ofV2_MU is higher than update frequency of VI.
[0062]
Here, the mobile station performs calculation using a plurality of types of
10 VI when the mobile station selects VI. As described in "1-2. Transmission
weight (VI and V2)", load of the mobile station in the case of selecting VI becomes
large because load of calculation using V1 is larger than load of calculation using
V2 MU.
[0063]
15 On the other hand, it is conceived that calculation using VI is not desired in
the case of selecting V2. However, the idea is wrong, and the mobile station
performs calculation using VI in the case of selecting V2. This is because the
mobile station obtains a channel matrix H from a newly received CSI_RS, multiplies
the channel matrix H by already determined VI, and evaluates optimal V2_MU for
20 the channel matrix H that is multiplied by the VI. As described above, in the
determination method of transmission weight using the comparative example, the
amount of calculation in the mobile station is increased undesirably because it is
desirable that the mobile station performs calculation using VI in any update of VI
and V2.
25 [0064]
Next, a determination method using a comparative example of transmission
weight in a case in which MU-MIMO and SU-MIMO are present is described with
reference to Fig. 5.
[0065]
30 Fig. 5 is an illustrative diagram illustrating the determination method using
a comparative example of transmission weight in the case in which MU-MIMO and
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SU-MIMO are present. As illustrated in Fig. 5, in the case in which MU-MIMO
and SU-MIMO are present, the base station and the mobile station updates V2_SU
for all a CSCRS in addition to VI and V2_MU. Therefore, calculation load in the
mobile station is further increased undesirably because the V2_SU is updated.
5 However, in order to realize dynamic switching of MU-MIMO and SU-MIMO, it is
important to evaluate both ofthe V2_MU and V2_SU all the time.
[0066]
The above-described determination method of transmission weight by a
comparative example is summarized as follows:
10 (1) Calculation load in the mobile station is high
Reason: As described with reference to Fig. 4, calculation using already
determined VI is performed even in the case of evaluating V2_MU.
(2) Calculation load in the mobile station is further increase when dynamic switching
ofMU-MIMO and SU-MIMO is tried to be realized.
15 Reason: As described with reference to Fig. 5, both of the V2_MU and
V2 SU are evaluated all the time.
[0067]
In addition, when dynamic switching is performed in a communication
system using a plurality of subcarriers of an OFDM modulation scheme, etc., there
20 has been no an allocation method of a frequency subcarrier that can effectively
reduce the amount ofcalculation.
[0068]
Therefore, the embodiments of the present disclosure have been led to
creation by regarding the above circumstances as a point of view. According to
25 each embodiment of the present disclosure, calculation load in the mobile station 20
for determining transmission weight can be suppressed. Each of such embodiments
of the present disclosure is described below in detail.
[0069]
<2. Basic configuration of a base station>
30 A technology according to the present disclosure can be implemented in
various forms as described in detail in "4-1. First embodiment" to "4-7. Seventh
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embodiment" as examples. In addition, the base station 10 according to each of the
embodiments includes:
A: a communication unit (an antenna 110, an analog processing unit 120,
etc.) that transmits a reference signal (CSI_RS),
5 B: a first multiplication unit (VI multiplication unit 154) that performs
multiplication of first transmission'weight (VI) that is determined on the basis of
reception of the reference signal by a communication partner (the mobile station 20),
and
C: a second multiplication unit (V2_MU multiplication unit 156) that
10 performs multiplication of second transmission weight (V2_MU) that is determined
on the basis of reception of the reference signal by the communication partner. In
addition,
D: the communication unit transmits a reference signal with weight
(VI *CSI_RS) obtained by multiplying the reference signal by the first transmission
15 weight after determination ofthe first transmission weight.
[0070]
First, a common basic configuration in the base station 10 according to such
embodiments is described below with reference to Figs. 6 to 8.
[0071]
20 Fig. 6 is an illustrative diagram illustrating a configuration of the base
station 10 according to the embodiment of the present disclosure. As illustrated in
Fig. 6, the base station 10 according to the embodiment of the present disclosure
includes the plurality of antennas 110, a switch SW 116, an analog processing unit
120, an AD/DA conversion unit 124, a demodulation processing unit 128, an upper
25 layer signal processing unit 132, a scheduler 136, a modulation processing unit 140,
and a weight multiplication unit 150.
[0072]
The antennas 11OA to lION function as a reception unit that converts a radio
signal that is transmitted from the mobile station 20 into an electrical reception signal
30 and supplies the converted signal to the analog processing unit 120, and a
transmission unit that converts a transmission signal supplied from the analog
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processing unit 120 into a radio signal and transmits the converted signal to the
mobile station 20. Note that the number of the antennas 110 is not particularly
limited, and may be, for example, 8 or 16.
[0073]
5 The switch SW 116 is a switch for switching a transmission operation and a
reception operation by the base station 10. The base station 10 performs the
transmission operation when the antennas 110A to lION are connected to a
transmission circuit of the analog processing unit 120 through the switch SW 116,
and performs the reception operation when the antennas 110A to lION are connected
10 to a reception circuit of the analog processing unit 120 through the switch SW 116.
[0074]
The analog processmg unit 120 includes the transmission circuit that
performs analog processing for a transmission signal, and the reception circuit that
performs analog processing for a reception signal. In the transmission circuit, for
15 example, up-conversion, filtering, gain control, etc. of a transmission signal, in an
analog form, which is supplied from the AD/DA conversion unit 124 are performed.
In the reception circuit, for example, down-conversion, filtering, etc. of a reception
signal that is supplied from the antenna 110 through the switch SW 116 are
performed.
20 [0075]
The AD/DA conversion unit 124 performs analogue/digital (AD) conversion
of a reception signal that is supplied from the analog processing unit 120, and
performs digital/analogue (DA) conversion of a transmission signal that is supplied
from the weight multiplication unit 150.
25 [0076]
The demodulation processing unit 128 performs demodulation processing of
a reception signal that is supplied from the AD/DA conversion unit 124. The
demodulation processing that is performed by the demodUlation processing unit 128
may include OFDM demodulation processing, MIMO demodulation processing,
30 error correction, etc.
[0077]
SP306449WOOO
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The upper layer signal processing unit 132 performs processmg for
inputting and outputting transmission data and reception data between the upper
layer signal processing unit 132 and an upper layer, control processing of the
scheduler 136, the modulation processing unit 140, and the weight multiplication unit
5 150, determination processing of each transmission weight based on feedback
information from the mobile station 20, etc.
[0078]
In addition, the base station 10 according to the embodiment transmits a
VI*CSCRS (reference signal with weight) obtained by multiplying a CSCRS by VI
10 in addition to a CSI_RS (reference signal) after determination of the transmission
weight VI on the basis of feedback information from the mobile station 20 as
described later in detail. The upper layer signal processing unit 132 includes a
function as a reference signal management unit that manages a resource for
transmitting the CSCRS and a VI*CSCRS. In addition, the upper layer signal
15 processing unit 132 controls the weight multiplication unit 150 so that transmission
of the CSI_RS or VI *CSI_RS is performed in the allocated resource.
[0079]
The scheduler 136 allocates a resource for data communication to each of
the mobile stations 20. The resource that is allocated by the scheduler 136 is
20 reported to each of the mobile stations 20 by a control channel, and each of the
mobile stations 20 performs data communication in uplink or downlink using the
reported resource.
[0080]
The modulation processing unit 140 performs modulation processing such
25 as mapping based on a constellation on transmission data that is supplied from the
upper layer signal processing unit 132. The transmission signal obtained after
modulation by the modulation processing unit 140 is supplied to the weight
multiplication unit 150.
[0081]
30 The weight multiplication unit 150 multiplies the transmission signal that is
supplied from the modulation processing unit 140 by the transmission weight V1 and
• SP306449WOOO
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transmission weight V2_MU that are determined by the upper layer signal processing
unit 132 at the time of execution of MU-MIMO. On the other hand, the weight
multiplication unit 150 multiplies the transmission signal that is supplied from the
modulation processing unit 140 by the transmission weight V2_SU that is
5 determined by the upper layer signal processing unit 132 at the time of execution of
SU-MIMO. In addition, the weight multiplication unit 150 multiplies a CSCRS by
VI in a resource that is allocated for transmission of a VI *CSCRS (the n*" is
complex multiplication) by the upper layer signal processing unit 132. Such
configuration of the weight multiplication unit 150 is described below in more detail
10 with reference to Fig. 7.
[0082]
Fig. 7 is an illustrative diagram illustrating a configuration of the weight
multiplication unit 150. As illustrated in Fig. 7, the weight multiplication unit 150
includes selectors 151, 157, and 158, a V2_SU multiplication unit 152, the VI
15 multiplication unit 154, and the V2_MU multiplication unit 156.
[0083]
The selector 151 supplies a transmission signal that is supplied from the
modulation processing unit 140 to the V2_MU multiplication unit 156 or the V2_SU
multiplication unit 152. More specifically, the selector 151 supplies a transmission
20 signal to the V2_MU multiplication unit 156 when setting of MIMO is MU-MIMO,
and supplies a transmission signal to the V2_SU multiplication unit 152 when setting
ofMIMO is SU-MIMO.
[0084]
The V2_SU multiplication unit 152 multiplies the transmission signal that is
25 supplied from the selector 151 by V2_SU that is determined by the upper layer signal
processing unit 132.
[0085]
On the other hand, the V2_MU multiplication unit 156 multiplies the
transmission signal that is supplied from the selector 151 by V2_MU that is
30 determined by the upper layer signal processing unit 132. In addition, the VI
multiplication unit 154 multiplies the transmission signal that is multiplied by the
• SP306449WOOO
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V2_MU, byVl.
[0086]
The selector 157 selectively outputs the multiplication result by the VI
multiplication unit 154, or the multiplication result by the V2_SU multiplication unit
5 152. More specifically, the selector 157 outputs the multiplication result by the VI
multiplication unit 154 when setting of MIMO is MU-MIMO and outputs the
multiplication result by the V2_SU multiplication unit 152 when setting of MIMO is
SU-MIMO.
[0087]
10 A selector 158 supplies a CSI_RS to the former part or the latter part of the
VI multiplication unit 154. More specifically, the selector 158 supplies a CSI_RS
to the latter part of the V1 multiplication unit 154 in a resource that is allocated for
transmitting the CSI_RS. In this case, the base station 10 transmits a CSCRS that
is not multiplied by VI.
15 [0088]
On the other hand, the selector 158 supplies a CSI_RS to the former part of
the VI multiplication unit 154 in a resource that is allocated for transmitting a
VI *CSI_RS. In this case, the base station 10 transmits a VI*CSI_RS because the
CSI_RS is multiplied by VI in the VI multiplication unit 154.
20 [0089]
Note that, in Fig. 7, the example is described in which the VI multiplication
unit 154 is arranged in the latter part of the V2 multiplication unit 156, however, the
configuration of the weight multiplication unit 150 is not limited to such example.
For example, as described below with reference to Fig. 8, the VI multiplication unit
25 154 may be arranged in the former part ofthe V2 multiplication unit 156.
[0090]
Fig. 8 is an illustrative diagram illustrating a configuration of a weight
multiplication unit 150' according to a variant. As illustrated in Fig. 8, the weight
multiplication unit 150' according to the variant includes the selectors 151, 155, 157,
30 and 159, the V2_SU multiplication unit 152, the VI multiplication unit 154, and the
V2_MU multiplication unit 156.
• SP306449WOOO
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[0091]
In the weight multiplication unit 150' according to the variant, as illustrated
in Fig. 8, the VI multiplication unit 154 is arranged in the former part of the V2_MU
multiplication unit 156. In addition, in the weight multiplication unit 150'
5 according to the variant, the selector 159 supplies a CSI_RS to the former part of the
VI multiplication unit 154 or the latter part of the V2_MU multiplication unit 156.
[0092]
More specifically, the selector 159 supplies a CSI_RS to the latter part of
the V2_MU multiplication unit 156 in a resource that is allocated for transmitting a
10 CSI RS. In this case, the base station 10 transmits a CSCRS that is not multiplied
byVl.
[0093]
On the other hand, the selector 159 supplies a CSCRS to the former part of
the VI multiplication unit 154 in a resource that is allocated for transmitting a
15 VI *CSI_RS. In this case, the CSCRS is multiplied by VI in the VI multiplication
unit 154, and the VI *CSI_RS that is the multiplication result is supplied from the
selector 155 to the selector 157 so as to bypass the V2_MU multiplication unit 156.
As a result, the base station 10 transmits the VI *CSCRS.
[0094]
20 As described above, the base station 10 according to the embodiment starts
to transmit a VI *CSI_RS after determination of transmission weight VI. By such
configuration, calculation load of V2_MU, etc. in the mobile station 20 that is
described below can be suppressed.
[0095]
25 <3. Basic configuration of a mobile station>
Fig. 9 is an illustrative diagram illustrating a configuration of the mobile
station 20 according to the embodiment. As illustrated in Fig. 9, the mobile station
20 according to the embodiments includes a plurality of antennas 210, a switch SW
216, an analog processing unit 220, an AD/DA conversion unit 224, a demodulation
30 processing unit 228, an upper layer signal processing unit 232, a modulation
processing unit 240, a channel matrix obtaining unit 244, and a weight determination
SP306449WOOO
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unit 248.
[0096]
The antennas 210A and 210B function as a reception unit that converts a
radio signal that is transmitted from the base station 10 into an electrical reception
5 signal and supplies the converted signal to the analog processing unit 220, and
function as transmission unit that converts a transmission signal that is supplied from
the analog processing unit 220 into a radio signal and transmits the converted signal
to the base station 10. Note that the number of antennas 210 is not limited, and for
example, may be four, or eight.
10 [0097]
The switch SW 216 is a switch for switching a transmission operation and a
reception operation of the mobile station 20. The mobile station 20 performs the
transmission operation when the antennas 210A and 210B are connected to a
transmission circuit of the analog processing unit 220 through the switch SW 216,
15 and the mobile station 20 performs the reception operation when the antennas 210A
and 210B are connected to a reception circuit of the analog processing unit 220
through the switch SW 216.
[0098]
The analog processing unit 220 includes a transmission circuit that performs
20 analog processing on a transmission signal and a reception circuit that performs
analog processing on a reception signal. In the transmission circuit, for example,
up-conversion, filtering, gain control, etc. of a transmission signal in an analog form,
which is supplied from the ADIDA conversion unit 224 are performed. In the
reception circuit, for example, down-conversion, filtering, etc. of a reception signal
25 that is supplied from the antenna 210 through the switch SW 216 are performed.
[0099]
The AD/DA conversion unit 224 performs AD conversion of a reception
signal that is supplied from the analog processing unit 220 and performs DA
conversion of a transmission signal that is supplied from the modulation processing
30 unit 240.
[0100]
SP306449WOOO
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The demodulation processing unit 228 performs demodulation processing of
a reception signal that is supplied from the AD/DA conversion unit 224. The
demodulation processing that is performed by the demodulation processing unit 228
may include OFDM demodulation processing, MIMO demodulation processing, and
5 error correction.
[0101]
The upper layer signal processmg unit 232 performs processmg for
inputting and outputting transmission data and reception data between the upper
layer signal processing unit 232 and an upper layer. In addition, the upper layer
10 signal processing unit 232 supplies feedback information that indicates transmission
weight that is determined by the weight determination unit 248 to the modulation
processing unit 240, as transmission data.
[0102]
The modulation processing unit 240 performs modulation processing such
15 as mapping based on a constellation on transmission data that is supplied from the
upper layer signal processing unit 232. The transmission signal obtained after
modulation by the modulation processing unit 240 is supplied to the AD/DA
conversion unit 224.
[0103]
20 The channel matrix obtaining unit 244 obtains a channel matrix H between
the base station 10 and the mobile station 20 when a CSI RS is received from the
base station 10.
[0104]
The weight determination unit 248 determines transmission weight of VI,
25 V2_MU, V2_SU, etc. on the basis of the channel matrix H obtained by the channel
matrix obtaining unit 244. Here, as described above with reference to Fig. 4, when
V2_MU is updated on the basis of the channel matrix H obtained from the CSI_RS,
the mobile station according to a comparative example multiplies the channel matrix
H by already determined V1 and evaluates optimal V2_MU for the channel matrix H
30 that is multiplied by the VI. Therefore, in the mobile station according to the
comparative example, calculation using VI is performed even at the time of update
SP306449WOOO
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ofV2 MU.
[0105]
On the contrary, in the embodiment, after determination of VI, VI*CSCRS
that is a CSI_RS multiplied by the VI is received from the base station 10. A
5 channel matrix H that is obtained from a VI *CSCRS by the channel matrix
obtaining unit 244 is already in a form of being multiplied by VI. Thus, the weight
determination unit 248 can update V2_MU on the basis of the channel matrix H that
is obtained from the VI *CSI_RS without performing calculation using VI. As a
result, calculation load in the mobile station 20 for update of V2 MU can be
10 significantly reduced.
[0106]
<4. Description of each ofthe embodiments>
The basic configurations of the base station 10 and the mobile station 20
according to each of the embodiments of the present disclosure are described above.
15 Next, each of the embodiments of the present disclosure is described in detail.
[0107]
[4-1. First embodiment]
Fig. lOis an illustrative diagram illustrating a first embodiment of the
present disclosure. As illustrated in Fig. 10, the base station 10 transmits a
20 VI*CSCRS to update (determine) V2_MU when VI is determined after transmitting
a CSI RS. As described above, the mobile station 20 that has received a
VI*CSCRS can evaluate optimal V2_MU without performing calculation using VI.
[0108]
In addition, the base station 10 transmits a CSI_RS to update VI after
25 transmitting a VI*CSCRS multiple times. After that, the base station 10 transmits
a VI *CSI_RS to update V2_MU.
[0109]
In Fig. 10, an example is described in which the update frequency of V2 is
about 4 to 5 times the update frequency of VI, however relationship of update
30 frequency is not limited to the example. In practice, it is conceivable that the
update frequency ofVI is more than 10 times the update frequency ofV2.
SP306449WOOO
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[0110]
[4-2. Second embodiment]
As described in the first embodiment, when the base station 10 transmits a
VI *CSCRS, the mobile station 20 can evaluate optimal V2_MU without calculation
5 using VI. Here, in order to realize dynamic switching of MU-MIMO and SUMIMO,
it is desirable that the mobile station 20 obtains V2_SU. However, it is
difficult for the mobile station 20 to evaluate V2 SU from the VI *CSI RS.
[0111 ]
Therefore, the upper layer signal processing unit 132 of the base station 10
10 according to a second embodiment allocates a resource for transmitting a CSCRS to
update (determine) V2_SU in addition to allocation of a resource for transmitting a
VI *CSI_RS to update (determine) V2_MU. An operation of the base station 10
according to such second embodiment is described in detail with reference to Fig. 11.
[0112]
15 Fig. 11 is an illustrative diagram illustrating the second embodiment of the
present disclosure. As illustrated in Fig. 11, the base station 10 according to the
second embodiment transmits a VI*CSIyS to update V2_MU after determination
of VI, and transmits a CSCRS to update (determine) V2_SU. By such
configuration, the dynamic switching of MU-MIMO and SU-MIMO can be realized
20 because V2- MU is obtained on the basis of the VI *CSI- RS and V2 SU is obtained
on the basis of the CSI_RS.
[0113]
Note that the mobile station 20 can determines that a radio signal that is
received from the base station 10 is a CSI_RS or a VI *CSCRS, for example, by a
25 method that is described below.
(1) The base station 10 reports timing, order, etc. of transmission of a
CSI_RS or a VI *CSI_RS through RRC signaling beforehand, to the mobile station
20.
(2) The base station 10 reports timing, order, etc. of transmission of a
30 CSI RS or a VI *CSI RS to the mobile station 20 by broadcasting system
information.
SP306449WOOO
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(3) The base station 10 transmits a CSCRS and a VI *CSI_RS after
performing addition of identification information that indicates a CSI RS or a
V1*CSI RS.
[0114]
5 [4-3. Third embodiment]
As described in "1-4. Dynamic switching", in SU-MIMO, for example,
MIMO transmission of eight independent streams is performed. On the other hand,
in MU-MIMO, for example, MIMO transmission of two independent streams is
performed for each of the four different mobile stations 20. Thus, V2_SU and
10 V2_MU are different in terms that V2_SU is used for eight streams and V2_MU is
used for two streams.
[0115]
In this case, it is effective to set update frequency of V2_SU higher than
update frequency of V2_MU because higher accuracy is desired for V2_SU that is
15 used for eight streams.
[0116]
Therefore, the upper layer signal processing unit 132 of the base station 10
according to a third embodiment allocates more resources for transmitting a CSCRS
to update (determine) V2_SU than that for transmitting of a VI *CSI_RS to update
20 (determine) V2_MU. An operation of the base station 10 according to such third
embodiment is described in detail with reference to Fig. 12.
[0117]
Fig. 12 is an illustrative diagram illustrating the third embodiment of the
present disclosure. As illustrated in Fig. 12, the base station 10 according to the
25 third embodiment transmits, on a time direction, a CSCRS to update (determines)
V2_SU at higher frequency than that of a VI *CSI_RS to update (determines)
V2_MU after determination ofVl. By such configuration, highly accurate V2_SU
can be obtained while suppressing calculation load in the mobile station 20 at the
time of update ofV2_MU.
30 [0118]
[4-4. Fourth embodiment]
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In the third embodiment, the description is made in which the base station
10 transmits, in the time direction, a CSCRS at higher frequency than that of a
VI*CSCRS in order to make the update frequency ofV2_SU higher than the update
frequency of V2_MU. In a fourth embodiment, similarly to the third embodiment,
5 arrangement of a VI *CSCRS and a CSI_RS on the frequency direction in a
subcarrier of OFDM has been devised in order to make the update frequency of
V2_SU higher than the update frequency of V2_MU. A resource allocation
example according to the fourth embodiment is described below in detail with
reference to Fig. 13.
10 [0119]
Fig. 13 is an illustrative diagram illustrating a resource allocation example
of a VI*CSCRS and a CSI_RS according to the fourth embodiment. As illustrated
in Fig. 13, the upper layer signal processing unit 132 of the base station 10 according
to fourth embodiment arranges, on the frequency direction, a CSCRS more densely
15 than a VI *CSCRS. As described above, similarly to the third embodiment, highly
accurate V2_SU can be obtained while suppressing calculation load in the mobile
station 20 at the time of update of V2_MU, by devising the arrangement of a
VI *CSI_RS and a CSI_RS on the frequency direction.
[0120]
20 [4-5. Fifth embodiment]
In a fifth embodiment, resource allocation for data communication using a
determined transmission weight is described.
[0121]
Fig. 14 is an illustrative diagram illustrating a specific example of resource
25 allocation according to the fifth embodiment. The horizontal axis in Fig. 14
indicates a time, and the vertical axis indicates a frequency. In addition, the time
width of a square block in Fig. 14 may be one resource block or one subframe. In
addition, the frequency width of the square block may be one resource block (12
subcarrier portions) or another band width.
30 [0122]
As illustrated in Fig. 14, when the base station 10 transmits a CSCRS first,
SP306449WOOO
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the mobile station 20 obtains VI, V2_MU, and V2_SU for each frequency on the
basis of the reception of a CSCRS. In addition, the mobile station 20 provides
feedback ofVI, V2_MU, and V2_SU to the base station 10.
[0123]
5 After that, as illustrated in Fig. 14, the scheduler 136 of the base station 10
allocates four resource blocks from the bottom included in a frequency range B for
MU-MIMO (fIrst scheme) with the mobile stations 20A to 20C. On the other hand,
as illustrated in Fig. 14, the scheduler 136 of the base station 10 allocates two
resource blocks from the top included in a frequency range A for SU-MIMO (second
10 scheme) with the mobile station 20D.
[0124]
Here, the scheduler 136 according to the fIfth embodiment keeps the
resource blocks that are included in the frequency range B as an area for MU-MIMO
and keeps the resource blocks that are included in the frequency range A as an area
15 for SU-MIMO.
[0125]
Therefore, for example, when the scheduler 136 according to the fIfth
embodiment performs dynamic switching of setting of MIMO of the mobile station
20C from MU-MIMO to SU-MIMO, the resource block that is allocated to the
20 mobile station 20C is moved to the resource block that is included in the frequency
range A, as illustrated in Fig. 14.
[0126]
As described above, according to the fIfth embodiment, dynamic switching
of MU-MIMO and SU-MIMO can be realized by moving a resource block of the
25 mobile station 20 in a frequency direction.
[0127]
[4-6. Sixth embodiment]
Fig. 15 is an illustrative diagram illustrating a specifIc example of resource
allocation according to a sixth embodiment. As illustrated in Fig. 15, the upper
30 layer signal processing unit 132 according to the sixth embodiment allocates resource
blocks that are included in the frequency range B for MU-MIMOthat is described in
SP306449WOOO
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the fifth embodiment, for transmitting a VI *CSCRS, after determination ofVl. In
addition, the upper layer signal processing unit 132 allocates resource blocks that are
included in the frequency range A for SU-MIMO that is described in the fifth
embodiment, for transmitting a CSI_RS.
5 [0128]
By such configuration, V2_SU can be updated in frequency range A while
suppressing the amount of calculation in the mobile station 20 and updating V2_MU
in the frequency range B. Therefore, the frequency range B can be used for
communication by MU-MIMO, and the frequency range A can be used for
10 communication by SU-MIMO.
[0129]
[4-7. Seventh embodiment]
In the above-described fifth embodiment and sixth embodiment, the
example is described in which a frequency range for MU-MIMO and a frequency
15 range for SU-MIMO are fixed, and alternatively, as described below with reference
to a seventh embodiment, a frequency range for MU-MIMO and a frequency range
for SU-MIMO can be dynamically changed.
[0130]
Fig. 16 is an illustrative diagram illustrating a specific example of resource
20 allocation according to a seventh embodiment. As illustrated in Fig. 16, it is
assumed that, in the time tl, resource blocks in a frequency range Z and a frequency
range X are allocated for transmitting a CSI_RS, resource blocks in a frequency
range Yare allocated for transmission of a VI *CSCRS.
[0131]
25 Here, in a frequency in which a CSCRS is transmitted, VI, V2_MU, and
V2_SU can be obtained. On the other hand, in a frequency in which a VI*CSCRS
is transmitted, V2_MU can be obtained, however, V2_SU is difficult to be obtained.
That is, the frequency in which a VI *CSI_RS is transmitted can be used for MUMIMO,
the frequency in which a CSI_RS is transmitted can be used for both ofMU-
30 MIMO or SU-MIMO.
[0132]
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Therefore, the scheduler 136 according to the seventh embodiment handles
resource blocks in the frequency range X and the frequency range Z to which a
CSCRS is transmitted as an area in which switching of SU-MIMO and MU-MIMO
can be performed. On the other hand, the scheduler 136 handles resource blocks in
5 the frequency range Y to which a VI *CSCRS is transmitted as a MU-MIMOdedicated
area.
[0133]
For example, as illustrated in Fig. 16, at the time t2, the scheduler 136
allocates resource blocks in the frequency range X for communication by SU-MIMO,
10 and allocates resource blocks in the frequency range Y and the frequency Z for
communication by· MU-MIMO. After that, at the time 13, the scheduler 136 can
switches resource blocks for MU-MIMO to resource blocks for SU-MIMO in the
frequency range Z, and can switches at resource blocks for SU-MIMO to at resource
blocks for MU-MIMO in the frequency range X.
15 [0134]
<5. Operation of the base station and the mobile station>
Each of the embodiments of the present disclosure is described above.
Next, operations of the base station 10 and the mobile station 20 according to the
embodiments of the present disclosure are described with reference to Figs. 17 and
20 18.
[0135]
Fig. 17 is a flowchart illustrating an operation of the base station 10
according to the embodiments of the present disclosure. Note that Fig. 17
particularly corresponds to the operation of the base station 10 according to the
25 seventh embodiment.
[0136]
As illustrated in Fig. 17, first, the base station 10 determines update
frequency of VI and update frequency of V2_MU in the time direction (S304).
After that, the base station 10 determines update frequency of V2_SU in the time
30 direction (S308).
[0137]
SP306449WOOO II 33M2
After that, the base station 10 detennines a density of a resource for MUMIMO
and a density of a resource for SU-MIMO in the frequency direction (S312).
In addition, the base station 10 detennines a ratio, which is illustrated in Fig. 16, of
the MU-MIMO-dedicated area and the area in which dynamic switching can be
5 perfonned in the frequency direction (S316). Note that in the example illustrated in
Fig. 16, the ratio of the MU-MIMO-dedicated area and the in which dynamic
switching can be perfonned in the frequency direction is 1:2, and a density ratio of a
resource for MU-MIMO and a resource for SU-MIMO in the frequency direction is
2:1.
10 [0138]
After that, the base station 10 allocates a resource for transmitting a CSI_RS
and a resource for transmitting a VI *CSI_RS (S320). More specifically, in S316,
the base station 10 allocates a resource of a frequency that is determined as the MUMIMO-
dedicated area for transmitting a VI *CSI_RS and allocates a resource of a
15 frequency that is detennined as the area in which dynamic switching can be
perfonned for transmitting a CSI RS. In addition, the base station 10 allocates a
resource in the time direction to a VI *CSI- RS and a CSI- RS on the basis of the
determination results of S304 and S308. In addition, the base station 10 transmits a
CSI_RS and a VI *CSI_RS in accordance with the determined resource.
20 [0139]
Fig. 18 is a flowchart of an operation of the mobile station 20 according to
the embodiments. As illustrated in Fig. 18, in a case in which the mobile station 20
receives a radio signal from the base station 10 (S404), when the radio signal is a
CSI_RS (S408), a channel matrix H is obtained from the reception result of the
25 CSI_RS (S412). In addition, the mobile station 20 detennines transmission weight
such as VI, V2_MU, and V2_SU on the basis of the channel matrix H obtained in
S412 (S416). In addition, the mobile station 20 provides feedback of VI, V2_MU,
and V2_SU to the base station 10 (S420).
[0140]
30 On the other hand, when the received radio signal is a VI *CSI_RS (S408),
the mobile station 20 obtains a channel matrix H that is multiplied by VI from the
• 8P306449WOOO
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reception result of a VI*C8CR8 (8424). In addition, the mobile station 20
determines V2_MUon the basis of the channel matrix H that is multiplied by VI
without performing calculation using VI (8428). In addition, the mobile station 20
provides feedback ofV2_MU to the base station 10 (8432).
5 [0141]
In addition, when the received radio signal is a data signal (8408), the
.mobile station 20 demodulates the data signal and obtains data that is transmitted
from the base station 10 (8436).
[0142]
10 <6. Conclusion>
As described above, the base station 10 according to the embodiments ofthe
present disclosure starts to transmit a VI *C8I R8 after determination of
transmission weight VI. By such configuration, calculation load such as V2_MU in
the mobile station 20 that is described below can be suppressed. In addition, the
15 base station 10 according to the embodiments of the present disclosure continues to
transmit a C8I_R8. By such configuration, the mobile station 20 can determine
V2_8U on the basis of reception of a C8I_R8. As a result, dynamic switching of
MU-MIMO and 8U-MIMO can be realized.
[0143]
20 The preferred embodiments of the present invention have been described
above with reference to the accompanying drawings, whilst the present invention is
not limited to the above examples, of course. A person skilled in the art may fmd
various alternations and modifications within the scope of the appended claims, and
it should be understood that they will naturally come under the technical scope of the
25 present invention.
[0144]
For example, two or more of the first embodiment to the seventh
embodiment may be combined. For example, the resource allocation in the time
direction that is described in the third embodiment, the resource allocation in the
30 frequency direction that is described in the fifth embodiment, and the resource
allocation for 8U-MIMO and MU-MIMO that is described in the sixth embodiment
• SP306449WOOO
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can be combined.
[0145]
In addition, the steps in the processmg of the base station 10 or the
processing of the mobile station 20 in this specification are not necessarily processed
5 in chronological order in accordance with the order that is described as the flowchart.
For example, the steps in the processing of the base station 10 or the processing of
the mobile station 20 may be processed in order different from the order that is
described as the flowchart, or may be processed in parallel.
[0146]
10 In addition, a computer program can be created that exerts hardware such as
a CPU, a ROM, and a RAM, which is built in the base station 10 or the mobile
station 20 as a function equivalent to each configuration of the above-described base
station 10 or the mobile station 20. In addition, a storage medium that stores the
computer program is also provided.
15
Reference Signs List
[0147]
10 base station
20, 20A, 20B mobile station
20 110,210 antenna
116,216 switch SW
120,220 analog processing unit
124,224 AD/DA conversion unit
128, 228 demodulation processing unit
25 132, 232 upper layer signal processing unit
136 scheduler
140, 240 modulation processing unit
150 weight multiplication unit
152 V2_SU multiplication unit
30 154 VI multiplication unit
156 V2_MU multiplication unit
244 channel matrix obtaining unit
248 weight determination unit
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CLAIMS
Claim 1
A wireless communication device comprising:
a communication unit that transmits a reference signal;
5 a first multiplication unit that performs multiplication of first transmission
weight that is determined based on reception of the reference signal by a
communication partner; and
a second mUltiplication unit that performs multiplication of second
transmission weight that is determined based on reception of the reference signal by
10 the communication partner,
wherein the communication unit transmits a reference signal with weight
that is obtained by multiplying the reference signal by the first transmission weight
after determination of the first transmission weight.
15 Claim 2
The wireless communication device according to claim 1, further
comprising:
a reference signal management unit that manages a resource for transmitting
the reference signal with weight.
20
Claim 3
The wireless communication device according to claim 2,
wherein the reference signal management unit allocates a resource for
transmitting the reference signal with weight and a resource for transmitting the
25 reference signal after determination ofthe first transmission weight.
Claim 4
The wireless communication device according to claim 3,
wherein the reference signal management unit allocates more resources for
30 transmitting the reference signal than the resource for transmitting the reference
signal with weight.
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Claim 5
The wireless communication device according to claim 4,
wherein the reference signal management unit allocates a resource so that
5 transmission frequency of the reference signal on a time axis becomes higher than
transmission frequency of the reference signal with weight on the time axis.
Claim 6
The wireless communication device according to claim 4,
10 wherein the reference signal management unit allocates a resource so that a
density of a resource for transmitting the reference signal on a frequency axis
becomes higher than a density of a resource for transmitting the reference signal with
weight on the frequency axis.
15 Claim 7
The wireless communication device according to claim 3, further
comprising:
a scheduler that allocates a resource for communication of a fIrst scheme or
a second scheme to each communication partner, and
20 wherein the scheduler allocates a resource within a fIrst frequency range for
the communication of the fIrst scheme, and allocates a resource within a second
frequency range for the communication ofthe second scheme.
Claim 8
25 The wireless communication device according to claim 7,
wherein the fIrst frequency range is a frequency range to which a resource
for transmitting the reference signal with weight is allocated, and
wherein the second frequency range is a frequency range to which a
resource for transmitting the reference signal is allocated.
30
Claim 9
f
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The wireless communication device according to claim 8,
wherein the first scheme is multi user multi input multi output (MU-MIMO),
the second scheme is single user multi input multi output (SU-MIMO).
5 Claim 10
The wireless communication device according to claim 3, further
compnsmg:
a scheduler that allocates a resource for communication of a first scheme or
. a second scheme to each communication partner, wherein,
10 the scheduler allocates, for the communication of the first scheme, a
resource within a frequency range to which a resource for transmitting the reference
signal with weight is allocated, and allocates, for the communication of the first
scheme or the second scheme, a resource within a frequency range to which a
resource for transmitting the reference signal is allocated.
15
Claim 11
The wireless communication device according to claim 3,
wherein update frequency of the second transmission weight is higher than
update frequency of the first transmission weight.
20
Claim 12
The wireless communication device according to claim 11,
wherein the fust transmission weight is weight for forming directivity, and
the second transmission weight is non-directional weight for adjusting a phase.
25
Claim 13
A program for causing a computer to function as a wireless communication
device that includes:
a communication unit that transmits a reference signal;
30 a first multiplication unit that performs multiplication of first transmission
weight that is determined based on reception of the reference signal by a
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communication partner; and
a second multiplication unit that performs multiplication of second
transmission weight that is determined based on reception of the reference signal by
the communication partner, and
5 wherein the communication unit transmits a reference signal with weight
that is obtained by multiplying the reference signal by the fIrst transmission weight
after determination of the fust transmission weight.
Claim 14
10 A wireless communication method comprising:
transmitting a reference signal;
multiplying the reference signal by fust transmission weight that is
determined based on reception of the reference signal by a communication partner;
and
15 transmitting a reference signal with weight that is obtained by multiplying
the reference signal by the fIrst transmission weight.
Claim 15
A wireless communication system comprising:
20 a fIrst wireless communication device; and
a second wireless communication device that includes,
a communication unit that transmits a reference signal,
a fust multiplication unit that performs multiplication of fust
transmission weight that is determined based on reception of the reference signal by
25 the fIrst wireless communication device, and
a second multiplication unit that performs multiplication of second
transmission weight that is determined based on reception of the reference signal by
the fust wireless communication device, and
wherein the communication unit transmits a reference signal with weight
30 that is obtained by multiplying the reference signal by the fIrst transmission weight
after determination of the fIrst transmission weight.
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Claim 16
A wireless communication device comprising:
. a communication unit that receives a reference signal from a communication
5 partner; and
a weight determination unit that determines first transmission weight and
second transmission weight based on a reception result of the reference signal by the
communication unit, and
wherein when a reference signal with weight thafis obtained by multiplying
10 the reference signal by the first transmission weight is received by the
communication unit, the weight determination unit determines the second
transmission weight based on a reception result of the reference signal with weight.
Claim 17
15 A wireless communication device comprising:
a scheduler that allocates a resource for communication of a first scheme or
a second scheme to each communication partner,
wherein the scheduler allocates a resource within a first frequency range for
'.
the communication of the first scheme, and allocates a resource within a second
20 frequency range for the communication of the second scheme.
Claim 18
The wireless communication device according to claim 17,
wherein the first scheme is multi user multi input multi output (MU-MIMO),
25 and thesecond scheme is single user multi input multi output (SU-MIMO).