Description
Title of Invention
BASE STATION, COMMUNICATION SYSTEM AND COMMUNICATION
5 METHOD
Technical Field
[0001]
The present invention relates to a base station, a communication system, and
10 a communication method.
Background Art
[0002]
Recently, introduction of a 4 generation cellular system (4G) has been
15 under discussion in order to achieve improvement of additional performance of
wireless communication. In 4G, techniques such as a relay technique, a carrier
aggregation, and a coordinated multiple point transmission and reception (CoMP) are
attracting attention.
[0003] j
20 The relay technique refers to a technique by which a relay node relays
communication between a base station (for example, a macro cell base station) and a
communication terminal, and the relay technique is important in improving the
throughput at a cell edge of a base station. The carrier aggregation is a technique in
which a use bandwidth is increased and a maximum throughput is improved by
25 collectively treating a plurality of frequency bands each having a bandwidth of 20
MHz. CoMP is a technique by which a plurality of base stations collaborate with
each other to perform data communication with a communication terminal, and the
coverage of high-data-rate communication can be increased.
[0004]
30 In further detail, CoMP refers to a technique by which a plurality of base
stations simultaneously perform data communication with one communication
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terminal. According to this technique, since branches of a plurality of base stations
can be used for data communication, an antenna gain and a signal to interference plus
noise ratio (SINR) can be improved.
[0005]
5 Here, it is assumed that a base station has calculated a weight of a branch
based on a channel matrix of an uplink from a communication terminal and then has
obtained reception directivity. In this case, when a weight of a branch is used even
at the time of transmission, transmission directivity matching reception directivity is
considered to be obtained. However, since a transfer function of a transmission
10 analog unit and a transfer function of a reception analog unit of each branch are
different from each other, actual transmission directivity does not match reception
directivity.
[0006]
Problems caused due to the difference between the transfer function of the
15 transmission analog unit and the transfer function of the reception analog unit of each
branch are solved such that each base station individually performs branch
calibration and a calibration coefficient of each branch. The calibration coefficient
is a coefficient used to regularize a ratio of the transfer function of the transmission
analog unit and the transfer function of the reception analog unit of each branch in
20 one base station. The branch calibration is disclosed in, for example, Patent
Literature 1 and Patent Literature 2.
Citation List
Patent Literature
25 [0007]
Patent Literature 1: JP 2009-188546A
Patent Literature 2: JP 2007-116489A
Summary of Invention
30 Technical Problem
[0008]
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However, in the above-described individual branch calibration, it is possible
to obtain the calibration coefficient used to regularize the ratio of the transfer
function of the transmission analog unit and the transfer function of the reception
analog unit of each branch in one base station, but it is difficult to regularize the
5 ratios of the transfer function of the transmission analog unit and the transfer
function of the reception analog unit of all branches in a plurality of base stations.
For this reason, using only a method in which each base station individually
performs branch calibration, it is difficult to treat all branches in a plurality of base
stations performing CoMP equivalently to a plurality of branches in one device in
10 which branch calibration has been completed. In other words, when CoMP is
performed using branches of a plurality of base stations in an aggregate manner, it is
difficult to match uplink directivity with downlink directivity.
[0009]
Further, when each base station individually performs branch calibration,
15 each base station individually forms directivity and performs a CoMP, but efficient
communication is expected to be difficult to perform. For example, when three
base stations having two branches individually perform branch calibration, it is
possible to implement MIMO communication of 2*N of 3 sets (N is the number of
branches at a communication terminal side), but it is difficult to implement MIMO
20 communication of6*N of a higher throughput.
[0010]
In this regard, the present invention is made in light of the above-mentioned
problems, and it is an object of the present invention to provide a base station, a
communication system, and a communication method, which are novel and
25 improved, and which are capable of efficiently performing collaborative branch
calibration through branches in a plurality of base stations.
Solution to Problem
[0011]
30 In order to solve the above-mentioned problems, according to an aspect of
the present invention, there is provided a base station including a plurality of
1
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branches that perform CoMP transmission with another base station and a
multiplying unit that multiplies a transmission signal from each of the plurality of
branches by a calibration coefficient of each of the plurality of branches, wherein the
calibration coefficient is a coefficient obtained by adjusting an individual calibration
5 coefficient acquired by branch calibration between the plurality of branches in the
base station based on a branch calibration result between a branch of the base station
and a branch of the other base station.
[0012]
The calibration coefficient of each of the plurality of branches may be a
10 coefficient obtained by adjusting the individual calibration coefficient of each of the
plurality of branches based on an adjustment coefficient obtained by dividing a
collaborative calibration coefficient of the branch of the base station acquired by
branch calibration between a branch of the base station and a branch of the other base
station by the individual calibration coefficient of the branch of the base station.
15 [0013]
The calibration coefficient of each of the plurality of branches may be a
value obtained by multiplying the individual calibration coefficient of each of the
plurality of branches by the adjustment coefficient.
[0014]
20 Further, in order to solve the above-mentioned problem, according to
another aspect of the present invention, there is provided a base station including a
plurality of branches that perform CoMP transmission with another base station, a
storage unit that stores a calibration coefficient for each of the plurality of branches,
and a multiplying unit that multiplies a transmission signal from each of the plurality
25 of branches by the calibration coefficient, wherein the calibration coefficient of each
of the plurality of branches is updated by adjusting an individual calibration
coefficient acquired by branch calibration between the plurality of branches in the
base station based on a branch calibration result between a branch of the base station
and a branch of the other base station.
30 [0015]
The calibration coefficient of each of the plurality of branches may be
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updated by adjusting the individual calibration coefficient of each of the plurality of
branches based on an update coefficient obtained by branch calibration between a
branch of the base station and a branch of the other base station, the update
coefficient may be a coefficient obtained by dividing a value obtained by multiplying
5 a collaborative calibration coefficient of the branch of the base station acquired by
branch calibration between a branch of the base station and a branch of the other base
station by a correction coefficient by the individual calibration coefficient of the
branch of the base station, and the correction coefficient may be a coefficient causing
a collaborative calibration coefficient of the branch of the other base station acquired
10 by branch calibration between a branch of the base station and a branch of the other
base station to be used as an in-use collaborative calibration coefficient of the branch
of the other base station.
[0016]
Further, in order to solve the above-mentioned problem, according to
15 another aspect of the present invention, there is provided a communication system
including a plurality of base stations, each of the plurality of base stations including a
plurality of branches that perform CoMP transmission with another base station, and
a multiplying unit that multiplies a transmission signal from each of the plurality of branches by a calibration coefficient of each of the plurality of branches, wherein the
20 calibration coefficient is a coefficient obtained by adjusting an individual calibration
coefficient acquired by branch calibration between the plurality of branches in the
base station based on a branch calibration result between a branch of the base station
and a branch of the other base station.
[0017]
25 Further, in order to solve the above-mentioned problem, according to
another aspect of the present invention, there is provided a communication system
including a plurality of base stations, each of the plurality of base stations including a
plurality of branches that perform CoMP transmission with another base station, a
storage unit that stores a calibration coefficient for each of the plurality of branches,
30 and a multiplying unit that multiplies a transmission signal from each of the plurality
of branches by the calibration coefficient, wherein the calibration coefficient of each
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of the plurality of branches is updated by adjusting an individual calibration
coefficient acquired by branch calibration between the plurality of branches in the
base station based on a branch calibration result between a branch of the base station
and a branch of the other base station.
5 [0018]
Further, in order to solve the above-mentioned problem, according to
another aspect of the present invention, there is provided a communication method
including, performing, by each of a plurality of base stations, each of which includes
a plurality of branches and performs CoMP transmission, branch calibration between
10 the plurality of branches in a base station, and acquiring an individual calibration
coefficient corresponding to each of the plurality of branches, performing branch
calibration between branches of the plurality of base stations, acquiring a calibration
coefficient by adjusting the individual calibration coefficient corresponding to each
of the plurality of branches based on a branch calibration result between branches of
15 the plurality of base stations, and multiplying a transmission signal from each of the
plurality of branches of the base station by the calibration coefficient of each of the
plurality of branches.
Advantageous Effects of Invention
20 [0019]
As described above, according to the present invention, it is possible to
efficiently perform collaborative branch calibration through branches in a plurality of j
base stations.
25 Brief Description of Drawings
[0020]
[Fig. 1] Fig. 1 is an explanatory view illustrating a configuration of a
communication system 1 according to an embodiment of the present invention.
[Fig. 2] Fig. 2 is an explanatory view illustrating a configuration of a branch
30 of the base station 10.
[Fig. 3] Fig. 3 is an explanatory view illustrating an individual branch
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calibration process.
[Fig. 4] Fig. 4 is an explanatory view illustrating an individual branch
calibration process.
[Fig. 5] Fig. 5 is an explanatory view illustrating a configuration of the base
5 station 10.
[Fig. 6] Fig. 6 is a flowchart illustrating an operation of the base station 10.
[Fig. 7] Fig. 7 is an explanatory view illustrating a process of initially
acquiring calibration for CoMP.
[Fig. 8] Fig. 8 is an explanatory view illustrating a process of initially
10 acquiring calibration for CoMP.
[Fig. 9] Fig. 9 is an explanatory view illustrating a process of initially
acquiring calibration for CoMP.
[Fig. 10] Fig. 10 is an explanatory view illustrating a process of initially
acquiring calibration for CoMP.
15 [Fig. 11] Fig. 11 is a flowchart illustrating an operation of the base station
10.
[Fig. 12] Fig. 12 is an explanatory view illustrating a process of updating
calibration for CoMP.
[Fig. 13] Fig. 13 is an explanatory view illustrating a process of updating
20 calibration for CoMP.
Description of Embodiments
[0021]
Hereinafter, preferred embodiments of the present invention will be
25 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
omitted.
[0022]
30 Further, in this specification and the drawings, a plurality of elements
having substantially the same function and structure may be distinguished from each
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other such that different letters are suffixed to the same reference signal. For
example, a plurality of elements having substantially the same function and structure
are distinguished from each other such as base stations 10A, 10B and IOC as
necessary. However, when it is unnecessary to individually distinguish a plurality
5 of elements having substantially the same function and structure, only the same
reference signal is attached. For example, when it is unnecessary to particularly
distinguish base stations 10A, 10B, and IOC, they are referred to simply as a base
station 10.
[0023]
10 Further, an "embodiment for embodying the invention" will be described in
the following order.
1. Overall Configuration of Communication System
2. Configuration of Base Station
3. Initial Acquisition of Calibration Coefficient 15 4. Update of Calibration Coefficient
5. Summary
[0024]
<1. Overall Configuration of Communication System>
First, an overall configuration of a communication system 1 according to an
20 embodiment of the present invention will be described with reference to Fig. 1.
[0025]
Fig. 1 is an explanatory view illustrating a configuration of the '
communication system 1 according to an embodiment of the present invention. As
illustrated in Fig. 1, the communication system 1 according to an embodiment of the
25 present invention includes a plurality of base stations 10 and a communication
terminal 20.
[0026]
The communication terminal 20 (UE: User Equipment) performs
communication with the base station 10 under control of the base station 10. For
30 example, the communication terminal 20 performs a reception process in a downlink
resource block assigned by the base station 10, and performs a transmission process
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in an uplink resource block.
[0027]
The communication terminal 20 may be an information processing device
such as a personal computer (PC), a video processing device for home use (a DVD
5 recorder, a videocassette recorder, and the like), a personal digital assistant (PDA), a
game machine for home use, or a household electrical appliance. Further, the
communication terminal 20 may be a mobile communication device such as a
portable telephone, a personal handyphone system (PHS), a portable music
reproducing device, a portable video processing device, or a portable game machine.
10 [0028]
The base station 10 performs communication with the communication
terminal 20 located within its coverage. For example, a base station 10A can
perform communication with a communication terminal 20A located within the
coverage of the base station 10A. In this disclosure, the description will proceed
15 under the assumption that the base station 10 is a macro cell base station (eNodeB),
but the base station 10 is not limited to the macro cell base station. For example,
the base station 10 may be a pico cell/micro cell base station which is smaller in
maximum transmission power than a macro cell base station or may be a relay node
or a femto cell base station.
20 [0029]
Each base station 10 is connected in a wired manner, and can exchange
information with another base station 10 through wired communication. The base
station 10 can implement CoMP which is expected as a next generation technology
based on this information exchange. CoMP is classified roughly into joint
25 processing, and coordinated scheduling and/or beamforming.
[0030]
The joint processing of the former is a technique by which a plurality of
base stations 10 simultaneously perform data communication with one
communication terminal 20. An example in which the base station 10A, the base
30 station 10B, and the base station 10C simultaneously transmit data to the
communication terminal 20A as illustrated in Fig. 1 corresponds to the joint
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processing. According to the joint processing, branches (antennas and analog
circuits) of a plurality of base stations 10 can be used for data communication, and
the antenna gain and the SINR can be improved.
[0031]
5 Further, when downlink joint processing is performed, it is necessary to
distribute transmission data to be directed to the communication terminal 20 to a
plurality of base stations 10 in advance using a wired communication path, called, for
example, a backhaul, between the base stations 10. Further, uplink joint processing
is performed by aggregating data which a plurality of base stations 10 have received
10 from the communication terminal 20.
[0032]
For example, a method of aggregating data at a bit level after decoding by
each base station 10, a method of aggregating data at a soft bit stage before decoding
by each base station 10, or a method of aggregating data before de-mapping by each
15 base station 10 may be used as a data aggregation method. As an amount of
aggregated data increases after a subsequent demodulation process is performed by
each base station 10, an amount of data exchanged through a backhaul increases, but
a performance tends to be improved.
[0033]
20 The coordinated scheduling and/or beam forming of the latter is a technique
by which data transmission is performed only by the one base station 10, and
scheduling (control of deciding a resource block to be assigned to each
communication terminal 20) is performed based on collaboration of a plurality of
base stations 10. According to the coordinated scheduling and/or beam forming,
25 interference between a plurality of base stations 10 can be easily avoided by
scheduling adjustment.
[0034]
The present invention is focused particularly on the joint processing of the
former among the two types of CoMPs described above. The joint processing is
30 classified roughly into non-coferent joint processing and coferent joint processing.
[0035]
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The coferent joint processing is a method in which a transmission timing of
data from each base station 10 is adjusted such that phases of pieces of data arriving
at the communication terminal 20 from the base station 10 match each other. On
the other hand, the non-coferent joint processing is a method in which each base
5 station 10 transmits data without adjusting a transmission timing of data from each
base station 10. Thus, the coferent joint processing is higher in performance than
the non-coferent joint processing. However, in order to perform the coferent joint
processing, it is necessary to calculate an adjustment amount of a transmission timing
of each base station 10 for each communication terminal 20, and thus there is a
10 disadvantage that processing becomes complicated.
[0036]
In this regard, it is desirable to treat all branches in the plurality of base
stations 10 performing CoMP (which represents the joint processing; the same
hereinafter) transmission equivalently to a plurality of branches in one device in
15 which branch calibration has been completed. Here, when such treatment can be
made, it is possible to match uplink directivity with downlink directivity when CoMP
is performed using the branches of the plurality of base stations 10 in an aggregation
manner, and thus it is unnecessary to adjust a transmission timing of each base
station 10 for each communication terminal 20.
20 [0037]
However, even when each base station 10 individually performs branch
calibration, not all branches in the plurality of base stations 10 are treated
equivalently to a plurality of branches in one device in which branch calibration has
been completed. Thus, even when each base station 10 individually performs
25 branch calibration, it is difficult to match uplink directivity with downlink directivity
when CoMP is performed using the branches of the plurality of base stations 10 in an
aggregation manner. The reason will be described below together with the details
of individual calibration and a branch configuration of the base station 10.
[0038]
30 (Individual Branch Calibration)
Fig. 2 is an explanatory view illustrating a configuration of a branch of the ;
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base station 10. As illustrated in Fig. 2, an analog unit 110 of the base station 10
includes a branch bO, a branch bl, and a branch b2. Each branch includes an
antenna A, a switch S, a transmission analog unit, Tx (which may include a digital toanalog
(DA) converting unit), and a reception analog unit Rx (which may include an
5 analog-to-digital (AD) converting unit). Although Fig. 2 illustrates an example in
which the base station 10 includes three branches, the number of branches included
in the base station 10 is not limited to three. For example, the number of branches
included in the base station 10 may be two or may be four or more.
[0039]
10 At the time of transmission, the antenna A configuring each branch is
connected to the transmission analog unit Tx through the switch S. The
transmission analog unit Tx executes analog processing on a transmission signal
supplied from a digital unit 150, and then supplies a high frequency signal which has
been subjected to the analog processing to the antenna A. The antenna A converts
15 the high frequency signal supplied from the transmission analog unit Tx into a radio
signal, and then transmits the radio signal.
[0040]
Meanwhile, at the time of reception, the antenna A is connected to the
reception analog unit Rx through the switch S. The antenna A converts a received
20 radio signal into a high frequency signal, and then supplies the high frequency signal
to the reception analog unit Rx. The reception analog unit Rx executes analog
processing on the high frequency signal supplied from the antenna A, and then
supplies the reception signal which has been subjected to the analog processing to the
digital unit 150.
25 [0041]
The antenna A, the transmission analog unit Tx, and the reception analog
unit Rx have a transfer function (characteristic) that differs according to a branch.
In addition, even inside the same branch, the transfer function of the transmission
analog unit Tx differs in phase from the transfer function of the reception analog unit
30 Rx. The problems caused due to the difference between the transfer function of the
transmission analog unit Tx and the transfer function of the reception analog unit Rx
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of each branch in the base station 10 are solved such that the base station 10
individually performs branch calibration. The branch calibration individually
performed by the base station 10 will be concretely described below.
[0042]
5 Let us assume that a branch number is i, a transfer function of a
transmission analog unit Tx of an ith branch is Tx(i), and a transfer function of a
reception analog unit Rx of the i* branch is Rx(i). In this case, the branch
calibration corresponds to a process of acquiring a calibration coefficient K(i) for
each branch satisfying the following Formula 1. In a broad sense, the branch
10 calibration corresponds to a process of complex-multiplying the transmission signal
or the reception signal by the calibration coefficient K(i).
[0043]
Tx(0)*K(0)/Rx(0)=Tx(l)*K(l)/Rx(l)=Tx(2)*K(2)/Rx(2) (Formula 1)
[0044]
15 In order to acquire the calibration coefficient K(i), first, the branch bO
transmits a radio signal, and the branch bl and the branch b2 receive the radio signal
transmitted from the branch bO as illustrated in Fig. 3. Next, the branch bl and the
branch b2 transmit radio signals, and the branch bO receives the radio signals
transmitted from the branch bl and the branch b2, as illustrated in Fig. 4.
20 [0045]
As a result, the following loop-back transfer function D(i,j) is measured.
The loop-back transfer function D(i j ) is a coefficient which is measured from a radio
signal which passes through a transmission branch i and a transmission branch j . A
branch which transmits a radio signal to a plurality of branches and receives radio
25 signals from a plurality of branches is referred to as a "reference branch."
[0046]
D(0,l)=Tx(0)*Rx(l)
D(0,2)=Tx(0)*Rx(2)
D(l,0)=Tx(l)*Rx(0)
30 D(2,0)=Tx(2)*Rx(0)
[0047]
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The base station 10 can acquire the calibration coefficient K(i) based on the
loop-back transfer function D(i j ) according to the following Formula 2.
[0048]
K(0)=1.0
5 K(l)=D(0,l)/D(l,0)={Rx(l)/Tx(l)}*{Tx(0)/Rx(0)}
K(2)=D(0,2)/D(2,0)-{Rx(2)/Tx(2)}*{Tx(0)/Rx(0)} (Formula 2)
[0049]
Here, when verification of Formula 2 is performed, Formula 1 used as the
calibration condition is verified to be satisfied as expressed in the following Formula
10 3.
[0050]
Tx(0)*K(0)/Rx(0)=Tx(0)/Rx(0)
Tx(l)*K(l)/Rx(l)=Tx(0)/Rx(0) (Formula 3)
Tx(2)*K(2)/Rx(2)=Tx(0)/Rx(0)
15 [0051]
Further, as expressed in Formula 2, a calibration coefficient K(0) of the 0th
branch bO becomes 1.0 because branch calibration has been performed using the
branch bO as the reference branch. Thus, when branch calibration has been
performed using the branch bl as the reference branch, a calibration coefficient K(l)
20 of the 1st branch bl becomes 1.0.
[0052]
(Problem of Individual Branch Calibration)
As described above, according to individual branch calibration, it is possible
to regularize the ratio of the transfer function of the transmission analog unit Tx and
25 the transfer function of the reception analog unit Rx of all branches in each base
station 10. However, even when the individual branch calibration is performed by
each base station 10, since reference antennas of the individual branch calibration by
the base stations 10 are different from each other, it is difficult to regularize the ratio
of the transfer function of the transmission analog unit Tx and the transfer function
30 of the reception analog unit Rx of branches in a different base station 10. In other
words, it is difficult to treat all branches in a plurality of base stations 10 performing
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CoMP transmission equivalently to a plurality of branches in one device in which
branch calibration has been completed.
[0053]
Meanwhile, when the plurality of base stations 10 perform branch
5 calibration together using the same branch as the reference branch, it is possible to
regularize the ratio of the transfer function of the transmission analog unit Tx and the
transfer function of the reception analog unit Rx of all branches in the plurality of
base stations 10. In other words, it is considered possible to treat all branches in a
plurality of base stations 10 performing CoMP transmission equivalently to a
10 plurality of branches in one device in which branch calibration has been completed.
[0054]
However, in the method in which the plurality of base stations 10 perform
branch calibration together using the same branch as the reference branch, for
example, it is necessary to sequentially transmit radio signals from all branches of a
15 calibration target, and thus a commensurate time is expended. As a result, it is also
feared that the branch calibration will adversely affect communication performed by
the communication terminal 20.
[0055]
In this context, an embodiment of the present disclosure has been made in
20 light of the foregoing. The base station 10 according to an embodiment of the
present invention can efficiently perform collaborative branch calibration with
another base station that performs CoMP transmission together. The base station 10
according to an embodiment of the present invention will be described below in
detail.
25 [0056]
<2. Configuration of Base Station>
Fig. 5 is a functional block diagram illustrating a configuration of the base
station 10 according to an embodiment of the present invention. As illustrated in
Fig. 5, the base station 10 according to an embodiment of the present invention
30 includes an analog unit 110, a backhaul communication unit 120, a digital unit 150,
an upper layer unit 180, and a storage unit 190.
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[0057]
The backhaul communication unit 120 is an interface used to exchange
information with another base station through a wired communication path. For
example, the base station 10 transmits/receives a loop-back transfer function
5 obtained in the process of collaborative branch calibration or calibration coefficient
update, which will be described later, to/from another base station through the
backhaul communication unit 120.
[0058]
The digital unit 150 includes an AD/DA converting unit 152, a
10 demodulation processing unit 160, and a modulation processing unit 170 as
illustrated in Fig. 5. The components of the digital unit 150 may be disposed for
each branch. '
[0059]
The AD/DA converting unit 152 converts a reception signal of an analog
15 format supplied from the analog unit 110 into a signal of a digital format, and
converts a transmission signal of a digital format supplied from the modulation
processing unit 170 into a signal of an analog format.
[0060]
The demodulation processing unit 160 performs various kinds of processing
20 to demodulate the reception signal supplied from the AD/DA converting unit 152.
For example, the demodulation processing unit 160 performs a Fourier transform, demapping,
error correction, or the like on the reception signal. The demodulation
processing unit 160 includes a synchronizing unit 162 and a transfer function
acquiring unit 164.
25 [0061]
The synchronizing unit 162 acquires synchronization with the reception
signal based on a synchronous signal included in the reception signal. The transfer
function acquiring unit 164 acquires a loop-back transfer function corresponding to a
signal transmission path based on the radio signal received in the process of
30 collaborative branch calibration or calibration coefficient update.
[0062]
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The modulation processing unit 170 performs various kinds of processing to
modulate a transmission signal supplied from an upper layer 180. For example, the
modulation processing unit 170 performs mapping of a transmission signal, an
inverse Fourier transform in an IFFT 174, addition of a guide interval, and the like.
5 A calibration coefficient multiplying unit 172 (multiplying unit) of the modulation
processing unit 170 complex-multiplies a transmission signal from each branch by a
calibration coefficient of each branch read from the storage unit 190 in a frequency
domain.
[0063]
10 The upper layer unit 180 includes an individual calibration coefficient
acquiring unit 182, a calibration coefficient adjusting unit 184, and a calibration
coefficient update unit 186.
[0064]
The individual calibration coefficient acquiring unit 182 acquires a
15 calibration coefficient K for each branch in the base station 10 through the
calculation described in "Individual Branch Calibration." In the following, the
calibration coefficient K for each branch in the base station 10 acquired by the
individual branch calibration is referred to as an "individual calibration coefficient."
[0065] ' :
20 The calibration coefficient adjusting unit 184 initially acquires a calibration
coefficient used when the base station 10 performs CoMP with another base station
by adjusting the individual calibration coefficient acquired by the individual
calibration coefficient acquiring unit 182. Although the details will be described in
"3. Initial Acquisition of Calibration Coefficient," the calibration coefficient
25 adjusting unit 184 adjusts the individual calibration coefficient based on a branch
calibration result between any one branch of the base station 10 and a branch of
another base station. The calibration coefficient obtained through this adjustment is
recorded in the storage unit 190.
[0066]
30 The calibration coefficient update unit 186 updates the calibration
coefficient for CoMP acquired by the calibration coefficient adjusting unit 184.
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This is because the accuracy of the calibration coefficient is considered to be
obsolete after a half day due to a change in temperature or the like. However, it is
difficult for all the base stations 10 performing CoMP to simultaneously update the
calibration coefficient. Further, when the calibration coefficients of some of the
5 base station 10s are updated, mismatching with the calibration coefficient of another
base station may occur.
[0067]
For example, even when some of the base stations 10 update the calibration
coefficient using the same branch as at the time of initial acquisition as the reference
10 branch, the transfer function of the reference branch may change. In this case,
mismatching occurs between the updated calibration coefficient of some of the base
stations 10 and the existing calibration coefficient of another base station.
[0068]
In this regard, the calibration coefficient update unit 186 can update the
15 calibration coefficient by an adjustment based on the branch calibration result
between any one branch of the base station 10 and a branch of another base station.
The calibration coefficient update will be described in detail in "4. Update of
Calibration Coefficient."
[0069]
20 <3. Initial Acquisition of Calibration Coefficient
The configuration of the base station 10 according to an embodiment of the
present invention has been described so far. Next, an initial acquisition method of
the calibration coefficient used when the base station 10 performs CoMP with
another base station will be described in detail.
25 [0070]
First, the terminology related to the calibration coefficient initial acquisition
is defined as follows.
• Individual Calibration Coefficient (i,j)
A calibration coefficient of an ith branch of a base station lOi, which is
30 acquired by performing branch calibration closed by the base station lOi.
[0071]
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• Reference Branch of Individual Calibration
A reference branch set when branch calibration closed by the base station
1 Oi is performed.
[0072]
5 ' Forward Loop-Back Transfer Function D(i,reference)(i j)
A loop-back transfer function from the reference branch of the base station
lOi to ajt h branch of the base station lOi.
[0073]
• Backward Loop-Back Transfer Function D(ij)(i,reference)
10 A loop-back transfer function from the j t h branch of the base station lOi to
the reference branch of the base station lOi.
[0074]
• Use Branch of Each Base Station of Collaborative Calibration
A branch selected for each base station when a plurality of base stations
15 perform collaborative branch calibration. This branch may be different from the
reference branch of the individual calibration.
[0075]
• Reference Branch of Collaborative Calibration
A reference branch set when a plurality of base stations perform
20 collaborative branch calibration. This branch may be one branch set for each
communication terminal 20 or for each relay node.
[0076]
• Forward Loop-Back Transfer Function D(reference)(i,use)
A loop-back transfer function from the reference branch of collaborative
25 calibration to the use branch of the base station lOi
[0077]
' Backward Loop-Back Transfer Function D(i,use)(reference)
A loop-back transfer function from the use branch of the base station 1 Oi to
the reference branch of collaborative calibration.
30 [0078]
• Collaborative Calibration Coefficient (i,use)
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A calibration coefficient of the use branch of the base station lOi acquired
by collaborative calibration
[0079]
• Adjustment Coefficient (i)
5 A coefficient used to adjust the individual calibration coefficient (ij) of the
base station lOi and acquire a final calibration coefficient. The adjustment
coefficient (i) is calculated according to the following Formula 4. In Formula 4, the
j * branch is the same as the use branch of the collaborative calibration.
Adjustment coefficient (i)
10 =collaborative calibration coefficient (i,use)
/the individual calibration coefficient (i,j)
(Formula 4)
[0080]
• Calibration Coefficient (ij)
15 Aj calibration coefficient of the base station lOi, which is used when the
base station lOi performs CoMP with another base station. The calibration
coefficient (i,j) is calculated according to the following Formula 5.
Calibration coefficient (i,j)
= individual calibration coefficient (ij)* adjustment coefficient (i)
20 (Formula 5)
[0081]
(Outline)
Next, an outline of a calibration coefficient acquisition method will be
described with reference to Fig. 6. Fig. 6 is a flowchart illustrating a calibration
25 coefficient acquisition method. First, each of a plurality of base stations 10
performing CoMP acquires the individual calibration coefficient, for example, by the
method described in "Individual Branch Calibration" (step 1).
[0082]
Thereafter, the plurality of base stations 10 perform calibration in
30 collaboration with each other, and acquire the collaborative calibration coefficient
(step 2). This collaborative calibration is branch calibration performed between the
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use branch selected one by one by each base station 10 and the reference branch.
The base stations 10 exchange the loop-back transfer function necessary to acquire
the collaborative calibration coefficient through the backbone communication unit
120. The number of use branches selected by each base station 10 may be two or
5 more rather than one.
[0083]
Subsequently, each base station 10 calculates the adjustment coefficient
based on the individual calibration coefficient and the collaborative calibration
coefficient according to Formula 4 (step 3). Further, each base station 10 acquires
10 the final calibration coefficient by complex multiplying the individual calibration
coefficient of each branch by the adjustment coefficient calculated in step 3 as
expressed in Formula 5 (step 4). Each step will be described below in detail using a
concrete example.
[0084]
15 (Step 1: Acquisition of Individual Calibration Coefficient)
Figs. 7 and 8 are diagrams for describing an individual calibration process.
As illustrated in Fig. 7, each of the base stations 10A to 10C performing CoMP first
transmits a radio signal through the branch bO selected as the reference branch, and
receives the radio signal through the branches bl and b2. Through this operation,
20 each of the base stations 10A to 10C can acquire the forward loop-back transfer
function D(i,reference)(ij). In this example in which the branch bO is selected as
the reference branch, "reference" in (preference) corresponds to "0," and " j " in (ij)
corresponds to " 1 " or "2."
[0085]
25 Subsequently, each of the base stations 10A to 10C transmits the radio
signal through the branches bl and b2 and receives the radio signal through the
branch bO as illustrated in Fig. 8. Through this operation, each of the base stations
10A to 10C can acquire the backward loop-back transfer function D(i,j)(i,reference).
[0086]
30 Then, each of the base stations 10A to 10C acquires the individual
calibration coefficient (i,j) according to the following Formula 6.
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Individual calibration coefficient (i,j)
=D(i,reference)(i,j)/D(i,j)(i,reference)
(Formula 6)
[0087]
5 Here, it is assumed that the following values have been obtained as the
forward loop-back transfer function D(i,reference)(i,j) and the backward loop-back
transfer function D(i,j)(i,reference) as illustrated in Figs. 7 and 8. In the following,
for the sake of simplification of description, each loop-back transfer function D is a
real number, but the loop-back transfer function D may be a complex number.
10 D(A,reference)(A,l)=2.0
D(A,reference)(A,2)=3.0
D(A, 1 )(A,reference)=4.0
D( A,2)( A,reference)= 1.5
D(B,reference)(B,l)=2.0
15 D(B,reference)(B,2)=1.0
D(B,l)(B,reference)=1.0
D(B,2)(B,reference)=2.0
D(C,reference)(C,l)=3.0
D(C,reference)(C,2)=4.0
20 D(C,l)(C,reference)=1.5
D(C,2)(C,reference)=2.0
[0088]
In this case, the individual calibration coefficient (ij) is calculated based on
Formula 6 as follows.
25 Individual calibration coefficient
(A,0)=1.0
(A, 1 )=D(A,reference)( A, 1 )/D(A, 1)(preference)
=2.0/4.0=0.5
(A,2)=D(A,reference)(A,2)/D(A,2)(A,reference)
30 =3.0/1.5=2.0
(B,0)=1.0
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(B, 1 )=D(B,reference)(B, 1 )/D(B, 1 )(B,reference)
=2.0/1.0=2.0
(B,2)=D(B,reference)(B,2)/D(B,2)(B,reference)
=1.0/2.0=0.5
5 (C,0)=1.0
(C, 1 )=D(C,reference)(C, 1 )/D(C, 1 )(C,reference)
=3.0/1.5=2.0
(C,2)=D(C,reference)(C,2)/D(C,2)(C,reference)
=4.0/2.0=2.0
10 [0089]
(Step 2: Acquisition of Collaborative Calibration Coefficient)
Fig. 9 and Fig. 10 are diagrams for describing a collaborative calibration
process. As illustrated in Fig. 9, the use antenna bO selected from each of the base
stations 10A to 10C performing CoMP first receives the radio signal transmitted from
15 the branch of the communication terminal 20A selected as the reference branch.
Through this operation, the base stations 10A to 10C can acquire the forward loopback
transfer function D(reference)(i,use).
[0090]
Subsequently, each of the base stations 10A to 10C transmits the radio
20 signal to the reference branch of the communication terminal 20A through the use
antenna bO as illustrated in Fig. 10. Through this operation, the communication
terminal 20A can acquire the backward loop-back transfer function
D(i,use)(reference).
[0091]
25 Then, each of the base stations 10A to 10C acquires the collaborative
calibration coefficient (i,j) according to the following Formula 7.
Collaborative calibration coefficient (i,use)
=D(reference)(i,use)/D(i,use)(reference)
(Formula 7)
30 [0092]
The loop-back transfer functions are dispersively acquired by the base
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stations 1OA to 1OC and the communication terminal 20A. Thus, each of the base
stations 10A to IOC may exchange the loop-back transfer function necessary to
acquire the collaborative calibration coefficient using a backhaul or wireless
communication.
5 [0093]
Here, it is assumed that the following values have been acquired as the forward loop-back transfer function D(reference)(i,use) and the backward loop-back
transfer function D(i,use)(reference) as illustrated in Figs. 9 and 10.
D(reference)(A,0)=1.0
10 D(A,0)(reference)=0.5
D(reference)(B,0)=3.0
D(B,0)(reference)=1.0
D(reference)(C,0)=2.0
D(C,0)(reference)=2.0
15 [0094]
In this case, the collaborative calibration coefficient (i,use) is calculated
based on Formula 7 as follows.
Collaborative calibration coefficient
(A,0)=D(reference)(A,0)/D(A,0)(reference)
20 =1.0/0.5=2.0
(B,0)=D(reference)(B,0)/D(B,0)(reference)
=3.0/1.0=3.0
(C,0)=D(reference)(C,0)/D(C,0)(reference)
=2.0/2.0=1.0
25 [0095]
(Step 3: Calculation of Adjustment Coefficient)
Each base station 10 calculates the adjustment coefficient (i) according to
Formula 4. Specifically, when the individual calibration coefficient (i,j) and the
collaborative calibration coefficient (i,use) have been obtained, each base station 10
30 calculates the adjustment coefficient (i) as follows.
Adjustment coefficient (A)=collaborative calibration coefficient (A,0)
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/individual calibration coefficient (A,0)
=2.0/1.0=2.0
Adjustment coefficient (B)=collaborative calibration coefficient (B,0)
/individual calibration coefficient (B,0)
5 =3.0/1.0=3.0
Adjustment coefficient (C)=collaborative calibration coefficient (C,0)
/individual calibration coefficient (C,0)
=1.0/1.0=1.0
[0096]
10 (Step 4: Acquisition of Final Calibration Coefficient)
Each base station 10 calculates the final calibration coefficient (i,j) of each
branch according to Formula 5. Specifically, when the individual calibration
coefficient (i,j) and the adjustment coefficient (i) have been obtained, each base
station 10 calculates the final calibration coefficient (i,j) of each branch as follows.
15 Final calibration coefficient
(A,0)=individual calibration coefficient (A,0)*adjustment coefficient (A)
=1.0*2.0=2.0
(A, 1 )=individual calibration coefficient (A, 1 )*adjustment coefficient (A)
=0.5*2.0=1.0
20 (A,2)=individual calibration coefficient (A,2)*adjustment coefficient (A)
=2.0*2.0=4.0
(B,0)= individual calibration coefficient (B,0)*adjustment coefficient (B)
=1.0*3.0=3.0
(B, 1 )=individual calibration coefficient (B, 1 )*adjustment coefficient (B)
25 =2.0*3.0=6.0
(B,2)=individual calibration coefficient (B,2)*adjustment coefficient (B)
=0.5*3.0=1.5
(C,0)=individual calibration coefficient (C,0)*adjustment coefficient (C)
=1.0*1.0=1.0
30 (C,l)=individual calibration coefficient (C,l)*adjustment coefficient (C)
=2.0*1.0=2.0
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(C,2)=individual calibration coefficient (C,2)*adjustment coefficient (C)
=2.0*1.0=2.0
[0097]
<4. Update of Calibration Coefficient
5 As described above, a plurality of base stations 10 perform branch
calibration in collaboration with each other, and thus it is possible to acquire the
matching calibration coefficient among all branches of a plurality of base stations 10.
Next, a method of updating some calibration coefficients will be described in detail.
[0098]
10 First, the terminology related to calibration coefficient updating is defined
as follows.
• Target Base Station
A base station whose calibration coefficient is to be updated.
[0099]
15 • Cooperative Base Station
A base station that cooperates to update the calibration coefficient of the
target base station.
[0100]
• Individual Calibration Coefficient (i,j)
20 A calibration coefficient of the i-th branch of the base station lOi, which is
acquired by performing branch calibration closed by the base station 1 Oi.
[0101]
• Forward Loop-Back Transfer Function D(reference)(i,use)
A loop-back transfer function from the reference branch of collaborative
25 calibration to the use branch of the base station lOi
[0102]
• Backward Loop-Back Transfer Function D(i,use)(reference)
A loop-back transfer function from the use branch of the base station 1 Oi to
the reference branch of collaborative calibration.
30 [0103]
• Collaborative Calibration Coefficient (i,use)
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#
A calibration coefficient of the use branch of the base station lOi, which is
acquired by collaborative calibration.
[0104]
• Correction Coefficient
5 A coefficient used to match the collaborative calibration coefficient (i,use)
of the use branch of the cooperative base station with the current calibration
coefficient of the use branch of the cooperative base station.
[0105]
• Corrected Collaborative Calibration Coefficient (i,use)
10 A collaborative calibration coefficient (i,use) corrected by the correction
coefficient. Specifically, a value obtained by multiplying the correction coefficient
by the collaborative calibration coefficient (i,use).
[0106]
• Update Coefficient (i)
15 A coefficient used to adjust the individual calibration coefficient (ij) of the
target base station, whereby the updated calibration coefficient is acquired. The
update coefficient (i) is calculated according to the following Formula 8. In
Formula 8, the j t h branch is the same as the use branch of the collaborative calibration.
Update coefficient (i)=corrected collaborative calibration coefficient (i,use)
20 /individual calibration coefficient (i,j)
(Formula 8)
[0107]
• Calibration Coefficient (i,j)
Aj* calibration coefficient of the base station lOi used when the base station
25 lOi performs CoMP with another base station. The calibration coefficient (i,j) is
calculated according to the following Formula 9.
Calibration coefficient (i,j)
individual calibration coefficient (ij)*update coefficient (i)
(Formula 9)
30 [0108]
(Outline)
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Next, an outline of a calibration coefficient update method will be described
with reference to Fig. 11. Fig. 11 is a flowchart illustrating a calibration coefficient
update method. As illustrated in Fig. 11, first, a target base station whose
calibration coefficient for CoMP needs to be updated and a cooperative base station
5 that cooperates in updating are decided (step 1). Subsequently, the target base
station performs individual calibration, and acquires the individual calibration
coefficient of each branch (step 2).
[0109]
Thereafter, the target base station and the cooperative base station perform
10 calibration in collaboration with each other, and acquire the collaborative calibration
coefficient (step 3). This collaborative calibration is branch calibration performed
between the use branch selected individually by the target base station and the
cooperative base station and the reference branch.
[0110]
15 Subsequently, the cooperative base station calculates the correction
coefficient used to match the collaborative calibration coefficient of the use branch of
the cooperative base station acquired in step 3 with the calibration coefficient of the
use branch currently stored in the storage unit 190 (step 4).
[0111]
20 Further, the target base station multiplies the collaborative calibration
coefficient of the use branch of the target base station acquired in step 3 by the
correction coefficient calculated in step 4, and calculates the corrected collaborative
calibration coefficient (step 5). Then, the target base station calculates the update
coefficient according to Formula 8 (step 6), and then acquires the final calibration
25 coefficient according to Formula 9 (step 7). Each step will be described below in
detail using a concrete example.
[0112]
(Step 1: Decision of Target Base Station and Cooperative Base Station)
The target base station is the base station 10 whose calibration coefficient
30 for CoMP is to be updated as described above. Here, the accuracy of the calibration
coefficient degrades with the lapse of time. In this regard, the base station 10 may
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decide itself as the target base station when a predetermined time elapses after the
calibration coefficient for CoMP is acquired or updated. Further, the base station 10
may decide a base station present at the position at which collaborative calibration
with the target base station is performed as the cooperative base station. In the
5 following, the process will be described under the assumption that among the base
stations 10A to IOC whose calibration coefficients are acquired by the process
illustrated Figs. 9 and 10, the base station 10A is decided as a target cell, and the base
station IOC is decided as a cooperative cell.
[0113]
10 (Step 2: Individual Calibration by Target Base Station)
The base station 10A decided as the target cell base station acquires the
forward loop-back transfer function D(A,reference)(A,j) and the backward loop-back
transfer function D(A,j)(A,reference), and then acquires the individual calibration
coefficient (A,j) based on the functions. Here, it is assumed that the following
15 individual calibration coefficient (A,j) has been acquired. As will be described
below, the individual calibration coefficient (A,j) acquired at the time of update is
expected to be different from the individual calibration coefficient (A,j) acquired at
the time of initial acquisition.
Individual calibration coefficient
20 (A,0)=1.0
(A,l)=0.6
(A,2)=2.2
[0114]
(Step 3: Collaborative Calibration)
25 Fig. 12 and Fig. 13 are diagrams for describing a collaborative calibration
process. As illustrated in Fig. 12, the use antennas bO selected from the base station
10A serving as the target base station and the cooperative base station 10C first
receive the radio signal transmitted from the branch of the communication terminal
20A selected as the reference branch. Through this operation, the base stations 10A
30 and 10C can acquire the forward loop-back transfer function D(reference)(i,use).
[0115]
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Subsequently, each of the base stations 10A and IOC transmits the radio
signal to the reference branch of the communication terminal 20A through the use
antenna bO as illustrated in Fig. 13. Through this operation, the communication
terminal 20A can acquire the backward loop-back transfer function
5 D(i,use)(reference).
[0116]
Then, each of the base stations 10A and IOC acquires the collaborative
calibration coefficient (i,j) according to Formula 7. The loop-back transfer
functions are dispersively acquired by the base stations 10A and IOC and the
10 communication terminal 20A. Thus, the base stations 10A and IOC may exchange
the loop-back transfer function necessary to acquire the collaborative calibration
coefficient using a backhaul or wireless communication.
[0117]
Here, as illustrated in Figs. 12 and 13, it is assumed that the following
15 values have been obtained as the forward loop-back transfer function
D(reference)(i,use) and the backward loop-back transfer function D(i,use)(reference).
D(reference)(A,0)=0.9
D(A,0)(reference)=0.6
D(reference)(C,0)=2.1
20 D(C,0)(reference)=1.9
[0118]
In this case, the collaborative calibration coefficient (i,use) is calculated
based on Formula 7 as follows.
Collaborative calibration coefficient
25 (A,0)=D(reference)(A,0)/D(A,0)(reference)
=0.9/0.6=1.5
(C,0)=D(reference)(C,0)/D(C,0)(reference)
=2.1/1.9«1.1
[0119]
30 (Step 4: Calculation of Correction Coefficient)
The base station 10C serving as the cooperative base station calculates a
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coefficient used to match the collaborative calibration coefficient (C,0) of the use
branch of the cooperative base station acquired in step 3 with the current calibration
coefficient (C,0) of the use branch of the base station IOC. Here, when the current
calibration coefficient (C,0) of the use branch of the base station IOC is "1.0," the
5 correction coefficient is calculated as follows.
Correction coefficient=current calibration coefficient (C,0)
/collaborative calibration coefficient (C,0)
*0.909
[0120]
10 (Step 5: Calculation of Corrected Collaborative Calibration Coefficient)
The base station 10A serving as the target base station multiplies the
collaborative calibration coefficient (A,0) of the use branch of the base station 10A
acquired in step 3 by the correction coefficient calculated in step 4, and calculates the
corrected collaborative calibration coefficient (i,use). Specifically, the corrected
15 collaborative calibration coefficient (i,use) is calculated as follows.
Corrected collaborative calibration coefficient (i,0)
=collaborative calibration coefficient (A,0)*correction coefficient
=1.5*0.909*1.36
[0121]
20 (Step 6: Calculation of Update Coefficient)
The base station 10A calculates the update coefficient (A) according to
Formula 8 based on the corrected collaborative calibration coefficient (A,0) and the
individual calibration coefficient (A,0). Specifically, the update coefficient (A) is
calculated as follows.
25 Update coefficient (A)=corrected collaborative calibration coefficient (A,0)
/individual calibration coefficient (A,0)
=1.36/1.0=1.36
[0122]
(Step 7: Acquisition of Final Calibration Coefficient) , '
30 The base station 10A serving as the target base station calculates the final
calibration coefficient (A,j) of each branch according to Formula 9. Specifically,
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when the individual calibration coefficient (A,j) and the update coefficient (A) have
been obtained, the base station 10A calculates the final calibration coefficient (Aj) of
each branch as follows.
Final calibration coefficient
5 (A,0)=individual calibration coefficient (A,0)*update coefficient (A)
=1.0*1.36=1.36
(A,l)=individual calibration coefficient (A,l)*update coefficient (A)
=0.6*1.36*0.82
(A,2)=individual calibration coefficient (A,2)*update coefficient (A)
10 =2.2*1.36«2.99
[0123]
<5. Conclusion>
As described above, the base station 10 according to an embodiment of the [
present invention can acquire and update the calibration coefficient for CoMP by j
15 adjusting the individual calibration coefficient acquired by individually performing
branch calibration to match the individual calibration coefficient of another base j
station. I
[0124] j
The preferred embodiments of the present invention have been described !
20 above in detail with reference to the accompanying drawings, whilst the technical
scope of the present disclosure is not limited to the above examples, of course. A
person skilled in the art may find 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 present disclosure.
25 [0125]
For example, steps of the processes of the base station 10 of the present
disclosure need not necessarily be processed in time series according to an order
described as a flowchart. For example, steps of the processes of the base station 10
of the present disclosure may be processed in an order different from an order
30 described as a flowchart or in parallel.
[0126]
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Further, a computer program may be created that causes hardware, which is
installed in the base station 10 such as a central processing unit (CPU), a read only
memory (ROM), and a random access memory (RAM) to perform functions
equivalent to the components of the base station 10. Further, a storage medium
5 storing the computer program is also provided.
Reference Signs List
[0127]
10 base station
10 20 communication terminal
110 analog unit
120 backhaul communication unit
150 digital unit
160 demodulation processing unit
15 164 transfer function acquiring unit
170 modulation processing unit
172 calibration coefficient multiplying unit
180 upper layer unit
182 calibration coefficient acquiring unit
20 184 calibration coefficient adjusting unit
186 calibration coefficient update unit
190 storage unit

CLAIMS
Claim 1
A base station, comprising:
a plurality of branches that perform CoMP transmission with another base
5 station; and
a multiplying unit that multiplies a transmission signal from each of the
plurality of branches by a calibration coefiFicient of each of the plurality of branches,
wherein the calibration coefficient is a coefficient obtained by adjusting an
individual calibration coefficient acquired by branch calibration between the plurality
10 of branches in the base station based on a branch calibration result between a branch
of the base station and a branch of the other base station.
Claim 2
The base station according to claim 1,
15 wherein the calibration coefficient of each of the plurality of branches is a
coefficient obtained by adjusting the individual calibration coefficient of each of the
plurality of branches based on an adjustment coefficient obtained by dividing a
collaborative calibration coefficient of the branch of the base station acquired by
branch calibration between a branch of the base station and a branch of the other base
20 station by the individual calibration coefficient of the branch of the base station.
Claim 3
The base station according to claim 2,
wherein the calibration coefficient of each of the plurality of branches is a
25 value obtained by multiplying the individual calibration coefficient of each of the
plurality of branches by the adjustment coefficient.
Claim 4
A base station, comprising:
30 a plurality of branches that perform CoMP transmission with another base
station;
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a storage unit that stores a calibration coefficient for each of the pluraUty of
branches; and
a multiplying unit that multiplies a transmission signal from each of the
plurality of branches by the calibration coefficient,
5 wherein the calibration coefficient of each of the plurality of branches is
updated by adjusting an individual calibration coefficient acquired by branch
calibration between the plurality of branches in the base station based on a branch
calibration result between a branch of the base station and a branch of the other base
station.
10
Claim 5
The base station according to claim 4,
wherein the calibration coefficient of each of the plurality of branches is
updated by adjusting the individual calibration coefficient of each of the plurality of
15 branches based on an update coefficient obtained by branch calibration between a
branch of the base station and a branch of the other base station,
the update coefficient is a coefficient obtained by dividing a value obtained
by multiplying a collaborative calibration coefficient of the branch of the base station
acquired by branch calibration between a branch of the base station and a branch of
20 the other base station by a correction coefficient by the individual calibration
coefficient of the branch of the base station, and
the correction coefficient is a coefficient causing a collaborative calibration
coefficient of the branch of the other base station acquired by branch calibration
between a branch of the base station and a branch of the other base station to be used
25 as an in-use collaborative calibration coefficient of the branch of the other base
station.
Claim 6
A communication system, comprising:
30 a plurality of base stations,
each of the plurality of base stations including
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a plurality of branches that perform CoMP transmission with another base
station, and
a multiplying unit that multiplies a transmission signal from each of the
plurality of branches by a calibration coefficient of each of the plurality of branches,
5 wherein the calibration coefficient is a coefficient obtained by adjusting an
individual calibration coefficient acquired by branch calibration between the plurality
of branches in the base station based on a branch calibration result between a branch
of the base station and a branch of the other base station.
10 Claim 7
A communication system, comprising:
a plurality of base stations,
each of the plurality of base stations including
a plurality of branches that perform CoMP transmission with another base
15 station,
a storage unit that stores a calibration coefficient for each of the plurality of
branches, and
a multiplying unit that multiplies a transmission signal from each of the
plurality of branches by the calibration coefficient,
20 wherein the calibration coefficient of each of the plurality of branches is
updated by adjusting an individual calibration coefficient acquired by branch
calibration between the plurality of branches in the base station based on a branch
calibration result between a branch of the base station and a branch of the other base
station.
25
Claim 8
A communication method, comprising:
performing, by each of a plurality of base stations, each of which includes a
plurality of branches and performs CoMP transmission, branch calibration between
30 the plurality of branches in a base station, and acquiring an individual calibration
coefficient corresponding to each of the plurality of branches;
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performing branch calibration between branches of the plurality of base
stations;
acquiring a calibration coefficient by adjusting the individual calibration
coefficient corresponding to each of the plurality of branches based on a branch
5 calibration result between branches of the plurality of base stations; and
multiplying a transmission signal from each of the plurality of branches of
the base station by the calibration coefficient of each of the plurality of branches.