Description
Title of Invention: COMMUNICATION DEVICE AND COMMU¬
NICATION METHOD
Technical Field
[0001] The present invention relates to a communication device, and a communication
method.
Background Art
[0002] Recently, a cellular system of fourth generation (4G) is discussed to achieve further
improvements on the performance of wireless communication. In the 4G, relay
technology, carrier aggregation, and Coordinated Multiple Point transmission and
reception (CoMP) technology are paid attention.
[0003] The relay technology is a technology by which a relay node relays communication
between a base station (for instance, a macrocell base station) and a communication
terminal, and is important in improving cell-edge throughput of the base station.
Moreover, the carrier aggregation is a technology that extends a usage bandwidth (for
instance, 20 MHz*5 = 100 MHz) and achieves an improvement in maximum
throughput by collectively treating a plurality of frequency bands that have a
bandwidth of 20 MHz. Moreover, the CoMP is a technology by which a plurality of
base stations called a CoMP set cooperates to communicate data with a communication
terminal, and can expand the coverage that can support communication at high data
rates. The CoMP is disclosed in Patent Document 1, for example.
[0004] Moreover, in the 4G, it is being discussed to improve the coverage by introducing
base stations other than macro-eNodeBs, for example, by introducing Home eNodeBs
(femtocell base stations, micro-base stations for mobile phones), remote radio heads
(RRHs), and pico-eNodeBs.
Citation List
Patent Literature
[0005] PTL 1: Japanese Patent Application Laid-Open No. 201 1-091785
Summary
Technical Problem
[0006] In this way, in a heterogeneous environment in which various kinds of base stations
such as RRHs, macro eNodeBs, and the like are dispersed, it is anticipated that even
the CoMP set might dynamically change. However, methods of determining the CoMP
set in the heterogeneous environment are not sufficiently discussed.
[0007] Accordingly, the present disclosure proposes a novel and improved communication
device, communication method, program, and communication system for appropriately
determining a combination of base stations used to communicate with a commu
nication terminal.
Solution to Problem
[0008] According to the present disclosure, provided is a communication device including a
receiver that receives information indicating timing at which a predetermined signal is
transmitted a transmitting base station of a plurality of base stations having the same
cell ID. The receiver determines that the predetermined signal has been transmitted
from the transmitting base station based on the timing observed by the receiver
[0009] Moreover, according to the present disclosure, further provided is a communication
method that includes receiving wirelessly at a user equipment receiver information in
dicating a timing at which a predetermined signal is transmitted from a transmitting
base station of a plurality of base stations having a same cell ID; and
determining that the predetermined signal has been transmitted from the transmitting
base station based on the timing observed by said user equipment receiver.
[0010] Moreover, according to the present disclosure, yet further provided is a commu
nication a communication controlling device and method that uses a setting unit that
sets a timing at which a predetermined signal is transmitted only from some base
stations of a plurality of base stations having a same cell ID so a user equipment can
determine that the predetermined signal has been transmitted from a transmitting base
station based on a receive timing observed by the user equipment.
Advantageous Effects of Invention
[001 1] According to the present disclosure as described above, it is possible to appropriately
determine a combination of base stations used to communicate with a communication
terminal.
Brief Description of Drawings
[0012] [fig. 1]Fig. 1 is an explanatory diagram illustrating a configuration of a communication
system according to an embodiment of the present disclosure.
[fig.2]Fig. 2 is an explanatory diagram illustrating a frame format of 4G.
[fig.3]Fig. 3 is an explanatory diagram illustrating an example of an embodiment of
CoMP.
[fig.4]Fig. 4 is an explanatory diagram illustrating another example of the embodiment
of the CoMP.
[fig.5]Fig. 5 is a functional block diagram illustrating configurations of an eNodeB and
an RRH according to a first embodiment.
[fig.6]Fig. 6 is an explanatory diagram illustrating a subframe which is set as an ABS.
[fig.7]Fig. 7 is an explanatory diagram illustrating subframes which are set as an ABS
and a Multimedia Broadcast multicast Single Frequency Network (MBSFN).
[fig.8]Fig. 8 is an explanatory diagram illustrating an example of setting an ABS.
[fig.9]Fig. 9 is an explanatory diagram illustrating another example of setting an ABS.
[fig.lO]Fig. 10 is an explanatory diagram illustrating an example of setting an ABS
when base stations are grouped.
[fig. 1l]Fig. 11 is an explanatory diagram illustrating an example of information that is
held by an RSRP holding unit.
[fig. 12] Fig. 12 is a functional block diagram illustrating a configuration of a UE
according to the first embodiment.
[fig.l3]Fig. 13 is a flowchart illustrating an operation of a communication system
[fig. 14] Fig. 14 is an explanatory diagram illustrating a modification of a method of
setting an ABS.
[fig.l5]Fig. 15 is a functional block diagram illustrating configurations of an eNodeB
and an RRH according to a second embodiment of the present disclosure
[fig. 16] Fig. 16 is an explanatory diagram illustrating a specific example of a CSI-RS
insertion period.
[fig.l7]Fig. 17 is an explanatory diagram illustrating an example of setting the CSI-RS
insertion period when RRHs are grouped.
[fig.l8]Fig. 18 is a functional block diagram illustrating a configuration of a UE
according to the second embodiment.
[fig. 19] Fig. 19 is a flowchart illustrating an operation of a communication system.
[fig.20]Fig. 20 is an explanatory diagram illustrating a modification of the CSI-RS
insertion period.
[fig.21]Fig. 2 1 is an explanatory diagram illustrating CSI-RS + Enhanced_Muting
according to the second modification.
Description of Embodiments
[0013] Preferred embodiments of the present disclosure are described below in detail
referring to the accompanying drawings. Throughout the present specification and
drawings, components having substantially the same functional configuration are
denoted by the same reference letters or numbers and thus a redundant description
about such components will not be made.
[0014] Moreover, a plurality of components having substantially the same functional con
figuration may be distinguished sometimes by different alphabets added to the last part
of the same reference letters in this specification and the drawings. For instance, a
plurality of components having substantially the same functional configuration may be
distinguished like RRHs 30A, 30B, and 30C if necessary. However, when a plurality
of components having substantially the same functional configuration need not nec
essarily be distinguished from each other, such components may be denoted only by
the same reference letter. For instance, when RRHs 30A, 30B, and 30C need not be
necessarily distinguished from each other, they are only referred to as RRHs 30.
[0015] Moreover, the present disclosure is described in the following order of items.
1. Overall configuration of communication system
2. First embodiment
2-1. Configuration of base station
2-2. Configuration of UE
2-3. Operation of communication system
2-4. Modification
3. Second embodiment
3-1. Regarding CSI-RS
3-2. Configuration of base station
3-3. Configuration of UE
3-4. Operation of communication system
3-5. First modification
3-6. Second modification
4. Conclusion
[0016] <1. Overall configuration of communication system>
The technology according to the present disclosure may be executed in various
modes as described in detail, for example, in sections from "2. First embodiment" to
"3. Second embodiment". Moreover, a communication device (UE 20) according to
each of embodiments includes:
A. a receiver (antenna group 204 and the like) that receives information that indicates
timing at which a specific signal is transmitted only from some base stations of a
plurality of base stations having the same cell ID;
B. a measuring unit (DL signal detector 230) that measures reception power at the
timing; and
C. a transmitter (antenna group 204 and the like) that transmits the measurement
result obtained by the measuring unit.
[0017] Hereinbelow, basic components that are common in respective embodiments are
described first by referring to Figs. 1 and 2.
[0018] (Overall configuration of communication system)
Fig. 1 is an explanatory diagram illustrating a configuration of a communication
system 1 according to an embodiment of the present disclosure. As illustrated in Fig. 1,
the communication system 1 according to the embodiment of the present disclosure
includes an eNodeB 10, a core network 12, a user equipment (UE) 20, and a plurality
of RRHs 30A to 30F.
[0019] The UE 20 is a communication device that performs reception processing for a
down-link resource block that is allocated by a base station such as the eNodeB 10, and
performs transmission processing for an up-link resource block.
[0020] The UE 20 may be a smart phone shown in Fig. 1 for instance, or may be an in
formation processing device such as a personal computer (PC), a home-use video
processing device (DVD recorder, VCR, and the like), a personal digital assistants
(PDA), a family-use game console, or a home electric appliance. In addition, the UE
20 may be a mobile communication device such as a mobile phone, a personal
handyphone system (PHS), a portable music player, a portable video processing
device, or a portable game console.
[0021] The eNodeB 10 is a radio base station that communicates with the UE 20 in the
coverage (in this specification, the eNodeB 10 indicates a Macro_eNodeB unless
specifically described otherwise). Moreover, the eNodeB 10 is connected to a plurality
of RRHs 30A to 30F through a communication path such as an optical fiber for
instance. Therefore, the eNodeB 10 can transmit a down-link signal to the RRH 30
through the communication path and cause the RRH 30 to transmit the down-link
signal to the UE 20, or can receive an up-link signal, which the RRH 30 has received
from the UE 20, from the RRH 30. In addition, it is also possible for the eNodeB 10 to
perform CoMP communication by cooperating with the plurality of RRHs 30A to 30F.
Details of the CoMP communication will be described later. Although not illustrated in
Fig. 1, a lot of the eNodeBs 10 are actually connected to a core network 12.
[0022] The core network is a service-provider's network including management nodes such
as a mobility management entity (MME) and a serving gateway (GW). The MME is a
device that sets a session for data communication, and controls opening and hand-over.
This MME is connected to the eNodeB 10 through an interface called X2. The S-GW
is a device that routes and forwards user data.
[0023] The RRH 30 is a radio base station which communicates with the UE 20 with
relatively small power compared with the eNodeB 10. Specifically, the RRH 30 is
connected to the eNodeB 10 through a communication path such as an optical fiber and
transmits the down-link signal, which has been received from the eNodeB 10 through
this communication path, to the UE 20. Moreover, the RRH 30 transmits the up-link
signal, which has been received from the UE 20, to the eNodeB 10 through the com
munication path. The communication system 1 according to the present disclosure
includes the RRHs 30 so that the coverage and the quality in the vicinity of the cell
edge can be improved.
[0024] (Frame configuration)
Next, a radio frame shared between the UE 20 and a base station such as the eNodeB
10 is described.
[0025] Fig. 2 is an explanatory diagram illustrating a frame format of 4G. As illustrated in
Fig. 2, a radio frame of 10 ms includes ten subframes #0 to #9 each of which is 1 ms.
Each subframe is one resource block including twelve subcarriers/fourteen orthogonal
frequency division multiplexing (OFDM) symbols, and scheduling is assigned in units
of a resource block. Moreover, a single OFDM symbol corresponds to a unit used in a
communication system of an OFDM modulation system, and is the unit for outputting
data which is processed through one time of fast Fourier transform (FFT).
[0026] Moreover, as illustrated in Fig. 2, each subframe includes a control region and a data
region. The control region includes first one to three OFDM symbols (Fig. 2 shows an
example in which the control region includes three OFDM symbols) and is used to
transmit a control signal that is called phy downLink control channel (PDCCH).
Further, the data region following the control region is used to transmit user data or the
like that is called phy downLink shared channel (PDSCH).
[0027] In addition, a cell-specific common reference signal (CRS) that is a cell-specific
reference signal is disposed in the control region and the data region. The UE 20
performs channel estimation by receiving this CRS, and can demodulate the PDSCH
and the like on the basis of the channel estimation result.
[0028] (Regarding CoMP)
Next, the CoMP that relates to the present disclosure is described. The CoMP is a
technology by which a plurality of base stations called a CoMP set cooperates to com
municate data with the UE 20, and can extend the coverage which can support commu
nication at high data rates. This CoMP is divided roughly into Joint Processing and Co
ordinated Scheduling and/or Beamforming.
[0029] The former, Joint Processing, is a technology by which a plurality of base stations
communicates data with one UE 20 at the same time. For instance, as illustrated in Fig.
3, an example in which the eNodeB 10 and the RRHs 30A to 30F transmit data to the
UE 20 at the same time comes under the Joint Processing. According to this Joint
Processing, since branches (antennas and analog circuits (wireless processing units)) of
a plurality of base stations can be used for data communication, the antenna gain and
SINR can be improved.
[0030] When Joint Processing for down-link is performed, transmission data to the UE 20
should be distributed to the RRHs 30A to 30F through a wired communication path,
for example, called a backing hole between the base stations beforehand. Moreover,
the Joint Processing for up-link is performed by integrating the data received by a
plurality of base stations from the UE 20.
[003 1] Examples of the data integration method include a method of integrating data of a bit
level which has been demodulated by each of the base stations, a method of integrating
data of a soft bit level which has not yet been decoded by each of the base stations, a
method of integrating data which has not yet been demapped by each of the base
stations, and the like. As the data is integrated after latter part of the data is de
modulated in each base station, the amount of data which is exchanged through the
backing hall increases, but the performance tends to improve.
[0032] The latter, the Coordinated Scheduling and/or Beamforming, is a technology by
which data transmission is performed only by one base station and scheduling (control
that determines resource blocks to be allocated to respective UEs 20) is performed co
operatively by the plurality of base stations. According to this Coordinated Scheduling
and/or Beamforming, interference among the plurality of base stations can be easily
avoided by performing scheduling adjustment.
[0033] The technology according to the present disclosure especially focuses on the former,
that is, Joint Processing, among the two kinds of CoMPs. This Joint Processing is
roughly classified into Non-Coherent Joint Processing and Coherent Joint Processing.
[0034] The Coherent Joint Processing is an adjustment method of adjusting timing of data
transmission from each of the base stations so that phases of data, which arrives at a
communication terminal 20 from the respective base stations, match. On the other
hand, the Non-Coherent Joint Processing is a method in which each of the base stations
transmits data without adjusting timing of data transmission from each of the base
stations. Therefore, the Coherent Joint Processing is superior in performance to the
Non-Coherent Joint Processing. However, in order to perform the Coherent Joint
Processing, it is necessary to calculate an adjustment amount of transmission timing of
each of the base stations 10 for every communication terminal 20. Accordingly, it is
disadvantageous in terms of complex processing.
[0035] (Regarding CoMP set)
The CoMP set is a term used in 3GPP, and it means a combination of base stations
which cooperatively perform transmission for the purpose of performing the CoMP.
Usually, it is assumed that about three eNodeBs 10 compose the CoMP set. On the
other hand, three or more base stations, such as five or ten, compose the CoMP set in
an heterogeneous environment in which cells such as Pico_eNodeBs, Home_eNodeBs,
PvRH_eNodeBs (in this specification, simply called RRHs), and the like are overlaid.
Moreover, it is anticipated that the CoMP set dynamically changes.
[0036] By the way, since the distances to the respective base stations are different depending
on the UEs 20, the best CoMP set is different for each of the UEs 20. Therefore, it is
important to determine the best CoMP set for each of the UEs 20. For instance, the
CoMP set can be determined in such a manner that the base stations receive the reports
of reference signal received power (RSRP) of CRS that each of the UEs 20 has
acquired in a frame-synchronized manner with each of the base stations and the base
stations where the RSRP is large are selected from among the plurality of base stations
that are reported from the UEs 20.
[0037] (Relation between cell ID and CoMP)
The above-mentioned Macro_eNodeBs 10 usually have cell IDs which are different
for each of the Macro_eNodeBs 10. Similarly, it has been assumed for the RRHs 30 to
have cell IDs different for each of the RRHs 30. However, recently, a scenario is being
discussed in which the plurality of RRHs 30 that belongs to a certain Macro_eNodeB
10 shares the same cell ID with the Macro_eNodeB 10. In this case, since the
Macro_eNodeB 10 and the plurality of RRHs 30 transmit the same signal, there are ad
vantages that an intercell interference of the RRHs 30 does not occur and it is easy to
execute the CoMP while there is also a disadvantage that the cell gain is not improved.
[0038] (Point aimed by this embodiment)
Since the cell ID and the reference signal like the CRS are in one-to-one corre
spondence when the eNodeB 10 and all of the RRHs 30 have the same cell ID as
described above, it is considered that the CRSs that are transmitted by the eNodeB 10
and each of the RRHs 30 are identical. Therefore, even if the UE 20 attempts to
measure and report the RSSP of the CRS transmitted from each of the RRHs 30, it is
difficult to distinguish the sending station of the CRS. Therefore, it is also difficult for
the eNodeB 10 to select the best CoMP set for the UE 20. As a result, as illustrated in
Fig. 3, a method is considered in which the eNodeB 10 and all of the RRHs 30 perform
the CoMP with respect to the UE 20.
[0039] Fig. 3 is an explanatory diagram illustrating an example of the embodiment of the
CoMP. When the eNodeB 10 and all of the RRHs 30 perform the CoMP with respect
to the UE 20 as illustrated in Fig. 3, the UE 20 improves the reception quality by
receiving the same signal from the eNodeB 10 and all of the RRHs 30.
[0040] However, when it is discussed in detail, the signal transmissions from the RRHs 30D
and 30E do not really contribute to the improvement of the reception quality of the UE
20 because the reception power from the RRHs 30D and 30E that are far from the UE
20 is low. The signal transmissions from the RRHs 30D and 30E act as an interference
wave and thus is considered to cause degradation of the throughput of the entire
system.
[0041] Therefore, ideally as illustrated in Fig. 4, it is preferable that the CoMP be performed
by using only a part of the RRHs 30 (for instance, RRHs 30A and 30B) that contribute
to the improvement of the reception quality of the UE 20. However, there was no
means to select the best CoMP set for the UE 20 as described above. In this respect,
since the conventional UEs of Rel8, Rel9, and RellO expect the same signal to be
transmitted from each of the RRHs, if the respective RRHs 30 transmit signals by
which the respective RRHs can be distinguished while the respective RRHs 30 have
the same cell ID, the compatibility may be lost.
[0042] Therefore, in view of the above-mentioned circumstances, each embodiment of the
present disclosure has been made. According to each embodiment of the present
disclosure, the best CoMP set for the UE 20 can be determined by obtaining the RSRP
of each of the RRHs 30 in the UE 20. Hereinbelow, each embodiment of the present
disclosure is described in detail as follows.
[0043] <2. First embodiment
(2-1. Configuration of base station)
Fig. 5 is a functional block diagram illustrating configurations of an eNodeB 10-1
and RRHs 30 according to a first embodiment. As illustrated in Fig. 5, each of the
RRHs 30 includes an antenna group 304 and a wireless processing unit 310, and
transmits a down-link signal, supplied by the eNodeB 10-1 through an optical fiber, to
a UE 20- 1 according to the first embodiment. Moreover, each of the RRHs 30 supplies
an up-link signal received from the UE 20-1 to the eNodeB 10-1 through the optical
fiber. Each of the RRHs 30 has the same cell ID as the eNodeB 10-1, and transmits the
same cell-specific reference signal (for instance, CRS).
[0044] Moreover, as illustrated in Fig. 5, the eNodeB 10-1 includes an antenna group 104, a
wireless processing unit 110, a DA/AD converter 120, an up-link (UL) signal detector
130, a scheduler 140, a down-link (DL) signal generator 150, an ABS setting holding
unit 160, an RSRP holding unit 170, and a CoMP set determining unit 180. Almost
blank subframe (ABS) is a technology that is decided to be adopted in RellO of 3GPP,
and the ABS is a subframe most of which is stopped from being transmitted. For
instance, only PDCCH and CRS are transmitted in a subframe which is set as the ABS.
The first embodiment is made by paying attention to the ABS.
[0045] The antenna group 104 receives a radio signal from the UE 20-1, acquires an electric
high frequency signal, and supplies the high frequency signal to the wireless
processing unit 110. Moreover, the antenna group 104 transmits the radio signal to the
UE 20-1 on the basis of the high frequency signal supplied from the wireless
processing unit 110. Since the eNodeB 10-1 includes the antenna group 104 including
a plurality of antennas, the eNodeB 10-1 can perform MIMO communication and
diversity communication.
[0046] The wireless processing unit 110 converts a high frequency signal supplied by the
antenna group 104 to a baseband signal (up-link signal) by performing analog
processing such as amplification, filtering, or down conversion. Moreover, the wireless
processing unit 110 converts the baseband signal (down-link signal) supplied by the
DA/AD converter 120 into the high frequency signal.
[0047] The DA/AD converter 120 converts the up-link signal of an analog format supplied
from the wireless processing unit 110 into a digital format, and supplies the converted
signal to the UL signal detector 130. Moreover, the DA/AD converter 120 converts the
down-link signal of the digital format supplied from the DL signal generator 150 into
the analog format, and supplies the converted signal to the wireless processing unit
110.
[0048] Moreover, the down-link signals for the respective RRHs 30 are supplied to the DA/
AD converter 120 from the DL signal generator 150. Therefore, the DA/AD converter
120 converts the down-link signal for each of these RRHs 30 into the analog format,
and supplies the converted signal to the corresponding RRH 30 through the optical
fiber. The DA/AD converter 120 is supplied with the up-link signal from each of the
RRHs 30 through the optical fiber, converts the up-link signal into the digital format,
and supplies the converted signal to the UL signal detector 130.
[0049] The UL signal detector 130 detects a control signal such as PUCCH or user data such
as PUSCH from the up-link signal supplied by the DA/AD converter 120. In particular,
the UL signal detector 130 according to this embodiment detects an RSRP mea
surement result obtained through CRS measurement in the UE 20- 1 from the up-link
signal supplied by the DA/AD converter 120. The RSRP measurement result may be
included in the PUSCH.
[0050] The scheduler 140 schedules resources to be used by the eNodeB 10-1, each of the
RRHs 30, and the UE 20-1 for communication. In particular, the scheduler 140
according to this embodiment performs scheduling on the basis of the base station (the
eNodeB 10-1 or each of the RRHs 30) where the ABS is set by the ABS setting
holding unit 160 and a position of the subframe. Moreover, the scheduler 140
schedules the communication with the UE 20- 1 by using the CoMP set for the UE 20- 1
which is determined by the CoMP set determining unit 180.
[0051] The DL signal generator 150 generates the down-link signal to be transmitted from
the eNodeB 10-1 and each of the RRHs 30. Specifically, the DL signal generator 150
generates PDCCH, PDSCH, and the like according to the scheduling by the scheduler
140. In addition, the DL signal generator 150 according to this embodiment sets the
position of the subframe, which is specified by the ABS setting holding unit 160 as the
ABS, in the ABS for the eNodeB 10-1 and each of the RRHs 30. Moreover, the
PDCCH or PDSCH may contain information on the ABS which is set by the ABS
setting holding unit 160. Hereinbelow, the subframe which is set as the ABS is
described in detail referring to Figs. 6 and 7.
[0052] Fig. 6 is an explanatory diagram illustrating a subframe which is set as an ABS. In
the subframe which is set as the ABS as illustrated in Fig. 6, the PDSCH is not
transmitted in a data region. On the other hand, transmission of the PDCCH and the
CRS (reference signal) is not stopped in the data region.
[0053] Fig. 7 is an explanatory diagram illustrating a subframe which is set as both an ABS
and a multimedia broadcast multicast single frequency network (MBSFN). As i l
lustrated in Fig. 7, all transmissions except a transmission of a CRS can be stopped in
the control region by setting both the ABS and the MBSFN to the subframe. In this
embodiment, as described in detail later, the ABS and the MBSFN are set in the
eNodeB 10-1 and each of the RRHs 30 so that the RSRPs of the respective RRHs 30
can be obtained in the UE 20-1.
[0054] Here, returning to the description about the configuration of the eNodeB 10-1 with
reference to Fig. 5, the ABS setting holding unit 160 sets the ABS (which may contain
the MBSFN, the same hereinbelow) with respect to at least part of subframes of the
eNodeB 10-1 and the RRHs 30A to 30F. The ABS setting holding unit 160 associates
and holds information that indicates the subframe set as the ABS and information that
indicates the base station where the ABS is set.
[0055] The ABS setting holding unit 160 sets the same subframe as the ABS in the base
stations except one base station, or except two or more base stations among the
eNodeB 10-1 and the RRHs 30A to 30F. As a result, in the subframes that are set as
the ABS, only one base station or only two or more base stations will transmit a CRS
in the data region. Hereafter, setting of such an ABS is described more specifically
referring to Figs. 8 to 10.
[0056] Fig. 8 is an explanatory diagram illustrating an example of setting the ABS. When a
subframe #3 of radio frames #M to #N is set as the ABS in the eNodeB 10-1 and the
RRHs 30B to 30F excluding the RRH 30A as illustrated in the first row of Fig. 8, only
the RRH 30A transmits the CRS in the data region of the subframe #3 of the radio
frames #M to #N as illustrated in the upper part of Fig. 9.
[0057] Similarly, when the subframe #3 of the radio frames #N+1 to #0 is set as the ABS in
the eNodeB 10-1, the RRH 30A, and the RRHs 30C to 30F excluding the RRH 30B as
illustrated in the second row of Fig. 8, only the RRH 30B transmits the CRS in the data
region of the subframe #3 of the radio frames #N+1 to #0 as illustrated in the lower
part of Fig. 9. By repeating such a setting, it is possible to generate the subframes with
the data region in which only each of the RRHs 30A to 30F can transmit the CRS.
[0058] Although the example of setting the ABS excluding only one RRH 30 has been
described above, this embodiment is not limited to the example. For instance, the ABS
setting holding unit 160 may group the eNodeB 10-1 and the RRHs 30A to 30F into
two or more base station groups, and the ABS may be set excluding some base station
groups. Hereafter, it will be described specifically referring to Fig. 10.
[0059] Fig. 10 is an explanatory diagram illustrating an example of setting the ABS when
base stations are grouped. As illustrated in Fig. 10, the ABS setting holding unit 160
may group the RRHs 30A to 30F into a base station group including the RRHs 30A to
30C and a base station group including the RRHs 30D to 30F. In this case, the ABS
setting holding unit 160 can cause only the base station group including the RRHs 30A
to 30C to transmit the CRS in the data region of the subframe #3 by setting the
subframe #3 of the radio frames #M to #N as the ABS for the eNodeB 10-1 and the
base station group including the RRHs 30D to 30F.
[0060] Similarly, as illustrated in the lower part of Fig. 10, the ABS setting holding unit 160
can cause only the base station group including the RRHs 30D to 30F to transmit the
CRS in the data region of the subframe #3 by setting the subframe #3 of the radio
frames #N+1 to #0 as the ABS for the eNodeB 10-1 and the base station group
including the RRHs 30A to 30C. As a result, though details will be described later, it is
possible to determine the base station group where the RSRP measurement result in the
UE 20-1 is excellent as a CoMP set.
[0061] In addition, the ABS setting holding unit 160 may set the ABS such that the base
station group where the RSRP measurement result in the UE 20-1 is excellent is dis
tinguished first and then the RSRPs of the respective RRHs 30 that compose the corre
sponding base station group can be acquired. According to this configuration, since the
RRHs 30 where the RSRP in the UE 20-1 is excellent can be specified in stages, such a
configuration is effective in terms of the time required and efficiency.
[0062] Here, returning to the description about the configuration of the eNodeB 10-1 in
reference to Fig. 5, the RSRP holding unit 170 holds the RSRP measurement results in
the UE 20-1 detected by the UL signal detector 130 in association with timings (for
instance, radio frame numbers and/or subframe numbers) for measurement by the UE
20-1.
[0063] Fig. 11 is an explanatory diagram illustrating an example of information that is held
by the RSRP holding unit 170. When the ABS setting holding unit 160 sets the ABS,
for example, as illustrated in Fig. 8, the RSRP holding unit 170 holds information
shown in Fig. 11 on the basis of the feedback from the UE 20-1. Specifically, the
RSRP holding unit 170 associates and holds the radio frames #M to #N which are set
as the ABS and the RSRPs measured by the UE 20-1 in the corresponding radio frames
so that the CRS can be transmitted from only the RRH 30A. Similarly, the RSRP
holding unit 170 associates and holds the radio frame numbers to which the ABS is set
and the RSRPs measured by the UE 20- 1 in the corresponding radio frames so that the
CRS can be transmitted only from any one of the RRHs 30.
[0064] The CoMP set determining unit 180 determines the CoMP set for performing the
CoMP with each of the UEs 20-1. Specifically, the CoMP set determining unit 180
determine which RRH 30 the RSRP in each of the radio frames which are held by the
RSRP holding unit 170 is associated with by collating the RSRPs with the ABS setting
information which is held by the ABS setting holding unit 160. The CoMP set de
termining unit 180 determines a suitable CoMP set for the UE 20-1 on the basis of the
RSRP of each of the RRHs 30.
[0065] For instance, the CoMP set determining unit 180 may determine a predetermined
number of the RRHs 30 from among ones where the RSRP is excellent as the CoMP
set. Alternatively, the CoMP set determining unit 180 may determine the RRHs 30
where the RSRP exceeds a predetermined value as the CoMP set. In addition, the
CoMP set determining unit 180 may determine the RRHs 30 selected from ones where
the RSRP is excellent in a manner that the total value of RSRPs reaches a prede
termined value as the CoMP set. The CoMP set may contain or may not contain
eNodeB 10-1.
[0066] (2-2. Configuration of UE)
Configurations of the eNodeB 10-1 and the RRH 30 according to the first em
bodiment have been described hereinabove. Next, the configuration of the UE 20-1
according to the first embodiment is described.
[0067] Fig. 12 is a functional block diagram illustrating the configuration of the UE 20-1
according to the first embodiment. As illustrated in Fig. 12, the UE 20-1 includes an
antenna group 204, a wireless processing unit 210, a DA/AD converter 220, a DL
signal detector 230, a UL signal detector 240, and an ABS setting position holding unit
250.
[0068] The antenna group 204 receives a radio signal from the eNodeB 10-1 and the RRHs
30 to acquire an electric high frequency signal, and supplies the high frequency signal
to the wireless processing unit 210. Moreover, the antenna group 204 transmits the
radio signal to the eNodeB 10-1 and the RRHs 30 on the basis of the high frequency
signal supplied from the wireless processing unit 210. The UE 20-1 includes the
antenna group 204 including a plurality of antennas as described above so that the UE
20- 1 can perform the MIMO communication or the diversity communication.
[0069] The wireless processing unit 210 converts the high frequency signal supplied by the
antenna group 204 into a baseband signal (down-link signal) by performing analog
processing such as amplification, filtering, or down conversion. Moreover, the wireless
processing unit 210 converts the baseband signal (up-link signal) supplied by the DA/
AD converter 220 into the high frequency signal. Thus, the wireless processing unit
210 cooperates with the antenna group 204 so as to function as a transmitter and a
receiver.
[0070] The DA/AD converter 220 converts the down-link signal of the analog format
supplied by the wireless processing unit 210 into the digital format, and supplies the
converted signal to the DL signal detector 230. Moreover, DA/AD converter 220
converts the up-link signal of the digital format supplied by the UL signal generator
240 into the analog format, and supplies the converted signal to the wireless processing
unit 210.
[0071] The DL signal detector 230 detects a control signal such as PDCCH, user data such
as PDSCH, or the like from the down-link signal supplied by the DA/AD converter
220. In particular, the DL signal detector 230 according to this embodiment extracts in
formation that indicates an ABS setting position from the PDCCH or the PDSCH. The
information that indicates the ABS setting position corresponds to a location to
measure an RSRP and is held in the ABS setting position holding unit 250. Moreover,
the DL signal detector 230 functions as a measuring unit that measures the RSRP at the
ABS setting position which is held in the ABS setting position holding unit 250.
According to this embodiment, since only some base stations out of the eNodeB 10-1
and the RRHs 30A to 30F transmit the CRS at the ABS setting position, the DL signal
detector 230 can measure the RSRP of only a part of the base stations.
[0072] The UL signal generator 240 generates an up-link signal to be transmitted to the
eNodeB 10-1 and each of the RRHs 30. Specifically, the UL signal generator 240
generates a control signal like PUCCH and a user data signal like PUSCH. In
particular, the UL signal generator 240 according to this embodiment generates the
PUCCH or the PUSCH including the RSRP measurement result obtained by the DL
signal detector 230.
[0073] (2-3. Operation of communication system)
Hereinabove, the configurations of the eNodeB 10-1, the RRHs 30, and the UE 20-1
according to the first embodiment have been described. Next, the operation of a com
munication system including the eNodeB 10-1, the RRHs 30, and the UE 20-1 is
described referring to Fig. 13.
[0074] Fig. 13 is a flowchart illustrating the operation of the communication system. As i l
lustrated in Fig. 13, when the ABS setting holding unit 160 of the eNodeB 10-1 first
sets the ABS (S404), the eNodeB 10-1 notifies the UE 20-1 of information that
indicates the ABS setting position by dedicated signaling (S408). When the in
formation that indicates the ABS setting position is received, the UE 20-1 transmits a
receipt acknowledgement to the eNodeB 10-1 (S412).
[0075] Subsequently, the eNodeB 10-1 and the RRHs 30 perform a regular operation as
usual until the ABS setting position arrives (S416, S420). Then, when the ABS setting
position arrives, only the RRHs 30 where the ABS is not set transmit the CRS in the
data region, but neither the eNodeB 10-1 nor the other RRHs 30 transmit the CRS in
the data region (S424).
[0076] On the other hand, the UE 20-1 measures the RSRP at the ABS setting position on
the basis of the information notified in S408 (S428). Then, the UE 20-1 transmits the
RSRP measurement result to the eNodeB 10-1 (S432).
[0077] After that, the eNodeB 10- 1 determines a suitable CoMP set for the UE 20- 1 on the
basis of the RSRP of each of the RRHs 30, or the RSRP of each group of the RRHs 30
when the RSRP of each of the RRHs 30 or the RSRP of each group of the RRHs 30 are
completely gathered (S436). Then, the eNodeB 10-1 and the RRHs 30 that compose
the determined CoMP set perform the CoMP communication with the UE 20-1 (S440).
Specifically, the eNodeB 10-1 supplies the down-link signal to the RRHs 30 that
compose the determined CoMP set, and the RRHs 30 that compose the CoMP set send
the supplied down-link signal to the UE 20-1 in cooperation with the eNodeB 10-1.
Further, if the eNodeB 10-1 supplies the down-link signal to the RRHs 30 that
compose the CoMP set as described above, the down-link signal is transmitted from
the corresponding RRHs 30 so that the CoMP communication can be achieved. Ac
cordingly, the determined CoMP set is not necessarily notified to the RRHs 30.
[0078] As described above, according to the first embodiment, the RSRP in the UE 20-1 of
each of the RRHs 30 can be measured even in the situation in which each of the RRHs
30 transmits the same CRS. Therefore, the eNodeB 10-1 can determine the suitable
CoMP set for the UE 20-1 on the basis of the RSRP of each of the RRHs 30 in the UE
20-1.
[0079] (2-4. Modification)
Although the example where the ABS setting holding unit 160 sets the ABS to
different radio frames for different RRHs 30 has been described above by referring to
Fig. 9 and the like, this embodiment is not limited to the example. For instance, the
ABS setting holding unit 160 may set the ABS to a plurality of subframes within the
same radio frame for different RRHs 30 as described referring to Fig. 14.
[0080] Fig. 14 is an explanatory diagram illustrating a modification of the method of setting
the ABS. As illustrated in Fig. 14, the ABS setting holding unit 160 may set the ABS
for the base stations other than the RRH 30A in the subframes #3 of the same radio
frame, and set the ABS for the base stations other than the RRH 30B in the subframe
#4. In this case, since only the RRH 30A transmits the CRS in the data region of the
subframe #3, the UE 20-1 can measure the RSRP of the RRH 30A in the subframe #3.
Similarly, the UE 20-1 can measure the RSRP of the RRH 30B in the subframe #4.
[0081] In this modification, the UE 20-1 may report the RSRP measurement results and the
subframe numbers where the RSRP is measured, in association with each other to the
eNodeB 10-1 so that the eNodeB 10-1 can distinguish which RRH 30 the RSRP
notified by the UE 20-1 is associated with.
[0082] Like this modification, when the ABS is set in different RRHs 30 with respect to a
plurality of subframes of the same radio frame, the time to acquire the RSRPs of the
respective RRHs 30 can be shortened.
[0083] <3. Second embodiment
Hereinabove, the first embodiment of the present disclosure has been described.
Next, a second embodiment of the present disclosure is described. The second em
bodiment acquires an RSRP of each of RRHs 30 by measuring a reference signal that
is called CSI-RS not by measuring the CRS that is described in the first embodiment.
In the following, the CSI-RS is described first, after which details of the second em
bodiment are described.
[0084] (3- 1. Regarding CSI-RS)
A channel state information reference signal (CSI-RS) is a reference signal defined
by LTE-Advanced (RellO). This CSI-RS is used to measure a channel quality, not for
the purpose of data demodulation. Therefore, the CSI-RS is thinned out in the d i
rections of frequency and time and inserted comparatively sparsely. For instance, an
insertion period of the CSI-RS can be set within the range of about 5 ms to 80 ms like
10 ms. Since the setting of the CSI-RS (for instance, settings such as adjusting the
insertion period to 5 ms or to 10 ms) can be performed for each UE, it can be said that
the setting (configuration) is UE_Specific.
[0085] Moreover, as specified in Section 36.21 16.10.5.1 of RellO, a pseudo-random
sequence is used for the CSI-RS. However, an initial value of the random sequence is
different for each cell (cell ID). Therefore, since the CSI-RS is originally cell_specific,
the base station which is a sending station of the CSI-RS can be distinguished by the
UE.
[0086] However, when the respective RRHs 30 have the same cell ID, the CSI-RSs that are
transmitted by the respective RRHs 30 are also identical. Moreover, although the
insertion period of the CSI-RS can be set in units of a cell, when each of the RRHs 30
has the same cell ID, the CSI-RS insertion periods (timings) of the respective RRHs 30
become also identical. Therefore, it has been difficult to distinguish the RRH 30 which
is a sending station of the CSI-RS measured by the UE, and to determine a suitable
CoMP set for the UE.
[0087] The second embodiment of the present disclosure is a technology that is conceived
by taking the above-mentioned circumstances into consideration. According to the
second embodiment of the present disclosure, it is possible to distinguish the RRH 30
which is a sending station of the CSI-RS received by the UE. The second embodiment
of the present disclosure is described in detail below.
[0088] (3-2. Configuration of base station)
Fig. 15 is a functional block diagram illustrating configurations of an eNodeB 10-2
and RRHs 30 according to the second embodiment of the present disclosure. As i l
lustrated in Fig. 15, each of the RRHs 30 transmits a down-link signal supplied by the
eNodeB 10-2 through an optical fiber to a UE 20-2 according to the second em
bodiment similarly to the first embodiment. Moreover, each of the RRHs 30 supplies
an up-link signal received from the UE 20-2 to the eNodeB 10-2 through the optical
fiber. Each of the RRHs 30 has the same cell ID as the eNodeB 10-2, and transmits the
same cell-specific reference signal (for instance, CSI-RS).
[0089] Moreover, as illustrated in Fig. 15, the eNodeB 10-2 according to the second embodiment
includes an antenna group 104, a wireless processing unit 110, a DA/AD
converter 120, an up-link (UL) signal detector 130, a scheduler 140, and a down-link
(DL) signal generator 150, a CSI-RS period setting holding unit 162, an RSRP holding
unit 172, and a CoMP set determining unit 182. Since the antenna group 104, the
wireless processing unit 110, and the DA/AD converter 120 have been described in the
first embodiment, detailed description thereof will not be given here.
[0090] The UL signal detector 130 detects a control signal such as PUCCH and user data
such as PUSCH from the up-link signal supplied by the DA/AD converter 120. In
particular, the UL signal detector 130 according to this embodiment detects an RSRP
measurement result obtained through a CSI-RS measurement in the UE 20-2 from the
up-link signal supplied by the DA/AD converter 120. The RSRP measurement result
may be contained in the PUSCH.
[0091] The scheduler 140 schedules resources to be used by the eNodeB 10-2, each of the
RRHs 30, and the UE 20-2 for communication. In particular, the scheduler 140
according to this embodiment performs scheduling according to the CSI-RS insertion
period set by the CSI-RS period setting holding unit 162. Moreover, the scheduler 140
schedules the communication with the UE 20-2 by using the CoMP set, which is de
termined for the communication with the UE 20-2 by the CoMP set determining unit
180.
[0092] The DL signal generator 150 generates the down-link signal to be transmitted from
the eNodeB 10-2 and each of the RRHs 30. Specifically, the DL signal generator 150
generates PDCCH, PDSCH, and the like according to the scheduling performed by the
scheduler 140. In addition, the DL signal generator 150 according to this embodiment
inserts a CSI-RS into the eNodeB 10-2 and each of the RRHs 30 according to the
period set by the CSI-RS period setting holding unit 162. In addition, the PDCCH or
the PDSCH may contain information about the CSI-RS insertion period set by the CSIRS
period setting holding unit 162.
[0093] The CSI-RS period setting holding unit 162 sets the CSI-RS insertion period for the
eNodeB 10-2 and each of the RRHs 30. For instance, the CSI-RS period setting
holding unit 162 sets different insertion periods (insertion timings) for the eNodeB
10-2 and each of the RRHs 30. As a result, it is possible to specify a sending station of
the CSI-RS when the UE 20-2 receives the CSI-RS at a certain timing. Hereafter, the
CSI-RS insertion period is described more specifically referring to Fig. 16.
[0094] Fig. 16 is an explanatory diagram illustrating a concrete example of the CSI-RS
insertion period. As illustrated in Fig. 16, the CSI-RS period setting holding unit 162
sets the CSI-RS insertion periods such that there may be timings at which only some
base stations out of the eNodeB 10-2 and each of the RRHs 30 transmit the CSI-RS.
[0095] For instance, the CSI-RS period setting holding unit 162 sets the CSI-RS insertion
periods named tl, t3, t5, and tl for the eNodeB 10-2 as illustrated in Fig. 16, and sets
the CSI-RS insertion periods named t2 and t4 for the RRH 30A. Therefore, only the
RRH 30A transmits the CSI-RS for t2 and t4. Similarly, the CSI-RS period setting
holding unit 162 sets the CSI-RS insertion periods named t6 and t8 for the RRH 30B.
Therefore, only the RRH 30B transmits the CSI-RS for t6 and t8. Similarly, it is
possible to generate timings at which only each of the RRHs 30 transmits the CSI-RS
by setting CSI-RS insertion periods different from those of the eNodeB 10-2 for each
of the RRHs 30.
[0096] The example of setting the CSI-RS insertion periods named tl, t3, t5, and t7 only for
the eNodeB 10-2 is shown in Fig. 16, but these CSI-RS insertion periods may be set
for each of the RRHs 30. In such a case, the UEs up to RellO receive the CSI-RSs from
the plurality of RRHs 30 for the same periods named tl, t3, t5, and t7 and acquire
channels without distinguishing sending stations of the respective CSI-RSs. On the
other hand, the UE 20-2 down from Rell 1 can receive the CSI-RSs at the timings at
which only each of the RRHs 30 transmits by setting a plurality of periods as the CSIRS
reception periods. That is, the method of setting the CSI-RS according to the
second embodiment can ensure compatibility with existing UEs.
[0097] Moreover, though the example of setting different CSI-RS insertion periods for each
of the RRHs 30 has been described in the above-mentioned embodiment, this em
bodiment is not limited to the example. For instance, the CSI-RS period setting holding
unit 162 may group the RRHs 30A to 30F into two or more groups, and set the same
SCI-RS insertion period for the RRHs 30 that compose the same group. Hereinbelow,
such a setting is described in detail referring to Fig. 17.
[0098] Fig. 17 is an explanatory diagram illustrating an example of setting CSI-RS insertion
periods when the RRHs 30 are grouped. As illustrated in Fig. 17, the CSI-RS period
setting holding unit 162 may group the RRHs 30A to 30F into a group including the
RRHs 30A to 30C and a group including the RRHs 30D TO 30F. In this case, the CSIRS
period setting holding unit 162 can cause only the RRHs 30A to 30C to transmit
the CSI-RS for t2 and t4 by setting the CSI-RS insertion periods named t2 and t4 for
the group including the RRHs 30A to 30C.
[0099] Similarly, the CSI-RS period setting holding unit 162 can cause only the RRHs 30D
to 30F to transmit the CSI-RS for t6 and t8 by setting the CSI-RS insertion periods
named t6 and t8 for the group including the RRHs 30D to 30F. As a result, it is
possible to determine the group where the RSRP measurement result in the UE 20-2 is
excellent, for instance, as a CoMP set.
[0100] In addition, the CSI-RS period setting holding unit 162 may set the CSI-RS insertion
periods such that the group where the RSRP measurement result in the UE 20-2 is
excellent is distinguished first and then the RSRP of each of the RRHs 30 that
compose the corresponding group can be achieved. According to this configuration,
since the RRHs 30 where the RSRP in the UE 20-2 is excellent can be specified in
stages, the configuration is effective in terms of the time required and efficiency.
[0101] Here, returning to the description about the configuration of the eNodeB 10-2 in
reference to Fig. 15, the RSRP holding unit 172 holds the RSRP measurement results
in the UE 20-2 detected by the UL signal detector 130 in association with timings (for
instance, radio frame numbers and subframe numbers) for measurement by the UE
20-2.
[0102] The CoMP set determining unit 182 determines the CoMP set for performing the
CoMP with each of the UEs 20-2. Specifically, the CoMP set determining unit 182 de
termines which RRH 30 the RSRP in each of the radio frames held in the RSRP
holding unit 172 is associated with by collating the RSRP with setting information of
each base station held in the CSI-RS period setting holding unit 162. The CoMP set de
termining unit 182 determines a suitable CoMP set for the UE 20-2 on the basis of the
RSRP of each of the RRHs 30.
[0103] For instance, the CoMP set determining unit 182 may determine a predetermined
number of the RRHs 30 from among ones where the RSRP is excellent as the CoMP
set. Alternatively, the CoMP set determining unit 182 may determine the RRHs 30
where the RSRP exceeds a predetermined value as the CoMP set. In addition, the
CoMP set determining unit 182 may determine, as the CoMP set, the RRHs 30 selected
from among ones where the RSRP is excellent such that the total value of the RSRPs
reaches a predetermined value. The CoMP set may contain or may not contain eNodeB
10-2.
[0104] (3-3. Configuration of UE)
Hereinabove, the configurations of the eNodeB 10-2 and the RRHs 30 according to
the second embodiment have been described. Next, the configuration of the UE 20-2
according to the second embodiment is described.
[0105] Fig. 18 is a functional block diagram illustrating the configuration of the UE 20-2
according to the second embodiment. As illustrated in Fig. 18, the UE 20-2 includes an
antenna group 204, a wireless processing unit 210, a DA/AD converter 220, a DL
signal detector 230, a UL signal detector 240, and a CSI-RS period holding unit 252.
Since the antenna group 204, the wireless processing unit 210, and the DA/AD
converter 220 have been described in the first embodiment, a detailed description
thereof is not given below.
[0106] The DL signal detector 230 detects a control signal like PDCCH and user data like
PDSCH from a down-link signal supplied by the DA/AD converter 220. In particular,
the DL signal detector 230 according to this embodiment extracts information that
indicates the CSI-RS insertion period from the PDCCH or the PDSCH. The information
that indicates the CSI-RS insertion period corresponds to a location for
RSRP measurement and is held in the CSI-RS period holding unit 252. Moreover, the
DL signal detector 230 measures the RSRP for the CSI-RS insertion period held in the
CSI-RS period holding unit 252. According to this embodiment, since only some base
stations of the eNodeB 10-2 and the RRHs 30A to 30F transmit the CSI-RSs for the
CSI-RS insertion periods, the DL signal detector 230 can measure the RSRPs of a part
of the base stations.
[0107] The UL signal generator 240 generates an up-link signal to be transmitted to the
eNodeB 10-2 and each of the RRHs 30. Specifically, the UL signal generator 240
generates a control signal like PUCCH and a user data signal like PUSCH. In
particular, the UL signal generator 240 according to this embodiment generates the
PUCCH or the PUSCH including the RSRP measurement result obtained by the DL
signal detector 230.
[0108] (3-4. Operation of communication system)
Hereinabove, the operations of the eNodeB 10-2, the RRHs 30, and the UE 20-2
according to the second embodiment have been described. Next, the operation of a
communication system including the eNodeB 10-2, the RRHs 30, and the UE 20-2 is
described referring to Fig. 19.
[0109] Fig. 19 is a flowchart illustrating the operation of the communication system. As i l
lustrated in Fig. 19, when the CSI-RS period setting holding unit 162 of the eNodeB
10-2 first sets a CSI-RS insertion period for each of the RRHs 30 (S504), the eNodeB
10-2 notifies the UE 20-2 of information that indicates a CSI-RS insertion period by
dedicated signaling (S508). When the information that indicates the CSI-RS insertion
period is received, the UE 20-2 transmits a receipt acknowledgement to the eNodeB
10-2 (S512).
[0110] After that, the eNodeB 10-2 and the RRHs 30 perform a regular operation as usual
until the CSI-RS insertion period arrives (S516, 5420). When the CSI-RS insertion
period arrives, the CSI-RS is transmitted only from the RRH 30 for which the coming
insertion period is set (S524).
[0111] On the other hand, the UE 20-2 measures the RSRP for the CSI-RS insertion period
on the basis of the information notified in S508 (S528). Then, the UE 20-2 transmits
the RSRP measurement result to the eNodeB 10-2 (S532).
[0112] After that, the eNodeB 10-2 determines a suitable CoMP set for the UE 20-2 on the
basis of the RSRP of each of the RRHs 30 or the RSRP of each group of the RRHs 30
when the RSRP of each of the RRHs 30 or the RSRP of each group of the RRHs 30 are
completely gathered (S536). The eNodeB 10-2 and the RRHs 30 that compose the de
termined CoMP set perform the CoMP communication with the UE 20-2 (S540).
Specifically, the eNodeB 10-2 supplies the down-link signal to the RRH 30 that
composes the determined CoMP set, and the RRH 30 that composes the CoMP set
transmits the supplied down-link signal to the UE 20-2 in cooperation with the eNodeB
10-2. In addition, if the eNodeB 10-2 supplies the down-link signal to the RRH 30
which composes the CoMP set as stated above, the down-link signal is transmitted
from the corresponding RRH 30 so that the CoMP communication can be achieved.
Accordingly, the determined CoMP set is not necessarily notified to the RRH 30.
[0113] As described above, according to the second embodiment of the present disclosure,
the RSRP can be measured in the UE 20-2 of each of the RRHs 30 even in the situation
in which each of the RRHs 30 transmits the same CSI-RS. Therefore, the eNodeB 10-2
can determine the CoMP set that is suitable for the UE 20-2 on the basis of the RSRP
of each of the RRHs 30 in the UE 20-2.
[01 14] (3-5. First modification)
Although the example where the CSI-RS period setting holding unit 162 sets the
CSI-RS insertion period for different RRHs 30 in different time frames has been
described referring to Fig. 16, but this embodiment is not limited to the example. For
instance, the CSI-RS period setting holding unit 162 may set different CSI-RS
insertion periods for different RRHs 30 in the time frame that overlaps as illustrated in
Fig. 20.
[0115] In this case, the UE 20-2 may report RSRP measurement results and RSRP
measuring periods in association with each other to the eNodeB 10-2 so that the
eNodeB 10-2 can distinguish which RRH 30 the RSRP reported from the UE 20-2 is
associated with.
[0116] Like the first modification, the time to acquire the RSRP of each of the RRHs 30 can
be shortened by setting different CSI-RS insertion periods for different RRHs 30 in the
overlapping time frame.
[0117] (3-6. Second modification)
By the way, the technology called CSI-RS Muting is standardized in RellO con
sidering the fact that the reception of CSI-RS of the adjacent cell is disturbed by
PDSCH or the like of high power from a serving base station. Muting is the technology
which stops the transmission from the serving base station by using the resource block
corresponding to the position from which the CSI-RS of the adjacent cell is
transmitted. Actually, it is considered that the transmission of the PDSCH is stopped
not only at the position from which the CSI-RS of the adjacent theory is transmitted
but also at around the transmission position. In short, the CSI-RS muting is a
technology which protects the CSI-RS of the adjacent cell from interference by the
PDSCH of the serving base station.
[0118] Therefore, according to the second modification, the RRH 30 which is a sending
station of the CSI-RS received by the UE 20-2 can be distinguished by using a method
named CSI-RS + Enhanced_Muting that improves the CSI-RS muting like the second
embodiment.
[0119] Specifically, the eNodeB 10-2 mutes the CSI-RSs from the RRHs 30 except a part of
the RRHs 30 in the situation in which the CSI-RS insertion periods of the eNodeB
10-2 and each of the RRHs 30 are identical. As a result, since only some RRHs 30 of a
plurality of RRHs transmit the CSI-RS, the RRH 30 which is the sending station of the
CSI-RS received by the UE 20-2 can be distinguished. Hereafter, such an operation
will be described in detail referring to Fig. 21.
[0120] Fig. 2 1 is an explanatory diagram illustrating CSI-RS + Enhanced_Muting according
to the second modification. As illustrated in Fig. 21, the CSI-RSs from the RRHs 30
other than the RRH 30A is muted for a period PI. Therefore, the RRH 30A can be
specified as the sending station of the CSI-RS received by the UE 20-2 for the period
PI.
[0121] Moreover, since the CSI-RSs from the RRHs 30 other than the RRH 30B are muted
for a period P2, the RRH 30B can be specified as the sending station of the CSI-RS
received by the UE 20-2 for the period P2. Moreover, since the CSI-RSs from the
RRHs 30 other than the RRH 30C are muted for a period P3, the RRH 30C can be
specified as the sending station of the CSI-RS received by the UE 20-2 for the period
P3.
[0122] In Modification 2, the eNodeB 10-2 notifies the UE 20-2 of the period of a single
CSI-RS beforehand, and the UE 20-2 may measure the RSRP for this CSI-RS period
and report the measurement result to the eNodeB 10-2. As a result, the eNodeB 10-2
can determine a suitable CoMP set for the UE 20-2 on the basis of the RSRP mea
surement result reported from the UE 20-2.
[0123] <4. Conclusion>
As described above, according to the embodiments of the present disclosure, the
RSRP can be measured in the UE 20 of each of the RRHs 30 even in the situation in
which each of the RRHs 30 operates based on the same cell ID. Therefore, the eNodeB
10 can determine the CoMP set that is suitable for the UE 20 on the basis of the RSRP
of each of the RRHs 30 in the UE 20. As a result, it is possible to achieve an im
provement of system throughput and a reduction in power consumption because the
transmission from the RRHs 30 that do not really contribute to the improvement of the
reception quality of the UE 20 can be avoided.
[0124] Although the preferred embodiments of the present disclosure have been described in
detail referring to the accompanying drawings, the technical scope of the present
disclosure is not limited to the examples. It is understood that those ordinarily skilled
in the technical field of the present disclosure may certainly conceive various a l
terations or modifications within the scope of the technical spirit described in the
claims, and be aware that these naturally fall within the technical scope of the present
disclosure.
[0125] For instance, although the examples of determining the CoMP set on the basis of the
measurement result of the RSRP as a reference signal which is measured by the UE 20
have been described above, the technical scope of the present disclosure is not limited
to the examples. As a modification, the UE 20 may feedback an index that indicates a
reception quality such as an error occurrence rate of a signal sent from each of the
RRHs 30 to the eNodeB 10, and the eNodeB 10 may determine the CoMP set on the
basis of the index.
[0126] Moreover, each step in the processing performed by the eNodeB 10 and the UE 20 of
this specification is not necessarily processed in a time series manner along the order
described in the sequence diagram. For instance, each step in the processing of the
eNodeB 10 and the UE 20 may be processed in order different from the order
described in the sequence diagram or may be processed in parallel.
[0127] Furthermore, the second modification of the second embodiment has been described
by using an example in which the RSRPs corresponding to the respective combinations
of the RRHs 30 are acquired by using CSI-RS Muting, but the signals used are not
limited to the CSI-RS. For example, a mechanism similar to the above-described
mechanism can be provided by preparing an RS other than the CSI-RS, or a new RS.
Especially when a plurality of RRHs 30 (or a plurality of eNodeBs 10) sends the RS
using the same resource element, the RSRPs corresponding to the respective com
binations can be obtained using the same mechanism as the present technology.
[0128] Furthermore, though the CoMP set is determined by using an estimation of a desired
signal and an estimation of an interference signal, the method of acquiring these e s
timations has not been sufficiently studied yet. Moreover, the estimation of the in
terference amount in CoMP environment can be used not only for the determination of
the CoMP set but also as information for controlling other interferences, such as ICIC
(Inter-Cell Interference Coordination) of the LTE Release 8. Accordingly, the e s
timation of the interference amount from each eNodeB also becomes important.
[0129] That is, the technology of the present disclosure is used not only for the purpose of
acquiring a desired RSRP, but also for the purpose of acquiring an intensity of an in
terference component. That is, according to the technology of the present disclosure,
the interference component from the base stations such as the RRHs 30 or the eNodeBs
10 that have the same cell ID can be acquired for each of different combinations of the
base stations. This is implemented, for example, in a way that the UL signal detector
130 of the eNodeB 10 acquires a detection result of the interference component which
is obtained from the uplink signal through RS measurement in the UE 20, and the
RSRP holding unit 170 stores the detection result of the interference component. A
specific method of acquiring the interference component in each of the UEs 20 is as
follows: for example, a correlation with a reception signal is obtained by using an RS
(Reference Signal) of each of the eNodeBs 10 as a known signal, and the interference
amount of each eNodeB 10 can be acquired by using the magnitude of the correlation.
It can be said that the method of acquiring the magnitude of this interference
component and the method of acquiring the magnitude of the desired component
among the reception signals are the same.
[0130] Moreover, it is possible to produce a computer program which causes hardware
embedded in the eNodeB 10 and the UE 20, such as a CPU, a ROM, and a RAM to
perform the same functions as those of the respective components of the eNodeB 10
and the UE 20 that have been described above. Moreover, a storage medium which
stores the computer program is provided.
[0131] Moreover, the following configurations also belong to the technical scope of the
present disclosure.
According to a communication device embodiment, the device includes
a receiver that receives information indicating a timing at which a predetermined
signal is transmitted from a transmitting base station of a plurality of base stations
having a same cell ID, wherein
said receiver determines that said predetermined signal has been transmitted from the
transmitting base station based on the timing observed by said receiver.
According to one aspect of the embodiment, the communication device further
includes
a transmitter that transmits an indication of measurement results made by said
receiver of said predetermined signal so that a subset of said plurality of base stations
are assigned for future communications with said communication device based on said
measurement results.
According to another aspect
the receiver is configured to receive the predetermined signal from the subset of said
plurality of base stations in a data portion of a predetermined subframe, and
other base stations of said plurality of base stations not transmitting said prede
termined signal in said predetermined subframe so that the receiver can distinguish
whether the predetermined signal is from one of the subset of said plurality of base
stations or from the other base stations.
According to another aspect
the predetermined subframe is an almost blank subframe that includes the prede
termined signal.
According to another aspect
the predetermined subframe is located in different respective time slots for different
base stations of the plurality of base stations.
According to another aspect
the receiver is configured to measure a received signal power of said predetermined
signal for each of the plurality of base stations.
According to another aspect
said transmitter is configured to transmit an indication of said received signal power to
the transmitting base stations for assisting in setting the subset of said plurality of base
stations.
According to another aspect
the receiver determines an interference component as part of said measurement result.
According to another communication device embodiment, the device includes
a communication controlling device that includes a setting unit that sets a timing at
which a predetermined signal is transmitted only from some base stations of a plurality
of base stations having a same cell ID so a user equipment can determine that the pre
determined signal has been transmitted from a transmitting base station based on a
receive timing observed by the user equipment.
According to one aspect of the embodiment, the device further includes
a wireless processing unit that receives a measurement result from a user equipment of
said predetermined signal as received at said user equipment and assigns a subset of
said plurality of base stations having a same cell ID to provide future communications
with user equipment.
According to another aspect
the communication controlling device sets a format of said predetermined signal to be
included in a predetermined subframe transmitted from the subset of said plurality of
base stations having a same cell ID.
According to another aspect
the communication controlling device positions said predetermined subframe as an
almost blank subframe that includes the predetermined signal.
According to another aspect
the predetermined subframe is located in different respective time slots for different
base stations of the plurality of base stations.
According to another aspect
the wireless processing unit receives a signal from the user equipment that includes a
measure of a received signal power at said user equipment of said predetermined signal
transmitted from respective of the plurality of base stations.
According to another aspect
said wireless processing unit receives an indication of said received signal power for
assisting the communications controlling device in setting the subset of said plurality
of base stations in association with a subframe number of said predetermined signal.
According to another aspect
the wireless processing unit receives an interference component as part of said mea
surement result.
According to a method embodiment, the method includes
receiving wirelessly at a user equipment receiver information indicating a timing at
which a predetermined signal is transmitted from a transmitting base station of a
plurality of base stations having a same cell ID; and
determining that said predetermined signal has been transmitted from the transmitting
base station based on the timing observed by said user equipment receiver.
According to one aspect of the embodiment, the method further includes
transmitting an indication of measurement results made by said receiver of said prede
termined signal so that a subset of said plurality of base stations are assigned for future
communications with said communication device based on said measurement results.
According to another aspect
the receiving includes receiving the predetermined signal from the subset of said
plurality of base stations in a data portion of a predetermined subframe, and
other base stations of said plurality of base stations not transmitting said predetermined
signal in said predetermined subframe so that the receiver can distinguish whether the
predetermined signal is from one of the subset of said plurality of base stations or from
the other base stations.
According to another aspect
the predetermined subframe is an almost blank subframe that includes the prede
termined signal.
According to another aspect
the predetermined subframe is located in different respective time slots for different
base stations of the plurality of base stations.
According to another aspect
the receiving includes measuring a received signal power of said predetermined signal
for each of the plurality of base stations.
According to another aspect
said transmitting includes transmitting an indication of said received signal power to
the transmitting base stations for assisting in setting the subset of said plurality of base
stations.
According to another aspect
said receiving includes determining an interference component as part of said mea
surement result.
According to another method embodiment, the method includes
setting a timing at which a predetermined signal is transmitted only from some base
stations of a plurality of base stations having a same cell ID; and
transmitting said predetermined signal to a user equipment so the user equipment can
determine that the predetermined signal has been transmitted from a transmitting base
station based on a receive timing observed by the user equipment.
According to one aspect, the method further includes
receiving a measurement result from a user equipment of said predetermined signal as
received at said user equipment and assigning a subset of said plurality of base stations
having a same cell ID to provide future communications with user equipment based on
said measurement result.
According to another aspect
setting a format of said predetermined signal to be included in a predetermined
subframe transmitted from the subset of said plurality of base stations having a same
cell ID.
According to another aspect
said setting includes setting said predetermined subframe as an almost blank subframe
that includes the predetermined signal.
According to another aspect
the predetermined subframe is located in different respective time slots for different
base stations of the plurality of base stations.
According to another aspect, the method further includes
receiving a signal from the user equipment that includes a measure of a received signal
power of said predetermined signal from the plurality of base stations at said user
equipment.
According to another aspect
said receiving includes receiving an indication of said received signal power for
assisting in setting the subset of said plurality of base stations in association with a
subframe number of said predetermined signal.
According to another aspect
the receiving includes receiving an interference component as part of said mea
surement result.
REFERENCE SIGNS LIST
10, 10-1, 10-2 eNodeB
12 Core network
20, 20-1, 20-2 UE
30 RRH
104, 204, 304 Antenna group
110, 210, 310 Wireless processing unit
120, 220 DA/AD converter
130 UL signal detector
140 Scheduler
150 DL signal generator
160 ABS setting holding unit
162 CSI-RS period setting holding unit
170, 172 RSRP holding unit
180, 182 CoMP set determining unit
230 DL signal detector
240 UL signal generator
250 ABS setting position holding unit
252 CSI-RS period holding unit
PCT7JP2012/004066

Claims
A communication device comprising:
a receiver that receives information indicating a timing at which a pre
determined signal is transmitted from a transmitting base station of a
plurality of base stations having a same cell ID, wherein
said receiver determines that said predetermined signal has been
transmitted from the transmitting base station based on the timing
observed by said receiver.
The communication device of claim 1, further comprising:
a transmitter that transmits an indication of measurement results made
by said receiver of said predetermined signal so that a subset of said
plurality of base stations are assigned for future communications with
said communication device based on said measurement results.
The communication device of claim 2, wherein
the receiver is configured to receive the predetermined signal from the
subset of said plurality of base stations in a data portion of a prede
termined subframe, and
other base stations of said plurality of base stations not transmitting
said predetermined signal in said predetermined subframe so that the
receiver can distinguish whether the predetermined signal is from one
of the subset of said plurality of base stations or from the other base
stations.
The communication device of claim 3, wherein
the predetermined subframe is an almost blank subframe that includes
the predetermined signal.
The communication device of claim 4, wherein
the predetermined subframe is located in different respective time slots
for different base stations of the plurality of base stations.
The communication device of claim 2, wherein
the receiver is configured to measure a received signal power of said
predetermined signal for each of the plurality of base stations.
The communications device of claim 6, wherein
said transmitter is configured to transmit an indication of said received
signal power to the transmitting base stations for assisting in setting the
subset of said plurality of base stations.
The communications device of claim 1, wherein
the receiver determines an interference component as part of said meaPCT7JP2012/
004066
surement result.
A communication device comprising:
a communication controlling device that includes a setting unit that sets
a timing at which a predetermined signal is transmitted only from some
base stations of a plurality of base stations having a same cell ID so a
user equipment can determine that the predetermined signal has been
transmitted from a transmitting base station based on a receive timing
observed by the user equipment.
The communication device of claim 9, further comprising:
a wireless processing unit that receives a measurement result from a
user equipment of said predetermined signal as received at said user
equipment and assigns a subset of said plurality of base stations having
a same cell ID to provide future communications with user equipment.
The communication device of claim 10, wherein
the communication controlling device sets a format of said prede
termined signal to be included in a predetermined subframe transmitted
from the subset of said plurality of base stations having a same cell ID.
The communication device of claim 11, wherein
the communication controlling device positions said predetermined
subframe as an almost blank subframe that includes the predetermined
signal.
The communication device of claim 12, wherein
the predetermined subframe is located in different respective time slots
for different base stations of the plurality of base stations.
The communication device of claim 10, wherein
the wireless processing unit receives a signal from the user equipment
that includes a measure of a received signal power at said user
equipment of said predetermined signal transmitted from respective of
the plurality of base stations.
The communication device of claim 14, wherein
said wireless processing unit receives an indication of said received
signal power for assisting the communications controlling device in
setting the subset of said plurality of base stations in association with a
subframe number of said predetermined signal.
The communication device of claim 10, wherein
the wireless processing unit receives an interference component as part
of said measurement result.
A communications method comprising:
WO 2013/005382 PCT/JP2012/004066
receiving wirelessly at a user equipment receiver information indicating
a timing at which a predetermined signal is transmitted from a
transmitting base station of a plurality of base stations having a same
cell ID; and
determining that said predetermined signal has been transmitted from
the transmitting base station based on the timing observed by said user
equipment receiver.
[Claim 18] The communications method of claim 17, further comprising:
transmitting an indication of measurement results made by said receiver
of said predetermined signal so that a subset of said plurality of base
stations are assigned for future communications with said commu
nication device based on said measurement results.
[Claim 19] A communications method comprising:
setting a timing at which a predetermined signal is transmitted only
from some base stations of a plurality of base stations having a same
cell ID; and
transmitting said predetermined signal to a user equipment so the user
equipment can determine that the predetermined signal has been
transmitted from a transmitting base station based on a receive timing
observed by the user equipment.
[Claim 20] The communications method of claim 19, further comprising:
receiving a measurement result from a user equipment of said prede
termined signal as received at said user equipment and assigning a
subset of said plurality of base stations having a same cell ID to provide
future communications with user equipment based on said mea
surement result.